Experimental and Numerical Simulation Study on the Influence of Gaseous Water on the Mechanical Properties of Red-Layer Mudstone in Central Sichuan

Water has a significant effect on the mechanical properties of rocks, especially those containing expansive clay minerals. The red-layer mudstone contains various clay minerals, which easily collapse in water. To further study the effect of water on the mechanical properties of red-layer mudstone, uniaxial and triaxial tests were first conducted on samples with different moisture contents, prepared using the gaseous moisture absorption method in the laboratory. The effect of water on the fracture mode, mechanical behaviour and strength of the red-layer mudstone was subsequently studied at a heterogeneous particle scale using the three-dimensional numerical simulation program 3DEC. The results demonstrated that the strengths of the mudstone samples (uniaxial compressive and triaxial compressive strengths) decreased with an increase in the moisture content. As the moisture content increased, the elastic modulus and residual strength of mudstone decreased. The Mohr–Coulomb strength envelope under different moisture contents was constructed, and it was found that with an increase in the moisture content, the cohesion of the mudstone decreased significantly and the internal friction angle remained almost unchanged. This numerical model accurately demonstrates the damage evolution (tensile and shear cracks) at a heterogeneous particle scale. Simultaneously, the macroscopic mechanical behaviour, strength and failure patterns observed in the laboratory were reproduced. Finally, this study reveals the weakening mechanism of water on the mechanical properties of red-layer mudstone at macroscopic and Ümesoscopic scales.