Dear reader we were discussing about filled deposit type collapsible soil. Such loose soil deposit has structure that is collapsed due to reduction of negative pore water pressure; also called capillary tension. The capillary tension reduced under wetting of fill.
The factors that influences degree of 1-D collapse for a specimen of fill submerged in water (considered distilled water) are
- Soil type
- Moisture content at compaction
- Dry density of compacted fill
- Vertical pressure
Generally 1-D collapse of a fill will increase when
- Dry-density is decreased
- Moisture content is decreased
- Vertical pressure is increased
For a moisture content and dry density, 1-D collapse is decreased with increase in clay fraction when clay content exceeds optimum value (generally small percentage).
2. Natural soil
The natural soil deposits of collapse behavior are found in arid climatic condition of south western part of United States, the general mechanism involved in collapse is a result of breaking down of bonds within soil particles.
Bonds break down due to weathering, at contact of coarse particles, of fine-particles brought by the surface tension within evaporating water.
In some cases, colluvium or alluvium having unstable structure (like pin hole porosity) may collapse while wetting cycle passes through soil.