Innovative protection of urban areas – Experimental research on the blast mitigating potential of hedges

Abstract

The increasing threat of terrorist attacks requires the protection of urban spaces. The protective function of currently available protection systems is often clearly visible, which can even increase the perceived threat. This is acceptable for temporary solutions, but in the long run it contradicts the idea of a modern and open society. For continuous use, new solutions should be considered that are not perceived as protective elements and unfold their protective potential inconspicuously. This includes elements of street furniture and landscape architecture. This paper addresses theoretical and experimental investigations on the protective potential of plants against blast loads. The aim of the study presented here was to quantify this protective potential for selected needle and leaf plants and to identify the decisive parameters that contribute to the pressure reduction in the event of an explosion. The results of the free-field explosion studies show that plants with certain properties can reduce the overpressure of blast waves by more than 40% compared to an unimpeded propagation. All examined plants achieved significant overpressure reductions in the close range behind the hedges. Especially thujens and yew trees reduced the peak overpressure by 39% to 45%. Furthermore, two numerical methods have been developed and successfully applied, with which the volume of the plants can be determined on the basis of point clouds from terrestrial laser scans. The two methods allow a mutual validation of the results. Thus, it is possible to prove a direct relationship between the growth density and the reduction of the peak overpressure by the plants. These results shall enable urban planners, landscape architects and engineers to specifically integrate plants into future protection concepts and enhance the resilience of urban areas in case of bomb attacks.