## 4 Discussion  
### Discussion on Influencing Factors of Adhesion Properties of Raw Coal  
This section systematically examines the effects of moisture content and compaction force on the adhesion properties of raw coal. By integrating existing research findings, the intrinsic mechanisms of interfacial property changes between particles are analyzed in detail. The results demonstrate that increasing moisture content significantly enhances  
Figure 27: Dynamic wall pressure changes during the discharge process at different coal storage heights.  
the cohesion at both the coal-coal and coal-wall interfaces. This phenomenon is primarily attributed to the formation of liquid bridges and negative pressure effects by adsorbed water between coal particles, thereby strengthening the adhesive force between particles. These findings align with the conclusions of [PERSON] (12), [PERSON] (13,14), and [PERSON] (15), who identified liquid bridge forces generated by adsorbed water at particle interfaces as the primary drivers of particle agglomeration. The variation in internal friction angles further underscores the significant role of moisture content. At lower moisture levels, the internal friction angle increases rapidly, but as the moisture content rises further, the growth rate diminishes. This trend is consistent with the findings of [PERSON] (34) and [PERSON] (35), which indicate that adsorbed water enhances friction between particles at low moisture levels, while lubrication effects become dominant at higher moisture levels. Moreover, under identical moisture conditions, the cohesion and internal friction angle at the coal-wall interface consistently exceed those at the coal-coal interface. This can be attributed to the smoother and more uniform surface of the bunker wall, which allows for more substantial interfacial contact. This also explains why raw coal is more prone to adhering to the bunker wall. Unlike previous studies that primarily focused on particle-particle interfaces, this research provides new data insights into the characteristics of the coal-wall interface, offering a deeper understanding of coal bunker adhesion issues.  
Additionally, increasing compaction force also enhances the cohesion at both interfaces. The results indicate that higher compaction forces intensify the mechanical interlocking of particles at the interfaces, consistent with the findings of [PERSON] et al. (36) on the effects of particle compression. However, this study further reveals that beyond a certain threshold of compaction force, the cohesion at the coal-wall interface approaches saturation. This is because the degree of interfacial contact under high-pressure conditions approaches its limit, resulting in a diminished increase in mechanical interlocking. In contrast, the coal-coal interface, with its larger interstitial voids, exhibits a more pronounced increase in cohesion with rising compaction force. This suggests that reducing the friction coefficient of the bunker wall could be an effective strategy to mitigate coal adhesion. Regarding the internal friction angle, compaction force significantly elevates its values at both interfaces, with the coal-wall interface consistently exhibiting higher internal friction angles than the coal-coal interface. Under high-pressure conditions, tighter particle contacts amplify frictional effects, further increasing the internal friction angle.  
By comprehensively analyzing the mechanisms of moisture content and compaction force, this study reveals the differences in adhesion properties between coal-coal and coal-wall interfaces and their influencing factors. These findings not only align with previous research on liquid bridge and frictional force mechanisms but also expand the scope of analysis to include the coal-wall interface. This extension provides novel insights for addressing adhesion issues in coal bunkers.