GB2418948A

GB2418948A - Scour protection using fabric formwork to resemble rock armour protection

Info

Publication number: GB2418948A
Application number: GB0422345A
Authority: GB
Inventors: Andrew Mountain
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-10-08
Filing date: 2004-10-08
Publication date: 2006-04-12
Anticipated expiration: 2024-10-08
Also published as: ATE453018T1; GB2418948B; AU2005291055A1; WO2006037976A2; EP1809815A2; US20080101862A1; DE602005018526D1; WO2006037976A3; GB0422345D0; EP1809815B1; WO2006037976A9

Abstract

The invention relates to a system of providing scour protection to structures, using grout, concrete or similar 5 filled fabric formwork bags (1, fig 1). The invention utilises fabric bags which are treated and shaped, possibly coloured and textured, to resemble and act hydraulically more like traditional rock armour scour protection, to increase the roughness of the concrete protection and improve the visual appearance of the concrete protection works. It aims to provide a more environmentally acceptable form of scour protection than traditional fabric formwork mattresses. The individual concrete blocks, formed by the bags, may have regular basal sections 2 to allow for complete and regular bed/bank coverage, improve the simplicity of the design and allow for "off the shelf" application. An internal diaphragm may also be included to allow for safer use, particularly within environmentally sensitive areas. Blocks may also be attached to one another using a variety of means to produce a coherent system of protection, or may be simply placed using butt joins. Internal stiffeners may be incorporated into the bagwork to improve the shape and regularity of the block bases.

Description

1 2418948

METHOD OF SCOUR PROTECTION USING FABRIC FORMWORK TO

RESEMBLE ROCK ARMOUR PROTECTION

DESCRIPTION

Scour, caused by the action of moving water on the bed and banks of raters, for example, can have serious consequences to structures, for example bridges, due to undermining of the structure's foundations. This has resulted in the catastrophic collapse of many structures, leading to potential loss of life and significant rebuilt costs. Structures can however be protected against these effects and there are several forms of protection currently in use around the world, in both fluvial and marine situations.

One such method of scour protection is the use of "Filter Point", or "fabric formwork", mattresses.

Filter point or fabric formwork mattresses have been used within the construction industry for approximately 40 years for the protection from scour and erosion to riverbanks, river and sea beds, particularly around structures. Fabric formwork mattresses, essentially form a hard layer of protection, which is designed to resist the effects of scour and as such protect structures from undermining, or river banks against lateral erosion. They consist of a sandwich of high strength, porous, typically woven, synthetic fabric, into which micro-concrete, grout or aggregate concrete is pumped. Mattresses placed below water are laid and filled insitu, using divers. Typically they form extensive mats, similar in shape to bedding mattresses, ranging in thickness between 100 and 350mm. The result, once the concrete has set, is a solid layer of protection that can be very effective and resistant to scour. Fabric formwork bags are also available, for underpinning works, or to form "massive" protection to structures such as pipelines, however, these bags are amorphous in shape, resembling sand filled bags. These bags are smooth textured and when formed are white/light grey in colour. Preformed concrete blocks, for example articulated or interlocking concrete blocks are also available, however these are considerably different from the proposed invention and do not enable construction below water.

The distinct advantage of fabric formwork protection is that it enables the placement of concrete or grout below water, without significant risk of environmental pollution that would otherwise occur if concrete were allowed to freely enter the river, or marine environment. The use of concrete can be very effective protection against scour, however, in most instances concrete cannot be placed without complete dewatering of the area to be protected, to protect against fouling and environmental pollution from the concrete, and to provide the necessary formwork.

The ability to place concrete without the need for dewatering has significant advantages over many other forms of scour protection and can lead to significant cost savings for any scour protection scheme. In addition to forming an effective means of protecting a structure, river bank or indeed any interface between water and land, the mattresses form a relatively thin form of protection, which has the advantage of requiring minimal excavation to form, and is relatively quick to install.

The disadvantages of fabric formwork mattresses however are significant and have resulted in this method of protection becoming unfavourable over the last 10 years or so, particularly within the UK. The main disadvantages with this method of scour protection are summarised below: It forms a hydraulically smooth surface (a low mannings "n" value), which typically results in the scour being deflected elsewhere. Smooth surfaces will not absorb any of the erosive force of the river and can even exacerbate the scour problem elsewhere.

It produces a very un-natural appearance, being smooth, dimpled and mattress looking, the colour of which is off-white/concrete looking, particularly when first placed.

Extensive mats are relatively inflexible and the extremities are particularly vulnerable to undermining and cracking of the protection.

It provides no environmental benefits.

Mattresses are very difficult to form protection for anything other than simple flat mattresses. Non-standard shapes/designs can be custom made but require significant time to manufacture.

They are very difficult to repair and the benefits gained by using extensive mattresses can be lost if small repairs are needed.

These disadvantages make the use of fabric formwork mattresses very unfavourable with the Environment Agency in the UK or other consenting bodies around the world and as a result are presently of limited use as a method of protecting structures or river banks against scour.

Consequently, alternative forms of protection such as Rock Amrour or RipRap, are usually preferred, which are environmentally more natural and largely preferred by numerous environmental consenting groups.

Specifically, the Invention in question relates to a distinct improvement in the use of fabric formwork for providing scour protection, by removing many of the disadvantages listed above.

The invention utilises the same simple system of using fabric to provide the "formwork" for the concrete or grout, but also aims to provide a simpler block (not mattress or bag) form of design and construction, utilising standard, typically 1m, sized blocked sections.

This form of construction means that the bagwork blocks can be used universally, be manufactured and stockpiled (as empty fabric bags) and therefore always available "off the shelf'. The overall scour protection scheme would also be much easier to design and is more flexible to accommodate and remove variations in bed profile around any scour feature.

It is intended that each individual block will have a regular base profile, to allow complete and regular coverage of the bed, which makes this system unique to the fabric formwork systems currently available. The seams of the fabric to form the individual formwork "bags" can be sewn or heat welded (due to the synthetic fibres).

The top surface of the individual blocks however, will make this method of protection unique and significantly superior to existing formwork systems by significantly improving its appearance. The top surface of the blocks will be manufactured to resemble large diameter rock armour. This will be achieved by a process of heat or physical deformation of the synthetic fibre fabric forming the top surface of the fabric formwork, which, when filled with concrete or grout will inflate to form a rough, irregular, rock like top surface.

Alternatively, similar results can be achieved by tailoring the fabric forming the top surface of the individual blocks, to produce a rough and irregular surface. The purpose of this deformation and irregular surface is to create a high mannings "n" value so that the protection acts more like rock armour scour protection in absorbing some of the energy of the flow. By using a coloured or textured fabric (for example a sand coated fabric), the colour and general appearance of the blocks, particularly in the short term, can be greatly improved. It is however worth noting that discolouration of the blocks would occur naturally, so the texturing and colouring is only of particular importance for areas that are easily visible.

Another significant advantage of this system of blockwork, which makes the system unique, is that it utilises relatively small, discrete units (blocks) rather than extensive mattresses. This is particularly useful if ever damaged, where individual blocks can be replaced and the damage essentially patch repaired. Simple repairs like this are difficult with extensive mattresses. In addition, if any problems occur whilst filling with concrete, for example hose blockages or burst bags, only small individual bags need to be aborted and replaced. Should this occur with a em wide mattress for example, the entire mattress would need to be removed and re-laid A preferred embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows diagrammatically an individual fabric formed, filled block, designed to act with other blocks to cover an area and surfaced to act like and resemble rock armour. The fabric skin, 1, forming the bag formwork will be formed from high strength, synthetic (Polypropylene, Polyester or similar), or other fabric, be permeable to allow the escape of trapped air or water within the bag, or be impermeable/permeable but incorporating an internal diaphragm (see figure 3) and optional bleed valve/filter to enable controlled escape of water/air from within the diaphragm. The purpose of the diaphragm is to provide for better control of the concrete and reduce the likelihood of environmental pollution from the concrete fines. Alternatively, heavy duty cotton, or similar type, fabric could be used, however the ability to heat or physically deform such fabrics is limited and it is likely that the top surface, at least, would need to be tailored. The individual blocks will include a uniformed and regular basal section, 2, to allow regular joining and coverage of numerous blocks to cover an area (in the same way a blocked driveway would be laid). Thickness of the basal section will vary depending on the degree of protection required and velocity of the flow experienced by the protection. Typically this would range between 0.1m and 1.0m. The seams of the fabric would be joined either by sewing, with thread for example, or a process of heat welding of the synthetic fabric. The top surface of the individual blocks, 3, shall be irregularly shaped to resemble rock armour and provide a less "artificially formed" appearance. Colouring of the fabric (either dyed or surface coating) and possibly texturing using a sand type coating, for example, will greatly improve the overall appearance of the individual blocks. The fabric forming the individual blocks will incorporate a valve or attachment, 4, to which the filling hose (see figure 3) can be attached. The valve may incorporate a simple one way or cut off valve to prevent escape of concrete once the hose has been removed and the valve is exposed to the water. These may be situated on the basal section or on the top surface of the individual blocks. Filling of the individual bags to form the blocks is to be carried out using grout (fine consistency), micro-concrete, regular concrete, specialist underwater concrete, or similar, 5, to fill the bags to form the finished block. They can be inflated individually, insitu below water, or a number of bags joined (refer to Figure 7) above water, placed, and then filled with grout, micro-concrete or similar, a number at a time.

The general "squared" basal section of the blocks can be attained using either stiffened fabric, or fabric of suitable thickness, or using internal tailoring of the fabric to restrain and retain the desired shape, or using internal stiffeners within the bags. These internal stiffeners may be required depending on trials and may be in the form of plastic or metal stiffeners inserted into the fabric sides, or by an internal or integral plastic or metal frame within the bags.

Figure 2 shows in three-dimensions an individual, filled block, showing the basal section, 2, the irregular top surface, 3, and valve/attachment, 4, used to fill the formwork with grout, micro- concrete, regular concrete, specialist underwater concrete, or similar, 5.

Figure 3 shows an individual bag being filled with concrete by a diver, using a hose. The concrete, or similar, is pumped into the bag, from plant located out of the water. In particularly environmentally sensitive areas the attachment of the hose to the bag can be made out of the water to reduce the possibility of leakage from the hose between filling of a number of bags below water. The inclusion of an internal diaphragm, 6, formed from a suitable impermeable expanding membrane within the individual bags could be added to reduce the leakage of fines or cement through the fabric skin of the bag and into the river or marine environment. To be effective though, it is likely that the diaphragm will need to include a bleed valve or filter, to allow the escape of any trapped air or water from within the diaphragm (voids within the concrete would otherwise weaken the concrete protection).

Figure 4 A to C show the method of construction, in plan, showing how the individual blocks can be arranged to form the protection. They can be arranged "offset" as shown in Figure 4A, similar to a brick wall, or in regular row/columns, i.e. not offset, see Figure 4B. Figure 4A and 4C show, in plan, how the system can be assembled with Figure 4A showing it part complete and Figure 4C showing the protection complete. Each instance of its use will however differ, depending on the size of the scour feature, orientation of the bed and of the structure, for example.

Figure 4A shows an example in plan where a bridge abutment, 7, with a scour feature, 8, in which individual blocks, 9, are formed to cover the bed and prevent further undermining. A special edge toe detail block, 10, (see Figure 6), shown hatched on Figures 4A and 4C, is included at the extremities to reduce the possibility of undermining of the extremities of the protection. This edge toe detail block is typically thicker than the regular blocks, typically in excess of 1m. An optional rock armour falling apron, 11, can be included, surrounding the block protection, for example. Figure 4C shows a typical arrangement, in its completed form.

Figure 5 shows a typical arrangement of the individual blocks in section, showing how the blocks interact and work to form the protection. The individual, formed, fabric formwork blocks, 12, protect the bed from further erosion and scour, with the toe detail block, 10, forming and protecting the extremity. This system of protection protects the abutment, 7, from the scour feature, 8. The diagram also shows a typical pre-scour bed profile, 13, and the scoured bed profile, 14.

Figure 6 shows a typical toe detail block arrangement, which can be used to protect the extremities of the protection. This toe block has a significantly extended base, 15, which would be more resistant to undermining. It retains the regular basal shape to allow integration into the general blockwork arrangement. Overall depth will vary, dependent on the degree of scour anticipated, but is likely to exceed 1 m.

Figure 7 shows a range of optional joining arrangements of the individual bags forming the blocks. The blocks can be unattached to one another, shown in Figure 7A, forming the simple butt join, 16, between the individual blocks. In reality this butt join will more closely resemble the simple butt join shown on Figure 7B, due to some deformation of the bags as they are being filled, which will provide some degree of interlocking of the individual blocks. Figure 7C shows two possible zip attachment arrangements, incorporating a zip, 17, which could be formed from nylon or similar, or less suitable, metal. Other configurations of zip attachment are possible.

Figure 7D, shows a possible bolt style attachment, 18, incorporating in this instance, a backing plate with attached bolt, 19, that would form an attachment using a washer, 20 and nut, 21. The bolt style attachment would be fed through pre-formed holes within the bags and allow joining of the empty bags. The bolt arrangement would then be cast into the block as the bag is filled with concrete, or similar. Alternatively, this simple bolt and plate type attachment could be used to attach any style of bag, where holes through the bags, through which the bolts are inserted, could be formed on site, during construction.

Finally, Figure 8 shows a possible concertina or bellows effect to the fabric forming the basal section of the fabric formwork to create the block. By including this folded edge, 22, within the fabric of the base, this will allow a regular and controllable expansion of the bag/block as it is being filled. This would accommodate some degree of flexibility in the filling of the bags, to better accommodate irregularities in the ground profile beneath the block and allow a range of thicknesses of the block that can be created on site.

Claims

1. A system of grout, concrete or similar filled fabric formwork bags shaped on their upper surface to resemble rock armour scour protection

2. A system of grout, concrete or similar filled fabric formwork bags shaped on their upper surface to resemble rock armour scour protection, as claimed in claim 1, but including a regular shaped base to the individual bags to allow regular and uniform coverage.

3. A system of grout, concrete or similar filled fabric formwork bags shaped on their upper surface to resemble rock armour scour protection, as claimed in claims 1 or 2, fabricated partly or wholly from coloured fabric, to resemble natural rock.

4. A system of grout, concrete or similar filled fabric formwork bags shaped on their upper surface to resemble rock armour scour protection, as claimed in claims 1, 2 or 3, fabricated partly or wholly from textured fabric, to resemble natural rock.

5. A system of grout, concrete or similar filled fabric formwork bags shaped on their upper surface to resemble rock armour scour protection, as claimed in claims 1, 2, 3 or 4, incorporating an internal diaphragm to reduce the possibility of leakage.

6. A system of grout, concrete or similar filled fabric formwork bags shaped on their upper surface to resemble rock armour scour protection, as claimed in claims 1, 2, 3, 4 or 5, with simple butt joins, zip joins or similar direct attachment to the bags, to link the separate blocks.

7. A system of grout, concrete or similar filled fabric formwork bags shaped on their upper surface to resemble rock armour scour protection, as claimed in claims 1, 2, 3, 4, 5 or 6 incorporating a bellows/concertina arrangement to the side of the individual bags to allow for more controlled and uniformed expansion and allow for undulations/variations in block thickness.

8. A system of grout, concrete or similar filled fabric formwork bags shaped on their upper surface to resemble rock armour scour protection, as claimed in claims 2 to 7, incorporating internal stiffeners or frame within the bags to maintain a regular base or shape to the individual blocks when filled.

9. A system of grout, concrete or similar filled fabric formwork bags shaped on their upper surface to resemble rock armour scour protection as herein described above and illustrated in the accompanying drawings or description.