Comprehensive analysis method and experimental vertification for in-situstress measurement by acoustic emission tests

The Kaiser effect (KE) point where there is a substantial increase in acoustic emission (AE) is to be determined for the evaluation of the in-situ stress by using rock AE tests. However it is hard to get the point accurately by means of the graphing method. A comprehensive method is proposed based on the theoretical and experimental analyses. First, we can get the approximate KE point by projecting the tangent at the turning point of the AE activity curve although it is not very accurate. Second, the relevant fractal dimensions of AE energy in the whole AE tests are calculated by using the G-P algorithm. One of the points with the minimum value of the relevant fractal dimension adjacent to the approximate KE point is taken as the final KE point and its corresponding stress is the value of the pre-stress. To validate the effectiveness of the proposed method, in-situ stress experiments are carried out by means of the overcoring stress relief method. The rock cores are obtained from boreholes used in the overcoring stress relief method. And the pre-stress of rock core specimens along the loading direction is determined. AE tests on the 11 rock specimens are carried out. The results indicate that it has higher accuracy in estimation of the pre-stress by using the proposed comprehensive method compared with the graphing method. It can be used as a new method in the evaluation of pre-stress in AE tests.