Abstract: In order to study the crack initiation mechanism of rock under hydraulic coupling, hydraulic coupling triaxial test and acoustic emission test were carried out on Xiluodu basalt. The test results show that the peak strength of basalt increases with the increase of confining pressure, showing a typical hard brittle behavior. When the confining pressure remains unchanged, the peak strength decreases gradually with the increase of initial water pressure, and the hard brittleness decreases at the same time. The acoustic emission test results show that the crack initiation of basalt under hydraulic coupling is tensile failure, which is mainly tensile failure and supplemented by shear failure in the stable crack propagation stage, and these failures mainly occur in the middle of the rock. In the post peak stage of unstable crack propagation, the rock fracture is mainly characterized by shear failure. Based on the understanding of crack initiation mechanism, the critical hydraulic failure criterion of rock crack initiation under hydraulic coupling condition is derived with the help of the single circular hole theory, which is then introduced into the numerical simulation of basalt hydraulic coupling triaxial test. The hydraulic coupling failure process and water pressure distribution law of basalt are analyzed. The rationality of the critical hydraulic failure criterion is verified, and it has a good reference value for the study of rock failure process under hydraulic coupling.

Key words: hydraulic coupling, basalt, acoustic emission, critical water pressure, failure criterion