In a significant breakthrough, engineers have completed the first mountain tunnel on the Mumbai-Ahmedabad high speed rail corridor through which trains will zip past at a speed of 350 km per hour, officials said. The 350-metre-long horse-shoe shape tunnel has been built to perfect alignment in the mountains of Zaroli village near here as even a minor flaw could play spoilsport.
The National High Speed Rail Corporation Limited (NHSRCL) plans to build six more tunnels on the 508-km route between Mumbai and Ahmedabad that will be connected with state-of-the-art Shinkansen trainsets to be procured from Japan.
“What makes us celebrate it is that it is the first tunnel in India through which a train with a speed of 350 kmph will pass,” S P Mittal, Chief Project Manager of the Valsad section, told PTI on Thursday.
He said his team did not face a single untoward incident over the entire construction period.
“The biggest challenge for us was how to keep the alignment of the tunnel absolutely straight because the bullet train will run at a speed of 350 kmph and a minor alignment flaw can play spoilsport. So every specification has to be followed precisely and you will not find a deviation of even a single millimetre,” Mittal said.
The NHSRCL has awarded the contract to Larsen and Toubro and the technique that has been used to make the tunnel is the well-established New Austrian Tunnelling Method (NATM), which has already been used in India for rail and road projects in several mountain areas.
“We have just dug the skeleton structure of the complete tunnel and the finishing work will start now,” he added.
According to Mittal, it took more than a year and a large workforce to complete the tunneling work.
He also expressed great satisfaction as it happened to be the first mountain tunnel built under his direct supervision.
When blasts are carried out for such tunnels, the safety of the workers and people residing in the vicinity are paramount, he said.
“We took every precaution so that stones, boulders or any other such material did not spread in the nearby area and hurt villagers or our workers,” Mittal said.
After coming into existence in 2016, the NHSRCL laid the foundation stone of the bullet train project in 2017 and it was proposed to be ready by December 2023. However, land acquisition issues delayed the ambitious project.
Though the construction work is going on in full swing, the new deadline for the project’s operationalisation is yet to be announced.
“A commuter using this bullet train can finish the 508-km journey in two hours and seven minutes. At present, the train journey takes about five hours,” the spokesperson of the NHSRCL told PTI.
In a statement, NHSRCL said the tunnel was located around one kilometre away from Zaroli village of Umbergaon taluka in Valsad.
“The tunnel structure comprises a tunnel, tunnel portal, and other connecting structures like tunnel entrance hood. NHSRCL has achieved a major milestone with the breakthrough of the mountain tunnel,” it said.
The mountain tunnel is 350 metres long, 10.25 metres high with a diameter of 12.6 m.
The six other mountain tunnels for which contracts have been awarded are in Kasabekaman, Chandrapada, Chandasar, Mithagar, Vasantwadi and Ambesari in Maharashtra’s Palghar district, some 100 kilometres from Mumbai, officials said.
The tunnels are being built using the New Austrian Tunnel Method (NATM) which includes drilling holes on the tunnel face, charging of explosives, controlled blasting, removal of muck (blasted rock pieces), and installation of primary support, which includes steel ribs, lattice girder, shotcrete, and rock bolts based on the type of rocks as assessed by geologist after each blast.
The NATM was used to build tunnels in the Austrian Alps and has proved to be very useful in diversified geological conditions where forecasting of the rock mass is difficult due to rapidly changing geology.
The high-speed train corridor also has a 21 kilometre tunnel between Bandra-Kurla Complex in Mumbai and Shilphata in Thane district. Seven kilometres of this structure will be under Thane creek, making it the first undersea tunnel in the country.