A Unified Framework of Vulnerability Assessment for Valley-Crossing Bridges Exposed to Compounding Mountain Geohazards

Under the changing climate, extremely massive landslides, destructive avalanches, glacial debris flows, and dam-breaching outburst floods occur frequently on the Tibetan Plateau, posing severe threats to valley-crossing bridges of the railways and highways. Previous studies examined bridge-landslide interactions corresponding to separate geohazard scenarios. However, in reality, hazard type can transform from one to another. Considering generic physical mechanisms of bridge-landslide interactions under different geohazard types or evolutions of hazard chains, a unified vulnerability assessment framework is established in this study. The resultant impact forces in various geohazards are categorized into three components: boulder impact, coarse particle impact, and slurry impact. Four failure modes of the bridge are revealed under different combinations of impact forces. The integrated vulnerability of a bridge is calculated as the union failure probability of different failure modes. As an example, the proposed methodology framework is applied to assess the vulnerability of the Zhibai Bridge, which was damaged by a high mobility debris flow on September 10, 2020.