Experimental investigation on cyclic failure criteria for marine clay based on energy method

The reasonable determination of the cyclic strength of marine clay is critical for ensuring the stability of marine structures throughout their service life. In order to study the cyclic failure criteria for the marine clay, a series of constant-volume cyclic direct simple shear tests are performed on the undisturbed saturated marine clay in the Yangtze River Estuary with different plasticity indexes (I_P) under different cyclic stress ratios (CSRs). The cyclic responses of the marine clay specimens are presented. The cyclic failure criteria are investigated by employing the energy method. The results indicate that there is a threshold cyclic stress ratio (CSR_th) in the undisturbed marine clay. When the CSR is smaller than the CSR_th, the energy dissipation per cycle (W_i) develops linearly only within a limited range that does not contribute to the cyclic failure of marine clay. However, when the CSR exceeds the CSR_th, the development curve of W_i with the number of cycles (N) shows an inflection point due to the serious damage of the soil structures. This point serves as the critical point for cyclic failure to determine the number of cycles to failure (N_f) and the double-amplitude shear strain to failure (${\gamma _{{\text{DA,f}}}}$). The CSR_th of the marine clay in the Yangtze River Estuary exhibits a power function relationship with the increasing I_P. Additionally, with the increasing CSR and I_P, both W_i and ${\gamma _{{\text{DA,f}}}}$ tend to increase, while the N_f gradually decreases. Furthermore, the data points of ${\gamma _{{\text{DA,f}}}}$/I_P^1.5 ~ CSR-CSR_th for all the tests are distributed in a narrow band, and a virtually positive linear relationship exists between the ${\gamma _{{\text{DA,f}}}}$/I_P^1.5and CSR-CSR_th. Finally, a ${\gamma _{{\text{DA,f}}}}$ evaluation method applicable to the marine clay in different seas is proposed for practical geotechnical engineering.