RU2486309C2 - Dam of soil materials - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: dam of soil materials, both frozen and thawed types, is erected on a frozen base. The soil dam comprises an anti-filtration core 1, upper and lower thrust prisms 2, transition zones 3 and 4 between the core 1 and thrust prisms 2. The core 1 of the dam consists of a low-filtering cohesive soil. Thrust prisms 2 are made of stone rip-rap. The slope of the lower thrust prism is covered with a layer of fine stone 5. At the same time in the lower thrust prism with the help of an air impermeable screen 6 there is an area of seasonal active convection 7. The screen 6 is made of thin rubberised fabric or cemented stone. The area of seasonal-active convection 7 is equipped with a hangar 8 and a detachable air impermeable cover 9 arranged on the lower slope. The hangar 8 is located on the dam ridge.

EFFECT: permanent temperature mode in a core and in a transition area at the side of a lower reach, when operating both thawed and frozen soil dam under severe temperature conditions of a northern construction climate area.

6 dwg

Description

As part of the hydropower facilities being built in the permafrost zone (the same: in the permafrost zone), dams of soil materials are mainly provided. Among them, the most economical in severe climates are stone dams. Such dams attract an invariable advantage - the ability to use local building materials and simplicity in construction technology, as well as year-round work.

According to the source [4], the location in the zone of permafrost is a serious risk factor for damage to dams and their reservoirs. 48% of accidents at hydroelectric power stations occur precisely in such regions (with a small number of hydroelectric stations located here). The main cause of damage is the underestimation of cryogenic processes in the body of dams, their foundations and in the adjoining areas, associated with changes in the conditions of heat transfer, temperature conditions, physico-technical properties of frozen rocks under the influence of hydropower, leading to the development of thermokarst, thermal erosion, ice formation, etc.

According to the source [7], by the end of the 20th century, over 800 low-pressure hydroelectric facilities were built in the permafrost zone in Russia, including more than 400 in Yakutia. All of them are more or less subject to deformations. An analysis of the operation of industrial water supply hydraulic systems indicates that more than 40% of failures occurred due to violation of the temperature regime of structures. Moreover, for the first time three years of operation, up to 53% of failures occurred, between three and five years - 31%, the rest - in subsequent years. Up to 90% of low-pressure reclamation waterworks in Yakutia for the above reason are destroyed in the first year of operation.

A stone-earthen dam is known (dam of the Kolyma hydroelectric station), in which the lower prism periodically freezes, forming an ice-ground mass that adjoins the permafrost base and the dam core. Under such conditions, the frozen bottom zone of the transition layers cannot drain the filtered water, and the remaining local thawed areas operate in unpredictable extreme conditions, which can lead to emergency situations [5].

A stone-earthen dam (dam of the Ust-Ilim hydroelectric station) is known, in which subsidence in the body was found during construction and operation, as a wedge of the frozen body formed in its stone draft, which then melted. That is, in severe winters, due to the formation of a temporary layer of frozen rocks, the building is sedimented [4].

From the foregoing, it is clear that for trouble-free, reliable operation in harsh climatic conditions of stone and earth dams, it is necessary to be able to regulate their temperature regime taking into account the diversity and interconnection of heat and mass transfer processes occurring in individual elements.

It is known that stone-earth dams, like other soil dams in the permafrost zone, are built according to two principles:

- during construction according to the I principle, a frozen dam is obtained, called non-filtering;

- during construction according to the II principle, a thawed type dam, called a filter dam, is obtained.

A frozen dam is known with a frozen anti-filter core made of low-filter cohesive soil, a persistent upper and lower prism from a stone outline, a transition layer between the core and persistent prisms and a frozen curtain. The dam is additionally equipped with an embankment of low-filtering soils with a height not less than the depth of seasonal thawing of the soil, sprinkled along the bottom of the lower slope, from the crest of which columns of the permafrost curtain are installed, and a cloak of cohesive soil located under the lower pressure prism [3].

The disadvantages of this design are:

1. The dam is supposed to be used only in the frozen state. The operation of the dam in a melted state when regulating the temperature regime of the proposed method is impossible.

2. Installation of expensive columns of permafrost.

3. There is no regulation of the temperature regime of the dam itself. It is not possible to guarantee the preservation of the core and the transition zone from the bottom of the persistent prism. As a result of the warming effect of the reservoir and the absence of an ice-soil curtain along the axis of the core, it is quite possible to thaw both the core itself and the transition zone. In the summer period (during the period of positive temperatures of atmospheric air) as a result of natural convection of air in the lower persistent prism, it will warm up with the movement of the zero isotherm to the core of the dam.

The closest in technical essence to the claimed one is a dam of soil materials on a frozen base with a frozen anti-filtration central core, upstream and downstream resistant prisms. The lower prism has an inner zone of coarse-grained stone, covered with soil from smaller fractions, and the crest of the dam and the lower slope are covered with a waterproof clay layer. The dam is equipped with exhaust pipes along the ridge and the bottom berm, as well as a ventilation system, through which natural and forced convection of air is carried out in the pores of the inner zone of the lower prism from the stone outline [6].

The disadvantage of the dam of this design is the low reliability during operation. Firstly, the dam is supposed to be used only in the frozen state. Secondly, into the lower prism, which has an inner zone of coarse-grained stone, it is possible that smaller fractions are sprinkled on top of the soil. As a result, the efficiency of convection cooling of the base and the anti-filter element of the dam will decrease. Thirdly, there is a high probability of clogging with ice by the horizontal pipes-outlets with which the dam is equipped, and they are practically impossible to clean.

The present invention is aimed at solving the problem of creating a design of both thawed and frozen soil (stone-earthen) dam, providing a constant temperature regime in the core and transition zone from the downstream side when it is used in severe temperature conditions of the northern building and climatic zone.

The solution of this problem for a soil dam (both thawed and frozen), consisting of an anti-filtration core 1 from a low-filter cohesive soil, a top 2 and a bottom prism from a stone outline and transition zones 3, 4 between the core and thrust prisms (Fig. 1, Fig. .2) is achieved as follows.

1. For thawed (filtering) dam (figure 1):

In order to prevent freezing of transition zones 4 of the dam from the side of the lower prism, as well as to reduce freezing of the upper part of the core 1 during the operation of the dam, it is proposed to regulate its temperature. This regulation is as follows:

a) in order to reduce air convection in the lower prism and thereby reduce the deep cooling of the prism during the cold season, the slope of the lower stone-filling prism is covered with a layer of fine stone 5 (quarry fines or sand and gravel);

b) to ensure that part of the lower prism is maintained near the transition zone in a thawed state in the lower prism, an area of seasonally active convection 7 is created using an airtight screen 6 made of thin rubberized fabric or cemented stone, which is activated in the warm season. This inclusion is as follows.

In the warm season, hangar 8, located on the crest of the dam, opens, additionally, airtight cover 9 is removed on the lower slope, after which flow convection occurs in the zone of the lower prism with seasonally developed convection from a coarse-grained outline. In addition, to enhance flow convection in the subscreen zone in the upper hangar, it is possible to create a vacuum of up to -1 kgf / cm ² (for example, using exhaust fans). This rarefaction will lead to the appearance of the wind tunnel between the screen 6, the downstream water in the lower prism and the core 1 with increased air velocities in the pores of this “pipe” in the desired - warm season.

In the cold season, the hangar 8 is closed, an airtight cover 9 is additionally installed on the downhill slope, after which the flow convection in the zone of the lower prism 7 with seasonally developed convection is stopped. Only limited thermogravitational convection is possible, caused by the density stratification of pore air due to differences in its temperature.

2. For the frozen (non-filtering) dam (figure 2), the temperature control is carried out in the same way as for a thawed dam, except that the hangar 8, located on the crest of the dam, opens in the cold season, in addition, the airtight cover is removed on the downhill slope 9. In the warm season, hangar 8 closes, and an airtight cover 9 is additionally installed on the lower slope.

The screen and hangar do not allow atmospheric precipitation and melt water to enter the “pipe” zone, as a result of which pores will not fill with ice sketches in areas with negative temperature.

There will be no sublimation of ice in the pores of the outline of the “pipe” for the melt dam, since the “pipe” is warm, the atmospheric air penetrating into the pipe is warm. For a frozen dam, on the contrary, the “pipe” is cold, the atmospheric air penetrating into the pipe is even colder, the saturation elasticity of which is lower than that of the air in the pipe pores.

To assess the effectiveness of the proposed method for regulating the temperature regime of stone-earth dams, its computer simulation was performed for the operational period. Modeling was performed using the NORD.3D software package [1]. The NORD.3D software package implements a physical and mathematical model of the temperature-filtration regime of stone-earth dams described in [2]. The reliability of the results obtained as a result of modeling by the NORD.3D software package has been repeatedly verified by comparison with field data (see, for example, [1]), where the initial data for modeling are the data at the time the facility was commissioned, and the results are compared with field data at the time of diagnosis of the structure.

As an example, here are the results of modeling the temperature regime for two variants of the Telmama hydroelectric dam. The Telmama hydroelectric facility is projected on the Mamakan River in the Bodaibo District of the Irkutsk Region near the mouth of the Telmama River.

The site of the Telmama hydroelectric complex is included in the zone of continuous development of permafrost with a through talik under the Mamakan River, the width of which does not exceed the width of the river along the low-water winter water edge. At the base of the permafrost is a merging type.

The rocky-and-earth dam of the hydroelectric complex is 154.5 m high, 1120.50 m long along the crest, designed with a loam core of 40.00 m bottom thickness and 7.5: 1 face laying, has two transition zones with an average thickness of 3 m. (figure 3). According to the temperature state of the melt dam, it assumes the free filtration of water through the core with its unhindered discharge into the lower pool along transition zones.

For the thawed channel dam of the Telmama hydroelectric complex, modeling showed that during operation there is a real danger of freezing of the transition zones from the bottom prism, as well as deep freezing of the central part of the dam due to significant winter runoff of the reservoir by a hydroelectric power station (Fig. 4). These circumstances can lead to the transfer of free filtration in the core of the dam to pressure or pressure-free. Such a situation cannot be allowed, since it will take the structure beyond the design state.

Modeling the temperature regime under the regulation of the proposed method showed that the near-core zone of the lower prism of the dam under conditions of temperature regulation will remain in a guaranteed thawed state, which, in fact, is required (figure 5).

Thus, we can conclude that the invention using the melt channel channel of the Telmam dam as an example is very effective and can be applied to other melt stone and earth dams designed in the permafrost zone.

For floodplain sections of the Telmama hydroelectric dam, where permafrost rocks are more than 80 ... 100 m thick, it is possible to erect a frozen stone and earth dam with temperature regulation. To confirm the effectiveness of the proposed control method, the temperature regime of the frozen left-bank stone-and-earth dam of the Telmama hydroelectric complex was simulated for 10 years. The core of the loam dam without a permafrost curtain is frozen at the temperature of -1 ° C by the beginning of the forecast.

The results indicate that in the 10th year of operation of the frozen dam under conditions of temperature control, the core is in a guaranteed frozen state, which also confirms the effectiveness of the proposed invention (Fig.6).

Information sources

1. Gorokhov E.N. The NORD software package for three-dimensional modeling of the temperature regime of stone-earth dams / E.N. Gorokhov, V.I.Loginov // Materials of the Intern. conf. "Engineering and geological surveys in the permafrost zone" IGK-2000 ". - SPb .: VNIIG them. B.E. Vedeneeva, 2000 .-- S. 64-73.

2. Gorokhov E.N. The theory and method of calculating the temperature-cryogenic regime of dams from stone drafts in the permafrost zone / E.N. Gorokhov // News of higher educational institutions. Construction. 2005. - No. 9. - S. 32-39.

3. Soil dam of frozen type / Bukatnikov VD, Maul VK, Shamaitis Yu.I. // Patent RU No. 2029016. Publ. 02/20/1995 g.

4. Malik L.K. Risk factors for damage to hydraulic structures. Security Issues / L.K. Malik; (ed. N.I.Koronkevich) // - M .: Nauka, 2005.

5. Pekhtin V.A. On the safety of dams in the northern climatic zone / V.A. Pekhtin // Hydrotechnical construction. - 2004. No. 10, p.6.

6. Dam from soil materials / Balyasnikov G. G., Maksimov I. A. // Patent SU No. 1714030. Publ. 02/23/1992

7. Zhang R.V. Temperature and stability of low-pressure hydroelectric facilities and soil channels in the permafrost zone / RVZhan // Abstract of dissertation for the degree of Doctor of Technical Sciences. - Yakutsk, 2001.

Claims (1)

A dam from soil materials of both frozen and thawed types, erected on a frozen base, including an anti-filtration core from a low-filter cohesive soil, upstream and downstream thrust prisms made of stone outline, transition zones between the core and thrust prisms, characterized in that the downhill slope a stone-prism prism is covered with a layer of small stone, in the bottom prism with the help of an airtight screen made of thin rubberized fabric or cemented stone, create a seasonal-active zone convection, equipped with a hangar located on the crest of the dam, and a removable air-tight coating located on the lower slope.

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