EFFECTS OF SATURATION AND BACK PRESSURE ON SAND LIQUEFACTION

The influence of saturation and back pressures on the liquefaction resistance of a sand is investigated by conducting cyclic triaxial tests on four sets of sand samples with different degrees of saturation and on five sets of samples with different back pressures. The tested sand is taken from the site of Tong Jaizhi Water Power Station in China. Test results show that the conspicuous effect of saturation on the liquefaction resistance of the tested sand cannot be improved by keeping back pressures on samples during the test. On the other hand, the application of back pressures otherwise results in higher liquefaction resistance. The effect of back pressures is further explained by analyzing the internal interaction of soil particles. It is concluded that the back-pressure method should not be used in cyclic liquefaction tests for improving the degrees of saturation of sand, and Terzaghi's effective stress principle is not valid unless additional conditions are included for the actions of interparticle forces in soils.