## 1 Introduction  
Salt rock, a medium with low seepage characteristics (permeability of less than \(10^{-20}\) m\({}^{2}\)) and good damage repair ability, has been an ideal storage medium for energy and nuclear waste [1; 2]. However, following years of use, the volume of underground salt caverns will fall because of changes in internal fluid pressure and rock creep. During this process, dislocations and slip among adjacent grains will occur and lead to severe rock damage. According to statistical analysis [3; 4; 5; 6; 7; 8; 9; 10; 11], 29 major accidents have occurred in the last 40 years, 20% of them due to rock damage. Therefore, it is of great significance to study the damage law of salt rock. However, this was a difficult task because of the micro-scale and extremely slow creep, which needed to be studied using special instruments or methods. Acoustic emissions (AE) technology provides an indirect means of monitoring the internal deformation and damage process of salt rocks in the laboratory. In recent years, a wide range of studies on 'hard' rocks, such as granite and shale, indicated that AE technology provide a convenient tool for the study of deformation and failure of geologic materials [12; 13; 14; 15; 16; 17]. For example, [PERSON] [12] and [PERSON] [13] studied the AE characteristics and the energy release law in granite at different stress stages, and demonstrated that energy accumulation was the root cause of crack growth, and a quiet period of AE events occurs before rock fracture. [PERSON] [15] analyzed AE information under uniaxial compression to evaluate the dynamic damage process; they obtained a 3D distribution of AE events to illustrate the generation, growth, and connection of micro-cracks. Unfortunately, AE technology has not been extensively applied in the study of damage behavior of salt. Only a few studies have focused on the AE characteristics of salt rock, a'soft' rock with coarse grains and non-uniform structures, whose AE characteristics are very different from others. [PERSON] [18] studied the AE features of salt rock during different strain phases in triaxial compression tests to determine the expansion and dilatancy boundary. [PERSON] [19] analyzed the influence of stress level and loading rate on AE frequency, and summarized that the higher the loading rate, the more obvious the rock's brittle features, and the lower the AE counts. [PERSON] [20] and [PERSON] [21] conducted AE monitoring in fatigue tests of salt under cyclic loading paths to reveal memory effects. However, they did not research the AE location owing to the limitations of experiments. Ultrasonic waves, an active method and good indicator, can be used to evaluate pore structure, rock damage processes, and anisotropy. [PERSON] [22] found that the increasing saturation of shales decreased the difference between seismic and ultrasonic stress-sensitivities. [PERSON] [23] showed that rock internal structure changed with variations in ultrasonic wave velocity and amplitude. [PERSON] [24] and [PERSON] [25] investigated the relationship between ultrasonic velocity and stress response in concrete, magmatic rocks, and sedimentary rocks; they found that ultrasonic velocity in rocks had a rising trend in the elastic loading stage. Although scholars have conducted many ultrasonic wave studies into rock damage, most focused on P-waves, not S-waves. Comparatively little work has been done on laboratory studies of ultrasonic velocity in salt rock under load [26; 27; 28]. The above studies are of great value; however, they only focused on either the variation of ultrasonic velocity or AE activity. In addition, because of the limitations of testing equipment, most did not concentrate on AE location and S-shear. In this study, we developed an integrated experimental apparatus of ultrasonic wave and AE activities, which was used to study the deformation properties and damage evolution of salt rock under uniaxial loading.