Cavity Radius Scaling for Underground Explosions in Hard Rock

Abstract

The main objective of this study was to examine the relationship between the explosive yield and the cavity sizes for chemical explosions in granite. We performed borehole studies in the two cavities produced by chemical explosions in Vermont, including the caliper, acoustic, and optical televiewer logs. The two irregularly shaped explosive cavities imaged during this study have the equivalent scaled radii of 8.26 and 8.34 m/kt1/3. Comparison of the cavity radii, determined in this study, with historical data from other chemical and nuclear explosions in hard rock (e.g., granite) demonstrates that the cavity radius as a function of yield obeys cube root scaling law. The empirical linear fit calculated for the nuclear cavity radii as a function of yield also provides a good approximation for the chemical cavity radii, even though the mechanisms responsible for the creation of cavities during chemical and nuclear shots are different. The depth dependence of the cavity size in hard rock appears to be weaker than proposed by the classical source theory, although there is not enough data to unambiguously resolve the depth dependence. The experimental field measurements of the cavity sizes (determined from geophysical log measurements) agree with the numerical simulations using the hydrodynamic code GEODYN (Antoun et al. , 2000; Lomov et al. , 2005), which confirm approximate cube root scaling with yield assuming that the quality of the rock mass is similar for all events. Online Material: Composite logs for the boreholes S1‐3, S2‐2, and S2‐4.