Chennai Metro Rail has carried out a special study that reportedly shows train vibrations do not affect the buildings close to the underground stretch. This is of significance in the backdrop of tunnelling work leading to several road cave-in incidents across the city and the first underground stretch is all set to open in a few days.
According to officials of Chennai Metro Rail Limited (CMRL), the lining of tunnels are built in such a way that it can withstand a substantial amount of vibrations of trains. Also, a low vibration technology has been carried out before laying tracks at places where hospitals or laboratories are located, they said.
“We place ‘rubber pads’ between stage one and stage two concrete of tunnel; after this process, the tracks are laid. The ‘rubber pads’ of 40 mm will dampen the vibrations from trains. These have been placed in 12 locations across the city, including Kilpauk Medical College, Rajiv Gandhi Government General Hospital and Vee Care Hospital. Hospitals have sensitive equipment which may feel even the slightest of vibrations and disrupt its functioning; hence this idea,” an official said.
In other areas too, though such pads are not laid, they claim the study and subsequent trials with trains show the vibrations are not beyond the permissible limit.
Experts from IIT Madras said the precast segments that a tunnel is made of will take in the vibrations from trains. “Unlike the tunnelling process, here the earth is not being directly disturbed. So, even in areas where rubber pads aren’t used, the precast segments will substantially lessen the vibrations thereby not disturbing the foundations of buildings on ground,” an expert who didn’t wish to be named said.
B.N. Rao, another professor of civil engineering at IIT Madras, said, “I haven’t looked at the report but they may have arrived at values and consequently gone ahead with operations based on varied factors. This is because, usually, the vibration values will vary depending on the soil structure, the depth of tunnel and the speed of trains and it’s acceleration and deceleration in various areas.”
