Experimental and numerical study on peak strength, coalescence and failure of rock-like materials with two folded preexisting fissures

Natural preexisting fissures are often overlapped, and these preexisting fissures greatly influence the stability of rock mass engineering; hence, it is necessary to investigate the strength and mechanical behaviour of rock materials with folded preexisting fissures. In this paper, for rock-like materials containing two folded preexisting fissures at different inclination angles and undulation angles, the folded preexisting fissures were overlapped by several preexisting fissures at the ends. The peak strength, coalescence patterns and failure modes were comprehensively investigated. It can be clearly found that the peak strength monotonically increased with increasing of the inclination angle; however, the influence of the undulation angle on the peak strength is not obvious through comparison with the inclination. Four coalescence modes can be summarized, and the failure mode can be classified into two types. By combining the crack number-strain curve and stress-strain curve, the failure process of the specimen with two folded preexisting fissures can be divided into four stages. In stage I, no cracks were generated; subsequently, some cracks were generated in stage II; however, the increment of the crack number was small. Many microcracks appear mainly in stage III and stage IV.