A SPORTS FIELD HAVING A TOP LAYER IN WHICH PUMICE IS INCORPORATED

Abstract: This invention relates to a sports field, consisting of layers of material of a distinguishing kind and/or composition lying on each other, the top layer comprising a mixture of pumice and sand. Such a sports field is used for purposes of sports and/or leisure. In the top layer according to this invention pumice having a dry bulk density of 400 to 900 kg/m<3> is used. It is preferred here that the percentage by volume of pumice is in the range of 50 to 75 %. The advantage of said top layer is a high drainage capacity and high structure stability of the sports field resulting in a high playing durability and a low burden to the environment.

Description: A sports field having a top layer in which pumice is incorporated. The present invention relates to a sports field, consisting of layers of material of a distinguishing kind and/or composition lying on each other, the top layer comprising a mixture of pumice and sand. Such a sports field is used for purposes of sports and/or leisure. The playing durability of regular sports fields varies from approximately 250 hours a year for a sports field without special provisions to approximately 700 hours a year for a specially prepared sports field. In favourable to normal weather conditions prepared sports fields have an average playing durability of approximately 400 hours a year. Because of intensive use of a sports field or because of extensive precipitation the playing durability of a sports field may even be lower. When a sports field is played on longer than the indicated playing durability a lot of damage is caused and the sports field has to be disused for a certain period of time or it may have to be replaced. In order to extend the playing durability of sports fields, a sports field is proposed in the state of the art consisting of layers of material of a distinguishing kind and/or composition lying on each other, the top layer comprising a mixture of pumice and soil. In the international application WO 96/32540, for instance, a nutritive layer for grass is proposed containing soil and up to 1 5% by volume of pumice grains (grain size of 5 to 14 mm) or up to 1 5% by volume of pumice sand (grain size of 0.5 to 1 .5 mm). The Italian pumice used has a high dry bulk density. Additionally the nutritive layer contains volcanic gravel (30 to 80% by volume) and green vegetable compost (0.8 to 60% by volume). Apart from the above-mentioned components other components may be added to said nutritive layer. Said nutritive layer is placed directly on top of a layer containing a drainage system. A drawback of the nutritive layer from international application WO 96/32540 is its relative low drainage capacity. The nutritive layer contains a relatively high quantity of green vegetable compost and therefore a relatively high quantity of organic substances as a result of which the drainage capacity of the nutritive layer, which is low anyhow, becomes even lower in time. In a top layer of a sports field other kinds of stone than pumice can also be used. For instance Dutch patent application 8500946 relates to a sports field of which the top layer consists of a mixture of poor leaf mould and fine foam lava in a mixing ratio determined beforehand through preventive laboratory research. The fine foam lava's primary object is to increase the water permeability. The fine foam lava used (German lava stone) has a high dry bulk density ( 1 21 4 kg/m 3 ) . In said document a high dry bulk density of the top layer of 1 ,245 to 1 ,450 kg/m 3 is mentioned. The maximum playing durability of a sports field having such a top layer is approximately 700 hours a year. Additionally within 1 .5 years after applying the top layer at a depth of 10 cm rooting of the grass in the top layer is achieved. The top layer of the sports field according to Dutch patent application 8500946 also has the drawback of having a relatively low drainage capacity. The object of the present invention is providing a sports field having a high drainage capacity and high playing durability. Surprisingly it was found that when the pumice in the top layer of the sports field has a dry bulk density of 400 to 900 kg/m 3 , a high drainage capacity can be guaranteed. The present invention accordingly provides a sports field, consisting of layers of material of a distinguishing kind and/or composition lying on each other, the top layer comprising a mixture of pumice and sand, and the pumice having a dry bulk density of 400 to 900 kg/m 3 . The general advantage of the sports field according to the present invention is its high drainage capacity and its high structure stability. As a result the sports fields according to the present invention suffer less playing damage and they are able to quickly recover from possible playing damage as a result of which the playing durability is high. Sports fields according to the present invention can be intensively used as a result. In addition to pumice, sand is used in the top layer of the sports field according to the present invention. Sand is a mineral type of soil and therefore, just like pumice, it is not subject to decomposition. As a result the structure stability of the top layer will be high and the values for the physical properties of the top layer, such as amongst others the drainage capacity, will be constant in time. Furthermore a small quantity of soil having a high organic substance content, which is indeed subject to decomposition, will in general be used in the top layer. The drainage capacity can be expressed in the so-called K-value, which stands for the saturated water permeability of a layer and indicates how quickly water flows through the layer. The K-value is indicated by m/day. The K-values of for instance the following types of soil are known: heavy clay 0.1 -0.2 clay/loamy soil 0.2-0.4 fine/normal sand 5-7 crude sand 7-1 0 Top layers of sports fields known up until now have a K-value of 1 -2.5 m/day, which value becomes even lower in the course of time. The K-value of the top layer according to the invention is considerably higher and may even be up to 1 3 m/day. The K-values mentioned here are determined by the analysis method "saturated water permeability" in conformity with NEN 51 23: 1 993 ONTW.NL. The present invention is further elucidated below on the basis of the drawing in figure 1 which is an upright cross-section of the sports field according to the present invention. In the drawing of figure 1 , 1 is the terrain the soil of which can by dug off to a certain depth 2. On the bottom of the deepened part 2 drainage means 3 can be arranged. Said drainage means may be of any kind and in this case are drawn as drainage pipes which may be connected to a self-acting discharge system or to a suction pump and the like. The pipes preferably run near the edges of the sports field and are laid at a distance of approximately 4 meters from each other. The deepened part 2 is filled with a high-draining layer 4. It is preferred to use a layer of a same kind of material having a thickness of approximately 40 cm so that the water column height in this layer is relatively large and as a result the water suction tension is high as well. Sand can for instance be used in this layer. After that a top layer 5, comprising pumice, sand and soil having a high organic substance content, of a certain thickness is applied on the sand layer 4. Depending on the country (climate) in question and the specific local field conditions and technical conditions the thickness of the top layer 5 usually lies in the range of 1 5 to 25 cm. In a dry climate the pumice grains lying on top in the top layer 5 will dry faster than the underlying pumice grains. Said underlying pumice grains may ensure that the water shortage in the upper layer of the top layer is supplemented. Such a process can however only occur when the top layer is relatively thick and the pumice in it is homogeneously distributed. Finally grass seed is sown on the top layer 5 in the usual manner as a result of which after a while a grass layer 6 is formed. It is also possible to apply grass sods on the top layer 5. Preferably grass sods are used that have been grown on an under-layer of the same composition as the top layer according to the present invention, or the so- called washed grass sods are used the roots of which have been stripped of soil residues. As a result "stress", which the grass is usually subject to when applying grass sods on the top layer, occurs less frequently. This ensures that the grass plants will penetrate deeply into the underlying top layer 5. Additionally it is preferred that the under-layer on which the grass sods have been grown contains poor soil, i.e. soil poor of nutrients. As a result the grass roots of the grass sods are activated when said sods are applied on the top layer 5 and they will grow, as a result of which an optimal adhering to the under-layer is created. Moreover more nutrients are consumed which can then no longer end up in the ground water. When the terrain 1 consists of sand, the sand is dug off to such a depth (not shown in the drawing) that the top layer 5, having a thickness equal to the depth of the deepened part, can be applied. The pumice used in the top layer of the sports field according to the present invention may be a type of pumice that is extracted in Iceland. The pumice has a dry bulk density in the range of 400 to 900 kg/m 3 . Of the type of pumice having a dry bulk density of 400 to 900 kg/m 3 those having a lower density such as 400 to 600 kg/m 3 , provide the largest drainage capacity. For intensively used and heavily burdened sports fields it is desirable to use a type of pumice having a higher density, such as 600 to 900 kg/m 3 . Each type of pumice having a dry bulk density between 400 and 900 kg/m 3 can be used, such as for instance pumice from Japan, Greece or Madeira (Spain). Because the dry bulk density of the top layer, in which the pumice is incorporated, is relatively low, the top layer does not end up in lower layers but forms a stable plate on top of the sand layer. Because of the high drainage capacity and the high percentage by volume of the pores of the pumice, the top layer can also quickly absorb excess water after abundant rainfall and subsequently discharge it from the top layer. The optimal quantity of pumice in the top layer depends on the type of climate. In a relatively dry climate the quantity of pumice used will be larger because a large quantity of pumice retains a lot of water as a result of which more water is available to the grass layer on the top layer. In a relatively wet climate the quantity of pumice will be lower because, in order to keep the sports field in a condition to be played on and for the prevention of grass root rot, it is important that a lot of water is passed through to the lower layers. The prevention of grass root rot is of importance because the grass can easily get infected by pathogens through the root skin opened as a result of rotting. The quantity of pumice in the top layer of the sports field according to the present invention may be in the range of 25 to 75% by volume and preferably in the range of 50 to 75% by volume, on the basis of the total volume of pumice, sand and soil having a high organic substance content. Preferably pumice of a relatively low grain size is used in the top layer of the sports field according to the present invention. The use of relatively small pumice grains namely has the advantage that over the entire thickness of the top layer the percentage by volume of water is nearly the same. As a result of such a homogeneous distribution and a suitable quantity of pumice, the pumice grains that are present in the lower part of the top layer, pass on water to the pumice grains that are present in the upper part of the top layer, and vice versa, by means of capillary action. The passing on of water however does not occur until the moment the pumice grains contact each other. Because of the homogeneous distribution and the use of a relatively large quantity of pumice contact between the pumice grains is strongly guaranteed. Additionally pumice grains having a grain size below 10 mm, and preferably below 4 mm, have less sharp edges as a result of which they lead to less injuries to the players on the sports field. The grain size of the pumice used in the top layer of the sports field according to the present invention may therefore be in the range smaller than 10 mm. A preferred grain size is in the range of 0.5 to 4 mm. Another preferred grain size, particularly for intensively used and heavily burdened sports fields, is in the range of 0 to 2 mm. The percentage by volume of the pores and solids of the pumice used in the present invention may be in the range of 70 to 90% by volume and 30 to 10% by volume, respectively. At a pressure head of -1 0 cm the pores contain water and air in the range of 40 to 70% by volume and 40 to 5% by volume, respectively, on the basis of the volume of the pumice. The values mentioned here for bulk density, pore volume, water and air contents and organic substance content are determined by means of the analysis methods as described in "Uitgebreid fysisch onderzoek" [Extensive physical research] in conformity with G. Wever and M.H. Pon, Fysische analysemethoden voor potgrond en veen [Physical analysis methods for potting compost and peat], Proefstation voor de Bloemisterij en Glasgroente (PBG), report no. 31 , December 1 990. In order to prevent the drainage capacity from decreasing in the course of time, it is of importance that the structure stability of the top layer is high. During decomposition of a relatively large quantity of organic substances in a certain kind of soil, such as for instance peaty soil, settlement occurs of a top layer which substantially contains such a kind of soil and pumice, i.e. the structure stability is relatively low. As a result the values for the physical properties of the top layer, such as for instance the percentage by volume of air and water as well as the drainage capacity, are less stable. Pumice and sand on the other hand do not contain organic substances as a result of which settlement of the top layer does not occur. Additionally the pumice has an angular and rough surface as a result of which there is a large hook resistance. By mixing the pumice with sand, preferably sand having a grain size of 1 00 to 250 μm, a heterogeneous grain structure is obtained. The stability of the top layer is increased in this way. Because sand does not absorb water it has a positive effect on the drainage capacity of the top layer. The top layer of the sports field according to the present invention, in addition to pumice and sand, also contains a small quantity of soil having a high organic substance content, which ensures that sufficient organic substance is present in the top layer. It is preferred here to use a quantity of soil having a high organic substance content in the range of 10 to 1 5% by volume. The quantity of organic substances in the entire top layer preferably is 6% by weight at the most. As soil having a high organic substance content for instance garden peat can be used, which has an organic substance content of approximately 96% by weight. Other examples are peaty soil, humus, composted bark products, etc. In addition to the organic substances the top layer of the sports field according to the present invention will usually contain relatively small quantities of manure and carbonated lime. Manure is added in such a quantity that the electrical conductivity of the top layer is approximately 1 .5 mS/cm. The electrical conductivity (EC) is a measure for the nutrient content; the higher the electrical conductivity the higher said content. Both artificial manure and organic manure may be used. Carbonated lime is added to buffer the pH of the top layer so that it has a pH-value of approximately 6.0 (measured in a water solution) . Adding carbonated lime is necessary because the pH of the top layer cannot be adjusted with the mineral substances present in it, i.e. the pumice and the sand. Because a small quantity of soil having a high organic substance content is used in the top layer, however, its pH, when necessary, has to be adjusted by adding a carbonated lime. The pH-values and EC-values mentioned here are determined by the analysis method " 1 : 1 14 volume extract" in conformity with C. Sonneveld, J. van den Ende and P. A. van Dijk, Analysis of growing media by means of a 1 : 1 .5 volume extract, Soil Science and Plant Analysis, 5(3), 1 83-202, ln addition to a high drainage capacity and a high structure stability of the top layer it is also of importance that the top layer is capable of buffering sufficient water and nutrients. This is also achieved by adding soil having a high organic substance content. The top layer of the sports field according to the present invention has a limited capacity for buffering water and nutrients because a large quantity of pumice and sand is used in the top layer. Only the pumice grains plus the soil having a high organic substance content in the top layer absorb a limited quantity of water and nutrients. In order to prevent shortages of water and nutrients the sports field needs to be regularly sprinkled and slightly manured. The limited capacity for buffering water and nutrients and the high per- centage by volume of air of the top layer of the sports field according to the present invention results in a relatively fast and intensive rooting of the turf on the top layer. This is caused by the roots growing in the direction of lower layers where a larger quantity of water and nutrients is present. Because of a strong and healthy turf damage through playing of such a turf occurs less quickly and the turf recovers quickly in case of damage through playing. Additionally the chance of grass root diseases is small as a result of the optimal air/water volume ratio. As a result the sports field has a high playing durability and burdens the environment little. As a result of the high playing durability replacement of the turf is less frequently necessary which leads to a considerable lowering of costs. When the top layer is dug off anyway after some time, no high costs for the discharge and processing are involved in such an operation because the top layer according to the invention only consists of natural substances. Additionally the sports field burdens the environment little. Because grass root diseases seldom occur in the turf on the top layer the use of herbicides, that are often expensive and harmful to the environment, is only necessary to a limited extent. Pumice moreover is not harmful to any kind of life in the soil; it is entirely inert and does not retain harmful substances. There are two methods for applying the top layer of the sports field according to the present invention. One method relates to the digging off of the soil on a terrain and mixing it on the site with the other components of the top layer. Another method relates to the digging off of the soil on a terrain after which a top layer, which is prepared beforehand by mixing all components of the top layer, is applied. The method wherein the top layer is prepared on the terrain itself can particularly be used when the dug-off soil contains sand or soil having a high organic substance content of a suitable quality. By using the dug-off soil an economic advantage is realised. The method wherein after digging off the soil a top layer which is prepared beforehand is applied, can particularly be used when it is not wanted to mix the dug-off soil with the above-mentioned pumice. This is for instance the case when the dug-off soil consists of clay or loamy soil. In both of the above-mentioned methods it is of importance that the top layer is homogeneous. This can be achieved by mixing the various com- ponents of the top layer with a mixing device. Additionally in both methods the top layer preferably contains 50 to 75 % by volume of pumice, 35 to 1 5 % by volume of sand and 1 5 to 10 % by volume of garden peat, based on the total quantity of pumice, sand and garden peat. The quality of the sand used has a dry bulk density in the range of 1 250 to 1750 kg/m 3 . The dry bulk density of the top layer is in the range of 600 to 1000 kg/m 3 . The quantities of other components in the top layer are: approximately 1 kg of carbonated lime and approximately 1 .5 kg of manure per m 3 of the top layer. In a preferred embodiment of the present invention the pumice, prior to being incorporated into the top layer, is sifted such that the pumice grains having a grain size of over 4 mm are removed. Subsequently the remainder of the pumice is sifted such that pumice grains having a grain size of under 0.5 mm are removed. The pumice that is left then substantially has a grain size of 0.5 to 4 mm. Said pumice is then treated such, amongst others removal of sludge particles, that it has the following physical properties. After moistening at a pressure head of -3 cm and subsequent drying, the pumice has a dry bulk density of approximately 520 kg/m 3 . The grain size of said pumice is in the range of 0.5 to 4 mm. The percentages by volume of the pores and solids of said pumice are 80% by volume and 20% by volume, respectively, based on the volume of the pumice. Said percentage by volume is measured after moistening the pumice at a pressure head in the range of -3 cm to -100 cm and subsequent drying. The pores of the pumice are filled with water and air. The percentage by volume of water at a pressure head of -10 cm is approximately 50% by volume, based on the volume of the pumice. The percentage by volume of air at a pressure head of -10 cm is approximately 30% by volume, based on the volume of the pumice. The percentages by weight of water and organic substances are 40% by weight and 2% by weight, respectively, based on the weight of the pumice. In another preferred embodiment of the present invention which is preferred for intensively used and heavily burdened sports fields, the pumice, prior to being incorporated into the top layer, is sifted such that pumice grains having a grain size higher than 2 mm are removed. The pumice that is left substantially has a grain size in the range of 0 to 2 mm. Said pumice is then treated such that it has the following physical properties. After moistening at a pressure head of -3 cm and subsequent drying, the pumice has a dry bulk density of 600 to 650 kg/m 3 . The grain size of said pumice is in the range of 0 to 2 mm. The percentages by volume of the pores and solids of said pumice are < 75% by volume and > 25% by volume, respectively, based on the volume of the pumice. Said percentage by volume is measured after moistening the pumice at a pressure head in the range of -3 cm to -100 cm and subsequent drying. The pores of the pumice are filled with water and air. The percentage by volume of water at a pressure head of - 1 0 cm is > 55% by volume, based on the volume of the pumice. The percentage by volume of air at a pressure head of -1 0 cm is < 20% by volume, based on the volume of the pumice. The percentages by weight of water and organic substances can for instance be approximately 40% by weight and 2% by weight, based on the weight of the pumice. Example 1 In a dry climate and on a terrain having a loamy under-layer, the under- layer is dug off to a depth of 45 cm after which a sand layer of 20 cm is applied on the bottom. The dug-off loamy soil is then taken away and the underlying layer of loamy soil may be further dewatered by means of arranging drainage means. A top layer is prepared by homogeneous mixing of 70% by volume of pumice, 1 5% by volume of sand, 1 5% by volume of garden peat, manure and carbonated lime. Subsequently the top layer having a thickness of 25 cm is applied on the sand layer. The sports field with the top layer is regularly sprinkled with water, preferably with large quantities on the less warm moments of the day. Water is used in such a quantity that the top layer is almost entirely saturated. The top layer of the sports field is characterized by a reasonable moisture buffer, a quick water absorption, a high drainage capacity, and a good rooting capability. Example 2 In an average climate with normal precipitation and on a terrain having a sand under-layer, the under-layer is dug off to a depth of 20 cm. On the terrain a top layer is prepared by homogeneous mixing of 65% by volume of pumice, 20% by volume of the dug-off sand, 1 5% by volume of garden peat, manure and carbonated lime. Subsequently the dug-off part is filled with the top layer. The sports field with the top layer only needs to be sprinkled with water during dry spells. The top layer of the sports field is characterized by a limited moisture buffer and good drainage capacity. Example 3 In a humid climate and on a terrain having a clay under-layer, the under- layer is dug off to a depth of 55 cm. Drainage pipes are placed on the bottom of the dug-off part. Subsequently the dug-off part is filled with a sand layer of 40 cm. The dug-off clay soil is then taken away. A top layer is prepared by homogeneous mixing of 50% by volume of pumice, 35% by volume of sand, 1 5% by volume of garden peat, manure and carbonated lime. Subsequently the top layer having a thickness of 1 5 cm is applied on the sand layer. The sports field with the top layer is only sprinkled with water during dry spells. Additionally nutrients are regularly added when they have been flushed away as a result of a large quantity of precipitation. The top layer of the sports field is characterized by a low moisture buffer and high drainage capacity. (octrooi\161939\des PB/NG 4389)

Claims: _ _ Claims 1 . A sports field, consisting of layers of material of a distinguishing kind and/or composition lying on each other, the top layer comprising a mixture of pumice and sand, and the pumice having a dry bulk density of 400 to 900 kg/m 3 . 2. A sports field according to claim 1 , characterized in that the pumice has a dry bulk density of 400 to 600 kg/m 3 . 3. A sports field according to claim 1 , characterized in that the pumice has a dry bulk density of 600 to 900 kg/m 3 . 4. A sports field according to claim 1 , 2 or 3, characterized in that the pumice has a grain size in the range smaller than 1 0 mm. 5. A sports field according to claim 1 or 2, characterized in that the pumice has a grain size in the range of 0.5 to 4 mm. 6. A sports field according to claim 1 or 3, characterized in that the pumice has a grain size in the range of 0 to 2 mm. 7. A sports field according to any one of the preceding claims, characterized in that the top layer further comprises a small quantity of soil having a high organic substance content. 8. A sports field according to claim 7, characterized in that the top layer contains a quantity of pumice in the range of 25 to 75 % by volume, based on the total quantity of pumice, sand and soil having a high organic substance content. 9. A sports field according to claim 8, characterized in that the top layer contains 50 to 75 % by volume of pumice, 35 to 1 5 % by volume of sand and 1 5 to 1 0 % by volume of soil having a high organic substance content. 10. A sports field according to any one of the preceding claims, characterized in that the top layer contains manure and carbonated lime. 1 1 . A method for laying out a sports field according to any one of the preceding claims on a terrain, comprising digging off the subsoil of the terrain to a certain depth, applying a layer of sand on the bottom of the deepened part and applying the top layer on the layer of sand. 1 2. A method for laying out a sports field according to any one of the claims 1 -1 0 on a terrain, the subsoil of the terrain consisting of sand, comprising digging off the subsoil of the terrain to a certain depth and applying the top layer on the bottom of the deepened part. 1 3. A method according to claim 1 1 or 1 2, characterized in that the sand or the soil having a high organic substance content in the top layer originates from the subsoil of the terrain. 14. A method according to claim 1 3, characterized in that the top layer is prepared on the terrain of the sports field. 1 5. A method according to any one of the claims 1 1 -14, characterized in that grass seed is sown on the top layer or sods are laid on the top layer. PCT/NLOO/00454 1 6. A method according to claim 1 5, wherein sods are laid on the top layer, characterized in that the sods have been grown on a layer the composition of which corresponds to the composition of the top layer of the sports field according to any one of the claims 1 -10. 1 7. A method according to claim 1 5, wherein sods are laid on the top layer, characterized in that the sods are washed sods, of which the roots have been stripped of soil residues.

Inventors: DE BAAT MARIUS CORNELIS, DE BAAT, MARIUS, CORNELIS
Applicants: BAAT MARIUS CORNELIS DE, MABA B V, DE BAAT, MARIUS, CORNELIS, MABA B.V.
Application year: 2000
Main classification: E01C13
IPC codes: A01G1, E01C13