GNGTS 2016 - Atti del 35° Convegno Nazionale

612 GNGTS 2016 S essione 3.3 algorithm, we performed a numerical simulation for a synthetic embankment dam with a simple 2D geometry (Fig. 2). A leakage is reproduced by adding a permeable pipe located inside the dam core that simulates the existence of a preferential ground water flow pathway with permeability much higher than the permeability of the surrounding area. The petrophysical properties used in the simulation are reported in Ikard et al. (2012). The self-potential synthetic data were referenced to a point located at infinity. Boundary conditions were defined as follows: water head pressures were imposed along the lateral boundaries using a Dirichlet condition. At the bottom of the dam and at the ground surface we imposed an insulating boundary condition (n·j=0) where n is the unit vector normal to the ground surface). Fig. 2 – Triangular meshes used to discretize the domain for the finite element simulation. For the electrical problem, the Neumann boundary condition was imposed at the insulating air-ground interface and a Dirichlet boundary condition was imposed at the other boundaries. The numerical model was performed for steady-state flow conditions with a leakage. The groundwater flow due to the hydraulic gradient between the upstreamand downstreamof the dam is illustrated in Fig. 3. The hydraulic gradient and the average velocity in the conduit resulted, respectively, on the order of 0.17 and on the order of 0.017 ms -1 . The magnitude of the simulated self-potential signals is in the same range than those obtained by the authors using a commercial finite element code, COMSOL Multiphysics. Using dataset from other studies as the reference, we have demonstrated that the developed numerical code implemented in MATLABperforming the forward modeling for self-potential works well and its numerical solutions are reliable. In fact, the result of the sign and the magnitude of the computed self-potential signals agrees well with the values of field and synthetic data. Future works will include development of a strategy to solve the inverse problem in order to reconstruct 2D distribution of the source current density responsible of the observed self-potential anomalies. Fig. 3 – Solution of the Darcy velocity obtained by solving the groundwater flow problem.