Tunnel-boring machines (TBMs) are increasingly being used in India for metro, rail and other infrastructure projects. Choosing the right TBM is vital to work efficiently, speedily and safely. Here’s a guide on how to make the right choice.Geological compatibilityTBMs are specifically designed and customised to suit the unique geological and geotechnical conditions of the area where tunnelling will take place. So, an extensive and thorough geotechnical investigation is conducted prior to the machine’s design and fabrication. “The tunnelling company accurately compiles soil sampling findings, rock quality assessments, groundwater studies and analysis of geological faults or anomalies and provides these to the TBM original equipment manufacturers (OEMs), who use this critical data to engineer and manufacture a TBM that can efficiently and safely navigate the anticipated ground conditions, while minimising risks and maximising performance,” explains Kapil Raman, President and COO, Building and Infrastructure SBU, Tata Projects.For instance, the TBM company will ensure that the cutterhead diameter, opening ratio and disc cutter configuration match the rock strength and abrasiveness, explains Sanjoy Sanyal, Founder & Managing Director, Bouw Consultants. For instance, in Pune, the TBM used to tunnel through basaltic rock to create the metro line had specially hardened disc cutters.The thrust and torque capacity must also be adequate for the ground resistance. “In weak rock, excess thrust can cause over-excavation; in hard rock, insufficient torque can stall progress,” he adds.Sanyal recommends engaging experienced TBM suppliers to customise the cutterhead, support systems and backup logistics based on past learnings from similar projects. When selecting a machine, he also recommends considering the outcome of a site-specific risk assessment, drive length, overburden, urban sensitivity and groundwater conditions. Machines enabling the automated recording of machine parameters and remote diagnostics facilitate performance optimisation and maintenance planning.By and large, shielded TBMs have been more commonly deployed for Indian projects in soft soils than open-type TBMs that work better in hard rock conditions with stable geology such as in Europe, observes Sanyal. “Earth pressure balance (EPB) shielded TBMs have been deployed in alluvial soil for Delhi Metro Phase 3, while the slurry TBM variant, best for granular soils and high water pressure, was deployed for the Mumbai Coastal Road Project.”According to Raman, “More India-specific research on the performance of TBMs in diverse geology would help improve the overall performance of these machines.”User feedback can also help manufacturers introduce new features that allow machines to work better. As Neeraj Gupta, Tunnel Manager, L&T, tells us, “New TBMs can take on tunnel seismic prediction and come with a 60-m borehole facility, whereby grouting can happen through the machine itself more effectively than earlier.”Gupta is engaged in a railway tunnel project in Uttarakhand where a single-shield hard rock TBM set a world record by boring 36 m in one day and 661 m in a month. “Many new features are an outcome of the feedback we give manufacturers,” he says. “They are receptive to our feedback.”Logistics & electricalsWith an eye on long-term performance, when selecting a TBM, go beyond the basic dimensions and the compatibility of the machine with geological and hydrological conditions. Consider the efficiency of support systems such as ventilation, lighting and logistics; safety and adaptability in urban or challenging conditions; and the lifecycle cost and maintainability. Explaining how these systems can impact performance, Sanyal says, “The efficiency of the screw conveyors in EPB-shielded TBMs or slurry pipelines in slurry TBMs is the key to high advance rates. Faster muck handling is vital for high-speed tunnelling in long drives for rapid rail transportation system projects.”Coming to electricals, “Grid power must be made available and appropriate transformers arranged, for example, 11 kV, 22 kV or 33 kV, along with emergency power supply to ensure proper visibility for safe operations, ventilation and communication in case of power failure,” explains Mihir Mishra, Vice President, Construction Plant and Equipment, Afcons Infrastructure. “A standby diesel generator placed in the TBM backup helps to mitigate this issue.”A few other caveats, according to him: the cables, lights and components must conform to recommended IS codes, the TBM must use flame-retardant low smoke cables, and the electrical components must be insulated with an ingress protection rating of IP 65 or higher. Lighting & ventilationProper lighting ensures onsite safety, performance and compliance. In that context, Mishra points out that working areas need 100 to 150 lux, walkways need 50 lux and emergency areas need at least 10 lux. Sanyal emphasises adequate lighting for both the operational zones and escape routes, with a focus on energy-efficiency. “LED-based low-voltage lighting was used in the Chennai Metro TBMs,” he says.Recollecting the Silkyara Tunnel incident where poor ventilation posed life-threatening risks, Sanyal also points out that ventilation systems play a role in worker safety and equipment cooling, especially in long tunnels.Proper ventilation is crucial for fresh air; to remove dust, gas and heat; and maintain a breathable atmosphere, agrees Mishra. “If the ambient temperature is very high, temperature control helps to ensure a conducive working environment. The ventilation fan and the size of the duct must match the tunnel conditions.”Safety & communicationSensors also play a role in ensuring safety. “A TBM must have gas-detection sensors to mitigate risks from flammable, toxic or oxygen-deficit gases like methane, carbon dioxide and hydrogen sulphide,” says Mishra. “Also, integrating an automatic fire suppression system and fire alarm with the TBM electrical system helps mitigate fire hazards.”Real-time sensors can also help monitor the face pressure, soil conditioning parameters, cutterhead torque and thrust, and thus enable proactive maintenance and response to the geological conditions, according to Sanyal.CCTV systems enable the real-time monitoring of conditions and swift responses to incidents like accidents or smoke detection. A reliable communication system also plays a role in monitoring the TBM’s operational parameters and performance in real time, and operational coordination, adds Mishra. “Alongside conventional communication systems (radio, mobile phones, Wi-Fi, walky-talky), IP-based communication can be considered.”Skill shortagesIndia is still largely dependent on expats for team leadership positions in projects making use of TBMs, observes Gupta. “We’re gaining experience but it is likely to take at least five more years to overcome the existing shortage of skilled engineers.”Despite an increase in tunnelling engineers, many lack hands-on TBM experience, agrees Raman. “Limited formal training means contractors often rely on foreign experts, which hinders knowledge transfer to local teams. This also prompts current operators and crew to seek better experience opportunities abroad, worsening the shortage of experienced personnel here in India.”Training would help tide over this shortage. “Onsite, inhouse training by large construction companies such as L&T is very useful,” says Gupta.Mishra endorses pre and on-the-job-training in manufacturing units assembling TBMs. By enhancing the capability of local engineers, this would additionally help to reduce TBM downtimes. Of course, such training is limited to companies making in India, which is, so far, limited.Make in IndiaHeavy reliance on imported, specialised TBMs is a key challenge. “Herrenknecht is assembling TBMs in India but their capacity is nowhere near the demand for TBMs considering that these are being deployed for many metro projects in cities,” says Gupta. That said, Mishra points out that TBMs assembled locally are likely to fare better in India’s very price-sensitive market for being lower-priced – an outcome of lower labour costs (in comparison to Germany and the US) and lower import duties and transportation costs on components as against a complete TBM. Machines assembled in India can also be delivered faster, as the local components and imported components can be processed simultaneously and made available in a shorter period, he adds. In time, local assembly has improved but full manufacturing is still difficult owing to the need for precision, expensive inputs and inconsistent demand, in Raman’s view. “So, the core components and advanced designs are still largely sourced internationally.”Mishra endorses continuous engagement with local vendors to improve their workmanship and capability.That’s something the industry would like to see – soon. Imported or assembled? Sanjoy Sanyal, Founder & Managing Director, Bouw Consultants, weighs in on the choice between an imported or locally assembled TBM: Cost: TBMs assembled in India cost 10-20 per cent less on account of lower import duties and logistics. Delivery: TBMs assembled in India are delivered faster and so can be mobilised faster. Service: TBMs assembled in India are serviced by local support teams and spare parts are more easily available, reducing downtime. Customisation: TBMs assembled in India are adapted to Indian geology (mixed ground, curved drives). “Both TBM manufacturers making in India as well as those importing machines can cater to requests for any change to the cutterhead of the TBM after deployment but as this has a financial impact, it is important to study the geology well,” cautions Neeraj Gupta, Tunnel Manager, L&T. Compliance ready: TBMs assembled in India are more easily aligned with the Indian Government’s project specifications. Core technology (AI, sensors, automation): Imported TBMs may be more advanced than TBMs assembled in India. Brand perception: Imported TBMs are favoured for extreme geology. (Disclaimer: Neeraj Gupta has shared his views in his personal capacity.) Quick bytes TBMs must be customised to the project’s geological conditions.Cutterhead design must match material strength and abrasiveness to ensure optimal performance.Thrust and torque settings must be precisely calibrated to minimise risk and maximise efficiency.Smart TBMs with automation, sensors and remote diagnostics improve safety and reduce downtime.Adequate lighting, low-smoke cables and strong ventilation ensure a safe and breathable workspace.Advanced safety systems are critical for early hazard detection and rapid response.Indian-assembled TBMs offer quicker delivery, lower costs and easier servicing – but still depend on imported core parts.Imported TBMs remain the go-to for highly complex or extreme geological conditions. Quotes TBMs assembled locally are likely to fare better in India’s very price-sensitive market. - Mihir Mishra, Vice President, Construction Plant and Equipment, Afcons Infrastructure It is likely to take at least five more years to overcome the existing shortage of skilled engineers. - Neeraj Gupta, Tunnel Manager, L&T LED-based low-voltage lighting was used in the Chennai Metro TBMs. - Sanjoy Sanyal, Founder & Managing Director, Bouw Consultants More India-specific research on the performance of TBMs in diverse geology would help improve their overall performance. - Kapil Raman, President and COO, Building and Infrastructure SBU, Tata Projects