The Research On Bearing Characteristic And Settlement Of Composite Foundation Bidirectionally Reinforced By Stone Columns And Geocell

Due to maintaining the balance between the advantages of horizontal reinforcement and composite pile,bidirectional reinforced composite foundation has been more and more favored in engineering field in recent years,among which," Geocell + stone column" bidirectional reinforced composite foundation is well effective in treatment of soft soil foundation and has advantages in its construction costs and term,and thus is widely used in foundation treatment of high-speed transportation.However,at the present time,its theoretical research is still in the infancy,especially for the coaction of " embankment – geocell – pile and soil reinforcement area",remaining to be further studied.Therefore,funded by the program of National Natural Science Foundation of China(51078138),this paper conducted a through and systematic research on the bearing mechanism and deformation calculation method of the composite foundation bidirectionally reinforced by stone columns and geocell under the embankment load by the combination of theoretical analysis and laboratory model test.Firstly,this paper analyzed the generation mechanism of embankment soil arching,summarized the mechanism of geocell reinforced cushion,discussed the stress deformation mechanism of rigid pile,flexible pile and discrete material pile.On this basis,it deeply studied on the mutual deformation and the load transfer mechanism of the "embankment – geocell – pile and soil reinforcement area" system and proposed an idea of regarding the relation between the load distribution to various parts and their deformation differences as the main research object.Secondly,in terms of load distribution mechanism of embankment soil arch,based on the conventional embankment arch "soil column model",it took the relation among the internal,external soil column friction re sistance,stress state and the relative displacement into consideration,constructed the load transfer soil mode of soil column model,and used the way of argument transformation and combined with the boundary conditions of embankment bottom to initiate th e functional relationship between the relative displacement of internal and external soil column at the bottom of embankment(soil-pile of differential settlement)and load distribution;in terms of the load transfer law of rigid pile composite foundation,it introduced hyperbolic model of pile and soil interface and obtained the control equation of pile and soil load transfer,and by using argument transformation,it converted the control equation into the differential equation about pile body stress and pile-soil relative displacement.Besides,it combined the stress boundary conditions of pile top and pile end to obtain the series solution of the vertcial stress of pile,and combined with the improved embankment soil column model to propose calculation methods of the pile-soilstressratio and settlement of rigid pile composite foundation under embankment.Then,for the mechanical characteris tics of Geocell,considering that the embankment and the pile and soil reinforcement area have horizontal constraints on geocell,it improved thetraditionalelasticfoundationplatemodel,and regarded pile and soil as springs with different stiffness,and set the horizontal spring on the topandbottomsurface of the geocell in order to take interface friction resistance into consideration.Considering the vertical and horizontal coupling deformation of the plate,it elicited the governing equations of deflection of geocell and horizontal displacement of the surface,and using the Bessel complex function to solve the differential equations and obtain the analytical solution of deflection of geocell and horizontal displacement of the surface,and then elicited the calculation formula of two-way reinforced pile-soil stress ratio and settlement of rigid pile composite foundation.It deeply analyzed the bearing deformation mechanism of the stone column under the flexible foundation,and considered the integrity of macadam pile to construct the radial displacement mode of cross-section of the stone column and obtain cross-sectional shear stress distribution.Besides,considering the confining role of the second-order effect to the stone column,and at the same time basing on the theorem of conjugate shearing stress,it elicited the load transfer mode of the stone column composite foundation under the flexible foundation.Based on the Hook’s law,it obtained the control equations of stone column deformation and then obtained calculation methods of the pile-soil stress ratio and settlement of stone column composite foundation under the flexible foundation.Finally,combined with the obtained function relationship between the load distribution and deformation differences of the embankment,geocell reinforced cushion and stone column soil reinforcement area,and based on stress and deformation compatibility conditions at the top of the pile,it established the "embankment – geocell – stone column composite foundation" interaction model and proposed the calculation method of composite foundation bidirectionally reinforced by stone columns and geocell under embankment.During the process of iterative calculation,it also considered the influence of normal stress of the cell interface on frictionresistance effects;based on similarity theory,it designed and completed asetofindoormodeltest to verify the correctness of the theoretical and computational methods in this paper,and then further discussed the bearing and deformation mechanism of composite foundation bidirectionally reinforced by stone columns and geocell under embankment.