Thursday, February 14, 2013

Classification of the soil

The soil according to its mode of formation can be classified into two major categories:
(1) Residual Soil: Sometimes after the disintegration of the rocks into the soil particles, these particles remain at their original place of formation and gets deposited there. These soil deposits are known as the residual soils. Black cotton soils of India  is a well known residual soil. Such soil deposits have the larger boulders in the lower depth, and the soil particle size decreases in the upper layers. The layers at the top contain the soil with smallest particle size. These particles are the ones which are prone to the weathering attacks often so they are fine enough in their particle size.
(2) Transported Soils: The weathered rocks give away the soil particles, which can be transported by the various transporting agencies to different places, and deposited there. The main transporting agencies are the air, water and glaciers. Such soil deposits are known as the transported soils.
(a) Air Transported soils(Aeolian deposits): The soil which are transported by the fast moving winds are known as the aeolian deposits or the air transported soils. Loess is a type of such soil, which is deposited to greater depths at many places. It generally contains the silt and clay particles. Sand dunes are another kind of air transported soil deposits which are formed in the desert areas. Sand dunes are not the permanent deposits because they keep on changing their place under the action of the fast moving winds.
(b) Water Transported Soils: Water transported soil deposits are the ones which are transported by the water to different places and they get deposited there. The deposits which are deposited along the sides of the streams, or in the stream beds are known as the Alluvial deposits.  The soil deposits which are deposited from the water suspensions in the lake beds are known as the Lacustrine soils. The soil deposits which are deposited in the ocean beds are known as the Marine deposits.
(c) Glacial Deposits: These are the soil deposits which are deposited by the glaciers at the different places. The soil deposits which are deposited by the body of the glaciers at different places are known as the Moraines.  The soil deposits which are deposited by the glaciers after melting into water, are known as the drift. Drift are generally stratified in their physical structure.

Engineering Classification of the soil:
The Engineering properties of the soil largely depends upon the particle size in the soil samples. According to the particle size of the particles the soil is classified among the following major categories:
(a)Fine Grained soils: Soil having the particles of size lesser than 0.075 mm are known are known as the fine particles. Clay and silt are the examples of the fine grained soils.
(b) Coarse grained soils: Coarse grained soils are soil having the particle sizes greater than 0.075 mm and the examples are sand, gravels, and boulders etc. 

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