METHOD FOR THE CONSTRUCTION AND SUSTAINABLE MANAGEMENT OF A HYBRID TURF SPORTS GROUND WITH WATER TABLE AND HYBRID TURF SPORTS GROUND

Abstract

The invention relates to a method for the construction and sustainable management of a hybrid turf sports ground, with management of a shallow water table in the structure of the sports ground, which comprises: a first step of constructing a structure (S) placed on a base (F), the structure comprising N stacked porous layers (Ci); a second step of installing turf on the surface of the top layer (Ci), the installation of the turf possibly being carried out by sowing; and, of the N layers, one hybrid layer (H) is constituted either (i) by a cultivation substrate that comprises synthetic reinforcing elements, or (ii) by a cultivation substrate that shares the space of the hybrid layer (H) with synthetic reinforcing elements.

Claims

1. Method for the construction and management of a hybrid turf sports field characterized: in that it comprises a first step for constructing a structure (S) placed on a base (F), the said structure comprising N stacked porous layers (C.sub.i), N ≥1, the lower layer (C.sub.N) being erected first on the base (F) and each (C.sub.i) being then placed on the layer (C.sub.1+1) up to the top layer (C.sub.1) which is comprised between the surface of zero depth (Y.sub.o = 0) and the bottom of the layer (C.sub.1) at the depth Y.sub.1, all layers being comprised between the depth Y.sub.i-1 of the base of the next higher layer (C.sub.i-1), if > 1, or Yo, if i=1, and the depth Y.sub.i of the base of the layer (C.sub.i); in that the method comprises a second step of installing turf on the surface of the top layer (C.sub.1), said installation of said turf being carried out by sowing seeds, once said top layer (C.sub.1) has been placed in its definitive position during said first step, or can be carried out beforehand by pre-cultivating said grass on a layer of substrate which is then cut into a partition of sub-elements each comprising a volume of substrate of the same thickness with the turf pre-cultivated on its surface and the roots installed therein, these sub-elements being transported and then finally gathered and placed in order to finalize the construction of said structure (S); in that there is at least one hybrid layer (H) among the N layers, consisting of either (i) a cultivation substrate which comprises synthetic reinforcing elements or (ii) of a cultivation substrate which shares the space of the hybrid layer (H) with synthetic reinforcing elements; in that said method comprises a step to manage the depth (P.sub.piezo) of the piezometric level of the water table inside the structure (S), to allow for good hydration of the turf using capillary flow from said water table.

2. Method for the construction and management according to claim 1, characterized in that it also comprises a step for defining: the depth P.sub.TOR of an oxygenation range of the turf roots from the surface to said depth P.sub.TOR, which is greater than or equal to 5 cm and preferably between 5 and 15 cm; of the minimum air concentration θ required within said root oxygenation range, said minimum air concentration being greater than or equal to 5% and preferably between 5% and 15%; and in that, in order to allow for good hydration of the turf and to ensure good oxygenation of the roots within the oxygenation range of the roots between the surface and the said depth P.sub.TOR, the depth Piezo of the piezometric level of the water table within the structure (S) is maintained for at least part of the time of the year between a minimum depth P.sub.piezoMINTOR and a maximum value P.sub.piezoMAX which satisfy the following equations: ${\text{-P}}_{\text{piezo MAX}}\le 2\text{m}$ $\begin{array}{l}{\text{-P}}_{\text{piezo MINTOR}}\ge {\text{P}}_{\text{MIN TOR}}=\\ \text{MAX}{\left[{\text{Zi + h}}_{\text{c i drainage}}\left({\text{E}}_{\text{i}}\text{-}{\text{θ}}_{\text{AIR MIN TOR}}\right)\right]}_{1\le \text{i}\le \text{n}\left(\text{PTOR}\right)}\end{array}$ where n(P.sub.TOR) is the number of layers entirely or partially above said minimum root oxygenation slice (TOR) of thickness PTOR and by considering as a definition of a layer entirely or partially included in said surface root oxygenation slice (TOR) the fact that Y.sub.i-1 .sub.< P.sub.TOR, which makes it possible to define the integer n (P.sub.TOR) ≤ N by the equation: $1\le \text{n}\left({\text{P}}_{\text{TOR}}\right)\le \text{N with Yn}\left({\text{P}}_{\text{TOR}}\right)\text{-1}<{\text{P}}_{\text{TOR}}{\text{and Y}}_{\text{n}}\left({\text{P}}_{\text{TOR}}\right)\ge {\text{P}}_{\text{TOR}}$ where ε.sub.i, is the characteristic total porosity of the layer (C.sub.i) in its in situ state of compaction; where the function h.sub.c i .sub.drainage is the function characterizing the theoretical capillarity of the layer (C.sub.i) in its state of in situ compactness, defined as the function which has a value θ.sub.water of water concentration by volume strictly comprised between the water concentration ε.sub.i at saturation and the water concentration at the wilting point corresponds to the value h.sub.cdrainage (θ .sub.water), which is the equivalent capillary height expressed in cm corresponding to θ.sub.water on the strictly decreasing water concentration versus capillary pressure curve on a quasi-static drainage path from the initial saturated state; by defining Z.sub.i, for i ≤ n (P.sub.TOR), by the relation Z.sub.i = Y.sub.i, for i < n (P.sub.TOR) and Z.sub.n (P.sub.TOR) = P.sub.TOR.

3. The method for the construction and management according to claim 1, characterized in that: it comprises a step to define the minimum summer air concentration θ.sub.AIR .sub.MIN .sub.SUMMER .sub.5 cm required at 5 cm from the surface at theoretical capillary balance, θ.sub.AIR .sub.MIN .sub.SUMMER .sub.5 .sub.cm is greater than 10%. to allow for good hydration of the turf and to meet this requirement of summer air concentration near the surface, the said depth P.sub.piezo of the piezometric level of the water table inside the structure (S) is maintained, during the times of the year when the night temperature exceeds 18° C., in such a way that the following equation is satisfied: $\begin{array}{l}{\text{P}}_{\text{piezo}}\ge {\text{P}}_{\text{piezo AIR MIN SUMMER 5cm}}=\\ 5{\text{cm + h}}_{\text{c j drainage}}\left({\text{ε}}_{\text{j}}\text{-}{\text{θ}}_{\text{AIR MIN SUMMER 5cm}}\right)\end{array}$ where j is the number of the layer (C .sub.j) which comprises the points at 5 cm depth.

4. A hybrid turf sports ground, characterized: First of all, in that it comprises a structure (S) placed on a base (F), with said structure comprising: (i) N porous layers (C.sub.i) with 1 ≤ i ≤ N stacked, with the first layer from the top being between the surface of zero depth Yo = 0 and the base of the layer (C.sub.1) with a depth Y.sub.1 and with all layers being between the depth Y.sub.i-1 of the base of the next higher layer (C.sub.i-1) if i > 1 or Y.sub.0 if i =1 and the depth Y.sub.i, of the base of the porous layer (C.sub.i), and with at least one hybrid layer (H) among the N layers, (ii) a turf whose roots are anchored in this hybrid layer (H); (iii) means (m) for introducing water into or removing water from the structure (S), for forming a water table therein and for managing the depth (P.sub.piezo) of the piezometric level of said water table inside said structure (S); Secondly, in that the hybrid layer (H) consists of either (i) a cultivation substrate which comprises synthetic reinforcing elements, or (ii) a cultivation substrate which shares the space of the hybrid layer (H) with synthetic reinforcing elements.

5. The sports ground according to claim 4, characterized in that, in order to be able to address the requirement of air concentration near the surface for minimum oxygenation of the roots, the structure verifies the equation: ${\text{Y}}_{\text{N}}\ge \text{MAX}{\left[{\text{Z}}_{\text{i}}{\text{+ h}}_{\text{c i drainage}}\left({\text{E}}_{\text{i}}\text{-}{\text{θ}}_{\text{AIRMINTOR}}\right)\right]}_{1\le \text{i}\le \text{n}}\left({\text{P}}_{\text{TOR}}\right)$ with P.sub.TOR = 5 cm and θ .sub.AIRMINTOR = 5 % where ε.sub.i, is the characteristic total porosity of the porous layer (Ci) in its compactness state in situ; where the function h.sub.C i .sub.drainage is the function characterizing the theoretical capillarity of the porous layer (Ci) in its state of compactness in situ, said function h.sub.C .sub.i .sub.drainage being defined as the function which to a value θ.sub.water of water concentration by volume strictly comprised between the water concentration at saturation and the water concentration at the wilting point associates the value h.sub.C i .sub.drainage (θ .sub.water) which is the equivalent capillary height expressed in cm corresponding to θ .sub.water on the main drainage curve, a strictly decreasing curve of water content at capillary equilibrium with respect to the capillary pressure on a quasi-static drainage path from the initial saturated state; where the number n(P.sub.TOR) of layers fully or partially above P.sub.TOR is an integer defined by the equation: $1\le \text{n}\left({\text{P}}_{\text{TOR}}\right)\le {\text{N and Y}}_{\text{n}}{\left({\text{P}}_{\text{TOR}}\right)}_{\text{-1}}<{\text{P}}_{\text{TOR}}{\text{and Y}}_{\text{n}}\left({\text{P}}_{\text{TOR}}\right)\ge {\text{P}}_{\text{TOR}}$ by defining Z.sub.i where i ≤ n(P.sub.TOR) by the equation Z.sub.i = Y.sub.i where i < n (P.sub.TOR) and Z n(P.sub.TOR) being equal to P.sub.TOR.

6. The sports ground according to claim 4, characterized in that the structure (S), in order to be able to meet the requirement of the air concentration near the surface so as not to promote summer illnesses during a heatwave, verifies the equation Y.sub.N ≥ 5 cm + h.sub.Cj .sub.drainage (ε.sub.j - 15%) where j is the number of the layer in which the points are located at a depth of 5 cm and ε.sub.j is the total porosity characteristic of the porous layer (C.sub.j) in its state of compaction in situ.

7. The sports ground according to claim 4, characterized in that the hybrid layer (H) comprises: a substantially sandy cultivation substrate (SUB sab) synthetic reinforcing elements (SYNT renf) which may be: (a) fragmented and incorporated into the substrate (SUB sab) during the manufacture of the substrate; or, (b) fragmented or continued and incorporated in situ into the substrate after the substrate (SUB sab) has already been placed in situ; or (c) consisting of an organized structure previously placed in situ at the location of the play layer, the substrate (SUB sab) itself being subsequently incorporated into said structure.

8. The sports ground according to claim 4, characterized in that the hybrid layer (H) is comprised of one of the following configurations: the synthetic reinforcing elements (SYNT renf) are fibers, and the substrate (SUB sab) and the fibers are premixed; the synthetic reinforcing elements (SYNT renf) are long fibers that are incorporated into the substrate, once the turf is placed. the synthetic reinforcing elements (SYNT renf) are long fibers that are incorporated into the substrate, once the turf is installed. the synthetic elements are a synthetic carpet with a substrate incorporated between the strands of the synthetic carpet, a seeding is then carried out to finally constitute a sown synthetic carpet in which a real natural turf grows.

9. The sports ground according to claim 8, characterized in that the hybrid layer consists of the substrate marketed under the name Radicalé.

10. The sports ground according to claim 4, characterized in that it has a pool structure with a formed base (F) and edges and an impermeable membrane placed on said formed base (F) and under the structure (S) and extending up to the edges of said pool structure, so that the structure (S) has its base and its vertical peripheral edges isolated from the outside by said impermeable membrane.

11. The sports ground according to claim 4, characterized in that one of the layers of the structure (S) consists of a porous concrete, with very coarse porosity, which is both very permeable and very porous, marketed under the brand name Capillary Concreete by the company Capillary Concreete.

12. The sports ground according to claim 4, the structure of which comprises a substrate layer with a thickness of 10 to 40 cm placed on a capillary storage layer with a thickness of 5 cm to 200 cm and located between the depth P.sub.ROOF of its roof and P.sub.BASE of its base, and characterized: in that P.sub.ROOF ≥ P.sub.Min and P.sub.BASE = P.sub.Max and in that the said capillary storage layer has natural capillary characteristics or by the artificial addition of suitable means enabling water to rise into the layer of substrate placed above it, whatever the piezometric level of the water table between P.sub.ROOF and P.sub.BASE, with a capillary flow at least equivalent to that which would result from the same evaporative demand at the top of the same substrate placed on a medium sand (between 250 .Math.m and 500 .Math.m) with a water table at the same depth.

13. The sports ground according to claim 12, characterized in that the capillary storage layer comprises a combination of 1 to 7 layers including: a layer of sand with a D10 of between 200 and 800 .Math.m, with a thickness of 5 cm to 200 cm, if present, a layer of substrate marketed under the name Radicalé with a thickness of 4 to 20 cm, if present a layer consisting of a juxtaposition of containers of the type known and marketed under the trade name Permavoid with a thickness of 7 cm to 15 cm, if present, said containers being provided with a bundle of vertical capillary columns allowing capillary rise through the air-filled void above the level of the water table a layer of gravel from 7 cm to 150 cm, if present, said layer of gravel being provided with a bundle of vertical capillary columns or capillary wicks allowing capillary rise through the capillary barrier constituted of the essentially air-filled porosity of the gravel above the water table a layer of the product marketed under the brand name Capillary Concreete from the company Capillary Concreete, with a thickness of 5 to 15 cm, if it is present a layer of sand having a D10 between 200 and 800 .Math.m located under the layer of the product marketed under the brand name Capillary Concreete, with a thickness of 10 to 250 cm, if it is present. A layer composed of hard or soft fibrous materials, natural or artificial, fibrous materials crushed or in pieces such as coral, chalk, crushed wood or clusters or balls of fibers, natural balls of Posidonia, pieces of carpet, all constituting a porous medium with high macroporosity between the aggregated constituent elements and a capillary network within the aggregated constituent elements.

14. The sports ground according to claim 12, characterized in that the capillary storage layer is an artificial capillary storage layer specifically designed for this purpose and which comprises: either a layer consisting of a juxtaposition of containers of the cell-type known under the trade name Permavoid, with a thickness of 8 cm to 15 cm, said boxes being provided from the top to the bottom of the layer with a bundle of vertical capillary columns allowing capillary ascent through the air-filled void above the level of the water table or a layer of the product marketed under the brand name Capillary Concreete from the company Capillary Concreete, with a thickness of 5 to 15 cm.

15. The sports ground according to claim 12, characterized in that the capillary storage layer is an artificial capillary storage layer specifically designed for this purpose with a thickness of ≥ 5 cm and that the cultivation substrate placed on it has a thickness between 12 cm and 19 cm.

16. The sports ground according to claim 12, characterized in that the capillary storage layer is an artificial capillary storage layer specifically designed for this purpose with a thickness of ≥ 8 cm and that the cultivation substrate placed on it has a thickness between 13 cm and 22 cm.

17. The sports ground according to claim 12, characterized in that the capillary storage layer is an artificial capillary storage layer specifically designed for this purpose with a thickness of ≥ 15 cm and that the cultivation substrate placed on it has a thickness of between 16 cm and 25 cm.

18. The sports ground according to claim 4, characterized in that the structure comprises a combination of 1 to 5 layers amongst which: a top dressing layer from 1 to 3 cm located, if present at the very top of the stack of overlapping layers, a substrate layer marketed under the name Radicalé with a thickness of 4 to 20 cm, a layer of sand having a D10 between 200 and 800 .Math.m located under the substrate marketed under the name Radicalé, with a thickness of 5 cm to 250 cm, if present, a layer of the product marketed under the brand Capillary Concreete from the company Capillary Concreete with a thickness of 5 to 10 cm, if it is present, a layer of sand having a D10 between 200 and 800 .Math.m located under the product marketed under the brand name Capillary Concreete from the company Capillary Concreete, with a thickness of 10 to 250 cm, if it is present.

Description

[0615] The description, which is in no way exhaustive, should be read in conjunction with the following figures:

[0616] FIG. 1 is a schematic cross-sectional view of a soil comprising 5 layers according to this invention.

[0617] FIG. 2 comprises the 4 FIGS. 2A, 2B, 2C and 2D which are 4 examples of compositions from 3 types of layers which can be identified by the pattern used to represent them: [0618] a type of layer consisting of the Radicalé substrate, marked on FIGS. 2 with ovals and noted (Ra), [0619] a type of layer consisting of Capillary Concreete, which can be identified in FIGS. 2 by triangles and is noted (CC) [0620] a type of layer composed of siliceous sand, identifiable on FIGS. 2 by rectangles with a cross and noted (SS)

[0621] In the 4 cases, the figures represent the aerial part of the turf which is noted (g) and shows an impermeable membrane that is noted (1 M) and the means shown as in FIG. 1 by an arrow connecting the layers to a container full of water whose level determines the piezometric level of the water table.

[0622] The highest and lowest levels predicted by the water table management process and the level at the moment t of the water table are represented as Ppiezo mini, Ppiezo mini and P piezo respectively, and the tidal range is noted (Δ) which is the difference between the highest and lowest level of the water table.

[0623] Comparing the four figures showing different examples, we can see that the tidal ranges are not necessarily the same.

[0624] FIG. 2A is a schematic cross-sectional view of a soil according to the invention comprising a single layer, consisting of the Radicalé substrate,

[0625] FIG. 2B is a schematic cross-sectional view of a field according to the invention comprising 2 layers: a layer of the Radicalé substrate at the top and a layer of sand at the bottom.

[0626] FIG. 2C is a schematic cross-sectional view of a field according to the invention, also comprising 2 layers: the layer of the Radicalé substrate at the top and a layer of Capillary Concreete at the bottom.

[0627] FIG. 2D shows from top to bottom: Radicalé substrate at the top, then Capillary Concreete and finally a layer of sand at the bottom.

[0628] FIG. 3 is a graph comparing 4 matrix pressure curves corresponding to 4 types of soil.

[0629] The 4 types of soil are a clay soil (T1 type curve), a silty soil (T2 type curve), a sandy soil (T3 type curve) and a substrate soil corresponding to the type of water profile intended in the invention (T4 type curve).

[0630] The curves show the relationship between the capillary pressure in logarithmic scale on the vertical axis in relation to the water content by volume θ.sub.WATER in normal scale

[0631] In the example of FIG. 1, we have N = 5 and in this example, the hybrid layer is the 2nd layer (C.sub.2), represented with a graphic pattern to suggest the draining and elastic aspect of this layer.

[0632] FIG. 1 shows a block of 5 layers C.sub.1, C.sub.2, C.sub.3, C.sub.4, C.sub.5 on a base (f), and the construction parameters Y1, Y2, Y3, Y4 and Y5.

[0633] The depth of 5 cm corresponding to the summer aeration criteria is given and P.sub.TOR is the depth of the root oxygenation layer (TOR). In the example in FIG. 1, we have n (P.sub.TOR) = 3.

[0634] Also on the right side of this block, there is a silt system communicating with a reservoir (R) that rises and falls and whose water level dictates the water table and with an impermeable membrane (IM). The figure also shows the tidal range (Δ) between the minimum and maximum water table. Farther right, vectors represent the conditions to be met.

[00030]${\text{Z}}_1\le {\text{P}}_{\text{Min}}{\text{- X}}_{1,}{\text{Z}}_2\le {\text{P}}_{\text{Min}}{\text{- X}}_2{\text{and Z}}_3\le {\text{P}}_{\text{Min}}{\text{- X}}_{3,}\text{with:}$

[00031]$\begin{array}{l}{\text{X1 = h}}_{\text{c1}\text{drainage}}\left({}_1\text{-}{\text{θ}}_{\text{AIRMINTOR}}\right){\text{and X}}_2=\\ {\text{h}}_{\text{c2 drainage}}\left(2\text{-}{\text{θ}}_{\text{AIR MIN TOR}}\right)\end{array}$

[0635] In FIG. 1, these quantities Z.sub.1, Z.sub.2, Z.sub.3 and X.sub.1, X.sub.2 and X.sub.3 which correspond to the example are also represented by vectors. These quantities appear on the right-hand side of FIG. 1 as vectors directed upwards with their origin at the depth P.sub.Min and this makes it possible to see whether the tip of the vector Xi is lower or higher than the tip of the vector Zi directed downwards from the surface because the condition to be respected according to the invention is diagrammatically to have the tip of the vector Zi situated higher than the tip of the vector Xi.

[0636] Thus, it can be seen that in the example shown in FIG. 1, the 3 equations are indeed satisfied, since Z.sub.1 ≤ P.sub.Min - X.sub.1, Z.sub.2 ≤ P.sub.Min - X.sub.2 and Z.sub.3 ≤ P.sub.Min - X.sub.3.

[0637] Moreover, FIG. 1 also illustrates the possibility of complying with the summer condition. In fact, in order to be able to respect the summer condition according to the invention when we will lower the level of the water table to the maximum up to P.sub.piezo .sub.Max, we must also verify in this example the following equation: 5 cm ≤ P′.sub.piezo .sub.Max - X′ with: X′ = h′.sub.c .sub.drainage (ε.sub.2 - θ.sub.AIR .sub.MIN .sub.SUMMER .sub.5 cm), where h′c is the profile function from the depth P.sub.piezo .sub.Max.

[0638] According to this example, it can be seen that if P.sub.piezo .sub.Min had been smaller and/or X3 had been a little larger, the relationship would not have been respected. We also see that if the substrate of layer 2 had been the substrate of layer 1 we would have had X1 = X2 and in this case we would have had: Z.sub.2 > P.sub.piezoMin - X.sub.2.

[0639] If the θ.sub.AIR .sub.MIN .sub.TOR requirement had been a higher air content, we would have had larger X1, X2 and X3 and therefore at least for layer 3, the equation would not have been satisfied.

[0640] Similarly, if the θ.sub.AIR .sub.MIN .sub.TOR requirement had been that of the example in FIG. 1, but the substrate of layer 3 had been a finer grained substrate, the h.sub.c .sub.3 .sub.drainage function would have decreased more rapidly and as a consequence X3 would also have been larger, and the equation would not have been satisfied either.

[0641] Finally, on the right-hand side of FIG. 1 are the 5 cm vector from the surface and the X′ vector from the maximum depth P.sub.piezo .sub.max, to check whether the peak of this vector is lower than the peak of the 5 cm vector, which corresponds to the summer conditions, which are indeed observed in the example shown in FIG. 1.

[0642] Thus, FIG. 1 represents all the elements that allow one to visually observe in a graphic manner that the example shown is indeed in conformity with the conditions sought by the invention.

[0643] An example of 4 typical embodiments is illustrated by FIG. 2, which represents 4 particular structures.

[0644] Furthermore, the link between the intrinsic characteristics of the soil and the structure according to the invention will then be illustrated by the analysis of 4 soils representing 4 relatively typical cases and represented on the same FIG. 3 by their capillary pressure curves.

[0645] Different combinations of diversified layers can be found, starting from the surface, such as the following example: [0646] On the surface, a top layer with a thickness of a few millimeters to 1 or 2 cm can be found to provide specific functionalities to this interface, in particular for slip management. [0647] On the surface or just below the top layer, the hybrid layer is normally present, as it is this surface layer that must play a mechanical, biomechanical role that gives the surface its specific qualities. This layer can be between 5 and 25 cm thick, depending on the sport and the requirements, bearing in mind that the thickness of this layer has a significant impact on the overall cost of the structure. [0648] Under the hybrid layer, a layer of sand can be used to take over the role of the hybrid layer, which is less effective from a mechanical and hydraulic point of view but more economical.

[0649] Underneath these layers, a layer of a material (CC) known under the brand name Capillary Concreete, which is an extremely porous capillary concrete. Ideally, this layer of (CC) has a very high macro-porosity and therefore has a maximum storage capacity per centimeter of the layer and a particularly low mechanical flow resistance, which allows for a perfect horizontal homogenization of the convection flows and an almost negligible mechanical flow resistance power.

[0650] Under the hybrid layer, a layer of sand may be found, which may be several dozen centimeters to 1 or 2 meters thick, and which serves both to lower the water table for the summer and to store winter rainwater for summer use.

[0651] Finally, underneath these layers, one can find an impermeable membrane that otherwise extends to the edges of the structure.

[0652] The following examples of preferred embodiments, which are not exhaustive either, illustrate in a concrete manner various methods of construction and management of sports fields according to the invention.

[0653] Since the invention concerns a structure comprising one or more stacked layers, the examples below will be given by taking examples with 1 then 2 then 3 layers, mainly chosen for their different characteristics and functions.

[0654] Thus, a first embodiment is possible with a single layer, as illustrated in FIG. 2A.

[0655] This is a single layer of the Radicalé substrate with a thickness of 20 to 40 cm, placed on an impermeable membrane that extends peripherally along the edges to the surface.

[0656] A second embodiment illustrated by FIG. 2B is possible, according to the same model but replacing the single layer of the Radicalé substrate with a Radicalé layer of 8 to 30 cm (depending on the sport considered and the level of performance sought) on a layer of coarse sand of 20 to 200 cm.

[0657] This two-layer structure does not excessively alter performance, as long as the upper layer of Radicalé is thick enough to withstand the mechanical stresses of the sport in question. A very deep structure with a thick sand layer and a deeper layer at the end of a prolonged summer drought in arid climates is certainly less effective, but it does allow the turf to play an important ecological role with economical water storage.

[0658] Ideally, from the point of view of turf quality, one can have a top Radicalé layer of 8 to 12 cm thick and a layer of sand 30 to 50 cm thick, with a water table of 40 cm at the time of the July heat wave and which can continue to drop to 60 cm until the first rains in autumn. Thus, the water table can vary between 15 cm and 60 cm in depth, and is mostly below 20 cm and around 40 cm at the time of the heat waves.

[0659] A third embodiment shown in FIG. 2C, also in two layers, is also possible by replacing the sand with a product known as CC or Capillary Concreete, which is a very porous concrete with very large pores and at the same time with high capillarity.

[0660] A first advantage of CC is that the additional storage volume per 10 cm of additional layer is 7 cm of water and that, above all, there is no need for a water filter. There is no need for drains to distribute the air or water horizontally under pressure or lack of pressure to create an upward or downward movement of air or water, because the permeability is such that the CC provides a perfect distribution layer without any delay and without any significant mechanical resistance, which makes it possible to create vertical convection in the substrate above it from a homogeneous horizontal base.

[0661] A second advantage of CC is that it is a perfectly stable surface on which vehicles can be driven or stands installed and that a Radicalé layer can be installed on CC and removed and put back on later, leaving a perfectly clean, load-bearing and draining surface that can be used for multi-functional stadiums.

[0662] However, the question of the economic cost remains problematic if one wants very thick layers of CC for large storage capacity.

[0663] Other important examples have already been described in the section on structures consisting of a thin substrate layer on a specially designed artificial storage layer, such as: [0664] sports grounds where the capillary storage layer is an artificial capillary storage layer specifically designed for this purpose with a thickness of ≥ 5 cm and where the cultivation substrate laid on top is between 12 cm and 19 cm thick. [0665] sports grounds with a capillary storage layer specifically designed for this purpose with a thickness of ≥ 8 cm and with a substrate thickness of between 13 cm and 22 cm. [0666] sports grounds whose capillary storage layer is an artificial capillary storage layer specifically designed for this purpose with a thickness ≥15 cm and with the cultivation substrate laid on top of it having a thickness between 16 cm and 25 cm.