This document discusses two common soil classification systems: the Unified Soil Classification System (USCS) and the American Association of State Highway and Transportation Officials (AASHTO) system. The USCS classifies soils based on grain size determined through sieve and hydrometer analysis as well as plasticity tests such as the liquid limit and plastic limit. The AASHTO system also considers grain size and plasticity but additionally calculates a group index value. Both systems aim to characterize soils to help evaluate their engineering properties and behavior.

1. Soil Classification Basics
Dr. Mohanad Alfach
Ph.D. in Earthquake Geotechnical Engineering

2. Contents
• Soil Classification Systems
• Criteria's of (USCS) soil classification
 Soil Grain Sizes
 Hydrometer analysis
 Soil Plasticity – Atterberg Limits
• AASHTO soil classification
 Classification Steps according to AASHTO
 Group Index (GI) Formula

3. Soil classification usually based on grain size and soil consistency.
Several classification systems exist :
1- Unified Soil Classification System (USCS) according
to (ASTM D2487-11)
2- American Association of State Highway and
Transportation Officials AASHTO according to
(ASTM D3282-09)
3-U.S. Department of Agriculture (USDA).
4- Burmister Soil Identification System.
5-Massachusetts Institute of Technology (MIT)

4. Sieve Analysis
Grain Size Distribution, Cc, Cu
Hydrometer Analysis
Percent Clay
(% < 2mm)
Liquid Limit Plastic Limit
Plasticity Chart
PI
LL
Coarse-Grained
•Gravel
•Sand
Fine-Grained
•Silt
•Clay
Sieve Analysis
Hydrometer Analysis
Liquid Limit
Plastic Limit
Grain Size Distribution, Cc, Cu
Percent Clay
(% < 2mm) Plasticity Chart
PI
LL
Steps of USCS Process

7. Mechanical Sieve Analysis (ASTM D422 , D1140 and AASHTO T88)

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13. In general….
PI Degree of Plasticity
0 Non plastic
1-5 Slightly plastic
5-10 Low plasticity
10-20 Medium plasticity
20-40 High plasticity
40+ Very high plasticity
(from Burmister, 1949)

16. #200
#40
#10

29. Questions?
Thanks for your time and
attention!