Vertical Vibration Theory Of Single-row Pile Group With Elevated-cap And Its Application

The single-row pile groups with elevated-cap are widely utilized for the foundations of piers and bridges. The pile groups beneath those structures are especially vulnerable to damage or even destruction induced by natural or man-made disasters due to the structural characteristics and service environment. The reliability of pile needs to be assessed after suffering possible damage. Dynamic nondestructive testing methods are more applicable for the detection of in-service pile while the corresponding dynamic theory is lagging behind. In addition, pile vibration theory provides the theoretical basis for dynamic foundation design and earthquake-resistance design, but the vibration theory of the single-row pile groups with elevated-cap is seldom studied. Therefore, theoretical study for vibrations of single-row pile groups with elevated-cap would be necessary and meaningful. Based on Timoshenko beam theory and soil-pile coupling vibration theory, the vibrations of single-row pile groups with elevated-cap are analytically investigated, and the principal researches are as follows:1. Based on Timoshenko beam theory and plain strain model, the mathematical model for motion of single-row pile group with elevated-cap in layered soil is established when the vertical transient excitation is applied to beam or pile. Two kinds of integral transform techniques including Laplace transform and inverse discrete Fourier transform are adopted to derive analytical solution in the frequency domain and quasi-analytical solution in the time domain successively. Comparisons with numerical simulation and model testing are conducted to verify the rationality of the present solution. On this basis, parametric analyses are conducted to give insight into the effects of beam-pile-soil parameters on the dynamic behavior of single-row pile groups with elevated-cap.2. The Timoshenko beam theory and longitudinal vibration theory for one-dimensional rod are introduced to simulate the lateral and longitudinal vibrations of pile group, respectively. The lateral and longitudinal vibrations of pile group are assumed to be independent but coupled with beam vibration. The integral transform techniques are also used to derive the frequency-domain and time-domain solution. A comparison with numerical simulation is carried out to verify the rationality of the present solution and reveal the difference in the impulse responses of single-row pile group with elevated-cap when the transient excitation is applied to pile side or different locations of beam. Related factors of the difference are further discussed.3. A pile-soil coupled vibration model is constructed when considering the transverse inertia effect of pile and the three-dimensional wave effect of surrounding soil layers, in which both vertical and radial displacement continuities at the pile-soil interface are taken into account. The integral transform techniques are used to derive the frequency-domain and time-domain solution for longitudinal vibration of a single pile, and then the solution for transient vibration of single-row pile group with elevated-cap is obtained. On this basis, a parametric analysis is conducted to investigate the effects of transverse inertia on the dynamic responses of an intact pile and a defective pile for different design parameters of the soil-pile system. Besides, the effect of the transverse inertia on the dynamic behavior of single-row pile group with elevated-cap is also analyzed.4. By introducing pile-soil-pile interaction factor to describe dynamic pile-soil-pile interaction, and considering the coupling relationship between beam and pile group in which both lateral and longitudinal deformations of pile group are allowed, the frequency-domain solution for the vertical vibration of single-row pile group with elevated-cap in layered soil is derived by using Laplace transform technique. Based on the present solution, the effects of flexible deformation of beam, lateral deformation of pile group and dynamic pile-soil-pile interaction on the frequency-domain response of single-row pile group with elevated-cap are investigated. Meanwhile, related factors of the effect are also discussed.5. To eliminate the impacts of the upper structures and adjacent piles on the low strain integrity test result of the test pile, two methods are proposed based on the foregoing derivation process-virtual isolation single pile method and universal frequency response function method. Both the present solution for the transient vibration of single-row pile group with elevated-cap and the numerical simulation are used to verify the rationality of these two methods and analyze the relevant factors affecting the test results.The present work is of theoretical significance and application prospect in integrity assessment and dynamic foundation design for single-row pile group with elevated-cap.