Geotechnical characterization of collapsible salty sands subjected to monotonic and cyclic loadings – A case study for areas with high seismicity

Collapsible soils are typically found in arid regions and often have an aeolian or alluvial origin. In their natural states, they may have a low moisture content and cemented structure that can contribute to high strength and stiffness; however, wetting or saturation can reduce the strength and stiffness due to loss of the cementation. This paper presents a geotechnical characterization of collapsible salty sands in the highly seismic southern coast of Peru, which makes the characterization of their dynamic properties and expected response to earthquake-induced demands (e.g., liquefaction) of primary importance. The geotechnical characterization was performed on intact and remolded samples utilizing various field and laboratory tests, including oedometer, direct shear, static triaxial, cyclic simple shear, torsional resonant column, plate loading, and MASW tests. The results revealed insights on the geotechnical properties and mechanical response of collapsible soils and the effects of salt cementation. The results indicated: 1) a decreasing brittle and collapsible behaviors with decreasing cementation while maintaining consistent post-collapse residual strength; 2) oedometer and in situ plate loading tests showed a sudden increase in deformations once cementation is broken; 3) higher dilation potential of collapsible soils as compared to natural sands; 4) decrease in the maximum shear modulus due to the loss of cementation; 5) increase in the stress dependence of the maximum shear modulus with loss of cementation; and 6) a higher resistance to liquefaction for the collapsible soils, even after washing, as compared to natural sands, which may be ascribed to the more pronounced dilation potential.