---
title: "Merits and demerits of percussion drilling"
subject: "Foundation Engineering"
chapter: 2
key: "semester_5/foundation_engineering:percussion-drilling"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/percussion-drilling
site: BCT Engineering
---

# Merits and demerits of percussion drilling

Foundation Engineering · Chapter 2: Soil Exploration

- Asked in: 2080 Baisakh, 2 marks
- Video: [Foundation Engineering | Percussion drilling | Types of exploration methods | #Soilexploration](https://www.youtube.com/watch?v=ebnHY68t7PI) — Digitech education
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/percussion-drilling
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-2

## Question

What are the merits and demerits of percussion drilling?

## Short answer

Merits: can penetrate hard soils, boulders, gravel, and rock; simple, cheap, reaches large depths. Demerits: slow in soft soils, gives disturbed mixed samples, disturbs soil below the bit making undisturbed sampling difficult, and strata boundaries are hard to identify.

## Answer

In percussion drilling a heavy chisel bit is repeatedly raised and dropped to break the soil or rock, and the cuttings are removed by a bailer.

#### Merits
- Can penetrate hard soils, boulders, gravel and rock.
- Simple, rugged equipment, cheap and suitable in remote areas.
- Gives a good idea of groundwater and depth to rock; reaches large depths.

#### Demerits
- Slow in soft soils and gives disturbed, mixed samples.
- Soil below the bit is disturbed, so undisturbed sampling is difficult and strata boundaries are hard to identify.
- Not suitable for soft clays or loose sands below the water table (need casing).
- Cannot give proper records of thin layers.

## Check yourself

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

1. In percussion drilling
   A. a diamond bit rotates with water
   B. a heavy chisel bit is raised and dropped and cuttings are removed by a bailer
   C. a hand auger is turned
   D. the soil is jetted with air only
   Answer: B. Repeated impact breaks soil or rock. (Key point: Method)

2. A merit of percussion drilling is that it
   A. gives perfect undisturbed samples
   B. can penetrate boulders, gravel and rock using simple rugged equipment
   C. is fastest in soft soils
   D. needs no casing ever
   Answer: B. It copes with hard ground cheaply. (Key point: Merit)

3. A demerit is that it
   A. cannot go deeper than 1 m
   B. cannot penetrate rock
   C. disturbs soil below the bit and gives mixed samples
   D. gives undisturbed clay
   Answer: C. Strata boundaries are hard to identify and undisturbed sampling is difficult. (Key point: Demerit)

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