Tunnelling activities in India have gained momentum in the past few years owing to a plethora of growth drivers. These include increased government support, adoption of latest technologies and techniques, accelerated investments and the need to provide connectivity in remote areas. Hence, tunnel construction is poised to become a vital aspect of various upcoming infrastructure projects. In a panel discussion at Infrabuild India, government and industry stakeholders, discussed the experience so far in the construction of tunnels, various techniques of tunnelling deployed, implementation of key tunnel projects, impact of Covid-19, issues and challenges faced, and upcoming opportunities…
S.K. Gupta, Director (Projects), Mumbai Metro Rail Corporation (MMRC)
The MMRC, a joint venture of the Government of India and the Maharashtra government, is responsible for implementing Line 3 of the Mumbai metro corridor. The 33.5 km long stretch is totally an underground corridor. It will have 27 stations, of which 26 are being built underground. The initial ridership on this line is expected to be around 1.4 million at the time of commissioning. It is expected to increase to 1.7 million by 2031.
Construction of tunnels on this stretch is being carried out through deployment of latest tunnelling techniques and equipment such as tunnel boring machines (TBMs), the New Austrian tunnelling method (NATM) and cut and cover. At one stage, a total of 17 TBMs had been positioned for the construction of twin tunnels on Line 3. As of now, 50 km of tunnelling, out of 55 km, is already completed.
The construction of tunnels posed a number of challenges as their alignment passed through densely populated and congested parts of the city. At many locations, tunnels pass directly under existing buildings and structures. The ingress of water pockets and weak geology further created barriers in tunnelling work. Further, tunnelling through the NATM faced problems as controlled blasting was required in hard rock conditions, besides the need for extensive use of lattice girder and rock bolt. However, each of the structural challenges were analysed with design modelling and calculations.
M.M. Madan, Chairman, Tunnelling Group, ASSOCHAM’s National Council on Construction Equipment
Tunnelling activity in India has witnessed significant improvement in the past few years, owing to the availability of better construction material, skilled personnel, advanced technology and implementation of better planning and execution strategies. Valuable experience in the Himalayan region has also been gained over the past few years due to which tunnelling activities have accelerated in the country’s hilly terrain. The completion of the Atal tunnel in Rohtang is one such example of successful tunnel construction in difficult terrain.
Tunnel construction under the Loktak hydroelectric project was another challenging task as it was located in a clay terrain with squeezy rock conditions. The tunnel area also had a high concentration of methane due to which welding and cutting activities suffered. All electrical equipment had to be flame-proof. Further, the area had to be vacated every time the level of methane concentration at the project site breached the 5 per cent mark.
The cost aspect of tunnelling is one of the areas that require utmost attention. Every project is implemented in different geological conditions and through different techniques due to which cost estimations differ. Hence, there is a need to ensure that the most efficient mix of tunnelling technologies is deployed to reduce the cost of tunnel construction.
Currently, heavy tunnel equipment in the country is being imported from Europe, the US and Sweden. Imports from China have witnessed a significant decline over the past one year. While domestic manufacturing of heavy tunnel equipment is yet to begin, assembling of imported machine parts has started taking place in the country. Indigenous manufacturing is expected to take place once the domestic demand reaches a significant level.
Going forward, the highways, railways and metro sectors will offer maximum opportunities in the tunnelling segment. Hydropower has currently taken a back seat due to a number of issues involved with hydro tunnels including socio-economic, environmental and forest issues. Meanwhile, microtunnelling also has a huge scope in the urban water supply and storm water drainage sectors.
Colonel Parikshit Mehra, Commander 42, Border Roads Task Force, Border Roads Organisation (BRO)
The Atal tunnel is touted as the world’s longest highway tunnel at an altitude of 10,000 feet. The strategically important, all-weather tunnel between Manali and Leh has instilled confidence to tunnel in any kind of geology in the country. The commissioning of the 9 km long tunnel has had a highly positive impact on the country’s tunnelling segment.
Construction activities on this tunnel faced a number of issues related to excavation works and ensuring proper ventilation. The most formidable task was to continue with the excavation work during heavy snowfall in the winter season. The Seri Nala fault zone, a 588 metre stretch from the south portal, was the most difficult challenge that the tunnelling team faced. Almost after four years of toil, works on the Seri Nala fault zone were completed.
The Atal tunnel was developed on a bill of quantities (BoQ) contract as it had a long construction period and required regular cash flow. Such deep tunnelling projects that are being implemented in difficult terrain are feasible only through BOQ contracts as they face various delays and require unit price contracts with time-related costs. Meanwhile, alignment works on some other projects being implemented by the BRO are being done on an engineering, procurement and construction basis.
Technological advancements such as the deployment of TBMs have significantly optimised tunnel construction activities. The work rate through the drill- and -blast method can also be optimised by carrying out well informed exploration and investigation. Moreover, work rates for tunnels in hilly areas can be at par with the work rate for roads if the right technique is deployed, monitoring is carried out efficiently and skilled manpower is employed.
Going forward, carrying out site investigation much before the project execution is of utmost importance. The executing agency will then be able to provide accurate data to the contractor, who can then mobilise the right set of machinery for project implementation. The BRO is aiming to construct tunnels of 100 km length in the next few years. Of this, nearly 60 per cent of the tunnel length is expected to be located in Arunachal Pradesh and Jammu & Kashmir only.
B. Vijaykumar, Senior Vice-President, ITD Cementation (with Virender Thakur and Brajesh Sinha)
ITD Cementation India Limited has recently completed 11 km of TBM tunnelling in Mumbai Metro Rail Project Line 3. ITD Cementation has been involved in successfully building underground metro corridors through TBM tunnelling in Delhi and Kolkata in the past and associated with Bangalore metro underground project also. The key challenges faced in tunnel construction in Mumbai were transportation of TBMs from Mumbai port to sites in congested roads, presence of old and dilapidated buildings over tunnel alignment with no foundation details, crossing TBMs below live railway lines of Indian Railway, issues in availability and retaining skilled workforce and logistic problems like long distance to designated dumping yards and restricted traffic timings for plying of dump trucks. However, support from the MMRC and the state government ensured completion of the tunnel as per schedule.
As far as the work rate of the project is concerned, an average of 8.3 metres of drive was achieved per day. While construction activities were halted due to the Covid-induced lockdown, work was accelerated from August 2020 onwards to make up for the lost time.
Moving forward, the company is aiming to take part in more tunnelling projects as it has gained valuable experience from the Mumbai metro project in terms of planning and cost estimation. Hence, TBMs deployed for tunnelling activities of the Mumbai metro’s Line 3 are expected to be redirected to other tunnel construction projects.
Future outlook: Hence, tunnels are being actively constructed in difficult terrain to ensure that a strong ecosystem is established for swift implementation of tunnelling activities in the country.