When a soil mass is subjected to a compressive force, its volume decreases. The property of the soil due to which a subtract in volume occurs under compressive gravity is known as the compressibility of soil. The pinch of soil can occur due to
- Compression of solid particles and water in the voids
- Compression and expulsion of air in the voids
- Expulsion of water in the voids
The compression of saturated soil under a steady static pressure is known as consolidation. It is entirely due to expulsion of water from the voids
INITIAL, PRIMARY AND SECONDARY CONSOLIDATION
When a load is applied to a partially saturated soil, a decrease in volume occurs due to expulsion and compression of air in the voids. A small decrease in volume occurs due to compression of solid particles. The reduction in volume of the soil just after the application of the load is known as initial consolidation or initial compression. For saturated soils, the initial consolidation is mainly due to compression of solid particles.
After initial consolidation, remoter reduction in volume occurs due to expulsion of water from the voids. When a saturated soil is subjected to a pressure, initially all the unromantic pressure is taken up by water as an glut pore water pressure. A hydraulic gradient will develop and the water starts flowing out and a subtract in volume occurs. This reduction in volume is tabbed as the primary consolidation of soil
The reduction in volume continues at a very slow rate plane without the glut hydrostatic pressure ripened by the unromantic pressure is fully prodigal and the primary consolidation is complete. The spare reduction in the volume is tabbed as the secondary consolidation.