Liquefaction Behaviour and Dynamic Soil Properties of River channel deposit in Kolkata City

Abstract

The present works studies the Liquefaction resistance and dynamic soil properties of sandy soil collected from Tollygunge region of Kolkata city. In connection with this, a series of strain controlled cyclic triaxial tests have been performed at the laboratory on prepared soil sample (75 mm diameter and 150 mm height) under undrained condition. The sample was collected from the Tollygaunge area in Kolkata city. In this work, the effect of relative density, peak shear strain and frequency of loading on dynamic behaviour of the sandy soil has been investigated. Soil samples have been prepared using moist tamping method to achieve desired relative densities. To study the effect of relative density, the tests have been performed at four different relative densities, i.e., 35, 60, 75 and 90%. All the tests are carried out at an effective confinement of 100 kPa. For studying the effect of peak shear strain, tests have been conducted at three different peak shear strain, i.e., 0.50, 1.0 and 1.5%.The effect of frequency of loading is examined by conducting tests at 0.1, 0.5 and 1Hz frequencies with constant relative density of 60%. So, in this study a total 11 numbers of cyclic triaxial tests have been performed. The results are presented in the form of excess pore pressure ratio vs no of cycle to liquefaction, relative density of soil vs excess pore pressure ratio and cyclic shear strain vs excess pore pressure ratio. From the results, it can be observed that as the relative density of soil increases the no. of cycle for liquefaction also increases. The peak shear strain is found to have a significant effect on liquefaction resistance of soil. As the peak shear strain increases liquefaction resistance of soil drastically decreases. In this study, the dynamic soil properties in terms of shear modulus and damping ratio have also been determined for different parametric variations. Finally, attempt has also been made to obtain the modulus reduction and damping curves for the soil and the same is proposed for the study region. These curves might play an important role to study the site specific dynamic response of the soil for the region.