---
title: "Short note: Underground excavation process"
subject: "Engineering Geology II"
chapter: 4
key: "semester_4/engineering_geology_ii:short-note-underground-excavation"
source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/short-note-underground-excavation
site: BCT Engineering
---

# Short note: Underground excavation process

Engineering Geology II · Chapter 4: Engineering geology in site selection, investigation & construction/excavation

- Asked in: 2079 Jestha, 2 marks
- Video: [How Do They Dig Tunnels Through Solid Rock?](https://www.youtube.com/watch?v=wRkYzzMcn8M) — Cold Ledger
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/short-note-underground-excavation
- Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-4

## Question

Write a short note on the underground excavation process.

## Short answer

The process includes portal preparation, excavation by drill-and-blast or TBM, mucking, immediate rock support (bolts, shotcrete, steel ribs), geological mapping and convergence monitoring, and final lining. Major geological problems are squeezing, rock burst, water inflow and overbreak.

## Answer

**Underground excavation** is the construction of tunnels, caverns and shafts below ground.

**Process:**
1. **Investigation and design** of the alignment, shape and support, based on rock mass classification.
2. **Portal construction:** slope cutting, support and drainage at the entrance.
3. **Excavation:**
   - *Drill and blast:* drilling holes, charging them with explosives, blasting and ventilating.
   - *Mechanised:* roadheaders in soft to medium rock; tunnel boring machines (TBM) in a wide range of rock, including hard rock.
   - Full-face or top-heading-and-bench method, chosen according to rock quality.
4. **Mucking:** removing the broken rock.
5. **Support:** rock bolts, shotcrete, wire mesh and steel ribs; installed immediately in poor rock.
6. **Geological mapping and monitoring** of convergence.
7. **Drainage and ventilation,** then the final concrete lining.

**Geological problems:** squeezing, rock burst, water inflow, overbreak and faults.

## Check yourself

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

1. Which is a mechanised underground excavation method?
   A. Drill and blast only
   B. Open cut and cover with bulldozers
   C. Manual dredging
   D. TBM or roadheader
   Answer: D. TBMs and roadheaders are mechanised; drill and blast uses explosives. (Key point: Excavation methods)

2. What follows excavation and mucking in underground excavation?
   A. Support with rock bolts, shotcrete, mesh or steel ribs
   B. Final lining before excavation
   C. Portal construction
   D. Investigation and design
   Answer: A. Broken rock is removed (mucking), then support is installed, immediately in poor rock. (Key point: Process order)

3. Which is a geological problem in underground excavation?
   A. Soil erosion by rain
   B. Squeezing, rock burst, water inflow, overbreak, faults
   C. Only traffic noise
   D. Lack of sunlight
   Answer: B. These are the typical hazards met underground. (Key point: Geological problems)

## Related in Engineering Geology II

- [Role of RMR in underground design](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Armr-importance-underground) — Engineering Geology II, chapter 6, asked 2×

## 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