Distant Plain Events 6 and 1A : Project 3.02A, earth motion and stress measurements
Murrell, Donald W.
Technical reportAbstract: The objectives of this study were to measure and analyze the earth motions produced by Events 6 and 1A of Operation Distant Plain. Event 6 was 100 tons of TNT stacked in a sphere, tangent to the ground surface. Event lA was 20 tons of TNT also stacked in a sphere, but detonated on a tower at a height of burst of 29.5 feet. Acceleration, particle velocity, and soil stress gages were installed for both events in order to measure the ground motion. For Event 6, these gages were placed in the region of 2,000- to 10-psi overpressure (49 to 680 feet from ground zero) and at depths of 1.5 -to 30 f'eet. For Event lA, gages were placed between the expected 10,000- and 500-psi overpressure levels (directly beneath the tower to 80 feet away) and at depths of 1.5 to 10 feet. Time histories obtained by this instrumentation are included in Appendixes A (Event 6) and B (Event 1A). For Event 6, ground shock arrival times indicated development of outrunning ground motion at about the 30-psi level. Shock propagation velocities were calculated to be 1,100 ft/sec for the soil layer above the water table and 5,500 ft/sec below it. Vertical particle accelerations for both events were correlated with overpressure. The ratio of acceleration to overpressure for the 1.5-foot depth was about o.4 g/psi at the 1,000-psi level, and increased to 1.0 at the 20-psi level. At depths of 5 and 10 feet, accelerations averaged 20 and 7.5 percent of the shallow data, respectively. Vertical particle velocities at the 1.5-foot depth were also correlated on the basis of overpressure; the ratio of velocity to overpressure varied from 0.03 ft/sec/psi at 1,600 psi to 0.08 ft/sec/psi at 10 psi. Velocities attenuated less sharply with depth than did accelerations. Velocities at the 5-foot depth were about 4o percent of those at 1.5 feet, while those from the 10-foot depth were about 30 percent of those at 1.5 feet. Horizontal velocities were dominated by the cratering-induced motion. These motions attenuated as the -2.7 power of distance. Vertical stresses attenuated more rapid cycle than did the velocities, with stresses at the 5-foot depth averaging 25 percent of those at the 1.5-foot depth. Horizontal stresses measured below the water table behaved similar to free-water measurements, attenuating as the -1.15 power of distance, versus -1.13 power for water. Calculations of shear stress were made for three locations on each shot. Peak values ranged from 40 to 70 psi.
Weapons Effects Laboratory (U.S.)Engineer Research and Development Center (U.S.)
Distant Plain (Operation); Earth movements; Explosion effects; Ground motion; Stress gages (soils)
Technical report (U.S. Army Engineer Waterways Experiment Station) ; N-70-14.
Approved for public release; distribution is unlimited.