EP0286662B1 - Buffer tank with alveolar structure for retaining and regulating natural waters - Google Patents

Abstract

Buffer tank for the storage of waters collected in urban environments or on surfaces such as roads or sport fields, when the water flow rates exceed the capacity of the evacuation network of natural waters. The tanks according to the invention comprise a drainage layer (2) consisting of porous materials, particularly gravel (7) or blocks (8) distributed on the bottom of the tank, and at least one layer consisting of an alveolar structure (3) formed by juxtaposition of vertical pigeon holes (4). This structure may be covered on its horizontal faces with a filtering material (9, 10). The surface of the tank is covered with earth or with a pervious or impervious coating (11). The sides and the bottom of the tank may be covered with a sealing film (16). According to an alternative, certain pigeon holes are filled with hydrophilic material which preserves the moisture of a coating (11) consisting of a lawn.

Description

The present invention relates to the field of natural water drainage. It relates more particularly to a retention and regulation buffer tank which can be connected to a drainage network.

The urbanization of soils and road works in rural areas create large areas of rainwater collection. In order not to weaken the soil by a disturbance of their hydrological situation, the water which can no longer be evacuated by natural way of infiltration through the soil must be collected and evacuated generally in the fluvial network.

To do this, networks are created to collect rainwater, and drainage networks leading to rivers. Collection areas being particularly important in urban areas, and cities being often built along a river, the evacuation network is generally built in the underground of cities, and the increase of their capacity of flow in view of the collection networks of recent peri-urban areas is excessively expensive.

These collection, collection and evacuation networks are constructed so as to allow the evacuation of water from the maximum precipitation known as "decennial rain", corresponding to approximately 60 mm of water, once in twenty four hours.

As such precipitation is very rare, approximately once every ten years as their name suggests, the dumping of collection networks directly into the evacuation network would lead to unnecessary and very expensive oversizing of the latter. We therefore thought of inserting a buffer basin between the water collection network and the drainage network. Its role is to allow a flow compatible with the capacities of the evacuation network, even if precipitation leads to higher collection flows, and to "smooth" the evacuation flow curve over time. These buffer tanks are generally connected to the drainage network via an orifice allowing the flow to be controlled, and a calibrated orifice is often used.

A first type of buffer basin is produced in the form of an open basin. This type of pool is unsuitable for use in urban areas, where building land is scarce and in demand. In addition, this type of pool causes unacceptable aesthetic pollution.

There has been proposed in the prior art a moving rising basin as described in French patent application FR-A-2 300 855 of February 11, 1976 corresponding to the preamble of claim 1, such a moving rising dam allows raise the maximum reservoir of a basin whose structure has a fixed threshold. The type of riser used is connected to a float that goes up and down with the water level. This type of basin is technologically advanced and has the disadvantage of deteriorating rapidly.

It has been proposed in the prior art to remedy these drawbacks by making buried buffer basins filled with gravel so as to support loads on its upper surface. This basin can be covered with a permeable coating allowing the collection of rainwater.

Due to the low porosity of the gravel, this type of tank requires large volumes. For a storage capacity of one cubic meter of water, the volume of the basin will be more than three cubic meters when using gravel with a porosity of thirty percent, which is the largest porosity currently known.

This involves excavation and transport of materials (evacuated earth, gravel), very significant resulting in high construction costs and delays. In addition, the reduced porosity results in a speed of diffusion of water which in some cases is insufficient to absorb rainwater during heavy precipitation.

The buried buffer tank according to the invention overcomes these drawbacks. It indeed has a honeycomb structure, consisting of juxtaposed vertical cells resting on a draining structure allowing the horizontal circulation of water and has in its lower part an evacuation orifice. The honeycomb structures are advantageously manufactured by extrusion from a thermoplastic material, using the devices and methods described in French patent applications 8023188 and 85 09 554 of the applicant.

According to a preferred embodiment, the basin comprises a first layer constituted by a draining structure allowing the horizontal circulation of the water in the bottom and its evacuation in the evacuation network by an orifice or device with controlled flow. The draining structure can be made of a porous material, in particular gravel with a large particle size. The honeycomb structure rests on this layer of porous materials. The height of this alveolar layer is substantially equal to the height of decennial precipitation, multiplied by the ratio between the surface of water collection and the surface of the basin. The honeycomb structure is advantageously covered on its upper surface or on its two horizontal surfaces with a filtering material avoiding obstruction of the cells. This filtering material can be chosen of the nonwoven polyester or polypropylene fiber sheet type, and can be fixed to the cellular structure by thermofusion. The honeycomb layer is covered with a concrete coating or a bituminous coating to support loads. This coating can be replaced or covered by a layer of soil allowing the planting of a lawn or a flower bed in order to completely hide the basin.

The basin is connected to the water collection network by means of a known type of sand separator, opening into the lower layer made of porous material. When the flow of collected water is greater than flow authorized by the evacuation orifice, it causes the filling of the alveolar structure. When the precipitation stops, the stored water is evacuated regularly in the evacuation network without causing an overflow.

The porous structure may, according to a variant, be replaced by studs maintaining a spacing between the lower surface of the honeycomb structure and the bottom of the basin. The size and distribution of the studs are chosen so that one percent of the bottom surface of the honeycomb structure rests on these studs.

Depending on the nature of the soil, the walls of the basin will be waterproofed using plastic films, bituminous sheets or bitumen coatings, or even masonry.

According to another embodiment, the basin according to the invention is buried at the edge of the carriageway and covered with a layer of soil sown with grass. The slope of the roadway collects water in the event of rain. These waters flow along the slope of the roadway towards the curbs and reach the buried basin by infiltration through the lawn. They feed the honeycomb structure through its upper surface.

The basin is advantageously completed by a gutter circulating between the roadway and the grassed edge. Said channel collects the water flowing on the roadway, and feeds the drainage layer of the basin through communication orifices.

According to an urban variant of this embodiment, the layer of grassy soil is replaced by porous pavers or non-porous pavers associated with a gutter.

It is thus possible to make a pedestrian path in an urban environment by laying porous pavers on a basin according to the invention. According to a variant, the basin is covered with a non-porous coating and it is fed at the level of the drainage layer by means of a gutter communicating through orifices.

According to another variant, a traffic pavement is produced by covering the basin according to the invention with a permeable coating. In order to avoid deformation of the soils surrounding said basin, the walls are covered with a sealing film.

The horizontal hold can be improved by the insertion of a mesh or mesh of plastic or stainless metal between the honeycomb layer and the covering.

According to a variant, the gutter communicating with the drainage layer of the basin under road surface has a double function of collecting water and evacuating the water stored towards the evacuation network. According to another variant, the evacuation of the water is carried out by a pierced pipe of the "AQUADRAIN" type deposited in the drainage layer parallel to the axis of the roadway.

According to another embodiment, certain cells are filled with a hydrophilic material.

The pools according to this embodiment are particularly useful for maintaining the humidity of lawns and in particular sports stadiums under which the buffer pool is buried. The buffer tank according to this embodiment, communicates with the drainage network by means of a valve making it possible in dry periods to maintain the storage of water in the alveolar layer and the drainage layer, and to serve to maintain the humidity of the lawn by feeding by capillarity through the alveoli filled with hydrophilic material, and diffusion at the interface of the alveolar layer and the grassy ground thanks to the sheet of nonwoven fibers.

According to a particular embodiment, the honeycomb layer consists of an assembly of plates which can fit together to form large basins.

• La figure 1 représente une vue en coupe d'un premier mode de réalisation du bassin selon l'invention.
• La figure 2 représente une vue en coupe d'une variante de bassin comprenant deux couches alvéolaires superposées.
• La figure 3 représente une vue en coupe d'un bassin enterré sous une bordure de chaussée.
• La figure 4 représente une vue en coupe d'un bassin enterré sous une chaussée.
• La figure 5 représente une vue en coupe d'un bassin enterré sous une pelouse et comportant une structure alvéolaire partiellement remplie d'une matière hydrophile.
• La figure 6 représente une vue d'un panneau permettant de constituer une couche alvéolaire.

Other advantages and non-limiting embodiments will emerge more clearly from the description of a few examples of embodiments which are illustrated by the following drawings:

• Figure 1 shows a sectional view of a first embodiment of the basin according to the invention.
• 2 shows a sectional view of a variant of the basin comprising two superimposed honeycomb layers.
• Figure 3 shows a sectional view of a basin buried under a curb.
• FIG. 4 represents a sectional view of a basin buried under a roadway.
• FIG. 5 represents a sectional view of a basin buried under a lawn and comprising a honeycomb structure partially filled with a hydrophilic material.
• FIG. 6 represents a view of a panel making it possible to constitute a cellular layer.

The buffer tank (1) represented in FIG. 1, comprises a drainage layer (draining structure) (2) and a cellular layer (3) consisting of a juxtaposition of vertical cells (4), preferably made of polypropylene by extrusion of thermoplastic material. These cells have a hexagonal profile with a diameter between 6 and 20 mm. The thickness of this alveolar layer is equal to the height of the decennial rains multiplied by the ratio:

The basin has in its lower part an evacuation orifice (5) communicating the drainage layer (2) and the evacuation network (6).

This orifice may consist of a calibrated orifice or of a valve.

The drainage layer (2) consists of a layer of gravel (7), preferably between 15 and 50 cm thick, or a series of studs (8). The honeycomb layer (3) is advantageously covered, on its horizontal surfaces, a sheet of non-woven polyester or polypropylene fibers (9), (10). The sheets (9), (10), can be fixed, during the manufacture of the cellular structure, by thermofusion at a temperature of approximately 250 ° C. This layer (10) prevents clogging of the cells (4) and retains particles with a diameter greater than 50 microns.

The honeycomb layer is covered with a coating layer (11) which may consist of earth, concrete, bitumen or any other known coating. When the surface has to support heavy loads, for example when it constitutes a parking area, a non-oxidizable plastic or metallic mesh (15) can be inserted between the covering and the honeycomb layer, improving the horizontal holding of the buffer tank ( 1) and in particular of the alveolar layer (3).

When the soils surrounding the buffer tank are deformable, the vertical edges (13) and the bottom (14) of the tank are covered with a sealing film (16) consisting of an impermeable plastic or bituminous sheet or a coating of bitumen.

This film can be removed when the pool is made in soil that is not very deformable and draining, for example, clean sand or gravel. The basin is supplied with water collected by an orifice (17) formed at the level of the drainage layer (2).

According to a variant presented in Figure 2, the basin comprises a first honeycomb layer (3) and a second honeycomb layer (18) separated by a separation layer (19) consisting of studs (20). The supply of collected water is, according to this variant, carried out at the level of the separation layer (19).

The supply of collected water can be done by means of a settling and degreasing device (21) of known type.

According to another embodiment shown in Figure 2, the basin is buried under a curb (22) covered with a coating layer (11) formed of grassy earth. The water flowing from the roadway (23) produced in a known manner with a slope descending towards the edge of the roadway, feeds the buffer tank by infiltration through the coating layer (11).

A perforated pipe (24) with a diameter of between 10 and 50 cm is placed in the drainage layer (2) and is used to collect the water and discharge it into the drainage network into which it opens out through the 'through an orifice allowing flow control. The diameter of the cells is preferably chosen between 5 and 12 mm.

According to a variant, the diameter of the perforated pipe (24) is calculated so as to limit the flow rate to a value lower than the maximum flow rate admissible by the evacuation network.

According to a variant represented in FIG. 4, the basin is buried under the roadway or more generally under a surface for collecting rainwater. If no other collection surface feeds the buffer basin, the thickness of the alveolar layer is substantially equal to the height of the decennial rains, or about 60 mm in most French regions.

The drainage layer consists of clean sand or gravel with a thickness of 20 to 40 cm. This layer is used both for water drainage and for absorbing local deformations. The edges (12) and the bottom (14) of the basin are covered with a sealing film (16) avoiding the degradation of the soil, in particular during frost.

According to a variant of the invention, a gutter (25) is produced along the roadway used both for collecting water from neighboring collection surfaces, and for discharging the water stored in the regulation network. . Said channel (25) communicates with the drainage layer (2) of the basin through orifices (25) regularly spaced about one meter apart. The depth of said channel is substantially equal to the thickness of the basin and of the covering, ie substantially equal to 50 cm. It is advantageously covered with a grid (27).

According to another exemplary embodiment represented in FIG. 5, a buffer pool is produced under a lawn serving in particular as a sports ground. It comprises a honeycomb layer (3) having a thickness substantially equal to the height of the decennial precipitation and a drainage layer (2) preferably produced in the form of a layer of gravel with a thickness of 15 to 30 cm. The honeycomb layer (3) consists of a juxtaposition of vertical cells, some of which are filled with a hydrophilic material (28) forming a wick allowing the water stored in a part of the basin to feed the upper surface (9 ) of the honeycomb layer covered with a nonwoven web.

The drainage layer communicates with the drainage network (6) to prevent stagnation of water in the event of heavy precipitation. The communication orifice (5) consists of a valve making it possible, on the contrary, during periods of drought to store the water collected in order to maintain the humidity of the lawn. The drainage layer (2) also communicates with water inlets (29) distributed along the lawn to maintain a sufficient level of stored water even in the absence of precipitation. An electrical probe (30) can be placed in one or more cells distributed over the surface of the ground and detecting the height of stored water. In the event of insufficient level, this probe can trigger an alarm or control the valves (23) and (5).

According to a preferred embodiment shown in Figure 6, the honeycomb layer (1) consists of panels (31) which can fit into each other easily by vertical sliding of a panel to be laid along the complementary edge (34) of a panel already installed.

Claims (13)

1. An underground tank (1) for retention and control of natural water, the upper portion of which is capable of sustaining a load, and which can be connected to a water evacuation network (6), characterized in that said tank (1) comprises at least one honeycombed layer (3) consisting of adjacent vertical honeycombs (4) resting on a draining structure (7) that permits a horizontal flow of water and comprises an outlet opening (5) at its lower portion.

2. An underground tank according to Claim 1, characterized in that said draining structure (2) consists of blocks (8) resting on the base (14) of the tank.

3. A tank according to Claim 1, characterized in that said draining structure (2) consists of a layer of porous material.

4. A tank according to Claim 3, characterized in that said draining structure (2) consists of a layer of coarse alluvial gravel (7).

5. A tank according to any Claim 1-4, characterized in that the upper surface of the honeycombed layer is covered by a filtering material (3).

6. A tank according to any Claim 1-5, characterized in that the lower surface of the honeycombed layer is covered by a filtering material (10).

7. A tank according to any Claim 5 and 6, characterized in that said filtrating material (9), (10) is made of a mat of non-woven fibres.

8. A tank according to any Claim 1-7, characterized in that at least a few of said vertical honeycombs are filled with a hydrophilic material (28).

9. A tank according to any claim 1-8, characterized in that said honeycombed structures are made of panels (31) that can be placed side by side horizontally and can be fitted one into the other through a vertical sliding motion of two panels along their complementary vertical edges (34).

10. A tank according to any Claim 1-9, characterized in that at least a portion of the walls (12), (14) is covered with a watertight film (16).

11. A tank according to any claim 8-10, characterized in that it comprises at least one conduit connected to the circuit of supply of running water.

12. A tank according to any claim 1-11, characterized in that it comprises two honeycombed layers (3), (9), superimposed and separated from the blocks (20).

13. A tank according to any claim 1-12, characterized in that the honeycombed structures (3) are obtained by extrusion process from a thermoplastic material.

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