Chenani-Nashri Tunnel (Patnitop Tunnel), India, India

The Chenani-Nashri Tunnel (or Patnitop Tunnel) in Udhampur, in the Indian state of Jammu and Kashmir, will be the longest road tunnel project in the country when opened for traffic in 2016.

The 9km long Patnitop tunnel, being built at the foot of the Himalayan mountains, will connect the districts of Chenani and Nashri. Its construction is estimated to cost about INR37.2bn ($723m).

The Patnitop tunnel is a part of the planned four-lane widening of the National Highway 1A (NH1A) between Srinagar and Jammu. The tunnel will act as an alternative to the existing NH1A section, which faces geometris and safety concerns, as it passes through steep mountain terrains.

The highway remains closed for 40 days a year due to bad weather conditions.

The two-line bi-directional traffic tunnel will be an all-weather and reliable road throughout the year. It will reduce the travelling distance from 41km to 10km.

Another 8.45km tunnel between Quazigund and Banihal on Jammu-Srinagar highway is also being constructed as part of INR100bn ($2.2bn) road projects in Jammu and Kashmir.

Indian Patnitop tunnel project specifics

The project involves construction of a single-tube, two lane main tunnel of 13.3m diameter along with a 5m diameter escape tunnel running parallel to it.

The main tunnel will be connected to the escape tunnel through pedestrian and vehicular emergency cross passages at every 300m and 1,200m respectively. It will run in the lower Himalayan mountain range to connect Chenani to Nashri villages.

The horseshoe-shaped tunnel will bypass the four-lane Udhampur to Ramban Section of NH-1A and have two rotary junctions. It will cross through the flyshoid geological formation in the Patnitop range of the Himalayas.

The tunnel will have a maximum overburden of 1,050m. The tunnel will reduce the elevation and hairpin bends associated with the existing highway. The gradient will also be reduced from 4.5% to about 0.5%.

Construction of the Chenani-Nashri tunnel

Construction uses New Austrian Tunnelling method (NATM) technique. Under NATM, the tunnel is sequentially excavated and supported.

The project is of complex nature sd it involves cutting of the Himalayan rocks. Advanced tunnelling and drilling equipment are being used for the project.

Construction of the tunnel began in September 2011 and is expected to be completed by mid-2015. The remote location of the tunnel in the mountain ranges, geology and logistic constraints raise several engineering and management challenges to the contractors.

Trinitrotoluene (TNT) explosions were used during the initial phase of tunnel construction through the hills.

The works will include overall construction of a 10.9km highway. It will include the 9km tunnel, a 50m single span bridge at north portal of the tunnel and a 40m single span approaching bridge at the south portal.

The south section also requires surface works of 1.3km, while the north approaching portal requires 0.6km of embankments and slope cuttings. Other infrastructure will include technological and service buildings, toll plazas, other project facilities and soil dump areas.

Financing India's longest road tunnel project and contractors involved

IL&FS Transportation Networks (ITNL) was selected for four-laning of the 41km NH1A highway (from 89km to 130km, which includes the Chenani-Nashri tunnel) on design, build, finance and operation basis in May 2010.

The concessionaire will receive annuity from the National Highways Authority of India (NHAI) for 20 years. ITNL established a special purpose vehicle Chenani Nashri Tunnelway (CNTL) for execution of the project.

The project is being funded by a consortium of 12 banks led by the State Bank of India, Project Finance Strategic Business Unit.

Feasibility studies for the highway upgrade projects were conducted by NHIA and Louis Berger Group during 2006 and 2007. D2 Consult Prague was a sub-consultant.

ITNL awarded about $570m engineering, procurement and construction lump sum, fixed price contract to Leighton Welspun Contractors for the Patnitop tunnel project in July 2010.

Scope of the contract includes architectural, structural, civil, electrical and mechanical works, SCADA, lighting and ventilation, fire protection, traffic control, video surveillance, emergency call and communications works.

GEODATA is providing the detailed design and construction supervision for the project.