Numerical modelling of submarine landslides and their impact to underwater infrastructure using the material point method

[Truncated] Oil and gas developments in deep waters pose increasing challenges for offshore geotechnical engineers. One of the major concerns is potential geohazards for pipelines and other subsea infrastructures. Submarine landslides, usually initiated by the failure of an unstable soil mass on the continental shelf, could impact nearby pipelines and lead to severe damage or even failure. Geohazard assessment for new offshore developments therefore tends to be dominated by establishing the potential for submarine landslides, the probability of sliding material impacting a pipeline, and assessing the potential consequences. From the engineer’s perspective, quantitative characterisation of velocity, run-out distance of the slide and the impact force between the sliding material and the pipeline is essential to avoid disastrous events such as the failure of a pipeline.

The ultimate aim of this research is the numerical simulation of the run-out of sliding material and the impact forces on pipelines. In order to achieve this, a new numerical method, the material point method (MPM) has been adopted as this approach has the capability of simulating the extreme material deformation involved in landslides and impact of the debris flow on structures. The major part of the thesis is therefore devoted to the development and implementation of MPM, leading eventually to exploring impact forces against a fixed rigid pipe.

Numerical modelling of submarine landslides is very challenging even for a total stress analysis. During the event of a submarine landslide, as the sliding material is remoulded and entrains water, it transforms into a debris flow and eventually a turbidity current that may travel for several hundreds of metres to hundreds of kilometres. This poses significant challenges for numerical simulation as the sliding material undergoes extreme deformation and the constitutive properties are history dependent. Moreover, as the stiffness of the pipeline is much greater than that of the sliding material, impact would lead to extremely large localised deformations and failure of the sliding material.