Abstract:

To enhance the predictive precision of rock strength using the true-triaxial Hoek-Brown criterion and to further broaden its potential applications in deep underground engineering, this study proposes an improved true-triaxial strength criterion. This criterion integrates both the critical confining pressure effect observed under conventional triaxial conditions and the intermediate principal stress effect inherent in true-triaxial stress states. On the basis of the modified Hoek-Brown criterion considering the critical confining pressure, the intermediate principal stress coefficient is introduced via the weighted averaging method, and the stress substitution method is adopted to establish the improved true-triaxial strength criterion composed of combined curved segments and linear segments. The research results show that when the intermediate principal stress (σ₂) exceeds its critical value, the relationship between the parameters σ₁ and σ₂ changes from nonlinear to linear, and the intermediate principal stress becomes the dominant factor to control the rock strength. A comparative analysis conducted against the Priest criterion, Zhang-Zhu criterion and Li criterion reveals that the proposed improved criterion attains the lowest average value of mean absolute error (MAE) of 4.946 5% in the strength prediction of ten types of rocks. It is verified that the novel criterion can remarkably enhance the prediction precision of rock strength under complex stress conditions. Moreover, the established criterion demonstrates favorable applicability and exhibits promising potential for engineering applications in the strength assessment of deep rock mass projects and the quantitative determination of the critical effect exerted by the intermediate principal stress.

Key words: critical confining pressure effect, intermediate principal stress effect, true triaxial Hoek-Brown criterion, rock strength, mean absolute error