Centrifuge modelling of the behaviour of buried pipelines subjected to submarine landslides

The assessment of the potentially destructive impacts of subaqueous landslides on offshore pipelines is required when the pipeline route passes through zones with a risk of mass movements. Therefore, quantifying and evaluating the ultimate load/pressure acting on the pipeline is one of the key factors in geotechnical safety design of the pipeline. One of the triggers of subaqueous soil mass movements is the monotonic loads, which induce the trigger relative displacement between a soil layer and a pipe under both drained and (partially) undrained conditions. Two approaches based on geotechnical and fluid dynamics perspectives have been proposed for estimating the ultimate load/pressure for different stages of a submarine landslide. Traditionally, the former method focuses on the analysis of pipelines installed under flat seabed experiencing relative movements to the surrounding soil, whereas, the latter method focuses on the behaviour of pipelines laid on the surface of the seabed and subjected to debris flows. However, offshore pipelines are often buried under the seabed, which is not always flat and has a modest inclination in some cases. This engineering condition normally differs from that of the simplifying assumptions and boundary conditions (such as seabed inclination, and soil strength) commonly imposed to the geotechnical and fluid dynamics approaches. Accordingly, a better understanding of the soilpipeline interaction when the pipelines are buried in subaqueous slopes is essential for evaluating the ultimate load/pressure that would be caused by the slope failures.
This thesis presents a research effort on investigating the soilpipeline interaction during subaqueous slope failures using advanced physical modelling. In this research, the experiments can be divided into two main groups according to the soil drainage conditions. The first group of tests were carried out in the drained condition by using dry sand as the soil material for the slopes. The pipe was buried at 5 different locations inside the slopes to study the pipe burial position and pipe embedment ratio effects on the ultimate pressure during slope instability. Particle image velocimetry analysis was conducted to study the pipe movement and slope failure mechanisms. The results of these tests reveal that the slope angle and the pipe distance to slope crest play significant roles on the ultimate loads acting on the pipe.