Analysis Of Bearing Capacity Of Single Pile In Composite Foundation With CFG Pile

Using CFG Piles for foundation treatment method has been widely used in our country.But in the bearing capacity test of practical engineering,the problem of " bearing capacity of composite foundation is enough but bearing capacity of single pile is insufficient" have happenned frequently.Therefore,in a bearing capacity test of composite foundation,the bearing capacity test of single pile become a problem worth studying.In this article,the development of test cases in composite foundation with CFG pile was summarized first,second,according to selecting three typical engineering cases,namely,the project in Ordos,Beijing and Tangshan.They have a same engineering problem,namely,in test of the composite foundation with CFG pile,oftenly the composite foundation of the fspk value have reached the design requirements,and the R_a value of the single pile have not reached the design requirements.Finally,in this paper,the reason of this phenomenon have been discussed from three aspects through theoretical analysis: calculation,experiment and construction.In addition,based on the original model of Tangshan project,this paper simulated the influence of partial single pile failure on the settlement deformation and bearing capacity of composite foundation.It took the damage in two ways: body failure of pile and end failure of pile.The simulated results showed that the load carrying capacity of single pile directly affected the bearing capacity and deformation of composite foundation.Therefore,it is necessary to do the test for the tensile strength of the single piles when testing the bearing capacity of the composite foundation.This article mainly completed the following works.(1)According to the field test results of composite foundation with CFG pile of the project in Ordos,a project in Beijing and a project in Tangshan,the paper summarized the cases of qualified bearing capacity of composite foundation and the failure of bearing capacity of single piles.The results showed that,in the three engineering cases,the measured bearing capacity of the single pile is 40~78% of the designed value,and the unqualified proportion of the bearing capacity of single piles is 40%~100%.(2)The bearing capacity of single pile of the smaller reasons was analyzed from the aspects of calculation,test and the construction.In terms of calculation,the bearing capacity R_a of single pile is determined by the formula in the code,and the selection of the parameter in the calculation formula is a range value,which leads to the calculated value of R_a could be a wide range.From the experimental aspect,The size of the board,the construction of the mattress,and the termination of the two tests have a direct effect on the test results.From the construction point of view,the site of geological conditions and the construction quality of the test pile directly determine the value of the test pile bearing capacity.(3)In order to avoid the failure of the foundation of the single pile,the design scheme of the composite foundation with CFG pile of the 2# of a project in Tangshan was redesigned by modifying the design value of the bearing capacity of the single pile,and using the PLAXIS 3D finite element software to do the numerically simulation of the modified design scheme.The results of field testing and simulation show that the maximum settlement or the maximum diffrential settlement of the foundation plate in the new design both can meet the code requirements.(4)In order to study the effect of single pile failure on the bearing capacity and deformation of composite foundation with CFG pile,the influence of pile foundation failure and end failure of pile on foundation settlement is simulated by PLAXIS 3D finite element software.The results show that,both the failure of pile body and the failure of pile end,the deformation and differential settlement of the top on pile are increased after the failure,the base plate deflection also exceeds the limits of the code's requirements.It showed that the failure of pile end on the foundation deformation is more significant.