Analysis Of Load Transfer Behaviors Of Stiffened Deep Mixed Pile Under Flexible Foundation

Stiffened deep cement mixing(SDCM)pile is a new type of pile,which is composed of high strength concrete core pile inserted in deep mixing cement soil pile,and has high bearing capacity and good economic benefits.At present,the interaction and load transfer mechanism of SDCM pile under flexible foundation are lack of systematic and in-depth theoretical research.Considering the shear behavior of the interface between core pile and cement-soil pile under flexible foundation,the load transfer and settlement characteristics of SDCM piles with different core pile lengths are studied.(1)On the basis of deeply investigating the stress-deformation modes of the SDCM pile under the flexible foundation,then in reference to some experimental results,the double-exponential function load transfer model is introduced to characterize the interface shear softening process between core pile and cemented soil,and the ideal elastic-plastic load transfer model is introduced to describe the interface shear deformation properties between cemented soil and the surrounding soil,based on load transfer method,the load transfer relationship among core pile,cement soil pile and soil is established,and combined with the iterative calculation method,a method for analyzing and calculating the load transfer law of SDCM pile with equal core under flexible foundation is proposed.Then,field test,engineering case and finite element numerical simulation are used to verify the method.The results show that the method has high reliability and can be used in practical engineering efficiently and conveniently.(2)In view of the stress-deformation models of short-core SDCM pile under flexible foundation,the cement-soil pile below the projection plane of the end of the core pile is regarded as the cement-soil core pile,and the analysis model of the internal cement-soil virtual pile is established,furthermore,based on the load transfer method,the load transfer relationship and its iterative calculation method among the components of the short-core SDCM pile are established,and a calculation method for load transfer law of short-core SDCM pile under flexible foundation based on internal cement-soil virtual pile model is proposed.At the same time,the reliability of the method is verified by an engineering case.(3)In view of the stress-deformation models of long-core SDCM pile under flexible foundation,the tubular soil which is around the core pile and below the projection surface of the cement-soil pile tip to the depth of the core pile tip is considered as soil pile,and the analysis model of the external soil virtual pile is established,then,based on the load transfer method,the load transfer relationship and its iterative calculation method among the components of the long-core SDCM pile are established,thus,a calculation method for load transfer law of long-core SDCM pile under flexible foundation based on external virtual soil pile model is proposed.The reliability of the method is verified by the contrast analysis of an engineering case.(4)Based on the proposed engineering example,the distribution law of side friction and axial force of equal-core,short-core and long-core SDCM piles under flexible foundation are studied,the influence of parameters of load transfer function models and resistance model on the calculation results of equal-core SDCM pile is analyzed.Finally,according to the calculation method proposed in this paper,the variation of the load transfer characteristics of the SDCM pile with equal core,short core and long core with curing age are discussed.