## Abstract  
The Kaiser effect of rock has been extensively studied due to its wide application in in-situ stress measurement and rock damage quantification. The uniaxial cyclic loading and unloading (UCLU) test is commonly employed to examine the rock Kaiser effect. However, how the two critical parameters, including prescribed stress in the first loading cycle (\(\sigma_{\rm A}\)) and loading strain rate (\(l_{\rm sr}\)), affect the appearance of the Kaiser effect lacks thorough understanding. We systematically performed UCLU tests on 75 sandstone specimens under 25 combinations of \(\sigma_{\rm A}\) and \(l_{\rm sr}\). \(\sigma_{\rm A}\) spans from \(0.5\sigma_{\rm c}\) (\(\sigma_{\rm c}\) is the uniaxial compressive strength) to \(0.9\sigma_{\rm c}\), and \(l_{\rm sr}\) ranges from \(10^{-5}\) s\({}^{-1}\) to \(10^{-3}\) s\({}^{-1}\), respectively. The acoustic emission characteristics of all the rock specimens are continuously monitored over the entire tests. We find that the Kaiser effect is unanimously observed in the stable crack growth stage, corresponding to the stress levels of \(0.5\sigma_{\rm c}\) to \(0.7\sigma_{\rm c}\) because under a lower stress, the [PERSON] effect is easily covered by the acoustic emissions generated by microcrack friction. The loading strain rate also heavily affects the occurrence of the [PERSON] effect. When \(l_{\rm sr}\) does not exceed \(10^{-4}\) s\({}^{-1}\), the Felicity ratio (\(FR\)) rises quickly as \(l_{\rm sr}\) ascends, whereas \(FR\) increases less pronouncedly once \(l_{\rm sr}\) exceeds \(10^{-4}\) s\({}^{-1}\). Therefore, a relatively high loading strain rate, i.e., \(l_{\rm sr}\) higher than \(10^{-4}\) s\({}^{-1}\), is suggested to facilitate the appearance of the [PERSON] effect. practical stress; loading strain rate; sandstone specimens; acoustic emission; Felicity ratio +
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the Kaiser effect is the UCLU test [18; 19; 20]. [PERSON] and [PERSON] [21] carried out UCLU test for eight rock types and revealed the influence of delay time on the [PERSON] effect. [PERSON] [22] found that the [PERSON] effect could be observed only when the follow-up cyclic loading rate was higher than the previous cyclic loading rate in the UCLU test of limestone under different loading rates. [PERSON] et al. [23] carried out a UCLU test on three rock types: limestone, sandstone, and halite, and analyzed influences of loading rate on Felicity effects of the three rock types. In the UCLU test, uniaxial stress is applied and raised to a certain level (\(\sigma_{\rm A}\)), followed by constant loading for a certain period. Then, the uniaxial stress is unloaded, and then increased again to examine the stress magnitude at which the [PERSON] effect appears (\(\sigma_{\rm AE}\)). The occurrence of the [PERSON] effect is affected by several factors, including rock lithology, magnitude of the prescribed stress (\(\sigma_{\rm A}\)) in the first loading cycle, duration of the constant loading, and loading strain rate (\(l_{\rm sr}\)). For instance, when \(\sigma_{\rm A}\) is low, the AE produced by the friction of the microcracks cannot be eliminated, which complicates the identification of \(\sigma_{\rm AE}\)[18; 24; 25]. On the other hand, if \(\sigma_{\rm A}\) is very high, the Kaiser effect vanishes, and due to that, unstable cracking takes place within the rock and AE happens before the maximum history stress is reached [11; 26; 27]. It has been also reported that the loading strain rate strongly affects the crack evolution and propagation [18; 19; 28]. However, how these factors, particularly \(\sigma_{\rm A}\) and \(l_{\rm sr}\), influence the occurrence of the Kaiser effect are rarely reported. In this paper, we carried out a series of UCLU tests on specimens of a typical sedimentary rock, red sandstone.