Types and Distribution of Collapsible Soils

Abstract

Collapsible soils are metastable and must have an open structure, that is the soil particles must be in an open packing which is capable of becoming a (significantly) closer packing. A granular material with angular particles compacted on the dry side of optimum can form a structure which is capable of significant further densification, but the classic collapsible soils are natural materials where the combination of particle type and sedimentation mechanism combine to give collapsibility. There is a fierce debate about what soils should be considered as collapsible and this has spawned several definitions of a collapsible soil, all of which are in some way limiting. The debate is advanced hereafter by consideration, from a geotechnical viewpoint, of what is not a collapsible soil. Thereafter a simple hierarchical, systematic classification can be produced which allows both compacted and natural materials to be included. A geographical classification which places all types of natural collapsible systems on a convenient base map is also required. This paper aims to address both of these issues by considering collapsible soils in their widest possible sense.