Metro phase 2: Tunnelling through rocky soil to commence by November

Tunnelling on one of the toughest stretches of CMRL phase-two between Kolathur junction and Villivakkam MTH Road metro (earlier Nadhamuni metro), covering 7.8km, may commence by November.

The stretch, which is the only underground section on corridor-five, is likely to pose a challenge to engineers as they may have to drill through hard rocky soil to build twin tunnels and five stations.

Tata Projects, which was awarded the construction contract for 1,450 crore, is importing a tunnel boring machine (TBM) and advanced equipment from China to build the line. Corridor-five covers 44.6km from Madhavaram Milk Colony to Sholinganallur.

K Ramesh, project director, CMRL, Tata Projects, earlier said the TBM, assembled in China, will undergo a factory acceptance test this month before the machine is shipped to India by Oct and launched in Kolathur in November

“This stretch has a mixed geology — some soil and rock. We collected soil samples and based on that we placed an order for some advanced equipment, including a TBM. We have also hired experts from abroad, who will provide their expertise. The TBM will go below the buildings; we will be careful and take all precautions by installing instruments to monitor the buildings,” he said.

The 116.1km phase-two is likely to be opened in stages between 2025 and 2028.

CMRL had earlier built tunnels and stations in hard rock on Anna Salai, but not before work was stalled for nearly a year, and new contractors had to be assigned.

At Villivakkam MTH Road station construction site, engineers are facing a challenge in the pre-construction stage as they have to change a 230kV overhead electricity cable to underground.

They also must relocate newly fabricated transmission towers. This is to prevent equipment such as a 25m-tall trench cutter, used for building an underground station, from coming in contact with the cables.

Former CMRL director R Ramanathan said that before tunnelling commences, one metre-thick diaphragm walls or the outer walls of the stations will be built by cutting through the soil from the surface of the road. Then the soil within the four walls will be excavated before tunnel boring machines are assembled and deployed through a shaft cut through the soil. Building the walls may take few months

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