Experimental characterisation of blast-induced ground shock by high-speed digital image correlation of structural response

Subsurface explosions result in the propagation of stress waves through the soil, known as ground shock. This can damage buried and surface structures in events such as the detonation of unexploded ordnance from previous conflicts or deliberate attack. However, understanding of the mechanisms and magnitude of loading imparted to buried structures is limited by a lack of high-quality experimental data. Past testing utilised discrete measurement devices within the soil; results have often been characterised as incident, free-field values, when in fact they are influenced by the materials, size and shape of the measurement device. This paper describes an innovative approach to experimental determination of ground shock loading on a buried structure.Uniquely, digital image correlation from high-speed video at 100 k frames per second has been utilised to determine ground shock loading at reduced scale on a deformable plate. Testing was conducted using a steel pipe with a deformable aluminium base plate, filled with varying depths of uniform sand at a consistent bulk density and moisture content. A constant scaled burial depth of 0.434m/kg<inf>TNTe1/3</inf> was maintained using spherical PE10 charges with a varying stand-off distance. Two charge sizes were used, with nine tests conducted in total.Displacement histories from over 2500 locations across the plate were extracted from each test, greatly increasing the resolution of data capture possible. The experimental data has been used to validate numerical modelling approaches, using an existing soil material model. The numerical results show good agreement with the experimental data.