Study On The Vertical Dynamic Characteristics Of Single Pile With Cushion Cap

Fruitful achievements regarding the research of single pile vibration theory can be found in a number of papers. The issues of single pile with cushion cap vibration, however, are scares and relatively fewer. This paper investigates the vertical free vibration of single pile with cushion cap by considering the influence of the properties of cushion cap-pile-soil on dynamic response. The principal contents and detailed work are shown as follows:(1)Based on Voigt model, the vertical free vibration of single pile with exposed cushion cap is theoretically investigated considering the viscosity of pile material. First, pile top impedance is calculated according to impedance transformation principle. Then the top impedance which serves as the supporting rigidity was substituted into the dynamic equilibrium equation of free vibration exposed cushion cap in order to derive the frequency-domain analytical solutions for the dynamic response of exposed cushion cap embedded in layered foundation according to integral transform technique. Finally, a semi-analytical solution for time-domain free vibration displacement of exposed cushion cap can be obtained by using inverse Fourier transform technique. Based on these solutions, a parametric analysis is conducted to explore the effects of parameters of cushion cap-pile-soil on free vibration characteristic of pile with exposed cushion cap.(2)Based on plane strain model, a research regarding the free vibration issue of pile with buried cushion cap which is commonly used in engineering world is performed. With the viscosity of pile material, the frequency-domain analytical solutions are derived from integral transformation. Then, a semi-analytical solution for the free vibration displacement of the cap can be obtained for the desired time domain according to inverse Fourier transformation. The effects of parameters of cushion cap-pile-soil on free vibration characteristic of pile with buried cushion cap are evaluated based upon the numerical analysis results.(3)Vertical free vibration test and vertical forced vibration test for single pile with cushion cap are operated by vibrate-excitation test in order to demonstrate the principles and calculation methods of dynamic properties tests of pile. Finally, the compressing rigidity and vertical vibration damping coefficients are thus been proposed. A comparison between the theoretical curve andmeasurement value validates the applicability of the present approach. The analysis results from this paper can serve as a supplementation of the pile foundation vibration theory. The conclusions and suggestions demonstrated in the paper are also applicable in the design and analysis process of dynamic machine foundation.