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PROCEEDINGS OF THE EIGHTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY
Edited by: B.H.V. Topping, G. Montero and R. Montenegro
Microtremors from Railway Traffic
Department of Structural Mechanics, Civil Engineering Faculty, University of Zilina, Slovakia
J. Bencat, "Microtremors from Railway Traffic", in B.H.V. Topping, G. Montero, R. Montenegro, (Editors), "Proceedings of the Eighth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 241, 2006. doi:10.4203/ccp.83.241
Keywords: microtremor, wave propagation, train-induced ground vibration process, railway vibration transmition, traffic effect on structures and environment, railways structures dynamics.
The operation of modern railways has been attended by an increase in train speed, train weight and wagon axle load. There seems nevertheless to be a few scattered complaints by wayside residents of vibration due to the passage of trains. The experimental evidence points out that the impact from the wheels passing over the rail joints have significant influence on the ground vibration transmitted from railway to nearby regions and the spectral characteristics of the ground-borne vibration can be significantly dependent on: (i) a unit train of identical vehicles produces ground vibration at frequencies which are related to wagon length, (ii) vibration which are produced by passing a steady wheel load over the discrete support provided by sleepers this effect is independent of inertia effects, (iii) vehicle vibrations (inertia effects) and (iv) track irregularities. The transient stress variations are produced in the ground below the track, they will propagate away from the track as ground-borne vibration. In the ideal case when the ground is homogeneous the compression and shear waves propagate in all directions away from the source, and thus they have substantial geometric attenuation, as well as losses due to the damping properties of the ground. The Rayleigh's waves, being surface waves, do not have the same geometric attenuation, but are still subject to loss by damping. In practice the ground is far from homogeneous: it can be stratified and possess discontinuities. In such a case additional modes of vibration can propagate along the interfaces of strata, and mode conversion from one type of wave to another may be encouraged.
The experimental tests have been performed in the several test fields near the railways of the ZSR (Slovak Railway Company). The object of the experimental measurements was to find: (i) spectral characteristics of the vibration components of the railway structure near the nearest rail joints and in the long distance from rail joints (rails, heavy concrete ties, ballast, roadbed and ground) by the power spectral densities , , (ii) the soil frequency characteristics expressed by frequency response function or by the gain factor of the response function , respectively, (iii) the Rayleigh´s wave velocities , by the cross correlation function and then calculation the initial tangent shear modulus , and (iv) the attenuation coefficients from the equation , where , are standard deviations of the amplitude of vibration at the distance , from the source of the vibration obtained from power spectral densities , , and represents the effect of geometrical attenuation [1,2].
According to performed of the theoretical and the experimental analysis of the railway track and ground vibrations, the following summary and conclusions can be made:
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