Sports field with controlled water content

Abstract

The invention relates to a sports field comprising a playing layer (1) laid on an underlayer (2), with the surface of said field being divided into two complementary sub-surfaces, the respective surface areas of which are both strictly positive, wherein: • vertically in line with a first sub-surface, the structure of said sports field is equipped with means for creating a layer (3) of liquid, such as, for example, a water table, in the volume of the sub-layer (2) located under the playing layer (1) and vertically in line with the first sub-surface, and for managing the level thereof; • the sub-layer (2) comprises a multitude of capillary trenches (4) located vertically in line with the first sub-surface, said capillary trenches being configured to ensure permeability and capillary continuity between the playing layer (1) and said liquid layer (3).

Description

[0001] SPORTS FIELD WITH CONTROLLED WATER CONTENT

[0002]

[0001] The present invention relates to a sports field whose playing layer rests on a sub-layer in which a plurality of drainage and capillary trenches are arranged, with means for installing a water table in said drainage and capillary trenches and controlling the level thereof to control the supply of water and the evacuation of excess water from said playing layer, in particular by the capillary forces in the playing layer above the water table, themselves controlled by the depth, or the level of said water table in said capillary trenches, said capillary forces controlling on the one hand the capillary rise from the water table present in the trenches located in the underlying layer and on the other hand the quantity of water evacuated from said playing layer by gravity drainage.

[0003]

[0002] With elements for filling the capillary trenches giving them permeability and capillarity characteristics which allow upward capillary flows and downward gravity flows to meet the water supply and water drainage needs of the playing layer, this allows satisfactory operation of the ground, taking into account the objectives, the capillary and permeability characteristics of the playing layer, the foreseeable evaporative demands, and the method of adjusting the water table level in the different seasonal situations.

[0004]

[0003] The present invention relates primarily to a natural grass sports field, and preferably to a hybrid grass sports field.

[0005]

[0004] However, even if the following description is made in the context of a sports ground where natural grass is cultivated, the playing layer then being the substrate layer in which the roots of the grass grow, the present invention also finds application in the case of synthetic grounds where the playing layer is simply the upper layer, where it is desired to maintain a satisfactory humidity level in order to control the temperature, the slipperiness and the mechanical characteristics by controlling the level of a water table in the capillary trenches arranged in the sub-layer on which said playing layer rests.

[0006]

[0005] The present invention relates primarily to a sports ground in which the adjustment of the water inputs or extractions in the playing layer is carried out in a quasi-permanent regime from the adjustment to a stable level of the level of a water table located lower in the drainage and capillary trenches, said water inputs or extractions in the playing layer then taking place spontaneously above the water table simply due to the flows resulting from the balance of the forces of gravity and surface tension in the unsaturated porosity above the water table located lower in the drainage and capillary trenches, depending on the level of said water table.

[0007]

[0006] However, even if the following description is made in this priority context of a sports ground where the input or extraction of water in the playing layer is done indirectly by the balance of surface tension and gravity forces in quasi-permanent regime above a sheet of water,the present invention also finds application in the case of sports grounds whose playing layer rests on a sub-layer in which a plurality of drainage and capillary trenches are arranged and having means for periodically directly adding water to the playing layer without passing through the upward flow of water resulting from the balance of surface tension forces above a sheet of water but by periodically installing a sheet of water in said capillary trenches and by directly raising this sheet of water from the capillary trenches into the playing layer by sufficient pressure or having means for directly extracting water from the playing layer more quickly and in greater quantity than would be possible by simple gravity drainage limited by the capillary forces in the playing layer,by directly exerting a strong depression in said drainage and capillary trenches making it possible to create a rapid flow of water descending through the drainage and capillary trenches from the play layer.,

[0008] Technical field

[0009]

[0007] The present invention relates in particular to a sports ground comprising a system for controlling the level of a water table, making it possible in particular to control the gravity drainage of the playing layer of this sports ground as well as its supply of water by capillarity from said water table, said system comprising according to the invention means for installing said water table in capillary trenches arranged according to the invention in the sub-layer on which said playing layer rests, and for controlling the level thereof, the permeability and capillary continuity being ensured between the playing layer and the water table located in the capillary trenches.

[0010] Previous Art

[0011]

[0008] In the prior art, the explicit use of capillary forces in a sports ground most often concerns capillary irrigation systems from a sheet of water installed in the sub-layer on which the playing layer rests and occupying up to the level of the sheet of water the entire volume of the porosity of this sub-layer, the volume occupied by the sheet of water therefore having as its base, that is to say as its surface projected onto the horizontal plane, the entire ground.

[0012]

[0009] However, although implicitly and sometimes even unrecognized and including in the case of grounds without a water table but irrigated by sprinkling and laid on a draining layer, it is in fact the capillary forces which actually play an essential role in limiting the quantity of water which can be evacuated from the playing layer by gravity drainage, since the substrates concerned are very permeable, which concerns most grounds with developed substrates used for sports grounds for more than 10 years.This role of capillary forces, which is often ignored or poorly understood, is therefore decisive in the functioning of gravity drainage and the impact of capillary forces is therefore in fact major on the construction cost of sports grounds because it has long been observed that playing layers that are too thin laid on a drainage layer retain a very high, or even too high, water content throughout the winter, the real cause, although often ignored, being excessively strong capillary forces linked to the too small thickness of the substrate layer above the drainage layer.Also, based on this observation, and even when a playing layer thickness of around ten centimeters would be sufficient for satisfactory root development and for the mechanical response of a sports field, it is commonly accepted, and in particular through the USGA standards known from the state of the art, that the playing layers above a drainage layer must have a thickness of between 20 cm minimum and preferably 40 cm, to prevent the water content of the playing layer from being too high in winter, even if the playing layer is made of an extremely permeable material.

[0013]

[0010] Apart from the case of conventional grounds on a draining layer, which still represent almost all the grounds developed today, the principle is also known from the state of the art of a forced supply or respectively a forced drainage of water or air into or respectively from the playing layer of a sports ground by means of an overpressure or respectively suction of drains connected to a system comprising pumps, water supply and outlet and a control system, said drains being installed at a certain depth in the sub-layer on which the playing layer rests or possibly at a certain depth in the playing layer itself. This type of system known from the state of the art, such as the SUB AIR system, is used to create rapid cycles of saturation and / or drainage of water or air in the transient phase.

[0014]

[0011] This type of means already known from the state of the art and used for a fairly long time in the transitional phase for the supply or extraction of water in the ground by drains placed in the playing layer for periodic forced emptying operations or for submersion-emptying cycles would be a type of means potentially usable also for introducing a water table into the ground and regulating its level for quasi-permanent management of the water content of the playing layer by controlling the forces of capillarity and gravity above such a table but was not used until recently, due to a lack of adequate knowledge of the spontaneous operating conditions of water flows above a table under the combined effect of gravity and surface tensions depending on the capillary characteristics of the substrate,

[0015]

[0012] In an operation closer to the invention, document FR-3112152-A, by the same author, describes a method which, by balancing the forces of gravity and surface tension, allows the water content in the playing layer of a sports ground to be controlled by a method of managing the variable level of a water table located in an entire sub-layer located under said playing layer, by explaining the necessary links between the depth of the water table and the capillary characteristics of the different layers and sub-layers of the structure.

[0016]

[0013] However, for these grounds managed in the long term by a water table in an entire sub-layer of the structure on the one hand as on the other hand for these grounds equipped with drains connected to means making it possible to create in a transient phase a pressurized water table for a rapid episode of forced saturation or to create in a transient phase a depression for a rapid episode of forced emptying of the substrate of the play layer and just as finally in the same way for conventional grounds on a draining layer, the same problem of construction cost and ecological impact of the construction of the ground arises each time.

[0017]

[0014] Indeed, whatever the water content management technique, the need to be able to have a relatively deep water table in the structure, for example at a minimum depth of 30 cm or 50 cm, ultimately represents the same major constraint as for a conventional terrain laid on a draining layer requiring an identical depth according to the USGA standards known from the state of the art, involving for terrains with a water table in the structure or for terrains with water supply or extraction by drains in the structure of the terrain known from the state of the art the same type of problems of cost and ecological impact of construction of the structure as for terrains with a draining layer.

[0018]

[0015] Certainly, in comparison with grounds on a draining layer, the fact of being able to vary the height of the water table makes it possible to reduce the minimum thickness of the structure with respect to the constraint of good oxygenation of the ground (at the cost of a strategy of episodes of rising and falling of said level which allows oxygenation of the turf which would not be possible with conventional grounds on a draining layer), but the fact remains that the minimum water content level remains unchanged for a given structure thickness, so that only hybrid grounds make it possible to present a suitable mechanical quality in winter despite a thickness lower than that recommended by the USGA standards.

[0019]

[0016] Thus, in all cases known from the state of the art where water is extracted or supplied from the bottom of the structure, the obligation to have a sufficient thickness of structure poses an ecological problem during the construction of the land, linked to the preservation of aggregate resources and the impact of the transport of materials and this also poses an economic problem as to the cost of construction of the land.

[0020]

[0017] The present invention provides a solution which addresses this problem both ecologically and economically by reducing the quantity of materials required for the construction of the land.

[0021]

[0018] On the other hand, for grounds with a water table in the structure, and in another version aiming at an additional functionality, it is also known in the prior art (cf. document FR-3112152-A) that it is useful to install water storage tanks under the playing layer to conserve the rainwater which falls during the rainy season, so as to be able to have this water available in periods of drought for the subsequent capillary irrigation of the lawn.However, in these water storage tanks and in the most classic case where the volume available for storing water in said tanks is a fixed volume over time, the level of the water table in the water storage tanks at a given time then depends directly on the quantity of water stored in the storage tanks at the time in question, while managing the water content of the playing layer of the ground requires, on the contrary, a depth of a water table that is totally independent of the quantity of water stored in the tanks. It is true that the possibility (see in particular document FR-3112152-A) of tanks with a movable bottom is known to regulate the water level in the tanks independently of the quantity of water stored therein: but this quality solution represents an additional cost that is justified especially in configurations with high storage requirements.The possibility of a sub-layer connected by a pump to the storage tanks is also known, but since this sub-layer is located above the tanks, all the solutions already known, although very effective in operation, therefore involve additional costs at the time of construction because the water level of the storage tanks with a non-moving bottom is not at all suitable for controlling the water content of the play layer by capillary forces. Apart from the solution of tanks with a moving bottom, the known solutions therefore also pose a problem of the quantity of material to be added to the sub-layer, a problem to which the present invention provides a solution.

[0022]

[0019] Finally, the method known from the prior art for controlling the level of a water table consists of connecting said water table to an open-air well by a network of pipes and having means for adjusting the height of the free surface of said well connected to the water table in the trenches: by the interplay of communicating vessels, this water level is then the same for the well and for the water table in the trenches.

[0023]

[0020] Certainly, this method makes it possible to meet the lawn quality objectives with trenches and a well of approximately 50 cm depth (optimal irrigation for the growth of the lawn and roots and ideal water content gradient for the health of the lawn). However, if we add the additional objective of saving irrigation water during the summer period of water restriction, the tests show that it is preferable to have greater trench and well depths, preferably up to 1.5 m to 2 meters. This therefore poses again, during the construction of the field, a possible feasibility problem or at least an economic problem regarding the cost of construction of the fields.

[0021] The present invention provides a different solution which makes it possible to obtain the same effect of controlling the forces and flows of gravity and capillarity and thus to respond to this problem both in terms of feasibility and in terms of economy.

[0024] Description of the invention

[0025]

[0022] The main objective of the present invention is to be part of the control of the water and air content of the playing layer of a sports field by capillary forces controlled by the level or pressure of a water table located in the structure of the field or by the pressure or depression of water exerted in the structure, whether it is a field comprising or not water storage tanks but with the additional objective of overcoming the drawbacks of the current state of the art and in particular the ecological and economic objective of minimizing the consumption and transport of the materials necessary for the construction of the fields.

[0026]

[0023] In this context and according to these objectives, the present invention relates both, on the one hand, to land having water storage reservoirs making it possible to store rainwater which falls during the rainy season, so as to have this water available during periods of drought for irrigating lawns and, on the other hand, to land not having such water storage reservoirs.

[0027]

[0024] The present invention therefore relates to new sports grounds but, as there is no creation of additional sub-layers in addition to the main sub-layer in which capillary trenches are created, it can therefore also be perfectly applied to the inexpensive renovation of an existing ground to change it from a conventional ground to a ground according to the invention, with a very low ecological impact.

[0028]

[0025] The advantage of this solution concerning the quantity of draining and capillary materials necessary to obtain a sufficient depth of water table is that these materials only concern the capillary trenches whose base, that is to say the surface projected on the horizontal plane can be a very small proportion of the surface of the ground, implying a volume of material reduced in the same proportion but making it possible to obtain a comparable effect.

[0029]

[0026] The additional advantage in the operating phase of a pitch according to the invention is that the control of the water content of the entire playing layer is not done by the level of a water table in a large volume having as its base the entire surface of the pitch or by the pressure or depression in a large volume having as its base the entire surface of the pitch but by the level of a water table in a very restricted volume because its base is restricted to the capillary trenches only, this base having a surface which may represent only a very small portion of the surface of the pitch.

[0030]

[0027] Similarly, in the case of controlling the supply or extraction of water in the play layer by the pressure or depression applied to the volume of the capillary trenches alone, the additional advantage in the operating phase of a terrain according to the invention is that the volume under the play layer to which the pressure or depression is applied is that of the capillary trenches alone, which may represent only a very small portion of the volume of the entire sub-layer located under the play layer of the terrain, which makes it possible to reduce the total volume of water to be raised or lowered during the operations of supplying or extracting water to or from the play layer.

[0031]

[0028] The quantities of water to be raised or lowered to control the water content of the ground are therefore limited quantities of water, which can be done with lighter infrastructures and lower peak energy requirements and also requiring a lower quantity of immediately available water.

[0032]

[0029] It should be noted, however, that it is possible according to the invention to sometimes raise the level of the water table up to the play layer (1), that is to say above the top of the capillary trenches located in the sub-layer (2) located under said play layer (1). In this use, even if the part of the water table located under the play layer (1) has a restricted base, the part of the water table located in the play layer (1) has the entire terrain as its base and raising the level of the water table by a given height in the play layer (1) located above the sub-layer (2) therefore requires more water than raising the water table by the same height given in the capillary trenches alone in the sub-layer (2).

[0033]

[0030] However, this use by rapid submersion-draining cycles is of complementary interest compared to the long-term management of the water content of the play layer by the quasi-stationary level of water tables in the capillary trenches in that these cycles allow convection of oxygen or calories (or frigories).

[0034]

[0031] Furthermore, these trenches in the sub-layer, located under the play layer, can be made in renovation of an existing ground without having to remove the play layer in place, the trenches being separated from the rest of the sub-layer by the installation of a membrane which will be held by the installation of the draining and capillary material inside the capillary trenches, material which can also be the same as that of the play layer. It is simply necessary to install perforated corrugated pipes at the bottom of the trenches which will allow water to be evacuated or supplied for controlling the level of the water table, these pipes themselves being connected to collectors which will be installed in a large trench outside or at the edge of the ground.

[0035]

[0032] Taking into account this essential advantage, the invention can thus be applied both in the case of land having a water storage reserve and in the case of land not having one.

[0036]

[0033] Another particularly important advantage of controlling the water in the substrate by layers in separate capillary trenches is to be able, according to a preferred version of the invention, to make a differentiated adjustment of the layer heights in the capillary trenches, by imposing a potentially separate layer height for each capillary trench.

[0037]

[0034] In other words, in a preferred version of the invention, the structure of the sports field comprises an independent or separate network of pipes for each capillary trench. This makes it possible to have independence of the water tables or water pressures applied to the different drainage and capillary trenches, each trench having its own liquid table whose level is not linked to the levels of the tables located in other trenches. It is then possible to adjust the liquid level or the air or water pressure in each capillary trench, independently of the liquid levels or the air or water pressure applied in the other capillary trenches.

[0038]

[0035] However, most old grounds do not have a horizontal surface. A first advantage of this differentiated management of the heights of water tables located in capillary trenches is to allow, according to the invention, the renovation of grounds with a non-horizontal surface (roofed grounds for example), by constituting the equivalent of a virtual water table parallel to the surface of the ground, that is to say by adjusting the water table height of the different trenches to obtain a constant depth of the level of the different water tables in relation to the surface of the ground.

[0039]

[0036] Another advantage of this possibility according to the invention of differentiated adjustment by zones of the water heights in the capillary trenches is to also allow, if desired, differentiated irrigation and drainage between zones always in the sun and zones always in the shade of the stands as is often observed in stadiums.

[0040]

[0037] Finally, another particularly important advantage of this possibility of adjusting the water heights in the capillary trenches differentiated by zones is to make it possible to raise the water level in one zone while simultaneously lowering the water level in another zone, so as to use the water extracted by the drainage of another zone to supply one zone.

[0041]

[0038] Now, it is known that regular cycles of submersion-drainage of the substrate allow oxygenation and air conditioning of the substrate to provide ideal growing conditions. Thus, by using drainage water from one area to saturate another area, such saturation-drainage cycles can be carried out according to the invention without having to introduce water from the network or discharge water into the sewers.

[0042]

[0039] Thus, even in the absence of storage water, there is no need to waste water to carry out these operations which are very favorable for the oxygenation or air conditioning of the substrate.

[0043]

[0040] Another object and advantage of the invention is to make it possible to impose a downward humidity gradient, with a low water content near the surface and an upward capillary flow sufficiently high for satisfactory irrigation, as well as good oxygenation of the soil and a controlled temperature of the substrate to allow the lawn to have optimal growth making it possible to compensate for wear and tear from the game, and to promote deep, dense, thick and white roots.

[0044]

[0041] The tests carried out show that with capillary trenches equidistant from 1 to 2 meters and by filling the capillary trenches as well as the play layer with an essentially sandy substrate, an ideal gradient of water content and an ascending capillary flow are obtained which in no way limit the growth of the grass and the roots when a depth of water table in relation to the surface of around 50 to 60 cm is imposed in the capillary trenches.

[0045]

[0042] Another object and advantage of the invention concerns the possibility of minimizing water consumption during possible periods of summer water restriction. In addition to the main objective of promoting the health and growth of the lawn during periods when saving water is not a priority objective (in general, depending on the climate, in autumn, winter and spring and sometimes or even often all year round), another secondary but very important object of the invention in certain circumstances is also to be able to reduce and limit water consumption by evapotranspiration to the strict minimum so as not to stress the lawn during periods of water restriction, when these restrictions exist.

[0046]

[0043] However, during certain summer periods, to further limit water consumption it is possible and effective to increase the depth of the water table to shift the capillary balance and thus limit the upward capillary flow, so that evapotranspiration becomes significantly lower than it could be with a water table closer to the surface.

[0047]

[0044] Certainly, it is possible for this purpose of reducing water consumption to carry out operations of variation of the water level resulting, as in sprinkler irrigation, in a fractionated supply of water instead of a constant supply, but stress control is not optimum in this type of strategy and a strategy of controlling the flow in a quasi-permanent regime is a preferred strategy, favored according to the invention to reduce uncontrolled risks.

[0048]

[0045] The tests carried out have shown that in order to favour this additional criterion of saving water consumption during periods of restriction but whilst ensuring that the turf can survive without excessive stress, it is effective to lower the level of the water table in the capillary trenches to depths of the order of 150 cm to 200 cm.

[0049]

[0046] However, in many situations, the creation of capillary trenches of such depth is not feasible (concrete support or other infrastructure under the ground) or too expensive to create and requiring more excavation and filling with materials to be supplied.

[0050]

[0047] It is another object of the invention to propose additional means for lowering the “virtual level” of the water table by another method, that is to say to act on the water tables present in the trenches so that their effect on the capillarity in the substrate of the play layer is the same as actually lowering the piezometric level of the ceiling of the water table.

[0051]

[0048] Another aim and advantage of the invention concerns the possibility of controlling the level of the water table by a means which is easy to manage and makes it possible to control the capillarity in the play layer not only when the water table has reached its equilibrium level but also when the top of the water table descends or rises towards this equilibrium controlled by a parameter which is known to be reached and kept stable over time.

[0052]

[0049] However, it is already described in document FR-3112152-A that in the embodiments where the pressure in the water of the play layer which determines the capillary and gravity flows is controlled by the pressure of a water table at equilibrium directly controlled by its piezometric level in the strict sense, that is to say by the depth H1 of a free surface of water in a well connected to the water table, the water pressure P in the water of the substrate of the play layer above the water table at a point M located at the depth H2 relative to the surface is P = Pa - H1 + H2, Pa being the atmospheric pressure (expressing here in a simplified (abusive but usual) way the pressure in water height, that is to say approximately 10 meters equivalent to 1 bar for atmospheric pressure).

[0053]

[0050] However, according to another preferred version of the invention, the water table is this time controlled not by the level of a free surface at equilibrium but by the non-free water surface located in a closed enclosure and connected to the water table of the capillary trenches. In this situation where said water surface in said enclosure is surmounted by a volume of air in depression and whose pressure is equal to ,P = Pa-Hl where H1 = hl + AP , hl being the depth relative to the surface of the ground of the water surface in the closed enclosure and AP the depression of the air expressed as the height of water obtained in the air overcoming the water in the closed enclosure, the result in terms of water pressure in the substrate at a point M located at the depth H2 relative to the surface of the ground is also P = Pa - HI + H2 .

[0054]

[0051] Assuming for example that the enclosure is located at the height hl from the ground, the expression becomes P = Pa - HI + H2 where Hl = hl + AP, AP being the overpressure (positive AP) or depression (positive AP) of the air above the water, expressing AP in equivalent water height), AP being kept constant in the closed enclosure using appropriate means.

[0055]

[0052] Thus, according to this preferred version of the invention, is it possible:

[0056] - to virtually lower the water table level to depth Hl (with for example Hl = 2 meters), even if the depth of the bottom of the drainage and capillary trenches is only 60 cm

[0057] - and to keep this level of the water table constant (at least for a certain time) even if during this time the "real" depth of the roof of the water table in the capillary trenches slowly descends to the bottom of the trenches, going for example from 30 cm to 60 cm deep in a few days. However, this means of constantly controlling the pressure in the water of the porosity of the substrate of the play layer by the constant level Hl of the air pressure in a closed enclosure above a volume of water connected to the water table in the capillary trenches only works during the time when said water table remains present inside said capillary trenches and connected to said closed enclosure where the water is topped by air at the pressure P = Pa - H1, which ends when the progressive emptying of the water present in said capillary trenches results in the complete emptying of the latter.

[0058]

[0053] In the example, assuming the enclosure is at ground height and hl = 0, P = Pa - 2 decibars, or approximately Ibar - 2 decibars or P = approximately 10 meters - 2 meters of water, expressing the pressures in water height).

[0059]

[0054] Now, the water pressure in the water table in the trenches is the parameter determining the balances and the gravitational and capillary flows in the play layer located above. Thus, we see that we obtain the same physical effect on the balances and the gravitational and capillary flows:

[0060]

[0055] - either by the "virtual level" P of the water table defined by P = Pa- Hl where Hl = hl + AP, hl being the depth relative to the surface of the ground of the water surface in the closed enclosure and AP the overpressure or depression of the air expressed as the height of water obtained in the air overcoming the water in the closed enclosure using an air pump, said closed enclosure being hydraulically connected to the water table of the capillary trenches (AP being in this case a depression, i.e. a negative value in the case considered where the level of the water table is lowered)

[0056] - or more conventionally by the depth Hl of a water table in the capillary trenches obtained in the version of the invention where the control of the level of the water table is done by a free surface of a water table in equilibrium at the depth Hl.

[0061]

[0057] Thus, in both cases, the water table level P = Pa - Hl obtained using two different methods does not have exactly the same physical meaning but has the same effect on the water pressure above the water table and in particular in the play layer and consequently on the balances and circulation of the water in the substrate of the play layer located above the water table.

[0062]

[0058] We can therefore consider the level of the water table in the same way in both cases since the effect is the same on the water flows in the substrate of the play layer, whether it is the piezometric level of a water table at equilibrium or the virtual level of a water table heading towards its real or possibly virtual depth at equilibrium.

[0063]

[0059] Furthermore, it is possible to combine the preferred mode of the invention where the level of the water table Pa - Hl is obtained in a closed enclosure where the air above the water in said enclosure undergoes an overpressure or a depression Hl and the mode of the invention of differentiated control of the water table levels where each capillary trench (or group of capillary trenches) is connected to a dedicated enclosure, which makes it possible to separately adjust the (virtual) levels of the water tables of different trenches to allow, for example, to equip a pitch of which a part is always in the sun and a part always in the shade of the stands.

[0064]

[0060] In other words, in a preferred version of the invention, the structure of the sports ground comprises a closed enclosure connected to at least one capillary trench. The air pressure Pa + AP above the liquid in said closed enclosure is then the tool for controlling the gravitational and capillary flows of the playing layer above said capillary trench to which said enclosure is connected and the level of the water table H1 is defined as the sum H1 = hl + AP, hl being the depth relative to the surface of the ground of the water surface in the closed enclosure and AP the overpressure or depression of the air expressed as the height of water obtained in the air above the water in the closed enclosure.

[0065]

[0061] It should be noted in this regard that the effect on the balance between gravity and surface tension which determines the capillarity in the play layer is not modified over time while the water table rises or falls in a capillary trench to find its equilibrium level determined by said air pressure in said closed enclosure connected to said water table, as long as the level of the air pressure above said water table is maintained. Therefore, the level of the water table in the capillary trenches which governs the management of the water in the play layer is not the instantaneous depth of the water table but the depth of the water table at equilibrium, that is to say the level towards which the instantaneous depth of said water table tends.

[0066]

[0062] It should also be noted that what works with a depression P a - AP also works with overpressure P a + AP with positive AP.

[0067]

[0063] It is thus possible, in a preferred version according to the invention, to adjust the level of a layer by a layer level defined by an air pressure adjusted and maintained for a certain time at a constant pressure P a more or less AP, this air surmounting in a closed enclosure a small sheet of water connected to the sheets in the capillary trenches.

[0068]

[0064] As soon as the layer connected to said enclosure is in a capillary trench descending or rising towards its level, the effect is the same for the capillarity in the water layer as that of a layer at equilibrium at the level considered, even if this level is lower or higher than the bottom or top of the capillary trenches.

[0069]

[0065] However, the implementation of this method for managing the water table level defined and controlled by the pressure maintained substantially constant of a volume of air in a closed enclosure, said volume of air surmounting in said closed enclosure a volume of water connected to said table must respect certain constraints which will be explained below in more detail, in relation to a figure illustrating the operation of the method.

[0070]

[0066] Furthermore, if it is possible and advantageous according to the invention to periodically raise or lower the water tables in the capillary trenches rapidly by the action of water or air pumps, so as to supply water or drain the substrate particularly rapidly, in particular for oxygenation or air conditioning cycles of the substrate or to meet an urgent drainage need, it remains however preferable for the lawn in the long term to have stable conditions between these exceptional operations so that permanent controllable regimes with a controlled effect concerning the needs of the lawn and the need to save water are established over sufficient time periods.

[0071]

[0067] Taking into account these essential advantages, the invention can thus be applied both in the case of land having a water storage reserve and in the case of land not having one.

[0072]

[0068] Another aim also sought and achieved according to the invention, perfectly distinct from the objective of limiting the use of water, although complementary from the perspective of saving water from the network, is in fact to allow water to be stored in the ground during periods without water restriction in order to use this water stored under the ground for irrigating the lawn during periods of water restriction.

[0073]

[0069] The first scenario concerned by the invention is that of a sports field where water storage tanks are arranged under the playing layer to store rainwater that falls, particularly during the rainy season, so as to have this water available during periods of drought for irrigating the lawn. However, in these water storage tanks and in the most conventional case where the volume available for storing water is fixed over time, the water level at a given moment then depends directly on the quantity of water stored in the storage tanks at the time in question, whereas managing the water content of the playing layer of the field requires, on the contrary, a depth of a water table that is completely independent of the quantity of water stored in the tanks. This water level of the storage tanks is therefore not at all suitable for controlling the water content of the playing layer by capillary forces.

[0074]

[0070] However, in this case, the problem is solved according to the invention by installing the water storage tanks under the play layer and arranging them in parallel lines, while providing a space between two successive lines of water storage tanks and filling said space with a draining and capillary material. The capillary trenches thus formed between the lines can also have a different depth, generally greater than the depth of the tanks. It is sufficient to dig a trench of the difference in depth in the well-leveled ground in place, at the level of said trenches. These capillary trenches, which thus alternate with the lines of storage tanks, are equipped according to the invention with means for installing a water table there and for managing its level.This alternation of reservoir lines and capillary trenches makes it possible to independently manage the depth of the storage reservoirs according to the water storage needs and the depth of the capillary trenches according to the capillary force objectives to be applied at a given time for a given substrate as part of the management of the water content of the play layer.

[0075]

[0071] Thus, according to the invention, a rake structure is obtained, with permeability and capillary continuity between the play layer and the water table located in the capillary trenches arranged between the lines of water storage tanks.

[0076]

[0072] However, so that the level of the water table inside the reservoirs does not influence the capillary forces inside the play layer, it is necessary according to the invention that there is no capillary continuity between the water table inside the reservoirs and the play layer located above the reservoirs. However, even if there is according to the invention capillary discontinuity between the play layer and the water storage reservoirs, the interface between these reservoirs and the play layer is not necessarily impermeable and may possibly allow gravity drainage to take place directly from the play layer to the storage reservoirs. The important thing is that the water level in the trenches is the only one to control by means of capillary forces the quantity of water that the play layer retains by capillarity or allows to drain away by gravity.By taking care to choose water storage tanks which do not have capillary continuity between said storage tanks and the play layer located above, the water level in the water storage tanks then has no influence on the water content in the play layer.

[0077]

[0073] This is particularly the case, in a preferred solution according to the invention, where the storage tanks are almost empty tanks, apart from the structural elements necessary for the mechanical solidity of said tanks, with in the upper part a permeable surface serving as an interface with the clearance layer, the capillary discontinuity being obtained and maintained as long as the tank is not completely full and a layer of air between the water and the permeable upper membrane ensures the capillary discontinuity.

[0078]

[0074] In this case, in the absence of a capillary effect of the water level in the reservoirs, the only tool for controlling the water content of the play layer by capillary forces is the level of the water table inside the capillary trenches which are arranged between the water storage reservoirs, said capillary trenches themselves being supplied by the means provided according to the invention with water which can come, depending on the needs, either from the water stored in the storage reservoirs, or possibly from another network, while, depending on the needs and circumstances, the excess rainwater flowing by gravity drainage is used to supply the water storage reservoirs or is evacuated to the sewers.

[0079]

[0075] The advantage of the invention in this first case is to allow the control of the play layer without movable bottom reservoirs and without underlay between the play layer and the reservoirs but with a very small volume of draining and capillary material in the trenches made according to the invention between the lines of reservoirs and a very small volume of water inside said trenches.

[0080]

[0076] The second application relates to a sports ground without a water storage reserve under the ground. With the aim of minimizing the transport of materials, this ground is constructed according to the invention with a playing layer laid on a sub-layer of ground in place in which are installed capillary layers filled with draining and capillary material in capillary continuity with the playing layer laid on said sub-layer.

[0081]

[0077] In this case, the fact of only having to fill the volume of the drainage and capillary trenches with a high-performance material (draining and capillary) makes it possible to optimize the ecological and economic impact of the construction of the land by saving the resource of aggregates and their transport to the construction site of the land. Once the land is in the operating phase, it will be irrigated by capillarity and drained by gravity with control of the ascending capillary flows and descending gravity flows by the level of the water table in the trenches filled with draining and capillary material, which makes it possible to ensure ecological and qualitative operation of the land by minimizing water requirements in summer and promoting aeration and especially oxygenation of the land in winter.

[0082]

[0078] So that, according to the invention, the means for supplying or removing water into said trenches to create a water table there and control its level only concern the volume of water present inside said trenches and not the volume of water inside the strips of natural ground on either side of said capillary trenches, a preferred solution according to the invention is to install an impermeable membrane at the bottom of the capillary trenches and on the vertical edges of these trenches.

[0083]

[0079] However, it is not always necessary to install such a vertical waterproof membrane at the edge of a capillary trench. Thus, for example, when the trenches are simply spaces provided between rows of storage tanks whose vertical walls are already waterproof, it is not necessary to add a waterproof membrane at the edge of the trench. Similarly, it is also not necessary to install a horizontal waterproof membrane at the bottom of the trench in the case where the bottom on which the entire underlay rests is already waterproof or waterproofed, for example an underlay comprising a waterproof membrane beneath it.

[0084]

[0080] In any event, having the volume of the trenches separated at the bottom and on the sides from their environment in a sufficiently impermeable manner is one of the means of installing a water table there and managing its level.

[0081] Perfect waterproofing between the capillary trenches and their environment is, however, neither necessary nor easily achievable in practice, the important thing being that these flows are marginal. In any event, the flows between the capillary trenches and their environment on the vertical edges and the bottom of the trenches must not represent more than 1% of the vertical capillary or gravity drainage flows in said trenches.

[0085]

[0082] These aims and advantages, as well as others which will appear subsequently, are achieved by a sports ground comprising a playing layer laid on a sub-layer, with a partition of the surface of said ground into two complementary sub-surfaces, the respective surface areas of which are both strictly positive, in which:

[0086]

[0083] - directly above a first sub-surface, the structure of said sports ground is equipped with means for creating a layer of liquid, such as for example a layer of water, in the volume of the sub-layer located under the playing layer and directly above the first sub-surface, and for managing its level;

[0087]

[0084] - the sub-layer comprises a multitude of capillary trenches located directly above the first sub-surface, said capillary trenches being configured to ensure permeability and capillary continuity between the clearance layer and said sheet of liquid.

[0088]

[0085] Preferably, the sub-layer is configured such that at the level of the second sub-surface there is no capillary flow between a sheet of liquid, such as for example a sheet of water, located at the level of the second sub-surface and the clearance layer located above.

[0089]

[0086] According to a particular technical characteristic of the invention, the sub-layer is configured such that at the level of the second sub-surface there is a capillary boundary between said layer of liquid at the level of the second sub-surface and the playing surface located above.

[0090]

[0087] This condition is an essential condition of the invention but here again the perfect capillary impermeability of the capillary boundary is neither easy to achieve nor necessary, the important thing being that the flows through these capillary boundaries are marginal.

[0091]

[0088] In any event, the sum of the upward capillary flows through this capillary boundary between the clearance layer and the sub-layer directly above surface B must not represent more than 5% of all the vertical flows between the clearance layer and the capillary trenches.

[0092]

[0089] Preferably, the sub-surfaces are respectively made up of a multitude of first parallel strips, all of equal width on the one hand, and a multitude of second parallel strips, all of equal width on the other hand, each first strip being inserted exactly between two second strips, the volume of the sub-layer directly above the first strips defining a multitude of capillary trenches, of height E2 and width WA.

[0090] Advantageously:

[0093]

[0091] the sub-layer on which the play layer rests comprises a multitude of rectilinear strips consisting of an alignment of water storage tanks, parallel to each other, of the same width, crossing the ground in the longitudinal or transverse direction, two successive parallel strips of water storage tanks being separated by a space of width WA allowing capillary trenches of said width WA to be installed therein;

[0094]

[0092] the sub-layer is configured such that at the level of the second sub-surface there is a capillary boundary between said water storage reservoirs and the play layer located above.

[0095]

[0093] Preferably, the sports field is such that the ratio R = WA / (WA+WB) is greater than or equal to 10% when the width WA of each capillary trench is substantially equal to 10 cm and the width WB of each second rectilinear strip is less than 1 m.

[0096]

[0094] Preferably, the sports field is such that the ratio R = WA / (WA+WB) is between 3% and 4% when the width WA of each capillary trench is substantially equal to 10 cm and the width WB of each second rectilinear strip is substantially equal to 2.5 m, or is substantially equal to 5% when the width WA of each capillary trench is substantially equal to 10 cm and the width WB of each second rectilinear strip is substantially equal to 2 m.

[0097]

[0095] Advantageously, the height of the capillary trenches is greater than or equal to 15 cm and the maximum depth Pmax of the bottom of said capillary trenches relative to the surface is greater than or equal to 35 cm.

[0098]

[0096] Advantageously, the sports ground further comprises a network of pipes and a perforated ringed drain, the network of pipes connecting all of the capillary trenches together and itself being capable of being connected to a water network, the perforated ringed drain being connected to the network of pipes and being arranged at the bottom of the capillary trenches.

[0099]

[0097] Advantageously, the sports ground further comprises an impermeable membrane arranged at the bottom of the capillary trenches and / or on vertical edges of said capillary trenches.

[0100] Figures

[0101]

[0098] [Fig 1] is a top view of a sports field according to the present invention.

[0102]

[0099] [Fig 2] is a vertical sectional view of this land along line II-II of Figure 1.

[0103]

[0100] [Fig 3] is a schematic view of Figure 2 showing a rake-like structure form.

[0104]

[0101] [Fig 4] is a vertical sectional view of a plot of land according to the present invention comprising a water storage tank.

[0105]

[0102] [Fig 5] is a top view of a sports ground according to the present invention which differs from Figure 1 in that on the one hand the capillary trenches shown are longitudinal and not transverse and on the other hand and above all in that individually controlled valves (12) are shown at the head of each capillary trench

[0106]

[0103] [Fig 6] is a detail or zoom of a vertical sectional view along line II-II' of figure 5 of a sports ground according to the present invention illustrating the means implemented allowing differentiated management of the water table levels of the capillary trenches in a version adapted to the renovation of sloping grounds.

[0107]

[0104] [Fig 7] is a schematic view in vertical section along line II-II' of figure 5, illustrating the means implemented allowing differentiated management of the water table levels of the capillary trenches in the particular case of a renovation according to the present invention of a “roof” plot.

[0108]

[0105] [Fig 8] is a schematic view in vertical section illustrating a particular version of the invention where the water table is connected to a closed enclosure, to control the water pressure and therefore the drainage and capillarity in the play layer (l) not by the level of a water table at equilibrium in the capillary trenches (4) but by the level of the water table in the capillary trenches in relation to a closed enclosure where the water is overcome by air at pressure P a+ AP and where the level Hi of the water table in the capillary trenches in quasi-permanent regime is defined, according to this preferred control method of the invention, by the sum Hi = hi - AP, where hi is the depth from the ground of the level of the free surface of the water in said closed enclosure and where the pressure difference AP is expressed in an abusive but usual way in equivalent water height (i.e. 10 meters of water for 1 bar of pressure).

[0109]

[0106] [Fig 9a] and [Fig 9b] represent schematic views illustrating in 2 different cases the fact that a water table at equilibrium and connected with the water in the closed enclosure is indeed at depth H1 and the fact that the water table level Hi corresponds to the depth of the roof of the water table in the capillary trenches once equilibrium has been reached since this level Hi is a depth located between the top and the bottom of the capillary trenches.

[0110] Detailed description of the invention

[0111]

[0107] Even if the present description and the figures primarily concern terrains with a partition of the surface of the terrain into parallel strips (BA) and (BB) all of the same width (WA) and (WB) respectively and capillary trenches (4) defined as the volume of the sub-layer directly above the strips (BA) because this type of geometry seems the simplest and most logical to implement, it is however important to specify that this geometric aspect of a partition of the surface of the terrain into rectilinear, parallel strips of the same width is not an essential point of the invention.

[0112]

[0108] Similarly, if the liquid used in the trenches and the play layer in the following description is water, this is not an essential aspect of the invention, which is therefore not limited to this liquid alone. The person skilled in the art can apply the concept with any type of liquid suitable for a play layer, in particular with a view to fertigation or phytosanitary treatment of the environment or water.

[0113]

[0109] In general, the invention relates to any sports ground comprising a playing layer (1) of thickness (El) placed on a sub-layer (2) of thickness (E2), with a partition of the surface of the ground into two complementary sub-surfaces (A) and (B), the respective surface areas SA and SB of which are both strictly positive, with permeability and capillary continuity between said playing layer (1) and the sub-volume of the sub-layer (2) located directly above the sub-surface (A) and with, on the contrary, an absence of capillary continuity between said playing layer (1) and the sub-volume of the sub-layer (2) located directly above the sub-surface (B),and the ground being furthermore equipped with means for creating a water table (3) in said sub-volume of the sub-layer (2) located directly above the sub-surface (A) and for managing its level at equilibrium or in quasi-permanent mode or equipped with means for introducing or extracting water from the bottom of the structure into or from drains (10) installed in said capillary trenches (4), even if this introduction or extraction of water in the transient phase is too rapid to allow the management at equilibrium or in quasi-permanent mode of a water table in said capillary trenches (4).,

[0114]

[0110] In the preferred version of the invention described below as a priority, it is precisely this level of the water table (3) in the capillary trenches (4) directly above the sub-surface (A) which makes it possible, thanks to the permeability and capillary continuity between the play layer (1) and said water table (3) directly above the sub-surface (A), to control the humidity level of the play layer (1), by the effect of the capillary forces which depend on said level of the water table (3), said capillary forces in turn controlling the gravitational drainage of said play layer (1) on the one hand and the capillary flows feeding said play layer (1) from said water table on the other hand.

[0115]

[0111] Also, in the preferred version of the invention described below as a priority, a field according to the invention is a sports field comprising a playing layer (1) of thickness (El) placed on a sub-layer (2) of thickness (E2), with a partition of the surface of said field into two complementary sub-surfaces (A) and (B), the respective surface areas SA and SB of which are both strictly positive, in which:

[0116] - The sub-volume of the sub-layer (2) located directly above the sub-surface (A) is made up of a multitude of capillary trenches (4), said capillary trenches (4) located directly above the sub-surface (A) being configured to ensure permeability and capillary continuity between said clearance layer (1) and said capillary trenches (4);

[0117] - The sub-volume of the sub-layer (2) located directly above the sub-surface (B) is configured to ensure, on the contrary, an absence of capillary continuity between said play layer (1) and said sub-volume of the sub-layer (2) located directly above the sub-surface (B);

[0118] - directly above the sub-surface (A), the structure of said sports ground is equipped with means for creating a layer of liquid (3), such as for example a layer of water, in the capillary trenches (4) constituting the sub-volume of the sub-layer (2) located under the playing layer (1) and directly above the sub-surface (A), and for managing its level;

[0119]

[0112] It should also be specified that the description does not only concern a flat terrain in which all the capillary trenches are connected together but that Figure 7 illustrates on the contrary the very classic and frequently encountered case of a so-called "roof" sports ground because the surface of the ground has a shape which evokes a roof with a high level in the axis of the ground and an altimetry which descends transversely on either side with a slope often of the order of 1%. In this figure, we notice in each capillary trench a water table whose level is managed individually for each trench, so as to constitute under the ground a "virtual water table" parallel to the surface of the ground.

[0120]

[0113] In this context, Figure 6 is a detail of section II-II' indicated in the top view of Figure 5 and which illustrates more generally and schematically the means implemented to allow individual management of the water table levels of the different capillary trenches; These means comprise for each drain installed at the bottom of the trench in each capillary trench (4) an individual and individually controlled valve.

[0121]

[0114] It should also be specified that the level of the water table (3) in a capillary trench (4) can be defined according to the invention as the piezometric level of said water table (3) (i.e. the depth relative to the ground of the free surface in a well of a volume of water in the open air connected to said water table) since said water table (3) in a capillary trench (4) is in equilibrium, but that this is only a particular case of the invention, and that the notion of controlling the water pressure in the play layer (1) by the level of a water table (3) in the capillary trenches (4) is not limited to water tables (3) having reached equilibrium and controlled by their piezometric level.

[0122]

[0115] On the contrary, the notion of the level of a water table in the capillary trenches can be extended according to the invention to water tables which have not yet reached their equilibrium and a preferred version of the invention makes it possible precisely in this configuration to define an extended notion of the level of the water table and provides the means to reach and maintain this level.

[0123]

[0116] Figure 8 illustrates the principle of a water table (3) located in the capillary trenches (4) and which has not yet necessarily reached its equilibrium (and whose roof (16) therefore sees its depth vary while tending almost permanently towards its future equilibrium position) but whose level can however be defined and controlled according to a particular version of the invention where said water table (3) located in the capillary trenches (4) is hydraulically connected by a circuit (20) to a volume of water (14) located in a closed enclosure (13) and surmounted in said closed enclosure (13) by a volume of air (15), said closed enclosure (13) (commonly referred to as a bell) being equipped with means for adjusting and maintaining the volume of air above the volume of water at the pressure Pa + AP (i.e. in overpressure AP or in depression AP relative to the atmospheric pressure Pa depending on whether AP is respectively positive or negative).

[0124]

[0117] In this configuration and according to this preferred method of the invention, the level H1 of the water table (3) in the capillary trenches (4) in quasi-permanent regime is defined in a broad manner by the formula H1 = hl - AP , where hl is the depth from the ground of the level of the free surface of the water in said closed enclosure, by expressing the algebraic pressure difference AP in equivalent water height, (in an abusive but usual manner), i.e. a height of 10 meters of water for a pressure of 1 bar.

[0125]

[0118] In the particular example illustrated by Figure 8, this is a depression (AP is negative and its absolute value / AP / = - AP) and said depression AP is kept constant for a certain time by keeping the volume of air above the water in the bell (13) constant, for example using a water pump whose function is simply to extract from the closed enclosure the flow of water necessary to compensate for the flow of water arriving from the water table (3) of the capillary trenches (4) in said enclosure closed by the circuit (20), so as to keep the volume of air (15) constant and therefore the air depression above the volume of water (14) in said enclosure (13);A downward pointing arrow symbolically indicates that the variable depth h2(t) of the roof (16) of the water table (3) in the capillary trenches (4) is descending to gradually move towards the equilibrium level of the water table, at depth Hl, because we are in a quasi-constant regime but not at equilibrium.;

[0126]

[0119] Meanwhile, for a fixed point M located in the play layer (1) at the depth hM, we consider a continuous water path represented as a tube (19) resting on the roof of the water table (3) in the capillary trench (4) at the depth h2 (t).

[0127]

[0120] It can be noted that the tube (19) receives at the level of the point M an atmospheric pressure Pa The water pressure at the bottom of the "tube" (19) is therefore (Pa + AP - (hl - h2 (t)). The tube (19) undergoes an upward force equal to the surface tension, and to the water pressure at the bottom of the tube and a downward force equal to the weight of the tube and to the atmospheric pressure which prevails in the unsaturated porosity, that is, by expressing all the pressures in the form of water height and by considering the resulting pressure Pbilan directed downwards: We have the formula Pbilan = Pa

[0128] + (h2 ( t) - hM ) - (Pa + AP - hl+ h2 ( t) ) = -AP + hl - hM = Hl - hM which means that the forces which determine drainage and capillarity in the play layer depend only on the level H1 = hl + AP and the depth of the point M considered and not on the instantaneous depth h2(t) of the roof (16) of the water table (3) in the capillary trenches (4).

[0129]

[0121] As long as there is water in the water table (3) located in the capillary trenches (4) and connected by the hydraulic path (20) to the closed enclosure (13), the water pressure in the unsaturated layer (1) is constant and therefore the capillary forces are constant as with a water table at equilibrium.

[0130]

[0122] It is also noted in Figure 8 that the hydraulic path (20) which connects the water table (3) located in the capillary trenches (4) to the closed enclosure (13) undergoes a narrowing (21). The reason for this is that the objective is to have a relatively long period of time with water in the water table (3) located in the capillary trenches (4) and connected by the hydraulic path (20) to the closed enclosure (13), which ends as soon as the descending water table (3) finally reaches the level of the bottom of the capillary trenches (4). The purpose of the narrowing is to slow down the descent of said water table (3) because the emptying speed of the table depends at any time on the pressure difference hl - h2 (t) between the roof (16) of said table and the free boundary between the water and the air inside the closed enclosure (13) while the flow rate is equal to the product of this speed by the section of the tube (21) at the entrance to the enclosure (13).

[0131]

[0123] The 2 cases presented in Figures 9a and 9b then make it possible to illustrate two different situations: a. In the configuration of Figure 9a, we see that this depth H' 1 = h' 1 -AP' corresponds to the case of an overpressure and that at equilibrium there is coincidence between this level H' 1, the level (18) in the pipe for viewing the water table level at equilibrium and the depth of the roof (16) of the water table (3) at equilibrium in the capillary trenches (4). b. In a configuration of Figure 9b, we have the case of a depression and all the water in the water table empties before reaching equilibrium and only water remains in the control pipe shown, and the water level (18) at equilibrium in said control pipe (17) is indeed Hi = hl -AP.

[0132]

[0124] Figures 9a and 9b illustrate on the one hand the fact that at equilibrium, the expanded concept of water table level (overpressure or depression of air in a closed enclosure) and the piezometric level of said water table coincide well, the depth of the roof of the water table (3) at equilibrium in the capillary trenches (4) defining the concept by the piezometric level having the value Hl = hl + AP defining the expanded concept by the depression of air in a closed enclosure with air-water separation surface at depth hl.

[0133]

[0125] It can be seen in Figures 9a and 9b that the depth of the roof 16 of the water table (3) at equilibrium in the capillary trenches (4) is indeed at the depth H1 since this level Hi is a depth located between the top and the bottom of the capillary trenches.

[0126] In the opposite case, that is to say in the case where this level cannot be reached by the water table (3) in the capillary trenches (4) because this level is located lower than the bottom of the trenches (4) (or higher than the surface of the ground), Figures 9a and 9b illustrate on the other hand that the situation would be the same as if these capillary trenches were virtually extended lower down to the depth H1

[0134]

[0127] This situation is in fact illustrated by adding, for the sole purpose of understanding, an additional pipe (17) connected at one end to the water of the closed enclosure and open to the open air at the other end; This pipe first descends lower than the level Hi and then rises to open into the open air and this makes it possible to visualize the level of the free surface (18) of the water in this pipe and to note that we then find at equilibrium that this free surface (18) is indeed located at the level Hi = hl -AP (i.e. Hi = hi + / AP / in depression and Hi = hi - / AP / in overpressure).

[0135]

[0128] Furthermore, even if preferably the means are configured as in figures 8, 9a and 9b to allow the water pressure in the playing layer (l) to be controlled by the level of the water tables (3) located in the capillary trenches (whether these water tables are in equilibrium or in permanent or quasi-permanent regime and whether or not this level is located between the top and the bottom of the capillary trenches (4),) the invention also relates to the possibility of saturation-drainage cycles and any modification in transient regime of the level of the water tables (3) in the capillary trenches (4) and more generally the invention also relates to all configurations of sports grounds comprising air or water pumps, valves, enclosures,probes and automation of pumps and generally all the numerous means already known which can be installed in the control system of a rake structure ground according to the invention and which make it possible to introduce air or water directly from the bottom of the structure, into or from drains (10) installed in said capillary trenches (4).,

[0136]

[0129] More generally, the invention also relates to any sports ground comprising a playing layer (1) of thickness (El) placed on a sub-layer (2) of thickness (E2), with a partition of the surface of the ground into parallel strips (BA) and (BB) all of the same width (WA) and (WB) respectively and capillary trenches (4) defined as the volume of the sub-layer directly above the strips (BA) characterized by the existence of capillary permeability and continuity between said playing layer (1) and said capillary trenches (4) and by the absence of capillary continuity between said playing layer (1) and the sub-volume of the sub-layer (2) located on the contrary directly above the strips (BB), said sports ground being further equipped with means for introducing or extracting water from the bottom of the structure into or from drains (10) installed in said capillary trenches (4),even if this introduction or extraction of water in the transient phase is too rapid to allow the management of a water table in said capillary trenches at equilibrium or in a quasi-permanent regime (4).,

[0137]

[0130] In Figure 2 or in Figure 4 or in Figure 6 which schematically present a sports ground with a rake structure according to the invention, the control system is therefore simply presented in a generic manner, without having to specify the details of the means already known for controlling the level of a water table, particularly in the transient phase.

[0138]

[0131] However, even if it is possible according to the invention to simply manage the water in the capillary trenches (4) by cycles in a transient phase, as is a practice already known with terrains not having this rake structure characterized by capillary trenches in capillary continuity with the play layer (1) located above and absence of capillary continuity between said play layer (1) and the underlayer strips (2) located between said capillary trenches (4), it remains however preferable according to the invention to use the rapid saturation-discharge cycles only for oxygenation or air conditioning by convection and to manage the capillarity and drainage between these transient cycles by the use of water tables at equilibrium or tending in a quasi-permanent regime towards equilibrium at a real water table level in the capillary trenches (4) or at a virtual water table level below the low point of the capillary trenches (4).

[0139]

[0132] The fact of being able to lower the level of the water table (3) lower than the depth of the bottom of the capillary trenches (4) during the time of slow descent of the top of the water tables (3) in the capillary trenches (4) makes it possible to meet the need for saving water in irrigation by capillary flow controlled by the level of said water table (3) in the capillary trenches (4) which is one of the important aims of the present invention.

[0140]

[0133] Furthermore, the reason for this preference for managing the water pressure in the unsaturated porosity of the play layer (1) above a water table (3) located in the capillary trenches (4) and in a situation of equilibrium or quasi-steady state is that this makes it possible to control the water content in the substrate of the play layer (1) by capillary forces and thus to control the water consumption by the roots in a system where the gradient is well oriented over long periods of time.

[0141]

[0134] It should also be specified that ensuring permeability between the play layer (1) and said capillary trenches (4) simply means that any filling elements of the capillary trenches (4) and the contact surface (BA) between the play layer and said capillary trenches (4) do not prevent the establishment of a gravitational flow descending spontaneously under the effect of the forces of gravity through the play layer (1) and down to said water table (3), since the water content contained in the play layer is in excess compared to the water content corresponding to the capillary equilibrium, that is to say since the forces of gravity pulling the water downwards prevail over the capillary forces pulling the water upwards, taking into account the depth of the table and the capillary characteristics of the substrate of the play layer.However, if ensuring permeability is a necessary condition of the invention, it is also necessary to ensure that this permeability is sufficient to reduce the excess water in a sufficiently short period of time to be truly satisfactory.

[0142]

[0135] It is known that this permeability condition, in the absence of an obstacle specially installed to waterproof the column, is fulfilled in any vertical column filled with any granular medium.

[0143]

[0136] Thus, ensuring permeability between the play layer (1) and said capillary trenches (4) does not involve additional means other than the absence of an impermeable barrier preventing the gravity flow from flowing to the water table, knowing that the gravity flow for a given surplus of water is all the faster as the permeability is high and that the assessment of satisfactory permeability is a subject already well known in the state of the art.

[0144]

[0137] In the same way, it should be specified that ensuring capillary continuity directly above the sub-surface (A) between the play layer (1) and said water table (3) in the volume of the sub-layer (2) located under the play layer (1), simply means that directly above the sub-surface (A) the structure of the ground allows the water to rise from the water table (3) to the play layer (1) by the effect of capillary forces when the water content of the play layer (1) is lower than the water content at capillary equilibrium.

[0145]

[0138] Also, for a capillary flow to spontaneously start feeding the upper part, there is no need for additional means because the force that makes the water rise is found in the surface tension at the air-water interface in the play layer and this force makes the water rise from the water table as long as there is a continuous column of water between the water table and the play layer and the gravitational force of the weight of this column of water is less than the traction of the surface tension which pulls said column. The only means necessary to ensure capillary continuity is therefore simply to have a structure which does not create a discontinuity of the water column between the water table and the play layer.

[0146]

[0139] It is known in particular that in any granular medium and in the presence of a water table and an evaporative demand, an ascending vertical capillary flow spontaneously begins to feed the upper part of said granular medium from said water table, said spontaneous capillary flow having the effect of partially and more or less effectively compensating for the deficit in water content compared to the capillary equilibrium created by said evaporative demand, which therefore makes it possible to bring the water content of the medium closer to its water content at capillary equilibrium.

[0147]

[0140] The effectiveness of the capillary continuity considered here is defined by the fact that the capillary continuity is considered all the more effective as the capillary flow generated to partially compensate for the deficit in water content compared to said capillary equilibrium created by an evaporative demand has the effect of bringing the water content in the clearance layer (1) closer to the water content at capillary equilibrium. In other words, in periods of intense evapotranspiration, the more effective the capillary continuity is, the smaller the difference between the water content of the clearance layer and the water content at capillary equilibrium.

[0148]

[0141] In this case, it is known that in a sandy-type granular medium and even for a very high Potential Evapotranspiration (PET) of up to 1 cm per day, the ascending capillary flow which spontaneously starts to act is capable of supporting the climatic evaporative demand, that is to say that the ascending capillary flow is capable of equalling the PET value on a daily average, as long as the water table has its piezometric level at less than 50 cm deep.

[0149]

[0142] On the other hand, and contrary to what is often accepted, fine granular media such as silt or a fortiori clay do ensure capillary continuity but with very low efficiency in terms of flow; also, contrary to generally accepted ideas, this type of fine granular media, which is also not very effective in terms of permeability, is not recommended for ensuring effective capillary continuity.

[0150]

[0143] Surprisingly, however, tests carried out with gravel have revealed that 2-6 or even 3-8 mm gravel (especially unrolled and unwashed) also ensures relatively satisfactory capillary continuity.

[0151]

[0144] Coarse gravels can also provide some capillary continuity provided there is a film of water on the surface of the aggregates but again, since the efficiency in terms of flow decreases with the specific surface area of ​​the aggregate, it is not desirable in terms of capillary flow efficiency to choose a gravel coarser than 2-6 gravel.

[0152]

[0145] Furthermore, whatever the environment, the presence of fibers (including possibly roots) is a factor of strong improvement in the efficiency of capillary continuity.

[0153]

[0146] Finally, the capillary trenches according to the invention are not necessarily filled with a single granular material and may comprise, according to the invention, a set of elements each having a specific function, the important thing being to ensure capillary continuity between the capillary trenches and the clearance layer above.

[0154]

[0147] The important thing in the context of the invention is that at the level of the surface (A), a water content lower than the water content at capillary equilibrium in the play layer (1) generates from the water table (3) located in the sub-layer (2) at the level of said surface (A) an ascending capillary flow supplying water to said play layer (1), unlike the situation at the level of the sub-surface (B) where there is no capillary flow between a water table located at the level of the sub-surface (B) and the play layer (1) located above, for example because there is then a capillary boundary between this water table at the level of the surface B and the play surface (1) located above, that is to say an impossibility of capillary flow from this water table to the play layer (1) located above.

[0155]

[0148] This condition of capillary continuity directly above the subsurface (A) and only the subsurface (A) between the water table (3) located in the capillary trenches (4) and the clearance layer (1) is an essential condition of the invention.

[0156]

[0149] However, even if this condition is an essential condition of the invention, perfect impermeability of the capillary boundary is neither easy to achieve nor necessary, the important thing being that any flows through these capillary boundaries due to a functional, although imperfect, capillary boundary remain marginal.

[0157]

[0150] A criterion for satisfactory effectiveness of the capillary boundary is according to the invention that the sum of the ascending capillary flows through this capillary boundary between the clearance layer and the sub-layer directly above the surface B never represents more than 5% of all the ascending vertical flows between the clearance layer and the capillary trenches.

[0158]

[0151] Naturally, for each terrain according to the invention, this necessary condition is not necessarily sufficient and it is also appropriate to ensure a relevant choice concerning the elements filling the capillary trenches, the width of said capillary trenches (4), the surface ratio SA to SB, the geography of the implantation of the surface (A), in such a way that the ascending capillary flow is sufficient to ensure the irrigation of the lawn, taking into account the local climate of the terrain considered and the irrigation objectives chosen for the terrain considered.

[0159]

[0152] Indeed, evapotranspiration is proportional to the total surface area of ​​the lawn SA + SB while the capillary flow allowing irrigation of the lawn is proportional to the sole surface area SA through which said capillary flow passes.

[0160]

[0153] Also, the lower the ratio R = SA / (SA + SB), the more efficient means are required to compensate for the low ratio R in order to ensure sufficient flow. Indeed, for perfect irrigation, the flow between the water table (3) and the clearance layer (1) which only passes through the surface SA must compensate for the evapotranspiration which takes place over the entire surface (SA + SB).

[0161]

[0154] As seen above, these means for obtaining a higher flow for a given surface area are, on the one hand, a material comprising a lot of fibers for better capillary efficiency and, on the other hand, raising the level of the water table in the event of high evaporative demand.

[0162]

[0155] In the same way, in the preferred case described below of rake structures, the ratio WA / (WA + WB) where (WA) and (WB) are respectively the widths of the capillary trenches (BA) and the strips BB between which the latter are inserted is a good approximation of the ratio R and in the same way as in the general case, the lower the ratio WA / (WA + WB), the more efficient means are required to ensure flow in the capillary trenches.

[0163]

[0156] Furthermore, so that it is indeed the level of the water table directly above the sub-surface (A) which determines the capillary pressure in the play layer (1), it is also appropriate to check that the volume (5) of the sub-layer located under the play layer (1) and directly above the sub-surface (B) does not contain any water table in capillary continuity with the play layer.

[0164]

[0157] This is the case for the terrains according to the invention in which there is no water table in the sub-layer (2) directly below the sub-surface (B).

[0165]

[0158] In practice, as illustrated by Figure 1, a preferred embodiment of land according to the invention without storage tanks under the surface B consists of making a set of equidistant parallel trenches crossing the land in the transverse or longitudinal direction of 10 to 2 cm in width and 50 cm to 70 cm in depth, with an equidistance of 1 to 2 meters between 2 successive trenches, all of the trenches and strips of land between the trenches covering the surface of the land.

[0166]

[0159] On the roof of the underlay (2) already in place (renovation) or installed and stabilized (creation) and before installing the substrate of the play layer (1) over the underlay (2), said trenches are first dug in the underlay in a first step, with extraction of the earth.

[0167]

[0160] Preferably, in a second step, rolls of waterproof membrane strips of a width approximately equivalent to the equidistance between 2 neighboring trenches are unrolled between 2 neighboring parallel trenches, in the direction parallel to said capillary trenches, the edges of the strip reaching or not reaching these capillary trenches, said edges of the strip descending where appropriate along the vertical edge of the capillary trenches.

[0168]

[0161] In a third step, a roll of membrane with a width significantly greater than the sum of twice the depth of the capillary trenches and their width is then unrolled above each of the capillary trenches, in the direction of the capillary trenches and extending on either side by a width sufficient to be able to be subsequently pushed into said capillary trench so as to match its edges, while maintaining on either side of the trench a horizontal width placed on the membrane placed in the previous step, respecting an overlap of at least 30 cm.

[0169]

[0162] A fourth relevant step consists of welding the membrane laid in the third step to the membrane laid in the second step and which it covers.

[0170]

[0163] In the case of welding the strips, it is preferable to provide an overlap of the strips greater than 10 or 15 cm on average for easier welding and to take into account the difficulty of precise positioning of the strips.

[0171]

[0164] This welding step, preferable to keep the strips in place when subsequently filling the trenches, is however not obligatory. The strips may not be welded together but in this case the overlap of 2 strips is preferably greater than 30 cm to properly press the upper strip onto the strip covered by the weight of the substrate placed on top, and even 50 cm to facilitate installation.

[0172]

[0165] In the fifth stage, the corrugated pipes are installed at the bottom of the trench, obviously protruding from the ground, to subsequently make the connections with the entire water supply and drainage system up to the system management and control organs.

[0173]

[0166] The sixth step consists of filling the capillary trenches and the seventh step is to install the play layer, these last two steps possibly being carried out simultaneously if the filling material is the same for the trenches and the play layer.

[0174]

[0167] In such an embodiment, the covering of the strips and their quality of impermeability and resistance ensure a satisfactory capillary barrier, in principle perfect but whose imperfections can allow a little water to pass through at the level of possible tears or possible passages of water between the superimposed membranes due to a non-existent or imperfect weld or an imperfect covering at the level of the edges. The essential thing according to the invention is that such possible flows linked to the imperfections of the installation only allow marginal capillary flows to pass through.

[0175]

[0168] In another type of embodiment according to the invention, a terrain may possibly be provided with means for managing a water table in the sub-layer (2) directly below the sub-surface (B), as is the case in particular with the storage tanks presented above, provided however that there is no capillary continuity between the play layer (1) and the volume of water possibly present in the sub-layer (2) directly below the sub-surface (B).

[0176]

[0169] In the particular case of storage tanks (RS) with an air layer (RSA) above the water table (RSW) inside said storage tanks (RS) or in the case of tanks (RS) with a watertight roof, there is indeed in this case a water table in the storage tanks and possibly the possibility of controlling the level by a network of pipes (6B) connected to a water level control member; but there is no capillary continuity between this water table (RSW) inside said storage tanks (RS) and the clearance layer (1) above.Thus, in this case according to the invention, and even if there are means in the structure of the ground to create a water table in the volume located under the play layer and directly above said second complementary sub-surface (B), the level of said water table cannot create capillary forces constraining the water content of the play layer located above because there is no capillary continuity between the play layer (1) and said volume (5) located under the play layer (1) and directly above said complementary sub-surface (B). The level of the water table (RSW) located in the reservoirs (RS) therefore has no influence on the capillary forces acting in the play layer.

[0177]

[0170] In practical terms, the following description concerns a “rake” terrain structure, the principle of which is a partition of the surface of the terrain into parallel rectilinear strips crossing the terrain with alternating strips belonging to the sub-surface (A) and strips belonging to the complementary sub-surface (B), the strips directly above said sub-surface (A) and located in the sub-layer (2) corresponding to the rectilinear capillary trenches (4) of width (WA) and the strips of the complementary sub-surface (B) being strips of width (WB), spaced apart from each other by the width (WA) of the capillary trenches (4) and the strips directly above said sub-surface (B) and located in the sub-layer (2) corresponding to the strips (5) interposed between the capillary trenches (4). These strips are preferably oriented to cross the terrain in the longitudinal direction or in the transverse direction.

[0178]

[0171] Thus, considering in section the clearance layer (1) and the plurality of vertical capillary trenches (4) located below, the structure appears as a rake, the clearance layer (1) playing the role of the horizontal crosspiece and the vertical capillary trenches (4) located in the sub-layer (2) playing that of the teeth of the rake, as shown in figure 3.

[0179]

[0172] Preferably, the invention relates to a sports field with such a rake structure, that is to say, in more detail, a field comprising a playing layer (1) laid on a sub-layer (2), and with a partition of the latter into two complementary sub-surfaces (A) and (B) which are respectively in the form of a multitude of parallel strips (BA), all of equal width (WA) on the one hand and a multitude of parallel strips (BB), crossing the field in the longitudinal direction or in the transverse direction, all the strips (BA) being of equal width (WA) and all the strips (BB) of equal width (WB); the strips (BA) alternate with the strips (BB), each strip (BA) interposing exactly between 2 parallel strips (BB) spaced apart from each other by the width (WA) of the strips (BA).In this preferred solution context, the volume of the sub-layer (2) directly above each strip (BA) of width (WA) corresponds to a capillary trench (4), defined as a parallelepiped of width (WA) and depth (E2) located in the sub-layer (2) directly above each of the strips (BA).

[0180]

[0173] These capillary trenches (4) arranged in the sub-layer (2) are equipped with means for installing a water table (3) in capillary continuity with the play layer (1) and with means for adjusting the level of this water table (3). Thus, by the level of the water table in the capillary trenches, it is possible according to the invention to control the water and air content of the play layer (1) by means of the capillary forces which depend on said level of the water table and which in turn control the gravitational drainage of said play layer (1) and the capillary flows feeding said play layer (1) from said water table located in the capillary trenches (4).

[0181]

[0174] According to the invention, the capillary trenches (4) are filled with a set of elements making it possible to ensure permeability and capillary continuity between the play layer and said capillary trenches (4).

[0182]

[0175] In practice, it is preferable to choose for the capillary trenches an overall permeability equivalent to or greater than that of the play layer. This choice is more particularly indicated when the main objective is rapid drainage of the surfaces.

[0183]

[0176] However, in certain circumstances, particularly with very dry climates where the objective of saving water is a priority, the choice of an overall permeability in the trenches lower than that of the play layer, with trenches filled with a relatively fine sandy material is another option according to the invention, interesting for slowing down the capillary flow for a given depth and thus limiting water consumption in summer.

[0184]

[0177] In the case where the capillary trenches (4) are filled with a single material, said material must be both draining and capillary. A sufficiently “dirty”, unrolled and unwashed sand may be suitable in certain cases, but the lower the surface area ratio of the capillary trenches to the total surface area of ​​the ground WA / (WA + WB), the more appropriate it is to have a truly capillary material.

[0185]

[0178] A truly satisfactory preferred solution is filling with fiber sand, which can also preferably be the material used for the play layer (1).

[0186]

[0179] Furthermore, the permeability between the play layer and the water table (3) in the capillary trenches (4) being a condition required according to the invention, it is also appropriate to ensure that the downward gravitational flow will be sufficient so that the drainage does not take too long.

[0187]

[0180] However, this is not a particularly difficult requirement to meet, because the drainage time is not really an essential element, as long as it is not excessive in relation to the chosen drainage objectives, knowing that the conditions for gravity drainage through seepage slots are already well known in the state of the art.

[0188]

[0181] On the other hand, and unlike the upward capillary flow from the water table which takes place only in the capillary trenches (4), the gravity drainage does not necessarily pass through the capillary trenches (4) alone but, according to the invention, can possibly also pass through the volume (5) of the sub-layer directly above the strips (BB).

[0189]

[0182] This latter option is not ruled out according to the invention, even if it is not of interest in the case of industrial tanks, the volume of which is essentially empty and capable of being filled with water, supplied from the drainage water from the trenches by a set of pumps because the drainage between said tanks works perfectly and the filling of said tanks can easily be done by a high flow pipe and filling the tanks by gravity would not present any advantage.

[0190]

[0183] This option may however be of interest in a more rustic version of the invention if, for example, a play layer (preferably thick) is placed on a porous sub-layer capable of being used to store water in winter or during storms, such as, for example, an old drainage layer whose outlets are closed by valves or a layer of permeable natural ground with coarse porosity placed on an impermeable sub-layer and therefore having an interesting capacity to store water so that it can be used in dry periods.

[0191]

[0184] In this case, as it would not be easy to simultaneously recover the large volume of water which falls in a short time on a piece of land during a storm to make it percolate directly through the reduced surface area of ​​a possible pipe to introduce the drained water into the sub-layer of the land which would offer significant resistance to the percolation of a high flow rate through a very reduced surface area, it is on the contrary possible and relevant to let this water infiltrate naturally by gravity through the entire surface of the land to thus supply the natural water reserve under the land by simple effect of gravity.

[0192]

[0185] A solution according to the invention is in this case to install above the old drainage layer or above the porous sub-layer serving as a water reservoir a suitable grid, topped with a geotextile, and providing an air gap to create a capillary barrier between the play layer and the sub-layer on which it rests, but while allowing the precipitation water to percolate through the geotextile and this suitable grid and which therefore serves as a capillary barrier while allowing the water to percolate by gravity to fill the water reserve constituted by the porous sub-layer under the play layer.

[0193]

[0186] Even if in absolute terms the surface of the grid structure may possibly allow the creation of a slight capillary flow, this flow, which remains marginal, is compatible with the control of drainage according to the invention by the capillary trenches alone.

[0194]

[0187] In reality, however, the level of the capillary trenches only controls the pushed drainage because minimal gravity drainage in the complementary subsurface of the capillary trenches takes place anyway, corresponding to a water table level at the bottom of the play layer.

[0195]

[0188] However, the principle of the invention of controlling drainage and capillary flow is maintained when the water table level in the trenches is lower than the bottom of the clearance layer.

[0196]

[0189] In this case, it is the drainage trenches dug and sealed at the edges by a membrane which alone serve for capillarity and which alone allow “advanced drainage”, that is to say drainage going beyond the minimal drainage of surplus storm water in the porous medium serving as a natural storage reservoir.

[0197]

[0190] However, in order to retain water in the porous sub-layer during a storm, gravity drainage must be allowed to take place in the sub-layer under the ground and for this purpose drainage through the trenches must be temporarily blocked, while the excess water in the play layer is evacuated into the sub-layer compared to the capillary equilibrium for atmospheric pressure at the top of the sub-layer.

[0191] Once this first limited but useful drainage for retaining rainwater has been carried out through the grid serving as a capillary boundary, it is then possible to continue further drainage in said capillary trenches until the desired water content is reached by adjusting the water table of the capillary trenches to the desired level.

[0198]

[0192] Thus, in this case, it is the drainage trenches dug and sealed at the edges by a membrane which alone serve for capillarity and which alone allow for extensive drainage.

[0199]

[0193] Also, by exception, complete control of capillary flow and control of "pushed drainage" only for water table levels in capillary trenches lower than the bottom of the playing layer is acceptable according to the invention for this type of rustic terrain.

[0200]

[0194] Furthermore, even if it is implicit, it can also be specified that the solutions according to the invention differ from the already known situation of a uniform sub-layer with a water table in the whole of said sub-layer by the fact that, in the case of the invention, the capillary trenches (4) are distinct and separated from the volumes (5) located in the sub-layer (2) located under the clearance layer (1) and in line with the strips (BB) and that, moreover, the means according to the invention for creating a water table (3) in the capillary trenches (4) and for controlling its level do not make it possible to create a water table and to manage its level in said volumes (5) in line with the strips (BB). In this context, having a sufficiently impermeable separation at the bottom and on the sides between the capillary trenches (4) and their environment is one of the means for installing a water table (3) there and for managing its level.

[0201]

[0195] A network of pipes (6) is also shown in Figures 2 and 4. This network of pipes (6) connects the drainage trenches (4) to each other and to a control center (9) equipped with the necessary means for adding water from a network (7) or discharging the water to sewers (8).

[0202]

[0196] Figure 2 shows the bands (BB), of width (WB) alternating with the capillary trenches (4) of width (WA) but also shows on the section the depths (El) and (E2) corresponding respectively to the play layer (1) and the sub-layer (2).

[0203]

[0197] In the section of Figure 2, the presence in the capillary trenches (4) of a water table (3) having its level at depth (P) relative to the surface (S) of the ground is illustrated. The bottom of the trenches is at depth (P MAX).

[0204]

[0198] The water table (3) located between the bottom of the capillary trenches and the piezometric level of said water table has the following thickness: PMAX - P. We therefore have P < PMAX

[0205]

[0199] The network of pipes (6) connects the drainage trenches (4) to each other and to the control center (9) equipped with means for adding water from the network (7) or for discharging the water to the sewers (8).

[0200] A perforated ringed drain (10) arranged at the bottom of the capillary trenches (4) is also shown; it is connected to the network of pipes (6) and allows distribution throughout the capillary trench of the water supplied or, on the contrary, extracted by the network of pipes (6).

[0206]

[0201] An impermeable boundary (11) separates the capillary trenches (4) from their environment and in particular provides a vertical separation with the volume (5) of the strips (BB) and a horizontal separation with the bottom on which said capillary trenches (4) rest, but this boundary (11) does not separate the capillary trenches (4) from the play layer (1).

[0207]

[0202] Figure 3 is a simple extract from Figure 2 which simply shows the rake shape of the structure seen in section with the layer (1) playing the role of the horizontal crosspiece and the vertical capillary trenches (4) that of the teeth of the rake, separated from each other by the volume (5) of each strip (BB).

[0208]

[0203] Figure 4 is a sectional view of a raked terrain according to the invention in a particular preferred embodiment where the structure comprises water storage tanks (RS) arranged in non-contiguous parallel lines which constitute strips of width WB with a space of width WA between the tank lines.

[0209]

[0204] Preferably, on a practical level, in this case where the structure comprises water storage tanks (RS) arranged in non-contiguous parallel lines which constitute strips of width WB with a space of width WA between the tank lines, a preferred solution for the creation of such a structure consists in starting by digging in the well-leveled ground in place parallel trenches of width (WA) and depth (E2 - HMAX), with (E2) = (PMAX - El), said parallel trenches being spaced apart by a distance WB corresponding to the width of the water tanks.

[0210]

[0205] The water storage tanks of width (WB) and height (HMAX) are then installed on the existing ground, between the trenches of width (WA) and depth (E2 - HMAX) previously dug in the existing ground.

[0211]

[0206] Thus, between the top of the water storage tanks and the bottom of the trenches between 2 successive parallel lines of water storage tanks, a capillary trench (4) of width (WA) and depth (PMAX - El - HMAX) + HMAX = (PMAX - El) = (E2) is provided.

[0212]

[0207] An impermeable membrane (11) separates the capillary trenches (4) from the form bottom and the water storage tanks. A perforated corrugated pipe is then placed at the bottom of each capillary trench (4). The capillary trenches (4) are then filled with a suitable material.

[0213]

[0208] The thickness clearance layer (El) is then installed above the upper surface of the sub-layer (2) comprising the top of the trenches (4) and the water storage tanks (RS).

[0214]

[0209] The bottom of the capillary trenches (4) is thus at the depth (PMAX - El) + El = PMAX

[0210] These water storage tanks (RS) are filled with water to a height (H) from the bottom of the storage tanks. We have (H) strictly less than (HMAX), which is the height of the storage tanks (RS), so that there remains a layer of air (RSA) above the layer of water (RSW), said layer of air having a strictly positive thickness and equal to HMAX - H.

[0215]

[0211] This air layer constitutes a capillary boundary which prevents the existence of a capillary flow between the water table inside the storage tanks and the clearance layer. This capillary boundary makes it possible to eliminate any influence of the level of the water table in the storage tanks on the capillary forces inside the clearance layer.

[0216]

[0212] It is also noted in Figure 4 that the capillary trenches (4) of width (WA) descend to the depth (PMAX), that is to say deeper than the bottom of the reservoirs placed on the ground in place which descend to the depth El + HMAX, because we have chosen to illustrate in Figure 4 a classic situation where we have PMAX > El + HMAX.

[0217]

[0213] As a result, it is also noted in Figure 4 that the strips (5) inserted between the capillary trenches (4) comprise on the one hand the soil in place in the lower part of the sub-layer (2) located under the play layer (1) and on the other hand the water storage tanks (RS) placed on said soil in place in the upper part of said sub-layer (2).

[0218]

[0214] In the section of figure 4 is also shown in the capillary trenches (4) a water table (3) at the depth (P) from the surface of the ground with P < PMAX.

[0219]

[0215] Figure 4 shows a depth (P) of the water table (3) which is also shown to be greater than the depth of the bottom of the storage tanks (RS). However, this depth being variable can also be less than the depth of the bottom of the storage tanks (RS) at another time.

[0220]

[0216] As in Figure 2, the space between two successive parallel strips of storage tanks (RS) of widths (WB) is filled with draining and capillary material and in direct contact with the clearance layer (1), and which defines a capillary trench (4). This capillary trench (4) is separated horizontally from the bottom and vertically from the strips (5) i.e. from the storage tanks (RS) and from the ground in place above the storage tanks (RS) by a membrane (11) also shown in this Figure 2.

[0221]

[0217] Also shown in Figure 4 is a network of pipes (6) which connect the capillary trenches (4) on the one hand and the water storage tanks (RS) on the other hand, this network of pipes (6) being connected to a control center (9).The particularity of the section in Figure 4 is that the network of pipes (6) is broken down into a sub-network of pipes (6A) which connects the capillary trenches (4) and the control center (9) and another sub-network of pipes (6B) which connects the storage tanks (RS) and said control center (9) to each other, which allows, by appropriate means, such as valves and possibly pumps, to add water or remove water from the storage tanks (RS) or from the capillary trenches (4), to pass water from the storage tanks (RS) to the capillary trenches (4) or in the other direction from the capillary trenches (4) to the storage tanks (RS) or to add water from an external network (7) or to evacuate water to sewers (8).

[0222]

[0218] Preferably, on a practical level, a preferred solution for controlling the level of the water table in the trenches is to have all the pipes (6 A) filled with water and connected to a control member which measures the piezometric level of the water table which, by the principle of communicating vessels, is the same in all the trenches and in a controllable reservoir where the level is measured permanently, water being added or respectively extracted if the level is lower or respectively higher than the set piezometric height assigned to the water table (3).Thus, the water consumed by evapotranspiration, which tends to lower the water table level, will be compensated by a supply of water as a drop in the level is observed during continuous monitoring of the water table level, while conversely, excess water following precipitation will be evacuated as a rise in the level is observed during continuous monitoring of the water table level.

[0223]

[0219] The surplus water in the water table (3) may advantageously be evacuated to the water storage reserves (RS) as long as these have not reached their maximum expected filling level and the water supplies to the water table (3) may advantageously come from the water storage reserves (RS) during periods when network water must be saved.

[0224]

[0220] If there is no more space in the storage tanks when it is desired to lower the level of the water table (3), the excess water can be discharged into the sewers (8) and if it is necessary to add water at a time when water is available and inexpensive and it is not desired to draw on the water storage reserves (RS), it is possible to add water to the water table (3) from the network (7).

[0225]

[0221] Also shown at the bottom of each capillary trench (4) is a perforated corrugated drainage pipe (10) which is connected to the network of pipes (6A) described above, which allows rapid and homogeneous distribution over the entire capillary trench (4) of the water supplied or evacuated passing through the network of pipes (6A).

[0226]

[0222] Thus, the means which preferably make it possible to create a sheet of water (3) in the capillary trenches (4) comprise, on the one hand, a connection between said capillary trenches (4) and a network of pipes (6A) making it possible to introduce or extract water into said capillary trenches (4) and, on the other hand, an impermeable boundary (11), such that the volume of the capillary trenches (4) is thus impermeably isolated from its environment, with the exception, on the one hand, of the connection with the network of pipes (6A) making it possible to introduce or extract water therefrom and with the exception, on the other hand, of the upper surface of said trenches (4) which ensure the continuity of circulation of the gravitational and capillary water between the sheet of water (3) located in said capillary trenches (4) and the clearance layer (1) located above.

[0227]

[0223] The network of pipes (6A) is itself connected to a water level control member (9) of the water table (3) in the capillary trenches (4), which makes it possible to introduce or extract water through said network of pipes (6A) into said water table (3) located in said capillary trenches (4).

[0228]

[0224] In this context, and taking into account the choice according to the invention of a very permeable composition of the substrate of the play layer and of the draining and capillary substrate for filling the capillary trenches under the play layer, it is indeed the level of the water table in the capillary trenches (4) which makes it possible to control by capillary forces both the gravitational drainage of the play layer (1) and the upward capillary flow from the capillary trenches (4) towards the play layer (1). The excess water compared to the characteristic curve of the substrate of water content at capillary equilibrium as a function of the capillary height is evacuated very quickly given the high permeability of the substrate but the water content which is maintained by capillarity in the play layer (1) and cannot therefore be evacuated by gravity given the depth of the water table (3) depends entirely on the level of the table (3).The highly permeable composition allows the excess to be quickly evacuated compared to the quantity retained by capillarity, but this quantity retained by capillarity and which will therefore not be drained by gravity depends exclusively, for a given substrate, on the depth of the water table (3).

[0229]

[0225] The depth Pmax relative to the surface of the ground of the capillary trenches is adjusted to allow the control of the air and water content of the play layer while the height Hmax of the water storage tanks (RS) is calculated according to the volume of water that one wishes to store there and these two depths having no reason to coincide, there is therefore no reason for the bottom of the capillary trenches (4) to correspond to the bottom of the storage tanks (RS).

[0230]

[0226] The depth Pmax relative to the ground surface of the capillary trenches (4) from the ground surface is preferably greater than 25 cm, but it is preferable that it is greater than 35 cm and for an optimal solution will be between 40 and 60 cm.

[0231]

[0227] Depending on this maximum depth Pmax and the capillary characteristics of the substrate of the play layer, it is necessary to adapt the strategy for raising and lowering the water table level, the efficiency of a rise-fall cycle being greater for a large amplitude between the high level and the low level of the water table depth during the cycle and this amplitude being necessarily lower than this maximum depth Pmax which therefore limits said amplitude, which implies for a low maximum depth Pmax to compensate by a greater frequency of the cycles for a suitable effect in terms of oxygenation of the substrate. On the other hand, only a sufficient maximum depth Pmax makes it possible to significantly reduce the water content in winter, so that, for low depths Pmax, only a hybrid terrain will be able to have a suitable mechanical response in winter despite a high water content.

[0232]

[0228] Raising and then lowering the water table level in the capillary trenches has the effect of increasing and then decreasing the water content of the play layer. It is therefore paradoxically advantageous for oxygenating the substrate to start by increasing the water content by raising the water table level very high (or even to the surface) because it is the subsequent reduction by gravity drainage of the water content of the play layer (1) which follows the increase in the water content of said play layer (1) during the lowering of the water table level (3) in the capillary trenches (4) which is accompanied in said play layer (1) by an entry of atmospheric air of a volume equal to the drained water.The water added to the playing layer when the water table (3) rises is then drained when the water table (3) falls and replaced by "new" air coming from the atmosphere above the surface of the ground, this air being loaded with oxygen. These operations of raising and then lowering the water table level are an extremely effective and useful way of bringing the necessary oxygen to the playing layer (1) for the roots and the ecosystem of the lawn (bacteria and fungi in the soil).

[0233]

[0229] The advantage of this structure with capillary trenches according to the invention in general and in particular of this “rake” structure comes from the fact that the water content in the play layer (1) in the presence of a water table located (3) below is not controlled by the quantity of water contained in the whole of the layer located under the play layer but only by the depth of the water table in capillary continuity with the play layer in the “capillary trenches” alone (4).Thus, in this configuration of "capillary trenches" disseminated in the underlying layer and even if the surface of the roof of said capillary trenches represents only a small proportion of the contact surface between the play layer and the underlying layer, this is sufficient to control the water content of the play layer because gravity drainage and capillary irrigation by the trenches can be as effective as if the entire layer located under the play layer provided the function of drainage layer and capillary layer with a water table occupying the entire volume at the same depth. Thus, the drainage and capillary materials to be provided to constitute the sub-layer according to the invention only concern the trenches and the rest of the volume of the underlying layer can be free for another function or even simply be the natural subgrade present on the site.

[0234]

[0230] Thus, the volume of draining and capillary material to be provided to fill the capillary trenches and water to control the system is divided with respect to a continuous capillary draining layer occupying the entire surface of the ground in the proportion of the surface of the capillary trenches relative to the surface of the ground and moreover all the surface not used by the trenches is potentially available for another function, in particular for the installation of water storage tanks.

[0235] Examples of achievements

[0236]

[0231] As seen above, the lower the WA / (WA + WB) ratio, the more efficient means are required to ensure flow in the capillary trenches.

[0237]

[0232] In all cases, the rise of the water table will always ultimately ensure sufficient capillary flow but at the cost of a water content that is all the higher the higher the level of the water table is, while we are seeking not only to obtain irrigation that allows evapotranspiration to be compensated at a level close to potential evapotranspiration (PET) but at the same time to have as low a water content as possible near the surface for a given capillary flow in order to limit the risks of disease.

[0238]

[0233] Now the two ways to reduce the water content near the surface for a given capillary flow are to lower the level of the water table within the limit of the depth of the rake teeth and to increase the performance of the substrate by seeking a substrate that is both draining and capillary.

[0239]

[0234] For this reason, it is necessary for each land to seek a compromise as relevant as possible by simultaneously considering the aspect of performance requirement and the consequences in terms of land creation budget.

[0240]

[0235] The advantage of the invention in terms of cost-effectiveness ratio is to concentrate the essential capillary function on the teeth of the rake alone. The lower the WA / (WA + WB) ratio, the more economical the construction of the land, by reducing the volume of extractions and inputs of materials.

[0241]

[0236] On the other hand, for the rake structure to be effective, and even if the strips of width WA corresponding to the rake teeth represent only a small proportion of the surface area of ​​the ground, the rake teeth must be long enough to be able to lower the water table level sufficiently, in order to allow good drainage in winter in the absence of ETP and capillary flow and a low water content near the surface in summer despite capillary flow necessary to irrigate the lawn.

[0242]

[0237] However, if the rake teeth are insufficiently long and even if the examples given below concern water tables where the water table level is controlled by a free surface at depth H1 with H1 less than or equal to the depth of the bottom of the rake teeth, there still remains the possibility according to the invention of having a virtual depth greater than the depth of the rake teeth, in the more complex version of the invention where the water table height is not controlled by a free surface at depth H1 but is controlled by the air depression above the water in a closed enclosure connected to the capillary trenches.

[0243]

[0238] The function of the capillary trenches is to allow the capillary zero level to be lowered at low cost, i.e. the piezometric level of the water table relative to the bottom of the clearance sub-layer (1).

[0244]

[0239] The examples below illustrate different possibilities for varying the parameters which make it possible to act on both the performance and the installation prices of the land according to the invention.

[0245]

[0240] Preferably, in an economical version, the height (E2) of the capillary trenches (4) is between 7 cm and 15 cm.

[0246]

[0241] Thus, considering for example a playing layer (1) of 15 cm, capillary trenches with a height (E2) of 7 cm, this gives a maximum depth Pmax of the capillary trenches from the surface of the ground of 22 cm and in the case of a low thickness of water table of 1 cm, this gives a depth of water table at 21 cm, which is sufficient to have relatively suitable drainage of the playing area in winter.

[0247]

[0242] However, in a more qualitative preferred version, the height (E2) of the capillary trenches (4) is greater than or equal to 15 cm and the maximum depth Pmax is greater than or equal to 35 cm.

[0248]

[0243] Thus, considering for example a play layer of thickness (E2) equal to 10 cm, with capillary trenches of a height (E2) of 25 cm, this gives a maximum depth Pmax of the capillary trenches from the surface of the ground of 35 cm and still in the case of a low thickness of water table of 1 cm, this gives a depth of water table at 34 cm, which allows to have a very good drainage of the water table in winter, despite a thin play layer and therefore more economical.

[0249]

[0244] From a perspective which aims not only at drainage allowing quality of the lawn and the playing surface to be obtained but also at reducing water consumption, the preferred depths of the bottom of the rake are rather from 60 cm to more than 1 meter, which increases the interest of the rake structure from an economic and ecological point of view.

[0250]

[0245] In another type of configuration with water reserves for watering and taking as an example the case of a 10,000 m2 football pitch, a water storage volume of approximately 4,000 m3 can be constituted by the installation over an area of ​​approximately 9,000 m2 distributed under the pitch of storage elements 50 cm thick with a filling rate of 90%.

[0251]

[0246] Such a storage volume is obviously considerable, thanks to the very large surface area occupied by a large-scale sports field. If, for comparison, one wanted to build under the field or outside the field a storage element of equivalent volume but occupying only 1,000 m2 for example, it would be necessary to excavate under the field or to raise the height by more than 4 m, involving considerable constraints and work costs, whereas the same storage volume on a surface area of ​​only 100 m2 would have to occupy a height of 40 meters. Thus, with only 10% of the surface area, for example capillary trenches with a trench width WA of 10 cm and an equidistance between trenches of 1 meter, corresponding to a width WB of 1 meter, it is possible according to the invention to combine the function of controlling the water content by capillary forces from the capillary trenches and the function of storing a very large quantity of water.

[0252]

[0247] Furthermore, in order for the water content in the playing layer to remain homogeneous on the horizontal plane over the entire terrain, the width WB of the strips of terrain without capillary continuity between two capillary trenches must not be too large and the width WA of the capillary trenches (4) must be sufficient to allow both sufficient capillary drainage flows to counterbalance evapotranspiration in summer and precipitation in winter over the entire surface.

[0253]

[0248] The effective equidistances for drainage trenches are already known from the state of the art and moreover the invention does not imply that the strips without capillary continuity between the playing layer and the layer below are separated by an impermeable boundary, so that the fact of reserving the drainage and capillary trenches to a surface representing a low surface ratio compared to the surface of the ground is not a new or serious problem.

[0254]

[0249] In the case in particular of water storage tanks in which the absence of capillary continuity is obtained by simply maintaining in said tank a layer of air above the water table, the roof of the tanks may be a permeable membrane, so that the gravity drainage of the clearance layer takes place not only in the direction of the capillary trenches but also in the direction of the storage tanks by percolation through the permeable roof of these storage tanks, even if it is the level of the water table in the capillary trenches which determines the capillary pressure and therefore the capillary forces exerted in the clearance layer and therefore, in said clearance layer, the quantity of water retained by capillarity and the quantity of water which flows by gravity.

[0255]

[0250] On the other hand, for the system according to the invention, a new difficulty arises with regard to the irrigation capacities by capillarity across a very restricted surface. Indeed, for a given nature of capillary medium the maximum capillary flow capacity under the effect of an evaporative climatic demand is proportional to the surface area of ​​the capillary trenches alone through which all the flow passes.

[0256]

[0251] However, surprisingly, the tests carried out show that this difficulty can be overcome according to the invention in two complementary ways:

[0257] - on the one hand by multiplying the capillary paths in the trenches, which can be achieved extremely efficiently by increasing the fiber density in a fibered sandy substrate

[0258] - on the other hand by raising the water table level as much as necessary but not permanently but only during periods of high evaporative demand.

[0259]

[0252] Thus, it is possible to have deep capillary trenches (4) to allow the water table (3) to be lowered and to obtain effective drainage of the play layer (1) in winter, but to raise the water table (3) in summer to increase the capillary flow in the capillary trenches (4) and thus compensate for the low WA / (WA + WB) ratio during periods of high evaporative demand.

[0260]

[0253] Thus, in practice, with a Radical type substrate with a high fiber density and with a depth that is varied in summer between 30 cm and at times 15 cm from the surface, the tests have surprisingly shown that a surface ratio R = WA / (WA + WB) of 3% is sufficient to ensure irrigation of the lawn with an ETP of the order of 1 cm per day.

[0261]

[0254] On the other hand, in winter and in the absence of significant ETP, the water table level in the drainage trenches must be lower.

[0262]

[0255] The depth of the water table to obtain by gravity drainage a given low water content in the play layer depends of course on the capillary equilibrium water content curve characteristic of the substrate of said play layer. In practice, however, to obtain in the case of a very permeable substrate as preferably used in the context of the invention, the order of magnitude of the depth necessary to obtain a low water content by gravity drainage is around 40 cm.

[0263]

[0256] Ideally, a satisfactory result can easily be obtained in this perspective with trenches of a depth of approximately 40 cm less the thickness of the play layer, as is the case, for example, with a play layer of 12 cm with trenches of a depth of 28 cm. When the water table has dropped to 40 cm, the water content is low and the air content high in the substrate.

[0264]

[0257] It is however possible according to the invention, not to aim to obtain a permanently low water content but to manage the winter drainage differently if it is accepted that the substrate of the play layer keeps a high water content in winter but with the concern for good oxygenation of the substrate. The principle of the cycles of rises followed by falls of the level of the water table explained above makes it possible to meet this objective.

[0265]

[0258] In this case, in fact, the important thing is not so much to obtain in the substrate of the playing layer the lowest possible water content and the highest possible air content thanks to a significant depth of the water table in the drainage trenches, but rather to obtain a sufficient amplitude between 2 levels of water (or air) content at Tissue drainages obtained at two successive times with 2 different depths of water table in the capillary trenches, so that the difference in water content in the playing layer obtained at Tissue of a rise followed by a fall of the level of the water table in the capillary trenches is compensated by a supply of fresh air loaded with oxygen from the atmosphere at the surface of the turf.

[0266]

[0259] In this perspective, a depth of 25 to 30 cm is sufficient to obtain both oxygenation of the substrate and a substrate that is not too wet

[0260] A preferred embodiment according to the invention concerns terrains characterized by a depth of the bottom of the trenches PMAX > 30 cm.

[0267]

[0261] This can be achieved for trenches 30 cm deep minus the thickness of the clearance layer, for example with a clearance layer (1) 10 cm thick (El) and capillary trenches (4) 20 cm deep inside the sub-layer (2).

[0268]

[0262] If we accept that the substrate remains fairly close to saturation in winter but still requires that it be sufficiently oxygenated for the health of the roots and therefore of the turf, this can be achieved with a 10 cm play layer and drainage trenches with a depth of only 10 cm, but this simply requires sufficiently frequent rises and falls of the water table level between the top and bottom of the trenches. However, it must be taken into account that a play layer always close to saturation is mechanically compatible with play only for hybrid lawns and a PMAX depth < 20 cm is therefore not recommended for a non-hybrid natural lawn.

[0269]

[0263] However, even with trenches 20 cm deep and even for a non-hybrid lawn, it remains possible according to the invention to have a virtual depth greater than 20 cm, for example of the order of 60 cm, if the water table height is controlled by the air depression above the water in a closed enclosure connected to the capillary trenches.

[0270]

[0264] In practice, concerning the specific effect of the rake structure, tests carried out show that a result is obtained which is practically as satisfactory in terms of controlling the water content of the play layer as what would be obtained with a 10 cm play layer on a 30 cm sub-layer and with a water table of 5 cm relative to the bottom of the sub-layer with a play layer 8 to 12 cm thick placed on the natural ground, having made trenches 30 cm deep and with a width WA of 10 cm every meter, i.e. WA = 10 cm and WB = 1 m and with a water table of 5 cm at the bottom of the trenches, i.e. a water table at depth P relative to the surface of 35 cm.

[0271]

[0265] Similarly, for a water table depth of 60 cm, tests carried out show that a result is obtained which is practically as satisfactory in terms of controlling the water content of the play layer as what would be obtained with a play layer of 20 cm on a sub-layer of 45 cm and with a water table of 5 cm in relation to the bottom of the sub-layer with a play layer 20 cm thick placed on the natural ground, having made trenches 45 cm deep and with a width WA of 10 cm every meter, i.e. WA = 10 cm and WB = 1 m and with a water table of 5 cm in the bottom of the trenches, i.e. a water table at the depth P in relation to the surface of 60 cm.

[0272]

[0266] In these cases, even if the drainage and upward capillary flow functions are probably slowed down due to a capillary trench surface representing only about 10% of the total surface, the result in terms of controlling the water content of the play layer is not noticeably affected.

[0273]

[0267] With a result practically as satisfactory as with a water table in a sub-layer whose surface is that of the ground, the advantage is that such a rake construction will be done with only 10% of the supply and transport of the quantity of draining and capillary material which would have been necessary for the creation of a sub-layer of 30 cm or respectively 60 cm thick under the influence of the entire surface of the sports ground in a solution without a rake structure according to the invention.

[0274]

[0268] However, the tests carried out also show that for a temperate climate of the European type, a water table depth of 60 cm seems more suitable in winter than a depth of 30 cm, which makes the rake structure all the more interesting.

[0275]

[0269] The tests carried out under the above conditions of trench surfaces 10 cm or 7 cm wide every 2.50 m with a filling of the play layer and capillary trenches in Radicalé substrate and with water reservoirs 2.50 meters wide and whose upper surface is permeable but without capillary continuity due to the fact that the reservoirs are empty and that there is a layer of air above the body of water, obviously show perfect drainage while the upward capillary flow, although reduced, seems sufficient to ensure suitable capillary irrigation in summer conditions with an ETP of 3 or 4 cm per day, when a geotextile which rises along the vertical walls of the capillary trenches is then extended horizontally under the play layer above the water storage reservoirs between 2 capillary trenches before the installation of the play layer.

[0276]

[0270] Other tests carried out with trenches 20 cm wide every 2 m with a filling of the play layer and capillary trenches in Radical substrate and with water tanks 2 meters wide and whose surface greater than Z cm of the surface is permeable but without capillary continuity due to the maintenance of a layer of air above the mass of water in the storage tanks show perfect drainage while the upward capillary flow from the capillary trenches although disturbed by the walking effect above the storage tanks is sufficient to ensure sufficient and visually homogeneous capillary irrigation in summer situations with high ETP

[0277]

[0271] The addition of a geotextile which rises along the vertical walls of the capillary trenches is then extended horizontally under the play layer above the water storage tanks between 2 capillary trenches before the installation of the play layer is an element promoting the horizontal homogeneity of the ascending capillary flow when the width of the storage elements and therefore the equidistance between capillary trenches is increased.

[0278]

[0272] Preferably, the substrate of the play layer and the porous and draining medium of the capillary trenches will be made with a sandy substrate containing fibers.

[0273] The best results have been found with the substrate marketed under the name Radicalé or with the substrate marketed by the company Natural Grass under the French trademark n°4044209, AirFibr, made up of sand, cork and fibers because this substrate has both characteristics of high permeability and high capillarity and, on the mechanical level, high resistance and high flexibility. This substrate will preferably be chosen for the realization of the present invention.

[0279]

[0274] Preferably, with a view to horizontally homogenizing the capillary flow from the capillary trenches, a geotextile which rises along the vertical walls of said capillary trenches may be extended horizontally under the clearance layer between 2 capillary trenches, which allows, by a privileged capillary path, the water to be conducted horizontally to the interface from where it may continue to rise vertically by capillarity in the substrate.

[0280]

[0275] With under the subsurface (B) strips without capillary control on the playing layer of a width WB and capillary trenches of width (WA), the ratio R of surface occupied by the capillary trenches on the total surface of the ground is approximately equal to R= WA / (WA+WB)

[0281]

[0276] With 10 cm wide drainage trenches every 2.5 meters, this gives an R ratio representing a little less than 4% while with 7 cm wide drainage trenches distributed every 2.5 meters, this gives an R ratio representing a little less than 3%. The result is not as satisfactory as with a higher R ratio but it remains however suitable in the case of a very fibrous substrate in the drainage trenches and the play layer, and by placing a geotextile on the entire contact surface between the play layer and the sub-layer.

[0282]

[0277] With drainage sections 5 cm wide every 2.5 meters, this gives an R ratio representing a little less than 2%. Under these conditions, the system still works but with a very significant loss of performance, both in terms of drainage and irrigation in the phase of significant evapotranspiration, even if it is possible to compensate for this loss of summer efficiency by raising the water table during periods of high summer heat, which allows irrigation but in a less homogeneous way and, as a result, with a profile that is too humid.

[0283]

[0278] Preferably, even if it is possible to lower the ratio even lower, and even if this allows further savings on materials, it does not seem desirable to go below a ratio of 2% or 3% because the resulting savings in relation to the structural cost are marginal while the drop in the quality of the ground is too significant.

[0284]

[0279] It is preferable to choose a ratio greater than 4% for a result which remains convincing with very fibrous substrates in the capillary trenches and the clearance layer.

[0285]

[0280] For satisfactory and easy-to-manage operation, it is preferable to choose an R ratio greater than 4% and a capillary trench depth relative to the ground surface greater than 35 cm.

[0281] Thus, for optimal conditions of use, it is preferable to provide an R ratio > 10%, which is found in the case of 10 cm slots with an equidistance less than 1 meter.

[0286]

[0282] For comfortable conditions of use it is preferable to provide a ratio R > 5%, which is found in the case of 10 cm slots with an equidistance of less than 2 meters.

[0287]

[0283] However, to optimize the manufacturing and transportation cost of water storage tanks, a width of 2.5 meters may be desirable and a solution according to the invention which is suitable because it is economical and still technically acceptable then gives a ratio R of the order of 3% or 4%.

Claims

Claims 1. Sports ground comprising a playing layer (1) laid on a sub-layer (2), with a partition of the surface of said ground into two complementary sub-surfaces (A, B), the respective surface areas of which are both strictly positive, said sports ground being characterized in that: - directly above a first sub-surface (A), the structure of said sports ground is equipped with means for creating a layer of liquid (3), such as for example a layer of water, in the volume of the sub-layer (2) located under the playing layer (1) and directly above the first sub-surface (A), and means for extracting or adding liquid or air into said volume of the sub-layer (2) located under the playing layer (1) and directly above the first sub-surface (A) and for managing its level; - the sub-layer (2) comprises a multitude of capillary trenches (4) located directly above the first sub-surface (A), said capillary trenches being configured to ensure permeability and capillary continuity between the clearance layer (1) and said liquid layer (3).

2. Sports ground according to claim 1, characterized in that the sub-layer (2) is configured such that at the level of the second sub-surface (B) there is no capillary flow between a sheet of liquid, such as for example a sheet of water, located at the level of the second sub-surface (B) and the playing layer (1) located above or there is a capillary flow between the sheet of liquid located at the level of the second sub-surface (B) and the playing layer (1) located above, said capillary flow being less than 1% of a vertical flow between the capillary trenches at the level of the first sub-surface (A) and the playing layer (1).

3. Sports ground according to claim 2, characterized in that the sub-layer (2) is configured such that at the level of the second sub-surface (B) there is a capillary boundary between said sheet of liquid at the level of the second sub-surface (B) and the playing surface (1) located above.

4. Sports ground according to any one of claims 1 to 3, characterized in that the sub-surfaces (A, B) are respectively made up of a multitude of first parallel strips (BA), all of equal width (WA) on the one hand, and of a multitude of second parallel strips (BB), all of equal width (WB) on the other hand, each first strip (BA) interposed exactly between two second strips (BB), the volume of the sub-layer (2) directly above the first strips (BA) of width (WA) defining a multitude of capillary trenches (4), of height (E2) and width (WA).

5. Sports ground according to claim 4, characterized in that: - the sub-layer (2) on which the play layer (1) rests comprises a multitude of rectilinear strips consisting of an alignment of water storage tanks, parallel to each other, of the same width (WB), crossing the ground in the longitudinal or transverse direction, two successive parallel strips of water storage tanks being separated by a space of width (WA) allowing the installation of capillary trenches (4) of said width (WA); - the sub-layer (2) is configured such that at the level of the second sub-surface (B) there is a capillary boundary between said water storage tanks and the play layer (1) located above.

6. Sports ground according to claim 4 or 5, characterized in that the ratio R = WA / (WA+WB) is greater than or equal to 10% when the width (WA) of each capillary trench (4) is substantially equal to 10 cm and the width (WB) of each second straight strip is less than 1 m.

7. Sports ground according to claim 4 or 5, characterized in that the ratio R = WA / (WA+WB) is between 3% and 4% when the width (WA) of each capillary trench (4) is substantially equal to 10 cm and the width (WB) of each second rectilinear strip is substantially equal to 2.5 m, or is substantially equal to 5% when the width (WA) of each capillary trench (4) is substantially equal to 10 cm and the width (WB) of each second rectilinear strip is substantially equal to 2 m.

8. Sports ground according to any one of claims 1 to 7, characterized in that the height (E2) of the capillary trenches (4) is greater than or equal to 15 cm and the maximum depth Pmax of the bottom of said capillary trenches (4) relative to the surface is greater than or equal to 35 cm.

9. Sports ground according to any one of the preceding claims, characterized in that it further comprises a network of pipes (6) and a perforated corrugated drain (10), the network of pipes (6) connecting all of the capillary trenches (4) together and itself being capable of being connected to a water network (7), the perforated ringed drain (10) being connected to the pipe network (6) and being arranged at the bottom of the capillary trenches (4).

10. Sports ground according to any one of claims 1 to 9, characterized in that it comprises a first capillary trench connected to a first layer of liquid and a second capillary trench connected to a second layer of liquid.

11. Sports ground according to any one of claims 1 to 10 characterized in that the structure of the sports ground comprises an independent network of pipes for each capillary trench, each capillary trench then having an independent layer of liquid.

12. Sports ground according to the preceding claim, characterized in that the structure of the ground comprises means for controlling the level of liquid in each independent layer of liquid.

13. Sports ground according to any one of the preceding claims, characterized in that it further comprises an impermeable membrane (11) arranged at the bottom of the capillary trenches (4) and / or on vertical edges of said capillary trenches (4).

14. Sports ground according to any one of the preceding claims, characterized in that the structure of the sports ground comprises a closed enclosure connected to at least one capillary trench, the structure of the sports ground further comprising means for controlling the air pressure in the closed enclosure, said air pressure in the closed enclosure being linked to the height of the liquid layer in said at least one capillary trench.

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