Research On Bearing Behavior Of Rigid-flexible Piles Composite Foundation With Reinforced Cushion Under Cyclic Loading

The rigid-flexible plies composite foundation with reinforced cushion is a cost-effective ground improvement method.At present,the research on the bearing behavior of the rigid-flexible plies composite foundation with reinforced cushion under cyclic loading is still lagging behind the engineering applications.In this paper,the bearing performance of rigid-flexible plies composite foundation with reinforced cushion under cyclic loading is analyzed by model test and three-dimensional finite element method.The effects of loading method,rigid piles,layers of reinforced cushion,load amplitude and load frequency on settlement,pile strain and geogrid strain of composite foundation under cyclic loading were studied by indoor model test.The result of indoor model test was compared with the results of three-dimensional finite element analysis.The effects of piles spacing,length and elastic modulus of flexible piles,length of rigid plies,tensile stiffness of geogrid and layers of reinforced cushion on settlement,axial force of piles,load sharing percent and tensile force of geogid of composite foundation under cyclic loading were studied by using three-dimensional finite element method.The results of the study show that the settlement of composite foundation increases with load,cyclic number,load amplitude and load frequency.The cumulative settlement of composite foundation under cyclic loading is obvious.The settlement of composite foundation can be reduced by adding rigid piles,reducing piles spacing and increasing reinforced layers and length of rigid piles.The strain of piles increases first and then decreases along the pile depth.As the reinforced layers increases,the effect of overall reinforced is better and the pile strain is larger.The stress between piles and soil is redistributed with the addition of rigid piles,and the pile strain is reduced.With the increase of pile spacing,the axial forces of rigid piles and flexible piles are obviously increased,but the load sharing percent of piles are decreased.The elastic modulus and the length of piles have a significant effect on the axial force and load sharingpercent of the piles.The tensile stiffness of geogrid has no obvious effect on the axial force and the load sharing ratio of piles.The distribution of the geogrid strain was influenced obviously by the arrangement of piles with different rigidity.The geogrid strain has the maximum value at the edge of piles,followed by the top of piles,and has the minimum value at soil between the piles.The strain of multi-layer reinforced geogrid is less than that of single-layer reinforced geogrid,and the strain of the upper-layer reinforced is larger than that of bottom-layer reinforced.The tension of geogrid increases with the increase of pile spacing and geogrid tensile stiffness.This study can provide the technical support for the ground treatment of soft foundation,it can also provide the basis for the promotion and use of the rigid-flexible plies composite foundation with reinforced cushion.