---
title: "RMR class II support and excavation"
subject: "Engineering Geology II"
chapter: 6
key: "semester_4/engineering_geology_ii:rmr-class-ii-support"
source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/rmr-class-ii-support
site: BCT Engineering
---

# RMR class II support and excavation

Engineering Geology II · Chapter 6: Measurement, analysis and interpretation of structural geological data

- Asked in: 2079 Asoj, 2 marks
- 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-class-ii-support
- Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-6

## Question

Discuss the support system and excavation method in class II rock type according to RMR.

## Short answer

For Class II good rock, full-face excavation with 1–1.5 m advance is used, and support is completed 20 m from the face. Local rock bolts (3 m long at 2.5 m spacing) with occasional mesh and 50 mm shotcrete in the crown suffice; steel sets are not needed.

## Answer

Class II is **good rock** with RMR 61 to 80 (cohesion 300 to 400 kPa, friction angle 35° to 45°, stand-up time about 1 year for a 10 m span). Guidelines for a 10 m span tunnel:

- **Excavation:** full face, advance of **1.0 to 1.5 m**; complete support about **20 m** from the face.
- **Rock bolts:** locally in the crown, 3 m long, spaced 2.5 m, with occasional wire mesh.
- **Shotcrete:** 50 mm in the crown where required.
- **Steel sets:** not required.

The rock is mostly self-supporting, so only local support for loose blocks is needed.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Class II rock is which quality and RMR range?
   A. Fair, 41-60
   B. Poor, 21-40
   C. Good, 61-80
   D. Very good, 81-100
   Answer: C. Class II is good rock, RMR 61-80. (Key point: Class II)

2. What excavation method does Class II use?
   A. Full face, advance 1.0 to 1.5 m, support complete about 20 m from face
   B. Top heading and bench, 1.5-3 m
   C. Multiple drifts
   D. Top heading, 0.5 m
   Answer: A. Good rock allows full-face excavation. (Key point: Excavation)

3. What support is used?
   A. Heavy steel ribs at 0.75 m
   B. Systematic 5 m bolts at 1 m
   C. Locally in crown 3 m bolts at 2.5 m, occasional mesh and 50 mm shotcrete; no steel sets
   D. Full concrete lining
   Answer: C. Rock is largely self-supporting so only local support is needed. (Key point: Support)

## Close variants set in other exams

- [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×
- [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×

## Related in Engineering Geology II

- [RMR rock mass classification](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Armr-classification) — Engineering Geology II, chapter 6, asked 8×
- [Rock classes needing steel rib and shotcrete](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Armr-steel-rib-classes) — Engineering Geology II, chapter 6
- [Meaning of rock class and shear parameter](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Armr-class-shear-meaning) — Engineering Geology II, chapter 6

## Related in other subjects

- [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×
- [Earthwork excavation in soft soil, hard rock, wet soil](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aexcavation-soft-hard-wet) — Building Technology, chapter 2