Tunnelling machines to chew mud from Sunday

Two giant tunnel boring machines (TBMs) will begin burrowing beneath the city’s surface from Sunday to link the proposed Nehru Park and Egmore underground Metro Stations. Chennai Metro Rail Chairman and Union Urban Development secretary Sudhir Krishna pressed the button to kickstart the operations at Nehru Park on Saturday.

The ceremony to launch the tunneling work was a low-key affair in the wake of an accident at the Metro worksite in Vadapalani on Thursday when a 50-tonne scaffolding collapsed while concreting was going on to make a pillar arm. “Today, it was just an opening ceremony. From Sunday, the tunnel boring machines (TBMs) will begin drilling,” a Metro rail spokesman said.

The distance between Nehru Park to Egmore is 939 metres and the tunnelling is expected to be over in about five months, CMRL sources said. The tender for design and construction of the twin tunnels plus three underground stations at Nehru Park, Kilpauk Medical College, and Pachiyappa’s College has been awarded to Larsen and Toubro, in joint venture with Chinese firm Shanghai Urban Construction Group (SUCG).

Initially, two TBMs will be operated under the guidance of experts in both the shifts with automatic alignment and monitoring control system developed with Japanese technology. 

“The cut soil will be disposed. All the necessary precautions with regard to the plugging of old bore wells and utility diversions have been taken well in advance and all the buildings enroute will be monitored round the clock when TBMs are in operation,” the CMRL official said. Heavy circular concrete linings will be fixed simultaneosly as the drilling goes on. The linings are manufactured at the state of the art casting factory at Vayalanellur, which has so far produced 1,400 segment rings.

“There will be cross passages between the two tunnels every 245 meters for ensuring operational fire safety,” he said. Metro rail is using 11 TBMs, each costing `60 crore, to drill 24 km with 19 stations under the city for the two Metro corridors.

An L & T official, who is involved in the tunneling operations, said that each day the machine will drill about six metres based on the soil conditions.