Seabed thickness - wave - buried pipeline interaction

An experimental investigation has been presented in this paper to predict the dynamic pore pressure on a pipeline buried in a sand bed due to the action of water waves. Laboratory experiments were conducted in a 2 m wide, 30 m long and 1.7 m deep wave flume. A PVC (Poly Vinyl Chloride) pipe of 160 mm outer diameter, 1.9 m length was used as a model pipeline. A parametric study was carried out to investigate the influence of various parameters like time period, wave height, water depth and burial depth on wave-induced pressure on the buried pipeline. Seepage force that is acting on the pipeline is also calculated by integrating this pressure distribution. Experimental result indicates that the magnitude of the dynamic pore pressure was observed to be maximum on the top of the pipeline and minimum at the bottom and intermediate at the sides. This trend continues for relative burial depths of 0.0, 0.25 and 0.5, for all time periods, wave heights and water depths. For relative burial depths of 0.75 and 1.0, the same trend as mentioned above is continued for time periods upto 1.5s. Beyond 1.5 s, the pressure at the bottom of the pipeline is higher than that at sides. For this range of relative burial depths and time periods the distribution of pressure around the pipeline seems to be quite interesting. This peculiar behaviour of pressure distribution has been explained with the help of a new term 'Relative Seabed Thickness factor' (RST), ratio of total seabed thickness to wave length. It is observed that for relative burial depth of 0.75 and 1.0, the pressure at the bottom of the pipeline is higher than that at sides when RST is less than 0.17. It has been concluded that the Relative Seabed Thickness factor has a predominant influence on the wave-induced pressure on buried pipeline.