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I I I 1 I t I I, BARREL I I, t l 26m as LEVEL, FIGURE 1 East west section through the shaft alld ancillary excavations. 84 MINING SHAFTS, a Pre liminary est imates of the s tress Numerical methods used. strain deformation fo r planni ng The comp uter program FREEFS wa s ex t ensivel y. modifications to the shaft timbering modified and adapted for use at. b Th e correct schedu11ng and sequencing Blyvooruitzicht by the Rock Mechanics. of the extraction of th e ore reserves Department staff A number of pre and. to minimi ze the above and R R post processing programs have been. c Det ermination of the stabil ity of the deve l oped i n order t o. satellite pi l lars a all ow easy modell ing, b generate grid pat terns from dig iti zed. The role of modelling, face position data, Traditionally the desi gn of underground c permit automati c windowing. exc avat10ns has been based on empirical and d provide visual output in the form of. obs ervati ana 1 methods More recently comp uter generated li ne drawings. numeri ca l met hods hav e become available A feature of the system i s that any area. whi ch are able to model stresses and dis of intere st can be selec t ed from dis k files. placements around underground exca va t ions and anal ysed 1l l1led iate ly The entire mine. Emp i rica l design methods depend on with portions of adj acent mines is. relating experience gained elsewhere in modelled using 512 x 333 blocks each. similar s ituations Th e observational representing a 15 m x 15 m square area Any. method is that method which is changed to area of 60 x 60 blocks 900 m x 900 m can. suit changing circ umstances and has no be selected for mi ning s imulati on in each. scientific base case the effect of mining outside thi s area. Ana lyt ica l design me thods howe ver rel y on being taken i nto account See Figure 2. model s tudies in which the performa nce of The Rock Mechan ics Department has. an excavat ion can be analy sed before it is available its own computer facilities which. created are also used for seismic research The, Ana lytical design methods al lowed for system s constructed aro und two Hewlett.
mod el studies to be made of the shaft Packard HP 21 MX E series mini computers. pillar extraction at t he mi ne before any of See Figure 3. the ore reserves contained i n the pillar The f trst unit with 64 Kb has a 12 bi t. were mi ned Th is numeri ca l modelling was AID sub system H P 2313 a 20 Mb di sk. only a part ia l component in the I, drive H P 7906 wi t h con troller and. inves t igation and it wa necessary to swi tch se 1ectab 1e use of graph i c termi na 1. combine analytical with empirical and H P 2648 This unit and AID i s. observa ti ona 1 methods to ensure a dedicated to cont1nuou s acq uisition of. sati sfa ctory design The cycle was dat a detection of seismic events and. a Site characterization collecting storage of eve nt data on disk. geolog ica l data and rock strength The second unit with 1 Mb has a 20 Mb. data dis k dr ive and t he graphi c terminal, b Geotechnical model the site was tog ether with a 1i ne pri nter HP 2608. divided into areas of s imilar geotech plotters HP 987 2 and HP 2648A and. nical properties magnetic tape drive HP 7970, c Modelling and design analysis a mod The graphics terminal has a fully refre sh. elli ng techni u e was se l ec ted graphics display with 720 x 360 add ressab le. EXTRACTION OF NO 1 SHAFT PILLAR AT BLYVOORUITZICHT. ENT Y POINT 1, EDIT FACES, TEMP OFACE TEMP, MSET ERRR f I. OF OFF REEF, REEFS MEDIT MEOIT I, FIGURE 2 Flowchart of FREEFS Program.
points and communicates at 9600 Baud A 50 of a centrally mined block with two square. Mb disk drive HP 7920 and a Summagraphics stabilizing satellite pillars in the upper. dig t zer were also later added east and west corners of the pillar with a. Modelling approach NE SW striking pillar downdip from the. Ten different stope phasing schemes were shaft enclosing a dyke was used in each. examined each scheme having up to ten case study I t was reasoned that this dyke. separate mining steps The general layout would present a barrier both from a mining. 86 MINING SHAFTS, OPHo 7 OG r, I 0 ELEPHCN DE, CA8LE I MQDU AID. COMPUTER 1, LATOR 128 Kb, UNDERGROUND ANO COOED, SURFACE GEOPHONE I CLOCK t RAPHICS. SITES r ERMINA, DATA I H P2648 I, AQUISITION, ANALYSIS SYSTEM. J PRINTERhL, I DISPLAY SE1SMOGRAM COMPUTER DiSK I, SELECT P S ARRIVALS PLOTTE I I. r I Mb 20Mb, OETERMlfIE LOCAT IONS AND, H CA O SIS.
SUMMAGRAP HICS, r l 1 1 1 1 sTRESS, 4 TERMNAlS ANALYSIS. I TAPE 50Mb DISK, FIOURE 3 System d ign Rock Me hanics Department Blyvooruirzichl Gold Mine. a nd seismic vi ewpo int hence the decision Strai ns and displ aceme nts induced al ong. not to mi ne it but to bracket 1t wi th the vertical axis of th e s haft were. unmined ore re serves updip and downdi p conSi dered 1n eva lua ti ng it s long term. The gen eral layout is shown in Figure 4 stability To calculate the se parameters. Inten s i ve examinatio n of old ge ological f ourt een of f re ef pO i nts we re modelled. data showed no other major discont i nuitfe s al ong t he vertical axis of t he s haft at. which would slow down or impede mining 50 0 m interva ls above and bel ow the reef. thus no al t erati ons we re necessa ry to t he horiz on. origina l min ing concept A reef project ion of the point s was used. Furt her detail s of the parameters used i n thu s th e di sta nce above and be low the reef. t he FREEFS model are hori Zon s the norma 1 di stance Above. Young s Modul us 70 Gpa reef being regarded as positive and be low. Poiss on s ratio 0 2 as negati ve Vert i ca 1 di spl acements were. Grid si ze 15 m computed at each of these off r ee f points. Stop ing width Srn 1 0 m Maximum principal s tresses were a l so. Reef dip 20 calculated at ea ch of these off reef points. Vertical stress gradient 0 027 Mpa m f or each stage of mining in each of t he. Hor i zontal t o ve rtical phasing schemes A limita t ion of the. virgin stress ra tio k 0 5 program was that off ree f paints were. I n each of th e mo dels examined extrac required to be one grid squ are away f rom. tion was simul ated in a n ea sterly and the reef horizon. westerly direc t i on symmetrically outwards The on reef solution was considered. from the shaft up to a maximum of nine important and on reef stresses and. mini ng steps convergences were al so ca lcul ated E R R s. EXTRACTION OF NO 1 SHAFT PILLAR AT BLYVOORUITZICHT 87. PILLAR 5 PILLAR, 2 i STAGES OF t lNINC3, FIGURE 4 Plan of sto pe phasing scheme accepted for the extraction o f No shaft pillal. 88 MINING SHAFTS, were also calculated as multiple mining Table 1 Maximum values and maximum change. steps were modelled ofC calculated along shaft barrel. The stope phas i ng scheme eventually, chosen by the mine offered the optimum Distance above Maximum 0 Maximum.
combination of these design parameters reef Im IMp change Mpa. Reef level stresses, 550 27 3 9 2, Two aspects of the stress field at the reef. 500 31 1 11 0, elevation were considered to be important. 450 35 4 13 4, to the stability of the shaft barrel. 400 41 2 17 5, a absolute value of the stress, 350 46 5 21 7. b change in stress experienced, 300 52 3 27 4, It was considered that should the stress.
250 58 0 34 2, level er be above a certain fraction of. 200 64 3 41 4, the uniaxial compressive strength of the. 150 67 3 43 6, rock Oe failure would occur Rockmass. 100 66 3 43 0, strength in the range 180 200 Mpa was. 50 55 4 36 7, used A proportion O Oc 0 5 was used as.
50 51 8 16 1, the limiting ratio, 100 65 2 35 0, A tabulation of maximum principal stress. 150 72 5 38 4, versus distance above and below reef shows. that at no place except in the inmediate, reef intersection area was the ratio Horizontal and vertical displacements and. exceeded The shaft barrel was bolted and strains, meshed for a distance of 20 m above and The discontinuity in displacement which. below the reef intersection to counteract occurs at the shaft reef intersection. expected rock failure and subsequent during mining is most conveniently resolved. dilation of the sidewalls of the shaft into horizontal and vertical components. Yielding stope support in the form of low when deal ing with modification to shaft. load to compress i on packs was a 1so timbering as opposed to nonnal convergence. installed for a radius of 10 m around the and ride components used in rock mechanics. shaft barrel at the shaft reef inter Since the timbering in the shaft was braced. section Crush pillars in the form of 1 5 m against the sidewalls distortion of it. wide strips of reef were left in the would occur if this predicted movement was. immediate vicinity of the shaft to inhibit not catered for. the initial convergence in the reef In dipping strata the direction of the. horizon horizontal displacement is such that the, In Table 1 the relationship of the hangingwall moves updip relative to the.
maximum principal stress and the maximum footwa 11 Mode 11 i ng of the extracti on was. change in the principal stress at each of symmetrical in the strike direction so that. the off reef points modelled along the the horizontal component of dislocation was. vertical axis of the shaft may be seen in the dip direction This was considered. to be important because if the mining is, not symmetrical an additional component of. EXTRACTION OF NO 1 SHAFT PILLAR AT BLYVOORUITZICHT 89. DISTANCE ABOVE REEF IN METERS, ACTUAL SMOOTHED VALUES 7 lO. THEORETICAL VALUES, 0 0050 0 23 DISTANCE BELOW, REEF IN METERS. DECOMPRESSIVE COMPRESS1VE, FIGURE S Theoretical and actual strain plotted along sha Ft axis for stope phasing stages J 2 3 5 6 and 9. hori zontal di s locat ion in t he strike where k rat i o of hori zonta l to vert ical. di rec tion wil l be i nduced vi r gi n s t re s s. The maximum va lues of the hor i zon ta l 0 d i p of stra t a. dis l oca ti on was cal culated fr om A ma x imum of 18 2 rrm har t zonta 1 movement. Horizon ta l was cal cul at ed This wa s inco rporat ed i nto. 6 h 2 k sinOC Srn the pl anned modificati ons The vert i ca l. 1 k T l k cos 20 mo vement was calcu l at ed at 680 mm and was. 9 MINING SHAFTS, res olved into 27 0 mm upward s and 410 Illl1 were con s i dered on the ba s is of.
downward s A limiting verti ca l st rain of dist ingui s hab l e con centra tions of. 0 001 was used This fi gure was derived sei smicity These regions were t hen. emp i rica 11y f r om exami nat i on of pr evious gr ou ped i n fou r E R R range s of namely. sha ft pillar extractions 0 20 21 40 41 80 and 81 1 60 MJ ml In. Th e vertical strai ns cal cul ated for the Figu re 6 it ca n be seen that the r ate of. accep ted stope pha s ing are shown on Figure se ismici ty ex pres sed as t he number of. 5 se ismi c eve nts with ML 1 5 pe r 1 000 m2, mi ned i s proporti onal to the E R R. Energy Release Rat E R R The stope phas i ng s cheme accep t ed f or. Examination of some 10 000 l oca ted se ismi c implement at i on was t he mo de l which al l owed. events at Blyvooruitzicht had e nable d th e for the lowes t E R R and co nsequently th e. Rock Mechanic s Depa rtment to derive a l owest predi cte d seismicity Table 2 s hows. r elat ion shi p between se i smic ity and E R R the ca l cul ated E R R f or each mi ni ng s t ep. Eighteen region s within Blyvooruitzi ch t modelled. 25 50 75 100 12l, E nergy release rate MJ m1, FIGURE 6 Relationship between number of seismic events of M 1 5 per I 000 m1 mined and E R R. as found at Biyvooruilzicht Gold Mine, EXTRACTION OF NO I SHAFT PILLAR AT BLYVOORUITZICHT 91. Table 2 E R R ca lc ul ated for each mining taken mont hl y. step Ride a nd c los ure was calcu lated from, measu r ements obtained from two th ree. Mi ning step Average E R R in MJ m2 dime nsional ride c l osure rr eters insta ll ed. in the ree f h o riz on close to the s ha ft, 1 10 Th ree hol es were drilled i n t he fo otwal J of.
2 11 t he stoped out a rea to f orm the corners of. 10 an approximate right angled triangle with, 37 1 one side a l ong dip and one side along. 61 0 strike Pegs we re grouted into these holes, 57 1 and the distances between them were. 64 9 measured us ing a metallic tape A hole was, 54 4 drill ed in the hang ngwall approximately. 62 0 vert i ca lly abov e the apex of the footwa 11. triangle The distances between the hang, Pillar stresses i ngwa 11 and f oo twa 11 pegs were a 1so. The dimens ions of t he two stabilizing measured, satellite pillar s a nd the NE SW s t rik i ng To monitor t he se ismicity induced by the.
pillar downd1p from the sha f t were mi ning n the pill ar area three additiona l. cal culated us ing t he on ree f stress option geophone s SENSOR M 6 9 8 14 Hz were. of t he FRE EFS program An ave rage plllar i nstalled in excavations below the reef. stress of 400 Mpa was t he design parameter hor izon These geophones were l inked to. Thi s parameter bei ng obta i ned from the mine wide seism i c network operated by. i nvestigations conducted previously on the t he Rock Mechanics Department. mine The average pillar stress of a EvalualloD, stable pillar on the mi ne was calculated The relative displacement between the. using the well known analogue at the measuring stat ion s in the shaft was. Chamber of Mines The calculated stress of r e lated to the off reef points to enable a. NOBLE K R The extraction of the No 1 shall pillar at Blyvooruitzicht Gold Mine APCOM 87 Proceedings of The planned extraction of the No 1 shafi pillar at Blyvooruitzicht Gold Mine highlighted a number of potential problems In spite of the relative shallowness careful thought had to be given to stope phasing owing to the detrimental effect of the anticipated geology and the fact

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