ITMI20110028A1 - METHOD AND DEVICE FOR LAYING AND TENSIONING OF A WATERPROOF COVER, FOR HYDRAULIC WORKS IN LOOSE MATERIAL. - Google Patents

Description

DESCRIPTION FOR INVENTION PATENT

Entitled: â € œMethod and device for laying and tensioning a waterproof covering, for hydraulic works in loose materialâ €.

BACKGROUND OF THE INVENTION

The present invention refers to a method and to a device, or system, for laying and tensioning a waterproof covering or geomembrane for the protection of hydraulic works in natural material in the loose state, such as for example clay, earth, gravel, rock material and / or their combination, in particular dams, canals and / or natural and / or artificial basins, or similar hydraulic structures, which achieve simultaneous locking and controlled tensioning of the waterproof covering during its installation and construction.

For the purposes of the present description, by `` geomembrane '' is meant an impermeable coating consisting of a plurality of strips and / or flat sheets connected together in a sealed manner, in which each strip or sheet comprises at least one or more layers of any geosynthetic material of the type defined below, suitable for use in contact with the ground; for example, the geomembrane may consist of a single impermeable layer of a polymeric resin, both natural and synthetic, or of bituminous material as defined below, or of several coupled layers of any geotechnical material, such as a geocomposite formed for example by a assembled structure comprising an impermeable layer as defined above, coupled with a layer of a geotextile suitable for the intended use.

STATE OF THE ART

As is known, the surface intended to come into contact with the water of hydraulic works, in particular hydraulic works in loose material, such as dams, canals and / or basins, must be suitably protected with a waterproof coating also known as â € œgeomembraneâ €, both to prevent a loss of water through the body in loose material of the dam or basin, and to prevent any infiltration of water and a possible subsidence and / or erosion of the same body in loose material, and / or surface in contact with water.

Over time, various methods and systems have been developed to cover and protect, by means of a geomembrane, hydraulic works in general and hydraulic works in loose material in particular, according to which special metal profiles for locking and tensioning the geomembrane have been used, which they had to be previously anchored to the surface to be protected.

For hydraulic works in loose material it has also been proposed to use strips of thermoplastic material, for example strips in PVC or other polymeric material suitable for geotechnical use, that is able to come into contact with the ground, partially incorporating them into the same soil. , to which a geomembrane was subsequently heat-sealed during its construction and installation.

The use of geomembranes has proved extremely advantageous, in particular for systems with exposed geomembranes, both for the quality and for the efficiency of the waterproofing system, for the comparatively reduced cost, and for their duration in the time.

A suitable channeling system obtained through the same anchoring profiles, also allowed the drainage and evacuation of water infiltrated into the body in the loose material of the dam or basin, and of any water losses caused by breakages and / or perforations of the protection geomembrane; in this way it was avoided that the membrane was subjected to swelling and / or strong stresses that could compromise its structural integrity.

Anchoring systems for geomembranes are described for example in EP-A-0 459 015, EP-A-0 722 016 and EP-A-1 137 850.

In the case of exposed geomembranes, in addition to the possible stresses caused by water infiltrating the ground, it is also necessary to take into account a possible wave motion of the water, or the action of strong winds, for example caused by cyclones, which they tend to suck up the geomembrane when the water does not cover it, tearing it from the anchor points.

AIMS OF THE INVENTION

However, systems of this kind have proved to be extremely complex and expensive, not always suitable for an adequate application to hydraulic works in loose material.

Therefore, there is a need to find an alternative solution that is easy to install, comparatively less expensive, and which at the same time allows a firm anchoring and controlled tensioning of the covering geomembrane during its laying and installation, also providing a suitable drainage system.

The tensioning of the geomembrane is important because it avoids the formation of folds and / or bags, which, if unfortunately perforated during operation, would constitute large preferential passages in which water would infiltrate coming into contact with the surface support, generating all those problems that you want to avoid thanks to the use of the same waterproof geomembrane; the use of a correctly tensioned geomembrane therefore allows to prevent a loss of water through the body in loose material of the dam or basin, as well as any infiltration of water and a possible subsidence and / or erosion of the same body in loose material , and / or the surface in contact with water.

BRIEF DESCRIPTION OF THE INVENTION

The above can be achieved by means of a method for laying and tensioning a waterproof geomembrane for hydraulic works in loose material, according to claim 1, as well as by means of a system or device according to claim 9.

According to a first aspect of the invention, a method has therefore been provided for laying and tensioning a waterproof geomembrane, comprising a plurality of strips of a geomembrane, or geo-strips, in elastically extensible synthetic material, on a surface of a € ™ hydraulic work in loose material, including the phases of:

digging in the surface of the hydraulic work a plurality of spaced trenches, which extend in one direction;

shaping the individual trenches conforming them with a regular, finished surface in contact with the geomembrane strips;

lay a plurality of geomembrane strips in an extended condition in contact with the surface of the hydraulic work, with a bridge arrangement on the trenches;

push the geomembrane strips connected tightly to each other making them penetrate into the cavities of alternate trenches, blocking them by superimposing a first ballast; And

then put the geomembrane strips under tension by pushing them into the cavities of trenches adjacent to the previous ones, blocking them in a taut condition by superimposing a second ballast.

According to another aspect of the invention, a system or device has been provided for laying and tensioning a waterproof geomembrane for covering hydraulic works in loose material, in which the geomembrane is made up of a plurality of geo-layers in elastically extensible synthetic material, stretched and tensioned according to the method referred to above, comprising:

a plurality of trenches for anchoring the geostrips extending in one direction, in which the trenches are shaped with a finite surface in contact with the geostrips;

a plurality of geo-strips, in elastically yielding synthetic material, laid transversely and / or longitudinally to the anchor trenches; and in which said geo-strips are kept adherent to the surface of the hydraulic work, in a taut condition and blocked in the cavities of the individual trenches by means of ballast.

If the surface of the hydraulic water to be protected is made up of clayey soil or an inert material with a fine grain size, for example less than 0.4-0.6 mm, the individual trenches can be directly shaped and shaped with a finished regular surface in contact with the geomembrane, consisting of the same inert material as the ground; otherwise, if the surface of the ground in which the trenches are dug includes rocky material, gravel and / or larger aggregates, in each trench it is possible to arrange a first bottom layer consisting of inert material of suitable grain size and consistency, for example gravel , superimposing on the latter a second layer of a filter material in the loose state of fine particle size, for example sand, clay and / or silt which is subsequently shaped with a large longitudinal cavity having a finished regular surface in contact with the geomembrane.

The filling of the trenches and the shaping of the contact surface are necessary in soils with a greater granulometry than sand which, if excavated, would not allow to obtain smooth and regular excavation walls. Failure to shape would cause the geomembrane to settle at the edges of the trench, according to an irregular line, thus giving rise to a laying with wavy edges of the geomembrane, which would make it difficult, if not impossible, to weld the strips, causing the formation of folds which would decrease the tensioning effect. The filling material also allows a secondary drainage and filtration function. The presence of the layers of draining and filtering material can be limited only to the trenches, or extend over the entire surface covered by the geomembrane.

The presence of the filtering and drainage layer therefore makes it possible to intercept and collect any water leaks through the geomembrane, or to discharge any negative pressures due to the presence of water, for example groundwater, on the back of the geomembrane.

The geomembrane strips can be laid transversely to the trenches and subsequently sealed together, i.e. they can be pre-welded and laid longitudinally to the trenches, as long as the total width of the pre-welded geomembrane strips or sheets is greater than the existing width between the extreme edges of at least three contiguous trenches.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further characteristics of the method and of the system or device for laying and tensioning a waterproof geomembrane, for hydraulic works in loose material, according to the present invention, will become clearer from the following description, and from the example of the attached drawings, in which:

Fig. 1 is a perspective view of a water basin, comprising a waterproof coating consisting of a geomembrane installed and tensioned according to the invention;

Fig. 2 is an enlarged view of a part of the bottom surface of the basin of figure 1, suitable for showing the excavation of the anchor trenches;

Fig. 3 is a section along the line 3-3 of figure 2;

Fig. 4 is an enlarged cross-section of a trench, made along the line 4-4 of figure 2;

Fig. 5 is a section similar to that of figure 4, designed to show the formation of a draining layer;

Fig. 6 is a section similar to that of the previous figures, designed to show the formation of a filtering or transition layer, after the drainage layer;

Fig. 7 is a view similar to that of figure 2, suitable for showing the laying phase of a certain number of geostretches, transversely and straddling the trenches;

Fig. 8 is a section along the line 8-8 of figure 7;

Fig. 9 is a view similar to that of figure 7, designed to show a first phase of penetration of the geostretches in alternating trenches;

Fig. 10 is a section along the line 10-10 of figure 9;

Fig. 11 is an enlarged cross section of a trench along the line 11-11 of figure 9;

Fig. 12 is an enlarged cross section of a trench, along the line 12-12 of figure 9;

Fig. 13 is a view similar to that of figure 9, designed to show the subsequent phase of penetration and final tensioning of the geo-strips in the trenches adjacent to the previous ones;

Fig. 14 is a section along the line 14-14 of figure 13;

Fig. 15 is a schematic view, summarizing the main steps of the method according to the previous figures.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows, by way of example, a generic hydraulic work in loose material, consisting of a basin 10 comprising an embankment 11 having an internal inclined surface 12, and a bottom 13 for containing a certain volume of water.

Both the internal surface 12 and the bottom 13 of the basin, in order to avoid water leaks by infiltration into the ground, are normally protected by a waterproof coating consisting of a geomembrane comprising a plurality of strips of an elastomeric synthetic material, that is elastomeric yielding, called â € œgeostrisceâ €, which must be suitably sealed together along the edges, stretched and anchored to the ground below.

The material used for the geomembrane making up the waterproof coating can be any, as long as it is suitable for the intended purpose; in particular, it can be chosen from the synthetic materials in the following table, taken individually or in combination with each other.

BASIC MATERIAL TYPE ABBREVIATION

THERMOPLASTICS - HDPE high density polyethylene

- Low and / or polyethylene

high density LLDPE

- PE polyethylene

- CPE chlorinated polyethylene

- Ethylene-vinyl copolymer

EVA / C acetate

- Polypropylene PP

- Polyvinyl chloride PVC RUBBERS - Chlorosulfonated polyethylene THERMOPLASTIC CSPE - E / P ethylenepropylene copolymer

THERMOSTABLE - Polyisobutylene PIB

- CR chloroprene rubber

- EPDM ethylenepropylene diene monomer

- IIR butyl rubber

- NBR nitrile rubber

BITUMINOUS - Prefabricated GM oxidized bitumen - Polymer bitumen -----

The above list is not exhaustive and also includes those materials that technically and commercially are attributable to the elastomer and bituminous family.

The geomembrane strips can have a thickness between 0.2 and 40 mm, with a modulus of elasticity between 10 and 5,000 MPa, possibly coupled to a geotextile.

According to the present invention, in order to install and anchor the geomembrane to the surfaces 12 and 13 of the basin 10, as shown in Figures 1 to 4, a plurality of trenches 14 are initially excavated in the ground, parallel to each other or oriented at a given direction; the trenches 14 must have sufficient dimensions to accommodate, if necessary, a predetermined quantity of a draining material and / or filtering material in the loose state, as explained below. The trenches 14 can have any suitable shape, for example they can have a rectangular, or trapezoidal, or semicircular cross section. As shown in the detail of figure 4, the dimensions in width L and depth S of the trenches 14 can be any, depending on the nature of the soil and the quantity of draining and / or filtering material to be contained, while the spacing or pitch P between contiguous trenches, must be much greater than the dimensions in width L, for example between four and ten times L, or greater, so that between contiguous trenches there is a section of geomembrane of sufficient length to allow a required elongation due to elastic yielding, necessary to put it in tension by means of a suitable ballast.

By way of example only, it should be noted that during some experimental tests trenches were dug with a maximum width L between 600 and 1000 mm, and a depth S between 400 and 700 mm, maintaining a pitch P or center distance between 4 and 10 m.

As previously reported, in the event that the ground is made up of inert material of fine size, equal to or less than 0.5-0.6 mm, for example sand or clay, once the trenches 14 have been excavated, adequately compact the soil, shaping the individual trenches with a longitudinal groove shaped with a finished regular surface, suitable for coming into contact with the geomembrane strips 14.

Optionally, if the characteristics of the soil in which the trenches 14 are dug are such as to include larger aggregates, once the trenches 14 have been dug, after having adequately compacted the soil, the individual trenches 14 are partially filled with a first layer 15 of drainage material, consisting for example of large gravel; in this way a sort of drainage channel is formed, suitably inclined towards a peripheral collector.

The layer 15 of drainage material can only be distributed in the trenches 14 of the bottom 13 of the hydraulic work or basin 10, while in the case of the inclined surface 12, facing the water in the basin 10, it is advisable that the drainage layer 15 is spread over the entire surface, as schematically represented in figure 5.

In all cases, the layer 15 of draining material in the trenches 14, must be distributed in such a way as to form a longitudinal cavity 16 sufficient to contain a second layer 17 of filtering material, as shown in Figure 6, in particular shaped loose material, for example earth, fine sand or small gravel, rounded and without sharp edges, which in this way forms a transition layer between the underlying drainage layer 15 and the protective geomembrane subsequently laid.

Once the filtering layer 17 has been distributed in the trenches 14, by means of a suitable tool, for example the bucket of an excavator, a longitudinal channel 18 is shaped as shown in figure 6.

The thicknesses of the draining layer 15, of the filtering layer 17, and consequently the shape and dimensions of the longitudinal channels 18, must be calculated so that the channels 18 can accommodate a stretch of geomembrane sufficient to cause the desired tensioning as well as to guarantee the due anchoring force necessary to resist external elements such as wind, wave motion, ice, etc.

Once the preparation of the trenches 14, or part of them, and their filling with the draining layer 15 and the filtering layer 17 have been completed so as to create a finished surface in contact with the geomembrane, and after having possibly superimposed a layer of a geotextile of protection, not shown, according to the example under consideration, the geomembrane is built by spreading a certain number of geo-strips 20, in a direction transversal or orthogonal to the trenches 14, as shown in the example of figure 7, unwinding them from special rolls ; as an alternative to the transversal laying of the geo-strips 20, shown in figure 7, it is possible to lay several pre-welded geo-strips 20, parallel to the trenches 14, as long as the total width of the pre-welded geo-strips is greater than the distance existing between the extreme edges of at least three contiguous trenches 14.

The geostrips 20 are initially laid in a flat form adhering to the ground or surface of the hydraulic work to be protected, so that they are arranged as a bridge across the individual trenches 14, as shown in figure 8; by providing a suitable overlap 21 between the edges of the contiguous geoblasts, it is possible to make a watertight connection between them, for example by heat sealing, vulcanization or suitable adhesive.

After having laid and sealed a certain number of geo-strips 20, they must be tensioned and anchored; this is done gradually in successive phases, shown in figures 9 to 14 of the attached drawings.

In particular, as shown in figures 9 and 10 and in the detail of figure 11, the geostrips 20 are first pushed in sequence into the cavity of the channels 18 of alternate trenches 14, for example the odd-order trenches as indicated by the numbers of reference 1 and 3 in figure 9, by means of a suitable ballast 22.

More precisely, by ballasting the geo-strips 20 in correspondence with a first series of alternate trenches 14, the geo-strips 20 remain adherent to the ground with a bridge arrangement on the remaining series of trenches 14 of even order, adjacent and interposed to the previous ones, as indicated for the trench 2 in figures 9, 10 and in the detail of figure 12. Once the first ballasting phase of the geostrips 20 in the cavities of the odd-order trenches has been completed, we proceed in the same way to ballast the geo-strips in the cavities of the even-order trenches, as shown and indicated with 22A in figures 13 and 14.

By ballasting in the previously indicated order, a final tensioning is imparted to the geo-strips 20 which makes them adhere perfectly to the surfaces 12 and 13 of the hydraulic work to be protected. Obviously, care must be taken to ballast the geostrips 20 with appropriate weights to create the desired elongation and the desired tension, by means of an elastic yielding, for example, between 2% and 4% in the section of the geostrips 20 between adjacent trenches 14, such as indicated by arrows W1 and W2 in figures 13 and 14.

The ballast material 22 and 22A may be of any desired type; for example it can be chosen from the following: gravel, sand, earth, concrete, or their combination.

Optionally, as indicated with 23 in figure 14, in correspondence with each trench 14 it is possible to cover the ballast 22, 22A with a geostrip 23, which extends longitudinally to the individual trenches, heat-sealing it along the edges to the geostrips 20.

The geosynthetic strips 20 and 23 can be of any type, for example they can be constituted by simple strips of geosynthetic material, or by a geocomposite consisting in the coupling of strips of geosynthetic material and a geotextile.

In some cases, in the stretch between contiguous trenches, the transition layer may include a geotextile, a geocompound, a geonet or other suitable anti-perforation material for the protection of the geomembrane; in the same way the drainage layer can be made up of any geodrain material, such as gravel, geonet, geogrid, geomat or their combination.

Figure 15 summarizes by way of explanation the various main steps from S1 to S5 of the laying and tensioning method for geomembranes according to the present invention; in particular:

S1 shows the excavation phase of the trenches 14;

S2 shows the step of filling the trenches with the optional draining layer 15;

S3 shows the step of filling the trenches 14 with an optional filtering layer 17, shaped with a longitudinal slot 18 able to provide a regular, finished surface in contact with the geomembrane strips.

S4 shows the step of laying the geo-strips 20 as a bridge on the trenches 14; S5 shows the phase of pushing and blocking the geo-strips by means of ballast, in the cavities of the odd-order trenches;

Finally, S6 shows the final tensioning and anchoring phase of the geo-strips, pushing and ballasting them into the cavities of the remaining trenches of even order.

However, it is understood that what has been said and shown in the attached drawings has been given purely by way of example of the general characteristics of the method and system according to the present invention; therefore other modifications or variations may be made to the shape, dimensions, arrangement and distance between trenches 14, to the type of material of the drainage and / or filtration layers and to the ballast material, achieving the same effects and the same results, without thereby move away from claims.

Claims (17)

CLAIMS 1. A method for laying and tensioning a waterproof geomembrane, comprising a plurality of geo-strips (20) in elastically extensible synthetic material, on a surface (12, 13) of a hydraulic work in loose material, comprising the phases from: digging in the surface of the hydraulic work, a plurality of spaced trenches (14), which extend in one direction; shaping the individual trenches (14) conforming them with a regular, finished surface in contact with the geomembrane strips; laying and sealing a plurality of geo-strips (20) in an extended condition in contact with the surface of the hydraulic work, maintaining a bridge arrangement on the trenches; push the geo-strips (20) making them penetrate into the cavities of alternate trenches, blocking them by superimposing a first ballast (22); And then put the geo-strips (20) under tension by pushing them into the cavities of trenches adjacent to the previous ones, locking them under tension by superimposing a second ballast (22A). The method according to claim 1, wherein the shaped surface of the trenches (14), in contact with the geoblasts (20), consists of an inert, fine material, having dimensions equal to or less than 0.5 mm. The method according to claim 1, comprising the additional steps of: partially filling each trench (14) with a first layer (15) of drainage material, and subsequently with a second filtering layer (17) of a fine, compactable inert material; And shaping the second filtering layer (17) with a longitudinal channel (18) conforming it with a finished regular surface in contact with the geostrips (20). The method according to claim 1 wherein the geostrips (20) are spread in a direction transverse to the trenches (14). The method according to claim 1 wherein a plurality of pre-welded geo-strips are stretched longitudinally to the trenches (14). The method according to claim 3 wherein the material of the drainage layer (15) consists of a geodrain. The method according to claim 6 wherein the material of the drainage layer (15) is selected from the following: gravel, geonet, geogrid, geomat or a combination thereof. The method according to claim 1, wherein the material of the filter layer (17) is selected from the following: silt, sand, rounded fine gravel, geonet, geotextile, or a combination thereof. 9. A device for laying and tensioning an impermeable geomembrane for hydraulic works in loose material, in which the geomembrane comprises a plurality of geo-strips (20) in elastically extensible synthetic material, spread and tensioned according to the method of claim 1 , comprising: a plurality of trenches (14) for anchoring the geostrips (20) extending in one direction, in which the trenches (14) are shaped with a cavity having a finished regular surface of contact with the geostrips (20); a plurality of geo-strips (20), in elastically yielding synthetic material, laid transversely and / or longitudinally to the anchor trenches (14); And in which said geo-strips (20) are held adherent to the surface of the hydraulic work, in a taut condition, blocking them in the cavities of the individual trenches (14) by means of ballast (22, 22A). The device according to claim 9 wherein the drainage material comprises: gravel, geonet, geogrid, geomat, taken individually or in combination. The device according to claim 9 wherein the material of the filter layer comprises: sand, earth, clay, silt, taken singly or in combination. The device according to claim 11 wherein the filter layer (17) further comprises a geotextile, a geonet, a geocomposite, or a combination thereof. The device according to claim 9 wherein the ballast material comprises: sand, gravel, earth, concrete or a combination thereof. 14. The device according to claim 9 in which the synthetic material of the geo-strips (20) is selected from the materials listed in the following table: BASIC MATERIAL TYPE ABBREVIATION THERMOPLASTICS - HDPE high density polyethylene - Low and / or polyethylene high density LLDPE - PE polyethylene - CPE chlorinated polyethylene - Ethylene-vinyl copolymer EVA / C acetate - Polypropylene PP - PVC polyvinyl chloride RUBBERS - Chlorosulfonated polyethylene THERMOPLASTIC CSPE - Ethylenepropylene copolymer E / P THERMOSTABLE - Polyisobutylene PIB - CR chloroprene rubber - EPDM ethylenepropylene diene monomer - IIR butyl rubber - NBR nitrile rubber BITUMINOUS - Prefabricated GM oxidized bitumen - Polymer bitumen ----- The device according to claim 13, in which the geo-strips (20) have a thickness of between 0.2 and 40 mm, and a modulus of elasticity of between 10 and 5000 MPa. The device according to claim 9 wherein the spacing (P) between trenches (14) is comprised between four and ten times the maximum width (L) of the trenches. The device according to claim 9, characterized in that it comprises an additional geo strip (23) for covering the ballast (22, 22A), sealedly connected to the strips (20) of the geomembrane.