2nd Herrenknecht TBM Breaks Through in Himalayas

By TBM Staff
August 7, 2025


Assembly of one of the two Single Shield TBMs in front of the portal, on the jobsite directly above the Ganges. (Photo: Herrenknecht.)

The young Himalayas were long considered virtually unconquerable for tunneling. Only a few projects in the region’s complex geology have been crowned with success to date. In late June, however, the second of two Herrenknecht Single Shield TBMs successfully completed its drive for the new railway line between Rishikesh and Karnaprayag in the Indian Himalayas. The first machine had already reached its destination in mid-April. Now both parallel tubes of the more than 20-km long tunnel system are complete.

Once operational, the new railway line between Rishikesh and Karnaprayag will reduce the journey time from seven hours to just over two. This represents significant improvements for the region, which serves as an important starting point for Hindu pilgrimages to the sacred Char Dham shrines. Every year, millions of pilgrims take the arduous route along winding roads through deep gorges, which are frequently blocked by landslides and rockfalls in the seismically active zone.

Pioneering work in the Himalayas

The project owner, Rail Vikas Nigam Limited (RVNL), awarded the contract for the line’s centerpiece — a 10.5-km long twin-tube tunnel — to civil contractor Larsen & Toubro Limited (L&T). … “Indian miners have extensive experience in conventional tunneling. For a long time, mechanized tunnelling technology was hence viewed by them with skepticism,” explains Sumit Gaur, Herrenknecht’s project manager on site. This skepticism had historical reasons: until now, machine technology has had too few successes in the Himalayas. This project was to change that. L&T therefore opted for two Herrenknecht Single Shield TBMs with a diameter of 9,110 millimeters, designed to meet the challenges of Himalayan geology.

Complex geology calls for innovative solutions

The biggest challenge was the predominant rock type: phyllite. L&T Project Leader & Tunnel expert Chris Cooper explains: “Phyllite is soft but stable. It disintegrates with water. Too much pressure and it clumps together and blocks the cutterhead. That doesn’t exactly make the drive easy.” … To make matters worse, the young, active rock mass is still moving. This can result in subsidence, causing rock to be deposited on the shield skin of the machine and block its progress. To prevent this, the crew can use so-called torque box cylinders. They were integrated into the cutterhead design. “It’s the first time we’ve had this system on a machine in India,” says Sumit Gaur. These allow infinitely variable horizontal and vertical adjustment of the main drive and can increase the excavation diameter by up to 100 millimeters if necessary.


The segments are stored in front of the main portal before being transported with a multi-service vehicle from Herrenknecht subsidiary TMS. (Photo: Herrenknecht.)

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