Experimental and numerical modeling of lateral pipeline-trench interaction backfilled with sand

Esmaeilzadeh, Mehdi (2019) Experimental and numerical modeling of lateral pipeline-trench interaction backfilled with sand. Masters thesis, Memorial University of Newfoundland.

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Abstract

Subsea pipelines are usually buried for physical protection in shallow waters. Pipelines may undergo large lateral displacements duce to ice gouging, ground movement, extreme thermal gradients, fish traps, pulling by anchors, etc. Sand backfills that have a different stiffness relative to the native ground are sometimes used for backfilling of the pipelines. The different stiffness of the sand backfill and the native ground affects the failure mechanism around the laterally moving pipe, and consequently the ultimate laterally mobilized soil resistance. This important effect is not considered by design codes in the lateral design of pipelines due to less explored failure mechanisms in pipeline-backfill-trench interaction process. In the current study, the lateral interaction between trenched pipeline backfilled with loose sand was investigated by performing centrifuge model tests. Soft slurry and lose sand backfills were used to facilitate investigation of the backfill stiffness effect. Transparent observation window was used with digital cameras to conduct Particle Image Velocimetry (PIV) and capture the internal soil deformation mechanisms. State-of-the-art instrumentation was used to collect high-quality data from the pipe, backfill, and trench. Partially drained condition was adopted to allow for full development of interaction mechanisms. Advanced numerical simulation of the conducted the tests was also conducted by using Coupled Eulerian-Lagrangian (CEL) analysis and built-in constitutive soil models in ABAQUS/Explicit. The study showed the significant influence of the relative backfill-trench stiffness on the lateral response of pipeline to large displacements. Comparisons with design codes revealed that the proposed equations by design code underestimate the lateral response inside the backfill, overestimate the lateral response for pipe penetrating into the trench wall, and propose no prediction for the pipe approaching the trench wall.

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