Deep Impact

By drilling 300m deep pilot holes on the mountain surface Afconians create record for constructing India’s deepest pressure shafts in the Pakal Dul Hydro Electric Project in J&K

After setting the record for constructing the highest single-arch railway bridge in the world in Jammu and Kashmir, Afconians have created another record in the region by constructing the deepest pressure shafts in any hydro project in India. What makes this initiative extra special is the use of Raise Boring Machine (RBM) for the first time in a hydro project in the country. Conventionally, full-face, or, raise-climber methodologies are used for shaft excavations in India. RBMs were introduced because the depth of the pressure shafts exceeded 290m.

Achieving this feat in the rugged terrains of Kishtwar in J&K makes this another piece of Extreme Engineering and Construction by Afcons. Afcons is constructing 1000MW Underground Powerhouse Package for Pakal Dul Hydro Electric Project on the Marusudar river, a tributary of the Chenab River, in Kishtwar district of Jammu & Kashmir. The project consists of construction of underground powerhouse, four vertical pressure shafts of 292m depth each, two surge shafts of 200m, main access tunnel, transformer cavern with others.

Around 300m deep holes have been made in the mountains to construct these deepest shafts. Several challenges had to be overcome like procurement of specialised equipment, extreme geology, and maintaining vertical accuracy from the beginning of the project. Of the four vertical pressure shafts, two have been completed and the remaining are work in progress.

Equipment procurement
Specialised equipment was needed to drill pilot holes (279mm dia followed by reaming of 1.8m dia) as deep as 300m into the hard mountain surface. Afcons deployed a Raise Boring Machine (RBM), which is not available in the Indian market. The procurement was difficult under Covid-19 pandemic and no agency or skilled manpower was readily available for installation and operation of the equipment. Handpicked skilled workers were taught how to assemble the RBM while the team scouted around for specialised operators and finally operators were deployed from Zambia.

Extreme geology
But the challenges were not over yet. “After commencement of the pilot hole drilling, we encountered unforeseeable physical conditions due to change in rock strata and poor geological conditions. Due to the water loss during drilling, it resulted in severe worn out of drill bit and damage to the thread strings of the drill rod,” said Afcons’ project manager Ravindra Singh Chauhan.

During drilling the change in rock strata caused huge vibrations in the machine that led to threads of drill rods getting damaged and the drill bit getting worn out before its designed life of drilling length. “So, it consumed all the arranged spare drill bits and drill rod threads forcing us stop the drilling midway,” Chauhan added.

Subsequently, additional drill rods, bits and reaming cutters were procured from four different countries in January 2022 and the drilling was resumed. “In spite of challenges beyond our control, we were able to complete the drilling in effective time of 62 days. The reaming activity to enlarge the bored hole dia from 279mm to 1.8m, was immediately taken up, and completed in 40 working days,” the project manager said.

Vertical accuracy
Ensuring the accuracy in vertical drilling of 292m depth in poor geological conditions was a rigorous task. But the team managed to drill accurately with a lot of patience and perseverance. “The accuracy achieved is commendable and the final dia of each of the pressure shafts will be 5.4m after the final excavation,” Chauhan said.

“We were able to apply our learnings from the first pressure shaft and that has helped to plan the remaining ones in a more time-bound manner. The use of the RBM for the first time under poor geological conditions reinforces our extreme engineering capabilities and our ability to innovate under constraints,” the project manager added.

The Pakal Dul Hydro Electric Project will significantly increase power-generation capacity of Jammu and Kashmir. As Afconians, we are extremely proud to contribute towards the social and economic well-being of the people of the region with significant infrastructure development.