Benches & Haul Roads

Benches and haul roads are where the mining happens. Learn how bench height is matched to equipment, berm width rules (modified Ritchie criterion), haul-road width for one- and two-way traffic, safety berms, ramp grades and lengths, road construction layers and drainage.

Haulage often represents 40–60 % of open-pit operating cost, and haul-road accidents are a leading cause of fatalities. Well-designed benches and roads raise productivity, cut tyre and fuel costs, and save lives.

An analogy

A haul road is a highway for 400-tonne trucks: lane width, gradient, surface quality and guard rails (safety berms) determine speed and safety just like on public roads.

Bench height and equipment

Bench height matches loading equipment reach — the shovel or excavator should dig a full face safely. Larger machines allow taller benches (12–15 m); selective mining in narrow ore zones uses smaller benches (5–10 m) or flitches.

Haul-road geometry

Two-way roads are ≈ 3.5× the widest truck; add a safety windrow (half wheel height) on open edges and a drainage ditch. Sustained grades 8–10 %; curves with superelevation; switchbacks flattened. Separate light vehicles where possible.

Road construction

Layered design: compacted subgrade, sub-base, base and a wearing course of well-graded crushed rock; CBR-based thickness design. Water carts control dust; graders maintain a smooth surface because rolling resistance of 2 % vs 5 % changes truck speed dramatically.

Road optimisation

Rolling resistance monitoring via truck payload/strut sensors, road maintenance dispatching, trolley-assist electrified ramps, and autonomous traffic management rely on consistent, well-built roads.

Formulas

• Modified Ritchie berm: B ≈ 4.5 + 0.2 H_b (m)
• Two-way road width: W ≈ 3.5 × W_t (+ safety berm + drain)
• One-way road width: W ≈ 2 × W_t
• Ramp length: L_r = vertical rise / G
• Safety berm height: h ≥ ½ tyre diameter of largest vehicle

Worked example: Berm and road width

Given: Bench 15 m; Largest truck width 7 m

Find: Berm width and two-way road width.

• Berm = 4.5 + 0.2 × 15 = 7.5 m
• Road = 3.5 × 7 = 24.5 m running surface
• + windrow ≈ 3 m + ditch ≈ 2 m ≈ 30 m total

Answer: 7.5 m berm; ≈ 30 m road corridor

Worked example: Ramp length

Given: Pit depth 300 m; Grade 10 %

Find: Ramp length.

• L = 300/0.10 = 3000 m

Answer: 3 km (plus flat switchback sections)

Common mistakes

• Wrong: Undersized windrows on road edges. — Right: At least half the tyre height of the largest truck.
• Wrong: Steep ramps to save waste. — Right: Excessive grades cut speed and increase fuel and brake risk.

Applications

• Haul-road design: Widths, grades and berms per mine standards.
• Road maintenance: Grading and watering scheduled by fleet data.
• Trolley assist: Electrified ramps for diesel-electric trucks.

Key takeaways

• Bench height matched to loading equipment.
• Berm ≈ 4.5 + 0.2H.
• Two-way road ≈ 3.5× truck width + windrow + ditch.
• Ramp length = rise/grade.

Going further

• CBR design: Layer thicknesses from wheel load and subgrade strength.
• Road condition monitoring: Vibration sensors detect potholes and ruts.
• Traffic simulation: Discrete-event models for congestion at intersections.