Effect of Loading Rate on the Felicity Effect of Three Rock Types

Excerpt

Given that the acoustic emission (AE) technique is low cost, easy, and efficient compared with other in situ stress test methods, many results of experiments performed under uniaxial and triaxial cyclic loading are available (Seto et al. 1997; Grosse and Ohtsu 2008; Tuncay and Obara 2012; Zhao et al. 2015; Yu et al. 2015). Kanagawa et al. (1976) first used the AE method to obtain the Kaiser effect and to estimate the in situ stress from the accumulative AE count of rocks. The basic principle of Kaiser effect states that a material emits a noticeable AE when the reload stress exceeds the previously applied stress (Kaiser 1953; Lockner 1993; Lavrov 2003; Tensi and Maria 2004; Tuncay and Ulusay 2008; Lehtonen et al. 2012). By contrast, for the Felicity effect, the AE intensifies before the previous maximum load (Hamstad 1986; Li and Nordlund 1993). The associated quantitative measure of the effect is known as the Felicity ratio (FR), which is the ratio between the AE onset stress and the maximum of the previous stress, reflecting the development of previous damage and the structural defects of the material. …