Design and watertight effectiveness of the underground contour of the Sayano-Shushenskoe dam

Conclusions

Seepage in the foundation of the SSh hydrostation has a nonuniform but regular character and substantially depends on the acting head and SSS. At an elevation of the UPL of less than 520 m, a change in the permeability of the rock mass is observed mainly on the upstream side of the grout curtain. The intensity of decompression of the rocks increases with increase of elevation of the UPL, especially above 534 m. At 540 m the zone of decompression of the contact part of the foundation in some places intersects the grout curtain and in individual cases intercepts the drainage; the discharge of the drain wells increases by 5–7 times in comparison with the discharge at an elevation of the UPL of 500 m. The width of the joints near the drainage (according to calculation) averages from 0.3–0.5 to 0.73 mm; here and there it can reach 1.5–2 mm. The average gradient of the head in the grout curtain is within 10–15; at individual places near the drainage it reaches 26, which is at the level of the allowable for a rock mass.

A method of controlling seepage is mainly used in such cases — repeated grouting at low elevations of the UPL, including with the use of plastic grouts, which in individual cases accelerate setting of the additives.

As measures for improving the seepage conditions and quality of monitoring, we can recommend plugging places of water shows through the grouting holes at an elevation of the UPL of 500–510 m, intensifying drainage in stretches of increased inflows and passages of the head beyond the drainage line, and broadening of geophysical and hydrogeological investigations for a detailed study of the character of change in permeability and seepage during fluctuations of the reservoir, especially at high elevations. During operation of the dam it is necessary not to exceed the attained rates and level of filling the reservoir (elevation 540.25 m), since at levels close to the NPL, the seepage discharge increases intensely.

The underground contour of the Sayano-Shushenskoe dam is of high quality and operates effectively and reliably under conditions of a varying stress-strain state of the foundation during fluctuations of the reservoir level.