Strength of ultra-high rockfill dam concrete face

The problem of providing safety to ultra-high rockfill dams with concrete faces is urgent and unresolved. It is proved by the facts of face structural failure of several ultra-high dams. As a rule, these facts are attributed to the face non-uniform bending deformations or are explained by high compressive stresses in the face central part. With the aid of numerical modeling the author investigated the conditions of forming stress-strain state (SSS) of ultra-high rockfill dams with concrete faces. Analysis was made of internal forces appearing in a concrete face: longitudinal forces and bending moments. It was established that high tensile stresses are most dangerous for concrete face strength in ultra-high rockfill dams. They create a threat by formation of horizontal and inclined cracks oriented along the contact with the foundation. These tensile stresses are the result of not only concrete face transverse bending deformations but also the presence of longitudinal tensile forces and longitudinal bending deformations in it. It is possible to minimize the impact of these adverse effects by decreasing friction at the contact of the face with the dam, however, this does not provide favorable SSS of the concrete face. It is necessary to take special measures on concrete face SSS regulation. Namely, it was established that rockfill deformation modulus should make up at least 300÷400 MPa. Absence of precedent cases of crack formation in the faces of the existing ultra-high rockfill dams may be explained by relaxation of stresses due to creep of concrete.