The study relies on the concepts of various mechanisms of explosives decomposition at supersonic propagation of the under-compressed detonation reaction zones, and examines the structured charges explosion effect on compressible obstacles. In such charges, artificially or naturally, there can appear rod-like formations highly capable of detonation, penetrating the charge and ensuring the propagation of the complete heat release zone at a speed greater than the normal, and the ideal detonation speed of a monodisperse charge is of the same density. We introduce a simple algebraic model of the explosive process of structured charges, the process proceeding in the form of under-compressed detonation. We obtained algebraic expressions that make it possible to compare the peak pressures at the obstacles depending on the direction of detonation propagation relative to the obstacle and on the mode of detonation, i.e. whether it is normal or “under-compressed”.