Pore Pressure Response of Natural Soils Under Various Testing Conditions

Abstract

Soil behavior under undrained conditions is governed by several factors, including soil density, fines content, plasticity index and loading conditions among many others. Constitutive behavior of soil being pressure-dependent, the undrained response of soils is dictated by the development of excess pore water pressure during the applied loading. In this study, the pore pressure response of the natural Kutch soils under monotonic compression triaxial (TX), cyclic triaxial (CTX), and cyclic simple shear (CSS) conditions was investigated at their in-situ density. The explored soils vary greatly in terms of gradation, fines content, and nature of fines. The development of excess pore water pressure was compared under the three loading conditions and was analyzed in the context of fines content and plasticity index of the soils. The excess pore pressure ratio at peak stress for TX was found to be lower than that during the first cycle for both the CTX and CSS. However, at critical state, the excess pore pressure ratio for TX was higher than that during the 5th cycle for CTX and CSS. Under cyclic conditions, for a given number of cycles, the excess pore water pressure ratio under CSS conditions was always higher than that under the CTX conditions, signifying overestimation of liquefaction resistance as evaluated from the CTX tests. With an increase in the fines content and plasticity index, excess pore water pressure was observed to decrease under all the three loading conditions.