UNCONFINED FLOW THROUGH AN EARTH DAM UNCONFINED FLOW THROUGH AN EARTH DAM This document verifies that groundwater flow principles are correctly implemented in PLAXIS. The water flow through an earth dam with drain in the downstream toe is studied. The flow in such a case is unconfined due to the unknown phreatic level and the unknown area of the seepage surface. This constitutes a problem which can be solved by the flow net method (Lambe & Whitman, 1979). Used version: • PLAXIS 2D - Version 2018.0 • PLAXIS 3D - Version 2018.0 Geometry: On the upstream side, the water is at the reservoir level, at 12.19 m, which results in an equipotential line along AB with total head equal to 12.19 m. On the downstream side, the water is at the ground surface level which results in an equipotential line with a total head equal to 0 m. The equipotentials and the stream lines determined by the flow net method are presented in Figure 1 (Lambe & Whitman, 1979). Figure 1 Earth dam geometry and groundwater equipotentials and stream lines The model geometry (including coordinates) and the groundwater flow boundary conditions used in PLAXIS 2D are illustrated in Figure 2. The bottom flow boundary is set to be Closed, while every other is set to be Open. In PLAXIS 3D, the model is extended by 1 m in the y-direction, as depicted in Figure 3. Both groundwater flow boundaries in y-direction as well as the bottom boundary are set to be Closed. Every other flow boundary is set to Open. In addition to the global model conditions, an inclined water level is used to generate the hydraulic head of 12.19 m at the left side and 0.0 m at the right side. The internal part of this water level has no meaning and it will be overwritten by the results of the groundwater flow analysis. Materials: The Rock at the toe is simulated by using a relatively high coefficient of permeability (1 m/s). The Standard hydraulic model (Coarse material) is used to model the unsaturated flow in all layers. The adopted material parameters are: Soil: Linear elastic Drained E ' = 1 kN/m 2 k = 1.52 ×10 -4 m/s Rock toe: Linear elastic Drained E ' = 1 kN/m 2 k = 1 m/s Meshing: In both PLAXIS 2D and PLAXIS 3D models, the Very fine option is selected PLAXIS 2018 | Validation & Verification 1