Civil Engineering ⇒ Topic : Soil and its classifications
Soil is a non-homogeneous, porous earthen
mixture of inorganic material (consisting of soft
clays, loams, silts and gravel or hard stiff clay in
various proportions) formed by disintegration and
decomposition of rocks.
On the geological basis the soils are classified into two main groups :-1. Residual soil : It is found at the place of disintegration of the parent rock. Igneous rocks such as granite or basalt and sedimentary rocks such as sandstone, shale or limestone are the parent rock material for residual soils.
2. Transported soil : It is carried away from its place of disintegration to some other place by the transporting agencies like force of gravity, water, wind, ice etc.
On the basis of transportation and deposition the transported soils may be classified as :-
Main categories of soils are :-
Liquid limit is the boundary between the liquid and plastic states.
Plastic limit is the boundary between the plastic and semi-solid states.
Shrinkage limit is the boundary between the semi-solid and solid states.Liquid limit is the minimum moisture content at which the soil is still in liquid state, but has started exhibiting a small shear strength against flowing.
Plastic limit is the minimum moisture content at which the soil can be rolled into 3 mm threads without showing any sign of cracks.
Shrinkage limit is the maximum moisture content at which a reduction in water content will not cause a decrease in volume of the soil.
Plasticity index = Liquid - Plastic limit
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