Civil and Mining Product: India’s longest rail tunnel

Engineer’s spree of developing the human skills to indulge themselves into making the sparkling changes in the society has got magnificent accomplishment.  Civil engineering deals with design and construction while mining engineering deals with excavation but when construction has to be dealt with excavation in underground; it’s time to step into a new field, Underground Space Technology. It deals with planning, design, construction and maintenance of underground structures. Construction of a tunnel is one of the challenges in this technology. Though there are very few tunnels in India, presently India is one of the emerging markets in tunneling projects.

In the recent times, India has accomplished its longest railway tunnel network named “Pir panjal Railway Tunnel”, one of the most challenging and marvelous project of Indian history. The 10.96 Km. long tunnel is the India’s first and Asia’s second longest railway tunnel connecting the Jammu Kashmir with other parts of India throughout the year. The methodology adopted for the construction of this tunnel was New Austrian Tunneling Method (NATM) with latest technology in 3D monitoring system. This is the India’s first large scale project where NATM has been implemented. NATM is based on the concept whereby the surrounding ground itself becomes a load bearing structure through activation of a ring like body of supporting ground. It’s most suitable for soft ground excavation and where smooth profile can be obtained for establishing load bearing ring.

A Himalayan mountain in which the tunnel has been excavated consists of eight geological strata’s based on geological investigations. The condition of the rocks made them to adopt different techniques to excavate using tunnel excavator for soft ground, road header for rocks having Unconfined Compressive Strength less than 100 Mpa and drill & blast method for hard rocks. The first ever use of road header for excavation in India. The excavation area of the tunnel varied with the geological conditions and the final cross sectional area being 48 Sq. m. The total area of the tunnel was excavated in three parts i.e. top heading, benching and invert. For early completion of the project, the excavation was started from three faces each from either sides and third from adit towards north. The excavation sequence of NATM is:

1. Mobilization of the strength of rock mass to its maximum extent.
2. Installation of initial primary support.
3. 3D monitoring to assess the deformation in initial support    system.
4. Sequentially excavation, closure of invert and support system.
5. Finally applying the permanent lining.

The tunnel is almost straight having a height of 7.3m and width of 8.4m with highest ever overburden of about 1,100m. The adit and shaft were excavated to shorten the critical length of drive and to set apart the difficulties near portals. They were used for the maintenance and ventilation purpose during the operation and they will be serving as the escape routes during emergency conditions. The midpoint of the tunnel is heightened from either side to provide an excellent drainage system. The tunnel has been made waterproof and fire fighting system is provided. Adjacent to the rail track, 3m wide concrete road is constructed throughout the tunnel for maintenance and emergency purposes.

 Routine work proves to be unbearable because of the boredom it produces, that’s where challenges keep you active. This project too had its major challenges which were like slope stability near the portals, the geological conditions, high water ingress, restricted drill & blast due to existence of village over alignment of tunnel and low performance of road header. They have excellently overcome the challenges offered by the environment and the climate.

 Being India an emerging market in tunneling projects, India is having lots of projects going on and some of the highlighted projects are metro railways in New Delhi and under river tunnel in Kolkata. The technologies used in these new projects are turning the face of the engineering works in India making on par with that of the world class tunnels. 

Source: economictimes.com