Abstract
Abstract. The risk of failure of transportation embankments due to seepage induced by temporary and occasional impoundments taking place on the upstream side as a consequence of exceptional rainfalls is frequently underestimated. These failure events result from a combination of three main factors, i.e. the flooding event, the hydraulic weakness and the geotechnical weakness of the embankment. Based on the case study of a railway embankment in Southern Italy that collapsed in 2005 due to an upstream impoundment that occurred after few hours of a very intense rainfall, the paper describes a methodological approach aimed at assessing hazard of failure of transportation embankments induced by flooding and seepage. In particular, according to hydrological, hydraulic and geotechnical studies performed to define the factors affecting the process of the embankment failure, three subsequent activities are proposed: the historical analysis of flood damages at the watershed scale; and the assessment of the upstream peak impoundment based on hydrological analysis and the embankment stability analysis, these latter to be carried out at the site specific scale. The approach here proposed is planned to be further validated and improved by means of the application to other case studies, characterised by different contexts and embankment structures.
Highlights
Seepage due to upstream hydraulic head can sometimes represent the cause of general failure of embankments. Hazard associated to this process is well recognised for dam embankments and levees (El Shamy and Aydin, 2008; Serre et al, 2008), but is frequently underestimated for transportation embankments located in critical points, where a railway or a road intersects the drainage network
The second condition is represented by the “hydraulic weakness” of the transportation embankment, which is determined by drains, culverts, bridges, and, in general, hydraulic sections that can be obstructed during a flood or are underdesigned from a hydraulic point of view for the specific flood event
The paper proposes a methodology to approach the problem of assessing hazard associated with failure of existing transportation embankments due to flooding
Summary
A historical analysis might istence of past cases is verified, the analysis should high- give evidence of significant modifications produced by natulight the recurrence period of damaging floods and discuss ral disasters or floods (Glaser and Stangl, 200247; Petrucci and each specific event in order to check if embankment insta- Polemio, 2007) This activity can represent a rebility events due to upstream impoundment were observed liable tool in order to assess the existence and the level of in the past or could be identified for recently built infras- hazard due the effects of flood events on railways and roads tructures. In such case, the specific contribution of the event to embankment damages can be considered If some of these documents include quantitative data concerning rainfall, maximum flood head or stage, discharge yield and/or submerged area, they might be used for the numerical analysis typical of the second activity.
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