Shear Behaviors of Soil Under Freeze–Thaw Cycles: Experiments and Discrete Element Simulation

Canal slope failures caused by freeze–thaw action frequently occur in cold regions. Most of the failures are closely associated with shear behaviors of slope soil. In this study, the shear behaviors of canal soil under freeze–thaw cycles (FTCs) are measured and analyzed. Then, a discrete element model is constructed and its accuracy is verified by experimental data. The mesostructural evolution of soil under different FTCs during the shear process is simulated. The results show that the FTCs lead to a significant degradation of peak stress and cohesive force of the soil. After five FTCs, the cohesive force decreases to 28.99 kPa. The internal friction angle shows a slight decreasing trend as the number of FTCs increases, and its value ranges from 9° to 16°. The simulated peak values agree well with the experimental data, with a maximum mean bias error (MBE) within 2.27% for samples when the FTCs range from zero to five. FTCs can promote the continuous propagation of microcracks within the soil, and the number of tensile cracks is greater than that of shear cracks. After five FTCs, the numbers of shear cracks, tensile cracks and total microcracks reach 1798, 6779, and 8577, respectively. The FTCs disrupt the original network of contact force chains, causing the number of particle contacts to decrease initially and then increase. The displacement of soil particles and the extent of the shear band during shearing increase significantly after FTCs. The findings of this study reveal the mesoscopic mechanism of shear degradation of canal slope soil under freeze–thaw conditions, and provide experimental evidence and numerical analysis methods for the stability evaluation of canal slopes in cold regions.