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The experience of carrying out grouting works during construction of high concrete dams attests to a substantial change in the stress state of adjacent columns under the effect of a comparatively small pressure on the surface of the joint between the columns [1]. In this connection the authors as early as the stage of working out the specifications for suppressing seepage through the stretched zone of concrete of the Sayano-Shushenskoe hydrostation dam gave special attention to possible consequences (positive and negative) of injecting grouts into seeping cracks at pressures considerably greater than those observed during grouting of the joints between columns and sections of the same Sayano-Shushenskoe dam during its construction. The firm approved to carry out the grouting works was supposed to inject comparatively viscous grouts of the "Rodur" type, as on other objects in past years, at a pressure exceeding 40 MPa at the pump outlet, which rapidly dropped on advancing along the injection path with a length of 15-20 m and at the mouth of the crack varied within 6-8 MPa with a 3 x 3-m arrangement of the holes and delivery of the polymer material through two holes. Only such a pressure made it possible to provide high-quality and continuous filling of the cracks with grout even with a small opening.During approval of the specifications specialists of the firm asserted that the effect of the grout pressure was limited to a small zone near the hole and additional opening of the cracks would not exceed the compressive strains from the unique press plate, which in cross sections with through cracks usually did not exceed 1 mm.Different regularities of additional opening of cracks that partially disturbed continuity of a cross section about 80 m high to a depth of 15-17 m ought to be expected in the particular case of grouting. The more so as grouting was to be done at upper pool levels (UPLs) close to the normal pool level (NPL), when the cracks without additional interference were in an equilibrium state.In the first years of normal operation it was established during drilling of exploratory holes and inspecting the walls by means of TV cameras that cracks were prevalent in the mass in the form of numerous small disturbance of the solidity of the concrete in zones 1.5-5.6 m high. Exploratory drilling before the start of grouting in 1996 showed the presence in each section of one to three zones with several cracks with a comparatively small opening. According to the readings of long-base deformometers, the openings of the cracks immediately before the start of industrial grouting at an UPL close to elevation 540 m were from 0.33 to 0.98 mm. At the dead storage level all cracks were practically closed. A plan was drawn up for grouting 40 zones in 24 sections to fill the main and small, intensely seeping cracks with grout into the depths of the mass. During grouting one could not assume penetration of cracks into the depths of the mass of the dam in connection with the fact that calculations established a zone of tensi...

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The Geodynamic Observations Service of the Electric Power Industry (GOSEPI) was created on the basis of the decree of the government of the Russian Federation for the purpose of developing measures to ensure the operating safety of electric power facilities in Russia as well as to prevent or reduce damages which can be inflicted by various natural and technogenic geodynamic processes and phenomena, including earthquakes occurring in regions of these facilities. Functioning of the GOSEPI is based on principles of continuous monitoring of natural and technogenic geodynamic processes in regions of a given power-generating facility by geological, geophysical, geodetic, seismological, and other types of on-site observations and a comprehensive analysis of the data obtained with consideration of the technical characteristics of the facility being monitored.The Sayano-Shushenskoe hydrostation represents a system composed of a concrete gravity-arch dam more than 240 m high, a reservoir, and the surrounding geological environment. Each component of the system undergoes changes with time.The dam was constructed in accordance with the SR-78 seismic regionalization map for an initial seismic vulnerability of 7. Later surveys revealed the existence near the dam of paleoseismic dislocations, the formation of which could have been accompanied by earthquakes exceeding the design one given above. During construction and operation observations of the dam were and are being carried out by the hydrostation service (hydraulic structures laboratory), specialists of the State Planning, Surveying, and Research Institute (Gidroproekt), and other organizations. The main types of observations are aimed at evaluating the stress-strain state of the dam, seepage phenomena depending on the water level in the upper pool (fluctuations of about 40 m), air temperature, hydrodynamic actions, and geodynamic phenomena. The creation of a local network of seismic stations began in 1990 for observing seismicity in the dam zone. These observations were an integral part of the seismogeological works begun earlier for refining the initial seismic vulnerability of the region of the dam.A natural development of the comprehensive observations of the Sayano-Shushenskoe hydro development is the decision made in 1995 by the Russian joint-stock company "United Energy Systems" concerning the creation here of a geodynamic observations test area, which is an integral part of the federal seismological observations and earthquake prediction system. In connection with this, the Siberian Branch of the Russian Academy of Sciences jointly with the "Sayano-Shushenskoe Hydrostation" Corporation drew up the draft of a program in which it is suggested to broaden the types of geophysical observations, including hydrogeological, of the condition of the surrounding rocks of the near-dam geological masses whose reaction must be taken into account both in connection with the operation of the hydrostation dam and with natural geological processes.The program of geophysical and hydr...