On the Kaiser Effect of Rock under Cyclic Loading and Unloading Conditions: Insights from Acoustic Emission Monitoring

Abstract

The Kaiser effect reflects the memory of the loaded rock to the irreversible damage and deformation. The stress level, loading rate and lithology are the main factors affecting the Kaiser effect of the rock. To identify the accurate stress point of the Kaiser effect, the MTS 816 rock mechanics testing system and the DS5-A acoustic emission testing and analysis system were adopted. The uniaxial cyclic loading–unloading and acoustic emission characteristic test of 90 rock specimens from three types of rocks under different stress level and loading rate was carried out. The evolution of acoustic emission under uniaxial compression of the rock corresponds to the compaction stage, elastic stage, yield stage and post-peak stress drop stage of the rock deformation and failure process and is divided into the quiet period, transition period, active period and decay period of the acoustic emission. The larger the hardness of rock is, the earlier the stress point of the Kaiser effect appears. The loading stress level (σA) has appreciable influence on the Kaiser effect of the rock. When σA ≥ 0.7σc, the Kaiser effect disappears. Usually, the dilatancy stress (crack initiation stress) does not exceed 70% of the uniaxial compressive strength (σc) of the rock, and the stress point can be the threshold to determine whether the Kaiser effect occurs. The influence of loading rate (lr) on Felicity rate (FR) is relatively large when lr < 0.01 mm/s, and FR rapidly grows with increase of the loading rate. When lr ≥ 0.01 mm/s, the influence of the loading rate on FR is relatively small. The findings facilitate the future application of the Kaiser effect and improvement of the accuracy of the acoustic emission data interpretation.

Assessment of Appropriate Experimental Parameters for Studying the Kaiser Effect of Rock

“…This prevents an unfavorable effect generated by the separation of the loading platen from the end face. To avoid that the test is stopped due to unexpected and quick rupture of the rock specimen under the loading mode of stress-control, the displacement-controlled loading mode is used in the 2nd loading stage, and the loading strain rates (l sr ) are 10 −5 s −1 to 10 −3 s −1 , which falls into the region of strain rate from low to medium [18,32,33]. The detailed experimental schemes of the UCLU refer to Table 1.…”

“…Extensive experimental studies have been carried out to examine the applicability of the Kaiser effect for history stress measurement [12,[15][16][17]. A widely used experimental configuration to study the Kaiser effect is the UCLU test [18][19][20]. Li and Nordlund [21] carried out UCLU test for eight rock types and revealed the influence of delay time on the Kaiser effect.…”

“…The occurrence of the Kaiser effect is affected by several factors, including rock lithology, magnitude of the prescribed stress (σ A ) in the first loading cycle, duration of the constant loading, and loading strain rate (l sr ). For instance, when σ A is low, the AE produced by the friction of the microcracks cannot be eliminated, which complicates the identification of σ AE [18,24,25]. On the other hand, if σ 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].…”

“…On the other hand, if σ 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 σ A and l sr , influence the occurrence of the Kaiser effect are rarely reported.…”

Effect of Axial In-Situ Stress in Deep Tunnel Analysis Considering Strain Softening and Dilatancy

“…Extensive laboratory tests and field observations [11][12][13][14][15] show that a strain softening model can better describe the post-peak mechanical behavior of most rock masses than perfectly elastoplastic and elasto-brittle-plastic models can. Dilatancy is closely associated with the deformation and failure of a rock mass [16][17][18]. Many rock mechanical tests [19][20][21] show that a rock mass exhibits significant dilatancy in the post-peak stage and that the dilation angle strongly depends on the confining stress and plastic shear strain, decreasing nonlinearly with an increase in the confining stress or plastic shear strain.…”