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OPEN CAST MINING
METHOD
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Open Cast Mining Method
• Open cast mining is a surfaceexploitation method, used mainlyfor coal It resem!les open pit mining
!ut di"ers in one uni#ue respect$
The overburden is nottransported to waste dumps for
disposal but cast or hauleddirectly into adjacent mined-out panels.
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Continued%%
• OC Mining is su!di&ided into t'o methodsi Strip Mining
iiTerrace Mining
i. Strip Mining
• This method is ideal under the follo'ingconditions$
a)Relatively thin overburdenb)Extensive area of reserves
c)Regular horizontal/at topography and seams
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Strip Mining) cont
• The deposit is mined in a series ofstrips
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Strip mining) cont
• The o&er!urden from each strip iscast directl* into the &oid created !*the pre&ious coal e+traction
• Strip Mining is normall* a largetonnage operation using largemining machines such as Draglines
and Power shovels for Coal andOverburden strippingrespectively.
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ii, Terrace Mining
a, This method is used 'here $
The overburden is too thick or
The oor is too steeply dippingto permit direct across the pit casting ofo&er!urden material- Theoverburden (spoil) must !e
transported !* other means andtipped back into the void left backby previous mining.
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Cont
!,This is a multi !ench lateral ad&ance
method- the 'hole mine mo&ingacross the deposit- !ut not in asingle stage operation as with
strip mining
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Cont
• c, .pper le&els are usuall* transported!* truc/ and sho&el- or !* acom!ination of !uc/et 'heel e+ca&ators
012E,- con&e*ors and stac/ersd, If a dragline is used in terrace mine
it can onl* operate on the bottom
benches 'here direct casting ofo&er!urden is possi!le
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Terrace mining) cont
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Terrace Mining)cont
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Opening up into a coalseam3
• The initial opening into a coal seam iscalled a Bo cut. a trench or box cut4is made through the o&er!urden to e+posea 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 theo&er!urden material from this cut is placedin the void of the !rst cut
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Position of !o+ cut
A bo cut is either made in the shallo"estpart of a pitching deposit, to mine to thedip or
1
bo cut
For a thick deposit a box cut may be madenear the center or at the highest part so thata series of benches may be ta!en out"ards
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1o+ cut ) cont%
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1o+ cut 5cont
• 6rom the !o+ cut coal miningproceeds down the dip or acrossthe mining lease O&er!urden isremo&ed from in front of thead&ancing high!all and thro'n intothe mined out area as in 7gure
!ello'
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1o+ cut) cont Striping Dragline
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1ac/ 7lling or 1ac/ Casting
• 2hen the dip angle# $, of a coaldeposit is less than the angle ofrepose of the spoil heaps plus a
factor of safet*- it is possi!le todump spoil8o&er!urden 'aste insidethe e+ca&ated area 01ac/7ll, Dip angleof coal seam 9:
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Direct 1ac/ 7lling
• 2here possi!le the o&er!urden'aste is direct back%cast acrossthe cut 'ith a Dragline or stripping
Po'er sho&el
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Indirect 1ac/7lling
• 2hen either the overburden orcoal seam is too thick the reachof the dragline or stripping sho&el
!ecomes small- and the o&er!urdenhas to go round the pit and !e 7lledin from !ehind
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Indirect !ac/7lling)cont
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Ma;or Open Cast Operations
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Ma;or OC operations cont
i) &ush clearing and leveling This in&ol&es the remo&al of the &egetation to
ensure homogeneous topsoil A bulldo'er ortractor does this 'ith a ripper !ehind The area isthen graded to allo' smooth tra&eling of haul
Truc/s
ii, Top soil removal$???@ Topsoil is remo&ed separatel*- and ultimatel* re)
placed upon graded spoils 0o&er!urden 'astedumps,
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Cont
Top soil can !e stoc/piled at the sideof the pit area for later redistributionor ma* !e hauled immediatel* to the
graded area for redistri!ution The method of redistri!uting the topsoil
is dictated !* economics considering
#uantit* and distance it ma* !e !*oader8Truc/ method or !* self)ele&ating scrapers- etc
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cont.
iii) verburden stripping The overburden benches ma* !e one
or more depending on 3
) The thickness of the overburden andthe reach of the stripping euipment.
) In a !ench 'here a dragline is used-
cast or * bu+er blasting is used toloosen the roc/ !efore the dragline can'or/ on the material
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Cont
• 2here the o&er!urden is &er* thic/-eg. -m. /t 0ankie colliery inBim!a!'e- o&er!urden stripping is
di&ided into )1enches1 m on top is "orked by a po"er
% shovel bench- or 0supplementar*
strip !ench, andThe bottom 21m. is 'or/ed !* a
Dragline hence called Dragline !ench
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Cont
iv) 3oal 4xtraction• 3oal mining ma* !e !* $
• A single !ench or t'o depending onthickness or uality of the coal seam.
Eg at 'an/ie collier* in Bim!a!'e a 5 mthick seam is mined in t"o benchesbecause the top m is po"er coal andthe !ottom m is coking coal The maine#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 !efore topsoil is
re)placed
&i, Top Soil 6eplacement• Scrapers- doers- loaders and truc/s are
used in this operation A la*er of fertilesoil is spread on top of graded spoils
•
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OC Operations
vii) 6e%vegetation orreplanting $
• ???@
• Planting of &egetation is accomplished !*a con&enient farm implement- and is doneas soon as practical Seed selection is!ased on post mining land use
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deposits for open cast
mining.
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Coal Open Cast machines
8ragline 4xcavators
• The dragline is a &ersatile attachmentcapa!le of a 'ide range of operations at
and !elo'ground le&el The dragline candig through loose to mediumcompacted soil
• The !iggest ad&antage of the dragline
o&er other machines is its long reach forboth digging and dumping Anotherad&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 MF and 'ith lo' abrasiveproperty.
• The machines are electricall* operated A
dragline !uc/et s*stem consists of a largebucket 'hich is suspended from a boom 0alarge truss)li/e structure, 'ith 'ire ropes The!uc/et is maneu&ered !* means of a num!er
of ropes and chains The hoist rope- po'ered !* large diesel or
electric motors- supports the !uc/et and hoist)coupler assem!l* from the !oom
http://en.wikipedia.org/wiki/Trusshttp://en.wikipedia.org/wiki/Wire_ropehttp://en.wikipedia.org/wiki/Dieselhttp://en.wikipedia.org/wiki/Dieselhttp://en.wikipedia.org/wiki/Wire_ropehttp://en.wikipedia.org/wiki/Truss
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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 ! schematicdiagram of a large dragline
buc"et system is sho'n !elo'
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Dragline 5cont
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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
ropeA 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 thebuc"et to tilt and empt* This is called a dumpoperation
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Draglines in mining 5sieand cost
• A large dragline s*stem used in the openpit mining industr* costs appro+imatel*.S )> million A t*pical !uc/et has
a &olume ranging from F to cu!icmetres- though e+tremel* large !uc/etsha&e ranged up to >J cu!ic metres Thelength of the !oom ranges from #$ to
%&& metres In a single c*cle it canmo&e up to K metric tonnes ofmaterial
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Dragline L po'er source
• Most mining draglines areelectrically po"ered.. Their po'erconsumption 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 upto Mega'atts during normaldigging operations
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Dragline po'er sourcemo&ement
• In all !ut the smallest of draglines-mo&ement is accomplished !*'al/ing using feet or pontoons- as
caterpillar trac/s place too muchpressure on the ground- and ha&egreat dicultl* under the immense'eight of the dragline
• Ma+imum speed is onl* at most a fe'hundred metres per hour since the feetmust !e repositioned for each step
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imitation of .se ofDraglines
• The primar* limitations of draglines are $boom height andboom length-
'hich limits 'here the dragline can dumpthe 'aste materialdig depth- 'hich is limited !* the length
of rope the dragline can utilie Inherent
'ith their construction- a dragline is mostecient e+ca&ating material !elo' thele&el of their !ase can,
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Draglines 5cont
• Despite these limitations- and theire+tremel* high capital cost,draglines remain popular 'ith man*
mines- due to their reliability, ande+tremel* lo" "aste removal cost
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PO2E= SHOE
• A :o"er shovel 0also called a Stripping or;ront Shovel in some mar/ets, is a !uc/ete#uipped machine- usuall* electricall*po'ered- used for digging and loading earth
or fragmented roc/- and mineral e+traction• A po'er sho&el is second to the dragline in
sie- !ut is more po"erful 'hen it comesto digging hard coal or overburden
• arge machines are electricall* operatedSmall sie of sho&els ma* ha&e$ ac- dc-diesel- diesel h*draulic or diesel electric-transmission
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:o"er Shovel 8esign
• Sho&els normall* consist of a revolvingdeck 'ith a po"er plant, driving andcontrolling mechanisms, usuall* acounter"eight, and a front attachment,such as a boom or crane 'hich supports ahandle 'ith a digger at the end Themachiner* is mounted on a !ase platform'ith tracks or "heels
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Capacit* of sho&els anddraglines3
• measured in bucket volume. Theregular range of sho&el !uc/ets is '&.#-%() m* + popular si,es
• 6or truc/ loading in metalliferous openpits or #uarries% FQ)K mF
• 6or truc/ loading in opencast coalmines-large iron ore mines- and large coppermines >)>> mF
Po'er Sho&el digging
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Po'er Sho&el diggingo&er!urden
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Cont
• O&er!urden stripping in opencastcoalmines
0Not used for truc/ loading, up to >FJ mF
• 1uc/et 7ll factor for hard roc/ is a!outR- !ut small !uc/ets in soft roc/s canha&e o&er ?R 7ll factor
• A sho&el should 7ll a truc/ in K) passes-as a rule of thum!
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Cont
• Normall* a sho&el runs on the oorle&el it digs for itself and 'or/s fromthat height up
• A !ulldoer is /ept for clean upduties and oor grading- the sho&elis not sucientl* mo!ile to performits o'n cleanup
Si f P
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Sie of Po'ersho&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 !* itso'n moti&e po'er A machine that had an
operating "eight of 21=5 tons- s'ung a >1cubic yard bucket that took 55 ton !ites ofearth and roc/- and mo&ed it over the lengthof a football !eld to place it on top of a giantspoil pile this stripping sho&el- 'as t*pe Qand 'as manufactured and erected !* the
Marion Po'er Sho&el compan* during >? 8 in .SA This sho&el 'as !etter /no'n under itsunocial name- the Mountaineer.
PO2E= SHOE 2O=ING
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PO2E= SHOE 2O=INGP=INCIPE
• There are three to four motions onthe shovel+
• a, 8ig !* pulling on the rope that goes
o&er the end of the !oom to the !uc/et ordipper 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 into the roc/ pile as it mo&esfor'ard
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Cont
c) S"ing )to ta/e the !uc/et round and empt* itthrough its !ac/ doord) propel ) mo&ing the sho&el unit to di"erent locationsor dig positions
•A sho&elUs 'or/ c*cle- or digging c*cle- consists of fourphases$•digging•
s'inging•dumping•returning
•
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Cont
• The cro"ding action of the dipper stic/and its hea&*- stiV*)mounted !uc/et- gi&ea sho&el a much stronger loading
breakout force than either a dragline ora front end loader- eg a -.> m? po"ershovel has a breakout force of @5T'hile a =.> m? loader has a breakout
force of ?1T A sho&el can break outshales or coal "ithout blasting andalso gi&e a smooth !ench surface
3h i b t 8 li
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3hoice bet"een a 8raglineand a po"er shovel.
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Cont
• There are other small machinesused in open cast mining for au+iliar*operations eg &ackhoes for
ditching etc- "heel loaders-graders- &ulldo'ers, scraperloaders- tractors etc
Oth hi th
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Other machines) the1ac/hoe
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)The 1ull doer
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)The 2heel loder
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Grader
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Scraper loaders
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Tractor
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