Undrained cyclic loading behavior of cemented sand in hollow torsional shear tests considering the minor principal stress

In the seismic design of nuclear power plants in Japan, a liquefaction evaluation is required from a conservative standpoint even for cemented Pleistocene sand, which is normally considered to be non-liquefiable. However, research on the undrained cyclic loading behavior of cemented sand under simple shear conditions has been limited. Therefore, hollow torsional shear tests were performed in this study on artificially cemented sand at various degrees of cementation to investigate its behavior under undrained cyclic loading, especially with respect to the minor principal stress. The test results showed that weak cementation led to the deterioration of the behavior under undrained cyclic loading, and that the excess pore water pressure ratio exceeded 95%. However, strong cementation led to a decrease in effective stress under undrained cyclic loading. The minor principal stress became negative and resulted in failure under the combined effect of tensile and shear stresses. Even when the excess pore water pressure ratio did not reach 95%, the shear strain increased after the minor principal stress had reached its local minimum value, eventually leading to failure. Based on these results, a new criterion for the undrained cyclic resistance of cemented sand was proposed, focusing on the local minimum value of the minor principal stress. Use of this criterion has the potential to serve as an effective method for adequately evaluating the undrained cyclic resistance of cemented sand under strong seismic ground motions.