==>>CLASSIFICATION OF SOILS FOR HIGHWAY USE<<==

                    ==>>CLASSIFICATION OF SOILS FOR HIGHWAY USE<<==

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Soil classification is a method by which soils are systematically categorized according to their probable engineering characteristics. It therefore serves as a means of identifying suitable subbase materials and predicting the probable behavior of a soil when used as subgrade material.

The classification of a given soil is determined by conducting relatively simple tests on disturbed samples of the soil; the results are then correlated with field experience. Note, however, that although the engineering properties of a given soil to be used in highway construction can be predicted reliably from its classification, this should not be regarded as a substitute for the detailed investigation of the soil properties.

Classifying the soil should be considered as a means of obtaining a general idea of how the soil will behave if used as a subgrade or subbase material.

The most commonly used classification system for highway purposes is the American Association of State Highway and Transportation Officials (AASHTO) Classification System. The Unified Soil Classification System (USCS) also is used to a lesser extent. A slightly modified version of the USCS is used fairly extensively in the United Kingdom.

==>>AASHTO Soil Classification System==>>


The AASHTO Classification System is based on the Public Roads Classification System that was developed from the results of extensive research conducted by theBureau of Public Roads, now known as the Federal Highway Administration. Several revisions have been made to the system since it was first published. The system has been described by AASHTO as a means for determining the relative quality of soils for use in embankments, subgrades, subbases, and bases.

==>>Unified Soil Classification System (USCS)==>>


The original USCS system was developed during World War II for use in airfield construction. That system has been modified several times to obtain the current version which also can be applied to other types of construction such as dams and foundations. The fundamental premise used in the USCS system is that the engineering properties of any coarse-grained soil depend on its particle size distribution,whereas those for a fine-grained soil depend on its plasticity. Thus, the systemclassifies coarse-grained soils on the basis of grain size characteristics and fine-grained soils according to plasticity characteristics.


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