Synthesis Analysis Of Longitudinal Wave And Torsional Wave In Pile Dynamic Testing

The method of reflected stress wave is the most representative and most widely used dynamic testing method because of its simplicity. However, it mainly adopts the method of reflected stress wave based on the theory of one dimensional longitudinal wave both in analysis and field testing. Whereas the diagnosis ability of the small defect and shallow-seated defect of piles still exist limitation. The propagation characteristic of torsional wave along pile is similar to that of the longitudinal wave, but more elevated in diagnosis of small defect and shallow-seated defect. Therefore the introduction of synthesis analysis of longitudinal wave and torsional wave has a broad application prospect for quantitative analysis of all sorts of defects.The propagation characteristics of both longitudinal wave and torsional wave along pile are simulated using MFC program based on characteristic line method. The research suggested that diagnosis ability of defects is influenced by the impulse width of exciting force. Besides, the effect of impulse width on longitudinal wave is more significantly than that of torsional wave under the same condition. Meanwhile, Material damping and soil damping will cause the exponential decay of reflection. The former effects the width of curve and attenuation degree, a fierce attenuation can be caused by the latter. With the increase of shape factor, the ratio of defect reflection wave to incident wave increases by exponential law. A contrast study on propagation characteristic of longitudinal wave and torsional wave is also discussed in this paper. The result shows that it's easier to interpret small defects and shallow-seated defects by torsional wave curve. Furthermore, the paper suggests that the result of synthesis matching method of longitudinal wave and torsional wave based on simplex method is more rational, and gives the coupling coefficient of pile-soil and coupling coefficient of pile-bottom. In the end, the problem of welded joint of pre-stressed concrete pipe pile is studied. Reflection on welding joint would be weakened and even be invisible when impedance ratio of steel-concrete and welding area satisfies some specific conditions. Moreover, large impulse width of exciting force is also the cause of reflection attenuation in welding joint.