Research On Working Properties Of Composite Pile With Cement-soil Column And Tapered Rigid Core Pile

Stiffened deep cement mixing（SDCM）pile is a kind of composite pile based on SWM method,which is formed by driving rigid core pile into deep cement mixing（DCM）pile.Two different materials are used in the composite pile.Due to the existence of rigid core pile,the cross-section strength of composite pile is improved.The external load on pile top is transferred from core pile to cement-soil pile,and then from cement-soil pile to soil,which solves the problems that cement-soil pile is prone to occur pile strength failure,and the material of lower part of pile is not fully utilized.Stiffened deep cement mixing（SDCM）pile makes full use of the advantages of the two materials and has a good application prospect in China’s coastal areas.Based on the stiffened deep cement mixing（SDCM）pile and the excellent bearing characteristics of tapered pile,this paper proposes a new pile foundation technology of cement-soil composite pile with tapered rigid core,which is suitable for strengthening deep layer of soft soil.In order to further explore the working properties of composite pile with cement-soil column and tapered rigid core pile under vertical load,four groups of model tests of composite pile with different taper angle,different core-pile length ratio and different average area core ratio were designed,combined with the numerical simulation analysis,this paper discusses the influence of different influence parameters and different combination forms on the vertical bearing capacity of composite pile,and puts forward a calculation method suitable for the load-settlement relationship of composite pile with cement-soil column and tapered rigid core pile.Through the research of this paper,the following achievements have been achieved:1)Through the comparison of large-scale indoor model tests of multiple groups of composite pile with cement-soil column and tapered rigid core pile,the load-settlement relationship of composite piles under vertical load,the distribution of axial force of tapered core pile and cement-soil pile along the depth,the shaft resistance distribution of tapered core pile,the load-sharing ratio of pile side and pile end are obtained,and the bearing mechanism of composite pile with cement-soil column and tapered rigid core pile is deeply studied.2)The reasonable three-dimensional numerical analysis models of the composite pile with cement-soil column and tapered rigid core pile are established by the finite difference software FLAC^3D,the working characteristics of composite piles under vertical load are studied,the model test results are verified and additionally analysed.It mainly expounds the stress distribution of each test pile,systematically studies the influence of different core pile parameters,cement-soil pile parameters,soil parameters and different combination forms on the vertical bearing capacity of composite piles,and comprehensively discusses the working behavior of composite pile with cement-soil column and tapered rigid core pile under vertical load.3)Based on Mohr-Coulomb theory and load transfer method,the shaft resistance increasing factorωof composite section of composite pile is introduced with reasonable assumption,the load transfer differential equation of composite pile with cement-soil column and tapered rigid core pile under vertical load is obtained.According to the differential equation of load-settlement relationship of composite pile with cement-soil column and tapered rigid core pile,the corresponding iterative calculation model is established,and the load-settlement relationship of pile top of composite pile with cement-soil column and tapered rigid core pile is obtained through a series of iterative calculation.