Soil Classification

O: 1/XI-3/GTK/10


Purpose

Classifying soils into groups with similar behavior, in terms of simple indices, can provide geotechnical engineers a general guidance about engineering properties of the soils through the accumulated experience.

The accumulated experience:

1. Simple indices
2. Classification system
3. Estimate engineering properties
4. Achieve engineering purposes

A. Unified Soil Classification System (USCS)

This system was first developed by Professor A. Casagrande (1948) for the purpose of airfield construction during World War II. Afterwards, it was modified by Professor Casagrande, the U.S. Bureau of Reclamation, and the U.S. Army Corps of Engineers to enable the system to be applicable to dams, foundations, and other construction

Four major division:

1. Coarse-grained
2. Fine-grained
3. Organic soils
4. Peat

Definition of Grain Size:
Boulders            > 300 mm
Cobles                   75 mm -   300 mm
Gravel :         
Coarse                  19 mm -     75 mm
Fine                   4,75 mm -     19 mm
Sand :
Coarse                 2,0 mm -  4,75 mm
Medium             0,425 mm -    2,0 mm
Fine                 0,075 mm  - 0,425 mm
Silt and Clay    < 0,075 mm

B. American Association of State Highway and Transportation Officials system (AASHTO)
This system was originally developed by Hogentogler and Terzaghi in 1929 as the Public Roads Classification System. Afterwards, there are several revisions. The present AASHTO  (1978) system is primarily based on the version in 1945.

Definition of Grain Size:
Boulders               > 75 mm

Gravel                   4,75 mm -     75 mm
Sand
Coarse                0,425 mm -     4,75 mm
Fine                    0,075 mm - 0,425 mm
Silt and Clay      < 0,075 mm

C. United States Depatment of Agriculture (USDA)

D. Wenworth Scale