RTR

Reprint from
RTR 1/2011

EUROPEAN RAIL TECHNOLOGY REVIEW

Stefan Potocan MSc.

Vibration protection for Birmingham’s
Arena TunnelVibration protection for Birmingham’s
Arena Tunnel
In the so-called Arena tunnel, right in the heart of the City of Birmingham (UK),the padded wooden sleepers of the ballasted track were replaced by concrete
sleepers fitted with under sleeper pads. Vibration measurement at the lining ofthe tunnel following track renewal showed that the under sleeper pads deliveredby the Getzner company were able to prevent any increase of train-born vibration.
Renewal of the tracks in the Birmingham
Arena Tunnel was carried out at the beginning of 2010. This included replacing therails, sleepers and ballast. In the course of
the project, the old wooden sleepers featuring 20 millimetre rubber cork sleeper pads
were replaced with new padded concrete
sleepers. The use of under sleeper pads
should provide a specified level of elasticity
for the superstructure.
There were no data available concerning
the elasticity of the rubber cork pads incombination with the wooden sleepers. In
retrospect it is nearly impossible to isolate
and evaluate the effect of those pads.
The newly built ballasted track with its concrete sleepers should have such properties(elasticity and damping) that no increase invibration propagation from the heavy trafficked railway line to the surrounding buildings would occur.
Experts from railway engineering specialist DeltaRail took vibration measurements
before and after the track renewal to determine whether this goal had been achieved.

1 Details of the reconditionedline
The renovated line is part of the two-track
Stour Valley line running west from Birmingham New Street Station to Wolverhampton.

Stefan Potocan MSc.

Fig. 1: Situation of the Birmingham Arena Tunnel

The 161-metre long tunnel runs directly beneath the International Convention Centre,
Symphony Hall and the National Indoor Arena (Fig. 1). The entire length is walled andruns through sandstone at a depth of about
25 metres. Both tracks are used by varioustypes of trains. To account for differencesin the vibration spectrums, measurements
were performed for diesel trains (DMU),
electric trains (EMU) and the Class 390
Pendolino train. The maximum train speed
allowed in this track section is 64 km/h
(40 mph). Renewal work on the track heading to New Street Station was performed on
the 24 and 25 January 2010. The tracks,
rail pads and ballast were replaced withsimilar new components, and padded concrete sleepers were installed in place of theprevious padded wooden sleepers.

where it was clipped in place. This meansthat the protective layer also served to fix
the under sleeper pad. During the renewal it
was discovered that some of the pads had
separated from the sleeper. As a result,bedding material had become lodged between the geotextile layer and the sleeper.
An example is shown in Fig. 2. According to
information from Network Rail, the sleeper
pads had been in service since 1991.
These were replaced with concrete sleep-

2 Sleeper pads compared
Product Manager,
Railway Applications
Getzner Werkstoffe GmbH, Bürs
stefan.potocan@getzner.com

2RTR 1/2011

The original pads were made of a 20 millimetre thick rubber cork mat, protectedagainst the ballast on the underside by ageotextile layer. This protective layer extends to the sides of the wooden sleeperFig. 2: Removed wooden sleeper withdamaged mounts

Vibration protection for Birmingham’s Arena Tunnel Grpa id madGdePro etzne of stecr S ynthLtion m S 10 etics
10atGers equipped with 10 millimetre thick polyurethane pads. The elastic sleeper pads
feature Getzner’s Sylomer® SLS 1010 G.
The static stiffness (bedding modulus) of
this model, determined in accordance with
DIN 45673-1 (Secant bedding modulus
between 0.02 N/mm3 and 0.16 N/mm3),
is 0.1 N/mm3. Geotextile has again beenused to protect the resilient layer of the padagainst perforation by the ballast, while an
installation grate secures the pad to theconcrete sleeper. The pad is pressed directly into the wet concrete during the production process to join it to the sleeper (Fig. 3).

3 Vibration measurements

To determine the effect of the track workon vibration emissions, measurements
were performed before and after the trackrenewal. The automatic measuring equipment was installed next to the rebuilt trackon the tunnel wall, adjacent to a safety
niche. In doing so, the accelerometer wasaligned vertically, laterally and longitudinallyto the track. The measuring equipment wasinstalled in a metal box affixed to the tunnel wall using plaster at a height of about
0.1 metres (Fig. 4). The control unit, datalogger and power supply were fitted in theadjacent niche.

Elastic

3.1 Measuring techniqueFig. 3: Sylomer® SLS 1010 G sleeper design

In order to compare vibration levels before
and after renewal, a reference target value
was determined on 17 January 2010. A
measuring system was then installed on
the same day and removed at the start ofthe renewal work on January 24. To ensure
consolidation of the tracks, comparison
measurements were performed ten weeks
after project completion on 6 and 7 April
2010. During the measurement process,the vibration spectrums were calculated for

Vibration velocity level [dB, v0=5 ∙ 10-8 m/s]

Fig. 4: Measuring
equipment

before renewal
after renewal
Frequency [Hz]Fig. 5: Vibration
spectrum measured
before and after trackrenewal – EMU class
323 only

RTR 1/20113

Reduction of vibration insertion [dB] Vibration protection for Birmingham’s Arena Tunnel

Frequency [Hz]Train type

recorded train speed[km/h]
beforerenewalafterrenewal

Class 153
DMU51

46

Class 220
DMU

3949

Class 323
EMU5957Class 350
EMU

50

46

Class 390
EMU

3830

Tab.1: Train types and speeds

five different train classes and averaged inorder to estimate variations in emissions.
To establish a correlation between the individual types of trains and the measurement
results, the trains travelling through the tunnel were observed and documented froma public space next to the tunnel opening.
Additional measurement of the transit time

made it possible to determine the speed ofeach train.

3.2 Results
The acceleration data collected were used
to calculate the vibration velocity spectra. The results were grouped according
to train type and speed for comparison(Tab. 1).
Since vertical acceleration is dominant,these values were used as the basis ofcomparison. The majority of the vibrationenergy has a frequency of between 12.5 Hz
and 40 Hz. Fig. 5 shows the vibration velocity levels recorded at the wall of the tunnel
when an EMU class 323 passes by, measured before and after the track renewal.
Prior to renewal, the peaks ranged from
25 Hz to 31.5 Hz, but after completion of
the work, they stood at 20 Hz to 31.5 Hz.
This indicates a slight downward shift in frequency. Very remarkable reductions in vibration were measured for frequencies below
6.3 Hz and above 40 Hz.

Elastic solutions
for track superstructure

Getzner Werkstoffe GmbH
Herrenau 5, 6706 Bürs, Austria
T +43-5552-201-0
F +43-5552-201-1899
info.buers@getzner.com
www.getzner.com

Class 153
Class 220Class 323
Class 350
Class 390
mean value(all trains)

Fig. 6: Reductionof vibration energy
insertion due to trackrenewal – five types oftrains and mean values

The reduction of vibration insertion (sometimes also called “insertion loss”) can becalculated using these two spectra for eachtrain. Fig. 6 shows this difference in vibration levels before and after the renewal.
Positive values report that reduced vibration levels at the tunnel lining were detected after completion of the track renewal
work. The mean reduction is a calculated
value, derived from the arithmetic mean ofthe vibration level of the five train classes.

4 Conclusion
A very remarkable reduction of the insertionof vibration energy into the tunnel structure
due to the new track construction featuringconcrete sleepers fitted with under sleeper
pads was measured for frequencies below
6.3 Hz and above 40 Hz. Furthermore there
was virtually no change recorded in the insertion of frequencies between 6.3 Hz and40 Hz. So the objective of the project wasachieved by using Getzner Sylomer undersleeper pads.