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News Entry# 58762  
Feb 18 2012 (8:45AM)  The rumblers of metro won’t cause a tumble (timesofindia.indiatimes.com)

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New Facilities/TechnologyCMRL/Chennai Metro  -  

News Entry# 58762     
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Posted by: rdb**  82688 news posts  
It seems humble springs can muffle the rumbles of metro trains. In Delhi, as metro trains dart through the underground corridors at precise intervals, the clatter of the rail is amplified by the corridor walls, rattling the neighbourhood homes above. But for the sake of our neigbourhoods, the Chennai Metro Rail is planning to install a noise and vibration reduction mechanism, likely a mass spring system, on the underground tracks here. The wheels of running trains clang against the rail, making a huge noise, which is further ballooned inside the cloistered tunnel, and escapes to the surface as vibrations. The noise and vibrations need to be hushed up because neither the heritage and old buildings nor our sleepy neighbourhoods will tolerate it. Mass spring system is considered the best antidote for rumbles. Tracks will be laid over an elastic layer made of steel coil...
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spring. The springs will absorb the vertical vibrations caused by the running train and turn down the noise. For the railways, cutting down on noise is not a priority. So, the sleepers are laid over coarse gravel beds. Then the tracks are fitted over the sleepers, with no aid to cut down the clatter. Metro systems across the world use various techniques to minimize noise and vibrations. Chennai Metro Rail has on its tables an alternative to mass spring system -- a rubber-based suspension system. In this, spring coils will be replaced with rubber pieces or sheets. "We are considering two technologies - mass spring and a rubber-based system. The general consultants will decide which is best for our conditions. The selection of the technology will depend on the stretch and the type of buildings located near the underground line. Nothing has been finalized yet," said a senior official of Chennai Metro Rail. Delhi Metro Rail Corporation ( DMRC) has decided to install a mass spring system in the tunnels being built as part of its phase III project. The line burrows through Old Delhi, where buildings are really old. Besides, residents from other parts of the city where metro rail is up and running have complained to the corporation that they could feel the jitters at home as trains pass through underground corridors. Taking a cue from Delhi's experience, Chennai metro officials have started discussing the technology that should be adopted. Though buildings of archaeological and historic importance are not located too close to the alignment of the underground corridor, Chennai metro has indentified 14 buildings that could be susceptible to vibrations. Vibration levels will be monitored constantly in the vicinity of these buildings. Metro will also lay ballast-less tracks with long welded rails to minimize noise and vibrations. Mass spring system or rubber-based system will be needed on those stretches where vibrations need to be reduced considerably. "Our trains are light and will make less noise. The noise will be lesser than that generated by road traffic. Still, we are looking at ways to tone it down further," said an official. The move comes after residents and conservationists expressed concern about the impact metro will have on heritage buildings. George Town residents even dragged metro rail to court to prevent the line from running underneath their neighbourhood. "Underground corridors will be built around 20 metres below the surface. The depth is too much for rumble or vibrations to affect heritage buildings and residences," said another official.
Tunnel-boring machines get ready to roar
Metro Rail is ready to burrow. Four tunnel-boring machines for underground work have arrived at Shenoy Nagar and Washermenpet and the groundwork is almost over at various places across the city. Two more tunnel-boring machines will arrive soon - one for Saidapet station works and another for Nehru Park, which is one of the locations where the machines will start roaring. "Factory acceptance test for these machines are done. One will come by the end of this month while the other will be here next month," said a senior official of Chennai Metro rail. Construction of diaphragm walls, which will help shore up the earth from caving in while digging, is progressing at places where underground stations will be built - Washermenpet, Madras high court, Egmore, May Day Park, Nehru Park, KMC, Shenoy Nagar, Anna Nagar Tower and Tirumangalam. Soil test is over and utilities like water pipelines and power cables have been shifted out of these places. "Works on the diaphragm wall began this month at spots where underground station will be built near new government secretariat complex on Anna Salai. Work sites are getting ready to hoist and launch tunnel boring machines at Thiru Vi Ka Park, Egmore, Nehru Park and Washermenpet," a metro rail official said. Precast concrete rings will be installed on tunnel walls as soon as boring is complete. Moulds to fabricate precast concrete tunnel walls have arrived from abroad and trials have begun at Vanagaram and Vayalanallur where metro rail has set up a factory to make precast concrete rings. A senior official said tunnel boring work would begin in the first quarter of this year.
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