Concrete slab beneath ballast bed - An Abatement Measure For Railway Induced Vibration

Abstract

In this research project, an assessment of an abatement measure for mitigating railway induced vibrations is carried out. Ground-borne vibrations, which are primarily generated due to wheel-rail interaction, may also result in ground-borne noise in the buildings located in vicinity of railway tracks. An example of adverse environmental impact caused by ground-borne vibration and noise is the annoyance to people living those buildings. Assessing ground-borne vibration and noise is of crucial importance, especially in soft soils in which Rayleigh wave velocity is low and amplification of vibrations is more likely to occur. For mitigating the ground-borne vibration and noise exceeding the threshold values defined by technical standards in each country, abatement measures are applied. The main objective of this research is assessing the effectiveness of ‘concrete slab beneath ballast bed’ used as the abatement measure for reducing vibrations. For this purpose, Plaxis 3D based on Finite Element Analysis method is employed. Numerical model is created and validated through measurement data available from field tests conducted in the Netherlands. After having numerical model validated, several simulations are performed in order to study the factors influencing ground-borne vibrations.
From the results of this study, one can conclude that ‘concrete slab beneath ballast bed’ is effective in reducing vibration strength at all distances when train speed is considerably lower than Rayleigh wave velocity of the uppermost soil layer. It is notable, however, that the application of this measure may bring about amplification of the vibration strength in the vicinity of the track for trains running at higher speeds. Nevertheless, regardless of the train speed, there is always a reduction in the vibration strength at further distances from the railway track. From practical standpoints, this aspect is of interest for the buildings located in the far field. From the results of a sensitivity analysis on changes to the width and thickness of the concrete slab, it can be concluded that an optimal solution of concrete slab dimensions can be found. It is observed that by changing concrete slab dimensions, the maximum vibration strength is mostly affected in close proximity to the railway track. In addition, the dispersion lines and oscillatory moving load in the Wavenumber-Frequency plane are analyzed. Their intersection indicates that the moving oscillatory load excites a wave of frequency and wavenumber given by the intersection point. If these frequencies are harmful for the environment then concrete slab application can diminish their content from response. Sleeper passing frequency content increases when the concrete slab is applied. The obtained results and recommendations from this study can be used for further studying the other factors influencing the effectiveness of the measure. Examples of these factors include, among others, various ground conditions (e.g., soft soils of different stratification, local changes in soil proper-ties, etc.), and optimization of concrete slab dimensions, material parameters, as well as, cracked and uncracked concrete stage. The numerical model developed during this research study can be further employed to analyze different aspects of railway induced ground-borne vibrations.