Wave-Induced Pipeline On-bottom Stability: Comparisons Between Pipe -Soil And Wave-Pipe –Soil Interaction Models

Gao, Fuping (Institute of Mechanics, Chinese Academy of Sciences) | Wu, Yingxiang (Institute of Mechanics, Chinese Academy of Sciences) | Jeng, Dong-Sheng (Department of Civil Engineering, The University of Sydney) | Jia, Xu (China Offshore Oil Research Center, China National Offshore Oil Company)

OnePetro 

ABSTRACT

To have a better insight into the mechanism of wave-induced pipeline on-bottom stability, the pipe-soil interaction model (Wagner et al., 1987) and the wave-pipe-soil interaction model (Gao et al., 2003) are compared intensively in this paper. This includes the comparisons of their experimental setups, procedure of tests, phenomena of pipe losing stability etc. The comparison indicates that the critical lines for the instability of anti-rolling pipeline and freely-laid pipeline in the empirical wave-pipe-soil interaction model overall agree with the design values , based on both simplified and generalized methods in DnV standard, respectively. However, with the increase of Froude number, the generalized method in DnV standard becomes more conservative than the wave-pipe-soil interaction model for the on-bottom stability design of pipeline. Therefore, wave–pipe-soil coupling effects should be taken into account when we analyze the on-bottom stability pipeline under wave loading.

INTRODUCTION

One of the main problems encountered with the use of the pipeline in offshore engineering is the wave-induced pipeline instability (Herbich, 1985). When a pipeline is installed upon seabed and subjected to wave loading, there exits a complex interaction between wave, pipeline and soil. To avoid the occurrence of pipeline on-bottom instability, the pipeline has to be given a heavy weight of concrete coating or alternatively be anchored/trenched. Both methodologies are expensive and complicated from the aspects of design and construction. Recently, considerable efforts have been devoted into the interaction between pipeline and seabed.

The state-of-the-art in pipeline stability design has been changing very rapidly recently. Three major investigations have addressed the problem of pipeline-seabed interaction, which include PIPESTAB project (Wagner et al., 1987), the American Gas Association (AGA) project (Brennodden et al., 1989) and a project at Danish Hydraulic Institute (DHI) (Palmer et al., 1988).