Research on Strength Softening Characteristics and Microscopic Mechanism of Sandstone After Absorbing Water Available to Purchase

The deformation of the surrounding rock in roadways occurs because of the coupling effect of water and rock, which decreases the strength of the surrounding rock. The microscopic pore structure in the rock mass develops through and develops into microcracks, which further the rock mass strength. Based on the rock mass strength reduce observation, this article selects Shandong Wanfu coal mine sandstone samples, based on XRD mineral composition and scanning electron microscopy testing, using nuclear magnetic resonance (NMR) and 2,000 kN rock single triaxial rock mechanics experimental equipment to perform NMR experiments and uniaxial compression tests under different water content. Quantitatively study the pore structure and strength change law of water to rock. The experimental results show that with the increase in water absorption time, the water absorption law of sandstone has three stages: accelerated water absorption, decelerated water absorption, and uniform water absorption. The microscopic pore structure of sandstone is gradually filled with water molecules. The water molecules first occupy the micropores, then the mesopores, and finally the macropores. After reaching the saturation state, the micropores account for 51.87%, the mesopores account for 42.76%, and the macropores account for 5.37%. Because sandstone contains hydrophilic iron dolomite and clay minerals, it dissolves and adsorbs hydrophilic minerals after encountering water. The micropores gradually decrease, the mesopores increase, and the macropores do not change. It can be seen from the mechanical strength of rock samples with various water contents that the dry state has the highest mechanical strength, with a strength of 171.58 MPa, a saturated state with the lowest mechanical strength, with a strength of 91.78 MPa, and a softening coefficient of 0.53. The surrounding rock strength is relatively unstable because the pore water pressure increases after the surrounding rock interacts with water. The increased pressure reduces the compressive stress between the particles, decreasing the strength of the surrounding rock.