Tunnelling |
Precision blasting for tunnels
Blasting techniques used to excavate a diversion tunnel at the Pakal Dam site in India have addressed the challenges posed by complex geological conditions in large-scale tunnelling projects.
methodology and specific techniques employed in the excavation of the diversion tunnel using the drill and blast method. This technique, the authors say, is widely used due
to its adaptability to various geological conditions and cost-effectiveness compared to mechanical methods like tunnel boring machines.
Challenging geology The regional geology of the project area comprises
Above: The Chenab River in Jammu and Kashmir in India. The surrounding geology can be quite a challenge for tunnel construction
NEW RESEARCH HAS INVESTIGATED the blasting techniques used to excavate a large diversion tunnel at the Pakal Dul Dam site in India, which is part of the country’s initiative to enhance hydroelectric capacity. Described as being on the cusp of a significant transformation, Indian hydropower capacity sat at approximately 46,928MW, equating to about 11% of the country’s total installed power capacity, as of March 2024. However, plans are afoot to increase this significantly and by 2031-32 total capacity is expected to reach 67GW. To achieve these targets, Chenab Valley Power
Projects Limited (CVPPL) is set to play a crucial role. Established in June 2011 as a joint venture between the Indian government and regional governments of Jammu and Kashmir, CVPPL is tasked with harnessing the hydropower potential of the Chenab River basin in Jammu and Kashmir. Indeed, CVPPL has been entrusted with the construction of four hydroelectric projects – the Pakal Dul, Kiru, Kwar and Kirthai-II projects which will have an installed capacity of 3094MW on a build, own, operate and maintain basis.
Major scheme Located on the Marusudar River, a main tributary of
Reference
Blasting techniques for excavating a large diversion tunnel at Pakal Dul Dam site by N.K. Bhagat, R.K. Singh, C. Sawmliana & A.K. Mishra, V. Anand & R. Mukhiya. Tunnelling into a Sustainable Future – Methods and Technologies – Johansson et al (Eds) 2025. ISBN 978-1-032-90462-7. DOI: 10.1201/9781003559047-256
the Chenab River in the Kishtwar district, Pakal Dul hydroelectric project is one of the major schemes being undertaken by CVPPL, and the biggest in the union territory of Jammu and Kashmir. The project involves construction of a 167m high CFRD and a horse-shoe shaped diversion tunnel, spanning 12.2m and 847.7m of a total 859.7m excavated in hard rock. Construction of the Pakal Dam will divert water
through a headrace tunnel into the power station on the Dul Hasti Dam reservoir on the Chenab River. This diversion is likely to improve the flow of water available for the dam’s 390MW hydropower plant, potentially enhancing operational efficiency and power generation capacity. Research by Bhagat et al has presented a detailed examination of the
34 | January 2026 |
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predominantly rock of the Kishtwar group and Kibar/ Pipran formation. The Kibar is the oldest formation of the Kishtwar window zone and comprises granitic gneiss, quartzite, and mica schist. While seismicity of the area falls in the zone where events of a magnitude more than or equal to 7 are anticipated. The research focused on the key blasting
techniques which were employed, such as V-cut patterns. As the authors explain, the V-cut pattern is characterised by shorter stab holes and offers several advantages in tunnel blasting. It reduces the requirements for drilling and explosives, as well as the time needed, particularly when dealing with complex geological challenges such as quartz veins and jointed rock masses. This makes it more suitable than the parallel cut pattern for excavating a 12.2m wide diversion tunnel. It’s also compatible with mechanised double boom drilling machines, enhancing efficiency and cost-effectiveness compared to wedge and parallel cuts. The shorter stab holes create initial cavities that facilitate optimal breakage of the first set of V-cut holes. As this study found, the V-cut patterns were effective in achieving an average advance per round of 80.7%, despite challenges such as quartz veins, shear seam, hard rock masses, and four to five joint sets. Bhagat et al’s research also outlined the blast design parameters. These included the use of emulsion explosives and non-electric detonators, to achieve optimal excavation results while minimising overbreak and vibrations. This approach not only enhances the cost-effectiveness of the tunnelling process but also ensures that environmental impacts, such as vibrations near public structures, remain within acceptable limits.
Carefully designed Overall, the research demonstrates that carefully
designed blasting techniques can successfully address the challenges posed by complex geological conditions in large-scale tunnelling projects. Furthermore, the authors say their research contributes valuable insights into cost-effective tunnelling practices for future hydroelectric developments in similar terrains
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