Some remarks on the cyclic response of non-plastic and high-plasticity natural silty soils of the Kathmandu valley (Nepal)

This note presents the results of constant-volume equivalent-undrained cyclic simple shear tests performed on saturated natural silty soils obtained from two different locations in the Kathmandu valley (Nepal) and characterized by different plasticity. Two simple shear devices were employed: the DSDSS (Double Specimen Cyclic Simple Shear) device and a modified NGI-type DSS device. The above two types of tests complemented each other and jointly covered a wide range of cyclic shear strains amplitudes. Nonlinear soil behavior (i.e. variation of shear stiffness and damping with shear strain level) and liquefaction resistance of the non-plastic silty soil were investigated. The results of the experimental investigation presented in this paper, albeit limited, increase the knowledge on the cyclic response of natural silty soils, especially those of very low plasticity, and provide first geotechnical data on the soft fluvio-lacustrine deposits of the Kathmandu Valley, responsible for site effects and liquefaction phenomena during the 2015 Mw=7.8 Gorkha earthquake.