Waterproofing system for hydraulic structures with rigid sheets in synthetic material

Abstract: A waterproofing system for hydraulic structures by rigid sheets (14, 15) in synthetic material. Localized points (17, 18) of the surface area of the hydraulic structure to be waterproofed are chosen and prepared for applying of mechanical anchoring means for an impermeable sheathing; the sheathing comprises rigid or semi-rigid sheets (14, 15) in synthetic material, which are mechanically and watertightly connected between each other, laid down on the surface (10, 11) of the hydraulic structure fastening them to the anchoring points (17, 18). The previous steps are repeated till completing the impermeable sheathing of part or of the whole surface area of the hydraulic structure.

Description: The present invention relates to a method of waterproofing bottom and side walls of a canal and the like by rigid and/or semi-rigid sheets in any synthetic material, for example PVC, polypropylene, polyethylene or other, of flat or type, suitable for maintaining their stiffness for the envisaged applications. For the purposes of the present description, by the wording "sheet of rigid, semi-rigid or non-extendable material" reference is made to any sheet or plate in synthetic material, having a suitable formulation and a thickness comprised between few millimetres and a ten of millimetres or greater, so that the space between either of two points of the sheet, be substantially unchanged when said points are stressed by external forces; consequently said sheet or plate has a substantial indeformability and "self-supporting" properties, after being applied to the surface to be waterproofed, allowing for a suitable anchoring at separated points. As well known, the aging of canals and the like, involves some problems due to water losses which, soaking the surrounding ground, causes variations of the humidity content, thus affecting the ground strength. Said water losses, if not suitably limited and controlled, over time, may cause land-slide phenomena which may also involve a risk for the stability of the canal itself. The economic loss in relation to water losses should also be considered. Therefore suitable maintenance and waterproofing of the canals is very important both for safety and for economic management purposes. So far, several solutions have been proposed to reduce or eliminate water losses, providing for simple localized repairs of the damaged canals, for example by suitable mortars or other concrete material, resin based paints, bituminous or synthetic membranes adhered to the surface to be waterproofed, or sometimes reconstructing a new surface which will come in contact with the water to be contained. EP-A-0 459 015 proposes other solutions which provide for- the use of flexible sheets in synthetic material, more simply known as geomembranes, for example based on PVC, PP, PE and PDM. According to said proposal the sheets are mechanically fastened to the back surface to be waterproofed, by metal profiles and/or mechanical fastening means, thus providing for an air chamber between the impermeable sheathing and the back surface, in such a way to collect and discharge the seepage waters on the back of the plastic sheathing, producing at the same time a dehydration effect of the masonry. This known use of flexible material for sheathing has proved to be of particularly efficiency where the water inside the canal is at standstill condition or flowing at very low speeds, in such a way not to cause substantial tensile stresses on the sheathing, which however should be firmly anchored to the back surface by a substantial set of mechanical anchoring means, watertighting by simply pressing the overlapped edges of the adjacent sheets. Even if the use of impermeable membranes in flexible material has proved to be a valid solution for various applications, besides being cost-saving with respect to other conventional waterproofing systems, however, remarkable problems have been involved when flexible sheets have been used for waterproofing canals in presence of whirling waters, flowing at high speeds, in particular in the areas where strong turbulence occurred. Merely by example purpose, reference can be made to covered or uncovered hydroelectric canals, pressurized hydraulic tunnels or areas of any hydraulic structure subjected to the inflow and outflow of strong current of water, such as weirs and the like. In all these cases the dynamic effect of the stream, or the water turbulence, may damage a flexible geomembrane, tearing or stripping the same from its fastening points; therefore the flowing water could seep under the sheathing till totally damaging the same, or damaging the hydraulic structure itself, or the hydraulic apparatus connected to the same. Such situations become more critical when the impermeable sheathing is fastened to a support which does not allow the use of an adequate number of fastening points; furthermore a structural inadequacy of the surface of the hydraulic canals or the like requires long and expensive repairing works in order to provide for anchoring forces compatible with the mechanical features of the same geomembrane. Sometimes, the extension of the preliminary works on the supporting surfaces for the impermeable sheathing, are such to rend the geomembrane solutions expensive and not advantageous. US-A-3 854 292 discloses the most relevant prior art, providing a rigid liner for irrigation ditches, in which prefabricated grass-fibre reinforced sheets having the same cross-section of the ditche, are overlapped and coated with resin at the apposite ends thereof. Therefore, the need still exist for impermeable sheathings of hydraulic canals and the like which, besides maintaining all the advantages of the well known solutions, allow to effect the laying down and the anchoring of the same sheathings in an extremely rapid and cost-saving way, by using a relatively reduced number of anchoring points; a high reliability degree in the management of the structure is at the same time required, especially in the case of localized damages of the sheathing, allowing possible defects to occur on the sheathing, within acceptable safety and economic limits, during use. Therefore, the general object of the present invention is to provide a method for the waterproofing of hydraulic canals and the like by sheets in synthetic material, which may resist to high mechanical stresses caused by the turbulence of flowing waters, by using an extremely reduced number of anchoring points, such to allow for the laying down of impermeable sheathings by an extremely simple mode, directed to assure a cost-saving and reliable waterproofing. According to the invention, a method for waterproofing bottom and side walls of a canal is provided as defined in claim 1. Sheets in rigid or semi-rigid synthetic material are laid down and anchored on the surface of the canal to be protected by mechanical anchoring means in a limited number of predetermined points, suitable arranged to allow for a firm and safe anchoring of the same sheets. The stiffness of the sheets in synthetic material by which the impermeable sheathing is constituted of, allows for remarkably increasing of the anchoring force to be applied to the same plates; furthermore fastening of the sheets to a back surface to be protected, usually in concrete material or in masonry, may be performed directly or by the disposition of a geonet or of a intermediate layer in a draining material for the pressurized waters which possibly may seep between the impermeable sheathing and the back surface of the protected canal. The greater force exerted at each single fastening point, together with the self-supporting of the single rigid or semi-rigid sheet in synthetic material, allow for the distribution of the same anchoring force on the whole surface of the same sheet; a limited number of the anchoring points is therefore required. This solution, in case the back surface to be waterproofed and to which anchoring the sheathing has a limited mechanical strength, allows for a considerable reduction of the extension of the surface area of the canal which will be preset or prepared to make it compatible with the desired fastening force. Therefore, by considering a same surface area of the impermeable sheathing, the proposed solution to use flat rigid sheets in synthetic material, compared with the conventional techniques, in particular with the use of flexible synthetic sheets, allows for a fewer number of fastening points and consequently a great save of costs. Also the roughness degree of the surfaces on which applying the sheathing is less critical and it could be greater when employing rigid sheets with respect to the use of flexible sheets or membranes according to the conventional techniques. In the case of canals and tunnels, the sheets in synthetic material may be applied on the side walls and the bottom surface, by watertight connecting the same sheets in a suitable way. For example longitudinal and/or cross welding, achievable for example by hot air thermal welding and cold chemical welding systems may be used, or watertight connection of the sheets may be made by means of bands in flexible synthetic material; in this case said bands define a suitable flexible hinge between adjacent sheets, which allows for the preparation of the same sheathing directly in the job site, or during their laying down. The limited overall dimensions of the flat sheet and the relatively reduced weight, allow also for their easy transport and assembly even in difficulty reachable areas, either in the job site or along the canal to be waterproofed. The fastening of the sheets in synthetic material, of rigid or semi-rigid type, could be carried out by any suitable way; for example anchoring studs of any type, or rigid profiles in synthetic or metal material, always fastened by studs when a better distribution of the anchoring force is required. Preferably the anchoring studs or profiles are provided along the edges of the impermeable sheathing, by positioning the same above the maximum level that can be attained by the water. The watertight connection among the various sheets and the flexible hinges, as already explained, is preferably obtained by means of hot welding systems, for example hot air thermal welding; cold welding should also be considered for example by THF or other chemical welding techniques, or by a combination of the previous systems. The advantages and the objects obtained with the present invention may be resumed as follows: greater anchoring force of the sheets in rigid or semi-rigid synthetic material; possible drainage of the seeping waters; minimum preparation of the support surface area to be waterproofed minimum number of the anchoring points, preferably localized outside the areas lapped on by the water; easy transport and rapid assembly of the sheets constituting the impermeable sheathing connection of the various rigid sheets by flexible covering bands, which assure for a continuous waterproofing and the possibility of hinge turning of the same sheets already welded to the same bands, for easy transport and laying down purposes; high mechanical strength of the impermeable sheathing, as well as withstanding to attacks by external agents including vandalism; lastly, high strength to the dynamic action of the waters with strong turbulence flow. Summing up, according to the invention, a method for waterproofing canals and the like by an impermeable sheathing system has been provided of self-supporting type, not at all conditioned by the state of the support and the resting surface of the canal which is to be protected. These and other objects and advantages of the present inventions are obtainable with a method for waterproofing a bottom and side walls of a canal and the like by sheets of rigid or semi-rigid synthetic material, according to claim 1. More precisely the invention is directed to a metod for waterproofing bottom and sides walls of a canal and the like, the method comprising the steps of: forming a waterproofing sheathingby, sealably and mechanically connecting a bottom sheet of rigid or semi-rigid synthetic material to side sheets of rigid or semi-rigid synthetic material along adjacent edges thereof by a synthetic flexible material forming a hinge; inserting the folded waterproofing sheating with inside-turned side sheets into the canal with the bottom sheet resting on a bottom surface of the same canal; raising the side sheets away from each other onto side walls of the canal; providing anchoring means in predetermined anchoring points of the surface area of the canal, and anchoring the side sheets into position at said anchoring means. The invention will be better hereinafter illustrated with reference to the attached drawings, relating to the waterproofing of a canal, in which: Fig. 1 is a sectional view of a canal provided with an impermeable sheathing according to a the invention; Fig. 2 is an enlarged view of figure 1, in correspondence to the connecting point between the bottom and a side wall of the canal; Fig. 3 is an enlarged view of the anchoring point at the left top end of figure 1; Fig. 4 is an enlarged view of the anchoring point at the right top end of figure 1; Fig. 5 schematically shows the application and laying down method for the impermeable sheathing of figure 1; Fig. 6 shows further embodiment in which a drainage layer is provided for seeping water. With reference now to figures from 1 to 4, we will describe a first embodiment and two different anchoring systems of the impermeable sheathing. In figure 1 the cross sectional view of a generic water conveying canal is shown, comprising a bottom surface 10 and side flat walls 11 sloping towards the outside. Reference 12 in the same figure indicates the level of the water in the canal. The side walls 11 of the canal, in the example shown, may end with the upper edge in correspondence to a horizontal concrete beam 13, which longitudinally runs along the canal at ground level. From the same figure, it results that the inner surface of the canal is protected by a suitable impermeable sheathing constituted by rigid plates in synthetic material, mechanically anchored in predetermined points to the same side walls of the canal, and or to the beams 13, over the level of the water 12 as hereinafter explained. More particularly, in the case of figure 1, the impermeable sheathing which longitudinally extend along the canal, comprises sheets 14 simply laying on the bottom surface 10 of the canal, and side sheets 15 laying against the side walls 11; the side sheets 15 are connected to the bottom sheets 14 by covering bands 16 which extend longitudinally to the canal; the bands 16 are suitably shaped and made in synthetic flexible material, to form a kind of flexible hinge, allowing for the inside turning of the plates 10 and 11 during the preparation and laying down steps of the impermeable sheathing, as hereinafter explained with reference to figure 5. The mechanical watertight connection of the bands 16 to the opposite edges of two adjacent sheets; as previously indicated, may be performed by any suitable means; for example use may be made of thermal welding, carried out in advance in the factory or directly on the job site, as well as before applying the sheets to the internal surface of the canal to be protected. More precisely, the working mode is the following: locating and preparing the anchoring points for the sheets, for example at the top edge of the side walls of the canal, more generally in localized points of the hydraulic canal to be protected; preparing said anchoring points to make them suitable for the insertion of the anchoring means; a predetermined length of the sheathing is performed by fastening the sheets to the selected anchoring points sufficiently spaced apart, as schematically shown with reference 17 or 18 in figure 1. The previous steps are repeated more times, till covering the selected part of the canal or the entire canal length to be protected, providing for the required cross watertights between subsequent sheathing portions of the sheets, for example by overlapping and welding the edges of the same sheets; at the beginning and at the end of the sheathing, the necessary cross watertight connections will be obviously executed. Figure 2 shows, as an example, an enlarged detailed view of the covering band 16 between the facing edges of adjacent sheets 14 and 15, where reference 19 indicates the welding lines. Figure 3 shows an enlarged detailed view of an anchoring point 17 according to a first embodiment of the invention. As shown, in this case the anchoring 17 is effected to the side beam 13, on the horizontal ground line, by using an angular section 20 in metal or in the same material of the sheet 15, suitably bent by simple deformation. From said figure 3 it can be seen that one wing of the angular element 20 is partially overlapped to the longitudinal edge of the sheet 15 and welded along the welding line 21; the other wing of the angular element 20 is leaned against the horizontal surface of the beam 13 fastening it by stud bolts, screws and washers 22, threaded into corresponding holes already pre-formed in longitudinally spaced apart positions in the wing of the angular element, forcing them in the concrete of the beam 13. Another alternative is shown in the enlarged view of figure 4, corresponding to the anchoring point 18 of figure 1; in this case the anchoring stud 23 presents a protruding threaded portion 23' on which a nut 24 is screwed on, which, by a washer 25, a strap 26 and a rubber gasket 27 presses the plate 15 against the sloping part of the beam 13, or against the side wall of the canal. In the same figure, reference 28 indicates a layer in a suitable resin material for leveling and preparing the anchoring surface. Figure 5 of the drawings shows the laying down scheme for a part of an impermeable sheathing, according to the solution of figure 1. The already welded and inside-turned sheets 14 and 15, as shown with a continuos line in figure 5, are firstly laid down with care on the bottom 10 of the canal. Successively the upper plate 15 is raised, making the same to rotate against the left side wall, then the other plate 15 is made rotate against the right side wall; lastly the various anchoring steps in the points indicated by references 17 or 18 are performed. This solution, which employ flexible hinge means for the watertight connection between the adjacent sheets, is particularly advantageous in all the applications involving difficulties in transporting as well as in anchoring the sheathing to the surface to be waterproofed. Figure 6 shows a further embodiment according to the example of figure 1, wherein a drainage layer 33 for the seeping water has been provided between the rigid sheathing sheets 14, 15, the walls 11 and bottom 10 of the canal, said layer being for example a net structure for collecting possible waters which seep in the bottom chamber between the impermeable sheathing and the canal walls, for example for accidental ruptures of the sheathing itself, and from there convoyed towards the discharge conduit 34; the conduit 34 may be constituted by a perforated pipe enveloped by a gravel, along a trench 35 at the bottom of the water canal. Also in this case, all the remaining parts, similar or identical to those of the previous case, have been indicated with the same reference numbers. From what above said and shown, it is now clear that it has been provided a method for waterproofing canals and the like with rigid or semi-rigid sheets in synthetic material, which presents a great versatility and efficiency in use as the limited overall dimensions of the flat sheets and their relatively reduced weight, make easy to transport and assembling them also in areas of difficult access, and therefore the delivery of the material in the job site of the canal to be repeared and protected, may be easily effected along the canal or tunnel, to be waterproofed. Moreover, the installation of the sheathing sheets may be carried out either in a dry mode, that is without water in the canal, or directly operating underwater with suitable apparatus and with a staff suitably equipped, by using appropriate watertight fastening systems.

Claims: A method for waterproofing bottom and sides walls of a canal and the like, the method comprising the steps of: forming a waterproofing sheathing (14, 15, 16) by, sealably and mechanically connecting a bottom sheet (14) of rigid or semi-rigid synthetic material to side sheets (15) of rigid or semi-rigid synthetic material along adjacent edges thereof by bands (16) in a synthetic flexible material forming a hinge (16); inserting the folded waterproofing sheating (14, 15, 16) with inside-turned side sheets (15) into the canal with the bottom sheet (14) resting on a bottom surface (10) of the same canal; raising the side sheets (15) away from each other onto side walls (11) of the canal; providing anchoring means (17, 18) for the sheating (14, 15, 16) in predetermined anchoring points of the surface area of the canal, for at least part of the waterproofing sheets, and anchoring the side sheets (15) into position at said anchoring means (17, 18). A method for waterproofing according to claim 1, characterised by providing mechanical anchoring means (17) for the side sheets (14, 15) along the upper edges of the side walls (11) of the canal, above the level (12) of the water usually flowing into the canal. A method for waterproofing according to the preceding claim 2, characterised by providing angular sections (20) for fastening the upper edges of the side sheets (15), said angular sections (20) being fastened to said predetermined anchoring points (17) and comprising a wing overlapping the longitudinal edges of the side sheets (15) of sheathing. A method for waterproofing according to the preceding claim 1, characterised by providing at least a layer (33) of draining material between the sheathing (14, 15, 16), the bottom and side walls (10, 11) of the canal. A method for waterproofing according to the preceding claim 4, characterised by providing a water collecting conduit (34) for the seeping waters at the bottom (10) of the canal.

Inventors: SCUERO ALBERTO, SCUERO, ALBERTO
Applicants: CARPI TECH ITALIA S R L, CARPI TECH ITALIA S.R.L.
Application year: 1996
Main classification: E02B5
IPC codes: E02B3, E02B5