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Application of expanded polystyrene (EPS) geofoam for the mitigation of dynamic vibrations and distress of civil infrastructure

Lyratzakis Alexandros

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Summary

Traffic congestion is one of the most important issues related to the conventional means of transportation (e.g., cars or busses). This disadvantage has led to the development of alternative comfort, fast and environmentally friendly transportation means, such as high-speed trains (HST). Nonetheless, in order to safely operate relatively new transportation means such as HST, several important aspects should be properly addressed. The most important issue related to the safety of high-speed railway infrastructure and the disturbance/comfort of the residents of nearby buildings, is the vibrations developed due to the high passing velocity of the trains. In recent decades, the developing noise and vibrations induced by the HST passage, as well as their mitigation, are considered as very crucial issues in structural dynamics. For this reason, several studies have been carried out aiming to propose optimal mitigation approaches in order to reduce ground-borne vibrations. These mitigation approaches can be grouped into four categories: (a) track modification, (b) track maintenance, (c) retrofitting to reduce vibrations of adjacent buildings and infrastructure, and (d) installation of wave barriers. The most popular mitigation measure to reduce the vibrations developed by the passage of HST is the construction of wave barriers/trenches across the railway. For this purpose, several types of wave barriers and filling materials have been proposed over the last decades. However, the most effective wave barriers have also high construction and maintenance costs. Hence, the proposal of an effective, low-cost mitigation measure is still a challenge for the engineering community.An additional challenge for the researchers is to establish numerical, experimental or analytical approaches capable of predicting the developing vibrations in a reliable and accurate manner. For this purpose, several numerical approaches have been proposed, i.e., finite differences, finite element and boundary element-based methods. Furthermore, this complex phenomenon has been investigated via two-dimensional (2D), two-and-a-half-dimensional (2.5D) and three-dimensional (3D) models. Sophisticated computational models have been implemented in order to examine various issues, such as the critical speed of HST, the properties of the track and the subsoil, ground vibrations generated by two passing trains, mitigation measures of induced vibrations, train-structure interaction, etc.One of the main aims of the current doctoral research is to present an efficient computational methodology, with low computational cost, capable of accurately predicting the HST-induced vibrations. For this purpose, the finite element method has been selected and advanced 3D models have been developed. In order to ensure the reliability of the numerical model, the numerical results have been compared with pre-available in-situ measurements. More specifically, field data from the passage of Thalys HST at three sites in Paris-Brussels line have been used in order to validate the developed numerical methodology. In the sequence, an extensive investigation of several mitigation measures based on the application of expanded polystyrene (EPS) geofoam at embankment and cutting sites has been performed in order to determine the optimal mitigation configuration. Accordingly, the impact of the subsoil conditions, the geometrical properties of the site or the HST passing speed have been investigated. Furthermore, the protection of nearby buildings and buried pipelines, using optimal configurations of EPS geofoam has been thoroughly examined and the results illustrate the efficiency of the proposed mitigation measures.

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