Seepage regime of the hydraulic-fill dam of the mingechaur hydropower development

Abstract

1. The anomalies of the seepage regime of the Mingechaur hydraulic-fill dam established during on-site observations are not related to intensification of the seepage flow and at present do not pose a danger for operation of the structure within the normal pool level of the reservoir, 83.0 m, which is also indicated by the temporal constancy of the seepage discharge being intercepted by the toe drain. The static calculations of slope stability under various most unfavorable operating conditions and an investigation of its earthquake resistance show a safe condition of the dam. 2. To judge from the results of investigating the soils of the core zone in the upper part, the Mingechaur hydraulic-fill dam in its current condition should be regarded not as a core-wall dam but as a gravel-sand dam with a lean central zone. About 10 such hydraulicfill dams, although of smaller height, have been constructed in the Soviet Union (Plyavinyas, Dubossary, Kaunas, etc.). 3. The presence of layers of increased permeability in the upper part of the core zone and the very high values of the permeability coefficient (up to 50 m/day) within the coreless “cap” of the dam (above elevation 84.0 m) give rise to the probability of a substantial increase of seepage discharge in the case of raising the level above the normal at reservoir elevations within 83.00–85.50, which can cause overfilling of the drainage system. At the same time we cannot preclude the possibility of the occurrence of contact erosion on the crest of the core zone under these operating conditions. With consideration of the aforesaid, it is recommended to take the elevation of the maximum water level with some margin equal to 83.50 m (the design specified 85.50 m). 4. To ensure safe operating conditions of the Mingechaur hydropower development at the designed maximum operating level above the elevation of the normal reservoir level of 83.0 m, it is required to strengthen the upper part of the core zone and “cap” by creating a watertight barrier. The design of the barrier should be selected on the basis of a technical and economic comparison of possible variants.