# Research on the Characteristics of Seepage Failure in the Surrounding Rock (Coal) of the Goafs
## 3 Results and Discussion
### Implications of Fissure Seepage for Water Gushing-Out from Simulation Result  
The pressure distribution within the fractures, as simulated and shown in Figure 6a, provides valuable insights into how water flows through these narrow and complex pathways. Pressure variations were examined by selecting eight key points along the fractures, comparing different fracture widths. The data from Table 4 demonstrate a clear trend: narrower fracture widths lead to greater pressure reduction. This finding emphasizes the critical role of fracture geometry in controlling fluid dynamics within fractured rock formations. When comparing fractures 1-1, 1-2, and 1-3, significant differences in pressure reduction were observed due to varying fracture widths. For instance, water entering fracture 1-1, with an average pressure reduction intensity of 0.196 MPa, experienced a moderate pressure drop, which can be attributed to its relatively larger width. As the water progressed into fracture 1-2, the pressure reduction intensity increased sharply to 1.33 MPa due to the narrower width of the fracture, which constricted the flow path and increased resistance to water movement. In contrast, fracture 1-3 showed a pressure reduction intensity of 0.28 MPa, reflecting a lower reduction due to the already diminished inlet pressure as water moved through successive fractures. Moreover, the data indicate a strong relationship between fracture width and pressure reduction. For fractures with widths greater than 0.11 mm, the pressure reduction intensity  
Figure 5: Coal sample after seepage failure (**a**), the residue of slack on the plug of gripper (**b**), and slack in water after seepage (**c**). remains relatively low, typically \(\leq\)0.28 MPa. However, for fractures narrower than 0.11 mm, the intensity exceeds 0.4 MPa, illustrating the significant impact of microfracture dimensions on pressure dynamics. Fracture 1-1, with a width of 0.09 mm, exhibited a higher pressure reduction intensity than subsequent fractures with narrower widths, driven by the higher initial pressure at its entrance, amplifying the pressure drop as the water passed through this narrow space. The water flow velocity distribution, shown in Figure 6b, further clarifies the impact of fracture width on fluid dynamics. In areas where the fractures narrowed, flow velocity increased dramatically, reaching localized peaks of up to 30 m/s. This acceleration occurred due to the constriction caused by narrower fractures. However, this effect was not uniform across the fracture network, with overall seepage velocity decreasing significantly as water exited the system. The outlet velocities often dropped to almost 0 m/s, highlighting how narrow microfractures effectively regulate and restrict fluid flow. The relationship between fracture width and pressure reduction intensity, visualized in Figure 6c, reveals that when fracture widths are less than 0.11 mm, a pronounced reduction in water pressure occurs. This trend, represented by a fitted curve, identifies a critical threshold below which abrupt changes in fracture seepage behavior may be expected. These findings underline the importance of microfracture widths in dictating pressure and flow characteristics in fractured systems. Figure 6: Pressure distribution of fissure fluid (**a**), velocity distribution map in fissure (**b**), and relationship between fissure width and the value of pressure reduction (**c**). The results from the simulated pressure distribution and water flow velocity reveal key insights into the effects of fracture width on fluid dynamics in fractured coal formations. Narrower fractures were found to significantly increase both pressure reduction and flow velocity, with microfractures serving as critical bottlenecks that control overall fluid movement. Specifically, fractures narrower than 0.11 mm were associated with heightened pressure reduction, emphasizing their role in dictating fluid resistance and permeability.