Page 4 - Structural Highway Design_Neat
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Unified Soil Classification System (USCS) was commonly based on:
- Grain Size ➔ Sieve Analysis
- Plasticity ➔ Liquid Limit & Plastic Limit ➔ > 50% LL = High
< 50% LL = Low
The plasticity characteristics are determined by the Atterberg limit tests.
These tests are the liquid limit (LL), the Plastic Limit (PL), and the Plasticity
Index (PI). The PI = LL – PL.
Generally, the basic components of soils are differentiated on a grain-size
basis.
The following table contains a summary of the soil components as defined in
the Unified Soil Classification System of the Corps of Engineers.
Component Size Range
Cobbles Above 3 in.
Gravel 3 in. to No. 4 sieve (4.76 mm)
Course 3 in. to ¾ in.
Gravel
Fine Gravel ¾ in. to No. 4 sieve (4.76 mm)
Sand No. 4 sieve (4.76 mm) to No. 200 sieve
(0.074 mm)
Course Sand No. 4 sieve (4.76 mm) to No. 10 sieve (2.0
mm)
Medium No. 10 sieve (2.0 mm) to No. 40 sieve (0.42
Sand mm)
Fine Sand No. 40 sieve (0.42 mm) to No. 200 sieve
(0.074 mm)
Fines (Silt or Clay) Finer than No. 200 sieve (0.074 mm)
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