The Influence of Specific Factors Affecting Spall in Explosively Loaded Soil.

Abstract : The purpose of this investigation was to evaluate the influence of explosion yield, soil hysteresis, and site layering on the shape and size of the spall zone due to directly coupled energy from a near surface explosion in soil. The investigation was done numerically on the contractor's HP1000 computer, using the Lagrangian, explicit, dynamic, finite difference computer code, STEALTH. The most important result is the observation that the computed directly coupled spall zone is pear shaped. The directly coupled spall zone size scales consistently with the cube root of the yield in the neighborhood of one megaton yield, and it dramatically reduced by hysterisis. The presence of a hard layer in one calculation had no effect on the maximum directly coupled spall depth on axis, but did increase the apex angle of the vertical cone within which directly coupled spall occurred. The calculations demonstrated conclusively that spall can be studied numerically using the STEALTH computer code. A more extensive numerical study should now be accomplished on a large mainframe computer, in which cratering and spall are investigated simultaneously. The purpose of such a study would be to evaluate the influence of early time source region details, and computational procedural details such as zone size, rezoning, and time step. Keywords: Spall; Ground motion; Nuclear weapon effects; Directly coupled energy.