Bearing Capacity And Deformation Behavior Reasearch Of CFG Pile-raft And Pile-net Composite Foundation Based On Centrifugal Model Test

With the development of railway, highway and embankment engineering, the bearing capacity and deformation behavior research of pile-raft and pile-net composite foundation is payed more and more attention by rock engineering field, and has gradually become the industry hotspot. In view of the immaturity of the bearing capacity and deformation behavior research about pile-raft and pile-net composite foundation under flexible, calculation method of bearing capacity and stability still has many unfavorable factors. It has very important engineering value for foundation treatment in railway to study the bearing capacity and deformation behavior of CFG pile composite foundation under flexible and improve the railway embankment design specifications.Taking theoretical analysis as basic, this paper through centrifuge model test, physical and mechanical tests indoor, numerical simulation etc, mainly studied the bearing capacity and deformation behavior of pile-raft and pile-net composite foundation, deeply analyzed sensitive factors of bearing capacity and deformation behavior affecting CFG pile composite foundation under flexible, to guide design and construction and provide reference for the same type of foundation consolidation treatment.This paper obtained the following main conclusions and recognitions.1. Under the same load level, the pile soil stress ratio and settlement of CFG pile composite foundation is closely related to the structure form. The greater the foundation stiffness, the larger the pile soil stress ratio, and the more full the pile strength play, which reduces the composite foundation settlement effectively.2. Settlement and pile-soil stress ratio are both increased with increasing basement inclination, compared to friction pile composite foundation, pile-soil stress ratio of end-bearing pile composite is more sensitive to basement inclination.3. Cushion modulus and thickness has less influence on the settlement of composite foundation. Pile-soil stress ratio and bearing capacity of composite foundation are increased by increasing cushion modulus and thickness, which exceeds a certain value, continuing increase has little effect on pile-soil stress ratio. Cushion modulus has a significant effect on bearing characteristics of composite foundation. In order to fully utilize pile bearing capacity, it should be appropriate to enhance the stiffness of the cushion. If necessary, it should be doped proper amount of cement to cushion.4. Piles in different locations play different role in composite foundation stability. In the range of embankment center piles are mainly confined, at toe of slope mainly bended and resist bending and shear between them. Therefore, local stability leads to overall is the failure law of CFG pile composite foundation under flexible, it is suggested using the calculation method by Code of practice for strengthened/reinforced soils and other fills about composite foundation stability that is reinforced by rigid piles and combined with allowable shear strain of cushion as control standard and judgment basis to analyze composite foundation stability.5. Composite foundation settlement is mainly controlled by pile length located at the range of shoulder,pile spacing etc, aiming at medium compression soil, it could increase pile spacing or decrease pile length, which could reduce the project cost and not cause significant foundation settlement.6. Composite foundation settlement and pile-soil stress ratio could be obviously influenced by pile spacing and length. Within the range of effective pile length, it is significant to reduce composite foundation settlement by increasing pile length. It has little effect to composite foundation settlement reduction to increase pile length, if pile length exceeds effective pile length. When using CFG pile foundation to reinforce ground, it is not appropriate to decrease settlement by increasing pile length.7. At same embankment height, safety factor using the treatment method that CFG piles reinforced to the slope toe is significantly greater than the method that to the center of slope, which leads to the potential slip surfaces gradually penetrate from the surface to the slope toe or outside a certain distance from the slope toe. Keeping constant embankment height and changing pile spacing, when the pile spacing 1.5m, composite foundation modulus increases, and the potential failure surface appears inside roadbed filling, but not penetrated into the ground soil. When the pile spacing 5m, geogrid is pulled out and piles appear apparent bending through strength reduction by finite element method.