Noise & vibration
4Hz 2.8 8Hz 1.4 16Hz 0.69 31.5Hz 0.35 63Hz 0.18
40km/h 80km/h 160km/h 320km/h 5.6 2.8 1.4
0.70 0.35
125Hz 0.089 0.18
11.0 5.6 2.8 1.4
0.71 0.36
250Hz 0.044 0.089 0.18
21.0 10.0 5.2 2.6 1.3
0.67 0.33
Table 1: relation between irregularity wavelength (m) and excitation frequency (Hz) at a given vehicle speed.
vibration energy into the soil which then propagates into the ground causing the foundations of the surrounding buildings to vibrate and potentially disturb residents. By focusing exclusively on the track parameters (excluding the vehicle and the propagation path effects), two methods have been identified to reduce the energy transmitted to the sub-layers
and the ground: reducing the excitation force at the
contact point, and reducing the vibrations of the track components.
As far as railway infrastructure is concerned, the excitation force is driven by track defects and the track receptance (displacement for a unit load) at the contact point.
In Rivas, track defects are classified according to their impact on the generation of ground vibration. The project has assessed the effect of standard maintenance
operations on these defects and the
corresponding reduction in vibration. In parallel, studies of track design have been carried out to identify means to control the track receptance at the contact point and track mobility in order to suggest ways to reduce the extent of vibrations transmitted to the sub-layers.
Contributions to railway-induced
ground vibration are generated by both the quasi-static and dynamic components of vehicle excitation. The quasi-static excitation is determined by rolling stock characteristics such as the static component of axleloads and axle distances, and vehicle speed, while the dynamic excitation is induced by wheel/rail irregularities and irregularities in track support stiffness. It is the latter that dominates the
vibration levels felt by the residents living close to a railway line. The dynamic component of the vertical wheel-rail contact force is an important source of ground vibrations and ground-borne noise. This can be generated by irregularities in track geometry brought about by differences in longitudinal level, isolated defects, insulated joints, rail corrugation, switches and crossings; track stiffness caused by transition zones, hanging sleepers or culverts; and/or misshaped wheels. Each type of irregularity induces specific vibrations, depending on the type of vehicle, its speed, the soil conditions and a number of track dependent parameters. The perceivable ground vibration has
a frequency content ranging from a few Hz up to around 80Hz, while the ground-borne noise typically contains frequencies in the range of 30-250Hz. At vehicle speed v, a periodic wheel/track irregularity with wavelength λ will generate a dynamic excitation at frequency f = v/λ, so when running at 80km/h, the irregularities between 0.09m and 5.6m have an influence on ground-borne noise and ground-borne vibrations, while when
Example of joints in bad (left) and good (right) condition and their respective impact on low-frequency vibrations (Graph 1 below).
20 18 16 14 12 10 8 6 4 2 0
-2 -4 -6 -8
-10 -12 -14 -16 -18 -20
1/3 octave band center frequency 38
sq229_rec08.mat
sq229_rec20.mat
sq229_rec26.mat average
20 18 16 14 12 10 8 6 4 2 0
-2 -4 -6 -8
-10 -12 -14 -16 -18 -20
1/3 octave band center frequency IRJ June 2013
sq144_rec08.mat
sq144_rec20.mat
sq144_rec26.mat average
dB [re 1e-09m/s]
Ground-borne noise Noticeable vibrations
dB [re 1e-09m/s]
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