## 4 Simulation Results and Discussions
### The Influence of Water Table Level  
Considering that particle friction coefficients above 0.3 yielded soil displacement that was not significantly different, a uniform particle friction coefficient of 0.1 was adopted for subsequent investigations.  
This choice allowed for a comparative analysis between Figures 16 and 17, highlighting the significant influence of groundwater levels on soil loss. By the 400,000 th simulation step, the high groundwater scenario exhibited pronounced soil subsidence, with substantial displacements observed in the middle of the top layer, forming a distinctive funnel-shaped configuration. The surrounding soil on both sides of the leakage opening symmetrically slid towards it, while the soil from the ninth layer above the leakage opening was also affected. In contrast, the low groundwater scenario exclusively affected the seventh layer.  
In regions with high water table levels, a greater proportion of soil particles are located within the saturated zone. Buoyancy effects weaken the interlocking behavior among particles, and the higher hydraulic gradient induced by the elevated water level increases their susceptibility to displacement. Consequently, during the initial simulation stages, particles in the high groundwater scenario experience significantly larger displacements compared to those in the low groundwater scenario. Upon comparing the computed values of soil particles in Figures 18 and 19 at the end of the simulation, it becomes evident that a considerable amount of soil particles has been lost. The contact resistance between particles  
Figure 16: The subsurface displacements at 5000 simulation steps.  
Figure 17: The subsurface displacements at 400,000 simulation steps.  
further diminishes, and under the influence of high hydraulic gradients, a stable leakage channel forms within the soil mass. As a result, the displacement of particles in both scenarios is significantly higher at the end of the simulation compared to the initial stages.  
Upon comparing Figures 20 and 21, it is evident that at the end of the simulation, the contact force chains between soil particles in both groundwater level scenarios have become sparser and weaker than in the initial stages. In the high groundwater level scenario, a substantial number of particles have been lost due to soil subsidence, resulting in a considerable loosening of the force chains in the top region. At this point, most soil particles are submerged in the groundwater, rendering them saturated. Consequently, under the influence of buoyancy and hydrodynamic forces, the interparticle friction gradually weakens, leading to a significantly weaker force chain strength compared to the low groundwater level condition.  
Figure 19: The subsurface particle displacements at 400,000 simulation steps.  
Figure 20: The internal force chains within the subsurface at 5000 simulation steps.  
The computed results clearly indicate that groundwater levels significantly affect soil particle displacement and stratum subsidence. When a pipeline rupture occurs, it disrupts the previously stable groundwater flow field, creating a noticeable hydraulic gradient between the unpressurized pipeline's interior and the surrounding soil. This hydraulic gradient becomes more pronounced with higher groundwater levels, leading to a higher flow velocity of groundwater into the pipeline. Consequently, the water flow exerts a stronger erosive action on the soil particles. Furthermore, in areas with high groundwater levels, a larger portion of the subsurface becomes saturated, weakening the interlocking behavior between particles. When combined with the increased hydraulic gradient, the soil becomes more susceptible to significant damage and erosion.