Rail irregularities, corrugation and acoustic roughness: characteristics, significance and effects of reprofiling

Abstract

Railway noise is excited by irregularities on the running surfaces of wheels and rails, with rails being more significant for most of the wavelength and frequency range of interest. Measurements are presented that demonstrate the significance of irregularities in the 100-1000 mm wavelength range (corresponding roughly to 25-250 Hz) on ground-borne noise, and show that a reprofiling specification to address reductions in low frequency noise should address these longer wavelengths. Differences are demonstrated between irregularities in the 6.3-2000 mm wavelength range on a dedicated high speed line, and on heavy haul, mixed traffic, metro and light rail systems. Although the sample size is small for the high speed and heavy haul systems, the lowest levels of irregularity were nevertheless found on the high speed line. Heavy haul systems also have low levels of irregularity, which are below the limit specified in the acoustic standard ISO 3095. Metro systems are distinguished by corrugation, higher levels of short wavelength roughness corresponding perhaps to roughening from consistently high traction and braking, and significant differences between high and low rails in some curves. In one case shown here the high rail is amongst the smoothest in an entire sample of dozens of rails whereas the corresponding low rail is by far the most heavily corrugated and irregular. Light rail systems have relatively high levels of irregularity, particularly at short wavelengths. This may result from sanding to enhance adhesion. Reprofiling in general reduces irregularities below the level stated in ISO 3095, except at wavelengths of less than 30 mm for which irregularities are consistently greater after reprofiling than before. Reprofiling is particularly effective in reducing irregularities in the 30-500 mm wavelength range, in which irregularities are typically reduced by 10 dB but in some cases by 20-30 dB. Irregularities to the ISO 3095 limit spectrum exist immediately after some forms of grinding. The best results are obtained from reprofiling that is undertaken to an appropriate specification that is conscientiously monitored.

Modelling, simulation and evaluation of ground vibration caused by rail vehicles

“…On the wheels, short wavelength unevenness is again caused by wear whereas discrete wavelengths up to about 3 m are present due to out-of-roundness. However, it has been shown in [81] that although the typical wheel irregularities are of a similar order of magnitude to the rail irregularities at short wavelengths (below 0.1 m; "acoustic roughness"), the magnitude of wheel irregularities is very much smaller than those of the rail at longer wavelengths and thus can be neglected for ground-borne vibration generation. Thus, all irregularities can be assumed to be on the rail surface.…”

The Effect of Track Unevenness Correlation on Railway Induced Ground Vibration

“…The principle is shown in Figure 5 It should be noted that, in the present work, the wheel irregularities are neglected, so that all irregularities are assumed to be on the rail surface. Nonetheless, it has been shown in [16] that although the typical wheel irregularities are of a similar order of magnitude to the rail irregularities at short wavelengths (below 0.1 m; "acoustic roughness"), the magnitude of wheel irregularities is very much smaller than those of the rail at longer wavelengths and thus can be neglected for ground-borne vibration generation. This smooth-wheel assumption is a useful starting point for a more realistic input excitation in comparing the effectiveness of various ground-borne vibration prediction models.…”

“…This shows that the mobilities are equal for the two ground types at low frequencies, where the transmission is dominated by the underlying half-space. Above 6 Hz the soft ground shows higher vibration levels (up to 20 dB at 16 Hz, close to the cut-on frequency of the soft ground). At higher frequency, above 50 Hz for 8 m and 35 Hz for 16 m, the soft ground shows lower vibration levels due to a greater influence of damping since the wavelengths in the soil are shorter.…”

Measurement methods and analysis tools for rail irregularities: a case study for urban tram track

“…The obtained spectrum k-r(k) thus can be compared with standard limits according to the needs: limits that are not univocally established if not for rail used during [12]. Figure 9 shows both acoustic roughness spectra of a tramway rail and standard limits for railway rail.…”

“…Since the vehicle/track interaction produces a wideranging vibratory phenomenon, this results in different types of noise: besides the rolling noise, the ground-borne noise and the structure-borne noise are generated as reflection of ground-borne vibration [12]. In general, the effect of ground-borne vibration is related to people discomfort (high-frequency vibration affects concentration ability, low-frequency vibration may cause muscular or internal organ injury, both depending on exposure time), rather than damage to buildings.…”