AU649874B2

AU649874B2 - Method of forming a barrier

Info

Publication number: AU649874B2
Application number: AU22110/92A
Authority: AU
Inventors: Ivan Wesley Lane; Peter John Steen
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-09-02
Filing date: 1992-09-02
Publication date: 1994-06-02
Anticipated expiration: 2012-09-02
Also published as: AU2211092A

Description

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AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant(s): Actual Inventor(s): Address for Service: Invention Title: LANE, IVAN WESLEY STEEN, PETER JOHN LANE, IVAN WESLEY STEEN, PETER JOHN CULLEN CO., Patent Trade Mark Attorneys, 240 Queen Street, Brisbane, Qld. 4000, Australia.

METHOD OF FORMING A BARRIER The following statement is a full description of this invention, including the best method of performing it known to us.

2 The present invention relates to a method of forming a barrier to prevent erosion of the foreshore behind revetment walls of canals, quays, groynes and the like.

Conventional revetment walls have been constructed from masonry such as blockwork, concrete slabs or pre-cast concrete section or other suitable porous material installed along a foreshore extending an appropriate distance into the seabed and rising above the high tide level. A problem encountered with these walls is that over a period of time, wave action and tidal action draw particulate matter such as sand and soil from behind the wall causing subsidence of the foreshore behind the wall.

To this end it must be borne in mind that revetment Swalls by their very nature are designed to allow for water to pass through the wall but also inhibit the passage of particulate material such as sand. However, such walls will often have cracks occurring along joints between adjacent masonry blocks and sand may pass through these cracks along with water and thus erosion may occur in regard to the foreshore behind the revetment wall.

To overcome the problem a number of different approaches have been followed. United States patent US5087150 entitled "Method of Constructing a Seawall Reinforcement or Jetty Structure" relates to a method using a water permeable filter fabric to overlay a sediment layer extending from the foreshore side to the shore side of the seawall and held in position by a series of concrete blocks.

Alternatively, the filter fabric may overlay the sediment on the shore side of the sea wall and be attached to the sea wall. United States patent US4655637 similarly relates to the positioning of a filter fabric liner beneath a frame structure for a revetment system. The filter fabric liner allows water to pass but prevents the passage of soil particles.

Another approach was taken with the method disclosed in the United States patent US4666334 where drains are installed beneath the soil on the foreshore side of the sea wall to remove water from the foreshore side of the sea wall.

Removal of water decreases hydrostatic pressure from the foreshore side of the sea wall and reduces the tendency to force soil particles through the wall.

Yet a further approach was developed with the beach .oo..i erosion control structure disclosed in the United States patent US3894397. The structure comprises a wall of individual concrete blocks arranged in multiple rows and courses. The blocks have reed or flap type valves which swing open by an incoming wave and then move to a partially closed position to restrict the return flow of water.

The disadvantages associated with the above methods and associated structures resides in that they are often difficult to construct because of their complexity. Because S of this complexity the formation of the prior art structures was often expensive and inefficient. In particular, the current methods do not adequately address the problem of established revetment walls that are in need of repair or improvement.

Thus, it is an object of the present invention to provide a method for forming a barrier which overcomes at least some of the aforementioned disadvantages.

4 The present invention is a new approach to an old problem that instead of forming a barrier on the seaward side of the revetment wall as had been previous practice, the present invention covers a method of forming a barrier on the foreshore side of the wall.

The novelty of this lies in the barrier itself and how it is formed.

Thus, in one aspect, the invention resides in a method of forming a barrier to prevent the erosion by tidal and wave action of particulate matter from a foreshore side of a revetment wall comprising: locating a spacer adjacent the foreshore side of the revetment wall at a selected site; (ii) placing a liner between the wall and the :spacer; and (iii) retaining the liner in desired position to •••leo S 15 inhibit particulate material passing through the revetment wall.

Another aspect of the invention is the formed barrier S: itself.

Preferably the method includes an initial step of excavating a gap between the foreshore side of the wall and ease •e 20 surrounding foreshore material comprising sand and/or soil.

~The method of forming a barrier may be used to repair a revetment wall or improve a revetment wall. The method may be •.applied to an old or new revetment wall. 'The selected site for installation of the barrier is preferably at a construction joint, a place 4a of weakness in the wall such as a crack, or where there has been subsidence of the foreshore adjacent the wall.

The method includes the location of a spacer adjacent or abutting the foreshore side of a revetment wall. The spacer may be located by initially excavating the gap at the selected site. Excavation may be performed by using high-pressure water, air or a suitable water/air mix to remove particulate matter from the selected site, or alternatively, may be carried out manually although this may be time consuming. In this step the particulate matter removed may S* o ee9 oo: .00.

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include sand or soil or other suitable fill. Preferably, the gap is excavated to a depth below the level of the adjacent seabed. The spacer may be located in the gap.

The spacer may be a form member or of any suitable configuration to maintain a selected width of the gap. The spacer is preferably a channel member and thus may be Ushaped, J-shaped, C-shaped or W-shaped. A channel member may include a member with a half-circular section, a concave section, or a three-sided rectangular section. The member with a half-circular section is suitably a semi-cylindrical pipe. The semi-cylindrical pipe may suitably be made of plastic such as PVC or of metal such as steel.

A liner is placed between the wall and the spacer.

The liner preferably comprises of material that is water permeable but restricts the passage of particulate matter.

The liner may be a geotextile, geocomposite or geomembrane liner. A geotextile liner is a blanket of synthetic fibres S whereas a geomembrane liner is a geotextile liner with interwoven plastic fibres, and a geocomposite liner is a combination of geotextile layers which may be spaced by artificial fibres. Suitable material that is water permeable *o* and impermeable to particulate matter is sold under the trade name "Terrafix" and in particular "Terrafix 360R" or "Terrafix 1200R".

The liner preferably extends the length of the excavated gap from at. or below the level of the adjacent seabed to at or above the average high water mark. The liner preferably extends across at least the width of the excavated hole. Alternatively, the liner may completely or partially 6 surround three sides of the excavated hole where one of the three sides is the wall side.

The liner may be placed into position by a guide.

One or more guides may be used. A guide may be used to position the liner under water. One guide may be used to hold the liner against the form and a second guide may be used to hold the liner against the wall. The guide may be a T-shaped device which in use has the cross-bar of the T-shaped device located downwardly. The cross-bar of the T-shaped device may also have protrusions to hold the liner in position. The guide is preferably removed as material to hold the liner in position is added.

eoooa Any suitable retaining means may be utilised to .I retain the liner in desired position. However, preferably the 1 5 gap is filled with particulate material to retain the liner in position adjacent the revetment wall. The particulate .i material added to the excavation gap may be of any size, depending on the particular application. Preferably, the granular material is gravel or other suitable bedding ~material. The spacer may be removed after the granular S material has been added although it may be retained in the gap if appropriate.

A preferred embodiment of the present invention will now be described by way of example with reference to the drawings in which Figure 1 is a sectional view of a revetment wall where the foreshore has been eroded; Figure 2 is a sectional view of a revetment wall where particulate matter is removed by jets of high-pressure air and water; Figure 3 is a sectional view of a revetment wall where a liner is positioned in an excavated site; Figure 4 is a sectional view of a revetment wall where material to hold the liner in position is added to the excavation site; Figure 5 is a top view of a revetment wall and formed barrier; Figure 6 is a sectional view of a revetment wall and a formed barrier.

Figure 1 shows a revetment wall 10 where sand 11 on the foreshore side of the revetment wall 10 has been eroded at eeseo site 15. The average high and low tide marks are represented by 12 and 13 respectively. The seabed is represented by 14.

A method for forming an erosion-resistant barrier is illustrated in Figures 2 to 6. High-pressure air and water S jets indicated by arrows 16 are used to excavate a hole 16B and remove sand particles. There is also provided a flexible conduit 16A connected to a source of compressed air such as a compressor (not shown) and a water supply (not shown). A rigid rod 16C is attached to the flexible conduit 16A in order to control and direct the excavation of the hole 16B. The nozzle of the flexible conduit 16A is attached to the rigid rod 16C. The hole or gap 16B is excavated to below the level of the seabed 14 and a spacer 17 is positioned in the hole 16B. Spacer 17 is a semi-cylindrical PVC pipe with the concave side facing the revetment wall 10. The spacer 17 is located in the hole 16B so that the upper ends of the spacer 17 protrude from the hole 16B and prevent excavated material from re-entering the hole 16B. A liner 18 is placed in the hole 16B against the wall 10 and held in position by guides 19 and 20 which holds the liner 18 against the wall 10 and at the bottom of the hole 16B, respectively. The liner 18 extends above the average high tide mark to just below the level of the foreshore surface. The liner 18 is also below the level of the adjacent seabed 14. The liner 18 extends across the width of the excavated hole 16B. The liner 18 is sold under the trade mark TERRAFIX. Granular material 21 is gradually added to the hole so that the granular material 21 fills the hole 16B keeping in place the liner 18 at the bottom of the hole. The granular material 21 is suitably 5 mm gravel. The

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guide 20 is withdrawn and guide 19 is moved upwardly against the wall as the granular material 21 is added maintaining liner 18 against the side of the wall 10. The liner 18 is held in position by the weight of the granular material 21.

At an appropriate stage, spacer 17 is removed. In Figure the liner 18 is shown to extend across the width of the excavation or hole 16B and partially around each side. There is also shown crack or gap 24 occurring in the joint between adjacent masonry blocks 25 and 26 where projection 27 is retained in mating socket 28.

In operation, water can pass through the liner 18 but sand particles are maintained behind the liner 18. The sand particles as a result are retained behind the barrier 22 and subsequently there is little, if any, erosion of sand from the selected site 15 which is suitably located adjacent a gap 24.

Not only are sand particles retained by the barrier 22, but the barrier 22 also assists in alleviating water pressure built up behind the revetment wall Advantages of the present invention include that it is simple and economical to form the barrier; the barrier may be formed quite quickly; and it can be appli4ad to a number of different walls of various structures and shapes.

It should be appreciated that the foregoing describes only one embodiment of the invention and various changes and modifications may be made to the embodiment without departing from the spirit and scope of the invention.

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Claims

1. A method of forming a barrier to prevent the erosion by tidal and wave action of particulate matter from a foreshore side of a revetment wall comprising: locating a spacer adjacent the foreshore side of the revetment wall at a selected site; (ii) placing a liner between the wall and the spacer; and (iii) retaining the liner in desired position to inhibit particulate material passing through the revetment wall.

2. A method as claimed in Claim 1 wherein a gap is initially excavated between the foreshore side of the wall and surrounding S: foreshore material comprising sand and/or soil and the spacer is located in the gap. 0 15

3. A method as claimed in Claim 2 wherein high-pressure water, air or air/water combination is used to excavate the gap.

4. A method as claimed in Claim 2 or 3 wherein a gap is excavated at the selected site to a depth below the level of the adjacent seabed. 20

5. A method as claimed in any one of the preceding claims wherein the spacer is a channel member.

6. A method as claimed in Claim 5 wherein the channel member is a semi-cylindrical pipe.

7. A method as claimed in any one of the preceding claims 11 wherein the liner is positioned against the revetment wall and extends at least between a bottom level of the seabed and an average high tide mark and to at least the width of the excavated selected site.

8. A method as claimed in any one of the preceding claims wherein one or more guides are used to position and temporarily hold the liner in desired position.

9. A method as claimed in any one of the preceding Claims 2 to 8 wherein the liner is retained in desired position by filling the gap with particulate material.

10. A method as claimed in any one of the preceding claims wherein the liner is a geotextile, geocomposite or a geomembrane liner.

11. A method substantially as herein described with °reference to the accompanying drawings. 15

12. A barrier when formed by the method of any one of the preceding claims. DATED this seventh day of April 1994. IVAN WESLEY LANE and PETER JOHN STEEN, 20 by their Patent Attorneys, FISHER KELLY. *000 ABSTRACT The present invention relates to a method of forming a barrier 22 on the foreshore side of a revetment wall 10 to prevent subsidence of the foreshore behind the revetment wall The method comprises excavating a hole 16B at a selected site 15, locating a spacer 17, positioning a liner 18 against the wall 10 and filling the excavated selected site 15 with granular material 21. The barrier 22 allows water to pass through but resists the passage of particulate matter such as sand. *i