This paper presents the results of an experimental programme aimed at evaluating the degradation phenomena of an argillaceous rock due to the application of hydraulic cycles. The degradation of shear strength parameters was detected using direct shear equipment on unaltered samples subjected to different controlled suction cycles. The experimental results were used to evaluate the influence of the rock degradation and the progressive reduction of the shear strength parameters on the stability of typical geotechnical structures, such as a slope on claystone with bedding planes and a concrete dam founded on marls. The analyses of the reduction of shear strength (specially the loss of cohesion) showed a great influence on the stability.