Uttarakhand Tunnel Collapse: All you need to know about


The year 2023 marked a pivotal moment in Uttarakhand, India, as a construction tragedy unfolded in the heart of the Himalayas. The Silkyara-Barkot tunnel (Yamunotri National Highway) in Uttarkashi district, a crucial segment of the Char Dham all-weather road project, faced a catastrophic collapse on 12th November 2023, leaving 41 workers trapped in its depths. This incident sparked a massive rescue operation that lasted 16 days and involved multiple agencies and experts.

Silkyara-Barkot Tunnel

Location: The National Highway's Brahmakhal-Yamunotri segment is getting a 4.5-kilometer tunnel constructed by Navayuga Engineering Construction Limited (NECL) which will link Silkyara and Dandalgaon.This tunnel is a pivotal component of the Char Dham all-weather road project, strategically connecting four sacred Hindu pilgrimage sites.

The Chardham Mahamarg Vikas Pariyojana represents a significant initiative by the Central government to enhance road connectivity to the four sacred sites in Uttarakhand, namely Gangotri, Yamunotri, Kedarnath, and Badrinath.

Objective: The primary goal of this undertaking is the comprehensive upgrade and expansion of 1100 kilometers of highways, transforming them into resilient all-weather roads. This initiative aligns with the broader vision of ensuring seamless accessibility to the revered pilgrimage destinations.

Operation Zindagi: A Glimmer of Hope

The state government launched "Operation Zindagi," deploying tunnel boring machines to break through the debris. Drilling commenced, but cracks in the tunnel halted progress, prompting the initiation of alternative access tunnels. Oxygen, dry food, and hot meals were supplied through pipes, maintaining a lifeline for the trapped workers.

The Defence Research and Development Organisation (DRDO) has deployed the Remote Operated Vehicle - Daksh, which is specifically designed to be used on a pan-tilt platform, in order to access risky terrain. 

  • It is capable of continuous operation for up to 3 hours, covering distances ranging from 100 to 500 meters.

What could be the probable causes behind the tunnel's collapse?

Hidden Loose Patch of Fractured or Weak Rock

  • The collapsed section, being 200-300 meters from the tunnel mouth, might have contained an unseen loose patch of fractured or weak rock.

Characteristics of the Loose Patch of Rock

  • The loose patch of rock may have consisted of fractured or fragile rock with numerous joints, making it inherently weak.This patch may not have been detectable during the construction phase.

Water Seepage

  • Water could have entered through the compromised rock, leading to erosion over time.
  • The erosion may have created an unseen void atop the tunnel structure.

Shear Zone

  • If there was movement between two rocks, creating a shear zone, it could lead to the crushing of rocks.
  • The crushed rock might undergo changes in behavior, possibly containing clay or becoming weathered over time.

Excavation Methods

In the field of tunnel construction, there are different techniques used to cut through the rough terrain of the Earth. The Drill and Blast method (DBM) and the Tunnel Boring Machine (TBM) method are two primary approaches used to overcome various geological challenges.

Drill and Blast Method (DBM)

This conventional technique involves a meticulous process of drilling holes into the formidable rock face and subsequently employing controlled explosives to shatter it into manageable fragments. This method finds its forte in shorter tunnel applications, typically spanning up to 3 kilometers. Widely adopted in challenging terrains like the Himalayan regions, particularly in Jammu & Kashmir and Uttarakhand, DBM is particularly suited for navigating through hard rocks and high mountainous landscapes.

Tunnel Boring Machine Method

In contrast, the Tunnel Boring Machine method introduces a technological marvel in the form of a shielded machine equipped with a rotating cutter head. This mechanical giant burrows through the rock, creating a tunnel with precision. Noteworthy for its application in lengthy tunnels, the Tunnel Boring Machine method is optimized for projects with tunnel lengths of up to 25 kilometers. Embraced for underground tunnels such as those in the Delhi metro, this method shines in traversing softer rock formations and low mountainous terrains.

Comparative Chart

CriteriaDrill and Blast Method (DBM)Tunnel Boring Machine Method
Tunnel LengthSuitable for tunnels up to 3 kmSuitable for tunnels up to 25 km
SuitabilityIdeal for hard rocks and high mountainsSuited for soft rock and low mountains
Environmental ImpactGenerates more vibrations, noise, dust, and gas emissionsOffers faster, safer, and environmentally friendly construction
CostCost-effective for shorter tunnels and smaller projectsRequires a higher initial investment and more technical expertise
Example ApplicationsApplied in Himalayan regions, including Jammu & Kashmir and UttarakhandUtilised for underground tunnels in the Delhi metro

What are the Challenges in Constructing Tunnels in the Himalayan Region?

1. Geological Dynamics
- The young mountain range is still growing due to the collision between the Indian and the Eurasian tectonic plates, resulting in geological complexity characterized by a combination of rock types, fault lines, and seismic activity.

2. High Altitude Hurdles
- The high altitude of the region poses logistical complexities, limits accessibility, and increases transportation costs for manpower and construction materials.

3.Seismic Concerns
- The Himalayas are situated in a seismically active zone, making earthquake preparedness a top priority during tunnel construction.

4.Weather Extremes
- Extreme weather variations ranging from heavy snowfall and freezing temperatures in winter to intense monsoons and landslides during the rainy season also significantly impact tunnel construction projects.

5. Rock Examination
- Thoroughly examining the rock's strength and composition through seismic waves and petrographic analysis is necessary to assess its load-bearing capacity and stability.

6. Continuous Monitoring
- The tunnel must be continuously monitored using stress and deformation meters, along with various support mechanisms like shotcrete, rock bolts, steel ribs, and specialized tunnel pipe umbrellas.

Rescuing trapped workers in the Silkyara tunnel involved employing various methods:

1.Vertical Drilling

Using a boring machine equipped with electrical tools, a vertical drill was employed to dig straight  down from the ground. An 800-mm pipe was inserted through this drill to extract the trapped workers during the Uttarakhand tunnel collapse.

2.Auger Mining (Horizontal Drilling)

Horizontal drilling was attempted using an auger machine or directional drill. These specialized tools are designed for drilling horizontal bores or creating underground tunnels without disturbing the ground. Unfortunately, in the case of the Uttarakhand tunnel collapse, the auger machine faced challenges, hitting metal obstructions and eventually breaking down irreparably.

3.Rat-Hole Mining

Rat-hole mining, a manual drilling method common in Meghalaya, involves skilled workers digging narrow pits into the ground. These pits are just wide enough for one person to fit into. The term "rat hole" refers to these narrow pits used for descending and extracting coal. The process is hazardous, involving miners descending into the pits using ropes and bamboo ladders. Rat-hole mining is considered illegal in many countries due to the high risk of asphyxiation, oxygen depletion, and hunger.

Another variant of rat mining involves creating a rectangular opening (10 to 100 sqm) through which a vertical pit (100 to 400 feet deep) is dug. Once the coal seam is located, rat-hole-sized tunnels are dug horizontally to extract the coal.

Way Forward

  1. Maintain the tunnel effectively with a strict schedule. Regular inspections cover structural integrity, drainage systems, and ventilation, ensuring quick identification and resolution of issues.
  2. Before starting the tunnel project, it is crucial to invest time and resources in studying the rock.
  3. Use sensors and monitoring tech for ongoing structural health assessments. This helps catch any potential weaknesses or anomalies at an early stage.
  4. Periodically conduct third-party risk assessments, factoring in geological, environmental, and usage considerations. Have contingency plans and emergency protocols in place for any structural concerns.
  5. Consider integrating advanced technologies like Artificial Intelligence, drones, or robotics for more efficient inspections, maintenance, and early issue detection.
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