EP1789632A1

EP1789632A1 - Fascines

Info

Publication number: EP1789632A1
Application number: EP05777581A
Authority: EP
Inventors: Richard Charles Connor; Nathan Michael Gray
Original assignee: Qinetiq Ltd
Current assignee: Qinetiq Ltd
Priority date: 2004-09-10
Filing date: 2005-09-05
Publication date: 2007-05-30
Also published as: WO2006027559A1; US20070292206A1

Abstract

Fascines for filling ditches or smoothing other discontinuities in or on the ground to facilitate the passage of vehicles across the discontinuity are composed of inflatable members (1) of the kind comprising an inflatable chamber (4) configured to define a hollow tube when inflated. These tubes, or at least selected lengths thereof, are reinforced internally against deformation under applied load, by means of additional inflatable chamber (5) which may themselves be of hollow or “solid” form, or by means of flexible tension members tied across the interior of the tube to resist expansion of the tube cross-section in the plane perpendicular to the load.

Description

Fascines

The present invention relates to fascines and more particularly to fascines comprising inflatable members.

Fascines are structures comprising at least one, and usually several, elongate members which are used to fill ditches or to level or smooth other discontinuities in or on the ground sufficiently to facilitate the passage of personnel or vehicles across the discontinuity, and sets of such members are commonly carried by tanks and other military vehicles when in the field for the temporary levelling of such discontinuities which would otherwise halt or impede the passage of the vehicle and/or of others which follow. Fascines comprising bundles of high density polyethylene or similar pipes are known from US4312601 and US4566821 and fascines including inflatable members are known from US5122400, US5215401 and US5406662.

Inflatable fascine members have the advantage over rigid pipes of reduced weight and of much reduced bulk whilst uninflated; they can be stored and carried uninflated and need be inflated only when required for use, e.g. by a suitable compressor or from cylinders of compressed air or other gas (such as an inert mixture of carbon dioxide and nitrogen) carried for the purpose. The members known from US5122400, US5215401 and US5406662 are "solid" members in the sense that substantially the whole of the gross volume encompassed by the outer periphery of the member must be pressurised to achieve inflation, its walls being akin to a closed sausage skin. An alternative form of inflatable member is proposed in copending United Kingdom patent application no. 0310906.3 filed on 12 May 2003 and published under no. 2401640 on 17 November 2004. In this case the inflatable fascine members comprise chambers with double walls configured to define hollow tubes when inflated, so that the pressurised volume at any section along the length of the member is of annular rather than solid disc-like form. More particularly such members may be formed from sealed sheets of so-called drop thread fabric comprising two textile layers which define the respectively outer and inner cylindrical walls of the tube when inflated and which are interconnected by a plurality of internal threads the lengths of which determine the spacing between the two textile layers - or in other words the wall thickness of the tube - when inflated. This has the advantage of requiring much less gas for inflation than a "solid" counterpart of equivalent diameter. Such hollow tube inflatable fascine members do however have the tendency to deform, and may eventually collapse, under significantly lower applied loads than their "solid" inflatable counterparts when inflated to similar pressures, and in one aspect the present invention seeks to alleviate this problem.

In a first aspect the present invention accordingly resides in a fascine member comprising an inflatable chamber configured to define a hollow tube when inflated, and means located or adapted to be located within said tube for reinforcing the same against deformation under applied loads in use, at least at a predetermined location or locations along the length of the tube.

In one preferred class of embodiments the or each reinforcing means comprises a second inflatable chamber located within the tube defined by the first-mentioned inflatable chamber when in use, and such second inflatable chamber(s) may be of hollow tubular or "solid" form. These second chamber(s) may be constructed separately from the first-mentioned chamber and nested therein either before or after inflation, or there may be an integral construction where the outer circumferential wall of an inner chamber is defined by at least a respective length of the inner wall of the outer chamber. In the latter case the two chambers .may be sealed from each other and inflated separately which, as in the case of separate nested chambers, would provide some structural redundancy in the event that one of the chambers fails, or they may be in fluid communication, e.g. through a port between them to permit common inflation at equal pressures or possibly at different pressures if equipped with a pressure-sensitive valve.

In an alternative embodiment the or each reinforcing means may comprise a rigid (non-inflatable) tube located within the tube defined by the first-mentioned inflatable chamber when in use. Such an arrangement would not have the same weight and space saving benefits of an all-inflatable structure, but in some circumstances may represent a useful compromise between strength and weight/stowed volume.

Another form of reinforcement in accordance with the invention recognises that increasing the stiffness of hollow tubular inflatable fascine members principally in the plane perpendicular to the applied load can be effective to resist deformation. That is to say the tendency of such members when subject to loading from above, as by a vehicle crossing a fascine comprising such members, is to deform in a downward flattening mode, with the horizontal "diameter" (cross-sectional dimension) of the tube increasing and the vertical "diameter" decreasing. This can cause excessive bending and eventually failure of the tube. In another preferred class of embodiments, therefore, the or each reinforcing means comprises one or more flexible tension members, such as straps, cords or fabric sheets, attached to the inflatable chamber so as to lie across the interior of the tube when inflated and resist expansion of the cross sectional dimension of the tube in the direction of the flexible tension member(s). In this way, if the fascine member is oriented in use with the flexible tension member(s) extending generally horizontally across the interior of the tube they will resist horizontal expansion of the tube diameter under loads applied vertically from above, and consequent flattening of the tube, in a manner akin to a so-called tied arch. Preferably there will be a plurality of such flexible tension members extending across the interior of the tube between respective positions spaced around the circumference of the tube, akin to the spokes of a wheel, so that flattening of the tube can be resisted in this way substantially irrespective of the rotational orientation of the fascine member and direction of the applied load. Members reinforced in this way can comprise a smaller inflated volume than all-inflatable reinforced members (e.g. as described above) of the same external dimensions, leading to faster inflation and reduction of the cost, weight and bulk of the compressed gas cylinders required to be carried for the purpose when that is the chosen means of inflation. It may also permit inflation to a lower pressure, thereby further reducing the amount of air required.

In any case the reinforcing means (of any of the above forms or combinations thereof) may be provided along substantially the whole length of the tube defined by the first-mentioned inflatable chamber or only at selected locations. For example reinforcements may be provided only at opposite end portions of the tube, at a spacing to accommodate the widthwise track or wheel spacing of vehicles intended to cross a fascine comprising such members. In such a case the wall thickness of the outer tube may be reduced in comparison to an unreinforced tube without loss of strength at the locations where loads are concentrated in use, thereby reducing the gas volume required for inflation. Alternatively shorter tubes may be produced, reinforced along their whole lengths, for use in pairs side by side (with or without a space between and optionally tethered together by rigid or flexible ties or spacers), each for supporting only one side of vehicles crossing the respective fascine. This allows greater structural redundancy and may save gas volume and overall weight/stored volume and will allow adjustment for vehicles of unusual width.

In another aspect the invention resides in a fascine comprising at least one inflated member according to the first aspect as defined above. These and other aspects of the invention will now be more particularly described, by way of example, with reference to the accompanying schematic drawings, in which:-

Figures 1 and 2 illustrate typical uses in the field of fascines composed of inflatable members;

Figure 3a is a longitudinal cross-section through a first embodiment of an inflatable fascine member in accordance with the invention and Figure 3b is a transverse cross-section through an end portion of the same;

Figure 4a is a longitudinal cross-section through a second embodiment of an inflatable fascine member in accordance with the invention and Figure 4b is a transverse cross-section through an end portion of the same; and

Figure 5 is a three-quarters view from one end and side of a third embodiment of an inflatable fascine member in accordance with the invention.

Figure 1 illustrates a typical use of inflatable members 1 forming a fascine to fill a discontinuity in the ground such as a ditch or gully 2. In this case a bundle of ten elongate fascine members 1 each of generally circular cross-section (but not otherwise illustrated in detail), and each having been inflated on-site, have been placed in the ditch so that the uppermost members collectively define a surface extending between the banks of the ditch which is sufficiently level to facilitate the passage of vehicles, such as tanks or other military vehicles, over the fascine and across the ditch. While Figure 1 shows the ditch substantially entirely filled with the members 1 , for wheeled vehicles with multiple sets of axles or tracked vehicles designed to have some degree of innate ditch crossing ability it is only necessary to fill a sufficient portion of the ditch to reduce its width to that which can be crossed by the vehicle's innate ability.

Figure 2 illustrates another typical use of such members 1 , in this case a bundle of three forming a fascine which has been placed against a wall, ridge or other sharply rising discontinuity 3. In this case the fascine presents a ramp-like surface which is sufficient to enable vehicles such as tanks and the like to climb over the fascine from the lower to the upper level of the discontinuity, or vice versa. Referring to Figures 3a and 3b there is illustrated the general structure of one embodiment of an inflatable fascine member 1 according to the invention. It comprises an outer inflatable chamber 4 configured to define a hollow tube when inflated. For ease of visualisation, in Figures 3a and 3b the inflated volume of the chamber 4 is denoted by forward broken hatching. Within the tube defined by chamber 4 there are two further inflatable chambers 5 each configured to define a hollow tube when inflated, and occupying opposite end portions of the outer tube. For ease of visualisation in Figures 3a and 3b the inflated volumes of the chambers 5 are denoted by backward broken hatching.

The chamber 4 may be formed from a rectangular sheet of drop thread fabric with its longer edges connected together and its ends closed as described in GB2401640. The chambers 5 may similarly be formed from respective sheets of drop thread fabric and nested within the outer tube either before or after inflation. For example the fascine member may be constructed with the outer walls of the fabric defining chambers 5 attached to the inner wall of the fabric defining chamber 4 at the respective locations. A three walled fabric could alternatively be used for the construction of a unitary member of this kind where the intermediate wall forms both the inner wall of the outer chamber and the outer wall of the inner chambers.

Figures 4a and 4b illustrate the general structure of another embodiment of an inflatable fascine member 1 according to the invention. It comprises an outer inflatable chamber 6 configured to define a hollow tube when inflated, equivalent to the chamber 4 of Figures 3a and 3b, and its inflated volume is similarly denoted by forward broken hatching for ease of visualisation. Within the tube defined by chamber 6 there are two "solid" inflatable chambers 7, occupying end portions of the outer tube. For ease of visualisation, in Figures 4a and 4b the inflated volumes of the chambers 7 are denoted by backward broken hatching.

The chambers 7 may be formed from respective sausage shaped fabric enclosures which are nested within the outer tube either before or after inflation. For example the fascine member may be constructed with the fabric of the outer walls of the "sausages" defining chambers 7 attached to the inner wall of the fabric defining chamber 6 at the respective locations. Alternatively and as depicted in Figure 4a the chambers 7 could be formed by the gastight attachment of four circular sheets of fabric 8 to the inner fabric layer of the material of chamber 6, so that that layer forms both the inner wall of the outer chamber and the outer wall of the inner chambers. In the embodiments of Figures 3 and 4 the inner chambers 5 or 7 serve to reinforce respective regions of the outer chambers 4 or 6 against deformation or collapse under the loading applied by the passage of vehicles over a fascine composed of respective members 1. The axial length of the members and the spacing of the inner chambers 5 or 7 is chosen so that the locations of the reinforced regions coincide with the widthwise track or wheel spacing of vehicles intended to cross the fascine. As previously indicated however, shorter individual fascine members constructed with inner and outer chambers similarly to the end portions of the illustrated embodiments could be used in pairs instead.

Turning to Figure 5, this illustrates the general structure of another approach to the reinforcement of fascine members comprising hollow inflatable tubes.

In Figure 5 the fascine member 1 comprises an inflatable chamber 9 configured to define a hollow tube when inflated, similarly to the chambers 4 and 6 of Figures 3 and 4. Within the tube defined by chamber 9 is a cruciform arrangement of four fabric strips 10-13, each fastened together (e.g. by stitching, welding or adhesive bonding) at the centre of the cross along one of their side edges, and each similarly fastened to the inner wall of the chamber 9, at a respective circumferential position, along their outer side edges. In use the fascine member is deployed with one of the opposed pairs of fabric strips (strips 11 and 13 as depicted in Figure 5) lying - generally horizontally across the width of the tube defined by chamber 9, although this need not be precise so long as the widthwise direction has a substantial horizontal component. The effect is as follows. When the member 1 is loaded by the passage of a vehicle across a fascine in which it is included the tendency will be for the inflated chamber 9 to be flattened downwards so that the vertical "diameter" of the tube decreases and the horizontal "diameter" increases. This will,- however, place the strips 11/13 into tension and their presence will serve to restrain, this mode of deformation of the tube.

The above analysis applies at least to fascine members at the top of a fascine where loads from passing vehicles are applied essentially in the vertical direction. Depending on the arrangement of any particular fascine and the position of any individual member within it loads may be experienced in other directions. By utilising the cruciform arrangement of reinforcing strips depicted in Figure 5, however, at least one opposed pair 10/12 or 11/13 should have a significant directional component perpendicular to the direction of loading and can thereby restrain deformation of the tube in the requisite direction. By increasing the number of strips extending from the centre of the assembly to the inner wall of the chamber 9 at closer spacings around the circumference of the tube it can be still further assured that any fascine member of this kind is capable of resisting deformation under loading applied from any radial direction and irrespective of the rotational orientation of the member.

Other forms of flexible tension members may be used in place of the fabric strips 10- 13 in figure 5 with similar effect, for example individual straps, chains or cords tied across the interior of the tube at axial spacings chosen to provide resistance to deformation of the tube along a chosen length of the tube. Furthermore while Figure 5 illustrates a relatively short fascine member 1 with the internal tension members providing reinforcement along the whole of its length, in other embodiments they may be provided only at selected locations e.g. equivalent to the positioning of the inflatable reinforcements in Figures 3a and 4a.

Combinations of the types of reinforcement exemplified by Figures 3 to 5 my also be employed if desired. For example the embodiment of Figure 3 may have additional tubular or "solid" inflatable chambers located within the chambers 5 or tension members such as described with reference to Figure 5 located within the chambers 5.

Although not shown separately in Figures 3 to 5 the fascine members 1 may be equipped with outer hoop-like sheaths of wear-resistant fabric, at least around those portions of the outer inflatable chambers 4, 6 or 9 which are intended to bear the tracks or wheels of passing traffic. The fabric of these sheaths can be selected for resistance to abrasion, puncturing and other damage which might otherwise be imparted to the gastight fabric of chambers 4, 6 or 9 by the tracks or wheels of vehicles passing .over them. If the sheaths of different fascine members are connected together, such as by zips, stitching or lacing, this will provide a simple and lightweight method of holding the members together in the assembled fascine. Small groups of such members may be interconnected in this manner prior to inflation and deployed as a unit. For example three members may be held together in this manner by interconnecting their sheaths along parallel edges at the positions indicated at A, B and C in the case of three members within the fascine exemplified in Figure 1 , or connections at only two of those positions may suffice. This method of interconnecting inflatable fascine members represents an independent aspect of the invention and may be applied not only to members in accordance with the above-described aspects of the invention but to inflatable fascine members of all kinds. In particular it avoids the complexity and mass of the conventional method of joining fascine members into groups by means of fabric loops attached to the ends of the members and metal karabiner clips attached through the loops.

Claims

1. A fascine member comprising an inflatable chamber configured to define a hollow tube when inflated, and means located or adapted to be located within said tube for reinforcing the same against deformation under applied loads in use, at least at a predetermined location or locations along the length of the tube.

2. A fascine member according to claim 1 wherein said reinforcing means comprises a second inflatable chamber.

3. A fascine member according to claim 2 wherein said second inflatable chamber is configured to define a hollow tube when inflated.

4. A fascine member according to claim 2 wherein said second inflatable chamber is of "solid" form.

5. A fascine member according to claim 1 wherein said reinforcing means comprises a rigid tube.

6. A fascine member according to claim 1 wherein said reinforcing means comprises one or more flexible tension members attached to the inflatable chamber so as to lie across the interior of the tube when inflated and resist expansion of the cross-sectional dimension of the tube in the direction of the flexible tension member(s).

7. A fascine member according to claim 6 wherein said reinforcing means comprises a plurality of such flexible tension members adapted to lie across the interior of the tube between respective positions spaced around the circumference of the tube.

8. A fascine member according to any preceding claim wherein said reinforcing means are provided along substantially the whole length of said tube.

9. A fascine member according to any one of claims 1 to 7 wherein said reinforcing means are provided only at opposite end portions of said tube.

10. A fascine comprising one or more inflated members according to any preceding claim.

11. A plurality of inflatable members adapted to be incorporated in a fascine, each said member comprising an outer sheath of wear-resistant material in addition to the fabric of the respective inflatable chamber, and means interconnecting or adapted to interconnect said sheaths of at least some said members.

12. A fascine comprising a plurality of inflated members according to claim 11.