RU2309219C1 - Earth-fill dam of frozen type - Google Patents

Abstract

FIELD: hydraulic structures, particularly to construct dams of frozen type.

SUBSTANCE: dam comprises core of fixed earth, upper and lower fills created of rockfill and separated from core with transition zone, as well as impervious curtain joined with frozen base in watertight manner through frozen shield. Frozen shield includes lower embankment part made of low-permeable earth along bottom of low dam slope. To provide impervious curtain watertightness polymeric film is included in impervious curtain. Polymeric film has upper part arranged under dam core in transversal dam section. Embankment crest projects over polymeric film for height of not less than seasonal embankment thawing depth. Frozen shield is created by freezing device including freezing pipe laid in trench. In the case of shallow bed talik frozen shield bottom coincides with that of talik. In the case of deep talik frozen shield section located in talik zone is created by means of freezing column row formed from embankment crest.

EFFECT: increased dam reliability due to accelerated freezing thereof with the use of natural ambient cold and decreased dam construction costs.

7 cl, 5 dwg

Description

The invention relates to the field of hydraulic engineering in harsh climatic conditions and can be used in the construction of frozen dams.

Known soil dam on a frozen base containing a core of cohesive soil, top and bottom prisms made of stone sketches and separated from the core by transition zones, and a frozen curtain in the core and base created by a freezing device in the form of freezing columns [1].

Such a dam is not reliable enough, and its construction and operation are associated with high costs. These drawbacks of the dam are due to the fact that the height of the freezing columns usually significantly exceeds the height of the dam. As the height of the freezing columns increases, the reliability of their work decreases, and the costs of their installation and operation increase.

The closest in technical essence and the achieved result is a frozen ground dam, blocking the river channel between its sides and containing a core of cohesive soil, top and bottom prisms made of stone sketches and separated from the core by transition zones, and an anti-filter cloak placed under the bottom prism made of cohesive soil and watertightly mated to a frozen base by means of a permafrost curtain. This curtain is created by a freezing device in the form of freezing columns buried in the dam base to a predetermined depth, and includes the lower part of the embankment made of low-filtering soils along the bottom of the bottom slope of the dam [2].

This dam is also not reliable enough and relatively costly. In the first years of operation of the dam, erected in the summer, under the core and under the antifiltration cloak, at least the upper layer of the base, usually highly permeable, and especially in the channel talik area, is in a thawed state. On this layer, water from the reservoir penetrates under the core and under the cloak. One part of this water enters the core through its sole and increases the filtration through the core as a whole, and the other, and many times the first, filters through the cloak. All the water that has filtered through the core and cloak brings heat to the bottom prism. This prevents freezing of the bottom prism, core, cloak and filtering melt layer at their base by freezing, which reduces the reliability of the dam. At the same time, through this thawed soil layer, water pressure is transmitted from the reservoir to the water-resistant frozen layer in the raincoat, which in the initial period of freezing forms in the form of a frozen crust at the upper surface of the raincoat. This, from the condition of stability of the lower prism, leads to an increase in the height of the embankment, and, consequently, an increase in the height of the freezing columns made from the crest of this embankment, which increases the cost of dam construction. In addition, firstly, the creation of a permafrost curtain by freezing columns along the entire length of the dam is expensive; secondly, the implementation of the cloak is associated with the expenditure of cohesive soils, which are scarce for the conditions of the northern construction and climatic zone, the volume of which is comparable to the volume of thawed soils of the dam core; thirdly, the water filtered through the core and the raincoat rolls down the raincoat into the channel section of the dam, where it accumulates and overflows through the embankment, which leads to an unorganized formation of ice at the bottom of the lower slope of the dam; fourthly, it is not possible to move from a cohesive (usually loosely coupled) soil of the core to a stone sketch of the bottom prism by placing between them one thin transition zone made only of soil material either due to the detachment of the soil from the core and / or due to spillage ground transition zone in a stone outline.

The challenge to which the claimed frozen dam is directed is to increase the reliability of the dam and save money on its construction. The technical result in the implementation of the invention is, firstly, to accelerate the freezing of thawed soils of the core, cloak and base under them, secondly, to reduce the amount of work and expense of scarce building materials and labor costs in the construction of the dam, and thirdly, to prevent the formation of unorganized ice soles of the bottom slope of the dam during its operation.

The specified technical result is achieved by the fact that in the frozen dam of the frozen type, overlapping the river between its sides and containing a core of cohesive soil, an upper prism, a lower prism made of stone sketches and separated from the core by a transition zone, and an anti-filter cloak placed under the lower prism, water-tightly coupled to the frozen base by means of a permafrost curtain created by a freezing device and including the lower part of the embankment made of low-filtering soils along under seams downstream side of the dam according to the invention is made waterproof impervious cloak with the inclusion of a polymer film. The upper part of the cloak in the cross section of the dam is placed under the core, and the crest of the embankment rises above the polymer film not less than the depth of its seasonal thawing.

Additionally:

- the freezing device is made in the form of a freezing pipe placed at the bottom, made at the base of the embankment of the trench, which is filled with soil of a permafrost curtain, which includes the bottom edge of the polymer film of the cloak;

- a pipe is placed on the channel section of the dam in its lower prism, which leads out of the lower prism to the downstream water, filtered through the core (in the first years of the dam operation);

- the transition zone includes a layer of gravel and pebble soil and a layer of synthetic filter material, the latter directly adjacent to the core;

- if there is a channel talik at the base of the dam with the bottom of the trench bottom, the freezing device in the channel talik section is made in the form of two or more freezing pipes in a trench in a trench;

- in the case of a deep channel talik, the permafrost curtain created by the freezing pipe on the side of the dam is watertightly connected to the permafrost curtain created on the channel section of the dam with an embankment next to the freezing columns buried at the bottom of the dam to a predetermined depth;

- the exhaust pipe is coaxially placed in the heat-insulating pipe with the formation of an annular gap, while the water receiving part of the exhaust pipe is T-shaped and perforated, and the heat-insulating pipe is provided with external thermal insulation.

The main essence of the technical solution lies in the fact that the polymer film is included in the composition of the anti-filtration cloak, which ensures the waterproofness of the cloak and its small thickness, as well as the fact that this film is placed under the core. It is these two differences that provide the main technical result: acceleration of freezing of talik, cloak and base underneath by means of natural external cold, and also the fact that, in contrast to a dam with a cloak, only from cohesive soil, the formation of an active water-resistant layer at elevated elevations is prevented. Such a technical result for frozen dams of the frozen type with a permafrost curtain created along the bottom of the lower slope of the dam is not known from the prior art. This allows, according to the applicant, to conclude that the claimed technical solution meets the condition of "inventive step".

It is also new that the freezing device in such a dam is made in the form of one or more freezing pipes placed in a trench made according to special rules, and an outlet pipe is placed in the bottom prism, as well as the fact that the transition zone includes a layer of synthetic filter material.

Figure 1 shows the dam, a longitudinal section, combined with the view from the downstream; figure 2 is a section aa in figure 1; figure 3 is a section bB in figure 1, case 1 of a shallow channel talik; figure 4 is the same as in figure 3, case 2 deep channel talik; figure 5 is a section CC in figure 3.

A soil dam overlaps the channel of the river 1 (Fig. 1) between its sides, right 2 and left 3, and is built on the permafrost base 4 in severe climatic conditions with a limited amount of high-quality clay (cohesive) soils in explored quarries and during short rainy summers. The dam includes a core 5 (FIG. 2) of cohesive soil, a lateral elevation prism 6 of gravel sand and a lateral lower prism 7 of stone outline. A transition zone 8 is placed between the core 5 and the bottom prism 7. An anti-filtration cloak 9 is placed on the prepared base 4 at the bottom of the dam, which is made waterproof by including a polymer film 10. In the cross section of the dam, the upper part of the polymer film 10 is placed under the core 5 (at least under the bottom half of the base of the core), the largest, medium in size, is under the bottom prism 7, and the bottom is watertightly mated to the frozen base 4 by freezing its edges into the permafrost curtain 11. The film 10 is placed on the underlying layer 12, which within the bottom prism 7 is made of sand, and within the core 5 is made of cohesive soil. On top of the film 10 is covered with a layer 13 of high-strength geotextiles, and within the lower prism 7, the film 10 is additionally covered with a layer 14 of gravel and pebble soil. The permafrost curtain 11 includes the lower part of the embankment 15 made of cohesive soils along the bottom of the lower slope 16. The crest 17 of the embankment 15 rises above the polymer film 10 not less than the seasonal thawing depth of the embankment 15.

The permafrost curtain 11 is created by a freezing device in the form of a freezing pipe 18, placed in a trench 19 at its bottom 20. If there is a shallow channel talik 21 at the base of the dam 21 (Fig. 3), with the bottom 22 of which the bottom 20 of the trench 19 is combined (case 1) the freezing device in this section is made in the form of two (or 3) freezing pipes 18, which are tiered in a trench 19, in the case of a deep channel talik 21 (case 2), a frozen curtain 11 created by a freezing pipe 18 on the side of the dam, waterproof it is interfaced with a permafrost curtain 11 created in the section of the channel talik 21 from the crest 17 of the embankment 15 next to the freezing columns 23 (Fig. 4), which are buried with their lower part into the base 4 of the dam to a predetermined depth.

In these cases, on channel section 1 and on-board sections 2 and 3, freezing devices are made mainly by seasonally acting and autonomous sections. In this case, the freezing pipes 18 are made in an aerial view, and the freezing columns are of any kind (fans and other equipment of freezing devices are not shown in the drawings).

An outlet pipe 24 (Fig. 1) is placed on the channel section of the dam in its lower prism 7, which leads water from the lower prism 7 to the downstream, filtered through the core 5 in the first years of operation of the dam. The exhaust pipe 24 is coaxially placed in the heat-insulating pipe 25 with the formation of an annular gap 26 (figure 5). The heat-insulating pipe 25 is outside coated with a layer 27 of heat-insulating material, and the water receiving part of the exhaust pipe 24 is made T-shaped and perforated (not explained in the drawing).

The transition zone 8 includes a layer of gravel and pebble soil 28 and a layer 29 of synthetic filter material, the latter directly adjacent to the core 5.

In the drawings, other elements of the dam are indicated:

30 - natural relief

31 - removable layer in the base,

32 - position of the zero isotherm before the first spring rise in water level in front of the dam,

33 - thawed soil layer under a polymer film,

34 - the calculated position of the zero isotherm,

35 - collector of freezing pipes,

36 - fastening of the slope of the dam,

37 - the boundary of the channel section of the dam.

The dam is constructed as follows.

The unconsolidated and peaty layer 31, the thickness of which is determined by geological conditions, is removed from the natural topography 30. In the warm season, an antifiltration cloak 9 and work are carried out to ensure the creation of a permafrost curtain: a trench 19 digs, a freezing pipe (one or more) 18 is laid in it, a trench 19 is filled with cohesive soil, and an embankment 15 is poured from the cohesive soil.

Soil elements of the dam body are constructed in the usual way. Laying cohesive soil is carried out mainly in the warm season, and incoherent - all year round. At the same time, conditions are created for freezing or at least cooling the core and prisms of the dam. Laying layer 28 of gravel-pebble soil in the transition zone 8 is expediently carried out using special shields that are variable in height at the junction of the transition zone 8 with the core 5. This will allow the transition zone 8 to be thin, and its conjugation with the core - in the form of a plane (without "Christmas trees") and at the same time lay a layer of synthetic filter material 29 on the side face of the core [3].

With the onset of the cold season, the freezing pipe 18 is activated, and freezing columns 23 are activated in the deep channel talik 21 section. By the onset of the warm season, the permafrost curtain 11 is created with the boundary of the zero isotherm 32. The permafrost curtain 11 together with the core 5 and cloak 9 forms the dam a single impervious barrier. After this, the dam is ready to take on the pressure of water.

The dam works as follows.

In the pressure-filled dam, there is no movement under the polymer film 10 in the highly permeable hoist layer 33, which was formed during the execution of the cloak 9 or is a natural channel talik 21. Water from the reservoir penetrates into the core 5 through its upper face in small quantities, therefore, filtering through core 5, this water introduces a small amount of heat into the bottom prism. Further, the water along the cloak 9 slides into the channel section of the dam, where it accumulates and is discharged through the exhaust pipe 24 to the downstream to a distance safe for the dam.

In each subsequent cold period of the year, the freezing increases first of the bottom prism 7, and then the core 5 and the base under them. The zero isotherm will occupy the calculated (safe) position 34, first on the lower side sections of the dam, and then on the higher channel section, the latter, after about 7-10 years at a dam height of 25-35 meters.

In the process of freezing the dam, the polymer film 10 does not undergo alternating freezing and thawing, which is dangerous for it, while the polymer film 10 does not perform any special useful functions in the frozen part of the dam. The preservation of the film in case of uneven deformations of the base, especially over the sides of the talik 21, is substantially ensured by a layer of high-strength geotextile 31. A similar layer of geotextile can also be placed under the film 10. In the frozen dam, the outlet pipe 24 ceases to function, heating of which in the initial period of operation, if necessary carried out by creating a circulation of the coolant in the annular gap 26; means for circulating the coolant are not shown.

In this frozen state, the dam has high reliability, and with further operation of the dam, its reliability will usually increase, and it will be able to operate without interruption for an unlimited number of years.

Information sources

1. SNiP 2.06.05-84 ^* . Dams from soil materials. / Gosstroy USSR.-M .: ALL TsITP, 1991, p.24, damn. 6.1 a.

2. Patent of the Russian Federation No. 2029016, cl. ЕВВ 7/06, publ. 02/20/95.

3. Copyright certificate of the USSR No. 1802034, cl. ЕВВ 7/06, publ. 15.03 95.

Claims (7)

1. Frozen type soil dam that overlaps the river bed between its sides and contains a core of cohesive soil, an upper prism, a lower prism made of stone sketches and separated from the core by a transition zone, and an antifiltration cloak placed under the lower prism that is watertightly connected to the frozen base by means of a permafrost curtain created by a freezing device and including the lower part of the embankment made of low-filtering soils along the bottom of the lower slope of the dam, characterized in that the tivofiltration cloak is waterproof with the inclusion of a polymer film, the upper part of which in the cross section of the dam is placed under the core, and the crest of the embankment rises above the polymer film by at least a depth of seasonal thawing of the embankment. 2. The dam according to claim 1, characterized in that the freezing device is made in the form of a freezing pipe placed at the bottom of a trench made at the base of the embankment, which is filled with soil of a permafrost curtain, including the bottom edge of the cloak polymer film. 3. The dam according to claim 1, characterized in that an outlet pipe is placed on its channel section in a downstream prism, leading water filtered out through the core from the downstream prism to the downstream. 4. The dam according to claim 1, characterized in that the transition zone includes a layer of gravel and pebble soil and a layer of synthetic filter material, the latter directly adjacent to the core. 5. The dam according to claim 2, characterized in that if there is a channel talik at the base with the bottom of the trench bottom, the freezing device in the channel talik section is made in the form of two or more freezing pipes located in the trench. 6. The dam according to claim 2, characterized in that in the presence of a deep channel talik, the permafrost curtain created by the freezing pipe on the side of the dam is watertightly connected to the permafrost curtain created on the channel of the dam from the embankment crest, next to the freezing columns, recessed lower part to the base of the dam to a predetermined depth. 7. The dam according to claim 3, characterized in that the exhaust pipe is coaxially placed in the heat-insulating pipe with the formation of an annular gap, while the water receiving part of the exhaust pipe is T-shaped and perforated, and the heat-insulating pipe is provided with external thermal insulation.

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