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Ground Support Capacity Calculator

Converts a regular rock-bolt or dowel pattern into the uniform equivalent support pressure it provides across the excavation surface. Mining and tunnelling ground-control engineers use it to check a bolting pattern against the support-pressure demand from a rock-mass classification or a wedge weight.

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How to use this calculator

Enter Values

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Enter the capacity per bolt T (kN) and the two pattern spacings sx and sy (m).
  2. Read the equivalent support pressure p (kPa) provided by the pattern.
  3. Compare p against the support-pressure DEMAND (from Barton Q / RMR, or a wedge/loosened-block weight) and check the bolt density.

How it works

Each bolt supports the plan area around it, sx·sy. Smearing one bolt's capacity T over that tributary area gives a uniform equivalent pressure p = T / (sx·sy).

With T in kN and the area in m², p is in kPa (1 kN/m² = 1 kPa). The tool also reports bolt density = 1/(sx·sy) and the area supported per bolt. This 'smeared' pressure lets you compare a discrete bolt grid against a required support pressure, but real support is a system (bolts plus mesh/shotcrete) and local block stability still needs checking.

Worked example

120 kN bolts on a 1.5 m × 1.5 m grid. Area per bolt = 2.25 m². Support pressure p = 120 / 2.25 = 53.3 kPa. Bolt density = 0.44 bolts/m². If the Q-system demand were, say, 40 kPa, this pattern would be adequate on a pressure basis.

Common mistakes

  • Comparing the supply pressure to nothing — it only means something against a demand (Q/RMR support pressure or a wedge weight).
  • Entering bolt capacity in the wrong units; T must be in kN so that p comes out in kPa.
  • Assuming uniform pressure guarantees stability — a large individual wedge can still fail between bolts.

Frequently asked questions

Why is the pressure in kPa?

kN divided by m² is kN/m², and 1 kN/m² is exactly 1 kPa. So T (kN) over sx·sy (m²) gives support pressure directly in kPa.

What should I compare this pressure against?

The support-pressure DEMAND: Barton's Q-system roof support pressure, an RMR-based estimate, or the weight-per-unit-area of a defined wedge or loosened zone above the excavation.

Does bolt capacity T mean yield or ultimate?

Use the design capacity consistent with your demand — typically the working/design capacity of the bolt. Keep supply and demand on the same basis.

What is bolt density used for?

Bolts per square metre is a quick way to compare or specify patterns and to cross-check installation quantities against a target areal density.

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Tip: Enter any known values to calculate the remaining results.

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