Numerical Study on the Undrained Response of Silty Sands Under Static Triaxial Loading

Abstract

The silty soils are more susceptible to liquefaction, even under static loading, than the coarse sands. Pore pressure developed during dynamic events may not dissipate easily due to the presence of more number of small voids. Hence, the rate of pore pressure build-up under static/dynamic loading conditions is much faster in silty sands, which lead to a reduction in the soil strength. This phenomenon may be assessed in terms of either contraction or dilation behaviour under triaxial loading. Therefore, it is necessary to analyse the undrained response of silty sands under triaxial loading so that the damages occurring during future dynamic events may be predicted. The present study involves both the experimental and numerical simulations on various silty sands, which contain 0, 10, 20, 30 and 40% silt fines. Initially, experimental static triaxial testing was performed to determine the undrained response of silty sands moulded to cylindrical specimens at medium relative density. The saturated samples are isotropically consolidated at 100 kPa pressure before shearing. Further, numerical simulations were performed on silty sands by inputting the material parameters into the hypoplastic model. This model requires eight material constants as input including critical friction angle, hardness coefficients, limited void ratios, peak state and stiffness coefficients. These constants were determined for each silty sand combination after conducting basic laboratory tests according to the formulations build in the hypoplastic model program. The experimental trends were compared with numerical model simulations under triaxial testing. The effect of the initial state of soil and the amount of silt fines on the undrained response of fine sands is discussed in detail. The liquefaction susceptibility of silty sand is described based on steady state line concept. The results indicate that the silt sands behave as highly contractive, i.e. more liquefiable when compared with sands.