What is a good RMR value?

RMR values above 60 are generally classified as good or very good rock, but “good” does not automatically mean unsupported excavation is safe. Orientation, span, stress condition, blasting damage, and water can still control support.

Why can the orientation adjustment be negative?

A joint set that dips unfavourably relative to a tunnel, foundation, or slope can reduce stability even when the basic rock quality looks strong. The orientation adjustment accounts for this directional effect.

Should I use point-load strength or UCS?

Use the data that is available and most reliable for the project. The RMR table allows ratings based on point-load strength index or uniaxial compressive strength. When both are available and conflict, a geotechnical engineer should review the test quality and rock variability.

Can RMR be used for slopes?

It can help with preliminary classification, but slopes are strongly controlled by discontinuity orientation, persistence, groundwater, weathering, and kinematic failure modes. A slope stability assessment should not be based only on the total RMR number.

Why does this calculator use selected ratings instead of raw lab values?

The published RMR system is rating-table based. Using ratings keeps the calculator transparent and lets field engineers enter the class they have already determined from logs, lab results, and mapping.

Engineering

Rock Mass Rating Calculator

Estimate the Bieniawski Rock Mass Rating score from the six common RMR inputs and classify the rock mass from very poor to very good.

Select field ratings for intact rock strength, RQD, joint spacing, discontinuity condition, groundwater, and orientation adjustment. The result is a screening classification and does not replace geotechnical design judgment.

Intact rock strength rating

RQD rating

Discontinuity spacing rating

Discontinuity condition rating

Groundwater rating

Orientation adjustment

Rock mass classification

—

Basic RMR before orientation—

Orientation adjustment—

Class interpretation—

Design note—

—

What is included in the RMR score?

The Rock Mass Rating system sums ratings for intact rock strength, RQD, discontinuity spacing, discontinuity condition, groundwater condition, and an orientation adjustment. In Hoek’s Practical Rock Engineering chapter, the RMR system is described as using these six parameters and summing the ratings to arrive at the final RMR value in the Bieniawski classification table.

For deeper background, see the Rocscience-hosted chapter on rock mass classification and the RMR system.

Worked example

Example inputs: Strength rating = 12 RQD rating = 13 Spacing rating = 10 Discontinuity condition = 22 to 25 depending on details Groundwater = 7 Orientation adjustment = -5 RMR ≈ 59 to 62, near the fair/good boundary.

A score near a class boundary should not be treated as exact. Logging quality, joint orientation, water inflow, scale effects, and excavation method can move the practical support requirement.

Limitations of RMR calculations

RMR is a classification method, not a complete tunnel, slope, or foundation design. It does not replace discontinuity mapping, stress analysis, groundwater assessment, numerical modelling, or local code and project-specific geotechnical review.

Common questions

RMR values above 60 are generally classified as good or very good rock, but “good” does not automatically mean unsupported excavation is safe. Orientation, span, stress condition, blasting damage, and water can still control support.
A joint set that dips unfavourably relative to a tunnel, foundation, or slope can reduce stability even when the basic rock quality looks strong. The orientation adjustment accounts for this directional effect.
Use the data that is available and most reliable for the project. The RMR table allows ratings based on point-load strength index or uniaxial compressive strength. When both are available and conflict, a geotechnical engineer should review the test quality and rock variability.
It can help with preliminary classification, but slopes are strongly controlled by discontinuity orientation, persistence, groundwater, weathering, and kinematic failure modes. A slope stability assessment should not be based only on the total RMR number.
The published RMR system is rating-table based. Using ratings keeps the calculator transparent and lets field engineers enter the class they have already determined from logs, lab results, and mapping.