Tunnel T-49 of USBRL, Jammu & Kashmir, India

The Project which is part of the strategic USBRL line, connecting the Kashmir Valley with the rest of the Indian railway network, consists in a 38.5m2 Main Tunnel of approximately 12km long, including 625m of double track (80m2 area) near Khari station, becoming the longest railway tunnel in India at the time of its completion. Along with the Main Tunnel, a parallel escape tunnel interconnected by cross passages every 375 meters and 4 underground substation caverns. The long length of T-49 demanded the excavation of 3 adits for the simultaneous excavation of the various mining fronts.

T-49 excavation was strongly affected by squeezing phenomena over more than 300 meters caused by a combination of relatively low overburden in a strongly tectonic metamorphic formation with low rock strength and intercepted by a sub-parallel shear zone. Significant heterogeneous deformation led to required reprofiling works after stress stabilization. The decision for the staged excavation (heading & benching) associated with consolidation cement grouting ahead of the tunnel face, drainage works and the use of steel ribs with pipe roofing umbrella revealed successful.