Study On Optimization Design For The Axial Bearing Capacity Of Large Diameter Bored Piles Of Highway Birdge

At present, the design of large diameter bored piles for highway bridge is tooconservative that the pile foundation size is large anf the cost is high. To solve thisproblem, this paper relys on the field static load test to analys systemically the bearingcharacteristic, load transfer law and the effective pile lengh. On this basis, this paperoptimize the geometry of large diameter piles with MATLAB genetic algorithm toolbox.Thus the optimal scheme of large diameter piles of highway bridge can be obtained, whichcan meet the requirement of bearing capacity and economical. The research conclusionsfrom this paper are listed as follows:1. Relying on the construnction of new airport Highway Bridge, the scene verticalload experiment of four large diameter bored piles is carreed on. It can be seen that theload-settlement curve of large diameter bored piles is different from middle or small piles’.The large ones have no obvious inflection point and present the slow changing trend. Insand soil, the pile side resistance distributes as a parabola. The pile axial force isdecreasesed with the depth.2. The conception of efficient length of pile is introduced. Based on the test data, thispaper calculates the efficient length of single pile with Mindlin solution considering theeffect of pile diameter. The result shows that the efficient length of single pile relates tothe diameter of pile, the modulus of compressibility of soil, the Poisson’s ratio and theelastic modulus of pile. It provide a reference for pile length selected in the design of pilefoundation.3. Based on the vertical load transfer process of large diameter bored pile, the loadtransfer mechanism of single pile is discussed and the load transfer model is established.The improved load transfer method is use to solve the load transfer differential equation.Then the influencing factors of transfer behavior of large diameter single pile is analyzed.4. Based on the theory of nonlinear programming optimization criterion, the geneticalgorithm and MATLAB M language are used to optimize the design of large diameterbored pile. Then the calculation program of optimization diameter and length of singlepile can be obtained， which can satisfy the requirement of bearing capability and economic.The research findings of this paper can be a reference for actual engineering.