Abstract:

In order to study the influence of hydraulic coupling on the mechanical properties and permeability characteristics of sandstone, a numerical calculation method using finite difference method to discretize the seepage field and the influence of crack formation on permeability was proposed based on the particle flow dispersion element numerical calculation platform. By conducting numerical experiments on the hydraulic coupling of sandstone samples under different osmotic pressures, the following conclusions were drawn: As the ratio of water pressure to confining pressure increases, the mechanical strength and elastic modulus of sandstone samples decrease exponentially, while Poisson's ratio and permeability increase approximately linearly and exponentially, respectively. When the ratio of water pressure to confining pressure is 0.03 to 0.40, the mechanical strength of the rock samples decreases by about 0.8% to 4.8%, and the permeability increases by about 2.2% to 8.0%. When the ratio of water pressure to confining pressure is 0.40 to 0.75, the mechanical strength of rock samples decreases by about 3.9% to 20.3%, and the permeability increases by about 15.0% to 85.3%. The strong contact force chain in the samples under hydraulic coupling is mainly concentrated in the vicinity of the shear rupture slip zone, and shows the characteristics of “dendritic” structure; With the increase of osmotic pressure, the evolution curve of the number of tensile-shear cracks changes from an S-shaped growth to a stepwise growth, which is mainly dominated by tensile cracks, and the cracks are mainly distributed along the strength of the seepage velocity field throughout the rock samples; The hydraulic coupling weakened the particle cementation strength and weakened the ability of the samples to accumulate elastic strain energy, while enhancing the ability to dissipate energy at the peak stress, and the dissipation of energy within the samples and the growth of cracks were positively correlated with the permeability characteristics. The numerical calculation method proposed in this article can provide a new approach for discrete element simulation of rock hydraulic coupling effects.

Key words: hydraulic coupling, mechanical properties, penetration characteristics, destructive mode, discrete element method, finite difference method