The influence of water, dry sand, and unsaturated sand constitutive behavior on the blast response of a rigid target

• We applied soil mechanics theory and computations to gain insight into target loading from buried explosives.
• Materials with lower yield strength demonstrated a greater propensity toward flow and toward higher target momentum loading.
• Water with no strength produced the highest loading; dry sand with the highest shear strength produced the least loading.
• The strength and target loading for partially saturated sand were intermediate between those of the other two materials.
• Less important factors were those associated with compressibility and initial bulk density.

A combination of soil characterizations, computations and small-scale experiments were performed in order to better understand the behavior of shallow-buried explosives. The constitutive behavior of the soil was determined using a combination of high pressure quasi-static tests and effective stress theory; the motion of rigid objects impacted by the material flow resulting from blast experiments was measured by use of high-speed digital video photography. Computations that simulated the blast experiments were performed by use of an arbitrary Lagrangian Eulerian (ALE) treatment in a nonlinear finite element code. We used a factorial design approach to deduce the underlying mechanics of such systems. Using this approach, we found that, for water and for dry and partially saturated granular materials lower deviatoric yield strength was a key factor which caused sand or water to flow more readily thereby producing higher levels of momentum loading to bodies in close proximity to the buried explosive. We found that higher bulk stiffness and mass density were moderately important factors although they were less significant than was the shear strength of the medium containing the explosive.