A series of wave flume experiments are carried out to investigate the seabed response around a trenched pipeline. The trench is backfilled with three kinds of sand (d50=0.15mm, 0.3mm and 0.5mm) and to different backfilled depths. The incident waves change with height and period. The results show that higher pore pressures are recorded at the top of the pipeline and lower pore pressures at the bottom. The amplitude of pore pressure is larger in coarser sand and the variation of pore pressure with the increase of backfilled depth is varied in different kinds of sand.
Submarine pipelines are widely used for the transportation of oil and gas in ocean engineering. Like other offshore structures, pipelines may be damaged by the complicated marine environment. Due to wave- induced seabed instability, many offshore pipelines have been reported to be damaged in the past years (Herbich et al., 1984; Christian et al., 1974). In general, ocean waves propagating over the seabed can exert dynamic pressure fluctuation in the soil skeleton, and further generate excess pore pressure accompanied with a decrease in effective stress within the seabed soil. As a result, the seabed underlying the pipeline may become unstable or even liquefied. Therefore, a proper evaluation of the wave-induced soil response is particularly important for the protection of offshore pipeline.
Extensive investigations on the wave-induced seabed response have been carried out in both theoretical and experimental approaches. Based on Biot's model (Biot, 1941), Madsen (1978) proposed an analytical solution for the wave-induced effective stresses in an anisotropic seabed and concluded that the effect of partial saturation on soil response is of great significance. Madga (1990) developed a finite difference model to examine the influences of saturation and compressibility on time phase in pore pressure. Tzang (1992) conducted a series of wave tank experiments and obtained the relationship between the build-up of pore pressure and fluidization. In additional to laboratory experiments, Zen and Yamazaki (1991) reported several field observations of wave-induced pore pressure and found that liquefaction was closely related to the upward seepage flow in seabed under wave troughs.
