为改善Hoek-Brown强度准则未考虑中间主应力对岩石强度的影响，通过岩石真三轴试验结果分析了岩石强度的演化规律，引入中间主应力系数，量化分析主应力系数对岩石真三轴强度的影响，考虑Hoek-Brown强度准则中的参数和岩石应力水平间的关联性，提出了基于拉格朗日插值方法的修正岩石真三轴Hoek-Brown强度准则，分析了其空间包络特征。最后，利用7种岩石的真三轴试验数据与其它3种真三轴强度准则进行最优拟合误差分析，探讨了修正强度准则的合理性。研究结果表明：岩石强度随着最小主应力的增加逐渐增大，随着中间主应力的增加则呈现先增大后减小的变化规律，表现出显著的区间效应；修正强度准则不仅能够继承Hoek-Brown强度准则在子午面上的非线性优点，且能够表征岩石强度在应力空间中的基本特性；线性和非线性插值形式的修正强度准则空间包络面分别为非等边的六棱锥面以及能够满足拉压子午面区间连续光滑要求的圆锥面；修正强度准则能够较好地预测岩石真三轴试验强度，较为合理地反映中间主应力对岩石强度的影响；相比于线性插值形式强度准则，二次插值形式强度准则能够提高岩石强度的预测精度1.2～2.0倍；相较于其他真三轴强度准则，修正强度准则对不同硬脆性岩石的真三轴试验结果均具有良好的强度预测精度，体现了修正强度准则的适用性和可靠性。

In order to improve the Hoek-Brown strength criterion not considering the influence of intermediate principal stress on rock strength, the evolutions of rock strength were investigated according to the results of the rock true triaxial compression test. The intermediate principal stress coefficient was introduced to quantify the effect on rock strength. Considering the relationships between the parameter of the Hoek-Brown strength criterion and the rock stress levels, the modified Hoek-Brown strength criterion for the true triaxial stress was then established with the Lagrange interpolation method. The spatial envelope characteristics of the modified strength criterion were analyzed. The best-fitting errors of seven rocks with true triaxial test results were finally compared with the three other three-dimensional strength criteria to verify the rationality of the modified strength criterion. The research results indicate that the rock strength increases gradually with the increase of minimum principal stress, and increases first and then decreases with the increase of intermediate principal stress, which presents a significant interval effect. The modified strength criterion not only has the advantage of the Hoek-Brown strength criterion in the nonlinear characteristics of the meridian plane but also describes the basic characteristics of rock strength in stress space. The spatial envelope surfaces for the modified strength criteria with the linear and quadratic interpolation are the non-equilateral hexagonal pyramidal surfaces and conical surfaces, which can meet the requirement of continuous smoothness in the tension-compression meridian plane interval. The modified strength criterion can better predict the true triaxial strength of rocks and reasonably reflect the influence of intermediate principal stress on the rock strength. The modified strength criterion with the quadratic interpolation improves the prediction accuracy of rock strength by about 1.2 to 2.0 times compared to the criterion with linear interpolation. The modified strength criterion has good agreement with the true triaxial test results of different hard and brittle rocks compared with other true triaxial strength criteria, which shows the applicability and reliability of the modified strength criterion.