A series of wave flume experiments are carried out to investigate the pore pressure distribution around twin pipelines in fine-sandy seabed. Typical characteristics of the pore-water pressures have been summarized for different wave periods, burial depths and the interval spacing. The differences between single and twin pipeline conditions are also studied. Results show that the identical cylinder close to the existing pipeline has significant impacts on the distribution of pore-water pressures around the pipelines. The pore-water pressures increase with the increase of wave period, while the amplitude of pore pressure decreases with the increasing interval spacing and the burial depth.
With the rapid development of fossil energy exploitation in the ocean, submarine pipelines have been playing a significant role in the offshore transportation of oil and gas in the past decades. Pipelines placed on an erodible seabed may undergo several kinds of destroys when exposed to sufficiently strong waves/currents. One potential danger is the wave-induced liquefaction in a porous seabed, which may cause damaging instability of buried pipelines, like sinking or floatation (Dunlap et al., 1979; Herbich et al., 1984). Thus, the evaluation of the pore pressure response in seabed is of great importance to pipeline engineers involved in the design of offshore pipelines.
Yamamoto et al. (1978) proposed and verified an analytical solution for the pore pressure and the displacements of the porous medium in a poroelastic seabed exposed to the propagating waves on the basis of Biot's model (Biot, 1941), and concluded that the permeability and stiffness ratio of the soil are significant parameters in investigating the seabed response. A one-dimensional model was developed by Magda (1990) to analyze the phase delay in pore pressure in consideration of the saturation and compressibility of both water and soil skeleton, and Magda (1996) further promoted this model to a two-dimensional one. Zen and Yamazaki (1990) introduced a new concept of "oscillatory" excess pore pressure and developed a one-dimensional criterion for liquefaction with this new concept, while Jeng (1997) further developed this criterion to three-dimensional. In order to study the complete sequence of sediment behavior under progressive waves, Sumer et al. (2006a) conducted a series of experiments and divided the whole liquefaction process into four parts including pressure buildup, liquefaction, dissipation of pore pressure and the generation of ripples.
