SLBC Tunnel Mishap in Telangana Introduction
- The recent collapse of the Srisailam Left Bank Canal (SLBC) tunnel in Telangana’s Nagarkurnool district has once again highlighted the importance of safety in tunnel construction.
- The tragic incident, which resulted in eight workers being trapped after a section of the tunnel roof caved in, underscores the urgent need for stricter safety measures and improved engineering practices.
- Complicating rescue efforts were the accumulation of water and silt, with nearly 200 meters of debris obstructing access.
- To tackle the crisis, rescue teams including the Indian Army, National Disaster Response Force (NDRF), State Disaster Response Force (SDRF), and a specialized team of ‘rat miners’ from Uttarakhand were deployed.
What is Srisailam Left Bank Canal (SLBC) Tunnel?
-
- The SLBC tunnel plays a crucial role in Telangana’s irrigation infrastructure, transferring water from the Krishna River to the drought-prone regions of Nalgonda and Mahbubnagar districts.
- It is a part of the Srisailam Lift Irrigation Scheme, which is designed to enhance water accessibility for both agricultural and drinking purposes.
- Key Features of the SLBC Tunnel:
-
- Purpose: Designed to transport water from the Srisailam Reservoir to regions frequently facing water shortages.
- Location: The tunnel runs through the Nallamala Hills in Nagarkurnool district, Telangana.
- Length: At approximately 50 km, it ranks among India’s longest irrigation tunnels.
- Challenges: The project has been marred by delays caused by geological challenges, financial constraints, and technical complexities.
Possible Causes of the Tunnel Collapse
- Water Seepage and Leakage: The maintenance work that was being conducted aimed at repairing a leakage, pointing to pre-existing structural weaknesses caused by water infiltration.
- Geological Weaknesses: The tunnel passes through the fragile rock formations of the Nallamala Hills. Over time, continuous exposure to water pressure can weaken these rock structures. Additionally, the presence of fault lines or loosely bound rock formations may have exacerbated the instability.
- Lack of Timely Repairs and Poor Maintenance: The tunnel has been under construction for over two decades and has seen multiple delays. Insufficient inspections and a failure to address early signs of deterioration may have worsened its structural integrity.
- Structural Instability: The sudden collapse of a three-meter section of the tunnel’s roof suggests weak reinforcement or erosion of support structures over time.
- Absence of Real-time Monitoring: A lack of early detection systems to identify minor cracks, vibrations, or structural shifts further increased the risk of collapse.
Types of Tunnel Construction Methods in India
| Technique | Methodology | Applications & Advantages |
| Tunnel-Boring Machines (TBMs) | TBMs use a rotating head to cut through rock while installing precast concrete segments for reinforcement. | Suitable for tunnels with rock cover up to 400m; used in Delhi Metro projects due to precision and enhanced safety. |
| Drill and Blast Method (DBM) | This method involves drilling holes into rock, placing explosives, and detonating them to break the rock apart. | Commonly used for tunnels in high-altitude regions (1000-1200m), including the Himalayas, Jammu & Kashmir, and Uttarakhand. |
While TBMs provide safer excavation, they are significantly more expensive compared to the DBM method.
Government Initiatives to Improve Tunnel Safety
- Expert Committee for Tunnel Projects: A dedicated committee has been formed to address technical challenges in tunnel construction projects.
- Implementation of Indian Standard Codes: The IS 15026 (2002) and IS 4756 (1978) codes provide essential guidelines on tunnel design, lighting, and ventilation to ensure safety.
- Adoption of IRC Codes for Road Tunnels: The 2019 IRC code mandates international-standard safety measures for tunnel construction.
- Creation of a Tunnel Zone Department (MoRTH): The Ministry of Road Transport and Highways (MoRTH) has set up a specialized department to enhance tunnel construction expertise and safety protocols.
- Integration of Advanced Safety Protocols: Various safety standards, including the Integrated Tunnel Control Systems (ITCS), Work in Compressed Air Regulations (1996), and emergency evacuation protocols, have been introduced to improve safety in tunnel operations.
- Adoption of Global Best Practices: The International Tunnelling and Underground Space Association has outlined safety standards that include dedicated escape routes and contingency plans for tunnel emergencies.
Ensuring Safer Tunnel Construction: Way Forward
- Continuous Geological Monitoring: Regular inspections by independent geologists can help assess rock stability and detect early warning signs of failure.
- Robust Support Systems: Tunnel supports, including shotcrete (sprayed concrete), rock bolts, steel ribs, and tunnel pipe umbrellas, must be rigorously tested to ensure they can withstand geological stresses.
- Stronger Emergency Response Measures: Construction companies must include detailed safety plans as part of project proposals. Provisions should be made for deploying NDRF personnel, integrating real-time monitoring systems, and establishing well-defined evacuation routes.
- Training and Capacity Building: Engineers and construction workers should receive specialized training in advanced tunneling techniques, structural risk assessment, and emergency response preparedness
- Comprehensive Geotechnical Studies: Currently, tunnel design and construction often occur simultaneously, leading to unforeseen complications. Conducting in-depth geotechnical studies, including petrographic analysis, before construction begins can mitigate risks.
