Effects of Asymmetrical Vertical Soil Stiffness on Strain Demand of Steel Pipelines Subjected to Transverse Vertical Permanent Ground Deformation: Fid-Bau Portal

Effects of Asymmetrical Vertical Soil Stiffness on Strain Demand of Steel Pipelines Subjected to Transverse Vertical Permanent Ground Deformation

Agbo, Sylvester / Roy, Kshama / Adeeb, Samer / Li, Yong

Abstract

Buried transmission pipelines generally traverse long distances, which potentially increase their susceptibility to geotechnical hazards. Geohazards triggered by permanent ground deformation (PGD) in the vertical plane, e.g., subsidence, frost heave, thaw settlement, and uplift, can potentially induce large plastic strain on buried pipelines. Not only the magnitude and direction but also the pattern of this vertical ground movement can result in different pipeline strain demands, which are crucial for assessing the structural performance of pipelines. This paper presents the effects of the asymmetrical soil stiffness in the vertical plane on the response of buried pipelines subjected to two different patterns of transverse vertical PGD (Step and Block) patterns. Using the nonlinear beam-spring finite-element modelling technique in Abaqus, the analysis is conducted for an NPS 42 X70 pipe with a uniform wall thickness of 14.3 mm buried in four different types of soil and subjected to a PGD magnitude of 3.0 m. The pipeline is internally pressurized to the maximum operating pressure of 9.93 MPa and temperature variation of 50°C. The results show a significant variation in the strain demand of buried pipelines subjected to the Step PGD pattern due to the asymmetric soil stiffnesses in the vertical direction. Not only the ratio of upward and downward soil resistances but also their values affect the strain demand of the pipeline against the Step pattern.