Abstract：In the anisotropic stress condition, the existence of the intermediate principle stress effect on the strength of rock has been verified by a large number of true triaxial tests of rock. Based on analysis of the true triaxial test data of four rock types and the polyaxial strength criterions, the relationship between the polyaxial strength and conventional triaxial strength of rock at the same intermediate principle stress coefficient was studied in this paper. The results indicated that the same function type of the polyaxial strength curves with the conventional triaxial strength curves could be obtained at the same intermediate principle stress coefficient. For the rock types of which the strength features can be described by the Mohr-Coulomb criterion, the influence on the cohesion action of the polyaxial strength of rock is remarkable. The cohesion action will increase firstly and then decrease with the growth of the intermediate principle stress coefficient which hardly influences the friction action of rock strength. The strength effect of different rock types is controlled by the corresponding angle of internal friction. The larger the internal friction angle is, the stronger this effect is. The results also indicated that the strength parameters obtained by the conventional triaxial tests can be directly applied in the polyaxial strength criterion after the intermediate principle stress effect function has been obtained. It will be of the important value for the application of polyaxial strength criterions in the stability analysis of rock engineerings lacking true triaxial test data.
2011, Vol. 32 
