Boring by TBM of Inclined Pressure Shaft Planning and Infrastructure

Parbati HEP, Stage-1 (800 MW) is located in lesser Himalayan zone. The project is situated in Kullu district of H.P. The project is located on Parbati river and comprises of 85 m high concrete dam and a concrete lined head race tunnel of 6m diameter and of length 31.6 km on the left bank of the river. This tunnel carries water to surface powerhouse located on the right bank of Sainj river. From the head race tunnel, the water is carried to powerhouse through two numbers of inclined pressure shaft, each of 1542 m having a bored diameter of 4.8m and finished diameter of 3.5m. The pressure shaft is totally lined by high grade steel to bear the high pressure. A surgeshaft of 17m diameter and 130m depth is to be constructed to take care of the surge. The surge shaft is also having two surge galleries. With two inclined pressure shafts @ 48m c/c (inclined at 30 degree to horizontal), with an excavated diameter of 4.8m will be excavated by TBM. This TBM has been specially selected to work in inclined tunnel having precautionary measures like anti-back slip device, auxiliary thrust cylinder. The excavated tunnel will be simultaneously lined with the honeycombed precast segments. This paper illustrates/elaborates the meticulous and flawless planning along with the enormous infrastructure required to be done for the successful completion of inclined tunnel of such a large length for the first time in India.