Numerical Modeling of Subsurface Blasts

摘要

When an explosion occurs on or below the ground surface, a phenomenon known as "ground shock" immediately follows. Ground shock is the propagation of compressive, shear, and tensile waves through earth media. Peak ground shock propagation in an earth medium is a complex function of the dynamic constitutive properties of the soil, the detonation products, and the geometry of the explosion. Due to the complexity of this type of problem, prediction of displacement and particle velocity and acceleration in the earth media resulting from a blast can be a very difficult task. The state-of-the-practice for describing and predicting these blast response parameters utilizes empirical formulas. These empirical formulas typically represent the earth medium as a homogeneous, isotropic mass and thus characterize the blast response within the medium using basic measures of linear elasticity. Unfortunately, natural earth deposits are seldomly isotropic, homogeneous masses and due to the large strains associated with a ground shock loading event, the dynamic response of the mass cannot be adequately described using linear elasticity. This paper presents the results of a study that evaluated the performance of a finite element model developed to predict peak particle velocity and pressure for free-field blast conditions. The influences of domain size, boundary conditions and the damping coefficients on the model performance were analyzed and the results are presented. The results of the numerical model were compared against case histories where empirical equations and monograms were developed to relate dynamic properties of soils to ground shock predictions. Finally, the influence of the soil constitutive model used in the numerical model is presented.