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Borehole water-inflow tests allow measurement of discharges and water pressures in isolated sections of drains and piezometric boreholes. A series of water-inflow tests and water electrical conductivity analysis were carried out in an area of the foundation of an arch dam.Detailed three-dimensional numerical models developed for the analysis of the tests data in two foundation areas are presented. Results of rock mass permeability tests and areas where seepage paths cross each drain, identified with both water-inflow tests and water electrical conductivity analysis, were taken into account. Models were validated against flow rates and water pressures recorded in situ. By examining water-inflow tests using numerical models, the main flow processes are identified and quantified. Test results and conclusions drawn from the detailed 3D models were used to elaborate a global model of the foundation. The present study shows that borehole water-inflow tests add valuable information to the usual monitoring data, which improves our ability to analyse the behaviour of concrete dam foundations. It is also concluded that although discontinuum models provide a more natural representation of flow in jointed rock masses, equivalent continuum models can still be used successfully to study both global and local hydraulic behaviour of dam foundations.

Evaluation of the sliding stability of concrete dams requires the use of numerical tools not only able to simulate the coupled hydromechanical behavior but also able to adequately represent the foundation discontinuities and the specific features of dam foundations. The formulation of a three-dimensional (3D) small displacement finite element model based on interface elements to simulate the discontinuities is presented. In this model, the hydraulic behavior is simulated assuming that the water flow occurs only along channels located at the edges of the triangular interface elements that simulate the discontinuities. The model is used to perform coupled hydromechanical analysis of a large arch-gravity dam and to assess safety against dam base sliding, assuming different constitutive models at the dam/foundation interface and two different approaches: (i) strength reduction method and (ii) amplification of the hydrostatic pressure, assuming an increase in the reservoir level. The present study shows that consistent results are obtained with the proposed numerical model and that stability analysis should preferably be carried out using the method of increasing the hydrostatic pressure and the corresponding uplift pressures, as this methodology leads to significantly lower safety factors.

This paper presents the application of a methodology which can be used to assess arch dam foundation stability, using the discrete element method (DEM) and the code 3DEC. A global three-dimensional model of a dam foundation was developed, in which some discontinuities were simulated and both the grout and drainage curtains were represented. The model, calibrated taking into account recorded data, was used to carry out nonlinear mechanical analysis. The same model was employed to perform a hydraulic analysis, based on equivalent continuum concepts, which allowed the water pressure pattern within the foundation to be obtained. These water pressures were applied on discontinuities involved in the possible sliding mechanism along the dam/foundation interface, and the safety of the dam/foundation system was evaluated using a process of reduction of strength characteristics, with the aim of calculating the minimum safety factors that ensure stability. Results were compared with those obtained with the usual bi-linear uplift pressure distribution at the base of the dam, commonly used in concrete dam design. The relevance of carrying out hydraulic analysis in arch dam foundation failure studies is highlighted.