Collapsible Soils and Subsidence

There are soils which are quite stable when dry and they show large volume changes on wetting under load. Examples of  these soils are loess (which  is wind borne),  residual soils which have high void ratios and are weakly cemented and also have crumbling structure. The structure of  these soils  is so unstable that upon saturation or vibration, collapse will occur. Foundations cannot be placed on such soils unless they are densified.  Prewetting and consolidation will help to improve the load carrying capacity. Alternatively deep foundations should be provided to take the load to firm underlying strata.