The Self-balanced Test Technology For Pile Bearing Capacity And Its Engineering Application

As an efficient, advanced static loading test technology, self-balanced test method at domestic and abroad has been widely approvaled and applied, but the load-box laying position, equivalent conversion method of test data and determination of bearing capacity needs to furtherly study.In addition the testing purpose is to provide calculation reference for design, the current tests which are mostly made of single pile and the bearing performance of pile groups can not be fully reflected, providing test data is only macro evaluation, and it can't be directly introduced into the calculation and analysis of the whole bridge. Based on the improvement of self-balanced test technology and pile group calculation model, the main innovative achievements of this article is as follows.(1) Research the methods for determining the install location of load-box according to different known conditions, and amend the side friction and end resistance of similarity analogue test technology unsing side roughness factor based on pile hole-shaped test and the pile end bearing capacity reduction factor for more accurate calculating load box location.(2) With the super-long piles in bridge engineering, design the dedicated load-box for super-long pile to avoid stucking the tube through the load-box, and obtains the national patent. A load-box for taking load test in working-pile is designed, to ensure the pile quality and effective transmission of axial force and bending moment.(3) A new simplication equivalent conversion method of self-balanced test data is proposed, which considers the compression of upper pile under self-balancing load mode and the top load mode to amend pile top displacement for additional compression, and gives formula for calculating the load-box location of single-layer and double-layer. A equivalent conversion method based on improved load transfer function is proposed, which considers the pile end displacement caused by side friction, it more accurately simulates the load transfer mechanism of pile, in line with the actual pile status.(4) Research results has been successfully applied to large-tonnage Pile of domestic and foreign bridge projects, to provide the measured values of design parameters, and optimize the calculation of pile foundation.(5) According to the neural network and genetic algorithm put forward multi-parameter inversion method based on improved genetic neural network, and prepare a back-analysis program using MATLAB.(6) To take the pile-side contact surface tangential stiffness, pile-end contact surface normal stiffness and the ratio factor between contact surface and soil for friction characteristics as the inversion parameters, make back-analysis using self-balanced test data; under the inversion results are based on static load test for single pile the vertical load-bearing characteristics of group pile foudation is calculated, and take the group pile foundation into the bridge structure model in the form of displacement boundary, to provide a calculation pattern based on measured data for considering the upper structure-pile-soil interaction terms.(7) To conclude this research work and forcast the direction that should be in-depth study and the aspects that need improvement.