Unsaturated soil blast: Flying plate experiment and numerical investigations

This paper presents the results of a combined experimental and numerical investigation into the blast loading generated by an explosive charge buried in an unsaturated soil. The dynamic response of the soil blast is quantified by its impulse imparted onto a high strength steel plate in a flying plate experiment. A 50 mm-thick plate of exposed area 500 mm by 500 mm is located at a constant stand-off distance of 400 mm above the surface of the soil. Upon detonation, the plate's heights are recorded and analysed using the initial velocity of the plate calculated from the flying time, while the rotation of the plates was shown to have negligible influence. Detailed unsaturated soil preparation, in-situ and laboratory characterisation as well as experimental setup are reported and compared to obtained meaningful parameters of the soil for the tests. The numerical model for the soil blast impact on the steel plates is developed based on the Arbitrary Lagrangian-Eulerian (ALE) method in the commercial simulation package LS-DYNA. Key soil properties, such as density, moisture content, bulk and shear moduli are characterised and utilised as input parameters into the FHWA material model in the numerical model. Results from a series of soil blast tests with 0.5 kg TNT charges on different plate sizes are presented and validated numerically. The numerical models agree generally well with the unsaturated soil blast test results, while the observed variations in the plate height are clearly attributed to the sensitivity of the soil properties.