## 3 Results and Discussion
### Strength Characteristics of Coal Samples
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Coal**} & \multicolumn{2}{c}{**Sample Size**} & \multirow{2}{*}{\begin{tabular}{c} **UCS \(\sigma_{c}\)** \\ **(MPa)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Mean** \\ **(MPa)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Blackic** \\ **Value of** **Value of** **\(\sigma_{c}\)** \\ **(MPa)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Mean** \\ **Value of** **\(\sigma_{c}\)** \\ **(MPa)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Mean** \\ **(GPa)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Values of** **\(\varepsilon\)** \\ **(GPa)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Values of** **\(\varepsilon\)** \\ **Ratio** \(\
u\)** \\ **Value of** **\(\
u\)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Mean** \\ **Value of** **\(\
u\)** \\ **(MPa)** \\ \end{tabular} } \\ \hline RS-1 & 48.55 & 100.17 & 6.22 & & 0.867 & & - & \\ RS-2 & 48.69 & 100.05 & 5.57 & & 0.923 & 1.014 & & 0.310 \\ RS-3 & 48.80 & 99.40 & 5.89 & & 1.255 & & 0.32 & \\ RS-4 & 49.10 & 104.14 & 4.83 & & 1.011 & & 0.30 & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of the uniaxial compression tests for raw coal samples. suppressing detectable AE signals. Prior to macroscopic failure, AE activity intensified as axial stress approached peak strength, reflecting frequent interparticle shear motions, microcrack nucleation, and stable crack propagation. These processes culminated in the formation of interconnected macro-weak planes. Final failure occurred under combined axial and frictional forces, accompanied by a rapid surge in both instantaneous and cumulative AE event counts. Post-failure analysis identified the dominant failure mode as X-shaped conjugate inclined shear failure, characterized by intersecting shear bands. Furthermore, Specific UCS values are shown in Table 4. The experimental results demonstrated a direct linear proportionality between the UCS, elastic modulus, and forming pressure for briquette coal samples (Figure 3b). As forming pressure increases, interparticle cementation within the briquette matrix becomes denser, significantly enhancing resistance to intergranular slippage and shear-induced motion. This consolidation mechanism drives a progressive improvement in both the UCS and elastic modulus of the specimens. Similarly, triaxial compression tests were conducted under varying confining pressures for five sets of raw coal samples and under a fixed confining pressure of 2 MPa for briquette coal samples prepared at different forming pressures, with results exhibited in Figure 4. The cohesion, and internal friction angle were systematically evaluated, as listed in Tables 5 and 6. As shown in Figure 4a, the anisotropic nature of coal introduces variability in the conventional triaxial test results of raw coal samples, as evidenced by differing stress-strain curve slopes. The triaxial compressive strength of raw coal samples increased with higher confining pressures, accompanied by enhanced deformation capacity and elevated elastic limits. Based on experimental data, the calculated cohesion and internal friction angle of raw coal were 1.35 MPa and 49.43\({}^{\circ}\), respectively (see Table 5). Figure 4b illustrates that the triaxial compressive strength and load-bearing capacity (\(\sigma_{1}-\sigma_{3}\)) of briquette coal samples increased with forming pressure. Furthermore, both cohesion and internal friction angle exhibited a linear dependence on forming pressure (see Table 6), which is consistent with the consolidation-driven enhancement of interparticle bonding.