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When fracture occurs in a concrete dam, the crack mouth is typicallyexposed to water. Very often this phenomenon occurs at the dam-foundation jointand is driven also by the uid pressure inside the crack. Since the joint is theweakest point in the structure, this evolutionary process determines the load bearingcapacity of the dam. In this paper the cracked joint is analysed through the modelproposed by Cocchetti, Maier and Shen [1] which takes into account the coupleddegradation of normal and tangential strength. The water pressure inside the crack,which reduces fracture energy and increases the driving forces, is analysed throughthe model proposed by Reich, Bruhwiler, Slowik and Saouma [2]. Some numericalresults are presented which refer to the benchmark problem proposed in 1999 bythe International Commission On Large Dams [3]. In concrete dams, cracks arepresent and may be of considerable dimensions since the beginning of dam life. Whenctitious process zone is completely developed and the water penetrates inside thecrack, a small cycle in water level is enough to make locally a complete unloadingand reloading cycle.