RU2382139C1 - Riverbed-diversion structure of seasonal waterway on permafrost - Google Patents

Abstract

FIELD: construction. ^ SUBSTANCE: structure of seasonal waterway on permafrost comprises dam, which blocks riverbed and talik of waterway, water channel arranged as bypassing protected mountain object, having foot below riverbed bottom, and low-flow water conduit, which provides for passage of riverbed talik underground waters that are capable of ice crust formation within the limits of the structure in cold season of the year as bypassing mountain object. Dam is equipped with antifiltration device adjoining permafrost, in water channel bottom in supply channel and bottom plate of inlet head are arranged at the level or below riverbed bottom adjoined to them, height of cavity and value of bottom longitudinal inclination permanently provide for nonpressure mode of water flow at underground section of water tunnel, provided with lining, bottom and walls of which produce water-impermeable tray, and output head, by means of diversion channel, is coupled with waterway. Low-flow water conduit comprises influent chamber installed in filtering water collector, and flow cavity of low-flow water conduit is heat insulated, besides supply channel of water tunnel within the borders of permafrost is equipped with antifiltration coat, which directly at the border of riverbed talik is coupled with permafrost in a water-permeable manner. ^ EFFECT: invention provides for reliability of structure. ^ 12 cl, 7 dwg, 1 ex

Description

The invention relates to the construction, namely, hydraulic structures, carrying out the diversion of seasonal watercourse from a protected mountain object in areas of permafrost and severe snow tolerance.

The development of irrigated deposits is associated with a series of works on their drainage, and the capital and operating costs of drainage reach 20 and 15% of the total cost of raw materials, respectively [1].

In areas of permafrost spreading with open-pit mining of minerals, drainage costs can be small, and work can be limited mainly by diverting surface runoff from a mountain object. However, if the field in the plan crosses a seasonal watercourse, then an expensive channel drainage construction is performed (the same: an artificial channel), mainly gravity. Such a structure consists of a water-lifting dam and a water conduit made in the form of a hydraulic channel [2, p. 210-230] or a hydraulic tunnel [2, p. 248-265]. This hydraulic plumbing tunnel (hereinafter: the tunnel) includes a supply channel, an inlet head, an underground section arranged without removing the ground mass above, an outlet head and a discharge channel [2, p. 250, Fig. 28.2].

The disadvantages of such a channel structure on permafrost are as follows.

1. Inserts into the permafrost, carried out during the implementation of channel channel construction, can lead to disruption of the upper water-gas-tight ice-ground layer of permafrost soils (the same: raincoat). Such a raincoat was formed in the initial period of the last (Late Holocene) cooling during unilateral freezing of soils from top to bottom under conditions of continuous penetration of precipitation from above into frost-pores and pores of water and migrating from below to freezing zone. The formation of the raincoat took place almost everywhere below the boundary of seasonal thawing of soils within the weathering crust, and the penetration of water into the raincoat occurred in a quantity dosed naturally. At the same time, along the largest stress cracks formed in previous periods of glaciation-warming, under the influence of a hydraulic slope, water from the cloak flowed to the nearest discharge sites. The gases accumulated in places under the cloak created a pressure exceeding atmospheric, which accelerated the flow of water from such "brook" (the same: channel) cracks to the discharge points. As a result of this, as the lower boundary of the permafrost soils further lowered below the cloak, part of the deep cracks turned out to be ice-free - hollow cracks [3].

Such a high-quality cloak was formed in conditions of abundance of moisture at the sole of taliks of shallow reservoirs.

Inserts in permafrost, including well drilling, sometimes violate the integrity of the cloak, which often leads to the development of intensive filtration of water from a reservoir filled with a channel or tunnel and, correspondingly, an abnormally fast thawing of frozen soils: the Irelyakhsky waterworks in Yakutia [4], the tailings of the Nadezhda Metallurgical Plant in Norilsk [5], tailing dump No. 8, Aikhal settlement in Yakutia and others.

Moreover, for example, when developing a deep quarry, the stress state of the rocks in the sides changes, which leads to the opening of existing cracks in the rocks and the formation of new ones. This is facilitated by natural and man-made shocks.

The degree of permeability of frozen rocks under the cloak can be judged, for example, by a study conducted at Vilyui HPP-3, where air with smoke was pumped into a prospecting adit, performed on the river side (the same side of the quarry). In this case, smoke exited through hollow wells at a distance of 90 to 160 meters from the smoke source [6].

The initial penetration of water from a cut-in tie-in into a quarry can occur only along one of the largest fissures. This will be facilitated by the possible mineralization of water in the fracture, which will lower the freezing temperature of water. In the future, intensive and uncontrolled thawing (thawing) of permafrost will inevitably take place.

2. A water-lifting dam blocks both the ground channel part of the watercourse and its underground talik part. After the onset of negative air temperatures (cold season), between the termination of surface runoff from the slopes and the complete freezing of the seasonal thawing layer and channel talik, low-temperature groundwater can penetrate the water conduit (channel and / or tunnel) and form ice in it. This ice, especially in conditions of heavy snow cover, complicates the passage of spring floods through the water conduit and, as an extreme case, can make the passage of floods impossible.

3. In the case of the tunnel (more precisely: its underground section) in the pressure mode, the channel branch structure additionally has the following disadvantages:

- from the operating conditions, the preferred form of the tunnel is round or at least oval, which is less convenient from a production point of view;

- preferably continuous flow flow throughout the tunnel, which with frequent changes in flow rate is difficult to achieve, especially in a multi-kilometer tunnel, since the tunnel is required to be switched to pressure mode (segmented shutter at the output end);

- the operation of the tunnel in pressure mode increases the load on the lining and is inevitably associated with a significant increase in the water level in front of the inlet head and the formation of a reservoir, which can lead to the thawing of a large amount of permafrost between the channel structure and the protected mountain object, which will create a problem that will be difficult to eliminate even at high cost.

The problem to which the invention is directed, is to increase the reliability of the channel structure. The technical result achieved in this case is to prevent permafrost from thawing between the channel structure and the protected mountain object, to prevent the formation of ice in the tunnel and to free the entry end of the tunnel from ice and snow naturally.

This problem is solved, and the technical result is achieved by the fact that the channel drainage structure of a seasonal operating watercourse on permafrost contains a dam blocking the channel and the talik of the watercourse, a tunnel bypassing the protected mountain object, having a sole below the bottom of the channel, and a low-flow water conduit. This low-flow conduit provides, in the cold season, bypassing a mountain object, the passage of groundwater of channel talik, capable of forming ice within the structure. The dam is equipped with an anti-filtration device associated with permafrost. In the tunnel, the bottom of the inlet channel and the bottom plate of the inlet head are located at or below the channel bottom mating with them, the height of the cavity and the longitudinal slope of the bottom constantly ensure a non-pressure mode of water flow in the underground section of the tunnel equipped with a lining, the bottom and walls of which form a waterproof tray, and the output tip through the outlet channel is connected to the watercourse. The low-flow conduit contains a water intake located in the filtering catchment, and the flow cavity of the low-flow conduit is thermally insulated. The tunnel inlet channel within the permafrost is equipped with an anti-filter coating, which is directly waterproofed with permafrost directly at the boundary of the channel talik.

Additionally:

- the anti-filter device of the dam is made in the form of an ice-soil wall formed by freezing columns;

- the entrance end of the tunnel is made of a corridor type and forms a continuation of the lining tray of the underground section of the tunnel, while the top of the side walls of the corridor is located at a level that is not flooded in the warm season;

- a low-flow conduit is located in the tunnel and gravity drains ground water from the channel talik to the cavity of the underground section of the tunnel or to the outlet end of the tunnel;

- water intake low flow conduit is made in the form of a pipe perforated by longitudinal slots;

- the filtering catchment of a low-flow water conduit is made of coarse soil and is part of the powder to the dam;

- the inlet head is equipped with an anti-icing threshold, the crest of which is located above the water intake of a low-flow water conduit;

- low water conduit along the length partially or completely made of polyethylene pipes;

- the outlet channel of the tunnel within the permafrost is equipped with an antifiltration coating, which is directly waterproofed with permafrost directly at the boundary of the channel talik.

- the combination of the antifiltration coating of the inlet channel and the antifiltration coating of the outlet channel with permafrost at the boundary of the channel talik is carried out by means of a tooth from clay soil frozen during its implementation;

- at least a portion of the corridor directly adjacent to the underground section of the tunnel is provided with a water-permeable overlap on which the filter prism from coarse soil is located and which hydraulically communicates the pore space of the filter prism with the cavity of the underground section of the tunnel;

- the permeable ceiling is equipped with a snow canopy.

It is the non-pressure mode of operation of the tunnel that allows water to be taken from the watercourse by means of a low-pressure earthen bulk dam with virtually no increase in the water level in the watercourse, i.e. without creating a reservoir, and the antifiltration coating of the flooded insets allows you to equivalently restore a waterproof raincoat damaged by insets (channels). This prevents the filtering of water under the cloak through hollow cracks, which prevents permafrost thawing. In addition, the implementation of the low-flow conduit and the inlet head of the tunnel according to the previously mentioned rules prevents the formation of ice in the tunnel, and when filling the inlet head with ice and filling it with snow, as an extreme case, it ensures that the inlet head is free of ice and snow naturally in the beginning of the warm season. All this allows you to achieve the previously specified technical result.

The invention is illustrated by drawings:

- figure 1 shows the channel structure, a schematic plan;

- figure 2 - node I in figure 1, plan;

- figure 3 is a section aa in figure 2;

- figure 4 is a section bB in figure 2;

- figure 5 is a section CC in figure 4;

- figure 6 is a section DD in figure 4;

- Fig 7 is a design of a pair of antifiltration coating of the inlet channel with permafrost, a section along the longitudinal axis of the inlet channel.

The permafrost facility 1 diverts a seasonal watercourse 2 that crosses in plan a mineral deposit planned for open pit mining by developing a deep quarry 3 (the same: a mountain object). The structure contains a dam 4, blocking the channel 5 and the channel talik (temporary or permanent) 6 of the watercourse 2 (Fig. 3), a water tunnel (the same: tunnel) 7, bypassing the protected quarry 3, having a sole 8 below the bottom 9 of the channel 5 , and a low-flow conduit 10. This conduit 10 provides, in the cold season, bypassing a mountain object, the passage of ground water of channel talik, capable of forming ice within the structure (Fig. 2).

The dam 4 is equipped with an anti-filtration device, which is made in the form of an ice-soil wall 11 formed by freezing columns (thermosiphons) 12 and conjugated with permafrost 1 (Fig. 3). The bottom 13 of the inlet channel 14, the bottom plate 15 of the inlet head 16 of the tunnel 7 is located at or below the bottom of the channel 9, which is connected with the tunnel 7 (Fig. 4). The height h _{m of the} cavity 17 and the longitudinal slope of the bottom i _m in the underground section 18 of the tunnel 7 constantly ensure a non-pressure mode of water flow in the underground section 18 of the tunnel 7. In this section 18, the tunnel 7 is equipped with a carrier and / or facing lining 19, the bottom 20 and the walls 21 which form a waterproof tray 22 (Fig.6). The output tip 23 by means of a discharge channel 24 is coupled to a watercourse 2.

Low water conduit 10 contains a water inlet 25, which is made in the form of a pipe perforated by longitudinal slots 26 (figure 3). The water intake 25 is located in the water collector 27, which is made of filtering (coarse) soil in the form of the lower part of the powder 28 to the dam 4 (Fig.2). This powder 28 forms an unsinkable platform 29 in front of the dam and insulates the water intake 25. The low-flow water conduit 10 is located in the tunnel 7 and by gravity drains ground water from the channel talik 6 into the cavity 17 of the underground section 18 of the tunnel 7 to a predetermined location or to the outlet head 23 of the tunnel 7. The flow cavity 30 of the low flow duct 10 is thermally insulated, first of all, by the fact that this duct 10 is partially or completely made of polyethylene pipes and covered with soil powder material 28.

The inlet channel 14 of the tunnel 7 within the permafrost 1 is provided with an anti-filter coating. This coating is made, for example, in the form of a polymer film enclosed in geotextile (the same: a membrane) 31, laid on a clay layer made of clay soil 32, and covered with protected plates 33. Such a coating is impermeable to water directly from the border of the channel 6 by means of an anti-filter tooth 34 is associated with permafrost 1, more precisely, with a natural waterproof raincoat 44 (Fig.7).

The input tip 16 of the tunnel 7 is made of a corridor type, while its corridor 35 is a continuation of the tray 22 of the lining 19 of the underground section 18 of the tunnel 7, and the top of its side walls 36 is located at a level that is not flooded in the warm season (Fig. 4).

The inlet head 16 is equipped with an anti-slip threshold 37, the crest of which is located above the water inlet 25 of the low flow duct 10. The place of water discharge from the low flow duct 10 and the structural insulation of its flow cavity 30 is established by the design based on the heat engineering calculation, and the fastening design of the low flow duct 10 in the tunnel 7 is based on research.

The part of the corridor 35 immediately adjacent to the underground section of the tunnel 18 is provided with a permeable ceiling 38, on which the filter prism 39 from coarse soil is located and which hydraulically communicates the pore space of the filter prism 39 with the cavity 17 of the underground section 18 of the tunnel 7 (Figs. 4 and 5) .

The need to provide the outlet channel 24 within the permafrost 1 with an anti-filter coating and its waterproof connection with the permafrost 1 directly at the boundary of the channel talik 6 is established by the project depending on local conditions.

Low drainage conduit 10 under favorable conditions can be laid bypassing a mountain object on the surface of the area, and the supply of ground water from the channel talik 6 can be carried out by pumps.

In the drawings, other elements of the structure and environment are indicated, namely:

40 - free surface of the stream (in the corridor);

41 - maximum level of flow in the inlet channel (same: in front of the dam);

42 - maximum level of flow in the underground section of the tunnel;

43 - thawed layer (seasonal thawing-freezing layer);

44 - waterproof raincoat;

45 - calibration level of ice and snow;

46 - snow shield;

h _m is the height of the cavity of the tunnel;

h _o - normal depth in the tunnel;

i _m is the longitudinal slope of the bottom in the tunnel;

i _in - the longitudinal slope of the channel of the watercourse.

A feature of the creation of such a channel-discharge structure is that at the time of the start of operation, by the first warm period of the year, all three main technological units of the structure should be erected: dam 4, tunnel 7 and anti-slip means (low flow conduit 10 and filter prism 39). At the same time, the effectiveness of anti-slip agents and the refinement of their design are evaluated during the operation of the structure, and quarry 3 is developed within the drained section of the channel 5 of watercourse 2 after the first year of operation of the structure and the creation of an ice-soil wall 11 in dam 4.

The construction works as follows.

In the warm season, dam 4 without a significant rise in water level, i.e. without creating a reservoir, directs the surface and ground runoff of watercourse 2 to tunnel 7. In the inlet head 16, within its corridor 35, an intensive decrease in the free surface 40 of the stream occurs. This surface 40 decreases from the maximum level 41, which was established in the inlet channel 14 at the maximum flow rate, to the maximum level 42, which was established on the underground section 18 of the tunnel 7 with a normal depth h _o <h _m , where h _m is the height of the cavity 17 of the tunnel 7. This circumstance provides the ability to perform the cavity 17 of the tunnel 7 with a constant height h _m . At the same time, groundwater flow is carried out through a low flow conduit 10.

In the cold season, surface runoff ceases. The ground drain, by means of a heat-insulated low-flow conduit 10, is discharged from the channel talik 6 and concentratedly directed into the cavity 17 of the underground section 18 of the tunnel 7. In this case, the anti-slip threshold 37 provides a gravity flow in the low flow conduit 10 and prevents the entry of ground water into the inlet head 16, therefore, prevents education in it ice. At the same time, the anti-filtration tooth 34 (Fig. 7) prevents the very dangerous penetration of ground water from the channel talik 6 side into the frozen layer (seasonal thawing-freezing layer) 43, which can form in permafrost below the waterproof raincoat 44 removed in the inlet channel 14 warm season.

The input tip 16, as a last resort, can become blocked by ice and snow to a reference level of 45, and the water level in front of the top tip 16 may temporarily rise above the permeable ceiling 38 with the onset of the warm period of the year. In this case, water will flow through the filter prism 39 through the ceiling 38 into the cavity 17 of the underground section 18 of the tunnel 7 and will open the inlet head 16. This circumstance should be taken into account when assigning the mark of the dam crest 4.

The example describes the simplest and most preferred variant of a drainage structure that creates an artificial channel under permafrost conditions to divert a watercourse from a mountain object.

Various modifications and changes may be made to the present invention without departing from its scope, for example:

- low flow pipe 10 can be placed in a closed tray, which runs at the base of the tunnel 7;

- low flow pipe 10 can be coaxially placed in an additional pipe of larger diameter with the formation of an annular gap filled with heat-insulating material;

- the permeable ceiling 38 can be equipped with a stationary or removable snow protection canopy 46 (the canopy in FIGS. 4 and 5 is indicated by a dotted line), and the pore space of the filter prism 39 can be hydraulically communicated with the cavity 17 of the tunnel 7 with a short conduit (not shown);

- ground water in the cold season can be accumulated in the drainage well and, if necessary heated, can be supplied to a low-flow conduit 10, the design and operation of which is specified in the first year of operation.

Additionally, the anti-filter coating of the insert in the channel 14 and 24 can be performed without a polymer film 31, i.e. may consist of a geotextile layer and a clay layer 32 made of clay soil. Such a coating allows water to penetrate under it in a very limited amount. This water in the form of drops penetrates possible hollow cracks and, under the influence of negative temperatures of permafrost 1, turns into ice and thus restores the waterproofness of the cloak 44.

The proposed channel discharge structure in the form of a tunnel can be implemented, for example, during the development of one of the largest in Russia, the Nezhdaninsky gold ore deposit (Yakutia).

In mountainous areas, the condition is usually satisfied: i _m <i _p , where i _m is the longitudinal slope of the tunnel; i _p , is the longitudinal slope of the channel of the watercourse.

Based on this condition and assuming the flow regime in the tunnel is non-pressure, and the tunnel tray is made of concrete, the following tunnel design sequence is recommended:

- on the basis of hydrological data and the assigned capitality class of the tunnel, the water discharges of the main Q _main and calibration Q _{pov are} determined _; ;

- taking into account the sediment flow, a permissible average flow velocity ν _dop is assigned and the cross-sectional area of the flow w _nom = Q _main / ν _{dop is} determined;

- based on the analysis of possible rock pressure, the profile of the tunnel is taken, including the width b _m , and the height h _{m of the} cavity after lining, as well as the normal depth of flow h _o at Q _main and Q _pov; ;

- when Q _basic hydraulic analysis determines the longitudinal slope of the tunnel i _m , which ensures the above flow regime in the tunnel: flow velocity ν _dop and its depth h _o ;

- the design of the heads and channels of the tunnel is adopted, after which the height position of the free surface of the flow along the entire length of the tunnel is determined for Q _main and Q _sw .

Example: Q _main = 150 m ³ / s; ν _extra = 10 m ² / s; the rock is solid, rock pressure is negligible, and lateral pressure is absent (f> 8). We take the cross section of the tunnel rectangular with a gently sloping arch and cavity dimensions after lining: width _m = 4.5 m and height h _m = 5.5. Such cavity dimensions correspond to a flow depth h _o = 3.5 m. Next, the hydraulic calculation of the tunnel should continue, i.e. determine the longitudinal slope of the tunnel i _m and the position of the free surface of the flow.

Used sources

1. Tsygelnyuk E.Yu., Ryzhkov AN, Kravtsov A.V. Testing cement slurry mix at the Koashvinsky quarry of the East mine of Apatit OJSC // Mining Journal. 2006. No1.

2. Waterworks: Textbook. for universities: In 2 hours, Part 2 / L.N. Rasskazov, V.G. Orekhov, Yu.P. Pravdivtsev and others; Ed. L.N. Rasskazova. - M.: Stroyizdat, 1999.

3. Yagin V.P., Vaikum V.A. The basic hydrogeological scheme is the hypothesis of permafrost, taking into account the history of geocryological development of the territory and with regard to hydraulic engineering construction. Intellectual product. 2007. The Federal State Unitary Enterprise VNTIC is registered under the number 73200700080.

4. Biyanov G.F. Dams on permafrost. - M .: Energoatomizdat, 1983. S.144-148.

5. Yagin V.P., Vaikum V.A., Povarenkin V.A., Davydov I.A., Neyland N.N. On the issue of placement of solid water-containing wastes of thermal power plants and other industries // Hydrotechnical construction. 1998. No. 6.

6. Frunkin V.N., Sherman M.M. About the construction of the Vilyui HPS-3 on a permafrost semi-rock base. // Hydraulic engineering. 2003. No. 12.

Designations

1 - permafrost

2 - watercourse

3 - quarry

4 - dam

5 - channel (watercourse)

6 - channel talik (temporary or permanent)

7 - water tunnel (same: tunnel)

8 - sole (career)

9 - bottom (channel)

10 - low consumption water conduit (hereinafter: water conduit 10)

11 - ice wall

12 - freezing columns (thermosiphons)

13 - bottom (inlet channel)

14 - inlet channel

15 - bottom plate (inlet head)

16 - input end (tunnel)

17 - cavity (tunnel)

18 - underground section (tunnel)

19 - lining of the tunnel (bearing and / or facing)

20 - bottom (lining, the same tunnel)

21 - walls (lining)

22 - tray (lining)

23 - output tip

24 - outlet channel

25 - water intake (anti-icing conduit)

26 - longitudinal slots

27 - catchment basin (anti-icing conduit)

28 - powder (to the dam)

29 - playground

30 - flow cavity (anti-icing conduit)

31 - polymer film

32 - underlying layer

33 - protective plates

34 - antifiltration tooth

35 - corridor (inlet head)

36 - side walls (corridor)

37 - anti-slip threshold

38 - permeable floor

39 - filter prism

40 - free flow surface (in the corridor)

41 - maximum level of flow in the inlet channel (same: forward dam)

42 - maximum flow level in the underground section of the tunnel

43 - frozen layer (seasonal thawing-freezing layer)

44 - waterproof raincoat;

45 - calibration level of ice and snow;

46 - snow shield;

h _m - the height of the cavity of the tunnel

h _o - normal depth in the tunnel

i _m - longitudinal slope of the bottom in the tunnel

i _in - the longitudinal slope of the channel

Claims (12)

1. The channel structure of a seasonal watercourse in permafrost, characterized in that it contains a dam blocking the channel and the talik of the watercourse, a water tunnel made to bypass a protected mountain object with a sole below the channel bottom, and a low-flow water conduit providing during the cold season in bypassing a mountain object groundwater pass of channel talik, capable of forming ice within the structure, while the dam is equipped with an anti-filter device paired with permafrost d, in the water tunnel, the bottom in the inlet channel and the bottom plate of the inlet head are located at or below the channel bottom that mates with them, the height of the cavity and the longitudinal slope of the bottom constantly ensure a non-pressure mode of water flow in the underground section of the water tunnel equipped with a lining, the bottom and walls which form a waterproof tray, and the output tip through the outlet channel is interfaced with a watercourse, a low-flow conduit contains a water intake located in the filtering catchment, and malorashodnyh-lingual cavity is thermally insulated conduit, wherein the supply channel plumbing a tunnel within the permafrost impervious covering is provided, which is directly at the border of the channel talik waterproof associated with permafrost. 2. The construction according to claim 1, characterized in that the dam filter is made in the form of an ice-soil wall formed by freezing columns. 3. The construction according to claim 1, characterized in that the inlet head of the water tunnel is made of a corridor type and forms a continuation of the lining tray of the underground section of the tunnel, while the top of the side walls of the corridor is located at a level that is not flooded in the warm season. 4. The construction according to claim 1, characterized in that the low flow conduit is located in the water tunnel and gravity drains ground water from the channel talik into the cavity of the underground section of the tunnel in a given place or in the outlet head of the water tunnel. 5. The construction according to claim 1, characterized in that the intake of low flow conduit is made in the form of a pipe perforated by longitudinal slots. 6. The construction according to claim 1, characterized in that the filtering drain pan of a low-flow water conduit is made of coarse soil and is part of the powder to the dam. 7. The construction according to claim 1, characterized in that the inlet head is equipped with an anti-icing threshold, the crest of which is located above the water intake of a low-flow water conduit. 8. The construction according to claim 1, characterized in that the low flow conduit along the length is partially or completely made of polyethylene pipes. 9. The construction according to claim 1, characterized in that the outlet channel of the water tunnel within the permafrost is equipped with an anti-filter coating, which is directly waterproof from the permafrost directly at the boundary of the channel talik. 10. The construction according to claims 1 and 9, characterized in that the conjugation of the antifiltration coating of the inlet channel and the antifiltration coating of the outlet channel with permafrost at the boundary of the channel talik is carried out using a tooth from clay soil frozen during its implementation. 11. The construction according to claim 3, characterized in that at least a portion of the corridor directly adjacent to the underground section of the water supply tunnel is provided with a permeable ceiling, on which a filter prism from coarse soil is located and which hydraulically communicates the pore space of the filter prism with a cavity underground section of the water tunnel. 12. The construction according to claim 9, characterized in that the permeable ceiling is equipped with a snow canopy.

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