---
title: "Physical and chemical disintegration"
subject: "Soil Mechanics"
chapter: 1
key: "semester_4/soil_mechanics:physical-chemical-disintegration"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/physical-chemical-disintegration
site: BCT Engineering
---

# Physical and chemical disintegration

Soil Mechanics · Chapter 1: Introduction

- Asked in: 2078 Poush, 2 marks
- Video: [Chemical Weathering Processes](https://www.youtube.com/watch?v=JzsmkVUEy0Q) — Professor Dave Explains
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/soil_mechanics/physical-chemical-disintegration
- Whole chapter: https://www.bctengineer.com/md/semester_4/soil_mechanics/chapter-1

## Question

Differentiate between physical and chemical disintegration process.

## Short answer

Physical disintegration breaks rock into smaller pieces without mineral change (by temperature, frost, abrasion), producing coarse soils. Chemical decomposition alters minerals via oxidation, hydrolysis, etc., forming clay minerals and fine soils.

## Answer

Both are types of **weathering**: the breakdown of rock into soil.

| Basis | Physical disintegration | Chemical decomposition |
|---|---|---|
| Nature | Rock breaks into smaller pieces | Minerals change to new minerals |
| Composition | Unchanged | Changed |
| Agents | Temperature change, freezing of water, abrasion, wind, roots | Water, oxygen, CO$_2$, acids |
| Processes | Exfoliation, frost action, abrasion, unloading | Oxidation, hydration, carbonation, hydrolysis, leaching |
| Product | Coarse soils: gravel, sand, silt | Fine soils: clay minerals |
| Climate | Cold and dry regions | Warm and humid regions |
| Particle shape | Angular, bulky | Flaky, very small |

Example: granite breaking into sand-size quartz by frost is physical; feldspar of granite turning into kaolinite by hydrolysis is chemical.

## Check yourself

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

1. What is the basic difference between physical and chemical weathering?
   A. Neither forms soil
   B. Physical changes minerals; chemical only breaks rock
   C. Both change composition
   D. Physical breaks rock without changing composition; chemical changes minerals into new minerals
   Answer: D. Physical disintegration leaves composition unchanged; chemical decomposition alters minerals. (Key point: Core difference)

2. Chemical decomposition typically produces:
   A. Gravel and sand
   B. Fine soils: clay minerals, flaky and very small
   C. Boulders
   D. Angular bulky grains
   Answer: B. Chemical weathering gives fine clayey soils with flaky particles. (Key point: Products)

3. Chemical weathering is most active in:
   A. Cold dry regions
   B. Polar regions
   C. Deserts only
   D. Warm and humid regions
   Answer: D. Warm, humid conditions speed up chemical reactions; physical weathering dominates in cold, dry regions. (Key point: Climate)

4. Feldspar in granite turning into kaolinite by hydrolysis is an example of:
   A. Physical disintegration
   B. Chemical decomposition
   C. Frost action
   D. Abrasion
   Answer: B. Hydrolysis changes the mineral, so it is chemical. (Key point: Example)

## Related in Soil Mechanics

- [Compare montmorillonite and kaolinite](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Acompare-montmorillonite-kaolinite) — Soil Mechanics, chapter 4

## Related in other subjects

- [Physical and chemical weathering](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aphysical-and-chemical-weathering) — Engineering Geology I, chapter 6, asked 5×
- [Chemical versus physical weathering; factors](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Achemical-versus-physical-weathering-factors) — Engineering Geology I, chapter 6
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