Research On Bearing Performance Of Scoured Single Piles Under Combined Loading

Pile foundations are widely used in large-scale projects such as bay bridges and offshore wind farms.Under deep-water conditions,the combination of scouring and combined loading is the normal state of piles.Ignorance of this may lead to failure of the entire system.Therefore,it is significant to investigate the bearing performance of single piles under combined loading and scouring.In this paper,theoretical methods and numerical simulation are mainly used.The main contents and conclusions are as follows:Based on Boussinesq's theory,the vertical stress distribution of the soil around scoured pile is derived.The results show that the stress of soil is weakened under scouring.The shallow soil is more affected and the deep soil is less affected.Friction piles with smaller aspect ratio are more likely to fail under local scouring.Based on the obtained stress distribution and ? method,the shaft resistance under scouring is derived,and the reduction factor of the shatf resistance is defined.By comparison,it is found that the FHWA for driven piles will lead to a dangerous design,and JTG D63-2007 is conservative.Among three parameters of scour hole dimensions,scour depth has the greatest influence on the shaft resistance under local scour,followed by the bottom width.The influence of slope angle is minimal.The cone tip resistance before scour were corrected to obtain the results after scour.The correction method is verified by a test in literature.The solutions of soil parameters considering stress history and local scour are derived.The evolution of soil parameters and shaft resistance are analyzed through an engineering case.The results show that the parameters of shallow soils change significantly.Below a certain depth,the parameters are basically not affected by the change of stress history.Ignoring the influence of stress history can lead to an underestimation of the shaft resistance.When the ratio of scour depth to pile length is relatively large,the influence of stress history cannot be ignored.A simplified pile-soil model under local scour is presented.The PLAXIS 3D simulation results of the simplified model are moderate between the local scour model and the general scour model.Compared with the general scour model,the design surplus is reduced.FLAC 3D was used to simulate the typical single pile under scouring and combined loading for the V-H failure envelope.The simulation results show that the existence of the residual soil above the scour line increases the bearing capacity of the pile in all directions.Its existence also improves the flexibility of the piles,which results in external expansion of the failure envelope.More flexible systems lead to more outward failure envelopes.