Concrete dams are constructed on rock foundations because of their enormous weight. Rock foundations have a very large load bearing capacity, resist erosion, and reduce permeability. A soil with a high permeability allows water to flow underneath the dam. With a strong foundation there are no height restrictions of RCC dams. RCC dams have been constructed at heights of up to 510 feet (156m). Engineers try to select a site with no shears or faults because remediation to correct these problems can be expensive. Soils at depths between 30 and 60 feet (10 to 20m) are considered to be the most important because they have the greatest effect on the foundation’s ability to withstand loads without producing major short-term and long-term deformations. The foundation designed is considered to be more important than the design of the dam itself because a dam is more likely to fail in its foundation than in its own section. For this reason, engineers spend a great deal of effort on foundation research and remediation.

Engineers must determine the soil’s compressive strength, shear strength, deformation modulus, poisson’s ratio and permeability in order to judge the adequacy of the material. The compressive strength of the soil determines how thick the dam’s base must be in order to distribute the weight of the dam. The shear strength of the foundation rock results from the soil’s friction between its particles. The magnitude of the deformation modulus is usually not as critical as the rate at which it changes across the foundation. Many dams to date have been constructed on fairly low modulus soils that do not have any drastic changes across the dam foundation. If a foundation soil does have drastic changes in deformation modulus, the soil may settle at different rates and cause cracking in the dam. In order to complete a more intensive mathematical study of the foundation, poisson’s ratio is must be determined. Poisson’s ratio is the ratio between the transverse and axial strain in the soil. The permeability of the soil must be obtained in order to determine the flow rate under the soil. Depending on how much water flows through the soil determines the remediation measures required.