Stressed state of gravity dam with tension permitted in upstream face

Abstract

1. The dam was designed on the basis that small tensile stresses would occur at the upstream face of a continuous profile. At first it was proposed, in order to avoid tension, to provide joint-notches; however, the tensile stresses obtained were acknowledged to be safe for concrete placed by the layer-by-layer method, as the strength of the construction joints under tension (according to data from full-scale tests carried out during construction of the Toktogul hydroelectric development) was considerably in excess of 6.1 kg/cm2. 2. The alternative investigated, namely, a narrow-profile concrete gravity dam with a reinforced-concrete apron, grout curtain, and a steel upstream membrane, should be regarded as safe from the viewpoint of the stressed-deformed state under the principal loadings acting during the service period. In a monolithic profile of the dam, the maximum tensile stresses on horizontal planes attain a value of 6.1 kg/cm2 at the upstream face; the maximum compressive stresses at the downstream face are 40.4 kg/cm2; at the dam-foundation contact surface the maximum tensile stresses on the horizontal planes are 8.5 kg/cm2, the maximum compressive stresses being 45.9 kg/cm2. 3. In the foundation of the dam under its upstream face there is a zone of all-directional tension extending 4.5 m dowstream from the upstream face and 3 to 4 m deep. Inasmuch as the drains are located here, the creation of a single infiltration zone will contribute towards an outflow of water, without impeding the normal operation of the subsurface contour. In the grout-curtain zone the normal stresses on horizontal planes will remain compressive. 4. Provision of a joint-notch 7.2 m deep along the contact line slightly improves the stressed state at the upstream face, in the lower part in the foundation of the dam. However, over the length of the joint-notch, a concentration of tangential stresses occurs, and this gives rise to principal stresses of up to 13.7 kg/cm2. The joint-notch at the contact line does not have a significant effect on the stresses due to the main combination of loadings, and can be regarded as a supplementary measure for improving the stressed state of the contact zone under seismic loading.