When an explosion occurs in a tunnel, the study of the blast wave quickly becomes complicated, due to the multiple propagation patterns of the blast wave (Incident wave, regular and Mach reflections) and to the geometrical conditions. Considering this problem, two patterns can be revealed. Near the explosive, one can see the well known free-field pressure wave. This overpressure, during its propagation, after multiple reflections on the tunnel's walls, can behave like a one-dimensional wave. The aim of this paper is to determine the position of this transition zone along the tunnel with reduced-scale experiment and hence to validate the dedicated law established in a previous work. Both numerical and experimental methods are presented. Previous experimental works have been done on this topic, based on a real scale [1]. In this present study, the experiments are realized in the laboratory using a 1/30th scaled model, simulating T.N.T. detonations ranging from 0.1 kg to 12 kg in a tunnel of 25 square meter cross section and 30 meters in length. The experiment on scaled models allows us to realize many inexpensive experiments; an accurate profile of the overpressure can be determined along the tunnel. The transition zone between the free-field and the one-dimensional decay law is presented using non-dimensional parameters and is also compared with the numerical simulation.
