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|Title:||Operation Prairie Flat. Project LN302, Earth motion and stress measurements|
|Authors:||United States. Defense Nuclear Agency.|
Murrell, Donald W.
Prairie Flat (Operation)
|Publisher:||Weapons Effects Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Technical report (U.S. Army Engineer Waterways Experiment Station) ; N-72-2.|
Abstract: The objectives of this study were to measure and interpret the earth motions and stresses produced by the Prairie Flat 500-ton TNT detonation. Acceleration, particle velocity, and soil stress gages were installed to measure the ground motions and stresses encompassed by the 2,000- to 10-psi predicted airblast overpressure region (84 to 1,150 feet from ground zero) and depths below the ground surface of 1.5 to 30 feet. Time histories of all successful measurements are included in Appendixes A and B. Ground shock arrival times indicated the occurrence of outrunning ground motion at a distance of about 560 feet, or the 35-psi pressure level. Peak vertical particle accelerations varied from 1,200 to 1.9 g's at the extremes of the instrumented region, attenuating sharply with both distance and depth. Peak acceleration to peak overpressure ratios, used as a basis for correlation, were observed to be both pressure and yield dependent, increasing with lower pressures and higher yields. Vertical particle velocities varied from 84 to 0.33 ft/sec over the area instrumented, also attenuating rapidly with distance and depth. Vertical velocities were also correlated on the basis of velocity to pressure ratios, and the ratios were again observed to be pressure and yield dependent. Peak horizontal velocities were found to vary from about 20 to 0.3 ft/sec over the same region, with little or no attenuation with depth. These velocities were compared with those obtained on Distant Plain Event 6 by means of cube-root scaling, and excellent comparability was noted. Both horizontal and vertical displacements were calculated from measured accelerations and velocities. Peak transient displacements were 20 feet upward and 20 feet outward at the 84-foot range and 1.5-foot depth. The upward displacement attenuated more rapidly with distance, so that at 400 feet it was only one-half of the outward displacement. Soil stress measurements were generally of poor quality from a signal-to-noise standpoint. Data at the 1.5- and 30-foot depths, where good measurements resulted, were exceptions. Vertical stresses at the 1.5-foot depth averaged 40 percent of the surface overpressure.
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