Rock-mass classification
Rock Mass Rating (RMR)
RMR combines ratings for intact strength, RQD, discontinuity spacing and condition, groundwater, and an orientation adjustment into a rock-mass classification.
Core relationship
RMR = R₁(σci) + R₂(RQD) + R₃(spacing) + R₄(condition) + R₅(water) + orientation adjustment
Inputs & units
- Intact rock strength
- Rock Quality Designation (RQD)
- Discontinuity spacing
- Discontinuity condition
- Groundwater condition
- Discontinuity orientation relative to the excavation
Assumptions
- The selected RMR edition and rating tables are stated.
- Field descriptions and test results represent the geotechnical domain being classified.
- Orientation adjustment matches the excavation type and geometry.
Limitations
- A single total can hide materially different input combinations.
- Class boundaries do not remove geological uncertainty or spatial variability.
- Empirical support guidance must be checked against project geometry, loads, construction sequence and observed behaviour.
Synthetic worked example
Synthetic workflow: retain every component rating beside its evidence, calculate the base score, then apply and report the orientation adjustment separately. Never store only the final class.
Engineering use boundary
This page is educational and supports preliminary assessment. It does not replace site investigation, competent engineering judgement, final design, independent review or permitting requirements.