---
title: "Rotary versus percussion drilling"
subject: "Engineering Geology I"
chapter: 1
key: "semester_3/engineering_geology_i:rotary-versus-percussion-drilling"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/rotary-versus-percussion-drilling
site: BCT Engineering
---

# Rotary versus percussion drilling

Engineering Geology I · Chapter 1: Geology and Civil Engineering

- Asked in: 2059 Chaitra (old course), 4 marks
- Video: [Types of Drilling - Principles of Percussion Drilling Explained | in English](https://www.youtube.com/watch?v=bGVn2iNEK5g) — Success Guru
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/rotary-versus-percussion-drilling
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-1

## Question

Differentiate between rotary drilling and percussion drilling.

## Short answer

Rotary drilling uses a rotating bit with downward pressure to cut rock and recover continuous core, suitable for hard rock and deep holes. Percussion drilling lifts and drops a chisel bit to crush material, yielding only disturbed cuttings, and is slower, shallower, and cheaper, used for hard soils and boulders.

## Answer

| Basis | Rotary drilling | Percussion drilling |
|---|---|---|
| Action | Rotating bit with downward pressure cuts the rock | Heavy chisel bit is lifted and dropped to crush the rock |
| Bit | Diamond, tungsten carbide or roller bit | Chisel or star-shaped steel bit |
| Material drilled | Hard rocks and also soils | Hard soils, gravel, boulders and rock |
| Sample | Continuous solid **core** recovered | Only crushed cuttings (disturbed) |
| Circulating fluid | Water or drilling mud/air removes cuttings | Water added, cuttings removed by bailer or sand pump |
| Speed | Fast and smooth | Slower |
| Depth and accuracy | Deep holes, good alignment | Shallower, less accurate |
| Cost | Higher | Lower |
| Use | Dam, tunnel and bridge investigation | Water wells and shallow investigation |

## Check yourself

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

1. Rotary drilling gives:
   A. Continuous solid core
   B. Only crushed cuttings
   C. No sample
   D. Only water
   Answer: A. Percussion gives disturbed cuttings. (Key point: Sample)

2. Percussion drilling works by:
   A. Rotating a diamond bit
   B. Lifting and dropping a heavy chisel bit
   C. Pushing an auger
   D. Using explosives
   Answer: B. Crushing by impact. (Key point: Action)

3. Rotary drilling suits:
   A. Only shallow water wells
   B. Only soft soils
   C. Dam, tunnel and bridge investigations in hard rock
   D. None of these
   Answer: C. Rotary handles hard rock and deep holes accurately. (Key point: Application)

## Related in Engineering Geology I

- [Weathering versus erosion](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aweathering-versus-erosion) — Engineering Geology I, chapter 6, asked 5×
- [Primary versus secondary geological structures](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aprimary-versus-secondary-geological-structures) — Engineering Geology I, chapter 5, asked 4×
- [Convergent versus divergent plate boundary](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aconvergent-versus-divergent-plate-boundary) — Engineering Geology I, chapter 2, asked 3×
- [Intrusive versus extrusive igneous rocks](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aintrusive-versus-extrusive-igneous-rocks) — Engineering Geology I, chapter 4, asked 3×
- [Engineering geology versus geology; disciplines](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aengineering-geology-versus-geology-disciplines) — Engineering Geology I, chapter 1, asked 2×
- [Body waves versus surface waves](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Abody-waves-versus-surface-waves) — Engineering Geology I, chapter 2, asked 2×

## Related in other subjects

- [Merits and demerits of percussion drilling](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apercussion-drilling) — Foundation Engineering, chapter 2