Drifts, slopes, and shafts

Name: Drifts, slopes, and shafts
Author: International Correspondence Schools

International Correspondence Schools

Drifts, slopes, and shafts

International Correspondence Schools · 1921 · Historical

First stage of excavation; Plumbing the shaft; Lining the shaft; Sinking through rock; Method of drilling, charg ing, and firing holes; Shaft lining

Overview

Drifts, slopes, and shafts is a 1921 historical mining reference by International Correspondence Schools, preserved in the Mountain Man Mining research library, focused on mine timbering. First stage of excavation; Plumbing the shaft; Lining the shaft; Sinking through rock; Method of drilling, charg ing, and firing holes; Shaft lining…

This 1921 document, Drifts, slopes, and shafts, is preserved in the Mountain Man Mining Library for research and reference. Original source: archive.org.

Drifts, Slopes, and Shafts

By

I.C.S. Staff

DRIFTS, SLOPES, AND SHAFTS Parts 1-2

Published by

International Textbook Company

Scranton, Pa.

.If

Drifts, Slopes, and Shafts, Part 1: Copyright, 1920, 1906, by International Text book Company.

Drifts, Slopes, and Shafts, Part 2: Copyright, 1921, 1906, by International Text book Company.

Copyright in Great Britain

Printed in U. S. A.

Grd

j i t

International Textbook Press Scranton, Pa.

Note. — This book is made up of separate parts, or sections, as indicated by their titles, and the pa*?e numbers of each usually begin with 1. In this list of 5untun , the titles the parts are given ip the order in which they appear in the book, and under each title is a full synopsis of the subjects treated.

Drifts, Slopes, And Shafts, Part 1

Location of Mine Opening . 1- 8

Definitions . 1

Conditions That Determine Position of Opening . 2- 4

Conditions That Determine Form of Opening . 5- 8

Drifting . 9- 15

Dimensions and Grade of Drift . - . 9- 10

Methods of Drifting . 11- 15

Beginning a drift; Narrow work; Location of shots; Cost of drifting; Blasting without preliminary cutting.

Tunnels . 16- 26

Tunneling in Loose or Running Ground . 16- 17

Forepoling a tunnel ; Wedging methods.

Tunneling in Hard Rock . 18- 21

Tunnel and Drift Portals . 22

Tunnel Linings . 23- 26

Slopes . 27-28

Dimensions; Construction; Shelter holes; Safety dog;

Safety blocks ; Derailing switch.

Principal Forms of Shafts. . . 29

Factors That Determine Shaft Dimensions . 30- 36

Disadvantages of small shafts; Usual shaft dimensions;

Speed of hoisting; Table of well-known shafts; Output of hoisting plant; Width of shaft; Length of shaft.

Sinking Tools and Appliances . 37- 41

Buckets ; Rope hooks and bridle chains ; Guides for buckets ; Shaft coverings ; Dumping the bucket ; Hoist ing engine ; Portable boiler.

Head Frames and Other Shaft Structures . 42- 46

Sinking head frame; Temporary head frame; Ventilation;

Manway or pumpway.

Methods of Lighting and Drainage . 47- 48

Drifts, Slopes, And Shafts

Serial 846A Edition 2

Location Of Mine Opening

Preliminary Considerations

Introduction

1. Definitions of Terms. — Excavations for the purpose of developing coal seams are termed mine openings. They may be horizontal, inclined, or vertical, depending on the geological conditions, economy and efficiency in bringing the coal to the surface, and requirements of drainage and ventila tion.

If all or a considerable portion of a coal seam lies close to the surface, the overlying earth and shale, or rock, may be removed and the coal mined by the open quarry method. The removal of the overlying earth and shale is known as

stripping.

If the coal seam crops out on the surface, an opening driven horizontally into the seam is known as a drift. If driven horizontally through rock from the surface to a coal seam or underground from one coal seam to another, it is called a

tunnel.

If drifts and tunnels are at such a level in the seam, or if they cut the seam at such a level that all drainage from the workings above the elevation of their floors will flow to the surface by gravity, they are usually called water-level drifts and water-level tunnels, respectively.

Copyrighted By International Textbook Company. All Rights Reserved

Drifts, Slopes, And Shafts, Part 1

If an opening is driven down the pitch in an inclined coal seam, it is known as a slope; if it is driven down grade through rock to a coal seam, it is known as a rock slope.

If the opening is sunk vertically through overlying strata to a coal seam, it is called a shaft.

2. The surface end of a drift or tunnel is known as its mouth. The upper, or surface, end of a slope or shaft is known as its head, top, or mouth, and the lower, or bottom, end is known as its foot, or bottom.

Haulage roads, that are horizontal or nearly so, when turned off a slope are known as levels, or lifts. They are numbered successively from the mouth downward, as first level , second level, or first lift, second lift, etc.

Conditions That Determine Position Of Opening

3. Position of Main Opening'. — The character and location of the main opening of a coal mine can be determined only after a careful study of the inclination and thickness of the coal seam and its overlying strata. In addition to this, it is necessary to take into consideration the extent and topog raphy of the property; the best location for the tipple or breaker and the balance of the surface plant ; also, the maxi mum daily output desired, and the capital available for future development.

While it is desirable that the main opening of a coal mine should be near the tipple or the breaker and at such a height relative to either one as to cause a minimum expense in outside haulage and handling, it is also possible that, ultimately, greater economy will be secured by having the opening at a consider able distance from the tipple or breaker.

If the capital available for development work is limited, it becomes necessary to have such an opening as will permit quick shipment of coal, from the profits of which more extensive development work may be done. Under such conditions the opening may be of such a nature as to allow its future use as a second opening, or at least as part of a second opening.

Drifts, Slopes, And Shafts, Part 1

4. Position of Tipple or Breaker. — Whenever pos sible, the position of the tipple or breaker and outside improve ments should be dependent on the location of the main opening, rather than that the location of the opening should be depen dent on the location of the tipple.

W hether the coal is to be shipped to market by railroad, by water, or partly by either means, will have an important bear ing on the location of the tipple or breaker.

If the coal is to be shipped by rail, the tipple or breaker must be located at such a point that a connecting branch railroad or sidings may be constructed and operated at a reasonable cost per ton of output. Should the mine mouth be high up on a hill and the existing railroad be in the valley, it often pays to locate the tipple or breaker in the valley and to use a self-acting plane for running the coal to it.

5. The main opening of a mine may be located several hundred yards away from the railroad and the surface forma tion be such as to make the cost of a branch line and sidings to a point near the mine opening prohibitive. In this case a narrow-gauge railroad may be constructed over which to haul the mine cars from the mine to the tipple or breaker. How ever, when the output will warrant the expense, it is preferable to locate the tipple or breaker near the mine opening and run a branch track to it from the main railroad.

If shipments are to be made by water, or part by water and part by rail, the tipple or breaker must necessarily be located on the bank of the river or canal, at a point most convenient to the mine opening and where a branch track can be constructed to it.

G. Connecting: Tipple or Breaker Witli Railroad.

If the mine opening and the tipple or breaker must be located at a considerable distance from the main railroad, the branch connecting with the mine may be constructed wholly by the railroad company, partly by the railroad company and partly by the mine owners, or entirely by the latter. When con structed jointly by the railroad company and the mine owners, the latter do the grading under the direction of the engineer-

Drifts, Slopes, And Shafts, Part 1

ing officials of the railroad, and the railroad company furnishes the ties and rails and lays them.

When the branch is constructed by the mine owners, a map showing its location, grades, curves, and the point where it is proposed to connect with the main line must be submitted to the railroad officials for their approval, because, as the haulage will be done by the railroad, they will require that the grades, curves, and point of connection with the main road shall be such as to make the operation of the branch line safe and as economical as possible.

7. Extent of Mine. — The amount of territory that can be economically worked from one main opening will depend on the physical characteristics of the seam and the contour of its floor. A general idea of the contour of the floor of the seam will in most cases have been obtained from prospect holes and geological cross-sections. The opening should, preferably, be placed at the lowest part of the seam, so that the workings will drain by gravity and so that haulage grades favorable to the load may be secured.

If the seam is flat and is opened by a shaft, it should be placed in the center of the field, if possible, so that the inside haulage costs will be at a minimum by reason of the shorter distances from the working faces to the shaft.

With locomotive haulage it is practicable to have main haul age roads extending a distance of 6,000 to 8,000 feet from the opening of the mine. Hence, if a shaft is sunk in the center of a flat seam it would be possible to work a tract of from 12,000 to 16,000 feet square, or from 3,000 to 5,000 acres. But, con ditions are generally such that it is advisable to restrict the acreage reached from one hoisting shaft to about 1,000 acres.

8. Position of Second Opening. — In locating a sec ond, or escape, opening, it is necessary to consider the use to which this opening is to be put and the requirements of the law regarding such openings. The law usually specifies a minimum distance between the main opening and the second opening inside of which it is not permissible to go. In general, it is desirable to make this distance as small as the law will

Drifts, Slopes, And Shafts, Part 1 5

allow, so as to quickly as possible provide a good circulation of air.

At slope and shaft mines the second openings are generally utilized for lowering timber and supplies, and lowering and hoisting men. Often they are also utilized for conducting elec tric wires, as well as steam pipe and compressed-air pipe into the mines, and for column pipe from the pumps; they are also used for main airways. While it is usually preferable to place the ventilating apparatus at the second opening, the posi tion will, to some extent, also be governed by the system of ventilation and the kind of ventilator used. If the second open ing is an upcast opening for the mine, the location of its mouth at a higher elevation than that of the main opening will assist the ventilation to some extent.

Conditions That Determine Form Of Opening

9. Effect of Local Conditions. — No definite rules can be given as to the most suitable form of mine opening. The choice of opening depends to a great extent on local conditions, of which the most important are the geological formation, the topography of the surface, and the distance between possible openings and the railway or waterway over which the coal must be shipped to market.

When all the coal in a seam, or a considerable portion of it, can be mined by a drift or a tunnel from the surface, and such an opening is not too long, as compared with the tonnage of coal that can be won through it, then such an opening is pref erable. It is assumed in this case that the mouth is within a reasonable distance of the tipple or breaker and that the topog raphy is such that the expense of getting the coal to the tipple or breaker will not be excessive.

10. Flat Seams. — If a coal seam is flat, or nearly so, and crops out on the property, a drift opening is best, provided it enters the seam at a point low enough to insure gravity drain age; provided also that its mouth is so located that the coal can be transported to the tipple or breaker at a cost per ton

Drifts, Slopes, And Shafts, Part 1

that will not exceed the sum of the costs per ton for hoisting, pumping, and transporting the coal from a shaft mouth to the tipple or breaker. In addition to this, it is necessary to con sider the difference in the costs of the openings and their maintenance.

A drift is the most inexpensive type of mine opening because its cost is wholly or partly covered by the value of the coal taken out.

A tunnel costs considerably more per yard of length than a drift or a slope driven in the seam, but it usually requires little or no timber.

11. When a coal seam that is flat, or nearly so, does not crop out on the property, and the overlying strata are too thick for profitable stripping, it must be opened by a shaft or a rock slope. Under such conditions the shaft or rock slope should be so located that the drainage will flow by gravity to the shaft or slope bottom and that the grades of the haulage roads will be in favor of the load. Also, its location should be such that the length of haul from the working faces on each side of the shaft or slope should be as nearly as possible of equal length.

12. Inclined Seams With Outcrop. — In case a seam has a comparatively light inclination and crops out on the property, it may be so situated that the mouth of a slope can be located more conveniently to the tipple or to the breaker than can be the mouth of a shaft. A slope is then, generally, preferable to a shaft.

But, if the seam has a comparatively heavy inclination and crops out on the property at a point where a slope can be located advantageously, a slope may be the best type of open ing through which to mine the coal for several lifts. For mining the deeper coal a well-located shaft may be advisable.

If an inclined seam dips with, or against, the slope of a hill, and a drift cannot be driven on its strike, it may be opened by a water-level tunnel driven at a right angle to the line of inclination of the rock strata, provided there is sufficient coal in the seam above the tunnel level to warrant the cost of the tunnel.

Drifts, Slopes, And Shafts, Part 1

13. Sometimes an inclined coal seam is cut through by a ravine or a valley in such a way that the end of the seam is exposed, or can be exposed by removing a comparatively small amount of "wash," or earth. In this case the best opening is a drift driven in the seam, provided the seam extends for a distance of 300 feet or more, measured on its pitch, above the level of the drift, and that it is practicable to convey the coal from the drift mouth to the tipple or breaker. Such a drift is said to be driven on the strike of the seam.

1-1. Even when conditions are such that most of the coal in an inclined seam lies below water level, if 300 feet or more of the seam, measured on the pitch, lies above the level of a conveniently located drift or tunnel, that coal is usually mined through a drift or water-level tunnel, and the coal below water level is mined through a slope or a shaft.

After the coal above water level has all been mined, the drift or water-level tunnel is frequently used as part of a second opening. Or it is utilized as part of a main airway or as an egress for water that is pumped to its level instead of being pumped to a higher elevation, as might be necessary if the drift or tunnel was not available.

15. In an inclined seam, the coal below water level may be mined through a slope or a shaft. If the outcrop of the seam is high on a mountain, and the basin of the seam is very deep and under a valley, a shaft sunk in the valley may be much more economical than a long slope sunk from the outcrop, because the length of hoist will be much shorter, the height to which the drainage must be pumped will be less, and the cost of upkeep of the shaft will be less than that of a long slope. Besides, in many cases, the mouth of such a shaft will be located more conveniently to the tipple or the breaker.

16. In the deep basins of the southern and middle anthra cite fields of Pennsylvania, the coal above water level was opened by water-level drifts or tunnels. For several lifts below water level the coal was mined through slopes sunk from the outcrops of the seams. Finally, when the length of the

Drifts, Slopes, And Shafts, Part 1

slope became such as to require a very long hoist and a high lift for the pumps, besides excessive costs for keeping the slope timbers in good order, shafts were sunk from points lower on the hills, or in the valleys, through which the coal below the lower levels of the slopes was won.

17. Inclined Seams Without Outcrop. — For an inclined coal seam that does not crop out on the property, the best opening is a shaft, though in case the seam has an anti cline at the determined location of the opening, it will be best to sink a rock slope from the surface on about the same pitch as that of the seam where the slope is to cut it. Which open ing to choose will depend largely on whether the top of the shaft or the top of the rock slope will be in the best location to get the coal to a well-located tipple or breaker.

18. Inclined Seams Worked From One Opening.

When two or more inclined seams are worked from the same opening, they are generally connected by tunnels and the coal is brought to the surface through one opening. When the coal is above water level, the connecting tunnel or tunnels are usually extensions of the water-level tunnel from the first seam cut by it. When the tunnels are below water level, they are usually called cross-cuts or underground tunnels, the term cross-cuts being used when the connecting tunnel is only about 20 yards or less in length.

Drifts, Slopes, And Shafts, Part 1

Drifts, Tunnels, And Slopes

Drifting

Dimensions And Grade Op Drift

19. Introductory. — As the work of driving a drift, or drifting , is so closely related to entry driving, these subjects will be treated together. Drifts are used for prospecting pur poses, for airways, haulage roads, traveling ways, and drainage purposes. In planning their size, shape, and timbering it is necessary to consider the purpose for which they are to be used.

20. Dimensions of Drift. — The size of a drift depends on the output desired, the size of mining cars to be used, the character of the haulage, the thickness and character of the seam, and the character of the top and bottom rock. A weak rock often necessitates a narrow opening. The height of the drift should not exceed the thickness of the seam, unless abso lutely necessary, as brushing (taking down) the roof or lifting (taking up) the bottom is always expensive dead work. The average height is from 5 to 7 feet, but when possible there should be 6 feet clearance above the top of the rail, so that a man can walk without stooping. The width varies from 6 to 12 feet, for a single-track drift, to 12 to 18 feet for one that is double-tracked. A fair, average-sized single-track drift is 6 feet wide at the top, 8 feet at the bottom, and 7 feet high in the center. Ample space should be allowed along the side for men to pass moving cars in safety and for a drainage ditch, air pipes, electric wires, etc.

21. Number of Tracks. — The question of a single or double track should be decided before the work is started, but

10 Drifts, Slopes, And Shafts, Part 1

a single-track opening may be widened for a double track at any time in the later development of the mine, if a pillar of sufficient size is left along the passageway. Fixed rules can not be given as to the size of a drift or as to when it should be built for single and when for double tracks, but the tendency is toward double tracks for short distances, and single tracks for long distances with partings or turnouts for the passing of cars going in and out of the mines.

When double tracks are required two or three openings are frequently used instead of a single wide opening, particularly when the top and bottom of the seam are of such a character that a wide opening is impracticable. Separate single openings are safer and often cost less to maintain than wide openings, but wide passageways are generally more cheaply driven than two single passageways of the same combined area. The mate rial left between two openings is called a pillar. The weight of strata resting on the pillars increases with the depth below the surface, hence the thickness of the pillars should increase as the depth of cover increases, or a sufficient thickness should be provided at the start to meet all future requirements. The thickness of the pillar between openings depends on the char acter of the rock and coal, depth of cover, and the method of mining to be employed.

22. Grade of Drift. — The grade of a drift should be sufficient for drainage, and be inclined toward the mouth of the opening, i. e., in favor of the loads. The theoretically per fect grade is one on which the pull required to return the empty car to the face is exactly equal to that necessary to bring out the loaded car ; but, as timber and supplies must be taken in, and since the track is not in uniformly good condition, this perfect grade is never attained. The grade should be at least 5 inches in 100 feet and should not exceed 1 or 2 per cent. With a grade under 1 per cent., the drainage is apt to be sluggish unless the side ditch is kept perfectly clean.

A gutter, or ditch, is usually cut along one rib to carry off the water, and if the bottom is clay or other material that will wash away, a wooden trough is laid in it. If for any reason

drifts, slopes, and shafts, PART 1

the grade of a drift or tunnel is such that drainage is not accomplished by gravity, a pump or a siphon is used, the drain age pipe being usually laid on the floor at one side of the track or hung on the side timbers.

Methods Of Drifting

23. Beginning* a Drift. — Before beginning the drift proper it is necessary to start an open cut in the side hill. The cut should be begun somewhat wider than the drift, the two

Fig. 1

side walls gradually converging toward the point where the drift goes under cover. As seen from Fig. 1, the cut should be continued until its height at the point where timbering begins is about 3 to 4 feet greater than the desired drift open ing. At this point, if the roof rock has been exposed, or if the strata are sufficiently firm to be supported by timbering, a sub stantial set of timbers is placed in position and drifting in coal is begun. If the material forming the roof is loose, the method of jorepoling, which is described later, is used until a firm roof is reached.

12 Drifts, Slopes, And Shafts, Part 1

Drifting may be carried on either by first undercutting and shearing the coal, as shown in Fig. 2, and then, if the coal does not fall by its own weight, wedging it or blasting it down ; or by bringing down the coal entirely by blasting, as is the case in tunneling in rock.

When the drift is from 6 to 12 feet wide, the work is called narrow work ; when it is wider than this, it is wide zvork.

24. Narrow Work. — In driving narrow drifts, the miner shears the rib on one side, as in Fig. 2, and undercuts the coal to a depth approximately equal to the thickness of the seam, if

the seam is not over 5 to 6 feet thick. A shot is then placed near the unsheared rib. It is essential to avoid a tight shot , or a shot that is not given sufficient oppor tunity to work, and a shot should not be placed too far on the solid. There is not the opportunity here, as in driving a room, to grip the shot, that is, to incline the hole at an acute angle to the face; but in narrow work the hole must be drilled more nearly parallel to the rib. The holes are generally shorter than in room work.

The position and depth of the hole depend wholly on the shooting character of the coal. This varies in every seam, and the judgment and experience of the miner alone will dictate the best position and direction. Some seams may be worked by a single hole, but, in general, two holes are required to give the best results. In almost every seam, there is a softer and a harder stratum of coal. It is necessary to give the hole such a position and direction as to locate the charge so that its force will be expended more against the

Drifts, Slopes, And Shafts, Part 1 13

harder stratum. The hard coal may be at the roof of the seam, or it may lie next to the floor ; or the hard coal may be central in the seam with a soft stratum above and below it. The coal may break freely at the roof, or it may have a tendency to hold fast to the roof. No rule can be given for these conditions except the general rule that the charge must always be located behind the greatest resistance. A charge located in a soft stratum will often cause the coal to seam out; that is, only the soft stratum will be blown out by the force of the blast, leaving the harder coal in place. When coal tends to seam out, the hole should always be inclined upwards or downwards across the strata, so that the charge is located in the harder stratum.

25. Location of Shot in Narrow Work. — In Fig. 3 (a) is shown the position and direction of the hole where a

Fig. 3

single shot is used for bringing down the coal in narrow work. The harder stratum lies next to the roof and the coal breaks freely at the roof. Such a hole in a 5-foot seam may be started 2 feet from the floor, 4 feet from the right rib, and inclined upwards and to the right at an angle of about 30°. The hole may be bored 4 feet deep, the shearing and under cutting being 2 feet in depth; this will locate the charge but slightly on the solid or beyond the face of the shear.

Fig. 3 ( b ) shows the position and direction of the holes when two shots are used to bring down the coal, owing to the upper stratum being harder and not breaking freely from the roof. The holes are fired separately.

It must be remembered, in locating a shot, that the weight of the coal is downwards, and with a good undercut and shear the weight assists in bringing down the coal shattered by the

14 Drifts, Slopes, And Shafts, Part 1

force of the blast. In the cases illustrated in Fig. 3 (a) and ( b ) the charge has been located in the upper stratum where the coal is harder. Fig. 3 (c) shows the position and direction of a hole when the lower stratum of coal is the harder. The undercut is in the underclay, and the coal breaks freely at the roof. It will be observed that the position of the shot is about central in the seam and inclines slightly downwards, having been started at a higher point in the face than in Fig. 3 (a) or ( b ). This position of the charge will cause the fracture of the hard stratum of coal at the back of the undercut, and the soft stratum above will also be broken.

When the coal is down, it is broken by sledges, if necessary, and loaded on the car. The rib on the opposite side from the shear is then trimmed as may be necessary. The operation is repeated by putting in another undercut and a new shear either

on the same or the opposite side of the face.

26. Wide Work.— In driving a wide drift, the coal is sheared close to one rib and undercut as before ; but the shot, more or less inclined, is placed toward the center of the entry. The shearing and undercutting are usually made deeper than in narrow work. When the coal has been removed from one side of the drift, or entry, the same operation is repeated by undercutting the coal, the shot being placed near the center of the solid coal. The place is thus advanced in steps — first on one side and then on the other.

When a drazv slate overlies the coal, it is usually allowed to remain up at the face. If necessary, one or two props are stood a short distance back from the face to protect the miners. The slate is either allowed to fall in the entry, say 20 or 25 yards back from the face, or it may be wedged down later to secure greater headroom for the timbering and the cars. In order to avoid removing too large an amount of dirt from the mine, when there is a heavy draw slate, or to provide

Fig. 4

Drifts, Slopes, And Shafts, Part 1 15

headroom in a thin seam, a wide drift, or entry, is driven and the draw slate, as it falls, is built along the rib as shown in Fig. 4.

27. Cost of Drifting-. — The cost of drifting varies according to the width of the opening and the conditions of the seam. For narrow work, the miner is usually paid yard age; i. e., a certain sum per linear yard of advance, the amount depending on the locality, the size of the drift or entry, and the character of the coal. He is sometimes also paid for the coal mined. In some localities, instead of yardage, the miner is paid an extra price per car or ton. In wide work, the miner is paid by the car or ton and is very seldom paid yardage. In ordinary coal, two men will drive an 8-foot entry from 4 to 6 feet in a shift of 8 hours.

28. Firing Time. — The specified time at which the firing of shots in the mine begins is known as the firing time. In entry driving or drifting, it is necessary to fire at shorter intervals than in room work; in many mines, firing is permitted in entries as soon as the holes are ready, although it may be prohibited in the rooms in the same mine except at firing time.

29. Blasting Without Preliminary Cutting. — If the coal is neither undercut nor sheared, the method of driving differs from the methods already given only in the effect of the shot. Thus, if a short hole is driven at an acute angle with the face, it will, when fired, produce an opening at one side or in the center, known as a loose end. This loose end is of the nature of a shear or an undercut. When drifting in coal, care must be exercised in locating and charging the holes so that the coal will be broken as little as possible.

16 Drifts, Slopes, And Shafts, Part 1

Tunnels

Tunneling In Loose Ground

30. Preparatory Work. — The preceding description of the size, number of tracks, grade, drainage, etc. of a drift applies equally to a tunnel. When a tunnel is driven from the surface, an open cut is started, as in the case of a drift, but the subsequent work of driving, its rapidity, and the method of securing the sides and top, depend on the character of the strata through which the tunnel passes.

31. Forepoling a Tunnel. — When tunneling in loose ground, the top, and sometimes the sides, of the tunnel must be

supported by an arrangement of plank or lagging known as forepoling'. It consists in driving sharpened pieces of nar row plank, or lagging, into the roof at a very slight pitch. The lagging rests on the collar of one timber set and is firmly held by having its end underneath the timber in the next set toward the entrance.

In Fig. 5, a are the posts of the timber sets, b the caps, and e the top bridging. The front ends of the spiles g from any given set rest on the bridging e of the next advanced set, and the spiles for advancing the work are driven between the bridging and the cap, as shown. To force the spiles into the ground, so as to provide room for the placing of the next set,

Drifts, Slopes, And Shafts, Part 1 17

tail-pieces i are placed behind the back end of the spiles as they are being driven. After the spiles have been driven for wards the desired distance, another set is placed, the tail pieces knocked out, and the front end of the spiles allowed to settle against the bridging of a new set. Where the face is composed of extremely bad material, it may be necessary to hold it in place with breast boards k held in place by props l that rest against the forward timber set. In a similar manner the side lagging h is placed in position. When breast boards are used, it is generally necessary to employ foot and collar braces between the sets, so as to transfer the pressure of the breast back through several sets.

32. Forepoling a Drift. — The method of starting the forepoling at the mouth of a drift is shown in Fig. 1. Several sets of timbers are set up and long lagging driven over them into the earth beyond. By balancing the pressure of the earth on the points of the lagging with a weight of stone or timber on the outside end, they are held up and enough earth removed to allow another set being placed to support the lagging nearer the tunnel face. While practicable in rather loose ground, this method is not available in material containing boulders, and is dangerous when used in loose sand.

Tunneling In Running Ground

33. Available Methods. — The several methods em ployed for excavating in running ground or loose sand are wedging, the use of metal shields, and the pneumatic process. As the latter two methods have been developed chiefly in con nection with shaft sinking, they will be described in detail under that heading.

34. Wedging Methods. — In some cases, it has been possible to drive through very fine, loose sand by simply wedging all or most of the material out of the way by means of wedges. An example of this kind is shown in Fig. 6, in which a are the posts of regular timber sets ; b, the side plank ing ; c, the spiling driven, as in forepoling, to support the top ;

18 Drifts, Slopes, And Shafts, Part 1

d, the wedges ; e, the tailing pieces ; f, the floor ; g, the bridging pieces ; and h , the cap pieces. The timber set below e is only a temporary one, and is removed after the spile c is driven forwards.

The wedges d are driven into the face oy means of a ram made of a piece of timber swung from the roof. They simply

Fig. 6

crowd the material away from in front of the excavation; if the pressure becomes so great that they cannot be driven any farther, a few auger holes are bored into the face to relieve the pressure by allowing some of the material to flow into the drift. Wedges are driven into the floor with a mallet as fast as those in the face advance, and are ultimately covered with a plank floor /.

TUNNELING IN HARD ROCIv

35. Drilling' and Blasting. — If rock crops out at the point selected for the location of a tunnel, a face must be cleared away by drilling and blasting. The work differs from that previously described, in that no undercutting and shearing is done. The rock is removed entirely by blasting, for which

Drifts, Slopes, And Shafts, Part 1

purpose one or more series of holes are drilled more or less inclined to the face. These holes should be so arranged as to permit the drills to be easily handled and to give the smallest possible number of holes and require a minimum weight of explosives.

36. If a solid face of rock is exposed, it is necessary first to make a wedge-shaped opening, known as a key hole, in the face. This key hole is produced by drilling the holes at such an angle to the face that the hole produced by the blast

ing will be shaped as a wedge, known as a key cut, with its pointed end innermost. The succeeding shots will then do deeper and more effective work.

37. The common method by which to produce a key hole is known as the square cut, or American, method, which is illus trated in Fig. 7 in several views. Thus, a front elevation of the face is shown at (a); a sectional elevation at (h) ; a sec tional plan at (c) ; and at ( d ) a sectional elevation taken at the

20 Drifts, Slopes, And Shafts, Part 1

near wall of the tunnel. In all views the drill holes are indi cated by dotted lines and the outer openings by blackened circles. The arrangement of the holes corresponds with that used in driving an ordinary 7 ft.X7 ft. mine tunnel.

The rows of drill holes, shown in a and b, view (a), are placed symmetrically on either side of an imaginary, ver tical center line of the face and at a distance of from to 3J feet, center to center. The angle of inclination to the face is shown in the various views. Other rows c and d are placed near the rib as shown. These rows and the top and bottom holes of the center rows are placed as near as possible to the

rib, to the roof, and to the floor, respectively. It is to be noted that the more nearly parallel the holes are to the general direction of the tun nel, the straighter will the cut be made.

38. As the number and inclination of the holes de pend on the character of the rock, no definite rules can be given that will apply to all cases ; experience must be the general guide. Under ordinary conditions it is found that 14 to 16 holes are ample for the face of a 7 ft.X7 ft. tunnel. In the first volley the holes i to 8 are fired, and in the second volley the side holes p to 16. In large tunnels these holes are sometimes as long as 10 feet and bring out from hard rock a cut of from 2 to 3 yards in length.

39. The drill holes may be arranged so that the key cut is produced either in the center, at the side, or at the bottom of the face, depending on the structure of the rock. If the rock texture is uniform and there are no joints, or slips, the holes are placed symmetrically with respect to the face center line, as in Fig. 7. They may also deviate from the American method

drifts, slopes, and SHAFTS, PART 1 21

by being arranged in circles about the key cut instead of in rows parallel to the ribs.

When a slip, or joint, occurs in the rock as at a b, Fig. 8, advantage may be taken of it by locating the holes for the first volley near the joint, and by inclining them toward the plane of fracture. Only the holes that are needed for cutting the opposite rib, such as p, io, and n, are inclining in the opposite direction. The order of firing is as follows : First, / and fired together; second, J, 4, and 5, fired consecutively; third, 6, 7, and 8 , fired consecutively; and, fourth, p, 10, and 11, fired consecutively.

40. It should be remembered that a rock that is hard to drill is not necessarily difficult to blast, and vice versa. Thus, a granite or some form of metamorphic rock, such as a very

hard sandstone that is jointed or brittle, may be difficult to drill, but will break easily with the use of comparatively few holes and a small amount of powder. A clay shale, however, which is soft and tough and easily drilled, may not yield as readily to the blast.

41. Removal of Material. — At first, the material pro duced by blasting is removed by shoveling it to the mouth of the tunnel. As the work proceeds, wheelbarrows are used; and, finally, wooden or iron rails are laid on which a small car is run, similar to that shown in Fig. 9. Unless the material excavated from the tunnel is coal or ore of some value it is simply dumped at its mouth and spread to form a nearly level surface with a slight grade away from the mouth and toward the dump. This will furnish track room and a convenient site

22 Drifts, Slopes, And Shafts, Part 1

for the necessary surface buildings. The cars are at first pushed out by hand, but as the face of the tunnel advances, a mule or a horse is used for pulling them.

Tunnel And Drift Portals

42. Various Forms of Portals. — A tunnel or drift mouth, or portal, is frequently constructed as in Fig. 10 (a)

Fig. 10

and (b), the mouth being surrounded by a frame of sawed timber and rough walls. Some of the more recently built portals have masonry arches built over the mouth of the

Drifts, Slopes, And Shafts, Part 1 23

tunnei or drift, as in Fig. 10 (c), ( d ), and ( e ). Or, the portal may be constructed of concrete, as shown at (/). The stonework or concrete construction at the portal is carried out wards in the form of side wing walls; it is also frequently con tinued underground to a point where a solid formation is encountered.

Tunnel Linings

43. Reasons for Lining; a Tunnel. — Usually, a tunnel does not require lining and sometimes no timber at all is required after a solid rock face is encountered. Under some conditions, however, either a portion or the entire length of the tunnel must be timbered or lined with brick or stone or con crete. When the roof of the tunnel must be supported, it is customary to employ timber or steel supports, the same as in a drift, though brick, stone, or concrete lining may also be used.

In case the bottom or the sides of the tunnel are soft, and the weight of the overlying rock tends to cause the floor to rise and the sides to bulge, it is necessary to line the tunnel.

44. Various Forms of Lining;. — Various forms of lined tunnels of rather large sectional area are shown in Fig. 11. The systems of lining shown will apply to tunnels of any sectional area. For a hard bottom, the form of arch shown in Fig. 11 (a) is often used. It consists of a full semi circular arch that has its spring lying a few feet above the floor of the tunnel. The side walls may or may not be carried below the floor of the tunnel, according to the character of the floor. The spring; of an arch is the point where the vertical side of the arch joins the curved portion.

For a soft bottom, the form of lining shown in Fig. 11 ( b ) is used. The lower portion a, which is an inverted flat arch, is laid first; it is kept in advance of the side walls and the arch forming the roof of the tunnel for the purpose of allowing the work a short time for setting before the weight of the arch is placed on it. In constructing the arch forming the roof of the tunnel, it is supported at intervals by centers, or wooden frames, cut to the required outline of the arch. These centers are

24 Drifts, Slopes, And Shafts, Part 1

placed from 2 to 3 feet apart, and are covered above with short lengths of lagging on which the arch rests while being' built. As each section of masonry is completed, the space behind the masonry is firmly packed with sand, ashes, cinders, slack, or other fine material in order to distribute the roof pressure evenly on the arch. A short time is given for the

work to set, when the centers are taken down and moved for wards to another section. Sometimes iron centers are used instead of wooden ones.

45. Where the side pressures are heavy, one of the forms of arch shown in Fig. 11 (c) and ( d ) is employed. In that shown at (c), the side walls are made to conform with the

Drifts, Slopes, And Shafts, Part 1 25

segments of a circle or of an ellipse. Should the tunnel be sub jected to a very heavy pressure all around, due to the soft nature of the ground, the section of the tunnel may be entirely elliptic, as shown at ( d ).

In the building of tunnel walls, very little mortar should be used between the joints, and no old wood or material liable to decay should be left in or behind the wall.

46. Material of Lining'. — The material used in con structing tunnel linings is generally stone, brick, or concrete . Concrete possesses the advantage of affording an even dis tribution of pressure, of being very rapidly constructed, and much less costly than masonry.

Concrete is composed of cement, sand, and crushed stone (or some substitute) mixed in such proportions as to be suit able for the purpose for which the concrete is to be used. Gravel, furnace slag, cinders, brickbats, broken slate, etc. are often substituted for the broken stone, because they are cheaper and often more readily obtained, but they do not give so good a concrete.

47. The cement generally used in making concrete that is subjected to heavy pressure, is that known as Portland, cement. This cement is made by mixing certain kinds of crushed limestone and clay or other materials rich in silica, alumina, and lime, then burning the mixture to a clinker and grinding this clinker until it is reduced to a nearly impalpable powder. From the nature of this process, involving the arti ficial mixture of the different ingredients, the resulting product is sometimes called artificial cement , but is more generally known as Portland cement.

When cement is mixed with water to a stiff paste and allowed to stand a sufficient time, the paste undergoes chem ical change and a solid mass results. This setting, as it is called, usually requires but a few hours at most. After the setting, a slower chemical action sets in, and the mass grad ually gains in strength. Usually this gain of strength, or hardening, extends over a period of from 6 months to a year — sometimes even beyond this period. Chemists who have

26 Drifts, Slopes, And Shafts, Part 1

examined the chemical composition of cement do not agree as to the changes that it undergoes when it sets.

48. In mixing concrete, the best proportions of the ingre

dients will depend on their character and the purpose for which the concrete is to be used. For engine foundations, mine open ings, tunnel and shaft linings, the following proportions will produce a satisfactory mixture : 1 part, by measure, of Port

land cement ; 3 parts sand ; 6 parts broken stone.

The sand should be clean, sharp, gritty, and free from dirt or other foreign matter; when it contains any considerable amount of mud or dirt, it should be washed. The broken stone or slag should be of suitable sizes, preferably such as will pass through a ring with a 2-inch opening. Modern engi neering practice does not object to the presence of the finer particles of stone in the mass. It will, consequently, not be necessary to screen the stone before using.

49. It is important that the concrete be thoroughly mixed, to insure that all the spaces between the broken stones are filled by the cement and sand. Mixing may be done by machine or by hand. Machine mixing is the better and gives more uniform results; it is also more economical where large quantities of concrete are to be used. Hand mixing may be resorted to where the quantities of concrete required are not sufficiently large to warrant the use of machinery.

In mixing concrete by hand, the sand and cement should first be mixed dry on a platform. Water is then added and the mixture is worked into a mortar. The use of too much water should be avoided; just enough to form a stiff paste is sufficient. The stone is first wetted and then added to the mortar, and the whole mass is thoroughly incorporated by turning over several times with shovels, until each stone is coated with mortar and the stones are evenly distributed through the mass. Concrete, after being mixed, should be placed in position immediately and not allowed to stand long enough to get an initial set before placing. After being placed in position, it should be well tamped with wooden or iron rammers. The tamping should be just sufficient to bring the

Drifts, Slopes, And Shafts, Part 1 27

water to the surface. Excessive tamping will disturb the intimate mixture of the ingredients that is so desirable.

Slopes

Slope Timbering And Safety Appliances

50. Dimensions of Slopes. — A slope may be classified as an inclined drift or tunnel dipping into a coal seam or other strata at any inclination between horizontal and vertical. Slopes vary in width and in height. The width depends on whether they are to be single-or double-track slopes and whether extra space is to be allowed on one side for electric wires and for steam, compressed-air, or column pipes. The height depends on the thickness of the coal seam or on the height of the cars to be used on the slope. Whether a slope should be single or double tracked depends on the extent of the body of coal to be worked and on the daily production.

51. Construction of Slope. — The material excavated in sinking a slope is generally removed by means of a temporary hoisting engine, and the drainage is effected by pumps placed on trucks that can be lowered as the work progresses.

The timbering of slopes of very light pitch corresponds with that employed in a drift or in a tunnel having the same char acter of roof and floor. As the pitch of a slope increases, the timbers are underset , or made to lean slightly up the pitch. The amount of undersetting varies with the inclination of the slope.

On steep slopes, the feet of the props, or legs, usually rest on heavy squared or hewn timbers, known as mud-sills, extending across the floor of the slope at right angles to its center line. These mud-sills are set into the ribs of the slope, and the props, or legs, are mortised into them. On very steep, wide slopes, the mud-sills often have posts, known as buntons, between them; and in addition, the rails of the track are laid on squared timbers that run longitudinally with the rails, these timbers being spiked or bolted to the mud-sills.

28 Drifts, Slopes, And Shafts, Part 1

Safety Appliances

52. Shelter Holes. — When slopes are of light pitch and are used by the men as traveling ways, refuge, or shelter, holes should be provided ; in particular, if men are frequently employed on them in making repairs. In some states, they are required by law, owing to the liability to accident to men by being caught and squeezed between the rib and a trip of cars, or by the breaking of the hoisting rope or car couplings, or by the possibility of cars descending the incline before being attached to the rope.

53. Safety Dog. — Hoisting and lowering of cars, while men are employed on the slope, is not permitted in most states. On slopes of light pitch, a heavy trailing iron bar, known as a safety dog, is often attached or coupled to the drawbar at the rear of the ascending car or trip of cars. The lower end of this dog, which may be either pointed or split, is allowed to drag along the track as the car proceeds up the slope. If the hoisting rope or a coupling breaks, the weight of the car on the incline forces the dog into a sill or into the floor, and the cars are either stopped or derailed.

54. Safety Blocks. — Devices known as safety Mocks are necessary at the knuckle or at the head of all inclines, and in some states are required by law. They consist of blocks so arranged as to prevent cars descending the incline before all is ready and the signal given. These blocks are shaped and arranged so that ascending cars will pass them without diffi culty, but they automatically return to place when the car has passed. They will, however, stop a car moving toward the knuckle, unless the blocks are moved aside by the topman, or by the engineer in the engine room.

55. Derailing Switch. — A derailing switch is some times employed either in place of or in conjunction with safety blocks. This is an automatic spring switch that permits an ascending car to pass on the main track but will derail a car passing to the slope unless the switch is properly set by the topman or from the engine room.

Drifts, Slopes, And Shafts, Part 1 29

Forms And Dimensions Of Shafts

Principal Forms Of Shafts

56. European and American Forms. — A shaft may be either circular, elliptic, polygonal, or rectangular in crosssection. The first three forms are better adapted to withstand pressure than the rectangular, but they are more difficult to timber, and there is always a considerable area of the crosssection that is not available for hoisting. Such shafts are usu ally lined with brick, masonry, concrete, or metal instead of timber and are common in many European countries, while rectangular shafts are generally used in the United States. The practice of lining shafts with concrete is growing in the United States and many of these have their sides and ends made as arcs of circles, so as to present an arch to the side and end pressures. The approximate section of the shaft is then elliptical. Rectangular shafts are either oblong or square, the former being the usual form for a hoisting shaft, while the latter is often used for a small prospect shaft, or for a second opening to be used as an escape shaft or an air-shaft. Rec tangular shafts are not usually lined with masonry on account of the danger of the walls bulging, owing to the pressure of the strata behind them, although a number of rectangular shafts have been lined with concrete ; timber of sufficient size is gen erally used for the lining in these shafts, and when bulging takes place, any of these timbers can be taken out and replaced by others after the trouble has been removed.

57. Shaft Compartments. — A shaft is usually divided into two or more compartments, either by buntons or cross timbers placed one above another and spaced from 6 to 8 feet apart, or by solid partitions formed of 3-inch or 4-inch plank-

30 Drifts, Slopes, And Shafts, Part 1

ing. If there are but two compartments, both of them may be hoistways or one may be a hoistway and the other a pumpway and ladderway. If there are three compartments, two of them are hoistways, and the third, and smaller, compartment, which is at the end of the shaft, is used for a manway and pumpway and for carrying steam or compressed-air pipes or electric wires into the mine.

Factors That Determine Shaft Dimensions

58. Disadvantages of Small Shafts. — The size of a shaft depends on the use for which it is intended, and is determined by the hoisting, drainage, and ventilating condi tions at the given mine. Before commencing to sink, a careful estimate should be made as to the size required for all future developments of the mine. Nothing is saved in sinking a shaft of too small dimensions, for the work of excavation is more easily accomplished in a large shaft, while the serious annoy ance and limitations of a small shaft, and the great expense of enlarging a shaft already sunk, warrant a shaft of generous size. A tight shaft is one in which there is but little space between the curbing and the edge of the cage. In such a shaft, the cage acts like the piston of an air pump, moving the doors in the mine, and causing a general disarrangement of ventila tion. In such a shaft, also, a very small amount of ice will interfere with hoisting.

59. Usual Shaft Dimensions. — Shafts for coal mines vary in size from 5 ft.XlO ft. to 12 ft.X54 ft. inside the timbers. Interesting data about some leading American coal shafts are shown in Table I.

60. Speed of Hoisting. — The size of a hoisting shaft is determined by the output of material required, the depth of the shaft, the speed of hoisting, the size of the mine car, and the number of cars hoisted at one time. The speed of hoisting is commonly understood to mean the maximum speed at which the cage moves during the hoist. This speed and the time lost in starting and stopping vary with the depth of the shaft. In general, the deeper the shaft the greater is the speed

Table I

Table Of Well-Known Shafts

I L T 87B

Depth completed, 1,150 feet.

32 Drifts, Slopes, And Shafts, Part 1

of hoisting allowed, and the greater the speed the greater is the proportional loss due to starting and stopping the engine. This loss of time in starting and stopping varies from 3 to 10 sec onds. The time consumed, between hoists, in caging and uncaging cars varies according to the style of equipment and the manner of caging cars employed. For ordinary conditions, it can safely be assumed to be from 5 to 15 seconds; and this amount added to the allowance made for the loss of time in starting and stopping the engine, or from 3 to 10 seconds,

makes a total allowance be tween hoists of from 8 to

Table Ii

Depth of Shaft

Speed of Hoisting Feet per Second

The speeds of hoisting for shafts of different depths are given in Table II.

61. Output of Hoist ing* Plant. — In estimating the output of a hoisting plant it is necessary to make a cer tain allowance for delays, varying from 5 to 10 per cent., according to the char acter of the hoisting plant. Thus, if hoisting is performed in 10 hours and if a delay of 5 per cent, is allowed, the net time of hoisting will be 95 per cent, of 10 hours, or .95 (10X60) =570 minutes. The total daily output divided by the net time of hoisting, in minutes, gives the required output per minute. The depth of the shaft, in feet, divided by the speed of hoisting, in feet per second, gives the time per hoist, in seconds, approximately, though it does not take account of the time lost in accelerating the engine in starting. The time per hoist plus the time for caging and uncaging gives the total time for each trip of the cage, in seconds. Then, 60 seconds divided by the time per trip gives the number of trips per minute. The output per minute divided by the trips per minute gives the weight of material hoisted at each trip of the cage. If one car is hoisted at a time, this will give the capacity

Drifts, Slopes, And Shafts, Part 1 33

of the car ; if two cars are hoisted at a time, the capacity of the car is obtained by dividing the weight hoisted by two, etc. The capacity of a car, in cubic feet, is found by dividing the weight of material, in pounds, carried by the car by the weight of a cubic foot of the material hoisted. A cubic foot of any solid material equals the weight of a cubic foot of water (62.5 pounds) multiplied by the specific gravity of the material. Table III shows the weight, per cubic foot, of anthracite and bituminous coals of different specific gravities solid and broken, the latter being given for both loose and moderately shaken

Table Iii

Kind

Specific

Gravity

Weight, Pounds per Cubic Foot

Solid

Broken

Loose

Moderately Shaken

Anthracite

' 1.6

' 1.2

Bituminous

coal. Coal, when broken, occupies about 1.5 the space occupied by the same amount when solid ; the weight of the broken coal is, therefore, about two-thirds that of the solid coal.

62. Width of Shaft. — The size of the car to be hoisted determines the width of the shaft. The length of the box of a mine car is determined by the formula

in which inside length, in feet ;

c capacity, in cubic feet ;

b average breadth, in feet ;

d depth, in feet, including the topping.

34 Drifts, Slopes, And Shafts, Part 1

To the inside length of the car calculated by this formula, must be added the thickness of the end planks, each end being from 1 to 2 inches thick, and the length of the bumpers at each end of the car, from 4 to 10 inches, according to the style of car used, in order to obtain the length of car, out to out of bumpers. To this must be added 6 to 8 inches for clearance between each end of the car and the cage, and 6 to 9 inches more for clearance between each end of the cage and the shaft timbers, to obtain the width of the shaft in the clear.

Cars, for use in coal mines, vary from 4 to 6 feet in width, from 5 to 10 feet in length, and from 2 to 5 feet in height. Their capacities vary from 1,000 to 8,000 pounds of coal and their weight from 500 to 4,000 pounds.

Example. — Find the width of a shaft required for hoisting an out put of 1,200 tons of bituminous coal per day of 8 hours, from a depth of 500 feet; the seam is 5 feet 6 inches thick, and has a good roof and floor; the specific gravity of the coal is 1.3.

Solution. — Allowing 5 per cent, for delays, the net time of hoisting is

nearly.

Referring to Table II, it is found that the speed of hoisting in a shaft 500 ft. deep varies from 25 to 40 ft. per sec. Assuming 25 ft. per sec., the time of hoisting one trip is-2™=20 sec. Assuming 10 sec. for the time of caging and uncaging, the total time for each hoist is 20+10 60 sec.

=30 sec. Then (j — hoists per min., and if one car is hoisted at a time, the weight of material per hoist is -Mr4- =2,632 lb. of coal.

In Table III, the weight of bituminous coal having a specific gravity of 1.3 is given as varying from 45 to 50 lb. per cu. ft., when broken (loose). For the ordinary mine run, assume 48 lb. per cu. ft.; then the capacity of a car is Jif1=about 55 cu. ft.

Assuming that the depth of coal on the car, including topping, is 30 in. (24 ft.) and the inside width 40 in. (34 ft.), then the inside length is

bd 34X2+ YXf 50 Adding, to the inside length, 4 in. for the ends of the car and 12 in. for bumpers, the total length of car will be 8 ft. Then adding 3 in. clearance, between each end of the car and the cage, and 9 in. at each end for shaft clearance, the required width of the shaft is 10 ft. in the clear. Ans.

Drifts, Slopes, And Shafts, Part 1 35

63. Length, of Shaft. — Ordinarily, the length of the shaft must be such as to provide for two hoistways, and a pumpway or manway. The width of each hoisting compart ment should be such as to give at least 6 inches of clearance between the greatest width of the car, out to out, and the guides. Allowance must be made also for the width of buntons separating the two hoistways, the thickness of the guides, and the width of buntons separating the hoisting compartment from the pumpway. According to the size and depth of the shaft and the character of the strata, the thickness of the

buntons will vary from 4 to 12 inches. The size of the guides often employed in hoisting shafts is 4 in.X4 in., and the guides are commonly bolted or spiked to the buntons, the heads of the bolts or spikes being countersunk in the guides.

In Fig. 12, the width of the car is shown as 40 inches, out to out, while the clear width between the guides in each hoist way is 4 feet 10 inches, giving a clearance of 9 inches on each side of the car. The size of the guides is 4 in.X4 in., making the total width of each hoistway 5 feet 6 inches. The buntons shown in the figure are 6 inches wide and the pumpway 5 feet

36 Drifts, Slopes, And Shafts, Part 1

wide, making the total length of the shaft, in the clear, 17 feet. The width of the hoistway also depends on the number and size of cars hoisted at one time, and whether two cars are placed side by side on the cage, cr one above the other on a double-deck cage.

G4. Fig. 13 shows a sectional elevation of a shaft where two cars are hoisted side by side on the cage. The entire length of the shaft in the clear, including hoistways and pumpways, is 28 feet, giving two hoistways each 9 feet 10 inches in

Fig. 13

the clear, between guides, and a pumpway 5 feet in the clear. The guides are each 4 inches and the buntons 6 inches wide ; the width of the cars is 46 inches, giving a clearance of 8 inches on each side, and 10 inches between the cars. This is a very large shaft, being capable of accommodating an output of between 3,000 and 4,000 tons per day.

Drifts, Slopes, And Shafts, Part 1 3/

Sinking Tools And Appliances

Hoisting Excavated Material

65. Buckets. — A large number of tools and appliances are required in sinking, but the most of them are used only in special cases, where the conditions of the strata make them necessary.

The buckets used for hoisting the material excavated in sink ing are usually made of boiler iron or steel ; two of the many shapes are shown in Figs. 14 and 15.

The bucket shown in Fig. 14 is sup ported from chains attached by a spring hook to ears on its sides and is dumped by being tilted by means of the handle shown. These buckets are from to 3 feet in height, about 27 inches in diameter at the top, 18 inches in diameter at the bottom, and hold about 6 cubic feet. They weigh about 150 pounds.

66. The form of bucket shown in Fig. 15 varies from 16 to 28 inches in diameter at the top, from 14 to 28 inches in diameter at the bottom, and from 26 to 38 inches in height ; it varies in weight from 180 to 470 pounds and in capacity from to 14 cubic feet. The bail a is attached at a point below the center of gravity of the bucket so that the bucket has a tendency to turn over and empty itself. To prevent this while hoisting, a short pin b is riveted to the side and an ordinary chain link sliding on the bail is slipped over it. While these buckets are easily dumped, numerous accidents have been caused by their overturning in the shaft while hoisting men or material.

A bucket is often made by sawing an oil barrel just above the second hoop from the top, and riveting to the lower part

38 Drifts, Slopes, And Shafts, Part 1

substantial eyes for securing the bail to the bucket. Boxes with drop bottoms are sometimes used instead of buckets for hoisting, and those using them claim a greater speed in the removal of material than with buckets ; they are, however, dan gerous, on account of premature opening of the bottom during hoisting, and sinkers should not be allowed to ride in them.

67. Rope Hooks and Bridle Chains. — The hoisting rope is usually attached to the bail of the bucket by a spe cial hook provided with a clip or extra link and pin for securing the hook fastening while the bucket is being hoisted, as shown in Fig. 16 (a) ; or two hooks are arranged with a drop link, as shown in Fig. 16 (&). At times, bridle chains are used, the hoisting rope being attached permanently to the bridle chain by a socket, as in Fig. 16 (c), or a clevis, as in Fig. 16 ( d ).

68. Guides for Buckets. — When the bucket has a ten dency to revolve while being hoisted from a deep shaft, the

difficulty may be overcome by the use of a yoke and guides. A simple form of this kind, known as a rider , and shown in

Drifts, Slopes, And Shafts, Part 1 39

Fig. 17, consists of a cross-bar connecting two vertical legs, the upper and lower ends of the legs being provided with eyes d loosely embracing the guide ropes c. These guide ropes are either coiled on a drum and lowered as the sinking proceeds, or are hung from the timbers across the top of the shaft. Large weights are attached to the lower ends to keep them steady. At the bottom of the shaft timbers stop-blocks h hold the rider while the bucket goes to the bottom of the shaft, thus keeping the rider and the guide ropes out of the way of the sinkers.

As the bucket is hoisted, the rope socket picks up the rider when it is reached. Considerable time is lost in steadying the bucket before it goes up and down, unless some such rider is used.

69. Fig. 18 shows a form of yoke that slides on guides the same as a cage. In each crosspiece of the yoke, there is a ferrule through which the rope passes, the bottom ferrule being conical to receive the cone on the rope socket. At the bottom of the timbering, two blocks are bolted on each side of the guides

40 Drifts, Slopes, And Shafts, Part 1

to prevent the yoke from descending below the timbers, while the bucket passes down to the bottom of the shaft.

In using yokes or crossheads, great care should be taken to have the guides parallel and with good joints, for many acci dents have occurred from the crosshead sticking and hanging in the shaft, while the bucket continued to go down. If the hanging crosshead jars loose after the bucket has gone 50 or

the bucket, it may carry it to the bottom. This is more likely to occur in lowering men than when lowering the empty bucket, for in the lat ter case the lowering is quickly done, taking the crosshead past the tight spots.

Cages are sometimes used in sinking, in which case false guides must be put in from the lower end of the permanent timber to the bot tom of the shaft. As these guides must be removed be fore each blast, and then re placed, the use of cages is not favored.

70. Shaft Coverings. In order to prevent material falling into the shaft, the top should be covered with 3-inch or 4-inch plank, excepting the portion that must be left open for the passage of the hoisting bucket. This opening may be simply covered by the larry, as shown in Fig. 21 ; but it is better to have a pair of doors meet ing in the middle and closing down flat, or as shown in Fig. 19. In the lowered position, they rest on a triangular boxing at each end and may be so arranged that the ascending bucket will open the doors for its own passage, while they are closed

100 feet below, and then falls on

Drifts, Slopes, And Shafts, Part 1 41

by means of weights not shown ; or the doors may be opened and closed by the levers shown in the figure. The balance weights should not be hung inside the shaft as is sometimes done, for if the ropes break they will drop to the bottom. When the doors are closed, the hoisting rope passes through a small hole cut in the two edges of the doors.

71. Dumping: the Buckets. — At the top, the bucket may be dumped automatically by placing a catch hook so that it engages one side of the bucket rim and tips it as the hoisting is continued, dumping the material either into a chute or into a car. Any method of dumping the bucket while over the shaft is dangerous, as small stones may fall down the shaft through the hole provided for the hoisting rope. It also throws a considerable strain on the headframe, hoisting gear, and rope; and if an accident occurs to the hoisting rope while dumping, the bucket and its load may fall on the shaft cover with sufficient force to break through and fall to the bottom. A

better arrangement is to swing the bucket clear of the shaft by means of a short snatch rope that hangs from a point in the top of the head-frame and at one side of the shaft opening. The hook is quickly put into the bail of the bucket as it comes up, and when slack is given by the engineer, the bucket is swung

clear of the shaft and dumped or transferred to a car.

Several buckets are often used for hoisting material, and as soon as the bucket has passed through the shaft opening, a larry, or truck, running on a broad track that spans the shaft

42 Drifts, Slopes, And Shafts, Part 1

opening is pushed underneath it, the bucket is lowered onto the larry, the hooks are snapped, and an empty bucket attached in its stead. The larry is then moved to one side and the empty bucket lowered into the shaft.

The larry, or truck, is a low flat car similar to that shown in Fig. 9 but without sides. An old railroad hand car that has had its axles made to fit the gauge of the track is often used.

72. Hoisting' Engine. — The hoisting engine used in con nection with the sinking is either a special engine that forms part of the shaft sinker's outfit and can easily be moved from place to place, or any engine that can be readily had and used until the shaft or slope is finished, when it is dismantled and disposed of to the best advantage.

A second-motion engine is safer for sinking purposes than a first-motion engine, as it is not so quick and positive in its movement of cages or buckets and the engine can be run rap idly with less danger to the sinkers. A good hoisting engine should be able to pick the bucket off the bottom at any time, without getting stuck on center or having to run back for slack.

The engines for sinking are usually placed on a temporary foundation made of heavy timbers. The tower backstays are sometimes used as part of this foundation, though this is not good practice, as they may move.

73. Portable Boiler. — A portable boiler of the locomo tive type is generally used, and the engineer frequently does his own firing. When a second shaft is sunk within 300 to 400 feet of the main hoisting shaft, steam is sent direct to the sinking engine at the second shaft through a pipe large enough to prevent excessive condensation. A steam separator is used, or the steam pipe is covered, to reduce condensation. Some times a steam separator is used in connection with a covered steam pipe.

Head-Frames And Other Shaft Structures

74. Sinking Head-Frame. — When an air-shaft or escape shaft is supplied with cages or a bucket for hoisting, the sinking tower, or head-frame, may be left in place after

Drifts, Slopes, And Shafts, Part 1 43

the shaft has been sunk. Otherwise, the head-frame is designed for temporary use only. It is usually built of 8"X8" or 10"X12" pine timbers that are mortised and cross-braced, or tied, with heavy iron rods. Fig. 20 shows an unusual form of

sinking head-frame that was used in sinking one of the largest shafts ever sunk; the shaft was 12 ft.X54 ft. in cross-section.

Sinking frames are sometimes built of 2J"X2J" angle iron ; in some cases these are cheaper than those made of timber, as they are put together with bolts and rivets, which can be easily removed with less damage to the parts than in the case of a timber frame put together with mortise and tenon. Railroad

44 Drifts, Slopes, And Shafts, Part 1

rails are laid across the shorter dimension of the shaft mouth midway of its length for a larry track.

Ordinarily, the towers are from 20 to 30 feet high and carry on top a single sheave of from 6 to 8 feet in diameter, so arranged that the bucket will hang in the center of the shorter dimension of the shaft. Instead of using a head-frame, a derrick is frequently used, at least until after the shaft has been sunk through the surface wash.

75. Temporary Head-Frame. — In order that the work of sinking may not interfere with the progress of the per

manent work about and over the shaft, such as the erection of the main tower, or head-frame, and the building of the foun dations for the permanent hoisting engine, buildings, etc., the temporary hoisting engine should be located at one end of the shaft (at the end opposite the manway if possible), as shown in Fig. 21, which gives a side and an end view of a temporary head-frame. This shaft is to be a three-compartment shaft, having two hoisting compartments and a manway. The man way is divided from the hoisting compartments by a close par-

Drifts, Slopes, And Shafts, Part 1 45

tition of heavy timber. The buntons separating the two hoistways are put in later, or when the sinking is completed. In the side view, Fig. 21, the head-frame is shown set on the cross-sills, just inside the main sills, so as not to interfere with the erection of the outer posts of the permanent head-frame. By this arrangement, the hoisting of the excavated material may continue uninterrupted while the permanent head-frame and buildings are being erected.

The waste material hoisted out of the shaft is dumped about the shaft frame and about the foundations of the permanent

machinery and a level surface is thus gradually built up. If the ground slopes away rapidly from the shaft, it may be necessary to build a trestle for the larry track. A smaller car is sometimes placed on a larger truck and run out on a trestle at right angles to the main dumping trestle.

46 Drifts, Slopes, And Shafts, Part 1

76. Ventilation. — An air-shaft of boards is erected over the manway at the surface, as shown in Fig. 21 ; this serves the double purpose of protecting the manway and ventilating the shaft, as a natural current is produced in the shaft. The parti tion separating the manway from the hoistway should be kept close to the bottom of the excavation. If this does not pro vide sufficient ventilation, a steam jet or small blower, such as is used in a blacksmith's forge, may be used.

77. Manway or Pumpway. — When the small compart ment at the end of the shaft is used as a manway, it is

Fig. 23

equipped with stairways. Fig. 22, inclined ladders, Fig. 23 (a) and ( b ), or vertical ladders. The mining law in some states provides that such stairs or ladders shall not have an inclination steeper than 60°, and that proper landings shall be made at the top and bottom of each flight of stairs. Vertical ladders are particularly dangerous. The ladders are sometimes arranged one above another, with a suitable staging or plat form connecting the top of each ladder with the foot of the

Drifts, Slopes, And Shafts, Part 1 47

next ladder above, all the ladders being inclined in the same direction, Fig. 23 (a) ; sometimes they zigzag across the shaft, the foot of one ladder being placed alongside the top of the ladder below it, as in Fig. 23 ( b ).

Methods Of Lighting And Drainage

i 8. Lighting:. — As sinking operations are frequently con tinuous, day and night, some good form of artificial light is essential at the top as well as at the bottom of the shaft ; water proofed incandescent lamps are most satis factory. A group of these protected by a metal basket forms by far the most conve nient method of light ing the bottom, as they give ample illu mination and can be easily hoisted out of the way during blast ing and can also be easily run up and down the shaft for an examination of t h e timbering. Electric lights do not load the air with the impure fumes that come from the ordinary miner's lamp, especially where kerosene oil is burned. Also, the water dripping down the shaft causes an incrustation to form on the wick of a miner's lamp, which must be removed constantly in order to maintain a good light. The top of the shaft should be provided with a strong and steady light, and for this pur pose a protected lamp or lantern with a good reflector should be used.

Fig. 24

48 Drifts, Slopes, And Shafts, Part 1

79. Drainage. — Surface water is kept out of the shaft by banking about the shaft sill the clay and other material taken out during the sinking. The water pumped or hoisted from the shaft is carried away in tight wooden troughs that lead in the direction in which the surface dips, and extend far enough from the shaft to prevent the water from returning. During the sinking, a hole, or sump, is excavated at one end or in the center of the shaft somewhat in advance of the general work. The water is either bailed out of this hole and hoisted in buckets, or a sinking pump of special form is employed. These pumps may be hung by hooks from the timbering, as in Fig. 24, at any point or simply hung by ropes, and may be hoisted and lowered as desired. Instead of a special sinking pump, a small horizontal pump of ordinary pattern is often set up on a temporary staging, which is moved downwards as the work advances. Either of these pumps is connected with the steam and water pipes in the manway by short lengths of wirewound rubber hose.

Drifts, Slopes, And Shafts

Serial 846B Edition 2

Work Of Sinking

Preparatory Work

1. Supply of Material and Appliances. — Before the actual sinking of the shaft begins the preparatory work is of vital importance. All materials and appliances that are liable to be required, or at least a sufficient supply for immediate need, should be on the ground and ready for use before the excavation work is begun. Prospect holes or shafts located in the vicinity, as well as a geological cross-section of the tract, will give the needed information about the character of the strata to be penetrated. These data will also help to determine the kind of material and appliances that will be required.

2. Position of Shaft. — A suitable site for the shaft hav ing been selected and a plan of the surface tracks and connec tions having been submitted, and approved by the railroad company, the exact position is staked out by driving eight stakes a, b, c, d, e, f, g, h in line with the ends and sides of the shaft and outside the area likely to be disturbed by the sinking operation, as shown in Fig. 1. These stakes are located with a transit so that the lines a d and h e are parallel and at a dis tance from each other equal to the width of the shaft. The lines b g and c f are also parallel to each other and at right

Copyrighted By International Textbook Company. All Rights Reserved

50 Drifts, Slopes, And Shafts. Part 2

angles to the lines a d and h e. The distance between the lines b g and c f is equal to the length of the shaft. If cords are

stretched between opposite 9® stakes so as to occupy posi

tions as indicated by the dotted lines, the points of in tersection i, 2, 3 , 4 indicate the four corners of the shaft. By measuring the distances a i, b i, c 2, d 2,

If the shipping tracks are near the shaft, the long side of the shaft should be made, as nearly as possible, parallel to these tracks. If the seam to be developed is inclined, the long side should be, as nearly as possible, parallel to the line of dip of the seam.

3. Shaft Templet, or Sill. — After the shaft has been staked out, shallow trenches are dug on each end line in which are laid the end sills, or cross-sills, which extend from 6 to 8 feet outside the shaft line on each side. Similar side sills, or main sills, are then laid across the end sills ; these ex tend from 4 to 5 feet beyond each end line, as shown in Fig. 2.

These timbers are usually of carefully selected 12"X 12" or 12"X16" oak. Square boxings from J inch to 2 inches deep are cut in the upper faces of the end timbers and in the lower faces of the side timbers and a drift pin is inserted at each corner

Drifts, Slopes, And Shafts. Part 2 51

to pin the sills together. The length of the long tim bers between the notches, or boxings, is equal to the clear length of the shaft, and that of the cross-timbers between the notches is equal to the clear width of the shaft, so that these timbers form a templet for the size of the shaft in the clear for all future excavation. When these timbers are laid in position, instead of being laid in trenches or on the surface of the ground, the sills are frequently raised and clay dumped about them to a sufficient height to prevent surface water running into the shaft. The timbers thus raised are supported on blocking and carefully leveled and squared. The work of sinking and the methods of timbering vary greatly according to the character of the ground and will therefore be treated under separate headings.

Sinking Through Ground That Does Not Run

4. First Stage of Excavation. — The excavation is started with pick and shovel by throwing the material from within the timber frame or sills. The earth is excavated a sufficient distance from the face of the timbers all around the shaft to allow the face of the shaft lining to be set flush with the face of the sills. The face of the timbers is the ex posed surface on the inside forming the face of the shaft when timbered ; the surface against the strata is called the back of the timbers. The excavation is carried down without timbers to support the side and end walls, as far as is considered safe, when the work is squared and the curb ing, or shaft lining, put in place. The depth thus excavated without supporting timbers will depend on the nature of the ground and will vary from 6 to 20 feet. With a long-handled

52 Drifts, Slopes, And Shafts, Part 2

shovel, a man can generally throw the dirt to the surface from a depth of 10 feet, after which a temporary staging must be erected, similar to that shown in Fig. 3, on which the dirt is thrown and thence to the surface. The pick used is the ordinary heavy dirt pick with wide point, while the shovel is the round-pointed D-handled shovel ; when the material is thrown to a considerable height, a long-handled shovel is used. Wedges may be employed for wedging loose sandstone and slate from the bottom and for trimming the sides and ends of the excavation, but no powder is used. The walls and corners of the shaft are neatly trimmed and carefully watched for any sign of yielding, as the excavation must not be carried unsupported far enough to cause any caving,

bulging, or weakening of the ground about the head of the shaft.

5. Plumbing: the Shaft. — As it is important that the shaft be kept verti cal, a plumb-line b c, Fig. 4, is usually suspended from each corner of a rectangular shaft, or from the center of a circular shaft. It may be hung from a block b , spiked in the corner of the sills, or from a cast-iron plate about 1 foot square screwed on one of the sills at one corner, the plumb-line passing through a small hole in the plate. It is arranged so as to hang 4 or 6 inches from the face of the shaft timbers. In excavating the earth, or in setting the shaft lining, measurement is made from these lines, allowing, when excavating, for the thickness of the wall ing or timbers forming the shaft lining. Thus, if the plumblines are hung 4 inches from the face of the shaft, and the thickness of the shaft lining is 6 inches, a measurement of 10 inches will clear the timbers. It is customary, however, to allow about 2 inches behind this to insure clearance at all points, as time is saved in the setting of the timbers by so doing.

Drifts, Slopes, And Shafts, Part 2 53

G. Lining' the Shaft. — In lining the shaft, the walling, or timbering, is often built up in sections from the bottom of the excavation as the sinking progresses, the space behind being filled with sand or other fine material that will distribute the pressure evenly over the lining. In wet strata, the space behind the walling should be well rammed with clay to prevent the inflow of silt or fine sand between the timbers. Except when sinking in rock, the shaft lining must be kept within

Fig. 5

a short distance of the bottom of the excavation ; this distance depends on the character of the strata, but seldom exceeds 6 or 8 feet except in unusually firm ground. The work of excavating is thus carried on in short stages, alternating with the work of extending the shaft lining.

7. Sinking Through Rock. — As soon as the strata become hard or firm enough to hold the explosive charge, powder is employed and percussive, hand, or machine drills

54 Drifts, Slopes, And Shafts. Part 2

are used, the type of drill depending on the character of the rock. In soft rock, a hand percussive drill is used and a light lifting shot is employed to dislodge the material from its bed. This material is afterwards broken by wedges and hammers or sledges. For this class of work, a slow large-grained powder is required. A quick powder exploded in soft material will find vent by a single rupture of the strata without exerting the lifting force on a great mass of material, as is done when a slower powder is used. If, however, the strata are full of seams and cracks, a small charge of a quick powder is used, since such rock will not confine the explosive force sufficiently

to do effective work when a slow powder is used. In hard rock, dynamite is used, and power drills, operated by compressed air or steam and usually mounted on shaft bars, are emoloyed.

.rase

P/an of //. ft. Cut

Fig. 6

8. Location of Holes. — The general position of the holes and their depth are about the same as described under Tunneling, in Drifts, Slopes, and Shafts, Part. 1. The first shots in a level floor should be inclined at a fairly sharp angle with the floor, and are usually cen tral in the shaft. These holes are often called sumping holes ; their purpose is to start the excava tion by blowing out a wedge-shaped piece of rock from the center of the floor. The holes are generally arranged in series, or rows, on each side of the center and across the width of the shaft, and are spaced an equal distance from one another. The general position of these holes is illustrated in Fig. 5, which also shows the position of the shaft bar on which the drills were mounted. The dimensions given are those that were employed in the sinking of a shaft in a white crystal line limestone. In this shaft, at first, only 6-foot cuts were made, a single series of shots excavating the material to this

Drifts, Slopes, And Shafts, Part 2 55

depth. The depth of the cut, however, was afterwards greatly increased by boring the side holes deeper, as shown in Fig. 6, until the cuts averaged 11 feet, six successive cuts excavating the shaft a depth of 66 feet.

9. Method of Drilling, Charging, and Firing Holes. — An example taken from the southeastern Missouri lead region illustrates the sinking of a 6'X18' shaft in lime stone of varying hardness. The position of the shaft bar on which the drills were mounted is shown at a, ax, a2, b , bl9 b2, in the lower view of Fig. 7, which is a sectional elevation, the upper view being a plan. The two center rows of holes, I, or the sumping holes, were drilled first, and each hole filled with from five to seven -§-pound sticks of giant powder or dynamite, con taining 50 per cent, of nitro glycerine. The depth of the holes varied from 3J to 6 feet.

Beginning at the center, the suc cessive rows of holes, marked j, 2 , 3, and 4, respectively, on both sides of the center line of the shaft, were drilled, charged, and fired in pairs, the material being loaded and hoisted between each operation. The end holes required but four or five sticks of 40-per-cent, dynamite apiece; the entire cut of twenty-six holes used from 50 to 60 pounds of dynamite, and excavated the material to a depth averaging from to 6 feet. The average quantity of 40-and 50-per-cent, dynamite in this material was 12 pounds per foot of depth, or 3 pounds of dynamite per cubic yard of excavation. The sinking was carried on by three shifts of four men each, and the record of the sinking showed a depth of 100 feet in 30 working days.

56 Drifts, Slopes, And Shafts. Part 2

The record of the sinking of a shaft at Rossland, British Columbia, shows an average of 25 pounds of dynamite per foot of depth in a shaft 9 ft.X20 ft., or practically 4 pounds of dynamite per cubic yard of material excavated ; the rock in this case was a hard, igneous formation composed mostly of diorite. These examples illustrate the practice of sinking in rock in different localities.

b

'*1

f

9a

9b

aJ

Fig. 8

10. Tlie Long-Hole, or Continuous-Hole, Method.

As in sinking in rock much time is ordinarily lost in drilling, and as machine drills cannot work close to the sides, ends, or corners of the shaft, the continuous-hole method is sometimes used. By this method, a number of diamond-drill holes are put down at definite distances apart, and from 100

to 300 feet deep, over the area where the shaft is to be sunk. They are arranged in rows, from 3 to 4 feet apart, with the outside rows close to the sides and ends of the shaft, so that they will nearly square it up and save much digging and trimming. They are then filled with sand or water, preferably the former. The sinkers prepare for the work of blasting by removing 3 to 4 feet of the sand from the holes and filling this space with explosives, which are tamped and fired.

Fig. 8 shows how the holes are arranged. The holes marked a are first cleaned and fired to give a loose end to the holes b on the outside, which are next cleaned out and fired. This work is continued until the bottom of the hole drilled by the diamond drill is reached, when another series of long holes is drilled.

This method probably originated from one that is sometimes used in the coal fields of the Central Basin. The shaft is sunk about the diamond-drill hole that was drilled for prospecting purposes. The sinkers charge a section of the hole, using a false bottom, and blow out a center cut.

Drifts, Slopes, And Shafts, Part 2 57

11. When shafts are sunk to workings already opened, a diamond-drill or churn-drill hole is sometimes put down into the open works below, and this hole kept open during sinking, thereby avoiding all hoisting of water. A long chain is used to clean out the hole when it becomes stopped up.

Both this plan and the long-hole plan are apt to cause crooked shafts on account of the divergence of the drill hole from the vertical. The advantages of the long-hole system are that sinkers need not wait while holes are being drilled ; and blasting can be done as soon as debris from shots is removed. The method is said to be very much quicker than the ordinary prac tice of using power drills driven by air or steam, but is more expensive.

12. Shaft Lining-. — Timbering is usually not required for securing the sides of the excavation when sinking in hard rock. Cross-buntons to support the cage guides, pipes, wires, etc. are set in hitches in the face of the rock, and are spaced 6 or 8 feet apart. They are carefully lined and placed verti cally over each other and then tightly wedged. In sinking through soft shale or loose crumbling rock, a greater amount of timber is needed for securing the sides. The sides are trimmed with the pick ; and when the material is dry, a closefitting lining of 3-inch or 4-inch planking is sufficient, the thick ness of the planking increasing with the depth of the excava tion. In wet material, 4-inch timber should be used at the surface, 6-inch at 100 feet, and 8-inch at 200 feet.

13. Sinking in Swelling Ground. — Clay or marl that swells when brought in contact with air and water is difficult to excavate and support. There is no timbering that can resist this swelling; it will burst any timber or break any frame that can be put in. In sinking a shaft or a slope under such conditions, the strata should be excavated for a certain depth back of the lining so as to give a good clearance between the formation and the lining all around the shaft. This space should be so arranged that a man can enter it and clear it from time to time as may be required. Drainage should be provided by cutting, in the hard pan or floor underlying such strata.

58 Drifts, Slopes, And Shafts. Part 2

a ditch connected by a pipe with the sump at the foot of the shaft. A good circulation of air should be made to travel around the space thus excavated so as to keep the clay as dry as possible.

The method of sinking through such ground does not differ materially from that used in other loose ground or rock, but the timbering of the excavation is of great importance.

Sinking Through Quicksand Or Running Ground

14. Nature of Quicksand. — Quicksand is sand that is so impregnated with water as to be semiliquid and therefore shifting and easily movable. Instances are on record where beds of quicksand were practically continuous for a depth of 75 feet, and as the semifluid material is often under great pressure, it sometimes bursts forth with great violence as the excavation approaches it, giving the sinkers barely time to escape. The bottom of the excavation may fairly boil, while the fluid material may rise several feet in the shaft. In differ ent localities, as in the Wyoming Valley of the Pennsylvania anthracite region, and in Central Illinois, these deposits occur in buried valleys of considerable extent, and sinking shafts in them by the ordinary methods is impossible. These conditions render sinking extremely hazardous, especially when they occur at a depth of from 50 to 100 yards below the surface.

15. Precautionary Measures. — The risks involved in meeting deposits of quicksand make it all the more important that the strata should be thoroughly prospected previous to sinking, and in localities where such deposits may be expected it is particularly important to have on hand an ample supply of the materials required during sinking. Timber of different sizes should be framed and ready for instant use, and pumps and piping of the proper kind and capacity should be on hand. Eight or ten pointed pipes, with perforated ends, are some times driven into the sand 6 or 8 feet apart and connected at their upper ends to a suitable pump. In some cases, a few hours' pumping draws off the water and the boiling sand settles

Drifts, Slopes, And Shafts, Part 2 59

and solidifies so that it may be removed with a shovel. Water can sometimes be drained from the soft ground within the area of the shaft into wells or small temporary shafts sunk adjacent to the larger shafts, thus leaving the sand within the shaft area compact and easily removable by shoveling.

16. When the watery sand is thus drained, there is a con siderable decrease in volume of the material surrounding the sides of the shaft ; the shaft lining is thus frequently robbed of all supporting material for a considerable distance up the shaft and begins to separate and sag, while the shaft may be swung out of line. This decrease in volume, or displacement of the strata, due to the draining off of the water, may be carried to such an extent that the surface of the ground will sink several feet over a large area surrounding the shaft. In removing the water, a large amount of sand is also removed ; the effect of its removal is often not appreciated until too late. The sand contained in the water will often cut out the pump linings in a short time, and render the pump useless ; but if a layer of straw or other light material is thrown into the shaft, it will form a mesh by which the sand will be largely filtered from the water.

The methods to be adopted when sinking through such mate rial are particularly methods of timbering, or supporting, the sides of the excavation; and the excavation must be kept timbered close to the bottom of the shaft. There are, however, certain methods of sinking that are particularly applicable to such ground, as follows: the use of cement, piling, forepoling, the use of shoes, the pneumatic process, and the freezing process.

17 Consolidating- Sand with Cement. — The shifting sand or loam in water-bearing strata may be consolidated by injecting powdered cement -into the soft ground by means of compressed air, steam, or water under pressure. The cement is first screened in order to free it from lumps, and the powder is taken by an injector that forces it through a flexible pipe into a perforated tube sunk in the soil to the required depth.

60 Drifts, Slopes, And Shafts, Part 2

18. Sand Beds Excluded by Piling:. — A bed of quick sand or other soft material lying near the surface is often best treated by piling. If the bed is shallow, it may be sufficient to drive a single set of piles all around the site of the proposed shaft. Where thicker beds of quicksand occur, it may be necessary to drive several series of piles, each successive series being driven inside the former after the material has been excavated to a point near the bottom of the first piles driven. The second set of piles having been driven, the material within these is excavated to a point near the bottom of the

piles, and, if necessary, a third set of piles is driven within the second. This method is illustrated in Fig. 9.

After the first set of piles a has been driven, they should be supported against external pressure, as the material is excavated from the space they enclose, by timber frames or timber sets at their top and middle. It is important that these frames should be set promptly and braced by cross-buntons supported by punch blocks e. As will appear from the illustra tion, it will be necessary to set the first sets of piles a sufficient distance back from the shaft to allow for the decreasing dimen-

Drifts, Slopes, And Shafts, Part 2 61

sions of the excavation, as each series of piles is driven. The required distance is easily calculated when the depth of the sand bed is known, and this information has already been obtained from the drill hole t.

19. In some cases, the soil at the surface may be firm for a considerable depth, but underlaid by a flowing bed of quick sand. In this case, the excavation of the overlying soil may be done in the usual manner, and after this is lined or curbed

Fig. 10

the piles may be driven from the foot of the excavation in the same manner as from the surface. In this system of sinking through watery strata, the permanent shaft lining is built up as soon as the rock is reached. The space between the shaft lining and the piles is then filled with clay, where this can be obtained, or the timbers are backed with a sufficient thick ness of cement, and this, in turn, with the material excavated.

62 Drifts, Slopes, And Shafts, Part 2

20. Forepoling in Quicksand. — The method of forepoling, described under Tunneling in the preceding Section, may also be applied for sinking through quicksand, as shown in Fig. 10. Strong timber sets j are framed to the sides of the shaft. As each set is put in, it is suspended from the next one above, as the set a, by light strips, or lath, /, while the punch blocks b are set between the frames to hold them apart. Twoinch planks with the ends sharpened are used for the spiles k , and are driven downwards in an inclined position behind the lower timber set. Before driving the spiles, the tail-pieces C are spiked to the lining just above the lower timber frame; the spiles are then driven as the excavation advances until their

tops reach this tail-piece. An other set of timbers is then placed in position at the floor and tied to the timbers above, and the same operation repeated, driving the spiles and excavating the material as rapidly as pos sible. This process of forepoling may be carried on at any depth below the surface where the strength of the timbers will resist the pressure of the sand.

21. Another method of forepoling, adapted to a greater depth below the surface and a greater thickness of sand, is illustrated in Fig. 11. This method is similar to that last described, except that the spiles are driven in at a greater inclination. The timber frames, however, are placed somewhat closer and no tail-piece is employed, the tops of the spiles bearing against the timber above instead of against the tail piece.

22. Fig. 12 illustrates the use of breast boards where the bottom has a tendency to rise and fill the shaft, and must be planked to keep it down. The material is removed a little at a

a

Drifts, Slopes, And Shafts, Part 2 63

time. A sump is carried ahead of the regular excavation, as shown, by driving short piles and putting in a small frame. The work is slow and tedious, and requires great care and caution.

23. In another system of forepoling interlocking channel bars are used in the manner shown in Fig. 13. In this system the shaft is started with dimensions that are 2 feet larger each

Fig. 12

way than the size required, and is sunk in the ordinary manner down to the sand; thus, an 8'X16' shaft must be started as 10 ft.X18 ft.

As seen from Fig. 13, the sides of the lining are composed of channels a and b alternately facing inwards and outwards. The channels a have Z bars c riveted to them, which engage and interlock the edges of the channels. The channels b have angle irons d riveted to them, thus forming grooves in which the sides of the channels a run. The corners of the shaft lining are made of three angles e riveted together, as shown, which interlock with the side and end channels a by means of the Z bar riveted to a. Heavier sections can be

64 Drifts, Slopes, And Shafts, Part 2

used, which would make the thickness of the metal about i inch. When sand is reached, these channels are set plumb in a solid frame inside of the shaft lining, and are driven vertically downwards through the sand to the solid material, if possible, before any sand is excavated. No one channel should be driven more than 2 feet ahead of the rest. A perfect fitting anvil, or clinker, is used to protect the head of the channel bar while driving. Channels 12 feet long are readily driven their entire length into the sand.

24. Channel sheathing can be driven in varying depths by feeding in pieces from the top, thus driving the preceding

Fig. 13

one down, in the same manner that a follower is used in driving piling. The individual members, engaging and interlocking, slide on each other so that one can be driven at a time, and thus afford an opportunity to drive channels all around a boulder, should one be encountered. The channels interlock nearly water-tight, and, by cementing above and below them, the water may practically be shut off. The channel lining may be assumed to be 5 inches thick, while 6 inches should be allowed for the timber. The channels are either left as a permanent lining or they may be drawn after a timber lining has been laid. They are cheaper than steel shoes , or drums, subsequently described.

Drifts, Slopes, And Shafts. Part 2 65

25. Shoes for Shaft Sinking. — The iron or wood structure known as a shoe has in its various forms been well known for many years to engineers and contractors in con nection with excavating work. It consists of a frame corre sponding in shape to the cross-section of the shaft. Attached to its bottom is the cutter, which is of steel and beveled so that it will sink easily into loose ground. The shoe is usually open top and bottom, but sometimes so arranged that the top can be closed tightly with steel plates, to resist the sand pressure

Fig. 14

from the shaft bottom. The upper part of the shoe is outside the shaft lining from 12 to 16 inches, and the lower part is usually divided into compartments by braces that brace the sides and ends.

In principle, the plan of sinking by a shoe is similar to the method of tunneling in soft ground with the use of an advance shield, except that shaft shoes, in America, are usually rec tangular in shape, while the shield in tunnel driving is cylin drical. As the material is excavated from beneath the shoe,

66 Drifts, Slopes, And Shafts, Part 2

the shoe drops by its own weight or on account of pressure applied to its upper surface by weights laid on it or by means of jacks, generally the latter, thus walling back the sand while the lining is being put in place. Only enough material is excavated from underneath the shoe and it is moved just far enough ahead to permit the placing of one set of timbers at a time; if planks are used for the shaft lining, they are put in flatwise. The shoe should descend uniformly at all points, and should be carefully leveled before the timber is placed.

26. Fig. 14 shows the plan and elevation of a steel shoe that is quite commonly used. It is made of f-inch steel boiler plate braced as shown, has a height of 30 inches under the shaft timbers, and a sheet-iron lap 18 inches deep extending outside of the timbers. Fig. 15 shows it in position at the bottom of the shaft, as well as the manner of supporting it and controlling its descent. Four hooks, or claws, are provided, which may be screwed into the lower coupling c, Fig. 16. To each of these hooks is fastened a strong chain attached to the frame of the shoe, as shown in Fig. 15; by this means, the downward progress of the shoe is controlled, and there is less liability of its becoming wedged.

One of the disadvantages of using the shoe is the fact that it is apt to be stopped by boulders, clay seams, or other obstruc tions, one part remaining stationary while the other goes down, thus throwing the shoe out of level and wedging it so tightly that it cannot be moved, and causing the shaft to be thrown out of line. Sometimes the shoe is tipped to such an extent that it has to be abandoned. By means of the chains shown in Fig. 15, this difficulty is partly overcome, as by their use the shoe can be held stationary until the obstruction is removed. The chain may also be slacked at any time to allow the shoe to move.

The cross-beams of the shoe frame furnish also a good sup port for the planks that are used in the shaft lining. As the shoe is lowered through a distance of 2 inches, corresponding to the thickness of a plank, the latter is slipped into place and spiked upwards from beneath, 40-penny nails being used for

Drifts, Slopes, And Shafts. Part 2 67

this purpose. The jacks for forcing down the shoe are shown in position in Fig. 17.

The shoe is sometimes forced downwards by the weight of the lining, if this rests directly on top of the shoe instead of hanging from the top of the shaft. The lining is then built from the surface by adding set on set, the increasing weight gradually forcing the shoe through the soft material.

27. Lining- Suspended From Surface Frame. — One of the chief difficulties encountered when sinking through sand

Fig. IS

beds of considerable thickness is the tendency of the shaft lining to settle and draw apart in places, accompanied also, very often, with a deviation of the shaft from a vertical line. This is caused by the removal of material from the strata sur rounding the shaft, due either to the running character of the material or to the removal of the water in the sand by pumping

68 Drifts, Slopes, And Shafts, Part 2

or by drainage. As the lining is robbed of its means of support, it will either settle vertically or move laterally, as a result of an excess of pressure on one side. To remedy this, the lining is often hung from a strong frame at the surface or at some point in the shaft where a firm foundation can be obtained.

28. In Fig. 15 the lining is shown suspended from a frame or trussed beam at the surface, by means of steel rods coupled to each other in lengths of 10 feet, and supporting at each coupling a cross-bunton on which rests the intervening lining. The rods may be of any convenient length until the sand is reached, when their length should be about 10 feet.

The diameter of the rods may vary from 1J to inches, according to dis tance from the surface, the size decreasing with an increase in depth of the shaft. The lower end of each section of the rods is passed through a hole in a crossbunton b, Fig. 16, and an iron bearing plate, or washer, a, is placed over the end of the rod under neath the bunton. A screw coupling c is then fitted to the end of the rod and screwed in place. This coupling furnishes the support for the next section of rod below, which is not, however, put in position until the excavation has reached the point where another cross-bunton is required. Until this time, the timbers of the shaft lining are supported by strips of lath nailed to their face, or by being spiked together from under neath when flat planks are used.

29. As an example of a suspended shaft lining the case may be cited where a sand bed 50 feet thick was encountered 60 feet below the surface. For the purpose of supporting the lining, four crucible-steel suspension rods capable of sustaining

Fig. 15

Drifts, Slopes, And Shafts, Part 2

a safe load of 132 tons (using a factor of safety of 5) were

used, one in each cor ner of the shaft; the length of the first set of rods was 20 feet, while all the other sections were 10 feet each. The diameter of the rods in the four upper sections was 1$ inches, that of the three next lower sec tions If inches, while that of the last three sections was If inches. By this means, the hard pan was reached at a depth of 110 feet from the surface. The frame from which the rods sup porting the lining were hung was made of 12"X 12" and 12" XI 6" timbers bolted together by drift pins to form a truss, as shown in Fig. 15.

A good frame is at least 3 or 4 feet high, and should extend from the shaft to solid ground so as not to be affected by any move ment at the surface due to shifting sands, as before described. It should be strong enough and sup ported in such a manner that it can carry the weight of tower

70 Drifts, Slopes, And Shafts, Part 2

and sheaves, as well as the lining, if necessary, although the tower should not be placed on the frame if it can be avoided.

30. The simple frame, shown in Fig. 15, is built directly on top of the shaft. The more elaborate one, shown in Fig. 17, in elevation and section, is constructed as follows : A 30 ft.X50 ft. platform of 2-inch plank a is first laid on the surface above the shaft. On top of this and running parallel to the long side of the shaft are steel rails b (about 60 pounds), which form the foundation of the solid timber trusses. Each truss shown is made of eight pieces of 12"X12" timber, the bottom piece c being 48 feet long and the next d 4 feet shorter,

and so on to the top one e, which is 20 feet in length. Across these trusses are placed two 16"X16" tim bers f, each 20 feet long; through these timbers and near the inside of the shaft walls pass the rods g, cf from which the lining is suspended. In this case, these rods are connected by couplings h, shown in detail in Fig. 18. The rods hold the lining by means of castings a fastened to it by means of lagscrews. The shoe, Fig. 17, is hung from the rods by the chains k and the swivels /.

31. Triger, or Pneumatic, Method.— Occasionally, a method of sinking is used for shafts and tunnels that is an adaptation of the caisson method, used in bridge work, and is known as the Triger, or pneumatic, method, as it was successfully applied by M. Triger, in France, a number of years ago. It has but rarely been used for sinking mine shafts and it is necessary, therefore, only to give the principle on which it is operated. In this method, a cylinder of cast iron, made by successively adding one ring to another at the surface, is made to sink slowly into the loose ground, either by its own

Fig. 18

Drifts, Slopes, And Shafts, Part 2 71

weight, by weights piled on top of the cylinder, or by means of pressure applied through jacks. In order to keep out the water from surrounding strata, compressed air is led into a closed chamber at the bottom of the iron cylinder, the pressure of the air being kept just sufficient to prevent an inflow of water and loose sand. This chamber forms the working space in which the material is excavated ; above it, and connected to it by suitable trap doors, is another closed space, known as an air lock. This air lock, by means of trap doors above and below, gives a means of communication between the working chamber and the surface. A person enters it through the upper trap door; after closing this door he allows the compressed air from the working chamber to enter, by means of suitable valves, until the air has reached the same pressure as that in the working chamber or caisson ; the lower trap door, which leads into the caisson, is then opened and he descends into the working chamber. In order to leave the caisson, the opposite procedure is adopted.

The excavated material can either be removed through the air lock, or it can be blown out through a pipe by means of air pressure after being mixed with water. If only a few boulders are found during the sinking, they are carried down in the caisson and are hoisted out after solid material has been reached and the roof of the caisson cut away. If many boulders are encountered, they must be blasted and the pieces hoisted out through the air lock. In some cases, the metal casing on top of the caisson forms a sufficient lining for the shaft; in other cases, it is necessary to build a lining of timber or metal inside of this casing.

32. Poetscli and Gobert Freezing Processes. — If a sufficient thickness of the fluid material of a sand bed is frozen to form a substantial wall about the proposed shaft, it is possible to excavate the enclosed material. Surrounding the shaft, a series of holes, Fig. 19, from 6 to 10 inches in diameter, are bored through the sand bed and cased with ordinary well casing; or if the sand is very fluid the casing may be driven through the sand. These holes if bored from the surface are

0 O

Oo0O00Oo

G

-e-

B

Fig. 19

Drifts, Slopes, And Shafts, Part 2 73

usually vertical, but if bored from a point in the shaft a few feet above the bed of sand, they are inclined as illustrated in Fig. 19. They are not more than 3 to 4 feet apart, in order to insure the thorough freezing of the sand between them. Inside these casing tubes, smaller ones, usually about 4 inches in diameter and closed at the bottom, are let down to the solid stratum, and the outer temporary casings withdrawn. The 4-inch tubes are closed at the top with metal cap pieces, and each contains a 1-inch tube that extends almost to the bottom. The 1-inch and the 4-inch tubes are connected at the surface to circular mains, each vertical tube being fitted with a screwdown stop-valve so that it can be cut off from the main.

33. The Poetsch system is distinguished from the Gobert system by the character of the freezing medium. The former uses a brine consisting of a solution of calcium chloride (or magnesium chloride) passed through a cooling machine on the surface, where its temperature is reduced to about 8° F. below zero. The solution of chloride of calcium is pumped through the smaller tube to the bottom of the hole, and then rises through the larger tube to the surface. In this process, the material is frozen first and hardest at the bottom where the greatest pressure is. Since this freezing mixture is much heavier than water, the pressure inside the pipes is greater than that outside, so that there is a tendency to burst the tube con veying the freezing solution, thus allowing it to escape into the sand outside and rendering it incapable of being frozen.

34. In the Gobert system, anhydrous ammonia is sent down the inner tube (which is then usually made of copper) and allowed to vaporize in the tubes, thus freezing the ground directly instead of allowing the ammonia to cool a mixture that freezes the ground indirectly, as in the Poetsch process. The ammonia gas is drawn off by a pump and reliquefied by com pression and used over again. As the pressure is less inside than outside the tubes, if a leak occurs in the tube any water entering will be immediately frozen and the leak thus stopped.

The .pipes may be driven well outside of the intended shaft area and a wall of earth frozen around the shaft, the central

74 Drifts, Slopes, And Shafts. Part 2

portion or shaft area being removed before it is frozen. In most cases, however, the ground has to be frozen solid and then blasted as though it were rock.

Kind-Chaudron And Lippman Systems

35. Kind-Chaudron System. — This system is appli cable only to circular shafts, and is adapted to sinking through strata with heavy feeders of water that render the work of sinking by ordinary methods wholly impracticable. The exca vation is carried down to water level by the ordinary methods of sinking, and the shaft is lined to this point with timber or masonry. Boring is then commenced by means of a large trepan, or rock-drilling tool, suspended in the shaft. The diameter of the excavation to water level must be sufficient to allow for the thickness of the walling, or timbering, so that the latter will not interfere with the use of the trepan for sinking below this level. The excavation is effected in two or more successive operations. The first trepan used cuts a hole in the center of the shaft from 4 to 5 feet in diameter; this is called the guide pit and is kept at least 35 feet in advance of the second cut, which is made by enlarging the guide pit by means of a special trepan. During the entire boring, the water is allowed to accumulate in the hole, which often stands full, and the boring is done underneath the water.

36. The first trepan, which is shown in Fig. 20, consists of a head a made of wrought iron and provided with steel teeth b on its under surface. The action of the cutting tool is the same as that of a churn drill. The trepan is suspended in the shaft by means of heavy iron rods attached to one end of a large walking beam at the surface, and the weight is partly balanced by a counterpoise at the other end of the beam. An engine operates the beam, raising the rod to a height varying from 10 to 20 inches and dropping it to the bottom. The trepan is turned by men who stand on a platform built above the level of the water in the shaft. In making this first cut, the hole is cleared by means of a sheet-iron sand

Drifts, Slopes, And Shafts. Part 2 75

Section on A- A

Fig. 20

pump about 6 feet long, which is raised and lowered by the trepan rods.

37. The second cut is an enlargement of the first and is made with a trepan that usually weighs from 36,000 to 50,000 pounds. It is quite similar to the first trepan, being formed of a wrought-iron bar having teeth attached to that por tion that extends beyond the diameter of the guide pit. It is guided by means of a cradle, or iron bar, that fits closely within the ex cavation made by the smaller trepan. The teeth on the large trepan are so set that they cut the bottom of the annular portion sur rounding the guide-bore pit in a conical, sloping surface, so as to allow the fragments and cuttings to roll into the smaller shaft, where they are caught in a sheet-iron bucket previously lowered to the bottom of the guidebore pit. Sometimes it has been found advantageous to use scrapers, which drag around after the trepan and sweep the material down the incline and into the bucket.

76 Drifts, Slopes, And Shafts, Part 2

The excavation having been made of the required size in two or more successive operations, the shaft is lined with iron tubbing, which is built in sections 4J to 5 feet high and added at the top as the whole is lowered from the surface.

To assist in supporting the great weight of the steel tubbing, it is provided with a water-tight bottom in which is a nozzle having a stop-cock by which a sufficient amount of water can be let into the tubbing to sink it gradually. The tubbing

is thus lowered in the shaft till it finally rests on the solid bed leveled to receive it. A special moss packing below the tubbing makes a water-tight joint when the water is pumped out.

38. Lippman System. — The Lippman system dif fers from the Kind-Chaudron system in that the shaft is bored to the desired diameter at one operation by using the cutting tool shown in Fig. 21. The tools are made and the cutting teeth are secured in a manner similar to that employed in the Kind-Chaudron method.

Shaft Timbering

timbering in various kinds op ground

39. Introductory. — In America, shafts are very gen erally lined with timber, hence the terms shaft timbering and shaft lining are often used synonymously. Although the term shaft timbering will be used in the succeeding descriptions, it is to be understood that many of the methods

Drifts, Slopes, And Shafts, Part 2 77

referred to apply equally well to masonry, steel, or any other form of shaft lining.

40. Effects of Local Conditions. — The object and character of shaft timbering vary with the nature of the enclosing strata and with the depth below the surface. Thus, the methods used in rock, in loose material, and in watery or running strata are very different. In a shallow shaft, however, it is not advisable to change the lining to suit changes in the strata, and the thickness is made throughout so as to meet the requirements at any point of the entire depth.

In hard material, only such timbers are introduced as are necessary to furnish support to the guides, pipes, wires, etc. that are carried down the shaft. In loose material, the object of timbering is to give support also to the sides of the excavation. In watery strata, the pressure of the water behind the timber is another point that must be con sidered. Water encountered in the sinking of a shaft finds its way at once to the excavation or follows down behind the lining and collects in the bottom of the shaft, unless kept out by the shaft lining. If the lining is built tightly against the sides of the excavation, so as to impede or stop the flow altogether, the water rises behind the lining to the water level of the strata, and the lining is subjected to a pressure dependent on the head of water. The strength of the lining must be sufficient to withstand this pressure.

41. Water Pressure Against Lining. — In cases where a lining has to resist the pressure resulting from a cer tain head of water, the following formula may be employed. It will determine the thickness of a white-pine lining that will possess a sufficiently high factor of safety to resist the pressure.

Let t thickness of white-pine lining, in inches ;

s clear unsupported span of timber, in inches; d depth, or head, of water, in feet.

Then, t

78 Drifts, Slopes, And Shafts, Part 2

It must be remembered that the water rarely, if ever, heads to the surface, hence the head of water supported by the curbing does not mean the depth of curbing below the surface.

Note. — While this formula seemingly applies only to white-pine timber, the same formula will give results that are practically correct for the other timber used in shaft linings.

Example— Find the thickness of white-pine curbing required for a coffer dam when the depth of the water head is 100 feet, the clear span of the end plates of the shaft being 7 feet.

Solution. — Substituting the given values in the formula, f=.016 (7X12) \/100= 13.44; hence a 14-in. timber would be used. Ans.

42. Material of Lining. — Yellow pine was formerly thought to be the only wood suitable for shaft lining, but on

account of its great cost it has been largely superseded by hemlock, black and white oak, and other woods. An ideal plan would be to have the tim ber cut of proper length and notched or framed before being delivered, but this is not often practicable, and, in general, the timber is framed on the ground by contract at so much per set (a set being one horizontal layer of timber of whatever size is used). If the framing is done by day labor, two men are kept busy cutting and carrying timber about one-third of the time, and are employed on drills or at other labor when not framing.

43. Timbering in Rock. — Where a shaft or a portion of a shaft is excavated from hard-rock strata, the only timber ing necessary is the cross-timbers, or buntons, to support the guides in the hoisting compartments of the shaft and the lines of pipes or wires. The buntons b. Fig. 22, are set in hitches h, cut in the rock face and firmly wedged in line, one above the other, by wedges w, w. At times the hitches are cut square and those on one side made deeper to permit the other end of the stick to be placed in the hole opposite.

Fig. 22

Drifts, Slopes, And Shafts. Part 2 79

The buntons are spaced from 6 to 8 feet apart, one above another, on each end of the shaft, and between the several compartments of the shaft. When it is desired to separate the compartments of the shaft, as in the case of an airway or man way, planks are spiked to the buntons or built between them to form the partition.

44. Timbering in Loose Dry Material. — In good ground, shafts have been sunk to a depth of 200 to 300 feet

Fig. 23

by using 3"X12" planking set on edge, but beyond this depth it is better to use 4-inch or 5-inch planks. When an especially soft, wet, or crumbling stratum is met, such as wet sand or fireclay, the planking is sometimes laid flatwise. If the sides of the shaft are not self-supporting and tend to crumble into fragments of varying size ; if boulders that are likely to become detached are found, or if the strata are jointed and faulty,

80 Drifts, Slopes, And Shafts. Part 2

then, in order to preserve the shaft and to avoid accident from earth or rock falling to the bottom from the side walls, it is necessary not only to line the entire excavation with plank, but this planking must be supported by heavy timber sets placed inside the planking as shown in Fig. 23.

The timber sets a are spaced equidistantly and are separated by the posts b. The lagging c, composed of closely fitting planks, may be driven in behind the timber sets, or it may be first placed in position and the timber sets or frames added afterwards. Cross-buntons d are also inserted in each set to separate the compartments. Where a greater strength of tim bering is required than is given by the form shown in Fig. 23,

the sets a may be placed one on top of the other, i. e., skin to skin.

45. An open crib of timbers, similar to that shown in Fig. 24, may also be employed in loose ground, the openings between the timbers being gradu ally filled up com pactly by the loose material. After the timbers have been placed in position, triangular strips, or corner pieces, A are spiked to them in each corner of the shaft. This open crib may be built either from the top downwards or from the bottom upwards.

46. Timbering From Bottom Upwards. — Instead of building the timbering from the top downwards, it is frequently built upwards from the bottom in sections of 10 to 15 feet, depending on the character of the ground. The bot tom of the shaft is carefully leveled with a carpenter's level and straightedge ; and, by measurements made from the plumblines hung from the shaft corners, a set of timbers is placed so that the inside is in line with the edge of the sills, or shaft

Drifts, Slopes, And Shafts. Part 2 81

templet. After the whole set is accurately leveled and joined, wooden wedges are driven between the timbers and earth at each corner. The wedges should be long and tapered through out, and while one man drives the wedge the other holds the set in place with a bar. Great care is taken to get this first set level and in line with the shaft templet, as it is the founda tion for the other sets.

47. After this foundation set has been placed in position and wedged, another set is placed on it and leveled and wedged in like manner. In this manner, the work is continued until the templet or next section of timbering is reached. If the sinker has measured correctly and has made due allowance for the number of sets required to close the distance between the shaft bottom and templet, his sets will close this space exactly. The inside edges of the planking are brought flush with the inside edges of the templet, and iron straps, about in.XJ in.X15 ft., provided with nail holes are hung from the surface downwards, con necting all the planking and suspend ing it from the templet. The straps, or hangers, are placed on the sides and ends of the shaft at distances of 2 to 3 feet apart, and they should break joints vertically as the timbering proceeds. If a small space is left between the last set and the templet and the planking does not close exactly, a closing set is necessary. For this purpose, a regular set is cut down to the required size by the rip saw or adz. How ever, the sinker should make his measurements and calculations so that no closing sets are required.

No cavities should be allowed to remain behind the timbering after it is completed, except in ground that swells. If cavities are found in the strata, or if more earth has been taken out than was necessary, the space must be filled with ashes, straw, etc.

82 Drifts, Slopes, And Shafts. Part 2

48. Timbering* in Swelling Ground. — A form of tim bering often employed in swelling ground is a cribwork of heavy timbers, such as is shown in Fig. 25. These timbers are notched together after the fashion of a log cabin. One side of the timbers may be faced, as shown in the figure, so as to form the face of the shaft, but the back of the timbers is preferably left round. When the ground swells, the material more readily works out between the timbers, and can be removed from time to time, as may be found necessary. An important feature of the work in dealing with swelling ground is to keep the material as dry as possible, since the moisture causes the swelling. In such swelling ground, a space at least 6 inches wide is sometimes cut out all around the sides and ends of the shaft, and filled in loosely with moss, straw,

Fig. 26

sand, or ashes, allowance being made for the probable expansion of the ground. When the timbering, by bulging, shows signs of excessive pressure behind, as shown in Fig. 26 (a), the diffi culty may be overcome by carefully removing two or more planks from the shaft at this point, and excavating such mate rial as may be necessary, all around behind the timbers, as shown in ( b ). The manway .thus formed should be carefully drained by a pipe conducting the water to the sump or other lodgment. This manway should be timbered and cleaned out from time to time, as may be necessary; the bulged timbers of the shaft should also be replaced by good ones.

49. Timbering* in Very Wet Ground or Quicksand.

In wet ground, timbers should be closely joined. At times, it is necessary to make a water-tight joint between each set of

Drifts, Slopes, And Shafts, Part 2 83

timbers to keep the water from entering the shaft; for this purpose, timbers have been laid in cement, but better results are obtained by backing the timbers with cement. A form of timbering that always gives good results, introduced for the first time in the sinking of the Ladd shaft at Ladd, Illinois, is that shown in Fig. 27, which illustrates a section of curbing passing through a stratum of quicksand, and through soft material overlying the same. At a point above the soft mate rial, the 3"X8" curbing plank employed for the shaft lining is laid flatwise, as shown at a, increasing the thickness of the curbing from 3 to 8 inches. When the quick sand is reached, the 8-inch plank is alternated by 6-inch plank, forming the corrugated backing shown at b ; the effect of this rough backing is to clog the drainage that would otherwise find its way down the back of the curbing, and greatly reduces the amount of water entering the shaft.

50. Setting1 Timber in Quicksand. — The chief difficulty in sinking through quicksand is that arising from the flow of the soft material into the excavation before the timbers can be placed in position. To prevent this as far as possible, the excavation should be timbered well down to the bot tom of the shaft. Fig. 28 is intended to give a gen eral idea of the inflow of sand and the method of Fig- 27 setting the timbers. The lower timbers have been set, jacked up, and spiked. Blocks a , used to support the back of the lining, are knocked out by the next set of timbers when it is driven to its place. It is necessary to provide a temporary foundation for the jacks, which in this case is afforded by the sills shown. The form of lining employed is the alternate narrow and wide plank laid flatwise. To reduce the flow of sand temporarily, spiling has been driven between the timbers ; but the spiles must be removed before they throw too much weight on the lining. To support the timber while the jacks under the set are being lowered far enough for a new timber to be placed over them, cleats are spiked on the timbers as fast

84 Drifts, Slopes, And Shafts, Part 2

as each timber set is laid in place. If the timbers cannot be forced into place by hand or driven with a sledge, a jack,

Fig. 28

similar to those shown in Fig. 28, is used, being fastened to a piece of 6"X6" or 8"X8" timber, about 1 foot shorter than the inside dimensions of the shaft.

51. Timbering' a Wet Surface and Subsoil. — It fre quently happens that much annoyance is caused in an other wise good shaft by a large amount of surface water finding its way into the shaft through the drift and subsoil overlying the hard pan. When this is the case, it will pay to enlarge the shaft through the drift and subsoil to the hard pan, and line the excavation in the ordinary manner by light timber

Fig. 29

frames and sheathing plank behind them. The excavation should be carried about 2 feet into the hard pan, in order to

Drifts, Slopes, And Shafts. Part 2

afford an opportunity of making a good water-tight joint, so as to prevent the surface water from finding its way into the shaft. The heavier permanent shaft lining is then built up from the bottom within this enclosure, the space between the two linings being filled with clay well rammed as the timbers are placed in position. This forms a water-tight shaft lining, as shown in Fig. 29. The thickness of the clay should not be less than 10 or 12 inches.

Provisions For Drainage Of Water

52. Water Rings. — In most shafts a certain amount of water collects during the sinking as well as after the shafts are completed. Some water will usually be found flowing over the rock or over the lining.

To draw this water away and prevent the annoy ance due to its constantly running down the shaft, a notch may be cut in the rock about the shaft as shown in Fig. 30, or, if the shaft is timbered, water rings, or curb rings, are built in the lining as shown in Fig. 31. These catch the water as it runs down the rock or lining and conduct it usually to one corner of the shaft, from whence a pipe leads to the sump at the bottom or to a lodgment or coffer dam.

53. Lodgments, or Basins. — Openings varying in height from 6 to 8 feet and of a width equal to that of the shaft are sometimes driven from the end of the shaft. These openings, known as lodgments , or basins , extend from 50 to 60 feet back from the shaft and are intended to serve as receptacles for large quantities of water collecting during sink ing operations. They are, as a rule, constructed on rock or other hard ledges through which the shaft passes. The hard stratum is smoothed and a floor made of heavy timber or

Fig. 30

86 Drifts, Slopes, And Shafts, Part 2

brick laid in cement ; the sides are treated in the same way, and the chamber thus made is arched over ; across the mouth, some 8 or 10 feet from the shaft lining, a dam of timber or brick laid in cement is built, as shown at Fig. 32 (a).

54. Instead of damming in the manner shown in Fig. 32 ( a ), the water may be caught in a basin, as shown at ( b ). An opening large enough to admit a man's body is left in the dam so that the lodgment can be periodically examined. In the opening a pump is erected, as shown in the illustration, and

the water pumped to the surface, the power for the pump being supplied from the surface. As much of the water in a shaft usually comes from within a comparatively short distance of the surface, the use of such lodgments saves pumping from the shaft bottom.

55. Sump. — As shown in Fig. 33, the shaft excavation is always carried far enough below the cage landing at the shaft bottom to provide a catch basin, or sump, large enough to hold the water draining into it from the shaft and from the

Drifts, Slopes, And Shafts, Part 2 87

workings during 24 hours. The depth of the sump will be limited by the suction of the pump, or the depth from which the pump will draw water. If the area of the shaft is not sufficient to afford the required capacity, the sump must either be extended at one end or a second sump provided.

56. Framing* Above Sump. — When the bottom of the shaft is reached and the sump has been made by carrying the excavation several feet below the floor of the seam, a heavy

Fig. 33

substantial frame must be built for the support of the shaft timbers. The cage landing is first made by placing two heavy square timbers a, Fig. 33, under each hoistway. These timbers should be 10 in.X12 in. or 12 in.X16 in., according to the size and weight of the cage, and should occupy a position about under the rails on the cage. They are well bedded in the strata on each side of the shaft, and set low enough to make the floor of the cage, when the latter is resting on the timbers, level with the floor of the landing. When this has been done

88 Drifts, Slopes, And Shafts. Part 2

in each hoistway, heavy longitudinal sills b are laid over them, one on each side of the shaft; cross-timbers c are boxed into

Fig. 34

the sills to keep them the right distance apart and to form a solid frame for the cage landing. Substantial posts d are then set at the corner of each compartment. Heavy caps, or col-

Drifts, Slopes, And Shafts. Part 2 89

lars e are framed to rest on these posts, and cross-timbers / are boxed into these caps above. The whole frame is brought to such a height as will correspond to the height of the heading, and the shaft timbers, or lining, g are made to rest on the top of this frame.

Underneath the cage timbers a heavy planks, not shown in the illustration, are inserted so as to cover the sump to pre vent material from falling in and avoid the necessity of fre quent cleaning. Without a cover, there is also the danger of animals falling into the sump and being drowned before they can be got out. This cover should be so arranged that it may be easily and quickly removed at any time.

57. Coffer Dam. — A coffer dam is a section of solid lining designed to dam back the water coming from a stratum of water-bearing rock encountered in the sinking of a shaft. An example of a coffer dam is shown at k , Fig. 34. At any point where a water-bearing stratum of rock is encountered, sufficient material is excavated from the watery strata to allow a good cement backing to be inserted behind the shaft timbers ; this excavation should be carried a short distance into the underlying and overlying strata so as to form a water-tight joint with each stratum. The space thus excavated is filled with concrete either at the same time that the timbers are put in place or later from an opening left in them. The timber ing is also often made much stronger and heavier at this point. The operation of damming back the water is known as coffering.

Examples Of Shaft Timbering

58. Three-Compartment Shaft. — Fig. 34 shows the general form of construction of a three-compartment shaft, the details of which have already been described. In the illus tration the two near sides of the hard-pan walls are broken away ; some portions of the sheathing are shown removed, and also the near portions of the concrete walling d. This walling is erected through the surface drift and subsoil into the hard pan, so as to form a water-tight joint at this point. The exca-

90 Drifts, Slopes, And Shafts. Part 2

vation was first lined in the ordinary way with timber frames and light board sheeting c, and the concrete d built up between this and the lining of the shaft. At a, a water-bearing stratum of rock was encountered and shut off by the coffer dam k and the concrete filling /. Below this point the ordinary shaft timbering was continued.

59. Shaft Sunk Through Quicksand. — The sinking of a water shaft at Gilberton, Pennsylvania, furnishes a good example of the heavy timbers required when sinking through

quicksand. It was estimated, in this case, that 6,000,000 gallons of water must be handled daily. This required a shaft mea suring 22 ft.X26 ft. 8 in., out to out of timbers. For the first 87 feet below the surface, the shaft passed through a peculiar formation composed of sand, clay, gravel, shale, and boulders, and containing so much water that it resembled quick sand. Fig. 35 is a plan of the timbering near the surface and Fig. 36 an elevation of the timbers, from the surface to the rock. As shown in Fig. 35 and in the upper part of Fig. 36, the timbering consisted of 20-inch round timbers a with 6-inch lagging b on the outside ; 4-inch planking c was spiked to the

Drifts, Slopes, And Shafts, Part 2 91

inside face of the round timbers a, and 12-inch square-timber frames d placed inside of these. Horn sets, or bearing tim bers, e, 28 to 30 feet long, were introduced at intervals of 7 feet, center to center, making a total of twelve sets of these timbers. After the shaft reached rock, at a depth of 87 feet, only the inner lining was used. Several streams of water were tapped during the sinking, and coffer dams were built in the shaft at these points ; the first was at a depth of 157 feet; the second, 250 feet; the third, 379 feet ; and the fourth, 482 feet.

All of these, except the last, were tem porary, being main tained during the sinking only. The last, or permanent, dam consisted of ten sets of 12"X 12" tim ber placed skin to skin, the last set rest ing on the rock, which was dressed to a level bearing or seat, and 1 foot of oakum placed about the bottom of the ring, while the back of the timbers was lined with clay.

92 Drifts, Slopes, And Shafts, Part 2

60. Timber Joints. — Several of the most simple forms of timber joints in common use are shown in Fig. 37. Each one of these has special advantages that make it more or less suitable for different conditions. At (a) is shown a simple square butt joint that requires no framing, but simply the cutting of the timbers to the exact length. The butt joints are made to alternate, as shown. By reason of its cheapness

and simplicity, this form is adapted to shallow shafts where the lining is from 2 to 4 inches thick. The triangular corner piece is spiked in place after the timbers have been inserted and wedged.

61. At Fig. 37 (b) is shown a simple half-and-half box joint made of timbers and capable of resisting heavy side pres sure. The joint shown at (c) is used when the timbers must be sprung into place, as in certain soft strata that are not self-

Drifts, Slopes, And Shafts, Part 2 93

supporting; also, in places where the space for the lining is limited. The joints in adjoining sets are generally made to alternate as in the joint at (a) ; but in some cases this is not done. This arrangement is illustrated in the view at (d), where the timber at the left is supposed to represent a side timber and the other an end timber. The recesses in the side timbers are all in line, vertically, but do not match with the correspond ing end timbers. On the contrary, the latter break joints, horizontally, being dropped one-fourth, one-third, or one-half its width, as at (d), below the corresponding side timber.

G2. A box-and-tenon joint is shown at Fig. 37. It is more expensive to make, but it is capable of resisting a great side pressure ; in this case both the side and end timbers alternate so as to break joints. These timbers cannot be sprung into place, but must be built up.

The joint shown at (/) is similar to that at (c) except that the timbers are boxed half and half, making the end timbers level with the side timbers of the shaft.

63. The form of framing shown at Fig. 37 ( g ) is princi pally used in the portions of shafts that pass through quick sand, where the lining must be kept close to the bottom of the shaft.

An expensive but very efficient joint capable of resisting a great side and end pressure is shown at where one view shows the complete joint and the other the timbers moved apart so as to show more clearly the construction of the joint. At (i) is shown what are called horn sets , or hearing timbers. These consist of a modification of the joint shown at (a), longer timbers being inserted at regular intervals in the lining. Gener ally, the long timbers in each of two adjoining sets are extended so as to project from 18 inches to 2 feet into the strata, giving

94 Drifts, Slopes, And Shafts, Part 2

a substantial support to the lining. The distance between these horn sets depends on the character of the strata. Examples of horn sets are found at e , Fig. 36.

Fig. 39

04. Fig. 38 shows a method of setting the buntons B into the wall plates, or timbers, A. The ends of the buntons rest in grooves cut inch deep in the wall plates, with which they break joints in a horizontal direction.

05. Square-set timbering is adapted to large shafts or where the timbers have to resist heavy pressures. This form

of timbering is wasteful in the use of timber on account of both the size and the quantity of the timber required. The

Drifts, Slopes, And Shafts. Part 2 95

form of the joint is simple, as the timbers are in general, slightly boxed into one another. Fig. 39 shows the general construction in the timbering of a three-compartment shaft by means of square sets. Some of the timbers are omitted or partly broken away for the purpose of showing the form of joint employed. A are the side plates, B the end plates, C cross-buntons, and D posts, punch blocks, or studdles.

66. The joints may be given any of the forms shown in Fig. 40. If the joint shown at ( b ) is employed, the crossbunton shown at (a) must be put in place from below. The advantage of this is that, if the timbering must be kept close to the bottom while sinking, the bunton going in from be low can be left out at first, so as to allow more room for the workmen.

If the side plate is re cessed as at (c), the bunton must be put in from above. In either case the post shown at ( d ) is placed in the recess provided for it on top of the plates shown at ( b ) and (c).

Fig. 41 shows another method of joining end and wall plates, the post F being boxed into the plates at its top as well as at its bottom. In this example, a 2-inch strip N is nailed to the plates on which the lagging is to rest.

67. Numerous other forms of joints are used in square-set timbering, but these will serve to illustrate the aim one should always keep in view, namely, that a timber should not be unnec essarily weakened by cutting away more than is absolutely required in making the joint.

In framing the timbers, regard must always be had to the manner in which they are put together in the shaft. When the timbering is done from the top downwards the sets are kept in position, while being lowered, by means of hanger bolts made

96 Drifts, Slopes, And Shafts, Part 2

of round-iron rods, bent into a hook at one end and provided with a thread and a nut at the other end. By arranging the

bolts as shown in Fig. 42, the various buntons and frame pieces will be held securely between the end and the cross pieces.

Curbs

68. Def i nitions. Applied to coal mining the term curb means a support, or foundation for the lining of a shaft, and is a term commonly used in England in con nection with circular shafts lined with ma sonry. The heavy frame, or sill, at the top of the shaft is also some times called the curb, since in some cases the entire shaft lining is hung from it.

The term curbing is also variously used in different countries and in different sections of the same country, giving rise to much confusion in describing shaft-sinking operations. Thus, in England, this term commonly means the lining that is placed on top of the curb, or shelf, made in the rock as a foundation for the shaft lining. In different parts of America, on the other hand, the terms shaft curbing, shaft cribbing, and shaft lining are used synonymously.

69. Wedging Curbs. — When the solid rock is reached in sinking, the length and the width of the excavation is slightly increased and the top of the rock is carefully leveled off, so as to form a shelf, or curb, on which to rest the lining above. This shelf should not be blasted out, as this will shatter the under rock and make it impossible to make a tight joint between

Drifts, Slopes, And Shafts, Part 2 97

the rock and the shaft lining. A wedging curb a, Fig. 43, made of iron or wood is laid on this shelf, a tight joint between the curb and the rock sometimes being made by means of a layer of cement under the curb and by ramming cement or concrete back of the timbers. If it is not desired to make a water-tight joint between the lining and the rock, a water ring similar to that shown in Fig. 31 is made in the wedging curb. Wedges b. Fig. 43, are placed between the curb and the rock, and on top of

the curb the tubbing c is laid. The tubbing is tightened by means of the wedges d, which are backed by the concrete e.

If a rectangular shaft is to be lined with timber, the wedging curb usually consists of a horn set made of heavy timbers cut longer than the length of the shaft and laid into excavations made in the surrounding strata and on a cement base.

Fig. 44 shows a more elaborate joint between loose ground and solid rock. The timbers a , b, c, d forming the lower

98 Drifts, Slopes, And Shafts. Part 2

portion of the sinking shoe are left in place and the shaft lining e is built up inside of them. A puddling k of clay or cement is forced under the bottom of the shoe or caisson to keep back the running material or quicksand /. Next a grout li of cement and gravel is built against this clay and around the point of the shoe. The space g between the inside lining of the shaft and the grout h is filled in with Portland cement.

70. Supporting: Curb. — It is sometimes necessary to employ what is called a supporting: curb. This consists of a strong wooden or cast-iron curb supported on horizontal bars located in holes drilled in the strata and projecting into the shaft. These bars are in a horizontal plane and furnish the required support for the curb laid on them. The masonry that is to form the shaft lining rests on this curb. This arrangement is generally temporary, and is used when the shaft lining is built in sections.

Timber, 31Asonry, And Metallic Linings

71. Masonry Shaft Lining*. — A lining that consists of brick, rock, or concrete is known as a masonry shaft lining,

and is used where tim ber is scarce or where the character of the strata is such as to render timber lining impracticable. Some times only a section of a shaft is lined with masonry. These linings are usually laid on a wedging curb and are carried upwards in sections, as shown in Fig- 45 Fig. 45. Each section

is laid on a ring a of cast iron or timber resting on a temporary shelf or seat b cut in the rock. As the lower sections are built up, the shelf b supporting the masonry above is cut away in

drifts, slopes, and SHAFTS. PART 2 9

places and the masonry below carried up to furnish the neces sary support for the upper section. In this manner, all the shelf is finally cut away and replaced by the masonry of the lower section.

72. Metallic Lining*, or Tubbing*. — The term tubbing is an English term applied to the metal, and sometimes to the timber, lining of a circular shaft, and is particularly used when such linings are employed to keep water from flowing into a shaft. The three kinds of metal tubbing are:

(1) That which is made in sections with outside flanges and is simply wedged firmly into place by wedges placed between the tubbing and the wall of the shaft; (2) that which is made in sections and bolted together on the inside both at the vertical and horizontal joints;

(3) that which is made up of complete rings of cylinders bolted together by means of horizontal flanges.

The metal tubbing.

Fig. 46 (a), consists of cast-iron segments vary ing'- from 18 to 36 inches

according to the pres sure to be resisted. The segments are flanged at top, pieces of pine are put

Fig. 46

bottom, and between them

as

ends and -|-inch they are put in

100 Drifts, Slopes, And Shafts, Part 2

place, thus making tight joints both horizontally and vertically. To prevent breaking the metal lining by the pressure of air or gas behind it, the metal is perforated ; these holes are loosely plugged, so that any particular pressure coming on them will force out the plugs. Fig. 46 ( b ) shows a method of walling a circular shaft with brick, the brick being laid on a cast-iron wedge curb s.

73. Wood Tubbing-. — Wood tubbing may be of two kinds: (1) Planks, 2 or 3 inches thick, placed vertically and having beveled edges like barrel staves; (2) thick blocks simi larly beveled and placed vertically. Fig. 46 (c) shows an example of plank tubbing. The planks have timber curves m placed inside them and spiked to them. The curves are kept apart by punch blocks n and are tied together and fastened to the shaft sills l by the stringers r. The sections of the shaft ( b ) and ( c ) are shown supported on a rock bench while the metal tubbing is being put in place below. When a shaft has been lined up to the rock bench, this is cut away and the metal tubbing joined to the other portion of the shaft lining by small metal sections called closers.

74. Calculating Thickness of Metal and Masonry Linings. — The following formula is proposed by Mr. W. Galloway for calculating the necessary thickness of a cast-iron tubbing, or of cement or brick lining :

wh d

in which t thickness of lining, in inches;

d internal diameter of shaft, in inches; head of water, in inches;

w— weight of cubic inch of water .0361 lb.;

r=33J per cent, (one-third) of crushing load per square inch of material used.

The crushing strength of the material used should be deter mined in each case by experiment, but the following may be used as a fair average value :

Drifts, Slopes, And Shafts, Part 2 101

Pounds Per Square Inch

Crushing strength of cast ironj . 80,000

Crushing strength of brick laid in lime mortar. . 1,000

Crushing strength of brick laid in cement and

lime . 1,500

Crushing strength of brick laid in best cement

mortar . 2,000

Crushing strength of concrete made from Port land cement and 1 month old . 1,000

Crushing strength of concrete made from Rosen-dale

cement and 1 month old . 500

Crushing strength of concrete made from Port land cement and 1 year old . 2,000

Crushing strength of concrete made from Rosen-dale

cement and 1 year old . 1,000

Example. — What should be the thickness of tubbing for a shaft 13 feet in diameter at a depth of 800 feet: (a) for cast iron? ( b ) for brick, assuming a mean crushing strength of 1,500 pounds per square inch? ( c ) for concrete made from Portland cement and one month old?

Solution.

"26, 666+347" lm* Ans'

2!

Ans.

~333£+347"39-7' say 40 in-

Ans.

75. Metallic Lining: Supported From the Surface.

When, on account of the presence of water in the shaft, it is necessary to build up the entire lining by adding successive sections at the surface, the method illustrated in Fig. 47 is used. A tight joint between the lining and the underlying rock is made by means of a moss box ; this consists of two rings of lining a, b, each of which has a flange turned outwards at the bottom and inwards at the top. The ring b slides over the ring a and the annular space between the ring a and the rock is

102 Drifts, Slopes, And Shafts, Part 2

filled with moss c. When the lower section a reaches the rock, the weight of the overlying sections forces the section b down on the moss, compressing it between the two flanges d and e and thus forming a water-tight joint. The sections of the tubbing above the moss box are bolted together by means of flanges that turn inwards, while a tight joint between the

flanges is made by means of a thin strip of lead. The weight of such a lining is enormous and in order to successfully lower it, a diaphragm f is fastened to the flange of one of the segments just above the moss box. In the center of this diaphragm is a tube g ; as the lining is being low ered the weight of the

that the tubbing meets in sinking through the water are so great that the weight of the tubbing is largely

counterbalanced. After the metal lining is in place, the space between it and the rock is usually filled in with concrete ; as soon as this is set the water can be pumped from the inside lining.

Fig. 47

76. Steel Shaft Lining. — The use of metal for lining shafts has, until recently, been restricted to circular shafts, in which iron tubbing was employed. Steel has now been introduced and used successfully in the lining of rectangular shafts. The method adopted at Ely, Minnesota, by the Oliver Iron Mining Company, and shown in plan and elevation in

Go

6u°l, ir/'oy q/ 9/

$C

a

Go

Co

jseyfo iff6ua-j

Fig. 48

104 Drifts, Slopes, And Shafts. Part 2

Fig. 48, has been to use rectangular frames, or sets, after the manner of timber frames. These are placed at suitable inter vals, with studdles s be tween to serve as posts or uprights. These frames have been lagged most successfully with corru gated steel. Flat plates stiffened by angles could be used, but for equal strength are more ex pensive. There is no framing of the sets, as in the use of timber, but the parts are put together, after the manner of ironwork, by riveted angle bars. Steel rails weigh ing from 25 to 30 pounds per yard are used for the wall plates a and end plates b, while 3-inch 7J-pound I beams are employed as center girts c to divide the shaft into compartments. The members of the set are connected together by angle pieces, or knees, d , 3J in.X3J in.XJ in., and inches long, each angle being secured by two J-inch rivets in each leg. The studdles ,y are pieces of 16-pound rail 4 feet long, the ends being slotted, as shown in the separate view at the right, to receive the flanges of the wall plates.

77. Fig. 49 shows in a perspective view a detail of the connection between a wall plate a, a center girt c, and a studdle s at one side of the shaft lining,

Fig. 48. The wall plates a are con nected to the end plates b, and studs s in a similar manner by angle pieces d , as shown. The studdles s are not riveted, but held firmly in position by the slot in each end, in which rest the flanges of the wall plates, while the head of the rail rests on the web of the end plate between the head and flange of that rail. In this position, the studdle is

H

Fig. 50

Drifts, Slopes, And Shafts, Part 2 105

held firmly and prevented from moving in any direction. No lagging is used, except where the strata require the support of the lining. For lagging, old wire ropes interlaced with wooden lath have been used ; but with the purpose in view of retarding the spread of fire, metal lath or corru gated steel plates may be used.

78. In sinking, the steel sets, shown in Fig. 48, are sus pended by hangers in the same manner as are timber sets. These hangers, Fig. 50, consist of simple bar iron having at each end a hook that passes over the flanges of the wall plates, a wedge being used, as shown, to force the hanger from the position occupied i:i view (a) into that shown at ( b ).

In a deep shaft, the weight of the steel lining is taken up at intervals by horizontal bearers, or bearing pieces, made of 30-pound rails set in hitches cut in the rock. The ends of the rail extending into the hitches rest in cast-iron chairs, Fig. 51. Small steel wedges are driven into the slots a, b, c, and d to hold the chair in position on the rail.

In order to give a firm footing to the steel set resting on the bearers, cast-iron chairs of the form shown in Fig. 52 are

used. These are slipped on the rails composing the side plates before the latter are placed in position; and when these chairs have been ad justed in their proper position, small steel wedges are driven in the slots g, h, i, k.

79. Concrete Lining' With. Expanded Metal. — The use of concrete as a shaft lining is rapidly gaining favor. This method has also been successfully used in relining shafts. The following are the details of the process

106 Drifts, Slopes, And Shafts, Part 2

used by the Lackawanna Company in relining a shaft near Scranton, Pa. : Concrete in the proportion of one part of cement, two parts of sand, and five parts of broken stone was used ; the broken stone is replaced at some places by fine ashes obtained from the boiler ash-pit, from which the large cinders are removed, or by slate or bony coal. These proportions were varied to suit conditions, the concrete being made strongest at

points of greatest pressure. The thickness of the lining varies from 8 inches to 2J feet, and as the shafts that were relined had originally been lined with an outer and inner lining, with a puddled space between, the inner lining and the puddled mate rial were removed and replaced by the concrete, the outer lining serving to hold back the walls as the work of laying the con crete progressed. A box made of 1J"X8" timber, well braced, as shown in Fig. 53, fitting closely against the inner lining and

Drifts, Slopes, And Shafts, Part 2 107

of the same size as the shaft compartment, was used as a form around which the concrete was placed. The work was begun on

Fig. 54

the rock at the shaft bottom, and carried upwards to the surface of the ground. The sheets of expanded metal were T3g inch thick and 6 ft.X8 ft. in size and overlapped at each meeting point. They were placed along the sides and ends and at the cor ners as indicated in Fig. 54 by the broken lines. The shaft buntons were taken out and re placed by concrete, the concrete partition being continuous from bottom to top of shaft, except for oval openings left to per mit examination of the guides, as shown in Fig. 55. These concrete partitions, as well as the concrete lining, are stayed by rods h and i set in the con crete, as shown by the dotted lines in Fig. 55. Bolts were set into the concrete partition to serve as fastenings for the cage guides.

Fig. 55

108 Drifts, Slopes, And Shafts, Part 2

Special Shaft Work

80. Retimbering- a Shaft. — As a rule, the shaft liningshould last until the shaft is abandoned. It frequently happens, however, that, owing to poor timber or bad ground, a shaft will need to be relined in places, or it may be desirable to replace the entire lining of an old shaft.

In the retimbering of a shaft, the timbers are removed only as new ones are put in their place. If the entire shaft is to be retimbered, the work is best performed from the bottom upwards. Starting at the bottom, the old timbers are with drawn two or three sets at a time, according to the character and condition of the strata, and solid substantial frames put in their places. It will often be necessary to support the curbing above by temporary blocks or posts set under the old frames and standing on the new ones. The position of these blocks can readily be changed as the new timbers are inserted. Care must be taken in this work to tamp good material behind the timbers as the latter are built up, so as to leave no cavities between the lining and the strata. The same provision must be made for the drainage of wet strata, as mentioned in refer ence to sinking. A scaffolding is carried up the shaft for the workmen to stand on as the work advances. Support for the scaffolding may be found in the center buntons and cleats spiked to the shaft lining below, or the platform may be hung from the advancing work.

81. Enlarging Shafts. — Though a shaft should always be sunk sufficiently large to meet every requirement, it often happens, in the later development of a mine, that the output cannot be maintained on account of the increased length of haul without increasing the size of the mine car, which gener ally requires, also, the enlargement of the shaft. The term widening is generally applied to any increase in the sectional area of a shaft by increasing the length or the width of the shaft, or both. As a rule, hoisting ceases during widening, but the shaft may be widened at night without interfering with day hoisting by using an auxiliary sinking cage.

Drifts, Slopes, And Shafts, Part 2 109

The plan ordinarily followed is to widen on one side or one end, as by this means timbering already in place is made use of, the alinement of the shaft is maintained, excavating is done easily, and less readjustment of hoisting sheaves, stops, etc. is necessary.

Fig. 56 represents the top of a shaft that is to be enlarged by increasing its length. The manway m is to remain unchanged, the end wall opposite to the manway being moved out from b to c. The end plates e are to be used again. The center partition j dividing the hoistways /, / is to be moved from g to h, the distance g li being one-half the distance b c, so as to make the hoisting compartments the same size. It is

Fig. 56

not customary to make the partition between the hoistways solid, but simply to use occasional cross-buntons, excepting where there is great pressure on the side timbers. Each alternate wall plate is cut at h, so that its end will rest against the center bunton h , and a new piece i, reaching from h to c, is substituted for the part cut out. The old center buntons j are sawed close to the wall plates and may be used again for short lengths at /, the buntons h being new timbers. The alternate wall plates k, remaining in position, are cut square on the line b ; the short fillers l butt against these and are framed into the wall plates at c ; w is a temporary working platform resting on the old end plates and center buntons and passing underneath the new center buntons. The material is excavated from the

110 Drifts, Slopes, And Shafts, Part 2

space o as the end plates e ' are removed. This material is hoisted to the surface by a temporary block and hoisting engine, or by the permanent hoisting engine.

82. A slightly different method of carrying on the work is shown in Fig. 57, which represents a plan and a sectional

elevation of the shaft. Cleats a are nailed on the old lining and buntons b placed on them across the shaft; on these is built a platform on which the men work. The enlarging is begun at the surface and car ried downwards, a sec tion usually about 8 feet high being taken out from each platform. The drillers work on the bench c d and load the waste directly into cars on the cage. The end e f is timbered and backed as in sinking a new shaft. The sides e h and / g are tim bered as shown. The timber joints at the corners g and h are left undisturbed, but new timbers must be used for the side timbers, except that for each al ternate timber the old timber is used, in part, a short length of new timber being joined to it by a feather-edge joint, so as to bring the length of the joined timbers up to that of the new side timbers. When

Fig. 57

Drifts, Slopes, And Shafts, Part 2 111

both the length and breadth of the shaft are to be increased, an entirely new shaft lining will be required; the excavation in this case may preferably be made on all sides of the shaft instead of on two sides only.

In some cases, shafts have been enlarged and retimbered very successfully by filling the shaft to the surface with cinders and ashes, using such a platform as is shown in Fig. 57 for a foundation for the filling. Then commencing at the surface the old timbering is

taken out, the shaft enlarged, if desired, and new timber put in place as if it were a new shaft. This is a costly procedure, but is often cheaper ul timately than endeav oring to use one or more sides or ends of the old shaft.

83. Deepening Shafts. — There are several methods of deepening-shafts when it is desired to extend them to a lower level than the

Fig. 58

one being worked. The following three are those most com monly used :

1. First Method. — A false bottom of heavy timbers is provided in the sump as a resting place for the cage, and sink ing is begun on the bottom of the sump. When the new seam is reached, a new sump is made, new guides are extended from the bottom upwards to meet the old guides, the false bottom is removed, and the cage ropes spliced, or new ones of sufficient length are substituted for the old ropes to allow the cages to hoist from the lower seam. This method is used often

112 Drifts, Slopes, And Shafts, Part 2

where material is being hoisted during the day and sinking done at night. A small sinking cage is slung under the regular cage or a bucket is used instead, the material being hoisted to the old shaft-bottom level and there taken back into the old workings and gobbed. The disadvantages of this method are that all the water from the old sump drains through the false bottom and down on the sinkers at their work, and there is

always danger of materials falling down the shaft on the sinkers.

2. Second Method. At a short distance from the shaft bot tom and on a passage way that is not much used, a steep slope a h, Fig. 58, or small shaft is sunk, the depth of sinking depending on the amount of rock necessary to be left as a support under the old sump while the deepening proceeds. At the foot of the slope a level heading h c is first driven to a point directly below the left-hand face of the shaft; the roof of this heading is strongly timbered by setting the collars in hitches cut in the sides, before the work of excavating the shaft below is commenced. When this is done, the excavation is begun and carried down in exact line with the shaft above, the material being removed by a hoisting bucket, operated by a windlass or temporary hoisting engine located at some point near the head of the slope. The further operation of sinking, timbering, etc. is the same as that previously described. When the sinking is complete and the shaft timbered, the main sump is drained

Fig. 59

Drifts, Slopes, And Shafts. Part 2 113

and the two shafts connected by driving upwards from below from a strong temporary staging erected at c or downwards from the bottom of the sump.

3. Third Method. — Fig. 59 shows the method of deepening a shaft while the upper part is in use, by opening only that portion of the shaft area not under the hoistway for a depth of 12 to 15 feet, and then widening it out the entire size of the main shaft. This leaves a roof of rock ( pentice ) that shields the men. When another lift has been sunk, the pentice is cut away and another started for the next drop. The hoisting is done by an underground engine or by bucket and windlass.

84. Upraising'. — It is often necessary, in order to gain time, to drive a shaft upwards from the inside workings as well as downwards from the surface. At times, shafts are driven entirely from below, this being often the case with escape shafts or air-shafts, which are frequently started from the workings below. Upraising, or driving upwards, is more expensive than sinking, so far as the labor of driving is con cerned ; but there is a saving when the work is wholly per formed by upraising, as it is then not necessary to set up a sinking plant on the surface, and an engineer's wages are also saved. The material is generally stowed in the old workings below, but sometimes when room is not available it is sent to the surface. Before commencing to drive upwards, a care ful survey is made to establish the four corners of the shaft in the mine immediately under the surface location. Four iron pins are driven in the bottom to mark these corners. If necessary, posts or timber cribs are set to secure the roof around the place before blasting is begun.

85. When the excavation has proceeded upwards 8 or 10 feet in the roof, the bottom is cleaned up, the pins located, and the shaft tested for alinement by hanging plumb-bobs in each of the four corners. Timbering is then begun by first setting a heavy square frame /, Fig. 60, in the roof, resting on substan tial posts and sills, as shown in the figure. The inside measure ment of the frame must correspond to the size of the shaft in the clear when timbered. This frame is exactly located by

114 Drifts, Slopes, And Shafts, Part 2

means of the plumb-bobs hanging over the four points pre viously established, and is then firmly wedged in place. The timbering of the shaft is built up on this frame after the ordi nary manner of shaft timbering. The timbering is carried as close to the roof as practicable, and a partition is carried up dividing the shaft into two compartments. This partition may later be used in the operation of the shaft as one of the perma nent partitions, and should be located accordingly.

A heavy bulkhead is now constructed at the bottom of the shaft, and a chute arranged under the large compartment h, by

which the loose ma terial excavated above and thrown into this compartment may be drawn and loaded as required. To control the descent of the loose material in this compartment, a door is arranged at the foot of the chute. The compartment m serves the double purpose of a manway and airshaft, and for this purpose it is divided by a temporary par tition. A ladder is constructed in the manway, by which the workmen travel up and down.

In the operation of upraising, the workmen ascend the man way by the ladder and stand on a temporary platform, or on the loose material that is allowed to fill the compartment h. The material is drawn from this compartment only as is required to furnish good standing room at the face.

8G. In upraising, the ventilation of the shaft is always more or less difficult, owing to the tendency of the smoke and

Drifts, Slopes, And Shafts, Part 2 115

hot bad air to remain at the top. The air compartment may be connected, by a box, to the main air-course while the man way is open to the return, or vice versa ; by this means, a fair current of air may be maintained at the top of the shaft or upraising. At times, a small blower is used to blow the air into the face. When compressed air is used to operate the drills, there will be air sufficient for the ventilation of the upraise without making other provision. The timbers required must be taken up the manway or the; air compartment. When blasting, the manway and air compartments are covered with heavy planks, to avoid the material loosened by the blast falling down the shaft and breaking the ladders or partitions.

Contracts For Shaft Sinking

87. Details of Contract. — A bore-hole record of the various strata to be passed through is usually available, and the sinking contractor therefore knows what he must expect and bids accordingly. His contract generally requires him to sink a certain distance, or to a certain coal or ore body, to properly timber the whole shaft, and to put heavy timber, horn sets, water rings, etc. where he is directed by the owner. The sinker is often required to give bond for faithful performance of work and only a certain percentage of the price agreed on is paid at the end of each month, the remaining part being with held until satisfactory completion of the contract. In order to protect the company against the filing of liens for unpaid labor or material, the contractor is often required to present all bills for material used in the prosecution of the work to the company; and to furnish the company with a correct pay roll of all labor employed each month ; such bills and pay rolls to be paid directly by the company and charged to the con tractor's account, and deducted from any amount due him on the contract.

88. The headframe, engines, pumps, and explosives may be furnished by either party as may be agreed on. The owner or operator of the property usually furnishes the power and men for hoisting the material excavated and any water above

116 Drifts, Slopes, And Shafts, Part 2

a certain limited amount, the lumber, and other supplies, such as cement, nails, etc. The contractor usually furnishes the drills and other tools and the drillers and laborers.

When inviting bids for a contract for sinking a shaft, the company is expected to provide a set of specifications giving such information as may be in their possession that will enable the bids for the work to be made intelligently, and stating the exact requirements that will afterwards form part of the contract.

A date is set by the company when all the bids received will be opened, examined, and the contract awarded, often "to the lowest responsible bidder." The company usually, however, reserves to itself the right to reject any or all bids. Where a bond is required, it is sometimes requested that the nature of the bond be submitted with the bid for the approval of the company.

89. Specimen Form of Contract. — No form of con tract can be given that will be of universal application, but the following form will serve as a guide in drawing up such contracts :

This Agreement made this day of A. D. 19 ,

between of , in the County of

and State of , party of the first part

and of , in the County of ,

State of , party of the second part.

Witnesseth, That the party of the first part, for and in consideration of the agreements hereinafter contained and for the further sum of one dollar ($1) to him in hand paid, the receipt whereof is hereby acknowl edged, agrees to sink a shaft upon the property of party of the second part located in , in accordance with the plans and specifi

cations furnished by the party of the second part and which form part of this agreement, and which shall remain the property of the party of the second part, and to turn over the completed work within the time hereinafter specified, free from all liens or encumbrances whatsoever, for the final inspection and acceptance of the party of the second part.

The party of the second part agrees to furnish the party of the first part from time to time, as requested, such further plans or explana tions as may be necessary to detail and illustrate the work to be done, and they shall form part of the contract, so far as they may be con sistent with the original plans and specifications.

Drifts, Slopes, And Shafts, Part 2 117

Art. I. Dimensions. — The shaft is to be ( ) feet

long and - ( ) feet wide in the clear, and in order to

keep the shaft true to size and plumb, six lines must be suspended, one in each corner and one in the middle on each side, as directed by the party of the second part, and no points in the ends or sides of the completed shaft shall project outside these lines. The corners to be well squared, and all loose rock in the walls of shaft must be trimmed down and made secure as the work advances.

Art. II. Depth. — The depth of shaft to be about

( - ) feet, or from the surface to a point feet below the

- vein or seam, the twelve feet below the vein

or seam being for a sump.

Art. III. Water. — The party of the first part agrees to make all lodgments or sumps for water where and when required and rings for conducting the water to the sump, to make all platforms for setting of pumps and roofs for protecting the same from falling debris from blasts or otherwise, and to do all necessary work in the shaft for the protection of machinery and pipes placed therein, as directed from time to time by the party of the second part.

Art. IV. Work. — The party of the first part agrees to prosecute the work with all possible vigor and despatch, and in a good work manlike manner. As many men must be worked on a shift as the party of the second part thinks proper and three (3) shifts of eight (8) hours each must be worked in every 24 hours except Sunday. Steam or air drills will be allowed after the first 25 feet, except in rock where in the judgment of the party of the second part it will be detrimental to the

shaft. If steam or air drills are used, at least machines must

be used at one time when required.

Art. V. — Should the party of the first part at any time refuse or neglect to supply a sufficiency of properly skilled workmen, or of mate rials of the proper quality, or fail in any respect to prosecute the work with promptness and diligence, or fail in the performance of any of the agreements herein contained, the party of the second part shall be

at liberty, after days' written notice to the party of the first

part, to provide any such labor or materials, and to deduct the cost thereof from any money then due or thereafter to become due to the party of the first part under this contract; or to terminate the contract and to enter upon the premises and take possession, for the purpose of completing the work comprehended under this contract, of all mate rials, tools, and appliances thereon, and to employ any other person or persons to finish the work, and to provide the materials therefor; and in case of such discontinuance of the contract the party of the first part shall not be entitled to receive any further payment under this contract until the said work shall be wholly finished, at which time, if the unpaid balance of the amount to be paid under this contract shall exceed the expense incurred by the party of the second part in finish-

118 Drifts, Slopes, And Shafts, Part 2

ing the work, such excess shall be paid by the party of the second part to the party of the first part; but if such expense shall exceed such unpaid balance, the party of the first part shall pay the difference to the party of the second part. The expense incurred by the party of the second part as herein provided, either for furnishing materials or for finishing the work, and any damage incurred through such default, shall be audited and certified by a board of three arbitrators, each party selecting one and these two choosing a third, and the certified findings of such board of arbitrators shall be conclusive upon the parties. If the party of the first part or any of his employes conduct himself improperly or does anything to injure the work, he shall be discharged immediately.

Art. VI. Labor and Material. — The party of the first part must furnish all necessary help and material for the execution of the work,

except as hereinafter mentioned, and render not later than the

day of each month the time and wage rate per day of each man and boy that has worked for him on said shaft during the previous month.

And the said party of the first part hereby authorizes and directs the party of the second part as far as the party of the second part shall be

indebted to the party of the first part, to pay on the day of each

month on a pay roll to be made out and approved by both the parties of the first and second parts, such sums as may be due as stated in said pay roll to the employes of the first party, and to charge the total of the amounts so paid to the account of first party, deducting such amount from any money due or that may become due later on the contract.

Art. VII. Machinery. — The party of the second part agrees to furnish machinery and power and a hoisting engineer for hoisting from

the shaft, and when the amount of water exceeds ( )

buckets per hour, he will furnish pump and one machinist to assist the party of the first part to put the pump and pipes in place. He will also furnish iron and ties for track to dump and cars for same, and all lumber and nails required inside the shaft.

Art. VIII. Timbering. — The work of timbering, putting in buntons, guides, and so forth, will be done by the party of the first part, and if not put in satisfactorily to the party of the second part, the party of the second part reserves the right of stopping the party of the first part and his men, and of putting them in himself with his own men, at the expense of the party of the first part.

Art. IX. Payment. — The said party of the second part hereby agrees to pay to the said party of the first part in the manner and at

the rates following, to wit : the sum of dollars ( )

per linear yard for each and every yard of surface or drift sunk, and

- dollars ( ) per linear yard for each and every linear

yard of rock driven. Gravel and boulders do not constitute rock, in the meaning of this contract, except boulders of considerable size and

Drifts, Slopes, And Shafts, Part 2 119

frequency requiring continued blasting. An occasional boulder requir ing to be blasted is not to be classed as rock.

The party of the second part shall be given monthly estimates of the amount of work done by the party of the first part.

And the said party of the second part further agrees that he will pay

to the said party of the first part on or before the ( )

day of each month for the work done during the preceding month at the prices hereinbefore agreed to be paid for said work, after deduct ing therefrom the amount paid to the men employed by the said party of the first part at the times and in the manner hereinbefore specified, provided that in no case shall the said party of the second part be liable for services rendered by any person or persons employed by the said party of the first part to any greater extent or amount than there shall be due the said party of the first part for work done as heretofore agreed.

And further, the said party of the second part shall have the right to retain from the monthly payments due first party and hereinbefore agreed to be made upon each monthly estimate, the sum of ten (10) per cent, of such estimate, for the first hundred feet or fraction thereof, seven and one-half (7i) per cent, for the second hundred feet or frac tion thereof, five (5) per cent, for the third hundred feet or fraction thereof, and two and one-half (2J) per cent, for any fraction of the remaining distance until the completion of said shaft, satisfactorily to the party of the second part. The amount so retained to be paid to the said party of the first part upon the acceptance of the work by the second party when the shaft shall have been completed in accordance with the terms of this contract and to the perfect satisfaction of the party of the second part.

Art. X. Acceptance of Work. — Upon the completion of the work and within the time hereinbefore specified, the party of the first part shall signify, in writing, his readiness to turn over the work for the final inspection and acceptance of the second party; such inspection and acceptance to be made by the duly qualified officers or agents of said

second party, within days after the receipt of the notice that

the work is ready for them.

The party of the first part shall not remove any of the machinery, tents, tools, or other implements used in the work from the ground, until after receiving the written acceptance of the work by the said second party, which machinery, tents, tools, and implements shall remain subject to attachment by said second party in case of a deficit in the final settlement.

After the final inspection and before accepting the work, the party of the second part shall have the right to advertise for any unpaid claims for labor or material used in the work, a certain length of time as may be required by law*, before writing the final acceptance of the work, permitting the removal of the chattels belonging to the first

120 Drifts, Slopes, And Shafts, Part 2

party. In case the total amounts paid by the second party for labor and material and chargeable to the first party shall exceed the total amount to be paid for the work under the terms of this contract, the said second party shall have the right to attach and hold the aforesaid chattels, machinery, tents, tools, and other implements used during the prosecution of the work, to recoup the amount of such deficit.

Art. XI. Responsibility. — The party of the first part will be responsible for all accidents on his own part, or on the part of any one of his men, and will save harmless the party of the second part from all claims for damage for injuries received by any of them in the prosecu tion of the work.

The party of the first part will provide for the ventilation of the shaft during sinking and will see that all the requirements of the Mine Law are strictly complied with.

In witness whereof the parties of these presents have hereunto set

their hands and seals this day of 19

Drifts, slopes, and shafts

Overview

I.C.S. Staff

International Textbook Company

Scranton, Pa.

Contents

Contents

Drifts, Slopes, And Shafts

Location Of Mine Opening

Preliminary Considerations

Introduction

Copyrighted By International Textbook Company. All Rights Reserved

Conditions That Determine Position Of Opening

Conditions That Determine Form Of Opening

Drifts, Tunnels, And Slopes

Dimensions And Grade Op Drift

Methods Of Drifting

Tunneling In Loose Ground

Tunneling In Running Ground

Tunnel And Drift Portals

Tunnel Linings

Slope Timbering And Safety Appliances

Safety Appliances

Forms And Dimensions Of Shafts

Principal Forms Of Shafts

Factors That Determine Shaft Dimensions

Drifts, Slopes, And Shafts, Part 1 3/

Sinking Tools And Appliances

Hoisting Excavated Material

Head-Frames And Other Shaft Structures

Methods Of Lighting And Drainage

Drifts, Slopes, And Shafts

Work Of Sinking

Preparatory Work

Copyrighted By International Textbook Company. All Rights Reserved

Sinking Through Ground That Does Not Run

Sinking Through Quicksand Or Running Ground

Kind-Chaudron And Lippman Systems

Shaft Timbering

Provisions For Drainage Of Water

Examples Of Shaft Timbering

Timber, 31Asonry, And Metallic Linings

Special Shaft Work

Contracts For Shaft Sinking