Assessment of Ground Vibration Caused by Underground Railroad Traffic close to High-rise Buildings
Successful performance of megacities is inseparably linked with the progress of underground transport, because so far there are no economically feasible alternatives. However, the metro, as any rail transport is the source of excessive vibration and noise. New subway lines are frequently laid within existing housing, which induces increased vibration in adjacent buildings above. The urgency of this problem was acknowledged in 2000 by launching of European project called CONVURT (CON trol of Vibrations from Underground Rail Traffic) aimed at development of the methods of predicting vibrations induced by metro as the base for the norms regulating max admissible vibration indexes depending on building typology. In 2007 the Moscow Government Directive № 896-ПП outlined the ways of reduction noise and vibration parameters within the city, which emphasizes urgency of decreasing negative metro issues in terms of vibration and acoustics.
Notwithstanding multiple relevant studies, none of existing approved evaluation methods considering dynamic influence of underground transport allow to solve universally the practical task of determining the levels of ground vibration. Unfortunately, there is no versatile tool facilitating this problem, which is the basic for development of strategies for zones adjacent to the underground railroad tunnels. In particular, the majority of empirical models dealing with the “tunnel-ground” system do not consider wave-like behavior of interaction between tunnel constructions and ground environment.
On the other hand, whereas the analytical methods of surface vibration assessment is reliable the most in terms of waves propagation, the set of tasks, related to this group of methods is limited by simple analytical models, whilst parameterization becomes problematic. In this article, in line with analytical studies on predicting of vibration structural load acting on high-rise buildings located close to subway lines, we describe the effective iterative- analytical procedure for determining surface vibration developed by VIBROSEYSMOZASHCHITA, applicable to plane problems.
The procedure successfully is used for determining the design vibration parameters for vibroprotection systems of buildings and facilities. The analytical complex allows prompt and well reliable prediction (experimentally proved) of anticipated levels of vibration at sites situated within the zone of influenced by existing and would-be subway lines.
If soil conditions and structure are complex, the results of applied analytical procedure are judged just as calibration, since they make it possible to predict the peculiarities of wave processes during subsequent application of numerical methods. It allows verification of complex finite-element models. The standard task is wave emission by absolutely rigid circular object - flat doughnut (simulating the underground tunnel) impacted with harmonic load applied to the tunnel.
Tunnel ground environment is simulated by semi-infinite plane with free boundary (“topographic surface”). To consider not only free-space attenuation of wave process, but also the losses as a result of the internal ground friction, analogous task is examined in elastic, and also in elasto-viscous conditions.
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Text by Mikhail DASHEVSKY, doctor of technical sciences, CTO at VIBROSEYSMOZASHCHITA plc,
Yuri KOLOTOVICHEV, assistant lecturer of MGSU Structural Mechanics Department