The Mining Technology of a Thick OverburdenLayer Covering a Group of Flat Dipping CoalSeamsS.I. Fomin and D.A. VedrovaNational Mineral Resources University, Saint Petersburg, RussiaAbstract. Horizontal mineral deposits with relatively thick sediment overburdenadvisable to practice using transtoptless overburden removal technology, that isusing a powerful stripping equipment - draglines. The main advantage of thistechnology is the placement of overburden directly into cut goaf, significantlyreducing the rented for the waste dumps disposing areas, and reduce the costs ofmining - reclamation works.Keywords: dragline, reexcavation ratio, waste dumping in to the cut goaf, coalmine, mining bench, overburden.1 Rising of Draglines Operating Parameters Expands theScope of Direct Dumping Method Deposits DevelopmentSystems with Application Overburden RehandlingHorizontal or flat dipping (up to 100) layers of minerals, which include most of thedeposits of sedimentary origin, such as oil shale, coal, peat, clay, limestone, with arelatively thick capping of overlying rock are advisable to develop by using directdumping method, that is using a powerful stripping equipment - draglines. Themain advantage of this technology is the back feeling into void, what cansignificantly reduce the land area rented for disposing of waste dumps, and reducethe costs of mining-technical stage of reclamation.Due to the increasing complexity of the mining and geological conditions offield development (increasing depth of mining works and reduction of developedspace parameters) and rising of draglines operating parameters expands the scopeof direct dumping method deposits development systems with applicationoverburden rehandling. Usually after the mining stope excavation in mined-outspace of a quarry the free bottomhole bandwidth remains. For the opening of thefollowing coal stope excavator ought to work out next overburden stope anddump the rock in the mined-out space. Due to the insufficient size of theoverburden excavator and a limited amount of free space to dispose a waste rock,overburden backfills quarries face. To remove it, and increase the capacity ofbottomhole excavator carries out rehandling of rock from the primary dump7 6 S.I. Fomin and D.A. Vedrovafreeing up bandwidth between lower bench slope edge and the edge of final wastedump location [1].An assessing indicator of the selected overburden bench mining processflowsheet is a rehandling ratio the parameter, that shows how much of the totalamount of a waste rock was excavated several times (being rehandled).Under the optimal parameters of the process flowsheet reexcavation ratio mustbe less than unity. As a result of insufficient working radius of overburdenexcavators and mudslides of waste dump multiplicity of the rehandling ratio maybe greater than 1 and up to 4.Economically acceptable rehandling ratioreh tr d reh k ( C ) /C , (1)Ctr, Cd, Creh - expenditures on 1 m3 of overburden removing with appliance oftrucks transportation, by using of direct dumping method and rehandling costsrespectively.2 Development Schedule of Izykhsky Strip MineFor cost-effective organization of production during the period of cut designingprocess flowsheet of overburden benches mining should be chosen according tothe principle of the additional costs on rehandling reduction. To successfullyresolve this task it is necessary to take into account a number of operationalparameters and indicators at drawing up of flowsheet process, such as: overburdenfragmentation index, sustainable slope angle of coal and overburden benches,loosened overburden natural slope angle, final angle of stability for internaldump, and the parameters of the dragline working the overburden bench.Consider the sequence of the process flowsheet designing for developing of thegroup of coal seams on example of the strip mine Izykhsky, Khakassia Republicof Krasnoyarsk region, Russian Federation. The deposit is represented by a groupof flat dipping (up to 90) hard coal seams with up to 5,8 m thickness.Interstratified layers of argillite and sandstone reach a thickness of 7 m. Depth ofworks increases from 40m in 2012 to 145 m by 2025, so overlying waste rocklayers thickness growth up to 111 m by the time of quarry closing. Annualdesign capacity of coal production is about 2 mln. t / year.Fig. 1 Profile of a Izykhsky coal mine development scheduleThe Mining Technology of a Thick Overburden L ayer Covering 773 Adjustment of the Maximum Output of Overburden byDirect Dumping MethodFor deposit development combined opening scheme was chosen: 1-st benchdevelops with appliance of shovels and railway transportation of waste rock to thenearest carried the work to completion open pit at the distance of 3 km, werewastes are discharged into the open space of a quarry; several of the next benches(total amount depends on the increasing depth of works) works out by complex ofhydraulic excavators and dumptrucks; the lowest and most thick (up to 27 m)layer of overburden, covering ore body, carries out by direct dumping methodwith appliance of draglines with different bucket capacity (11 and 20 m3), withrehandling ratio of 0,4.The main task is to determine the maximum height of the bench, which will beexcavated by a dragline, taking into account that the volume of developed space,were overburden should be replaced is limmited by the width of stope which isassumed according to the system of deposit development. Based on draglinesdischarging parameters and stability conditions a profile of inside dump stopemust be designed. This profile gives a square of dump, out of which the amount ofdischarged overburden can be calculated. Having the width and the square ofoverburden stope the maximum height of the bench can be found.As the annual design capacity of the coal production is also determined beforedesigning of the flowsheet process, the necessary draglines park due to its yearlycapacity should be counted: firstly a length of working front of a strip mine, whichallows to gain coal production must be evaluated; then by using the square ofoverburden stope total amount of overburden, that is to be removed, to open theaccess to coal and ensure the performance, can be found. If this value exceeds therating yearly capacity of one dragline, then several shovels should work out thatbench [2].When main parameters of working space, such as height of the bench, width ofstope, stability angles and working parameters of determined draglines arespecified the scheme with sequence of rehandling can be designed.Fig. 2 The profile of blasted overburden stope and a final inside dump position afterrehandling7 8 S.I. Fomin and D.A. VedrovaFig. 3 Dividing total bulk of blasted rock according to draglines capacities. Passes ofdraglines 1 and 2 with bucket capacity 11 m3, primary inside dump formation.Fig. 4 1st pass of dragline with bucket capacity 20 m3. Primary inside dump formation.Fig. 5 2nd pass of dragline with bucket capacity 20 m3 consisting of discharging from twodifferent positions. Final view of the inside dump and total bulk of rehandling.The Mining Technology of a Thick Overburden L ayer Covering 79Coal layers then are developed by complex of hydraulic excavators anddumptrucks: overburden of interstratified layers is taken away on a dumpinglandfill outside the quarry border.The thickest interstratified layer (more than 7 m) is to be excavated byadditional pass of a dragline from on-dump standing point.Fig. 6 Coal excavatingFig. 7 Additional pass of a dragline from on-dump standing point4 ConclusionsThe appliance of the proposed scheme will provide: Adjustment of the maximum output of overburden by direct dumping method; fully usage of draglines working parameters (maximum digging depth anddischarging heights, working radiuses) and taking into account safety workconditions according to dump stability; reducing the bulk of work on opening the deposit and duration of time periodpreceding the start of operational activities; reducing expenditures in rehandling works, due to the optimal formation ofthe inside dump by back feeling into void.