Operation MINE SHAFT, MINERAL ROCK Event : far-out ground motions from a 100-ton detonation over granite
Murrell, Donald W.
Technical reportAbstract: The objectives of this study were to measure all ground motions in the outrunning region produced by the Mineral Rock Event of Operation Mine Shaft. The Mineral Rock Event was a duplication of the Mine Ore Event of the same series, and was a 100-ton sphere of TNT placed with the center of gravity 0.9 charge radius (about 7.2 feet) above the ground surface. Accelerometers and velocity gages were installed from 200 to 500 feet from ground zero at depths of 2, 10, and 18 feet. Time histories of all successfully recorded gages are presented in Appendix A along with integrals of each record. The outrunning acceleration data were partially obscured by a cable noise problem. This noise was blast overpressure-induced and unfortunately was present during the significant outrunning motion onset, i.e., before air blast arrival at the gage locations. Although these data are limited, they are discussed along with the outrunning velocity data. Airblast-induced motions are treated in detail. Vertical airblast-induced accelerations were found to attenuate rapidly with distance and depth from the maximum downward acceleration of 32 g's at the 200-foot range and 2-footdepth. These accelerations were correlated with overpressure, and, for the 2-foot depth, acceleration-to-overpressure ratios averaged 0.2 g/psi, which is considerably less than for a similar detonation over soil. Vertical particle velocities also attenuated with distance and depth from the maximum value of 1.3 ft/sec at the 200-foot range and 2-foot depths. Horizontal velocities followed much the same pattern, with a peak value of 2 ft sec at the same location. Outrunning motion was noted on all horizontal velocity gauge records. For the vertical component, outrunning motion was not apparent at the 250-foot range, but was of significant magnitude at the 500-foot range. Vertical downward displacements of a high confidence level were limited to the 250-foot range and were found to be 0.0060 to 0.0075 foot. Horizontal displacements were successfully computed from acceleration and velocity records, and at were three to four times as large as the vertical at the 250-foot range were three to four times as large as the vertical displacements.
Weapons Effects Laboratory (U.S.)Engineer Research and Development Center (U.S.)
Detonation; Explosive effects; Granite; Ground motion; Mine Shaft (Series); Mineral Rock (Event)
Technical report (U.S. Army Engineer Waterways Experiment Station) ; N-72-6.
Approved for public release; distribution is unlimited.