Interesting and necessary information about building materials and technologies. Fundamentals of hydropower. Dam types Major dam disasters

In publications on the topic of hydraulic engineering and hydropower, there are often a lot of terms that are completely understandable to specialists, but not very clear to everyone else. In this regard, we are starting a series of publications on the basics of hydraulic engineering and hydropower. In them, we will talk about what dams and turbines are, why hydroelectric power plants need shutters and SF6 circuit breakers, and much more. Today I will talk about what types of dams exist; In the future, we will dwell on each of the types in more detail.

Roosevelt Arch Dam

All dams can be roughly divided into two groups: soil and concrete (we can ignore various exotics, such as metal, fabric or wooden dams, as they are practically not used in modern hydropower).

earth dams

As their name implies, earth dams are built from soil materials - sand, loam, stone. All of them are gravitational, i.e. their stability is ensured by their weight. The advantages of earth dams are the simplicity and manufacturability of their creation, the use of readily available local materials, and high seismic resistance. The disadvantages are the need for special measures to combat filtration, more complex and expensive spillways, instability when water overflows over the crest.
Soil dams are divided depending on the material used in their creation - into earthen, stone and stone-earth. Earth dams are the most widely used, especially in lowland waterworks, where they are part of the pressure front in 99% of cases.

Scheme of the dam of the Nurek hydroelectric power station

concrete dams

Concrete dams are divided into three large groups - gravity, buttress and arch.

Gravity dams remain stable due to their weight. They are simple, reliable, technologically advanced, easily combined with spillways and buildings of hydroelectric power stations, and therefore they have become very widespread. From low-pressure spillway dams in run-of-river waterworks to high-rise dams in the mountains, this type of dam can be seen everywhere. The main disadvantage is that such a dam requires a lot of concrete.

Gravity concrete dam of the Krasnoyarsk HPP

Buttress dams work mainly not due to weight, but due to the transfer of forces to the foundation with the help of special retaining walls - buttresses. This design of the dam requires much less concrete, but is much more difficult to construct.

Types of buttress dams.

Arched dams transfer water pressure to the banks. The concrete in them works in compression, and in this case its strength is very high. Therefore, arch dams can be very thin and economical. The disadvantages of arch dams are the impossibility of their construction in wide sections, as well as the presence of special requirements for the quality and configuration of the slopes.

Arch dam of the Enguri hydroelectric power station

Man is not just a child of nature. He tries to change the environment around him, to make it more comfortable for living. In this he differs from animals. Since ancient times, people have tried to curb the elements so as not to depend on the vagaries of nature and the weather. So, they learned to build dams so that there would always be water for irrigating fields and watering animals. This engineering device helps people conserve and rationally use both water and land resources, and also prevents destructive floods.

What is a dam?

A dam is a barrier that holds back or controls the flow of water. Thanks to them, artificial reservoirs are created in which life-giving fluid is accumulated, and then it is consumed as needed.

In addition to accumulative functions, a dam on a river can bring even greater benefits when the power of the water flow drives power plants that supply cities and towns with electricity. Over the years, people have learned not only to control the rivers, but also to force them to work for the good of the country.

complex structure

A dam is a hydraulic engineering structure with various functions. During the construction of each new structure, preliminary work is carried out, as a result of which an economic justification is made, the technical capabilities of the future structure are calculated. The construction of a dam is a complex and labor-intensive process that requires highly skilled workers both at the design stage and during its construction and further operation.

Types of dams

A dam is a structure that is not built according to a single pattern. Each specific object requires its own parameters and calculations. There are several types of dams.

Solid reinforced concrete have an almost unlimited margin of safety. This material is able to contain the most powerful streams of water. They are also called gravitational, because they are held on the surface of the earth due to the force of gravity, which firmly fixes the reinforced concrete in place. These dams are very expensive because they consist entirely of the specified material. Therefore, they are built only on the most powerful rivers and exploited for a very long time.

Hollow reinforced concrete dams are much cheaper than solid ones. Their insides are reinforced with steel reinforcement of various sections to increase the margin of safety.

Earthen ones are built from soil, stones, sand to hold back the flow of water. Often they are erected in places of river floods as temporary barriers around settlements.

Another type of dam is dams and embankments, which are supposed to prevent floods in the event of an increase in the water level in rivers. The height of the dam depends on its technical characteristics. Earthen ones are rarely poured above 15 meters, but reinforced concrete ones can be of almost any height that the project requires.

Historical facts

Dams are structures that have been built since ancient times. The oldest known is over 4,500 years old and was discovered in Egypt.

But one of the largest hydraulic structures in the world - the Hoover Dam on the Colorado River - was built back in 1930 in the United States and is still in operation. Its length is 379 m at a height of 221 m. The working dams claim that the reinforced concrete layer here is so thick that in the central part it still, after almost 90 years, has not yet frozen. Thanks to this construction, the largest artificial lake in the world appeared - Lake Mead, which supplies water to several arid states.

The dam is a peaceful structure. But there have been cases in history when such objects were used for military purposes. Often, during the siege of the city, the invaders blocked the riverbed with an earthen dam, changing the direction of the water flow. The besieged inhabitants, exhausted from thirst, opened the gates. There were also opposite situations, when a recalcitrant town was flooded with the help of a dam. Many such structures were blown up during World War II so that the Nazis could not go deep into the country.

By the way, according to one of the versions of historians, the unfound grave of Genghis Khan also rests at the bottom of the river, which is why the search for it took so long. The erection of dams is a technique often used by this mighty conqueror.

Modern dams often perform three functions at once - they protect against floods, allow the accumulation of water reserves and help generate electricity.

Dam was the first hydraulic structure that an ancient man learned to build. Dams of antiquity, of course, could not boast of height and elegance, but were built from improvised materials. The function of such a dam was to retain water in order to later use it for irrigation or as drinking water.

ATTENTION!

This article is under revision! Thank you for understanding!

Modern dam is a complex hydraulic structure designed to hold the required volume of water within specified limits. The most common use of a dam is to block a riverbed to create pressure and reservoir for a hydroelectric power plant. In addition to generating electricity at hydroelectric power plants, the rise in the water level in the river creates favorable conditions for timber rafting, navigation, irrigation and water supply. At the same time, when creating a reservoir, a significant area of ​​often fertile land is flooded, the natural migration of fish is hindered, and the climate near the reservoir is changing.

Dams are classified according to several criteria:
By role in the hydroelectric complex:

• deaf;
• spillway;
• station;

In terms of pressure:

• low-pressure;
• medium pressure;
• high-pressure;

According to the material used:

• concrete (reinforced concrete);
• ground;
• wooden;

On a constructive basis:

• gravity;
• buttress;
• arched;

A dam is called deaf if its design does not provide for spillways. spillway dam, as the name implies, is equipped with one of the types of spillway devices and is designed to pass excess water into the downstream. station dam equipped with water supplies.

The division of dams by pressure, as in the case of hydroelectric power plants, is conditional. Here are the most common values:

• low-pressure dams - up to 20 m;
• medium pressure dams - from 20 to 80 m;
• high-pressure dams - from 80 to 200 m;

Side by side with the head criterion is the dam material used. High-pressure dams are built of concrete or reinforced concrete, in the range of medium heads, earth materials can be used for construction, and low-pressure dams can be built of wood.

In turn, its structural feature is closely related to the material from which the dam is built. earth dams And wooden dams can only be gravitational. This means the stability of the dam, that is, the ability to withstand the pressure of water from the reservoir, is determined only by its weight. gravity dams can be erected on any grounds.
Reinforced concrete and concrete dams can be gravitational, arched and buttressed.

Arch dam provides stability in the reservoir by transferring water pressure from the front of the dam to the banks or coastal abutments. Its unusual design allows this to be done - an arc convex towards the upstream, resembling an arch from above (hence the name). But because of the same feature, it can only be built on a rocky foundation.

buttress dam is a concrete ceiling or vaults (arches), based on buttresses. At the same time, the pressure ceiling, in the form of slabs or vaults, does not stand vertically, but at a certain angle to the upstream. This design provides stability not only due to the weight of the dam, but also due to the pressure of water on its inclined surface. The construction of a buttress dam is possible only on a rocky foundation.

Diversified: the rise in the water level and the increase in depths in the upper pool favor navigation, timber rafting, as well as water intake for irrigation and water supply; the concentration of pressure at P. creates the possibility of energy use of the river flow; the presence of a reservoir allows you to regulate the flow, i.e. . increase the flow of water in the river during low periods and reduce the maximum flow in high water, which can lead to destructive floods. P. and the reservoir significantly affect the river and adjacent territories: the river flow regime, water temperature, and the duration of freeze-up change; hindered fish migration; the banks of the river in the upper pool are flooded; the microclimate of coastal areas is changing. P. is usually the main structure of the hydroelectric complex. Dam building arose as long ago as hydraulic engineering, in connection with the significant development of artificial irrigation of territories among the agricultural peoples of Egypt, India, China, and other countries. The construction of P. was required for the construction of hydropower plants, and then the construction of hydroelectric power stations. The energy use of water resources was the main stimulus for the increase in the size and improvement of the constructions of rivers, and the appearance of hydropower facilities on high-water rivers. On the territory of the USSR, water mills with P. were built in the times of Kievan Rus. In the 17-19 centuries. the mining, metallurgical, textile, paper, and other branches of industry in the Urals, Altai, Karelia, and the central regions of Russia mainly used the mechanical energy of hydraulic power plants; their P. were insignificant in size and were built from local materials. Powerful hydroelectric power plants with large concrete and earthen P. began to be built only under Soviet power, after the adoption of the GOELRO plan. In 1926, the first concrete spillway was built at the Volkhov hydroelectric station. In 1932, the high concrete P. Dneprovskaya hydroelectric power station was built (its highest height is about 55 m). Spillway P. Nizhnesvirskaya HPP - the first P., built on weak clay soils. In the 50-70s. on high-water rivers were built: alluvial earthen P. on the Volga near Kuibyshev and Volgograd; earthen P. Nurek HPP on the river. Vakhsh, the arched P. of the Sayan hydroelectric power station on the Yenisei (height 242 m, length along the ridge 1070 m; under construction, 1975), and many others. in the world. Of the P. built abroad, it should be noted: multi-arched P. Bartlett, height 87 m (USA, 1939), stone P. Paradela, height 112 m (Portugal, 1958), earthen P. Ser-Ponson, height 122 m ( France, 1960), stone and earth P. Miboro, height 131 m (Japan, 1961), gravity concrete P. Grand Dixans, height 284 m (Switzerland, 1961). The type and design of a building are determined by its size, purpose, and natural conditions and the type of basic building material. According to their purpose, reservoir reservoirs and water-lifting reservoirs (designed only to raise the level of the upper pool) are distinguished. According to the magnitude of the pressure, P. is conditionally divided into low-pressure (with a head of up to 10 m), medium-pressure (from 10 to 40 m), and high-pressure (more than 40 m). Depending on the role performed as part of a hydroelectric complex, a waterway can be: deaf, if it serves only as a barrier to the flow of water; spillway, when it is designed to discharge excess water and is equipped with surface spillways (open or with gates) or deep spillways; station, if it has water intake openings (with appropriate equipment) and conduits that feed the turbines of the hydroelectric power station. According to the main material from which the dam is built, earthen dams, stone dams, concrete dams, and wooden dams are distinguished. Earthen P. is erected wholly or partially from impermeable soil. Laid along the upstream slope of P., low-permeable soil forms a screen; when such soil is located inside the body of P., a core is created. The presence of a screen or core makes it possible to build the rest of the pit from permeable soil or from stone materials (stone-and-earth pit). At the bottom of the lower slope of the earthen P., drainage is arranged to drain the water that has filtered through the body and base of the P.. The upstream slope of P. is protected from the effects of waves by concrete slabs or rock fill. During the construction of earthen bulk P., the soil is mined in a quarry with excavators, transported to the construction site by dump trucks, placed in the body of the P., leveled with bulldozers, and compacted in layers with rollers. The erection of alluvial P. includes the excavation of the soil by dredgers or hydraulic monitors, the transportation of the pulp through pipes and its distribution over the surface of the P. under construction, after which the water leaves, and the subsiding soil becomes self-compacting. To prepare the foundation and erect an earthen waterway in the riverbed, its foundation pit is fenced off with bridges, and the river is diverted along pre-laid temporary conduits, which are closed after the construction of the waterway. In stone (throw) roofing, the screen or the central waterproof element (diaphragm) is made of reinforced concrete, asphalt, wood, metal, or polymeric materials. The requirement for low water permeability also applies to the base of the P. If the soil of the base is permeable to a great depth, it is covered in front of the P. with a droop (for example, from clay), which forms one whole with the screen. P. with a core is supplemented by a device at the base of a steel sheet pile wall or an impervious curtain. The stone in rockfill and rock-and-earth P. is poured in layers of great height. Concrete plinths are usually classified according to their structural features, depending on the shear conditions; accordingly, three main types of dams are distinguished (Fig. 2): gravity dams, arch dams, and buttress dams. Main The material for modern concrete concrete (mainly gravitational) is hydrotechnical concrete. One of the most important issues in the construction of concrete P. - the reduction of water filtration in the base. For this purpose, an impervious curtain is arranged at the base of a high concrete P. near the upper edge. In the rest of the area, the base is drained to reduce the pressure of water on the sole of the P., which increases the stability of the structure. Gravity and buttress P., in order to avoid the formation of cracks due to temperature fluctuations, are cut along the length into short sections, the seams between which are blocked by waterproof seals (see Waterproofing). To prevent the appearance of cracks as a result of shrinkage of concrete during hardening and to reduce thermal stresses, concrete blocks are concreted in separate blocks of limited dimensions, artificial cooling of the components of the concrete mixture and concrete laid in blocks is used by means of circulation of a cooling liquid (from a refrigeration unit) through a system of pipes laid in the body of the concrete Concrete P. in the riverbed is usually built in 2 phases under the protection of the cofferdams that enclose the pits. During the construction of the first stage of the river, the river flows along the free part of the channel; at the second - through the holes (holes) left in P., which are closed at the end of all construction work. If the riverbed is narrow, a concrete riverbed is built in one step, with the river temporarily diverted into coastal waterways. A low-pressure concrete spillway dam, which is widespread in the practice of hydraulic engineering construction, is built on a non-rocky foundation and is designed to pass large water flows, has a design shown in Fig. 3. It is based on spillway spans formed by concrete flutebet and bulls and blocked by hydraulic gates. Behind the weirs, a massive fastening of the channel is arranged - a water hole (sometimes buried in the form of a water well), then a lighter fastening is located - an apron. Drainage is arranged under the reservoir. With banks or earthen P. spillway P. is mated with massive abutments. A low-pressure concrete spillway is usually built using reinforcement, often the entire structure (see Reinforced Concrete Dam). headwater level, and ships and rafts go through the lock. In the high-water period, gates and bridges are removed, buttress trusses are laid on a flutbet, opening the way for ships and rafts through the dam. The general trend of modern dam construction is an increase in the height of the dam. often turns out to be more rational than one high. Improving the types of P. made of soil materials is carried out while simultaneously reducing the cost and speeding up their construction by increasing the power of construction mechanisms and vehicles. Increasing the efficiency of concrete concrete is achieved by reducing their volume, replacing gravity concrete with buttress concrete, and using arched concrete more widely. This trend is accompanied by the improvement and specialization of the properties of cement and concrete. It is very effective to combine a spillway dam and a hydropower plant building in one structure, which ensures the reduction of the concrete (the most expensive) part of the pressure front of the hydroelectric complex. This hydrotechnical work, M., 1970. A. . Mozhevitinov.

Of all the dams, the arch dams certainly make the biggest impression. It seems absolutely incredible how a thin curved concrete wall holds billions of tons of water, and even at the same time has a huge margin of safety. Well, in the end, arched dams are just very beautiful.

Xiaowan is the highest arch dam in the world. Photo from here

The principle of operation of arch dams is fundamentally different from all other types of dams. If gravity and buttress dams put pressure on the base, then arch dams transfer the load to the banks. An arch dam can even be specially cut off from the base with a special cut seam (this is sometimes done to relieve stress that occurs in some types of dams).

Lumei Dam with seam at the base

At the same time, the concrete in the arch dam works in compression, and in such a situation its strength is extremely high. Accordingly, the arch dam can be surprisingly thin - at a height of a hundred meters, its thickness can be only 2-3 m.

At the same time, such thin arch dams are not always built. Depending on the specific conditions, it may be more efficient to build a thicker or even arch-gravity dam, the stability of which is ensured both by the emphasis on the banks and by its own weight.

The main advantage of a concrete dam is significant savings in concrete, reaching 80% of the amount of concrete in a gravity dam. At the same time, arch dams impose special requirements on the banks - on the width of the valley, its shape and the quality of the rocks.

Enguri dam. Photo from here

In wide valleys, the construction of arch dams is inefficient. There is a special coefficient that reflects the ratio of the length of the arch dam along the crest to its height (L/H). The construction of arch dams is most effective if this coefficient does not exceed 3.5, although there are cases of construction of arch dams in relatively wide sections - for example, for the Sayano-Shushenskaya HPP L / H = 4.56, for the Pieve di Cadore dam in Italy L/H=7.45.

Pieve di Cadore Dam. Photo from here

They do not like arched dams and asymmetric valleys - the arch does not work normally in them. If necessary, they even resort to the construction of special tie-ins and retaining walls. And finally, the rocks against which the arch dam rests must be very strong. Accordingly, the ideal place for an arch dam is a mountain gorge, where they are actually mainly built.

Scheme of the Xiaowan hydroelectric dam.

The stability of arch dams is extremely high. In model experiments, they collapsed only at loads 3–5 times higher than the calculated ones. There is a well-known example of a disaster at the Vaiont dam (very high and very thin), when a landslide descended into the reservoir caused water to overflow through the dam with a layer of at least 70 m - the dam withstood and, moreover, was almost not damaged.

Vayont Dam. Photo from here

There are few arch dams in Russia - three purely arch dams (Chirkeyskaya, Miatlinskaya and Gunibskaya) and two arch-gravity dams (Sayano-Shushenskaya and Gergebilskaya). There is a project of the Aghvala hydroelectric power station on the Andiyskoye Koysu river with an arch dam 210 m high.

Chirkeyskaya HPP. Photo from here

The highest arch dam in the world is the dam of the Chinese hydroelectric power station Xiaowan on the Mekong River with a height of 292 m, put into operation in 2010. Before that, for a long time, the leadership was held by the Enguri hydroelectric dam in Georgia, its height is 271.5 m. Many high-rise arch dams are being built in China - for example, the Siluodu hydroelectric dam, 278 m high (by the way, the power of the hydroelectric power plant is also impressive - 13,860 MW!). The highest arched dam in the world, Jinpin-1, 305 meters high, is also being built there. However, this is not the limit - there is a beautiful project of the Abu Sheneila dam in Sudan, 335 meters high!