Study on mechanical properties and fracture surface characteristics of argillaceous sandstone under different stress paths

To study the differences in mechanical properties and failure characteristics of underground chambers surrounding rock under different stress conditions, triaxial loading and unloading tests were carried out on argillaceous sandstone. The three-dimensional topography parameters of the fracture surface were obtained by using high-precision three-dimensional topography scanning technology, including six height characteristic parameters and two texture parameters. Compared with the triaxial loading test, the strength, peak strain and residual strength of argillaceous sandstone with the same confining pressure under unloading conditions all decrease, and the stress–strain curve changes from ductility to brittleness. The Mogi–Coulomb strength criterion can better describe the strength properties of argillaceous sandstones than the Mohr–Coulomb and Drucker–Prager strength criteria. Under the unloading condition, the cohesion c decreased by 30.87% and the internal friction angle φ increased by 30.87% compared with the loading condition. The tensile cracks perpendicular to the unloading direction is formed during unloading, resulting in large roughness, dispersion and fluctuation of fracture surface.