Sela Tunnel Project: Overcoming the Impossible

Manpower: Tunneling work is both mechanised and labour intensive at the same time. During the winter months, the human output reduces drastically as the workmen were not able to continue for long hours at a stretch. The site work in these months was carried out by organising four shifts of six hours each. The workers were provided special clothing, work warming regimens, local heating arrangements on the working sites.

Machinery: The equipment on site faced major challenges wherein the filters of BS-IV engines would get choked and equipment would remain off road for days together. These issues were obviated by using winter grade diesel and using insulation layers on plants. Many of the vehicles and equipment would have their engines kept running throughout the winter nights.

Concrete Setting Cycles: The final arch lining of the tunnel was executed using 12 m long gantry based concrete shutters. Each arch lining segment consisted 150 – 250 cu m of concrete dependent on over breaks. Ordinarily the concrete setting time is around 12-18 hrs, however, at the Sela Tunnel site these setting times went upto 48 hours due to low ambient temperatures and wind chill. The setting times were brought down by using halogen lamps for local heating and wind screens placed on portals. Additional gantry based formworks were inducted to further compress timelines.

Freezing of Water: Natural sources get frozen in the winter months and sometimes during night even in summer months posing challenges. The issue was resolved by making sumps inside the tunnel and keeping the water in circulation to prevent freezing. Some artesian sources were identified within the tunnels to tap water as they were perennial due to the inherent rock mass heat.

Lack of Local Quarries: There is a dearth of local quarries in the region which could offer suitable quality and quantity of aggregates for road works and tunnel concrete works. This meant that most of the aggregates had to be recycled from within the site. The site team ensured that suitable tunnel muck and excavated material from the road were identified and stacked properly. These were recycled for aggregates.

Rarified Atmosphere: The tunnels are located above an altitude of 13000 feet which causes the atmosphere to be rarified. This posed serious challenges for ensuring required fresh air and oxygen content in the tunnels. The design of the ventilation system had to be carried out deliberately wherein twin jet fans of one meter diameter were at every 400m in each traffic tube to ensure adequate air volume inside tunnels throughout the year. There are fans in all cross pages to help evacuation in an eventuality of a tunnel fire.

Lack of Technical Manpower: Tunnel industry is currently overstretched in India with construction of vast number of tunnels for railway, roads and metro system. However, the core technical manpower still remains to be very limited. Sela Tunnel project was competing with such soft sites in the hinterland where people prefer to work and it was very difficult to recruit and motivate technical manpower to operate at altitudes above 13000 feet in a remote location. The project overcame this challenge by training supervisor level engineers for higher technical responsibilities. Many of the technical managers took upon themselves more than usual share of work load.

Safety Measures

The Sela Tunnel has been designed with state-of-the art safety systems that conform to the strict IRC standards as laid out in Special Publication-91 dealing with Tunnelling Projects. It has a Supervisory Control and Data Acquisition System, commonly known as SCADA that quickly gathers and analyses the real-time data.

The data is gathered through a supervisory system comprising CCTVs, Incident Detection System, Fire Detectors and various instruments for measuring visibility and gas concentrations within the tunnel. The data gathered is fed to the control rooms established at the mouth of each tunnel and based on the analysis, the alarm system comprising automatic fire alarms, fire extinguishers and emergency lighting get activated.

The escape tube in the main tunnel, a notch better that even Atal Tunnel, has been constructed adjacent to the main tunnel with an aim to not only allow movement of pedestrians out of the main tunnel in case of any contingency, but also to permit the movement of emergency vehicles. In addition to the SCADA system, the tunnel has essential equipment for communication and traffic regulation such as emergency telephones, PA system, lane signals, variable text signs, barriers, emergency, cautionary, prohibitory and informative road signs in place.

Electromechanical and Safety Provisions

The tunnels are being provided with a state of the art electromechanical system including jet fan based longitudinal ventilation system, firefighting devices, CIE norms based illumination system and SCADA controlled monitoring systems.

Though Project had witnessed significant delays in the days of commencement due to COVID conditions, the project picked up pace and is one of the fastest progressing tunnel works in the Himalayan region.

Currently, the tunnel is in the final stages of completion and will be inaugurated and dedicated to the Nation soon.