By Satish Paretkar, Director (Hydro, Underground and Water), Afcons Infrastructure
Tunnels have become a key component of modern infrastructure, playing a major role in enhancing connectivity and accessibility. Tunnel construction has evolved from being associated with hydropower projects and shorter tunnels in highways and water supply systems, to now serving as integral components for metro systems and roads, especially for long-distance links. The rapid expansion in infrastructure investments across sectors is also driving the construction of tunnels that serve as connectivity corridors and function as critical missing links.
Learning from experience
Tunnelling projects are faced with many geological bottlenecks. As tunnel geology and conditions cannot be fully determined in advance, construction proceeds with a certain degree of geological risk, requiring contractors to adapt to and tackle these conditions. Tunnelling projects face significant roadblocks in northern regions like Jammu & Kashmir and Himachal Pradesh owing to varying and complex geologies and terrain. Nonetheless, decades of tunnelling experience in the country has yielded a substantial amount of technical know-how and methodologies for addressing various challenges across different geologies. Over the years, several noteworthy tunnelling projects have been undertaken and successfully completed; reflecting the industry’s strong technical expertise and the ability to tackle challenges posed by topological and geological conditions. The 8 km twin Samruddhi tunnels, which are part of the Nagpur-Mumbai Super Communication Expressway in Maharashtra, stand out for having been completed in a record time of two years. Another example is the Atal Tunnel in Rohtang. The project suffered a major collapse, presenting significant bottlenecks to continued excavation. In response, various proposals were evaluated, and a drift method along with a three-tiered pipe arrangement was adopted. This enabled effective navigation of the 600 metre stretch. Further, tunnel T-49 under the Udhampur-Srinagar-Baramulla Rail Link (USBRL) witnessed squeezing and deformation in the main tunnel and the escape tunnel, which was then rectified.
Enhancing stakeholder coordination
Pre-construction investigations and geological surveys by consultants have improved with time. In certain conditions, consultants are able to carry out detailed geological investigations to carefully identify tunnel conditions. Findings are then used to identify rock masses and the support system required to proceed further. However, actual conditions experienced during excavation sometimes vary from initial findings. In such situations, the experience of engineers working on-site plays an important role in dealing with challenges. Hence, while opinions differ among stakeholders, timely decision-making can prevent potential problems.
While tender documents provide the baseline required for project execution and costing, unforeseen conditions are likely to arise during the construction process. In engineering, procurement, and construction projects especially, contractors are responsible for the costs. As a result, stakeholders now hold discussions on accommodating a certain level of variation, and allocating risk and responsibility in case of unforeseen circumstances.
Moreover, consultants can play a larger role in bringing about change. While contractors possess strong design teams and technical capabilities, consultants are better positioned to advise project owners. While the pace of speed remains gradual, progress is evident, with new contracts now integrating provisions that were absent earlier. Hence, continued, shared responsibility among all stakeholders is needed to drive further change.
For example, the Parbati Stage-II Hydroelectric project featured two inclined shafts of around 1.5 km each, with excavation carried out through tunnel boring machines (TBMs). Consultants and the NHPC proposed an open TBM, while the contractor, drawing on prior experience and ground conditions, advocated a double-shield TBM. This was later adopted and tunnelling works witnessed successful completion.
Focus on safety
Safety measures constitute a critical component in the entire tunnelling process. The Samruddhi Tunnel, for instance, features a high-pressure water mist fire protection system, the first of its kind in India. At Afcons, safety measures for the workforce are a key priority during tunnel construction. While promoting such a culture remains a challenge in India, significant efforts are being taken to meet safety standards, with strong involvement from top management as well. Personal protective equipment prior to entering the construction site, required equipment and other measures are mandatory. Afcons also has the AfconSafe mobile app that facilitates real-time reporting of hazards and unsafe conditions. It also records near-miss accidents for future prevention. Toolbox talks are also conducted prior to every shift for safety briefings.
In sum
Tunnelling continues to play a major role in enabling infrastructure development across challenging terrains. While issues like technical constraints, complex geologies and availability of the right manpower exist, efforts are under way to skill the workforce. In sum, tunnelling projects are evolving to better adapt to unforeseen situations. Continuous learnings from ongoing tunnelling experiences are strengthening resilience, and safety and execution quality.
