24-MMP-A2 Underground 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-A2 Underground Mining Methods and Design, 2013-May. 3 hours duration, closed book; only a Casio or Sharp approved calculator permitted. Question 1 is compulsory (40 marks, all seven parts 1.1–1.7); a candidate then selects FOUR of Questions 2–7 (each worth 15 marks).
Reference texts: Hartman & Mutmansky (eds.), SME Mining Engineering Handbook, 3rd ed. (underground mining methods, mine ventilation, shaft hoisting systems, backfill practice — the primary reference throughout this paper); BC Ministry of Energy, Mines and Low Carbon Innovation, Health, Safety and Reclamation Code for Mines in British Columbia (Canadian regulatory context for mine ventilation and hoisting-plant safety); Wills & Finch, Wills' Mineral Processing Technology, 8th ed. (tailings thickening/filtration and paste preparation for backfill).
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.
6.1 — the four services. Every underground mine depends on: (i) ventilation air, to dilute and remove blasting fumes, dust, heat and diesel exhaust and supply breathable air; (ii) electrical power, to drive fixed plant (hoists, pumps, fans, crushers) and, increasingly, mobile equipment; (iii) compressed air, historically for rock drills and still widely used for pneumatic tools, air-actuated valves and instrumentation; and (iv) mine water (both a service supplied — for drilling, dust suppression, cooling — and a service removed, via dewatering).
6.2 — infrastructure. Surface infrastructure typically comprises a main substation stepping down utility (or on-site generated) power to a mine distribution voltage, main ventilation fans (forcing or exhausting) at surface fan stations connected to the shaft/decline collar, a compressor house supplying the compressed-air ring main, and surface water/settling ponds feeding fresh water underground while receiving pumped mine water for treatment and discharge. Underground, this is mirrored by a distribution network: substations and transformers at each level feeding cable to loads, ventilation raises/ducting and regulators directing air to each working face, a compressed-air ring main with drops at each heading, and a dewatering system of sumps, pump stations and pipe ranges lifting water level by level to surface.
6.3 — transfer methods underground. Power is carried down the shaft or decline as armoured cable on cable-hangers or in a raise, then distributed level-by-level through trailing cables and cable reels to mobile loads. Ventilation air is drawn or forced through the shaft/decline itself and through purpose-built ventilation raises, then ducted or regulated (doors, stoppings, regulators) to individual headings. Compressed air travels down a shaft-column pipe range into an underground ring main with branch lines to each working area. Water (fresh supply and mine drainage) travels in dedicated borehole/shaft pipe columns, fresh water gravity-fed or pumped down, mine water pumped up in stages through a series of pump stations sized to the total lift.
6.4 — typical amounts and costs. Ventilation quantities scale with the diesel equipment fleet and heat load, commonly ranging from tens to several hundred m³/s for a mid-size to large mine, with main fan and airway (raise) capital in the low tens of millions of dollars and a significant ongoing power cost (fan power rises with the cube of quantity, per Q1.2's H–Q law). Electrical demand for a mid-size underground mine typically runs from a few MW to tens of MW, with substation/reticulation capital scaled accordingly and unit cost billed per kWh consumed. Compressed air demand is comparatively modest (a few hundred to a few thousand cfm) with compressor-house capital in the low millions and a notable power draw per unit of air delivered. Mine dewatering ranges from tens of L/s in a dry mine to hundreds of L/s in a wet one, with pump station capital and power cost (as in Q1.6) scaling directly with flow and lift.
6.5 — equipment supplied and consumption rates. Ventilation air is "consumed" primarily by diesel equipment (a typical diesel LHD or truck requires on the order of 0.03–0.06 m³/s per rated kW of engine power under current guideline dilution criteria) and by personnel/heat loads. Electrical power runs fixed plant — hoists (hundreds of kW to several MW each), main fans and pumps (tens to hundreds of kW each), crushers and conveyors — plus, on mines with trolley or battery-electric fleets, mobile equipment. Compressed air runs pneumatic rock drills, stopers, jacklegs, air-actuated loading-pocket gates and instrumentation, each drawing on the order of tens to a couple of hundred cfm per active tool. Water services drills (for flushing) and dust suppression at each active heading, at typical rates of a few L/s per active drill or muck pile, while the dewatering system must handle both this service water and any natural groundwater inflow.
