stemming

in blasting operations:

(1) The process of filling the empty part of a charge case, such as a blasthole or well, with an inert stemming material (sand, gravel, or clay) to retain the products of the detonation of an explosive charge in an enclosed space. Blastholes and wells are stemmed mechanically by pneumatic rammers and stemming machines. Stemming is performed after the charging operation is completed.

(2) The material used in charge cases to insulate an explosive charge. Friable materials that are inert to the action of an explosion and are sufficiently hard and have a high coefficient of internal friction are usually used for stemming. In blast-holes, the best stemming materials are crushed stone chips (with water filling the spaces between the grains), coarse sand, water-filled plastic ampuls, and fast-hardening concretes. In shafts in which there is a gas or dust hazard, various types of pulp and paste stemming materials are also used. Stemming made of finely crushed chips (to 20 mm) and siftings from crushing and sorting plants is used in wells. Water stemming of well charges is less effective, since its ejection resistance decreases sharply with an increase in diameter. Stemming made with pieces of rock no larger than 300 mm is advisable for case charges. Stemming increases the resistance to the escape of gaseous detonation products from the charge case, as well as the duration of application of the explosion energy to the performance of efficient crushing work or the removal of rock to a particular distance.

The length of the stemming may be only 8–10 times the diameter of the blasthole or well when the most effective materials and the most efficient explosive charge arrangements are used. In shafts with gas and dust hazards, the length of the stemming is governed by the Safety Regulations.