Study on stress relaxation and acoustic emission of fractured rocks with different fissure inclinations

In deep underground engineering, the rheological properties of fractured rock are prominent. This paper investigates the stress relaxation characteristics and damage development in rocks with different fracture inclinations. Uniaxial step-by-step loading relaxation and acoustic emission tests were carried out on five rock samples with intact and prefabricated fissure inclinations of 30 degrees, 45 degrees, 60 degrees and 75 degrees. The test results show that the stress relaxation is divided into a fast relaxation stage and a slow relaxation stage. The duration of the fast relaxation stage is relatively short, with significant time effect. The increase of stress relaxation before reaching the peak is negatively correlated with the fissure angle, and the fissure will have a serious effect on the relaxation of the rock. The initial relaxation rate increases and then decreases with the increase of the strain level, and the maximum initial stress relaxation rate occurs at the peak strain, which is 45 degrees, 75 degrees, 30 degrees,60 degrees fractured rock and intact rock from the largest to the smallest. The acoustic emission events are mainly concentrated in the loading section and the rapid stress relaxation stage, and there are sporadic acoustic emissions in the slow relaxation stage. The final cumulative AE counts were 45 degrees, 30 degrees, 75 degrees, and 60 degrees fractured rock in descending order, which is a solid fit with the damage results.