Standard one dimensional Consolidation Test

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Standard one dimensional consolidation test is usually carried out on saturated specimens of about 25.4 mm thick and 63.5 mm in diameter. The soil specimen is kept inside a metal ring, with a porous stone on the top and another at the bottom.

The load P is applied on to the specimen using a lever arm, and compression of the specimen is measured with the help of a micrometer dial gauge. The load is usually doubled every 24 hours.  The specimen is kept under water throughout the test.

For each load increment, the specimen deformation and the corresponding time t are plotted on a semilogarithmic graph paper. The graph consists of three distinct parts:

1. Upper curved portion(Stage I). It is mainly due to the result of pre-compression.
2. A Straight line portion (Stage II), is referred to as the primary consolidation. At the end of primary consolidation, a major extent of the excess pore water generated by the increased loading is dissipated.
3. A lower straight line portion (Stage III), is called the secondary consolidation. During this stage, specimen undergoes small deformation with time.
   

Note that at the end of of the test for each loading, the stress on the specimen is the effective stress. Once the specific gravity of the soil solids, the initial dimensions of the specimen, and the specimen deformation at the end of each load have been determined, the corresponding void ratio can be calculated.

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