Breakthrough in the Himalayas: Second tunnel boring machine reaches its destination near Rishikesh
Milestone for a strategic railway project: in late June, the last 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-kilometer-long tunnel system are complete.
The young Himalayas were long considered virtually unconquerable for tunnelling. Only a few projects in the region’s complex geology have been crowned with success to date. This makes the breakthrough of the second Herrenknecht machine in late June even more significant, after the first TBM had already reached its destination in mid-April. Once completed, 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-kilometer-long twin-tube tunnel — 
to civil contractor Larsen & Toubro Limited (L&T).
“Indian miners have extensive experience in conventional tunnelling. 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 Herrenknech 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.
High-tech configuration for extreme conditions
In addition to the innovative torque box technology, the TBMs are equipped with the Herrenknecht ISP system. This sends a surface wave along the tunnel wall, which turns into a spatial wave at the tunnel face. The system records the measurement and excavation data obtained during tunnelling in real time and translates it into a geology report. In an anomaly is detected, additional probe drilling is carried out to check the suspected fault zone. This contributes to safety and a smooth drive. “This is a great advantage for our customers and, of course, especially for our colleagues on the machine,” emphasizes Sumit Gaur. Additionally, a convergence measurement system continuously analyzes the distance between the shield and the rock. If the rock is getting too close to the machine, the machine operator is shown a limit signal.
Impressive advance rates
The comprehensive range of equipment installed on the machine paid off. In record time, 23 rings were installed in just 24 hours. Consequently, at peak times one of the machines advanced a good 39 meters in a day. “That’s impressive, especially in this rock and with this large diameter,” comments Cooper. Fast is also the transport of spare and wear parts. L&T Project Director Rakesh Arora says: “Herrenknecht has its own purpose-built warehouse less than three hours from here in Dehradun and can therefore easily supply new parts when needed. This gives us the flexibility we need.” With the successful completion of both tunnel drives, the experts have proven that modern tunnel boring machines can also cope with the extreme conditions of the Himalayas. “Here we’ve shown we can move faster with the technology used here than with conventional drill & blast,” emphasizes Cooper. The project provides important references for subsequent tunnelling projects in this geologically complex region.
PROJECT DATA RISHIKESH–KARNPRAYAG NEW RAIL LINE (RVNL)
› Client: Rail Vikas Nigam Limited
› Contractors: Larsen & Toubro Limited
› Application: Railway
› Drive length: 10,489 m + 10,317 m
› Geology: Chandpur Formation, phyllite
MACHINE DATA
› Machine type: 2x Single Shield TBM
› Diameter: 9,110 mm
› Cutterhead drive power: 4,200 kW
› Torque: 24,304 kNm