SECTOR | POWER, WATER & STORAGE
Above, figure 4: Inclined Pressure Shaft by TBM PHOTO CREDIT: GAMMON INDIA
Difficult tunnelling conditions were encountered
after about one year of TBM excavation. At about Ch. 9000m there was instability of a wedge block at the face of the TBM, which resulted stoppage of the machine. There was inrush of groundwater and fines up to rates of 800 l/s, and failure of a portion of the erected precast concrete tunnel ring. A 180m-long bypass tunnel was constructed, by
drilling & blasting methods, around the TBM to reach the front of the shield and rehabilitate the area. After a total downtime of about eight months, TBM boring continued. Second and third entrapments of the TBM occurred, in early and then in late 2012, after another 3000m of excavation, and prior to Ch. 6000m. All of these significant TBM stoppages appear to have
occurred near the intersection of inferred fault/fracture zones with very acute angles to the tunnel axis. The entrapment mechanism has been presented as a result of sub-vertical faults (Brandl et al., 2010 and Millen and Brandl, 2011). The TBM has remained trapped since 2012.
3.4 Kishanganga, India The 330MW Kishanganga hydro project includes a 23.7km-long headrace tunnel and was the fourth such tunnelling project in the Himalayas to use a TBM. The shield was used on a 14.75km-long portion of the headrace. Construction of the headrace tunnel commenced
in April 2011 and was successfully completed in June 2014 (after 38 months) – the first fully successful use of a TBM on a Himalayan hydro project, in entirely completing the planned portion of headrace, and therefore marking a turning point in major mountain range tunnelling. Mixed geology was present along the headrace tunnel
alignment comprising andesites, phyllitic quartzite and meta-siltstones and sandstones of variable rock quality and strength. The 6.2m-diameter double shield universal (DSU)
TBM was fitted with 483mm (19”) cutters and erected a 350mm-thick precast concrete segmental tunnel lining.
Above, figure 5: Complex geology of Tapovan headrace tunnel SOURCE: NAITANI & MURPHY (2006) 22 | October 2025
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