Research On Bearing Mechanism And Design Calculation Method Of Series Composite Pile Composite Foundation

Series composite pile composite foundation is a new type of pile composite foundation,upper and lower coaxial series piles composed of "Solid" and "Granular",the “Solid” is composed of two kinds of cement materials with different stiffnesses,namely plain concrete and slurry solid gravel,and “Granular” is gravel material.Under the action of the upper load,the new composite foundation type overcomes the defect that the strength of the Granular material pile is low and the lateral bulging deformation of the pile body is large or even destroys the soil structure when the soil layer property is poor.In addition,the upper and lower coaxial series combined piles composed of three different stiffnesses can effectively transfer the load to a deeper soil,improve the bearing capacity of the composite foundation and reduce the settlement deformation of the foundation.At present,with the further expansion of the concept of combined composite foundation,a variety of composite pile composite foundation models have been derived,which have improved the bearing capacity of the Granular materials to varying degrees,and have been successfully applied in engineering practice.However,The research results of the composite foundation of solid-discrete composite piles are few,especially the bearing mechanism,load-transfer mechanism and calculation theory of the force-deformation of the composite foundation of Solid-discrete composite piles are still in the exploration stage,which needs further study.To this end,this paper combines the National Natural Science Foundation of China(51478178)"Research on the bearing mechanism of rigid pile composite foundation under traffic moving load and its analysis method of force deformation",Based on theoretical analysis,numerical simulation and field test,based on theoretical analysis,numerical simulation and field test,the bearing mechanism and design calculation method of "Solid-Granular" series composite pile composite foundation under flexible foundation are systematically studied.In this paper,the physical properties and mechanical properties of composite materials of "Solid-Granular" series composite piles are systematically expounded,and the engineering application evaluation of various types of foundation soils is carried out.The characteristics of failure and stability of composite foundations based on granular materials are studied.Based on the study of the mechanical deformation characteristics of pile composite materials,the composite foundation of series composite piles is proposed,and the structural composition and structural characteristics of the "Solid-Granular" series composite piles are introduced.Research on construction technology of series composite pile composite foundation.Secondly,the pile load transfer mechanism of pile composite foundation and the load transfer mechanism of pile-soil system are analyzed.Based on the self-developed grading loading system and pressure test method,the under different pile length ratio conditions is revealed.The mechanical calculation model and differential control equation of the "Solid-Granular" series composite piles are established by the load mechanism of the series composite piles.It is clarified that the force deformation is not only related to the pile materials and specifications,but also the engineering geology the conditions are related,mainly because of the parameters of the cushion,the parameters of the pile section,the pile diameter,the pile spacing and the soil modulus parameters.Based on the analysis of the deformation characteristics of the composite foundation,the suitability evaluation of the bearing capacity and settlement deformation of the composite foundation with different stiffness piles is carried out.The calculation method of bearing capacity and settlement deformation of composite foundation with different stiffness piles is proposed.Based on the theory of sliding block failure,the calculation model of ultimate bearing capacity of two kinds of "Solid-Granular" series composite piles is established by calculating the Meyerhof method of deep foundation bearing capacity.The critical sliding surface is determined by stochastic optimization algorithm.Calculation method for ultimate bearing capacity of composite "series" composite pile foundation.Based on the mechanical deformation mechanism of the composite foundation of "Solid-Granular" series composite piles,the settlement deformation of the series composite pile composite foundation consolidation zone is divided into three sections,and the piles and soils of each section are proposed respectively.The calculation model of body settlement deformation,and based on the theory of thick-walled cylinder elasticity,the settlement calculation method of composite foundation of series composite pile considering pile-soil slip and pile bulging deformation is established,and the settlement calculation of composite foundation is proposed.The method and principle of three parameters in settlement calculation of composite foundation are proposed.At the same time,in order to consider the influence of the lateral restraint force of the pile on the settlement of the composite foundation caused by the bulging deformation of the pile,based on the improved strain wedge theory,the calculation method of the settlement deformation of the composite foundation of the series composite pile is proposed.The value of three parameters in the settlement calculation of composite foundation.Based on the engineering example,the calculation methods of settlement deformation of two kinds of series composite pile composite foundation are compared and analyzed.The calculation results of settlement deformation of composite foundation considering slip and bulging deformation are too large,but the calculation parameters are directly obtained.The design is conservative,and the settlement calculation of the composite foundation based on the improved strain wedge model can better reflect the engineering reality,but there is uncertainty in obtaining the calculation parameters.Thirdly,based on the physical properties of the materials of the piles of the series combination piles,combined with the discrete-continuous coupling theory,the gravel piles in the series combination piles are discrete elemental structures.The area around the discrete element solid structure adopts a continuous solid structure,that is,the solid-solid structure of the slurry-solid gravel pile section and the concrete pile section is established,and a discrete-continuous(FLAC-PFC)coupling numerical calculation model is established,and the parameters of the cushion layer are analyzed.The influence of concrete pile section parameters,parameters of slurry-solid gravel pile section,parameters of gravel pile section,pile diameter,pile spacing and soil modulus on the bearing behavior of composite foundation of "Solid-Granular" series composite piles is "Solid" The theoretical basis for the design of the composite foundation of the "sediment" series composite pile.Finally,relying on the new soft soil roadbed project of a station in Zhangzhou-Shenzhen passenger dedicated line,based on the technical standard of high-speed railway soft soil roadbed,the design principle of "Solid-Granular" series composite pile composite foundation controlled by post-construction settlement deformation is proposed.The method of determining the pile length,pile diameter,pile spacing and pile form of "Solid-Granular" series composite piles is combined with the calculation theory of bearing capacity and settlement deformation of composite foundation of series composite piles.Contrast and analyze the reinforcement effect of CFG pile composite foundation with the same design parameters,the reliability and rationality of the calculation theory of bearing capacity and settlement deformation are verified,the design concept of reinforcing soft soil foundation by series composite pile is realized.The series composite pile composite foundation expands the practice field of composite foundation engineering,enriches the design calculation theory of combined composite foundation,and provides a theoretical basis for the promotion and application of series composite pile composite foundation.