Application Research On High Stain Dynamic Testing Method For Pile Bearing Capacity

Bored cast-in-place pile is widely used in soil improvement. High stain dynamic testing method is adopted to obtain pile's ultimate bearing capacity quickly and accurately as a substitute for static loading testing method. When we deal with the signal which obtained by high stain dynamic testing method, there are two methods at present: Case method and signal matching analysis. The damping factor is actually a experiential factor in Case damping factor method, and its value influence greatly to determining pile's ultimate bearing capacity. In the first part, firstly, total soil resistance formula of Case method is deduced over again using absolute time coordinate; Secondly, Case damping factor method and its improved method are analyzed; at last, a assistant method of Case damping factor method is put forward to test the rationality of damping factor and its practical value is proved by an engineering case. Traditional signal matching analysis adjusting parameters of soil model uses manual way which has a fault of low efficiency and need the professional who processes engineering experience. In the second part, penetration and reflection laws of up traveling wave and down traveling wave and soil resistance influence on traveling wave are deduced when a continuous bar model and one dimension traveling wave theory are introduced. Then an inverse problem on parameters of soil model is formed. The genetic algorithm instead of manual way is applied to solve the inverse problem. Because of the big influence of the parameters of soil model, an improved soil model is adopted. According above all, by programming, the automatic signal matching analysis is implemented. At last, two engineering case are introduced to test the method, and through comparing with static tests, the feasibility and the reliability are proved.