POWER, WATER & STORAGE | SECTOR
grouting. Unfortunately, the initial launch cavern was not effective to allow for the launching of the TBM and a total delay of six years was realised before the TBM broke into bedrock, after 200m (Kahli and Potnis, 2023). Figure 10 presents the TBM portal area during the
initial excavation in 2016, when partially consolidated river deposits with boulders were discovered without bedrock. The TBM comprises a specially designed Terratec
9.0m-diameter double shield universal (DSU) TBM, and the tunnel lining is formed of 350mm-thick precast concrete segmental rings. The shield design was targeted to improve the TBM’s capability to advance through squeezing/converging rock formations under high cover. It includes a telescopic joint design (allowing the machine to operate in double shield mode in very weak rock), and capability to investigate and treat the ground around and ahead of the face (Grandori, 2016). Geology along the headrace tunnel alignment
comprises predominantly slates with dolomitic limestone. TBM excavation finally commenced in July 2023 and since April 2024 has progressed consistently at about 11m/day or 365m per month.
5.2 Pakul Dul, India The 1000MW Pakal Dul hydro project is under construction and includes twin, 7.5km-long headrace tunnels. Construction of the headrace started in November 2023. Two Herrenknecht 7.2m-diameter, single shield TBMs are being used for the excavations. Tunnel lining is precast concrete segmental rings. Geology along the headrace tunnel alignment
comprises mixed quartzites, phyllites, schists, and gneissic granites. Figure 11 presents the TBM at the starting portal platform. TBM launching and assembly took place in a limited area. TBM progress has been exceptional. Recent progress,
to early 2025, was of 46.6m on the best day and 630m in the best month. The success of the technical evaluation to use a TBM for the Pakal Dul project, along with the
TBM procurement, has been attributed to comprehensive risk management practices with all stakeholders (Armetti and Panciera, 2023).
6 PROPOSED TBM HYDROPOWER TUNNELS IN THE HIMALAYAS A TBM is to be used on a new major project including the 285MW Upper Tamor Hydropower Project, in eastern Nepal. Upper Tamor includes an 8.7km-long, 7.2m-diameter headrace tunnel. The headrace tunnel bore would be the third time
use of the same TBM in Nepal, for a total of 32km, and also the first use of a TBM for a private hydropower project in the country. The formal contract for the works was signed in mid-2025 with Robbins and also the contractor who constructed both the headrace tunnels at Bheri Babai and Sunkoshi-Marin Multiple-Purpose projects in Nepal. Figure 12 presents the longitudinal profile for the proposed Upper Tamor headrace tunnel. In addition, the Melamchi Water Supply Project -
Phase 2, in Nepal (that includes a mini-hydro station) has the 8.9km-long Yangri Tunnel under maximum cover of 1700m. The tunnel has been evaluated for TBM bored tunnelling, given that there is no possibility for an intermediate access adit and with difficult portal locations for access (Brox, 2022). Figure 13 presents the longitudinal profile for the proposed Yangri Tunnel.
7 OTHER RELEVANT TBM PROJECTS IN INDIA 7.1 Rishikesh-Karanprayag Rail Tunnel Project The Rishikesh-Karanprayag rail project has been in construction in the Himalayan foothills since late 2022 and includes two tunnels (upline and downline) of lengths 10.5km and 10.3km, respectively. The area is dominated by metamorphic rocks,
including schists, gneisses, and quartzites. Twin, 9.1m-diameter single shield TBMs have been used in conjunction with precast concrete segmental lining to construct the tunnel. The TBMs were specificallydesigned with accessories for overcoming the risks of squeezing conditions and include a cutterhead torque box, high thrust rams, and shield void measurement system. Progress to date has achieved an average of 630m per month with a maximum of 555m, with sustained daily progress from 12m-18m (Cooper, 2025).
7.2 AMR and Veligonda Water Transfer Projects The Alimineti Madhava Reddy (AMR) water transfer and supply project comprises a single, 10m-diameter, 46km-long tunnel located in southeast India, in the state of Andhra Pradesh. It is to transfer water below a Tiger Reserve from the Srisailam Reservoir to an area of farmland to the north. In addition, the Veligonda water transfer and supply
Above, figure 11: TBM assembly at Starting Portal
project comprises 19km-long tunnels of 7.9m and 10m diameter, respectively, located immediately south of the AMR project.
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