Energy characteristics during the progressive shear failure of rock joints and brittleness evaluation

The energy-driven progressive brittle shear failure of rock joints is a key mechanism behind deep engineering disasters such as joint-induced rockbursts and engineering earthquakes. To investigate the energy evolution mechanisms and disaster proneness, monotonic and stepwise loading-unloading tests were performed on regular dentate joints under constant normal stiffness boundary conditions. Results indicate a transition in damage mechanism from climbing wear of low-inclination asperities to brittle rupture of high-inclination ones, accompanied by a marked decrease in irreversible displacement. Energy analysis reveals a strong linear relationship between pre-peak elastic energy density and both input energy density and shear stress squared. The post-peak elastic energy release rate ( η ), and the self-sustaining instability coefficient ( μ ) increase with joint undulation. A dimensionless brittleness index ( BI ) integrating the complete energy conversion and release process was proposed to quantify the energy balanced budget. The highly undulated joint R 4 showed the most pronounced brittleness and instability intensity, with the highest BI value of 0.697, along with η = 0.774 and μ = 0.611 . This study provides deeper insight into the understanding of the disaster-inducing proneness and stability assessment in jointed rock mass.