These have included covers for cricket squares, tennis courts and football pitches. However, in many cases, the ground covers are somewhat cumbersome and easily fall into a state of disrepair. In addition, ground covers presently available tend to be relatively expensive, especially since many require permanent foundations. Other covers require a large underground trench, preferably with an artificial grass cover, to store the ground cover when it is not in use. In addition, permanent anchor points for securing the erected cover to the ground are often required. Other forms of ground cover presently available are simple plastic sheets laid on the ground and rolled up to one side of the ground to be protected when not in use. These have the disadvantage that they do not throw rainwater clear, and they also cannot be used for extensive periods since they are likely to cause grass disease.

The present invention attempts to overcome these problems since it does not require extensive permanent

securing means, can be easily stored, is relatively inexpensive and, in certain of its arrangements, is less likely to cause grass disease when in use.

According to the present invention, there is provided a ground cover comprising: a main sheet; and means for creating a sub-atmospheric pressure beneath the sheet.

Preferably, the sheet is hollow and divided into zones, and there is also provided means for creating a super-atmospheric pressure in the hollow zones within the shee .

The majority of the ground cover can be formed of a robust plastics material, but other robust materials could also be used.

The ground cover can have any desired shape, but conveniently is rectangular, for example square.

The main sheet is preferably in the form of a plurality of zones or compartments in the form of inflated tubes joined to each other. A positive pressure is maintained in these tubes whilst the ground cover is in use, for example by means of an attached fan pumping air into the tubes. Each tube may be joined to an adjacent tube by seams which may act as gutters on the outside of the sheet for rainwater, or the like. Preferably, the tubes taper and become smaller in height from one end to the other such that rainwater may travel along the seams which- act as gutters from the larger end to the smaller

end of the tubes to a collection point, from where it may be pumped away from the surface to be protected.

The tubes may be in any position relative to each other but are preferably parallel. The walls between the tubes may be solid, in which case each is inflated by passage of air around the perimeter of the cover into each tube separately, or may, for example, comprise netting thus allowing passage of air between the walls of adjacent tubes. If the walls between the tubes are solid, passage of air may be allowed into either end or both ends of the tubes.

Underneath the ground cover there is provided a reduced air pressure, which draws the cover downwardly towards the ground, thus opposing wind forces which may tend to lift' the cover due to the "vacuum effect" induced by the movement of the wind at speed over the upper surface of the cover, and also due to the wind getting under the edge of the cover and then lifting it.

In preferred embodiments of the cover of the present invention, the likelihood of grass disease is reduced due to the passage of air under the region of the seams between adjacent tubes making up the ground cover. In particularly windy conditions the fan speed can be adjusted to increase the sub-atmospheric pressure beneath the ground cover and therefore to increase the downward force. The fan speeds may also be adjusted in order to ease the movement of the cover from one part of a surface to be protected to another part of that surface.

The air pumped into the tubes may be warm in order to protect the ground from the cold due to frosty or snowy conditions, and to melt snow for removal. The introduction of warm air may enhance growing conditions under the cover, which could preferably be further improved by the secondary infiltration of warm air through perforations in any or all of the tubes, preferably only the outermost tubes, or similar means, to the underside of the cover which is at sub-atmospheric pressure. In addition, a simple guy rope and peg system may be provided as emergency backup in the event of power failure.

Although a wide variety of shapes and sizes of cover can be manufactured and used, very large areas may be protected by joining two or more ground covers to each other in order achieve the desired degree of protection. By way of example, the typical size of a single cover may be 22m x 44m and is suitable for covering, for example, the main area of wear on football pitches, that is the penalty area or centre circle.

Preferably, the super-atmospheric pressure for the inflation of the tubes is of the order of 1500 Pa gauge, and the sub-atmospheric pressure used beneath the ground cover is of the order of -356 Pa gauge. When not in use, the ground cover is deflated and, for convenience, a trailer can be provided, which can support the fan unit and the deflated cover for easy storage.

For a better understanding of the present invention, and to show how the same may be carried into effect, a preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a plan view of the cover; Figures 2 and 5 are respectively side views in the directions of the arrows Il-ll and V-V in Figure 1; and Figures 3, 4, 6 and 7 are respectively cross- sections taken along the lines Ill-Ill, IV-IV, VI-VI and VII-VII in Figure 1.

Referring firstly to Figure l, the cover 1 includes a plurality of tubes 2 joined together along seams 3 and having open ends 6 and partially closed ends

7, the ends 7 having end walls which are perforated and are formed of netting, for example. In use, air is pumped into the cover 1 through an inflation inlet 4 and then passes around a peripheral distributing tube 5 of the cover entering the tubes 2 at both their partially closed ends 7 and their open ends 6. The air is pumped into the cover 1 until the desired degree of inflation is achieved.

In the embodiment shown in Figure l, the ends 6 of the tubes 2 are greater in height than the ends 7 of the tubes 2, and, as a result, there is a slope from the ends 6 to the ends 7 down which rainwater or the like may fall. There may additionally be a gutter in the vicinity of the ends 7 of the tubes 2 which collects the rainwater

and from which the water can be pumped away.

A sub-atmospheric pressure is achieved beneath the cover 1 by extracting air through an outlet 8. The resulting reduced air pressure draws the cover 1 onto the ground, thus opposing wind forces which may lift the cover due to the "vacuum effect" induced by the movement of the wind at speed over the upper surface of the cover, and also due to the wind getting under the edge of the cover and then lifting it. The presence of the seams 3, as well as the provision of inflatable projections 10 (see Figure 6) on the bottoms of the tubes 2, means that the area of the underside of the cover in contact with the ground is relatively small, and this, in combination with the passage of air under the cover, reduces the likelihood of significant grass disease.

As may be seen in the view of the cover taken at the inlet/outlet end shown in Figure 2, as well as in the side view of Figure 5, the distributing tube 5 is itself provided with an inflatable lower rib 11 extending about the periphery.

The cross-sectional view in Figure 6 shows the slope of the tubes 2 from the larger ends 6 of the tubes to the smaller ends 7 of the tubes, whereas the cross- sectional view in Figure 7 shows the joining walls 9 at the seams 3 between the tubes 2.

Referring now to Figure 4 , the cross-sectional view at the larger ends 6 of the tubes 2 is shown in which the seams 3 are formed by the joining walls 9 between the

tubes. The walls 9 may be solid, in which case the tubes 2 are inflated by passage of air into one or both ends of the tubes, or may comprise netting thus allowing passage of air between adjacent tubes. Referring now to Figure 3, the cross-sectional view at the smaller ends 7 of the tubes 2 is shown. In this embodiment, the area of contact between adjacent tubes is small at the ends 7. Thus, the area of contact between adjacent tubes tapers from a maximum at the larger ends 6 of the tubes to a minimum at the smaller ends 7 of the tubes.