Post-Earthquake Inspection Zoning of Buried Pipelines in Liquefiable Ground Based on Manhole Uplift

Abstract Rapid post-earthquake inspection of buried pipelines in liquefiable ground is difficult because damage is concealed, whereas manhole uplift H can be measured at the surface. This study develops a three-level inspection-zoning method that links this visible field indicator to the internal response of an adjacent buried steel pipe. A coupled FLAC3D model was established for the manhole–pipeline–soil system, including pore-pressure accumulation, degradation of pipe–soil restraint, manhole–soil slip, and load transfer through the manhole–pipeline connection. The model reproduced a field case with approximately 0.50 m uplift; the calculated uplift was 0.553 m, a difference of 10.6%. Twenty-four analyses combined six pulse-like or non-pulse-like records with peak ground accelerations of 0.1–0.4 g. At 0.4 g, pulse-like motions produced a mean uplift of 0.585 m, 2.1 times the non-pulse-like mean of 0.280 m, while the corresponding mean maximum axial strains were 1.073 × 10⁻³ and 0.856 × 10⁻³. Across all cases, H and maximum pipeline axial strain were positively associated (Pearson r = 0.888; Spearman ρ = 0.883), but strain localization depended additionally on liquefied-zone boundaries and transient deformation compatibility. Accordingly, H is not used to invert actual strain. Instead, case-specific reference boundaries of 0.30 and 0.64 m define routine patrol, review, and priority-inspection zones, with leakage, pressure anomalies, pavement cracking, and joint offset used as escalation criteria. The resulting field chart provides a rapid, observable basis for allocating inspection resources after an earthquake.