---
title: "Factors for residual soil characteristics"
subject: "Soil Mechanics"
chapter: 1
key: "semester_4/soil_mechanics:residual-soil-characteristics-factors"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/residual-soil-characteristics-factors
site: BCT Engineering
---

# Factors for residual soil characteristics

Soil Mechanics · Chapter 1: Introduction

- Asked in: 2073 Bhadra, 1 marks
- Video: [How Soil is Formed? Parent Rock, Residual Soil, Transported Soil, Soil Horizon](https://www.youtube.com/watch?v=etJqCQnOJwo) — Kuwader Knows
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/soil_mechanics/residual-soil-characteristics-factors
- Whole chapter: https://www.bctengineer.com/md/semester_4/soil_mechanics/chapter-1

## Question

Write the factors that determine the characteristics of a residual soil.

## Short answer

Parent rock type, climate (temperature and rainfall), topography (slope), time, drainage and groundwater, vegetation, and the weathering-erosion balance determine the characteristics of a residual soil.

## Answer

The characteristics of a residual soil depend on:
1. **Parent rock:** type and mineral composition (granite gives sandy soil; basalt gives clayey soil).
2. **Climate:** temperature and rainfall control the rate of weathering; warm humid climates cause deep chemical weathering.
3. **Topography:** gentle slopes keep the weathered material in place; steep slopes remove it.
4. **Time:** the longer the weathering, the deeper and finer the soil.
5. **Drainage and groundwater:** leaching removes soluble minerals.
6. **Vegetation and biological activity:** add organic matter and acids.
7. **Rate of removal:** weathering rate must exceed the erosion rate for residual soil to build up.

## Check yourself

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

1. Which factor decides mineral composition of a residual soil, e.g. granite giving sandy soil?
   A. Vegetation only
   B. Topography
   C. Parent rock
   D. Wind
   Answer: C. Parent rock type and minerals control the soil formed. (Key point: Parent rock)

2. How does topography affect residual soil?
   A. Gentle slopes keep weathered material in place; steep slopes remove it
   B. Steep slopes build deep soil
   C. It has no effect
   D. Only flat land weathers
   Answer: A. Residual soil can accumulate only where the weathered material is not eroded away. (Key point: Topography)

3. For residual soil to build up:
   A. Erosion rate must exceed weathering rate
   B. Both must be zero
   C. Weathering rate must exceed erosion rate
   D. Rainfall must be zero
   Answer: C. If material is removed faster than formed, no residual soil accumulates. (Key point: Rate of removal)

4. Warm humid climate and long time give:
   A. Deep, finer, chemically weathered soil
   B. Shallow coarse soil
   C. No soil
   D. Only gravel
   Answer: A. More weathering time and humid warmth cause deep chemical weathering and finer soil. (Key point: Time and climate)

## Related in Soil Mechanics

- [Residual and transported soils](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aresidual-transported-soils) — Soil Mechanics, chapter 1, asked 2×
- [AASHTO classification of inorganic soil](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aaashto-classify-inorganic-soil) — Soil Mechanics, chapter 3
- [Compacted soil 17 kN/m³, OWC 16%](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Amax-dry-weight-17-void-ratio) — Soil Mechanics, chapter 5, asked 2×
- [Moist soil 20 kg numerical](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Amoist-soil-mass-numerical) — Soil Mechanics, chapter 2
- [Factors affecting compaction](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Afactors-affecting-compaction) — Soil Mechanics, chapter 5, asked 3×
- [Factors affecting capillary rise](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Acapillary-rise-factors) — Soil Mechanics, chapter 6

## Related in other subjects

- [Soil moisture forms; factors affecting CWR](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Asoil-moisture-forms-cwr-factors) — Irrigation and Drainage Engineering, chapter 2
- [Soil stabilization factors; mechanical; cement-soil base](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Asoil-stabilization-factors-mechanical-cement-soil) — Transportation Engineering II, chapter 3
- [Soil stabilization, equipment, mass haul characteristics](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Asoil-stabilization-definition-equipment-mass-haul) — Transportation Engineering II, chapter 3
- [Contour interval factors and characteristics](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Acontour-interval-factors-characteristics) — Surveying II, chapter 4