The tunnelling industry in India has seen rapid developments in the past few years with a large number of projects being commissioned or moving ahead. Major tunnelling projects such as the 9 km Chenani-Nashri tunnel in Jammu & Kashmir and India’s first underwater metro tunnel in Kolkata were completed in April 2017 and June 2017 respectively. Meanwhile another key project – the Katra-Qazigund railway project – in Jammu & Kashmir is under construction and involves the construction of 29 tunnels with a total length of 105 km.
According to India Infrastructure Research, the tunnelling segment offers a pipeline of over 1,190 tunnels spanning a total length of 3,578 km. This large number of projects is expected to drive the requirement for tunnelling equipment in the future. Tunnelling equipment such as tunnel boring machines (TBMs), tunnelling jumbos, roadheaders, backhoes, hydraulic cutters, crawler excavators, wheel loaders and crawler loaders are expected to show a significant growth in demand. The industry is also seeing a gradual move from conventional tunnelling methods to modern methods such as the New Austrian Tunneling Method (NATM).
Key trends observed
The drill and blast method (DBM) continues to be the most widely used for tunnelling in India, commanding an almost 60 per cent share of the industry. This method involves the controlled use of explosives and other methods such as gas pressure blasting pyrotechnics to break rock for excavation. Equipment such as tunnelling jumbos, roadheaders, backhoes and hydraulic cutters are used to dig the tunnel and clear the excavated rock. The Indian DBM and NATM equipment market is dominated by Atlas Copco and Sandvik, which together command a 95 per cent market share. Other players in the D&B equipment market include Caterpillar, JCB, Normet, Okamura, Soilmec, Akkerman, Doosan and Volvo.
With an increase in the size and depth of tunnels, there is an increasing shift towards the use of TBMs. According to India Infrastructure Research, at least 28 tunnels spanning a total length of over 215 km are either under construction or are planned to be taken up using TBMs. In the metro rail sector alone, tunnels spanning a length of at least 162 km are either under construction or are planned to be taken up using TBMs. For instance, the Delhi Metro in its initial phases had used one-two TBMs. However, under Phase III of the project, around 25 TBMs are boring at the same time.
TBMs offer several advantages over other tunnelling methods. They are a cost effective and speedier alternative to DBM. They are also suitable for all types of rocks and geology, and offer faster and smoother tunnelling without much disturbance to the surrounding rock mass. This makes TBM the method of choice for the industry. Various types of TBM equipment including open mode TBMs, earth pressure balance machines and mixed shield or slurry TBMs are available in the market. Major suppliers of TBMs in the country include Germany-based Herrenknecht, Australia-based Teratec, US-based Robbins and Japan-based Hitach Zosen.
Another tunnelling method which is seeing increasing acceptance is micro-tunnelling. Emerging as a new trend in India, it is being extensively used to lay water supply pipelines and sewers in congested areas. It is especially used for projects that require tunnels under roads with high traffic volumes, railways, rivers, etc. It is used for laying large diameter gravity sewers in cities where open cut installation is difficult, for installation of product pipelines in areas where the soil condition does not allow for horizontal directional drilling and for long individual crossings across rivers. This method is particularly used for constructing tunnels with diameters ranging from 600 mm to 3,000 mm.
Mumbai was the first city to experiment with micro-tunnelling for the World Bank-funded Mumbai Sewage Disposal Project. Other cities such as Delhi and Kolkata have also used this technology. The main equipment used in the micro-tunnelling method is the remote-controlled steerable boring machine, which is operated from a computer operator station using drive motor controls. The micro-tunnelling equipment market is dominated by foreign suppliers such as Herrenknecht, Teratec, Robbins, Caterpillar, Akkerman, etc.
The dominance of foreign players in the Indian tunnelling equipment market has increased considerably with the use of new techniques. This is led by China, which currently commands over 90 per cent of the Indian tunnelling equipment market. Imported equipment is widely preferred over domestically manufactured equipment. This is largely due to the taxation on tunnelling equipment. If a TBM is imported, there is a low customs duty, whereas if a TBM is manufactured domestically and sold to customers, full duties and taxes are applicable. This makes importing a better option and players are increasingly importing tunnelling equipment rather than procuring it from domestic players.
The size of tunnelling projects in the country is seeing an increase as well. Longer and larger tunnels are being increasingly developed. This increasing tunnel size requires an associated increase in equipment size. (The biggest machine now being used globally is over 19 metres in diameter.) Equipment size though has to fit well with the economics of the project. There is also an increased amount of electronic data available from equipment nowadays. This helps in making intelligent data-based decisions, which has increased the efficiency of project implementation.
With advancements in technology, TBMs can now be custom designed based on the geological conditions of a project. The TBM can be customised for hard rock, mixed rock, soft soil or a combination of all of these. Although advanced technologies allow geologists to determine the upcoming rock formation with a certain degree of certainty, there is always some degree of uncertainty that remains. Thus, TBM manufacturers have to ensure that their machines are robust and reliable and have the capability to cope with any surprises in the rock formation. In this context, risk mitigation becomes a key element for tunnelling projects.
Tunnels are also going deeper. For example, the Bosphorus crossing in Turkey and the Westerschelde tunnel in the Netherlands at their deepest points go up to 106 metres and 65 metres deep respectively. A major challenge faced while working at such depths is a variation in air pressure. The workers, especially those who work on physically repairing TBM equipment, have to stay in special chambers while working at these depths. Workers therefore require special training as the tasks need to be executed with high precision.
The way forward
Going forward, D&B is expected to continue as the major tunnelling method, particularly for the hydropower, road and railway sectors. Tunnels spanning a total length of 143 km are planned to be constructed using DBM. However, TBM is also expected to pick up significantly. The import of TBM equipment and machinery is expected to remain high with a low likelihood of TBM suppliers setting up new manufacturing or assembly units in the country. Given the high costs associated with this technology, TBM will continue to remain expensive as compared to other methods. However, in the case of tunnels longer than 3 km and diameters of 3.5 metres or more, the use of TBM will be more economical and advantageous, as it offers a production rate three-four times higher than conventional methods, with no additional cost on ventilation.
Another tunnelling method which is gaining prominence is NATM, especially in the road, railway and metro rail sectors. In the metro sector specifically, over 36 km of tunnel length is planned for implementation using this technique. The tunnels include those for the Kanpur Metro (13.5 km), Jaipur Metro (9.96 km), Lucknow Metro (6.55 km), Pune Metro (5.02 km) and Delhi Metro, Phase III (1.18 km) projects. With the demand for NATM expected to grow further, specialised equipment for NATM is likely to gain popularity.
With an increase in the size and depth of tunnels, the selection of the right equipment is likely to become even more critical for successful project execution. Equipment selection has to be based on a wide range of parameters including the geology of the project, the surrounding air pressure, the ambient environment and the adjoining infrastructure. This will be key in risk mitigation and successful project execution for the tunnelling industry going forward.
Based on presentations by Sandeep Sharma, Regional Sales Manager, VMT Gmbh, and Hans Greve, Director, Tunnelling, Royal IHC, at a recent India Infrastructure conference