Mechanisms of pipe embedment and lateral breakout on soft clay

Pipelines laid on the seabed expand and contract during operating cycles as a result of thermal loading, which can lead to lateral buckling. Analysis of this behaviour requires assessment of the vertical penetration and lateral breakout responses. This paper reports centrifuge modelling of these processes, using advanced image analysis techniques to observe the soil deformation. Simple mechanisms are fitted to the observed deformation patterns, allowing the mobilized soil strength to be back-calculated. The vertical embedment mechanisms closely match plasticity solutions. Even if heave is accounted for, the penetration resistance is slightly higher than calculations based on the undrained strength inferred from a T-bar penetrometer. This discrepancy can be attributed to the additional remoulding and softening during steady flow around a T-bar compared to shallow pipe penetration. The lateral breakout response is brittle, and the peak resistance is governed by the available tensile resistance behind the pipe. During steady lateral sweeping the pipe rises close to the original soil surface. At this stage the resistance is governed by the growth of a soil berm ahead of the pipe. Accurate assessment of the near-surface soil strength is difficult, hampering the use of theoretical solutions.