Analysis of soil state in the core of the Ust-Khantaika hydroelectric plant dam

Conclusions

In the core of the river-channel dam of the Ust-Khantaika hydroelectric plant rewetted, weakly compacted moraine soils and soil mixes were placed, which during the construction period were frozen, a very nonuniform core structure being formed with interbedding of thawed and frozen soils, which substantially differ in water content and density in the different zones: from hard to flowing (17%) and from loose (with γ_dr.d.≤1.4–1.5 g/cm³) to overcompacted (with γ_dr.d.≥1.8–1.9 g/cm³).

• 2. Control drilling permitted determining the actual core structure and the soil state as regards water content, density, and temperature, at the start of dam operation. The soil decompression regions under the upper frozen zone in the river-channel portion of the core were determined.

• 3. From field observations and controlled drilling data it was found that despite the nonuniform structure, composition, and state of the core soils, in the dam of the Ust-Khantaika plant there were no dangerous deformations or concentrated seepage centers during the first years after start of operation under the reservoir water pressure, and that thawing of the frozen zones and deformation of the dam take place very slowly.

• 4. Taking into account the unsteady temperature and seepage regimes of the core and the dam on the whole, as well as the established soil decompression zones, it is necessary to intensify the field observations on the unique river-channel dam of the Ust-Khantaika plant and to increase the control-measurement equipment and the frequency of the measurements.

• 5. In order to generalize and analyze the behavior of the river-channel dam during the first years of its operation and to determine the changes in the state and properties of the core soils, it is necessary to repeat control drilling and core inspection during 1979–1980.

• 6. The factual data on the structure, composition, and properties of the soils in the core of the Ust-Khantaika dam should be used in design practice for earth dams in the Far North, to improve their design features and the techniques for constructing their antiseepage components, as well as to work out long-term predictions of the behavior of such dams for operating under severe climatic conditions.