Patent Publication Number: US-2011058904-A1

Title: Stabilizing Reinforcement For Use In Reinforced Soil Works

Description:
The present invention relates to a stabilising reinforcement intended for use in reinforced soil structures, as well as the use of such a reinforcement for the construction of reinforced soil structures. 
     A reinforced soil structure combines a compacted fill, a facing and reinforcements that may or may not be connected to the facing. 
     The facing is for example made from precast concrete elements, in the form of slabs or blocks, juxtaposed to cover the front surface of the structure. A structure built in this way is known in particular under Terre Armée Internationale&#39;s brand name Terra Class. 
     The facing can also be made from a net, particularly constituted of metal rods welded together. Such facing can include a geosynthetic fabric and can receive planting. A structure built in this way is known in particular under Terre Armée Internationale&#39;s brand name Terra Trel. 
     Various types of reinforcement can be used: metal, for example comprising galvanised steel rods, or made from a synthetic material such as stabilising strips for example based on polyester fibres. The reinforcements are placed in the soil at a density that depends on the stresses that might be exerted on the structure, as the active earth pressure of the ground is taken up by the soil-reinforcement friction. 
     The stabilising reinforcements are attached to the facing and/or a wall located at a distance from the facing. 
     The stabilising reinforcements intended for use in reinforced soil structures comprise elongated longitudinal parts. Their length is of the order of magnitude of the metre. They can be several metres long. The longitudinal parts of the reinforcements can be arranged one by one in the soil, or be assembled together by various means. The width and thickness of such longitudinal parts are of the order of the centimetre, and do not generally exceed approximately ten centimetres. 
     The longitudinal parts can be arranged substantially perpendicular to the facing or be arranged slanting relative to the facing. In the latter case, the longitudinal parts are generally arranged on either side of an axis perpendicular to the facing. Generally, the longitudinal parts of the reinforcements are arranged in a substantially horizontal plane. 
     Metal stabilising reinforcements are often seen as advantageous in terms of price and are generally constituted of metal rods welded together to form for example ladders or a mesh. 
     A ladder reinforcement is generally constituted of two substantially parallel metal rods, each forming a longitudinal part, and transverse rods that connect the longitudinal rods to each other in order to stiffen the assembly. 
     By “transverse” is meant a part of a reinforcement that connects two longitudinal parts to each other. Such parts are for example constituted of rods. Consequently, the transverse parts are arranged so that they are substantially parallel or slanting relative to a facing. 
     The transverse rods of ladder reinforcements are generally arranged perpendicular to the longitudinal rods. They can however be inclined relative to the longitudinal rods. 
     The transverse rods are generally distributed over the entire length of the longitudinal rods and particularly evenly spaced. For example, the spacing between two transverse rods is of the order of several tens of centimetres for a normal ladder reinforcement. 
     A reinforcement that resembles a ladder is thus formed. 
     Generally, one end of the ladder reinforcement comprises a means of fixing to the facing, particularly hooks formed or arranged at one end of the longitudinal rods, or a flat, perforated piece connecting the ends of two longitudinal rods, in which the perforated part of said piece is intended to receive means of connection with the facing. 
     The metal rods used for such reinforcements are generally steel rods. They are often cylindrical and their diameter is generally of the order of the centimetre. These rods are advantageous to use as they are very moderately priced. However, the environment in which they are arranged is corrosive, particularly due to the pH of the soils and the ions they contain, which can moreover vary over time and as a function of rainfall or other parameters. 
     It is therefore convenient to protect the steel reinforcements in order to ensure a satisfactory service life of the structures built. 
     In order to produce a durable metal ladder stabilising reinforcement, the following steps are usually carried out:
         arranging two longitudinal rods substantially parallel to each other,   arranging the transverse rods, generally orthogonally to the longitudinal rods,   welding the transverse rods to the longitudinal rods,   galvanising the assembly.       

     Such a ladder stabilising reinforcement has several drawbacks. Firstly, it is often necessary to move it, or even transport it from a distant production site before installing it on a soil reinforcement site. The associated transport costs can be high as such reinforcements are bulky. 
     Furthermore, the inventors have established that the welds are sometimes weak points on a ladder reinforcement. It appears that the protection by galvanising is often imperfect in the weld zones, thus resulting in the risk of localised corrosion and a significant reduction in the strength of the assembly. One solution can be to increase the safety factors for a given structure, for example by increasing the density of reinforcements. Such a solution is however costly and unsatisfactory. 
     It is also possible, in order to form a ladder stabilising reinforcement, to use steel wires or bars, previously continuously coated with a zinc-aluminium alloy, which are cut to the desired dimensions and then welded. It has been found that the welds can significantly damage the protective coating and this damage can also reduce the strength of the reinforcement. 
     An object of the present invention is to overcome the aforementioned drawbacks and particularly to propose a reinforcement without the risks associated with the corrosion of the welds between longitudinal parts and transverse parts. 
     The invention thus proposes a stabilising reinforcement intended for use in reinforced soil structures, comprising two longitudinal parts forming a non-zero angle α+β with respect to each other and connected to each other by transverse parts which are movable relative to at least one longitudinal part and comprise angular limit pieces making it possible to limit the angular separation of said two longitudinal parts. 
     The invention also proposes a stabilising reinforcement intended for use in reinforced soil structures, comprising two longitudinal parts forming a non-zero angle α+β with respect to each other and connected to each other by transverse parts which are movable relative to at least one longitudinal part and comprise angular limit pieces making it possible to limit the angular separation of said two longitudinal parts, where the range of movement of the transverse parts occurs within a perimeter defined by the two longitudinal parts, their point of intersection or the line joining the two nearest ends of the two longitudinal parts and the line joining the other two, or most separated, ends of the two longitudinal parts. 
     By “movable transverse parts” is meant transverse parts capable of undergoing movement relative to at least one longitudinal part. This movement can correspond to a translation, in which case the transverse part moves as a whole relative to the two longitudinal parts. This movement can also be a rotation. In certain cases of rotation, one point, particularly one end of a transverse part, can remain fixed relative to one longitudinal part, while the rest of the transverse part moves relative to the two longitudinal parts. It is also possible to combine a translation and a rotation. 
     Generally, the movement of a transverse part relative to a longitudinal part can occur from the area of the reinforcement where the two longitudinal parts are furthest away from each other towards the area where the longitudinal parts are nearest to each other, particularly towards the point where the axes of the two longitudinal parts intersect, that is, in the direction from the inside of the fill towards the facing when the reinforcement is arranged in a structure. 
     By “angular limit pieces for limiting the angular separation of two longitudinal parts” is meant any means making it possible to limit the angular separation of the two longitudinal parts, particularly by limiting a distance between two points of two separate longitudinal parts. 
     Using a stabilising reinforcement according to the invention, it is possible to avoid welding the longitudinal parts to the transverse parts. As a result, such a reinforcement no longer presents a risk of preferential corrosion. 
     Furthermore, it is thus possible to produce the reinforcement on the site of the reinforced soil structure, for example using previously galvanised metal rods or wires that are commercially available and shaping them, for example by folding or bending, in order to obtain the desired configuration of the reinforcement. It is therefore no longer necessary to perform a prior galvanising operation on the reinforcement at a production location distant from the site. 
     Remarkably, the combination of two longitudinal parts forming a non-zero angle α+β with respect to each other and the use of transverse parts comprising angular limit pieces makes it possible to ensure the stiffening of the reinforcement when said longitudinal parts come into contact with said limit pieces on the transverse parts. 
     According to various embodiments, which can be combined:
         the longitudinal parts are metal, particularly galvanised steel, for example formed from cylindrical rods;   the transverse parts are metal, particularly galvanised steel, for example formed from cylindrical rods;   two longitudinal parts are connected to each other by material continuity to form a substantially V-shaped piece;   two longitudinal parts are independent and articulated so that they can form a non-zero angle α+β with respect to each other;   two independent longitudinal parts are articulated about the same axis, for example by means of hooks located at one of their ends;   two independent longitudinal parts are articulated about two different axes, for example by means of hooks located at one of their ends;   ends of two longitudinal parts are rigidly connected to each other;   the angular limit pieces on the transverse parts are hooks or heads located at each end of said transverse parts;   a plurality of transverse parts are of regularly increasing length and are capable of determining a plurality of maximum separation distances between two longitudinal parts;   one end of at least one transverse part is held movable in rotation in a housing in a longitudinal part;   one end of a longitudinal part is connected to a transverse part by material continuity by intermediate portions, for example substantially in the form of an elbow, V-shaped or U-shaped;   the transverse parts of the same stabilising reinforcement are connected to each other by material continuity by intermediate portions, for example substantially in the form of an elbow, V-shaped or U-shaped;   the angle α+β is comprised between 10° and 120°, preferably greater than or equal to 20° and/or less than or equal to 90°, or even substantially equal to 30°.       

     A further object of the invention is a reinforced soil structure comprising a facing running along a front surface of the structure and/or a wall delimiting a fill, where said fill is stabilised by at least one stabilising reinforcement according to the present invention. 
     A further object of the invention is a reinforced soil structure in which the angles α and β are substantially equal to each other, the angles α and β each measuring the angular separation between an axis orthogonal to the facing and one of the two longitudinal parts. 
     The structure built in this way is preferably obtained with a plurality of said stabilising reinforcements, each comprising two longitudinal parts, where the different reinforcements are separated from each other, without touching each other or being connected to each other by anything other than fill material. According to an embodiment, the different reinforcements are connected to the facing at regular intervals, both in a horizontal plane and in a plane parallel to the facing. A reinforced structure is thus obtained in a manner that is efficient and simple to implement. 
     The invention also relates to a construction method for a reinforced soil structure, in which a facing running along a front surface of the structure delimiting a volume to be filled is arranged at a distance from a wall, reinforcements are arranged in a zone of said volume, fill material is placed in said volume and the fill material is compacted, where said reinforcements are at least partly constituted of stabilising reinforcements according to the present invention. 
     According to an embodiment of the construction method, the stabilising reinforcements are arranged separated from each other, without touching or being connected to each other by anything other than fill material. 
     According to an embodiment of this method, two longitudinal parts are arranged, with one end of each longitudinal part connected to the facing or to the wall in a substantially horizontal plane, a plurality of elements comprising a transverse part are arranged and said transverse parts are moved relative to the longitudinal parts, for example in translation and/or rotation, in such a way as to delimit the angular separation α+β. 
     According to another embodiment of this method, two longitudinal parts are arranged, with one end of each longitudinal part connected to the facing or to the wall in a substantially horizontal plane, an element comprising a plurality of transverse parts with material continuity is arranged, in order to delimit the angular separation α+β. 
     According to another embodiment of this method, two longitudinal parts are arranged, with one end of each longitudinal part connected to the facing or to the wall in a substantially horizontal plane, one or both of the two longitudinal part(s) being connected by material continuity to a transverse part, the transverse part is moved in rotation relative to said longitudinal part in such a way as to delimit the angular separation α+β. 
    
    
     
       The invention will be more clearly understood on reading the following description, given by way of example only, with reference to the attached drawings, in which: 
         FIGS. 1 to 7  are diagrammatic views of different embodiments of a reinforcement according to the invention; 
         FIG. 8  is a diagrammatic cross-sectional view of a reinforced soil structure according to the invention, during construction. 
     
    
    
     For reasons of clarity, the different elements shown in the figures are not necessarily to scale. In the figures, identical reference numbers denote identical elements. 
       FIG. 1  shows a diagrammatic top view in which a stabilising reinforcement  1 , according to the invention, is connected to a facing (not shown) at a point along a line  2 . A facing is usually constituted of a plurality of facing elements, for example formed by a concrete block cast in a mould. The facing element can comprise one or more anchoring pieces, for example hook or ring, embedded in the concrete and extending beyond the concrete block along the line  2 . The line  2  is generally substantially parallel to the front surface of the facing. 
     The reinforcement  1  is connected to an anchoring piece on a facing element by means of a hook  3 . 
     The reinforcement shown extends generally substantially horizontally and rests on fill material. 
     The reinforcement  1  comprises two longitudinal parts  11 , connected by continuity of material by an elbow  12  to form a substantially V-shaped piece  10 , and a plurality of transverse parts  15 . Non-limitatively, three transverse parts are shown. The transverse parts are of regularly increasing length, d 1 , d 2 , d 3 . Each of their ends is equipped with a hook  16  the end of which faces towards the inside of the transverse parts. 
     The two transverse parts are angularly separated by a non-zero angle α+β, in this case of the order of 20° to 30°. In the configuration shown, the angles α and β are substantially equal, where the angles α and β each measure the angular separation between an axis orthogonal to the line  2  of the attachment points to the facing and the longitudinal part  11  located on the right of the figure and the longitudinal part  11  located on the left of the figure respectively. 
     The piece  10  can for example be formed on a site by bending a rod 2 L long in the middle to obtain two longitudinal parts 11 L long, separated by an angle α+β. 
     The transverse parts  15  can for example be formed on a site by bending the ends of a rod inwards in order to form the hooks  16 . 
     The transverse parts  15  are arranged in such a way that the hooks  16  on each end of each transverse part clasp a longitudinal part  11  of the piece  10  and thus form angular limit pieces for limiting the angular separation of the two longitudinal parts  11 . 
     Such a reinforcement  1  can be obtained by first placing the piece  10  on a fill, then sliding the transverse parts  15  in the direction from the elbow  12  towards the opposite ends of the longitudinal parts  11  until the hooks  16  abut against said longitudinal parts  11 . 
     The three transverse parts  15  are then separated from each other by a value E and prevent the longitudinal parts  11  from separating from each other by more than d 1 , d 2 , d 3  respectively at the contact points. 
     For example, a hook  3  can then be arranged in the elbow  12  of the piece  10  and be hooked to an anchoring piece on the line  2 . 
     Optionally, it is possible to prevent the longitudinal parts  11  from moving together by arranging nails  13  in the fill in contact with the longitudinal parts  11 , on the inside of the V of the piece  10 . 
       FIG. 2  shows a top view of another stabilising reinforcement  1  according to the invention. The reinforcement comprises two pieces  20  each comprising a longitudinal part  21  each with a hook  22  at one end. 
     The hooks  22  are arranged in a ring  27  that is connected to an anchoring plate  28 . This plate can be integral with a facing element or can be attached to it. The two longitudinal parts  21  are separated by an angle α+β and their angular separation is limited by transverse parts  15  of the type described above. 
     Optionally, the ends of the longitudinal parts  21 , opposite the ends on which the hooks  22  are arranged, are connected to each other. They can for example be connected to each other by parts  24  extending them. These parts  24  are substantially parallel to the transverse parts  15  and connected by material continuity by an elbow  23  to the longitudinal parts  21 . The parts  24  can for example be connected to each other by means of threaded ends  25  held by a reverse-threaded piece  26 . 
     A variant of the embodiment in  FIG. 2  is shown in  FIG. 3 , in which a stabilising reinforcement according to the invention comprises two pieces  30  each comprising a longitudinal part  31  and a head  32  at one end. 
     The heads  32  are arranged in one of the holes in an anchoring plate  28  of the type described above. The two anchoring plates are separated and the heads  32  of the pieces  30  are thus connected to the facing at separate points. It is thus possible to produce a wider stabilising reinforcement than those described above. 
       FIG. 4  shows a top view of a stabilising reinforcement  1  according to the invention that is a variant of the embodiment shown in  FIG. 2 . The reinforcement comprises two pieces  40  and  44  each comprising a longitudinal part  41  and  45  respectively each with a hook  42  at one end, arranged in a ring  27  connected to an anchoring plate  28 . 
     The longitudinal part  45  of the piece  44  is straight. 
     The longitudinal part  41  of the piece  40  comprises housings  43 . 
     This longitudinal part can be produced from a single rod by bending to form the housings  43  and the hook  42 . It is also possible to obtain a piece of this type from a straight rod to which the housings are added, for example by screwing, welding or any other appropriate means. 
     The transverse parts  46  comprise at each of their ends heads  47 ,  48 , for example obtained by bending a rod at 90°, or by adding an end  47 ,  48  forming a head by any other means known to a person skilled in the art. One of the heads  47  of each of the transverse parts  46  is arranged in a housing  43  on the longitudinal part  41 . 
     The heads  47  and the housings  43  are, in the example shown, produced in such a way that the heads  47  can only move in rotation relative to their axis in the housings  43 . 
     The reinforcement  1  shown in  FIG. 4  can be obtained by placing the pieces  40  and  44  on a fill, attaching these pieces using their hooks  42  to a ring  27  connected to the facing, separating the two pieces  40  and  44  by the desired angle α+β, inserting the heads  47  into the housings  43  in the piece  40 , and rotating the transverse parts  46  about the axis of the heads  47  until the heads  48  of said transverse parts come into contact with the piece  44  in order to limit the angular separation of the longitudinal parts  41  and  45 . 
       FIG. 5  shows a top view of a stabilising reinforcement  1  according yet another embodiment. This reinforcement comprises two longitudinal parts  11 , connected by material continuity by an elbow  12  to form a piece  10  and a piece  55  comprising a plurality of transverse parts  56  connected by material continuity by elbows  57 . It is entirely possible to replace the piece  10  comprising the transverse parts shown here by pieces  20  or  30  as shown in  FIGS. 2 and 3  respectively. 
     The piece  55  comprises at its ends hooks  58 ,  59 . Such a piece  55  can be produced by bending a rod. 
     The reinforcement  1  shown in  FIG. 5  can be obtained by sliding the piece  55  on the piece  10  from the elbow  12 , for example by inserting the longitudinal parts  11  into the loops formed by an elbow  57  and the two transverse parts  56  attached to it. The piece  55  thus passes above and below the piece  10 . The hooks  58 ,  59  form angular limit pieces for limiting the angular separation α+β of the longitudinal parts  11 . 
     It is possible to design the piece  55  in such a way that the inside part of the elbows  57  is in contact with the longitudinal parts  11  when the hooks  58 ,  59  contact said longitudinal parts. In this configuration, the elbows  57  also form angular limit pieces for limiting the angular separation of the two longitudinal parts. 
       FIG. 6  shows another embodiment of a stabilising reinforcement  1  according to the invention, constituted of a continuous piece  60 . This reinforcement comprises two longitudinal parts  61 , connected by material continuity by an elbow  62  and two transverse parts  65 ,  66 , each connected by material continuity by an elbow  63 ,  64  respectively to the longitudinal parts  61 . 
     A hook  67 ,  68  is arranged at the other end of each transverse part  65 ,  66 . Such a reinforcement can be obtained by bending a single rod. 
     The transverse parts  65 ,  66  can be moved, for example by rotation about the axis of the elbows  63 ,  64 , by slightly deforming the elbows, in such a way as to bring the hooks  67 ,  68  into contact with the longitudinal parts  61  and thus form angular limit pieces making it possible to limit the angular separation of the two longitudinal parts. 
       FIG. 7  shows another embodiment of a stabilising reinforcement  1  according to the invention that can also be obtained by bending a single rod and form a continuous piece  70 . 
     This reinforcement comprises two longitudinal parts  71 ,  73 , connected by material continuity by an elbow  72  and a plurality of transverse parts  75 ,  77 . The transverse part  75  is connected by material continuity to the longitudinal part  73  by an elbow  74 . The other transverse parts  77  are connected by material continuity to each other by elbows  76 , and one of them is connected by material continuity by an elbow  76  to the transverse part  75 . A hook  78  is arranged at the end of the transverse part  77  furthest from the transverse part  75 . 
     The hook  78  forms an angular limit piece for limiting the angular separation of the two longitudinal parts  71 ,  73 , as do the elbows  76 , which are designed in such a way that their inside part comes into contact with the longitudinal parts  71 ,  73  when the hook  78  is in contact with the longitudinal part  73 . 
     It will be noted that for all of the embodiments shown, the range of movement of the transverse parts  15 ,  46 ,  56 ,  65 ,  66 ,  75 ,  77  occurs inside a perimeter defined by the two longitudinal parts  11 ,  21 ,  31 ,  41 ,  44 ,  61 ,  71 ,  73 , their point of intersection or the line joining the two nearest ends of the two longitudinal parts and the line joining the other two, or most separated, ends of the two longitudinal parts. 
     In the examples shown in  FIGS. 1 ,  2 ,  4 ,  5 ,  6  and  7 , the perimeter is defined by the two longitudinal parts,  11 ,  21 ,  41  and  44 ,  11 ,  61  respectively, which meet at a point of intersection, respectively located in the elbow  12 , at the overlap of the hooks  22 , the hooks  42 , in the elbows  12 ,  62 ,  72  and by the line joining the other two, most separated, ends of these two longitudinal parts  11 ,  21 ,  41  and  44 ,  11 ,  61  respectively. 
     In the example shown in  FIG. 3 , the perimeter is defined by the two longitudinal parts  31 , the line passing through their two nearest ends passing through the heads  32  and the line joining the other two, most separated, ends of these two longitudinal parts  31 . 
     The invention also relates to a construction method for a reinforced soil structure. 
       FIG. 8  shows such a method. A compacted fill  81 , in which stabilising reinforcements  1  according to the invention are distributed, is delimited on the front side of the structure by a facing  84  constituted by juxtaposing prefabricated elements  85 , and on the rear side by the ground  83  against which the retaining wall is erected. 
     To ensure the cohesion of the retaining wall, the stabilising reinforcements  1  can be connected to the facing elements  85 , and extend over a certain distance within the fill  81 . These stabilising reinforcements  1  contribute to reinforcing the soil located in a reinforced zone Z behind the facing  84 . 
     In the reinforced zone Z, the fill material  81  is very strong due to the fact that it is reinforced by stabilising reinforcements  1 . It is thus able to withstand the shear stresses exerted due to the tensile loads to which the stabilising reinforcements  1  are subject. This reinforced zone Z must naturally be thick enough to support the facing  84 . 
     The simple connection of stabilising reinforcements to the back of the facing elements  85  thus allows for the facing to be held against the fill, which can be of a large volume. 
     The stabilising reinforcements are generally connected by connecting means, particularly hooks or rings, to the back of the facing elements  85 . 
     In the example of a structural configuration shown in  FIG. 8 , the stabilising reinforcements  1  are arranged in superimposed horizontal planes alternating over the height of the structure. 
     To build the structure shown in  FIG. 8 , the following method can be used: 
     a) position a part of the facing elements  85  so that fill material can then be placed over a certain height. In a known manner, the assembly and positioning of the facing elements can be facilitated by assembly components placed between them; 
     b) install stabilising reinforcements  1  on the fill already present; 
     c) place fill material on top of the layer of stabilising reinforcements  1  that has just been installed, up to the next level of stabilising reinforcements  1  on the rear side of the facing elements  84 . This fill material is compacted as it is placed; 
     d) repeat steps a) to c) until the top level of fill is reached. 
     According to a variant of said construction method for a reinforced soil structure, the stabilising reinforcements  1  are attached to the facing  83 . 
     It is possible to attach the stabilising reinforcements both to the facing  84  and the wall  83 . The attachment to the wall can be by means of nailing an anchoring element into the wall  83 , to which for example a ring is connected. A hook, for example, is then arranged allowing for said ring and a stabilising reinforcement to be connected. 
     By way of example, a reinforcement of the type of reinforcement shown in  FIG. 2  can be attached to the wall by a hook located along the parts  24  or in an elbow  23 , a reinforcement shown in  FIG. 6 , by a hook located in an elbow  63  or  64 , or a reinforcement shown in  FIG. 7 , by a hook located in the elbow  74 . The connection of a reinforcement on which one end of the longitudinal part  11 ,  31 ,  41 ,  44 ,  71  is free can also be envisaged by adding to that end a hook or a ring allowing for the insertion of a connection element to the wall. 
     It is also possible to use the reinforcements according to the invention and only attach them to a wall. In this case, it must be understood that the narrowest part of the stabilising reinforcements is facing the wall  83  to which it is connected. The line  2  represents in this case the line of the anchoring points to the wall. For example, the plates  28  can be connected to the wall by nailing. 
     It is also possible to alternate the attachment of the reinforcements according to the invention, with one reinforcing layer being attached to the wall and the reinforcing layer located above and/or below being connected to a facing. Preferably the projections in a horizontal plane of the reinforcements attached to the wall and those attached to the facing have an overlapping zone. 
     It must be noted that a great number of variants can be applied to the structure described above and to its construction method. 
     The invention is not limited to these types of embodiment and must be interpreted in a non-limitative manner that encompasses any equivalent embodiment.