DEM modeling of the effect of gravity on the onset and post-liquefaction characteristics in bi-axial test condition

抄録

The concern regarding the overestimation of liquefaction resistance in granular materials arises from the challenge of achieving a zero effective stress state in laboratory element tests. The influence of particle self-weight due to the gravity effect, is considered a significant contributing factor to the non-zero effective stress issue. To investigate the impact of gravity on liquefaction behavior, this study employed the discrete element method (DEM) to conduct a series of bi-axial loading simulations. A single layer of spherical particles was initially consolidated under normal gravity (1g) condition at a stress level of 100 kPa. Subsequently, constant-volume cyclic loading tests were performed at varying gravity levels ranging from 0g to 1g, with a cyclic deviator stress of 60 kPa. The findings demonstrate the substantial role of gravity in liquefaction behavior. Lower gravity conditions exhibited reduced stiffness, increased contractive behavior, and lower resistance to liquefaction. In the absence of gravity, specimens with initially highly mobile particles experienced a temporary loss of inter-particle contacts, resulting in a complete absence of frictional interactions at the zero effective stress state. This highlights vulnerability to liquefaction onset, significant accumulation of strain during liquefaction, and diminished resistance in the post-liquefaction stage. Conversely, the presence of gravitational forces enabled the development of frictional interactions between particles, even during liquefaction. This gradually evolving deformation process exhibited a lower likelihood of liquefaction and higher resistance in the post-liquefaction stage under higher gravity conditions. These findings underscore the importance of considering the potential influence of gravity in laboratory-based assessments of liquefaction resistance of soil.