Contour Blasting

a method of blasting in which the actual profile of underground mine workings or excavations is as close as possible to the projected profile, with preservation of the surrounding rock. It is used in mining during the development stage and in hydraulic-engineering and transportation construction during the building of tunnels and chambers in rock walls. There are two types of contour blasting: preliminary shaping and subsequent shaping. In preliminary shaping explosive charges are set off in peripheral blast holes, followed by the main charges, which are spread throughout the entire working area. In subsequent shaping, charges in blast holes located along the periphery are exploded after the detonation of the charges in the main set of holes.

The advantages of contour blasting are a reduction in the volume of rock ejected from the projected profile; an increase in the stability of the slopes of benches, cuts, and workings, making possible a reduction in their maintenance and repair costs during the period of use; and a decrease in the cost of materials for the erection of supports (in sufficiently strong rock, the more economical spray-concrete supports may be used successfully).

The disadvantages of contour blasting are a certain increase in the volume of drilling work and the necessity for more rigorous checking of the position and direction of holes during the drilling process.

Contour blasting is widely used in the USSR, Sweden, the USA, and Canada.