Sports field with water content of the playing surface controlled by liquid water table depth in a rake-like structure

Abstract

The invention relates to a sports field comprising a playing surface (1) laid on a sub-surface (2), with the surface of said field divided into two complementary sub-surfaces, each with a strictly positive area, wherein: directly above a first sub-surface, the structure of said sports field is equipped with means for creating a layer of liquid (3), such as, for example, a water table, within the volume of the sub-surface (2) located beneath the playing surface (1) and directly above the first sub-surface, and for managing its level; the sub-surface (2) comprises a multitude of capillary trenches (4) located directly above the first sub-surface, said capillary trenches being configured to ensure permeability and capillary continuity between the playing surface (1) and said layer of liquid (3). Figure 2

Description

Title of the invention: Sports field with water content of the playing layer controlled by liquid sheet depth in a rake-like structure

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

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

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

[0004] However, even though the following description is made in the context of a sports field where natural grass is cultivated, the playing layer being the substrate layer in which the grass roots grow, the present invention also applies to the case of synthetic fields where the playing layer is simply the top layer, where a satisfactory humidity level is to be maintained in order to control the temperature, slipperiness and mechanical characteristics by controlling the level of a water table in capillary trenches arranged in the sub-layer on which said playing layer rests. technical field

[0005] The present invention relates in particular to a sports field comprising a water table level control system enabling the control of gravity drainage of the playing surface of this sports field as well as its capillary water supply 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 its level, permeability and capillary continuity being ensured between the playing layer and the water table located in the capillary trenches. Previous Art

[0006] In the prior art, the explicit use of capillary forces in a sports field most often concerns capillary irrigation systems from a water table installed in the sub-layer on which the playing layer rests and occupying up to the level of the water table the entire volume of the porosity of this sub-layer, the volume occupied by the water table therefore having as its base, that is to say as its projected surface on the horizontal plane, the whole field.

[0007] However, although implicitly and sometimes even unrecognized, including in the case of fields without a water table but irrigated by sprinkler and laid on a drainage layer, it is in fact capillary forces which actually play an essential role in limiting the amount of water that can be evacuated from the playing surface by gravity drainage, provided that the substrates concerned are very permeable, which concerns most of the fields with elaborate substrates used for sports fields for more than 10 years.This role of capillary forces, often ignored or misunderstood, is therefore crucial to the functioning of gravity drainage and the impact of capillary forces is therefore in fact major on the cost of constructing sports fields 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 insufficient thickness of the substrate layer above the drainage layer.Therefore, based on this observation, and even when a playing surface thickness of around ten centimeters would be sufficient for satisfactory root development and for the mechanical response of a sports field, it is generally accepted that playing surfaces above a drainage layer should have a thickness of at least 20 cm and preferably 40 cm, to prevent the water content of the playing surface from being too high in winter, even if the playing surface is made of an extremely permeable material.

[0008] Apart from the case of conventional pitches on a drainage layer, which still represent almost all pitches constructed today, the principle of controlling the water and air content of the playing surface of a sports pitch by capillary forces controlled by the controlled and variable level of a water table located in a sub-layer located under said playing layer is already known and has recently been described in document FR-3112152-A.

[0009] However, for these pitches with a water table within the structure, and just as for pitches on a drainage layer, the need for a relatively deep water table within the structure, for example at a depth of 30 cm or 50 cm, ultimately represents the same major constraint. This constraint implies the same type of construction cost problems for pitches with a water table within the structure as for a conventional pitch laid on a drainage layer. While the ability to vary the water table level allows for a reduction in the thickness of the structure, at the cost of a strategy of raising and lowering this level, which provides turf oxygenation that conventional pitches do not allow, the minimum water content remains unchanged. Consequently, only hybrid pitches have adequate mechanical quality in winter due to an excessively high water content for a pitch structure that is too weak.Therefore, during the construction of the field, this poses an ecological problem related to the preservation of aggregate resources and the impact of transporting materials, and it also poses an economic problem regarding the cost of constructing the fields.

[0010] The present invention provides a solution which, by reducing the quantity of materials needed for the construction of the land, addresses this problem both ecologically and economically.

[0011] On the other hand, for fields with a water table in the structure, and in another version aimed at an additional functionality, it is also known in the prior art (cf. document FR-3112152-A) that it is useful to install under the playing surface water storage tanks to retain rainwater which falls during the rainy season, so that this water can be available during periods of drought for the subsequent capillary irrigation of the turf.However, in these water storage tanks, and in the most common scenario where the available water storage volume is fixed over time, the water table level in the tanks at any given moment depends directly on the amount of water stored at that time. Conversely, managing the water content of the playing surface requires a water table depth that is completely independent of the amount of water stored in the tanks. While it is known that movable-bottom tanks exist to regulate the water level independently of the stored water volume (see, in particular, document FR-3112152-A), this high-quality solution represents an additional cost that is primarily justified in configurations with high storage requirements.The possibility of a sub-layer connected by a pump to the reservoirs is also known. However, since this sub-layer is located above the reservoirs, all known solutions, while very effective during operation, consequently involve additional construction costs because the water level in storage reservoirs with fixed bottoms is completely unsuitable for controlling the water content of the playing surface through capillary action. Apart from the solution of reservoirs with movable bottoms, known solutions also present a problem regarding the quantity of material to be added to the sub-layer, a problem to which the present invention provides a solution. Description of the invention

[0012] The present invention aims to contribute to the control of the water and air content of the playing layer of a sports field by capillary forces controlled by the level of a water table located in the structure of the field, whether or not it is a field including water storage tanks, but with the additional objective of overcoming the disadvantages of the current state of the art and in particular the ecological and economic objective of minimizing the consumption and transport of materials necessary for the construction of the fields.

[0013] In this context and according to these objectives, the present invention relates both, on the one hand, to land having water storage tanks allowing the rainwater that falls during the rainy season to be stored so as to have this water available during periods of drought for the irrigation of the lawn and, on the other hand, to land not having such water storage tanks.

[0014] The present invention therefore relates to new sports fields 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 perfectly be applied also to the low-cost renovation of an existing field to make it evolve from a classic field to a field according to the invention.

[0015] The advantage of this solution regarding the quantity of drainage and capillary materials needed to obtain a sufficient water table depth is that these materials only concern capillary trenches whose base, i.e. the surface projected onto the horizontal plane, can be a very small proportion of the ground surface, implying a reduced volume of material in the same proportion but allowing a comparable effect to be obtained.

[0016] The additional advantage in the operating phase of a field 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 whole surface of the field 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 area which may represent only a very small portion of the surface of the field.

[0017] 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 infrastructure and lower peak energy needs and requiring a smaller quantity of immediately available water as well.

[0018] Furthermore, these trenches in the sub-layer, located beneath the playing surface, can be created during the renovation of an existing field without having to remove the existing playing surface. The trenches are separated from the rest of the sub-layer by the installation of a membrane, which is held in place by the drainage and capillary material inside the capillary trenches. This material can even be the same as that of the playing surface. It is simply necessary to install perforated corrugated pipes at the bottom of the trenches to drain or supply water for monitoring the water table level. These pipes are themselves connected to collectors installed in a large trench outside or at the edge of the field.

[0019] In view of this essential advantage, the invention is thus applicable both in the case of a site with water storage reserves and in the case of a site without such reserves.

[0020] The first scenario addressed by the invention is that of a sports field where water storage tanks are located beneath the playing surface to collect rainwater, particularly during the rainy season, so that this water is available for irrigating the turf during dry periods. However, in these water storage tanks, and in the most typical case where the available water storage volume is fixed over time, the water level at any given moment depends directly on the amount of water stored in the tanks at that time. In contrast, managing the water content of the playing surface requires a water table depth that is completely independent of the amount of water stored in the tanks. Therefore, this water level in the storage tanks is entirely unsuitable for controlling the water content of the playing surface using capillary action.

[0021] However, in this scenario, the problem is solved according to the invention by installing the water storage tanks under the playing surface and arranging them in parallel lines, while leaving a space between two successive lines of water storage tanks and filling said space with a capillary drainage 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 in the well-leveled existing ground to the difference in depth, at the level of said trenches. These capillary trenches, which alternate with the lines of storage tanks, are equipped according to the invention with means for installing a water table and for managing its level. This alternation The system of tank lines and capillary trenches allows for independent management of the depth of storage tanks according to water storage requirements and the depth of capillary trenches according to the objectives of capillary forces to be applied at a given time for a given substrate as part of managing the water content of the playing layer.

[0022] Thus, according to the invention, a rake-like structure is obtained, with permeability and capillary continuity between the playing layer and the water table located in the capillary trenches arranged between the lines of water storage tanks.

[0023] However, in order for the water table level inside the reservoirs not to influence the capillary forces within the playing surface, it is necessary, according to the invention, that there be no capillary continuity between the water table inside the reservoirs and the playing surface located above the reservoirs. However, even if, according to the invention, there is capillary discontinuity between the playing surface and the water storage reservoirs, the interface between these reservoirs and the playing surface is not necessarily impermeable and may allow gravity drainage to occur directly from the playing surface to the storage reservoirs. The important point is that the water level in the trenches is the only factor controlling, through capillary forces, the amount of water that the playing surface retains by capillary action or allows to drain by gravity.By carefully selecting water storage tanks that do not exhibit capillary continuity between said storage tanks and the playing surface above, the water level in the water storage tanks then has no influence on the water content in the playing surface.

[0024] 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 strength of said tanks, with a permeable surface in the upper part serving as an interface with the play layer, the capillary discontinuity being obtained and maintained as long as the tank is not completely full and an air layer between the water and the upper permeable membrane ensures the capillary discontinuity.

[0025] In this scenario, in the absence of a capillary effect of the water level in the reservoirs, the only tool for controlling the water content of the playing surface by capillary forces is the level of the water table inside the capillary trenches which are provided between the water storage tanks, said capillary trenches being themselves supplied by the means provided according to the invention with water which can come, as required, either from the water stored in the storage tanks, or possibly from another network, while, as required and as required, excess rainwater flowing by gravity drainage is used to supply the water storage tanks or is discharged into the sewers.

[0026] The advantage of the invention in this first case is to allow control of the playing surface without movable-bottom reservoirs and without sub-layer between the playing surface and the reservoirs but with a very small volume of drainage and capillary material in the trenches made according to the invention between the reservoir lines and a very small volume of water inside said trenches.

[0027] The second application relates to a sports field without an underground water storage reservoir. With the aim of minimizing material transport, this field is constructed according to the invention with a playing surface laid on an existing sub-layer of ground in which capillary layers filled with drainage and capillary material are installed in capillary continuity with the playing surface laid on said sub-layer.

[0028] In this scenario, only the volume of the drainage and capillary trenches needs to be filled with a high-performance material (drainage and capillary) to optimize the ecological and economic impact of the field's construction by saving on aggregate resources and their transport to the construction site. Once the field is operational, it will be irrigated by capillary action and drained by gravity, with upward capillary and downward gravity flows controlled by the water table level in the trenches filled with drainage and capillary material. This ensures ecological and high-quality field operation by minimizing water requirements in summer and promoting aeration and, above all, oxygenation of the field in winter.

[0029] In order that, according to the invention, the means of supplying or draining water into said trenches to create a water table 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.

[0030] However, it is not always necessary to install such a vertical impermeable membrane at the edge of a capillary trench. For example, when the trenches are simply spaces between rows of storage tanks whose vertical walls are already impermeable, it is not necessary to add an impermeable membrane at the trench edge. Similarly, it is also not necessary to install a horizontal impermeable membrane at the bottom of the trench if the base on which the entire sub-layer rests is already impermeable or waterproofed, for example, a sub-layer that includes an impermeable membrane underneath it.

[0031] In any event, having the volume of the trenches separated at the bottom and on the sides from their environment in a sufficiently impermeable way is one of the means of installing a water table and managing its level.

[0032] These goals and advantages, as well as others that will appear subsequently, are achieved by a sports field comprising a playing surface laid on a sub-surface, with a partition of the surface of said field into two complementary sub-surfaces, the respective areas of which are both strictly positive, in which:

[0033] - directly above a first sub-surface, the structure of said sports field is equipped with means to create a layer of liquid, such as for example a water table, in the volume of the sub-layer located below the playing layer and directly above the first sub-surface, and to manage its level;

[0034] - the sub-layer comprises a multitude of capillary trenches located vertically of the first subsurface, said capillary trenches being configured to ensure permeability and capillary continuity between the playing layer and said liquid layer.

[0035] Preferably, the sub-layer is configured so that, directly above the second sub-surface, there is no capillary flow between a liquid layer, such as, for example, a water sheet, located directly above the second sub-surface and the playing layer located above.

[0036] According to a particular technical feature of the invention, the sub-layer is configured such that, directly above the second sub-surface, there is a capillary boundary between said liquid layer directly above the second sub-surface and the playing surface located above.

[0037] Preferably, the subsurfaces are respectively made up of a multitude of first parallel bands, all of equal width on the one hand, and a multitude of second parallel bands, all of equal width on the other hand, each first band being inserted exactly between two second bands, the volume of the sublayer in front of the first bands defining a multitude of capillary trenches, of height E2 and width WA.

[0038] Advantageously:

[0039] the sub-layer on which the playing layer rests comprises a multitude of straight strips made up 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 the installation of capillary trenches of said width WA;

[0040] the sub-layer is configured such that, directly above the second sub-surface, there is a capillary boundary between said water storage tanks and the playing layer located above.

[0041] 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 straight strip is less than 1 m.

[0042] 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 approximately equal to 10 cm and the width WB of each second straight strip is approximately equal to 2.5 m, or is approximately equal to 5% when the width WA of each capillary trench is approximately equal to 10 cm and the width WB of each second straight strip is approximately equal to 2 m.

[0043] 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.

[0044] Advantageously, the sports field further comprises a network of pipes and a perforated corrugated drain, the network of pipes connecting all the capillary trenches together and being itself suitable for connection to a water network, the perforated corrugated drain being connected to the network of pipes and being arranged at the bottom of the capillary trenches.

[0045] Advantageously, the sports field further comprises a waterproof membrane disposed at the bottom of the capillary trenches and / or on vertical edges of said capillary trenches. Figures

[0046] [Fig. 1] is a top view of a sports field according to the present invention.

[0047] [Fig.2] is a vertical cross-sectional view of this land along line II-II of [Fig.1].

[0048] [Fig.3] is a schematic view of [Fig.2] showing a rake-like structure.

[0049] [Fig.4] is a vertical cross-sectional view of a plot of land according to the present invention including a water storage tank. Detailed description of the invention

[0050] Although the present description and figures primarily concern land with a partition of the land surface 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 below the strips (BA) because this type of geometry seems the simplest and most logical to implement, it is nevertheless important to specify that this geometric aspect of a partition of the land surface into straight, parallel strips of the same width is not an essential point of the invention.

[0051] Similarly, if the liquid used in the trenches and playing surface in the following description is water, this is not an essential aspect of the invention, which is therefore not limited to this liquid alone. Those skilled in the art can apply the concept with any type of liquid suitable for a playing surface, particularly from a fertigation perspective.

[0052] In general, the invention relates to any sports field comprising a playing layer (1) of thickness (El) placed on a sub-layer (2) of thickness (El), with a partition of the surface of the field into two complementary sub-surfaces (A) and (B), whose respective areas SA and SB are both strictly positive, the field being equipped with means for creating a water table (3) in the volume of the sub-layer (2) located under the playing layer (1) and above the sub-surface (A) and for managing the water level and with capillary continuity and permeability between the playing layer (1) and said volume of the sub-layer located under the playing layer (1) and above the sub-surface (A).It is this water level in the capillary trenches above the subsurface A which, thanks to the permeability and capillary continuity between the playing layer (1) and said water table (3) above the subsurface (A), allows the humidity level of the playing layer to be controlled, by the effect of capillary forces which depend on said water table level, said capillary forces in turn controlling the gravity drainage of said playing layer on the one hand and the capillary flows supplying said playing layer from said water table on the other hand.

[0053] Also, in the general case, a field according to the invention is a sports field comprising a playing layer (1) of thickness (E1) laid 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), whose respective areas SA and SB are both strictly positive, in which:

[0054] - directly above the subsurface (A), the structure of said sports field is equipped with means to create a liquid layer 3, such as for example a water table, in the volume of the sub-layer (2) located below the playing layer (1) and directly above the sub-surface (A), and to manage its level;

[0055] - the sublayer (2) comprises a multitude of capillary trenches (4) located at the vertical alignment of the subsurface (A), said capillary trenches (4) being configured to ensure permeability and capillary continuity between the playing layer (1) and said liquid layer (3).

[0056] It should be clarified that ensuring permeability between the playing surface (1) and said capillary trenches (4) simply means that any filling elements of the capillary trenches (4) and the contact surface (BA) between the playing surface and said capillary trenches (4) do not impede the establishment of a spontaneous downward gravitational flow under the effect of gravitational forces at through the playing surface (1) and down to the water table (3), provided that the water content in the playing surface exceeds the water content corresponding to capillary equilibrium, that is, provided that the downward gravitational forces pulling the water outward outweigh the upward capillary forces, taking into account the depth of the water table and the capillary characteristics of the playing surface substrate. However, while 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 within a sufficiently short period of time to be truly satisfactory.

[0057] It is known that this permeability condition, in the absence of an obstacle specially installed to waterproof the column, is met in any vertical column filled with any granular medium.

[0058] Thus, ensuring permeability between the playing layer (1) and said capillary trenches (4) does not imply additional means other than the absence of an impermeable barrier preventing the gravitational flow from flowing to the water table, knowing that the gravitational flow for a given surplus of water is all the faster as the permeability is greater and that the assessment of satisfactory permeability is a subject already well known in the state of the art.

[0059] Similarly, it should be specified that ensuring capillary continuity at the level of the subsurface (A) between the playing layer (1) and said water table (3) in the volume of the sublayer (2) located under the playing layer (1), simply means that at the level of the subsurface (A) the structure of the ground allows water to rise from the water table (3) to the playing layer (1) by the effect of capillary forces when the water content of the playing layer (1) is less than the water content at capillary equilibrium.

[0060] Therefore, for capillary action to spontaneously begin supplying the upper part, no additional means are needed because the force that causes the water to rise is found in the surface tension at the air-water interface in the playing surface. This force causes the water to rise from the water table as long as there is a continuous column of water between the water table and the playing surface, and as long as the gravitational force of the weight of this water column is less than the surface tension pulling on said column. The only means necessary to ensure capillary continuity is therefore simply to have a structure that does not create a discontinuity in the water column between the water table and the playing surface.

[0061] It is known in particular that in any granular medium and in the presence of a water table and evaporative demand, an upward vertical capillary flow spontaneously begins to supply the upper part of said granular medium from said water table, said spontaneous capillary flow having the effect of partially compensating and more or less effectively the deficit in water content compared to the capillary equilibrium created by said evaporative demand, which therefore allows the water content of the environment to be brought closer to its water content at capillary equilibrium.

[0062] The effectiveness of the capillary continuity considered here is defined by the fact that capillary continuity is considered all the more effective the more the capillary flow generated to partially compensate for the water content deficit relative to said capillary equilibrium created by evaporative demand has the effect of bringing the water content in the playing layer (1) closer to the water content at capillary equilibrium. In other words, during periods of intense evapotranspiration, the more effective the capillary continuity and the smaller the difference between the water content of the playing layer and the water content at capillary equilibrium.

[0063] In this case, it is known that in a granular medium of the sandy type and even for a very high Potential Evapotranspiration (PET) of up to 1 cm per day, the upward capillary flow which spontaneously comes into action is able to support the climatic evaporative demand, that is to say that the upward capillary flow is able to equal on average daily the value of the PET, provided that the water table has its piezometric level at less than 50 cm depth.

[0064] On the other hand, and contrary to what is often assumed, fine granular media such as silt or a fortiori clay do ensure capillary continuity but with very low efficiency in terms of flux; therefore, contrary to generally accepted ideas, this type of fine granular medium, which is also not very efficient in terms of permeability, is not recommended to ensure effective capillary continuity.

[0065] Surprisingly, however, tests carried out with gravel revealed that 2-6 or even 3-8 mm gravel (especially unrolled and unwashed) also provides relatively satisfactory capillary continuity.

[0066] Coarse gravels can also ensure some capillary continuity provided there is a film of water on the surface of the aggregates but here again, the efficiency in terms of flux decreases with the specific surface area of ​​the aggregate, it is not desirable in terms of capillary flux efficiency to choose a gravel coarser than 2-6 gravel.

[0067] Moreover, regardless of the environment, the presence of fibers (including possibly roots) is a factor in strongly improving the efficiency of capillary continuity.

[0068] Finally, the capillary trenches according to the invention are not necessarily filled with a single granular material and can comprise according to the invention a set of elements each having its own function, the important thing being to ensure capillary continuity between the capillary trenches and the playing layer above.

[0069] The important thing in the context of the invention is that, directly above the surface (A), a water content lower than the water content at capillary equilibrium in the playing layer (1) generates from the layer (3) located in the sub-layer (2) directly above said surface (A) an upward capillary flow supplying water to said playing layer (1), contrary to the situation directly above the sub-surface (B) where there is no capillary flow between a water layer located directly above the sub-surface (B) and the playing layer (1) located above, for example because there is then a capillary boundary between this water layer directly above surface B and the playing surface (1) located above, that is to say an impossibility of capillary flow from this water layer to the playing layer (1) located above.

[0070] This condition of capillary continuity directly above the subsurface (A) and only of the subsurface (A) between the water table (3) located in the capillary trenches (4) and the playing layer (1) is an essential condition of the invention.

[0071] Naturally, for each field according to the invention, this necessary condition is not necessarily sufficient and it is also necessary to ensure a relevant choice concerning the filling elements of the capillary trenches, the width of said capillary trenches (4), the surface area ratio SA to SB, the geography of the implantation of the surface (A), so that the upward capillary flow is sufficient to ensure the irrigation of the turf, taking into account the local climate of the field in question and the irrigation objectives chosen for the field in question.

[0072] Indeed, evapotranspiration is proportional to the total surface area of ​​the turf SA + SB while the capillary flow enabling the irrigation of the turf is proportional to the surface SA alone through which said capillary flow passes.

[0073] Therefore, the lower the ratio R = SA / (SA + SB), the more efficient the means required to compensate for the low R ratio in order to ensure sufficient flow. Indeed, for perfect irrigation, the flow between the water table (3) and the playing surface (1), which only passes through the surface SA, must compensate for the evapotranspiration that occurs over the entire surface (SA + SB).

[0074] As seen above, these means for obtaining a higher flux for a given surface are, on the one hand, a material comprising many fibers for better capillary efficiency and, on the other hand, the rise of the water table level in the event of high evaporative demand.

[0075] Similarly, 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 intercalated 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 ) is, the more efficient means are needed to ensure a flow in the capillary trenches.

[0076] Furthermore, in order for it to be the level of the water table directly above the subsurface (A) which determines the capillary pressure in the playing layer (1), it is also necessary to verify that the volume (5) of the sublayer located below the playing layer (1) and directly above the subsurface (B) does not contain any water table in capillary continuity with the playing layer.

[0077] This is the case for the land according to the invention in which there is no water table in the sub-layer (2) directly below the sub-surface (B).

[0078] In other embodiments, a field according to the invention may optionally be equipped 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 playing layer (l) and the volume of water possibly present in the sub-layer (2) directly below the sub-surface (B).

[0079] In the particular case of storage tanks (RS) with an air layer (RSA) above the water layer (RSW) inside said storage tanks (RS) or in the case of tanks (RS) with a sealed roof, there is indeed in this case a water layer in the storage tanks and possibly the possibility of controlling its level by a network of pipes (6B) connected to a water level control device; but there is no capillary continuity between this water layer (RSW) inside said storage tanks (RS) and the play layer (1) above.Thus, in this scenario according to the invention, even if there are means in the structure of the ground to create a water table in the volume located below the playing surface 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 playing surface located above because there is no capillary continuity between the playing surface (1) and said volume (5) located below the playing surface (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 playing surface.

[0080] In practical terms, the following description relates to a "rake-like" ground structure, the principle of which is a partitioning of the ground surface into parallel straight strips crossing the ground with alternating strips belonging to the subsurface (A) and strips belonging to the complementary subsurface (B), the strips directly above said subsurface (A) and located in the sublayer (2) corresponding to the straight capillary trenches (4) of width (WA) and the strips of the complementary subsurface (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 subsurface (B) and located in the sublayer (2) corresponding to the strips (5) interspersed between the capillary trenches (4). These strips are preferably oriented to cross the ground in the longitudinal or transverse direction.

[0081] Thus, considering in cross-section the playing layer (1) and the plurality of vertical capillary trenches (4) located below, the structure appears as a rake, the playing layer (1) playing the role of the horizontal cross member and the vertical capillary trenches (4) located in the lower sub-layer (2) playing that of the teeth of the rake, as represented in [Fig.3].

[0082] Preferably, the invention relates to a sports field with such a rake-like structure, that is to say, in more detail, a field comprising a playing layer (1) placed on a sub-layer (2), and with a partition of the latter into two complementary sub-surfaces (A) and (B) which respectively take 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 or 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) separated from each other by the width (WA) of the strips (BA).In this preferred solution context, the volume of the sublayer (2) directly below 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 sublayer (2) directly below each of the strips (BA).

[0083] 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 playing layer (1) and means for regulating the level of this water table (3). Thus, by adjusting 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 playing layer (1) through capillary forces that depend on said water table level and that in turn control the gravity drainage of said playing layer (1) and the capillary flows supplying said playing layer (1) from said water table located in the capillary trenches (4).

[0084] According to the invention, the capillary trenches (4) are filled with a set of elements to ensure permeability and capillary continuity between the playing layer and said capillary trenches (4).

[0085] 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," unwashed, and unwashed sand may be suitable in certain cases, but the lower the ratio of the surface area of ​​the capillary trenches to the total ground area WA / (WA + WB), the more important it is to have a truly capillary material.

[0086] A really satisfactory preferred solution is filling with a fiber sand, which can also preferably be the material used for the playing layer (1).

[0087] Furthermore, since permeability between the playing surface and the water table (3) in the capillary trenches (4) is a required condition according to the invention, it is also necessary to ensure that the downward gravity flow will be sufficient so that drainage does not take too long.

[0088] However, this is not a particularly difficult requirement to meet, since the drainage time is not really an essential element, provided that it is not excessive in relation to the drainage objectives chosen, knowing, on the one hand, that the conditions for gravity drainage through seepage slots are already well known from the state of the art and that, on the other hand, and unlike the upward capillary flow from the water table which takes place only in the capillary trenches (4), gravity drainage does not necessarily pass through only the capillary trenches (4) but, in many cases according to the invention, can also pass through the volume (5) of the sub-layer directly above the strips (BB).

[0089] In practice, however, it is preferable to choose for drainage trenches an overall permeability equivalent to or greater than that of the playing surface.

[0090] Furthermore, although 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 throughout said sub-layer in that, in the case of the invention, the capillary trenches (4) are distinct and separate from the volumes (5) located in the sub-layer (2) situated below the playing surface (1) and directly above the boards (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 allow for the creation of a water table and the management of its level in said volumes (5) directly above the boards (BB). In this context, having a sufficiently impermeable separation at the bottom and on the sides between the capillary trenches (4) and their surroundings is one of the means for installing a water table (3) and for managing its level.

[0091] A pipe network (6) is also shown in Figures 2 and 4. This pipe network (6) connects the drainage trenches (4) to each other and to a control center (9) equipped with the necessary means to add water from a network (7) or to discharge water into sewers (8).

[0092] We find in [Fig.2] the bands (BB), of width (WB) alternating with the capillary trenches (4) of width (WA) but also appear on the section the depths (El) and (E2) corresponding respectively to the playing layer (1) and the sub-layer (2).

[0093] The cross-section in [Fig. 2] illustrates 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. The bottom of the trenches is at depth (PMAX).

[0094] The water table (3) located between the bottom of the capillary trenches and the piezometric level of said water table has a thickness of: PMAX - P. Therefore, P < PMAX

[0095] The pipe network (6) connects the drainage trenches (4) to each other and to the control center (9) equipped with means to add water from the network (7) or to discharge water into the sewers (8).

[0096] A perforated ring drain (10) arranged at the bottom of the capillary trenches (4) is also shown; it is connected to the pipe network (6) and allows distribution throughout the capillary trench of the water supplied or, on the contrary, extracted by the pipe network (6).

[0097] An impermeable boundary (11) separates the capillary trenches (4) from their environment and provides in particular 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 playing layer (1).

[0098] Fig. 3 is a simple extract of Fig. 2 which simply shows the rake shape of the structure seen in section with layer (1) playing the role of the horizontal cross member and the vertical capillary trenches (4) that of the teeth of the rake, separated from each other by the volume (5) of each band (BB).

[0099] Fig. 4 is a cross-sectional view of a rake field according to the invention in a particular preferred embodiment where the structure comprises water storage tanks (RS) arranged in non-contiguous parallel lines that form strips of width WB with a space of width WA between the tank lines.

[0100] Preferably, from a practical point of view, in this case where the structure includes 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 is to start by digging in the well-leveled in-situ ground parallel trenches of width (WA) and depth (E2 - HMAX), with (E2) = (PMAX - El), said parallel trenches being separated from each other by a distance WB corresponding to the width of the water tanks.

[0101] Water storage tanks of width (WB) and height (HMAX) are then installed on the ground in place, between the trenches of width (WA) and depth (E2 - HMAX) previously dug in the ground in place.

[0102] Thus, between the top of the water storage tanks and the bottom of the trenches between 2 successive parallel lines of water storage tanks, there is a capillary trench (4) of width (WA) and depth (PMAX - El - HMAX) + HMAX = (PMAX - El) = (E2)

[0103] A waterproof membrane (11) separating the capillary trenches (4) from the subgrade and 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.

[0104] The thickness play layer (El) is then installed above the upper surface of the layer (2) comprising the top of the trenches (4) and the water storage tanks (RS).

[0105] The bottom of the capillary trenches (4) is thus located at the depth (PMAX - El) + El = PMAX

[0106] 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 equal to HMAX - H.

[0107] This air layer constitutes a capillary boundary that prevents capillary flow between the water table inside the storage tanks and the playing surface. This capillary boundary eliminates any influence of the water table level in the storage tanks on the capillary forces within the playing surface.

[0108] It is also noted on [Fig.4] that the capillary trenches (4) of width (WA) descend to the depth (PMAX), that is to say deeper than the bottom of the tanks placed on the ground in place which descend to the depth El + HMAX, because we have chosen to illustrate in [Fig.4] a classic situation where we have PMAX > El + HMAX.

[0109] Consequently, it is also noted on [Fig.4] that the strips (5) intercalated 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 playing 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).

[0110] On the cross-section of [Fig.4] is also shown in the capillary trenches (4) a water table (3) at the depth (P) from the ground surface with P < PMAX.

[0111] We observe in [Fig.4] 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, it may also be less than the depth of the bottom of the storage tanks (RS) at another time.

[0112] As in [Fig.2], the space between two successive parallel strips of storage tanks (RS) of width (WB) is filled with draining and capillary material and is in direct contact with the playing 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. the storage tanks (RS) and the soil in place above the storage tanks (RS), by a membrane (11) also shown in this [Fig.2].

[0113] Also shown in [Fig.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, this network of pipes (6) being connected to a control center (9). The particularity of the cross-section in [Fig.4] is that the pipe network (6) is divided into a sub-pipe network (6A) which connects the capillary trenches (4) and the control center (9) and another sub-pipe network (6B) which connects the storage tanks (RS) and said control center (9), which allows, by appropriate means such as valves and possibly pumps, the addition of water or the removal of water from the storage tanks (RS) or from the capillary trenches (4), the transfer of 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), the addition of water from an external network (7), or the discharge of water into sewers (8).

[0114] Preferably, from a practical point of view, a preferred solution for enabling control of the groundwater level in the trenches is to have all the pipes (6A) filled with water and connected to a control device which measures the piezometric level of the groundwater which, by the principle of communicating vessels, is the same in all the trenches and in a controllable reservoir where the level is constantly measured, water being added or respectively extracted if the level is lower or respectively higher than the piezometric setpoint height assigned to the groundwater (3).Thus, the water consumed by evapotranspiration, which tends to lower the water table level, will be compensated by water input as a drop in the level is observed during continuous monitoring of the water table level, while conversely, excess water following precipitation will be removed as a rise in the level is observed during continuous monitoring of the water table level.

[0115] Surplus water in the water table (3) may advantageously be discharged to the water storage reserves (RS) as long as these have not reached their maximum planned filling level and water inputs to the water table (3) may advantageously come from the water storage reserves (RS) during periods when network water must be saved.

[0116] 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 cheap and it is not desired to draw from the water storage reserves (RS), it is possible to add water to the water table (3) from the network (7).

[0117] Also shown at the bottom of each capillary trench (4) is a perforated corrugated drainage pipe (10) which is connected to the pipe network (6A) described above, which allows a rapid and homogeneous distribution over the entire capillary trench (4) of the water brought in or evacuated passing through the pipe network (6A).

[0118] Thus, the means which preferably allow the creation of a water table (3) in the capillary trenches (4) comprise, on the one hand, a connection between said capillary trenches (4) and a network of pipes (6A) allowing water to be introduced or extracted 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) allowing water to be introduced or extracted from it and with the exception, on the other hand, of the upper surface of said trenches (4) which ensures the continuity of circulation of gravity and capillary water between the water table (3) located in said capillary trenches (4) and the playing layer (1) located above.

[0119] The pipe network (6A) is itself connected to a water level control device (9) of the water table (3) in the capillary trenches (4), which allows water to be introduced or extracted by said pipe network (6A) into said water table (3) located in said capillary trenches (4).

[0120] In this context, and considering the choice according to the invention of a highly permeable composition for the playing surface substrate and the draining and capillary filling substrate for the capillary trenches beneath the playing surface, it is indeed the water table level in the capillary trenches (4) that allows control, by capillary forces, of both the gravity drainage of the playing surface (1) and the upward capillary flow from the capillary trenches (4) to the playing surface (1). Excess water relative to the characteristic curve of the substrate's water content at capillary equilibrium as a function of capillary height is evacuated very rapidly due to the high permeability of the substrate, but the water content that remains in the playing surface (1) by capillary action and therefore cannot be evacuated by gravity due to the depth of the water table (3) depends entirely on the water table level (3).The highly permeable composition allows excess water to be quickly evacuated relative to the amount retained by capillary action, but this amount retained by capillary action, and which will therefore not be drained by gravity, depends exclusively, for a given substrate, on the depth of the water table (3).

[0121] The depth Pmax relative to the ground surface of the capillary trenches is adjusted to allow the control of the air and water content of the playing layer while the height Hmax of the water storage tanks (RS) is calculated according to the volume of water that we wish 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).

[0122] The maximum 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 be greater than 35 cm and for an optimal solution will be between 40 and 60 cm.

[0123] Depending on this maximum depth Pmax and the capillary characteristics of the playing surface substrate, the strategy for raising and lowering the water table level must be adapted. The effectiveness of a rise-fall cycle is greater for a large amplitude between the high and low water table levels during the cycle, and this amplitude is necessarily less than this maximum depth Pmax, which therefore limits said amplitude. This implies that for a low maximum depth Pmax, a higher frequency of cycles must be used to compensate for a suitable effect in terms of substrate oxygenation. Conversely, only a sufficient maximum depth Pmax allows for a significant reduction in water content during winter, so that, for low depths Pmax, only a hybrid pitch will be able to provide a suitable mechanical response in winter despite high water content.

[0124] 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 playing surface. Paradoxically, it is therefore advantageous for oxygenating the substrate to begin by increasing the water content by raising the water table level very high (even to the surface), because it is the subsequent decrease in the water content of the playing surface (1) by gravity drainage that follows the increase in the water content of said playing surface (1) during the lowering of the water table level (3) in the capillary trenches (4), which is accompanied in said playing surface (1) by an influx of atmospheric air equal to the volume of water drained.The water added to the playing surface during the rise of the water table (3) is then drained during the fall of the water table (3) and replaced by "fresh" air from the atmosphere above the surface of the pitch, this air being rich in oxygen. These rising and falling water table operations are an extremely effective and useful way to supply the playing surface (1) with the oxygen necessary for the roots and the turf ecosystem (soil bacteria and fungi).

[0125] The advantage of this capillary trench structure according to the invention in general and in particular of this "rake" structure comes from the fact that the water content in the playing 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 below the playing layer but only by the depth of the water table in capillary continuity with the playing layer in the "capillary trenches" (4) only.Thus, in this configuration of "capillary trenches" disseminated within the underlying layer, even though the roof area of ​​said capillary trenches represents only a small proportion of the contact area between the playing surface and the underlying layer, this is sufficient to control the water content of the playing surface. This is because gravity drainage and capillary irrigation through the trenches can be as effective as if the entire layer beneath the playing surface acted as both a drainage and capillary layer, with a water table occupying its entire volume at the same depth. Therefore, the drainage and capillary materials required to create the sub-layer according to the invention are limited to the trenches, and the remaining volume of the underlying layer can be used for another purpose or simply be the natural subgrade present on the site.

[0126] Thus, the volume of drainage and capillary material to be brought in to fill the capillary trenches and of water to pilot the system is divided with respect to a continuous capillary drainage layer occupying the entire surface of the ground in the proportion of the surface of the capillary trenches with respect to the surface of the ground and furthermore all the surface not used by the trenches is potentially available for another function, in particular for the installation of water storage tanks. Examples of completed projects

[0127] As seen above, the lower the WA / (WA + WB) ratio, the more efficient means are needed to ensure flow in the capillary trenches.

[0128] In all cases, the rise of the water table will always ensure in the end sufficient capillary flow but at the cost of a water content that is all the higher as the level of the water table is high, whereas we seek not only irrigation that compensates for evapotranspiration at a level close to the potential evapotranspiration (ETP) and at the same time to have a water content that is as low as possible near the surface for a given capillary flow in order to limit the risks of diseases.

[0129] Now the three ways to decrease the water content near the surface for a given capillary flow are to increase the thickness of the playing layer, to lower the water table level and to increase the performance of the substrate by seeking a substrate that is both draining and capillary.

[0130] For this reason, it is necessary for each site to seek a compromise that is as relevant as possible, considering simultaneously the aspect of performance requirements and the consequences in terms of the budget for creating the sites.

[0131] The cost-effectiveness advantage of the invention is that it concentrates the essential capillary function on the rake's teeth alone. The lower the WA / (WA + WB) ratio, the more economical the soil construction.

[0132] On the other hand, for the rake structure to be effective, and even if the WA width strips corresponding to the rake teeth represent only a small proportion of the ground surface, the rake teeth must be long enough to lower the water table level sufficiently to allow good drainage in winter.

[0133] The function of capillary trenches is to allow, at a lower cost, to lower the level of the capillary zero, i.e. the piezometric level of the water table, relative to the bottom of the sub-layer of play (1).

[0134] The examples below illustrate different possibilities of varying the parameters which allow action on both the performance and the installation prices of the land according to the invention.

[0135] Preferably, in an economical version, the height (E2) of the capillary trenches (4) is between 7cm and 15cm.

[0136] Thus, considering for example a playing layer (1) of 15 cm, capillary trenches of 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 water table thickness of 1 cm, this gives a water table depth of 21 cm, which is sufficient to have relatively suitable drainage of the playing area in winter.

[0137] 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.

[0138] Thus, considering for example a playing 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 water table thickness of 1 cm, this gives a water table depth of 34 cm, which allows for very good drainage of the water table in winter, despite a thin playing layer and therefore more economical.

[0139] In another type of configuration with water reserves for irrigation and taking as an example the case of a 10,000 m2 football field, a water storage volume of approximately 4,000 m3 can be constituted by installing on an area of ​​approximately 9,000 m2 distributed under the field storage elements 50 cm thick with a filling rate of 90%.

[0140] Such a storage volume is obviously considerable, thanks to the very large area occupied by a full-size sports field. If, by way of comparison, one wanted to build a storage element of equivalent volume under or outside the field but occupying only 1,000 m², for example, it would require an excavation under the field or an elevation greater than 4 m, involving considerable constraints and construction costs, whereas the same storage volume on an 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, the invention allows one to combine, according to the invention, 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.

[0141] Furthermore, in order for the water content in the playing layer to remain homogeneous on the horizontal plane over the whole field, the width WB of the field strips 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 over the whole surface evapotranspiration in summer and precipitation in winter.

[0142] 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 reserving the drainage and capillary trenches to a surface representing a low ratio of surface to the surface of the field is not a new or serious problem.

[0143] In the particular case 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 can be a permeable membrane, so that the gravity drainage of the playing 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 that determines the capillary pressure and therefore the capillary forces exerted in the playing layer and therefore, in said playing layer, the quantity of water retained by capillarity and the quantity of water that flows by gravity.

[0144] On the other hand, for the system according to the invention, a new difficulty arises concerning the capillary irrigation capacities through a very small surface area. Indeed, for a given type 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 through which the entire flow passes.

[0145] However, surprisingly, the tests carried out show that this difficulty according to the invention can be overcome in two complementary ways:

[0146] - on the one hand by multiplying the capillary paths in the trenches, which is achievable extremely efficiently by increasing the fiber density in a fibrous sandy substrate

[0147] - on the other hand, by raising the water table level as much as necessary but not continuously, but only during periods of high evaporative demand.

[0148] Thus, we can have deep capillary trenches (4) to allow lowering the water table (3) and obtain efficient drainage of the playing surface (1) in winter, but raise the water table (3) in summer to increase the capillary flow in the capillary trenches (4) and thus compensate for the low ratio WA / ( WA + WB ) during periods of high evaporative demand.

[0149] Thus, in practice, with a Radicalized 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 the irrigation of the turf with an ETP of the order of 1 cm per day.

[0150] On the other hand, in winter and in the absence of significant ETP, the water table level in the drainage trenches should be lower.

[0151] The depth of the water table required to obtain a given low water content in the playing surface by gravity drainage naturally depends on the capillary equilibrium water content curve characteristic of the substrate of said playing surface. In practice, however, to obtain a low water content by gravity drainage in the case of a highly permeable substrate, such as that preferably used in the context of the invention, the order of magnitude of the depth required to obtain a low water content by gravity drainage is around 40 cm.

[0152] Ideally, a satisfactory result can easily be obtained in this respect with trenches approximately 40 cm deep minus the thickness of the playing surface, as is the case, for example, with a 12 cm playing surface and trenches 28 cm deep. When the water table is lowered to 40 cm, the water content is low and the air content is high in the substrate.

[0153] However, according to the invention, it is possible not to aim for a permanently low water content but to manage winter drainage differently if it is accepted that the playing surface substrate retains a high water content in winter, but with the aim of ensuring good oxygenation of the substrate. The principle of the cycles of Ascents followed by descents of the water table level described above make it possible to meet this objective.

[0154] In this case, 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 by means of a large 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 the end of the drainages obtained at two successive times with 2 different depths of the water table in the capillary trenches, so that the difference in water content in the playing layer obtained at the end of a rise followed by a fall of the water table level in the capillary trenches is compensated by a supply of fresh oxygen-laden air from the atmosphere to the surface of the turf.

[0155] 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

[0156] A preferred embodiment according to the invention relates to terrains characterized by a depth of the bottom of the trenches PMAX > 30 cm.

[0157] This can be achieved for trenches 30 cm deep less the thickness of the playing layer, for example with a playing layer (1) 10 cm thick (El) and capillary trenches (4) 20 cm deep inside the sub-layer (2).

[0158] If we accept that the substrate remains fairly close to saturation in winter, but require that it be sufficiently oxygenated for the health of the roots and therefore the turf, this can be achieved with a 10 cm playing surface and drainage trenches only 10 cm deep. However, this simply requires sufficiently frequent rises and falls in the water table between the top and bottom of the trenches. It should be noted, however, that a playing surface that is always close to saturation is only mechanically compatible with play for hybrid turf, and a maximum depth (PMAX) of less than 20 cm is therefore not recommended for non-hybrid natural turf.

[0159] In practice, tests carried out show that a result is obtained that is practically as satisfactory in terms of control of the water content of the playing layer as that which would be obtained with a playing layer of 10 cm on a sub-layer of 30 cm and with a water table of 5 cm relative to the bottom of the sub-layer with a playing layer of 8 to 12 cm thick laid on the natural ground, having made trenches of 30 cm deep and of a width WA of 10 cm every meter, i.e. WA = 10 cm and WB = 1m and with a water table of 5 cm in the bottom of the trenches, i.e. a water table at the depth P relative to the surface of 35 cm.

[0160] In this case, 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 area, the result in terms of controlling the water content of the playing surface is not noticeably affected.

[0161] With a result practically as satisfactory as with a water table in a sub-layer whose surface area is that of the playing field, the advantage is that such a rake-like construction will be achieved with only 10% of the supply and transport of the quantity of drainage and capillary material that would have been necessary for the creation of a 30 cm thick sub-layer under the entire surface of the sports field in a solution without a rake-like structure according to the invention.

[0162] The tests carried out under the above conditions of surface trenches of 10 cm or 7 cm wide every 2.50 m with a filling of the playing layer and capillary trenches in Radicalé substrate and with water reservoirs of 2.50 meters wide and whose upper surface is permeable but without capillary continuity because the reservoirs are empty and there is an air layer above the mass of water, clearly show perfect drainage while the upward capillary flow, although reduced, seems sufficient to ensure proper capillary irrigation in summer conditions with an ETP of 3 or 4 cm per day, when a geotextile which goes up along the vertical walls of the capillary trenches is then extended horizontally under the playing layer above the water storage reservoirs between 2 capillary trenches before the installation of the playing layer.

[0163] Preferably, the playing surface substrate and the porous and draining medium of the capillary trenches will be made with a sandy substrate containing fibers, 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 no. 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 of high resistance and high flexibility and which will be preferably chosen for the realization of the present invention.

[0164] Preferably, with a view to horizontal homogenization of the capillary flow from the capillary trenches, a geotextile which goes up along the vertical walls of said capillary trenches may be extended horizontally under the gap layer between 2 capillary trenches, which allows by a preferred capillary path to conduct the water horizontally to the interface from where it can continue to rise vertically by capillarity in the substrate.

[0165] 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 the area occupied by the capillary trenches to the total area of ​​the field is approximately equal to R= WA / ( WA+WB)

[0166] With 10 cm wide drainage trenches spaced every 2.5 meters, this gives an R-value of slightly less than 4%, while with 7 cm wide drainage trenches spaced every 2.5 meters, this gives an R-value of slightly less than 3%. The result is not as satisfactory as with a higher R-value, but it remains acceptable in the case of a highly fibrous substrate in the drainage trenches and the playing surface, and when a geotextile is laid over the entire contact area between the playing surface and the sub-layer.

[0167] With 5 cm wide drainage strips 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 during periods of high 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 with, consequently, a profile that is too wet.

[0168] Preferably, even though it is possible to lower the ratio even further, and even though this allows for 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 decrease in the quality of the ground is too significant.

[0169] It is preferable to choose a ratio greater than 4% for a result which remains conclusive with highly fibrous substrates in the capillary trenches and the playing layer.

[0170] 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.

[0171] 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 of less than 1 meter.

[0172] For comfortable conditions of use it is preferable to provide an R ratio > 5%, which is found in the case of 10 cm slots with an equidistance of less than 2 meters.

[0173] However, for the optimization of the manufacturing and transport costs of water storage tanks, a width of 2.5 meters may be desirable and a suitable solution according to the invention, being economical and still technically acceptable, then gives an R ratio of the order of 3% or 4%.

Claims

Demands

1. Sports field comprising a playing layer (1) placed on a sub-layer (2), with a partition of the surface of said field into two complementary sub-surfaces (A, B), the respective areas of which are both strictly positive, said sports field being characterized in that: - directly above a first sub-surface (A), the structure of said sports field is equipped with means for creating a layer of liquid (3), such as for example a water table, in the volume of the sub-layer (2) located below 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 playing layer (1) and said layer of liquid (3).- the sub-layer (2) is configured such that, directly above the second sub-surface (B), there is a capillary boundary between said liquid layer directly above the second surface (B) and the playing surface (1) located above.

2. Sports field according to the claim characterized in that the subsurfaces (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) being inserted exactly between two second strips (BB), the volume of the sublayer (2) in the vertical plane of the first strips (BA) of width (WA) defining a multitude of capillary trenches (4), of height (E2) and width (WA).

3. Sports field according to claim 2, characterized in that: - the sub-layer (2) on which the playing layer (1) rests comprises a multitude of straight strips made up of an alignment of water storage tanks, parallel to each other, of the same width (WB), crossing the field 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, directly above the second sub-surface (B), there is a capillary boundary between said water storage tanks and the playing layer (1) located above.

4. Sports field according to claim 2 or 3, 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.

5. Sports field according to claim 2 or 3, 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 straight 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 straight strip is substantially equal to 2 m.

6. Sports field according to any one of claims 1 to 5, 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.

7. Sports field 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 the capillary trenches (4) together and being itself capable of being connected to a water network (7), the perforated corrugated drain (10) being connected to the network of pipes (6) and being disposed at the bottom of the capillary trenches (4).

8. Sports field according to any one of the preceding claims, characterized in that it further comprises a waterproof membrane (11) disposed at the bottom of the capillary trenches (4) and / or on vertical edges of said capillary trenches (4).

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