LAUSR

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. The loading and unloading processes of rock in situ include complex paths with various loading rates, for instance, from a slow rate during the geological history to a fast rate when earthquakes occur. The reloading of the core sample in laboratory conditions is usually performed with the loading rates different from the stress memory formed in situ (Yamshchikov et al. 1994; Lavrov 2001; Filimonov et al. 2002). Determining the effect of loading rates on the Felicity effect is necessary to estimate the stress experienced by rocks during dynamic loading in the earth’s crust. Although several studies have focused on conducting laboratory tests to estimate the effect of parameters, such as time delay, water content, heat, and duration of load application, on the Felicity effect (Park et al. 2001; Lavrov 2003; Jin et al. 2009), the effect of loading rate has not been identified thoroughly. The AE study on rocks differs significantly from that on other materials because the energy frequency distribution of acoustic data is strongly dependent on rock properties (Zhang et al. 2015). The study is associated with the variation of mineral composition and microstructure of rocks. Therefore, the difference in the Felicity effect of different rock types should be examined to ensure its feasibility on practical applications. This paper presents the results of a series of AE tests, which aim to reveal the effect of loading rate on the Felicity effect of three different rock types through two uniaxial loading cycles. By analyzing the relationship between the loading rate and FR, the effects of different rock types on the Felicity effect and the mechanism of loading rate dependence during cyclic loading are discussed on the basis of the physical properties and mineralogical characteristics of the rock. & Yulong Chen [email protected]