For the first time since the project work commenced five years ago, Chennai Metro Rail plans to procure a few more tunnel boring machines (TBMs) as delays plague the underground construction work of the upcoming phase II project.

Cancellation of tenders floated for station construction in the initial stages of the project and shifting of utility pipelines are some of the major reasons contributing to this delay.

In the 118.9-km phase II project which will serve the city commuters through three corridors — Madhavaram to SIPCOT (corridor 3), Poonamallee to Light House (corridor 4), and Madhavaram to Sholinganallur (corridor 5), 42.6 km is built as underground network.

Tunnelling for a total length of 69.05 km has to be completed. But as of now, only 28.11 km of the tunnelling work has been done so far.

A total of 23 TBMs were purchased in the initial period of the project to carry out the tunnelling work, and they were subsequently engaged for work. Usually, when the TBM completes tunnelling in a stretch, it will be dismantled and again relaunched at another location.

TBMs stranded

In two locations in the city, the TBMs remain stranded for a long period ranging from months to sometimes even more than year, unable to make breakthroughs.

In corridor 3, TBMs have been stuck underground in the following stretches — Madhavaram to Moolakadai (upline and downline), Purasawalkam to Kellys (upline) — to make a breakthrough as the station shaft (from where the TBM will begin the boring process) is yet to be ready. The idling time of each of these TBMs runs beyond a year but will finally reach their destination shortly.

In some stretches, the TBMs were stranded for some time due to the delay in constructing the shaft.

In corridor 5 too, between Villivakkam Metro and Villivakkam Bus Terminus, the tunnelling started recently but there was a delay since they had to wait for permission from the Southern Railway to bore under the suburban station tracks at Villivakkam.

As a result, Chennai Metro Rail is yet to begin the tunnelling in the stretches including Royapettah to Thousand Lights (upline) Thiruvanmiyur to Indira Nagar (upline) and Perambur to Perambur Market (downline) and there exists a growing need for additional TBMs to accelerate the work and make up for the delays.

According to officials of Chennai Metro Rail Limited (CMRL), the delays in the underground construction work stemmed from the decision to cancel the tender floated for building the underground stations in corridor 3 and a part of corridor 5, five years ago. “This was inevitable. At that point, the bidders submitted unreasonable and inflated quotes. In the process to cancel, refloat the tender and award the contracts, we lost a little more than a year,” an official said.

Building of station shafts were delayed in corridor 3 and a part of corridor 5. As a ripple effect, the delay was felt in the tunnelling too. Besides, the shifting of utilities was extremely challenging in some of the locations.