Research On Bearing And Deformation Behavior Of Rigid-Flexible Piles-Supported Composite Foundation Reinforced With Geogrid Cushion Under Cyclic Load

Rigid-flexible piles-supported composite foundation reinforced with geogrid cushion is the foundation treatment method that sets rigid-flexible piles in the foundation as vertical reinforcing materials and sets horizontal reinforcing materials in the cushion.Because of its good reinforcement effect,short construction period and low cost,this technique is often used to reinforce soft soil subgrade.There are few researches on the bearing and deformation behavior of rigid-flexible piles-supported composite foundation reinforced with geogrid cushion under cyclic load at present.This paper studies the bearing and deformation behavior of rigid-flexible piles-supported composite foundation reinforced with geogrid cushion under cyclic load through laboratory model test and numerical analysis.Via large scale model test,the influence of the load frequency,the number of geogrid layers and the type of support piles on slope top settlement,geogrid strain,pile axial force distribution and pile load sharing ratio of rigid-flexible piles-supported composite foundation reinforced with geogrid cushion under cyclic load was explored.This paper simulating the model test through Plaxis 3D software and comparing the numerical simulation results with the test results.A numerical model of composite foundation was established based on typical geological conditions of Hangzhou area in actual engineering dimensions.How strong the influence of pile cap size,the number of geogrid layers,flexible pile length and grid stiffness to settlement and deformation of composite foundation under cyclic load was determined by numerical orthogonal test.The specific impact of two factors that have the greatest impact on settlement and deformation of composite foundation to the bearing and deformation behavior of composite foundation was studied by numerical control test.The results show that the slope top settlement of rigid-flexible piles-supported composite foundation reinforced with geogrid cushion increases with the increase of cyclic cycle numbers under cyclic load,but the growth slows down.The settlement of composite foundation increases with the increase of cyclic loading frequency.Increasing the number of geogrid layers can reduce the cumulative settlement of composite foundation.When only flexible piles are used for supporting,the settlement of composite foundation is obviously larger than that using rigid-flexible piles.The effect of the load frequency,the number of geogrid layers and the type of support piles on geogrid strain was similar to that of slope top settlement.Geogrid strain depends on its location.The strain of geogrid near the top of rigid pile is larger than that on soil between piles.The axial force distribution of rigid pile is different from that of flexible pile,and rigid pile plays the main bearing role.The load-sharing ratio can be improved obviously via rising the load frequency or increasing the number of geogrid layers.The settlement variation law of composite foundation under cyclic load,the strain distribution law of geogrid and the axial force growth law of pile body obtained by numerical simulation with Plaxis 3D software are similar to those of model test.This shows the practicability of using Plaxis 3D software to analyze the properties of composite foundation.The results of numerical orthogonal test show that size of rigid pile cap and the number of geogrid layers have maximum influence on settlement and deformation of composite foundation.The results of numerical control test show that increasing the size of pile cap can significantly improve the load sharing ratio of piles in composite foundation and reduce the maximum settlement of composite foundation while increasing the number of geogrid layers can slightly improve the load sharing ratio of piles in composite foundation and reduce the maximum settlement of composite foundation.The results can be used to optimize the design of rigid and flexible pile bearing reinforced soil composite foundation.