Experimental study and particle flow code numerical simulation of crack propagation and failure characteristics of prefabricated double-fissured rock samples

Primary fissures within rock masses in underground engineering severely affect their mechanical properties. The propagation and coalescence of cracks are the key factors influencing the stability of engineering rock masses, thereby posing challenges to retaining the long-term stability of underground engineering rock masses. In this work, Brazilian splitting tests were carried out on sandstone samples with prefabricated fissures with different inclination angles. The strain field cloud map of the sample was obtained via digital speckle technology. The crack propagation evolution law, displacement field and stress field distribution characteristics of the fissured rock were studied from a microscopic perspective, and the failure mode of the sample was analysed in combination with a strain field cloud map. The results show that the mechanical parameter curve presents a “W” shape as the fissure inclination increases. The presence of fissures reduces the bearing capacity of rock samples, making the strength of fissured rock less than that of intact rock. The crack initiation position around the inclined fissure (F1) progressively transitions from the midpoint to the tip as the fissure inclination angle increases. The compressive stress and tensile stress concentration areas are primarily distributed near the fissure tip. As the fissure inclination angle increases, the maximum displacement value tends to decrease initially, followed by an increase. The rock bridge coalesces in the form of tensile cracks, and the fissure inclination angle alters the failure mode of the fissured rock.