Loose blasting of rocks at quarries of the Petropavlovsk group ofcompanies

Abstract

At present, in most quarries of the Petropavlovsk group of companies, mining is carried out using  hydraulic excavators with bucket capacity up to 18 m3. Hydraulic excavators have mass three times lessthan the mass of mechanical shovels, therefore, given large scooping forces, they lose stability during operation and rotate relative to the front track rollers. The loss of stability complicates operation of excavators and requires fine crushing of rocks by blasting, which forces the increased powder factor, i.e. the increased material costs. In mines of the Petropavlovsk group of companies, experts of AVT-Amur LLC conducted the research aimed at essential increase in delay intervals up to 300 ms. The extended delay intervals during downhole blasting make it possible to increase the total duration of repeated alternating loads on rock mass, including the tensile stresses. The delay of 150 ms or more allows each blast to be directed not toward incipient cracks as with delays of 40–80 ms, but toward the free surface of ope n cracks, which provides a blasting muck pile almost within the limits of the block at minimal scatter of rocks and at the same fragmentation quality. The long-term use of the extended delay intervals of AVT-Amur LLC in mines proves the high quality of fragmentation of rocks by blasting at zero scatter, which enables approach of dump trucks to the block immediately after blasting, without cleanup. Experimental explosions show that blasting with long delays allows an increase in the yield of blasted rocks by 35% at the powder factor reduction by 21%.