Propagation and Effects of Vibrations in Densely Populated Urban Environments

Environmental vibration generated by sources such as rail lines, road traffic and construction work is a serious concern, especially in the urban environment. It leads to annoyance of the exposed population, creating uncomfortable living and working spaces. Thus, prediction and mitigation of these effects is an important research area, investigated by an increasing number of engineers and researchers. In this regard, computational models are especially useful. They enable the prediction of environmental vibration levels in the planning stages of a new project, reducing or, ideally, completely removing the need for in-situ investigations. Currently available numerical approaches are highly capable and can be used to model the complex cases encountered in the urban environment. However, the largest drawback of these approaches is the long computational times needed to obtain the solution, thus limiting their usage for real applications. The thesis aims to create environmental vibration prediction tools, with particular interest in their computational efficiency. This way, the created methodologies could be easier applicable to a wider audience. Modelling of the vibration propagation through soil, in most cases, is the most time consuming task. Thus, the thesis mostly focuses on this part of the system. A semi-analytical soil modelling approach was chosen to model the soil, using a Thomson-Haskell transfer matrix method. The method is advantageous, due to the analytical formulation of the soil, which does not require the discretization of the full soil domain and incorporates the infinite nature of the soil. The semi-analytical method is coupled to the finite element method, where the soil is accounted for using the semi-analytical approach, while the external structures can be modelled with finite elements. This way, the computational efficiency of the semi-analytical approach is combined with the modelling freedom of the finite elements method, allowing the application of the created model for a wide range of application cases. The thesis investigates a number of modelling cases that are commonly encountered when analysing dynamic soil–structure interaction and vibration propagation through soil. A railway bridge structure is analysed using lumped-parameter models to obtain a solution in the time domain. The work presents a novel lumped-parameter model fitting technique that is needed to obtain a numerically stable solution. Further, the semi-analytical soil model is used to analyse cases commonly encountered in the urban environment. For that purpose, various configurations of soil interacting with structure are tested, such as: rigid blocks, pile foundations, railway tracks, embedded structures, and cavities inside the soil. The proposed modelling methods are validated by comparison with other numerical methods. Very good agreement is found, demonstrating the high accuracy and the reduced computational effort of the proposed modelling approaches. A novel numerical method for predicting railway-induced vibrations is also proposed. The method utilizes the semi-analytical soil model formulated in both moving and fixed frames of reference. This way, it is possible to model the railway track and the vehicle in a moving frame of reference, while the nearby structures are formulated in a fixed frame of reference. The approach offers a flexible and numerically stable approach of modelling the full vibration propagation path, using a single-step solution procedure

Effect of structural design on traffic-induced building vibrations

Population growth and urbanization results in densified cities, where new buildings are being built closer to existing vibration sources, and new transportation systems are constructed closer to existing buildings. Potential disturbing vibrations are one issue to consider in planning urban environments and densification of cities. Vibrations can be annoying for humans but also for sensitive equipment in, for example, hospitals. In determining the risk for disturbing vibrations, the distance between the source and the receiver, the ground properties, and type and size of the building are governing factors. In the paper, a study is presented aiming at investigating the influence of various parameters of the building’s structural design on vibration levels in the structure caused by ground surface loads, e.g. traffic. Parameters studied are related to the type of construction material (if it would be a light or heavy structure), and to the slab thickness. The study is limited to the structural response at frequencies near the first resonance frequency of the soil. The finite element method is employed for discretizing the building structure that is coupled to a semi-analytical model considering a layered ground

Variation in models for simple dynamic structure–soil–structure interaction problems

To account for dynamic cross-coupling of structures via the soil, a computational model must be accurate enough to provide the correct overall behaviour of the scattered wave field. However, simplicity is also important when a model should be used for design purposes, especially in the early design stages and feasibility studies. The paper addresses the accuracy of simple models in which an array of structures is simplified into blocks placed on the ground surface or embedded within the soil. Comparisons are made between models that account or do not account, in a proper manner, for the inertia and embedment of the structures. Especially, the limitations of simplified models are discussed regarding their capability to quantify the insertion loss accurately

Variations within simple models for structure-soil interaction

The dynamic response of blocks sitting on a half-space is considered. Buildings and other structures placed on or within the ground influence the transmission of seismic waves. Hence, the presence of a building will have an impact on the dynamic response of neighbouring buildings. Furthermore, obstacles such as concrete blocks lead to wave scattering that may be beneficial or unfavourable for the response of a building close to, for example, a railway. To account for this dynamic cross coupling via the soil, a model must be accurate enough to provide the correct overall behaviour of the scattered wave field. However, simplicity is also important when a model should be used for design purposes, especially in the early stages of design and feasibility studies. The paper addresses two models in 2D and 3D based on different methodologies. Results are discussed regarding their capability to quantify vibration reduction when a periodic combination of masses are added on the ground to mitigate waves

Numerical modelling of ground vibration caused by elevated high-speed railway lines considering structure-soil-structure interaction

Construction of high-speed railway lines has been an increasing trend in recent years. Countries like Denmark and Sweden plan to expand and upgrade their railways to accommodate high-speed traffic. To benefit from the full potential of the reduced commuting times, these lines must pass through densely populated urban areas with the collateral effect of increased noise and vibrations levels. This paper aims to quantify the vibrations levels in the area surrounding an elevated railway line built as a multi-span bridge structure. The proposed model employs finite-element analysis to model the bridge structure, including a multi-degree-of-freedom vehicle model and accounting for the track unevenness via a nonlinear contact model. The foundations are implemented as rigid footings resting on the ground surface, while the soil is modelled utilizing Green's function for a horizontally layered half-space. The paper analyses the effects of structure-soil-structure interaction on the dynamic behaviour of the surrounding soil surface. The effects of different soil stratification and material properties as well as different train speeds are assessed. Finally, the drawbacks of simplifying the numerical model, in order to reduce the complexity of the calculations, are determined