Investigation of the rock failure effect on overcoring stress relief test in deep hard rock

The failure of a rock core will result in the inaccuracy of in situ stress tests when the overcoring stress relief method is used in deep rock engineering. To investigate the stress test error caused by rock failure, stress test simulations under different loading conditions and post-peak parameters are designed and implemented. The results show that the stress measurement error increases exponentially as the degree of rock core failure increases. The greater the severity of the rock failure, the greater the estimation error of each stress component. The strain test error is the primary cause of stress test error, not the residual stress at the rock core. Based on this, the applicable conditions of the overcoring stress relief method are analyzed. To keep the stress test error within an acceptable range, the test borehole axis should be kept close to the direction of the maximum principal stress. Additionally, the fracture depth should be less than 0.2 times the radius of the pilot hole. This research will provide the basis for the error analysis of stress test results and optimization of a borehole drilling process for the overcoring stress relief method in deep hard rock engineering.