2005 Volume 45 Issue 5 Pages 103-113
A series of undrained cyclic torsional shear tests was conducted to investigate liquefaction properties of Toyoura sand under low confining stress. Hollow-cylindrical specimens were prepared by air pluviation at a relative density of about 55%. After being saturated, they were anisotropically consolidated to an effective vertical stress of 9.8, 29.4 and 98.1 kPa, while keeping the effective horizontal stress to be half of the vertical one. They were subjected to undrained cyclic torsional shear without allowing any vertical displacement of the top cap. The amplitude of the cyclic shear stress was kept constant with correction for the effects of membrane force on the measured values. The liquefaction resistance was found to increase with the decrease in the confining stress, while correction for the effects of membrane penetration did not significantly affect this tendency. Analyses of the test results revealed that the liquefaction properties were affected by the mobilization of shear resistance under extremely low effective stress states and the stress level-dependency of shear modulus that was normalized by the confining stress. Finally, by introducing a concept of apparent increase in the effective mean principal stress, a simplified procedure to estimate the liquefaction resistance under low confining stresses was proposed.
