24-MMP-A5 Surface Mining Methods and Design · May 2013
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, 2013-May. 3 hours duration; one handwritten 8.5×11 in reference sheet permitted (not an open-book exam); only approved Sharp or Casio calculators allowed. Question 1 is compulsory (40 marks, parts 1.1–1.7); candidates then select FOUR of the six optional Questions 2–7 (15 marks each) to complete the paper.
Reference texts: Hartman & Mutmansky, SME Mining Engineering Handbook, 3rd ed. (dewatering, slope stability classification, dragline stripping geometry, truck dispatch, mine closure); Hustrulid, Kuchta & Martin, Open Pit Mine Planning and Design (moving-cone and Lerchs–Grossmann pit optimization, capital-cost estimating, truck-shovel match factor); Lerchs, H. & Grossmann, I.F. (1965) “Optimum Design of Open-Pit Mines,” CIM Bulletin (the graph-theoretic 2-D worked example this question is drawn from); O’Hara, T.A. (1980) “Quick Guides to the Evaluation of Orebodies,” CIM Bulletin, Feb. 1980, and Mular, A.L. & Poulin, R. (1998) CANCOST, CIM Special Volume 47 (capital-cost formulae); Bieniawski, Z.T. (1989) Engineering Rock Mass Classifications (RMR system).
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.
Open-pit dewatering keeps the working floor and haul roads trafficable and prevents pore-pressure build-up in the pit walls that would otherwise reduce the factor of safety of the slope. Six components recur in almost every pit dewatering system:
1. Pencil (or “stinger”) pumps are small-diameter, high-head submersible units (typically 100–150 mm barrel) lowered into a sump or a shallow well point. They move modest volumes – roughly 5–30 L/s (0.3–2 m³/min) – against heads of 30–100 m, and are used to chase a moving sump on an active bench floor because they are light enough for one labourer to reposition by hand.
2. Submersible pumps are the general-purpose sump pump of the pit: multistage electric or hydraulic units set directly in the water, sized from small floor pumps up to large 300–500 mm discharge units. Typical ranges are 50–500 L/s at heads of 20–150 m depending on stage count; because the pump is flooded it is self-priming and tolerates the silty, abrasive water typical of a pit sump.
3. Hydraulic pumps are driven by a remote hydraulic power pack through flexible hose rather than by an on-board electric motor, which lets the pump end be lowered into confined or hazardous sumps (or on a float) while the prime mover stays on safe, dry ground. They cover a similar duty to submersibles, roughly 20–300 L/s at heads up to 150–200 m, and are favoured where mains power is not yet available to a new cut.
4. Pumps with an attached generator are self-contained diesel-generator/pump skids used where the mine grid has not reached the working area or as an emergency backup during a power outage; they trade a lower duty point (commonly 10–100 L/s at 20–80 m head) for complete independence from the site electrical system.
5. Check (non-return) valves are fitted in the discharge riser immediately above the pump to prevent the full column of water in a long vertical or inclined discharge line from draining back through the impeller when the pump stops. Without one, the reverse flow can spin the impeller backwards at damaging speed and subjects the pump and column pipe to a pressure surge every time the pump cycles.
6. Water hammer is the pressure transient created when a valve closes (or a pump trips) and the moving column of water in the discharge line is decelerated almost instantaneously; the resulting pressure spike, which can be several times the static head, is the classic cause of split HDPE riser pipe and blown pipe joints in pit dewatering ranges. It is controlled with the check valve above, plus slow-closing valves, air/vacuum relief valves at high points, and surge chambers on long discharge runs.
