Effects of Permanent Ground Deformation Patterns on Strain Demand of Pressurized Buried Continuous Steel Pipelines

Abstract

The structural integrity of buried pipelines is often threatened by permanent ground deformation (PGD) within the pipeline route. Oil and gas transmission steel pipelines, which usually traverse several kilometers, are mostly buried. Inevitably, they can cross over areas with considerable geohazard concerns due to different soil types or extreme topographies. PGD usually occurs with various patterns, magnitudes, and directions relative to the pipeline axis with varying influences on the structural performance of buried pipelines. This paper discusses a comprehensive investigation of the effect of PGD patterns on the strain demand of pressurized buried continuous steel pipelines subjected to ground movement. The maximum strains induced in buried pipelines by longitudinal and transverse ground displacements of different patterns are presented. A three-dimensional nonlinear beam-Winkler spring finite-element (FE) analysis is used. The FE model accounts for the elastic-plastic behavior of pipe and nonlinear pipe-soil interaction. A straight NPS 42 Grade X70 steel pipeline with a wall thickness of 14.3 mm was considered and assumed to be fully embedded in two different soil types (stiff clay and dense sand). The pressurized pipeline was subjected to six different PGD patterns (i.e., sinusoidal, trapezoidal, ridge, ramp, block, and step) of three different magnitudes (1.0, 2.0, and 3.0 m). Each pattern was applied in the transverse (vertical and lateral) and longitudinal directions. The results show a significant variation in the strain demand of buried pipelines subjected to the various PGD patterns. The longitudinal strain induced in a pipeline due to PGD of the same magnitude but different patterns varies by up to 752%. Moreover, stiff clay is found to impose more strain on buried pipelines than dense sand. The results presented in this paper can be a useful reference in the safety assessment of straight sections of a similar buried pipeline under PGD.