Jamming analysis on the behaviours of liquefied sand and virgin sand subject to monotonic undrained shearing

It is well documented in the experimental literature that liquefied sands behave differently from virgin sands without a shearing history. In this study, undrained DEM simulations were performed on both a virgin sample and samples liquefied by cyclic loading. An identical critical state was reached regardless of liquefaction history. The fundamental mechanisms underlying the difference in the stress-strain responses between the liquefied sands and virgin sand were interpreted within the framework of jamming transition. The virgin sample was jammed throughout the simulation, characterised by a fully-percolated force transmission network of increasing resilience and mechanical stability. In contrast, the initially liquefied samples experienced an apparent phase transition from unjammed to jammed states. A fully-percolated force transmission network did not exist, and thus the unjammed samples flowed during the initial stage of loading. As loading proceeded, the force transmission network became fully percolated, and its resilience and mechanical stability developed. All of the micro-scale parameters reflecting the resilience and mechanical stability of the force transmission network reached identical values at the critical state independent of liquefaction history. Finally, a micro-scale approach based on the degree of indeterminacy was proposed to identify the four-stage post-liquefaction behaviour.