Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Bearing Capacity of an Obliquely-Loaded Pipeline on a Clayey Seabed: A Slip-line Field Solution
Ning Wang a,b, Wen-Gang Qi a,b, Yu-Min Shi a,b, Fu-Ping Gao a,ba Institute of Mechanics, Chinese Academy of Sciences, Beijing, Chinab School of Engineering Science, University of Chinese Academy of Sciences, Beijing, Chinaor semi-empirical solutions have been proposed by simplifying thecircular pipe-soil interface as a rectangular (Small et al., 1971) or awedged foundation (Karal, 1977). Based on the limit analysis ofplasticity theory, an upper bound solution for the pipe-soil interaction
was derived by Randolph and White (2008). The bearing capacity of thepipeline can be consequently solved using the upper bound solution;nevertheless the solution is implicit and mainly applicable to partiallyembedded pipelines. Based on the slip-line field theory, Gao et al. (2013)derived an explicit analytical solution for the vertical bearing capacity ofa pipeline partially-embedded or fully-buried in a clayey seabed. To
predict the lateral instability of a pipeline in ocean currents, a pipe-soil
interaction model was established by Gao et al., (2016) using the limit
equilibrium approach, in which the Coulomb’s theory of passive earthpressure for the sloping seabed is incorporated in their derivation.

ABSTRACT
Predicting the ultimate bearing capacity of a deep-sea pipeline on the soft
clayey seabed is crucial for on-bottom stability and global buckling
analyses. Based on slip-line field theory, an analytical solution is derived
for the undrained bearing capacity of an obliquely-loaded pipeline on aclayey seabed obeying Tresca criterion. For a wished-in-place pipeline,
the failure mechanisms and the corresponding pipe-soil interface
conditions are proposed for the vertical and the lateral instability mode,respectively. Based on the derived slip-line field solution, a series offailure envelopes are established for various pipe-soil interface
conditions. The analytical solution matches well with the previous
numerical and theoretical results. Parametric study indicates that theembedment-to-diameter ratio and the loading angle are the key
parameters for the bearing capacity of an obliquely-loaded pipeline.

Numerical models have been intensively employed for simulating pipesoil interactions. By applying the arbitrary Lagrangian-Eulerian (ALE)remeshing technique, Merifield et al. (2009) simulated the vertical
penetration procedure of a pipeline. A pipe-soil interaction model wasestablished by Tian and Cassidy (2011), which can predict large lateraldisplacements of the pipe in the calcareous sand. Martin and White (2012)
numerically investigated the effect of pipe-soil interface properties on
the failure mechanism and the corresponding bearing capacity. A largedeformation finite-element method was employed by Chatterjee et al.
(2012) for modeling the large lateral movements of the pipeline on aclayey seabed. The hardening and softening of the soil in correlation withstrain rate and accumulated shear strain were considered in theirconstitutive model. An elasto-plastic finite element model incorporating
the adaptive meshing technique and the contact-pair algorithm wasrecently proposed by Wang et al. (2022) for predicting the instability
trajectory of an obliquely loaded pipeline on a clayey seabed. Liu et al.
(2014) numerically simulated the lateral global buckling of a longpipeline with the implicit and explicit methods, respectively. However,the computational cost and the calculation stability remain to beunsatisfactory, especially when predicting the global buckling of a longpipeline with the three-dimensional analysis.

KEY WORDS: bearing capacity; deep-sea pipeline; oblique loading;slip-line field theory; failure envelope; pipe-soil interaction; clayey
seabedINTRODUCTION
Soft clayey sediments are widely distributed in the deep waters of South
China Sea (see Liu et al., 2021). The deep-sea pipelines are generally
laid directly on the seabed, where the pipelines may penetrate partiallyor even completely into the soil during their service period (DNV GL,2017). Under the action of ocean currents, a partially-embedded pipeline
would suffer an oblique hydrodynamic loading including the drag(horizontal) and the lift (vertical) forces. While the deep-sea pipelinetransports oil and gas with high temperature and high pressure, an axial
compressive force could be induced along the pipeline (Taylor and Gan,1986). Under the external (hydrodynamic forces) or/and the internal(axial compressive force due to the rise of temperature and pressure)loads, the pipeline may break away from its original location whilelosing on-bottom stability (Gao et al., 2007) and even buckle along theseabed surface (Bruton et al., 2006). As such, a reliable assessment of
the ultimate bearing capacity of an obliquely-loaded pipeline on theclayey seabed is necessary for predicting the instability of deep-sea
pipelines (Fredsøe, 2016; Gao, 2017).

In this study, a slip-line field solution is proposed for predicting thebearing capacity of an obliquely-loaded pipeline on a clayey seabed. The
analytical solution is verified with the previous numerical and theoreticalresults. A series of failure envelopes are established for various pipe-soil

To predict the vertical bearing capacity of submarine pipelines, empirical

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