# Experimental Study on the Features of Infrasonic Waves of Sandstone under Shear Load
## 2 Experiment to Acquire Infrasonic Signals during Sandstone Shear Destruction
### Rock Sample Preparation and Experiment Process
#### 2.2.1 Rock Sample Preparation  
(1) To determine the size effect of sandstone slopes, synchronous monitoring experiments of infrasounds generated during sandstone shear destruction were conducted on  
Figure 1: Experiment apparatus.  
sandstone samples of different sizes. A group of cubic samples with side lengths of 50, 100, 150, and 200 mm were prepared. Faces of the samples were planished. The samples were coded as a1-1, a1-2, a2-1, a2-2, a3-1, a3-2, a4-1, and a4-2 (Table 1).  
(2) Rainfall is the most important coefficient that causes landslides. To determine the effect of rainfall on the sandstone slope, synchronous monitoring experiments of infrasounds generated during sandstone shear destruction were carried out on the rock sample with different water saturations. The water cut of rock sample was calibrated by the weighing method.  
In this method, the first step is to put the sandstone samples of the same size into the oven for drying and dehydrate the core. During this period, the balance is continuously used to measure the change of rock sample quality until the rock sample quality no longer changes and the rock sample reaches the pure dry state. Then, the mass of the rock sample is recorded as M1. Second, after the rock sample cools, it is placed in a bucket to absorb water, and the water level exceeds the height of the rock sample. During this period, the balance is continuously used to measure the change of rock sample quality until the rock sample quality does not change and the rock sample reaches the state of pure water saturation. At this point, the mass of the rock sample is recorded as M2. The third step is to calculate the mass difference \(\Delta\)M between the saturated and dry states of each rock sample and divide the difference into five different saturations: M1, M1 + 1/4\(\Delta\)M, M1 + 2/4\(\Delta\)M, M1 + 3/4\(\Delta\)M, M2. The fourth step is to encapsulate pure dry rock samples and pure water-saturated rock samples with sealed bags. Other rock samples are placed in the oven to dry, and the mass changes of rock samples are continuously measured with a balance until the mass of rock samples reaches the weight of rock samples corresponding to the required saturation. These samples are then likewise encapsulated with sealed bags.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**No.** & **Size/mm3** & **Density/(g.cm\({}^{-3}\))** & **Saturation/\%** & **Axial Pressure/Mpa** \\ \hline a1-1 & \(50\times 50\times 50\) & 2.49 & 0.00 & 0.00 \\ a1-2 & \(50\times 50\times 50\) & 2.34 & 0.00 & 0.00 \\ a2-1 & \(100\times 100\times 100\) & 2.45 & 0.00 & 0.00  
Sandstone samples with different water saturations were prepared by the water absorption and weighing method and coded as b1, b11, b2, b21, b3, b31, b4, b41, b5, and b51.  
(3) In order to discuss the influence of different overburden pressures on sandstone slopes, infrasound synchronous monitoring experiments were carried out during the shear failure process under different axial pressures. A total of cubic sandstone samples 50 mm in side length were prepared and put into the oven to ensure the samples were dry. These samples were coded as c1, c11, c2, c21, c3, c31, c4, c41, c5, and c51.  
Prepared sandstone samples are shown in Figure 2. Sandstone can be classified according to its permeability. The sandstone used in this study has a low permeability and belongs to the category of tight sandstone.