OPEN CAST MINING METHOD
Open Cast Mining Method Open cast mining is a surface exploitation method, used mainly for coal It resem!les open pit mining !ut di"ers in one uni#ue respect$ The overburden is not transported to waste dumps for disposal but cast or hauled directly into adjacent mined-out panels. •
Continued%% OC Mining is su!di&ided into t'o methods i Strip Mining iiTerrace Mining •
i. Strip Mining This method is ideal under the follo'ing conditions$ a)Relatively thin overburden b)Extensive area of reserves c)Regular c)Regular horizontal/at topography topogra phy and seams •
Strip Mining) cont •
The deposit deposit is mined in a series of strips
Strip mining) cont •
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The o&er!urden from each strip is cast directl* into the &oid created !* the pre&ious coal e+traction Strip Mining is normall* a large tonnage operation using large mining machines such as Draglines and Power shovels for Coal and Overburden stripping respectively.
ii, Terrace Mining a, This This method method is is used used 'her 'here e$ The overburden is too thick or The oor is too steeply dipping to permit direct across the pit casting of o&er!urden material- The overburden (spoil) must !e transported !* other means and tipped back into the void left back by previous mining.
Cont !,This is a multi !ench lateral ad&ance method- the 'hole mine mo&ing across the deposit- !ut not in a single stage operation as with strip mining
Cont c, .pper le&els are usuall* transported !* truc/ and sho&el- or !* a com!ination of !uc/et 'heel e+ca&ators 012E,- con&e*ors and stac/ers d, If a dragline is used in terrace mine it can onl* operate on the bottom benches 'here direct casting of o&er!urden o&er!urden is possi!le •
Terrac Terrace e mining) cont cont
Terrace Terrace Mining)cont Mining)cont
Opening up into a coal seam3 •
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The initial opening into a coal seam is called a Bo cut. a trench or box cut 4 is made through the o&er!urden to e+pose a portion of the coal seam This trench is e+tended to the limits of the property 0Deposit, in the stri/e direction After coal removal- a second cut is made parallel to the !rst one - and the o&er!urden material from this cut is placed in the void of the !rst cut
Position of !o+ cut A
bo cut is either made in the shallo"est part of a pitching deposit, to mine to the dip or
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bo cut For a thick deposit a box cut may be made near the center or at the highest part so that a series of benches may be ta!en out"ards
1o+ 1o+ cut ) cont%
1o+ cut 5cont •
6rom the !o+ cut coal mining proceeds down the dip or across the mining lease O&er!urden is remo&ed from in front of the ad&ancing high!all and thro'n into the mined out area as in 7gure !ello'
1o+ cut) cont
Striping Dragline
1ac/ 7lling or 1ac/ Casting •
2hen the dip angle# $, of a coal deposit is less than the angle of repose of the spoil heaps plus a factor of safet*- it is possi!le to dump spoil8o&er!urden 'aste inside the e+ca&ated area 01ac/7ll, Dip angle of coal seam 9:
Direct 1ac/ 7lling •
2here possi!le the o&er!urden 'aste is direct back%cast across the cut 'ith a Dragline or stripping Po'er sho&el
Indirect 1ac/7lling •
2hen either the overburden or coal seam is too thick the reach of the dragline or stripping sho&el !ecomes small- and the o&er!urden has to go round the pit and !e 7lled in from !ehind
Indirect !ac/7lling)cont
Ma;or Open Cast Operations
Ma;or OC operations cont i)
&ush clearing and leveling
This in&ol&es the remo&al of the &egetation to ensure homogeneous topsoil A bulldo'er or tractor does this 'ith a ripper !ehind The area is then graded to allo' smooth tra&eling of haul Truc/s Truc/s
ii, Top soil removal $
???@ Topsoil Topsoil is remo&ed separatel*- and ultimatel* re) placed upon graded spoils 0o&er!urden 'aste dumps,
Cont Top
soil can !e stoc/piled at the side of the pit area for later redistribution or ma* !e hauled immediatel* to the graded area for redistri!ution redistri!ution The method of redistri!uting redistri!uting the topsoil is dictated !* economics considering #uantit* and distance it ma* !e !* oader8Truc/ method or !* self) ele&ating scrapers- etc
cont.
iii) verburden stripping The
overburden benches ma* !e one or more depending on 3 ) The thickness of the overburden and the reach of the stripping euipment. ) In a !ench 'here a dragline is usedcast or * bu+er blasting is used to loosen the roc/ roc/ !efore the dragline can 'or/ on the material
Cont 2here the o&er!urden is &er* thic/eg. -m. /t 0ankie colliery in Bim!a!'e- o&er!urden stripping is di&ided into )1enches )1enches 1 m on top is "orked by a po"er % shovel bench- or 0supplementar* strip !ench, and The bottom 21m. is 'or/ed !* a Dragline hence called Dragline !ench •
Cont iv) 3oal 4xtraction 3oal mining ma* !e !* $ A single !ench or t'o depending on thickness or uality of the coal seam. Eg at 'an/ie collier* in Bim!a!'e a 5 m thick seam is mined in t"o benches because the top m is po"er coal and the !ottom m is coking coal The main e#uipment here is the po'er sho&el
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OC operations &, 6egrading of Spoils •
arge 1ulldoers and Graders grade 7lled mined out areas areas !efore topsoil is re)placed
&i, Top Soil 6eplacement •
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Scrapers- doers- loaders and truc/s are used in this operation A la*er of fertile soil is spread on top of graded spoils
OC Operations vii) 6e%vegetation or replanting $ •
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???@ Planting of &egetation is accomplished !* a con&enient farm implement- and is done as soon as practical Seed selection is !ased on post mining land use
deposits for open cast mining.
Coal Open Cast machines 8ragline 4xcavators The dragline is a &ersatile attachment capa!le of a 'ide range of operations at and !elo'ground le&el The dragline can dig through loose to medium compacted soil The !iggest ad&antage of the dragline o&er other machines is its long reach for both digging and dumping Another ad&antage is its high cycle speed
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Cont The roc/s that is to !e handled must !e of lo" density of >) T8 M F and 'ith lo' abrasive property. The machines are are electricall* operated A dragline !uc/et s*stem consists of a large bucket 'hich is suspended from a boom 0a large truss truss)li/e )li/e structure, 'ith 'ire ropes ropes The !uc/et !uc/et is maneu&ered !* means of a num!er of ropes and chains The hoist roperope- po'ered po'ered !* large diesel diesel or or electric motors- supports the !uc/et and hoist) coupler assem!l* from the !oom •
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Cont The
dragrope is used to dra' the !uc/et assem!l* horiontall* 1* s/illful maneu&er of the hoist and the dragropes the !uc/et is controlled for &arious operations ! schematic diagram of a large dragline buc"et system is sho'n !elo'
Dragline 5cont
Dragline operation 9n a typical cycle of excavation $ the bucket is positioned above the material to !e e+ca&ated The bucket is then lo"ered on the material The dragrope is then dra"n or pulled so that the !uc/et is dragged along the surface of the material The buc"et is then lifted by using the hoist rope A swing operation is then performed to mo&e the !uc/et to the place 'here the material is to !e dumped The dragrope is then released causing the buc"et to tilt and empt* This is called a dump operation •
Draglines in mining 5sie and cost •
A large dragline s*stem used in the open pit mining industr* costs appro+imatel* appro+imatel* .S )> million A t*pical t* pical !uc/et !uc/et has a &olume ranging from F to cu!ic metres- though e+tremel* large !uc/ets ha&e ranged up to >J cu!ic metres The length of the !oom ranges from #$ to %&& metres In a single c*cle it can mo&e up to K metric tonnes of material
Dragline L po'er source •
Most mining draglines are electrically po"ered.. Their po'er po'er consumption is so great that the* ha&e a direct connection to the high% voltage grid at &oltages of !et'een to / / A t*pical dragline- 'ith a cu!ic metre !uc/et- can use up to Mega'atts during normal digging operations
Dragline po'er source mo&ement •
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In all !ut the smallest of draglinesmo&ement is accomplished !* 'al/ing using feet or pontoons- as caterpillar trac/s place too much pressure pressure on the ground- and ha&e great dicultl* under the immense 'eight of the dragline Ma+imum speed is onl* at most a fe' hundred metres per hour since the feet f eet must !e repositioned for each step
imitation of .se of Draglines The primar* limitations limitations of draglines draglines are are $ boom height and boom length'hich limits 'here the dragline can dump the 'aste material dig depth- 'hich is limited !* the length of rope the dragline can utilie Inherent 'ith their construction- a dragline is most ecient e+ca&ating material !elo' the le&el of their !ase can, •
Draglines 5cont •
Despite these limitations- and their e+tremel* high capital cost, draglines remain popular 'ith man* mines- due to their reliability, and e+tremel* lo" "aste removal cost
PO2E= SHOE •
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A :o"er shovel 0also called a Stripping or ;ront Shovel in some mar/ets, mar/ets, is a !uc/et e#uipped machine- usuall* electricall* po'ered- used for digging and loading earth or fragmented roc/- and mineral e+traction A po'er sho&el is second to the dragline in sie- !ut is more po"erful 'hen it comes to digging hard coal or overburden arge machines are electricall* operated Small sie of sho&els ma* ha&e$ ac- dcdiesel- diesel h*draulic or diesel electrictransmission
:o"er Shovel 8esign •
Sho&els normall* consist of a revolving deck 'ith a po"er plant, driving and controlling mechanisms, usuall* a counter"eight, and a front attachment, such as a boom or crane 'hich supports a handle 'ith a digger at the end The machiner* is mounted on a !ase platform 'ith tracks or "heels <2@ The !uc/et is also /no'n as the dipper dip per Modern !uc/et ! uc/et capacities range from J m F to nearl* J m F
Capacit* of sho&els and draglines3 •
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measured in bucket volume. The regular range of sho&el !uc/ets is '&.#%() m* + popular si,es 6or truc/ loading in metalliferous open pits or #uarries% FQ)K m F 6or truc/ loading in opencast coalmineslarge iron ore mines- and large copper mines >)>> m F
Po'er Sho&el digging o&er!urden
Cont O&er!urden stripping in opencast coalmines 0Not used for truc/ loading, up to >FJ mF •
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1uc/et 1uc/et 7ll factor f actor for hard roc/ is a!out R- !ut small !uc/ets !uc/ets in soft s oft roc/s roc/s can ha&e o&er ?R 7ll factor A sho&el should 7ll a truc/ in K) passesas a rule of thum!
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Normall* a sho&el runs on the oor le&el it digs for itself and 'or/s from that height up A !ulldoer is /ept for clean up duties and oor grading- the sho&el is not sucientl* mo!ile to perform its o'n cleanup
Sie of Po'er sho&el8Draglines • •
Marion 1=>5 The Mountaineer % The Story Imagine a machine that stood as high as a >% story building that 'as still a!le to mo&e !* its o'n moti&e po'er po'er A machine that had an operating "eight of 21=5 tons- s'ung a >1 cubic yard bucket that took 55 ton !ites of earth and roc/- and mo&ed it over the length of a football !eld to place it on top of a giant spoil pile this stripping sho&el- 'as t*pe Q and 'as manufactured and erected !* the Marion Po'er Sho&el compan* during >? 8 in .SA This sho&el 'as !etter /no'n under its unocial name- the Mountaineer.
PO2E= SHOE 2O=ING P=INCIPE •
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There are three to four motions on the shovel+ a, 8ig !* pulling on the rope that goes o&er the end of the th e !oom to the !uc/ !u c/et et or dipper thus lifting it through the roc/ pile
!, 3ro"d !* rolling the dipper do'n past the !oom to the !uc/et this forces the !uc/et !uc/et into the roc/ pile as it mo&es for'ard
Cont c) S"ing )to ta/e the !uc/et round and empt* it through its !ac/ door d) propel ) mo&ing the sho&el unit to di"erent locations or dig positions
A sho&elUs 'or/ c*cle- or digging c*cle- consists of four phases$ digging s'inging dumping returning •
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The cro"ding action of the dipper stic/ and its hea&*- stiV*)mounted !uc/et!uc/et- gi&e a sho&el a much stronger loading breakout force than either a dragline or a front end loader- eg a -.> m? po"er shovel has a breakout force of @5T 'hile a =.> m? loader has a breakout force of ?1T A sho&el can break out shales or coal "ithout blasting and also gi&e a smooth !ench surface
3hoice bet"een a 8ragline and a po"er shovel.
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There There are are other small machines used in open cast mining for au+iliar* operations eg &ackhoes for ditching etc- "heel loaders graders- &ulldo'ers, scraper loaders- tractors etc
Other machines) the 1ac/hoe
)The 1ull doer
)The 2heel loder
Grader
Scraper loaders
Tractor Tractor
