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The impact of water on the stability of onshore and offshore earth slopes under static and seismic conditions

Kavalieratou Evgenia-Evnomia

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Summary

In recent years, on one hand, there is a significant increase of offshore infrastructure, e.g., energy lifelines, while on the other hand, there has been a dramatic increase in the intensity and frequency of flooding phenomena due to climate change. Climate change, i.e., the change in weather conditions is mainly attributed to the increase of greenhouse gases, which leads to an increase of Earth’s temperature. Higher temperatures increase evaporation causing, among others, intense rainfalls, resulting in problems and landslides on natural and artificial soil slopes.The failure of soil slopes may result in large movements of soil masses, thus creating landslides, which constitute a crucial geohazard worldwide. The mechanical properties of the materials, the geometry of the slope, the location (onshore or offshore) affect the mechanisms of landslides. Especially for onshore slopes, the underground water table plays an important role, as well as the precipitation conditions, which are altered due to climate change. The influence of water on soil strength depends on the (drained or undrained) prevailing conditions in the area, interacting with the process of soil erosion, which is stalled by the presence of vegetation, but intensified by flooding phenomena. Adverse factors for the stability of a slope are high inclinations, low cohesion and/or angle of internal friction of the soil, as well as seismic and dynamic loads.In addition, water, either internally with the presence of a water table in saturated soils, or externally, due to floods, has an impact on slope stability, altering the safety factor. Moreover, due to climate change, there has been a significant increase (increased frequency and duration) of flooding phenomena. Under these adverse conditions, the infiltration of water into the soil (a factor affecting the aquatic horizon), as well as surface runoff (a factor affecting erosion and the slope inclination) are also different compared to normal rainfalls. Obviously, the combination of a heavy rainfall with a strong earthquake event cannot be ruled out in countries with high seismicity, such as Greece.Based on the aforementioned remarks, the present diploma thesis attempts to quantify the stability of onshore and offshore soil slopes under static and seismic conditions by analytical and numerical methods. For this purpose, analytical relationships as well as numerical simulations, utilizing the finite element software PLAXIS 2D, have been used. The parametric study confirms the crucial role of groundwater and surface water and indirectly demonstrates the potential (detrimental or beneficial) impact of climate change on the stability of soil slopes, as well as on the adjacent structures.

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