Numerical Investigation of Interaction Behavior in Large-Diameter Buried Parallel Pipelines Subjected to Variations in Internal Conditions

Buried parallel pipelines are increasingly common, and unlike single-line systems, adjacent pipelines exhibit mutual interactions. This study investigated their behavior under symmetric and asymmetric conditions, considering empty pipeline, water filling, and normal working, as well as the effects of diameter-to-thickness ratio, spacing, and burial depth. The results indicate that the pipeline–soil interaction differs significantly from single pipelines and is highly dependent on working conditions. Under symmetric conditions, vertical and horizontal deformations differ by 3.0–4.3 mm; contact pressure is nearly circular under empty pipeline and water filling conditions, but elliptical under normal working condition; tangential force follows a cloverleaf pattern; and soil pressure at the pipeline top and vertical soil support lose axial symmetry, with unequal horizontal resistance on either side. Under asymmetric operations, the largest differences occur under the water filling—normal working condition, with the soil pressure at the top of the #1 pipeline being 36.7% lower than that of the #2 pipeline. Moreover, smaller diameter-to-thickness ratios reduce sensitivity to working conditions, while greater burial depth linearly increases deformation and soil pressure, amplifying inter-pipeline differences. Pipeline spacing has only limited effects. These findings reveal the mechanical properties of parallel pipelines under various operating scenarios, providing a reference for the design of multi-pipeline systems.