Research On The Torsional-shear Method Applied To Dynamic Pile Testing

The low strain method is characterized as nondestructive and convenient. Therefore,it has long been one of the most popular measures of the pile integrity test at present.Because of complicated engineering geological condition as well as different types of pileinstallation, the code simply points out that the low strain method’s effective detectinglength of pile is determined by field test and it does not provide a quantitative calculationmethod. Besides, the mentioned method inclusively refers to the P-wave reflection method.This method is usually applied in the pile with exposed pile tops. However, it cannot bedirectly applied to quality test of pile foundation with existing superstructures such asbuilding, bridge and port. The torsional-shear method, whose mechanical theory is similarto that of P-wave reflection method, is extensively studied for more than ten years. It canto some extent overcome the difficulties in pile test caused by existing superstructure.However, due to the lack of simple and efficient methods of vibration excitation, thetorsional-shear method is not yet widely used in practical engineering.In this thesis, the attenuation characteristics of stress wave in the pile in soil, themethod of torsional wave signal extraction and the influence of the superstructures on thetorsional wave are systematically studied.Firstly, based on Winkel foundation model，the attenuation characteristics andinfluence factors are discussed. Then the difference between the attenuation characteristicsof P-wave and torsional wave in both circular pile and pipe pile are discussed. Thecalculation method of pile’s effective detecting length of the torsional-shear method insingle layer soil is proposed. Further amendment and improvement are performed, so thatit can apply to the P-wave method and complex engineering condition, and the method isverified using engineering practice.Secondly, a practical approach to extract the torsional wave signal from horizontal eccentric percussion excitation is put forward. Influencing factors of the method areanalyzed by numerical simulation. In order to guide engineering applications, a model testis conducted to investigate the torsional wave signal generated by different excitationapproaches.At last, when superstructure exists, the characteristics of incident wave, the influenceof different excitation method and the location of collection point on incident wave arediscussed. The characteristics of the interference wave from beam and pile cap in torsionalwave signal are also discussed.