Effect of fluctuation of water level on stability of dike
Date of Issue2013
School of Civil and Environmental Engineering
The increasing demand of dike construction from the past as prevention measure against land inundation to the current context for land reclamation project to meet the needs of increasing population has required attention to ensure the performance and safety of the dike as it protects many lives and great economic value. For the latter usage, sea water level will be higher than the water level inside the land imposing seepage flow through dike body that would affect the stability. In addition, water level is not constant, it fluctuates with time. Limitation of past studies not accommodating such two aspects has brought up this study. This paper presents a study to examine the effect of fluctuation of water level on stability of dike by conducting simulation study using finite-element analysis softwares, Plaxis and GeoStudio. Both softwares analyse flow using finite-element method. The difference is on the method calculating slope factor of safety, the first uses finite-element method and the latter uses limit equilibrium method. A total of 8 pairs of models, 8 models each for respective software with varying tide amplitudes, tide periods, and dike heights were evaluated to examine the performance of dike. Results both from Plaxis and GeoStudio show consistent trend of change in slope factor of safety due to effect of fluctuation of water level. Typically, upon increasing water level the likely occurrence of slope failure is at downstream slope and factor of safety is not affected much. Whilst, upon decreasing water level factor of safety reduces significantly to the most critical state, notably at low tide or at short period before low tide by 8% to 20% and the likely occurrence of slope failure is at upstream slope. The most critical state could also occur at high tide if some conditions are met. In summary, implication of fluctuating water level condition on slope stability varies depending on tide amplitude and tide period which constitute rate of change of water level, and ratio of water level to dike height. The larger the decrease rate of water level, the lower will be the factor of safety. Against the same profile of water level, dike with lower height yet sufficient enough to block water gives higher margin of safety in terms of slope stability.
Final Year Project (FYP)
Nanyang Technological University