Ground engineering · Rock mechanics
Rock bolt pattern for a loose block / wedge calculator
Bolt load from suspending a loosened zone of height h over the bolt tributary area, with bolt length guidance.
Standard: Dead-weight suspension design
Open the live calculator → All ground engineering calculators
Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Loosened zone height | 1.5 | m |
| Rock unit weight | 26 | kN/m³ |
| Bolt spacing (longitudinal) | 1.2 | m |
| Bolt spacing (transverse) | 1.2 | m |
| Factor of safety | 2 | |
| Bolt working capacity | 120 | kN |
| Bolt length | 3 | m |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Required load per bolt FS γ h sx sy | 112.3 | kN |
| Min length h + 1 m anchorage | 2.50 | m |
- ✓ Bolt capacity
- ✓ Bolt length
- ✓ Spacing ≤ L/2
Method, formulas and assumptions
- Required load per bolt FS γ h sx sy = 2*26*1.5*1.2*1.2 = 112.32 kN
- Min length h + 1 m anchorage = 1.5+1 = 2.5 m
Related ground engineering calculators
- Point load index (rock) — Is and size-corrected Is(50) for diametral or axial/block tests, AS 1726 strength term and estimated UCS.
- Rock wedge stability (3-D, Hoek & Bray) with stereonet — Tetrahedral wedge formed by two discontinuities, the slope face and the upper ground surface. Geometry by…
- Rock slope kinematic analysis (planar, wedge, toppling) — Discontinuity sets mapped in a rock cut are tested against the slope face. Planar sliding needs a set…
- Rock Mass Rating (RMR89) — Ratings for UCS, RQD and spacing from values, plus joint condition, groundwater and orientation adjustment…
- Q-system & support — Q = (RQD/Jn)(Jr/Ja)(Jw/SRF), equivalent dimension De = span/ESR, Q–RMR correlation and unsupported span.
- Hoek–Brown rock mass strength (GSI) — mb, s, a from GSI, mi and D; rock mass UCS, tensile strength, global strength and modulus.
- Joint shear strength (Barton–Bandis) — Peak shear strength τ = σn tan(φr + JRC log10(JCS/σn)) and equivalent friction angle.
- Block sliding / toppling criteria — Mode of a block of width b and height h on a plane of dip ψ with friction φ: stable, sliding, toppling or…
For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.