Research On Load Bearing Properties And Reasonable Parameter Determination Of Long Piles Used In Huge Bridges

In recent years,as Chinese highways,high-speed railway development,grand bridges are emerging,and the requirements of bearing capacity of the foundations which support the upper struetures have tunred out more and more strict.The long piles not only have stronger bearing capacity,but also have some other advantages:flexible in application,simple in computation,convenient for construction,and economical in materials consumption,etc.,thus long piles are widely used as the first priority in deep foundations.It is unreasonable to use the theory of ordinary piles to analyze the long piles,beeause there are distinguished differences in the mechanism of load transfer and deformation features between them.It is because long piles have higher bearing capacity that the load test in-situ for them is confined for many reasons,therefore the tested results and experiential information are seldom reported,thus the theoretical research on it lays behind.Based on the study about the field tests of the long piles used in the Huanghe bi-purposed bridge,the work has been carried out as follows:1.Firstly,the long piles has been defined,then the working principle of single pile has been described. At last,the research on the load transfer of long piles has been done,and summarize its characteristics.2.Based on the analysis about the date of the four test piles,the deep study on the load bearing properties of long piles has been done form the Q～S curve, Q～QS and Q～Qb curve, qst～z curve and N～z curve.3.in this paper,the Huanghe bi-purposed bridge test pile has been taken as a example,and the pile-soil interaction finite element model has been established.In this process,many problems have been solved.Then,the model has been proved reliable by the date of the filed tests.4.In the end of this paper,the research on how to assess the design parameters reasonably have been done in depth including ultimate side friction resistance,tip resistance,ultimate load capacity, effective length and pile diameter. In this process,the formula on computation of ultimate side friction resistance and ultimate load capacity has been proposed,and the concept of induction factor has been introduced.