1 Development of fragility curves for railway ballast and embankment 1 scour due to overtopping flood flow 2 3 Ryota Tsubaki 1* , Koji Ichii 2 , Jeremy D Bricker 3 and Yoshihisa Kawahara 2 4 1 Department of Civil Engineering, Nagoya University, Nagoya, Aichi, Japan 5 2 Department of Civil and Environmental Engineering, Hiroshima University, Higashi-hiroshima, 6 Hiroshima, Japan 7 3 International Research Institute of Disaster Science, Tohoku University, Sendai, Miyagi, Japan 8 * E-mail: rtsubaki@civil.nagoya-u.ac.jp 9 10 Abstract 11 Fragility curves evaluating risk of railway track ballast and embankment fill scour were developed. To develop 12 fragility curves, two well-documented single-track railway washouts during two recent floods in Japan were 13 investigated. Type of damage to the railway was categorized into no damage, ballast scour, and embankment 14 scour, in order of damage severity. Railway overtopping surcharge for each event was estimated via hydrologic 15 and hydraulic analysis. Normal and log-normal fragility curves were developed based on failure probability 16 derived from field records. A combined ballast and embankment scour model was validated by comparing the 17 spatial distribution of railway scour with the field damage record. 18 19 Key Words: railway embankment, fragility curve, overtopping, ballast scour, embankment scour 20 21 1. Introduction 22 Railway lines consist of components including tracks, power supply, and signaling infrastructure, all of which 23 can suffer damage during river floods, hurricane storm surge, and tsunamis, leading to interruption of 24 transportation service (see Figure 1 for two examples for damage due to surge in the USA). The most common 25 mechanism of track damage occurs when tracks are overtopped by floodwaters, leading to scouring of the 26 ballast and/or the embankment fill upon which the rail tracks are built. Even when only a short section of 27 track is washed out, the entire railway system can experience serious delays or malfunction due to a ripple 28 effect on the dispatch of engines and cars until the damaged section is repaired. 29 Since railcars (except those specialized for steep slopes like cable cars or rack railways) cannot handle 30 steep gradients in topography, railways are often built in areas of mild slopes, such as rivers, floodplains, and 31 Nat. Hazards Earth Syst. Sci. Discuss., doi:10.5194/nhess-2016-167, 2016 Manuscript under review for journal Nat. Hazards Earth Syst. Sci. Published: 31 May 2016 c  Author(s) 2016. CC-BY 3.0 License.