Technical Paper 379: Strength of Ore and Top Rock in the Red Iron-Ore Mines of the Birmingham District, Alabama
Technical Paper 379: Strength of Ore and Top Rock in the Red Iron-Ore Mines of the Birmingham District, Alabama by United States Department of Commerce…
Public-domain full text preserved in the Mountain Man Mining Library. Original source: archive.org.
San" wee Technical Paper 379 ) DEPARTMENT OF COMMERCE HERBERT HOOVER, SECRETARY
BUREAU OF MINES SCOTT TURNER, Drmecror
STRENGTH OF ORE AND TOP ROCK IN THE RED IRON-ORE MINES OF THE BIRMINGHAM DISTRICT, ALA.
Price 10 Cents
Sold only by the Superintendent of Documents, Government Printing Office Washington, D. GC Sn ee SS eg Le a ee, WASHINGTON GOVERNMENT PRINTING OFFICE
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Contents
TutrodUctione. 2.) geese teu ee ete eee eee ess ACKNOW IGG RINeN (8.55.25 22 oe Go te Gees eee eb es Occurrence of ore and top rock Compressive strength of iron ore
Size and shape of test pieces Effect of size and shape on compression Advantages of cubical test pieces
Methods of testing and results of tests
Tests under vibration.
Transverse strength of top rock
Results of bending-strength tests Tests of beams failing under their own weight Modulus of rupture ese eee gas Ete teye
Blasticity of ore eee een nen
Results of deformation tests Lateral expansion 0 22.005. c ees wobec cee eee el eee ese be Modulus:of elasticity ..2...2.2:0%02.. 5504454 bed bo oe Se eo
Publications on metal mining 2 2-2-2 eee eee eee
Illustrations
1. Section of ore bed brought to surface 2. Cubes of ore prepared for testing 3. Cubes after testing, showing failure forms 4. Failure forms resulting from crushing cubes of ore - 5. Failure of ore cubes under compression 6. Failing pillar forming inverted cone 7. Upright pyramid formed at base of failing pillar 8. Ore spalling from face of pillar 9. Failure of pillar by distortion
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STRENGTH OF ORE AND TOP ROCK IN THE RED IRON- ORE MINES OF THE BIRMINGHAM DISTRICT, ALA.
By W. R. Crane
Introduction
A wide choice of stone is usually available for building any type
of structure, but the native ore and rock must form the pillars and roof in amine. The character and condition of the ore and rock and the weight of the load to be supported are fixed; the only factors that can be varied are the dimensions of the pillars—that is, the crosssectional area—-and the height and width of openings. Evidently it is very advantageous to know as definitely as is possible the strength of the support in order that proper values may be given the variable factors. This paper presents the results of the writer's attempts to ascertain the strength of the ore and top rock in the hematite mines of the Birmingham district and to determine the size of pillars adequate to support the roof as the mines grow deeper. Surface cracks, excessive inflows of water, and the collapse of pillars have made it desirable, if not imperative, to obtain all possible information on the sufficiency of the roof support in those mines. Among the underground conditions that were studied carefully were the failure of pillars and top rock and their relation to the occurrence of ore in the bed worked. The investigation was extended to include determination of the strength of the ore forming the pillars and of the rock of the roof formations. The results are recorded herein.
Acknowledgments
Acknowledgment is made to the operators of the iron-ore mines for their cooperation. Particular acknowledgment is due to C. E. Abbott, general manager, Tennessee Coal, Iron & Railroad Co.; C. E. Bowron, chief engineer, Gulf States Steel Co.; W. M. Lacey, former general superintendent, and J. R. Moore, local superintendent of ore mines, Woodward Iron Co.; W. J. Penhallegon, general superintendent, Republic Iron & Steel Co.; J. E. Strong, vice president and chief engineer, Alabama Co.; and H. J. Thomas, general superintendent, Sloss-Sheffield Iron & Steel Co. -
Special acknowledgment is due the Reed Bros. Stone & Monument Works, of Birmingham, for assistance in preparing test pieces for crushing and bending tests; to the Carnegie Institute of Technology
2 Top Rock, Birmingham District
and the United States Bureau of Standards for making tests in its laboratories; and to many others whose advice and suggestions have been of much value.
Occurrence Of Ore And Top Rock
No study of the strength of rock formations can be complete unless it includes data on the formations as they occur in place. ill stratified formations may be cross-bedded in places, and the crossbedding planes, lying at an angle with the normal bedding, may seriously lessen the strength of a rock formation. Joints or slip planes, whieh are often called "headings," are another source of weakness.
Slip planes usually occur in two series that cut one another at
approximately right angles, and may be termed "'major slips'' and ''minor slips.'' If several series are present in a bed, the bed is broken into blocks whose dimensions range from a few inches to a number of feet. At those mines in the Birmingham district where the major and minor slips correspond with the strike and dip of the beds they may materially help development and the breaking of ore, but this advantage may be more than offset by the pillars and roof being weakened and rendered more liable to fail under pressure— pillars in particular tend to disintegrate most along planes parallel to their free faces. In the Birmingham district slip planes are seen to best advantage in the ore bed, but they occur in the top formations, where they are very persistent laterally and vertically. Both the top rock and the ore are weakened by slip planes and cross-bedding; the former are elements of inherent weakness in ore and top rock, and the latter affects the top rock most.
Compressive Strength Of Iron Ore
The load of the superincumbent formations is exerted in two ways— in compressing the ore in the pillars and in bending the top rock. The resistance to compression is the compressive or crushing strength; the resistance to bending the bending or transverse strength. The elasticity of a material under stress plays ari important part in the strength of the elements of support. The strength of ore and top rock is then of three kinds—compressive, transverse, and elastic.
In the investigation of the compressive strength of ore great care was taken to obtain masses of ore that were free of flaws and fractures caused by earth movements and blasting. Sections were cut—in fact, practically sawed out—by hand-power drills at points as far as possible from drill holes and between joints or slip planes. Figure 1 shows a section of the ore bed cut out for testing. In a similar manner pieces of top rock were removed from the roof after several
Compressive Strength Of Iron Orb 3
feet of top had fallen. Such pieces could not possibly have been weakened by shooting.
Size And Shape Of Test Pieces
The compressive or crushing strength of the ore must be the basis for determining the supporting strength of mine pillars. The collection and preparation of test pieces is therefore an important part of the work of determining the strength of ore, and great care must be taken in obtaining representative samples.
As determination of the compressive strength of each foot of the bed worked was desired, complete sections were taken and broken into foot sections, from which the test pieces were prepared. The masses of ore representing the feet in the sections were numbered
FIGURE 1.—Section of ore bed brought to surface
from the top of the bed down, the top of each section being marked to show its position in the bed with respect to bedding planes and dip.
The masses or sections of ore were then cut into cubes one-half inch oversize by gang and carborundum saws. The rough cubes were squared up and ground to hone finish on the rubbing bed, with no attempt to obtain definite sizes.1. Although most of the test pieces were cubes, many others were of odd sizes and shapes. Results of the tests of these irregular pieces will be given separately.
EFFECT OF SIZE AND SHAPE ON COMPRESSION Data and opinions on the effect of size and shape upon the result of compressive tests have been conflicting. In 1876 Q. A. Gilmore?
1 Cubes were prepared from masses of ore through the courtesy of Reed Bros. Stone & Monument Works, Birmingham, Ala.
2 Gilmore, Q. A., Report on the Compressive Strength, Specific Gravity, and Ratio of Absorption of the Building Stones of the United States. 1876, p. 28.
meee Gor gle UN VERSITY OF M CHIGAN
4 Top Rock, Birmingham District
made an extended series of tests of building stones, which seemed to indicate that the increase in resistance to crushing per square inch varied directly with the size of cube tested. The results of his tests are summarized as follows:
TaBLE 1.—Size and compressive strength of stones
Size of cubes. 1 inch 1% wy, inches inche Total 104,500 160,740 698, 200 Avernge ' 9, 500 16, 074 CQ oat Square inch 9, 500 10, 300 13 aw
Doctor Baker states that ''It has been conclusively proved that the strength per square inch of bed area is independent of the size of cube, and therefore the size of the test specimen is immaterial."
Tests made by the writer that show similar variations in compressive strength are as follows:
TABLE 2.—Compressive strength, in pounds, of iron-ore cubes, by mines and sizes
of cubes 7 0. 4, 0. d, oO. 4, Mine Mine sample No. buat 9.17 15.97 a pods inches square square square inches inches inches 2 ene One ne RY SQUAT chaise Gis ceaaues el apt was tae WAL eehitatiet coe Gece 10, 789 ar ee oe Merced co eek octane Oe ots ee ain It ee ne B ee ee ee ee 15 Dee eres Sree Peete it ey caer tank fae 13, 723 BAB utacnes ete ch tae We ole ad 11,75 7 ER ON TEIN iG OnE naet Ean arene ONE 13, 423 Dee eee aus te eae all pela Ae ee ee a 13, 660 {ee ee eon are ae 13, 7 eee See rer De en a fe tai cpap chortle, Ns write tek e O00 in cee le eessiccs ceases Bes Pcie Ra) eens ha Sac eS oar 13, 439 22--! CO. .1---enn ene e ee ne een e ee eee ene (ieee eh iat ir NE dC EON AN eI IRR NER) 14, 735 14, 09 Wig 22 ee acter 17, 280 PT ee ae reais tee Le shctateonbahes a cucereauras ped Duals Lede 17, 6% eee eee eee h, ARNON eS ateaat eoewiteor, acct' QO eo hh tye be BE Bal in teats 11,682 PAD Ae cst sony Stet beac estate ete Sees Me setae ro en ee sre eel ae. 14,707 IY 12242 Bid tect en 2 eas Gera so ae Nid yee ey eee ayes 13, 817 ds oot so ties Shean gh Maer te aetna ee ean 12, 359 NG von vie SeriG hoes: Re SBOAST eccete tesco atte Veh tetas : Same Seen ee a 14, 652 Pgeurceateee Sct te Mastzasrhcite 2b Boe Sete ds ted Sede na Wnadtrn sborae eau OM ee a 10, 160 OR eabeies 11, 709 eG Saat eae eeeae D1 B00 se sn ccus cecnecee: See eee re tenceseteefecnseneses BA isco 13, 755 33 Se Sak sotn SS eeu ens 10, 517 CSpot teresa ee Ne erereuetererd S haus ea euatecsterae ' Fc noe ene Hae tes) Cee cera game al Vests oats ¢ ane amen esate ween RRR Par Lice eeu inceton ee W700! aiccd oc ole (eet ees i$ 43, S90 ernie seueaed ieee a ant ee 11, 638 0.2... Aesth yet Gere Deonnich ck oe avis ich ciel es aan Jada clever ds 16, 97;
DO onsaeeie tide! ICO58/ vasecene PB Ah Srl gah cats APO 2 cae Ot cle NS, ceed 12,101 {022 .. iS Sie wie lad ede stata Sank Gee Wea tacthe acceso hee head seen es oa. 12 ADD coe ee Fee eetaete ceccsteeseeek fcr ee ene eel re re ee 13, 574 Nes eae eter ict a RU ce Reale eae 16, 219 AGO cid ince eton ech cose uses Me Bei atoll ects 15, 042 AVerage 2.--2---2 fa eden a eat 11,391) 12,002) 13, 522 Moo 12907 ia
+ Baker, Ira Osborn, A Trentise on Musonry Construction. 1909, p. 8.
Compressive Strength Of Iron Ore 5
The percentage differences noted between Nos. 1, 2, 3, and 4 are 5, 11, and 9. Subsequent tests indicate, however, that the increase in compressive strength noted is due not so much to the large cubes actually giving increased strength as to the smaller cubes making less perfect contact with the plates of the testing machine because of difficulties experienced in cutting plane faces. (See fig. 2.)
The tests given above were made primarily to determine the size of cube most desirable for tests; as a result it was decided to use test pieces with 3 to 4 inch sides.
Advantages Of Cubical Test Pieces
The cubical test piece seems to be the simplest and most readily made and is commonly used. Gilmore, speaking of tests made by Hodgkinson, says' that ''The cubical form of specimens adopted for the experiment affords sufficient security for the angular breakage which he proved to be necessary for a true result. This latter fact is corroborated by subsequent experiments."
Doctor Baker states that although theoretically the best form of test piece should be higher than broad, it is common practice to use cubes.°
Doctor Parks states ® that ''A broken cube tends to assume the form of two pyramids with their apexes at the center and their bases against the bearing plates of the machine. Doctor Buckley con-
siders these residual forms as indicative of the strength of the stone."' ' The consensus of opinion seems to be that good results are obtained when two pyramids are formed with their apexes centering in the cube and their bases against the plates of the testing machine. Such was true in the series of tests of iron-ore cubes. Almost invariably cubes that showed symmetrical angular fracture resulting in the abovedescribed form had the greatest strength. However, Doctor Parks states in the above connection that ''It was observed that the limestones of high strength from different parts of Ontario resulted in a series of vertical columns with scarcely any appearance of either cone or pyramid." A few of the writer's samples broke thus, but by far the most representative tests gave the pyramidal and conical forms.
Methods Of Testing And Results Of Tests
The preliminary tests of iron-ore cubes, by Prof. F. A. Simmons, Carnegie Institute of Technology, Pittsburgh, Pa., were made with Olson testing machines of 20,000 and 200,000 pounds capacity,
4 Gilmore, Q. A., Report on the Compressive Strength, Specific Gravity, and Ratio of Absorption of the Building Stones of the United States. 1876, p. 4.
§ Baker, Ira Osborn, A Treatise on Masonry Construction. 1909, p. 8.
¢ Parks, William A., Report on the Building and Ornamental Stunes of Canada: Canada Department of Mines, Mines Branch, 1912, vol. 1, p. 46.
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COMPRESSIVE STRENGTH OF IRON ORE y
. while the final tests, by D. W. Kessler, Bureau of Standards, Department of Commerce, Washington, D. C., were made with a Richle machine of 200,000 pounds capacity.
Doctor Baker gives the angular rupture of stone as 60° with the direction of the compressive force. From measurements of 200 or more iron-ore cubes the writer found that the average angle of fracture was 65.32° with the vertical; however, the larger number of breaks was approximately 60°, the range being from 55° to 80°. Observation of failing pillars shows that the natural angle of fracture is about 60°.
In the preliminary tests the cubes were centered on the bottom rigid plate. The upper plate had a universal or adjustable bearing to conform with possible lack of parallelism between the upper and lower faces of the cubes. In the final tests the plate with universal bearing was placed below to facilitate careful centering of the cubes.
Inequalities in the surfaces of the cubes next to the plates of the testing machine were largely eliminated in both series of tests by the use of hard, dense blotting paper. The efficacy of this material was shown by its adhering to the cube on the ore side and receiving a glossy surface on the upper or plate side.
The results of the tests are shown in Table 3.
TABLE 3.—Compressive strength of iron-ore cubes !
Cube No. Section Height Area eee Strength| of testing 3 as Pounds Square Y square Inches Inches inchea Pounds - inch Wet ccse et ectemets oid Oe ceue tio acaied 3. 37 by 3. 29 3. 42 11.08 106, 750 9, 640 N Dc oat ns Me ha i Pe VAP Re And eo 3.06 by 3. 09 2. 96 9. 46 124, 660 13, 170 Vv OB lM EE vata RN Saye Dat cat ts aca on koe 3. 65 by 3. 61 3. 44 13. 18 143, 050 10, 850 N ee cect tse oo ein ss ea ae bees Ses 3. 65 by 3. 57 3. 45 13. 04 206, 590 15, 850 V-A! OMe fa tal Fae Mak ho eke an Se eG 3. 66 by 3. 57 3. 45 13. 08 145, 000 11, 080 N Gee ee kes wu Rad ent lard 3. 42 by 3. 60 3. 50 12. 32 150, 100 12, 180 N Wiech ett See ae ee NS a Shee SoG ae Ah 3 27 by 3. 8 334 11. 55 120, 000 10, 390 N Se epee rere nee ony STO rt ete Re eR, 3. 46 by 3. 59 3. 46 12. 42 177, 000 14, 240 Vv 1! AEE Ae eam i NR ts MOLAR ee Ck oe EPR fee a a 3.38 by 3. 54 3. 33 11. 97 123, 330 10, 300 N 10 a eee oe oe ee 3.43 by 3. 57 3. 32 12.25] 131, 500 10, 740 N es ce eo oe ep ts PEE a Da 3. 43 by 3. 52 3. 29 12. 08 129, 600 10, 730 N Vio: k etal haath acces talent eee oe 3. 62 by 3. 44 3. 21 12. 46 193, 110 15, 520 V-A ae ete tis ts ni tal Ce SL aR eet 3.55 by 3.61 3. 51 12,82 144, 950 11, 310 N Vs. the sae ce Wie A tn eta A ee ceed ih 3.65 by 3. 50 3. 45 12 78 144, 850 11,320 N eRe ed eae A ace eR AT a A Le 3.76 by 3. 51 3. 34 13.20 146, 300 11, 080 N 163 2sen crt ose beh erie ce 8a DV 347 3. 33 13. 04 130, 650 10, 020 N DP ie sa Se tte a hel ance ayta ca fine 3.51 by 3. 85 3. 50 13.51 168, 400 12, 470 N DS tte Bore aes isha, Sn SE ea MCG 3.97 hy 3. 50 3.70 13. 90 208, 750 18, 010 Va 1G ose oe ah oe me Cede teottict taewae eal eae OM aCae 247 13.05 154, 900 11, 870 N BOF sb ha soba Cetera De Se aes ites 3. 82 by 3. 47 2 40 13. 26 210, 200 15, 850 V-Aé Woe hee a webu vie SOard ba acad conceal eae DM 3. 26 8. 83 RH, 100 9, 750 N 2. Oh ala elas aie nen eo! en SPR RR ay ae 4. 42 8.35 125, 20) 15, 010 Vv oe oS ae Gelato Peed Menges SN ath, ye oh, 2) 3.12 hy 3.27 272 10. 20 5, 500 9, 360 N DY oh ee te acobann ele ea Gute ol al aye a DY AG: 3. 28 10.52 175, 3%) 16, 660 V-A DSB icscctiach ietende wearers die a scashorviosin so vasediae el Ao TNCs AG 3. 22 10.42 160, 850 16, 300 OB ocd and sa eee ade rete adore nope as PONV AAG 2 21 10.39 116, 000 11, 160 V-A DES oe aed FetN Aa eod daa aici edu AAG DY Beak 2 6 10.59 132, 000 12, 460 N a ee Se oath) ia ca ahah 3.32 by 3.46 3.25 11.15 146, 140 13, 110 V-A POs 38 A555 oe ete a Ses Sais 3.14 by 397 3. 10 9. 96 101, 200 10, 160 N
1 Tests made by the U. 8. Bureau of Standards, Department of Commerce, Washington, D.C.
8 N, tests made under normal conditions; V, tests made under vibration; V-A, tests made with vibratory attachment but without vibration.
3 Specimen held minute at this load, then broke explosively.
4 Specimen broke after 2 minutes at this load.
5 Specimen broke in 15 seconds at this load.
(Go gle
8 Top Rock, Birmingham District
TABLE 3.—Compressive strength of iron-ore cubes—Continued
d Method Cube No. ' Section Height Area [Rresking Strength af
testing
ware [per square
Inches Inches inches i imca 90220525 5ecx a cagltaNee a te cheat Cd dae taal 3.29 by 2 84 3. 22 9.35 109, 700 11. 730 N Ey ea ane aroma Gna NO CER eae ea 3. 2B by 2.37 3. 28 & 30 142,900 17, 20 v 5 Sea phase ce. Le ened Sea 3.32 by 2.25 3. 30 7. 48 81, 200 10. 850 V-A oe renee Ae ae eC anne ' 3.29 by 3.19 3.31 10.49 130, 500 12, 450 V-A 34 RE ene ered tren 3. 33 by 3.35 3. 13 11.16 137, 800 12, 340 N Boi ane anes Sas eA Cac y oe wd ape eS 2.85 by 3. 20 2. 80 9.38 134,320 14, 320 Be Rc cite Ee. oeaknn mts euees Sc 3.30 by 3. 32 3. 30 10.95 114,650 10, 480 N Bice ea ite ae Bs we it eae urine ue hehe: CREE DY AC ae 3. 20 10. 86 130, 300 12, ovo N BR Sane tess ida Ve emer enna! Ge Oe ON Sk 2. 95 10.89 130, 600 11, 990 V-A BU ys stale Se 88 1 3.33 by 3.31 3. 33 11.02 112,370 10, 190 N BO ee inte iegitn ne, Px ey eine Ghee, 8a cites 3.31 by 3. 38 2.61 11.19 147,000 13, 140 V CER eee in pire 3.26 by 3.31 3.27 10.79 108, 320 10, 040 N Se no aha thd ono oe NA end 3.30 by 2.13 3. 03 7. 04 65, 570 9, 310 N Wn 5 nn G cose A ne ahs 8h heen ee 3. 30 hy 3.20 3. 31 10.57 138, 220 13, 070 V4 OA suet cae. Meee oo ee Mee ete 3.33 by 3. 30 3. 33 10.99 115.5 10, 510 N Bete Ae eas brie eas oth eto 3.10 by 3.19 2. 20 9.89 158,910 16, 070 Vv BG otc R St eRe Sorte as Pale eas 3. 36 by 3.00 3. 30 10.08 120,730 11, 980 N Dc eae ah aes ge hege daa nee Nees eens 3.35 by 2.77 3. 04 9.28 108,000 11, 640 N 1: EDO ie Ka AW A ES 3. 33 by 3.03 3. 34 10.09 127.500} 12.640 N Bos ss hee aes ip cata 3.36 by 3.30 3. 21 11.09 206, 340 18, 640 ve 1? SAR CECE OE ER A OO Rg MIE ee ENE: 3.25 by 3.28 2.70 10.67 191,110 17, 940 V-A Bd se eee es ee ae Pees 3. 59 by 3.54 3. 36 12.71 132, 900 10, 450 N Oc he hm he Ateste ae ciate 3.57 by 3.39 3.27 1210 157,200 13, 060 Vea aa Ate Era A a SL Ws, DUE EERO 3. 42 by 3. 41 3. 22 12.00 119, 300 9, 940 3 Dba creat coho on aes, Sa aeas tes Nee eG 3. 51 by 3.45 3. 20 12.10 125, 900 10, 400 N eee aS ve Cae eT nae Oe OR EN 3.28 by 3. 26 3.17 10.69 165,310 15, 460 Vv Ln iene aerate ee aaa eR ee 3. 39 by 3. 14 3.16 10.64 108, 500 9,740 N Bnet Se ahd alain re Vie ca nth tenet the 3. 46 by 3. 52 2. 59 12.19 184, 000 15, 100 V-4 GO eet cia tl kat ple ae Sei 3. 29 by 3. 21 3. 21 10.56 118, 800 11, 240 N Clic ae Serer Ott otk, ate oa ues 3. 34 by 3.19 3. 11 10.66 118, 950 11, 160 N Boe eine eae oe ee ne eae ee 3. 38 by 3. 40 3. 22 11.50 122,100 10, 620 N Ga tt oe hate ot oe act rene ike 3.40 by 3.14 3. G9 10.68 158, 200 14, 820 V-A OB cise acer es ye ete S 3.51 by 3. 36 3. 20 11.80 136,000 11, 520 N OF kit ot nan see ye Se Bane omnes aL ae A DS an ae 3.17 11.60 177,940 15, 340 Vv BBS eciec s eetlas i rtin fra hares Rinna ete aae a 3. 58 by 3. 41 2.70 12.21 128, 700 10, 5 N OF ag urs ee hens tee eee aati ened 3.48 by 3. 24 3. 42 11.28 128, 400 11, 200 N Gi he oak mate Pine, 5 Sasaht, om, Rea Meeauuta ead 3.39 by 3.18 3.05 10.7 175, 15 16, 250 COs aces eer St Od eee ee ae 3. 44 by 3.31 3.07 11.39] 133,400 11,710 N £1 eae eee ae ee te IN nk PN oe 3.41 by 3.24 3. 33 11.04 147,310; 13,340 V-A i] eee ae ener Serer mine Deanne 3.32 hy 3. 23 3.45 10.73 123, 430 11, 500 N DD gh MEE ok oe es et) pa erion, BaP eae 3.43 by 3.35 2.55 11.49 115, 350 10, 040 N TB oe eee ee eee ensue e.-.| 3.30 by 3.06 2.91 10.10 162, 960 16, 140 vV ff Secon Sere nae at pes mnent Oitee een tne eS 3.23 by 3.31 3. 33 10.69 100, 500 9, 400 N oS cre er ets Wace Loe aed 3.46 by 3. 43 3. 40 11.88 190, 460 16, 020 V-A TB x SSncte dis eethadecton Sat cote Het teal ae oe UN 2000 3. 26 9.86 110,5 11, 220 N i Oe a Ie CRE a ait Bee RE 3.28 by 3.21 3. 37 10.52 107, 820 10, 240 N Dae ites eh ich een eck eat Pk 3.32 by 3.11 3. 30 10. 32 97, 930 9, 490 N DO deciles cae Bhs pte sete ded ied tena ARDS BOO 3.34 10.18 115, 130 11, 310 N BO sss Bare redial ga tape des £4 6 canst etl 3.22 bv 3.21 3. 40 10.34 112,3c0 —-:10, 870 N eee ay ae ee 3.28 by 3.10 3.17 10.17 118,810 ; 11, 680 N (0 EE eet es aie me es gi 3.30 by 3.27 3.04 10.78 117,000 10, 860 N BE Ge ce Ba eat Ps So tee ak oul ae Ole 3. 32 10.55 104, 600 9, 910 N Ce ee are ee rene pein cat ite: aN 3.28 by 3.39 3.24 11.12 152, 100 13, 670 BRS ees na peated tc este eet 3.20 by 3.05 2. ¥2 9.77 108, 300 11, 100 N BG csi oe ed BB dae owebalskeeecce! 440 DY 2S 2. 18 9. 80 94, 100 9, GOV N Bre ee ie a haha eat 3.14 by 3.10 3.62 9.74 116, 500 11, 960 Vv BS oe i ook kine Bade us winoeeatardoscwell alae DY oo 3.01 11.21 124, 700 11, 130 N BD eh ros Ses ops Shots Soaalsiunt atone oe aoe AO BS Goal 3.17 11.26 117, 950 10, 480 N eae Neneh eine 8.30 by 3.25 3.10 10.72 150, 400 14, 020 Vv : 7 Re St ne ote 3.20 by 3. 12 3.17 10. 26 127, 900 12. 460 N O82 2 haere 3.30 by 3. 12 3. 4 10. 30 86, 000 8, 350 N' oe tah nA 3.00 by 2.80 3. 12 8. 40 7, 500 11, 610 Vv WV aces, Basu 22} 8.16 by 3. OS 3. 26 y. 7A 104, 200 10, 700 N Oech ek ee cen 3.20 by 3.08 3. 32 9.56 165, 400 16, 780 Det ae neti, gf. oc, ityacbtun eit 4.25 by 3.63 3.13 9.85 111, 860 11, 370 N ee 3.23 by 3.16 2. 9 10. 21 97, 600 9, 550 N GOs wae he ete nb. ce. paiknssuee 3.09 by 2.97 3.14 9.18 119, 800 13, 060 V FOO) ca ocate Pets t, Skits Saad ook LESS Sek ES lO 4. 32 9.96 114, 200 11, 460 N Wlosdeeccicdee ¢ Bact 5 iyi de Sake Ree Per ee: 3.23 by 3.11 2. 10.04 125,330 12, 480 Vv 1 ( 2a ae oe tN GR OE ee eta 4.27 by 3.14 3.11 10.26 146, 520 14,280) V-A POS eset con coat ea ho ate et oamcaaeh a eel 3.16 10.63 116, 500 10, 950 N LOG os sett Wes pd Sete eo en OO A 3.34 9.56 137, 570 14,400 V-A BO cs Sheetal a er ae cea kta seein, 3.20 by 3.07 3. 20 9.84 97,300 9,890, N TOG pbc oat hes atest taal ines Bale abies 3.24 by 3.05 2.92 9.89 102,000} 10,320; N
6 Specimen broke violently after minute at capacity of machine. ? Vertical crack.
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Compressive Strength Of Iron Ore 9
Tests Under Vibration
Careful study of failing pillars in the mines showed that most failures occur near falls of top rock, which led the writer to conclude that the intense vibration caused by falls might make pillars fail under less pressure than when the load was static. An attempt was made to demonstrate the correctness of this conclusion by subjecting the test pieces to vibratory action and gradually increasing pressure.
The results were surprising in that instead of showing that the ore failed under less pressure the converse was the case. The compressive strength of cubes cut from one mass of ore increased from 10 to 50 per cent over that in the normal tests. Obviously, however, the increase was not due wholly to vibration, therefore duplicate tests were made with the vibratory attachment in place but without the vibratory action. Asa result the compressive strength still remained high, being but 3 per cent lower than the strength obtained under vibration, which averaged 28.3 per cent above the strength obtained under normal conditions.
The reason for the relatively large increase in compressive strength under these conditions was easily found. The vibratory attachment consisted of a 6-inch cylinder with a 114-inch steel plate at the lower end; the upper end rested against the upper plate of the testing machine and was attached to it. Within the cylinder operated a 10-pound hammer actuated by an external mechanism. Thecylinder and plate, being lighter and consequently more flexible than the heavy plate of the machine, permitted more perfect contact between the cube and plate; thus more accurate testing was possible:
After higher compressive strengths were obtained with the vibratory attachment in place, a series of tests were made with other cubes, a number of which were duplicates of those tested under normal conditions. As duplicates were not available for all cubes tested, values for N, V, and V-A were calculated and are given in Table 4, except that averages of duplicates for the various feet in a section are given.
TaBLE 4.—Compressive strength of iron-ore cubes A from sections of ore t
taken from mines in the Big Seam, Red Mountain, Birmingham district, Ala., representing each foot of the bed worked, from the top down
' Strength in pounds per square Breaking
loa
Foot Section Height Area ae: Vibrat ory
Normal dion attach-
ment
MINE A Inches Inches Sq. in. Pounds
Mee ee heen as dag Matt 3.35 by 3.13 3. 04 10.50 118, 312 10, 133 13, 000 12, 696 2 Aa ella cet Sissheark chadete She 3. 22 by 3.10 3. 14 9. 98 124, 158 10, o8 1 13, 575 13, 258 Be eel eae out omc gees te A OB DY ae ld 3. 30 10.25 111,042 10,837 13, WO4 13, 579 4 ROS eeneseteeth Slee cote! Donde ate A 3. 22 by 3. 11 3.16 10. 08 119, 978 10. 800 13, 869 13, 44 eee ee 3.28 by 3. 22 3.13 10.55 120, 500 10, 631 13, 63y 13, 320 Pee GeO eeu Meee eit oe wita cb Go AO Dy 308 3. 31 10.19 109, 160 10, 730 13, 766 13, 445 ena is Aetaye: test yee 3.20 by 3.06 3. 28 9.82] 127,158 11,716 15, 032 14, 680 PR RGNE Eek Sites Con eS tes A ion a & 3.18 by 3.09 3. O9 9.84] 114, 232 10, 229 13, 124 12, S16 Avernge / 3.25 by 3.11 3.17 10.14 117,445 10,708 13, 738 13, 417 a a ames: pues :
Go gle
10 Top Rock, Birmingham District
TaBLe 4.—Compressive srelig of tron-ore cubes prepared from sections of cre taken from the mines in the Big Seam, Red Mountain, Birmingham district, Als., representing each foot of the bed worked, from the top down—Continued
eee) pee eee? noch ! Foot Section Height Area MINE B Inches Inches Sq. in. ese 8 eg ye Se ee ee heres 3. 58 by 3.46 3. 31 12. 40 Deo SIN a ele Re 3.51 by 3.43 3. 25 12 05 i PRA et te Gt OES Ree ae ae Ee 3.31 by 3.20 3. 16 10. 61 Oh a Ota een asi Ae be 3. 52 by 3. 46 2. 64 12.20 ES epee hes Naan fridge Dore Mase 3.33 by 3.20 3. 16 10. 66 Or ais Ss). cnet aa 3. 46 by 3. 37 3. 18 11.70 @ nc bee eee eeedi oie uecascecec| 3.80 DY 3. 27 3. 15 11.00 Average. 3.45 by 3. 34 3. 12 13. 8 MINE C Visteon Gordo teins 3. 65 by 3. 50 3. 44 Deeds Sten Dek ae A Meat ak 3. 76 by 3. 49 333 Dek Fle Son Sa niaca eee 3. 54 by 3. 68 3. 47 Be tn Been eee 3. 65 by 3.21 8. 14 Oe Sete cricket 3. 36 by 3. 56 3. 40 Gs recoils ee oe tee 3.21 by 3.19 3. 19 Ds Sa se eh bet ate Eh bist d dd ot 3. 40 by 3. 55 3. 32 Bo BE es asin Bee 3. 52 by 32. 48 3. 25 a pores Se oe Pact 3. 60 by 3. 55 3. 48 Average 3. 52 by 3. 46 3.33 MINE D Bee ne dtet eae tue aire 3.36 by 3.20 2. 73 DA he alana eee) Thee ie 3. 34 by 3. 37 3. 36 Oe ous ie en tee a uisoceute sce 3. 43 by 3. 21 3. 23 Wide Ditech aes late ote Ss) 3. 32 by 3.23 3. 45 Desa cih cane ere Nd Gare 8 3.42 by 3. 27 3. 20 Average 3.37 by 3. 26 3. 19 11.00 le eredece rete eeue aes 3. 22 by 3. 21 2. 99 10. 36 Die coca cb ae ays eth teeta 3 29 by 3 16 3. 21 10. 40 SGD eenratere Meierhans en ome 3. 26 by 3. 33 2. 95 10. 87 Woe Sag htt See tate Vole 3.14 by 3.17 3. 10 9. 06 ice AN Sarge eo 3. 26 by 2. 70 3 25 & 82 Ore et a eee 3.31 by 2.98 3. 24 9.71 Te ee eae 3.07 by 3.30 305] 1016 8.. een ., 3.30 by 3.29 307 10. 87 DS se Sacral Sse Laat 3. 30 by 3.33 3.07 11.00 VO he ee Bias Seta bat 3. 30 by 2. 66 3% 17 8 80 Veet eu acterer sees tide DY 3 Oo 3. 33 10. 99 V2 ise ens See eScavessss] 2 DY ZS 2. 87 9. 75 bE See ee Ace eT SE ee ee 3.32 by 3. 20 3. 02 10. 63 Saas eee Se ener NOE Ne eee etn de a 3. 30 by 3. 30 3. 00 10. 91 Average. 3.27 by 3.13 3. 09 10. 2 Grand average... 3.37 by 3.26 318 21.08 14, 216
More precise testing, with regard to equipment and procedure, may give results showing a still greater increase over those obtained in normal static tests.
That the results obtained approached proper testing conditions more nearly was evident from the failure forms and the angular fracture obtained. In the tests under normal conditions many cubes failed unsymmetrically, half cones and pyramids being formed, but single cones, pyramids, and wedges extending froin the top to
Compressive Strength Of Iron Ore
Sulioj Bulmoys
''g WUNODIg
Top Rock, Birmingham District
FIGURE 4.—Failure forms resulting from crushing cubes of ore
Compressive Strength Of Iron Ore 13
the bottom of the cubes predominated. (See figs. 3, 4, and 5.) When the vibratory attachment was in place and testing was done with or without vibration, symmetrical fractures and the formation of double cones, wedges, and
pyramids were the rule. (See fig. 5, a.) Further, while the failure of cubes was quiet under normal conditions, it became violently explosive when the
vibratory attachment was 7% Double wedge ? parscirhcd arora
used. For failure forms in erushing pillars, see Figures
eee eee EFFECT OF FRACTURES 7 eee aN
To ascertain the influence of defects in the test pieces used, each cube was examined with a microscope before it was tested, and the c Effect of hard layer on position and extent of frac- ee ee tures caref ully noted. The FIGURE 5,—Failure of ore cubes under compression fractures observed were classified as horizontal, vertical, diagonal, horizontal-vertical, and diagonal-vertical. The compressive strength of
FicurE 6.—Failing pillar forming inverted cone
cubes with such defects was: Horizontal fractures, 10,918 pounds; vertical, 9,520 pounds; diagonal, 11,156 pounds; horizontal-vertical, 10,000 pounds; and diagonal-vertical, 10,630 pounds per square inch,
Dates by (OK gle UN VERSITY OF MICHIGAN
14 Top Rock, Birmingham District
Cubes having no visible fractures gave 10,949 pounds per square inch. The average of all defective cubes was 10,701 pounds and of all nonfractured cubes 10,949 pounds, a difference of 248 pounds per square inch. The lowest strength of the defective cubes was 9,520 pounds, the highest 11,156 pounds per square inch, which would seem to indicate that vertical cracks or fractures weaken the cubes least of all, while the diagonal cracks are most weakening. This condition may, however, be apparent rather than real, as the number of test pieces showing distinctly vertical cracks was small compared with the number showing other classes of defects.
Tests of duplicate pieces from the same location show that the compressive strength varies but little, the difference being due probably to cracks or incipient fractures. Comparative tests of duplicate FIGURE 7.—U right pyres Raszaed at base of failing eyes are given in Table 5.
TaBLE 5.—Comparison of tests of duplicate test pieces of the same form
coal Section Height Area Breaking crrength Pounds per
€ Inches inches Pounds tnch
ie DY BBS TOS 5c oes as ax Steves vente nscrentctasenisuk 3. 59 13.51 168, 400 12, 470 AOE IT BOO ONION 8 2S 5 Soca ow cue nas Ba kect dens aeCereickeeke 3. 70 12.90 208,750 11, 689 9/3.23 by 3.31 PONG on 65nd Gi Apbsann twa Tstashsacasaweawnen 3. 33 10.69 100, 500 9, 400 3.46 by 3.43 inches ee ae ee en ee a oe ae ee ak 3. 40 11.88 190, 460 12, 785 Bk DY S.00 IMCNORS 5 coins a Soletateesn sc eee Ri che daeascedeades 3. 20 11.80 136, 000 11, 520, NS Ot RNID oe oe SE obo Bic, he. Sultry sk oe tale baw naes 3.17 11.60 177,940 11, 956 gidiad DY 8.19 INCHES. o8. 6. cowa canciawnrecdancaca= essesennuss 3. 31 10.49 130, 500 9, $36 Epa eee tes era be) kis] aa] eae : F BLE AO Oise sn na corsa dene sabes a eke keke seuku save 2 O2a DY a1 0 Ons as: gest Coe Siceceb est) Taeeteetkhe ceaeoeen 3. 34 10. 18 115, 130 11, 310 Bide Oe Sie TOR Sn bina Lads 20s Seed aNd ue ea ac oned Ehee soe 3. 40 10. 34 112, 300 10, 870 3.28 by 3.10 3.17 11, 680
The compressive strengths given above represent normal conditions.
Diattizes ty (SOK gle eeu aweln
Transverse Strength Of Top. Rock 15
Tests Of Other Forms Than Cubes
To show the effect of the form of test pieces upon the compressive strength of the ore, tests were made with cubes and other parallelepipeds whose dimensions and compressive strength are given in 'Table 6.
TABLE 6.—Compressive strength of cubes and other rectangular test pieces
Compres- Test piece Area Height sive strength Pounds per square Inches Inches inch Cube, approximately. 2.222 ee eee en eee eee eee 11. 02 3. 18 11, 244 Square hase, height less than sides 2 ee eee eee eee 10. 77 2. 69 11, 200
Rectangular base, height same as longer side 8.71 3. 18 10, 666
As the difference in height between the first two forms is only onehalf inch, it is not surprising that the compressive strength differs so slightly. The difference is, however, more marked in the form with narrow base—the third in the table.
Doctor Baker' gives the following compressive strengths for various stones; for comparison the average compressive strength of iron ore from the Birmingham district has been added:
TABLE 7.—Compressive strength of stones
Ultimate crush-
ing strength,
Stone eee Granite: 3230 eee eee ees oe Se 19, 379 Limes (ONG .Wc oe eetce otis tects Gases jueeaeaceen ss 9, 438 WATE uo os at ttt ty eB 2 See tS A TN 12, 709 Sandstone: cc oh ee ee eee eee eee eee 9, 333 Iron ore (hematite) ee eee eee 11, 081
The compressive strength given for iron ore was found under normal conditions. The compressive strength with the vibratory attachment in place but without vibration is 13,889 pounds per square inch. The latter value is more nearly accurate.
Transverse Strength Of Top Rock
The transverse or bending strength of the top rock largely determines the size of the openings made to extract the ore. The beds of rock forming the roof of workings must act as beams in resisting the weight thrown upon them. Such resistance depends upon the tensile strength of the beds, which is much less than the compressive strength.
7 Baker, Ira Osborn, A Treatise on Masonry Construction. 1909,p.1l. .
16 Top Rock, Birmingham District
The top rock that forms the roof of the mine workings is composed of slate and sandstone. The latter is often highly ferruginous, and the iron oxide undoubtedly adds materially to its strength. The beds of sandstone within 5 or 10 feet of the top of the ore bed are usually thick enough to constitute strong elements of support, although the beds of shale (locally called slate) are often thinly stratified and weaken on weathering.
Slip and cross-bedding planes adversely affect the conditions of support. They make necessary relatively narrow workings and the use of timber for temporary support. Even when such precautions are taken it often happens that the roof falls in a comparstively short time. When conditions permit, the most satisfactory procedure is to leave roof ore to support the weak shale top rock.
On the whole a reliable index of the strength of top rock and its ability to stand would seem to be the span at which beds of certain thickness will fail of their own weight.
Test pieces were cut from slabs of slate, sandstone, roof ore, and an intermixture of slate and sandstone or roof ore. The test pieces were difficult to prepare, because they disintegrated under the vibration of the saw and the excessive amount of water used in sawing. The selection made probably separated the specimens that had been exposed to air and moisture from those more recently exposed, and the pieces tested were probably more representative of the top rock in place. Of about 50 test pieces that it was planned to test, only 22 were obtained. This limited materially the tests made and the data
gathered. RESULTS OF BENDING-STRENGTH TESTS
Information concerning the bending-strength tests is given in
Table 8. As a number of the specimens were irregular, they were embedded
in plaster of Paris. Measurements of the cross section were taken at or near the fractured section, because of variations in cross section throughout the specimen.
yon A ry
Transverse Strength Of Top Rock 17
TABLE 8.—Bending-strength tests of top rock in the roof of ore mines
th Ultimate Modulus
Test piece P Span Breadth| De of rupture No. Kind of material (1) (b) 7 ona Ee me)
Pounds
per square
Inches Inches ne Pounds i
Psecwtieuss< Slate. cross cc hewecieso wast sens use sce 14 3. 18 coral 510 2, 340 Dose hecotebe dots OO se sda oee Sotto eee ocn eet 14 3. 00 i 24 360 1, 640 3. Jepstisen MOOG ak most hits Bee De ok ee SE, S 13 3. 12 1.81 710 1, 355 4._ aes 0 Boe Sidon ayate wit gee nae wae eosiciote ie 13 2. 90 1. 70 505 1, 140 Ossett loses OO 2 soso rate satel eee sche 12 2. 90 1. 30 610 2, 240 Gora tite dt) ere 3 M02 scutes ae ae da ee ee 10 3. 00 2.15 750 810 Vices ntitaxti ol ewe ook sisal, irae Woda No ier ne 10 2 95 1.00 110 560 octet eee ls PO St i ian DO tela ona hotter el 14 3. 00 1. 05 270 1, 710 Pia oseettes ta G0 aoe cet sace tel ae peas 14 2. 84 1.55 720 2, 220 10 okie SOO Set Jacl anen clot uate ten caae 14 2. 90 1. 670 1, 880 Wictcest dese eee Gs 283ion cei bee ete Set erate ee 1] 2 95 1. 70 910 1, 760 Ns 2s Sheed apee cal OOP ea iics cupid Mine tet Ae a eco 14 3. 10 1. 69 740 1, 750 Seeapaae eRehiae! Slate, ore, or sandstone ET eae a 14 2. 90 1. 50 500 1, 610 VA oe ee ee Os a ae ee Sct yt at ord 14 3. 20 1. 64 1, 930 Pp eee ines Bo seen een eee atten een erer ere 14 2. 72 2. 21 1, 610 2, 550 16... ee ener DO eis eu th tans oka te 9 3. 00 22 400 3, 160 Leioeeaitscscd ORG i cts ee ay oe Bete 14 3. 14 1. 65 580 1, 480 Bete Os eters te ee ae 14 3. 09 1. 45 540 1, 740 19... Soe se Otcaote noses wana ou cew ates 16 2. 80 2. 78 1, 700 1, 890 Sie Sek cielo we OS ee oor be Lia adel isi co ma a 14 2. 80 2. 98 1, 750 1, 500 ys eee eae nee eae! OG ees ce ees ao ee hr oe 11 3. 3 3. 32 6, 140 2, 640 Fb ole Loker He Sead G02 30s Ss ec ote eee eee 13 2. 93 L. 65 810 1, 980
The specimens tested were free from slip planes and of fairly uniform thickness, although cross-bedding was evident in practically all of them. The tests were therefore made with test pieces that represented better than normal conditions of top rock, and the results are probably much more favorable than could be expected with equal spans of top rock.
Tests Of Beams Failing Under Their Own Weight
Calculation in feet of the depth of beams with a given span that will fail under their own weight gives the following values:
TABLE 9.—Limits of depth of beams with given spans, feet
SAN Mt ao po ep tise s e ce d oe te etal eae ee as 10. 000 20. 000 30. 000 40. 000 Slate: IMAI oe ce cosas cs Set ac ccs tac sdececttleesse . 160 . 641 1. 442 2. 564 AV OCTARO@2 2002 pence ste eit ee ona shoo eeooewc as . 099 . 397 . 893 L. 590 Maximiim:2..c¢ 22 5S ee Gob ne ele eee eee ease cece . 038 183 . 45 . 613 Sandstone or roof ore: NEINIMU M2 20522 ooo seen ces ee Se ee ooee eee oe sees . 080 dal' . 724 1, 284 AVOTAR Gs heh ete ott oan ce settee Sete eS . 061 . 247 . 558 . 990 MAXSIMMUD 252 sec econ Sate bolic eee oases . 043 174 . 392 . 697 Sandstone and slate: WEI e ooo cece oe ceustcc aul eso carseueleose sees ee .071 . 285 . 643 1. 143 DOM OEA GO ci rad alt tk ta Oat GY ot . 053 .215 . 485 . 862
MASINI 2 soot eee cGetiwe oso wuseee seb ehuowue - 036 145 327 . 582
Table 9 shows that 30-foot spans of the top rocks constituting the roof of the ore mines average failing under their own weight as follows: Slate, 0.89 foot; sandstone or roof ore, 0.56 foot; and slate and sandstone, 0.48 foot. Shale and sandstone or oreantimately interstratified therefore give the most satisfactory roof material.
(Go gle
18 Top Rock, Birmingham District
Modulus Of Rupture
Table 10 gives the modulus of rupture of several kinds of stone, as determined with the testing machine at the United States arsenal, Watertown, Mass.°
TaBLE 10.—Transverse strength of stone
Stone Average modatus of rapture, pounds per square inch Bluestone, North River 5, 026 CVAD IGE oo 3 Sis ee Oe Si eee dee oes 1, 849 LAMOCstODG sesh ooh ta Ss ee or le 1, 377 MAP 6 sias eres eee Sn ee es Sate erotic 1, 390 BANGStONG: 22S ob ee ee Se ee els ees a 1, 378 Bibte Jost awe e ect oe re ek eee ee te els 7, 671 Iron ore (hematite) 2 ee eee 1, 765 Ore and "alate cn 5 8 eo Se ee 1, 863 OSA eres ee i a Sa Ae ee eta ee ioe 1, 617
To the above table have been added the results of tests by Prof. J. M. Daniels, at the Carnegie Institute of Technology, of 22 test pieces—12 of slate (shale), 6 of ore, and 4 of ore and slate.
The difference between the two sets of measurements of slate— 7,671 and 1,617 pounds per square inch—is probably due largely to the physical condition of the specimens. Practically all of the specimens last tested showed ripple marks and cross-bedding and were thinly stratified.
The test pieces were collected and prepared by the Bureau of Mines for bending-strength tests.
Elasticity Of Ore
The tests recorded in this section were made in the United States Bureau of Standards laboratories, Washington, D. C., under the direction of D. W. Kessler. Several columns were cut from masses of iron ore free from fractures, all but one test piece having the larger dimension at right angles to the bedding planes.
The evident failure of pillars through lateral expansion under roof pressure suggested the desirability of determining whether or not lateral expansion or deformation actually took place and if so to what extent. The spalling off of slabs of ore and the loosening of masses of ore as the height of pillars is reduced by roof pressure were checked by the observations made in the testing of cubes and hardly seem to need corroboration by actual deformation tests; however, such tests were made, with the results recorded in the tables that follow.
§ Baker, Ira Osborn, A Treatise on Masonry Construction. 1908, p. 13.
(Go gle
Elasticity Of Ore 19
The longitudinal compression was measured by a compressometer that consisted of an averaging lever system manipulating an Ames dial reading to one-thousandth inch. Deformation was measured on two opposite faces of the column, and as the lever mechanism gave a magnification of five to one, the actual values are one-fifth those recorded.
To determine the lateral expansion due to vertical compression, measurements were made with a single Ames dial so arranged that it could be shifted to any vertical position on the column. Measurements were taken on opposite faces. The dial read to cne tenthousandth inch and the values given showed actual expansion.
Results Of Deformation Tests
Deformation tests were made to show the vertical distortion of four columns of ore 4.47, 5.40, 11.88, and 13.29 inches long. Tho results are given below:
TABLE 11.—Deformation measurements of 4.47-inch tron-ore column, showing vertical distortion °
{Area of column, 11.22 square inches; bedding, horizontal; gauge length, 3.5 inches]
Load, in pounds: Inch BO: fe BOs oe ee 5 ee eae oe eee 0. 0000 7 ae ode nt ee ree Rn 0019 747A © IA ae Meet Ser eae TET ee Yosa0e Pee eC Re 0033 33,660 Bedi yal oad ae Ae 0051 MA OBO Secon lent ce inhale dante erate Eales 0068 BO NO ta a ee tes epee ee acoso 0089 7 AAS 7 ee ne ne eo ee 0111 74 ea ene ey SOC A OE ESE 0130 807608 a 5 ie ee he eee eee 0158
TaBLE 12.—Deformation measurements of 5.40-inch iron-ore column, showing vertical distortion ¢
[Area of column, 11.23 square inches; bedding, horizontal; gauge length, 4.50 inches]
Actual values are one-fifth those recorded.
t Actual values are one-fifth of those recorded. 8 Specimen began to crack at this load.
(So gle
20 Top Rock, Birmingham District
TABLE 13.— Deformation measurements of 11.88-inch tron-ore column, showing vertical distortion !
[Area of suena 11.56 square inches; peddling: vertical]
' 9-Ineh gauge 10!4-inch gauge
First Second Third Fourth Fifth Sixth test test test test test test
. SREREMSED Inch Inch Inch Inch Inch Inch
Ba cteabcieaceea 2 tat aa, Neher e tae 0.0000 @0000| 0000] 0000] 0.0000 @. 0000 Fr a ee ee re neck een em . 0042 . 0066 0049 : 0049 uso A 1 Rae ae Fone Aman Cue ee nat . 0001 -0119 102 .0110 0120 0108
(ORO oe nce te ae ee tate: 0151 0170! .0168 .0173 0192 0163 QB DAO eater ae en ale . 0199 . 0221 . 0245 . 0241 BT OU se she hi ana! atte eeeieh in Nata eh . 0260 0271 0287 . 0292 . 0333 (301 DBDs ata a Cracte Mctacal a ted tce . 0321 . 0830 0351 . 0358 _0397 0358
(7. aR MAE alll ot ee Rien eM RD eh . 0378 .0380 .0419 0418 . 0457 o4ry Dat ata hes Sc sea otto soen MO Mb aye ach 0438 OMS ose chess cede decay ee
Decreased
0 0605 oe ack es 1k in aca eels Liiaenase th eee cement A (ye eae 370 87,800 Mites Pee btaecwacen tes ceu|! se ORO lotesta ccs: 6311 46,240. - bs rch es emu ec eaart! OMB. ce ctectac: C2 34,680... Series hen Utah eae le Na detent 0206 0195 23,120... eas tet leas Rica hort Partie 0147 |...2.. 2. 0135 11,560... owes i eieneain ewan SOON eo. c. 0083
! Actual hid are one-fifth those recorded.
TABLE 14. — Deformation measurements of 18.29-inch tron-ore column, showing vertical distortion !
{Area of colamn, 11.36 square inches; bedding, horizontal)
11-inch gauge
'Load, In pounds
Increased
wee ee eee ewe ee ee ee ee ee te twee ee
' Actual values are one-fifth those recorded.
The results of these deformation measurements show a fair degree of uniformity, and the values for elastic measurements of different test pieces show about the same range as were obtained in the compressivo tests.
There was less vertical distortion in the column with bedding planes vertical than in the column of about the same height with the bedding horizontal; there was, however, greater vertical distortion in the shorter columns with bedding horizontal.
a
ad
aan
Elasticity Of Ore Pt Lateral Expansion
Measurements of lateral expansion under vertical compression were made on a 13.29-inch column. Two series of tests are shown.
TaBLE 15.—Measurement of lateral expansion of 13.29-inch iron-ore column; bedding, horizontal !
inch linch 2inches 3inches 4 inches 5inches 6 inches At center Load, in pounds from end from end from end from end from end from end from end end
Inch Inch Inch Inch Inch 0.00059 0.00122 0.00171 0.00070 0. 00080 . 00116 . 00191 . 00218 . 00088 . 00158
- 00028 . 00031 - 00102 - 00085 - 00115 - 00111 . 00180 COINS Meedwescge
1 Actual values not recorded.
' Results of the lateral expansion tests were not altogether satisfactory. It is probable that the number of tests made was too small and some of the test pieces may have been defective. Lateral expansion occurs, but is least in the middle of the column and greatest at or near the ends. How far lateral expansion contributes to the failure of pillars is, then, not definitely known, but it probably plays an important part. Figures 8 and 9 show the effect of lateral expansion.
Modulus Of Elasticity
The modulus of elasticity of stone varies with the load and is valuable in determining the distortion of a mass of stone or ore under weight. With ore the modulus of elasticity may give some indication of the distortion that will result under the weight of superincumbent strata.
Iron ore, like sandstone, FIGURE 8.—Ore spalling from face of pillar takes a permanent set for all loads. Ferruginous sandstone naturally does the same.
viatizes ty GOO
22 Top Rock, Birmingham District
TABLE 16.— Modulus of elasticity of stone between limits of 100 to 1,000 ®
The modulus of elasticity given for iron ore has been added to the table for comparison and is an average of 8 or 10 tests, the range being from 6,110,000 to 9,640,000. The tests were made between limits of 100 to 9,000 pounds per square inch.
The modulus of elasticity or compressibility is determined by dividing the length of a bar or column of material subjected to longitudinal pressure by the decrease in length and multiplying the quotient by the load in pounds per square inch. The amount by which a test piece fails to return to its original size and shape on the release of pressure has been defined as ''set.'' It represents per-
FiGuRE 9.—Failure of pillar by distortion manent distortion. PUBLICATIONS ON METAL MINING
A limited supply of the following publications of the Bureau of Mines has been printed. Requests for publications available for free distribution should be addressed to the Section of Publications, Bureau of Mines.
The Bureau of Mines issues a list of all publications available for free distribution as well as those purchasable at cost from the Superintendent of Documents, Government Printing Office. Interested persons should apply to the Section of Publications, Bureau of Mines, Washington, D. C., for a copy of the latest list.
3 Baker, Ira Osborn, A Treatise on Masonry Construction. 1909, p. 14.
Digitized by ( 5OX gle UN pares ; FM CHIGAN
Publications On Metal Mining 23
Publications Available For Free Distribution
BuLueTiIn 48. The selection of explosives used in engineering and mining operations, by Clarence Hall and S. P. Howell. 1914. 50 pp., 3 pls., 7 figs.
BuLLETIN 80. A primer on explosives for metal miners and quarrymen, by C. E. Munroe and Clarence Hall. 1915. 125 pp., 15 pls., 17 figs.
BuL_etin 204. Underground ventilation at Butte, by Daniel Harrington. 1923. 131 pp., 3 pls., 42 figs. .
BuLuetin 215. Timbering of metal mines, by E. A. Holbrook, R. V. Ageton, and H. EK. Tufft. 1923. 72 pp., 17 pis., 43 figs. .
BuLueTin 235. Mine timber: Its selection, storage, treatment, and utilization, by R. R. Hornor and H. E. Tufft. 1925. 115 pp., 16 pls., 3 figs.
BULLETIN 257. Review of safety and health conditions in the mines at Butte, by G.S. Rice and R. R. Sayers. 1925. 29 pp., 2 pls., 4 figs.
TECHNICAL Paper 174. Suggestions for the safe operation of gasoline engines in mines, by R. H. Kudlich and Edwin Higgins. 1917. 19 pp., 3 figs.
TeEcHNICAL Paper 314. Metal-mine fires, by Daniel Harrington, B. O. Pickard, and H. M. Wolflin. 1923. 20 pp., 7 pls.
TEcHNICAL Paper 363. Lessons from the Argonaut: mine fire, by B. O. Pickard. 1926. 39 pp., 4 pls., 5 figs.
Miners' CircutarR 13. Safety in tunneling, by D. W. Brunton and J. A. Davis. 1913. 19 pp.
Miners' Circutar 17. Accidents from falls of rock and ore, by Edwin Higgins. 1914. 23 pp.
Miners' Circutar 19. The prevention of accidents from explosives in metal mines, by Edwin Higgins. 1914. 16 pp., 11 figs.
Publications Obtainable Only From The Superintendent Of Documents
BULLETIN 57. Safety and efficiency in mine tunneling, by D. W. Brunton and J. A. Davis. 1914. 271 pp., 6 pls., 45 figs. 40 cents.
BuLLetin 75. Rules and regulations for metal mines, by W. R. Ingalls and others. 1915. °296 pp., 1 fig. 35 cents.
BuLLETIN 107. Prospecting and mining of copper ore at Santa Rita, N. Mex., by D. F. MacDonald and Charles Enzian. 1916. 122 pp., 10 pls., 20 figs. 25 cents.
BuLueTIN 121. The history and development of gold dredging in Montana, by Hennen Jennings, with a chapter on placer-mining methods and operating costs, by Charles Janin. 1916. 64 pp., 29 pls., 1 fig. 30 cents.
BULLETIN 127. Gold dredging in the United States, by Charles Janin. 1918. 226 pp., 63 pls., 23 figs. 50 cents.
BULLETIN 132. Siliceous dust in relation to pulmonary disease among miners in the Joplin district, Missouri, by Edwin Higgins, A. J. Lanza, F. B. Laney, and G. S. Rice. 1917. 116 pp., 16 pls., 6 figs. 25 cents.
BuLLETIN 188. Lessons from the Granite Mountain shaft fire, Butte, by Daniel Harrington. 1922. 50 pp., 5 pls., 2 figs. 15 cents.
TECHNICAL Paper 24. Mine fires, a preliminary study, by G. S. Rice. 1912. 51 pp., 1 fig. 5 cents.
TECHNICAL Paper 67. Mine signboards, by Edwin Higgins and Edward Steidle. 1913. 15 pp., 1 pl., 4 figs. 5 cents.
TECHNICAL Paper 132. Underground latrines for mines, by J. H. White. 1916. 23 pp., 2 pls., 7 figs. 10 cents.
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24 Top Rock, Birmingham District
TECHNICAL Paper 134. Explosibility of gases from mine fires, by G. A. Burrell and G. G. Oberfell. 1916. 31 pp., 1 fig. 5 cents.
TECHNICAL Paper 223. Cost keeping for small metal mines, by J. C. Pickering. 1919. 46 pp. 10 cents.
TECHNICAL Paper 250. Metal-mine accounting, by C. B. Holmes. 1920. 63 pp. 10 cents.
TECHNICAL Paper 251. Ventilation in metal mines, a preliminary report, by Daniel Harrington. 1921. 44 pp. 10 cents.
TECHNICAL PaPerR 260. Miners' consumption in the mines of Butte, Mont., by Daniel Harrington and A. J. Lanza. 1921. 19 pp. 5 cents.
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