Landmine explosions involve the generation of high velocity granular sprays due to the expansion of explosive gases under a layer of soil and the subsequent interaction of these granular sprays with structures such as the under-bodies of vehicles. This talk will focus on the physics of two separate "fluid-structure interaction" problems: (i) the acceleration of the dense/compacted granular media by high-pressure gases; and (ii) the interaction that occurs when high velocity granular media 4 impinge on deforming structures. The phenomena involved in these two problems are investigated by a combination of coupled discrete/continuum and Eulerian calculations along with laboratory-scale model experiments and full-scale blast tests. We shall demonstrate via both laboratory-scale experiments and Eulerian calculations that the interaction of high- pressure gases with water-saturated granular media results in the formation of instabilities similar to the Richtmyer- Meshkov instabilities observed in fluids. This instability causes the dispersion of the granular medium prior to it impacting the structure. On the other hand, dry granular media typically do not display such instabilities and the role of the granular friction angle in governing this behaviour will be discussed. Laboratory-scale experiments and coupled discrete/continuum calculations will be presented to reveal the underlying physics of the interaction of high velocity granular sprays with deforming structures. The loading by the granular media will be shown to be primarily inertial with pressure and loading time being the two parameters that fully characterise the loading. This understanding will be used in conjunction with numerical calculations to design sandwich structures that significantly outperform their equal weight monolithic counterparts. Laboratory-scale granular impact experiments and full-scale blast tests will be presented to demonstrate the efficacy of these predictions.