Theoretical Study On Vertical And Torsional Vibration Of Stepped Piles

Pile vibration theory is the theoretical basis for dynamic foundation design and various pile integrity tests.With the development of modern pile foundation engineering,various types of piles have emerged.Among them,stepped piles have been widely applied in both bridge engineering and soft ground improvement due to their significant economic benefits and remarkable performance.However,most of the research on stepped piles focuses on their staic characteristics such as bearing capacity and deformation laws,but there are few reports on their dynamic characteristics.In view of this,based on the wedged soil model,this paper analytically studied the vertical and torsional vibration characteristics of stepped piles in single-phase soil and saturated soil.The main work and results are as follows:1.A wedged soil model was established to simplify the dynamic interaction between the stepped pile and the surrounding soil.The wedged soil boundary was obtained by combining numerical modelling and the Mohr-Coulomb failure criterion.Based on plane strain model,ring soil pile theory and Rayleigh-Love rod theory,the analytical solution of vertical vibration of a stepped pile in single-phase soil is derived.The sensitivity of the vertical dynamic response of the stepped pile to the wedged soil boundary error was examined.Then the wedged soil model was compared with the Voigt model.Finally,the influence of pile geometry on the vertical dynamic response of the stepped pile was investigated.2.The analytical solution of torsional vibration of a stepped pile in single-phase soil was derived.From the perspective of earth pressure theory,the selection of wedged soil boundary was discussed and the influence of wedged soil boundary on the torsional dynamic response of the stepped piles was investigated.In addition,the influence of pile geometry on the torsional dynamic response of the stepped pile was studied.3.By combining plane strain model,Biot theory and ring soil pile theory,the analytical solution of vertical vibration of a stepped pile in saturated soil was derived.The accuracy of incorporating the plane strain model to Biot theory was examined.Then the derived solution was compared with the single-phase soil solution derived in Chapter 2.Finally,the influence of the properties of the saturated wedged soil on the vertical dynamic response of the stepped pile was studied.4.By combining the plane strain model,Biot theory and ring soil pile theory,the torsional vibration characteristics of a stepped pile in saturated soil was theoretically studied.The derived analytical solution is compared with the single-phase soil solution derived in Chapter 3.Then,the influence of the properties of the saturated wedged soil on the torsional dynamic response of the stepped pile was studied.