GB2212195A

GB2212195A - Cellular stabilization and protective structure

Info

Publication number: GB2212195A
Application number: GB8724282A
Authority: GB
Inventors: Charles Michael Waters
Original assignee: BUKASA Ltd
Current assignee: BUKASA Ltd
Priority date: 1987-10-16
Filing date: 1987-10-16
Publication date: 1989-07-19
Also published as: GB8724282D0

Abstract

A cellular structure for surface stabilization of ground or for protective covering of underlaying material or other items comprises a plurality of discrete substantially similar components (1), the components being arranged in one layer with the top surface of the components (1) being substantially aligned with one another to form an upper surface of the structure, the components being arranged in a close-packed hexagonal manner; the cross-section of the components being such that perforations are defined between the components, the collective arrangement of the components being such that the axes which are defined by their close-packed hexagonal collection passing through the central axis of each component define three discrete sets of parallel axes (2) which intersect one another at the centre points of the components, the components being coupled to one another in the structure such that components along all the axes in at least two of the sets are coupled to one another along said axes the connection between a pair of components being by means of a flexible elongate member (11) passing between the pair of components. <IMAGE>

Description

CELLULAR STABILIZATION AND PROTECTIVE STRUCTURE Field of the Invention The invention relates to a cellular structure for surface stabilization of ground or for protective covering of underlaying material or other items. The invention is applicable with particular advantage to providing a load bearing surface for use as, for example, an access roadway.

There are many areas such as embankments, beaches, coastal ramps, airfields, construction site access ways etc, where the ground surface needs to be stabilized and strengthened to reduce the effects of soil erosion and soil creep and, in some instances, to withstand traffic. Many different systems have been proposed and developed for use in such situations.

When the load bearing capacity of an area needs to be increased for purposes such as roads or runways, typically the work involved is extensive and the costs very high. This is because the materials used to surface such areas can necessitate sophisticated measures to withstand expansion and contraction, and because extensive excavation and foundation preparation is necessary. This is because it is usually impractical to produce the materials used to surface such areas with sufficient capability to withstand and distribute superimposed loads, and extensive excavation and foundational preparation is therefore undertaken to provide a sub structure with the adequate stability. Without such excavation and foundations superimposed loads can cause failure of the surface material which can be very dangerous.Various methods and products have been produced to provide surfaces involving minimal foundational preparation, however, such systems, which are made up of frictionally connected or interlocking blocks, on their own only marginally improve the load bearing capacity of the areas which they cover.

Other systems for stabilizing and paving ground surfaces consist of substantially rectangular discrete blocks which are linked together by cables or ropes. With such systems the interconnecting ropes usually pass through open galleries within the blocks, therefore they do not greatly add to load bearing and distributional capabilities and a rope breakage causes widespread effect. Because the ropes are not bonded within the blocks, the blocks can gather and separate which generally limits any deflective resistance which such systems can provide.

Summary of the Invention According to the invention there is provided a cellular stabilization and protective structure for protecting and/or strengthening an area of ground surface, or other underlaying material or items, the structure comprising a plurality of discrete substantially similar components, the components being arranged in one layer with the top surface of the components being substantially aligned with one another to form an upper surface of the structure, the components being arranged in a close-packed hexagonal manner; the cross-section of the components being such that perforations are defined between the components, the collective arrangement of the components being such that the axes which are defined by their close-packed hexagonal collection passing through the central axis of each component define three discrete sets of parallel axes which intersect one another at the centre points of the components, the components being coupled to one another in the structure such that components along all the axes in at least two of the sets are coupled to one another along said axes, the connection between a pair of components being by means of a flexible elongate member passing between the pair of components.

In this context "close-packed hexagonal" packing is intended to mean as in a plane of hexagonal close packing as in chemical crystallography. In such a plane the components are arranged in three sets of parallel rows with components in alternate rows being aligned with one another and with the components in adjacent rows having their centres off-set such that each component is surrounded by six other components. The term is intended to include cases where the components are in close contact with one another and cases where the components may be separated from one another by uniform spaces, but nevertheless maintain the relationship of each component being surrounded by six others within the body of the structure.

Such a structure in accordance with the invention is extremely efficient for stabilizing a ground surface without extensive foundational preparation since the flexibility between the components, whilst allowing the structure some degree of movement, can be engineered to minimize deflection and thereby widely distribute superimposed loads. A structure in accordance with the invention being cellular can be produced in very large areas without the need for expansion joints and can accommodate reduced levels of sub foundational stability without failure.

The components are preferably impact resistant and conveniently are primarily or wholly of concrete.

More preferably each component consists of a hollow outer mould which is filled by concrete.

The mould may be produced in a permanent material or in a temporary material. In cases where the flexibility of the connection between the components has to be minimized it is important that a gap between the tops of- the components is not allowed to develop and in this case any mould must be permanent. However, there are cases in which it is possible for the mould to be temporary when there is no reason to limit the flexibility of the structure. In this case the moulds can be made up of cardboard which will eventually erode away.

One reason why the moulds are useful is that their use enables the structure to be transported in a prefabricated form that can be filled in-situ with maximum convenience and economy. In this case it is preferred that the moulds have two open ends so that the prefabricated structure can be laid in place on the ground surface and the concrete which is then used to fill the moulds in-situ will take up any irregularities in the ground surface which might cause a gap between the ground and the underside of any of the moulds. This is of especial importance when the structure is to be used as a load bearing surface. Alternatively, the structure can be both prefabricated and concreted in a factory.

In ths case it is preferred that the moulds have only one open end at the top so that the concrete does not fall straight through the moulds when they are being filled.

Another reason for the use of the moulds is that they permit the use of flowing concrete which will set and bond to the contours and to the intersections of the rope network. In such a structure there is no possibility of a "string of beads" effect occurring if one of the components fails or if one of the interconnecting ropes fails.

Preferably the moulds can be produced in a durable material such as a plastic when deflection needs to be minimized, or can be produced in a perishable material such as cardboard when deflection does not need to be minimized and when increased flexibility is advantageous. Since the finished structure is to be perforate it is preferred that the components are either circular or elliptical in cross-section.

The components can be arranged in a regular close-packed hexagonal pattern or an irregular close-packed hexagonal pattern. In the case of an irregular close-packed hexagonal structure the triangles defined between the three sets of parallel axes would be isosceles triangles. In the case of a regular close-packed hexagonal structure the triangles would be equilateral. In the case of an irregular closepacked hexagonal structure in which perforations are advantageous, preferably the components are elliptical in crosssection. In the similar case of a regular close-packed hexagonal structure preferably the components are circular in crosssection.

Although it is possible for the structure to be produced with only the components along two of the parallel sets of axes being coupled together, preferably the components along all three sets of axes are connected together so that each component is connected triaxially to six other components.

This gives a very firm connection, and a very strong structure.

The flexible connection between the components may comprise a link rope or wire which extends along an axis and passes through the components on that axis. If the components are components which include moulds, the moulds each have bores through them to allow the link ropes to pass therethrough.

The concrete is cast about the link ropes to fix them firmly in position.

The components may be of constant cross-section such that they may resemble cylinders. Such a shape is of especial advantage if the structure is to be used as a load bearing surface in which a minimization of deflective capability is required. Such use is, for example, when the structure is to be used as an access roadway. In this case the components are pretensioned together so that each component is in tight contact with six adjacent components where the only spacing between the components is due to the shape of the component to allow growth of vegetation to assist environmental acceptibility and also to help the drainage of the surface. In such a case it is preferred that the link ropes which connect the components are positioned as low as possible in the components since this increases the lever moment between the components to give the best load bearing capacity.

It is also sometimes advantageous for the components to be coupled together with spacers consisting of incompressible but flexible tubing which extends between the components and which allows the components to flex with respect to each other, but does not allow distance between the components to vary. Such an adaptation is not suitable for use as a structure for producing a load bearing surface, but being more flexible can be used to stabilize a surface such as an embankment or to protect material or items of irregular surface contour.

The components can also have tapered or stepped side walls being interconnected by the rope network at a mid zone of the component's height which provides the maximum cross section of the component. Such shaped components allow flexing about the flexible connection between the components which is limited to either convex or concave capability.

This can provide controlled bending of the structure where it is required.

As has been mentioned before, it is advantageous to provide perforations between the components in the structure to allow growth of vegetation. Such perforations can also help the drainage of the surface. Clearly, whilst the moulds of the structure are being filled with concrete it is important that these perforations are not filled with concrete. This can be effected in one of two ways. The first method is to provide an insert which fits in the perforation between the moulds to block the perforation. Once the moulds have been filled the insert is removed. Such an insert can be re-usable.

An alternative method of filling the moulds is to provide a collar which fits into the top of each mould and then to provide a perforated sheet of polythene which is a tight fit around each collar of each mould. The polythene sheet is fitted into place over each collar and the moulds are then filled through the holes in the polythene. The polythene prevents any concrete entering the perforations between the moulds. After completion the polythene can be removed together with the collars, or the collars can be left in place.

Descriptions of the Drawings An example of a structure in accordance with the invention will now be described, together with some modifications of the structure with reference to the accompanying drawings, in which: Figure 1 is a perspective schematic view of a first example of a structure; Figure 2 is a schematic perspective view of a second example of a structure; Figure 3 is a plan view of the axes of connection between components within the first and second structures; Figure 4 is a plan view of the axes of connection within a third structure; Figure 5 is a plan view showing the position of the mould in the first structure; Figure 6 is a plan view showing the position of the mould in the third structure; Figures 7, 8 (A and B), and 9 (A and B) are perspective views of modifications of components for the structures;; Figures 10 (A and B) show alternative cross-sections through moulds for components for a structure; Figure 11 is a plan view of unfilled moulds of the first structure; Figure 12 is a perspective view of an unfilled mould of the first structure shown in Figures 1 and 11; Figure 13 is a schematic view of a method of anchoring a prefabricated structure to the ground prior to in-situ filling with concrete; Figure 14 is a longitudinal cross-section of the structure in place on a ground surface; Figure 15 is a schematic view of an insert for use in filling the components of the fourth blanket; Figure 16 is a schematic view of the structure when its installation is complete and vegetatidn is growing in the perforations;; Figure 17 is a schematic section through the structure in the form intended to minimize deflective capability showing the mechanical principle of restrained leverage which is involved; and, Figure 18 is a schematic section through a fourth structure.

Description of the Preferred Embodiments A first example of a structure in accordance with the invention will be described in detail with reference to Figures 11 to 17 of the drawings. However, variations of modifications of the structure will be described schematically with reference to Figures 1 to 10 and 18 of the drawings.

Each of the structures described is a perforate structure consisting of a plurality of discrete substantially similar components 1. In most cases the components will be identical.

The components are arranged in one layer with the tops of the components being substantially aligned to form an upper surface of the structure. In the case as shown in Figure 1 where the components are close together the upper surface is substantially planar. As can be seen clearly in Figures 1, 5 and 6, the components are arranged in a close packed hexagonal manner. The close-packed hexagonal arrange ment is such that the components are arranged in a plurality of rows 2 of components. Alternate pairs of rows are arranged such that the components 1 are aligned. This can be seen in Figures 5 and 6 where the components in alternate rows 3 and 4 are aligned and the components in alternate rows 5 and 6 are similarly aligned. The components in adjacent rows are off-set such that any component of one row always lies off-set between two components of any adjacent row.

The axes defined along each row of components pass through the central axes 7 of each component defining three discrete sets of parallel axes.

As shown in Figure 5 axes 8 are all parallel to one another - axes 9 are all parallel to one another - axes 10 are all parallel to one another. Any axis in one set is non-parallel to any axis in one other of the sets.

The components are coupled to other components in the structure such that components along all the axes in at least two of the sets are coupled to one another, the connection between components being via flexible elongate members 11 which pass through the components.

In all the structures specifically described herein the components along all the axes in each of the three sets are coupled to one another so that each component is coupled to each of its adjacent components.

The close-packed hexagonal arrangement of the structure can be regular as shown in Figures 3 and 5, or irregular as shown in Figures 4 and 6. In regular close-packed hexagonal structures the triangles 13 formed between the three axes 8, 9 and 10 are equilateral. In such a structure the components are conveniently circular in cross-section.

In irregular close-packed hexagonal structures the triangles 14 formed between axes 8, 9 and 10 are isosceles triangles and here conveniently the components are elliptical in cross section.

The close packed hexagonal arrangement can be as shown in Figure 1 in which each component is in contact with its adjacent components or can be as shown in Figure 2 where the components have a spacing between them. In Figure 2 the spacers 12 between each pair of components may be flexible and in the form of a plastics material similar to that used for making hose pipe. This material is flexible but incompressible which means that the distance between any pair of adjacent components is set and substantially maintained at constant dimension.Alternatively the spacers 12 may be produced in a temporary material such as cardboard, which will set the initial spacings between components but will ultimately perish to allow the components to gather to the degree of the flexibility of the free rope that interconnects the components as well as allowing the components to flex relative to one another. It may also be advantageous in certain applications for the spacers 12 to be produced in a rigid durable material. The length of the spacers 12 can be between one and two and a half inches long. Clearly such a structure will not form a deflection resistant surface and therefore can only be used in situations where stabilization of the ground surface or protection of irregularly shaped materials or items is required without providing a load bearing structure.

The first, second and third structures described in Figures 1 to 6 are all structures in which the components are concert in cross-section and are circular or elliptical cylinders.

However, as shown in Figures 7 to 9, modifications of the structure allow for different shapes of companents. The components may be shaped such that they each have a maximum cross-section at a waist zone 15 and taper from that waist zone to both ends 16. In this way if the components are connected closely together the components may bend with respect to one another by virtue of the taper 17 and the flexible bond provided by the flexible elongate connecting members. In Figure 9 there is shown a modification of this where the component tapers from the waist zone 15 to one end only. In this way components can be connected together so that flexibility remains multi-directional but is limited to convex or concave capability depending on whether the tapers are arranged towards the lower or towards the upper surfaces of the structure respectively.

Figure 8 shows another form of component in which its outer surface is shaped like two ajoined cylinders with different diameters. This component facilitates similar flexible capabilities to those shown in Figures 9 (A and B) and described above.

The components described are preferably components consisting of a mould 18 to be filled with a settable composition which is conveniently concrete. The mould 18 has an open top 19 through which the mould is filled. It can involve either of the configurations shown in Figure 10 so that it can be open at its lower end as shown in Figure l0A, or closed at its lower end as shown in Figure 10B. The moulds as shown in Figure 10B are primarily for use in situations where the structure is both prefabricated and concreted in a factory environment where the structures are advantageously delivered as completed units. However, in many cases it is preferred that prefabricated structures are delivered empty and the structures are put in place and connected together before the concrete is placed within the moulds 18.In this case it is preferred that the moulds have the configuration as shown in Figure 10A, because then if there are any irregularities in the ground surface any gaps beneath the bottom of the moulds 18 will be filled by concrete to give a steady surface. Structures can also be made having tapered thicknesses by arranging components of different heights adjacent to one another to vary the thickness of the structures. The moulds can be injection or blow moulded, or manufactured as extruded tubing which may be cut into equal or variable lengths as required.

Structures in accordance with the invention may advantageously be prefabricated into units of transportable dimensions and delivered and interconnected together on prepared ground.

Pins 20 are hooked over selected moulds and are driven into the ground beneath the structure to provide anchor points as shown in Figure 14.

The perforations 21 between adjacent components may be filled by temporary inserts 22, or covered by polythene or other sheeting positioned prior to the concrete being added. The concrete is inserted into the hollow moulds, thus anchoring the link ropes into position and filling any voids 23 beneath the structure caused by unevenness of the ground surface. The inserts or sheeting may then be removed and the gaps filled with soil to promote growth of grass as shown in Figure 16. This also helps drainage of the surface. Figure 17 shows the mechanical effect of stress on the completed structure when impacted. The tension between the components reacts and limits the blanket deflection six ways for each component. The gap 24 between the components is shown exaggerated in order to illustrate the principle.

Circular or elliptical components produce an environmentally attractive texture which is softened and camouflaged by the presence of vegetation growing in the perforations between adjacent components.

The finished surface has sufficient rigidity to dissipate operational impact of traffic which makes the surface ideal for a runway, or for an access roadway or ramp. This rigidity is provided without requiring extensive and expensive subsoil excavation and foundation preparatidn. The rope network gives sufficient flexibility to eliminate expansion, contractional or sheer failure, and the stepped surface irregularity that would normally resuIt in non-cellular surfacing materials.

During general movement caused by swelling or shrinkage of the subsoil structural failure will be eliminated because of the flexibility inherent in the cellular structure. However, the finished product will have sufficient tensile strength and elasticity to absorb the stress of traffic forces.

In applications where the structure will be subjected to very high superimposed loads or the subsoil has very low bearing capacity and/or it is necessary to maximize the structural integrity of the structure as a load bearing element, it would be advantageous to maximize the strength and closeness of contact of the point of the lever moment 25 between the upper surfaces of adjacent components and to maximize the tensile strength and stability of the interconnecting tie ropes between the lower surfaces. This is shown schematically in Figure 18 of the drawings.

Convex contours in the prepared sub foundation would tend to produce disadvantageous gaps at the lever moments which would negate the mechanical objective of the structure and concave contours would concentrate the lever moment too intensely onto the extreme top of the components which could fracture under compression and negate the mechanical advantage.

To counteract these problems the components could advantageously be produced with a very slightly tapered or stepped reduction in cross-sectional area 26, reducing from the point of the lever moment down to the lower end of each component.

This would enable the structure to conform to mild convex contours without reducing the essential tight contact between components at the lever moments.

In order to strengthen the points of contact forming the lever moments, very slight tapers 27 could advantageously be produced at the top of each component. Tie ropes of high tensile strength and low elongational characteristics could advantageously be used and could advantageously be stainless steel ropes.

These provisions would result in a prefabricated structure which when pretensioned would tend to adopt a slightly convex upper surface. This would assist in the production of a very regular surface to the completed structure which in its prefabricated form would have bedded tightly down onto any high spots in the prepared sub foundation and which would have bridged across any local low spots until the concrete fill had absorbed the irregularities.

There are some occasions in which it is advantageous to reduce the size of the perforations between the components of the structure. In this case the shape of the components can be chosen such that a minimal gap is produced between them.

Claims

1. A cellular stabilization and protective structure for protecting and/or strengthening an area of ground surface, or other underlaying material or items, the structure comprising a plurality of discrete substantially similar components, the components being arranged in one layer with the top surface of the components being substantially aligned with one another to form an upper surface of the structure, the components being arranged in a close-packed hexagonal manner; the crosssection of the components being such that perforations are defined between the components, the collective arrangement of the components being such that the axes which are defined by their close-packed hexagonal collection passing through the central axis of each component define three discrete sets of parallel axes which intersect one another at the centre points of the components, the components being coupled to one another in the structure such that components along all the axes in at least two of the sets are coupled to one another along said axes, the connection between a pair of components being by means of a flexible elongate member passing between the pair of components.

2. A structure according to Claim 1, in which the components are impact resistant and primarily or wholly of concrete.

3. A structure according to Claim 1, in which each cpm ponent consists of a hollow outer mould which is filled by concrete.

4. A structure according to Claim 3, in which each mould is formed from a temporary material which will erode away such as cardboard.

5. A structure according to Claim 3, wherein each mould is made from a durable material such as plastic.

6. A structure according to Claims 3, 4 or 5, in which the moulds have two open ends.

7. A structure according to any one of the preceding Claims, in which the components are either circular or elliptical in cross-section.

8. A structure according to any one of the preceding Claims, in which the components are coupled together with spacers consisting of incompressible but flexible tubing which extends between the components and which allows the components to flex with respect to each other, but does not allow distance between the components to vary.

9. A structure according to any one of the preceding Claims, in which the components are of constant cross-section.

10. A structure according to any one of the Claims 1 to 8, in which the components have tapered or stepped side walls being interconnected by the rope network at a mid zone of the component's height which provides the maximum crosssection of the component.

11. A method of forming a cellular stabilization and protective structure for protecting and/or strengthening an area of ground surface, or other underlaying material or items, comprising providing a plurality of discrete substantially similar moulds, and arranging the moulds in one layer with an open surface of the moulds being substantially aligned with one another to form an upper surface of the structure, the moulds being arranged in a close-packed hexagonal manner; the crosssection of the moulds being such that perforations are defined between the moulds, the collective arrangement of the moulds being such that the axes which are defined by their closepacked hexagonal collection passing through the central axis of each mould define three discrete sets of parallel axes which intersect one another at the centre points of the moulds, the moulds being coupled to one another in the structure such that moulds along all the axes in at least two of the sets are coupled to one another along said axes, the connection between a pair of moulds being by means of a flexible elongate member passing between the pair of moulds, covering the perforations and then filling the moulds with concrete.

12. A method according to Claim 11, in which an insert is provided which fits in the perforations between the moulds to block the perforation and once the moulds have been filled the insert is removed.

13. A method according to Claim 11, in which the method of filling the moulds comprises providing a collar which fits into the top of each mould and then providing a perforated sheet of polythene which is a tight fit around each collar of each mould, fitting the polythene sheet into place over each collar and then filling the moulds through the holes in the polythene and after completion removing the polythene together with the collars.

14. A cellular stabilization and protective structure arranged substantially as described herein, with reference to, and as illustrated in Figures 1, 3, 5, 11 and 12 of the accompanying drawings.

15. A cellular stabilization and protective structure arranged substantially as described herein, with reference to, and as illustrated in Figure 1, when adapted in accordance with Figure 2 of the accompanying drawings.

16. A cellular stabilization and protective structure arranged substantially as described herein, with reference to, and as illustrated in Figure 1, when adapted in accordance with Figures 4 and 6 of the accompanying drawings.

17. A cellular stabilization and protective structure arranged substantially as described herein, with reference to, and as illustrated in Figure 1, when adapted in accordance with Figures 15 and 18 of the accompanying drawings.

18. A cellular stabilization and protective structure arranged substantially as described herein, with reference to, and as illustrated in Figure 1, when adapted in accordance with Figures 7, 8 or 9 of the accompanying drawings.