The effect of backfilling stiffness on lateral response of the shallowly trenched-backfilled pipelines in clay

Abstract

Offshore pipelines need to be trenched and backfilled in shallow waters for physical protection against the environmental, operational, and accidental loads. These buried pipelines may encounter lateral pipe-soil interaction in various incidents such as ground movements, landslides, ice gouging, and dragging by embedment anchors and fishing gears. Using the pre-dredged material for backfilling is a common and cost-effective solution to fill the trenches. During the construction process and being exposed to the environmental loads, the backfill material is significantly remolded and becomes much softer than the native ground. The different stiffness of backfill and native ground along with trench configuration may significantly affect the internal soil deformations, failure mechanisms, and consequently the lateral soil resistance against the laterally displaced pipeline. However, this important and less-explored aspect is neglected by existing pipeline design standards. In this study, centrifuge tests, particle image velocimetry (PIV), and large deformation numerical analysis were conducted to investigate the effect of different backfilling stiffness on lateral pipeline-backfill-trench interaction and the failure mechanisms around a pipeline shallowly buried in clay. The study showed that ignoring the trenching/backfilling effects may overestimate the ultimate lateral soil resistance for large displacements and underestimate it in small to medium displacements.

Keywords:

• Lateral pipe-soil interaction
• pipeline-backfill-trench interaction
• p-y response
• large deformation analysis
• centrifuge testing

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors gratefully acknowledge the financial support of “Wood Group” that established a Research Chair program in Arctic and Harsh Environment Engineering at Memorial University of Newfoundland, the “Natural Science and Engineering Research Council of Canada (NSERC)”, and the “Newfoundland Research and Development Corporation (RDC) (now TCII)” through “Collaborative Research and Developments Grants (CRD)”. Special thanks are extended to Memorial University for providing excellent resources to conduct this research and also the technicians at C-CORE’s centrifuge lab for their kind technical support.