Calculation of Ground Shock Motion Produced by Airburst Explosions Using Cagniard Elastic Propagation Theory

摘要

This report describes a study which used elastic wave propagation theory to predict ground motion produced by airburst explosions of spherical charges. The air-earth environment was treated as three elastic layers (air, soil, and rock) separated by plane parallel boundaries. The explosion was approximated by a point source in an elastic fluid. The exact, closed form integral solutions of L. Cagniard for the reflection and refraction of spherical waves in elastic solids were extended to model the ground shock propagation in layered earth. Nonlinear empirical airblast arrival time and pressure source waveform formulae were developed and were used as source inputs for the elastic calculations. A computer code CAGGS was developed to evaluate the integral solutions to produce ground shock particle velocity waveforms. Calculations were compared with experimental records, for soil-soil, soil-rock, and rock sites. At gage locations where the airblast overpressures are less than approximately 40 psi for weak soils and over 100 psi for strong rocks, these comparisons show generally good agreement in the important characteristics amplitude, pulse shape, and arrival times. The results of the study indicate that the CAGGS code can be a valuable tool for studying the basic characteristics and effects of the controlling parameters of ground shock in layered earth media. (Author)