In this study, the vortex-induced vibrations of a cylinder near a rigid plane boundary in a steady flow are studied experimentally. The phenomenon of vortex-induced vibrations of the cylinder near the rigid plane boundary is reproduced in the flume. The vortex shedding frequency and mode are also measured by the methods of hot film velocimeter and hydrogen bubbles. A parametric study is carried out to investigate the influences of reduced velocity, gap-to-diameter ratio, stability parameter and mass ratio on the amplitude and frequency responses of the cylinder. Experimental results indicate: (1) the Strouhal number (St) is around 0.2 for the stationary cylinder near a plane boundary in the sub-critical flow regime; (2) with increasing gap-to-diameter ratio (e 0 /D), the amplitude ratio (A/D) gets larger but frequency ratio ( f / f n ) has a slight variation for the case of larger values of e 0 /D(e 0 /D > 0.66 in this study); (3) there is a clear difference of amplitude and frequency responses of the cylinder between the larger gap-to-diameter ratios (e 0 /D > 0.66) and the smaller ones (e 0 /D < 0.3); (4) the vibration of the cylinder is easier to occur and the range of vibration in terms of V r number becomes more extensive with decrease of the stability parameter, but the frequency response is affected slightly by the stability parameter; (5) with decreasing mass

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Two mechanisms for the wave-induced pore pressures in a porous seabed, i.e. oscillatory and residual excess pore pressures, have been observed in laboratory experiments and field measurements. Most previous investigations have focused on one of the mechanisms individually. In this paper, an analytical solution for the wave-induced residual pore pressure, which is not available yet, is derived, and compared with the existing experimental data. With the new solution, a parametric analysis is performed to clarify the applicable ranges of two mechanisms. Then, a simplified approximation for the prediction of wave-induced liquefaction potential is proposed for engineering practice.seabed, pore pressure, residual, oscillatory, wave loading One of the important marine geotechnical engineering considerations for many engineering installations in oceanic environments, such as platform, pipeline and anchors, is the liquefaction potential of seabed due to ocean waves. Numerous examples of liquefaction have been reported in the literature, such as, floatation of pipeline during storm [1] , sinking of several measuring instructions in Mississippi Delta [2] and subsidence of offshore breakwaters at Niagata Coast, Japan [3] . Two significant mechanisms accounting for wave-induced soil response, including oscillatory pore pressure and residual pore pressure, have been observed in laboratory experiments and field measurements [4] , as shown in Figure 1. The first mechanism, termed as transient or oscillatory excess pore pressure, is accompanied by the attenuation of amplitude and the phase lag in pore pressure changes [5,6] . This mechanism is more important for unsaturated marine sediments and deeper water region. The second mechanism, termed as the residual pore pressure, is the build-up of excess pore pressure caused by contraction of the soil under the action of cyclic loading [7,8] . This mechanism is similar to the earthquake-induced pore pressure accumulation.Numerous investigations for ocean waves propagating over a porous seabed have been carried

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Unlike previous mechanical actuator loading methods, in this study, a hydrodynamic loading method was employed in a flow flume for simulating ocean currents induced submarine pipeline stability on a sandy seabed. It has been observed that, in the process of pipeline losing lateral stability in currents, there usually exist three characteristic times: ͑1͒ onset of sand scour; ͑2͒ slight lateral displacement of pipeline; and ͑3͒ breakout of pipeline. An empirical linear relationship is established between the dimensionless submerged weight of pipeline and Froude number for describing pipeline lateral stability in currents, in which the current-pipe-soil coupling effects are reflected. Scale effects are examined with the method of "modeling of models," and the sand particle size effects on pipeline stability are also discussed. Moreover, the pipeline stability in currents is compared with that in waves, which indicates that the pipeline laid directly upon the sandy seabed is more laterally stable in currents than in waves.

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