Australian Research Council Centre of Excellence Geotechnical Science and Engineering

Thesis

Structural analysis of submarine pipelines under submarine slide and thermal loading

Summary

The proposed research is concerned with the interaction between seabed pipelines and submarine slides, as well as other loading conditions induced by thermal conditions. The research aims to support the transition of oil and gas developments into deeper water and more remote conditions. The principal motivation is the need for export and tieback pipelines to negotiate regions of instability or sloping, where ground movements may occur (i.e. submarine slides), and for these pipelines to withstand other forms of loading. The objectives are:

<1>To improve the techniques for assessing the axial and lateral pipe-soil interaction forces resulting from relative pipe-soil movement, including the passage of mobile slide material along or across a seabed pipeline. Parallels will be drawn with the ‘t-z’ techniques for assessing pile-soil interaction forces. Where appropriate, the theoretical techniques used for pile design will be transferred to pipeline conditions.

<2>To develop analytical models and conduct numerical simulations of pipeline-slide interaction (and also other pipeline loading conditions), to provide insights into the dominant governing parameters and to assess the sensitivity of the pipeline structural loading to the geotechnical (i.e. pipe-soil) input parameters.

<3> to develop nondimensionalised expression of critical lateral buckling load of submarine pipeline subjected to axial compression due to slide loading

<4> to derive expression for thermal walking of submarine pipeline with elastic-plastic soil response

<5> to analyse thermal walking of submarine pipeline with velocity dependent friction.

Why my research is important

A significant body of previous research has studied the related problems of earthquake fault – pipeline interaction (usually for pipelines fully buried in sandy materials) and passive or active lateral pile loading. The research will draw on these previous developments, but will also focus on advancing the analysis techniques for conditions relevant for deepwater pipelines: namely, soft clayey seabed sediments, high velocities of ground movement, and partial pipeline embedment.

Although the initial focus will be on slide-pipeline interaction, it is anticipated that the techniques will be equally applicable to pipeline loading that arises from changes in the pipeline temperature (due to the operating conditions), allowing the poorly-understood phenomenon of ‘pipeline walking’ to be tackled.

The research methods will include analytical modelling, supported by numerical modelling. The simplest combinations of loading and problem geometry will be treated analytically, with the intention of devising either closed-form solutions or solutions which can be solved analytically. More complex cases will be simulated using numerical analysis. The numerical results will be distilled into simplified guidance, in the form of analytical expressions, where possible