The T-48 Tunnel is part of the railway line linking the cities of Udhampur and Srinagar. The tunnel length is 10'250 m, including the two portals and the cut&cover section of approx. 70 m at the north portal. The gradient is 1.25% in straight and 1% in the curves. The layout comprises the single track railway main tunnel (internal section 40 sqm) and the parallel escape tunnel (internal section 18.4 sqm). Pedestrian cross passages are foreseen every 375 m (internal section of 9.2 sqm, 18.4 sqm for drivable ones equivalent to the escape tunnel). The overburden varies within the few tens of metres at the north portal up to 1'150 m in the central portion.
The major part of the tunnel shall be excavated in phyllite and quartzitic phyllite with possible presence of gypsum bands. Fault crossing cannot be excluded.
At approx. 2 km from the south portal, the overburden drops from 400 m to 80 m due to the crossing of a gorge.
Because of the geological conditions and the scarce information along the central tunnel section, drill&blast method was preferred. The excavation and support measures definition is done according to the observational method.
The suitability of the selection is constantly checked by means of the monitoring system and alarm limits defined according to the expected behaviour as evaluated by the geomechanical analyses. The calibration of the parameters on the base of the real behaviour is not excluded.
At present, approx. 15'000 m of excavation (corrisponding to 75%) has successfully been carried out from the various fronts and aroung 7'000 m of final concrete lining (35%).