---
title: "Short note: Weathering"
subject: "Engineering Geology II"
chapter: 1
key: "semester_4/engineering_geology_ii:short-note-weathering"
source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/short-note-weathering
site: BCT Engineering
---

# Short note: Weathering

Engineering Geology II · Chapter 1: Introduction to Engineering Geology

- Asked in: 2080 Chaitra, 2 marks
- Video: [CET 202 - Engineering Geology | Module 1 - Lec 2 | Weathering - Physical Weathering | S4 KTU Civil](https://www.youtube.com/watch?v=OjLHq8jPulw) — Alex -E Academy
- 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-weathering
- Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-1

## Question

Write a short note on weathering.

## Short answer

Weathering is the in-situ breakdown of rocks by physical, chemical, and biological processes. It reduces rock strength, increases porosity, and causes landslides. Weathering grades are used in rock classification for foundations and slopes.

## Answer

**Weathering** is the in-situ breakdown and decay of rocks at or near the earth's surface by the action of atmosphere, water and organisms, without transport of the material.

#### Types
- **Physical (mechanical):** frost wedging, temperature changes, salt crystal growth, unloading (exfoliation) and root action break the rock into pieces without changing its composition.
- **Chemical:** oxidation, hydrolysis, carbonation and solution change minerals (feldspar to clay, calcite dissolves).
- **Biological:** roots, burrowing animals, lichens and bacteria.

#### Factors
Climate (rain, temperature), rock type and mineral stability, joints, topography and time. Warm, humid climate gives deep chemical weathering.

#### Engineering significance
- Lowers strength, increases porosity and permeability of foundation rock.
- Weathered rock needs deeper excavation and flatter slopes.
- Causes landslides and rock falls on cut slopes.
- Weathering grades (fresh, slightly, moderately, highly, completely weathered) are used in rock classification.
- Weathered material forms residual soil and clay, which may swell.

## Check yourself

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

1. What distinguishes weathering from erosion?
   A. Weathering is breakdown in place without transport
   B. Weathering always involves transport by rivers
   C. Weathering happens only deep underground
   D. Weathering only builds rock
   Answer: A. Weathering is in-situ breakdown and decay of rock at or near the surface without transport. (Key point: Definition)

2. Which is an example of chemical weathering?
   A. Frost wedging
   B. Root action
   C. Feldspar changing to clay
   D. Unloading exfoliation
   Answer: C. Oxidation, hydrolysis, carbonation and solution alter minerals, e.g. feldspar to clay. (Key point: Chemical weathering)

3. Which climate gives deep chemical weathering?
   A. Cold and dry
   B. Warm and humid
   C. Dry desert
   D. Permanently frozen
   Answer: B. Warm humid conditions speed chemical reactions, giving deep weathering. (Key point: Climate factor)

4. What is an engineering effect of weathered foundation rock?
   A. Higher strength
   B. Lower permeability
   C. Lower strength and higher porosity and permeability
   D. No change in excavation depth
   Answer: C. Weathering weakens rock and raises porosity and permeability, needing deeper excavation and flatter slopes. (Key point: Engineering effect)