A study of preservation of the gypsiferous rock in the foundation of the Kama hydroelectric station

Conclusions

• 1. Preservation of the foundation rock of the Kama hydroelectric station, which was brought into service over 14 years ago, is not a source of danger, as confirmed by the following objective data:

• a) the stability factor of the structure is above the design specifications and regulations on all the sections;

• b) the maximum settlement does not exceed 20 mm, this process now being stabilized and subsidence and swelling sections being absent;

• c) permeability of the foundation rock is low on the whole;

• d) metamorphism and desalination processes of the ground water, associated with leaching and solution of the foundation rock, are proceeding fairly slowly.

• 2. Considering that seepage in the foundation of the Kama hydroelectric station is proceeding through a complex system of fissures in rock and semirock soil, at any moment in time there is the possibility of the filler's dissolving and washing out from the cracks directly under the building of the structure; and in connection with this, the existence in section IV of piezometers with high and increasing specific flow rates (225, 245, 244) necessitates the adoption of appropriate countermeasures (grouting, reinforcement of the grout cutoff, etc.).

• 3. Experimental inclusion of the vertical submerged drainage has confirmed its efficiency in reducing uplift and increasing the stability factor of the structure. Since the hydrochemical processes continue to develop regularly, it is advisable in the immediate future to develop an optimum system of bringing in the vertical submerged drainage on the basis of the results of observations and test modeling, giving rise to the minimum head gradients on the “middle impermeable bed” and providing a reliable dead zone directly under the hydroelectric station building, Following this, the vertical submerged drainage can be connected in permanent operation. Periodic inclusion of the drainage should be dispensed with, since this greatly disturbs the hydrodynamic and hydrochemical seepage regimes.

• 4. Investigation of the state and preservation of the rock making up the foundation of the Kama hydroelectric station, after 14 years' operation, has demonstrated the possibility of erecting headwater structures on gypsiferous rock if a network of protective antiseepage and drainage installations is set up, together with a piezometric network for observing variations in level and chemical composition of the water-bearing horizons, for monitoring the state of the foundation before and during construction and during the operating period.