Geotechnical characterization of collapsible soils cemented by salts–a case study

Collapsible soils are typically found in arid regions and often have an aeolian or alluvial origin. In their natural state, they have a low moisture content and high initial or peak shear strength and stiffness due to their cemented structure (e.g. by the presence of salts). However, when these soils are subjected to wetting or saturation, the salts can dissolve resulting in a reduction of cementation and the peak strength and stiffness. This paper presents a summary of the geotechnical characterization performed on a deposit of collapsible soil at a proposed mine site near the southern coast of Peru, with particular emphasis on the dynamic characteristics. The site is located in a very high seismic area, which makes the dynamic characterization of these materials of primary importance. The geotechnical field investigation included drilling of boreholes, excavation of test pits, collection of samples, and execution of in-situ field tests. Undisturbed samples were carefully collected and oedometer, direct shear, consolidated drained triaxial, cyclic simple shear and resonant column tests were performed on them, while disturbed samples were also collected and tested for index properties and soluble salts content. The testing on undisturbed specimens was carried out at their natural moisture content state and after being subjected to wetting and the results revealed interesting insights in terms of the geotechnical properties and mechanical response of these materials as they lose the effects of salt cementation.