--- title: "RMR rock mass classification" subject: "Engineering Geology II" chapter: 6 key: "semester_4/engineering_geology_ii:rmr-classification" source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/rmr-classification site: BCT Engineering --- # RMR rock mass classification Engineering Geology II · Chapter 6: Measurement, analysis and interpretation of structural geological data - Asked in: 2079 Jestha, 6 marks; 2079 Asoj, 1 marks; 2075 Bhadra, 3 marks; 2074 Bhadra, 4 marks; 2070 Bhadra, 2 marks; 2069 Poush, 5 marks; 2072 Asoj, 2 marks; 2081 Chaitra, 2 marks (asked 8 times) - Video: [How to Calculate Rock Mass Rating (RMR) | Real Example + Tunnel Adjustments](https://www.youtube.com/watch?v=jvEQeZuqydI) — Soil Mechanics and Engineering Geology - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/rmr-classification - Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-6 ## Question Define Rock Mass Rating (RMR). Describe the Bieniawski RMR classification system, its parameters and the condition of discontinuities in it. ## Short answer RMR (Rock Mass Rating) by Bieniawski rates rock mass from 0 to 100 using uniaxial compressive strength, RQD, spacing and condition of discontinuties, groundwater, and orientation adjustment. The condition of discontinuties rates persistence, aperture, roughnes, infilling and weathering, giving a maximum of 30 points. ## Answer **Rock Mass Rating (RMR)**, also called the **Geomechanics Classification**, was proposed by Bieniawski (1973, revised 1989). It gives a single rating from 0 to 100 that describes rock mass quality for tunnels, slopes and foundations, and guides support design. #### Parameters and ratings | Parameter | Range of rating | |---|---| | 1. Uniaxial compressive strength of intact rock | 0 to 15 | | 2. Rock Quality Designation (RQD) | 3 to 20 | | 3. Spacing of discontinuities | 5 to 20 | | 4. Condition of discontinuities | 0 to 30 | | 5. Groundwater condition | 0 to 15 | | 6. Adjustment for orientation of discontinuities | 0 to -12 (tunnels) | $$ RMR = R_1 + R_2 + R_3 + R_4 + R_5 + R_6 $$ Example ratings: UCS above 250 MPa = 15, RQD 90 to 100 % = 20, spacing above 2 m = 20, completely dry = 15. #### Condition of discontinuities (maximum 30) | Factor | Best (6) | Worst (0) | |---|---|---| | Persistence (length) | below 1 m = 6 | above 20 m = 0 | | Aperture (separation) | none = 6 | above 5 mm = 0 | | Roughness | very rough = 6 | slickensided = 0 | | Infilling | none = 6 | soft, above 5 mm = 0 | | Weathering | unweathered = 6 | decomposed = 0 | #### Rock mass classes | Class | RMR | Description | Cohesion (kPa) | Friction angle | |---|---|---|---|---| | I | 81 to 100 | Very good | above 400 | above 45° | | II | 61 to 80 | Good | 300 to 400 | 35° to 45° | | III | 41 to 60 | Fair | 200 to 300 | 25° to 35° | | IV | 21 to 40 | Poor | 100 to 200 | 15° to 25° | | V | below 20 | Very poor | below 100 | below 15° | **Use:** the class gives stand-up time (e.g. 20 years for 15 m span in class I, 30 minutes for 1 m in class V), shear strength parameters and recommended excavation and support. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What does RMR give and who proposed it? A. A 0-100 rating of rock mass quality, proposed by Bieniawski (1973) B. A 0-1000 index proposed by Barton C. A percentage of core pieces over 10 cm, by Deere D. A stress ratio by Terzaghi Answer: A. RMR is the Geomechanics Classification giving a single 0-100 rating. (Key point: RMR definition) 2. Which is NOT one of the six RMR parameters? A. Groundwater condition B. Spacing of discontinuities C. Stress reduction factor D. Uniaxial compressive strength of intact rock Answer: C. SRF belongs to the Q-system; RMR uses UCS, RQD, spacing, condition, groundwater and orientation adjustment. (Key point: Parameters) 3. Which parameter has the largest maximum rating? A. RQD (20) B. Spacing (20) C. Condition of discontinuities (30) D. Groundwater (15) Answer: C. Condition of discontinuities can contribute up to 30. (Key point: Largest rating) 4. In condition of discontinuities, what gets the worst rating (0) for roughness and infilling? A. Very rough, no infilling B. Slickensided, soft infilling above 5 mm C. Rough, hard infilling D. Smooth, no infilling Answer: B. Worst cases are slickensided surfaces and soft infill above 5 mm; the best are very rough with none. (Key point: Discontinuity condition) ## Related in Engineering Geology II - [Q-system of rock mass classification](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Aq-system-classification) — Engineering Geology II, chapter 6, asked 7× - [Properties of rock mass and discontinuities](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Arock-mass-properties) — Engineering Geology II, chapter 6, asked 3× - [Geo-mechanics classification of rock mass](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Ageomechanics-classification) — Engineering Geology II, chapter 6, asked 5× - [RMR fair rock support and excavation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Armr-fair-class-support) — Engineering Geology II, chapter 6, asked 6× - [RMR poor rock support and excavation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Armr-poor-class-support) — Engineering Geology II, chapter 6, asked 2× - [Rock mass versus intact rock](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Arock-mass-vs-intact-rock) — Engineering Geology II, chapter 6, asked 7× ## Related in other subjects - [Rock mass classification and discontinuities](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Arock-mass-classification-and-discontinuities) — Engineering Geology I, chapter 5 - [RMR system and its parameters](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Armr-system-and-its-parameters) — Engineering Geology I, chapter 5, asked 2× - [Rock mass, rock material, discontinuities](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Arock-mass-rock-material-discontinuities) — Engineering Geology I, chapter 5 - [Rock mass classification](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Arock-mass-classification) — Engineering Geology I, chapter 5