Wave-induced Residual Pore Pressure Response And Mechanical Proprety Analysis Of Silty Seabed Soil

The soil of silty seabed is widely distributed in 80% of the world's coastal areas with special engineering properties between clay and sand.The soil of seabed produces oscillating pore water pressure and residual pore water pressure under long-term wave loading in the marine environment,which causes the effective stress of the soil to descend.The effect of long-term wave loading has an important influence on the mechanical properties of soil.The mechanical properties directly determine the bearing capacity of the foundation,which is of great significant to the stability of the foundation of the marine structures.The wave-seabed interaction is established by numerical method in order to analyze the residual pore water pressure of the seabed with variable permeability in this paper.At the same time,the long-term dynamic response of the silty seabed under wave loading was studied by one-dimensional cylinder test equipment.And the soil samples of seabed before and after the wave loading action were analyzed.The research contents and conclusion of this paper mainly come into the following three points:1.A two-dimensional residual pore pressure model with variable permeability is established.The Biot's poro-elastic equations is used as the governing equation of the seabed,which is solved by fluid-soil coupling of Comsol.The Two-dimensional model can be accurate to simulate residual pore pressure of silty seabed with variable permeability under wave loading by comparing the solving results and the indoor wave tank test dates.The analysis results show that the residual pore pressure gradually increases with time,then tends to reach the maximum value gently.The distribution of maximum values of residual pore pressure along the depth direction increases and then decreases,and the residual pore pressure away from the middle part of the seabed is small.In the horizontal direction,residual pore water pressure of each position grows steadily with time.The maximum value of the residual pore pressure increases with the increment of the wave height and length,and decreases with the increment of the wave period and the average water depth.The effect of the wave height and the average water depth on the residual pore pressure is more significant.The maximum value of the residual pore pressure decreases with the increment of the soil saturation,shear modulus,transverse permeability coefficient and vertical permeability coefficient,which is more sensitive to the variation of the permeability in transverse direction than vertical permeability.2.The whole process of residual pore pressure of silty seabed under continuous wave loading is analyzed by one-dimensional cylinder equipment,and the pore pressure of uniform soil and layered soil is analyzed respectively.The research shows that the surface of the seabed mainly presents as oscillating pore pressure while the deep seabed has the obvious residual pore pressure,which rises slowly and reaches a maximum value.The pore pressure undergoes three processes of ascending,stabilizing and dissipating in the seabed under continuous action of wave loading.During the ascending process,the amplitude of the pore pressure increases,and during the dissipation process,the amplitude of the pore pressure decreases,and the residual pore pressure will maintain a constant after dissipating.The residual pore pressure increases with the increment of the wave height,and decreases with the increment of the wave period and the average water depth.For the layered seabed,the upper sand seabed is mainly the oscillating pore pressure accompanied by amplitude attenuation and the phenomenon of phase hysteresis,and the residual pore pressure of the lower silty seabed becomes insignificant.3.The mechanical properties of the fine sand seabed were tested and compared by using consolidation instrument and direct shear tester before and after wave loading experiment.The comparison shows that the change of the void ratio of the upper seabed after the wave loading action is equal to or slightly larger than that before the test,while the change of the void ratio before the test in the middle and deep seabed is more obvious than that after the test.For the deep seabed,the minimum void ratio of the seabed in not much different.As the depth of the seabed increases,the compressibility of the soil decreases significantly for silt seabed.The shear strength of the fine sand increased after the wave experiment,and the surface of the seabed is loose and viscous.The cohesive force on the surface of the seabed was greater than the middle and lower parts of the seabed for the fine sand and silt seabed.