Hydraulic and earth engineering – Bank – shore – or bed protection – Wave or flow dissipation
Patent
1991-08-15
1993-01-05
Corbin, David H.
Hydraulic and earth engineering
Bank, shore, or bed protection
Wave or flow dissipation
405 21, 405 17, E02B 304
Patent
active
051764695
DESCRIPTION:
BRIEF SUMMARY
One of the most effective methods of preventing erosion of the river or sea bed around underwater structures is by anchoring an array or mat of synthetic buoyant fronds close to the structure. The fronds exert a viscous drag which reduces the velocity of the fines (soil particles) in underwater currents to a point where the particles are deposited, and the deposited particles then accumulate to form a permanent consolidated sandbank.
The array of fronds generally consists of lines of fronds arranged in a predetermined pattern and interconnected by flexible ties, or the fronds may be secured individually or in bunches to a matting.
In either case, the difficulties of manufacturing the array in a simple but cost-effective manner, combined with the difficulties of deploying the array on the river or sea bed, have prevented the potential of the method being fully exploited.
There is therefore the need for a soil retention and reinforcement structure which can be easily deployed on the sea bed, and which is simple to produce on a commercial scale. Ideally, the method of deploying the structure should lend itself to automation.
It would also be an advantage if the density and/or height of the structure could be easily varied over a wide range without affecting the manufacturing process.
According to one aspect of the present invention, there is provided an underwater soil retention and reinforcement structure comprising a sequence of synthetic buoyant fronds arranged side-by-side to form a frond line, the line being folded back and forth to form an array of fronds, and the successive folded sections of the frond line having aligned openings threaded by at least one anchor line for anchoring the array to the soil bed. In this manner, a curtain of fronds is presented to the soil particles in almost every direction, and the pitch or spacing between the successive folded sections is infinitely variable from a virtual solid to whatever pitch or spacing is required.
In a preferred embodiment, the structure comprises a fan-folded continuous sheet with vertical slits forming the individual fronds. The folded sheet is initially packed in a box-like dispenser with the folded sections in a tightly bunched, compact state. As the anchor line is withdrawn from the dispenser, the sections are spread apart.
In this manner, the density of fronds in the structure can be regulated simply by controlling the pitch of the folded sections. Moreover, since the frond line is a continuous folded structure, manufacture of a complete array of fronds is greatly simplified. A change in frond height is obtained merely by changing the width of the sheet.
The base of the sheet is preferably reinforced, and the anchor lines pass through aligned holes in the reinforced base section of the sheet.
One particular example of the invention will now be described with reference to the accompanying drawings in which:
FIG. 1 is a diagrammatic perspective view showing a scour control structure partially withdrawn from a dispenser and anchored to the sea bed;
FIG. 2 is a diagrammatic underside plan view of the structure shown in FIG. 1; and
FIG. 3 is a detail of a part of the structure shown in FIG. 2 when viewed from one side and showing the attachment of a side anchor.
Referring to these drawings, the illustrated scour control structure consists of a continuous sheet 10 of buoyant synthetic material, such as polypropylene, slit into 25 mm vertical strips 11 to provide a sequence of individual fronds each having a height of up to 2 meters above the soil bed 12 when the structure is anchored to the bed 12.
The slits 15 terminate some distance above the bottom edge 16 of the sheet, and the bottom of the sheet is folded upwards to provide a reinforced base 18. A reinforcing strap 17 is encased within the base 18.
The sheet 10 is folded back and forth in a fan-folded configuration, and is dispensed from a box 13. As best shown in FIG. 2, the successive fan-folded sections 14 of the folded base strip 18 are stored at the bottom of the box 13 in a bunched compac
REFERENCES:
patent: 4437786 (1984-03-01), Morrisroe
patent: 4534675 (1985-08-01), Morrisroe
patent: 4722639 (1988-02-01), Alsop
Corbin David H.
Hydracor International, Inc.
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