The process of consolidation is often confused with the process of compaction. Compaction increases the density of an unsaturated soil by reducing the volume of air in the voids. Meanwhile, Consolidation is a time-related process of increasing the density of saturated soil by draining some of the water out of the voids.
According to Karl Terzaghi "consolidation is any process which involves decrease in water content of a saturated soil without replacement of water by air." In general it is the process in which reduction in volume takes place by expulsion of water under long term static loads. It occurs when stress is applied to a soil that causes the soil particles to pack together more tightly, therefore reducing its bulk volume. When this occurs in a soil that is saturated with water, water will be squeezed out of the soil. Consolidation is generally related to fine-grained soils such as silts and clays. Coarse-grained soils (sands and gravels) also undergo consolidation but at a much faster rate due to their high permeability. Saturated clays consolidate at a much slower rate due to their low permeability.
Generally Compression of saturated soil consists of two successive phases, namely the primary and secondary consolidation phases. The settlement is defined as the compression of a soil layer due to the loading applied at or near its top surface. The total soil settlement of a soil layer consists of three parts:
Immediate or elastic compression
Compression due to primary consolidation
Compression due to secondary consolidation
This method assumes consolidation occurs in only one-dimension. Laboratory data is used to construct a plot of strain or void ratio versus effective stress where the effective stress axis is on a logarithmic scale. The plot's slope is the compression index or recompression index. The equation for consolidation settlement of a normally consolidated soil can then be determined to...
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