India's First Undersea Rail Tunnel Underway As Mumbai-Ahmedabad Corridor Progresses; Get Latest Updates Here

Indian Railways is making notable progress on its first high-speed rail corridor linking Mumbai and Ahmedabad. The National High-Speed Rail Corporation Limited (NHSRCL) is working on the underground bullet train station at Bandra Kurla Complex (BKC) in Mumbai and the dual rail line underground tunnel for this Rs. 1.08-lakh-crore project.

Currently, work on the tunnel is nearing Thane Creek, where a section will be the country's first undersea rail tunnel. Engineers have constructed a unique 'T intersection' from the Additionally Driven Intermediate Tunnel (ADIT) at Ghansoli in Navi Mumbai, connecting to the main tunnel. This ADIT is 110 metres deep and serves as a key entry/exit point. It runs perpendicular to the main tunnel, with one branch heading towards BKC and the other towards Shilphata in Thane.

So far, 120 metres towards BKC and 110 metres towards Shilphata have been excavated. This work involved 218 blasts with gelatin explosives for the BKC section and 314 blasts for the ADIT.

"The tunnel will be around 25-30 metres deep from the bottom of Thane Creek," explained an NHSRCL engineer. "We are working very carefully using the New Austrian Tunnelling Method (NATM) due to the surrounding buildings and structures. Despite the heavy rains, our work is ongoing at this site."

NHSRCL is currently creating a single-tube rail tunnel for both Up and Down lines. So far, the earth's stratum has not caused significant issues. On average, four explosions are conducted each day. The process involves drilling nearly 180 to 200 holes, each two metres deep, using specialised Japanese equipment.

To provide fresh air, two large yellow rubber tubes powered by motors are used to ventilate the main tunnel through the ADIT. This setup also supports the 150 workers on site, who work in two shifts. "Before each detonation, we deflate the rubber tubes, turn off the high-powered lights, and ensure all workers are outside. After the explosions, we clear the tunnel of fumes by pumping in fresh air," added another engineer.

Before lighting multiple gelatin sticks, two warning sirens are sounded. After blasting and clearing fumes, a trained team inspects the tunnel to ensure there are no loose rocks or risk of collapse. The rocks are so hard that the blasts only remove about three to four metres of the mantle.

Large JCBs then remove the fallen rocks from the surface, followed by dumper trucks that transport the debris to a designated dumping ground at Turbhe. Once the rocks are cleared, a semi-tunnel is created and reinforced with specialised cement, steel bolts, and other materials. "We are installing various monitoring instruments in the tunnel to track soil changes, seismic activity, and the overall health of the tunnel. These instruments provide real-time updates and are connected directly to a server," explained an NHSRCL official.

The work is expected to be finished by December this year. Around the same time, three large tunnel-boring machines (TBMs) will arrive at Ghansoli, Vikhroli, and BKC to continue the tunnelling work. The first TBM is likely to start from Ghansoli and will help tunnel beneath Thane Creek.