Assessment of the consolidated breakout response of partially embedded subsea pipelines

Abstract

The changing soil strength due to consolidation around a subsea pipeline can alter the lateral breakout resistance. Results of elasto-plastic coupled consolidation finite element analyses are presented that quantify the effect of consolidation on the undrained breakout resistance and trajectory of partially embedded seabed pipelines. Breakout resistance is presented in terms of failure envelopes in vertical-horizontal load space, which also allow the trajectory of the pipe during breakout to be determined by normality. Observed responses for consolidated undrained breakout are described by simple algebraic expressions as a function of initial pipe embedment, pipe self-weight (and consequent consolidation pressure) and breakout load path.Consolidation and the associated enhancement of the shear strength of the surrounding soil can have a significant effect on the breakout response. The assumption in current practice of unconsolidated undrained soil behaviour may lead to underestimation of pipeline breakout resistance and inaccurate prediction of the trajectory of the pipe during breakout.

Consolidated undrained load-carrying capacity of subsea mudmats under combined loading in six degrees of freedom

“…Feb 2015 4 applied to predicting gains in lateral break out resistance of submarine pipelines as a result of relative vertical preload and degree of consolidation (Chatterjee et al 2014). …”

Effect of embedment on consolidated undrained capacity of skirted circular foundations in soft clay under planar loading

“…The effect of consolidation on the undrained vertical capacity of shallow foundations has been previously investigated (Zdravkovic et al 2003, Lehane & Jardine 2003, Lehane & Gaudin 2005, Chatterjee et al 2012, Fu et al 2015. A limited number of studies have addressed combined load capacity following consolidation for surface foundations (Bransby 2002, Vulpe et al 2016, shallowly embedded rectangular subsea frames (Feng & Gourvenec 2015) and pipelines (Chatterjee et al 2014).…”

Softening and consolidation around seabed pipelines: centrifuge modelling

“…where N is the enhanced normal force that takes into account the wedging effect around the pipe 369 as defined by Equation 8 (Chatterjee et al (2014)), whilst the factor f takes into account the 370 non-uniform distribution of the stress in the affected zone of soil. The resulting increase in 371 strength of the soil affected by consolidation is then calculated as: 372…”

“…In recent years, axial and lateral pipe-soil interactions have been studied extensively by 63 researchers, with a particular focus on the undrained conditions that generally prevail during using analytical approaches (Randolph and Houlsby (1984), Murff et al (1989), Martin and 66 Randolph (2006), Randolph and White (2008), Martin and White (2012), Randolph et al (2012)) 67 and finite element analysis (FEA) both through small-strain (Aubeny et al (2005), Merifield et al 68 (2008), Merifield et al (2009), Krost et al (2011), Chatterjee et al (2014)) and large-deformation approaches (Wang et al (2010), Chatterjee et al (2012c), Chatterjee et al (2012a), Chatterjee et 70 al. (2012b), Chatterjee et al (2013)) are plenty, and can provide a prediction of pipe axial or 71 lateral breakout capacity if the undrained shear strength conditions of the soil are known and 72 defined simply (such as uniform or increasing linearly with depth).…”