Influence of Material Strength on the Apparent Cohesion of Unbounded Gravity Dam Joints under Low Normal Stress

International audienceInternational gravity dam design guidelines consider that the different joints of a dam or its foundation (rock-rock, rock-concrete, and concrete-concrete joints) are unbounded and recommend using the Mohr-Coulomb criterion to evaluate their shear strength. By implementing these considerations into the calculations, it appears that an apparent cohesion value (C APP) can be used, even at low normal stress levels. It has been suggested that both the mechanical properties of the material forming the unbounded joint and the type of joint (uniform or composite) may influence the apparent cohesion. An experimental protocol comprising 24 shear tests on natural rock joint replicas was developed in this study. Replicas of the same granite joint were made with three types of mortars, exhibiting very different mechanical properties. These replicas were used to reproduce both rock-rock and concrete-concrete lift joints (uniform joints) and the rock-concrete foundation contact (composite joint). Tests were conducted under normal stresses of 100-1,000 kPa, corresponding to those found in gravity dam foundations. The results showed that the joint shear strength and apparent cohesion were not strongly influenced by the type of joint or joint material strength