Splitting characteristics of sandstone under the influence of water saturation and its mechanism of water rock interaction

The water saturation and distribution of rocks affect the roughness of the fracture surface, which in turn determines the seepage performance and friction effect of the fracture surface. It is crucial for analyzing the stability of the surrounding rock of the roadway and the effect of hydraulic fracturing induced permeability enhancement. In this paper, nuclear magnetic resonance analysis and Brazilian splitting experiments are performed on sandstones with different saturations(0, 25%, 50%, 75% and 100%). Three-dimensional morphology scanning of the rock sample splitting surface are also conducted. The effect of saturation on the splitting characteristics of sandstones was studied. The results show that:(1) From dry to saturated, the tensile strength of rock sample decreased from 3.05 MPa to 0.98 MPa, which conforms to the characteristics of Exponential function. Rock hardness decreased by 56.6% from dry to saturated. Plasticity enhances in highly saturated sandstone. (2) Splitting surface fractal dimension increases logarithmically with saturation. With saturation increasing, the mean value of joint roughness coefficient(JRC) increases from 5.598 to 13.306. The unsaturated JRC exhibits significant discrete. (3) The splitting surface of sandstone with different saturations was quantified using statistical principles. It is found that the roughness height, slope mean and standard deviation increase with saturation, while the slope direction gradually tends to be concentrated at 270°from a uniform distribution in drying. The increase in saturation promotes an increase in vertical fractures, ultimately leading to a rougher splitting surface. (4) NMR analysis shows that with water saturation increasing, water is transported from the periphery to the interior of the rock sample, and the pore wetting within the rock samples gradually increases. As the saturation increases from 25% to 100%, the wetting ratio of large and medium pores and microcracks inside the rock sample increases from 3% to 17%, which promotes the formation of weak structures in rock samples. It causes the transgranular cracks gradually evolve into intergranular cracks in splitting test, resulting in a coarser macroscopic appearance of the splitting surface. © 2024 Academia Sinica. All rights reserved.