Netting with hexagonal mesh for use in civil engineering in geotechnical applications

Abstract

A hexagonal mesh netting, particularly for use in civil engineering in geotechnical applications, preferably in the field of protection from natural risks, is composed of elongate elements which are twisted over at least one complete revolution about adjacent elongate elements, in twisting zones which define opposite sides of the hexagonal mesh of the netting. In each twisting zone, the elongate elements are twisted in a single rotational direction. All or most of the elongate elements are multiwire elongate elements which are each composed by a plurality of metal wires.

Description

[0001] NETTING WITH HEXAGONAL MESH IN CIVIL ENGINEERING IN

[0002] GEOTECHNICAL APPLICATIONS

[0003] Field of the invention

[0004] The present invention relates to a netting with hexagonal mesh for use in civil engineering in geotechnical applications , for example , in the field of protection from natural risks .

[0005] The invention has been developed with particular regard, even i f not exclusively, for a netting with hexagonal mesh with high resistance , for carrying out civil engineering works , such as protection barriers against rockfalls or avalanches , for covering the surface of rocky walls in order to contain detachments of rocks , for three-dimensional stabili zation of earth, scarps , dams , embankments , tunnels and road constructions , for constructing containment walls for embankments , for protecting banks of bodies of water, for constructing weirs and other debris-protection barriers along rivers and streams and water works in general , for constructing gabions and other similar products made of metal nettings or comprising a metal netting, and for any other use of the generally known civil and geotechnical type , in which it is necessary to provide a metal netting which is resistant and durable .

[0006] Technological background

[0007] The nettings to which the present invention relates are used in the field of civil and geotechnical works mainly for protection from natural risks . For example , using such nettings it is possible to avoid or in any case reduce the risk of rocks , debris , snow or other similar natural elements falling downstream as a result of natural instabilities , such as , for example , landslides , avalanches , flows of debris , river floods , detachments of rocks and other phenomena of the type , reaching and damaging roads , dwellings , bridges , etc . , or even putting at risk the safety of people . To this end, these nettings , together with the supports thereof , are configured to withstand great impacts and high pressures , such as the ones brought about by a rockfall , by a flow of debris or by an avalanche which strikes it .

[0008] Typical , even i f not limiting, uses of these nettings are the construction of barriers for protection from rockfalls or avalanches , covering rocky walls in order to contain detachments of rocks , three-dimensional stabili zation of earth, scarps , dams , embankments , tunnels and road constructions , constructing containment walls for embankments , protecting banks of bodies of water, constructing weirs and other debris-protection barriers along rivers and streams and water works in general , constructing gabions and other similar products made of metal nettings or comprising a metal netting, and for any other use of the generally known civil and geotechnical type which has to use a netting which is resistant and durable , both with respect to impacts and to corrosion .

[0009] In the geotechnical sector, there are generally known, for the obj ects mentioned above , so-called loose-mesh nettings which are also known as rhomboid mesh nettings . The geometry of these nettings is produced by helically bending a series of metal wires which are interlaced with each other in order to form the rhomboid mesh of the netting .

[0010] US 6279858 describes an example of such a netting with rhomboid mesh, wherein the metal wires which compose the netting are made from a high-strength steel which has an ultimate tensile strength between 1000 and 2200 N / mm2(MPa ) . These steel wires have a very high traction resistance so that the woven arrangement maintains the three-dimensional structure thereof which is defined similarly to a mattress , even under conditions with a very high force .

[0011] The rhomboid-mesh netting, which is known by the commercial name TECCO® and which is produced by Geobrugg AG, is constructed with metal wires having an ultimate tensile strength of approximately 1770 N / mm2and a diameter of 2 , 3 or 4 mm, with mesh which may have dimensions of the diagonals of approximately 62 x 95 mm, approximately 83 x 143 mm or approximately 102 x 177 mm .

[0012] A problem with nettings with rhomboid mesh which are constructed with metal wires is that gradually, i f the resistance of the wires increases , the greater is the di f ficulty of constructing the netting as a result of the substantial force necessary for bending the wires . Although US 6279858 describes the construction of metal wires with wires having a resistance of up to 2200 N / mm2, in practice there have not been constructed any nettings having wires with resistances greater than 1770 N / mm2.

[0013] Another example of nettings with rhomboid mesh with a high resistance used for stabili zing earth is described in US 2007 / 210214 . The mesh of the netting are not formed by single wires , as are the ones previously mentioned and described in US 6279858 , but instead by strands which are formed by metal wires which are helically wound or by strand-like ropes . At least two of the wires which form each strand or rope are made of steel with a traction resistance between 100 and 2200 N / mm2. A speci fic resistance value which is described in US

[0014] 2007 / 210214 is 1770 N / mm2in accordance with the DIN standard 2078 . An alternative which is described is the use of a spring steel according to the standard DIN 17223 . A wire thickness of 3 mm is described as an example . The wires which form the strands with which the mesh of this netting are constructed may be galvani zed and provided with a zinc / aluminium covering and / or a plastics covering or a chromium-plating which provide the necessary corrosion resistance . By way of example , a covering of the wires with zinc between 10 and 250 g / m2is described . According to what is indicated in US 2007 / 210214 , the characteristics of the netting given as an example , wherein the wires of the strands have a diameter of 3 mm and an ultimate tensile strength of 1770 N / mm2, make it very rigid so as not to be subj ected to virtually any deformation under load and so as not to require any ring-like fixing elements ( for example , cross-like clips ) .

[0015] A netting having the features described in US 2007 / 210214 is produced by Geobrugg AG with the commercial name Spider® . It is formed by 1 x 3 helical strands , that is to say, each one is formed by three metal wires wound together in a helical form about the common theoretical axis with a uni form lay length . The nominal diameter of each strand is 6 . 5 mm while each of the three metal wires which form the strand has a diameter of 3 mm and is made from a steel with a high resistance of 1770 N / mm2. The rhomboid mesh of this Spider® netting are very wide with respect to the mesh of the TECCO® netting mentioned above , because they nominally measure 164 mm ( smaller diagonal ) x 270 mm ( larger diagonal ) .

[0016] Both i f single metal wires are used and i f metal strands which are constituted by a plurality of metal wires are used instead, the main problem of the rhomboid-mesh nettings is that the netting does not maintain its integrity following the breakage of one of the wires or strands which form the mesh . However, the production of nettings with such wires or strands from high-strength steel is di f ficult , i f not impossible , as a result of the substantial rigidity of the individual wires which have to have in any case a minimum diameter of 2 mm in order to achieve a nominal ultimate tensile strength, taking into account the area of the crosssection of the wire , of at least 5 . 5 kN . In order to produce these rhomboid-mesh nettings with a high resistance , it is necessary to use very robust machines which in any case have an extremely high wear rate . It is further necessary to use special arrangements for bending the metal wires as a result of the fact that the wires or strands made of high-strength steel tend to behave like harmonic steel wires for springs with a substantial resilient return and a very poor tendency to become plastically deformed so as to maintain the form of the helical bending .

[0017] Another type of containment and protection netting which is widely used in the geotechnical sector is that of metal nettings with hexagonal mesh also commonly referred to as double-torsion nettings , sometimes also known as tripletorsion nettings . They are nettings as defined in the European standard EN 10223-3 which are constituted by mesh of hexagonal shape which are formed by means of torsion in a single direction of adj acent wires in pairs , which alternately form a torsion to the right and a torsion to the left . The term "torsion" is intended to be understood here to mean a strict helical winding of the two wires about each other, where the wires rotate in a single direction . In the hexagonal mesh nettings , the pairs of wires are wound in such a manner that each wire carries out around the other wire , in the nodes of the mesh, a winding by one and a hal f revolutions in a single direction, that is to say, by at least 540 ° , so as to leave from the same side of the hexagonal mesh as the one at which it entered . Apart from this torsion in the nodes of the netting, each wire forms the netting with a zig- zag path in a longitudinal direction . A hexagonal mesh netting is intrinsically more resistant to punching or one of the metal wires which form it being torn because the double-torsion nodes of the hexagonal mesh prevent the breakage from bringing about detachment of the metal wire beyond the limit of the nodes in which the breakage is confined . In other words , the strict helical winding of the wires of the nodes of the netting brings about proper binding which prevents the netting from "becoming unravelled" i f one of the wires breaks .

[0018] WO 2019 / 239220 describes a metal netting with hexagonal mesh which is constructed with steel wires which may be stainless steel , with an ultimate tensile strength between 1500 and 1900 MPa . The wires can be covered with a protection layer made of an alloy of zinc / aluminium comprising at least 150 g / m2. The mesh of this netting have a proportion between the width thereof , that is to say, the distance between two nodes , and the height thereof , that is to say, the distance between the vertices of the hexagon which are arranged in the longitudinal direction of the netting, of less than 0 . 75 . In other words , the mesh of this known netting are more oblong than the hexagonal mesh of the most common nettings which are constructed with steel wires with a lower resistance between 550 and 770 MPa, which typically have a nominal width and height of 60 x 80 mm, 80 x 100 mm or 100 x 120 mm . The reason described, for which the mesh are more oblong than normal , is that the known machines used to manufacture the doubletorsion nettings with steel wires with a lower resistance cannot use steel wires with a high resistance because this wire is more fragile and breaks when the preformed helixes leave the tubes in which they are received and are straightened in order to pass into the mandrels where they are woven with the adj acent wires , originating from the reels upstream of the machine .

[0019] WO 2022 / 152697 describes a metal netting with hexagonal mesh which is constructed with steel wires with high resistance of at least 1560 N / mm2, preferably at least 1770 N / mm2, and preferably at least 1950 N / mm2, having a diameter between 2 and 4 mm . The ratio between the width and height of the hexagonal mesh is at least 0 . 75 , preferably at least 0 . 8 , which is the proportion of the mesh of the nettings which are commonly constructed with steel of the lower resistance class . However, WO 2022 / 152697 does not provide information relating to how it is possible to solve the problem of fragility and consequently breaking of steel wires mentioned in WO 2019 / 239220 except for generally setting out the maintenance of a process temperature suitable for not embrittling the steel or slowing down the winding operations of the wires in the weaving machine of the double-torsion netting . WO 2022 / 152697 therefore does not provide any solution to the problem of producing a metal netting with hexagonal mesh with steel wires with high resistance .

[0020] Therefore , the problem of known nettings remains unsolved in relation to how to increase the resistance of the nettings themselves without having to use special or di f ferent machines from those used for manufacturing the nettings which use metal wires made of steel with low resistance .

[0021] Statement of invention

[0022] An obj ect of the present invention is to solve the problems of the prior art , providing a hexagonal mesh netting for use in civil engineering in geotechnical applications which require a high level of resistance of the netting, in addition to a high level of ease of handling and flexibility, with a relatively reduced weight .

[0023] Another obj ect of the invention is to provide a hexagonal mesh netting with high resistance which can be readily manufactured with existing machines which are normally used for manufacturing hexagonal mesh nettings which use relatively soft wires .

[0024] Another obj ect of the invention is to provide a doubletorsion netting which is suf ficiently flexible to adapt to the non-uni form formation of the ground of scarps , slopes , banks , etcetera .

[0025] Another obj ect is to provide a double-torsion netting which is relatively light in terms of weight per unit of measurement in order to be transported and installed readily with reduced costs , particularly in impassable regions , such as , for example , mountainous zones which are potentially subj ect to rockfalls , avalanches , landslides , debris flows , etcetera .

[0026] Another obj ect of the invention is to provide a doubletorsion netting which is economical , simple to produce and durable , with a saving of material with respect to the conventional double-torsion nettings .

[0027] The above-indicated obj ects are achieved by the invention as defined in the appended claims .

[0028] In the present description, the term "wire" is intended to be understood to be a flexible , elongate element with a solid cross-section, for example , a metal wire . The term " strand" is intended to be understood to be a rope with simple winding which is constituted by wires which are wound helically about the same axis ; this rope with simple winding is also known as a "helical rope" . The axis of the strand or helical rope can be virtual , as , for example , in the case of strands with three or four wires , or real , in which case it can be constituted by a metal wire , as , for example , in the case of strands with seven wires or helical ropes with several layers of wires .

[0029] In the present description, a distinction will be drawn between strands or helical ropes and the other ropes of di f ferent types which, for clarity, will be defined as "ropes with several strands" . These other ropes are generally of the type with double or triple windings and are in any case formed by several strands , each one being wound helically about the axis of this rope with several strands .

[0030] In the present description, the term "multiwire" is also used, this being intended to be understood to be a bundle or group of two or more wires j uxtaposed along their length, but not necessarily wound helically about a common axis .

[0031] According to a first aspect , there is described a hexagonal mesh netting, particularly for use in civil engineering in geotechnical applications , preferably in the field of protection from natural risks . The netting is composed of elongate elements which are twisted in a single direction over at least one complete revolution about adj acent elongate elements , alternately in a single clockwise rotation direction and in a single counter-clockwise rotation direction, in di f ferent twisting zones which define opposite sides of the hexagonal meshes of the netting, also known as "nodes" of the double-torsion netting . All or most of the elongate elements are multiwire elongate elements which are each composed by a plurality of metal wires .

[0032] I f not all the elongate elements of the netting are multiwire ones , the remaining elongate elements may be simple wires and / or ropes with several strands .

[0033] Such a netting has a number of advantages , including the fact of being very light and convenient to move , including by hand, facilitating the positioning operations , particularly in locations and in positions which are more impassable . Furthermore , this netting is very flexible , resistant and lightweight , therefore adaptable with ease to various ground formations . Being light and flexible , the netting is readily rolled for transport and unrolled where applicable at the installation site .

[0034] According to a particular aspect , at least two of the multiwire elongate elements are arranged so as to be adj acent and twisted with each other in the twisting zones . A particular case is the one in which the entire netting is composed of multiwire elongate elements which are in this case all twisted with two adj acent elongate elements - or with a single adj acent elongate element in the case of the edges of the netting . A netting of this type allows weaving machines to be used for the hexagonal mesh nettings of known type in order to obtain nettings with high resistance which would require special machines in order to be obtained by means of single wires which are twisted, as in the case of conventional hexagonal mesh nettings .

[0035] According to another particular aspect , this hexagonal mesh netting may comprise multiwire elongate elements which are composed by two or three metal wires , preferably by two metal wires but without excluding the use of multiwire elongate elements which are also composed of four or five metal wires or more . The use of ( relatively) few metal wires in place of the single metal wire used in conventional hexagonal mesh nettings allows , in accordance with the dimensions and the strength of the single wires of the multiwire element , a good rigidity of the structure , a greater resistance thereof and / or a saving of material and therefore a reduced weight to be obtained with respect to the hexagonal mesh and doubletorsion nettings .

[0036] According to another particular aspect , the multiwire elongate elements of the hexagonal mesh nettings can be strands or helical ropes , each one comprising at least two metal wires which are helically wound about a common axis . The use of strands , also known as helical ropes or simplewinding ropes , allows the weaving machine for the netting to be supplied with elongate elements which substantially behave like a single wire , therefore being easy to use during the construction of the hexagonal mesh netting .

[0037] According to an alternative aspect , the multiwire elongate elements of the hexagonal mesh netting can each be a group or bundle of single wires which are simply j uxtaposed . This solution is particularly economical because it does not require the previous provision of strands or helical ropes which generally have a higher cost than the cost of the same wires which are not helically wound .

[0038] According to another particular aspect , the metal wires of the multiwire elongate elements are made of steel , with an ultimate tensile strength greater than 770 MPa, preferably greater than or equal to 1500 MPa, for example , of approximately 1550 MPa . The ultimate tensile strength of the metal wires may advantageously be even greater, for example , preferably greater than or equal to 1700 MPa, for example , of approximately 1750 MPa, or 1860 MPa . Even more preferably, the strength of the metal wires may be greater than or equal to 1900 MPa, for example , of approximately 1950 MPa, and, for example , it may reach or even exceed 2160 MPa . The high strength of the metal wires which form the multiwire elongate elements from which the netting is made allows relatively thin wires which still ensure a high level of flexibility of the netting, in addition to a substantial lightness thereof , to be produced . Although the wires which form the multiwire elongate elements are intrinsically resilient due to the high level of strength of the steel , the netting generally has a speci fic plasticity which allows it to be shaped and to be adapted to the varied formation of the ground . This ef fect appears to be a result of the fact that , even i f not yet completely confirmed, the wires which form the multiwire elongate elements can slide slightly with friction on each other in such a manner as to maintain over time the configuration which is imposed thereon but without there being a signi ficant yield of the material as instead occurs with the plastici zation of a metal wire of the conventional nettings .

[0039] According to another particular aspect , the metal wires of each multiwire elongate element may have the same nominal diameter . Regardless of this , the metal wires of each multiwire elongate element may have a diameter less than 3 mm, preferably less than or equal to 2 . 5 mm, more preferably less than or equal to 2 mm, much more preferably less than or equal to 1 . 5 mm, even more preferably less than or equal to

[0040] 1 . 1 mm, it also being possible to be less than 1 mm . According to another particular aspect , the multiwire elongate elements which form the netting have a nominal diameter less than or equal to 5 mm, preferably less than or equal to 4 mm, preferably less than or equal to 3 mm, even more preferably less than or equal to 2 . 50 mm, for example , 2 . 40 mm .

[0041] According to another particular aspect , the strands or helical ropes of the netting are helical ropes with a single layer of wires , each one comprising at least two metal wires , more preferably at least three metal wires , even more preferably at least five metal wires , even more preferably at least seven metal wires . These helical ropes are flexible and are , however, rather compact so as to be also readily usable even in conventional weaving machines for hexagonal mesh nettings which are normally used for manufacturing nettings with single metal wires .

[0042] According to another aspect , the elongate elements and / or the metal wires of the multiwire elongate elements may have a protection covering . The protection covering may be made of metal , for example , an alloy of zinc and aluminium, or plastics material , for example , polyethylene PE , polyvinyl chloride PVC or polyamide PA, or a combination thereof .

[0043] According to another aspect , the mesh of the netting can have a dimensional ratio of the width to the height which is less than or equal to 0 . 9 and can measure in terms of width (measured between two adj acent nodes ) and height (measured between the longitudinal vertices of the hexagonal mesh) , for example , 60 x 80 mm, 80 x 100 mm or 100 x 120 mm, reproducing the same nominal dimensions of the double-torsion nettings constructed with single metal wires . According to another aspect , the netting may comprise elements with a transverse extent , preferably metal bars which can be inserted into at least a number of twisting torsions between adj acent elongate elements . The elements with a transverse extent can contribute to maintaining the nominal dimensions in terms of width of the netting and can prevent the necking as a result of the resilience of the metal wires .

[0044] Brief description of the drawings

[0045] Additional features and advantages will be appreciated from the following detailed description of a preferred embodiment with reference to the appended drawings which are given purely by way of non-limiting example and in which :

[0046] - Figure 1 is a perspective view of an exemplary strand ( or helical rope ) which is constructed with three metal wires and which is used to construct an exemplary netting according to the invention;

[0047] - Figure 2 is a front view of some of the hexagonal mesh of a first variant of the netting according to the invention; and

[0048] - Figure 3 is a front view of some of the hexagonal mesh of a second variant of the hexagonal mesh netting according to the invention .

[0049] Detailed description

[0050] Now with reference to Figure 1 , there is illustrated by way of example a multiwire elongate element in the form of a strand 1 which is also sometimes referred to in the sector as a "cord" , "braid" or "helical rope" , which is used for possibly constructing a hexagonal mesh netting according to the invention . The strand 1 is made of steel and can be provided in reels , thereby being able to be used in the same manner in which the single metal wires are used for the manufacture of known double-torsion nettings in known netting weaving machines .

[0051] More speci fically, the strand 1 which is simply a nonlimiting example , given solely for better comprehension of the invention, is constituted by three metal wires 2 which all have the same nominal diameter and which are wound together in helical form about the common theoretical axis with a uni form lay length . The strand can also be of the type in which one of the wires is central and forms a core , about which there are helically wound the remaining wires of the strand . Another example of a strand is , for example , the one referred to as 1x7 , which is constituted by seven metal wires . Naturally, the invention is not limited to the use of such a strand or helical rope , but may comprise using other types of ropes , for example , helical ropes with several layers .

[0052] The diameter of each wire may be less than 3 mm, preferably less than or equal to 2 . 5 mm, more preferably less than or equal to 2 mm, much more preferably less than or equal to 1 . 5 mm, even more preferably less than or equal to 1 . 1 mm, it also being possible to be less than 1 mm . In the case of the example illustrated, the 1x3 strand has a diameter of 2 . 4 mm and each wire 2 has a nominal diameter of approximately 1 . 1 mm . The ultimate tensile strength is approximately 1770 N / mm2. In another example , which is not illustrated, there is advantageously used a 1x7 strand with a nominal diameter of 3 mm, the wires of which have a diameter of 0 . 9 mm, still with an ultimate tensile strength of approximately 1770 N / mm2. Naturally, these values have to be considered to be exemplary but not limiting with respect to the invention, which can be carried out with strands or ropes which are di f ferent from those described here in detail . The strand 1 has its own nominal diameter D which may be less than or equal to 5 mm, preferably less than or equal to 4 mm preferably less than or equal to 4 mm, even more preferably less than or equal to 2 . 50 mm, for example , in the case of Figure 1 of approximately 2 . 40 mm .

[0053] The wires 1 which form the strand 2 are made of steel having a resistance greater than 770 MPa, preferably greater than or equal to 1500 MPa, for example , of approximately 1550 MPa . The ultimate tensile strength of the metal wires may be even greater, for example , preferably greater than or equal to 1700 MPa, for example , of approximately 1750 MPa, or 1860 MPa . Even more preferably, the strength of the metal wires may be greater than or equal to 1900 MPa, for example , of approximately 1950 MPa, such as , for example , it may reach or even exceed 2160 MPa . Experiments have been success fully carried out with strands constructed with metal wires having a nominal resistance of 1770 MPa .

[0054] As can be seen in Figure 2 , a first variant of a hexagonal mesh netting 10 according to the invention is constructed using a series of strands 1 , of the type illustrated in Figure 1 , which are wound with each other in order to form hexagonal mesh 12 . In particular, the mesh 12 are formed by means of torsion of adj acent strands in pairs , which alternately form nodes 13 with torsion to the right , alternating with nodes 14 with torsion to the left . The term "torsion" is intended to be understood here to mean a tight helical winding of the two strands about each other, where the wires rotate in a single direction . In order to obtain a hexagonal mesh, the strands 1 carry out a winding, one about the other, in the nodes 13 , 14 by a revolution and a hal f , that is to say, through 540 ° , so that each strand 1 leaves the node at the same side of the hexagonal mesh as the one at which it entered .

[0055] As a result of the flexibility of the strands 1 , it is possible to produce hexagonal mesh which are rather small , reproducing, for example , the dimensions of the mesh commonly used for double-torsion nettings having nominal dimensions M x H of 60 x 80 mm, 80 mm x 100 mm and 100 x 120 mm . Therefore , it is possible to obtain dimensional ratios of the mesh of the width to the height of less than or equal to 0 . 9 .

[0056] The strands 1 of the netting 10 may have a corrosion protection covering . This covering may be constructed both individually on each wire 2 and - alternatively - on the strand 1 already formed . The protection covering may be of the type which is generally known, for example , made of metal , such as an alloy of zinc and aluminium, such as the one commercially designated Gal fan, or plastics material , for example , of polyethylene , polyvinyl chloride or polyamide , or a combination thereof .

[0057] The netting 10 may comprise transverse bars 15 having the function of elements with a transverse extent which are merely schematically indicated in Figure 2 . The transverse bars 15 can be inserted in the nodes of the netting 10 at predetermined intervals along the longitudinal extent of the netting itsel f . These metal bars contribute to maintaining the nominal dimensions in terms of width of the netting, preventing the necking thereof as a result of the resilience of the metal wires , particularly i f they are constructed from steel with a high strength, for example , greater than 1700 MPa . The metal bars 15 particularly block the nodes 13 , 14 at the planned nominal distance M thereof . In order to construct the netting 10 , the strands 1 are used in the known machines for producing double-torsion nettings . The dimensions of the strands 1 , in particular the nominal diameter thereof , is compatible with the known machines because it does not exceed the dimension of the metal wires used in the construction of the double-torsion nettings which are known . It has been found experimentally that the helical winding of the strands 1 necessary for introducing them into the rods which are mounted on-board the known machines is possible without it being necessary to use special rods or special devices for removing the strands as otherwise described in the prior art which uses individual metal wires with high strength . The possible introduction of the transverse bars 15 is also brought about with known techniques and systems without any need for modi fying the existing machines .

[0058] Figure 3 illustrates a variant of a metal netting 20 with hexagonal mesh according to the invention which is constructed with multiwire elements 22 which are formed by two individual wires 24a, 24b which are placed beside each other without being helically wound about each other . The dimensions of the mesh and the characteristics of the wires which form the multiwire elements 22 are similar to what has been described above with reference to the embodiment of Figure 2 , wherein the embodiment of Figure 3 illustrates a variant which di f fers only in that the wires 24a, 24b do not form a strand .

[0059] In the preferred, though non-limiting embodiment , of Figure 3 , the two metal wires 24a, 24b all have the same nominal diameter . The values of diameter and strength of each of the multiwire elements 22 can be similar or correspond to those described in relation to the embodiment described above with reference to Figure 2 . The wires which form the multiwire elongate elements 22 are also made of steel having a strength and an ultimate tensile strength similar to those described in the embodiment of Figure 2 .

[0060] The metal wires 24a, 24b of the netting 20 may each have an individual covering for protection from corrosion of a type generally known, as described above .

[0061] Each metal wire may be provided in reels and can be supplied individually to a machine for weaving the netting near which it is placed beside one or more other metal wires in order to form a group or bundle of j uxtaposed wires . Each bundle of j uxtaposed wires can readily be used in place of the individual wires which, in known weaving machines , are used to construct the conventional hexagonal mesh nettings . The transverse dimension of the elongate elements 22 which are formed by the group or bundle of j uxtaposed wires 24a, 24b is compatible with the known machines because it can be selected in such a manner that it does not exceed the diameter of the individual metal wires used in the production of conventional double-torsion nettings which are known .

[0062] Naturally, the principle of the invention remaining the same , the forms of embodiment and details of construction may be varied widely with respect to those described and illustrated, without thereby departing from the scope of the present invention .

Claims

1 . A hexagonal mesh netting, particularly for use in civil engineering in geotechnical applications , preferably in the field of protection from natural risks , which is composed of elongate elements which are twisted over at least one complete revolution about adj acent elongate elements , in twisting zones which define opposite sides of the hexagonal mesh netting, in each twisting zone the elongate elements being twisted in a single rotational direction, wherein all or most of the elongate elements are multiwire elongate elements which are each composed by a plurality of metal wires .2 . A hexagonal mesh netting according to claim 1 , wherein at least two of the multiwire elongate elements are arranged so as to be adj acent and twisted with each other in the twisting zones .3 . A hexagonal mesh netting according to either of the preceding claims , wherein the multiwire elongate elements are composed by two or three metal wires , preferably by only two metal wires .4 . A hexagonal mesh netting according to any one of claims 1 to 3 , wherein the multiwire elongate elements are strands or helical ropes , each one comprising at least two metal wires which are helically wound about a common axis .5 . A hexagonal mesh netting according to any one of claims 1 to 3 , wherein the multiwire elongate elements are each a group of single wires which are j uxtaposed .6 . A hexagonal mesh netting according to any one of the preceding claims , wherein the metal wires of the multiwire elongate elements are made of high-strength steel , with an ultimate tensile strength greater than 700 MPa, preferably greater than or equal to 1500 MPa, even more preferably greater than or equal to 1700 MPa, even more preferably greater than or equal to 1900 MPa . . A hexagonal mesh netting according to any one of the preceding claims , wherein the metal wires of each multiwire elongate element have the same nominal diameter .8 . A hexagonal mesh netting according to any one of the preceding claims , wherein the metal wires of each multiwire elongate element have a diameter less than 3 mm, preferably less than or equal to 2 . 5 mm, more preferably less than or equal to 2 mm, much more preferably less than or equal to 1 . 5 mm, even more preferably less than or equal to 1 . 1 mm, or less than 1 mm .9 . A hexagonal mesh netting according to any one of the preceding claims , wherein the multiwire elongate elements have a nominal diameter less than 5 mm, preferably less than or equal to 4 mm, preferably less than or equal to 3 mm, even more preferably less than or equal to 2 . 50 mm .10 . A hexagonal mesh netting according to any one of the preceding claims , wherein the elongate elements are helical ropes with a single layer of wires , each one comprising at least two metal wires , more preferably at least three metal wires , even more preferably at least five metal wires , even more preferably at least seven metal wires .11 . A hexagonal mesh netting according to any one of the preceding claims , wherein the elongate elements and / or the metal wires of the multiwire elongate elements have an external protection covering .12 . A hexagonal mesh netting according to any one of the preceding claims , wherein the mesh have a dimensional ratio of the width to the height which is less than or equal to 0 . 9 .13 . A hexagonal mesh netting according to any one of the preceding claims , comprising elements with a transverse extent , preferably metal bars which are inserted into at least a number of twisting torsions between adj acent elongate elements .