24-MMP-A2 Underground Mining Methods and Design · December 2019
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Mining and Mineral Processing Engineering, 18-Mmp-A2 Underground Mining Methods and Design, 2019-Dec. Closed book exam, Sharp/Casio approved calculator plus one hand-written 8.5x11 in. reference sheet permitted. Question 1 is compulsory (40 marks, all five parts 1.1–1.5); a candidate then selects THREE of the five optional Questions 2–6 (20 marks each).
Reference texts: Hartman & Mutmansky (eds.), SME Mining Engineering Handbook, 3rd ed. (rock haulage systems, shaft hoisting design, ground support, mine ventilation, mine cost estimation — the primary reference throughout this paper); Hustrulid & Bullock, Underground Mining Methods: Engineering Fundamentals and International Case Studies (room-and-pillar, vertical crater retreat and shaft/incline material-handling comparisons); BC Ministry of Energy, Mines and Low Carbon Innovation, Health, Safety and Reclamation Code for Mines in British Columbia (Canadian regulatory context for hoisting-rope factors of safety, ground support and ventilation practice); O'Hara, "Quick Guides to the Evaluation of Orebodies," CIM Bulletin, Feb. 1980, and Mular & Poulin, CapCost, CIM Special Volume 47, 1998 (parametric underground capital-cost formulas used in Question 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.
Skip and vertical shaft. A vertical (or steeply inclined) shaft is sunk from surface to below the lowest planned mining horizon, equipped with a headframe, hoisting sheave(s) and a drum or friction hoist on surface. Ore is trammed or gravity-fed to a shaft-bottom loading pocket, metered into a skip that travels the full shaft length on guides, and dumped automatically at the top of travel into a surface bin or crusher feed. The shaft also typically carries the mine's men-and-materials cage, and often the primary intake or exhaust ventilation airway, making it a single piece of infrastructure serving several functions at once.
Truck and incline (decline). A ramp is driven from surface (or from an existing underground level) down into the orebody at a sustained grade (commonly around 1:7, or 15%), usually as a spiralling decline to keep the ramp length manageable within the available footprint. Rubber-tyred haul trucks, loaded by an LHD at or near the working face, drive the full haul distance under their own power to surface or to an underground crusher/transfer point. Unlike the shaft, the decline is a general-purpose access way — the same ramp also carries personnel, supplies and equipment into and out of the mine, rather than needing a separate access system.
| Component | Skip and vertical shaft | Truck and incline |
|---|---|---|
| Primary access excavation | Shaft sinking (slow, expensive per metre; specialised sinking crew/equipment) | Ramp/decline development (faster, uses standard production drill/blast/muck fleet, cheaper per metre) |
| Fixed hoisting/haulage plant | Headframe, hoist (drum or friction), sheaves, skip(s), guides — large, purpose-built, high fixed cost | None fixed; haul fleet itself is the "plant," and is mobile capital rather than fixed infrastructure |
| Mobile equipment fleet | Minimal (LHDs to feed the shaft loading pocket) | Full haul-truck fleet, sized to the haul distance and required tonnage — a major capital line unique to this option |
| Loading pocket / crusher station | Shaft-bottom loading pocket, usually with a crusher ahead of it | Portal/surface crusher station, comparable scope |
| Ancillary structural/electrical | Reinforced-concrete headframe structure, high-voltage hoist drive and control system | Ramp ground support (bolting/shotcrete over the full ramp length), lower-voltage distribution to mobile equipment charging/fuelling |
| Component | Skip and vertical shaft | Truck and incline |
|---|---|---|
| Energy cost per tonne | Electric hoist power, largely INDEPENDENT of shaft depth once built (fixed cycle time dominated by acceleration/deceleration, not distance) | Diesel fuel cost per tonne, RISING roughly linearly with one-way haul distance/depth |
| Labour | Small hoist-operator crew; loading-pocket crew | One driver per truck, scaling with fleet size |
| Maintenance | Rope replacement (scheduled, on a fatigue-life cycle), sheave/drum bearing maintenance — concentrated on a small number of large components | Tyres, engine/drivetrain wear, brakes — distributed across many mobile units, generally a higher total maintenance cost per tonne at depth |
| Ventilation load | Minimal incremental load (electric hoist, no combustion) | Significant — diesel exhaust dilution requirement grows with fleet size and ramp length, a real operating cost specific to trucking |
| Ground support upkeep | Shaft lining/guides, inspected and maintained over a fixed length | Ongoing ramp ground-support maintenance over a much longer excavated length than an equivalent-depth shaft |
Qualitatively, the skip/shaft option is capital-heavy and comparatively operating-cost-flat with depth (once built, hoisting cost per tonne changes little as the mine gets deeper, because cycle time is set mainly by acceleration/deceleration rather than travel distance at typical hoisting speeds), while the truck/incline option is capital-light but operating-cost-rising with depth (each additional metre of haul directly adds fuel, tyre wear and driver-hours per tonne, and ventilation cost for the diesel fleet grows with it). The crossover point between the two — the depth/tonnage combination at which a shaft's higher capital is repaid by its flatter operating cost — is exactly the quantity a real feasibility study computes from site-specific capital quotes and diesel/tyre/labour rates; the qualitative direction of every line in the tables above is what drives that crossover, regardless of the specific dollar figures used.
Skip and vertical shaft is favoured where: the mine is DEEP (the point past which trucking's per-tonne operating cost, compounding with depth, overtakes the shaft's flat operating cost and repays its higher capital); the orebody and mine LIFE are large enough to amortise the shaft's high capital over many years of production; sustained TONNAGE is high (a shaft's fixed hoisting capacity is used efficiently only at high, steady throughput); and rock strength/ground conditions support a long-lived, low-maintenance vertical excavation. It is the standard choice for major, long-life, deep base-metal and gold operations.
Truck and incline is favoured where: the deposit is SHALLOW to moderate depth, so the operating-cost penalty of a longer haul never grows large enough to offset the shaft's capital saving; the mine LIFE is short-to-moderate or production needs to start QUICKLY (a ramp can be driven and trucks running in a fraction of the time a shaft takes to sink and equip); production RATE requirements are modest-to-moderate, well within a truck fleet's flexible capacity; and the orebody geometry is IRREGULAR or not yet fully defined, since a ramp's flexible, incrementally-extendable access adapts far more easily to a moving or evolving mine plan than a shaft, whose location and depth must be committed to years in advance. Trucking is also generally preferred where existing surface infrastructure or permitting favours a portal/ramp over a new shaft collar.
| Condition | Favoured method |
|---|---|
| Deep, long-life, high sustained tonnage | Skip and vertical shaft |
| Shallow-to-moderate depth, shorter life, fast start-up needed | Truck and incline |
| Operating cost sensitivity to depth | Shaft roughly flat with depth; trucking rises with depth |
| Capital sensitivity | Shaft high fixed capital; trucking lower capital, scalable with fleet size |
| Flexibility to an evolving/irregular orebody | Truck and incline (ramp is incrementally extendable; shaft location is fixed at sinking) |
