The interaction between the seabed and unburied pipelines is one of the key uncertainties associated with deepwater and/or high pressure, high temperature (HPHT) pipeline design. Emerging research is shedding light on this important topic that is not currently well understood. BP has amassed a considerable quantity of data from different basins ranging from conventional in situ measurements of soil properties (supplemented by two campaigns using Fugro's SMARTPIPE®) to model testing at the Norwegian Geotechnical Institute (NGI) and the University of Western Australia (UWA). Added to this, standard and advanced low stress interface shear testing has been carried out in laboratories at the University of Texas, Austin, UWA and Fugro. These tests were designed to address the key mechanisms governing axial pipe-soil interaction behaviour, spanned a large range of pipe properties and sliding velocities, and included episodes of post-sliding reconsolidation. New data from all of these sources are given in this paper, along with a theoretical framework developed to synthesise these results and contribute to improved practice for the design of pipelines that are susceptible to walking, buckling and other forms of movement.

1. Introduction

It is well known that the interaction between surfacelaid pipelines and the seabed is extremely complex. The challenge for geotechnical and pipeline engineers is to model this interaction in a manner that can be efficiently applied in design calculations and analyses. In addition, this modelling will need to produce safe and reliable results, while faithfully reproducing the relevant physical processes in play. Design calculations for buckling and walking can be classified as either analytical or numerical. In analy-tical calculations, the pipe-soil response is modelled as rigid-plastic, characterised by a single parameter - the ultimate resistance. In numerical calculations, the response may be elastic-plastic (i.e. bi-linear), or may be a more complex piecewise linear variation.

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