Debris flow impacts on masonry arch bridges

Debris flows are a mountain hazard and present a risk to bridges in mountainous areas. Designers of modern bridges are able to consider loads related to debris flows but the designs for historical arch bridges lack this possibility. Although historical arch bridges still form a substantial amount of the total number of bridges in mountainous areas, most research investigations for this bridge type have considered vertical loadings; a few studies consider horizontal longitudinal loads but there are no reported investigations into horizontal transversal loads, which is the debris load direction. The research reported in this paper investigated, firstly, the impact force of debris flows against solid structures in terms of miniaturised laboratory tests. A variety of debris parameters was systematically investigated and an impact–force relationship was developed. Secondly, different horizontal transversal impacts on a slightly miniaturised arch were carried out in the laboratory. The behaviour of the arch under this loading was examined using different measurement techniques. Finally, both test results were combined in order to describe the behaviour of arch bridges under such debris flow impacts. Recommendations for engineers are given.