The influence of the geological origin on soil volume change through collapse settlement

• Refinement of collapse in sandy soils based on various origins.
• Geological origin influences the volume reduction in collapsible soils.
• Collapse in residual soils is due to closure of some voids.
• Collapse in transported soils is due to most of the voids being closing.
• Decrease in void ration after collapse are similar in both soil origin types.

Partially saturated soils are often dense with a high bearing capacity and will subsequently only suffer small amounts of compression under normal foundation loads. However, when wetted under load many such soils undergo a marked and sudden increase in settlement, the phenomenon that is known as collapse settlement.It was originally assumed that the collapse phenomenon is largely restricted to loose aeolian deposits, with the result that most of the research and work dealt almost exclusively with such deposits. However, the collapse phenomenon has since been identified in a number of different transported soils as well as residual soils, most notably the residual granitic soils associated with the Basement Complex of South Africa.Recent studies suggest that the geological origin of the material plays an important role in the collapse mechanism of the particular material. This paper highlights the differences between the collapse process in transported and residual soils by focusing on the geological origin of the material.