Chennai Metro Rail’s tunnelling for the 118.9-km phase II project from Perambur Barracks to Purasawalkam has been delayed due to challenges in the construction of shaft and diversion of utilities.

Shafts in metro rail constructions, which are deep and vertical structures, are built in underground stations to facilitate the launch of a tunnel boring machine (TBM) from the origin location.

In the phase II network, Purasawalkam and Perambur Barracks has been provided connectivity as part of the corridor 3 which starts from Madhavaram and ends at SIPCOT after passing via Purasawalkam. The first half of this corridor from Madhavaram up to Taramani is getting built as an underground network and then ascends into an elevated corridor from the next station, Nehru Nagar, in the IT corridor and terminates at SIPCOT.

The length of the Perambur Barracks-Purasawalkam tunnel stretch runs for 1.2 km. In the upline where the work began in September 2025, nearly 65 percent of tunnelling has been completed so far. According to officials of Chennai Metro Rail Limited (CMRL), while there was some delay in building the shaft at Perambur Barracks to launch the TBM, the main delay now is to construct the shaft at Purasawalkam.

“The retrieval shaft [where the TBM will be taken out after the tunnelling is completed] is coming up at Purasawalkam junction. At the junction, there were numerous utilities which had to be shifted. It took us a long time to move the utilities like metro water, sewer pipelines, and power cables. Recently, it was completed, the construction of the shaft is now in progress,” an official said.

The TBM has been boring through weathered rock at a depth of about 18 metres from the ground. “While the TBM will reach Purasawalkam in August this year, it may take another three months to build the retrieval shaft construction. By the end of November, we will complete this tunnel work,” he added.