Research on the mechanical characteristics and precursor patterns of failure in sandstone under different water contents

To address the challenges posed by complex deep underground environments, it is of significant practical importance to study the impact of water on the properties of surrounding rock. This paper conducts microstructural and mechanical experiments on sandstone specimens from the sandstone formations of the Chengjiao coal mine, exploring the mechanical properties and precursor patterns of failure in sandstone with different water contents. The results signify the following: The water absorption process of the rock specimens can be categorized into three stages. The uniaxial compressive strength of the sandstone specimens shows a linear inverse association with the water content. Combined with SEM observations, it can be concluded that clay mineral swelling, loosening of interparticle bonding, and partial dissolution of mineral particles contribute to the strength softening after water absorption. The AE signals of the rock samples mainly occur during the plastic deformation stage, signifying the development and propagation of microcracks during this stage. The AE count sequence exhibits distinct multifractal features. The phenomenon of sudden drop in multifractal parameter Delta f(alpha) and rapid increase in Delta alpha can serve as precursors to sandstone failure, and the warning time initially rose with the raise in water content before subsequently declining. The macroscopic failure cracks in the sandstone are predominantly a combination of shear and tensile fractures, with shear fractures accounting for approximately 70% of the total. With elevated water content, the percentage of shear fractures in the specimens initially increases and then decreases, with the degree of damage gradually decreasing.