Mechanical properties and crack evolution characteristics of fractured rock with hidden fissures

Natural defects, such as joints, structural surfaces and voids, significantly affect the mechanical properties and fracture modes of rock mass. Hidden fissures are widely distributed in magmatic rock, while their influences on the mechanical properties and the cracking mechanism are still unclear. Laboratory tests were conducted on prefabricating hidden-fissured rock-like specimens, as well as intact specimens and close-fissured specimens as a comparison. The real-time digital image correlation technology and acoustic emission monitoring technology were synchronously adopted to capture both the external and internal cracking process. The results show that the hidden fissures can weaken the uniaxial compression strength, while the deterioration effect of hidden fissures is weaker than closed fissures due to the internal cohesion among fissure internal particles. What’s more, the initiation behavior of the α = 90° hidden-fissured specimen is different from that of β = 90° closed-fissured specimen. Finally, the cracking mechanism of hidden-fissured specimens was revealed by analyzing the RA–AF relationship. The failure of the close-fissured specimens is mainly the tensile-shear mixed fracture mode, while the failure of the hidden-fissured specimens is mainly the tensile fracture mode and supplemented by the shear. The experimental results contribute to the understanding of cracking properties in hidden-fissured rock.