Method of excavating rock caverns by blasting

A method of blasting an essentially elongated rock cavern tunnel, or shaft, preferably with a large cross-sectional area, comprising driving at least one drilling drift in the longitudinal direction of the cavern, drilling from said drilling drift first drill holes in successive planes extending transversely to the longitudinal axis of the intended cavern, charging and blasting in said first drill holes for excavating said cavern layer by layer,

• said drilling comprising drilling said first drill holes in an essentially ring or fan-shaped pattern and partially outside the intended contour of said cavern, inserting rock strengthening means beyond said contour in said drill holes prior to blasting, whereby the cavern obtains such a degree of stability that work for reinforcing walls and roof subsequent to blasting can be carried out within the cavern, or that the cavern can be used for its intended purpose, for example for storing liquids, without any further reinforcement works following the removal of the blasted rock, and
• drilling from a previously excavated part of said cavern, second drill holes along said contour of said cavern in its longitudinal direction to a depth approximately equal to the distance between every two of said successive transverse drilling planes, and using said second holes for presplitting the rock along said contour of said cavern before the round, or smooth blasting of the roof and walls of said cavern concurrent with or subsequent to the round.