Physical and numerical modelling of extreme flow through rockfill dams
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Upon overtopping of a rockfill dam, the downstream shell is placed under duress by pore pressure build up and inertial forces from the flowing water. Including drainage toes in the downstream shell of the dam may decrease the pore pressure and increase stability of the dam. Design and effects of different drainage toes, is a field sparsely covered in international research and by the Norwegian authorities governing dam safety. In this project, a 1:10 physical scale model was constructed, examining the effects of different toe designs under controlled overtopping events. The model was constructed with four different configurations. One configuration featuring a shell without a drainage toe, and three configurations featuring different drainage toe designs. The model was tested with an external toe, internal toe and combined toe. Through the physical modelling it was concluded that the internal toe configuration provides the optimal reduction of pore pressures, reaching pressure reductions of 80% in the center of the downstream shell. The conducted tests were recreated through numerical modelling with FEM software, Seep/W. In order to replicate the non-linear flow regime through the dam, a non-Darcy supplementary program was utilised in Seep/W. The numerical model was calibrated to the physical results and found to replicate the pore pressure development with a root-mean-square error of 0.023 m, proving high accuracy. The numerical model indicates that non-linear flow is possible to model in Seep/W, and is suitable for optimising and future planning of experiments.