Abstract:The underground rock after failure forms cracked rock mass in a certain area,which represents great structural effect under effective support,namely,it has the capacity of load-carrying and resisting deformation. During the process of resisting the outer load or deformation,the cracked rock mass shows the stress hardening characteristic. Under outer-loading,the rock blocks within the cracked rock mass produce re-fracture and the degradation of rock mechanical behavior. The evolution of stress state and mechanical behavior of cracked rock mass when bearing outer load are determined by the integral mechanical performance of cracked rock mass,the stress state of hoop constraint and the characteristics of initial failure surface. When re-loaded on cracked rock mass,both the direction and magnitude of principal stress on the failure surface change gradually and the direction of principal stress on failure surface is different from that of rock mass,by which the new failure surfaces form and develop sequentially. This research reflects the load-carrying properties and re-fracturing process of cracked rock mass,which is very significant for study of stability of deep underground engineering.