Research On The Method Of Measuring Large Diameter Pile Bearing Capacity By Self-Balance System With Loading On Pile Top

Conventional static load tests have two types of reaction equipments, heap-weight and anchored-pile reaction frame, so the tests always cost much time, money and great efforts, especially to large diameter piles. This kind of tests often be abandoned or be substituted by model test in engineering because of difficulties in supplying enough reaction force. The self-balanced method has solved above problems in a certain extent. But because of series of problems, such as quality of the test pile, working mechanism and risk of loading system and so on, the self-balanced method has not been acknowledged in the country up to the present.This dissertation improves the self-balanced method and presents a new method for static load test: measuring pile bearing capacity by self-balanced system with loading on pile top. The specially set partition layer separates test pile into two parts. By using a ordinary jack or a few ordinary jacks, the inside pile is compressed, the outside pile is pulled and the two piles can get sufficient displacement simultaneously or successively. The back calculated parameters, according to measured axial shaft force and displacement of pile top during loading, are substituted into the simplified model, then the Q-S curve and axial force distributing are got, which can be used to determinate ultimate capacity of corresponding engineering pile.This method saves advantages of the self-balanced method, without using heap-weight and anchored-pile reaction frame, together with many other advantages, such as: big load tonnage, small testing site, without one-off load cell, simple and reliable choice of balance point, without influences induced by load equipment's breakdown, similar stressed state to static or engineering pile, and so on. In the research work, Q-S curve, axial force, side friction and the load transmission relation of a engineering pile are got firstly using ANSYS finite element analysis software. Then, after modeling improved self-balanced loading pile using finite element method, this dissertation analyzes the interactions between the two piles, relations between the piles displacement and parameters of the pile-soil system, relations between shaft friction and relative...