Chennai Metro rail completes one tunnel under Anna Salai

Chennai metro rail completed building of one of the two tunnels in arterial Anna Salai on Wednesday, a day after its engineers attempted in vain to achieve a break through. The tunnel will connect May Day Park to AG-DMS covering a distance of 3.7km. The line is expected to get operational by December 2018.

Metro rail officials said the giant tunnel boring machine broke the fibre reinforced concrete wall and entered AG-DMS station at around 3pm on Wednesday, signalling completion of one of the two tunnels. This comes a day after they suffered a setback when engineers found the boring machine’s cutter head had worn out when they had only 10cm of the wall left to bore through to complete the job. They attempted other means to break the wall, including the use of a hydraulic breaking equipment. “But the wall was strong,” a senior Metro rail official said.

It was after seven hours and restarting the machine several times, engineers gave up and decided to change the cutters again. They completed the task on Wednesday afternoon. “We now have the other tunnel to complete which is about 450m away from achieving break through. We will complete it by next month,” an official said.

The tunnel boring machine bores through a thick diaphragm wall of the underground station to enter the station box. The boring machine is then taken out using the space excavated for the station.

Once the tunnelling under Anna Salai is complete, officials said traffic will be restored to its original by December end after removing the tunnel boring machine from the site and closing the shafts cut to build the stations. Station work will progress faster.

It has been seven years since traffic restrictions were imposed on Anna Salai and the four-lane road has been converted into single lane or double lane at some stretches.
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