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Stability assessment of road and railway embankments under static, seismic and flood conditions

Kossioris Ioakeim

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Summary

In recent years, extreme weather events have become more pronounced due to climate change. Consequently, there is a substantial increase in the intensity of phenomena such as rainfall, snowfall, and extended drought periods. These phenomena can have a detrimental impact on the stability of slopes and increase the frequency of landslides. The stability of natural and artificial slopes (such as embankments and excavations) is a key issue in geotechnical engineering, as any potential failure can have catastrophic consequences. The physical and mechanical properties of slope materials significantly influence failure mechanisms, thereby contributing to landslides. Additionally, the groundwater table and the impact of flooding events play a crucial role. The effect of water on soil behavior depends on the prevailing conditions in the area of interest, in conjunction with the process of slope erosion, which is stalled by the presence of vegetation, but intensified by flooding. Adverse factors for the stability of a slope/embankment include steep inclination, low cohesion and/or internal friction angle of soil materials, as well as seismic/dynamic loads.Moreover, the presence of water, either internally due to the presence of groundwater in saturated soils, or externally due to floods, affects slope stability by altering the safety factor. It is important to emphasize that in recent years there has been a significant increase in the intensity and frequency of flooding events due to climate change. Therefore, the study of slope/embankment stability must consider not only static, but also seismic and flooding conditions. Gravitational forces are a determining factor in slope failure, and their combination with seismic or/and intense rainfall activity can be catastrophic in areas where these phenomena coexist, as it it has been observed in many incidents in seismic-prone regions.Based on the above, the aim of this diploma thesis is to investigate the impact of gravitational forces, seismic loads, and flooding phenomena on the stability of road and railway embankments, especially when a lightweight filling material, such as expanded polystyrene (EPS), has been used. For this purpose, analytical expressions were employed and parametric numerical analyses were performed utilizing Plaxis 2D filinite-element software. In conclusion, it is confirmed that the rise of water table level and seismic loads can have an unfavourable impact on embankment stability, while their combination is particularly detrimental. On the other hand, surface water may have even a beneficial impact on soil slope stability, depending on the circumstances.

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