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Reliable assessment of the lateral pile-soil interaction is of pronounced importance for the design of mono-pile foundations of offshore wind turbines. As the offshore engineering moves to deeper waters, the diameter of mono-piles is getting larger, usually about 5 m and could be up to 8 m, which may lead to partially drained behaviors of sand in the vicinity of the pile and thus imply limitations of conventional design methods in which fully drained conditions were assumed. To shed light on this issue, a fully-coupled finite element model was established using an in-house developed finite element code DBLEAVES, incorporating a cyclic mobility constitutive model that is capable of describing the instantaneous contractive and dilative response of sands simultaneously. Triaxial and centrifuge model tests were conducted to calibrate the constitutive model and validate the pile-soil interaction model respectively. This is followed by a parametric study primarily focusing on the effects of loading rates. The initial stiffness of the p-y curve was found to increase with the loading rate whilst the bearing capacity showed the inverse, and the mechanism behind this phenomenon is examined in detail. Then an explicit model was developed to evaluate the development of excess pore pressure in the pile front upon lateral loading, and an upper boundary of normalized loading rate was identified to distinguish fully and partially drained conditions.

Accurate assessment of pipe-soil interaction under cyclic wave actions is of pronounced importance for the stability analysis of submarine pipelines in sandy seabed. This paper presents a plane-strain numerical study on such a problem using a finite element program DBLEAVES, which incorporates an elasto-plastic soil model that is capable of capturing the cyclic mobility behavior of sandy soils under cyclic loadings. A detailed validation against analytical solution and model test results was provided to demonstrate the robustness of the present numerical model to mimic both pre- and post-liquefaction behavior of sands, before an extensive parametric study was introduced. It was found that the accumulation of excess pore pressure in the vicinity and far field of a pipeline was strongly affected by the existence of it, with an influential range of about two pipe diameters. The influences of wave and seabed properties (e.g. relative densities) on the uplift response of pipelines were then investigated, based on which an explicit model was developed to quantify the degradation effect of waves on the uplift bearing capacity of pipelines against thermally-induced buckling.

The application of marine pipelines prevails in offshore developments for the transportation of oil and gas products from offshore to onshore, and some of them are inevitably buried in continental slopes with moderate inclinations (mostly below 6°). Regrettably, very limited attention has been paid to the bearing capacity of these pipelines, which generates the very motivation of this study. A total number of 169 200 separate finite element limit analyses (FELA) were conducted on rigid plane-strain pipe sections in inclined clayey seabed, using a sound FELA code OxLim. The breakout resistances of the pipe along all possible directions are explored to determine the most vulnerable plane where a transverse displacement could most likely take place, and accordingly the minimum breakout resistance. Before reaching a full-flow state, this resistance was found to be considerably lower, mostly by 15% to 35%, than the uplift resistance. Design charts that can be immediately used for the modification of existing database are then provided, which promotes the safe design of pipelines regarding transverse displacement or buckling. The potential non-conservation of the most recent design approaches is highlighted through comparisons.