Quantification of dilatancy during undrained cyclic loading and liquefaction

The dilatancy characteristics of sand at liquefaction state is investigated using a method proposed to quantify dilatancy during undrained cyclic loading in discrete-element numerical tests. The method utilizes constant strain increment ratio dεv/|dγ| probes to gauge dilatancy at designated states. Undrained cyclic biaxial 2D DEM numerical tests are conducted and analyzed using the dilatancy quantification method. The measured dilatancy during undrained cyclic loading before initial liquefaction shows good agreement with current understanding of dilatancy-stress ratio relationship of sand, confirming the method’s effectiveness. The dilatancy characteristics of sand at liquefaction state during undrained cyclic loading is quantitatively assessed in detail. A contraction potential is discovered to exist for sand at liquefaction state, which causes large but limited shear strain to be generated at zero effective stress, explaining the physical basis of the well documented post-liquefaction shear strain phenomenon. A unique correlation is found between the fabric entity Mean Neighboring Particle Distance, dilatancy potential, and post-liquefaction shear strain. The new findings of the contraction potential at liquefaction state bridges the gap between current understanding of micromechanical fabric evolution and macroscale post-liquefaction shear deformation.