Simulation of Freeze–Thaw Damage and Fine Characterization of Water-Rich Sandstone Materials Based on PFC3D

This paper proposes a method for simulating freeze–thaw damage in water-rich sandstone using PFC3D (Particle Flow Code in three dimensions). Water-rich sandstone is idealized as a composite system consisting of rock particles, water particles, and three types of contact surface: rock–rock, rock–water, and water–water. The volume change in water particles is governed by temperature, unfrozen water content, and porosity. During thawing, the volume change in water particles is realized by increasing the porosity after each cycle because the expansion of water particles is reflected by pore enlargement and the accumulation of externally supplied water. The proposed approach is intended for saturated or highly water-rich sandstone under laboratory freeze–thaw conditions with external water replenishment. It represents freeze–thaw damage associated with pore water freezing expansion and porosity-controlled equivalent water replenishment, whereas ice segregation, cryogenic suction, moisture migration, and a moving freezing front are not explicitly considered. A comparison between simulation results and laboratory tests indicates that the proposed method can effectively reproduce the freeze–thaw cycling process in water-rich sandstone. The results show that the mechanical behavior of sandstone after freeze–thaw cycles, including uniaxial compressive strength and elastic modulus, deteriorates significantly. The failure mode changes from shear failure to splitting failure. Freeze–thaw cycling and subsequent uniaxial compression are dominated by tensile damage, with tensile cracks accounting for approximately 90% of the total cracks. The tensile damage rate, Rt, increases exponentially. Crack development induced by freeze–thaw cycling follows an S-shaped trend and can be divided into three stages: slow crack growth from 0 to 10 cycles, rapid crack growth from 10 to 32 cycles, and a reduced growth rate after 32 cycles. The results provide a reference for the freeze–thaw damage analysis of rocks in cold regions and numerical simulations of freeze–thaw cycling processes.