Flowlines and pipelines installed in deep-sea waters are submitted to axial and lateral loads due to the effects of flow stoppages and starts, thermal influences and internal pressure. To study the phenomenon of soilpipeline interaction, a physical model was used and special emphasis was given to the application of large horizontal loads coupled with vertical loads. This paper focuses on the experimental results of two sideswipetype tests with a pipeline model in a very soft soil with undrained shear strength of ~3kPa. Experimental yield envelopes are also included. The experimental tests revealed that for very shallow pipe embedments the maximum horizontal load is obtained for a value of V/Vmax = 0.5, and that for larger embedments this value is in the order of 0.2.

1. Introduction

The design of pipelines installed in deep-sea waters is still a challenge for offshore geotechnical engineering. Flowlines and pipelines can be submitted to combined vertical and horizontal loads, thermal expansion and internal pressure, among other loadings. The pipeline laying installation is not a guarantee of their penetration embedment and, consequently, their stability. The problem of untrenched pipelines has been studied and reported in literature (Murf et al., 1989; Brennodden and Stokkeland, 1992; Cassidy, 2004; Fontaine et al., 2004; Cathie et al., 2005; Zhang and Erbrich, 2005; Cheuk and Bolton, 2006; Dendani and Jaeck, 2007; Bruton et al., 2008; Tian and Cassidy, 2008; among others). A physical model was used to understand the mechanisms of interaction between pipe and soil through a lateral visualisation, and then to simulate the pipe response under combined vertical and horizontal loads. This paper concentrates on the results obtained using sideswipe tests with large and short horizontal displacements, in order to obtain an experimental yielding envelope of the pipe.

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