India builds safest and longest tunnel with integrated tunnel control system

chenaninashri-tunnel

Chenani Nashri Tunnel (also known as Patnitop Tunnel) in Jammu and Kashmir will be the country’s first tunnel with a world-class integrated tunnel control system (ITCS), where ventilation, fire control, signals, communication and electrical systems are automatically activated. The ITCS software platform will be a dedicated traffic SCADA (supervisory control and data acquisition), including traffic security system for the traffic control management of the tunnel. The system integrates the management and monitoring of all subsystems involved in traffic control. It allows for takeover in case of manual failure, and has two backup power systems, one at each end of the tunnel.

Safety features such as installation of SOS box, PA system and FM systems, lighting and ventilation systems, monitoring through CCTV cameras, fire extinguisher and fire-fighting system, cross passages for safe evacuation in case of fire, road signage, and speed limit and overtaking restrictions have been installed inside the tunnel. The tunnel has been designed to fight a 30-MW fire, i.e., fire caused in a fully loaded truck. There are fire hydrants at every 150 m (meter); in case of fire, the ventilation system is suitably regulated to extract the smoke to facilitate the safe evacuation of the users through the escape tunnel. At both portals, there is a pump room with a jockey pump, main electrical pump and backup diesel pump for supply of water at high pressure to hydrants installed inside the tunnel.

Maintaining air quality
There is a ventilation system at every 600 m. As soon as the air quality is below prescribed norms, the ventilation fans start functioning automatically. Air quality is monitored by 14 CO cu m (cubic meter) opacity sensors installed in the main tunnel. The project has installed five air velocity sensors across the main tunnel that provide real-time updates about the longitudinal air direction and its velocity. The air velocity is then controlled by automatic actions of banana jet fans in the event of fire so as to contain it in the shortest length of the tunnel.

Eight banana jet fans of 37 kW capacity have been installed in the main tunnel, while eight axial fans of 710 kW each (four at each portals) have been installed in the ventilation building. Of the eight, four are used for supply of fresh air inside the main tunnel and the other four as exhaust fans for extraction of smoke. There are two pressurization fans of 37 kW at each portal face in the escape tunnel. The project has adopted a fully transverse ventilation system. The air is circulated inside the tunnel via two separate ducts housed above the slab of the tunnel. One duct is for transmitting fresh air inside the tunnel through openings or dampers placed 8 m apart. The other duct is used to extract polluted air and smoke from the tunnel through openings or exhaust dampers placed 100 m apart. These exhaust dampers are motorized and can be opened and closed using the ITCS.

Preventing seepage
Waterproofing membrane has been provided before provision of final concrete lining with channelization of seepage water to the underground drainage system to prevent seepage in the tunnel. Further, central drainage has been placed throughout the tunnel to drain out the underground water collected from the subsoil PVC pipe of 75 mm behind the concrete lining, i.e., rock surface. There is also surface drainage to drain out the surface water along with the man holes. Also, for the fire-fighting hydrants, two water tanks with the capacity of 1.5 lakh liter, one at each portal, have been constructed. Further, a total of 124 CCTV cameras have been installed in the main tunnel.