Abstract：A study of the influences of the hydraulic uplift pressures underneath the base of a typical concrete gravity dam on its stability is presented. The dam is located at Cumbidanovu(Sardegna，Italy). The foundation of the dam is made of heavily fractured rock. Firstly，analytical calculations about the equilibrium of the dam as a free body have been employed to evaluate the maximum hydraulic pressure before collapsing and to assess the impact of an effective drainage system on the stability of the dam in a simple way. Secondly，numerical analyses by the distinct element method(DEM) using the code UDEC have been carried out to evaluate the hydraulic flow taking place within the fractured rock foundation，the uplift pressure distribution generated by the calculated flow，and its influence on the stability of the dam. For design purposes，it emerges that availability of reliable data on the hydraulic permeability of rock foundations and a computationally advanced distinct element modeling might lead to the acceptance of loads significantly higher than the more conservative estimations obtained from equilibrium analyses.
