## 3 Investigation of Adhesive Clogging Characteristics in Underground Coal Bunkers
### Numerical Calculation Model and Simulation Method  
(1) Numerical model  
The main body of the coal bunker in the II 1011 roadway of Taoyuan Coal Mine is cylindrical in shape, with a diameter of 3.1 m, a bottom opening diameter of 1 m, a total height of 28.39 m, a cylindrical segment height of 26.57 m, and a bottom conical segment height of 1.82 m. In the simulation, the linear parallel bond model [33] was used to represent the constitutive relationship between raw coal particles. Due to limitations in computational power, the simulation increased the gravitational density of the particle model by tenfold to simulate a gravity field similar to that of the actual coal bunker. The mechanical parameters for the interactions between coal particles and between particles and the wall were obtained through experiments, with key parameters listed in Table 8.  
(2) Simulation of the coal storage process in the bunker  
Before discharging, all coal particles must be loaded into the bunker, and the model must reach a stable state before proceeding to the next simulation step. A layer-by-layer particle generation method was used: 4000 coal particles were generated at the top of the bunker, allowed to fall freely as shown in Figure 12(a), and reached equilibrium after some time as shown in Figure 12(b). This process was repeated layer by layer until the bunker was filled to the specified height, as shown in Figure 12(c)-f.  
(3) Simulation of the coal bunker discharge process  
After completing the coal storage process, a \"receiving bunker\" was formed below the bunker outlet with three wall segments using the coal bunker unloading subroutine, and the barrier wall at the outlet was removed, allowing particles to flow out under gravity until equilibrium was reached inside the bunker. The proportion of adhesive coal and the morphology of clogging were recorded at equilibrium, with real-time monitoring of dynamic wall pressure. Since adhesive coal was mainly concentrated at the discharge outlet and the middle-to-lower straight cylinder wall, and the bunker was symmetrical, the analysis focused on the side walls with more adhesive coal, namely wall units 1-10 and 21-30, as shown in Figure 13(a). Figure 13(b)-e show the movement of coal particles during discharge at a storage height of 5 m and the condition of adhesive coal after unloading.  
Figure 12: Extraction of raw coal particle contours.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \begin{tabular}{c} **Particle Unit** \\ **Model** \\ \end{tabular} & \begin{tabular}{c} **Density** \\ **(kg/m3)** \\ \end{tabular} & \begin{tabular}{c} **Particle-Particle** \\ **Friction** \\ **Coefficient** \\ \end{tabular} & \begin{tabular}{c} **Particle-Wall** \\ **Friction** \\ **Coefficient** \\ \end{tabular} & \begin{tabular}{c} **Wall Normal** \\ **Stiffness** \\ **(N/m)** \\ \end{tabular} & \begin{tabular}{c} **Wall Shear** \\ **Stiffness** \\ **(N/m)** \\ \end{tabular} & \begin{tabular}{c} **Particle Normal** \\ **Stiffness** \\ **(N/m)** \\ \end{tabular} & \
\begin{tabular}{c} **Particle Shear** \\ **Stiffness** \\ **(N/m)** \\ \end{tabular} \\ \hline
\begin{tabular}{c} Raw coal \\ particles \\ \end{tabular} & \(1500\times 10\) & 0.65 & 0.5 & \(3.5\times 10^{6}\) & \(1.75\times 10^{6}\) & \(1.75\times 10^{6}\) & \(0.875\times 10^{6}\) \\ \hline \hline \end{tabular}
\end{table}
Table 8: Physical and mechanical parameters of particles obtained using the discrete element model.  
The figures show that the flow of coal particles inside the bunker exhibits central flow characteristics. Coal in the center moves downward first and quickly, while coal near the walls moves slower due to greater pressure, forming a \"V\" shape within the bunker. Ultimately, coal adheres to the wall due to the combined effects of friction and adhesion, consistent with real-world engineering, validating the simulation method.