Investigation of the Kaiser effect in anisotropic rocks with different angles by acoustic emission method

The utilize of Kaiser effect during acoustic emission testing is a novel approach for computing the amount of stress in the rock, which has been tremendously exploited due to the immense reduction in the cost and time of determining the in-situ stress. Several parameters influence the accuracy of the Kaiser effect. This paper investigates the effect of anisotropy on the Kaiser effect on the rock. For this purpose, acoustic emission effect in the uniaxial compression test and Brazilian tensile strength test on the Phyllites specimens with various angles of anisotropy (0, 30, 60, and 90 degrees) has been conducted. The results demonstrate that in all uniaxial compression tests, the Felicity ratio of acoustic emission, which is defined as the ratio of the stress at which the Felicity effect occurs to the previously applied maximum stress, is close to one. In other words, the anisotropy does not have a significant effect on the values of the Felicity ratio. In Brazilian tensile strength tests, only the sample with zero-degree angle of anisotropy has a Felicity close to one, which means that the Kaiser effect in this condition is predicted more accurately. In addition, the results show that the uniaxial compression tests are more accurate in determining the Kaiser effect than Brazilian tensile strength tests. (C) 2020 Elsevier Ltd. All rights reserved.