Abstract: As one of the most widely-used rock strength criteria, Hoek-Brown criterion mainly suffers two limitations. Firstly, the triaxial strength results predicted by Hoek-Brown criterion at high value of confining pressure do not agree well with experimental data. Secondly, the effect of intermediate principal stress to rock true triaxial strength is ignored by the criterion. In the present study, to overcome the limitations, Hoek-Brown strength criterion is modified by employing Barton’s critical confining pressure and Singh’s treatment of intermediate principal stress. The applicability of the modified criterion has been verified by its application to a large number of intact rocks experiment data. The analyzing result shows that the strength predicted by the two criteria are basically consistent when confining pressure is under critical confining pressure; otherwise the modified Hoek-Brown criterion agrees better with experimental data. Under the condition of true triaxial test, the average error between modified Hoek-Brown criterion considered intermediate principal stress and experimental data is the least. Thus,the modified Hoek-Brown criterion is more suitable to predict triaxial strength of intact rocks.

Key words: intact rock；Hoek-Brown strength criterion；triaxial, critical confining pressure； intermediate principal stress