Energy-based method for the failure criterion and resistance evaluation of marine clay under cyclic loading

Abstract

Energy dissipation can macroscopically synthesize the evolutions in the microstructure of the marine clay during cyclic loading. Hence an energy-based method was employed to investigate the failure criterion and cyclic resistance of marine clay. A series of constant-volume cyclic direct simple shear tests was conducted on undisturbed saturated marine clay from the Yangtze Estuary considering the effects of the plasticity index (I_P) and cyclic stress ratio (CSR). The results indicated that a threshold CSR (CSR_th) exhibiting a power function relationship with I_P exists in marine clay, which divides the cyclic response into non-failure and failure states. For failed specimens, the development of energy dissipation per cycle (W_i) with the number of cycles (N) exhibited an inflection point owing to the onset of serious damage to the soil structure. In this regard, the energy-based failure criterion was proposed by considering the inflection point as the failure point. Consequently, a model was proposed to quantify the relationships between failure energy dissipation per cycle (W_f) [or failure accumulative energy dissipation (W_af)], initial vertical effective stress, I_P, and the number of cycles to failure (N_f,E). An evaluation model capturing the correlation among CSR, I_P, and N_f,E was then established to predict the cyclic resistance, and its applicability was verified. Compared with the strain-based cyclic failure criterion, the energy-based failure criterion provides a more robust and rational approach. Finally, a failure double-amplitude shear strain (γ_DA,f) evaluation method applicable to marine clay in different seas was presented for use in practical geotechnical engineering.