Study on the deterioration characteristics and mechanism of physical and mechanical properties of natural gypsum rock under freeze–thaw action

Abstract

The physical and mechanical properties, microstructure degradation characteristics, and damage mechanism of natural gypsum rock under 15, 30, and 45 freeze–thaw cycles were studied by using a self-developed program-controlled freeze–thaw experimental device. The results show that compared with natural gypsum, with the increase in freeze–thaw cycles, the mass of the sample increases first and then decreases, Poisson's ratio increases, the density decreases, and the longitudinal wave velocity, the uniaxial compressive strength, and the elastic modulus decrease. Indexes decrease greatly in the early stage of freeze–thaw and slowdown in the later stage. With the increase in freeze–thaw cycles, the slope of the pre-peak stage of the stress–strain curve decreases, the compaction stage is significantly prolonged, and the brittleness of the post-peak failure process decreases. Failure cracks of the specimens after freeze–thaw cycles are mainly inclined shear failure and axial tensile cracks. The analysis shows that the freeze–thaw damage of gypsum rock is caused by the superposition and mutual promotion of water-rock softening and pore frost heave. The specific performance is the damage of crystal particles and the loose pore structure at the mesoscale. On this basis, the cracks gradually develop and expand, which is consistent with the macroscopic test results of the sample. The research results have reference significance for the construction scheme design and frost damage prevention of gypsum surrounding rock tunnels in cold regions.