Zojila Tunnel: The challenge of digging through the Himalayas, Pg6

Key Highlights:

• The Zojila Tunnel, a 13-km passage, achieved a significant breakthrough in its construction.
• Located at an altitude of 11,578 feet in the Himalayas, it is one of India's most challenging infrastructure projects.
• Tunnelling in the Himalayas faces unique geological and environmental risks, including highly variable rock strata and extreme temperatures as low as -30°C.
• The project incorporates safety measures such as three deep shafts, with the longest being 474.3m deep, for ventilation and rescue.
• The New Austrian Tunnelling Method (NATM) is being used for excavation, involving selective blasting and immediate structural reinforcement.

Zojila Tunnel.png

Detailed Insights:

• The Himalayas are a relatively new and tectonically active mountain range, making tunnelling inherently risky due to unstable rock formations.
• Geologists describe the Himalayan rock strata as highly variable, ranging from soft seabed rock to boulders, often differing significantly meter to meter.
• Extreme cold temperatures and high altitudes pose severe challenges for both human workers and machinery, impacting operational efficiency and safety.
• The mountains store significant amounts of water, and melting snow contributes to water ingress, which requires careful management to prevent pressure build-up and potential collapses.
• The NATM involves excavating the top half first, followed by the bottom, and immediately securing the walls with shotcrete and rock bolts to maintain structural integrity.
• Engineers can adjust the tunnel's alignment and the configuration of reinforcements like rock bolts based on real-time geological conditions encountered.

Scientific/Technical Concepts Involved:

• New Austrian Tunnelling Method (NATM): A modern tunnelling approach that uses the geological stress of the surrounding rock mass to stabilize the tunnel, employing shotcrete and rock bolts.
• Shotcrete: A type of concrete or mortar conveyed through a hose and pneumatically projected at high velocity onto a surface, used for structural support and lining.
• Rock bolts: Steel reinforcing bars or cables inserted into holes drilled in rock masses to stabilize rock excavations, preventing rock falls and improving overall stability.
• Tectonic activity: The movement and deformation of the Earth's crust, leading to phenomena like earthquakes, volcanic activity, and mountain building, prevalent in geologically young mountain ranges like the Himalayas.