Blast wave transmission along rough-walled tunnels

Abstract

There is a sizeable body of published work relating to the transmission of blast waves along smooth tunnels of both simple and complex geometry though relatively little has been presented on the propagation of blast waves along tunnels with roughened walls. This paper presents the results of experimental studies carried out at small scale into the propagation of blast waves along straight tunnels roughened by means of different-sized roughness elements fixed along the sides of two model tunnels in a range of configurations. First, small hemispherical charges of plastic explosive were detonated at a fixed scaled distance from the open end of one tunnel. Second, a small shock tube was used to provide a repeatable simulated blast wave pressure–time history at a second model tunnel entrance. For each tunnel, measurements of overpressure–time histories were made at different locations initially with roughness absent and then with different roughness configurations in place. Results from both sets of experiments are presented as graphs of scaled peak overpressure and impulse against non-dimensional parameters based on tunnel geometry. These graphs allow the effect of the different roughness element configurations to be assessed and effective attenuation geometries to be identified. It is concluded that the use of rough-walled tunnels could offer a means of providing an efficient protective entrance to a sensitive structure NOTATION B tunnel breadth H roughness element height i r(smooth) peak reflected specific impulse at the end of smooth tunnel i r(rough) peak reflected specific impulse at the end of rough tunnel L 1 location of elements relative to end of tunnel L 2 length of tunnel over which roughness elements extend n number of roughness elements p 0 atmospheric pressure p r peak reflected overpressure p r(smooth) peak reflected overpressure at end of smooth tunnel p r(rough) peak reflected overpressure at end of rough tunnel p s peak side-on overpressure S roughness element spacing t thickness of roughness element