Predicting the Instability Trajectory of an Obliquely Loaded Pipeline on a Clayey Seabed

Ning Wang,Wengang Qi,Fuping Gao

doi:10.3390/jmse10020299

Abstract

Predicting the instability trajectory of an obliquely loaded pipeline on the seabed is vital for the global buckling assessment. To numerically investigate the obliquely loaded pipe–soil interactions, a plane strain elastoplastic finite element model incorporating the adaptive meshing technique and the contact-pair algorithm is employed and verified with the existing experimental data and the analytical predictions. The evolution of slip mechanisms within the underlying soil is simulated, indicating the instability direction of the pipe, and the corresponding ultimate soil resistance is closely correlated. It is also indicated that the ultimate load angle is in the positive correlation with the movement angle, the dimensionless embedment of the pipe and the roughness coefficient of the pipe–soil interface. On the basis of numerous simulations, a force-resultant plasticity model including the bearing capacity envelope and the flow rule is proposed for predicting the behavior of a partially embedded pipeline on the clayey seabed. Finally, an explicit expression with respect to the critical submerged weight of the pipe is derived for distinguishing the lateral instability of a pipe between the ‘light’ and the ‘heavy’ mode.

Highlights

Submarine pipelines in deep waters are commonly laid directly on the seabed, which is a dominantly soft clayey deposit with low shear strength [1,2,3]
The deep-sea pipelines may penetrate into the clayey seabed by a fraction of a diameter due to self-weight and the dynamic effect involved in the laying process [4]
The process associated with the large lateral displacement of a pipeline was experimentally and numerically studied by Tian and Cassidy [30] and Chatterjee et al [31], respectively. Their results indicated that the movement trends for either the upward or the downward were mainly dependent on the overpenetration ratio and the dimensionless embedment of the pipe

Summary

Introduction

Submarine pipelines in deep waters are commonly laid directly on the seabed, which is a dominantly soft clayey deposit with low shear strength [1,2,3]. Two extreme cases were considered in their limit analysis, where the pipe– soil interface can sustain either zero shear stress (smooth pipe) or the full shear strength of the adjacent soil (rough pipe).Taking account of the geometric curvature effect of the pipe, the adhesion/friction at the pipe–soil interface, and/or the internal friction of the soil, Gao et al [14,15] presented slip-line field solutions of the vertical bearing capacity under undrained and fully drained condition, respectively. The process associated with the large lateral displacement of a pipeline was experimentally and numerically studied by Tian and Cassidy [30] and Chatterjee et al [31], respectively Their results indicated that the movement trends for either the upward or the downward were mainly dependent on the overpenetration ratio (e.g., the ratio of the vertical ultimate bearing capacity to the submerged pipe weight for a pipeline initially laid on the seabed) and the dimensionless embedment of the pipe. AcoknitnienmuuamticwciothupthlienfgaiclounrestdreasincrtibweadsbiymtphoesTerdesbceatywieelednctrhiteernioonde(Esqoufamtioondse(l2p)–ip(4e))a. nTdhethe recofehreesniocne pofotihnet acltatyheeypsoipilewcaesntcehra.rTahcteertirzaendslbaytitohneaul nddisrpailnaceedmsheenatrosftrtehnegmthosdue. l pipe was applied on the reference point, transferred to the pipe section by the coupling constraint

Constitutive Models

Properties of the Pipe and the Clayey Soil

Failure Mechanism

Numerical results:

Trajectory of Pipe Instability