## 2 Experimental Device and Sample Preparation
### Sample Preparation and Experimental Scheme  
The shale rock samples were collected via man-machine collaboration, and the sampling site was Dongnihe Village, Yijun County, Tongchuan City. Through the on-site collection, uniform shale rock blocks of the same strata were obtained. The shale rock blocks had good integrity and a stable structure. The shale rock blocks, without obvious damage, were transported to the geotechnical Laboratory of Xi'an University of Science and Technology. According to the \"Engineering Rock Mass Test Method Standard\", the shale rock blocks were processed via core drilling, cutting, and grinding. Then, standard shale rock samples with a diameter of 5 cm and a height of 10 cm were obtained. The shale rock samples here were massive and formed by the cementation of rock mineral particles. They were argillaceous siltstone samples with a dark red color. They were heterogeneous bodies composed of clay and clastic minerals from the Yanchang Formation of the Upper Triassic Series. Different mineral particles were bonded to each other by cementation to compose these samples. Through a D/max-2500 X-ray diffractometer (Rigaku, Tokyo, Japan), we determined that the mineral composition of the shale rock samples was mainly clay minerals and quartz, in which the average mass fraction of clay minerals was 35.28% and the average mass fraction of quartz was 40.56%. Organic pores, inorganic pores (intergranular pores and intragranular pores), and micro-fractures were developed in the test  
Figure 1: Electro-hydraulic servo control, high- and low-temperature, high-pressure dynamic rock three-axis test system.  
rock samples, and the pores were mainly micro- and medium-sized pores. According to the experimental procedures of the International Society of Rock Mechanics, samples with similar longitudinal wave velocities were selected with an acoustic test system (Crystal Instruments, Santa Clara, CA, USA) (see Figure 2), and the samples were vacuumized and saturated by the vacuum saturator (Vinci Technologies, Nanterre, France) for 24 h.  
1. Experimental scheme: In order to test the mechanical properties of shale rock, the effects of water sensitivity characteristics under different confining pressures and different water contents on its mechanical properties were analyzed. The samples of shale rock with water contents of 0%, 2%, 4%, 6%, and 8% were subjected to triaxial compression tests under confining pressures of 60 MPa, 70 MPa, and 80 MPa.
2. Experimental procedure: After the shale rock sample had been wrapped with rubber film, it was fixed on the pressurized platform, and the anisotropic strain gauge was installed. We then started the system to set the control parameters, installed the pressure chamber cover, and filled the oil to discharge the gas. After the oil had been filled, the confining pressure was applied, and the setting confining pressure was loaded at the rate of 2 MPa/min, after which the axial strain rate was set as \(10^{-6}\)/s for the loading experiment. After the sample had been damaged, the system automatically generated the test data. The physical parameters of the tested shale rock samples are shown in Table 1.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**ID**} & **Altitude** & **Diameter** & \multirow{2}{*}{**ID**} & **Altitude** & **Diameter** & \multirow{2}{*}{**ID**} & **Altitude** & **Diameter** \\  & **(cm)** & **(cm)** & **(cm)** & **(cm)** & **(cm)** & **(cm)** \\ \hline A-1 & 10.23 & 4.85 & B-1 & 9.86 & 4.85 & C-1 & 9.85 & 4.85 \\ A-1 &