The Study And Application On Vertical Bearing Capability Of Plain Concrete Pile Composite Foundation

Along with the foundation treatment requirement continuously improved,composite foundation technology also incessant development,composite foundation technology is the most widely used of foundation treatment technology.Plain concrete pile composite foundation with its high bearing capacity,small deformation,strong adaptability,good economic and social benefits is developed rapidly in recent years.Firstly,this paper analyzes the working principle of plain concrete pile composite foundation and reinforcement mechanism of concrete pile,explain the mechanism of the cushion,according to setting cushion,make the stress among the pile and soft between piles reached regulation and balance respectively,and to make full use of soil between piles,save the project cost provides some favorable means,and puts forward the reasonable selection of cushions exists an optimal value range.Also,the thickness of cushion have strict requirements,the thickness of cushion is too small,pile foundation will generate obvious stress concentration,make the pile-soil stress ratio n of composite foundation which behind the cushion is small,its means that shallow foundation soil bear high load,and the intensity of shallow layer soil is often low.Although the sharing load of shallow layer soil will soon Wansfer to pile(pile top have negative frictional resistance area),shallow layer soil compression deformation may cause too large settlement,in fact,the pile which setting in the composite foundation lose its significance.On the basis of the existing literation,the paper summarize factors of effecting vertical bearing capability of plain concrete pile composite foundation,generalization analysis of bearing calculation with limit equilibrium theory and Analysis of bearing calculation with elastic-plastic theory,comparision data of bearing capacity factor and analysis simply. According to area ratio formula of calculating vertical bearing capability of composite foundation,the paper derivate vertical bearing capability of plain concrete pile composite foundation and brief calculation parametes of formulating vertical bearing capability of plain concrete pile composite foundation.Secondly,this paper argues that use the building foundation processing technical specification(JGJ79-2002),the calculation of concrete pile composite foundation bearing capacity of composite foundation is less than average load test site characteristic value of bearing capacity of composite.The main reason is that the single pile in the composite foundation bearing capacity and freedom pile is different,the soil in the composite foundation between soil and the foundation pile soil have different load-bearing characteristics,in the calculation formula,the value of reduction factorβis too conservative.Finally,based on the field load test of concrete pile composite foundation reinforcement treatment in Cheng du Jinjiang district,and data analysis of pile integrity test,can determine the composite characteristic value of bearing capacity and compression modulus value is less than design.Study on the reason of the project concrete pile produce defects.These reasons,may caused by the construction technology of concrete pile,also may caused when using large excavator to clear the soil between piles.According to the analysis of the field test data,this paper thinks that the project use concrete pile composite foundation reinforcement,the purpose of foundation reinforcement is reached.By typical examples,the design method,construction method andloading test method were introduced and analysised in detail,which can be referenced tosimilar projects.Expect this paper could play an cative role in accumulating the regionally datum and researching method of the foundation bearing capacity.