Similitude laws and modeling experiments of explosion cratering in multi-layered geotechnical media

According to the scaling law of cratering explosions in a monolayer medium and the theory of similarity, this research derived a scaling law for cratering explosions in multi-layered media. Except for the influence of scaled depth of burial, for cratering explosions in multi-layered media, the wave impedance of the layered media will affect the distribution of the total energy, which ultimately affects the crater. At present, there are two main methods used to investigate cratering or underground explosions: centrifuge model tests and equivalent material model tests. Based on the use of a mini-spherical explosive charge and a pouring type of equivalent material, we carried out modeling experimental design and implementation of explosion cratering in multi-layered media. Specifically, a center-initiating explosive charge with the 1 gTNT equivalent yield was used to simulate the explosive source with 10 kg TNT equivalent yield on an equivalent material of low strength but high density to simulate high-strength geotechnical materials such as concrete and rock. There were 12 groups of blasting model tests, which were carried out to investigate the influence of wave impedance matching and the scaled depth of burial on the cratering effects in multi-layered media. A high-speed movie camera was used to capture the photographs of ejecting and bulging movement, and molten paraffin wax was poured into the explosion craters to obtain a mold of the crater. Generally, the basic law of explosion cratering in multi-layered media was obtained. The cone radius of the crater at the interface exhibited either expanding or necking phenomena. After analysis of the experimental data, the ejecting and bulging, and the crater geometries, as affected by the ratio of wave impedance and the scaled depth of burial, were assessed.