Saturation effects on the undrained shear behavior of loess: application to static liquefaction

This study investigates the critical moisture level required to trigger flow failure in silty loess, with the aim of enhancing liquefaction risk management. Determining appropriate saturation (Sr) criteria is essential for understanding the mechanics of loess flow failure. Silty loess may experience pore structural collapse and saturation shift during wetting and loading processes. To assess the influence of saturation on undrained hydraulic and mechanical behavior, isotropically consolidated undrained tests were performed on natural intact loose loess under varing saturation levels, indicated by Skempton coefficient B (ranging from 0.65 to 0.95). The results reveal that liquefaction resistance declines as B-value increases. Moreover, hydro-mechanical indices, including characteristic strain $${\varepsilon }_{ap}$$ ε ap , the undrained shear strength ratio Su/ $$p_{0} ^{\prime}$$ p 0 ′ , liquefaction potential index (LPI), and maximum pore pressure ratio rumax at the critical state, exhibit discontinuities or twists when B is between 0.8 and 0.85. This suggests that the threshold for the onset of static liquefaction in silty loess is within this range, aligning closely with the air entry value (SAEV) derived from the soil–water characteristic curve (SWCC) and the B–Sr curve. We propose standardizing the saturation criteria for silty loose loess to B-value between 0.8 and 0.85.