Multi-mechanism fragility surface assessment of buried steel pipelines subjected to landslide-induced permanent ground deformations

Landslide-induced permanent ground deformations (PGDs) pose a significant threat to the structural integrity and operational safety of natural gas pipelines. Existing vulnerability assessments often focus on a single failure mode, potentially underestimating overall risk. This study evaluates pipeline vulnerability by incorporating multiple failure mechanisms, specifically local buckling, beam buckling, ovalization, and tensile rupture, using an advanced 3D nonlinear continuum finite element model for API X52 steel pipelines ( D / t = 96). Quasi-static analyses were conducted for 18 landslide widths to characterize the dispersion of engineering demand parameters (EDPs). Multiple linear regression was subsequently employed to simultaneously account for the effects of landslide width and displacement on the EDPs, leading to the development of mode-specific fragility surfaces. While landslide width exhibits limited influence on the probability of failure exceedance, it significantly dictates the spatial distribution of failure mechanisms. Notably, a high degree of fidelity is demonstrated by the close agreement between the 3D continuum numerical results and the derived fragility surfaces. The findings indicate that local and beam buckling govern the failure response, occurring in close proximity, while ovalization remains less critical following tensile rupture. Finally, system-level fragility surfaces were derived using the first-order reliability bounds approach. This multi-mechanism framework offers a computationally efficient and high-fidelity basis for rapid probabilistic risk assessment of buried steel infrastructure subjected to landslide hazards.