Construction of Railway Tunnels in Highly Adverse Geological Conditions in Himalayas by Using NATM – A Case Study

Tunnel T-48 the railway tunnel, is one of the main stretches of the 273 km long Udhampur – Srinagar- Baramullah, a new broad gauge rail project in the state of J&K, India covering a length of 10.2 km comprising the Main Tunnel and the Escape tunnel of 10.20 km length, each of which are required to be bored with 7.12m and 4.5 m of finished diameter respectively.

Presently the tunnels- comprising 6 faces out of total 10 faces, i.e., 4 faces from Adit-1, 4 Faces from Adit-2 and 2 faces from North Portal -are under construction in accordance with the principle of New Austrian Tunnelling Method (NATM). The remaining 4 faces from Adit-2 are yet to be opened. Despite the very heterogeneous geological conditions, i.e., frequent changes of massy and completely fractured rock, and with partial high water ingress, the work is progressing without prolonged excavation related interruptions and delays. Tunnelling is a challenge on this stretch in the face of multifarious problems owing to extremely difficult and inaccessible terrain, compounded by technical problems and adverse security concerns.

These prestigious tunnels are driven by conventional mined tunnelling methods, such as drill and blast and also by the most modern equipments like telescopic boomers, Schaeff loader, Volvo tippers, CIFA Shotcrete machines, Side tilt Libherr Loaders, Terex Tunnel Loaders,PC-200 Excavators with hydraulic breakers, Transit Mixers and Swing stator Batching plant (60 m³/hr capacity) at each locations.

Notwithstanding the difficult geology, extreme weather situations in winter and the hostile conditions of the area, we have been able to achieve the progress of construction of the tunnel, 24 meter per day.

This paper deals with the planning process, with provisions for advancing with NATM in the very poor geological condition coupled with geological surprises, for and restoration of cavities with pipe roofing, SDR anchors, probe holes and extensive grouting to be followed by erection of lattice girders and shotcreting. The paper also interrogates the problems encountered as a result of extreme weather conditions and poor access available to the site where landslides owing to heavy rainfall during the winter season,are so common. The paper describes how we grappled with the adversities which broke our supply chain and how we overcame the same.