SUPPORTING FABRIC FOR BEARING BULK MATERIAL AND A METHOD OF BUILDING A ROAD EMBANKMENT, A DAM, A CONCRETE STRUCTURE OR SOME OTHER BODY FORMED OF BULK MATERIAL

Abstract: The invention relates to supporting fabric, such as a woven fabric, a knitted fabric, a web or a deposition made up of prac­ tically rightangularly crossing, substantially synthetic yarns and having a width of at least 30 cm, preferably more than 1 m, and a length of at least 3 m, more particularly for geotextile uses, such as for bearing one or more layers of sand, gravel, stones, clay, loam, asphalt, mortar or like bulk or other material, the fabric having a tensile strength in one or more directions of at least 50 kN/m. The yarns of the fabric are entirely or partly in the form of tapes or threads, the material of each of the tapes or threads chiefly being formed of a matrix of polypropylene incorporating a polyester, preferably poly­ ethylene terephthalate. The matrix is used in an amount of 75 to 85 per cent by weight, based on the total weight of the tapes or threads, and the polyester is used in an amount of 25 to 15% by weight, based on the total weight of the tapes or threads.

Description: The invention relates to a supporting fabric, such as a woven fabric, a knitted fabric, a web or a deposition made up of pre­ ferably practically rightangularly crossing, substantially synthetic yarns and having a width of at least 30 cm, preferably more than 1 m, and a length of at least 3 m, more particularly for stationary geotextile and/or constructional uses, such as for bearing one or more layers of sand, gravel, stones, clay, loam, asphalt, mortar or like bulk or other material, to a height of at least 5-10 mm, the fabric having a tensile strength in one or more directions of at least 50 kN/m. A supporting fabric of the type indicated above is known from EP 0 024 777 and the article "Kunststofweefsels in de praktijk" by Ir. J.H. van Leeuwen in "Land + Water", No. 7/8, 1975. These known fabrics are often successfully used in building road, dam or dike embankments on a subsoil having a low bearing capacity. On this relatively bad subsoil there is laid a supporting fabric on which subsequently a structure of sand, stones, clinker or other bulk material is formed. The embankment of bulk material may widely vary according to the locality and the structure to be made, such as simple road surfacing, a motorway, a dike or a breakwater in the sea. For instance, the height of the layer of bulk material may range from about twenty cm to 10-20 m. The use of a supporting fabric on a subsoil and/or as intermediate layer leads to improved stability of the raised structure and a proper, permanent separation between the subsoil and the raised struc­ ture. Furthermore, the load distributing effect of the supporting fabric consists in a reduction of point-to-point differences in consolidation, so that a re-distribution of stresses is obtained. The use of the known supporting fabric as a soil stabilizing means consequently leads to considerable savings, compared with the conventional method of working without the use of this type of soil stabilizing means. Of the commercially available supporting fabrics the warp yarns, which take up practically the entire loads, may be polyester multifilament yarns, and the weft yarns are generally multifi­ lament yarns of the same material or some different material, such as polyamide or polypropylene. Although in actual practice the well-known supporting fabrics of polyester warp and/or weft yarns are applied on a large scale and are found quite satis­ factory, use is made in actual practice and also on a fairly scale of supporting fabrics of which the warp yarns and possibly also the weft yarns are in the form of tape yarns of polypropy­ lene. A disadvantage to supporting fabrics containing polypropy­ lene warp yarns, however, is that the creep of the fabric in load direction is very high. The creep of a fabric is the deformation of material, particularly the extension of the material, under the influence of static loading. The magnitude of the creep is expressed as percentage extension with time, the time being a period of 1 year or 10 years. As in actual practice the creep of a supporting fabric is one of the most important properties, it will be clear that the high creep of a polypropylene supporting fabric will generally con­ stitute a restraint on its applicability. It should be added that FR 2 265 913 describes a fabric for use underneath the ballast bed of an asphalt paving. It also says that the fabric may consist of polyesters, polyamides or poly­ olefins. In FR 2 276 427 it is described that for reinforcing the subsoil of a road or an embankment an interwoven fabrication of crossing strips may be placed on the subsoil. The strips are of polyester monofilaments. DOS 1 965 737 describes a non-woven web of polyester filaments for the stabilization of the subsoil. There is the impression that the creep of a polypropylene suppor­ ting fabric may be 100 × as high as that of a supporting fabric of polyester multifilament yarns, depending on the acting load in relation to the breaking load. The invention has for its object to provide a supporting fabric of the type mentioned in the opening paragraph, which however does not display the disadvantage of the prohibitively high creep of a supporting fabric entirely formed of polypropylene. The supporting fabric according to the invention is characterized in that the yarns of the fabric are entirely or partly in the form of tapes and/or threads, the material of each of the tapes or threads chiefly being formed of a matrix of polypropylene incor­ porating a polyester, preferably polyethylene terephthalate, and in that the matrix is used in an amount of 75 to 85 per cent by weight, and preferably approx. 80 per cent by weight, based on the total weight of the tapes or threads, and the polyester of is used in an amount of 25 to 15% by weight, preferably about 20% by weight, based on the total weight of the tapes or threads. In a preferred embodiment the polyester is present in the polypro­ pylene matrix in the form of a large number of fibrils. A favourable embodiment is characterized according to the invention in that in one or more directions, particularly in warp direc­ tion, the fabric has a tensile strength of 50 to 1000 kN/m, preferably 75 to 600 kN/m, and that in the same directions the elongation at rupture is 5 to 20%, preferably about 8-20%. The supporting fabric of the type made up of warp and weft yarns having a tensile strength in weft direction of at least 15 kN/m is characterized according to the invention in that the fabric has a mass of 150 to 2500 g/m², preferably about 200 to 1000 g/m². According to the invention it is of advantage to use yarns, more particularly warp yarns, that are in the form of tape and may consist of a single, for instance twisted and fibril­ lated, tape having a thickness of about 60 to 100 µm and a width of at least 0,5 mm, preferably 1 to 150 mm, with the linear density of the yarns, more particularly the weft yarns of the fabric being in the range of about dtex 1500 to 25000. Surprisingly, it has been found that the creep properties of the supporting fabric according to the invention are considerably better than those of well-known wholly polypropylene supporting fabric. The creep of a supporting fabric according to the invention of tape yarn made up of 80% by weight of polypropylene and 20% by weight of polyethylene terephthalate is expected to be about 10 times as low as that of a well-known 100%-polypropylene suppor­ ting fabric. It is therefore possible for the supporting fabric according to the invention to be loaded in actual practice up to 30-35% of the tensile strength or breaking load for those uses where resistance to creep must constitute the essential property of the fabric. The well-known 100%-polypropylene supporting fabric, however, can in actual practice only be loaded up to about 20% of the tensile strength or breaking load. Moreover, with a supporting fabric according to the invention the weaving efficiency is higher, as a result of which the strength of the supporting fabric is 2,5 times that of the well-known polypropy­ lene supporting fabric. Consequently, the functional strength of a supporting fabric according to the invention is 3,5 to 5 times that of the well-known 100%-polypropylene supporting fabric. It should be noted that some properties of the supporting fabric according to the invention, such as tensile strength and creep, are somewhat less favourable than those of a supporting fabric of of polyester multifilament yarns. On the other hand the suppor­ ting fabric of tape yarn according to the invention is consider­ ably less susceptible to damage than the well-known supporting fabric of polyester filament yarns, and the supporting fabric according to the invention has a more robust appearance. On the strength of the various properties and the special com­ position of the supporting fabric according to the invention it has also surprisingly been found that of the supporting fabric according to the invention the cost price for a special func­ tional (useful) strength is lower, i.e. a lower price per useful kN/m, than that of the well-known wholly polypropylene or wholly polyester supporting fabric. The supporting fabric according to the invention may with advan­ tage have a plain weave or a twill weave. For relatively heavy loads the supporting fabric of the type with warp and weft yarns according to the invention is characterized in that the yarns extending in the warp direction of the fabric are formed by straight warp yarns and binder warp yarns, the straight warp yarns each having a higher tensile strength than the binder warp yarns, the construction being such that when the fabric is sub­ jected to a tensile load in the warp direction the straight warp yarns bear a higher proportion of the tensile load, preferably at least 80%, than the binder warp yarns. And the linear density of each of the straight warp yarns may be at least five times, and preferably ten to forty times as high as the linear density of the binder warp yarns. In various uses the supporting fabric according to the invention must be properly water permeable, but the meshes in the material must be dimensioned appropriate to the conditions under which it is to be used, so that no bulk material can pass through them. When the bulk material is in the form of sand, use may be made of meshes measuring, for instance, about 0,1 × 0,1 mm to 0,5 × 0,5 mm, depending on the grade limits of the sand. The afore-mentioned tensile strength and elongation at rupture are determined in accordance with DIN 53857, be it that before­ hand a pretension is applied until the supporting fabric has undergone 1% deformation. As to the state of the art it should be added that fibrillated or non-fibrillated tape yarns of 80% weight of propylene and 20% by weight of polyethylene terephthalate from which the supporting fabric according to the invention is made are known in themselves from GB 1 559 056. The invention will be further described with reference to the accompanying schematic drawing. Figure 1 is a view in perspective of the supporting fabric accor­ ding to the invention. Figure 2 is a plan view of the fabric of Figure 1. Figure 3 is a cross-sectional view of the supporting fabric according to the invention. Figure 4 is a cross-sectional view of a road embankment. The supporting fabric according to the invention shown in Figures 1 and 2 has a plain weave pattern and is formed by straight warp yarns or tapes 1, binder warp yarns or tapes 2 and weft yarns or tapes 3. Figure 3 shows this fabric in cross-section, like parts being referred to by the same numerals as given in Figures 1 and 2. As appears from the drawings, the straight warp yarns 1 extend practically rectilinearly in the fabric, whereas the binder warp yarns 2 strongly wind about the weft yarns 3. As the heavy straight warp yarns extend practically linearly in the supporting fabric, they will show a contraction of as little as 0-2%, i.e. straight warp yarns not present in the fabric will only be 0-2% longer than the straight warp yarns contained in the fabric. Upon the supporting fabric according to the invention being subjected to a tensile load in warp direction the fabric elongation will consequently be very small. As appears from the drawing, the binder warp yarns 2 show a much higher contraction. The contrac­ tion of the binder warp yarns is generally in the range of 25 to 70%. In the supporting fabric which is very schematically illustrated in Figure 1, 2 and 3 with a plain weave and of the straight warp type, i.e. straight warp and binder warp yarns, the straight warp yarns 1 may each consist of, for instance, a single fibrillated tape of a linear density of dtex 25000 to 50000. These tapes are of 80% by weight of polypropylene and 20% by weight of poly­ ethylene terephthalate (petp) and in the non-twisted state these tapes have a thickness of 60 to 100 µm and a width of 1 to 150 mm. For the use of these tapes as warp yarns in the supporting fabric they are given a twist of the order of, say, 10 to 40-50 turns per metre. The binder warp yarns 2 are considerably lighter than the straight warp yarns 1. Alternatively, the binder warp yarns 2 may each consist of a single non-fibrillated tape having a linear density of, say, dtex 800 to 1200 and a width of, say, 1 to 4 mm. Or the binder warp yarns may consist of 80% by weight of poly­ propylene and 20% by weight of polyethylene terephthalate. As other yarns that may be used for the binder warp may be mentioned multifilament yarns or monofilaments of nylon 6 or petp. Another suitable binder warp yarn is a wholly propylene tape yarn. The weft yarns 3 also may each consist of a single non-­ fibrillated tape having a linear density of, say, about dtex 5000 or higher and a width in the non-twisted state of, say, 1 to 150 mm. The weft yarns also may consist of 80% by weight of polypropylene and 20% by weight of polyethylene terephthalate. For the weft yarns, however, also other yarns may be used, such as multifilament or monofilament yarns of nylon 6, such as a nylon 6 or petp yarn of the dtex 940 f140 Z180 type. Another suitable weft yarn is a 100%-polypropylene tape yarn. Figure 4 shows a cross-section of a road embankment 4. The building of a road embankment first of all comprises covering a subsoil 5 of low bearing capacity with a supporting fabric 6 in such a way that the warp direction of the material is transverse to the longitudinal direction of the road embankment. Subsequently, for instance three different layers of bulk material 7, 8 and 9 are dumped onto the supporting fabric. The top layer 9 is provided in the usual manner with a road surface 10. A supporting fabric 6 thus placed in the foundation of the road embankment has a stabilizing effect until the subsoil has sufficiently consolidated for it to have a higher bearing capa­ city and may lead to a considerable economy on the cost of buil­ ding a road. Optionally, the supporting fabrics 11 and 12 accor­ ding to the invention may be placed between the boundary surfaces of the three layers of bulk material 7, 8 and 9. Further, the ends of the supporting fabrics 11 and 12 may be folded inwards, as indicated with the broken line 13. The favourable properties of the supporting fabric according to the invention will be illustrated with a few examples of which the data and measuring results are summarized in the following table. For comparison the table gives several properties of supporting of supporting fabrics I, II and III according to the invention along with those of two commercially availabe supporting fabrics A and B. For the supporting fabrics I, II, III and A a plain weave was used. For the supporting fabric B, however, use was made of a 6-ends filling rib. In the supporting fabric I according to the invention use is made both in warp and in weft direction of a single tape, each tape having a linear density of dtex 7500 and consisting of 80% by weight of polypropylene and 20% by weight of polyethylene tere­ phthalate. The tapes are twisted to 45 turns/m. In the supporting II according to the invention both the warp yarns and the weft yarns each consist of a single tape containing 80% by weight of polypropylene (PP) and 20% by weight of poly­ ethylene terephthalate (PETP). Each warp tape has a linear den­ sity of dtex 11100 and a twist of 45 t/m. The linear density of each of the weft tapes is dtex 5000 and the twist 0 t/m. Also in the supporting fabric III according to the invention both the warp yarns and the weft yarns each consist of a single tape containing 80% by weight of polypropylene (PP) and 20% by weight of polyethylene terephthalate (PETP). The linear density of each of the warp yarns is dtex 7400 and the twist is 45 t/m. The linear density of each of the weft tapes is dtex 5000 and the twist 0 t/m. In the conventional supporting fabric A both the warp and the weft are 100%-polypropylene yarns. The warp yarns each consist of a single tape having a linear density of dtex 16000 and a twist of 45 t/m. The weft yarns each consist of a single tape having a linear density of dtex 5500 and a twist of 0 t/m. In the conventional supporting fabric B use is made of poly­ ethylene terephthalate dtex 1100 f210 warp yarns having a twist of 130 t/m. The weft yarns are of polyamide dtex 1880 f280 and have a twist of 0 t/m. So both for the warp and the weft use is made of multifilament yarns. Comparison of the properties of the supporting fabrics III, A and B in the table shows that in the representative warp direction and at approximately equal tensile strength the supporting fabric according to the invention is considerably superior to the 100%-­ polypropylene supporting fabric A as far as weight (g/m²) and weaving efficiency are concerned. Of the warp yarns in the supporting fabrics mentioned in the table the creep in 1 month was measured under a load of the order of 50% of the breaking load and the following values were obtained: Creep of warp tapes of 80% PP and 20% PETP: 5,9% (supporting fabrics I, II, III according to the invention) Creep of warp tapes of 100% PP: 51,2% (supporting fabric A not according to the invention) Creep of multifilament yarns of 100% PETP: 0,5% (supporting fabric B not according to the invention) The creep of the fabrics made from these yarns will present a similar picture, so that it may be concluded that as regards the creep property of importance to this field of application a sup­ porting fabric according to the invention is far superior to a fabric wholly made up of propylene tape yarns. Surprising is that the addition of a relatively small amount of 20% by weight of PETP results in a decrease of the creep by a factor 8,7 = over a supporting fabric wholly made up of PP warp tapes. By said weaving efficiency is to be understood the ratio between the tensile strengths of the fabric and the sum of the tensile strengths of the yarns contained in it, expressed on a percentage basis. Within the scope of the invention various modifications may be made. For instance, for the weft of the supporting fabrics use may be made of yarns textured by means of air or in some other way. In building concrete structures or foundations use made be made of the supporting fabric according to the invention for bearing concrete or cement mortar and hence be used as flexible form work.

Claims: 1. A supporting fabric, such as a woven fabric, a knitted fabric, a web or a deposition made up of crossing, substan­ tially synthetic yarns and having a width of at least 30 cm, preferably more than 1 m, and a length of at least 3 m, more particularly for stationary geotextile uses, such as for bearing one or more layers of sand, gravel, stones, clay, loam, asphalt, mortar or like bulk or other material, to a height of at least 5-10 mm, the fabric having a tensile strength in one or more directions of at least 50 kN/m, characterized in that the yarns of the fabric are entirely or partly in the form of tapes or threads, the material of each of the tapes or threads chiefly being formed of a matrix of polypropylene incorporating a polyester, preferably poly­ ethylene terephthalate, and in that the matrix is used in an amount of 75 to 85 per cent by weight, based on the total weight of the tapes or threads, and the polyester is used in an amount of 25 to 15% by weight, based on the total weight of the tapes or threads. 2. A fabric according to claim 1, characterized in that the polypropylene matrix is used in an amount of about 80% by weight, based on the total weight of the tapes or threads and the polyester in an amount of about 20% by weight, based on the total weight of the tapes. 3. A fabric according to claim 1, characterized in that the polyester is contained in the polypropylene matrix in the form of a large number of fibrils. 4. A fabric according to claim 1, characterized in that in one or more directions, particularly in warp direction, the fabric has a tensile strength of 50 to 1000 kN/m, preferably 75 to 600 kN/m. 5. A fabric according to claim 1, characterized in that in one or more directions, particularly in warp direction, the fabric has an elongation at rupture of 5 to 20%, preferably about 8 to 20%. 6. A supporting fabric according to claim 1 of the type with warp and weft yarns, the tensile strength of the fabric in weft direction being at least 15 kN/m, characterized in that the fabric has a mass of 150 to 2500 g/m², preferably about 200 to 1000 g/m². 7. A fabric according to claim 1, characterized in that use is made of yarns, more particularly warp yarns, which are formed by a single tape which in the untwisted state has a thickness of about 60 to 100 µm and a width of at least 0,5 mm, preferably 1 to 150 mm. 8. A fabric according to claim 1, characterized in that yarns, particularly warp yarns are used having a linear density of about dtex 1500 to 75000. 9. A fabric according to claim 1, of the type with warp and weft yarns, characterized in that the fabric is so constructed that the yarns extending in the warp direction of the fabric are formed by straight warp yarns and binder warp yarns, the straight warp yarns each having a higher strength than the binder warp yarns, the construction being such that when the fabric is subjected to a tensile load in the warp direction the straight warp yarns bear a higher proportion of the tensile load, preferably at least 80%, than the binder warp yarns. 10. A fabric according to claim 9, characterized in that the linear density of each of the straight warp yarns is at least five times, preferably ten to forty times as high as the linear density of the binder warp yarns. 11. A process for constructing a road embankment, a dike, a dam, a concrete structure or some other body formed of bulk material, such as sand, gravel, stones, clay, loam, asphalt or cement mortar, and/or for stabilizing soil, a supporting fabric being laid on a subsoil and subsequently one or more layers of bulk material being placed on the supporting fabric, characterized in that use is made of the supporting fabric according to one or more of the claims 1-10.

Inventors: VAN DE POL, GUSTAAF MARIA WILHELMUS
Applicants: AKZO N.V.
Application year: 1987
Main classification: D03D15
IPC codes: D03D1, E02D17, E01C3, D03D15, D04B1