INVESTIGATING THE INFLUENCE OF A SECOND TUNNEL AND UTILITY CORRIDORS ON GROUND-BORNE VIBRATION INDUCED BY UNDERGROUND RAILWAYS

Abstract

Railway systems are an integral part of the transportation system. They play a vital role in bulk transportation, efficiently moving large volume of goods and large number of passengers. However, as they operate, they generate ground-borne noise and vibration that affect nearby structures, sometimes in levels that can hardly be tolerated. This thesis presents an investigation into the influence of a second tunnel and utility corridors on ground-borne vibrations, using the Finite Element (FE) method. The analysis is extended to assess the effect of changes in in-track parameters by incorporating a mass-on-spring system into the model. The baseline model considered in the thesis is a tunnel-soil model, where the tunnel is embedded in half-space and is subjected to a unit harmonic point load at the base of its invert. The analysis is conducted for a 2D plane-strain case in the frequency domain, considering the range of 0-250 Hz, which is relevant for ground-borne noise and vibration. The primary metric for assessing the results is the vertical vibration displacement presented in decibels (dB). For the parameters used in this thesis, considering the second tunnel in the model has resulted in a modification of the displacement field by ±26 dB, while the presence of the utility corridor resulted in a modification up to ±16 dB for the single tunnel case, and up to ±23 dB for the twin tunnel case. The mass-on-spring system resulted in vibration isolation across all frequencies beyond the natural frequency of the mass-on-spring system. It was found that the Insertion Gain (IG) derived from two natural frequencies of the mass-on-spring system remained unchanged for both single and twin tunnel configurations. This suggests that ignoring the second tunnel in modelling noise and vibration from underground tunnels is acceptable, when the target of modelling is predicting the change of vibration or noise due to the introduction of in-track countermeasure.