Question

What are the stresses developed in the soil during the time of consolidation and compression in soil?

Answer 1

Consolidation

Consolidation is the process in which reduction in volume takes place by expulsion of water under long-term static loads.

When stress is applied to a soil that causes the soil particles to pack together more tightly. When this occurs in a soil that is saturated with water, water will be squeezed out of the soil. When the stress is reapplied, the soil will consolidate again along a recompression curve, defined by the recompression index.The soil which had its load removed is considered to be "overconsolidated". This is the case for soils that have previously had glaciers on them.The highest stress that it has been subjected to is termed the "preconsolidation stress". The "over-consolidation ratio" (OCR) is defined as the highest stress experienced divided by the current stress. A soil that is currently experiencing its highest stress is said to be "normally consolidated" and has an OCR of one. A soil could be considered "underconsolidated" immediately after a new load is applied but before the excess pore water pressure has dissipated.

Primary 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.

When the final effective stress is greater than the preconsolidation stress, the two equations must be used in combination to model both the recompression portion and the virgin compression portion of the consolidation processes, as follows,

where

δc is the settlement due to consolidation.

Cc is the compression index.

e0 is the initial void ratio.

H is the height of the compressible soil.

σzf is the final vertical stress.

σz0 is the initial vertical stress

σzc is the preconsolidation stress of the soil.

Secondary consolidation

Secondary compression is the compression of soil that takes place after primary consolidation. Even after the reduction of hydrostatic pressure some compression of soil takes place at slow rate. This is known as secondary compression. Secondary compression is caused by creep, viscous behavior of the clay-water system, compression of organic matter, and other processes.Due to transfer of stresses to points of contact of soil grains some of the highly viscous water between the points of contact is forced out.