Tunnel construction activity in India has seen significant growth in the past few years, owing to the growing urbanisation and development across key infrastructure sectors. The growth has primarily been driven by a robust pipeline of projects as well as investments in developing hydropower projects, enhancing urban mass transit networks, augmenting road and rail interconnectivity, constructing underground crude oil repositories, and upgrading water supply and sewerage systems.
In recent years, the Indian tunnelling industry has witnessed significant traction in the adoption of modern and advanced technologies in tunnel design and construction. The demand for advanced tunnelling equipment and materials is also on the rise due to formidable geological intricacies that pose a major hurdle in tunnelling, particularly in regions such as the Himalayas and the Western Ghats.
Customised monitoring solutions have the potential to facilitate the continuous mapping of concrete coverings and reinforced bars, identifying cavities situated behind the coverings, while also recognising fractures, voids, delamination and water permeation within tunnels. There is also a growing focus on smart/intelligent tunnels that feature integrated traffic control systems, video surveillance, wireless communication systems, entrance detection control, electrical fire signalling systems, SOS call boxes, etc.
For instance, Intozi’s artificial intelligence-based video analytics solution has been implemented at Larsen & Toubro’s ADIT-2 tunnels for vehicle detection, number plate detection, optical character recognition, face detection, attendance via face matching, helmet detection, etc.
Recently, the Border Roads Organisation evinced a keen interest in the adoption of space technology to enable real-time monitoring of its strategic assets such as bridges and tunnels. As of May 2023, it has signed a memorandum of understanding with Innovations for Defence Excellence at Aero India, expediting the acquisition of the technology.
Manual monitoring of tunnels has a number of limitations, the most significant being that it does not provide an accurate depiction of the terrain. The integration of modern technology is of utmost importance to accelerate the construction of tunnels and bridges at key locations. This apart, automation is also becoming the new way of sustainable and faster tunnelling, with the introduction of computerised controls for two- and three-boom excavation rigs.
With the growing number of complex tunnels being constructed, advanced materials have replaced conventional raw materials. Some of the materials used in tunnel construction are explosives, concrete, steel, shotcrete, lattice girders, geomembranes, rock bolts/anchors, admixtures, fibres and rock reinforcement. Explosives, one of the key materials for blasting activities, have evolved from dynamite to emulsion-based and water gel-based explosives.
Moreover, contractors are increasingly utilising innovative materials such as fibre bolts, fibre-reinforced shotcrete, lattice girders, lining stress controllers, pipe-roof pre-support systems, geosynthetics, geomembranes, steel anchors and self-drilling rock bolts to increase the durability and strength of geologically challenging projects.
Delhi Metro Rail Corporation Limited used Tech Geo PR 30 non-woven geotextile in the tunnels of the Delhi metro. It provides protection, separation and drainage between the top shotcrete lining and the yellow geomembrane sheet. For the construction of the Rohtang tunnel, a unique self-adhesive waterproofing polyvinyl chloride membrane, LOGICROOF V-GR FB SA, was used. In the PirPanjal tunnel, located in the PirPanjal range in Jammu & Kashmir, geotextiles and waterproofing membranes have been used. Additionally, specialised work was carried out simultaneously across the block for their installation.
The need to establish a rigorous quality control framework for tunnelling projects across the country is crucial. Furthermore, it is important to highlight the significance of cost management while upholding standards. As per the Ministry of Road Transport and Highways, the construction of around 144 tunnels, spanning 357 km, at a cost of Rs 2 trillion is currently under way on national highways in India. To this end, the ministry is developing a policy to incorporate municipal waste in road construction. A potential switch back to item rate contracts from the prevalent engineering, procurement and construction contracts in these regions has also been proposed, to mitigate geological risks.
As the number of tunnels being constructed keeps on rising and the traffic volume in existing tunnels grows, safety measures are assuming greater importance. The development of safe tunnels necessitates the consideration of a diverse array of factors. Every aspect, ranging from the tunnel design, ventilation system and lighting to firefighting procedures, plays a crucial role in ensuring safety of labour as well as travellers.
Another essential safety consideration is the design of tunnel lights. Considering factors such as the black hole effect at the entrance, the glare effect at the exit, and sufficient reaction time/stopping distance when a hazard is identified, is essential. Electrically powered equipment, noise control mechanisms, robotic excavators (used in the Mumbai metro) and electric drum cutters are a few of the sustainable measures that have the potential to be scaled up.
The Dr Syama Prasad Mookerjee (formerly Chenani-Nashri) Tunnel is India’s first tunnel equipped with a fully transverse ventilation system (including exhaust and fresh air ducts). The Atal Tunnel, also known as the Rohtang Tunnel, has deployed many new technologies to monitor local and remote connectivity, ventilation, lighting, fire safety systems and power distribution. Additionally, in a bid to ensure fire safety, fire hydrants have been placed every 60 metres.
Recently, the National Capital Region Transport Corporation announced the construction of cross passages in parallel tunnels in the underground section of the Delhi-Ghaziabad-Meerut Regional Rapid Transit System corridor to increase safety along the route. For this, implementation of the New Austrian Tunnelling Method is being pursued, owing to its capacity to accommodate surfaces with a lot of curves.
Going forward, tunnel projects are expected to increasingly deploy smart and sustainable solutions
in order to enhance operations and safety efficiency, while enabling resource and cost savings.
In recent times, the preference has shifted to the use of refurbished tunnel boring machines (TBMs) as opposed to brand-new TBMs for each new tunnel project. In early 2023, TERRATEC, a renowned designer and manufacturer of TBMs, launched an earth pressure balance (EPB) TBM for the Surat metro, an under-construction rapid transit rail system in Gujarat. This unit is a refurbished 6.61 metre diameter EPB TBM, which will be used by J. Kumar Infraprojects for Phase I of the Surat Metro Rail Project (UG-02).
Similarly, a refurbished mixed-shield EPB machine called TBM Bhadra, manufactured by Herrenknecht, along with another machine, TBM Tunga, will be used to build a total of four tunnels in the Bangalore Metro.
Multi-utility tunnels (MUTs) should also be considered as a strategy for deploying integrated power distribution, telecom cables, water, sewerage and gas. In contrast to conventional methods, MUTs present a resilient and enduring strategy, particularly when evaluated in terms of project life cycles. MUTs reduce operation and maintenance costs while simultaneously enhancing the life of the equipment. They also effectively eliminate the necessity for recurrent excavations, which disturb city life and create pollution. Furthermore, these structures safeguard facilities against unwarranted public intervention and offer resilience against potential harm resulting from extreme events. MUTs also free up land for public and productive purposes.
Tunnelling activity in India has accelerated in recent years due to several growth factors. Increasing government support, adoption of cutting-edge technologies and processes, and initiatives to improve rural connectivity are a few of them. Going forward, tunnel projects are expected to increasingly deploy smart and sustainable solutions in order to enhance operations and safety, while enabling resource and cost savings. Digital advancements in the sector will help in ensuring safety and quality in tunnel construction, and lead to profitable returns on projects.