In offshore engineering, especially for the construction of offshore wind farms, vibratory driven piles are increasingly appealing. Compared with conventional impact piles, vibratory piles have the advantages of less noise pollution and faster penetration rate. In some specific cases, to meet the requirements of the projects, such as the noise level, the penetration time, and the disturbance to the environment, it is necessary to use the vibratory piles. However, the current level of understanding of the mechanics of vibratory pile installation is incomplete and more reliable predictive models are needed. Thus, a substantial need exists for a better understanding and improved prediction models for vibratory pile installation. This thesis first summarizes the historical development in vibratory pile driving and then develops a Wave Analysis & Stiffness Degradation Model (WASD) to study the nonlinear behavior of saturated sands during vibratory driving. This model features a hyperbolic constitutive model to characterize non-linear stress-strain behavior together with a cyclically-induced excess pore pressure model by Dobry (1984) to predict wave propagation and degradation in soil strength due to excess pore water pressure during the pile penetration process. The analyses are based on the one-dimensional wave equation theory. During this study, two cases of using vibratory driving are studied. One is a large steel pile driven in partially saturated sands reported by Dorp (2019), the other case is a sheet pile driven in fully saturated sands by Viking (2002). In the case studies, the predicted penetration times from the WASD model are compared with the actual results. Then the sensitivities of soil strength reduction to different pile-related and hammer-related parameters are analyzed by several sets of parametric studies.
