LIQUEFACTION RESISTANCE OF SOILS UNDER CYCLIC LOADING

Abstract

The liquefaction of saturated loose sand during earthquakes has been the cause of severe damages to various buildings, embankments and retaining structures. The catastrophic damages during past earthquakes, such as Alaska (1964), Niigata (1964), Northridge (1994), Kobe (1995), Kocaeli (1999), Chi-Chi (1999) and Bhuj (2001), due the liquefaction susceptibility of soil were encountered. Therefore, improvement of site conditions to eliminate liquefaction is necessary. Liquefaction of loose, saturated sands may be caused by cyclic undrained loading. An experimental investigation is undertaken to evaluate the stress conditions required to initiate liquefaction and the influence of various parameters on those stress conditions. The cyclic triaxial test is an easy and reliable method for measurement of liquefaction. A number of parameters for liquefaction study such as deviator stress, number of cycles, maximum pore water pressure ratio (r„)., axial strain (s), frequency were observed experimentally. The liquefaction resistance was evaluated in terms of maximum excess pore water pressure ratio. In the present study, an experimental investigation to obtain liquefaction potential of the locally available fine sand from the bed of Solani River was carried out. Total 47 tests were carried out to evaluate effect of relative density of soil, frequency of loading and confining pressure acting on the soil. It was observed that the Solani sand is susceptible to liquefaction at relative density of 35 % and 45 %. At higher relative density, i.e. 55 % there was only reduction in shear strength but the soil did not liquefied. From the test results it was observed that number of cycles required for liquefaction decreases with an increase in frequency. It was also observed that liquefaction resistance of soil increases with an increase in confining pressure. Soil samples were collected from Dhanouri and Roshnabad sites from different depths using SPT, were tested to evaluate the liquefaction potential. Cyclic triaxial tests were performed at a frequency of 1 Hz for and axial strain of 0.7% on the samples prepared at a relative density of 40%. A sample collected from Dhanouri site is susceptible to liquefaction for certain depths. However, sample from Roshnabad are not susceptible.