Experimental study on the mechanical of deep-buried soft rock under triaxial loading and unloading

Abstract

This study investigated the changes in the mechanical properties of the soft surrounding rocks in the deep-buried cavern during the excavation unloading process. The argillaceous sandstone in the main diversion tunnel of the Panlong pumped storage power station in Chongqing is the case study. Triaxial loading and unloading tests were carried out to discuss rock samples’ strength, deformation, and failure characteristics under different stress paths. The results showed that the soft rock’s peak strength, strain, deformation modulus, and cohesion in the triaxial loading test are greater than those of the unloading test. During the loading process, the soft rock’s elastic modulus and deformation modulus increase with the confining pressure. However, a more significant increase was observed in the deformation modulus. Under loading conditions, the soft rock suffers from double-shearing shear failure with a failure angle of about 65°. Under unloading conditions, single-shearing shear failure is dominant and accompanied by tensile failure. There are many tension cracks on the surface of the rock sample under low confining pressure, and lateral expansion occurs under high confining pressure.