Question 2 of 6: Room-and-Pillar Development/Production Cycle, Continuous Mining, Stope-and-Pillar and Trackless-Equipment Case Study

Question 2: Room-and-Pillar Development/Production Cycle, Continuous Mining, Stope-and-Pillar and Trackless-Equipment Case Study (20 marks)

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.

2.1 — Conventional hard-rock room-and-pillar development/production cycle

Each production round in a conventional hard-rock room follows a fixed cycle: (1) drill — a jumbo drills the blast-hole pattern into the face on the pre-surveyed room/pillar grid; (2) blast — the round is charged and fired, and the heading is cleared of personnel and re-ventilated to clear blast fumes before re-entry; (3) muck — an LHD loads the broken rock and trams it to an ore pass, truck or rail siding for haulage out; (4) support — the newly exposed back is scaled and bolted (roof bolts, mesh where needed) before the next drill pass advances the same room; and (5) services extension — compressed air, water, power and ventilation ducting are extended into the room as it advances. The cycle repeats room-by-room on the regular grid, leaving pillars un-mined at the design spacing for permanent ground support, with development (access drifts, ore passes, ventilation raises) staying one or more rounds ahead of the active production faces.

2.2 — Conventional hard-rock vs. continuous soft-ore room-and-pillar

Services. Conventional hard-rock mining needs high-pressure compressed air and water for jumbo drilling and blast-hole flushing, sized for peak drilling demand, plus explosives magazines and handling; continuous mining substitutes a single high continuous electrical load (trailing cable to the continuous miner) for the intermittent drill-and-blast air/water demand, and needs no explosives infrastructure at all.

Ventilation. The conventional cycle requires a mandatory stand-down and re-ventilation period after every blast to clear fumes before re-entry, which caps the achievable production rate per heading; continuous mining removes that blast-fume clearance requirement entirely (there is no blast), but it demands continuous, close-coupled dust control — water sprays at the cutting head and dust scrubber/ventilation ducting kept immediately behind the machine — because cutting, rather than blasting, is now the dominant dust-generation event and it runs constantly, not once per cycle.

Roof support. Conventional mining installs roof support as a discrete step after each blast-and-muck cycle, so there is a re-entry lag between exposing new roof and bolting it; continuous mining pairs the continuous miner with an integrated or immediately-following bolting machine (or a bolter operating in tandem in the same heading) so that support keeps pace with near-continuous advance, minimising the time any span of unsupported roof is exposed.

2.3 — Stope-and-pillar mining in thick (>6 m) seams

A single conventional room-and-pillar pass is limited by drill-jumbo/bolter reach and by roof-bolt length to roughly 5–6 m of face height; in a seam thicker than that, "stope-and-pillar" mining extracts the same room-and-pillar grid in multiple vertical lifts or slices rather than one full-height pass — typically a top slice mined and supported first, followed by one or more benched lower slices, sometimes with an intermediate sill left temporarily between lifts for stability until the lower lift is opened. This differs from 2.1's single-pass hard-rock cycle and from 2.2's continuous soft-ore cycle in that the SAME horizontal grid footprint is worked repeatedly at different elevations rather than once, so development, ventilation and ground support must all be re-established for each lift, and the overall extraction sequence (top-down vs. benching) becomes a key design decision to keep each lift's exposed span within what the rock can stand.

2.4 — Gaspe Copper trackless mechanised equipment, late 1960s

Advantages. Horizontal and vertical drill jumbos, small (2–3 m³) cable shovels and 30-tonne trucks were, for their era, a major step up in mechanisation from rail-bound hand/scraper mucking: the mechanised equipment fleet gave substantially higher productivity per worker and lower unit mining cost, and being rubber-tyred/trackless, it could follow irregular ramp and level geometry without the fixed-track constraint of a rail system, giving the mine layout far more flexibility to follow the orebody rather than a pre-built track network.

Disadvantages. The larger equipment needed correspondingly larger drifts and rooms to operate and turn in, increasing both waste dilution and the ground-support burden compared with a rail-scale opening; diesel-powered shovels and trucks introduced a substantial exhaust-ventilation demand that a rail/battery-electric system did not have, driving up the primary air quantity (and hence fan power) required; and the equipment's higher capital cost and greater maintenance/parts-supply complexity (relative to simple rail rolling stock) demanded a more sophisticated maintenance organisation than the mine may previously have needed.