Impact of Foundation Stiffness on Stress-Strain State of Concrete Faced Rockfill Dam

Hydraulics and Engineering Hydrology

Sometimes high concrete faced rockfill dams are constructed not on a rock foundation but on a soil foundation. Therefore, the urgent study is related to the impact of foundation stiffness on the stress-strain state (SSS) and strength of a concrete face. Method. The study was conducted using numerical modelling on the example of a 100 m high dam rested on a compressible foundation 100 m thick. There were considered five alternatives of foundation soil deformation modulus: from 40 MPa to 20 GPa. In addition, the impact of the seepage-control wall, which is arranged in the base, on the SSS of the hydrostatic pressure shield was investigated. High-order finite elements were used for modelling stiff thin-wall structures, which permitted obtaining a detailed pattern of stress distribution in the face. Results. Analyses showed that concrete face SSS of a dam located on a foundation of decreased stiffness is characterized not only by increased displacements but also by changing the character of their distribution. At the stiff foundation, the maximum deflections of the face are observed approximately in the middle of the dam height, and at the soft foundation, they are near the foot. Consequently, at the soft foundation, the face lower part's transversal deflection is expressed to a greater extent than in the upper part. The impact of the foundation stiffness decrease also results in the appearance of additional longitudinal forces. Conclusions. The study revealed a considerable role of the foundation stiffness in the formation of a rockfill dam concrete face SSS. Even at a strong rock foundation, the face SSS is more favourable than at an absolute stiff foundation. Therefore, in numerical modelling, it is necessary to take into account the real foundation stiffness. If a rockfill dam is constructed on the foundation more deformable than the dam's soil, then it may be expected considerable tensile, and compressive longitudinal forces may appear, which may result in loss of concrete strength. It can be recommended as a rule that the ratio of the deformation modulus of the soils of the dam and the foundation should not exceed 3. It was found that the hydrostatic pressure on the seepage-control wall at the base causes additional displacements of the base and the dam and a compressive longitudinal force in the concrete face. This leads to the growth of longitudinal forces perceived by the concrete face.