Specific blasting technique for tunnelling in hot zones

Abstract

Encountering hot zones while excavating tunnels for hydropower projects in the Himalaya, India, is a challenge for civil engineers. Blasting within the hot rock mass can pose serious threats due to possibility of temperature-induced unintended detonation of explosives. Moreover, the paucity of a suitable rock-blasting method for these hot zones sometimes compels engineers to realign the tunnel. Such a realignment is costly and time-consuming. A temperature of 50-98°C was encountered while excavating the rock mass for head race tunnel of Karchham-Wangtoo Hydro-Electric Project, Himachal Pradesh, India. The Directorate General of Mine Safety, India, suggests that blastholes with temperature greater than 80°C must not be charged and blasted. Similarly, the use of electric or non-electric detonators is discouraged above 70°C because of premature detonation. Hence excavation works were suspended for tunnel construction. A unique drill and blast method has been adopted for blasting the hot strata in the tunnel. The technique described in this study can be easily followed in similar situations for tunnel-rock excavation.