Every soil contains water in its pore spaces and in the grain too. Atterberg limits are the certain water limits in the soil which demonstrates the critical positions of water content.Behavior of fine grained soil changes with the percent of water it contains..
Depending on the percentage of water present in the soil ,there could be four states:
- Solid State
- Semi-Solid State
- Plastic State
- Liquid State
Transformation from each state to other takes place upon the content of water present and grain conditions of soil. Depending upon the characteristics shown by the soil each of the four stages and their relative positions could be demonstrated. These four limits were invented by a Swedish Chemist Albert Attreberg and later they were developed by Arthur Casagrande.
Definition of Shrinkage Limit:
Shrinkage is the volume change of soil. It is the minimum water content in which the soil changes its state from solid to semi-solid. It is the water content in which further reduction of water will not cause any volume reduction in soil. Shrinkage Limit of soil can be determined by the test method prescribed in ASTM D4943.
Definition of Plastic Limit:
Plastic Limit is the minimum water content at which the soil changes its state from semi-solid to plastic. Plastic Limit is determined by making a thread of 3.2 mm by rolling in a flat surface. When there is hair line crack arises. the corresponding water content is determined by oven-drying the specimen.This water content is known as plastic limit. The test procedure to determine the plastic limit was demonstrated in ASTM D4318.
Definition of Liquid Limit:
Liquid limit is the water content at which the soil changes its state from plastic to liquid.Clayey soil has very low shear strength at higher water content at liquid limit. Arthur Casagrande proposed a test procedure for determining the liquid limit. Casagrande proposed liquid limit determination method is mostly used method for liquid limit determination. Casagrande proposed a special apparatus with a groove.The test method is described on ASTM D4318.
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