Advanced and effective safety measures and systems have become critical in tunnel design with the growth of tunnel construction, and the increasing traffic volumes and utility of tunnels. As a result, safe and smart tunnels are being planned and developed to ensure proper functioning and prevent accidents. Key components of such advanced tunnels include new surveillance and monitoring technologies; effective firefighting systems; proper lighting; mechanical, electrical and plumbing (MEP) systems; and heating, ventilation and air-conditioning (HVAC) systems. In a bid to improve the overall quality and safety of tunnels, the National Highways Authority of India (NHAI) recently established a new design division for efficient review of the design and construction of tunnels, among other specialised structures. It also signed an MoU with Konkan Railway Corporation Limited to review the design, drawing and safety aspects of tunnel construction and slope stabilisation under NHAI’s projects. Such developments should improve the uptake of key safety components and create a more accident-proof environment for the sector.
New surveillance technologies
Advanced surveillance and mapping technologies such as digital twins, drones and artificial intelligence (AI) are being deployed to ensure the safety and security of tunnels. They help in mapping, monitoring and managing the condition of the tunnels, identifying any faults and anomalies and aiding in rescue operations. Digital twin models provide high resolution data to monitor rock bolts, precisely locate loose fall areas, allow overbreak and underbreak analysis, and monitor and fine-tune drilling and blasting. Similarly, drone-based LiDAR technology is being adopted for early detection of voids and cavities, and evaluation of cracks, water tables, humidity and leakages in tunnels. It also enables data collection, with the flight and radar status being monitored via Universal Ground Control Software. One such technology, called Hovermap, is being provided by a key player, Squadrone Infra and Mining Private Limited, in the sector. It is installed on a light motor vehicle with a total scan length of 6 km and a scanning time of 45 minutes. These drones are also used for underground tunnel mapping, and search-and-rescue following tunnel accidents. For instance, in November 2023, two advanced drones were deployed to access remote areas following the Silkyara-Barkot tunnel accident in Uttarakhand.
Another advancement is the use of AI-enabled system for vehicle identification in tunnels through number plate detection, optical character recognition, face detection, attendance recording via face matching and helmet detection. In May 2024, the Jammu and Kashmir Police activated an AI-based facial recognition system with high-focus CCTV cameras near a tunnel on the Jammu-Srinagar National Highway in Ramban district, to improve security.
Effective firefighting systems and lighting design
Upgraded firefighting measures are being integrated into tunnel design to ensure safety, tunnel integrity and stability. These include tracking the performance of the water mist system and full-scale fire testing by independent and recognised accredited test laboratories. Installing a high pressure water mist system is an effective firefighting measure. They utilise small droplets with greater coverage and superior cooling.
On similar lines, tunnel lighting design is another important safety feature that demands proper consideration of factors such as the black hole effect at the entrance, the glare effect at the exit, and ensuring sufficient reaction time or stopping distance when a hazard is identified. Factors that affect the quality of lighting include illumination levels, uniformity of light, and glare (threshold increment) on the tunnel road and walls. Key solutions for improving these factors include the installation of proper luminaires (daylight CCT 4000k) and connected and controlled lighting systems such as the Base Logic System by Signify. This system provides easy and cost-effective control of LED lighting, with limited capex, low opex and high modularity. Furthermore, light equipment should be properly positioned, with consideration for carrying out future maintenance work without hindering tunnel traffic. The interiors and geometry of a tunnel also have a big role to play in creating the right lighting environment. Detailed interiors with dry surfaces and curved and clear geometry are best suited to proper lighting.
Advanced MEP and HVAC systems
MEP systems must be integrated into tunnel design and construction processes for the proper alignment and safety of tunnels. During the design stage, building information modelling (BIM) is used to align and coordinate all the important parts of the MEP network. A centralised data platform helps in collating information on all MEP material and equipment to facilitate BIM. It also improves operational control and enables communication systems that detect, and raise alerts for, failures and faults.
Another important aspect of tunnel design is proper planning of the HVAC system. Several key functions such as smoke extraction, pollution ventilation and temperature-controlled air regulation must be considered. The main elements of tunnel ventilation are general ventilation through jet fans, centrifugal fans, planum fans, inclined fans, pressure blowers, etc.; and expulsion of harmful fumes produced by chemical processes, via fume exhausts. Fume exhaust fans must be made from spark-resistant material and special alloys and coatings based on the corrosiveness of the fumes, for high efficiency and long-lasting quality.
Meanwhile, variable frequency drives (VFDs) play an important role in maintaining safe and comfortable air movement inside tunnels. The use of efficient VFDs on tunnel fans also ensures optimised energy consumption. Danfoss, a key player in this space, providing VFDs with specific features such as fly start, dual DC chokes, 3C3 printed circuit board coating, fire mode and braking features. They are compatible with long cable lengths. Danfoss has installed over 1,500 VFDs across metro projects such as Delhi Metro Phases I, II and III; as well as the Chennai, Bengaluru, Mumbai and Pune metros. It has also installed them in India’s first underwater metro tunnel in Kolkata. Additionally, in the Z-Morh tunnel, high-rating VFDs of up to 710 kW have been installed in jet fans, allowing swift reversal of airflow direction via brake choppers and brake resistors, and minimising the need for manual interference.
Critical safety hurdles
The construction and operation of tunnels in India faces many challenges. Tunnel ventilation issues include drops in oxygen level, low visibility, fire and smoke circulation caused by accidents, high energy consumption, improper calculation of voltage drops and harsh operating environments. Continuous monitoring of air quality must be ensured to keep gases within permissible levels. For fire safety, care must be taken to check the operating temperatures of machines, and the presence of flammable gases must be checked at regular intervals. During hyperbaric interventions, the state of workers must be continuously monitored to check for air loss and ensure adherence to protocols.
Amongst other roadblocks, the age-old norms used for project contracts are unclear about the roles of the implementing agency and contractors. Moreover, the use of low-quality materials and redundant techniques lead to the failure of MEP and HVAC systems. For instance, the Pragati Maidan tunnel project has been facing passenger safety risks due to water seepage, cracks in concrete works and inadequate drainage systems. The Public Works Department of Delhi is scrutinising the construction and quality of the tunnel, and has issued multiple notices to the contractor for technical and design deficiencies.
Future growth
As the sector progresses, certain trends are expected to emerge and take centre stage in the development of safe tunnels. One such trend is the use of innovative materials such as mechanical single bolts, expanding friction bolts, self-drilling rock bolts, steel– and fibre-reinforced polymer active anchors, and steel passive anchors. These are increasingly being used by contractors for efficient tunnel construction.
Going forward, domestic manufacturing of equipment and development of indigenous techniques will need to be increased, especially with new metro systems being planned for Tier I and the II cities. Investments in modern, high quality safety equipment, including personal protective equipment for workers and advanced machinery, will be critical for high-risk actions. Government schemes and programmes such as Gati Shakti will provide a fillip to many tunnel projects. This will boost the infrastructure capabilities of the sector and encourage the use of more sophisticated safety measures. The sector must focus on strict enforcement of safety laws, regular safety audits, training and awareness programmes for workers, and emergency preparedness and response drills. In line with this, the central government announced plans to introduce new standard operating procedures for tunnel construction in January 2024. It is in the process of forming an audit team with experts from various IITs (such as Roorkee, Ropar and Delhi), and setting up a world-class tunnelling centre. The team will research and propose enhanced safety measures for tunnels, benchmarked against international metrics.