Show standard d rounds spano for blasting in ua w metal lula PV mining u d practice drilling soft jog medium and hard ground graphically described by aa charles S hunter S B E before ill the dp development A D of the dill Ak water 1341 hammer IP drills sll when piston machines were universally used ill the type 0 of round known su as the hammer cut was SUM very generally employed ui in metal mining PUE and it 41 is S IS still largely used where hand drilling ST is the dill practice such lions a I 1 round puno ST is shown in 11 figure A two om lines 0 of jo holes m are 0 drilled across the dill S face and lq blasted pIse ut in qi the 0 order numbered to 04 break a cut before drilling the al remaining holes which M are 0 used to ol square up the ay face the al principal reason for this sll round si is the dill fact that most of JO the holes have a I 1 downward slant PUL and with hand drills e pue and pu piston cm machines bore holes that will HIM hold water can be drilled more easily pue and more rapidly than hp dry holes the qa water prevents the dip bit from becoming au joil hot and losing aa temper jadud pui and keeps the qi D sludge in ui suspension so Os that the qi drill does 1 more effective work and the gauge 3 of JO the bit sr is not AA worn UIO down so OS fast 9 L r v as su ral 1 I agit J mk no figure a A IeH hammer Luu cut an round the dip water hammer drill was sum perfected the dill piston machine practically disappeared from underground work jom but the miners clautu s naturally continued with dili the same amus type cdx of jo round pum sv as they had been using with ilia the increase m in cost jo 01 lacor put and s supplies addo operators jua sao began a study of jo elal blasting chips th methods aed particularly ul in tight work such alons SU as drifting sink JUTS au g PUL and raising they discovered qa that with the hammer ina cut pue and cuts based on a 1 similar principle the dill full depth of jo the 01 round pun drilled was i rarely pulled pound unless aided by some feature in the ground this led to 01 some careful practical experimenting SUl lasting over two years UT in some MOS es pue and the dill eventual development qu of CIS standard rounds sv agthe qa depth of a round blasted out depends entirely the al depth of jo ground pulled by the ino cut holes the pulling 0 lo 10 qa depest possible cut em was s the dill principal problem to oi be sol pajas alved i in u the dill first place dould it I 1 is s not IOU economical e se as S a rule to 04 01 lind a im cut aper ump than the dimension of the face in th build i ta in ut which pip the dip cut holes are drilled the chief mod D Aap 10 01 pad III in these experiments was sm that in m order to 04 11 null qa acut properly to 01 the dill bottom of jo the holes it 41 si is au sD its 01 daia IL at least two OMI im cut holes patu meet to ol OJ form lu a vui vin va vu soft ground oa 02 pu one pair of holes will lla be sufficient uj in eq hard pi rn 41 may q be necessary to 04 have three Vs sa side ps by side or lipp drift 01 aale 7 three or io four holes meet in III the otje center of jo the dill the 01 t OJ tua m e a pyramid or jo center cut with the cut an out squaring up of the dill face st is a simple etu matter stach zal howing illustrations show different types of jo haap n rounds puno S alsap designed au p oj for a cap dl and fuse eig blasting cups which kind saull T aped Aap ui in some milos mining districts asp for different haap jo ground and different working conditions pue and which abati proved p method of shooting it is effective m in sn use with this arable Jr able se as a rule to 04 have the dill holes forming the ap first Ner t co ioa E ir c representative a q I 1 du wa font de A to 04 be shot meet so Os that their explosives charges will detonate dewill simultaneously this will lla result in a cleaner break in u the illustrations lle all bore holes DIU are numbered to OI show otis M the order in ul which they ag are shot figure el and figure D 3 represent egsa drifts which have a high arched top doi to ol provide for 9 CPS I 1 figure B E soft ground motor haulage both of jo these rounds use 4 the oil principle of jo the flat A cut the dill round ui in figure a is s for soft rock IDO where only 0 one au pair mud of jo V cut anza holes st is necessary A relief hole ON no 2 7 1 is sr placed below the wo cut so os sl as to oi widen it 41 wo out PUL and give the dill succeeding holes a better chance to oi break figure 0 shows aois st a i wis similar irl round designed P for hard ground which requires a flat A across the mud entire D uj face ul in addition IMPE 1101 to 04 the center A which it 4 should be observed sa s1 is drilled at a somewhat sharper angle than that UT in the soft rock jow round of jo figure B there is s a d pair 11 of JO A holes on a each e rib however on account of jo the dill height of jo the cut in broken out by the dill first A put and the al z lT relief jat hole below it 11 si is not necessary for the cut in holes of JO zm the Vs sa on the dill ribs sap to 04 meet er A 1 0 go C 0 1 A C paulj their bottoms ura can be ds spaced pu some aluos distance apart breaking more ground and giving the succeeding holes a u better chance to 04 break ivain uv an extra relief hole coq above the center A is s also used to 04 a break p into the aal cut in jq before ro rocq the atil top dol holes are am fired figure ca D shows another hard ground puna round with a flat A cut across the entire liqua uj face this was sem developed for a en ai topped drift P with a height of autu outu nine feet advantage 2 bs square 0 of j this height si is taken to 04 drill both the qa center uz I auz A and p the i pip relief holes above e alq and below it 4 at e a wide pla angle these after the dill center daud A and so Os relief holes are aa 9 fired pa immediately much material sr is thus snip taken out of jo will the center of the face agaj that eal I the side cut holes 5 PUE and 19 6 started a little lower than the bottom hole for the center A diu are adap depended papu upon lm with I 1 TJ the q D liff lifters siD to 04 square up the bottom of jo the face without appu additional relief holes the section of this ap drawing 2 illustrates a principle which has been isa established in ul iju all the later ja work on standard rounds namely that A inz cut holes which meet should be drilled a foot deeper than M the OT other millo holes for the round og 60 1 01 C li V 7 4 5 1 t i i j I 1 ai b 3 oa 02 c ay figure CE ich hard P 10 ground punO the next four illustrations figures a F j 0 and H represent 1 drifts with the ordinary round puno arched top do these rounds diu are iju all planned uld to 01 give su as many holes su as possible on an upward slant thus securing the i maximum u adds speed P from w the water hammer drills lP now mou universally used which drill faster on tio an upward slant because the cuttings diu are washed out of jo the hole su as soon su as they diu are formed figure a shows a round ui in ground sufficiently soft for boj it 41 to 01 be unnecessary for i the holes forming the A to 01 meet 40 to oil take advantage so of pointing the drill along the buol longest sixt axis of jo the drift c and pu thus giving the hole a greater slant 1 these holes diu are drilled on a diagonal line dull da 01 01 figure a soft ojo ground pun figure din F j shows a round in ui medium ground where blasting aul conditions diu are a little tighter 1211 iDIL than in m figure a here three D cut holes are u D used to ol make sure ans of jo pulling the cut out clean pui and it is si ut an advantage 13 P A U IT I 1 to ol have III all three itil 03 holes pau meet at u I 1 the bottom so 0 that their charges will explode simultaneously this is ST known su as the center or 0 a pyramid ind cut r 1 n A ol 01 r i so J Q B figure a medium ground figure 0 shows the development of the gunoa rounding ro ali fig ure din F J loj for hard ground with extra tj salo holes u above and bel olaa ow and the ribs the center ino cut on 7 A 6 4 S 1 1 ft 0 o I 1 I 1 V f T 10 0 9 fe figure 0 hard auh P io ground puno this round 1 is s j further n modified ut in figure H for extra i hard ground by giving I 1 the top dol cut an hole ox no 11 1 a greater slant 01 9 9 figure 11 1 extra IRH hard P ground the i rounds thus snip far discussed diu are designed for use in ground that will stand without the necessity of JO timbering 0 J close to 0 the face and the ulu aim in U IP all of JO them ST is ig first Is to 04 blast istia a good cut from the middle of the face and then to 04 develop this to oj a ino cut ij from wo rib qi to 01 i rib q in III this SIT lluLu manner Ja the inefficient practice of jo shooting against an arch ST is avoided P sl as muc su as possible when driving UI in aa ground puno that has to oi be timbered sojo close to 01 the face however i the A cut and the center wo cut generally have to 01 be abandoned because heavy blasts of JO this s type ar likely to 01 knock down the timber sets the procedure m U this sup I pup pupi of jo work pom must be to ol break aimaq su as I 1 much su as sod possible iqs is iro the center of JO the face with single q hole ajo blasts so Os that in holes with the qa lightest 1 sod around the edge can Z be blasted j sible charges sd and thus not endanger the timbering figure I 1 shows a round of jo this type for soft ajo grou where two oma slanting holes diu are sufficient W to 01 take out j center doad properly Xiao ah figure j I 1 soft ground A T tere figure r J sl is a round for medium tuni ground cut holes DJU are used ads drilled on a considerably redl PUT and also a center top hole 10 4 0 o figure J medium ground figure K represents a hard ground round showing how a maximum amount of ground can be taken from the center of the face by means of four cut holes thus lightening the burden on the remaining holes in all three of these rounds for timbered grounds advantage is taken to the greatest possible extent of the ability of the water hammer machines to drill faster on an upward slant 10 za 5 02 ao 00 figure K hard ground the rotation of shots in all the rounds illustrated is designed for hand mucking it will be noticed that the lifter inter holes are always fired last they are loaded heavy enough not only to break bottom but also to throw the muck back ack from the face so that the drill can be set up with a minimum amount of shoveling and can be operated while ane we muck is being shoveled out behind it where mechanical loaders are used this system of blasting is not advantageous because the heavy blasting of the lifters scatters the muck down the drift therefore when mechanical loaders are used the rotation of shots should be changed 0 o as to fire the lifters as soon as possible and the back holes oles last thus leaving the muck piled up against the face ln lna a shape that will allow the loader to do its most effluent efficient work iii I 1 all the operations where the standard rounds here illustrated lust rated were figured out it was found that it did not pay to 10 take into consideration local slips in the ground when la ying out thia rounds except in drifts that run long along veins where 0 there is a continuous free slip along the hang hanging ing ivall w wal n or under all other conditions the use of the autor jt or the center cut accomplished more than d did id cial 1 rounds ands local slips and laid out each day according to backs ks in in the face in connection with the development of standard rounds access has also been achieved in some mines in the stand ald izing of explosives Ps ives charges it is the practice in these operations gnp orations to classify all ground in the mine as ashard hard hardy met diun mor or soft or somei sometimes imes under four or five heads next of to determine the type or types of round used in each class ground and then to fix the size of the charge for each hole this th in each type pe of round for the several classes 0 of f ground s must he be worked out experimentally in each mine of course se and d the strength of explosive also specified this systematic method of fixing charges cha ages has proved much more economical econom ical of explosives th than anthe the old custom of leaving the size of the charge to the judgment of ithe the individual ind miner the writer wishes to acknowledge assistance received in the preparation of this article from mr N B braly bral of butte montana mr C A of bisbe arizona ariz ona and mr E leland of pilares de nacozari Naco zari sonora mexico d |