--- title: "RMR system and its parameters" subject: "Engineering Geology I" chapter: 5 key: "semester_3/engineering_geology_i:rmr-system-and-its-parameters" source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/rmr-system-and-its-parameters site: BCT Engineering --- # RMR system and its parameters Engineering Geology I · Chapter 5: Structural Geology - Asked in: 2064 Jestha (old course), 2+6 marks; 2066 Bhadra (old course), 6 marks (asked 2 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_3/engineering_geology_i/rmr-system-and-its-parameters - Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-5 ## Question Define the RMR system of rock mass classification. Describe the different parameters of the RMR system. ## Short answer The Rock Mass Rating (RMR) system (Bieniawski, 1973/1989) classifies rock mass by ratings 0–100 using five parameters: uniaxial compressive strength (0–15), RQD (3–20), joint spacing (5–20), joint condition (0–30), and groundwater (0–15), plus an orientation adjustment (0 to –12 for tunnels). It estimates stand-up time, support needs, cohesion and friction angle. ## Answer #### Definition The **Rock Mass Rating (RMR)**, or Geomechanics Classification, was proposed by **Bieniawski (1973, revised 1989)**. It classifies a rock mass by a rating from 0 to 100, obtained from five basic parameters plus an adjustment for joint orientation, to estimate the stand-up time, support requirement, cohesion and friction angle of the rock mass. It is widely used in tunnelling, slopes and foundations. #### Parameters and ratings (Bieniawski 1989) | No. | Parameter | Rating range | |---|---|---| | 1 | Strength of intact rock (uniaxial compressive strength or point-load index) | 0 - 15 | | 2 | Rock Quality Designation (RQD) | 3 - 20 | | 3 | Spacing of discontinuities | 5 - 20 | | 4 | Condition of discontinuities (persistence, aperture, roughness, infilling, weathering) | 0 - 30 | | 5 | Ground water condition (inflow per 10 m of tunnel, or water pressure ratio) | 0 - 15 | | 6 | Orientation of discontinuities (adjustment) | 0 to -12 (tunnels), 0 to -25 (foundations), 0 to -60 (slopes) | $$ RMR = R_1 + R_2 + R_3 + R_4 + R_5 + R_6 $$ The first five are summed to give the basic RMR, and the sixth is the adjustment for the orientation of joints relative to the engineering work (very favourable to very unfavourable). #### Parameter notes 1. **Intact strength** - higher UCS gives a higher rating (>250 MPa gives 15). 2. **RQD** - percentage of core pieces longer than 10 cm in a run; higher RQD gives a higher rating. 3. **Spacing** - wider spacing of joints gives a higher rating (>2 m gives 20). 4. **Condition** - tight, rough, unweathered, unfilled joints give a high rating; soft gouge, open or continuous joints give a low rating. 5. **Ground water** - completely dry rock gets the maximum rating (15); flowing water gets zero. 6. **Orientation** - a favourable direction needs little or no correction; unfavourable joints reduce the rating. #### Rock mass classes | RMR | Class | Description | |---|---|---| | 81 - 100 | I | Very good rock | | 61 - 80 | II | Good rock | | 41 - 60 | III | Fair rock | | 21 - 40 | IV | Poor rock | | < 21 | V | Very poor rock | Each class gives an average stand-up time, cohesion (kPa) and friction angle of the rock mass. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Who proposed RMR and what is its rating scale? A. Barton, with a rating 0 to 1000 B. Terzaghi, with a rating 0 to 10 C. Bieniawski, with a rating 0 to 100 from six parameters D. Deere, with a rating 0 to 100 from RQD only Answer: C. RMR (Geomechanics Classification) is Bieniawski's, summing six parameter ratings to 0-100. (Key point: RMR definition) 2. Which set lists the RMR parameters? A. Intact strength, RQD, joint spacing, joint condition, ground water, joint orientation B. Intact strength, Q value, Jn, Jr, Ja, SRF C. RQD, density, porosity, hardness, colour, grain size D. Strength, depth, span, support, cost, time Answer: A. These six are the RMR inputs. (Key point: Six parameters) 3. How is joint orientation treated in RMR? A. As a positive rating up to 30 B. As an adjustment from 0 to a negative value added to the sum of the first five C. It is ignored D. As the main parameter with the highest rating Answer: B. Orientation ranges 0 to -12 and reflects favourable or unfavourable joints for the work. (Key point: Orientation adjustment) 4. Which statement matches the parameter notes? A. Closer joints give a higher rating B. Flowing water gives the maximum rating C. Soft gouge infilling raises condition rating D. Wider joint spacing and higher RQD give a higher rating; dry rock gets the maximum water rating Answer: D. Better rock (wide spacing, high RQD, dry) gets higher ratings. 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