Thermo-stressed state of rockfill dam concrete face at reservoir impoundment
In Russia and China there considered the plans of constructing concrete face rockfill dams (CFRD) in the regions whose climate is characterized by considerable drops of temperature. Therefore, the issue about the role of thermal effects in formation of stress-strain state (SSS) of rockfill dam concrete face becomes urgent. We studied the impact on concrete face SSS without cooling effect of water during the reservoir impoundment. Materials and methods. A 100 m high dam was studied whose face was 0.5 m thick. Numerical modeling of the dam behavior was conducted with the aid of the finite element method. At first, the non-stationary temperature regime of the dam was studied at the reservoir impoundment. It was assumed that the rate of the water level rise comprised 1 m a day and water temperature was 20°С less than the dam temperature. Then the temperature distribution in the face was used for calculation of thermal forces in it. SSS analyses were conducted for two cases: with consideration of thermal forces and without it. Results. Analyses showed that by the moment of the reservoir impoundment completion the face temperature regime at a depth of more than 5÷10 m is close to the steady regime. It is characterized by nearly uniform cooling of the face, which results in appearance of additional tensile longitudinal force approximately 1 MPa in this part of the face. In the zone of water edge the thermo-stressed state of the face is much more unfavorable. The temperature regime of this zone is characterized by non-uniform distribution of temperatures along the face thickness and height; it intensively varies within several days after the reservoir impoundment completion. The most dangerous is the initial time interval when the zone of concentration of high tensile stresses (more than 3 MPa) appears in the water edge zone in the face upstream part. Conclusions. Cooling of the face at the reservoir impoundment is dangerous for the face concrete strength. At CFRD construction in severe climatic conditions it is reasonable to arrange heat insulation of the face upstream part.