A numerical study of the evolution of the blast wave shape in rectangular tunnels

When the explosion of condensed materials occurs in square or circular cross-section tunnel, the subsequent blast wave reveals two patterns: threedimensional close to the explosive charge and one-dimensional far from the explosion.Pressure decays for these two patterns have been thoroughly studied.However, when the explosion occurs in rectangular cross-section tunnel, which is the most regular geometry for underground networks, the blast wave exhibits a third, two-dimensional, patterns.In order to assess the range of these three patterns, several numerical simulation of blast waves were carried out varying the width and the height of the rectangular cross-section as well as the mass of the charge.Laws are presented to localize the transition zones between the 3D and the 2D patterns, and between the 2D and the 1D patterns, as functions of non-dimensional width and height.The numerical results of the overpressure are compared to existing 3D and 1Dlaws.An overpressure decay law is proposed to represent the 2D pattern.Knowing the two transition zones and the overpressure decays within these