As part of a national project to link the harsh, mountainous Himalayan terrain of the northern Jammu region with the Kashmir Valley by a 293-kilometer-long, broad-gauge railway line—the J&K Rail Link Project—government-owned Indian Railway Construction Co. Ltd has released an invitation for bids for two packages with a combined expected cost of about $140 million.
The packages, called T49A and T49B, are for the construction of tunnels, embankments and bridges for a 14.8-km-long link to be completed in 48 months. The last date for bid submission is Aug. 5.
Contenders for the projects are expected to include Hindustan Construction Co. (HCC), Larsen & Toubro, AFCONS Infrastructure Ltd. and Gammon India.
With its difficult, mountainous terrain, the state of Jammu and Kashmir always has been a challenge to transportation providers. The area is geologically unstable and prone to tremors and earthquakes, with deep gorges alternating between steep, rocky mountains. With long months of incessant rains and heavy snow, the weather is another factor that can put construction activity on hold.
One likely bidder, HCC, recently completed a 10.96-km-long tunnel, T-80, in the Pir Panjal range in the Himalayas. It is the longest tunnel in India, with overburden, or mountain height above the tunnel, reaching 1.1 km. It opened on June 26.
Sharnappa Yalal, HCC project manager, says he is confident that, if HCC wins the new bid, the company is ready to take on the challenge of two more tunnels. The new work is part of an overall rail project that includes 84 tunnels through an active seismic zone. One tunnel cuts across a main boundary fault, and many others cut through thrust and shear zones.
In the Himalayas, geology remains the biggest challenge. Even though surveys have been carried out, there are still surprises, Yalal says. “There are different kinds of rocks. In certain places they are weak, requiring support structure, so we cannot move speedily. During construction of the Pir Panjal tunnel, for instance, we expected loose soil in certain sections. Hence, we deployed a sophisticated equipment—road headers. However, we ended up with just 9% of the work [using] the equipment,” Yalal told ENR.
“We used the new Austrian tunneling method [NATM], which has advantages over conventional methods. In NATM, the complete support system is installed subsequent to excavation, where the surrounding soil and rock mass of a tunnel is integrated into overall support structure. Nothing is left loose, and the work remains sturdy,” says Yalal. If HCC wins the next work, he says NATM can be used on those tunnels, too.
NATM often has been referred to as a "design as you go" approach because it provides an optimized support solution based on observed ground conditions. Based on the computation of the optimal cross section, a complete support system—as per specific rock-class requirements—is installed for farther advancement. It is applied immediately after tunnel excavation to create a natural load-bearing ring and minimize rock deformation.
As in the Pir Panjal tunnel, the two tunnels now out for bid will be lined with concrete using ballastless track.