Uttarkashi Tunnel Collapse | 22 Nov 2023

Source: TH

Why in News?

Recently, an under-construction Silkyara-Barkot tunnel along the Yamunotri National Highway in Uttarkashi district, Uttarakhand, collapsed, trapping a significant number of workers inside.

• The incident raises concerns about tunnel construction, prompting closer examination of potential causes and preventive measures.

What Could be the Potential Cause of Tunnel Collapse?

• About:
  • The Silkyara-Barkot tunnel is part of the ambitious Char Dham all-weather road project of the Central Government.
  • The construction of the tunnel was tendered to Hyderabad-headquartered Navayuga Engineering Company by the National Highways and Infrastructure Development Corporation Ltd (NHIDCL), a fully owned company of the Ministry of Road Transport & Highways, Government of India.
• Potential Causes of Tunnel Collapse: The exact cause of the tunnel collapse is yet to be ascertained, but a possible factor could be:
  • The collapsed section, situated around 200-300 meters from the tunnel mouth, might have contained a hidden loose patch of fractured or weak rock, undetectable during construction.
  • Water seepage through this compromised rock could have eroded it over time, creating an unseen void atop the tunnel structure.

What are the Critical Aspects of Tunnel Construction?

• Tunnel Excavation Techniques:
  • Drill and Blast Method (DBM): Involves drilling holes into rock and detonating explosives to break it apart.
    • DBM is often used in regions like the Himalayas (Jammu & Kashmir and Uttarakhand) due to the challenging terrain.
  • Tunnel-Boring Machines (TBMs): It bore through rock while supporting the tunnel behind with precast concrete segments. It is a more expensive but safer method.
    • TBMs are ideal when the rock cover is up to 400 metres tall. Underground tunnels for the Delhi Metro were dug using a TBM at shallow depth.
• Aspects in Tunnel Construction:
  • Rock Investigation: Thoroughly examining the rock's strength and composition through seismic waves and petrographic analysis to assess its load-bearing capacity and stability.
  • Monitoring and Support: Continuous monitoring using stress and deformation meters, along with various support mechanisms like shotcrete, rock bolts, steel ribs, and specialized tunnel pipe umbrellas.
  • Geologist Assessments: Independent geologists play a crucial role in examining the tunnel, predicting potential failures, and determining the rock's stability duration.

Way Forward

• Regular Maintenance: Implement a stringent maintenance schedule, including inspections for structural integrity, drainage systems, and ventilation to identify and rectify issues promptly.
  • Employ sensors and monitoring technologies to continuously assess structural health, detecting any potential weaknesses or anomalies early.
• Risk Assessment and Preparedness: Conducting third party risk assessments periodically, considering geological, environmental, and usage factors.
  • Developing contingency plans and emergency protocols in case of any structural concerns.
• Training and Awareness: Training personnel in tunnel management and emergency response procedures. Public awareness campaigns can educate users and nearby residents about safety measures and reporting mechanisms.
• Technology Integration: Explore innovative technologies like Artificial Intelligence, drones, or robotics for more efficient inspections, maintenance, and early detection of potential issues.