Tunnel construction across infrastructure sectors, including railways, roads, urban rail, hydro, water supply and irrigation, has been on the rise over the past few years. Various developments in these sectors along with increased investments have contributed to this growth. Moreover, with the rising population and concentration in urban areas and limited land availability, there is a growing need for tunnel construction. Over the next few years, tunnelling activity is expected to witness a significant increase.
Railways
According to India Infrastructure Research, as of May 2024, there are more than 370 tunnels, spanning a total length of around 330 km, at various stages of implementation in the railway sector. These include under-construction, under-bidding and planned projects. Of these, more than 240 are under construction and more than 100 are at the planning stage. Some of the key under-construction projects, based on total length, are the Mumbai-Ahmedabad High Speed Rail Corridor Project with eight tunnels spanning a total length of 26 km, the Jiribam-Tupul-Imphal Railway Line Project with around 50 tunnels spanning more than 70 km and the Rishikesh-Karanprayag New Rail Project with around 17 tunnels spanning a length of 105 km. In the railway sector, techniques such as the cut and cover method and the New Austrian Tunnelling Method (NATM) are mainly used for tunnel construction.
The Udhampur-Srinagar-Baramulla Rail Link project is one of the key projects in the rail segment. The total project spans around 272 km and comprises around 38 tunnels. This has been one of the most challenging railway line projects, mainly owing to the geographical location. The line mainly passed through the young Himalayan ranges, which are characterised by geological and other problems. Given these geographical conditions, the construction of the access roads also proved to be difficult. Due to high risks involved, the project has especially adhered to safety provisions in line with international norms. Some measures include the provision of mechanical ventilation systems, firefighting systems including fire hydrants and fire extinguishers, and access roads to escape tunnels and adits. In terms of recent developments, in February 2024, the 12.77-km tunnel on the Khari-Sumber section was inaugurated. This is reportedly the longest transportation tunnel that currently exists in the country.
Roads
The road segment is also seen to have various projects involving the construction of tunnels. According to projects tracked by India Infrastructure Research, as of May 2024, there are more than 210 tunnels spanning a total length of more than 460 km under various stages of development. Under-construction projects account for over 100 tunnels spanning more than 150 km, and over 90 tunnels totalling a length of more than 250 km are in the planning stage. In terms of tunnelling techniques, the sector is witnessing an increased adoption of the tunnel boring method (TBM) and the NATM methods. As per the projects tracked, the TBM method seems to dominate. Further, upcoming tunnels majorly seem to be concentrated in Himachal Pradesh, Jammu & Kashmir and Maharashtra in terms of the total number of under-construction tunnels.
The construction of road tunnels is especially important owing to rising urban concerns. Road tunnels would act as an alternative route, overcoming challenges of narrow roads and traffic congestion. Road tunnels also pave the way for alternative uses of land spaces for purposes including commercial and residential developments.
In a notable development, the government inaugurated the Sela Pass Tunnel in March 2024, facilitating all-weather connectivity to Tawang in Arunachal Pradesh. Tunnels located on these roads provide all-weather access, in addition to better connectivity between remote locations. The development of these road tunnels has also led to a reduction in the travel time. A notable upcoming project in the sector is the Shinku La tunnel connecting Manali and Leh via Darcha-Padun-Nimmu. Works on the tunnel, spanning 4.1 km, are likely to commence by September 2024. Upon completion, this is expected to be the world’s highest tunnel, located at an altitude of more than 16,600 feet.
Metro
Metro tunnels have also seen expansion with increasing urbanisation. According to projects tracked by India Infrastructure Research, as of May 2024, there are more than 70 tunnels spanning a total length of approximately 220 km, which includes more than 40 under-construction tunnels (120+ km) and more than 20 in the planning stage (80 km). These majorly seem to be applying the TBM and cut and cover methods of tunnelling.
Looking at recent developments, the Kanpur Metro Rail project witnessed the completion of tunnelling on the Kanpur Central to Nayaganj stretch. The tunnel stretch, spanning around 1.25 km, achieved a breakthrough on the downline using TBM.
In a line of firsts, the first underwater metro in India commenced commercial services in March 2024. The tunnel spans around 520 m. It is a part of the 4.8-km stretch from Howrah Madian – Sealdah under the Kolkata East-West Metro Project.
Irrigation and water supply and sewerage
Looking at the water supply and sewerage segment, according to India Infrastructure Research, as of May 2024, there are more than 40 tunnels spanning more than 300 km under various stages of development. Among them, under-construction tunnels comprise more than 20, spanning more than 120 km and around nine tunnels stretching to over 160 km are in the planning stage. These tunnels majorly seem to be employing the TBM method of tunnelling.
Tunnel construction in the irrigation sector is also witnessing notable development. The sector has a total of more than 60 tunnels stretching to more than 560 km under various stages of development, including under-construction (more than 20 tunnels totalling over 140 km) and planned (over 30 tunnels with a total length of more than 400 km). The Sleemanabad Carrier Canal Tunnel Project located at Madhya Pradesh is an example of an under-construction tunnelling project. It comprises a 12-km long tunnel and is targeting completion by December 2024.
Hydro
From the tunnel construction perspective, hydro is the largest segment. Under this segment, according to India Infrastructure Research, as of May 2024, there are more than 800 tunnels spanning more than 900 km under various stages of development. Of these, more than 600 tunnels covering a total of over 500 km are under the planning stage. In terms of under-construction tunnelling projects, more than 100 tunnels covering over 200 km are spread across the country but majorly concentrated in states including Himachal Pradesh and Jammu & Kashmir. Some of the key under-construction projects include Stage I of the Luhri Hydro Electric Project comprising two tunnels with a total length of around 38.6 km; and Stage II of the Parbati Hydro Electric Project comprising six tunnels with a total length of more than 35 km. The Teesta-VI Hydro Power Project is also currently under construction. It includes six tunnels totalling more than 28 km. Hydro tunnels majorly seem to be deploying the drill and blast method for construction, with more than 77 per cent of the ongoing projects using this method.
Challenges
Tunnelling projects across different infrastructure sectors are being hit by various challenges. A notable number of projects are located in the Himalayan regions and other hilly terrains. These locations pose difficulties in terms of complex and varied geological conditions. Mobility of labour, equipment and material also prove to be a challenge in such geographical areas. Further, unpredictable conditions and the coming up of unforeseen circumstances such as breakages and flooding lead to increased costs and delays. Other challenges faced include water ingress, cavity formation, lack of skilled labour and delayed decision-making.
Conclusion
As is evident from the recent developments, the infrastructure sectors have witnessed increased tunnelling activity. The limited surface ground requirements and the ability to overcome challenges such as urban congestion and pollution have paved the way for the widespread implementation of tunnels. These sectors have also witnessed the use of advanced tunnelling methods and technology to help address key challenges. Looking ahead, these sectors promise sizeable opportunities for increased tunnelling activity.