Seepage control is a fundamental issue in the stability of concrete-faced rockfill dams. In this structure drains have a key role in reducing pore water pressure an‎d directing subsurface flow, thus optimal design of the drains is necessary. This study investigates the effect of the location an‎d length of a horizontal drain on reducing seepage discharge, pore water pressure, an‎d water level fluctuations within the body of a protective concrete-faced rockfill dam with stepped slopes. For this purpose, a physical model with a scale of 1:10 relative to a real stone-cement protective dam was constructed in a laboratory box with dimensions of 40×40×47.5 cm, an‎d was filled with gravel, having particle sizes ranging from 4 to 5 cm, In this structures installed 8 piezometers an‎d 7 perforated pipes. By examining the seepage velocity an‎d determining the Reynolds number from field studies in real dams an‎d aligning it with the laboratory model, both geometric an‎d dynamic similarity between the physical model an‎d the real structure were established. Two sets of experiments were performed including with an‎d without drain conditions. In both conditions seepage discharge, pore water pressure (via piezometers), the seepage line, an‎d the water level inside the dam body (via perforated pipes) were measured. Subsequently, the SEEP/W module of the GeoStudio software was used for numerical modeling. The hydraulic properties of the materials used in the laboratory model, such as saturated hydraulic conductivity, were initially estimated based on laboratory experience an‎d defined in the software. The numerical model was calibrated by gradually adjusting these parameters until the seepage line, pore water pressures, discharge, an‎d internal water levels at upstream heads of 10, 20, 25, 30, an‎d 35 cm matched those obtained from the physical model. Once good agreement between the numerical an‎d physical models was achieved, optimal positioning of the horizontal drain was investigated numerically. Various installation scenarios were considered in terms of drain height (0, 2, 4, 6, an‎d 8 cm above the base of the dam foundation) an‎d drain length (from 10% to 50% of the dam foundation length). The results indicated that increasing the drain length an‎d reducing its installation height relative to the base of the dam foundation, had a significant effect on reducing seepage discharge an‎d pore pressure, an‎d provided more effective control of the seepage line. The best performance was observed when the drain was installed at the base of the dam foundation (0 cm above the base of the dam foundation) an‎d with a length equal to 50% of the dam foundation length. The accurate performance of the SEEP/W module in replicating experimental results confirmed its reliability in seepage analysis an‎d in the design of protective structures.

محمد شايان نژاد

سعيد صالحي هفشجاني

محمدرضا مصدقي , منوچهر حيدرپوراسفرجاني