GS Paper III

News Excerpt:

40 workers are trapped due to the collapse of a section of the Silkyara tunnel in Uttarakhand.

About Silkyara tunnel:

• It is part of the Chardham Project of the Ministry of Road Transport and Highways (MoRTH) and is under construction.
• This Yatra or pilgrimage is a tour of four holy sites - Yamunotri, Gangotri, Kedarnath and Badrinath.
• The tunnel, once ready, will especially benefit the pilgrims providing an all-weather connectivity, shortening the distance to Yamunotri by 26 Km.

Ways in which tunnels are excavated in rock: 

• There are essentially two ways: the Drill and Blast Method (DBM), and by using Tunnel-Boring Machines (TBMs).
• DBM involves drilling holes into the rock and loading them with explosives. When the explosives are detonated, the rock breaks apart.
• TBMs bore the rock from the front (using a rotating head) while supporting the excavating tunnel behind the machine by installing concrete segments.
• Building a tunnel with a TBM is more expensive than DBM, but much safer. 

Impact of terrain on the method of excavation:

• A TBM cannot be used to drill through very tall mountains. Creating a void through a 1,000-2,000-metre-high mountain by using a TBM leads to rock burst — when a part of the rock suddenly falls due to high stress.
• 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.
• On the other hand, in places like Himalayas, including Jammu & Kashmir and Uttarakhand, DBM is usually used.

Current Rescue process:

Trenchless technology:

• The rescue operation involves the use of Trenchless Technology.
•  It will be the first time that a “tunnel inside a tunnel” will be created as part of a rescue operation in India.
•  It involves creating a passage through 900 mm wide mild steel (MS) pipes for the trapped workers to crawl through.
• It  is a non-invasive and minimalist approach to repair the collapsed tunnel without disturbing the loose rock and debris on the surface.
• It will minimize collateral damage compared to traditional excavation methods.

How safe are tunnels in Himalaya?

Scientists believe that the tunnel collapse are generally due to inadequate geological understanding or non-compliance with regulations.

Geological Understanding:

• The Himalayas are young and are still growing due to the collision between the Indian tectonic plate and the Eurasian tectonic plate. 

• Tunnel construction activities may alter the following:

• • Stability of Slopes: It can potentially increase the risk of landslides and rockfalls.

• • Local Hydrology: Tunnels may intersect with water sources  and any alterations to natural drainage patterns can affect water quality as well as availability downstream.

• • Nearby Communities: Noise and Air pollution as well as relocation of communities are major factors with tunnel construction.

Compliance with Regulations:

• Robust monitoring programs:  Monitoring management during and after construction allows for adaptive management, enabling the adjustment of strategies to mitigate unforeseen impacts.
• Conduct comprehensive EIA: A comprehensive Environmental Impact Assessment (EIA) before initiating tunnel construction helps identify potential environmental impacts and develop mitigation measures.

Way Forward: 

This collapse highlights concerns about the environmental impact of Himalayan tunnel construction. Balancing the need for infrastructural development with the preservation of the fragile Himalayan ecosystem requires careful planning, effective regulation, and a commitment to sustainable practices.