Strip Mining & Quarrying

Strip mining removes overburden in long panels to expose flat coal or mineral seams, casting it into the previous void; quarrying extracts aggregate or dimension stone. Learn dragline and truck-shovel stripping, volumetric stripping ratios, dragline productivity, swell factors, and quarry operations.

Flat-lying, shallow deposits — coal, phosphate, oil sands, bauxite — are mined in strips. Huge draglines (bucket 60–120 m³) dig overburden and cast it directly into the mined-out strip, avoiding haulage. Quarries supply billions of tonnes of crushed stone every year for construction.

An analogy

Strip mining is like reading a book one page at a time: you lift the page (overburden), read the words (coal), then lay the page on the stack you already read.

Strip mining sequence

Clear topsoil (stored for rehabilitation) → drill and blast overburden → strip it with dragline or truck-shovel → expose and mine the coal → backfill and reshape spoil → replace topsoil and revegetate. Strips are 40–80 m wide and kilometres long.

Units: bank vs loose

In-situ rock is measured in bank cubic metres (bcm). Broken rock occupies more space (swell 20–50 %), measured in loose cubic metres (lcm). Productivity must be reported consistently — mixing bcm and lcm is a classic error.

Quarrying

Aggregate quarries drill-blast-load-haul limestone, granite or basalt, then crush and screen to sized products. Dimension-stone quarries cut blocks with wire saws and splitters, minimising blasting to avoid cracks.

Dragline planning

Dragline reach, dump height and spoil geometry decide whether overburden can be cast in one pass or needs rehandle (extended bench, chop cut). Simulation software (e.g. Dragline 3D) optimises strip geometry and minimises rehandle.

Formulas

• Dragline productivity: Q = V_b × F / S_f × 3600 / t_c × E (bcm/h)
• Stripping ratio: SR = overburden thickness / (seam thickness × ρ_coal) (bcm/t)
• Swell: Loose volume = bank volume × S_f

Worked example: Dragline productivity

Given: Bucket 60 m³, fill 0.9, swell 1.3; Cycle 60 s, efficiency 0.8

Find: bcm/h.

• Bank m³ per cycle = 60 × 0.9/1.3 = 41.5
• Cycles/h = 60 → 2492 bcm/h × 0.8 = 1994 bcm/h

Answer: ≈ 2000 bcm/h

Worked example: Coal stripping ratio

Given: Overburden 30 m, coal 5 m, ρ_coal 1.4 t/m³

Find: SR.

• Per m²: 30 bcm over 5 × 1.4 = 7 t coal
• SR = 30/7 = 4.29 bcm/t

Answer: 4.3 bcm/t

Common mistakes

• Wrong: Mixing bank and loose volumes. — Right: Convert with the swell factor before comparing.
• Wrong: Ignoring rehandle. — Right: Rehandled spoil costs production — design strips to minimise it.

Applications

• Coal strip mines: Powder River Basin, Bowen Basin draglines.
• Oil sands: Truck-shovel stripping of muskeg and overburden.
• Aggregate quarries: Crushed stone for roads and concrete.

Key takeaways

• Strip: remove, expose, mine, backfill, rehabilitate.
• Q = V_b F/S_f × 3600/t_c × E.
• Keep bank vs loose units consistent.
• Quarries: aggregate vs dimension stone.

Going further

• Cast blasting: Explosives throw overburden into the void, reducing dragline work.
• Dragline automation: Automated swing and dump cycles improve consistency.
• Rehabilitation: Spoil reshaping and topsoil return for land use.