**PreConsolidation stress **:

It may be defined as

*” The maximum vertical effective stress the soil has ever experienced.”*

Or

*” The maximum effective past pressure is called the preconsolidation pressure.”*

** Why we need to calculate preconsolidation stress :**

When performing consolidation analysis, we need to compute the preconsolidation stress and the initial vertical effective stress. Preconsolidation stress may be determined from the laboratory data by using Casagrande procedure.

Initial vertical stress is determined with the original field conditions without the new load and the original hydrostatic pore water pressure. Both values may be determined at the same depth of the sample on which the consolidation test was performed.

This maximum effective past pressure (preconsolidation stress) may be equal to or less than the existing effective overburden pressure (initial vertical effective stress) at the time of sampling.

The reduction in effective pressure may be caused by the natural geologic process or human processes.When we take the sample, then the existing effective overburden pressure is also released. It results in soil expansion.

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