India's Underground Construction: Tunnels for Growth

Tunnels are fast becoming the lifelines of India's infrastructure growth — unlocking mobility, economic development, and engineering innovation beneath the surface.
R.K. Dhiman, AVSM, VSM, President, Tunnelling Association of India (TAI)

India’s underground construction industry is undergoing a seismic transformation. Driven by rapid urbanization, strategic infrastructure needs, and technological advances, the nation is tunnelling through mountains, rivers, and mega cities at an unprecedented pace. From metro systems and highway tunnels to hydropower conduits and strategic storage caverns, subterranean projects are reshaping how India connects, commutes, and conserves. As the world’s third-largest metro network expands and game-changing tunnels like Zojila and Atal bring remote regions into the national fold, India is emerging as a global leader in tunnelling excellence. This article explores the surge in underground construction, the cutting-edge technologies driving progress, and the critical challenges that lie ahead.

Key Drivers of Growth

India’s tunnel and underground construction activity has surged significantly in the past few years, fuelled by a robust pipeline of infrastructure projects across multiple sectors. Major drivers include:

Urban Mass Transit (Metro Rail)

The expansion of metro systems in dense cities like Delhi, Mumbai, Chennai, Bengaluru, and Kolkata has spurred extensive tunnelling to create efficient mass rapid transit corridors. For instance, during Delhi Metro’s Phase 3 expansion, a record 19 Tunnel Boring Machines (TBMs) were simultaneously used – one of the largest urban tunnelling operations globally. In Mumbai, the entire 33.5 km long Line-3 metro (Colaba-Bandra-SEEPZ) is underground, tunnels through hard basalt rock. Kolkata recently achieved India’s first underwater metro tunnel under the Hooghly River, showcasing engineering prowess in urban transit. Metro systems have transformed travel in India. Covering over 1,000 km across 11 states and 23 cities, millions of people rely on them for quick, easy and affordable travel. With this growth, India has become home to the third-largest metro network in the world. Metros are not just a way to get around— they are changing how we live and move in cities.

Road and Highway Tunnels

Improving all-weather road connectivity in mountainous regions has become a national priority. The roads and highways sector, which once had limited tunnel projects, is now delivering landmark tunnels in the Himalayas. The 9.02 km Atal Tunnel (Rohtang), inaugurated in 2020, now provides year-round access between Himachal Pradesh’s Kullu Valley and Lahaul-Spiti. It reduces travel distance by 46 km and travel time by 4–5 hours compared to the old route, ending the region’s winter isolation and boosting local economies. Further north, the under-construction Zojila Tunnel (14.2 km) – poised to be Asia’s longest road tunnel – will bypass the perilous Zojila Pass. Together with the adjacent Z-Morh Tunnel, this strategic project will ensure all-weather connectivity to Ladakh, slashing mountain drive down to 15 minutes and greatly enhancing tourism, trade, and military logistics. Banihal Qazigund Road Tunnel, situated at 1,790 meters in the Union Territory of Jammu and Kashmir, lies beneath the Banihal Pass in the Pir Panjal mountain range on National Highway 44; it was constructed between 2011 and 2021. Costal road project in Mumbai has been recently completed with largest slurry TBM.

Railway and Transit Tunnels

Indian Railways has historically been a pioneer in tunnelling (dating back to British-era hill railways), and continues to build ambitious tunnels. The signature project is the Udhampur-Srinagar-Baramulla Railway, carving through the Himalayas with long tunnels (including the 11.2 km Pir Panjal Tunnel) to connect the Kashmir Valley with the rest of India. Elsewhere, Indian Railways and Metro authorities are undertaking tunnels for upcoming high-speed and urban rail projects. A notable future endeavour is the Mumbai- Ahmedabad bullet train’s planned under- sea tunnel, which will be India’s first undersea rail tunnel – to be excavated by a TBM with a massive 13.1m diameter cutterhead. The Rishikesh-Karnaprayag railway line project features 16 main tunnels (104 km), 12 escape tunnels (97.72 km), and 7.05 km of cross passages, totalling an impressive 213.57 km of tunnels. Out of this, 195 km has already been constructed.

Recent breakthrough in package IV with TBM is ahead of schedule in this project. Hydropower and Water Resource Tunnelling The hydropower sector accounts for the largest share of India’s tunnelling projects by length, tapping rivers via headrace and diversion tunnels in mountainous terrain. Over 470 km of tunnels have been driven for hydroelectric projects to date. Ongoing schemes like the Pradhan Mantri Krishi Sinchayee Yojana (irrigation) and the Interlinking of Rivers Programme have also given a fillip to water-supply and irrigation tunnels. Under Jawaharlal Nehru National Urban Renewal Mission (JnNURM), cities undertook major water supply tunnel projects. Mumbai, for example, has constructed deep rock tunnels to convey water from lakes to the city (e.g. the Gundavali–Bhandup tunnel) and is expanding its underground sewer network as part of the Mumbai Sewerage Disposal Project. These projects improve urban utilities while avoiding surface disruptions.

Underground Storage and Caverns

Beyond transportation, India is leveraging underground space for strategic storage. The Indian Strategic Petroleum Reserve Ltd (ISPRL) has built vast underground crude oil storage caverns to bolster energy security. These facilities, essentially large underground chambers, shield India’s oil reserves and exemplify advanced excavation and ground support techniques in rock. A second phase to add more capacity (including a 2.5 MT cavern at Padur) is underway. Tunnel lengths are increasing and projects are being executed in some of the world’s most challenging geologies and terrains, from crowded mega cities to high Himalayan ranges. The past 4–5 years alone have seen a sharp uptick in the number and scale of tunnel projects as the nation pushes to upgrade infrastructure. This growth trend is expected to continue as urbanization and connectivity needs rise.

Technological Advancements and Innovative Practices

Meeting the demands of these ambitious projects has required significant technological advancements in tunnelling methods, equipment, and design. India’s engineers and contractors are increasingly adopting global best practices and modern techniques to address the unique challenges of underground works:

Tunnel Boring Machines (TBMs)

Mechanized tunnelling via TBMs has gained substantial traction, especially in congested urban areas where it minimizes disturbance to surrounding ground and structures. TBMs create smooth, circular tunnel walls lined with precast segments, which reduces lining costs and makes them ideal for city tunnels. High-end data management systems now allow TBM operators to continuously log and adjust for geological conditions, enhancing efficiency. However, TBM use also brings challenges – geotechnical uncertainties can stall machines, and there is currently a shortage of experienced TBM crew in India to meet the rising demand. Nonetheless, with over 63 TBM-driven tunnel projects (>600 km) already completed – largely in metros and water works – and dozens more underway, TBMs are set to dominate in urban tunnelling. Earth Pressure Balancing Machines & Slurry TBMs remain to be the mainstay for tunnelling in soft ground especially in urban settings.

Drill-and-Blast Method (DBM)

Conventional drilling and blasting remains indispensable for tunnels in hard rock and difficult access areas. In the Himalayan and Northeast regions, DBM is often preferred for its flexibility, since deploying huge TBMs in remote, rugged terrain can be impractical. Most hydropower tunnels and long road tunnels rely on controlled blasting techniques. It is noteworthy that over 700 km of tunnels (across 250+ projects) have been excavated using DBM in India, predominantly in the hydro sector, and dozens of new DBM-driven tunnels are currently under-construction or planned.

New Austrian Tunnelling Method (NATM)

NATM (also known as the observational method) has emerged as a flexible approach for uncertain ground, adjusting support based on actual ground behaviour. It is widely used for medium to large span underground openings like highway tunnels and underground caverns, especially when geology is variable. NATM relies on immediate ring closure and shotcrete lining with rock reinforcement, guided by instrumentation data to modify support patterns on the fly. India has applied NATM in many road tunnels and metros (e.g. tunnel portals, station tunnels), benefitting from its cost- effectiveness and adaptability. Sequential Excavation Methods (SEM), a refined form of NATM, have been deployed to carefully navigate challenging geology section by section, for example in large underground station boxes or soft ground tunnels. Over 300 km of tunnelling has been completed with NATM in India, with the hydropower sector seeing the highest use (23 projects) followed by metro rail projects.

Micro-Tunnelling and Trenchless Technology

For smaller diameter conduits like city sewers, water mains, and utility pipelines, trenchless micro-tunneling is increasingly popular. Micro-TBMs (or pipe-jacking machines) can install pipelines under roads, runways, and rivers without open excavation, a boon in congested urban environments. Indian cities like Mumbai, Delhi and Bengaluru have begun using micro-tunnelling to upgrade sewage and drainage systems with minimal surface disruption. This trend aligns with the push for smart city infrastructure, ensuring essential services are buried out of sight and harm’s way.

Ground Freezing and Sequential Excavation

Ground freezing – temporarily turning water in the soil to ice – can be tried to stabilize waterlogged ground during excavation, such as for shafts or cross-passages in metro tunnels. Each of these techniques, while used sparingly so far, expands the toolkit available to engineers to handle difficult ground conditions safely.

Innovative Materials and Design Tools Material science and digital design are also transforming underground construction. Projects are increasingly using high- performance materials like fibre-reinforced shotcrete, rock bolts with yieldable fibre components, geosynthetic membranes, and energy-absorbing anchors to improve tunnel support and waterproofing. These materials enhance the durability and safety of linings, especially in squeezing ground or seismic zones.

On the design front, adoption of Building Information Modeling (BIM) and geotechnical modeling software allows integrated 3D simulation of underground structures, detecting clashes and optimizing alignments before construction. Furthermore, operational tunnels now feature cutting-edge systems and are designed as “smart tunnels” with SCADA- controlled ventilation, fire detection, CCTV surveillance, and real-time air quality monitoring for safety. Such digital systems enable proactive maintenance and incident response, marking a leap in tunnel operation technology.

India’s underground construction is becoming more technology-intensive – combining mechanized excavation, improved conventional techniques, advanced materials, and digital monitoring. These innovations are enabling engineers to tackle greater depths and lengths than ever before. Continued R&D and knowledge exchange through forums like the Tunnelling Association of India will be key to keep pace with the growing scale of projects.

Challenges Beneath the Surface and Risk Factors

Despite the exciting progress, the underground construction industry in India faces a range of challenges that require careful management. Understanding these challenges is crucial for stakeholders to formulate solutions and policy support.

Geological Uncertainty

Mother Nature remains the ultimate boss in tunneling. India’s geology is diverse and often unpredictable – from the fractured young Himalayan ranges prone to collapses and water ingress, to the hard basalt and granite under cities that can hide fault zones. Unforeseen conditions can lead to collapses. Such events highlight the need for thorough geotechnical investigations, flexible designs, and robust emergency plans (e.g. providing escape tunnels or cross-passages in long tunnels).

Even with modern methods, tunnel projects frequently have to alter designs mid-course due to ground conditions, causing delays and cost overruns. Geotechnical risk mitigation – via better site investigations (boreholes, geophysical surveys), real- time monitoring (convergence gauges, ground penetrating radar ahead of TBMs), and adaptive support systems – remains a top challenge. It is imperative that national level geotechnical investigation campaigns are progressed for better mapping of underground geomorphology & allied details.

Safety and Risk Management

Underground construction is inherently hazardous. Ensuring worker safety in confined, underground environments is paramount. Traditional drill-and-blast tunnelling carries high accident risk if not meticulously managed – controlled blasting, ventilation of fumes, and rock support must be executed with precision. Even TBM drives have risks like machine entrapment, cutterhead interventions under pressure, or sudden inflows of water or gas. Contractors today must implement strict safety protocols: robust temporary supports, continuous gas monitoring, evacuation drills, personal protective equipment, and backup systems. Incident of Silkyara and Telangana demand detailed review of proposal before start for risk assessment and for mitigation plan in advance.

Skilled Manpower Shortage

Building tunnels demands specialized skills – geotechnical engineers, experienced miners, TBM operators, shotcrete experts, etc. India faces a shortage of skilled labour and engineers experienced in modern tunnelling techniques, partly due to the rapid escalation of projects. Developing domestic expertise through training programs, academic courses in tunnelling, and knowledge transfer from global firms is essential. The government and industry bodies like the Tunnelling Association of India are working to build capacity, but the skill gap remains a hurdle as projects multiply.

Equipment and Logistics Constraints

Deploying large TBMs or heavy equipment in remote areas poses logistical headaches. Transporting a 100-ton TBM shield to a hilly project site with poor road access can be an epic challenge. Mobilization and demobilization of TBMs across the country is cited as a key challenge by contractors – after one metro project finishes, shifting the machine to the next project may involve disassembly and weeks of haulage. Similarly, procuring spare parts quickly for sophisticated machines can be difficult domestically, leading to downtime.

There is a need to augment local manufacturing and inventory of tunneling equipment (aligning with the “Make in India” initiative) to reduce dependence on imports and improve response times.

Project Management and Financial Risks

Underground projects are notorious for cost overruns and schedule delays, often stemming from the factors above (geology surprises, design changes, etc.). Complex contracts, land acquisition for portals or shafts, and environmental clearances can further slow progress. Ensuring projects remain economically viable is a concern for contractors, especially when bidding on fixed-price contracts that don’t adequately account for geological risks. On the financing side, tunnels demand heavy upfront investment. Better contract forms with risk sharing mechanisms & provisions for dynamic changes of supports need to be put in practice. Risk can be mitigated to some extent by detailed investigation and DPR preparation by employing experienced geologist/engineers. This should be followed by expert review in all cases. Documentation in the form of record of experience in each project should be kept on completion which should act as a guide to our future projects.

Environmental and Social Concerns

Large underground works can have environmental impacts – tunneling in the fragile Himalayan ecosystem, for example, raises concerns about disturbing groundwater regimes and triggering landslides or loss of springs. Communities may worry about blasting vibrations affecting their homes. Urban tunneling has to manage settlement to prevent damage to adjacent buildings (as faced in some older parts of Kolkata and Chennai during metro construction). Thus, environmental impact assessments and management plans are crucial. The industry is moving towards more sustainable practices – precise blasting to reduce vibrations, tunnel spoil reuse (using excavated rock for aggregates), and careful monitoring of groundwater.

Engaging local communities with transparency and providing reassurance through compensation or rehabilitation (if needed) is part of responsible tunnel development. By investing in geotechnical research, enforcing stringent safety codes, training manpower, and improving project governance, India can mitigate risks and ensure its underground projects are delivered safely and efficiently.

Why Tunnels Matter

Contribution to Development and Economic Multiplier Effects

The underground construction industry is far more than a niche engineering endeavor, it is a significant contributor to India’s development story, with powerful multiplier effects on the economy.

By piercing through natural barriers, tunnels connect previously isolated regions. Shorter travel times reduce vehicle operating costs and save fuel, improving overall logistics efficiency. The Zojila tunnel, upon completion, is expected to drastically cut the cost and time of supplying essentials to Ladakh and boost tourism inflows, thereby increasing income for local communities. Atal Tunnel has already changed the social, commercial & economic contours of Lahaul valley for the better by bringing in all-weather connectivity.

Similarly, metro tunnels in cities enable reliable public transport, which attracts investment and business activity to those cities by improving urban mobility. In essence, underground infrastructure provides the arteries through which commerce and development flow.

Conclusion

The relevance of tunnels, whether to offer greenfield connectivity to remote areas or for decongestion of cities by providing underground transit systems, is increasing. The future, as they say, is truly underground. It is pertinent that government, academia and technical institutions ensure that necessary policy changes, technical interventions, and pragmatic research aspects are accelerated to set the pace for faster development of underground assets. Tunnels when built right, will be safe, cost- effective, and environmentally sustainable.