Experience with drilling-blasting work at the Ust'-Ilimsk hydroelectric plant (Russian Soviet Federated SR)

Conclusions

• 1. Horizontal rock contour blasting to a depth of 2 m permits obtaining a horizontal surface without visible defects as well as without internal defects susceptible of being detected by means of drilling tests.

• 2. Horizontal contour blasting may be recommended as a means for reducing the volume of work required for hand mucking of the protective layer at those sections in which elapsed time between preparation of the surfaces and placing of the concrete is insignificant and there is no danger that the rock exposed by the contour blasting will be disturbed by weathering processes or by lateral rebound.

• 3. The tests conducted indicate that by reducing the blasting hole charges it is possible in different cases to eliminate the borehole finishing of the protective layer.

• 4. The investigations on the state of the rock mass indicated that the zone of disturbance for both borehole and blasting hole charges of normal length is equivalent to 10–11 charge diameters for diabases.