Mix Designs of Low Modulus of Elasticity of Mass Concrete and Cushion Concrete Used in Yusufeli Dam Body

The construction of the Yusufeli Dam and Hydroelectric Power Plant on the Coruh River has been completed and the dam, which has a total water storage volume of approximately 2,2 billion cubic meters, has become the highest dam in Turkey and the fifth highest dam in the world with a height of 275 meters in the double-curvature concrete arch dam type. During the design process of the mass concrete body of the Yusufeli Dam, relatively low deformation modulus zones were encountered in some slope rock soils where the thin arch structure would create pressure. It was taken into consideration that these partially weak soil conditions would create structural risks in terms of the interaction of the rigid arch dam structure with the foundation, and instead of conventional mass concrete, a special concrete design defined as “cushion concrete” with low elasticity modulus and high unit deformation capacity was developed and implemented in the dam. The aim of this study is to present the theoretical basis, material properties and field application of this special concrete design developed to provide elastic compliance by reducing stress concentrations between the dam body and the foundation in the low rigidity foundation zones encountered during the construction of the Yusufeli Dam and to prevent crack formation under high elastic deformation. The changes on the left side required significant changes in the design of the low modulus rock material dam, requiring a larger left embankment concrete structure. However, the preservation of the less rigid base rock with the more rigid body concrete was deemed necessary on a transition zone basis, and the transition in question was called “Cushion Concrete”. The cushion concrete has a larger base area than the dam structure. With less deformable concrete on the more flexible rock mass, the cushion concrete tends to act as a rigid beam on a flexible foundation. Therefore, while significant benefits can be obtained from the cushion concrete structure acting as a rigid transition between the dam and the foundation, in return, the cushion concrete structure has to be constructed with a low E modulus value and maximum possible flexural stress capacity in the concrete. Analyses have determined that the maximum elasticity modulus of approximately 19 GPa and a slow-loading tensile strain capacity of 150x10-6 units are important design criteria in the “cushion concrete” design (1,2). In addition, in regional areas where the strain exceeds the concrete capacity, it has