On reducing the level of vibration transmitted by transport to the environment

Abstract

The paper considers problems in reducing the vibration activity of modern rail transport networks in big cities, primarily, the metro system, which provides the biggest carriage of passengers. The growing intensity of traffic in the lines and the ever-increasing load and necessity of building new subway lines, as well as of other kinds of rapid-transit rail transport (monorail roads, express tramways, and others) dictates the necessity to account for the possible impact of transport facilities on the surrounding buildings. Hence, recently, more strict norms are being introduced to relevant regulatory documents. They regulate the definitive physical parameters of vibration and noise admissible in urban rail transport. Metro system shallow subway lines are known to be a source of increased vibration, which propagates in the ground and is transmitted to the foundations of buildings located in the metro system land allocation area. Therefore, it is critical to reduce the level of vibrations and structural noise in the development area adjacent to the metro system lines being projected and built. Different technical solutions based on conventional vibration isolation schemes are not always effective. A development is known with a sleeper track design using separate rubber cushions. A technical solution is known, which is based on the design of the German firm GERB with the usage of metal springs. Also known are methods based on using rubber mats. All these solutions fail to meet sanitary norms. The design of a track vibration isolation system using any elastic elements has a service constraint. The track deflection under the weight of a car shall not exceed 4 mm. Hence, the eigen frequency of the entire mechanical system train - track – vibration isolation – tunnel lining - ground cannot be lower than 8 to 10 Hz. Hence, the vibration isolation factors for common vibration isolation schemes are insufficient. It is necessary to ensure stiffness with track depression within 4 mm and increase the level of vibration isolation at the same time. Presently, the metro system has no track vibration isolation system whose design would meet sanitary norm requirements to vibration and structural noise. The paper addresses the problem of suppressing vibrations created by metro trains. Vibrations occurring due to interaction of the railway train and rails in the railwheel point of contact are reduced by placing hydraulic vibration isolators with inner inertial elements under the track structure. The study builds models of systems of the metro stock. It is investigated using dynamic stiffness methods for both the case of using vibration isolators and without them. The result is comapred against experimental data. The vibration oscillation effect is predicted to increase (by 6 to 30 dB) whilst retaining the required static stiffness value.