Experimental and numerical study of the directional dependency of the Kaiser effect in granite

The significance of in situ stress has been well recognized in the oil and mining industries. In the oil industry, it controls both natural and induced fluid flow in the subsurface. In the mining engineering, the in situ stress field is fundamental for the design of excavations. The Kaiser effect, as one of the most important and interesting manifestations of the fundamental features of rock materials, refers to the phenomenon that, if a sample is subjected to cyclic loading, acoustic emission (AE) does not occur and the stress level exceeds the peak stress in the loading history. This effect can be used to determine the in situ stress in rock mass with rock memory recovery [1–5]. The Kaiser effect was first discovered in 1950 by Joseph Kaiser [23], who performed his experiments on metal specimens under cyclic loading. Other researchers subsequently obtained similar results in rock under compressive loading. In the past decades, many researchers have studied the Kaiser effect in rocks. Michihiro investigated the Kaiser effect in granite and tuff [6]. The load was previously applied on rock specimen up to 14.7MPa at a rate of 9.8MPa/min. The rock was loaded cyclically for 50 cycles, until no residual strain developed. The pre-load levels were found to be 14.81 and 15.06MPa using the Kaiser effect for granite and tuff, respectively. Kurita compared the difference of AE activities in elastic and plastic ranges for granite [7]. The experimental results