---
title: "Engineering vs index properties; index tests"
subject: "Soil Mechanics"
chapter: 2
key: "semester_4/soil_mechanics:index-engineering-properties-index-tests"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/index-engineering-properties-index-tests
site: BCT Engineering
---

# Engineering vs index properties; index tests

Soil Mechanics · Chapter 2: Solids- Water –Air Relations and Index properties of soils

- Asked in: 2079 Asoj, 3 marks
- Video: [Gate Q&A | Geo Technical | Index Properties of Soil - Part1](https://www.youtube.com/watch?v=oJNm76Ibg0s) — Learn U Live
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/soil_mechanics/index-engineering-properties-index-tests
- Whole chapter: https://www.bctengineer.com/md/semester_4/soil_mechanics/chapter-2

## Question

How do the engineering properties of soil differ from index properties? Mention different index tests done for coarse and fine grained soils.

## Short answer

Engineering properties are needed directly for design and depend on stress state; index properties identify and classify soil and depend on composition. Coarse-grained tests include sieve analysis, specific gravity, and relative density. Fine-grained tests include hydrometer analysis, Atterberg limits, consistency, and activity.

## Answer

**Difference**
| Engineering properties | Index properties |
|---|---|
| Needed directly for design (strength, settlement, flow) | Used for identification and classification |
| Examples: $c$, $\phi$, $k$, $C_c$, $c_v$ | Examples: $w$, $G$, $e$, grain size, $w_L$, $w_P$ |
| Complex and costly tests, undisturbed samples | Simple, cheap tests, disturbed samples often enough |
| Depend on the structure and stress state | Depend mostly on composition |

**Index tests**
- **Coarse-grained soils:** sieve analysis (grain size distribution, $C_u$, $C_c$), specific gravity, relative density (maximum and minimum density), in-situ density, water content, particle shape.
- **Fine-grained soils:** hydrometer/pipette analysis, Atterberg limits (liquid limit, plastic limit, shrinkage limit), plasticity index, consistency index, activity, sensitivity, and field tests (dilatancy, dry strength, toughness).

## Check yourself

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

1. Engineering properties differ from index properties in that they:
   A. Are used directly for design (strength, settlement, flow)
   B. Are only for classification
   C. Are simple tests
   D. Depend only on composition
   Answer: A. Engineering properties like c, phi, k and Cc are design inputs; index properties classify. (Key point: Difference)

2. Which test is for coarse-grained soils?
   A. Dilatancy test
   B. Atterberg limits
   C. Sieve analysis giving Cu and Cc
   D. Activity
   Answer: C. Coarse soils use sieve analysis and relative density. (Key point: Coarse soil tests)

3. Which tests are for fine-grained soils?
   A. Hydrometer analysis, Atterberg limits, plasticity index
   B. Sieve analysis only
   C. Relative density
   D. Cu and Cc
   Answer: A. Fine soils use hydrometer, Atterberg limits, activity, sensitivity and field tests. (Key point: Fine soil tests)

4. Engineering property tests usually require:
   A. Disturbed samples
   B. No sample
   C. Undisturbed samples
   D. Only sand
   Answer: C. They depend on structure and stress state, so undisturbed samples are needed. (Key point: Sample type)

## Related in Soil Mechanics

- [Field identification of fine-grained soils](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Afield-identification-clay-silt) — Soil Mechanics, chapter 3, asked 4×
- [Index tests for soil](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aindex-tests-list) — Soil Mechanics, chapter 2, asked 2×
- [Index and engineering properties](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aindex-vs-engineering-properties) — Soil Mechanics, chapter 2, asked 4×