There has been a surge in tunnelling activity in the country over the past few years. Tunnel construction in sectors such as hydropower, roadways and railways has also increased the demand for tunnelling equipment. The deployment of water treatment systems in urban and rural areas, and the growing need for clean water are also driving tunnelling activity in the country.
The cost of equipment is dependent on a number of variables, including the tunnel construction method employed, geological conditions and the level of technology. These machines comprise expensive elements and components such as conveyor belts, slurry pipelines, ventilation systems and electrical systems, which add to the product cost. Transporting these machines is a challenging endeavour with substantial costs. In addition, the lack of adaptability and compatibility of equipment is a market obstacle, which complicates the process of installation. These machines are energy intensive and require a robust backup system.
The different types of materials used in tunnel construction include explosives, concrete, steel, shotcrete material, lattice girders, geomembranes, rock bolts/anchors, admixtures, fibres and rock reinforcement. The demand for a particular type of material depends on its availability, site conditions, transportation costs, project location, manufacturing capabilities and local taxes. Other key factors that play a vital role in the selection of construction materials are tunnel life expectancy and capital costs. For example, for the construction of the all-weather Atal Tunnel, 15,000 tonnes of steel was used.
The growing complexity of tunnel construction in the Himalayan and peninsular regions has necessitated the use of new and advanced materials to improve the durability and strength of tunnels. Steel fibre-reinforced shotcrete, safer emulsion-based explosives, geosynthetics such as 5D steel fibres (for increased tensile strength), mineral admixtures, geotextile membranes, steel anchors and self-drilling rock bolts are some of the key advanced materials being used.
Construction method
The drill-and-blast method (DBM) and tunnel boring machine method (TBM) are the two most prevalent technologies for tunnel construction in India. Nearly 65 different categories of equipment are required to execute a tunnelling project through DBM. Double boom jumbo machines (underground drilling machines), road headers (self-propelled rock cutting machines for constructing tunnels without requiring explosives), and drilling rigs (used to dig holes in the subsurface) are some of the important pieces of equipment utilised in the drill-and-blast process. Other equipment includes survey instruments, and excavation, concrete, and workshop equipment. Some of the key providers of drill-and-blast equipment are Sandvik, Atlas Copco, Caterpillar, JCB, Normet, Okumura, Soilmec, Akkerman, Doosan and Volvo.
The TBM approach has also seen widespread use, particularly in the construction of metro tunnels in densely populated urban areas. In addition, it has acquired popularity in the water supply and sewerage industries. TBMs can be divided into four major categories — soft ground, slurry, hard rock and hybrid. In the TBM market in India, open-mode TBMs, earth pressure balance machines and mixed shield or slurry TBMs are deployed on the basis of soil content and geographical terrain of project sites. In a recent development, Afcons Infrastructure Limited launched a TBM without a diaphragm wall (D-wall) for the Underground (UG-1) Project of the Ahmedabad Metro. Such a strategy has been utilised for the first time on a metro project in India.
Technology intervention
Sophisticated drilling techniques, computerised jumbos and navigation systems are being increasingly used to improve precision and monitoring. The TBM navigation systems help to provide a continual reference point for the machine’s location. Under the navigation system, a beam is detected by the TBM’s rear targets. This enables the driver to compare the real-time location and altitude to the predetermined, preprogrammed position.
Moreover, the application of strength monitoring using thermal imaging (SMUTI) technology allows for real-time evaluation of the strength of the entire shotcrete lining from a safe vantage point, delivering enormous safety, quality control, and productivity benefits. In addition, SMUTI can be utilised during spraying to diagnose local issues such as unaccelerated cold patches, pulsation and lamination. In addition, the use of variable density TBMs provides enhanced safety and flexibility with regard to the selection of tunnel face support and muck discharge. These TBMs can be operated both as conventional slurry TBMs with an air bubble system to manage the face pressure and as earth pressure balance TBMs.
There is a need to indigenise tunnelling equipment as much as possible in order to promote the use of modern machinery, minimise prices and reduce servicing time. India must forgo imports in favour of increased self-reliance and promote indigenous production. Heavy duty loaders, Liebherr excavators (for loose strata), telehandlers, grouting pumps, Schaeff loaders, drum cutters, hydraulic crawler drill machines, side-dumping loaders (such as the CAT 850 model) are some of the essential machines that can be manufactured in India.
Recent developments
Chennai Metro Rail Limited is planning to utilise indigenous tunnel boring equipment for Phase II of the project. This is in contrast to the previous decade, when China, Russia and Germany supplied machinery. Around 12 of the project’s 23 TBMs will come from Tamil Nadu, five from China, one from Germany, and one from Pune.
Megha Engineering and Infrastructures Limited has utilised an advanced automatic boomer, a semi-automatic boomer, a shotcrete machine, a hagg loader, a hydraulic excavator, a wheel loader, dumpers, transit mixers, a scissor platform, a breaker, a truck-mounted grouting pump, diesel generator sets and a batching plant, and a mobile crusher for the Char Dham Railway Tunnel Project.
In order to construct underground parts of the Kanpur Metro, world-class and state-of-the-art TBMs have been utilised. In this underground portion of the Kanpur Metro, the total length of TBMs is around 80 metres.
For tunnelling in the Himalayan region, India relies primarily on New Austrian Tunnelling method-capable machinery, such as boomers/ jumbos, shotcreting, various types of grouting, and ground strengthening, rather than TBMs.
Challenges
There is a need for geological engineers to lead tunnelling projects in order to ensure that the right methods and equipment are utilised. To expedite the geological investigations that precede construction projects, mobile versions of boring machines or new technologies and models that provide exact data more quickly are required. Probing the geology in advance and making good predictions using technology can help TBMs avoid getting stuck in mountainous terrain as well as in city underground metro projects. Due to inadequate training, many tunnel
construction personnel lack machinery expertise and are unable to address the obstacles that occur. Proper operator training would increase workplace productivity and safety.
The sudden ingress of heavy water while executing tunnelling work, particularly in the Himalayan region, is a real challenge that can stall work for days. Another major challenge is the sudden changes in geology, which necessitate a change in the cutter head in the TBM), which is difficult and time-consuming because TBMs come with standard cutter heads.
Outlook
With the rise in tunnel construction in the country, the outlook for the tunnelling equipment market seems promising. It is, however, important to resolve issues such as shortage of skilled manpower for operating and maintaining TBMs, absence of spare parts inventories, and inadequate investigation resulting in high wear and tear of equipment.