SOIL REINFORCEMENT STRIP AND GRID

Abstract

A soil reinforcement strip (10, 30) for mechanically stabilizing earth structures. The strip (10, 30) has a polymer matrix (12, 32) which envelops elongated steel elements (14, 34) for reinforcing the matrix (12, 32). The steel elements (14, 34) may be steel cords containing a plurality of steel filaments (20, 22, 40, 42). Additionally, a reinforcement grid (60) for soil and ground. Furthermore, applications of this reinforcement strip (10, 30) and grid (60), namely to a reinforced soil layer (80) and to a mechanically stabilized earth structure or retaining wall (82).

Claims

1. A soil reinforcement strip, said strip having a polymer matrix, said strip further comprising elongated steel elements inside said polymer matrix as reinforcing elements, each of said elongated steel elements having a combined elastic and plastic elongation at break that exceeds 4%.

2. The strip according to claim 1, wherein said elongated steel elements are steel wires.

3. The strip according to claim 1, wherein said elongated steel elements are steel cords or comprise at least one steel cord having steel filaments and/or wherein at least one of the elongated steel elements or each elongated steel element comprises a plurality of steel filaments, wherein the steel filaments have a twisted configuration such that helical interstices are formed between at least some of the steel filaments at a periphery of the at least one of the elongated steel elements, wherein polymer material of the matrix penetrates into the helical interstices.

4. The strip according to claim 3, wherein the at least one of the elongated steel elements or each elongated steel element comprises a central steel filament and peripheral steel filaments stranded around the central steel filament.

5. The strip according to claim 4, wherein the helical interstices at the periphery of the at least one of the elongated steel elements or each elongated steel element reach the central steel filaments.

6. The strip according to claim 4, wherein the peripheral steel filaments are between 3 and 9, preferably between 3 and 6, peripheral steel filaments.

7. The strip according to claim 4, wherein the central steel filament has a diameter larger than at least some of the peripheral steel filaments.

8. The strip according to claim 3, wherein the at least one of the elongated steel elements or each elongated steel element is made of a group of at least two steel filaments twisted together as a group.

9. The strip according to claim 8, wherein the group has at most 5 steel filaments.

10. The strip according to claim 3, wherein the cord(s) is/are selected from the group of: n×1 cord(s), where n is the number of steel filaments and ranges between 2 and 5, preferably 3 and 5; 2×1 cord(s); 1+n cord(s) where n ranges from 3 to 9, preferably from 3 to 6 or wherein the elongated steel elements comprise at least one cord selected from the group of: n×1 cord(s), where n is the number of steel filaments and ranges between 2 and 5; 1+n cord(s) where n is a number of steel filaments arranged around a central steel filament and ranges from 3 to 9, preferably from 3 to 6.

11. The strip according to claim 1, wherein said elongated steel elements are coated with a material providing cathodic protection and/or wherein the strip comprises at least 2, preferably at least 3 steel cords or steel wires, further preferred at least 5 steel cords or steel wires, preferably between 5 and 50 steel cords or steel wires, further preferred between 10 and 45 steel cords or steel wires, further preferred between 15 and 40 steel cords or steel wires, further preferred between >15 and <30 steel cords or steel wires and/or wherein the steel cords or steel wires are arranged inside the polymer matrix parallel to each other, preferably in a way that they do not touch each other and/or wherein the steel cords or steel wires may be arranged inside the polymer matrix in one plane or in multiple planes, especially in 2, 3 or 4 planes and/or wherein the thickness of the polymer matrix between any point at the outside of the strip and any steel cord or steel wire inside the strip is at least 100 μm, preferably between >100 μm and <500 μm, further preferred between 150 μm and 400 μm, further preferred between 160 μm and 350 μm, further preferred between 175 μm and 300 μm and/or wherein the dimension of the outline of cross-section of the matrix in one direction is bigger than the dimension of cross-section of the matrix in another perpendicular direction, preferably wherein the outline of cross-section of the matrix is oval, rectangular or corresponds to a rectangle with rounded corners and/or wherein thickness of the polymer matrix and/or wherein the strip is arranged to be connected to or the strip is connected to at least one facing element, preferably stabilizing earth and/or arranged to be part of an embankment, further preferred a concrete block or a gabion and/or wherein said elongated steel elements have a combined elastic and plastic elongation at break that is more than 4.5%, preferably more than 5%, further preferred more than 6%, and/or further preferred less than 15%, further preferred less than 12%, further preferred less than 10% and/or wherein the strip has a width between 5 mm or mm and 80 mm, preferably between 20 mm and 70 mm.

12. The strip according to claim 1, wherein said elongated steel elements are in contact with a material providing cathodic protection.

13. The strip according to claim 1, wherein said elongated steel elements are of stainless steel.

14. The strip according to claim 1, wherein said elongated steel elements or at least one of said elongated steel elements are/is in a stress-relieved state.

15. The strip according to claim 3, wherein all of said steel filaments are in contact with polymer of said polymer matrix.

16. The strip according to claim 1, wherein said elongated steel elements have a cord tensile strength or tensile strength of at least 1800 MPa, preferably at least 2000 MPa, most preferably at least 2200 MPa, further preferred at least above 2500 MPa and/or further preferred below 4500 MPa.

17. The strip according to claim 1, wherein said polymer material comprises a functionalised polyolefin, preferably selected from grafted and/or blended HDPE (high density polyethylene), modified polypropylene and low-density polyethylene (LDPE), linear low density polyethylene (LLDPE), very low density polyethelene (VLDPE), ultra low density polyethylene (ULDPE) and/or ethylene based polymers or copolymers like for example ethylene-propylene copolymers, ethylene-vinyl acetate copolymers (EVA) or acrylate copolymers, especially for example modified, grafted or comprising some polar function like acrylate or acetate functions.

18. The strip according to claim 1, where said steel elements are provided with an adhesion promotor and/or where said steel elements may be individually or together coated in advance with a thin layer of a polymer that is a functionalized polyolefin or individually or together provided with a primer or adhesion promotor before all the steel wires or the steel cords are together extruded with a common, non-functionalized polymer.

19. The strip according to claim 1, wherein said strip has a strip breaking load ranging from 1 kN to 200 kN, preferably ranging for example from 10 kN to 150 kN, further preferred from 20 kN to 125 kN, even further preferred from 30 kN to 110 kN, even further preferred from 50 kN to 105 kN.

20. A grid for soil reinforcement, said grid comprising a set of first strips in a first direction and a set of second strips in a second direction, said set of first strips and said set of second strips crossing one another and being bonded to one another, said set of first strips or said set of second strips or both said set of first strips and said set of second strips having strips according to claim 1.

21. A soil reinforcement layer, said layer comprising one or more soil reinforcement strips or one or more grids for soil reinforcement, wherein the one or more soil reinforcement strips have a polymer matrix, further comprise elongated steel elements inside said polymer matrix as reinforcing elements, wherein each of said elongated steel elements has a combined elastic and plastic elongation at break that exceeds 4%, and wherein the one or more grids for soil reinforcement comprise a set of first strips in a first direction and a set of second strips in a second direction, said set of first strips and said set of second strips crossing one another and being bonded to one another, said set of first strips or said set of second strips or both said set of first strips and said set of second strips having the one or more soil reinforcement strips.

22. A mechanically stabilized earth structure, comprising one or more soil reinforcement strips, or one or more grids for soil reinforcement, wherein the one or more soil reinforcement strips have a polymer matrix, further comprise elongated steel elements inside said polymer matrix as reinforcing elements, wherein each of said elongated steel elements has a combined elastic and plastic elongation at break that exceeds 4%, and wherein the one or more grids for soil reinforcement comprise a set of first strips in a first direction and a set of second strips in a second direction, said set of first strips and said set of second strips crossing one another and being bonded to one another, said set of first strips or said set of second strips or both said set of first strips and said set of second strips having the one or more soil reinforcement strips.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

[0053] FIG. 1 illustrates a first strip;

[0054] FIG. 2 shows a cross-section of a first example of a steel cord;

[0055] FIG. 3 illustrates a second strip;

[0056] FIG. 4 shows a cross-section of a second example of a steel cord;

[0057] FIG. 5 shows a load—elongation curve of a steel cord;

[0058] FIG. 6 shows a first grid;

[0059] FIG. 7 shows a second grid;

[0060] FIG. 8 illustrates a mechanically stabilized earth structure.

MODE(S) FOR CARRYING OUT THE INVENTION

[0061] FIG. 1 illustrates a first soil reinforcement strip 10 according to the invention. The strip 10 has a polymer matrix 12 and between ten and fifty steel cords 14.

[0062] Suitable and preferable polymers or functionalised polymers for the polymer matrix 12 may be for example polyolefins such as grafted and/or blended HDPE (high density polyethylene), modified polypropylene and low-density polyethylene (LDPE), linear low density polyethylene (LLDPE), very low density polyethelene (VLDPE), ultra low density polyethylene (ULDPE) and/or ethylene based polymers or copolymers like for example ethylene-propylene copolymers, ethylene-vinyl acetate copolymers (EVA) or acrylate copolymers, especially for example modified, grafted or comprising some polar function like acrylate or acetate functions.

[0063] The strip 10 may have a width ranging from 5 mm or 10 mm to 80 mm, preferably 20 mm to 70 mm. Especially in case of a grid, the width of the strips for example may be less than 20 mm. The strip 10 may have a thickness ranging from 2 mm to 4 mm.

[0064] Referring to FIG. 2, the steel cord 14 is a (1+5)×0.37 steel cord having a core filament 20 with a diameter of 0.37 mm and five layer filaments 22 with a diameter of 0.37 mm twisted around the core filament and forming an unsaturated layer around the core filament 20. An unsaturated layer means that the layer is not closed, i.e. the layer filaments 22 do not contact one's neighbour and allow polymer to penetrate and adhere to the core filament 20. The unsaturated layer not only allows mechanical anchorage of the polymer to the steel cord 14 but also increased chemical adhesion as the contact surface between steel and polymer has increased substantially.

[0065] Alternative steel cords may be provided that also have a construction with one or more core filaments and an unsaturated layer.

[0066] An example is a 1×d.sub.1+6×d.sub.2 construction where the diameter d.sub.2 of the layer filaments is smaller than the diameter di of the core filament. Another example is a 1×d.sub.1+4×d.sub.2 construction with the diameter d.sub.1 of the core filament equal or somewhat thicker than the diameter d.sub.2 of the layer filaments.

[0067] The steel filaments of the steel cords preferably have a zinc or a zinc alloy coating. Most preferably, the zinc or zinc alloy coating is applied to the steel filaments by way of a hot dip operation. The thickness of the zinc coating may be smaller than four micrometer, e.g. lower than three micrometer. Preferably an alloy layer zinc-steel is present between the steel core and the zinc or zinc alloy coating. This zinc or zinc alloy coating is added to the steel wires or the steel filaments of the steel cord before any extrusion with a polymer or before any treatment with a primer or adhesion promotor.

[0068] A zinc alloy coating may be a zinc aluminium coating that has an aluminium content ranging from 2 per cent by weight to 12 per cent by weight, e.g. ranging from 3% to 11%.

[0069] A preferable composition lies around the eutectoid position: Al about 5 per cent. The zinc alloy coating may further have a wetting agent such as lanthanum or cerium in an amount less than 0.1 per cent of the zinc alloy. The remainder of the coating is zinc and unavoidable impurities.

[0070] Another preferable composition contains about 10% aluminium. This increased amount of aluminium provides a better corrosion protection then the eutectoid composition with about 5% of aluminium.

[0071] Other elements such as silicon (Si) and magnesium (Mg) may be added to the zinc aluminium coating. With a view to optimizing the corrosion resistance, a particular good alloy comprises 2% to 10% aluminium and 0.2% to 3.0% magnesium, the remainder being zinc.

[0072] An example is 5% Al, 0.5% Mg and the rest being Zn.

[0073] FIG. 3 illustrates a second soil reinforcement strip 30 according to the invention. The soil reinforcement strip has a polymer matrix 32 and is reinforced by various steel cords 34.

[0074] FIG. 4 shows a cross-section of a steel cord 34. Steel cord 34 has a 2×1 construction, i.e. steel cord 34 consists of two steel filaments 40, 42 that have been twisted with each other. An example is 2×0.54 (filament diameter 0.54 mm).

[0075] Other n×1 steel cord constructions may be provided with n the number of steel filaments and ranging from three to where nine. One or more of the steel filaments has a plastic deformation, for example an undulation, to avoid that all n steel filaments contact one another and form and enclose a central cavity where polymer would not be able to penetrate.

[0076] FIG. 5 shows a load elongation curve 50 of a steel cord used in the context of the present invention. The abscissa is the elongation A, expressed in per cent. The ordinate is the load R, expressed in MPa.

[0077] At small initial loads steel cord constructions may show in some cases a relatively large elongation A.sub.s, referred to as the structural elongation. This is the first phase. The structural elongation A.sub.s of the steel cord is that part of the elongation that is due to the twisted nature of the cord or due to plastic preformation of the individual steel wires. The cord is somewhat stretched, filaments come closer to each other and the twisting pitch increases somewhat. In case of an individual steel wire, the steel wire is stretched and becomes straight.

[0078] It is not necessary that this structural elongation is avoided. In some cases it may be useful to obtain a complete penetration by the polymer inside the steel cord.

[0079] In a second phase, the steel filaments in the steel cord show an elastic elongation A.sub.e. That part is the linear part according to Hooke's law.

[0080] In a third phase, the steel filaments are plastically deformed over an elongation A.sub.p until the steel cord breaks at an elongation of A.sub.t.

[0081] According to the present invention, the sum of the elastic elongation A.sub.e and the plastic elongation A.sub.p must exceed 4%, e.g. is more than 4.5%, e.g. more than 5%. The structural elongation A.sub.s, if any, must not be added, since this structural elongation gets lost due to embedment of the steel cord in the polymer matrix.

[0082] FIG. 6 shows a first example of a soil reinforcement grid 60, sometimes called a geogrid, according to the present invention. Grid 60 comprises a number of strips 62 in one direction and a number of strips 64 in another direction, e.g. preferably perpendicular to the direction of strips 62 although other embodiments are possible with angles different from 90°. Strips 62 may form the warp and strips 64 the weft. The strips 62, or the strips 64, or both the strips 62 and the strips 64 may be reinforcement strips according to the invention. The strips 62 are superimposed upon the strips 64. Strips 62 may be fixed to strips 64 by a heat operation like hot welding so that the polymers melt partially and adhere to each other. Another way of fixing strips 62 to strips 64 is by adhesive bonding, or by mechanical fixing by means of textile yarns forming stitches.

[0083] FIG. 7 shows another example of a grid 70 having strips 72 in one direction and strips 74 in another direction. The difference with the embodiment of FIG. 6 is now that the strips 72 are interwoven with strips 74.

[0084] FIG. 8 illustrates how strips 10 are used in a mechanically stabilized earth structure 80. The embankment structure 80 has a facing that may be composed of prefabricated concrete blocks 82, 82′ that are positioned one upon the other. Alternative facings may be constructed with welded or woven steel wire gabions. Strips 10 are connected to the facing 82, 82′ one by one, starting with the lowest level. Fill material 84 is gradually added and loaded. The fill material 84 may comprise sand, gravel, soil, crushed rocks, recycled materials from demolition of buildings or civil engineering structures, lime, cement.

LIST OF REFERENCE NUMBERS

[0085] 10 strip [0086] 12 polymer matrix [0087] 14 steel cord [0088] 20 core steel filament [0089] 22 layer steel filament [0090] 30 strip [0091] 32 polymer matrix [0092] 34 steel cord [0093] 40 steel filament [0094] 42 steel filament [0095] 50 load — elongation curve [0096] 60 grid [0097] 62 strip [0098] 64 strip [0099] 70 grid [0100] 72 strip [0101] 74 strip [0102] 80 mechanically stabilized earth structure [0103] 82, 82′ building blocks of the facing [0104] 84 fill material [0105] 86 natural ground