AbstractTraditional theoretical and experimental investigations of the mechanical behavior of granular media such as sand are restricted by the limited quantitative information about what actually happens internally. The discrete element method (DEM) was developed as a technique to examine the micromechanics of granular media for this purpose. In this paper, a new microscopic parameter in terms of redundancy factor is proposed to describe liquefaction for sand, and the evolution of redundancy factor is provided using DEM simulations under undrained conventional triaxial conditions. It is demonstrated that the phase transition dividing the soild-like behavior and liquid-like behavior is associated with a redundancy factor of 1, which corresponds to an average coordination number slightly above 4.