Design of openpit mining


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Design of openpit mining

  1. 1. DESIGN OF OPENPIT MINING I. Satyanarayana, M.Tech,MBA,MCADy. Manager, Project Planning, SCCL,, visit at ISN
  2. 2. OPEN PIT MINING ISNSource: WCI 2005
  3. 3. PRELIMINARY EVALUATION OF DEPOSIT Deposit Tech-Aspects Economic aspectsResources Production requirementsGR/MR Mining Technology Minelife requirementsMining depth Logistics,Strata Sequa Options and Suggestions Roads etc.Thickness of- coal Equipment Cash out flow- waste Cash inflow- inter burden Surface Constraints Required rate ofCoal Quality ReturnSlope stability Cut-off SRWater Conceptual Mine Plan (Open pit layout, equipment) Modification of concept and or optimization Pre-Feasibility Study Accepted – Management Not accepted – DPR ISN New attempt
  4. 4. Steps in design of OpencastA. Study of deposit exploration (GR)B. Final pit limits.C. Development sequence.D. Design of Access Ramp and Haul RoadsE. Pit designF. Annual production capacity – system availability – Mining technologyG. Main Mining EquipmentH. Optimizing Dumping strategy and balancingI. Year-wise / stage – wise plansJ. Financial viability (Capital & Revenue)K. Coal WashingL. Environment stipulations ISN
  5. 5. A. Study of GR on the deposit Exploration• Extent of deposit i.e. strike and dip rise widths.• Geology – Geological succession, sequence of beds, drilling, logging, no. of seams, sequence of coal seams, description.• Inter seam partings.• Structure – No. of faults, Throws, dip of seams and beds• Reserves – Quality wise/seam wise/depth-wise etc. based on Block model, Gridded seam model & polygonal Model• O.B. volumes & S.R. – Sector-wise, depth-wise etc.• Coal seam analysis, proximate and ultimate , Ash etc. & OB strata hardness etc.• Drilling details (Lithology)• Physiography• Climate and Vegetation ISN• Preliminary EMP information
  6. 6. B. DIMENSIONS OF OPENPIT FIELD The criteria for delineation of boundaries of an Opencast Project are:Rise side boundary - Usually incrop of the bottommost seamLateral sides - Usually by Geologicaldisturbances like faults, surface structures / features likenalah, river etc or limitation of the strike length of thedeposits.Dip side - Depends on the economical stripping ratio,in absence of natural constraints ISN
  7. 7. Cont.Delineation of boundariesQuarry Surface to be delineated based on the following stipulations:Vicinity of structures to the project.1. No person should be within the blasting zone2. As per CMR 170, Blasting Zone is 300m. As per DGMS Circular, It is 500m3. PPV (max. 10mm/s) to be maintained as per DGMS Technical Circular No.7 of 19974. However, by controlled blasting low charge / delay, muffling etc. permission was given even upto a distance of 125 – 150m. ISN
  8. 8. Contd.Haul analysisLead,lift increase cost – decides mode of transportDump limits available areDump area 100m from mine boundaryDump area 50 m from internal access road.Dump area 80-100 m. from mine infrastructureOB volumes - Final slopesMineable Reserves – various losses, batter, barrier etc. - dilution etc (0-1 m against Roof,floor)Maximum depth increases haul cost (30-40% of total cost at 1 1/2 Km lead. ISN
  9. 9. Estimation of Coal, OB & Stripping ratio Contd.Rough assessment is given below• Assuming Pit slopes of 450, the Quarry floor and Quarry surface are delineated• Volume of Coal & OB = Average area x Average depth - (A)• Average area = (Quarry surface area + Quarry floor area) / 2• Average depth = (Minimum depth + maximum depth) / 2• Volume of Coal=(Quarry floor area x Cumulative thickness of all coal seams) - (B)• Coal in tonnes = Volume of coal x Specific gravity – (C)• OB Volume = Coal + OB Volume (A) – Coal Volume (B) - (D)• Stripping ratio = OB Volume (D) / Coal in tones (C) For accurate S.R,the volumes of OB and coal are to be made seam wise ISN
  10. 10. Contd.The boundaries are firmed up based on the economicstripping ratio. Economic stripping ratio varies with: • Average sales realization i.e. higher the quality of coal, higher the realization. • Capital investment requirements • Operating cost. • Also surface constraints Projects are likely to be economically viable upto a maximum SR indicated against the grade of coal Grade Stripping ratio (Cum/T) F 8 E 9 D 10 C 12 ISN
  11. 11. C. Development Sequence-Opening the deposit – Access trench-Box cut – To accommodate all equipment-Mine phases – Depends on the shape of the property-Progress of Benches-Coal production schedules-OB excavation schedulesNote:- Maximize inventory of coal in the initial years -Differ OB stripping requirements as much as possible – Average SR versus natural SR -Income generated in the first 5 to 10 years but not remote economics will either make or break the project. -Profits for in the future have practically no impact on the project NPV. Each successive phase will be less profitable and the ultimate limit will be loss even after ploughing in earlier profits. ISN
  12. 12. D. Design of Access Ramp & Haul roads Location of Access ramp is guided by the following: 1) Generally located at the minimum depth of incrop of bottom most seam – So as to reduce initial waste stripping (unproductive work) 2) Should facilitate maximizing of internal dumping and sectional working. 3) Should be near the External dump / Coal yard / Mine service facilities etc. 4) Main haul road upto the pit limit should be planned in the beginning only. 5) Since haul costs constitute about more than 40% and tyre costs about 10% of the total mining costs,priority for design,construction and maintenance should be given. 6) Gradient,width,drainage,curves,super elevation,base,sub base,type and thickness of top dressing should be like that of national high ways for heavy traffic. ISN
  13. 13. D Contd.D. Design of Access Ramp & Haul roads Haul roads Sl.No Particulars 1 Width Should facilities two way traffic, dozer movement, formation of drains, lighting arrangement (Normal width – 30m,but depends on capacity of dumpers). 2 Gradient 1 in 16 Short ramps 1 in 10 3 Lesser number of curves 4 In flat seams of larger haul roads can be formed over the floor of the strike length seam 5 In steep seams Haul road for Coal & OB benches can be planned along highwall slopes say every 30m. This will also facilitate internal dumping. ISN
  14. 14. E. Pit design.General design parameters and planning data• Density of seams, total coal column thickness•Thickness of partings• Gradient• Geological disturbances• Strike lengths, shape of property• Geological Reserves• Surface constraints/adjacent habitat• Dump yards availability with lead and lift• Mining system, optimum mining concept• Depth of operation, mineable reserves after various losses, OB volumes, SR• Spoil characteristics• Work practices in the Area• Diggability characteristics ISN
  15. 15. E Contd.E. Pit designAs per Regulation 98 of CMR 1957,In alluvial soil etc. - Sides shall be sloped at 450 or Benched – height not more than 1.5m Width – not less than heightIn hard ground - Sides adequately benched/sloped so as to prevent danger from fall of sidesCoal - Sides shall be sloped at 450 or Benched – height not more than 3mHowever, exemption can be sought from Inspectorate. ISN
  16. 16. E Contd.E. Pit design Overall slope of a pit depends on several factors of the pit slope: a) Geological disturbances like faults etc. b) Hydrological condition of strata c) Orientation of slip planes d) Nature of strata – i.e. hardness, material consolidation etc. e) Depth of workings f) Design of haul roads & ramps in the highwall g) Stratigraphy – thickness, spacing of the clay bands or other weak layers ISN
  17. 17. E. Pit design E Contd.In general for OC mines upto a depth of 200m, overall slope angle of 450 ispermitted. ISN
  18. 18. E Contd.E. Pit designFor deeper mines flatter highwall slopes will be necessary from safety point ofview (for 35 T dumpers & above) ISN
  19. 19. E. Pit design E Contd.For deeper mines flatter highwall slopes will be necessary from safety point ofview (dumpers below 35T capacity) ISN
  20. 20. E Contd.E. Pit design Typical High wall layout ISN
  21. 21. E Contd.E. Pit designWorking benches:1) GeneralWidth - 40 – 45mHeight - Generally equal to height of the boom or in some cases upto 3m above the boom height. In case of Backhoe – digging height of machineBench slope - 560 to 7002) Dragline:Width of the cut - 60mHeight of bench - maximum digging depth3) In order to even out the yearly OB removal quantities and the economics sometimes alternative workings and non-working benches (around 25 m wide) are proposed. ISN
  22. 22. F. Fixing annual production capacityAfter defining the boundaries, the annual production capacity will be fixedbased on the following criteria :1) The available mineable coal reserves2) Geometry of the deposit - Strike & dip rise lengths3) Structure of the deposit - Thickness of seams, partings, faults, gradient etc.4) Linkage - Basket, Captive use etc.5) HEMM configuration - Capacity of HEMM.6) Surface structures - Limits the material to be blasted. ISN
  23. 23. F Contd.Excavator machine productivity –Based on ,-Dipper cycle time-Waiting time for truck spotting-Bad blast factor-Truck loading time etc.Annual capacity is based on-Equipment available hours-Utilization percentageProper fragmentation,less throw off material,benchheight,bench slopes ,avoiding toes and secondaryblasting,improves shovel efficiencyOptimum fragmentation-cost of drilling,blasting vis-à-vis cost of dozing,loading,hauling and dumping. ISN
  24. 24. ISN
  25. 25. Thank you all ISN