Effects of external water-level fluctuations on slope stability

There is a worldwide increasing need of land-use in costal/waterfront areas. All kinds of changes of geotechnical conditions in these areas pose potentially slope instability and jeopardized values of property and life. Soil slopes are affected by water-level fluctuations originating from as well tides and other waves, as non-natural sources such as watercourse regulation for irrigation, freshwater provision, and/or hydropower production. Due to a growing use of non-regulated energy sources (e.g. wind and solar), the need of energy balancing and storage is increasing. Also techniques such as pumped hydropower storage (PHS), which may be associated with significant water-volume changes in the reservoirs, are growing globally. This is expected to involve variations of hydropower reservoir water levels; hour to hour, day to day and/or seasonally. In this paper geotechnical effects of water-level fluctuations on slope stability are reviewed; relevant inter-disciplinary findings are presented, adventurous simplifications and/or inadvertencies are underlined, and potential improvement areas are identified. A lot of research has been carried out focused on coastal erosion; mainly aimed to investigate tide-water influence on slope-profile development, and quantification of sediment production. On the other hand, studies on effects of water-level changes on geotechnical conditions in adjacent soil structures have been predominantly concerning embankment dams. In addition, studies addressing processes in natural slopes and banks are often environmentally oriented, rather than focused on slope stability. Since also water-level rise (not only drawdown) has been shown to significantly influence slope stability, further investigation of processes of suction loss, effects of rapidly increased water pressures, and retrogressive failure development is needed. Long-term views are often missing; analyses tend to involve few rise-drawdown cycles, soil materials are deficiently described, and limited attention is put on constitutive models used. Reliable integration of seepage effects on soil-property changing requires consideration of as well acute effects as long-term changes. Therefore, proper consideration of internal erosion is central. Given the critical relationship between pore pressure, soil strength, and soil-deformation, analyses have to be performed using robust simulation approaches. The terms “simplicity” and “applicability”—promoting use of limit-equilibrium methods—should more often be set in relation to accuracy and robustness provided by use of methods considering also deformations.Validerad; 2014; 20140404 (johjen)