At present, there is a significant number of experimental and theoretical works devoted to the study of the properties of soft soils under explosive loading and experimental methods for determining the shock adiabats of soft soils. However, the results obtained are largely contradictory, and both further research into the basic properties of soft soils and an in-depth theoretical justification of the experimental methods themselves are required. This paper presents the results of a numerical study of the impact of a superimposed explosive charge on sandy soil through a metal impactor plate. The ground is modeled by S.S. Grigoryan’s compressible medium with irreversible volumetric and shear deformations. Numerical solutions obtained using various shock adiabats known in the scientific literature are compared with experimental data. As a result, a synthesized sand shock adiabat is proposed and justified in the range from low pressures up to 1 GPa. The influence of volumetric plastic deformations and friction forces on wave processes in the ground is analyzed.