Telangana Tunnel Collapse- Explained Pointwise

Eight workers have been trapped inside the collapsed Srisailam Left Bank Canal (SLBC) tunnel in Telangana’s Nagarkurnool district. The incident occurred when a three-meter section of the tunnel’s roof collapsed during maintenance work to repair a leak. Out of the 70 workers present, most managed to escape, but eight individuals remain unaccounted for. Telangana Tunnel Collapse

The rescue mission faces significant challenges due to the accumulation of water and silt in the tunnel, with approximately 200 meters filled with debris. Specialized teams of the Indian Army, National Disaster Response Force (NDRF), State Disaster Response Force (SDRF), and a group of ‘rat miners’ from Uttarakhand have been deployed to assist in the rescue operations.

What is the Srisailam Left Bank Canal (SLBC) tunnel? What are the key features of the SLBC tunnel?

The Srisailam Left Bank Canal (SLBC) tunnel is a crucial irrigation project in Telangana. It is designed to supply water from the Krishna River to drought-prone areas in the Nalgonda and Mahbubnagar districts. It is part of the larger Srisailam Lift Irrigation Scheme, which aims to improve water accessibility for agriculture and drinking purposes.

Key Features of the SLBC Tunnel:

a. Length: The tunnel is approximately 50 km long. It is one of the longest tunnels in India for irrigation.
b. Purpose: It has been designed to carry water from the Srisailam Reservoir to regions that face chronic water shortages.
c. Location: The tunnel runs through the Nallamala Hills in Nagarkurnool district, Telangana.

The project has faced multiple delays since its inception, primarily due to geological challenges, financial constraints, and technical difficulties.

What are the possible reasons behind the Telangana Tunnel Collapse?

1. Weak Geological Conditions- The tunnel passes through the Nallamala Hills, which consist of fragile rock formations. Continuous exposure to high water pressure may have weakened the rock structure over time. The presence of fault lines or loose rock formations made the tunnel section vulnerable to collapse.

2. Water Seepage and Leakage- According to reports, the maintenance work was being carried out to fix a leak. This indicates pre-existing structural weaknesses due to water seepage and leakage.

3. Poor Maintenance and Delayed Repairs- The SLBC tunnel has been under construction for over two decades, and has been facing multiple delays. Lack of timely inspections and maintenance could have allowed cracks and weak spots to go unnoticed.

4. Structural Instability- The caving in of 3-meter section of the tunnel roof suggests weak concrete reinforcement and erosion of support structures.

5. Human and Technical Factors- Lack of real-time monitoring for detecting early warning signs like vibrations or minor cracks, further exacerbated the risk of tunnel collapse.

What are the methods of Tunnel Excavation used in India?

In India, two methods of Tunnel Excavation are employed-the drill and blast method (DBM), and tunnel-boring machines (TBMs).

TBM method is much safer but expensive, when compared with the DBM method.

What are the initiatives taken for ensuring safe tunnel construction mechanism in India?

1. Creation of Tunnel Zone department in the MoRTH- A tunnel zone department  has been created in the Ministry with a mandate to build the capacity for excellence in tunnelling, preparation of guideline on design and construction of tunnel.

2. Constitution of Expert Committee on Tunnel- This expert committee has been created for resolving technical issues which arise in implementation of Tunnel Projects in the country.

3. Indian Standard Code for Tunnel Construction- The Indian Standard Codes-IS 15026 (2002) and IS 4756 (1978) have been issued for tunnel Construction. This code prescribes the guidelines for tunnel design, lighting and ventilation.

4. IRC Codes for Tunnels- IRC code 2019 for tunnels is being implemented to ensure the road tunnels which are constructed, are as per the international standards. 

5. Implementation of other standard codes in tunnel construction- Integrated Tunnel Control Systems (ITCS), The Work in Compressed Air Regulations 1996, Emergency Evacuation and Rescue Plans for tunnels & RDSO (Research Designs and Standards Organisation) guidelines must be properly implemented.

6. International Tunnelling and Underground Space Association safety practices in tunnel construction- According to these guidelines on the safety practices in tunnel construction, particular attention should be given to the means of escape in an emergency situation like specific escape routes marked by signs and contingency plan.

What should be the way forward to ensure safe tunnel construction?

1. Detailed geotechnical studies- Currently, in India the design and construction of a tunnel project is done simultaneously. More detailed geotechnical studies like the petrographic analysis, needs to be done to incorporate in the design and the construction of the tunnel project.

2. Regular monitoring by specialist geologist- Regular site visits of an independent specialist geologist must be conducted to check for probable failures and to determine the rock’s stand-up time. (Rock-stand up time- It is the duration for which a rock can remain stable without any support. Support is given to the rock within its stand-up time.)

3. Supports provided to the tunnel must be tested for adequacy- Supports of the tunnel like shotcrete (sprayed concrete that works as a membrane to prevent parts of the rock from falling), rock bolt (a long anchor bolt for stabilising rock excavations), steel ribs and tunnel pipe umbrella need to be properly tested for its adequacy to prevent tunnel collapse.

4. Arrangements for safe evacuation in case of collapse- There must be deployment of NDRF personnel & proper safety equipments to ensure safe evacuation in case of any mishap. The construction companies must submit a safety plan along with the bid for the projects.

Tunnel-building technology is around 200 years old and, if executed properly, tunnels aren’t dangerous.