Failure behaviors of granitic rocks induced by point/local loads under biaxial compression stress state

It is acknowledged that most surrounding rocks of underground engineering are subjected to biaxial static stresses and various dynamic fatigue loads. In most cases, the dynamic loads have a point or local acting area, which affect the failure properties of rocks greatly. To reveal the failure mechanism of rocks under the combined effects of biaxial static stress and dynamic fatigue loads, a series of biaxial compression tests and point/local fatigue-induced failure tests on cubic granite specimens with a side length of 50 mm were conducted out. In the biaxial compression tests (the maximum principal stress sigma(1) > the intermediate principal stress sigma(2) > the minimum principal stress sigma(3) = 0), the biaxial compressive strength of granite presents a monotonous increasing trend with the sigma(2) increasing from 0 to 40 MPa, while the increasing rate of biaxial compressive strength increases firstly and then decreases with the increase in sigma(2). The rock failure induced by point/local fatigue loads with 5 kHz frequency was analyzed in this study. It shows that the fatigue life of granite is much shorter than that in the traditional full-section fatigue tests, which increases with the increase in sigma(2) and decreases as the upper level of the fatigue stress or predefined stress of sigma(1) increase. From the acoustic emission properties, the failure of rocks under biaxial confinements induced by point/local static or fatigue loads are mainly because of tensile cracks. Meanwhile, the application of a disturbance bar with a smaller cross-sectional area induces rock broken more quickly. It seems that the following measures can be used to improve rock breakage efficiency: increasing the predefined stress in the breaking direction, reducing the lateral confinement, using the breaking bar with a small cross-sectional area, and changing the static loading into the dynamic loading of the breaking force.

Automated summary

This study reveals the failure mechanism of rocks under the combined effects of biaxial static stress and dynamic fatigue loads through a series of tests. The biaxial compressive strength of granite increases monotonically with the increase of the intermediate principal stress. The fatigue life of granite is shorter than that in traditional full-section fatigue tests and it increases with the increase of the intermediate principal stress. The failure of rocks under biaxial confinements induced by point/local static or fatigue loads is mainly due to tensile cracks.