Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Dr. Timothy A. Newson

Abstract

Offshore oil and gas pipelines are commonly buried below the seabed to provide environmental stability and protection. Many of these pipelines are prone to upheaval buckling following burial. Soil failure mechanisms can extend to the surface (shallow) or remain localised within the soil body (deep); the exact conditions that cause this transition are currently unclear. In very weak soils, rock fill or sand berms are added to the surface of the completed trench after burial, to increase the required pull-out capacity. Despite a relatively large body of research existing in the literature, much confusion still exists as to the appropriate design parameters and failure mechanisms involved for different homogeneous soils. The most appropriate approach for upheaval bucking design in layered materials is even less clear.

A literature review on the upheaval buckling of buried pipelines in cohesive, granular and layered materials was conducted, to identify issues of importance in the design process and appropriate failure mechanisms of soil around uplifting pipelines. A program of scaled physical models were carried out with synthetic clay (Glyben), sand and gravel, as single homogeneous and layered materials, addressing the quantification of the uplift behaviour of buried offshore pipelines. Soil deformation measurements were studied using the models, employing the particle image velocimetry (PIV) technique to investigate the velocity fields and failure mechanisms.

Numerical finite element analyses were conducted to study the resistance of undrained soils against upheaval buckling of buried pipelines to aid interpretation of the laboratory pullout tests and conduct further parametric studies.

Current state-of-the-art in upheaval buckling pipeline design was assessed; guidance for the design of buried pipelines for clays, granular soils and layered soils is provided and some aspects of uncertainty in this area are discussed.

Available for download on Sunday, December 31, 2017


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