The dynamic response of piles is a fundamental issue that significantly affects the performance of pile foundations under vertical cyclic loading, yet it has been insufficiently explored due to the limitations of experimental methods. To address this gap, a hydraulic loading device was developed for centrifuge tests, capable of applying loads up to 2.5 kN and 360 Hz. This device could simulate the primary loading conditions encountered in engineering applications, such as those in transportation and power machinery, even after the amplification of the dynamic frequency for centrifuge tests. Furthermore, a design approach for model piles that considers stress wave propagation in pile body and pile-soil dynamic interaction was proposed. Based on the device and approach, centrifuge comparison tests were conducted at 20 g and 30 g, which correspond to the same prototype. The preliminary results confirmed static similarity with only a 1.25% deviation in ultimate bearing capacities at the prototype scale. Cyclic loading tests, conducted under various loading conditions that were identical at the prototype scale, indicated that dynamic displacement, cumulative settlement, and axial forces at different burial depths adhered the dynamic similarity of centrifuge tests. These visible phenomena effectively indicate the rationality of centrifuge tests in studying pile-soil interaction and provide a benchmark for using centrifuge tests to investigate soil-structure dynamic interactions.

Bridge piers embedded in a riverain region are commonly supported by pile foundations. This provides a flexible restraint to the bridge pier instead of a theoretical rigid foundation type. In this work, a cylindrical bridge pier with a monopile foundation is introduced as an example. A modeling framework is proposed to investigate the dynamic response of bridge piers to the impact of flash flooding. The fluid-structure interaction is directly investigated via a two-way fluid-structure coupling approach and the p-y springs distributed over the interface between the soil and pile are adopted to model the lateral restraints from the soil. The effect of the soil-structure interaction (SSI) on the structural dynamic response is investigated on the basis of 3D numerical models with and without a pile foundation. Moreover, the soil around the pile foundation is vulnerable to erosion by flood flow. This continuous exposure of the pile foundation reduces the lateral load bearing capacity and consequently increases the dynamic responses of bridge structures to flash flooding. To demonstrate the effects of increased exposure of bridge pile foundations on structural dynamic responses, several different scour depths with scour ratios ranging from 0 to 0.5 are included in the numerical analysis. Two different considerations of the pile bottom are included in this study: completely fixed and only vertically fixed. The behavior of bridge piers subjected to flash flooding is thoroughly analyzed, and the damage mechanisms for these two foundation types are investigated. The relationships between peak responses and fundamental periods are determined via regression analysis.

The seismic excitations are potential hazards for offshore wind turbines located in earthquake prone zone. To investigate the dynamic characteristics of bottom-fixed offshore wind turbines (OWTs) under earthquakes, the influence of aerodynamic, hydrodynamic loads and pile foundation flexibilities is non-negligible. Hence, in this study, the fully coupled simulation tool FAST V8 for OWTs under earthquakes is updated based on the devised equations and the rotor-nacelle-assembly-tower-substructure numerical models considering different boundary conditions are established. The natural modes of a monopile substructure are compared to validate the accuracy of the established numerical model in the updated FAST V8. Subsequently, the OWT structural dynamic responses with different foundation boundary conditions under the combination of winds and waves, the combination of winds, waves, and earthquakes are analyzed and discussed, and a short-term damage equivalent load is adopted to assess the effect of pile foundation flexibility on OWTs. Finally, it is pointed out that the different foundation boundary constraint conditions have obvious influence on the OWT dynamic responses, especially for the model with coupled spring boundary condition under the action of earthquakes, the effect of second order frequency is more significant. In addition, the influence of different environmental loading frequencies on the OWT structure can also be observed.

Understanding the dynamic response of soil is crucial in geotechnical engineering. Based on the Biot's theory of poroelastic soil, the integral transformation method is used to solve the wave equation of multilayered poroelastic soil. Analytical solutions for the dynamic displacement and stress fields in the spatial domain are then derived. This method accounts for the transverse isotropy properties and the discontinuous contact conditions between adjacent layers. The accuracy of the algorithm is verified by the degradation models. On this basis, the effect of varying interlayer contact parameters on the displacement fields of the poroelastic layered soil is examined. The results show that the interlayer discontinuity condition state significantly affects the dynamic response, with a greater degree of separation leading to a greater dynamic displacement response and increased susceptibility of the pavement to damage. Finally, an example is given to analyze the effect of heterogeneous properties of soil on the dynamic response of multi-layered system. Due to the existence of discontinuous contact between layers, the influence of the heterogeneous properties of the soil on the dynamic response of the pavement structure is weakened, but it still has a great influence on the soil below the discontinuous contact layer.

This paper establishes an efficient model for simulating wave propagation in a multi-layered transversely isotropic (TI) saturated medium. The complex frequency shifted perfectly matched layer (CFSPML) is integrated into the thin layer method (TLM) framework to address instability issues associated with the classical PML in TI media. The three-dimensional closed-form fundamental solution for dynamic sources acting on a layered TI halfspace is derived in the frequency-space domain. By eliminating the necessity of double discrete Fourier transform of spatial coordinates, this approach provides an efficient and accurate tool for exploring wave propagation in saturated soils. Numerical examples are conducted to determine the parameters involved in CFSPML for an unbounded TI saturated medium across various material anisotropy ratios, including the total thickness of CFSPML domain HPML, the parameter Delta gamma related to the number of CFSPML elements, and the reflection coefficient within the discrete CFSPML domain R0. A comprehensive investigation systematically analyses the effect of material anisotropy on dynamic responses. Numerical studies highlight that the anisotropy in the shear modulus exerts the most substantial influence on the dynamic response, followed by Young's modulus and the permeability coefficient. The effect of permeability coefficient anisotropy cannot be disregarded, particularly in the context of fluid sources.

Recent field case study shows that the roadbed of ballastless high-speed railway experienced water-induced defect such as excessive fines pumping and even local subgrade-track contact loss affecting the normal operation of high-speed train due to water immersion through gaps of waterproof materials in expansion joints between the concrete base, particularly in rainy seasons. However, the study about the dynamic behavior of high-speed railway subgrade involving water is currently rare. Based on the theory of fluid dynamics in porous medium and the vehicle-track coupling vibration theory, a numerical method of hydraulic-dynamic coupling was established to evaluate the dynamic responses of saturated roadbed surface layer under the high-speed train loading with the validation by comparing the calculated values and field data. The temporal and spatial characteristics of dynamic behaviors (stress, pore water pressure, seepage velocity, displacement) of saturated roadbed surface layer are fully discussed. Also, the effects of train velocity, permeability, on aforementioned dynamic responses of the saturated roadbed surface layer are evaluated. The study shows that improving the drainage of ballastless track roadbed has a significant effect on minimizing the mud pumping of ballastless track, and the influence zone of hydraulic-mechanical coupling is mainly within 0.1 m of the roadbed.