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One of the principal progressive trends in the field of the design and construction of concrete dams is the regulation of their strength, which is directed toward improving the extent to which the strength properties of the concrete and bedrock are utilized, and providing equal strength to individual zones in the body of the dam, and ultimately reducing the volume of the structure and lowering its cost. Strength can be controlled either by varying the strength properties of the concrete, or what is more often practiced, by varying the stress-strain state (SSS) of the dam. Both structural, and also production methods can be used to regulate the strength. Structural methods directed toward the stress state of concrete dams, such as variation in the shape of the dam, the installation of a different kind of joints, hinges, interlayers, thermal insulation, prestressing of the dam, etc., are widely known, and many of them have become traditional for some time now. Rationalization of the building and loading sequence of the dam, optimization of closure temperatures, zoning of the concrete in the dam on the basis of strength, formation of favorable residual stresses in the construction period, use of concretes with different moduli to redistribute the stiffness of the structure, etc. are classed as production methods of strength regulation, which are favorably distinguished from structural methods by the fact that neither the shape of the dam, nor its operating scheme are changed, the static indefinableness of the structure is reduced, and no operating expenses are required. The decision to regulate strength using production measures can be adopted in virtually any stage of design or construction, since there is no need to alter basic design drawings. The cost to implement the production measures are, as a rule, low, and the saving may be significant. Despite the above-noted advantages of production methods of strength regulation, few studies have been devoted to their investigation (P. I. Vasil’ev, V. N. Durcheva, A. P. Epifanov, L. I. Malyshev, N. S. Rozanov, Ya. G. Skomorovskii, I. B. Sokolov, V. B. Sudakov, G. I. Chilingarishvili), particularly if we speak of these methods as applies to regulation of the stress-strain state (SSS) of the dam as a whole, and not its individual elements or regions of the structure’s body. Three types of production measures, the broad implementation of which promises no small technico-economic effect, are discussed below. Rationalization of Sequence of Construction, Monolithization, and Loading of Dam. Any possible acceleration of the start of commercial service of the generating sets at a hydroelectric plant to lower the volume of capital expenditures amortized over the long term is one of the most critical problems in hydraulic-power construction. This problem is solved by the staged introduction of generating sets when the dam is only partially completed. As a rule, the start-up complex includes the minimum volume of construction-assembly work required for

Use of the above-indicated basic positions of a single methodological base for the organization of planimetric surveys of the lower pools of hydroprojects makes it possible to obtain reliable information on their actual conditions, which is required for a safety declaration of the water-development works. Positive experience gained from the complex survey of the lower pools at the Volga-Lenin and Saratov hydroelectric power plants may also find application on other hydroprojects, when it is required to evaluate the condition of the underwater portions of structures.

It has become obvious in recent years that the primary purpose of engineering surveys is to ensure the reliability and safety of water-power projects. 76% of emergency situations at the world’s hydroelectric plants are associated with the development of natural and techno-natural processes. This superposes additional requirements on surveys.

1. A significant increase in the seismicity of the region - from 7 to 9 points - was accomplished essentially without implementing any measures to ensure the stability of the terminal section of the diversion channel, the daily-regulation basin, and the upper portion of the pressure conduit in the left bank alternate scheme of the Aushigersk hydroelectric project.

A three-dimensional geofiltration model of the area of the Plavinas hydro unit has been developed and calibrated from the results of full-scale,in situ observations. The model reproduces complex-interacting groundwater flows in the area and contains, for all practical purposes, a complete set of information on the regime-forming structural elements of the installation and on the intervening hydrogeologic environment subjected to technogenic influence during operation of the hydroelectric plant.

Hydroelectric power resembles other lines in electric power, particularly nuclear, in being at present under close public management, which cannot be ignored in plans for future development. On the other hand, today’s hydroelectric power is part of electrical power supplies and supports the economy, and it has technical and economic factors that can advance or retard its progress. What does one expect from Russian power engineering in the near future? Firstly, we must have some data on the electrical power supplies at present. The installed power of stations in Russia in 1999 was about 214 million kW, which was 1 million kW larger than in 1990. In 1999, the total electrical energy production was 847 billion kWh, including HES 161.4, nuclear stations 129, and balance thermal power stations. The structure of the station power is as follows: thermal power stations 148.7 million kW (70%), HES 44.1 million kW (20%), and nuclear stations 21.3 million kW (10%). The fuel structure in thermal stations in recent years has been as follows: gas 59.5-64%, coal 25.3-29.1%, and fuel oil 7-13.2%. In 1999, the gas consumption was 64% of the total volume of fuel required for electricity. This is about 130 billion m of gas. Energy consumption has always been an objective indicator of a country’s economic state. In 1990, Russia produced 1082 billion kWh of electrical energy, but by 1998, it had fallen to 827 billion kWh, but on the other hand, in 1999, the production in Russia rose to 847 billion kWh. This is evidence for a recovery in the economy and allows one to forecast the course of that rise and the increase in electrical power demand. A very important aspect of electricity economics is the cost of fuel. Up to the present, the government has regulated the prices for gas and the tariffs for electricity, which shows that market relationships still do not apply to electricity, and consequently there is a gross disproportion over the costs of individual forms of fuel on the internal market and large differences between domestic and international prices for the most valuable forms of fuel. In 1999, the price for coal was 530 rubles/tfe, while that for gas was 340 rubles/tfe, and that for oil 925 rubles/tfe. The average tariff for electrical power has been kept at the level of 26.5 kopeks/kWh or about 1 cent. In terms of United States dollars, the price of gas on the internal market at present is 13.6 dollars/tfe, whereas in Western Europe, it is 65-75 dollars/tfe. The price of gas on the domestic market is at present lower by a factor 1.5 than that of coal, although the technological, ecological, and other features of that fuel are much better than those of coal. There is clearly a paradox in the relation between the prices for these forms of fuel. That situation cannot persist for a long period. The price of gas within the country will rise, with the limit set by the price on the international market. The same tendencies apply to the prices for other forms of fuel; the only difference is that the price of gas will rise more rapidly. It is obvious that there will be a rise in the cost of making electricity at thermal stations primarily because of the increase in the fuel component. That is the economic aspect of the problem. However, recent attempts to overcome this economic paradox have led to a technical problem that is no less acute. This very inefficient gas use on the domestic market has forced restrictions on the use of gas in power stations on a scale constituting a danger to electricity supply, particularly in the European part of the country. It must be recognized that this is an objective tendency. However, converting many large thermal power stations to use coal instead of gas requires much time and major capital investment. One should not forget that one needs simultaneously to overcome some major ecological problems associated with the conversion. That is the price of the gas pause adopted as the basis for the development of electricity at the start of the 1970s. Finally, a consequence of the past decade has been the extensive ageing of all power plant, which needs upgrading and renewal. That problem exists at all types of station, and its resolution requires large capital investment, which very much complicates development. Russian power engineering is thus in a difficult state at the start of the new century. What should we expect of it? There has been a reduction in the rate of fall in demand for electricity in recent years, and a substantial rise in consumption in 1999 over the previous year, and the continuation of that tendency in the first half of 2000

The S. Ya. Zhuk All-Russian Scientific-Research Institute for Design and Exploration and the ScientificResearch Institute of Construction Economics on assignment to the Russian joint-stock company Unified Electric Power Systemof Russia have com pleted a four-year study on utilization of the renewable and ecologically safe power generated by the Mezen’ tidal electric plant in the pool of East-West power systems [1, 2]. The following were adopted as a basis for the studies: surveys and design materials on the Mezen’ tidal electric power plant, which were performed from 1940 through 1992 under the guidance of L. P. Bernshtein, basic positions of the feasibility study for the Tugur tidal electric plant (S. Ya. Zhuk Scientific-Research Institute for Design and Exploration, 1996), the 30 years of operating experience gained at the Rance tidal electric plant in France [3], and the Kislogubsk tidal electric plant in Russia [4], and developments of the Scientific-Research Institute of Construction Economics on the creation of a new orthogonal turbine for tidal electric plants, and small hydroelectric plants [2]. The Mezen’ tidal electric plant is planned for the coastline of the White Sea in the Gulf of Mezen’, where basic reserves of tidal energy are concentrated in the European portion of Russia, and the magnitude of the tide attains 10.3 m. Of the eight sites considered for the location of the tidal electric plant in the shallow gulf, the most prominent one, which will make it possible to place the powerhouse for the tidal plant and spillway dam at natural depths without underwater excavations, and in the channel portion, which is not subject to silting by detritus, has been adopted (Fig. 1). The potential capacity of the tidal electric plant is 19.7 million kW with a generation of 49.1 billion kWh. Based on the region’s power demand at the start of the century, 11.4 million kW with a generation of 38.9 billion kWh for 3,400 h of annual utilization is assumed for use in the domestic and foreign markets [1, 8]. Structures of Tidal Electric Plant. The powerhouse for the tidal electric plant consists of 150 floating 93.0 × 76.5 × 55.3-m blocks each with four generating sets manufactured by the Zultser Esher-Weiss Company (SEW) (Fig. 2); the blocks will employ 86.0 × 53.0 × 47.4-morthogonal sets. The water-passing damwill also be built of floating 100 .0 × 45.0 × 38.0-mblocks with four bottomconduits in each block. The reliability and strength of the thin-wall reinforced-concrete design of the large-scale floating blocks for the tidal electric plant, which will function jointly with an artificial foundation bed and under the action of complex loadcombinations, were substantiated on the basis of analysis of their stress-strain state and with consideration of the 33 years of monitoring experienced gained with the floating powerhouse for the Kislogubsk tidal electric plant, and the building of floating water-passing structures in the protective dike for Saint Petersburg. The left- and right-bank dams, which will extend over 53 km (deployed at depths to 8 m) will be built of local materials. A lock and fish-passing structures will be blended into the dam. Ice- and Marine-Growth-Resistant Concretes with Extra-High Frost Resistance. The action of ice and sea water on the reinforced-concrete structures of the tidal electric plant represents a complex set of concrete-destroying mechanical, physical, chemical, and biological effects. Operating experience with concrete structures in various countries bordering the northern seas is negligible, and contradictory in nature. Dams with a compressive strength of no less than 60 MPa are recommended as ice-resistant structures in Finland, while Norway uses concretes with microsilica additives for the construction of platforms in the North Sea. Concretes for the Mezen’ tidal electric plant were developed on the basis of field tests on marine benches at the Kislogubsk tidal plant [4]; this made it possible to determine the compositions for a sulfate-resistant cement with additives of ecologically safe biocides, microfillers, and super-plasticizers, which provide for durable and impermeable structures with the capacity to resist long-termabrasion and the impact action of ice over its service life; the structure should also exhibit extra-high frost resistance ( F> 1000), and resist marine encrustation for more than 10 years

for commercial and drinking water, and the creation of zones for recreation and possible navigation in previously inaccessible sections of the riw,rs [12]. In addition, the existence of reservoir-impounding dams. together with the above-indicated benefits will, by itself, generate different kinds of risks, which are apprecial)ly lower in magnitude than the expected benefit. and by their own nature, are probabilistic; of these risks, the most familiar in terms of negative consequences are social, material, constructive (operation in the design mode), hydroh)gical, geodynamic, ecological, etc. Here, risk is understood, in tire broad sense, to be tile incapability of the project to provide the expected benefit over a given period of time. About 3.000 reservoirs, each with a volume of 1 million m a and greater, have been impounded within tile territory of the Russian Federation. As analysis of the catastrophic failures of the Kiselevsk (1993) and Tirlyansk (1994) dams h~ indicated, study of the causes and htws governing different risks, and their consideration and regulation assume practical significanc'e. Provision for reliability and safety has always been a primary condition of dam building. Statistical data derived from emergency situations are being used to assess the actual magnitude of the risk of failure, especially in recent times. Dam Reliability. Figure I shows the distribution of tile risk of emergency situations (P is equal to tile ratio of the number of failures to tile number of dams in service: the figure is presented in logarithmic scale) at various types of darns as their number increased from 1,200 at the turn of the century to 44,000 at the present tinle. According to these data, the risk of emergency situations for all types of dams, which had reached 18% in the period from I920 to 1930, had been reduced by more than a factor of three by 1971-1980. For concrete dams, a similar reduction in failure risk amounted to approximately five times from 1981 through 1990. The risk of failure for all types of concrete dams, which had reached 4% in the 1920s and 1930s, had also been reduced by up to 0.7% from 1971 through 1980. Here, the failure risk of concrete dams had been lowered by a factor of approximately 30 (from 3% in 1911-1920 to 0.1% in 1981-1990). Social risk over the entire period has served as a principal criterion of reliability assessment - the safety of existing types of dams. Catastrophes have been timely beacons for tile inspection of existing design criteria and selection of more effective methods of monitoring dam safety, such that use of the social-risk criterion reached maturity long ago in design practice. The introduction of government monitoring of tile condition of dams has been associated with large-scale dam catastrophes: after tile Bois disaster in France in 189.5, after the disaster at the Saint Francis Dam in California in 1928, after the disaster at the Eidzhi Darn and Dollarog hydroelectric plant in England in I935, and, finally, after the disasters at the Kiselevsk and Tirlyansk Dams in Russia in 1997. Considering the increa.sed attention that society has given to the safety question in analyzing problems of social risk, we can utilize the most (:autious estimates. Figure 2. which is based on data derived from various publications [1, 2, 3, 5, 6], shows the distribution of the xmmber of human victims in the largest dam disasters during the period from 1900 through 1995, according to which an increase in tile number of human victims from 1,074 to 4,165, i.e., 3.9 times, was observed in the periods between 1920-1940 and 1940-1960, with a subsequent increase to 4,576 persons in the period from 1960 through 1980. A reduction in the number of human victims to 3.858 after 1980 is explained by the incompleteness of this period; the number of victims during this period w~, nevertheless, higher than during the entire 19th century'. It is possible to criticize tile method used to calculate the number of victims

The 25-year service of the Riga hydroelectric power plant has demonstrated reliable operation of the installed power-generating and hydromechanical equipment. The condition of the water-development works has also given no cause for special concern from the standpoint of ensuring their safe operation. A large amount of the monitoring-measuring equipment installed by service personnel are completely preserved and provide for reliable monitoring of structure behavior. Data derived from field observations have completely confirmed the correctness of solutions adopted in the design of both the earth and concrete structures. The computerized information-diagnostics system installed at the plant has made it possible to develop a data base of observational results, and process and analyze them on a qualitatively higher level. Service personnel have the capacity to assess independently the safe condition of a structure for the adoption of timely measures to prevent emergency situations.

The recommendations of par. 3.29 and 3.36 of the building codes SNiP 2.06-85 concerning the development of variants of dissipating the energy of the flow and comparing their technical economic indices were not realized. The construction of an artificial pit (scour pocket) or demolishing the bar for eliminating the downstream backwater were not provided for in the design. A reduction of the capacity of the hydrostation and production of electricity was not taken into account in the design, although the results of laboratory studies established a substantial backwater caused by the downstream bar.

1. The result of on-site observations of the behavior of section joints and horizontal displacements as well as of the stress state of the dam and strains of the rock foundation show that individual sections of the dam, primarily at high elevations, are able to shift relative to one another both in longitudinal and transverse directions. It is admissible to assume the existence of only constant local force contacts between the heads of individual sections. 2. A geodynamic effect on the structures from the surrounding rock masses undoubtedly takes place. However, the level of this effect and the reaction of the structure to it according to the data given in [2] with respect to the stress-strain state of the dam and foundation cannot be considered substantiated. 3. The actual characteristics of the geodynamic effect on the structure can be determined only after eliminating other factors influencing the monitored indices of its state. The values of the indices of the state of the structure should be determined with the use of a mathematical model of its behavior, with consideration of the entire spectrum of loads and climatic effects applied to it.

1. The seismicity of the region of the Zeya hydroelectric plant, which has been defined more precisely, is (for the MCE) nine points; this exceeds the computed seismicity adopted during the design of the structures for the hydraulic facility by two points. 2. The stress-strain state and stability of the Zeya Dam under basic load combination are in line with standard requirements. 3. It is impossible to substantiate the earthquake resistance of the dam within the framework of the linearelastic calculation for both the DE, and also, not to mention, the MCE. 4. Calculations performed with consideration of the actual strength and deformation properties of the concrete on the assumption of the possibility of crack formation indicated that damages sustained by the dam during a nine-point earthquake will not result in break through of the thrust face, and can be subsequently eliminated. 5. Considering the low effectiveness of measures taken to improve the earthquake resistance of the dam, and also the possibility of performing repairs and bringing the dam to a serviceable condition after passage of the computed earthquake, it is recommended preliminarily not to implement at the present time measures to improve the earthquake resistance of the dam, which were limited only to providing for the possibility of discharging the additional water flow that feeds into the drainage system of the dam via cracks formed on the upstream face during the earthquake. 6. The conclusion concerning the retention of the dam's bearing capacity corresponds to the effect of a single earthquake. It is impossible to assess the probability of the passage of a repeated seismic effect, and in the case of the high realization of this probability, to establish the level of the dam's earthquake resistance when subjected to a succession of earthquakes, when subsequent tremors (aftershocks) will be taken up by the structure, which has sustained damage during the initial earthquake.

1. The dam core from DM 5+00 to DM 7+80 and from DM 8+50 to DM 13+80 is in a limit state. These stretches require taking immediate antiseepage measures, the stretch from DM 6+10 to DM 7+60 is top-priority. 2. A diaphragm wall made by the method of secant piles with a diameter of 1000–1200 mm is recommended as the antiseepage measure. The diaphragm wall is made from the dam crest, cut through the entire core, sands, and loamy sands in the foundation, and is carried down into loams. Plastic soilcrete with a compressive cube strength of 1–2 MPa and modulus of deformation 1000–2000 MPa is recommended as the material.