GB2167795A - Flexible revetment panel - Google Patents

Abstract

The panel comprises a plurality of earth-armouring units (1) each constructed as a hollow generally tubular open ended cell and interconnected to provide said panel by a two-dimensional mesh or grid of cables (4,5) or flexibly joined links (Figs. 10-12). The hollow cells (1) are so arranged in said panel that the longitudinal tubular axes (2) of adjacent cells are mutually at right angles, with at least some said axes (2) lying parallel to the armoured earth surface. When water flows over the panel it is free to enter into each cell cavity and thereafter will lose energy therein, water borne material (6) being deposited therein. The length of the cells (1) may be equal to their internal diameter as shown, or less than their internal diameter, in which case the cells (1) overlap (Figs. 5-7). The said interconnecting mesh of cables or joined links may pass diagonally between adjacent cells (Fig. 12) or through holes (6) or openings (3) in the cell walls. The panel may rest on a geotextile mat (7). <IMAGE>

Description

SPECIFICATION Improvements in or relating to a method of, and flexible structures for, erosion control This invention relates to a method of, and flexible interconnected structures for, protecting earth or ground surfaces against wave or current attack and is particularly concerned with providing structures having improved wave-energy dissipating properties, a superior rapid release of porepressures, and a variable degree of flexibility.

Such earth-protecting or erosion-control structures are commonly referred to as Revetments, and are used in many and varied applications. For example they can be used to protect shorelines or coasts against sea-wave attack, or to prevent the erosion of canal or river banks against ship-induced waves or turbulence, or to armour off-shore islands or breakwaters.

Many methods at present in use for the revetting of embankments or shore-lines require the manual placing together of separate blocks or armour units either in random contact or in an ordered close juxtaposition; said separate blocks or units being either quarried rock boulders or a variety of preformed units manufactured from castable materials. All such separately placed units have indeterminate degrees of mutual interlock and their anticipated combined stability, as an engineered structure, is largely determined by their individual masses and chance contact.

Alternatively Revetments may be constructed from rock-filled gabions; or from pre-cast slabs or blocks, inter-keyed in the direction of at least one principal structural plane, whose stability or resistance to hydraulic attack may thereby be improved by said keying. However no pre-cast slabs or blocks, comprising a Flexible Revetment Structure can be inter-keyed in all three principal structural planes, and in revetments formed from keyed units there will remain one principal structural plane in which an unrestricted movement of adjacent blocks or units is possible.

To overcome this possibility rectangular-shaped slabs or blocks, comprising a Revetment, may be flexibly retained in mutual side-by-side proximity by a two-dimensional interconnecting mesh of cables or the like, which said mesh may contribute to a three-dimensional stability of the structure. However, due to the proximity of the slabs or blocks any interconnection of cables, and the controlled removal of slackness to achieve a structural effectiveness of the mesh are time-consuming and imprecise operations; as are any subsequent necessary mesh adjustments or component replacements during the life of the structure: Such operations being especially difficult when carried out below water level.

Revetment structures comprising single layer slabs or blocks being rectangular in shape and lying in close juxtaposition possess relatively poor wave-energy dissipating properties; and such structures must necessarily be extensive in directions which lie normal to anticipated wave attacks if the run-up of such attacks are to the absorbed without overtopping.

Moreover a rapid evacuation of high pore-pressures within a protected earth mass which may be generated during the run-up phase of a wave is much impeded during the subsequent drawdown phase by the considerable impervious base areas of the adjoining slabs or blocks; and this at the moment when the said slabs or blocks are themselves in a variable and indeterminate hydrodynamic situation.

It is one object of the present invention to provide an improved method of providing a flexible and orthogonally, or two-dimensionally, integrated revetment structure comprising interconnected armour units or cells which are at least partly hollow and within which the energy of waves from variable directions will be dissipated and their suspended or transported materials deposed and thereafter largely retained, said interconnected armour units or cells being so formed and interconnected as to provide improved pathways below the said structure for the rapid evacuation of short-term wave-induced pore pressures, and a variable and predetermined two-dimensional degree of flexibility of said structure.

It is a second object of the present invention to provide an improved flexible and orthogonally integrated revetment structure comprising interconnected armour units or cells which are at least partly hollow and within which the energy of incident waves will be dissipated and their suspended materials deposited and thereafter retained, said interconnected armour units or cells being so formed and arranged as to provide improved pathways at the base of said structure for the rapid release of short-term wave-induced pore pressure and a variable pre-designed degree of flexibility of said structures.

It is a third object of the present invention to provide a flexible integrated revetment panel of hollow cells which shall combine the efficient use of engineering materials with freely-available natural resources to produce a revetment structure having an improved mass stability by the deposition and retention of wave-transported materials therein, and which shall be economic to manufacture, simple to install, robust in use and difficult to remove from its installed position.

According to one aspect of the present invention there is provided a flexible revetment panel comprising hollow cylindrical open-ended cells or pipes in mutual contact and with each said cell or pipe having a cylindrical length equal to its external diameter and being so disposed within said panel that its longitudinal or cylindrical axis is at right angles to the longitudinal or cylindrical axies of surrounding or adjacent cells, each said cell having at least one pair of opposing holes in its cylindrical wall through which said opposing holes may freely pass cables or flexible links arranged as a two-dimensional or orthogonal flexible mesh, each of which said cables or flexible linkages of said mesh will lie alternately either in a diameter or chord of a one said cell or along or parallel to the longitudinal or cylindrical axis of an adjacent second cell.

In order that a flexible panel of hollow cells, inter-connected by cables, may be easily handled for example for installation the cables in said orthogonal mesh which lie in a one direction may, with advantage, he arranged below the cables in a second direction in order that when said flexible panel is suspended from two opposing ends by said cables in the one direction, said cables in said second direction will co-operate to mutually suspend all cells in said panel between continuous curved upper and lower surfaces.

It is well known that the disintegration of energy of a breaking wave during its run-up phase upon a shore-line is usually accompanied by the deposition or considerable volumes of materials such as sand, gravel and stones which are transported by said wave; and that during the subsequent draw-down phase of the wave much of these materials are also withdrawn for retransportation by the succeeding wave. In the present invention the, at least, partial loss of energy from a wave following its entry into the hollow cells of a revetment structure, as heretofore described, will bring about the deposition and retention within said cells of relatively large fractions of said wave-transported materials.

An assembly of interconnected hollow cylindrical cells or pipes in mutual contact with their cylindrical axies mutually at right angles and with lengths equal to their outer diameter will have a maximum two-dimensional degree of flexibility and will also overlie a maximum area of earth or ground to be protected. However, due for example, to embankment profile or to anticipated high pore pressures it may be desirable to reduce the design degree of structural flexibility of a revetment below said maximum or to restrain the deflection of revetment surfaces particularly in directions which are convex relative to a plane structural base.

According to a second aspect of the present invention there is provided a flexible revetment panel comprising an assembly of hollow cylindrical open-ended cells or pipes in mutual contact and with each said cell or pipe having a cylindrical length which is equal to or greater than the length of side of the inscribed square within said hollow cell but is less than its internal diameter said cells being so disposed within said panel that the longitudinal or cylindrical axis of any one cell is at right angles to the longitudinal or cylindrical axies of its adjacent or surrounding cells.

each said cell or pipe being provided with one or more pairs of opposing holes in its cylindrical side through which said opposing holes may freely pass cables or flexible links or the like so arranged as to form a two-dimensional or orthogonal mesh, each of which said cables or flexible linkages of said mesh will lie alternately in a diameter or chord of a one said cell and along or parallel to the longitudinal axies of adjacent second cells.

It will be apparent that for a major fraction of wave-deposited material to be retained within an assembly of cells as heretofore described, said cells must be in close juxtaposition, in order that said deposited materials, though freely distributable within and around the lower levels of all adjacent said cells, cannot easily escape from their upper levels but instead will establish equilibrium deposited regimes related to the energy characteristics of wave attack.

While a panel of hollow cylindrical open-ended cells or pipes in mutually transverse contact may be flexibly interconnected by a two-dimensional or orthogonal mesh of cables passing freely through diametrically, or otherwise opposed pairs of holes in the cylindrical wall of each cell, as heretofore described, there are other ways in which said cells may be flexibly interconnected.

One preferred alternative method is for the cells in each parallel row of a panel of cells to be mutually retained by at least one cable which passes through diametrically or otherwise opposed holes in the cylindrical walls of a first series of alternating cells in said row, said first series being defined by cells whose cylindrical axies are at right-angles to said cable, and in or parallel to the cylindrical axies of a second series of alternating cells in said row, each cell in said second series having at least one rod or bar passing freely through diametrically Qr otherwise opposed holes in its cylindrical wall and entering into associated cells in said first series of cells in adjacent rows, said rods or bars being provided with end eyes through which also pass said cables retaining said adjacent rows of cells. With advantage said eye at the end of each said rod or bar is formed as an open helix having a pitch equal to the diameter of said cable in order that said cable, when slack, may be engaged to pass rotationally within said helix in a manner analogous to the securing of a key upon a key-ring. It will be understood that the aforesaid orthogonal system for the flexible interconnection of hollow cylindrical open-ended cells by parallel cables and transverse rods or bars each having open helical eyes will greatly facilitate the tensioning control of a panel of cells and the interconnection, and any subsequent necessary replacement, of individual cells therein, and especially so when said undertakings are to be carried out below water.

A further alternative means of flexibly interconnecting adjoining hollow cylindrical open-ended cells or pipes when assembled with their cylindrical axies mutually at right-angles is for each said cell in said assembly to be provided with at least one pair of diametrically or otherwise opposed holes in its cylindrical wall through each of which said holes a separate rod or bar is free to pass having at its both ends an eye or similar means of linkage and being of a length approximating to the external diameter of its said cell so that the four end-eyes of four rods or bars proximal within each said hollow cell and radiating in two right-angled directions coincident with or parallel to the said cylindrical axies of the said assembly of cells, may be mutually interlinked within said cell by a common open helical ring or similar means.

It will be evident that the aforesaid orthogmal flexible mesh of rods or bars aligned with the cylindrical axies of said cells could be rotated through 45" to provide a linkage mesh whose rods or bars pass diagonally through each said cell in a diametrical plane thereof, in which alternative no diametrically opposed holes would be required in the cylindrical wall of said cell.

It is generally presumed that any single layer of flexible revetment armour must invariably be laid upon a geotextile fabric or similar permeable filter-layer, separating said flexible armour from the prepared surface of an earth mass to be protected against erosion. While the geomorphology of some earth masses may require such said separation, others, if protected by a revetment structure of integrated hollow cylindrical open-ended cells as heretofore described will exhibit a stable surface in hydrodynamic equalibrium with water-borne materials deposited within and around said cells of said revetment.

Embodiments of the invention will now be described by way of example, reference being made to the accompanying drawings in which: Figure 1 is a perspective view of an assembly of interconnected, hollow, cylindrical, openended cells or pipes according to the present invention wherein the cylindrical length of each cell forming said assembly is equal to the external diameter of said cells. In the drawing the adjacent edge cells are shown as being partly filled with wave-transported materials, although it is to be understood that all cells in an assembly or revetment panel or structure so combined will contain said deposited materials.

Figure 2 is a part-plan, part-sectional view of Fig. 1 said part-sections showing two ways whereby said cells may be flexibly interconnected.

Figures 3 and 4 are part-elevational, part-sectional views of Fig. 2.

Figure 5 is a part-plan, part-sectional view of an assembly of interconnected, hollow, cylindrical, open-ended cells according to the present invention wherein the cylindrical length of each cell forming said assembly is less than the internal diameter of said cells, said part-sectional views showing two alternative ways whereby said cells may be flexibly and mutually interconnected.

Figures 6 and 7 are part-elevational, part-sectional views of Fig. 5.

Figure 8 is an enlarged elevational view of a hollow cylindrical open-ended cell with Fig. 9, a longitudinal section of Fig. 8 showing its contact association with an adjacent cell whose cylindrical axis is at right-angles to the cylindrical axis of said longitudinal section, said association between said cells being set out in the Notes accompanying Figs. 8 and 9.

Figure 10 is a perspective view of one form of rod or bar passing through diametrically opposed holes in the cylindrical wall of a hollow cell and provided with open helical ends to accept flexible cables rotationally looped therein.

Figure ii is a perspective view of one arrangement of rods or bars mutually linked within a cylindrical hollow cell which is shown by pecked lines for clarity the opposing ends of each bar or rod being similarly interlinked in adjacent surrounding cells.

Figure 12 is a section in the diametrical plane of part of a flexible revetment panel comprising hollow cylindrical open-ended cells or pipes arranged in accordance with the present invention but having rods or bars lying diagonally within each said cell and being mutually interlinked therein to form a flexible mesh within which said mesh said cells are flexibly retained in a close mutual proximity.

The flexible revetment illustrated in Fig. 1 comprises an assembly of hollow cylindrical openended cells 1 each having a cylindrical length equal to its external diameter and so arranged that the cylindrical axis 2 of any one cell is at right-angles to the cylindrical axies of surrounding or adjacent cells.At least one pair of diametrically opposed holes 3 in the cylindrical wall of each cell freely accept a first flexible tendon or cable 4 passing therethrough said cable 4 being coincident with the cylindrical axies of adjacent cells and in like manner a second flexible tendon or cable 5 at right angles to cable 4 is coincident with the cylindrical axis 2 said cables 4 in the one direction passing below said cables 5 in the second direction so that when a revetment panel is lifted from the ground by the ends of the cables 4 in the said one direction, said cables 5 and their interconnected cells will be supported in the said second direction. Wave-transported materials 6 are shown deposited within cells along three sides of the illustrated assembly although it is to be understood that all cells therein may accept similar materials.The assembly is shown resting on a geotextile fabric 7 overlying the surface of a protected earth mass 8.

The reference numerals of Figs. 2, 3 and 4 conform to those of Fig. 1, the part sectional views in Fig. 2 lying in the diametrical planes A-A' of the elevational views in Figs. 3 and 4.

Additionally in the part-sectional views of Figs. 2, 3 and 4, bars or rods 9 passing through the diametrically opposed holes 3 in the cylindrical walls of cells 1 are shown with open helical ends 10 each engaged alternately with cables 4 in adjacent cells.

The reference numerals of Figs. 5, 6 and 7 conform to those in Figs. 2, 3 and 4, the partsectional views of Fig. 5 lying in the diametrical planes B-B' of the elevational views in Figs. 6 and 7. The extent to which any one hollow cylindrical cell 1 having a cylindrical length whhich is less than its internal diameter will extend into the cylindrical interior of an adjacent second cell whose cylindrical axis 2 is at right-angles to that of the first cell is shown in Figs. 6 and 7 by broken-line cylindrical minor segments 11.

In Figs. 8 and 9 the cylindrical minor segment 11 extended into the interior of an adjacent hollow cylindrical cell 1 is shown in section to an enlarged scale, the Notes thereto being referenced to the alphabetical annotation of said Figures and associating panel flexibility to covered ground area.

In Fig. 10 a rod or bar 9 is shown passing through opposing holes 3 in a cell 1 and having open helical eyes 10 formed at its ends through which said eyes parallel cables 4 may be passed, each cable connection or linkage being made while a said cable 4 is still slack so that a length 12 may be introduced into the helical eye 10 and thereafter rotated into its connected or linked position.

In Fig. 11 the one ends of four rods or bars 13 each approximating in length to an external cell diameter are shown as being flexibly interlinked within the interior of a hollow cylindrical cell 1, said cell being in broken lines for reasons of clarity, the second end of each said rod or bar 13 being similarly interlinked with an associated three other rod-ends in each surrounding or adjacent cell. It will also be apparent that said rods or bars 13 may be provided with simple closed eyes at their both ends four of which said eyes being interlinked by one helical ring or cruciform fastening.

In Fig. 12 rods or bars 14 lie diagonally in the diametrical plane of a sectional assembly of cells 1 said rods or bars 14 being mutually interconnected within each cell as heretofore described.

The description which follows originally accompanied Figs. 8 and 9: THE CONTROLLED FLEXIBILITY OF ONE SYSTEM OF SINGLE LAYER INTEGRATED FLEXIBLE REVETMENT Considering "n" interconnected Cylindrical hollow cells of Radii "R" and "r" and with Thickness "t" (=R-r) all adjacently in contact along diametrical planes, and arranged with their longitudinal axies, vertually at right angles.

There the ground area "A" covered by the n cells will be a maximum where the cell length LA=2R.

Also the two dimensional flexibility of the ''R'' cells will be a maximum where LA=2r and will decrease as L < 2r.

Let L,=cell length for a Minimum Flexibility corresponding to a maximum covered ground area "a," of the n cells.

There L,=L where "L" is the side of the inscribed square in the cell.

Claims (9)

1. A flexible revetment panel comprising a plurality of interconnected earth-armouring units each said armouring unit being constructed as a cell having a substantial open cavity therein or defined otherwise as a cell which is prediminately hollow or tubular in form said cells being arranged in said flexible panel so that some at least of their longitudinal tubular axies are parallel to the surface of the earth to be armoured and so that water when flowing over said panel is free to enter said cavaties within said cells and thereafter to lose energy through internal turbulence said interconnection of said earth-armouring units or cells to form said flexible revetment panel being by a two-dimensional mesh of cables or flexibly joined links or the like.

2. A flexible revetment panel according to Claim 1, in which said plurality of earth-armouring units or cells are so arranged in said panel that the longitudinal tubular axies of adjacent cells are mutually at right-angles.

3. A flexible revetment panel according to Claims 1. and 2. in which each interconnected earth-armouring unit or cell is a monolithic rigid tube or pipe.

4. A flexible revetment panel according to Claims 1. and 2. in which each interconnected earth-armouring unit or cell is constructed from an elastic material that is to say a material having a tendency to return to its original size or shape after having been stretched or compressed or deformed.

5. A flexible revetment panel according to Claims 1. 2, 3, or 4. in which one or more eartharmouring units or cells assembled therein are constructed from a plurality of conjoined annular casings or rings said casings or rings being either individually rigid or elastic.

6. A flexible revetment panel according to any of the preceding Claims in which the cavities of at least some armour units or cells contain a volume of castable or deposited material.

7. A flexible revetment panel according to any of the preceding Claims in which the interconnection of said earth-armouring units or cells comprising said panel is by a mesh of cables or flexibly joined links of which some at least pass through openings or holes in the walls of the said cells.

8. A flexible revetment panel according to any of the preceding Claims in which some at least of the cables or flexibly joined links interconnecting said earth-armouring units or cells comprising said panel pass between the ends of adjacent cells or the components thereof.

9. A flexible revetment panel substantially as described herein with reference to Figs. 1-12 of the accompanying drawings.