## 1 Introduction
### Uniaxial Compression Test Process of Gas-Containing Coal
#### 3.2.2 Test Steps  
1. The standard coal samples prepared from the Wuhushan Coal Mine in Wuhai Mining area, and they were divided into three groups and numbered; the original physical parameters of each group were recorded. 2. The first group of coal samples was numbered as A1\(-\)1, A1\(-\)2, and A1\(-\)3, which are subjected to conventional uniaxial compression tests. 3. The second group of coal samples were numbered as A2\(-\)1, A2\(-\)2 and A2\(-\)3. Uniaxial compression test was carried out on this group of coal samples under the gas pressure of 1 MPa. 4. The third group of coal samples was numbered A3\(-\)1, A3\(-\)2, and A3\(-\)3. A uniaxial compression test is carried out on this group of coal samples under the gas pressure of 2 MPa, and the process is the same as that of the second group of coal samples. 5. Experimentalists compared and analyzed the three groups of test data and summarized the rules. Influence Analysis of Different Gas Pressure on Mechanical Properties of Coal Samples Containing Gas  
1. Stress-strain curve analysis of coal samples  
The stress-strain curves of coal samples under different gas pressures are shown in Figure 3. The stress-strain curve of gas-containing coal does not change obviously in the initial compaction stage. With the continuous increase in the load on the coal sample, the gas-containing coal begins to fail and enters the elastic deformation stage, and the \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Test Plan** & **Gas Pressure/MPa** & **Loading Rate/mm/min** & **Water/Cement Ratio/g/g** &
\begin{tabular}{c} **Briquette Forming** \\ **Pressure/MPa** \\ \end{tabular} \\ \hline The first group & 0 & 0.02 & 9.50.5 & 15 \\ The second group & 1 & 0.02 & 9.50.5 & 15 \\ The third group & 2 & 0.02 & 9.50.5 & 15 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Uniaxial compression test scheme of gas-containing coal. Figure 2: Uniaxial compression test system. stress-strain in the elastic deformation stage shows obvious linear characteristics. As the load continues to increase, the cracks in the coal develop rapidly and form cracks, which is the stage of plastic deformation. The strain and peak strength of gas-containing coals near the final rupture decrease with the increase in gas pressure. It can be seen that the increase in gas pressure under conventional uniaxial loading can weaken the bearing capacity of gas-containing coal. The mechanical properties of the test results of coal samples containing gas under different gas pressures were fitted to the data, and the following fitting formulas were obtained. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Gas Pressure/MPa**} & \multirow{2}{*}{**Coal Sample Number**} & \multicolumn{2}{c}{**The Compressive Strength/MPa**} & \multicolumn{2}{c}{**Modulus of**} & \multirow{2}{*}{**Poisson’s Ratio**} \\ \cline{3-3}  & & A1-1 & 39.27 & 2.249 & 0.233 \\
0 & A1-2 & 43.83 & 2.327 & 0.267 \\  & A1-3 & 40.45 & 2.286 & 0.246 \\ \hline On average & & 41.18 & 2.29 & 0.25 \\ \hline \multirow{2}{*}{1} & A2-1 & 31.879 & 1.526 & 0.288 \\  & A2-2 & 37.236 & 1.998 & 0.242 \\  & A2-3 & 33.754 & 1.529 & 0.259 \\ \hline On average & & 34.29 & 1.68 & 0.263 \\ \hline \multirow{2}{*}{2} & A3-1 & 22.072 & 1.63 & 0.324 \\  & A3-2 & 21.478 & 1.14 & 0.261 \\  & A3-3 & 26.873 & 1.03 & 0.282 \\ \hline On average & & 23.47 & 1.27 & 0.29 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Test results of mechanical properties of coal samples under different gas pressures. Figure 3: Full stress–strain curve of coal sample under different gas pressure. (**a**) The gas pressure is 0 MPa; (**b**) the gas pressure is 1 MPa; (**c**) the gas pressure is 2 MPa. The relationship between compressive strength and gas pressure is as follows:  
\[y_{1}=41.835-8.855\text{x} \tag{4}\]  
where \(y_{1}\) is the compressive strength (MPa), and x is Gas pressure (MPa).