Numerical analysis and optimization design of vibroflotation gravel pile combined with uplift pile under U-shaped groove
[Objective]Due to insufficient urban road space,U-shaped grooves in road cuts are widely used because of their small deformation,high stiffness,and the ability to prevent road sinking and cracking.The design of U-shaped grooves in sandy strata under high water levels requires consideration of sand liquefaction and the anti-floating stability.As a continuation of previous research,here we further study the reinforcement effect and optimization design of the combination of vibroflotation gravel piles and uplift piles under the U-shaped groove of coastal underpass road engineering,providing design reference for similar projects.[Methods]The finite element software ABAQUS was used to model the combined uplift pile of vibroflotation gravel pile(VGP)under U-shaped groove in a coastal road project.The shear stress method was used to study the improvement effect of VGP on the anti liquefaction ability of sand,and the impact of VGP combined with uplift pile on the anti floating performance of U-shaped groove was explored.On this basis,NSGA2 genetic algorithm was adopted to optimize the design of U-shaped groove bottom plate thickness,length and diameter for uplift piles and VGPs with three objectives:sand liquefaction rate,uplift displacement,and engineering cost.[Results]The finite element software ABAQUS was used for modeling,and the improvement effect of VGP on the liquefaction resistance of sandy soil ground was analyzed.The duration of liquefaction in the sandy soil ground treated with VGP had been reduced from 30 seconds to 5 seconds when the diameter of the VGP was 0.8 m.And liquefaction rate had changed from 100％to only 4.7％.Meanwhile,increasing the diameter of VGPs can not only shorten the duration of liquefaction,but also reduce the number of units involved in soil liquefaction.When the diameter of the VGP increased from 0.8 m to 1.0 m,liquefaction occurred in 0-3 seconds and only 2.6％of soil underwent liquefaction.Subsequently,the influence of design parameters of U-shaped groove,VGP and uplift pile on the anti-floating effect of U-shaped groove was discussed.The thickness of the U-shaped groove bottom plate,the diameter and length of VGP and the uplift pile all had a significant impact on the upward displacement of the bottom plate,while the influence of the elastic modulus was relatively small.Increasing the pile diameter of the VGP can better enhance the anti-floating effect of the U-shaped groove than the pile length.When the diameter and length of the uplift pile was 0.7 m and 13.5 m,it could meet both safety and economic requirements.Finally,optimization design of VGP combined with uplift pile on the U-shaped groove of a coastal underpass road project was carried out based on NSGA2 genetic algorithm with three objectives(sand liquefaction rate,uplift displacement,and engineering cost).The original design scheme was:U-shaped groove bottom plate thickness du=1.5 m,uplift pile length lb=15.0 m,pile diameter db=0.8 m,and VGP diameter ds=0.8.The optimal scheme obtained was as follows:U-shaped groove bottom plate thickness du=1.25 m,uplift pile length lb=13.50 m,pile diameter db=0.9 m,and VGP diameter ds=1.00.Compared with the original design scheme,the cost was saved by 10.0％and the liquefaction rate of sandy soil ground was reduced by 45.7％.[Conclusions]VGP can significantly improve the anti-liquefaction effect of sandy soil ground.Increasing the diameter of VGP can enhance the anti-liquefaction ability of composite ground,shorten the liquefaction time of sandy soil ground,and reduce the proportion of soil liquefaction.The thickness of the U-shaped groove bottom plate,the diameter and length of VGP and the uplift pile all has a significant impact on the upward displacement of the bottom plate,while the influence of the elastic modulus is relatively small.The optimized design scheme of U-shaped groove bottom plate,VGP,and uplift pile based on NSGA2 genetic algorithm with the goals of sand liquefaction rate,bottom plate uplift displacement,and engineering cost can provide design guidance for similar projects in the future.
万方数据
维普
