Ore pass rehabilitation Case studies from Impala Platinum Limited

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1 Oe pss ehbilittion Cse studies fom Impl Pltinum Limited by L.J. Gdne* nd N.D. Fenndes* J o u n l Synopsis Oe pss systems ply citicl ole in moving boken ock fom the wokplce to sufce, nd the integity of the oe pss excvtions is cucil. Ove the life of the mine, oe pss integity deteiotes, which my eventully esult in the oe pss no longe being fit fo pupose. This ppe pesents sevel cse studies of successful oe pss ehbilittion execises. Intoduction A successful mine must stive to mintin constnt level of poduction. To chieve this, ock boken in the wokplce must be emoved to sufce on continuous bsis, with miniml inteuption. Oe pss systems ply citicl ole in this pocess, nd the integity of the oe pss excvtions is cucil to mintining poduction equiements. Ove the life of the mine, oe pss integity deteiotes. Oe psses e subjected to chnging stess envionments s esult of mining, to we nd bsion due to the flow of boken oe, s well s to the effect of ockwll filues ound nd on geologicl discontinuities. The esulting deteiotion my esult in the oe pss no longe being fit fo pupose, in which cse emedil mesues e equied. This ppe biefly summizes some of the technicl issues egding options fo the ehbilittion of oe psses, nd then discusses thee ehbilittion cse studies: No. 10 shft, inte-level oe pss No. 10 shft, stoge silos No. 9 shft, inte-level oe pss. Finlly, n Impl methodology fo oe pss ehbilittion is pesented. Loclity nd bckgound infomtion Impl Pltinum Limited is the wold s second lgest pltinum goup metl (PGM) poduce. The compny s min mining lese e is situted some 30 km noth of Rustenbug in the Noth West Povince, long the westen lobe of the Bushveld Complex (see Figue 1). The lese e mesues some hectes. The geologicl sequence in the lese e dips t ppoximtely 9 degees to the noth est. Two PGM-ich hoizons e exploited; the Meensky economic hoizon nd UG2 chomitite lye. These two hoizons e septed by n 80 to 100 mete middling. Aside fom opencst opetions, thiteen shft systems e cuently used fo ccess nd mining puposes, t depth of 30 to 1200 metes below sufce. Undegound mining opetions genelly follow tditionl tbul mining pctice. The oebody is ccessed by mens of tvelling wys emnting fom footwll hulges nd oe is extcted using scpe winch-clened now eef stoping techniques. Moe thn people e employed undegound on the lese e to extct moe thn 16 million tons of oe pe nnum, which poduces some 1.1 million ounces of pltinum goup metls. Technicl issues The integities of oe psses vy some hve to be ehbilitted befoe being used, othes my be in sevice fo numbe of yes befoe showing signs of deteiotion, nd some my emin intct nd seviceble thoughout thei woking life. Oe psses cn be developed in sevel wys: Conventionl mnul development with shot ounds nd blsting with explosives Dop-ising using long emotely dilled holes, then etet blsting up the oe pss Rise- o blind-boing, with no explosives involved. * Impl Pltinum Limited. The South Aficn Institute of Mining nd Metllugy, SA ISSN X/ This ppe ws fist published t the SAIMM Colloquium, Design, Development nd Opetion of Rockpsses, Novembe P p e The Jounl of The South Aficn Institute of Mining nd Metllugy VOLUME 106 NON-REFEREED PAPER JANUARY

2 Oe pss ehbilittion Cse study fom Impl Pltinum Limited Mokopne Rustenbug Lyeed Suite Mul Bel-Bel Bugesfot Kennedy s Vle Two Rives Impl Rustenbug Cocodile Rive Petoi Middelbug Johnnesbug 100 km Figue 1 Loclity mp of the Bushveld Complex Ech method hs its own poblems ssocited with ensuing the integity of the finl oe pss excvtion. In theoy, oe psses deteiote due to: Stess-induced filue of the ockwlls Absion due to the flow of ock though the pss Detchment of the ockwlls inside, o longside, geologicl discontinuities o wek geologicl hoizons tvesed by the oe pss. The ctul deteiotion often esults fom combintion of these cuses, which my be ggvted by fctos such s unfvouble loction, poo excvtion pctice, bsive mteil nd the pesence of wte. Signs of oe pss deteiotion include: Obvious inceses in oe pss dimension Iegul oe flow though the oe pss Lge wste ocks blocking the contol chutes t the bottom of the oe pss Mixing of eef nd wste in supposedly septe oe psses due to oe psses holing into one nothe. Unless the entie length of the oe pss cn be obseved fom its top o bottom ccess, deteiotion (nd indeed holing between oe psses) my continue undetected fo lengthy peiods. This is especilly tue fo longe oe psses (50 m plus). It is thus impotnt tht oe psses e physiclly inspected nd mesued t egul intevls. When oe psses deteiote to the point tht they e no longe fit fo pupose, mine mngement is fced with simple choice the oe pss cn eithe be ehbilitted o eplced. While this should be simple economic decision, it is often complicted by issues such s infstuctue, logistics nd time. If ehbilittion is chosen, thee e thee commonly employed sttegies: Reinfocement of pesent excvtion nomlly employed in cses whee deteiotion is detected ely, o whee sufficient middling exists between the oe pss nd djcent excvtions to povide stbility. The oe pss is einfoced to ccommodte its enlged size nd shpe, not estoed to its oiginl dimensions. Instlltion of tube nd bckfill nomlly employed in cses whee deteiotion is sevee o ongoing, o whee the oe pss hs indvetently holed into nothe excvtion. The use of tube mens tht the oe pss is etuned to size simil o possibly smlle thn its oiginl dimensions, nomlly in the sme position s the oiginl oe pss. Fill nd edevelopment though fill vition on complete eplcement, this method entils filling the oe pss with cemented wste ock, followed by edevelopment though the fill, usully by ise boing. Thee e no hd nd fst ules in mtching sttegies to scenios nd, depending on cicumstnces, it my even be necessy to use combintion of sttegies within single oe pss. Vious mteils hve been used successfully when ehbilitting oe psses, including: Gouted tendons, with mesh nd lcing ope Steel ings Andesite lv-bsed shotcete Coundum-bsed shotcete Concete fill. Fo the cement-bsed mteils, 70 MP compessive stength equiement is nomlly indicted. The bove mteils hve been used individully, but e nomlly pplied in combintion. The woking method fo the ctul ehbilittion pocess is dictted by the site-specific cicumstnces, but cetin bsic pinciples pply: In view of the hzdous ntue of the wok, sfety is pmount All pties involved need to clely undestnd thei ole, esponsibility nd duties A stuctued, systemtic ppoch is essentil this is best chieved by conducting specil plnning session/isk ssessment pio to beginning wok, s well s ongoing pogess meetings duing the ehbilittion pocess. 18 JANUARY 2006 VOLUME 106 NON-REFEREED PAPER The Jounl of The South Aficn Institute of Mining nd Metllugy

3 Oe pss ehbilittion Cse study fom Impl Pltinum Limited Cse studies No. 10 shft, level eef pss This oe pss, which uns fom 975 to 1040 metes below sufce, ws commissioned in ely 1986 nd ehbilitted in mid Although situted in noitic Footwll 16 host ock, with UCS of ove 200 MP, the oe pss tvesed vey blocky eplcement pegmtoid mteil, s well s sevel infilled lmpophye (kimbelitic) dyke stuctues, which deteioted due to exposue, wte flow nd bsion fom the oe flow. Pio to ehbilittion, the oe pss ws thooughly suveyed to detemine the extent of deteiotion (Figue 2), nd offsets wee tken t fixed intevls down the length of the oe pss (Figue 3). The suvey showed tht the oe pss s oiginl 3.5 m dimete hd incesed to mximum of 24 m in one e. Thee ws, howeve, sufficient clence emining between this nd the othe inte-level oe psses, nd theefoe einfocement sttegy ws dopted. In detemining woking method fo the ehbilittion pocess, expeience dictted the wok poceed fom the top of the oe pss downwds, to minimize the isk of ocks flling fom unsuppoted es bove. Wok would tke plce fom fixed pltfoms estblished t egul intevls, the thn simply stnding on muck pile (Figue 3). The pltfoms pesented sevel dvntges: Wok could tke plce on moe thn one level simultneously Additionl stoge plce ws vilble fo mteil nd equipment Ech pltfom could be custom-built to the dimensions of the oe pss t tht level Ech pltfom povided dditionl potection fom flling objects, s well s educing the distnce tht n object could fll. To estblish the pltfoms, the oe pss ws filled to the top with ock. The oe pss ws then bled until the ock level hd dopped by between 3 nd 5 metes. A sfety net ws plced bove the ock nd secued to the sidewll by mens of pigtil eye bolts. Howeve, muck pile plug would be left t the bottom of the oe pss s n dditionl sfety mesue. The following sevices wee povided in the oe pss (See Figues 4 to 6): Ventilting i ws supplied by mens of 406 mm foce ventiltion column, s the muck pile plug pevented the flow of though ventiltion A 570 mm pipe column ws instlled fo tnspoting mteil down the oe pss using sky climbe minihoist tht ws cetified by the Inspecto of Mchiney Compessed i nd sevice wte wee supplied in 50 mm dimete flnged pipes Veticl ingbck lddes llowed fo tvelling between the top of the oe pss nd the diffeent woking pltfoms. The longest ldde mesued 7.2 metes. In view of thei steep ngle of instlltion, the lddes potuded t lest 1.0 m bove the top woking pltfom. Additionl covege of the ingbck section ws povided by nylon netting Telephones wee instlled t the top of the oe pss nd the mteil dischge point. The ctul einfocement consisted of 1.8 nd 2.2 mete long, 16 mm dimete gouted tendons, instlled dilly J o u n l P p e OREPASS SCALE 1 : LEVEL 50m 48m 46m 44m 42m 40m 38m 36m 34m 30m 28m 26m 24m 22m 20m BOTTOM 16m 14m 12m 10m 8m TOP 6m 2m 0m 15 LEVEL 15 LEVEL Figue 2 Sections though oe pss Figue 3 Offsets down oe pss The Jounl of The South Aficn Institute of Mining nd Metllugy VOLUME 106 NON-REFEREED PAPER JANUARY

4 Oe pss ehbilittion Cse study fom Impl Pltinum Limited Figue 4 Section though oe pss duing ehbilittion pocess ound the oe pss on 1.0 mete ptten. These would be supplemented by meshing nd lcing to impove el covege nd igidity. This system would be coveed with 100 mm thick lye of high stength (70 MP) ndesite lvbsed shotcete, which would povide bsion esistnce. It ws oiginlly intended to begin ll wok t the top of the oe pss nd wok downwds, stipping fom the top s wok pogessed. This poved logisticlly impossible due to the difficulty of emoving ll the mteil nd equipment though the oe pss chute on 15 level. Insted, the gouting, meshing nd lcing wok pogessed downwds (Figue 7), fte which the shotceting ws done in evese (Figue 8), with stipping tking plce fom the bottom upwds behind the shotceting opetion. Figue 5 Typicl woking pltfom Figue 6 Typicl ingbck ldde instlltion 20 JANUARY 2006 VOLUME 106 Figue 7 Completed meshing nd lcing opetion NON-REFEREED PAPER The Jounl of The South Aficn Institute of Mining nd Metllugy

5 Oe pss ehbilittion Cse study fom Impl Pltinum Limited Figue 8 Oe pss fte completion of ehbilittion pocess Despite the til-nd-eo ntue of the execise, the ehbilittion pogessed smoothly with only mino delys due to mteil shotges nd excessive woking heights. No ccidents o injuies occued duing the ehbilittion pocess, which took ppoximtely 6 months nd cost R1.2 million. To dte, no futhe significnt deteiotion hs occued nd the oe pss continues to opete. No. 10 shft, decline silos The 10 shft decline system ws one of five simil pojects begun in the ely 1990s to sustin poduction levels. Given the depessed stte of the pltinum mket t the time, it ws decided to extend the life of existing veticl shfts vi sublevel decline systems, the thn sink new veticl shfts. Ech decline system compised septe mjo tunnels fo tnspoting men by chilift, mteil by il, nd ock emovl by conveyo, s well s ncilly excvtions such s connecting tvelling wys nd oe psses. The oiginl 10 shft decline system design poposed thee lge (30 m long x 7.0 m dimete) veticl bunkes to povide buffe nd stoge cpcity fo oe deliveed fom the decline section vi the conveyo. The bunkes would be situted close to the shft, in the sme geologiclly-distubed e s the inte-level oe pss tht hd ecently equied ehbilittion, nd would extend fom 15 level (1040 mbs) to loding inte-level 30 m below. Anlysis of the locl in situ stess egime nd oienttion of locl geologicl stuctues showed tht even if suppoted, the long-tem stbility of the bunke could not be gunteed. This nlysis, togethe with the histoicl evidence nd dvese gound conditions encounteed in the hoizontl development ends, pompted design chnge. The single bunke ws eplced by seven smlle (3.0 m dimete) veticl silos, which wee developed by iseboing, nd then fully suppoted pio to commissioning. As the silos would be fully suppoted, the middling between djcent silos ws educed to 9 m, hlf of the ccepted industy nom. The suppot fo the silos consisted of welded mesh, pinned into plce by 1.8 m long mechniclly-nchoed ockstuds. The ockstuds wee subsequently full-column gouted fo long-tem coosion esistnce. No lcing ws used due to the smll dimete of the silos. The tendons nd mesh wee coveed by 100 mm thick lye of 70 MP UCS ndesite lv-bsed shotcete. All wok ws conducted on mini-stge, which ws loweed fom skyjck ngement instlled on top of the oe pss. Suppot opetions pogessed down ech silo in 2 3 m stges, with both gouting nd shotceting being completed befoe loweing the mini-stge. The suppot of the seven silos, which ws conducted by contctos, took ppoximtely 9 months to complete, with no seious incidents being ecoded. Following thei commissioning in 1996, the silos hve functioned successfully to dte, with the only significnt deteiotion in the lining hving occued long the lmpophye dyke zone (see Figues 9 to 12). No 9 shft, level oe psses This ehbilittion execise ws well documented in ppe entitled An engineeed solution to multiple oe pss epis t Impl Pltinum Ltd, Wildebeest South mine by vn de Linde nd Moolmn (1995). To summize biefly, in August 1994 it becme ppent tht, fte some 10 yes of sevice the Meensky eef pss nd the wste pss hd holed into one nothe between 16 level (975 mbs) nd 17 level (1030 mbs), s eef tons wee being lost to wste. The holing ws initilly estimted to mesue 2 m x 3 m. An ttempt ws mde to sel the holing, but this hd to be bndoned due to dngeous gound conditions encounteed in the oe pss. The oe psses wee continully blocked by lge ocks scling off the oe pss ockwlls, nd it becme evident tht pope ehbilittion execise would hve to be conducted to ensue long-tem oe pss stbility. The selection of n optiml ehbilittion method ws hmpeed by uncetinty egding gound conditions nd the extent of filue. Afte ssessing the vilble options, the following methodology ws poposed: Both oe nd wste psses would be filled with ock fom 16 to 17 level Figue 9 Genel view of condition of suppoted silo Figue 10 Lining eoded on lmpophye dyke exposue J o u n l P p e The Jounl of The South Aficn Institute of Mining nd Metllugy VOLUME 106 NON-REFEREED PAPER JANUARY

6 Oe pss ehbilittion Cse study fom Impl Pltinum Limited Figue 11 Shotcete eoded to ptilly evel weld mesh Figue 12 Mino exposue of lmpophye dyke in silo The boken ock would be used s bse fo mking sfe nd suppot opetions, coveed by sfety net nd wooden pltfom Wok would begin on 16 level nd poceed downwds, with ock being bled fom the psses when necessy to lowe the woking level Suppot would consist of gouted tendons, with meshing nd lcing fo el covege, supplemented by shotcete when consideed necessy Once the psses hd been suppoted, they would be bckfilled fom the bottom up by low-stength concete, with steel shutteing used to keep the intended pss voids open Finlly, the voids would be lined with high (80 MP) stength concete ings to cete the new ockpss excvtions. The job equied extemely complex logisticl ngements the tip coss-cuts hd to emin ccessible fo ock being emoved fom the ffected levels, which wee still poducing, nd ock tipped on the shft s uppe levels hd to be moved though the single emining oe pss without mixing Meensky nd UG2 oe. In ddition, the 3 ton mss of the ssembled concete ings ment tht they hd to be loweed into plce by mens of specilly-instlled Fulton winde nd ssocited hedge. Seious delys wee expeienced duing the initil mking sfe nd suppot phse s the eef pss emptied fste thn the wste pss when bled, peventing simultneous wok fom tking plce until such time s the holing point hd been eched. When the holing cvity ws finlly exposed, the dmge ws found to be moe sevee thn initilly nticipted. The semi-ellipticl shped holing hd occued in the lyeed footwll 16 hoizon (see Figues 13 nd 14). The e ws tvesed by 45 degee-dipping evese fult, togethe with ne-veticl jointing, which esulted in blocky gound conditions. It ws lso likely tht the sitution could occu in the newly developed djcent UG2 oe pss, which intesected the sme fetues. Afte ssessing the extent of the dmge, it ws concluded tht the wste pss, being the lowe of the two, ws unlikely to migte futhe towds the footwll s substntil ded box of muck hd ledy fomed. Povided its hngingwll ws popely suppoted, futhe deteiotion ws unlikely. A chnge of poject scope ws poposed bttice wll would be constucted in the holing cvity to septe the two psses, then the wste pss would be ecommissioned (see Figue 15). Once the wste pss ws in use, the eef pss would be ehbilitted s oiginlly poposed, while simultneously ehbilitting the UG2 oe pss. This would hve both time nd cost dvntges, s well s ensuing the futue stbility of the UG2 oe pss. Following the chnge of scope, the ehbilittion pocess ws completed successfully, lthough poblems wee expeienced with the wokbility nd tnspot of the concete used fo the bckfilling opetion. The poject oven its plnned time fme, with delys expeienced with the mking sfe nd concete pouing opetions, nd cost R2.47 million. The emphsis plced on sfe woking pctices esulted in only two dessing cses being ecoded duing the shifts woked. Impl methodology The success of the einfocement ppoch used t No. 10 shft led to it being dopted s the pefeed mens of oe pss ehbilittion on Impl. The ppoch ws efined by til nd eo duing othe ehbilittion execises, nd ws eventully witten up s method sttement by one of the contcting compnies. This method sttement ws incopoted into set of guidelines issued by Impl s ock engineeing deptment in lte 2003, which cn be customized to suit diffeent situtions. The methodology incopotes most of the steps used in the oiginl level oe pss on No. 10 shft, but with few efinements: Pltfoms e limited to mximum of 3 m pt this hs been found to be optiml in tems of woking height nd ccessibility Acceleto hs been dded to the shotcete mix to povide bette binding, fste setting nd less ebound. Fluoescent lighting hs been included fo bette visibility. Sfety belts hve been eplced by full-body hnesses. In the mjoity of cses on new cpitl pojects, oe psses e suppoted pio to commissioning. Rehbilittion of typicl m long oe pss (55 m level intevls t 55 degees) tkes between 4 nd 6 months, t cost of between R nd R Although this ppoch delys the commissioning of the oe pss, it ensues its long-tem stbility. 22 JANUARY 2006 VOLUME 106 NON-REFEREED PAPER The Jounl of The South Aficn Institute of Mining nd Metllugy

7 Oe pss ehbilittion Cse study fom Impl Pltinum Limited J o u n l Figue 13 Holing between psses nd evese fult position P p e Wste pss Reef pss Figue 14 Pln view showing pofile of holing between psses t widest point Figue 15 Position of bttice wll nd filled e in eef pss Conclusions The Impl expeience hs shown tht t pesent depths in the Bushveld envionment, oe pss deteiotion occus due to filue long geologicl stuctues, the thn stesselted issues. The extent of such deteiotion cn be extensive, nd cn esult in the loss of the oe pss s functionl excvtion. While the cse studies pesented bove compise only smll numbe of the oe psses ehbilitted on Impl to dte, they showcse typicl engineeed ppoches to ensuing oe pss stbility nd continued functionlity. Expeience on Impl hs shown tht, fo Bushveld conditions, sttegy of oe pss einfocement ensues long-tem oe pss stbility. Adopting foml ehbilittion methodology lso educes the isk ssocited with the ctul oe pss ehbilittion pocess. Acknowledgement The uthos wish to thnk the mngement of Impl Pltinum Limited fo pemission to publish this ppe, s well s thei commitment to bette nd sfe mining using innovtive methods. REFERENCES VAN DER LINDE, A. nd MOOLMAN, B.D. An engineeed solution to multiple oe pss epis t Impl Pltinum Ltd, Wildebeest South Mine, Ass. Min. Res. Engs S. Af The Jounl of The South Aficn Institute of Mining nd Metllugy VOLUME 106 NON-REFEREED PAPER JANUARY

8 24 JANUARY 2006 VOLUME 106 NON-REFEREED PAPER The Jounl of The South Aficn Institute of Mining nd Metllugy