The load-penetration response of a pipe in clay is of fundamental importance to the on-bottom stability assessment of a pipeline and the interpretation of T-bar penetrometer data. This paper aims to summarize the findings of a series of large strain large deformation numerical analyses performed to simulate the continuous loadpenetration response of a smooth pipe section with particular emphasis on the transition from a shallow bearing capacity mechanism to a deep plastic flow mechanism and elucidates on the practical implications of the key findings.
In a deepwater oil and gas development, a pipeline is often laid directly on the seabed. The on-bottom stability of the as-laid pipeline is strongly influenced by the pipeline embedment depth. The pipeline embedment depth has a significant effect on both the hydrodynamic loads acting on the pipeline as well as the lateral soil resistance provided by the seabed. Therefore, an accurate prediction of the vertical load-penetration response of a pipe section, especially at embedment depths of up to 0.5 pipe diameter, is imperative for a reliable on-bottom stability assessment. The second area of interest in which the vertical load-penetration response of a pipe is of particular interest concerns the adoption of a Tbar penetrometer for measuring the undrained shear strength, su of cohesive soils, especially in soft deepwater sediments. The current state-of-practice involves the adoption of a constant T-bar factor of 10.5 for the conversion of T-bar penetration resistance to the undrained shear strength of the soil. White et al. (2010) pointed out that a constant T-bar factor is only applicable when the full-flow mechanism is operative. Puech et al. (2010) further noted that there is insufficient information on the failure mechanisms at very shallow penetration, especially within the first 0.2-0.3 m below seafloor.