Quantitative characterization and applicability analysis of critical confining pressure for rock brittle-ductile transition

The critical confining pressure for rock brittle-ductile transition is a key parameter in stability analysis and disaster prediction of deep engineering rock masses. To improve the accuracy of predicting critical confining pressure, an analytical expression for criti-cal confining pressure is established, which includes the uniaxial compressive strength σc, rock characteristic parameter m, and critical deviatoric stress ratio ζ. The analytical expression of the critical confining pressure is embedded into the improved Hoek-Brown criterion, and its rationality along with the parameter values is validated by employing a fitting method that combined the single parameter exhaustive search and the three-parameter global optimization algorithms. The results show that the deter-mined critical confining pressure, corresponding to the optimal ζ value obtained by the fitting method, can better aligns with the strength evolution laws from brittle to ductile stages. The comparison with traditional characterization methods shows that there is no fixed multiplicative relationship between the analytical expression and the uniaxial compressive strength. The average for mean absolute percentage error (MAPE) of the I-H-B-I criterion corresponding the analytical expression for predicting rock strength is only 1.0216%, and the error fluctuation range is the smallest, indicating that this quantitative characterization method demonstrates better applicability.