Abstract: How to evaluate the stress state in an engineering rock mass is one of the most fundamental problems that all the underground structure designers have to be faced with. Evaluating the stress state needs considering both sides of this problem, rock mass strength and stresses in the rock mass. The evaluation results reflect the deformation and failure responses of surrounding rock masses under the actions of secondary stresses when they observe a rock mass strength criterion. Most research findings in the past on high stress criterion are summarized to infer a general deformation and failure law for underground structures under the impact of high stresses. By analyzing the relation between the rock mass strength and the rock mass rating parameters and the uniaxial compressive strength (UCS) of rock specimens according to the Hoek-Brown criterion, a conclusion is come to that the ratio of the rock mass strength to the UCS should be less than 0.5 in most situations. With respect to the new high stress criterion put forward by the authors in 2009, basic relationships at different frictional coefficients between the rock mass strength and the maximum principal stresses present in the rock mass are obtained by analyzing the Hoek-Brown strength criterion and rock friction theory comprehensively; based on this relationship and the redistribution law of secondary stress field around an underground opening, the new high stress evaluation criterion is verified from the aspect of rock mechanics. The application of this criterion to some engineering practices all over the world proves that this new high stress evaluation criterion works very well. Finally, the authors put forward the general rules and procedures for how to use this new criterion, and some concerns that should be careful of.

Key words: high stresses, strength criterion, ratio of strength to stress, in-situ stresses