# Statistical Analysis of Acoustic Emission in Uniaxial Compression of Tectonic and Non-Tectonic Coal
## 2 Experiment  
### Materials for the Experiment  
The tectonic coal was collected from Shihao coal mine, located in Qijiang district of Chongqing (Southwest of China), and the non-tectonic coal was collected from Xieqiao coal mine, located in Huainan City of Anhui Province (East of China). The coal bearing strata in the two areas are both Permian. However, geological activity is more active in western China than that in eastern, and the tectonic coal from western China is affected by geological activity, which makes it different from the same period non-tectonic sample, such as the volatile content of tectonic coal is only 1/3 that of non-tectonic coal (see Table 1). Table 2 shows the maceral content analysis of the samples, the vitrinite content of tectonic coal is greater than the vitrinite content of non-tectonic coal, which also indicates that the geological influence leads to the enhancement of tectonic coal coalification. Tables 3 and 4 show the pore features of the coal samples. The porosity and specific surface area were acquired using the mercury intrusion method and low-temperature liquid nitrogen absorption, respectively. The macro pores in the coal mainly hosted laminar flow and slow laminar flow. Capillary condensation and gas diffusion occur in the meso pores. The proportion of meso pores in the tectonic coal was twice the proportion in the non-tectonic coal. In addition, the pore volume of the 10 to 20,000 nm pores was 3 to 7 times greater in the tectonic coal relative to the non-tectonic coal. Furthermore, the specific surface area of the tectonic coal was three times the specific surface area of the non-tectonic coal. These results indicate that the tectonic coal is good for methane gas absorption. The structure of tectonic coal is loose, and the mechanical properties of tectonic coal are poor. The pore characteristics and surface morphology of tectonic coal and non-tectonic coal were observed with secondary electron (SE) scanning electron microscopy (SEM, TESCAN VEGA 3 LMH). The tectonic coal and non-tectonic coal samples were made into about \(3\times 3\times 2\) mm cubes for observation. Figure 1a shows the rough surface morphology and some developed microcracks of tectonic coal. Compared with tectonic coal, non-tectonic coal (Figure 1b) has a relatively smooth surface. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Tectonic** & **Non-Tectonic** \\ \hline Moisture contents & M\({}^{\text{a}}\) & 2.17\% & 2.72\% \\ Ash content & A\({}^{\text{a}}\) & 8.50\% & 9.24\% \\ Volatile matter content & V\({}^{\text{daf}}\) & 10.67\% & 31.24\% \\ Elemental C content & C\({}^{\text{a}}\) & 79.63\% & 73.73\% \\ Elemental H content & H\({}^{\text{a}}\) & 2.02\% & 3.85\% \\ Elemental N content & N\({}^{\text{a}}\) & 2.62\% & 2.56\% \\ Elemental S content & S\({}^{\text{a}}\) & 1.96\% & 1.17\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Proximate analyses and elemental analyses of coal samples. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Tectonic** & **Non-Tectonic** \\ \hline
100–0.1 mm & 38.97\% & 70.34\% \\
10–100 nm & 61.03\% & 29.66\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Pore volume and specific surface area derived from low-temperature liquid nitrogen absorption. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Tectonic** & **Non-Tectonic** \\ \hline Vitrinite & 83.1\% & 58.2\% \\ Liptinite & 5.3\% & 9.0\% \\ Inertinite & 10.4\% & 31.2\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Maceral content. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Tectonic** & **Non-Tectonic** \\ \hline
100–0.1 mm & 38.97\% & 70.34\% \\
10–100 nm & 61.03\% & 29.66\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Maceral content. For both kinds of coal samples, four-prism test pieces were used. The four sides of the test pieces are perpendicular to the bottom surface, and the top surface and bottom surface are parallel. The height of sample is 100 mm, and the width of the bottom is 50 mm.