Dynamic characteristics of natural kutch sandy soils

摘要

Kutch region has experienced widespread liquefaction and related damage during a series of past earthquakes; however, cyclic behavior of sandy soils of the region is yet to be explored. The current study is focused on the dynamic characteristics of natural soil deposits of the high seismicity Kutch region. In the previous studies, variations in fines content (FC) and the nature of fines (plastic, non-plastic) has been controlled and systematic and based on either non-plastic or plastic fines using mostly standard or river sands. However, the present study is different in the approach as the dynamic characteristics of natural sandy deposits with simultaneous presence, and random variations of both the plastic and non-plastic fines are explored. Results from cyclic triaxial tests indicated sandy soils of Kutch region are severe to moderately prone to liquefaction with a strong dependence on plasticity rather than FC. Pore pressure ratio (r(u)), mean effective pressure (p') and cyclic stress ratio (CSR) for silty-sands signified effective stress failure, which was found to be coinciding with initial liquefaction. Clayey sands exhibited strength degradation instead of liquefaction, and the plasticity index (PI) was found to control the magnitude of degradation. Large degradation in secant shear modulus and reduction in damping ratio with the number of cycles was observed in silty-sands whereas clayey-sands exhibited relatively lesser degradation in secant shear modulus and damping ratio.