A rock brittleness index based on the postpeak energy release rate and damage surface characteristics for brittle hard rock

Rock brittleness is an important mechanical property that describes damage of rocks. This study proposes a rock brittleness evaluation index considering the postpeak energy release rate and damage surface morphology parameters. The accuracy of the brittleness index is verified by the triaxial direct shear test of granite under different confining pressures. By comparing the accuracy and precision of eight existing brittleness evaluation indexes, the results show that BI PERF can more accurately evaluate the postpeak brittleness of granite under direct shear conditions. The findings confirm that the brittleness of Beishan granite decreases with increasing confining pressure, with BI PERF declining by 23.5% as the confining pressure increases from 2 to 22 MPa. Similarly, brittleness decreases with increasing temperature, with BI PERF decreasing by 20.16% as the temperature increases from 30 to 110°C. The research findings provide significant guidance for evaluating the stability of engineering rock masses and predicting geological hazard risks.