SOIL CLASSIFICATION AND PROPERTIES BASICS AND TUTORIALS

BASIC PROPERTIES AND CLASSIFICATION OF SOILS
Soil Mechanics Tutorials


1. REFERENCE.
Soil designations in this manual conform to the Unified Soil Classification per ASTM D2487, Classification of Soil for Engineering Purposes.

2. UTILIZATION.
Classify soils in accordance with the Unified System and include appropriate group symbol in soil descriptions. A soil is placed in one of 15 categories or as a borderline material combining two of these categories. Laboratory tests may be required for positive identification.

a. Sands and Gravels.
Sands are divided from gravels on the No. 4 sieve size, and gravels from cobbles on the 3-inch size. The division between fine and medium sands is at the No. 40 sieve, and between medium and coarse sand at the No. 10 sieve.

b. Silts and Clays.
Fine-grained soils are classified according to plasticity characteristics determined in Atterberg limit tests.

c. Organic Soils.
Materials containing vegetable matter are characterized by relatively low specific gravity, high water content, high ignition loss, and high gas content. Decrease in liquid limit after oven-drying to a value less than three-quarters of the original liquid limit is a definite indication of an organic soil.

The Unified Soil Classification categorizes organic soils based on the plotted position on the A-line chart. However, this does not describe organic soils completely. For the characteristics of the Unified Soil Classification System pertinent to roads and airfields, see NAVFAC DM-5.4.

3. TYPICAL PROPERTIES. Some typical properties of soils should be based on laboratory and/or field testing, and engineering evaluation.

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