Using a meshless method to investigate the effects of confining pressure on the hydraulic fracturing processes of hydraulic tunnels.

Abstract

To reveal the dynamic evolution mechanism of hydraulic fracturing in hydraulic tunnels under different confining pressures and overcome the limitations of traditional tests and numerical methods in simulating complex crack propagation and multi-field coupling problems, a meshless numerical simulation framework suitable for hydraulic fracturing in hydraulic tunnels is constructed using the Smoothed Particle Hydrodynamics (SPH) method. Through the definition of the contact force transmission mechanism between matrix particles and water particles as well as the particle failure criterion, the dynamic tracking of the entire process of crack initiation, propagation, and penetration is realized. Multiple schemes with confining pressure ratios λ (σ_x/σ_y) of 0.2, 0.4, 0.6, and 0.8 are set up to systematically investigate the influence of confining pressure ratio on the hydraulic fracturing process. The research results show that the SPH method can effectively reproduce the evolution of complex crack networks in hydraulic fracturing and overcome the defects of traditional grid methods in dealing with discontinuity problems. The confining pressure ratio is a key parameter regulating the crack morphology. With the increase of λ, the crack network gradually transforms from a dendritic shape (λ = 0.2) to a m-shaped pattern (λ = 0.4) and a snowflake-like structure (λ = 0.6, 0.8). The increase in the proportion of horizontal stress significantly promotes the lateral propagation of secondary cracks. A common mechanism of "corner stress concentration dominating crack initiation" exists under different confining pressure ratios. Moreover, with the simultaneous increase of σ_x and σ_y, the degree of stress concentration decreases, and the crack propagation rate slows down. This study provides theoretical support and quantitative tools for the analysis of water-mechanics coupling disaster-causing mechanisms and engineering disaster prevention and control in hydraulic tunnels.