# Numerical Simulation Study of Cavity Formation in Soil under Blast Load
## 1 Introduction  
Since soil is a heterogeneous medium, and civil explosives such as ANFO or powdered ammonium nitrate explosives are characterized with a non-ideal detonation behavior, the aim of this study is to find a reliable numerical model that can predict soil behavior under a blast load. In order to predict soil deformation under an impact load, such as one that is produced by an explosion, it is important to identify the deformation mechanisms that can occur in high-strain conditions. The common practice in modeling soil behavior under a blast load is primarily based on empirical formulas from field tests [1]. For the last two decades, many researchers have been studying numerical simulation under a blast load, and numerical models were derived and validated on explosives with ideal detonation behavior, such as TNT or C4. Also, they have used sand (saturated or unsaturated) as the media [1; 2; 3; 4; 5]. Some correlations are established between the spherical cavity volume and the blasting charge mass and type of explosive used, as well as its detonation and blasting parameters [6]. However, there are a huge number of different soils in nature, with corresponding deformation mechanisms. This diversity has produced a great number of theories with different initial models of soil. Also, the theoretical problem that occurs is based on the fact that an explosion in a solid medium is a dynamic process [7]. According to the classification, soil can be cohesive or non-cohesive. In cohesive soils, two deformation mechanisms exist. In the first deformation mechanism at low pressure, the soil skeleton deformation is determined by the elastic deformation of bonds on the contact surfaces of grains; the first mechanism at high pressure is determined by a failure in bonding and the displacement of grains (plastic deformation). The second deformationmechanism is the deformation of all the soil phases. When soil is being compressed, both mechanisms act simultaneously, but at certain phases of the loading, one of the mechanisms predominates [7]. In terms of explosive performance in soil, the first stage is the impact effect. In that phase, pressed gasses act like a rigid barrier that hits the soil, and compaction occurs. In the next stage, expanded gasses can migrate in the soil layer next to the border with a cavity. That kind of process can occur when the action of several nearby blast holes or a free face exists in the charge vicinity zone. In the case of a buried charge when a cavity is produced, generally, gasses cannot migrate in the compacted soil, because the soil is compacted, densified, and acts like a barrier to the gasses in expansion. First, the impact effect on the explosion tends to make natural air and water migrate from the explosion zone. That process causes soil to be densified to values near crystal density because all-natural air and water do not exist in that zone anymore, and the soil particles are arranged and pressed. Different types of explosives are used in blasting practice. Also, they generally have different values of detonation parameters depending on the performance and workability under different conditions and surroundings. There are several methods to predict the workability of explosives in different materials and intendent functionality, such as lead block test, ballistic mortar, underwater explosion test, cylinder test, Hess test, Kast test, plate dent test, etc. [8]. One of the predictor methods that can be used is the TNT equivalent method. In that approach, the explosive of interest is compared with TNT in a manner of theoretic heat, pressure, velocity of detonation (VOD). The problem with that approach is that explosives with different explosion processes are compared. TNT is an ideal explosive that detonates in the most ideal manner. On the other hand, for the in-cylinder expansion test, which was used in the detonation model applied in Ansys 2020 R1 Autodyn 2D, experimental constants and real exact values of detonation parameters are crucial.