--- title: "Role of RMR in underground design" subject: "Engineering Geology II" chapter: 6 key: "semester_4/engineering_geology_ii:rmr-importance-underground" source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/rmr-importance-underground site: BCT Engineering --- # Role of RMR in underground design Engineering Geology II · Chapter 6: Measurement, analysis and interpretation of structural geological data - Asked in: 2072 Magh, 3 marks; 2073 Magh, 2 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_4/engineering_geology_ii/rmr-importance-underground - Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-6 ## Question Describe the role (importance) of the RMR system in underground excavation and support design. ## Short answer RMR quantifies rock quality to determine stand-up time, guide support design (bolt length/spacing, shotcrete thickness), select excavation method and advance rate, provide strength and deformation parameters, adjust for joint orientation, and enable cost estimation and clear communication among engineers. ## Answer The RMR system is one of the most widely used tools for design of underground openings (tunnels, caverns, mines, shafts) because it turns field observations into numbers that can be used directly in design. **Role / importance** 1. **Quality assessment:** divides the rock into five classes (very good to very poor), so the tunnel can be divided into sections of similar behaviour (geotechnical zoning). 2. **Stand-up time:** gives the unsupported span and time the rock will stand, which decides how soon support must be installed. 3. **Support design:** the class gives guidelines for rock bolts (length, spacing), shotcrete thickness, steel ribs and wire mesh. 4. **Excavation method:** suggests full-face, top heading and bench, or multiple drifts and the length of advance per round. 5. **Strength parameters:** cohesion and friction angle for each class, and the modulus of deformation $E = 2\,RMR - 100$ (GPa, for $RMR > 50$) for numerical models. 6. **Orientation adjustment:** the tunnel axis direction relative to joints (favourable to very unfavourable) can reduce RMR by up to 12, which helps choose the best alignment. 7. **Cost estimate and planning:** quantities of support and construction time can be forecast; it is also used at the face for quick checks during construction (updating the design). 8. **Communication:** a simple common language between geologists, designers and contractors. It is used together with the Q-system for cross-checking, and the empirical relation $RMR = 9\ln Q + 44$ links the two. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How does RMR help divide a tunnel? A. Into sections of similar behaviour (geotechnical zoning) using five classes B. Into equal-length sections C. By depth only D. By groundwater only Answer: A. Classes group the tunnel into zones of similar rock behaviour. (Key point: Zoning) 2. Why is stand-up time useful? A. It gives rock density B. It gives cohesion only C. It decides how soon support must be installed D. It gives permeability Answer: C. It tells the unsupported span and time the rock stands. (Key point: Stand-up time) 3. What is the role of the orientation adjustment? A. It increases RMR by 12 B. It has no effect C. It sets bolt diameter D. Tunnel axis relative to joints can reduce RMR by up to 12, helping choose alignment Answer: D. Unfavourable orientation lowers RMR, guiding the best tunnel direction. (Key point: Orientation adjustment) 4. Which empirical relation links RMR and Q? A. RMR = 9 ln Q + 44 B. RMR = 44 ln Q + 9 C. RMR = Q/9 D. RMR = 2Q - 100 Answer: A. RMR = 9 ln Q + 44; E = 2 RMR - 100 GPa is the deformation modulus for RMR above 50. (Key point: Relation to Q) ## Related in Engineering Geology II - [RMR class II support and excavation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Armr-class-ii-support) — Engineering Geology II, chapter 6, asked 7× - [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 class IV support and excavation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Armr-class-iv-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× - [Short note: Underground excavation process](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Ashort-note-underground-excavation) — Engineering Geology II, chapter 4 - [Selecting support type for underground opening](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Asupport-type-underground) — Engineering Geology II, chapter 6 ## Related in other subjects - [Underground water tank: excavation, brick, plaster](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Aug-tank-g-brick-plaster) — Estimating and Costing, chapter 6 - [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× - [Short note: Decision Support System](https://www.bctengineer.com/question.md?key=semester_7%2Fdata_mining%3Adss-note) — Data Mining, chapter 1, asked 2× - [Three phase system; role of aggregate phase](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Athree-phase-aggregate-phase) — Concrete Technology and Masonry Structure, chapter 2