With increased investment in infrastructure development, the country has transformed into one of the fastest growing markets for tunnel construction. A number of sectors such as railways, roads, hydropower, water supply and metro rail offer ample opportunities to contractors. The growth of tunnelling activity is largely being driven by projects entailing huge investments in these sectors. Of late, the size of tunnelling projects has witnessed a substantial increase. Longer and larger tunnels are beginning to be developed. Although these are still only a few in number, developers have started planning for larger-sized projects as they acquire greater confidence in tunnel construction.
With regard to construction methods, advanced technologies such as those using tunnel boring machines (TBMs) and the New Austrian Tunnelling Method (NATM) are being used extensively for tunnelling activity in congested urban areas. Excavation using TBMs has been quite successful in constructing metro, water supply and sewerage tunnels. However, the high cost of TBMs and the difficulty in mobilising these machines to job sites, especially in the Himalayan region, remain strong deterrents. Sector-wise, TBMs are the most widely utilised for tunnels in urban rail and water supply and sewerage projects in congested urban areas. This technique has been successful in projects such as the Delhi metro and the Srisailam Left Bank Canal. With regard to the irrigation sector, TBMs are slowly replacing the drill-and-blast method (DBM) of construction that was used earlier. In the water supply and sewerage sector too, the use of TBMs for tunnelling started only recently, primarily in urban areas. Heavy movement of traffic, space constraints and congestion have been the main reasons behind the use of this technology. Microtunnelling is another advanced method that is finding increasing uptake in congested urban areas. New advances are also being witnessed in microtunnelling. Herrenknecht has introduced the Direct Pipe® technology. This has opened up possibilities for installing pipelines in a more efficient way. The method combines the advantages of microtunnelling and the horizontal directional drilling technology. In recent years, the NATM, a flexible and cost-efficient technique, has also been gaining prominence, especially in the railway and metro rail sectors. However, tunnel construction in difficult terrains like the Himalayas and the Western Ghats is still carried out using the conventional DBM.
In addition, there is 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. The Chenani-Nashri tunnel is a case in point. Other challenging landmark projects are also under execution. These include the 9 km Rohtang tunnel on the Leh-Manali highway, 82 km of tunnels on the JiribamTupul-Imphal rail line, and the 33.5 km Mumbai Metro, Line 3. Underwater tunnels are also being constructed.
With the growing number of complex tunnels being constructed, advanced materials have replaced conventional raw materials. Explosives, one of the key materials used for blasting activities, have evolved from dynamite to emulsion-based and water gel-based explosives. These explosives are a safer and more sustainable alternative to destructive dynamite. Cement, another key raw material used to provide strength to the tunnel structure, has seen significant advancements. Reinforced concrete mixed with glued steel fibres is being used as shotcrete for permanent/temporary lining, cast-in-situ lining, precast segmental lining and for other flooring works. Further, compatible materials that can fill cracks/joints completely using the pressurised grouting technique are required. At present, ordinary Portland cement grout, which has larger particles, is primarily used to fill cracks, and thus gaps are left. To overcome this issue, grout with finer material referred to as microfine cement is being tested. Waterproofing of tunnels is another key requirement for which geotextile membranes are being widely adopted. To improve durability and add strength to tunnels, steel- and fibre-reinforced polymer active anchors and steel passive anchors are also being used by tunnel contractors. Besides, expandable friction bolts, self-drilling rock bolts, and mechanical single bolts that allow faster installation are being used to increase productivity. Though most of the materials used at present are still traditional, new materials are beginning to be used and are expected to be deployed even more in the future. At the same time, awareness about the suitability and use of new materials has increased among contractors.
Key tunnelling projects
A large number of tunnelling projects are being undertaken across sectors such as railways, metro rail, and roads and highways. The country’s longest electrified rail tunnel, between the Cherlopalli and Rapuru stations in Andhra Pradesh, was inaugurated in September 2019. The tunnel is part of the 112 km Obulavaripalli-Venkatachalam railway line project and has been constructed to provide connectivity between Krishnapatnam port and its hinterland areas for faster freight movement. The country’s first underwater metro tunnel, the 502 metre underwater metro rail tunnel below the Hooghly river was completed in May 2017. Further, the first undersea tunnel is planned to be constructed for the Mumbai-Ahmedabad high speed rail project. The project involves the construction of a 21 km long tunnel, of which 7 km will be under the sea. Estimated to entail an investment of Rs 35 billion, the tunnel will be constructed using a combination of the TBM technique and the NATM. In February 2020, the Ministry of Home Affairs gave its nod to the Brihanmumbai Municipal Corporation to appoint a Chinese contractor for the construction of two sewer water tunnels between Borivli and Goregaon. The tunnels, spanning a length of around 10 km, will be connected to the wastewater treatment plant at Malad. The tunnels will be part of the Mumbai sewerage disposal project. The first tunnel will be constructed between Borivli and the Malad plant and the second between Goregaon and the Malad plant.
The way forward
Tunnel development in the country is being driven by investments in the metro rail, railway, roads and highways, hydropower, underground crude oil storage, and water and sewerage sectors. Construction players have recently started using modern technology for tunnel development. Almost all the upcoming tunnel projects are of much higher value than had been the case in the past. However, the tunnelling segment continues to struggle with issues of inadequate investigation, geological complexities and mismanaged contracts although there has been some improvement on these fronts. Projects have also been stalled or surrendered due to contractual issues.
Overall, there is great scope for tunnel construction in India. In the next three to four years, there will be abundant opportunities across sectors, given the large pipeline of projects. Thus, over the long term, the tunnelling segment holds immense promise for engineering, procurement and construction contractors, and technology and equipment providers.
Recently, in February 2020, the central government emphasised the need for a tunnel system at strategic locations across the country. It announced plans to undertake tunnelling works worth over Rs 1 trillion over the next five years. The government also has plans to provide opportunities to competent players, both big and small, through relaxation in technical and financial bid parameters. However, these policy and project plans will be on hold until the ongoing lockdown is completely lifted. The lockdown has already delayed several ongoing and upcoming projects in the tunnelling segment due to disrupted supplies of raw material and shortage of labour. The invocation of force majeure by infrastructure players is expected to impact financial obligations in the case of both revenue generating projects and those awaiting financial closure. At present, construction contractors are facing issues such as availability of working capital for meeting their financial obligations – payments to workers, subcontractors, raw material and technology suppliers. These issues are expected to further delay projects, leading to substantial time and cost overruns. Moreover, contractors have had to devise new strategies to fast-track implementation, while adhering to physical distancing norms at construction sites and ensuring the safety of workers. Given the current situation, construction activity, particularly for tunnelling that requires a high degree of safety and the involvement of a number of workers and types of machinery, will take time to return to normalcy.