Rock Bolt Capacity Calculator

Formula Used

The calculator checks three common resistance limits and reports the lowest design value.

1. Steel area: A = π × (d × area factor)² ÷ 4
2. Steel nominal capacity: P_s = A × f_y ÷ 1000
3. Bar to grout nominal capacity: P_bg = π × d × L × τ_bg ÷ 1000
4. Grout to rock nominal capacity: P_gr = π × D × L × τ_gr ÷ 1000
5. Design capacity for each mode: P_design = P_nominal ÷ FS
6. Governing capacity per bolt: Minimum of steel, bar to grout, and grout to rock design capacities
7. Aligned capacity: Governing capacity × cos(load angle)
8. Total group capacity: Aligned capacity × number of bolts

How to Use This Calculator

1. Enter the bolt diameter, borehole diameter, and embedment length.
2. Enter the steel yield strength and the bar to grout bond stress.
3. Enter grout to rock bond stress directly, or estimate it from rock UCS.
4. Set the factor of safety, load angle, area reduction factor, and number of bolts.
5. Press the calculate button to view results above the form.
6. Review the controlling mode, per bolt design capacity, and total group capacity.
7. Use the required bond length outputs to compare alternative support options.
8. Download the results as CSV or PDF for reporting and checking.

Example Data Table