About this tool Calculate Rock Mass Rating per Bieniawski (1989) — the most widely used version (RMR89). Rate five parameters from field and lab data: UCS strength, RQD, discontinuity spacing, condition of discontinuities, and groundwater conditions.
An orientation adjustment accounts for the relationship between tunnel/slope/foundation direction and the dominant discontinuity set. The final RMR (0–100) maps to five rock mass classes with indicative stand-up times, cohesion, and friction angle.
RMR is used worldwide for preliminary tunnel support design, feasibility assessment, and as an input to the Hoek-Brown failure criterion (via GSI ≈ RMR - 5). Standard: Bieniawski (1989).
How to use this tool 1. Rate the five parameters — select the range that best describes each parameter from your field data.
2. Select orientation adjustment — based on the relationship between the excavation direction and the critical discontinuity set.
3. Read the RMR, class, and engineering parameters — the breakdown shows individual ratings so you can see which parameters dominate.
Technical information RMR = R₁ + R₂ + R₃ + R₄ + R₅ + adjustment
R₁ = UCS strength (0–15), R₂ = RQD (3–20), R₃ = Spacing (5–20), R₄ = Condition (0–30), R₅ = Groundwater (0–15). Orientation adjustment: 0 to -12 for tunnels.
Five rock mass classes: I (81–100, very good) to V (<21, very poor). Each class has indicative cohesion and friction angle ranges for the Mohr-Coulomb criterion.
Limitations RMR89 uses fixed parameter ranges. Real rock masses often fall between categories — use engineering judgement to interpolate or select the more conservative rating.
The orientation adjustment values differ for tunnels, foundations, and slopes. This tool uses the tunnel adjustment (most common). For slopes and foundations, refer to Bieniawski (1989) Table 6.
RMR does not account for in-situ stress magnitude, excavation size, or construction method. For detailed design, use RMR as one input alongside numerical modelling.
Revision history 2 June 2026: Initial release
Disclaimer This tool is provided for educational and general information purposes only. It is not a substitute for professional engineering advice, design or verification.
Diggy and its contributors are not licensed engineering consultants and no results generated by this tool should be used directly for construction, design or safety-critical decisions.
All values and outputs are based on published empirical correlations and should be independently checked and confirmed by a qualified geotechnical engineer before use.
By using this tool, you accept full responsibility for how you interpret and apply the information provided.
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