---
title: "Short note: Weathering profile"
subject: "Engineering Geology I"
chapter: 6
key: "semester_3/engineering_geology_i:short-note-weathering-profile"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/short-note-weathering-profile
site: BCT Engineering
---

# Short note: Weathering profile

Engineering Geology I · Chapter 6: Physical Geology

- Asked in: 2063 Baisakh (old course), 2 marks; 2062 Baisakh (old course), 2 marks (asked 2 times)
- Video: [Gr9 SS: Geography | Term 3 | Lesson 1 | Weathering](https://www.youtube.com/watch?v=DbhkPJrCr1Y) — Thuma Mina Teaching
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/short-note-weathering-profile
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-6

## Question

Write a short note on weathering profile.

## Short answer

A weathering profile is a vertical section from fresh bedrock (grade I) to residual soil (grade VI) per ISRM/BS 5930. Weathered zones have reduced strength and higher permeability, critical for foundation depth and slope design.

## Answer

A **weathering profile** is the vertical section from fresh bedrock up to the ground surface, showing zones of increasing degree of weathering.

```text
 Zone         Description
 ---------------------------------------
 VI  Residual soil   (fully altered, no rock fabric)
 V   Completely weathered (soil-like, fabric seen)
 IV  Highly weathered (more than half is soil)
 III Moderately weathered (less than half soil)
 II  Slightly weathered (discoloured joints)
 I   Fresh rock
```

- The classification is that of ISRM/BS 5930 (grades I to VI).
- The thickness of the profile depends on climate, rock type, structure and topography. It is deepest in warm, humid regions, where it can reach tens of metres (e.g. the thick red residual soils of the Nepal Midlands).
- Strength, bearing capacity and the safe cut-slope angle fall as the grade increases.
- It is important for foundation depth, tunnel portals and slope design, because the weathered zone is weak, permeable and easily eroded.

## Check yourself

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

1. What is a weathering profile?
   A. Plan map of rock types
   B. Graph of rainfall
   C. Section of river
   D. Vertical section from fresh bedrock to surface showing zones of increasing weathering
   Answer: D. It shows grades I to VI. (Key point: Definition)

2. Which grade is residual soil?
   A. VI
   B. I
   C. III
   D. II
   Answer: A. I is fresh rock; VI is fully altered soil with no rock fabric. (Key point: Grades)

3. How do strength and cut-slope angle change as the grade increases?
   A. They rise
   B. They fall
   C. They stay constant
   D. They rise then fall
   Answer: B. More weathered rock is weaker. (Key point: Strength)

4. Why does the profile matter in engineering?
   A. It decides rainfall
   B. It determines the colour of rock
   C. Weathered zone is weak, permeable and erodible, affecting foundations, portals and slopes
   D. It has no design role
   Answer: C. Used for foundation depth, tunnel portals and slope design. (Key point: Importance)