HYDERABAD: At first glance, Zoji La appears to be just another Himalayan pass — a 3,528-meter ribbon of broken asphalt winding through barren slopes before descending towards Ladakh from Kashmir. In summer, convoys of trucks, tourist vehicles and Army transport negotiate its narrow bends. Shepherds move livestock across alpine meadows. Meltwater streams cut across the road before disappearing into deep valleys. Traffic slows wherever fresh rockfall has narrowed the carriageway.
Then winter arrives. Traffic stops. For generations, winter has determined when movement was possible at all. It is tempting to think Zoji La is simply a victim of winter. If snowfall alone were responsible, wouldn’t engineering solutions perfected elsewhere — modern snowploughs, avalanche forecasting, and controlled blasting — have eased the problem? Roads through the Alps, Scandinavia and North America remain open despite winters. Why has civil engineering in Zoji La remained such a Himalayan task? The explanation, geologists point out, begins thousands of kilometres south of where the Himalayas stand, in rocks that have been compressed, fractured and uplifted by a continental collision. Around 50 million years ago, the Indian continental plate collided with the Eurasian plate, closing the ancient Tethys Ocean and initiating the uplift of the Himalayas. Satellites show the Indian Plate continues to move northwards by roughly four to six centimetres every year.
“The motion is imperceptible, but enough to reshape an entire mountain range. Parts of the Himalayas continue to rise even as rivers slice through them, glaciers grind them down and gravity relentlessly pulls them apart. The result is a landscape caught in a perpetual contest,” explains Sri Nagesh, former Chief Scientist at NGRI.
That restless geology explains why earthquakes continue to shake the region. Why the rocks beneath the pass are intensely folded, fractured and faulted. Why landslides and rockfalls are common. And why building a tunnel here demanded something more than engineering. Those exact forces confronted more than 1,200 personnel from Megha Engineering & Infrastructure Ltd., influencing every stage of construction of the Zojila Tunnel, which is set to become the world’s longest bi-directional single-tube road tunnel.
Deep beneath the Zojila range, two teams of engineers and miners spent six years excavating towards one another. One advanced eastwards from the Baltal portal in Ganderbal district of Kashmir, while the other drove westwards from the Minamarg portal in Drass, Ladakh. On June 9, they met. The last remaining 2.5 metres of rock inside the Tunnel were removed in a controlled blast, marking a major breakthrough in the construction of the 13.153-km tunnel. For the engineers, geologists, surveyors and miners who had tunnelled for years inside a living mountain at an altitude of 11,578 feet, it represented the culmination of 10 million safe man-hours, millions of calculations, thousands of controlled blasts and countless engineering decisions.
The scientific questions that made it possible have occupied geologists for decades. While longer, ultra-high-altitude projects such as China’s New Guanjiao Tunnel (32.65 km at 3,323 m) and Tianshan Shengli Tunnel (22.13 km at around 4,000 m) use twin-tube layouts that separate one-way traffic and simplify ventilation and emergency evacuation, Zojila is being built as a single-tube, bi-directional road tunnel. That configuration required engineers to manage opposing traffic aerodynamics, vehicle emissions and fire safety within a single high-altitude bore. Zojila also occupies a unique middle ground. Tunnels such as Mainling Tunnel (11.56 km) demonstrate high-altitude tunnelling, but either at shorter lengths or with different design constraints.
“Long enough to demand mega-tunnel safety systems yet confined to a single tube, Zojila is supported by a parallel 14.2-kilometre escape tunnel connected by cross-passages every 250 metres, making it the world’s longest single-tube bi-directional road tunnel at such an extreme altitude,” says Muhammad Rafi, Design Director. Engineers must constantly adapt to volatile, ‘alive’ rock strata that literally squeeze inward upon excavation, all while battling thin air that starves heavy machinery of power and punishing sub-zero winters that plummet to -30°C. “Long before excavation began, the one thing we tried to figure out may sound naive in its simplicity: what exactly lay beneath Zoji La?” recalls Chief Engineer Col. A K Shiv Kumar.
They pieced together the answer using satellite imagery, geological mapping, boreholes and geophysical surveys. Rock cores extracted from exploratory drilling revealed the type, strength and condition of the rock at specific locations. Seismic surveys, which measure how sound waves travel through the ground, helped identify changes in rock density that could indicate fault zones or fractured ground. Together, the investigations produced a geological model of the mountain.
But it’s not enough. A borehole samples only the rock through which it passes. Between two boreholes, separated by hundreds of metres, the geology may be entirely different. Hard rock can give way to crushed fault material. Dry conditions can suddenly become water-bearing. Stable rock can transition into heavily fractured ground incapable of supporting itself. “A tunnel, after all, is the only way to truly discover a mountain’s interior.” The solution was never to predict every surprise, but to adapt to each as it emerged. What they chose was the New Austrian Tunnelling Method, an engineering philosophy built on a simple premise: the mountain knows more than the engineer.
Rather than excavating long stretches at once, the teams advanced only a few metres before stopping. The geological model was constantly compared with what engineers encountered at the tunnel face. “At Zojila, engineers encountered 67 different geological formations,” says engineer Zahoor. The physics is simple: remove rock, and the forces inside redistribute. The engineering challenge is predicting that redistribution quickly to keep the tunnel stable. And, that was achieved.
