Cyclic behavior of saturated soft clay under stress path with bidirectional shear stresses

Under seismic loading, soil layers experience multidirectional cyclic shear stresses with different amplitudes and frequencies. Therefore, the deformation behavior of soft clay under complex stress paths is practically relevant. In this study, cyclic tests are performed on normally consolidated soft clay. To simulate the situation induced by seismic load, the complex figure-eight-shaped stress path is realized by applying shear stresses in two directions simultaneously. Under the figure-eight-shaped shear stress path, the cyclic strain, cyclic modulus, and cyclic strength of soft clay are found to be significantly dependent on the CSR (cyclic shear stress ratio) and the bidirectional shear frequencies. With an increase in the CSR and a decrease in the shear frequency, the dynamic shear modulus decreases and cyclic strain accumulation increases with an increasing number of cycles. Based on the test results, an empirical formula was presented to predict the cyclic strength under different shear frequencies.