DEM analysis of macro- and micro-mechanical behaviors of cemented sand subjected to undrained cyclic loading

Natural or artificial cementation formed between sand particles can strengthen the liquefaction resistance of sand. Hence, it is significant to investigate the dynamic behavior of cemented sand at the macro- and micro-scale. By introducing an existing three-dimensional (3-D) complete bond contact model into a 3-D distinct element method (DEM) code, a series of undrained cyclic triaxial shear tests on the cemented sand are simulated, where the effects of cementation and cyclic stress ratio are studied. The results show that the inter-particle cementation can restrain the development of axial strain and pore pressure, and increase the liquefaction resistance. In addition, there is an exponential relationship between the cyclic stress ratio and the number of cycles to trigger the initial liquefaction. These findings confirm the reliability of the DEM simulation in this study. When the value of cyclic stress ratio is relatively small, within the cemented specimen with given degree of cementation, a very small amount of bonds break, the mechanical coordination number remains almost unchanged, and the input work is mainly used to increase the elastic energy at the particle contacts and bond contacts. For the cemented sand before the initial liquefaction, as the cyclic stress ratio increases, the inter-particle bonds break more intensely, the mechanical coordination number declines faster. Likewise, as the cyclic stress ratio increases, the elastic energy at the particle and bond contacts tends to zero faster, and the dissipated energy reaches the maximum value in a shorter period of time. In addition, the contact normal orientation tends to be isotropic more rapidly.