---
title: "Soil classification systems"
subject: "Soil Mechanics"
chapter: 3
key: "semester_4/soil_mechanics:common-classification-systems"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/common-classification-systems
site: BCT Engineering
---

# Soil classification systems

Soil Mechanics · Chapter 3: Soil Identifications and Classification

- Asked in: 2074 Bhadra, 2 marks; 2076 Baisakh, 1 marks; 2078 Poush, 1 marks (asked 3 times)
- Video: [Soil classification System](https://www.youtube.com/watch?v=i9Q3hjFaAPI) — Elementary Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/soil_mechanics/common-classification-systems
- Whole chapter: https://www.bctengineer.com/md/semester_4/soil_mechanics/chapter-3

## Question

What are the common (important engineering) soil classification systems? Write down the types of soil classification.

## Short answer

Major engineering systems: Unified Soil Classification System (USCS) for general works, AASHTO for highways, IS Classification (IS 1498). Types include textural (e.g., MIT, USDA) based on grain size, plasticity/size systems (USCS, ISSCS, AASHTO), genetic classification, and purpose-based systems (airfield, agricultural).

## Answer

#### Types of soil classification
1. **Textural (particle size) classification:** based on percent of sand, silt and clay, e.g. USDA/triangular chart, MIT system.
2. **Classification based on plasticity and size (engineering classification):** Unified Soil Classification System (USCS), Indian Standard Soil Classification System (ISSCS, IS 1498), AASHTO, Casagrande's airfield system.
3. **Classification based on origin and genesis:** residual, transported, alluvial, etc.
4. **Classification for specific purposes:** AASHTO for highways, Federal Aviation Administration (FAA) for airfields, and agricultural (pedological) classification.

#### Important engineering systems
| System | Main use |
|---|---|
| Unified (USCS) | General engineering, foundations, dams |
| IS Soil Classification (IS 1498) | Indian/Nepali practice |
| AASHTO | Highways, subgrade |
| Textural (MIT, USDA) | Based on grain size only |

## Check yourself

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

1. Which are textural (particle size) classifications?
   A. USDA/triangular chart and MIT system
   B. USCS and AASHTO
   C. IS 1498 and USCS
   D. FAA and AASHTO
   Answer: A. Textural systems use sand, silt and clay percentages only. (Key point: Textural systems)

2. Which uses grain size and plasticity (engineering classification)?
   A. Triangular chart
   B. Residual/transported classification
   C. MIT system
   D. Unified Soil Classification System
   Answer: D. USCS, IS 1498 and AASHTO use both size and plasticity. (Key point: Engineering systems)

3. AASHTO classification is mainly used for
   A. dam foundations in general
   B. highways and subgrade
   C. agricultural land
   D. Indian practice only
   Answer: B. AASHTO is the highway system. (Key point: AASHTO use)

## Related in Soil Mechanics

- [Purpose of soil classification](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Apurpose-of-soil-classification) — Soil Mechanics, chapter 3, asked 3×
- [AASHTO classification of inorganic soil](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aaashto-classify-inorganic-soil) — Soil Mechanics, chapter 3
- [Define soil; soil engineering problems](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Adefine-soil-engineering-problems) — Soil Mechanics, chapter 1
- [Systems by size and plasticity; ISSCS chart](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aissc-plasticity-chart-systems) — Soil Mechanics, chapter 3
- [Describe one classification system, limits](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Adescribe-classification-system-limits) — Soil Mechanics, chapter 3
- [Classification for subgrade suitability](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Asubgrade-suitability-classification) — Soil Mechanics, chapter 3

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