POWER, WATER & STORAGE | SECTOR
Above, figure 6: Kishanganga headrace tunnel profile SOURCE: SWANNELL ET AL
The success and timely completion of Kishanganga
headrace tunnel is fully attributed to the experience and competence of the TBM tunneling contractor. The TBM typically achieved an overall average
progress rate of 12.5m/day or about 400m per month, with a maximum monthly progress of 816m. The shield was specifically designed by the TBM
tunnel contractor (Seli) based on extensive experience in difficult tunnelling conditions and including key design features to allow for de-risking and continued advance through challenging conditions. Figure 6 presents the longitudinal tunnel profile where
the maximum cover was 1400m and therefore there was a recognised risk of squeezing ground.
4 RECENT TBM HYDROPOWER TUNNELS IN THE HIMALAYAS
4.1 Bheri Babai Multi-Purpose Project, Nepal The 47MW Bheri Babai Multi-Purpose project was the first use of a TBM in Nepal. It was used for the construction of the entire 12.2km-long headrace tunnel. Construction of the headrace commenced in April
2017 and was completed in April 2019 (18 months - 12 months ahead of project schedule) and typically achieved an overall average of 24m/day or about 712m per month but with a maximum monthly progress of 1202m using a 5.0m-diameter Robbins double shield
TBM with 483mm (19”) cutters and erecting a 300 mm- thick precast concrete lining. The TBM-driven tunnel was completed one full year
ahead of schedule and, notably, the excavation passed without any delay through the Main Boundary Thrust fault, recognised to be the key construction risk for the project. A single delay of five days only was experienced due to uncemented sedimentary bedrock, requiring construction of a bypass tunnel to free the front of the TBM. Figure 7 presents the space required for the assembly
and launch of the TBM at the Bheri Babai headrace tunnel.
4.2 Sunkoshi-Marin Multi-Purpose Project, Nepal The 39MW Sunkoshi-Marin Multi-Purpose project was the second use of a TBM in Nepal for the construction of the entire 13.3km-long headrace tunnel. Construction of the headrace tunnel started in
October 2022 and was completed in May 2024 (19 months) and typically achieved an overall average of 25m/day (maximum 67m/day) and about 750m per month with maximum progress of 1224m. The same Robbins TBM from the Bheri Babai project was used, with the cutterhead enlarged to 6.2m-diameter and equipped with 483mm (19”) cutters. The precast concrete segmental lining had a thickness of 300mm.
Above, figure 7: Portal for assembly and launch at Bheri Babai PHOTO CREDIT: ROBBINS October 2025 | 23
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