Ground Support

Ground support keeps underground openings safe. Learn rock bolts (mechanical, resin, friction, cable bolts), mesh and shotcrete, dead-weight bolt design, empirical bolt length and spacing (Q-system rules), support for burst-prone ground, and quality control.

Falls of ground are among the most common causes of injury underground. Support systems combine reinforcement (bolts tying rock together) with surface support (mesh, shotcrete) so that loose blocks cannot fall and the rock mass works as a self-supporting arch.

An analogy

Rock bolts are like stitches holding a wound together, and mesh/shotcrete is the bandage that stops small pieces from falling out.

Support elements

Mechanical (expansion shell) bolts; fully grouted resin or cement bolts; friction bolts (Split Set, Swellex); cable bolts (6–25 m) for stope walls; welded mesh and fibre-reinforced shotcrete (50–100 mm) for surface support; steel sets and arches in very weak ground.

Design approaches

Empirical (Q-system chart, RMR tables), analytical (dead-weight suspension, beam building, wedge analysis with Unwedge), and numerical (FLAC, RS2). Bolt length must anchor beyond the loosened zone.

Installation and QA

Support must be installed promptly after blasting (no one under unsupported ground). Pull tests, grout quality checks and shotcrete thickness probes verify performance.

Dynamic support

Rockburst-prone ground needs yielding bolts (Durabar, D-bolt, Garford) that absorb energy (20–50 kJ/m²) while deforming, combined with high-capacity mesh and lacing.

Formulas

• Dead-weight design: FoS = C_b / (γ h s²) → s = √(C_b / (FoS γ h))
• Q-system bolt length: L_b = 2 + 0.15 B / ESR (B = span)
• Loosened height (rule): h ≈ B/3 to B/2 for blocky roofs

Worked example: Dead-weight bolt spacing

Given: Loose height 2 m, γ = 27 kN/m³; Bolt capacity 150 kN, FoS 1.5

Find: Spacing.

• s² = 150/(1.5 × 27 × 2) = 1.85 m²
• s = 1.36 m

Answer: ≈ 1.3 m × 1.3 m pattern

Worked example: Bolt length

Given: Span 6 m, ESR 1.6

Find: L_b.

• L = 2 + 0.15 × 6/1.6 = 2.56 m

Answer: ≈ 2.4–2.7 m bolts (use standard 2.4 or 3.0 m length ≥ loose zone + anchorage)

Common mistakes

• Wrong: Bolts shorter than the loosened zone. — Right: Anchor at least 0.6–1 m into stable rock.
• Wrong: Skipping surface support between bolts. — Right: Mesh/shotcrete stops small blocks falling.

Applications

• Development drives: Standard bolt + mesh patterns by ground type.
• Stope hanging walls: Cable bolts limit dilution.
• Burst-prone mines: Dynamic support systems.

Key takeaways

• Reinforcement (bolts) + surface support (mesh, shotcrete).
• s = √(C/(FoS γ h)).
• L = 2 + 0.15B/ESR.
• Dynamic support for burst-prone ground.

Going further

• Unwedge: 3D wedge analysis for support design.
• Ground reaction curves: Convergence–confinement method.
• Automated bolting: Bolters with instrumented installation records.