CT Logo

Tunnels play a crucial role in setting up hydropower projects, developing urban mass rapid transit systems, improving road and rail connectivity and facilitating water and irrigation projects. There has been a rise in tunnelling activity in the country, as a large number of infrastructure projects are being implemented across sectors such as railways, roads and highways, water supply and sewerage, and urban mass transit. Over the past few years, the tunnel segment has received greater attention due to increased congestion in urban areas, which has left little scope for on-ground construction. As a result, newly evolving tunnelling techniques offer greater flexibility to contractors.

The New Austrian Tunneling Method (NATM) is an innovative approach to tunnel construction that has been gaining popularity in recent years. NATM is a flexible and adaptable method that allows for the construction of tunnels in a variety of geological conditions, including soft ground, hard rock, and mixed conditions. This method also allows for the construction of tunnels with complex shapes and cross-sections. Additionally, the method is relatively fast and cost-effective, as it eliminates the need for extensive pre-support measures, while also improving safety and minimizing environmental impact. NATM is not just a construction method for performing tunneling operations, but also an approach towards a streamlined sequence of the necessary construction activities with security, safety, and economy being the pivotal elements. NATM is fast emerging as an alternative to traditional tunneling methods in congested urban areas especially in metro rail sectors. It is also a preferred method for tunnels in mountains with uncertain geological and hydrogeological conditions. Besides, it is appropriate for construction of approach roads of adequate geometry for caverns and mines.

The development of tunnel boring machine (TBM) has revolutionized the tunnelling industry by making tunnelling a safer, more economical solution for creating underground space and opening the possibility of creating tunnels where it was not feasible before. This highly mechanized tunnelling method, TBM is well known throughout the world for achieving very high tunnelling rates and adoption of such method in projects can speed up considerably the completion of the project within the stipulated time schedule. Tunnel boring machines are the best choice for use in densely populated regions since they minimize disruption in the excavation area. Additionally, they provide a smooth tunnel wall, which lowers the price of the finished lining. When compared to traditional excavation techniques, TBMs considerably shorten the overall excavation time of longer tunnels. The use of TBMs is the most prominent in the irrigation and water supply, sewerage and metro rail sectors for tunnel construction in congested urban areas. These machines are being custom-made to deal with site-specific requirements of projects.

Another advanced method gaining traction in tunnel construction is micro tunnelling, also known as trenchless or pipe jacking technology. This construction method is employed to accurately install pipelines under existing utilities, highways, railroads, levees, waterways, in sensitive wetlands, unstable ground conditions, and contaminated soils with minimum disruption to businesses and traffic on the surface. It is used for laying large diameter gravity sewers in cities where open cut installation is difficult, for the installation of product pipelines in areas where the soil condition does not allow for horizontal directional drilling (HDD) and for long individual crossings across rivers. This method is particularly used for constructing tunnels with diameters ranging from 500 mm to 4,000 mm. Microtunneling is desirable for its ability to reduce project risk, constrain the construction zone within easements and right of ways, minimize ground surface settlement, and is applicable to a wide range of geological and changing ground conditions with extreme accuracy. It offers precise line and level installations in various ground conditions. The main applications of microtunnelling are in sewerage, drinking water, oil and gas, communication and power supply networks. Despite being expensive, microtunnelling is preferred over HDD due to its accuracy and reliability and lower maintenance cost of pipelines. Unlike the drill-and-blast-method (DBM) that has a higher environmental impact, greater noise and vibration levels and disturbance to wildlife, the microtunnelling method involves minimal interface with the local environment, making it suitable for constructing tunnels, especially in congested areas.

Mechanical excavation of tunnels using Road header (RH) is getting widespread and popular due to their capability of excavating precisely soft to medium strength rock without weakening the surrounding rock. It can excavate smoothly various sizes, shapes, and types of tunnel openings. In civil construction, they find extensive use for excavation of tunnels (railway, roadway, sewer, diversion tunnels, etc.) in soft ground conditions, as well as for enlargement and rehabilitation of various underground structures. Their ability to excavate almost any profile opening also makes them very attractive to those civil construction projects where various opening sizes and profiles need to be constructed. High mobility, advance rates, reliability, low strata disturbance, safety and low labour deployment are some of the advantages of the RH. The main advantage of the roadheader is its high cutting power density provided by the small diameter of its cutting drum. This gives the RH the cutting edge over other mechanical excavators. Recent advances have made RHs more efficient in hard rock tunnelling.

However, despite the mechanised techniques on offer, the traditional drill-and-blast-method (DBM) continues to be the most used method of tunnelling across all sectors. One of the key reasons for the DBM being the preferred method is that it is flexible and is more capable of handling multiple challenges as against advanced mechanised techniques. Additionally, it is a cost-effective method that requires less specialized equipment than other tunnelling techniques. This makes it an attractive option for smaller projects or those with limited budgets. Another advantage of the drill and blast method is that it can be used in conjunction with other tunneling techniques, such as tunnel boring machines (TBM). This approach can speed up the tunneling process and reduce costs. In fact, the selection of the appropriate tunnelling method hinges on a thorough analysis of the project requirements, geological factors, tunnel length, budget constraints, and safety considerations.