Vibration Control Market Leader GERB Now Offers Cutting-edge Mass Spring System (Track-Bed Isolation) Technology to Mitigate Vibration Transmission From Metro Tunnels to Overlying Buildings

NOIDA, India, March 24, 2015 /PRNewswire/ --

The vibrations felt by residents in areas near or above metro lines/tunnels have always been a matter of concern and with numerous media reports in the recent past covering this pressing issue, it is important that we gain a perspective into this problem and understand how vibration isolation technology can prevent and mitigate this phenomenon.

     (Photo: http://photos.prnewswire.com/prnh/20150324/10118891-a )
     (Photo: http://photos.prnewswire.com/prnh/20150324/10118891-b )

Complaints from residents of buildings overlying the metro tunnel have been highlighted very well by a few media reports as under:

"The court has now sought a reply from the Centre on the allegation levelled by the residents of D-Block, Saket, that they are unhappy over the high levels of noise and vibration caused by the movement of the Delhi Metro Rail Corporation-run trains running on the Yellow Line connecting Jahangirpuri with HUDA City in Gurgaon". http://urbanupdate.in/governance/delhi-residents-seek-hc-intervention-metro-disruption

"My house shakes when the metro passes underground. What measures should I take?"- http://www.quora.com/My-house-shakes-when-the-metro-passes-underground-What-measures-should-I-take

"The residents of the Shahbad Mohammadpur, which is a residential colony, in the vicinity of the tunnel connecting Aerocity and IGI Airport Metro stations have complained of cracks and tremors in their houses."-  

http://asiabizz.com/13892/airport-metro-residents-complain-of-cracks-and-vibrations/

It is clear that buildings overlying or close to the metro track are prone to be affected by ground-borne-noise and vibration. Vibrations can be felt by people staying in buildings less than 10 meter distance from the line axis and in addition, structure borne noise can also cause disturbance.

Vibration propagation path is demonstrated in Figure 1. Typical vibration level at buildings above tunnel may reach more than 90 VdB easily as demonstrated in Figure 2.

Resulting vibration level of 90VdB inside the building is about 8 times  more than the threshold value of human annoyance of 72 VdB** as can be calculated from the following formula: 20LogT = 90VdB - 72VdB; 20LogT =18VdB ; LogT = 18/20=0.9 ; T = 10 ^ 0.9 = about 8.

**According to ISO 2631-2, the limiting RMS velocity is 0,0001m/s = 0,1mm/s for the residential buildings. The corresponding vibration level in VdB = 20*LOG (v / v_ref) = 20*LOG(0,1 / 0,0000254) = 72dBv. This is the threshold value of human annoyance and also corresponds to FTA-USA as adopted worldwide.

Appropriate measures are needed to attenuate the vibration levels by 20VdB (minimum), especially for the buildings overlying the tunnel. The best way to achieve this attenuation of resulting vibrations levels is through installing a Mass Spring System (MSS) which consists of a floating track-bed and have been adopted by many metro operators around the world. An MSS, as its name suggests, comprises of a mass, i.e., the concrete track-bed and a spring which could actually be a steel spring or an elastomeric pad supporting the concrete track-bed in a discrete manner.

The functioning of the mass spring system can be understood from the points below:

• Typical train emissions spectra shall be derived from the already available measurements of similar rolling stock in operation usually ranging between 95 VdB and 110 VdB.
• Soil-transfer-functions between the track and the neighbourhood buildings need to be either measured or theoretically assessed.
• Resonance between train emissions and natural frequencies of the building slabs induce increased vibration levels inside buildings. While calculating the required vibration mitigation of MSS, such resonance condition shall be considered with an allowance for the buildings.
• Based on the results of the above mentioned calculation proceedings, the lack of mitigation must eventually be compensated by the attenuation capacity of the proposed MSS in order to match the specified vibration limits.
• Based on calculated attenuation as required along the track, the natural frequency of MSS shall be demonstrated with appropriated elastic elements made out of steel springs, synthetic materials such as rubber compounds or elastomeric material and a suitable natural frequency shall be achieved in order to assure the calculated attenuation.
• The elastically supported track-bed consisting of MSS has to match the attenuation requirements. At the same time, the elastic elements of MSS must assure fatigue resistance of all track components acting together as a system. Furthermore, the ageing of the elastic elements of MSS leading to a change in their elastic properties and related consequence at their attenuation capacity must be prevented. MSS must be replaceable and must have to be retrofitted during the night maintenance period of 3 hours in case of an eventuality like inadequate mitigation.

About GERB 

GERB has been a forerunner in providing MSS solutions to urban mass rapid transit sector around the world. GERB MSS has been installed under more than 300 km of metro tracks in countries like Germany, France, Switzerland, UK, USA, China, Brazil, Russia etc. For more information, log on to www.gerb.in.

Primary Media Contact
Snigdha Dwivedi
[email protected]
+91-9560444968
Media Consultant
GERB Vibrations Control Systems Pvt. Ltd.

Secondary Media Contact
SK Mishra
[email protected]
+91-9717822331
Project Manager
GERB Vibrations Control Systems Pvt. Ltd.