## 4 Mechanical Response of Pipeline Under Mining Influence  
### Influence of Mining on Pipeline Strain  
From Figure 8, the longitudinal strain distribution along the pipeline was symmetrically aligned with respect to the center of the pipeline. The peak longitudinal strain consistently occurred at the midpoint of the pipeline: the maximum tensile strain was located at the center of the pipeline's lower surface, while the maximum compressive strain was found at the center of the upper surface. Additionally, there was a localized concentration of axial strain in areas unaffected by sedimentation, indicating minor variations in pipeline strain even outside the mining areas.  
Before excavation, the axial strain along the pipeline was minimal, maintaining an almost linear distribution. As the mining ratio reached 57%, the coal seam excavation began affecting the surface, leading to an increase in pipeline strain. At this stage, the strain along the upper part of the pipeline exhibited a symmetrical 'M-shape' distribution, characterized by convex ends and a concave middle. This strain pattern increased and then decreased from the periphery towards the center of the mining area, with a maximum recorded strain of 145.21 \(\times\) 10\({}^{-6}\) and a minimum strain in the center of the mining area of \(-\)44.21 \(\times\) 10\({}^{-6}\). This observation confirmed that different locations along the top of the pipeline simultaneously experienced tensile and compressive stresses during the subsidence process, a phenomenon consistent across various stages of mining. Conversely, the axial strain at the bottom of the pipeline displayed a 'W-shape' with upward convexity in the middle and downward concavity at both ends. This strain pattern firstly decreased and then increased from the edge to the center of the hollow zone, with a minimum value  
Figure 7: Settlement of soil around the pipeline.  
of \(-50.47\times 10^{-6}\) and a peak strain of \(156.75\times 10^{-6}\) at the center. The maximum and minimum strains at the bottom of the pipeline exceeded those at the top by 7.4% and 12.9%, respectively.  
As mining progressed and surface settlement became more pronounced, the surface experienced more obvious settlement, and under the combined influence of the pipe's overburden and its inherent gravitational forces, an increase in pipe strain was observed. Consequently, the axial strain concentration within the pipe shifted toward both ends, a shift prompted by the expanding range of surface settlement. Owing to these changes, the pipeline deformation within the mining site could be distinctly categorized into tensile and compressive zones. Within this framework, the tensile zone at the pipe's apex, centrally located in the mining zone, showed a gradual increase. Concurrently, the compressive zone shifted toward the periphery of the mining zone, with minor changes in its length; conversely, at the pipe's base, the compressive zone's presence in the middle of the mining zone became more pronounced, while the tensile zone migrated toward the mining zone's edges, again with minimal alterations in length. Particularly noteworthy was the significant change when the mining ratio reached 86%. At this point, the maximum tensile strain at the pipe's apex increased to 1075.25 \(\times\) 10\({}^{-6}\), marking a 184.72% rise from the strain observed at a 71% mining ratio. Similarly, the maximum compressive strain increased to 509.92 \(\times\) 10\({}^{-6}\), an increase of 246.02%. At the base of the pipeline, the maximum tensile strain rose to 1282.64 \(\times\) 10\({}^{-6}\), a 203.87% increase, and the maximum compressive strain increased to 340.32 \(\times\) 10\({}^{-6}\), a 146.78% rise compared to the strain at a 71% mining ratio. As mining concluded, the peak strain of the pipeline increased only slightly.