Abstract: In order to advance debris flow loss assessment from macroeconomic evaluation to service for civil engineering, the concept of engineering vulnerability based on structural devastation extent of civil engineering infrastructures is put forward. However, for those engineering harmed by debris flow hazards, such as bridges and tunnels, it is insufficient to determine the actual disaster loss merely according to structural devastation extent. When the engineering function is completely lost but structure slightly damaged, its vulnerability can be underestimated. Besides, when the engineering function is fairly workable but structure severely damaged, its vulnerability can be overestimated. Therefore, on the basis of the conventional assessment of structural devastation extent, the influencing factors for bridges and tunnels’ function is introduced, such as hazard-affected characteristics, railway/highway ranking and restoration cost. Thus, the engineering vulnerability assessment method for bridges and tunnels harmed by debris flow hazards is proposed, considering both structural devastation and function loss. In the case study, the assessing results show that the insufficiency of the conventional structural assessment can be overcome by this method. This method extends and develops the concept of engineering vulnerability, which makes the assessment more comprehensive and credible. Hence, it is concluded that this method is of great significance to correctly predict and verify the disaster situation of bridges and tunnels harmed by debris flow hazard, to properly prepare the emergency plans or to initiate a quick response.

Key words: debris flow, engineering vulnerability, bridge and tunnel engineering, structural devastation, function loss