24-MMP-A5 Surface Mining Methods and Design · May 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Mining and Mineral Processing Engineering, 09-MMP-A5 Surface Mining Methods and Design, 2015-May. 3 hours duration, closed book; one hand-written 8.5×11 inch reference sheet and an approved Casio or Sharp calculator permitted. Question 1 is compulsory (40 marks, all six parts 1.1–1.6); a candidate then selects FOUR of Questions 2–7 (each worth 20 marks).
Reference texts: Hartman & Mutmansky (eds.), SME Mining Engineering Handbook, 3rd ed. (equipment availability/utilization, dragline stripping systems, truck-shovel productivity, mine dewatering, mine cost estimation); Hustrulid, Kuchta & Martin, Open Pit Mine Planning and Design, 3rd ed. (block-model economics, floating/moving-cone algorithm, the Lerchs–Grossmann graph-theoretic pit-optimization method, discounted cash-flow scheduling); Kennedy, B.A. (ed.), Surface Mining, 2nd ed., SME (dragline range-diagram geometry, stripping methods); Lerchs, H. & Grossmann, I.F. (1965), “Optimum Design of Open-Pit Mines,” CIM Bulletin, 58, 47–54; O’Hara, T.A. (1980), CIM Bulletin (Feb. 1980), and Mular, A.L. & Poulin, R. (1998), CapCosts: A Handbook for Estimating Mining and Mineral Processing Equipment Costs, CIM Special Volume 47 (parametric capital-cost formulae used in Question 6); Theis, C.V. (1935) and Cooper & Jacob (1946) aquifer-test methods (standard hydrogeology references, Question 3.2).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
1.4.1 – Key cut. A key cut (or "keyway") is a narrow starter trench dug at one end of a new panel, normally by an auxiliary machine (dozer, scraper, or a smaller excavator) rather than the main production dragline, to create the very first spoil-side void the dragline needs before it can begin its own normal casting cycle. It is necessary at the start of every new panel/strip and at box-cuts, because a dragline sitting on virgin, unmined overburden has nowhere to cast its first bucket – the key cut gives it an initial void to throw into.
1.4.2 – Extended bench. An extended-bench operation lengthens the dragline's working bench (the along-strike length mined per machine position) beyond a normal single-pass width, by having the dragline work a wider swath through a combination of extra reach and lateral tub repositioning along the strike before advancing forward. It is used where higher production per dragline is needed from a fixed capital fleet, or where geometry (a locally wide, uniform overburden section) makes it more efficient to sweep a longer bench than to add another machine.
1.4.3 – Advanced bench. In an advanced-bench (pre-strip) arrangement, a second bench sits ahead of and above the main dragline bench and is stripped in advance (by dozer, scraper, or a smaller machine), so the dragline only ever casts the remaining lower portion of the overburden column. It is necessary whenever total overburden thickness exceeds the dragline's effective digging depth plus safe stacking height – splitting the column between an advanced upper bench and the dragline's own lower bench lets a single dragline handle overburden that would otherwise be beyond its geometric capability (exactly the stacking-height AND reach shortfall found for this dragline's own geometry in Question 4.6).
1.4.4 – Chop down. A "chop-down" (or "chopping") cut is a single-dragline, two-lift technique used when the overburden is only moderately beyond the machine's rated digging depth – not so far beyond it that a separate advanced-bench machine is justified. The dragline first digs and casts the UPPER portion of the overburden from its normal bench-top position (a shallow first pass across the full panel length), then walks down (or "chops down") onto the newly lowered surface and re-digs the SAME panel a second time to remove the remaining lower portion to full depth, casting it onto the already-placed first-pass spoil. It is necessary when a single full-depth pass would exceed the dragline's rated dig depth or stacking height by only a modest margin (as found for THIS machine's 17.6 m stacking-height shortfall in Question 4.6) – two shallower, self-contained passes by the same machine avoid the capital cost of a dedicated pre-stripping unit, at the cost of extra cycle time and one additional bucket pass per unit volume moved.
