Collapsible Soils

Collapsible soils are those that are susceptible to a rapid reduction of volume when wetted under load as the soil passes from a metastable condition to a normally consolidated state. The most common type of metastable soil is loess, which is of wind-blown origin and consists of angular grains of silt size that are well sorted. The silt is produced by glacial action before being moved by wind action and redeposited. However, there are a number of other types of soil that are susceptible to collapse particularly some young soils that are recently altered. These include soils derived from weathering of granite and some tropical red clay soils derived from volcanic ash deposits. Some nonengineered fills may also collapse. To reduce the risk posed by collapsible soils, their presence needs to be identified using geological and geomorphological information, their degree of collapsibility needs classifying and quantifying by geotechnical testing, and then appropriate engineering mitigation measures need to be applied.