Pseudo-Static Finite-Element Assessment of Seismic Soil–Pipeline Interaction in Multi-Line Buried Pipelines

This study investigates the seismic response of double- and triple-buried steel pipeline systems using finite-element modeling in RS2, with particular emphasis on soil–pipeline interaction and symmetry-breaking behavior under pseudo-static seismic loading. Although the pipeline systems are initially symmetric in geometry, material properties, and boundary conditions, the analysis demonstrates that directional seismic excitation induces quantitatively measurable asymmetric responses in shear force, displacement, and spacing due to nonlinear soil–pipeline interaction. Five parametric scenarios were examined, including burial depth (1–5 m), pipeline diameter (8–56 in.), groundwater table (1.4–20 m), peak ground acceleration (0.1–0.6 g), and soil type. The results show that maximum shear forces increase with burial depth and diameter, reaching approximately 15–17 kN in clayey soils at a PGA of 0.4 g, whereas sandy and heterogeneous soils produce lower shear forces (≈12–14 kN). Horizontal displacements are strongly governed by groundwater and PGA, increasing from about 1.2–1.8 m in dry or deep groundwater conditions to more than 2.8 m for shallow groundwater and exceeding 5 m at PGA = 0.6 g. Triple-pipeline systems exhibit higher shear demand due to confinement effects, with the middle pipeline often developing the largest shear force, while the pipeline facing the seismic load consistently experiences the greatest displacement. This study makes two primary contributions. First, it demonstrates that initially symmetric multilined buried pipeline systems exhibit systematic, quantifiable symmetry-breaking behavior under directional seismic loading, manifested as unequal shear forces, displacements, and interaction effects among adjacent pipelines. Second, it presents an integrated multi-parameter coupling analysis that simultaneously accounts for burial depth, pipeline diameter, groundwater level, soil type, and peak ground acceleration, revealing interaction mechanisms that cannot be captured through single-parameter or single-pipeline assessments.