Three-dimensional interaction between concrete gravity dam and foundation rock mass in presence of coupling with seepage

This paper presents a numerical study of dam-foundation system taking into account hydro-mechanical coupling and groundwater surface fluctuations in abutments. A finite element method formulated for the resolution of hyperelasto-plastic laws for unsaturated porous media is used to simulate the three-dimensional response of a concrete gravity dam to reservoir filling and drawdown. The diffuse presence of pre-existing discontinuities of geological origin (tectonic fractures, bedding planes) is considered in the characterization of drained response and permeability of the continuum equivalent to the rock mass. The numerical implementation of a strain-dependent law is used to account for permeability changes induced by joint opening variations. The calculated evolution of dam response to reservoir operation is consistent with typical monitoring data, in terms of displacements, uplift pressures and drain discharges, thus indicating the employed numerical method as an effective tool for the interpretation of long-term behaviour of dams.