Study on the mechanical response of HDPE pipelines under uneven settlement in soft soil foundations and its influencing factors

High-density polyethylene (HDPE) pipes, valued for their flexibility and corrosion resistance, are increasingly used in infrastructure, yet their behavior under uneven settlement in soft soil remains underexplored.Uneven settlement directly threatens the safety of buried pipelines. This study investigated the mechanical response of HDPE pipelines in soft soil foundations through a combined approach of model tests and numerical simulation (FLAC3D). The results indicate that, under single-factor conditions, increasing the pipe diameter significantly reduces the peak stress in the pipeline (by up to 44.78% in tests), while its effect on suppressing vertical displacement remains limited. Conversely, increases in burial depth and settlement range exacerbate the bending moment, stress, and displacement responses, leading to more pronounced structural deformation. Unlike single-factor studies, this study conducted a systematic multi-factor coupling analysis, which reveals that under shallow burial conditions(≤1.4 m), using a large diameter (≥480 mm) can effectively control both stress and displacement. For a small settlement range (<2.7 m), pipe diameter plays a dominant role in displacement control, whereas stress rebound may occur for a large settlement range (>5.4 m). The influence of burial depth is more significant within a small settlement range (<3.6 m) but diminishes for a large settlement range (>4.5 m). Based on the numerical results, a multi-factor coupled prediction model for stress and displacement was established using nonlinear surface regression, with a verified prediction error within ±10%. However, its applicability is strictly limited to the geological conditions and parameter ranges studied herein. In practical applications, it must be validated against site-specific conditions and should not be extrapolated to scenarios significantly different from those considered in this study.The findings of this study provide theoretical foundations and practical tools for the preliminary design and selection, monitoring point placement at critical sections, maintenance strategy optimization, safety assessment, and design refinement of HDPE pipes in soft soil regions.