Investigations and new insights on the relation between the valid interval of the Kaiser effect and the characteristic stress

Based on the systematic summary and analysis of a large number of relevant literatures, combined with the authors' related research findings, some new insights are presented on the relation between the valid interval of the Kaiser effect and the characteristic stresses of rocks. The acoustic emission activity of rocks exhibits a sudden increase when the largest previously experienced stress is exceeded during reloading, which is known as the Kaiser effect. The Kaiser effect has been widely used as one of the core-based methods to determine in-situ stress due to cheap, easy and less time consuming. However, the Kaiser effect is influenced by various factors, such as previous damage, rock type and porosity, and the largest previously experienced stress. Nevertheless, a standard method to determine stress has yet to be established due to the lack of a unified understanding of the mechanism concerning Kaiser effect. Since both the Kaiser effect and characteristic stress can be obtained through acoustic emission measurement, particularly in terms of crack initiation stress which is similar to the Kaiser effect stress measurement method. Therefore, it is crucial to conduct a thorough analysis of the relation between the valid interval of Kaiser effect and characteristic stress in order to estimate Kaiser effect stress. This paper provides an overview of the recent investigations that have explored the effect of the above factors on the Kaiser effect and how they can affect the identification of the characteristic stress. The relation between the valid interval of the Kaiser effect and the characteristic stress, which is influenced by the aforementioned factors, was discussed in detail. The valid interval of the Kaiser effect has been proposed in light of the aforementioned research, and corresponding arguments have been presented to support this proposal. These findings can serve as a theoretical foundation for estimating in-situ stress using the Kaiser effect.