Research On The Influence Of Suction Cylinder Foundation On Sand Liquefaction Resistance And Its Bearing Performance

China's offshore wind power industry is in a booming period.The tubular foundation attracts the attention of scholars from all over the world due to its simple structure,good bearing capacity and convenient construction.It is an inevitable trend in the future to apply it to the infrastructure of offshore wind power facilities.However,the cylindrical foundation needs to work in the seabed foundation.Compared with the foundation structure of onshore wind turbines,the complex and changeable marine environment places higher requirements on its carrying capacity and stability.Earthquakes occur frequently in the eastern coastal zone of China,and the saturated sand in the offshore soil layer is prone to liquefaction.In addition to its own weight and working load,the marine cylindrical foundation must also bear the cyclic effect of environmental loads such as ocean currents and waves for a long time,which has a non-negligible impact on the bearing capacity of the cylindrical foundation.Therefore,this article starts from exploring the effect of earthquake action and environmental load on the bearing capacity of the marine tubular foundation.Based on FLAC 3D technology,the three-dimensional elastoplastic model of Mohr Coulomb and considering the liquefaction of sand is established.Analysis of anti-liquefaction performance of cylinder foundation under earthquake load based on Seed effective stress principle.At the same time,the Swipe loading method was used to study the load-bearing performance of the cylinder foundation under different environmental load cycles.The main research contents are as follows:(1)Under the condition of applying a magnitude 7 artificial seismic wave,the law of pore water pressure,sand settlement and stress distribution at each observation point in saturated sand foundation under earthquake action is studied.Discrimination of the liquefaction of the seabed foundation based on the principle of effective stress and summarize the influence mechanism of cylindrical foundation on the liquefaction resistance of saturated sand under earthquake.The lateral hoop effect of the cylindrical foundation and the additional stress generated in the seabed soil by the uniformly distributed load on the top surface of the cylinder can restrict the increase of pore water pressure and improve the liquefaction resistance of the sand.However,the restriction effect of the cylinder wall will cause intense fluctuations in the dissipation phase of the pore pressure.(2)The environmental load is reduced to four unidirectional cyclic forces,vertical,horizontal,bending moment and torque,and the unidirectional cyclic load is applied by the displacement control method.Then it observes the damage mechanism of the seabed foundation under different working conditions.It records the relationship between the displacement of the cylinder base and the bearing capacity,and selects the loading value corresponding to the displacement at the inflection point of the curve development as the ultimate bearing capacity of the cylinder base in different directions.The load value corresponding to the vertical displacement of 7%D(D is the diameter of the cylinder base),5%D horizontal displacement,and 0.05rad angular displacement on the top surface of the cylinder base is the unidirectional vertical,horizontal,and flexural ultimate bearing capacity of the cylinder base.The cylinder base undergoes a large rotational displacement under the action of a low-strength torsional shear cycle force,and the torsional shear resistance is low.If it is necessary to bear a larger torsional shear effect,an additional structure needs to be added.Sand foundation is vibrated tightly after being subjected to low-strength vertical cyclic force,which improves vertical bearing capacity.(3)The failure mechanism of the cylindrical foundation under vertical-horizontal and vertical-bending moment load is similar.When the strength of the applied vertical cyclic force is low,the anti-instability and overturning ability of the cylindrical foundation is improved to a certain extent,and the damage envelope surface shows a trend of first rising and then falling.Under the condition of horizontal-bending moment composite cyclic loading in the same direction,the degree of instability and damage will be deepened.However,horizontal-bending moment reverse loading can restrict each other,thereby improving the ability of the tube base to resist bending moment overturning.Three vertical,horizontal and bending moment cyclic loads are applied to the tube foundation with different strength combinations.When the strength of the vertical cyclic force is low,the three-dimensional failure envelope surface has a clear outward expansion trend in both horizontal and bending cyclic loading directions.It proves that the application of low-strength vertical cyclic force can appropriately improve the ability of the tube base to resist overturning and instability.