Rock Mass Rating (RMR) Calculator
RMR Calculation Results
Calculation Method:
The RMR is calculated by summing the ratings for six parameters: UCS, RQD, spacing of discontinuities, condition of discontinuities, groundwater conditions, and discontinuity orientation.
Rock Mass Rating (RMR) Classification
Rock Mass Rating (RMR) is a widely used geomechanical classification system developed by Z.T. Bieniawski in 1973, with updates in 1989. It provides a systematic method to assess rock mass quality for engineering design and construction in rock environments. The RMR system evaluates six parameters that influence rock mass behavior and assigns numerical ratings to each parameter.
The RMR system is particularly valuable for tunnel design, slope stability analysis, foundation engineering, and mining operations. It helps engineers determine appropriate support measures, excavation techniques, and design parameters based on quantitative rock mass quality assessment.
The six parameters evaluated in the RMR system include:
- Uniaxial Compressive Strength (UCS) – Measures the intact rock strength
- Rock Quality Designation (RQD) – Quantifies the degree of fracturing
- Spacing of Discontinuities – Measures the average distance between joints
- Condition of Discontinuities – Evaluates joint roughness, persistence, separation, weathering, and infilling
- Groundwater Conditions – Assesses water inflow or pressure
- Orientation of Discontinuities – Considers the relationship between discontinuity orientation and engineering structure
The sum of these ratings provides the RMR value, which ranges from 0 to 100. Higher values indicate better rock mass quality. The RMR value classifies rock masses into five classes: very good (Class I), good (Class II), fair (Class III), poor (Class IV), and very poor (Class V).
How to Use the Rock Mass Rating Calculator
Step 1: Enter Rock Strength Data
Input the Uniaxial Compressive Strength (UCS) value in MPa. This value typically ranges from 1 to 250 MPa, with higher values indicating stronger intact rock. If you have Point Load Index values instead, convert them to UCS by multiplying by approximately 24.
Step 2: Input RQD and Joint Spacing
Enter the Rock Quality Designation (RQD) percentage (0-100%) which represents the percentage of intact core pieces longer than 10 cm in a total core run. Then input the spacing of discontinuities in millimeters, measuring the average distance between natural fractures in the rock mass.
Step 3: Select Discontinuity Conditions
Choose the appropriate option that best describes the condition of discontinuities in your rock mass. Consider factors such as roughness, persistence, separation, weathering, and infilling material. More favorable conditions receive higher ratings.
Step 4: Assess Groundwater and Orientation
Select the groundwater condition from the dropdown menu based on observations at your site. Then evaluate the orientation of discontinuities relative to the engineering structure (tunnel axis, slope face, etc.) and select the appropriate adjustment factor.
Step 5: Review Your Results
Click the “Calculate RMR” button to generate your Rock Mass Rating. The calculator will display individual parameter ratings, total RMR value, rock mass class, and a description of the rock quality. Use these results to inform your engineering decisions regarding support requirements and excavation methods.