What is Rock Mass Rating (RMR)?

Rock Mass Rating (RMR) is a geomechanics classification system developed by Bieniawski (1973, revised 1989). It rates a rock mass on six parameters — UCS, RQD, discontinuity spacing, discontinuity condition, groundwater, and orientation adjustment — producing a score from 0 to 100. It is the most widely used rock classification system in tunneling, mining, and slope engineering worldwide.

What is a good RMR score?

Scores of 81–100 (Class I) indicate very good rock. Scores of 61–80 (Class II) are good rock. Scores of 41–60 (Class III) are fair and require systematic support. Scores below 40 (Classes IV and V) represent poor to very poor rock requiring heavy, immediate support.

What is the difference between RMR76 and RMR89?

RMR89 (Bieniawski 1989) is the current industry standard. It has revised ratings for UCS and RQD, expands discontinuity condition into five sub-parameters, and updates the groundwater rating scale. Always use the 1989 version unless a project specifically requires the earlier edition.

How does RMR relate to the Q-System?

Both are empirical rock classification tools. The common correlation is: RMR ≈ 9 × ln(Q) + 44. On important projects, calculate both independently and compare. Significant divergence signals unusual site conditions worth investigating further.

How do I calculate RQD without core drilling?

Use Palmstrom's formula: RQD = 115 − 3.3 × Jv, where Jv is the number of joints per cubic meter. Alternatively use Priest and Hudson (1976): RQD = 100 × e^(−0.1λ) × (0.1λ + 1), where λ is mean joint frequency per meter.

Is this RMR calculator suitable for professional reports?

This calculator correctly implements Bieniawski 1989 and supports professional work as a computation aid. All input parameters must be assessed by a qualified geotechnical or mining engineer from actual field investigations and lab tests before use in final design.

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Rock Mass Rating Calculator · Last updated: April 28, 2026

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