Study On Self-balance Pile Load Test For Bearing Capacity Of Pile Foundation

Self-balance pile load test is a new test technique which is simple, fast and economical. In Chinese Code for Pile Foundation JGJ94-94, only the method to determine ultimate bearing capacity of pile foundation is given on the results of self-balance pile load test. Method of determining Q-S curve of pile from self-balance pile load test results is still not given. The mode of conversion from self-balance pile load test results to traditional load test results is mainly determined by the different behaviors between self-balance pile load test and traditional load test. So the key problem of self-balance pile load test is the behavior of pile's load transfer. Through comparing the mechanism of self-balance pile's side friction resistance with traditional load pile, the conclusion about behavior of side friction resistance, axial force and cross section displacement with different relative stiffness ratio is drawn out.The main difference and influence factors are drawn out through analyzing the different behavior of pile between self-balance pile load test and traditional load test. In displacement coordination exists, load transfer behaviors of self-balance pile are derived out by using load transfer method. The different behaviors between self-balance pile load test and traditional load test are proved by finite element simulation analysis of self-balance and traditional pile. Finite element simulation analysis use bored concrete pile model which works in condition of displacement coordination and can be simplified as a symmetric model comprised with pile, solid and pile-solid contact zone. Low elastic modulus materials are used for weakening contact zone to simulate relative slip under great load between pile and solid. Exertion disciplinarian of positive and negative friction resistance are drawn out through using D-P model to analyze of self-balance pile's behaviors which is the main difference between self-balance pile load test and traditional load test. Then, the similarity of stress and negative friction resistance between self-balance load pile and uplift pile is analyzed by using finite element simulation analysis method. Finally, basic principle and test approach of self-balance pile load test are introduced. The merits and demerits of two kind Q-S curve fitting method are analyzed.