Study On Bearing Capacity And Deformation Behavior Of CFG Pile Composite Foundation

With the development of the western region and the implementation of the One Belt One Road strategy,vigorous development of Construction Engineering in Western China.CFG pile composite ground gene has been widely used for its low cost and other advantages.It has been widely used in foundations of high-rise buildings,and it is not uncommon for it to be used for foundations of high-rise buildings with a height of more than 30 floors.The pile-soil interaction of the CFG pile composite foundation of high-rise buildings is relatively significant,and the existing design theories have not considered this well.The concept of pile-soil composite body is not reasonable for high-rise buildings.The design method only relying on the results of single-pile composite foundation load test may lead to risks.In recent years,many cases of high-rise building CFG pile composite foundation diseases also illustrate this.This paper conducts research on the bearing and deformation behavior of CFG pile composite foundation based on the pile-soil interaction,and discusses whether the test results of single-pile composite foundation can reflect the actual engineering behavior of composite foundation.Based on the load test and settlement observation of CFG pile composite foundation of a high-rise building in Xi’an.The differences between single pile composite foundation load test and actual composite foundation in foundation stress,bearing capacity and deformation are analyzed.It is pointed out that the settlement is difficult to be determined because the empirical correction coefficient of regional settlement is difficult to be determined.The bearing capacity determined by the field test deformation standard is also difficult to determine.The bearing capacity determined by the single-pile composite foundation load test meets the design requirements,but the actual composite foundation produces a lot of settlement.It shows that the load test results of single pile composite foundation can not reflect the engineering properties of the actual composite foundation,which indicates that the load test of single pile composite foundation has limitations in the application of high-rise buildings.Based on the numerical simulation of single pile composite foundation and actual multi pile composite foundation.The characteristics of axial force,lateral friction in different pile length,pile diameter and pile distance are analyzed.Under the same load,the axial force of single pile composite foundation gradually decreases along the depth,and the maximum axial force is located at the top of the pile,but the axial force of multi pile composite foundation first increases and then decreases along the depth,and the maximum axial force is located at a certain depth below the top.The side friction of single pile composite foundation is higher than that of multi pile composite foundation,but the side friction of single pile composite foundation is lower than that of multi pile composite foundation.Under the same load,the soil compression of single pile composite foundation is less than that of multi pile composite foundation,the compression of the soil between the piles reduces the side friction of the pile and makes the pile sink.The settlement of composite foundation is increased due to the phenomenon of pile-soil cooperative settlement,and the distribution of additional stress in the underlying layer is also quite different.Under the influence of superimposed load at the end of adjacent piles,the compression of the underlying layer of multi pile composite foundation is greater than that of single pile composite foundation.By comparing the load transfer characteristics of single pile composite foundation and composite foundation,the difference is summarized as follows: the “weakening effect” of the side friction at the top half of the pile body in the reinforcement area and the "strengthening effect" of the side friction at the lower part of the pile.The "superposition effect" of additional stress is applied to the underlying layer.According to the numerical simulation results,the main reason for the difference of settlement is the different compression of the lower lying layer.Based on the difference,the calculation method of bearing capacity of composite foundation is modified,and the calculation method of additional stress of the lower lying layer is proposed according to the transfer characteristics of the additional stress in the lower lying layer.Finally,the reliability of the proposed method is verified by the engineering example.