## 3 Experimental Results
### Young's Modulus, Uniaxial Compressive Strength and Axial Strain at Peak Stress  
To observe the effects of rock/coal strength on the deformation behavior and strength of the CRC specimen, the [PERSON]'s modulus, uniaxial compressive strength, and its corresponding uniaxial strain under uniaxial compressive loading were calculated. The effects of rock/coal strength on the [PERSON]'s modulus, uniaxial compressive strength, and its corresponding axial strain in the CRC specimen are shown in Figures 4-6. The deformation parameters and peak compressive strength of the pure rock/coal specimens are listed in Table 2.  
Figure 4: The Young’s modulus of the coal-rock combined (CRC) specimens. Figure 5: The compressive strength of the CRC specimens. Figure 4 illustrates the influence of the rock/coal strength on Young's modulus. As the pure rock strength increases, the Young's modulus tends to increase. When the coal sections of the CRC specimens were M\({}_{1}\) and the rock section was mudstone, the average Young's modulus of these types of CRC specimens was 1.93 GPa. However, for the M\({}_{1}\) and fine sandstone specimens, the average Young's modulus was 2.14 GPa. Moreover, with increasing coal strength, the average Young's modulus also tended to increase. For example, the average Young's modulus of a specimen of M\({}_{1}\) and fine sandstone was 2.14 GPa, while that of a specimen of M\({}_{2}\) and fine sandstone was 2.79 GPa, approximately 30.4% higher than that of the former. These phenomena indicate that the higher the uniaxial compressive strength of the pure rock/coal specimen is, the greater the stiffness is and the less likely it is to deform. The uniaxial compressive strength average values of the CRC specimens are presented in Figure 5. The results indicate that the uniaxial compressive strength of the CRC specimens depends on the pure coal strength. For all CRC specimens, the uniaxial compressive strength increased with increasing coal section strength and appears to be independent of the rock section strength. These findings agree with the results reported by [PERSON] et al. [35]. During the process of quasi-static loading, the coal part \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Group**} & **Specimen** & **Modulus/** & **Average/** & \multicolumn{2}{c}{**Uniaxial**} & \multirow{2}{*}{**Average/** **MPa**} & **Axial Strain** & \multirow{2}{*}{**Average** **at Peak Stress** (\(\times\)10\({}^{-3}\))**} \\  & **Label** & **GPa** & **GPa** & **Compressive** & & & **MPa** & (\(\times\)10\({}^{-3}\))** & \\ \hline \multirow{3}{*}{M\({}_{1}\)} & M\({}_{1}\)-1 & 1.23 & & 8.8 & & 9.28 & \\  & M\({}_{1}\)-2 & 1.52 & 1.4 & 12.3 & 10.53 & 9.52 & 9.39 \\  & M\({}_{1}\)-3 & 1.45 & & 10.5 & & 9.37 & \\ \hline \multirow{3}{*}{M\({}_{2}\)} & M\({}_{2}\)-1 & 1.72 & & 14.1 & & 9.26 & \\  & M\({}_{2}\)-2 & 1.58 & 1.75 & 12.7 & 14.3 & 9.20 & 9.26 \\  & M\({}_{2}\)-3 & 1.85 & & 16.2 & & 9.33 & \\ \hline \multirow{3}{*}{NY} & NY-1 & 6.82 & & 59.14 & & 11.95 & \\  & NY-2 & 7.05 & 6.86 & 62.32 & 59.7 & 12.04 & 11.95 \\  & NY-3 & 6.75 & & 57.65 & & 11.87 & \\ \hline \multirow{3}{*}{XS} & XS-1 & 7.54 & & 73.01 & & 12.17 & \\  & XS-2 & 7.32 & 7.51 & 69.22 & 72.67 & 12.06 & 12.16 \\  & XS-3 & 7.67 & & 75.78 & & 12.24 & \\ \hline \multirow{3}{*}{ZS} & ZS-1 & 8.37 & & 82.04 & & 12.31 & \\  & ZS-2 & 8.11 & 8.33 & 77.22 & 81.87 & 12.22 & 12.41 \\  & ZS-3 & 8.52 & & 86.34 & & 12.69 & \\ \hline \multirow{3}{*}{FS} & FS-1 & 9.04 & & 100.08 & & 13.02 & \\  & FS-2 & 8.75 & 9.02 & 92.58 & 101.03 & 12.92 & 13.09 \\ \cline{1-1}  & FS-3 & 9.26 & & 110.43 & & 13.32 & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Young’s modulus, uniaxial compressive strength and axial strain at peak stress of the pure coal/rock specimens. Figure 6: The axial strain at the peak stress of the CRC specimens. generally exhibits relatively weak properties compared to the rock part. Thus, it can be expected that the weak properties of coal contribute significantly to the bearing capacity of the CRC specimens once loaded.