Short-Delay Blasting

a method of blasting in which the detonation of several explosive charges takes place in a specified sequence over certain intervals of time, usually measured in milliseconds. In short-delay blasting, the initiation of each subsequent charge or group of charges occurs in an area of the rock mass that is under stress as a result of the preceding explosion, thus increasing the useful blast effect. The use of short-delay blasting increases the intensity of fragmentation of the medium by the blast, reduces disruption of the rock mass outside the crushing zone, provides localized disintegration of the rock mass, and decreases the seismic effect of the blast. In addition, short-delay blasting makes possible control of the direction of movement of the crushed rock, providing collision and additional crushing of the fragments. In shafts with hazardous gas and dust conditions, short-delay blasting makes possible the firing of an entire set of blast holes in one stage instead of several, with instantaneous blasting (charging and blasting of sumper holes and ventilation, charging, and blasting of auxiliary holes).

Short-delay blasting is performed by means of short-delay electric detonators or, when blasting with a detonator fuse, by means of pyrotechnic delay mechanisms (relays). Single-row and multirow short-delay blasting arrangements are used. The principal single-row short-delay blasting arrangements are sequential row blasting, in which the charges are detonated one by one from one end to the other, and consecutive-counter blasting, in which the detonation proceeds from the center of a row toward its flanks, providing head-on collision of the fragments and formation of a pile against the center of the face. In cases of a large face, the method can be repeated, forming several collision centers along the front (wave arrangement). The principal types of multirow short-delay blasting are sequential row blasting, in which the charges are detonated consecutively from one flank with the same delay interval (for example, 20 milliseconds between charges and, so that the moments of detonation of adjacent charges do not coincide, 30 milliseconds between rows); row blasting (parallel to the front of the face), in which the charges in each row are detonated simultaneously and the rows of charges are set off in sequence, starting from the face and going deep into the rock mass; diagonal row blasting, in which the rows of the simultaneously detonated charges are arranged at an angle to the front of the face; transverse row blasting, in which charges are detonated simultaneously in rows perpendicular to the front of the face and the rows of charges are detonated one after the other, beginning from the central row, called the cutting row; wedge blasting, in which rows of simultaneously detonated charges are arranged diagonally and are detonated sequentially from the center of the face toward the flanks; and trapeziform blasting, which is similar to wedge blasting but with a trapeziform configuration of the rows of simultaneously detonated charges. The last two methods provide the best fragmentation and heaping up of the rock mass. Short-delay blasting is widely used in mining (for breaking out minerals and sinking mine-shafts) and construction (building of dams and canals; deepening rivers).

The idea of short-delay blasting was first put forth and realized in the USSR by the engineer K. A. Berlin in 1934 during the sinking of a mineshaft; later, it was introduced in the USA (1945) and Great Britain (1949).