Document Type : Research Paper
Abstract
Analysis of seepage from an earth dam helps determine water loss and is very important for analysis of the stability of these structures. The present study examined the effect of material hydraulic properties and drawdown rate and ratio on the position and form of the phreatic line, pore water pressure and the stability of the shoulder of a homogeneous earth dam. For this purpose, the materials used in the homogeneous earth dam were selected from the unsaturated soil hydraulic database. Seepage and stability analysis were performed using the Geostudio
sub-programs of seep/w and slope/w (based on the finite element and limit equilibrium methods, respectively). Seepage and stability analysis were performed in steady and transient states by applying four different drawdown rates. The results showed that the lack of significant differences in safety factors means that application of constant or function conductivity does not affect downstream slope stability of a homogeneous earth dam and the phreatic line was independent of conductivity. Results from the numerical model shows the noticeable impact of the soil water characteristic curve and slope () on the rate of drainage and subsequent pore water pressure and shear strength. The safety factors and critical states changed as the degree of saturation decreased or increased. With rapid drawdown of the reservoir at constant volumetric water content, the state of the upstream shoulder became critical when the drawdown ratio (L/H) reached about 0.5. As the water content of the unsaturated zone and the capacity of drainage decreased, stability reached the minimum FOS at a reservoir water level of about 2/3 of the total drawdown height.
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