Parameters in Hoek-Brown's failure criterion considering intermediate principal stress of rock

The accurately establishing rock strength criteria is very important for stability analysis of the deep underground engineering. Using Hoek-Brown failure criterion for rock consideration of the intermediate principal stress, σ2+σ3 as a independent variable and σ1-σ3 as a variable, the seven group tests data on true triaxial compression strength for Dolomite, Limestone, Trachyte, Sandstone, Shale, Marble and Amphibolite were analyzed with multi-fitting approximation method. Based on the physics features of the parameters in Hoek-Brown criteria (σ1-σ3=σc [m(σ2+σ3)/ (2σc)+s]n), the reasonable parameter values and computational formula were presented. The analysis results show that for high stress state at stress-strength ratio κ from 1.5 to 8, the Hoek-Brown failure criterion for rock consideration of the intermediate principal stress is in accordance with the seven group tests results, where parameters n, s and m can approximatively equal to 0.4, 1 and 1.5κ1.8 respectively.