Longwall Mining

Longwall mining is the most productive underground coal method. Learn panel layout (gate roads, face, goaf), the shearer, armoured face conveyor and hydraulic shields, face production calculations, shield support capacity, subsidence, and automation.

A longwall face 250–450 m long is cut slice by slice by a shearer travelling along an armoured face conveyor, while a line of hydraulic shields holds up the roof. As the face advances, the roof behind the shields caves into the goaf. One face can produce 5–10 Mt of coal per year with a small crew.

An analogy

A longwall is like a bread slicer moving along a loaf, with a row of umbrellas (shields) protecting the slicer while the crust behind collapses.

Panel layout

Two gate roads (maingate for intake air and conveyor, tailgate for return) are developed first with continuous miners, defining a panel 250–450 m wide and 2–5 km long. The longwall retreats from the far end back toward the mains.

Equipment

Shearer with two cutting drums; armoured face conveyor (AFC) under the shearer; hydraulic shields (≈ 1.75–2 m wide, 800–1750 t yield) that advance after the shearer passes; stage loader and crusher; belt conveyor out-bye.

Strata behaviour and subsidence

Roof caves behind the shields forming the goaf; periodic weighting occurs as roof beams break. Surface subsides by ≈ 60–70 % of seam thickness over the panel — affecting buildings, rivers and farmland.

Automation

LASC (Longwall Automation Steering Committee) technology uses inertial navigation for face alignment and horizon control; shields advance automatically; remote operation from surface is common in Australia and China. Gas drainage and spontaneous-combustion control are critical in gassy seams.

Formulas

• Tonnes per cut: T_cut = L_f × h × d × ρ
• Daily production: T_day = T_cut × N
• Cuts per day: N ≈ 1440 × A / (L_f / v_s + t_turn)
• Face advance: Advance/day = N × d

Worked example: Daily production

Given: Face 300 m, height 3 m, web 1 m; Coal 1.35 t/m³, 12 cuts/day

Find: Daily tonnes.

• T_cut = 300 × 3 × 1 × 1.35 = 1215 t
• T_day = 1215 × 12 = 14 580 t

Answer: ≈ 14 600 t/day (≈ 5 Mt/yr)

Worked example: Face advance

Given: 12 cuts/day, 1 m web; Panel 3 km long

Find: Time to mine panel.

• Advance = 12 m/day
• 3000/12 = 250 days

Answer: ≈ 8 months per panel

Common mistakes

• Wrong: Assuming 100 % availability. — Right: Include breakdowns, shift changes, gas delays (often 40–60 %).
• Wrong: Ignoring gas make at high production. — Right: Gas emission rises with production — plan drainage and ventilation.

Applications

• Coal mines: Australia, USA, China — dominant underground method.
• Trona & potash: Longwalls in soft evaporites.
• Subsidence management: Planning under infrastructure and rivers.

Key takeaways

• Shearer + AFC + shields.
• T = L h d ρ × cuts.
• Goaf caves; surface subsides.
• Highly productive and automatable.

Going further

• LASC automation: Inertial navigation for face alignment.
• Top coal caving: LTCC for thick seams.
• Spontaneous combustion: Inertisation of goafs in reactive coals.