Chenani-Nashri Tunnel, the longest road tunnel in India: the "Himalayan challenge" for design in heterogeneous rock masses

The 9 km long Chenani-Nashri Tunnel, currently under construction, is the longest road tunnel in India and is part of the planned four-lane widening of the NH-1A between Udhampur and Banihal in the state of Jammu and Kashmir. Bypassing the existing NH-1A from km 89 to km 130, the tunnel crosses a sub-Himalayan formation with a maximum overburden of 1,050 m. With an escape tunnel running parallel to the main tunnel, excavation is performed by Leighton-Welspun Contractors using the drill and blast method. Geodata Engineering (GDE) is providing consultancy services for detailed design and construction supervision including 3D-geotechnical monitoring. Back-analyses of already-excavated sections are performed to better understand the behaviour of the heterogeneous rock mass in which the tunnels are excavated. The numerical models are fed with the actual geological and geomechanical conditions encountered during excavation and the monitoring results. The 3D-monitoring system, specially implemented by GDE for this project, has played a key role in understanding the real rock mass behaviour, allowing the highlighting of potential risks, selecting the correct tunnel support class, checking of the effectiveness of countermeasures, identification of the tunnel stretches in which the final lining needs to be reinforced and providing cost-effective solutions to speed-up the construction process.