The shear strength of discontinuities plays a key role in the stability of rock masses, particularly in the case of analyzing the sliding stability of the rock foundations of gravity dams. This paper proposes a methodology for analyzing the spatial variability of shear strength along the joints of rock mass, based on the input parameters of the Barton and Choubey's model. The aim of this approach is to evaluate the reduction of the variance of the parameters involved at full-scale by identifying a deterministic trend varying in depth and a spatial correlation calculated from a variographic analysis. An advantage of this methodology is to use a simple experimental protocol (a laser profilometer, a portable shear test apparatus and a concrete sclerometer), which generates large sets of shear strength properties for assessing their spatial variability. The methodology is illustrated in the case of the rock foundation of a concrete gravity dam. Analysis of the spatial variability conducted for this case study led to a significant reduction of the variance of the variable analyzed. The advantage of this method is demonstrated through the evaluation of the probability of failure performed in a study of this structure's stability. Taking variance reduction into account in the case study led to significantly reducing the probability of failure assessed through a reliability analysis.
