Characteristics of water-rich weakly cemented sandstone erosion and dewatering disaster mitigation mechanism via computational fluid dynamics–discrete element method coupled modeling

Weakly cemented sandstone is softened by water erosion, which increases the water content and seriously reduces the bearing capacity of the surrounding rock. In this paper, a numerical model is developed based on the bond contact state of the parallel bond model, which takes into account the macroscopic strength deterioration and pore space increase caused by the microscopic disbonding effect of the weakly cemented sandstone under water erosion, and introduces it into the computational fluid dynamics–discrete element method coupled fluid-solid method. In addition, the permeability evolution equation due to particle loss under erosion was established based on the Kozeny–Carman equation considering the clay-bearing effect. The sand inrush process of weakly cemented sandstone strata under different water levels was simulated. The results show that there is a hysteresis phenomenon of sand inrush with weakly cemented sandstone strata. The evolution of the sand inrush process usually consists of four stages: the erosion stage by disbonding; the erosion stage by flushing and disbonding; the upper-stratum collapse phase; and the continuous large deformation stage. As the water level lowers, the maximum height, length, and width of the collapsed area within the strata decrease dramatically. The increment of the supporting structural force also decreases, which reduces the risk of cracking of the tunnel support structure. The results of this study can be used as a scientific basis to study the prevention and control of sand inrush disasters in tunnel construction in water-rich weakly cemented sandstone strata.