A concrete lined Head Race Tunnel passing through very weak formations of quartzites and states, red shales and sandstones and claystones in young rocks of Himalayan terrain criss-crossed with thrusts and faults, is a unique engineering feat. The entire tunnel is heavily steel supported. Final concrete lining and grouping were done concurrently with the excavation. In the middle, one kilometre reach of the tunnel, a manifold of three smaller tunnelsinstead of a single one is provided due to poor geographical ground conditions.
The intrathrust zones are founded to be seismically active and special type of flexible lining is provided for seismic movements.
Features :
(a) Head Race Tunnel 7.5m. dia., 5.6 km. long with concrete lining 300mm to 750mm thick.
(b) Manifold of three tunnels of 5m. dia. one kilometre long.
(c) Construction of 7m. dia. D-shaped 150m. long at outlet end.
(d) Construction shaft 5.1m. dia. 66m deep on the bank of river Tons.
(e) Main surge shaft 21m. dia. 46m, deep with riser 12m. dia, 25m. deep, both concrete lined with sand-
wiched steel liner.
(f) Steel lined underground pressure shafts 2 nos. each 5.5m. dia., 82m. long with Y-shaped bifurcations,
and 4 nos. penstocks each 4.11 m. dia; 20m. long.

Underground Excavation 4,85,000 cu.m.
Open excavation 2,35,000 cu.m.
Steel support 20,000 tonnes
Concrete 2,30,000 cu.m.