CA1248802A

CA1248802A - Paving stones

Info

Publication number: CA1248802A
Application number: CA000458478A
Authority: CA
Inventors: Paul E. Loewrigkeit
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-07-09
Filing date: 1984-07-09
Publication date: 1989-01-17

Abstract

PAVING STONE

ABSTRACT
A paving stone is disclosed of the kind having open slots whereby grass can grow through the stone. Such stones are used for unobtrusive or landscaped hard-standing for vehicles. The disclosed stone has V-shaped ridges on the longitudinal walls of the slots. The ridges act to key the stone to the bar of turf that grows in the slot. The disclosed stone also has curved side edges, complementarily convex and concave; this feature lends greater stability in that the stones are interlocked with each other.

Description

BACKGROUND TO THE INVENT_ON
This invention is in the field of paving stones, particularly paving-stones of the kind that have through-slots.
The slots permit grass to grow through the stone for the purpose of blending the stones into the landscape. The slotted stones are used to provide hard-standing for vehicles, in car-parks and driveways for example, or to provide unobtrusive emergency access for vehicles across a grassed area, or to stabilize a grassed area on a slope such as an embankment or cutting.

PRIOR A~T
A stone of the above kind is described in USA Patent No. 4~052,131, issued 04 October 1977 to LOEWRIGKEIT.
Some aspects to be borne in mind when designing the stone ~or easy casting in concrete are these. The ribs of concrete between the slots, and the beams of concrete connecting the ends of the ribs, are preferably all of the same section, so that the concrete sets evenly. From the point of view of the strength of the stone in use, the ribs should not be long or khey might crack.
From the point of view of promoting a good healthy growth of grass, the slots between the ribs should be wide.
Also, the ribs and beams should be tapered in such a manner that the slots are wider below ground level than at the 27 surface. This provides room for the roots to spread.
Soil per se has little sheer strength. However soil with grass roots in it (i.e. turf) does have some tensile :

strength, a~d certainly some sheer strength. The bars of turf in the intercostal slots, once they become established, can therefore make an appreciable contribution to the stability of the stone against forces tending to displace the stone longitudinally, i.e., in the direction of the slots, or laterally, i.e., at right angles to the slots.
The tapered shape of the ribs and beams means that the bars of turf in the slots, and between the stones, have a good broad base.
ln However, the soil at the base of the bar does not contain such a thick profusion of root fibres as the turf at the top of the bar. The invention provides a means whereby the turf of high tensile strength at the top of the bar can be made to contribute to the overall rigidity and stability of an area paved with slotted stones. This is especially useful in paved areas which are subject to high sideways forces, such as when the stones are laid on the side of a banking. It is also useful in areas that are prone to being flooded or washed, since very wet soil has no strength whatsoever. Neither has very dry soil, and again the invention is useful to enhance the stability of an area that likely become dried out.

BRIEF DESCRIPTION OF THE INVENTION
In the invention, the ribs are provided with ridges arranged to protrude into the areas of the intercostal slots.
27 The ridges are such as to engage mechanically with the strongly-rooted turf in the slot. Now~ the bar of turf is very much more resistant to slipping along the length of the '' .~. .

slot. The resistance to longitudinal slipping of the stone is therefore much enhanced. The gradually diminishing tensile strength of the turf as the soil gets deeper is now of little consequence beca~se the ~hole of t~e bar can contribute.
Preferably, the ridge should extend right to the top of the slot. Moreover, the ridge should be small and thin:
small, in the sense of not protruding far into the slot; and tllin, in the sense of having little width in the direction of the slot. Such ridges interfere hardly at all with the size of the opening of the slot, and it is important that the slot should provide a large soil area to promote a vigorous growth. Slots which are very narrow, or narrowly necked along their length, do not promote the healthiest growth.
Besides, the slots should not have any intricacy of shape but should be straight~sided and parallel so that the ribs (and beams) can all have the same section. The ridges in the invention are small and thin enough to make substantially no difference either to the castability of the stone, nor to the size of the intercostal bar of turf.
The mechanical engagement, or meshing, of the turf bar with the ridges is provided for the purpose of restraining the turf bar against movement along the slot. The ridge should be so shaped as to fulfill this purpose, which means that the ridge should provide a surface which is directed against such movement. A ridge may be V-shaped for 27 easy castability. As mentioned, the ridge should have a surface that is at a substantial angle to the side-wall of the slot. A V with an included angle of less than 90 degrees :

serves very satisfactorily.
The invention includes another aspect1 which is concerned with the problem of lnterlocking 'che stones together. The manner of interlocking preferably should be such that the stability of each stone is enhanced by the other stones around it. In the invention, the stability may be enhanced not only by making use of whatever tensile strength the rooted turf possesses, but also by providing the stones with a curved outline.
The outline is such that opposite edges of the stone are complementarily curved, one convex, and the other concave.
Providing the stones are tightly packed together the interengaging curved edges ensure that no stone can slip sideways relative to its neighbours.
The stones could be arranged to engage each other over the whole length of the edge, but preferably the edges are provided with narrow shoulders: the gap created between the stones in this case can be filled with soil, and grass may grow in the soil.
The extra stability provided by the curved edges again is useful particularly when the stones are on the sides of a banking, or when the area is prone to being inundated.
Another advantage of the curved edges is this.
First, the stones are normally laid so that a vehicle in driving over the stones passes in the direction of the slots.
27 Passing across the slots produces an obtrusive fluttering of the vehicle's wheels. The second point is that it is important that the stone be reasonably short in the direction ` ~e~ ~88~
in which the vehicle pas s, since any slight unevenness of the foundation under the stone could produce rocking of the stone. The resultant bending stresses might crack the stone:
the shorter the stone, the less likely this is to happen.
The ribs are therefore short. The beams on the other hand may be long enough to accommodate three or four slots. Hence there can be a problem of the vehicle vibrating uncomfortably as a wheel passes alternately on and off the edges of the beams. Having the beams of a curved outline means that a wheel passes on and off the edge of the beam not suddenly but progressively, which reduces the jolts.
The stone might have a generally rectangular shape, notwithstanding the curved edges. Preferably, however~ the curved edges give the stone the shape of a parallelogram, which smoothes out the jolts even more.

DETAILED DESC~IP~ION OF PREFERR~D EMBODIMENT
In the drawings:
Figure 1 is a view of a paving stone;

Figure 2 is a section on line 2-2 of Figure 1, Figure 3 is a plan of a layout of stones.
The stone 10 shown in the figures is parallelogram-shaped. It includes a front beam 11, a back beam 12, and five ribs 13-17. The ribs define four slots 19, 20, 21, 22.
The walls of the slots are provided with V-shaped ridges 23, which protrude into the slots. The included angle 27 of the V is acute. The ridge 23 runs straight down from the top surface 24 of the stone to the bottom surface 25. The ridge 23 is of a constant section throughout its length.

In the invention, the shape of the ridge need not be as in the embodiment. The ridge could be rounded, or rectangular. It could protrude further at the top than at the bottom. It should not protrude so far, though, that the ridge would substantially interfere with the shape of the bar of turf in the slot~ since that could weaken the bar of turf, and render the bar less able to contribute to the stability of the stone.
The ridge 23, in addition to not protruding very far into the slot, is also thin. The ridge 23 is thin so as, again, not to interfere with the shape of the bar of turf.
It may be thought that the ridge is thin because its performance as a tooth is thereby enhanced: it may be thought that it is the action of the ridge in digging into the turf that causes it to grip the bar of turf. The ridges should be regarded however more as gear-teeth that mesh with complementary indentations in the turf.
The ridge does not need to be thick for strength purposes. The shear and tensile strength of turf is very much greater than tha~ of plain soil, and) as explained above, it is the aim of the invention to take advantage of that strength, but still the strength of turf is of course very much less than the strength of concrete. The ridges can easily support any force that might be transmitted to them through the bar of turf. The ridges are thin so as not to interfere with the general width of the slot, and hence of the bar of turf that will eventually fill the slot. Turf 27 will not grow strongly in a narrow confined space.
The stone is made as a unitary casting in concrete.
A wire framework is provided, embedded in the ribs and beams, ' to give the stone strength. The stone is provided with a draft taper on all its vertical walls, so that the stone may be easily removed from the mould.
The tapered shape also has another purpose. As may be seen in Figure 2, the bar of turf in a slot is thicker at the bottom The bar is also weaker at the bottom, since turf is at its strongest (as regards its resistance to tensile and shear stresses) at, or just below, ground level. The stone is normally laid on a foundation of cr~shed rocks, but the bars of turf should not be regarded as totally isolated from each other. There is a network of grass roots that passes underneath each rib, so that each bar of turf is connected to its neighbours. The soil itself does have some shear strength: in the absence of the ridges of the invention, much of the stability of the stone was provided by the shear strength, such as it is, of the soil at the bottom of the slots. The greater the taper, the thicker and stronger and more rigid is the bar of turf/soil at the bottom of the slot, in the plane about which the soil would have to shear if the 2Q stone were to slip sideways.
The front 26, back 27, right 29, and left 30 side edges of the stone are, in accordance with the invention, curved.
Figure 3 shows how the stones are arranged when packed tightly together. The stones would normally be arranged so that a vehicle drives over them in the direction 27 of the arrow 32? i.e., longitudinally relative to the slots.
The front and back edges 26,27 of the stone are inclined to this direction to ease the vehicles' wheels .

~%~
smoothly and progressively from stone to stone. The fact that the edges 26,27 are curved also assists in this aspect.
The curve also means that each stone is interlocked with its neighbours against slipping sideways. The curves have to be complementary to acheive this! i.e., a convex curve must engage a concave curve.
The concave curved edges 26, 30 are cut away so as to leave shoulders 33. The resulting spaces 34 become ~ occupied with further bars of turf.

-:

Claims

1. Paving stone with through-slots, where the slots have walls which define the shape of the slot, and the shape is long and narrow;
where the long side walls of the slots are provided with ridges;
and the ridges protrude from the side walls into the slots.

2. Stone of claim 1, where the ridges are small and thin.

3. Stone of claim 2, where the ridges are V-shaped.

4. Stone of claim 3, where the included angle of the V
is acute.

5. Stone of claim 1 where a ridge has the same cross section all down the wall.

6. Stone of claim 1, where the stone comprises parallel ribs joined at their ends by beams, and where the slots are the spaces between the ribs.

7. Stone of claim 6, where the ribs and the beams are all of the same, uniform cross-section.

8. Stone of claim 7, where the cross section is tapered, being narrower at the bottom of the ribs and beams.

9. Paving stone of claim 1 having a generally four-sided outline, where two opposite edges are longitudinally curved complementarily, one edge having a longitudinal convex curve, the other having a longitudinal concave curve.

10. Stone of claim 9 where the other two opposite edges are curved complementarily in a similar manner.

11. Stone of claim 10 where the stone has a generally parallelogram shapes, in that opposite edges are of equal length.

12. Stone of claim 11 where only one of a pair of opposite edges is provided with shoulders along that edge.

13. Stone of claim 12 where only one each of both pairs of opposite edges are provided with shoulders along those edges.

14. Stone of claim 13 where the shoulders are in the edges with the concave curves.

15. Stone of claim 1, having a generally four-sided outline, where the opposite edges are curved complementarily, one edge having a convex curve, the other having a concave curve.