Generalized predictive framework for lateral break-out resistance of submarine pipelines considering nonlinear seabed geometry and consolidation: Fid-Bau Portal

Generalized predictive framework for lateral break-out resistance of submarine pipelines considering nonlinear seabed geometry and consolidation

Ghorai, Bithin / Chatterjee, Santiram / Gourvenec, Susan

Abstract

Highlights • Effects of installation and consolidation on pipe break-out capacity are studied. • A range of pipe weights, embedment depths, and degrees of consolidation is explored. • Improvement in break-out capacity is linked with gain in soil shear strength. • Combined capacity of pipe is expressed in terms of normalized failure envelopes. • Generalized expressions are provided as predictive methodology for design.

Abstract The ultimate capacity of submarine pipelines under combined vertical and horizontal loading, so-called lateral break-out resistance, is influenced by the change in seabed geometry due to the installation process and subsequent drainage with associated gain in soil shear strength due to consolidation. The majority of existing solutions in the literature and the current design practices for the assessment of lateral break-out resistance are based on small-strain geometry assumptions and the unconsolidated undrained soil response, i.e. without considering the change in seabed geometry due to installation or improvement in shear strength of the surrounding soil due to post-installation consolidation. In this paper, the effects of installation and subsequent consolidation on the combined load carrying capacity of on-bottom pipelines in a soft clay seabed are investigated and quantified in a systematic manner. A large deformation finite element approach coupled with the Modified Cam Clay plasticity model is adopted to simulate the installation of pipelines, and a series of coupled small strain finite element analyses are performed to study the consolidation and break-out response. A comprehensive range of normalised pipe installation depth, preload level and consolidation time period is considered. Results are interpreted using a critical state framework, and expressed in terms of generalized equations for ease of application in engineering design. A predictive methodology is developed for the estimation of combined load capacity of submarine pipelines in soft clay, including the influences of installation, drainage and consolidated strength.