"STRENGTH & STRESS" COUPLING CRITERION AND ITS GRADING STANDARD FOR HIGH GEOSTRESS

The construction of many underground projects can be in high geostress environment,and the initial geostress is the precondition and dominate factor for deformation and failure of underground surrounding rock. The term and concept of "high geostress" are closely related to the abnormal failure of surrounding rock in underground engineering and belong to the engineering concept category. The failure of surrounding rock attributed to high geostress is becoming increasingly significant with increasing burial depth of underground projects,which seriously influences the stability of engineering projects. Although various quantitative classification criteria have been proposed,they are mostly established in the form of rock strength to geostress ratio,without fully considering the absolute magnitude and coupling relationship between rock strength and geostress. In this paper,a "strength & stress" coupling criterion and its quantitative grading standard for high geostress rock failure are proposed via discussing the existing classification criteria,collecting the related engineering cases,and analyzing the failure progress of high geostress rock. This coupling criterion is expressed by 3 boundary lines considering the saturated rock uniaxial compressive strength R_c and the initial maximum principal stress σ₁. The area enclosed by the boundary lines represents the high geostress zone,and that outside the boundary lines represents the low geostress zone. The coupling criterion is characterized by considering both the absolute boundary conditions of R_c and σ₁,as well as their coupling interval. Through an evaluation of geostress grades in 86 typical underground projects,it is found that the judgments of this two-dimensional "strength & stress" coupling criterion are favorably consistent with the in situ rock failure phenomena. Thus,this criterion can be applied to the practical underground engineering. Moreover,the rating standards of high geostress zone of this "strength & stress" coupling criterion can better identify the failure intensity of surrounding rock,which can provide a reference for the prevention of engineering disasters.