Mechanical properties and dilatancy angle model of jointed hard rock under true triaxial cyclic loading and unloading

Abstract Joints play a crucial role in the stability of surrounding rock in deep underground engineering. Studying the mechanical properties and evolution laws of rocks with different joint characteristics under true triaxial stress is highly significant. This paper presents the results of a series of true triaxial cyclic loading and unloading experiments conducted on natural stiff-jointed and artificially jointed granite, where the correlation between fracture characteristics and joint inclination was investigated. It was observed that the peak strength, plastic volumetric strain, and failure mode of the jointed granite varied considerably with joint inclination. This underscores the significant influence of joint inclination on the mechanical behavior of deep granite. Building upon a comprehensive understanding of the strength characteristics and deformation evolution in jointed granite with varying inclinations, a new dilation angle model was developed, incorporating the coupling effects of plastic volumetric strain and joint inclination. A strong agreement was found between our theoretical predictions and test data, suggesting that the proposed dilation angle model can effectively describe the dilatancy characteristics of granite with joints. This study is anticipated to offer a theoretical basis for excavation and support design, as well as stability analysis of deep jointed rock masses.