Blasting Crater Test for Underground Mine′s Long-hole Caving

For a long-hole mining test in some mine,a series of blasting crater tests were carried out with 12 single-holes and 4 variable distance holes laid out in a mining tunnel which has the similar rock property with the mining stope in that mining test.Characteristic curve of blasting crater for the emulsion explosives used,the relationship between blasting crater volume and charge embedment depth,the relationship between crater radius and charge embedment depth,the optimum and critical embedment depth for the blasting crater and blast fragmentation have been discussed.It is obtained from the tests that the optimum and critical embedment depth for blasting crater are 1.09 m and 1.65 m,the optimum blasting crater radius is 0.79 m,the optimum blasting crater volume is 0.37 m3,the hole spacing is 1.9 times of the optimum blasting crater radius,with an average 58.4% of blast fragmentation up to grade.Results show that blasting crater test is still of important guiding significance in long-hole blasting practice.