Experimental Investigation on Mechanical Behavior of Sandstone Containing Two Non‐Coplanar Fissures Under Triaxial Monotonic and Multilevel Cyclic Loading

ABSTRACT Natural rock masses with complex fissures are frequently subjected to multilevel cyclic loading during underground engineering construction. The effect of fissure layout patterns and confining pressure on the fatigue mechanical behavior of fissured rocks remains poorly understood. Therefore, triaxial multilevel cyclic loading tests were performed on sandstone specimens containing two non‐coplanar fissures with four layout patterns. The results indicated that: (1) Fissure layout patterns dominated the characteristics of stress–strain curves and the degree of mechanical deterioration of specimens. (2) Multilevel cyclic loading altered the inherent stress fluctuation features on the stress–strain curves of fissured specimens. (3) Multilevel cyclic loading generally reduced peak strength compared with monotonic loading, while gentle–gentle type specimens exhibited strength enhancement. (4) Multilevel cyclic loading and confining pressure both promoted the transition from tensile‐dominated crack coalescence to shear‐dominated crack coalescence. These findings could provide a reference for the stability assessment of flawed rock masses under cyclic engineering disturbance.