Seismic characteristics of cavity decoupled explosions in limestone: An analysis of Soviet high explosive test data

Abstract

During the summer of 1960, Soviet scientists conducted a series of high‐explosive, cavity decoupling tests in a mine in Kirghizia. These decoupled tests were carried out in a variety of mined cavities in limestone, including spherical cavities with diameters ranging from 3.5 to 10 m as well as nonspherical cavities with volumes of about 25 m3. The experiments of this test series consisted of 10 tamped and 12 decoupled explosions having yields of 0.1, 1.0, and 6.0 t, and seismic data were recorded at locations in the mine over a distance range extending from about 10 to 250 m from the sources. These data provide valuable new insight into the dependence of decoupling effectiveness on variables such as cavity volume, cavity shape, and charge emplacement geometry. In particular, analyses indicate that chemical explosions at a depth of 290 m in limestone are essentially fully decoupled in spherical cavities with scaled cavity radii larger than about 27 m/kt⅓ and that the low‐frequency decoupling effectiveness under such conditions is approximately independent of cavity shape for roughly cylindrical cavities with length‐to‐width ratios of as much as 6–12. These results suggest that the possibility of cavity decoupling in nonspherical cavities in hard rock media will have to be carefully evaluated in establishing the seismic verification regime for the Comprehensive Test Ban Treaty.