WO1995011350A1 - Geocomposite for reinforcement and containment works having high-elastic modulus and a locally differentiated deformability - Google Patents

Abstract

The present invention relates to a continuous material having high overall tensile strength (mono-and/or bidirectional) and having deformability properties which are locally differentiated and filtration or filtration-drainage properties. According to an embodiment, the material may also have water-proofing properties. The material may be used as a reinforcing structure or as a containment structure in earth construction works. The material is particularly suitable for reinforcement and containment works in that it allows to reduce or to avoid the pull-out phenomena.

Description

Geocomposite for reinforcement and containment works having high-elastic modulus and a locally differentiated deforma¬ bility

State of the art

The use of geosynthetics (such as geotextiles and the like articles and geocomposites) as reinforcing and containment elements in earth construction works is becoming increas¬ ingly wide-spread as a suitable modification of the conven¬ tional technologies.

It is known that linear or planar elements provide a ground reinforcing effect resulting from activation of the shear stresses and of resistance to pull-out originating from the interaction phenomena between the ground and the reinforc¬ ing element.

The use of geotextiles for making containment structures in foundation, reinforcement, support or hydraulic works is known.

For reinforcing works, elements made by geosynthetics are laid in horizontal layers, giving to the structure an im¬ proved resistance against the shear stress generated in the ground as a component of the compression stress. As a con¬ sequence, their elastic properties must be such as to pro¬ vide a low deformability of the structure.

Often, in these kinds of works there is the need that the same reinforcing or containment element may carry out - besides its main function (reinforcement or containment) - also other functions such as: filtration, drainage, separa¬ tion, water-proofing or other functions depending on the purpose of the structure. Often, such secondary functions are not taken into account both by designers and workers on the project site and by the producers of the materials; this fact brings about the use of monofunctional materials and - as a consequence - a substantial reduction with the passing of time of the overall functionality of the work.

The materials most commonly used for providing ground rein¬ forcing elements are: geogrids, geonets, woven geotextiles and geocomposites based on non-woven reinforced geotextil¬ es. Geotextiles (woven or non-woven) and geomembranes are, on the other hand, commonly used for providing containment elements.

A drawback relating to some reinforcing materials resides in the possibility that phenomena of pull-out from the ground may take place resulting from the low friction coef¬ ficient between the reinforcing element and the ground. Of¬ ten, containment materials may suffer a loss of functiona- luity due to tearing during the laying process or in opera¬ tion.

Among the above-mentioned materials, those which are pre¬ sently most often used for reinforcement are geogrids and geonets; these are open planar materials having a reticular structure which, as different from linear reinforcing metal elements generally used for reinforced earth works, reduce the pull-out phenomena.

The material by which geogrids and geonets are made (high- density polyethylene, high-resistance polypropylene, poly¬ ester filaments protected with polyethylene and the like) have a high elastic modulus and good friction properties in contact with the ground. Geogrids and geonets, however, have only a mechanical function and no hydraulic function. Often, in order to make up for this functional deficiency, it is necessary to make use of additional materials (such as filtering and draining materials and the like).

Furthermore, geogrids and geonets, as well as other linear metallic elements, may be used only with a limited number of types of ground (granular, non-cohesive grounds).

Both geogrids and geonets are poorly protected as to possi¬ ble damage resulting particularly during the laying opera¬ tion, with a consequent substantial reduction of the per¬ formances.

Woven geotextiles, having some filtering properties, used both for reinforcement and containment works, are more sub¬ ject to the risk of mechanical damage both during laying and in operation, even though they may sometimes have high mechanical properties. In view of the above, woven textiles are often protected by non-woven materials. In reinforcing works, woven geotextiles, as different from geogrids and geonets, tend to prevent the pull-out phenomena, since they are subject to deformation in their planes, such as to pre¬ vent the slip out of the ground.

Non-woven geotextiles, which are materials with excellent filtration properties have the relevant drawback of an ex¬ cessive deformability which does not allow their use in re¬ inforcement works, wherein the admissible deformation in the work are limited.

Geome branes, which are highly deformable water-proofing geosynthetics, often used for containment works, may be ea¬ sily damaged by piercing and tearing and as a consequence they are used only in a protected manner.

Geocomposites have been made in order to try to compensate for the above-mentioned drawbacks; these consist of combi¬ nations of textile materials (woven or non-woven) having different features or by textile materials coupled to other types of materials. It is thus possible to obtain products having mechanical and/or hydraulic properties suitable for use as reinforcing elements for any type of ground and also for peculiar hydraulic conditions. Among the geocomposites of this type, there are geocomposites based on reinforced non-woven geotextiles, geocomposites based on reinforced filtering and draining geocomposites, etc..

Summary of the invention

An object of the invention is to provide a geocomposite for reinforcement and containment works suitable to substan¬ tially reduce or avoid the pull-out phenomena.

Accordingly, the invention provides a geocomposite for re¬ inforcement ad containment works consisting of a continuous material having high overall tensile strength (mono- and/or bidirectional) , having an elastic modulus locally differen¬ tiated, comprising contiguous zones having a different ela¬ stic modulus and having deformability properties which change along its surface in an alternated and/or regular way and having filtering or filtering-drainage capacity which is preferably uniform throughout its surface.

The tensile strength of the geocomposites according to the invention is preferably between 20 kN/m and 1500 kN/m and the elastic modulus is preferably comprised between 25 kM and 150,000 kN.

According to an embodiment of the invention, the material may also have water-proofing functions. The material comprises at least three layers, one of which has high-tensile strength, preferably between 30 kN/m and 1500 kN/m and elastic modulus between 3,000 kN and 150,000 kN. The layer or layers having high-tensile strength and constituting a reinforcing structure are sandwiched between protecting layers having high strength against piercing or penetration (fig.la and fig.lb).

Such protecting layers may form an integral structure with the reinforcing layer or layers by being bonded throughout the overall surface or only along the edges (fig.2a and fig.2b) .

The reinforcing layer or layers may consist of linear ele¬ ments which are independent one from the other (fig.3a) or by linear elements having high-tensile strength included in a continuous planar structure (fug.3b and fig.3c).

One or both of the protecting layers may consist of a non- woven geocomposite having filtering or filtering-draining properties (fig.4a and fig.4b). One of such protecting la¬ yers may be water-proofing, that is it may be a geomembrane protected by a non-woven geotextile suitable for mechanical protection or by a filtering-draining geotextile (fig.5a and fig.5b). The reinforcing elements of the layer or la¬ yers forming the reinforcing structure may be made from synthetic polymeric materials (such as high-density poly¬ ethylene, high-resistance polypropylene, polyvinylalcohol , polyester, polyamide, etc.) or mineral materials (such as glass fibers) or metallic materials (steel, copper, brass, zinc-plated steel, etc.) or by combinations of such mate¬ rials.

The reinforcing elements may be obtained by means of texti¬ le technologies or by means of extrusion processes; in both cases, the reinforcing layer will be made from independent band or strip-like elements.

If the reinforcing layer is made in a planar form, both the reinforcing elements and the supporting structure will be preferably made by means of textile technologies; under such circumstances, the textile supporting structure should have deformability properties or elastic strain, which is at least twice higher than that of the reinforcing elements (fig.3b).

The protective layers (fig.la and fig.lb), whatever their function (filtration, filtration-drainage, water-proofing) should be made from materials having high elastic strain, preferably of at least 40%, preferably consisting of non- woven textiles.

If a planar reinforcing structure is used, the material shall be subject to deformations within the reinforced earth structure such as to make impossible the pull-out; this would be due to the fact that the material of the in¬ vention takes a configuration similar to that shown in figs.6a and 6b, which creates a number of joints between the structural reinforcing element and the ground.

If the layers forming the described material according to the invention are only partially connected (only along their edges), the reinforced structure will take a tubular shape suitable for containment works or for specific rein¬ forcement works.

In this case, filling material such as ground, concrete, may be introduced into the tubular structure by piercing a hole through the protecting layers. The connection between the various layers of the described material may be carried out by means of mechanical methods which are specific of the textile technology (particularly in the case of permeable structural elements), such as needling or stitching or by means of thermal processes, such as heat-sealing. In the latter case, the connection between the various layers of the structure may be carried out with the use of textile material made up of at least two types of polymeric fibers or yarns having different melting points and by subjecting the textile material to a thermal treatment suitable to melt the polymer with the lower melting point.

In this case, the connection may also be carried out by in¬ serting open heat-melting structure (such as thermoplastic nets) or by using direct extrusion processes. The connec¬ tion may also be made by means of mechanical and/or thermal processes carried out sequentially.

In the drawings:

figs.la, lb, 2a and 2b are sectional views of a geo¬ composite according to different embodiments of the inven¬ tion; figs.3a, 3b and 3c schematically show reinforcing structures for use within the geocomposite of the inven¬ tion; figs.4a and 4b are cross-sectional views of two embo¬ diments of the geocomposite of the invention having filter¬ ing-draining properties; figs.5a and 5b are cross-sectional views of two embo¬ diments of the geocomposite of the invention including a water-proofing layer; figs.6a and 6b are schematic views showing a geocompo¬ site of the invention laid and buried in the ground and showing the interaction between the geocomposite and the ground, preventing the pull-out phenomena.

As shown in the drawings, a geocomposite according to the invention comprises at least two protecting overlapping plies 2 and 4, which may comprise one or more layers, pre¬ ferably of a non-woven or woven geotextile material. The protecting plies are connected one to the other(s), by me¬ chanical connecting means 6, such as by needling or stitch¬ ing, throughout the overall surface of the geocomposite, as shown in figs.la and lb or only along the edge zones of the geocomposite as shown in figs.2a and 2b.

A reinforcing structure 8, 8a, 8b is sandwiched between the protecting plies; said reinforcing structure may consist of a plurality of discrete bands or strips 8, spaced apart one from the other, of a material having a tensile strength substantially higher than the material constituting the protecting plies, e.g. of a non-elastomeric polymeric mate¬ rial, a mineral material such as glass or metal materials. In the embodiment of fig.3b, the reinforcing structure con¬ sists of a continuous planar structure comprising spaced apart longitudinally extending portions 10 having high-ten¬ sile strength and low-elastic strain made e.g. of woven fa¬ bric of metal wires or glass filaments or filaments of a polymeric material, preferably polyamide; the portions 10, which provide tensile strength, are adjacent to portions 12 having substantially higher deformability consisting e.g. of fabric or web made of yarns of a material having prefe¬ rably the same elastic strain as the material constituting the protecting plies.

In the embodiment of fig.3c, the reinforcing structure con¬ sists of a continuous planar structure comprising a net-li¬ ke portion 14 having the same function as the portions 10 and providing tensile strength in two crossing directions. The net-like portion 14 surrounds discrete portions 16 con¬ sisting e.g. of a grid or web of high elastic strain mate¬ rial. The surface of the reinforcing structure correspond¬ ing to the portions having high-tensile strength is bonded or at least partially bonded to at least one of the protec¬ ting plies, preferably by non-mechanical connecting means such as by an adhesive or by heat-sealing.

In the embodiment of fig.4a, the geocomposite comprises a first protecting ply comprising two layers, namely a layer 20 having filtration properties and a layer 22 having drai¬ ning properties and a lower protecting ply 20a consisting of a geotextile layer having filtration properties.

In the embodiment of fig.4b, the geocomposite comprises two protecting plies comprising a filtering layer 20 and a draining layer 22.

In the embodiment of fig.5a, a water-proofing layer 26 is interposed between two filtering layers 20.

In the embodiment of fig.5b, a water-proofing layer 26 is interposed between a protecting ply consisting of a filter¬ ing layer 20 and a draining layer 22 and a lower protecting ply consisting of a filtering layer 20a.

The geocomposite of the invention, as the result of its structure, will therefore comprise portions having high de¬ formability and low-tensile strength, which are adjacent to surface portions featuring a step increase of the tensile strength, so that the elastic modulus of the material will be locally differentiated according to the tensile proper¬ ties of the adjacent portions. As shown in figs.6a and 6b, the geocomposite of the inven¬ tion is particularly suitable for reinforcement and con¬ tainment works, since when buried in the ground indicated with reference G, under the compression stress to which it will be subjected, it will create a number of joints with the ground which are suitable to avoid the pull-out pheno¬ mena. It is understood that, depending of the specific structure of the geocomposite of the invention, the resis¬ tance to pull-out may be monodirectional , as shown in fig. 6a or bidirectional as shown in the embodiment of fig.6b.

Claims

1. A geocomposite particularly for earth containment and reinforcing works comprising at least two interconnected protecting plies and a reinforcing structure sandwiched be¬ tween said protecting plies, wherein said reinforcing structure includes portions having tensile strength sub¬ stantially higher than the tensile strength of the protect¬ ing plies, said portions being at least partially bonded to at least one of the protecting plies, whereby the geocompo¬ site has a locally differentiated elastic modulus, the dif¬ ference between the elastic modulus of adjacent surface portions of the geocomposite being such as to substantially reduce the pull-out events when the geocomposite is laid in operation in the ground.

2. A geocomposite according to claim 1, wherein at least one of said protecting plies has filtering or filtering- draining properties.

3. A geocomposite according to claims 1 or 2, comprising a water-proofing layer.

4. A geocomposite according to any one of claims 1 to 3, wherein the reinforcing structure is formed by one or more layers.

5. A geocomposite according to any one of claims 1 to 3, wherein the reinforcing structure comprises linear indepen¬ dent elements in the shape of bands or strips, having an elastic modulus between 3000 kN and 150,000 kN.

6. A geocomposite according to any one of claims 1 to 4, wherein the layer or layers forming the reinforcing struc¬ ture comprises portions having an elastic modulus between 30,000 kN and 150,000 kN comprised within a continuous pla¬ nar permeable structure having a deformability which is at least twice higher than the deformability of said single reinforcing portions.

7. A geocomposite according to any one of claims 1 to 6, wherein the reinforcing portions or elements of said layer or layers forming the reinforcing structure are made of a polymeric material selected from the group consisting of high-density polyethylene, high-strength polypropylene, polyvinylalcohol , polyester and polyamide or of a mineral material particularly glass, or metallic material prefera¬ bly selected from the group consisting of steel, copper, brass, zinc-plated steel.

8. A geocomposite according to any one of claims 1 to 7, wherein the elements or portions having high-elastic modu¬ lus of the reinforcing structure are woven materials.

9. A geocomposite according to claim 5, wherein said li¬ near elements forming the reinforcing structure consist of extruded bands.

10. A geocomposite according to any one of the preceding claims, wherein said protecting plies are bonded together along edge portions of their surface thereby to form a tu¬ bular geocomposite structure suitable to contain a filling material .

11. A geocomposite according to any one of the preceding claims, wherein said plies are connected by mechanically connecting means conventionally used in the textile techno¬ logy.