Study On Load Transfer Mechanism And Optimization Design Theory Of Composite Foundation Under Rigid Base

Settlement calculation is an important problem in the optimization design of rigid foundation composite foundation,and has the role of the upper and lower links in the design of the composite foundation.On the one hand,settlement calculation involves a series of problems to be solved,such as effective pile length,cushion thickness,parameters of pile arrangement and the load transfer mechanism;On the other hand,it is also a key problem to solve optimal design.In order to solve the optimization design problem of composite foundation under rigid base in building construction,firstly,effective length of pile,the optimal cushion thickness,the optimal parameters of pile arrangement and the load transfer mechanism are analyzed,on this basis,settlement problems are studied.Finally,basis on the settlement calculation method proposed in this paper,an optimization design method of single-type-pile and multi-type-pile composite foundation is proposed.This article has carried on the contents of research:The upper bound solution of flexible pile composite foundation is put forward based on the pile strength condition.The calculation method of the effective pile length of the flexible pile is put forward by based on separation of pile and soil.The method of calculating the effective pile length of rigid piles is given by reducing the side friction of piles.The stress diffusion theory of cushion is established,and the relationship between the cushion thickness and the pile-soil stress ratio is determined,which solves the problem of cushion optimal design.The relationship between cushion stiffness,soil stiffness and pile stiffness and the stiffness of composite foundation is put forward based on load test,and then the calculation method of pile-soil stress and bearing capacity coefficient is obtained.Under the following four conditions that the different base width of same replacement,the different pile diameter of same replacement,the different pile arrangement modes of same replacement rate and the different base length of same base width,the bearing capacity and settlement characteristics of composite foundation are studied by three-dimensional numerical method,and the optimal parameters of pile arrangement is obtained.Based on the analysis of the "critical base width" of composite foundation,the nonlinear relationship between the stress,modulus and the foundation size in the reinforcement area and substratum is defined.By analyzing the load transfer mechanism of composite foundation,the load transfer mode of pile and soil is obtained.On this basis,combined with effective pile length and the optimal parameters of pile arrangement,the settlement calculation method of flexible pile and rigid pile composite foundation is put forward.A method for calculating the replacement rate of the multi-type-pile composite foundation is proposed by using the separate calculation of each pile type.In the case of load test and no load test,the defect of the composite modulus method and the bearing capacity improvement coefficient method are analyzed,and the solution of composite modulus is put forward.By analyzing the results of field test and model test,the value of bearing capacity coefficient of composite foundation is put forward.Based on the analysis of load transfer mechanism of multi-type-pile composite foundation,the settlement calculation method of multi-type-pile composite foundation is put forward.The design parameters of composite foundation are analyzed;The key design parameters are chosen as the design variables,and the bearing capacity and settlement calculation method proposed in this paper are used as the constraint condition,and the optimal design method based on settlement safety factor and engineering cost as control conditions of single-type-pile and multi-type-pile composite foundation is proposed.Meanwhile,The design principle of single-type-pile and multi-type-pile composite foundation is given,and the selection of design scheme in preliminary design stage is analyzed.