Metro work: four tunnel boring machines on a short break from drilling

Chennai Metro Rail's tunnel boring machines named after birds take a break for cutterhead intervention on phase II project.

Four tunnel Boring Machines (TBMs) – Flamingo, Eagle, Pelican and Peacock – are on a short break from drilling the earth. All four of them, named after birds, were deployed along Corridor 4 of the Chennai Metro Rail Limited’s (CMRL) phase II project.

The machines are on a break as they are undergoing ‘cutterhead intervention’, owing to challenging geological conditions. According to sources in the CMRL, one of the most crucial parts of a TBM is the cutterhead, which rotates and drills through the earth and helps build a tunnel. “Cutterhead intervention is a routine process through which we change the machine parts such as disc cutters. This is done due to wear and tear [that the machines undergo] from continuous drilling. It is incidental that all four machines in the corridor are going through this at the same time now. They will resume work shortly,” a source said.

The Corridor 4 of the ₹63,246-crore phase II project spans from Light House to Poonamallee via Mylapore and T. Nagar. Owing to various reasons, including cost, land availability and convenience of construction, half of the corridor would be elevated (from Poonamallee to Kodambakkam) and the other half, underground (from Kodambakkam to Light House).

On the underground stretch, the TBMs tunnel on two stretches — from Light House to Kutchery Road; and Panagal Park to Kodambakkam. “Changing of disc cutters may take anywhere between 3-10 days. In cases where all the disc cutters have to be changed, like the ones between Light House and Kutchery Road, it takes a little longer. We are encountering abrasive sand ground between Light House and Kutchery Road; and hard rock between Panagal Park and Kodambakkam. When we know that the machine has endured quite a bit of wear and tear, we halt for cutterhead intervention, after which we resume work,” another source said.

Cutterhead intervention happens more often when machines drill through rocks, sources added. Early this month, the tunnelling work between Light House and Kutchery Road was briefly halted, owing to leak of gases such as methane and carbon monoxide.

Sources said the issue had been resolved, and the machine resumed drilling until it was stopped for this cutterhead intervention.