Stemming Ejection and Burden Movements of Small Borehole Blasts.
Paper in Second Internatl Symposium on Rock Fragmentation by Blasting Keystone Colorado Aug; :7 pages
The types and amounts of stemming material that are desirable in underground metal and nonmetal mine blasting to improve fragmentation while containing the hot gases are largely unknown. U.S. Bureau of Mines researchers examined the effectiveness of differing lengths of stemming by measuring stemming ejection times as related to burden movement. Test blasts at two surface limestone quarries were evaluated using high-speed photography. Cooling of explosive gases was calculated assuming adiabatic expansion as the gas worked its way into the fractured burden region. For the conditions of these tests, a stemming length of at least 26 charge diameters was found to prevent premature stemming ejection. In tests with stemming lengths of 16 charge diameters, the stemming was effective, but there was early venting of hot gases through fractures in the rock.
Paper in Second Internatl Symposium on Rock Fragmentation by Blasting, Keystone, Colorado Aug.23-26