Abstract: The estimation method of rock mechanic parameters based on Hoek-Brown strength criterion could well reflect the nonlinear failure characteristics by taking into account multiple factors such as rock structure, rock block strength, rock mass stress state, etc. With the deep marbles at Jinping project as a research case, the intactness coefficient K_V of rock mass is introduced to improving the determination of GSI (geological strength index) value of deep rock mass, and the applicability of this estimation method to deep rock mass is analyzed in detail. Results indicate that the Hoek-Brown strength criterion is feasible in estimating the mechanics parameters of deep rock mass as the four parameters in Hoek-Brown strength criterion are independent and have no correlation with confining pressure state. The intactness coefficient K_V of rock mass enhances the objectivity of determining GSI value as it reflects the discontinuities development in rock mass and the excavation disturbance. It is appropriate to calculate parameter σ_ci and m_i according to indoor triaxial test results. The envelope curves of Jinping marbles obtained by the method are apparently nonlinear. Under high confining pressure state (15 MPa<σ₃<40 MPa), internal friction angle of Jinping marbles decreases by 32%, while cohesion is 3 times that under low confining pressure state.

Key words: deep rock mass, Hoek-Brown strength criterion, GSI, intactness of rock mass, mechanics parameters