PROJECT PRE-GONDOLA II SURVIVAL OF HYPOTHETICAL PREEMPLACED CHARGES.

Stress and particle velocity horizontal and vertical data were obtained from a 140-ton nitromethane row-charge detonation in a saturated clay-shale. The charge row consisted of two 40-ton and three 20-ton charges placed in a row with 80 ft between each charge. The charge line ran S 10 deg. W from the center of the existing Pre-GONDOLA I Charlie crater with the first charge 105 ft from the center. Three sand-filled survival holes 80 ft apart were located in line with the charge row at the south end, the first hole being 105 ft from the closest charge. Gages were placed at depths varying from 60 to 70 ft in the survival holes. The unsaturated sand in the survival holes had a much lower impedance rho c than the surrounding Bearpaw clay-shale. This impedance mismatch resulted in a reflective interface that greatly reduced the incident stress and motion measured at the survival hole gages. Initial peak horizontal velocity, input from charges H and I approximately 60 tons, compares well with the 20-ton charge data obtained from Pre-GONDOLA I and the main gage line of Pre-GONDOLA II. The closest survival hole J appears to have sustained damage, although additional data would be required to assess the extent. The remaining two survival holes K and L appear to have sustained light damage but would be usable. Author