This invention refers to the formation of protective and waterproof sheathings on surfaces of hydraulic structures, by means of which it is possible to drain off the seeped water that collects between the surface of the hydraulic structure and the protective sheathing, by means of an appropriate valve system provided in the waterproof sheathing itself.
The invention in particular relates to the formation of waterproof sheathings provided with automatic drainage of the seeped water, for any type of hydraulic structure, such as earth or concrete dams, such as RCC (roller compacted concrete) dams, hydraulic tunnels, reservoirs and canals, or for any other type of hydraulic structure for which a sheathing and a water drainage system is required.
Waterproofing devices are known and widely used for protecting the surfaces of hydraulic structures intended to come into contact with water, in order to prevent excessive, and in certain cases dangerous, leakage of water through the main body of the hydraulic structure itself.
A known waterproofing device substantially consists in applying a waterproof sheathing onto the surface of the hydraulic structure to be protected, comprising for example a geomembrane of elastomeric and/or thermoplastic material, such as PVC or other elastically deformable synthetic material, and providing a suitable mechanical anchoring system for fastening the geomembrane to a surface area of the hydraulic structure to be protected; a geonet, a geotextile, a draining spacer or “geospacer”, or a layer of highly permeable loose material, for example gravel or sand, with a permeability coefficient of K<10−7 m/s, may be disposed between the waterproofing geomembrane and the surface area of the hydraulic structure to protect the latter or to form a hollow space for collection of the seeped water which must be continuously discharged towards the outside, by means of a suitable system of drainage channels or conduits.
Devices for the protection of hydraulic structures by waterproof geomembranes can be found in several prior documents, for example in U.S. Pat. No. 4,913,513 and U.S. Pat. No. 5,720,576, insofar as the waterproofing of dams is concerned; in U.S. Pat. No. 4,371,288 and U.S. Pat. No. 4,915,542, insofar as the waterproofing of tunnels and hydraulic tunnels is concerned; in U.S. Pat. No. 5,806,252 and U.S. Pat. No. 3,854,292, for canals and the like; as well as in DE-A-2 734 514 and EP-A-1 157 168, insofar as the waterproofing of joints or cracks.
In all these applications there is a common need to provide a suitable drainage device for draining off or discharging the water seeped through the body of the hydraulic structure, which collects between the same body and the waterproof sheathing.
The absence of any device for draining off the seeped water, in hydraulic structures provided with a waterproof sheathing of elastically deformable synthetic material, would give rise to serious problems, due to the fact that the water which collects behind the sheathing, would cause the same sheathing to swell and form dangerous water pockets, with the severe risk of damaging and/or tearing the protective sheathing in correspondence with the anchorage points or the areas subjected to high stresses.
In order to partially obviate this problem, some solutions have been proposed; for example, U.S. Pat. No. 4,913,583, suggests to embed into the body of the dam, during its construction, a waterproofing membrane and a system of micro-perforated pipes for discharging the drained off water on the rear side of the sheathing.
Conversely, U.S. Pat. No. 5,720,576 makes use of the same structural sections used for anchoring the waterproofing membrane to the upstream surface of the dam, to flow the seeped water to the bottom of the structure, by providing a longitudinal manifold which subsequently discharges the water downstream or to the outside in given points of the hydraulic structure.
Although these solutions have provided satisfactory results, the construction of a drainage device is not always possible in a previously existing structure, or proves to be extremely difficult and expensive.
Consequently, whenever the hydrostatic level of the water on the upstream side, or inside the hydraulic structure, tends to decrease, in the absence of any discharging system, the pressure of the water, behind or on the rear side of the waterproof sheathing or membrane, under certain conditions could cause it to burst or become torn in the areas subjected to the greatest stress.
In order to maintain the efficiency of the drainage device it is therefore necessary to periodically carry out complicated and costly maintenance operations; moreover, in certain cases, for example in existing earth dams and hydraulic tunnels, or in certain canals, the construction and/or maintenance of a drainage system is, in fact, made impossible.
In an attempt to remedy to problems arising from previously known drainage devices, JP-A-2003055935 suggests the use of a check valve on the bottom of a waterway, allowing only inflow from the outside, nevertheless there is also the problem of maintaining the drainage system in efficient working condition, due to the fact that over time it tends to become clogged, preventing the water from flowing freely.
The main object of this invention is to provide a method for waterproofing and draining off seeped water in hydraulic structures, such as dams, tunnels, canals and the like, by means of which it is possible to achieve an effective automatic drainage of the seeped water, both in existing hydraulic structures, and during their construction.
A still further object is to provide a method as mentioned previously, by means of which it is possible to achieve a drainage both during and after the waterproof sheathing has been installed, at any point of the hydraulic structure, wherever required.
A further object of the invention is to provide a waterproofing device for hydraulic structures, by means of which it is possible to exploit the differential pressure of the water on both fore and rear sides of the waterproof sheathing, to cause an automatic discharge of the seeped water, while at the same time preventing the water normally contained or flowing in the hydraulic structure, from seeping towards the outside or into the surrounding soil.
A still further object is to provide a drainage device which is structurally simple, highly efficient, does not require costly maintenance operations, and at the same time is simple and inexpensive.
Advantageously, the construction of a waterproof sheathing for membrane provided with a drainage device according to this invention can be carried out both in the presence and in the absence of water upstream or inside the hydraulic structure, also over an already installed waterproofing membrane.
The above can be achieved by means of a method for waterproofing and draining off seeped water in hydraulic structures, according to claim 1, or by means of a sheathing and drainage device according to claim 18.
In particular, according to the invention, a method for waterproofing and draining off seeped water through the body of hydraulic structures, according to which a waterproof sheathing, consisting of elastically deformable geomembrane sheets, is applied and secured to a surface area of a wall of the body of the hydraulic structure, providing said sheathing with a one-way water drainage valve for draining off the seeped water collected behind the waterproof sheathing, comprising the steps of:
defining drainage points for draining off the water in pre-established positions of the waterproof sheathing;
providing, in each of the pre-established drainage point, a one-way drainage valve having a water discharging aperture in said waterproof sheathing;
orienting said water discharging aperture of the drainage valve in a natural downflow direction of the water and providing said drainage valve device with a flat flexible valving member, overlapping the discharging aperture;
subjecting the flat valving member to a differential pressure of the water acting on opposite faces of the waterproofing sheathing; and
causing automatic opening and closing of the drainage valve, by the pressure difference of the water arising on the opposite faces of the flat valving member of the drainage valve, characterised by the steps of providing said drainage valve on a wall surface of the hydraulic structure; and
downwardly draining the seepage water, by gravity.
According to a further aspect of the invention, a device has been provided for waterproofing and draining off seeped water through the body of hydraulic structures, comprising:
a waterproof sheathing, consisting by a geomembrane of elastically yieldable material;
fastening means to secure the geomembrane to a surface area of a wall of the hydraulic structure, and
drainage means for draining off the seeped water collected between the surface area of the hydraulic structure and the waterproof sheathing, said drainage means comprising:
a plurality of one-way drainage valves on the waterproof geomembrane; each drainage valve comprising:
a water discharging aperture in the waterproof geomembrane, said water discharging aperture extending in a direction transversal to the natural downflowing direction of the seepage water; and
a flexible flat valving member sealingly fastened to the waterproofing membrane, said flat valving member having a free edge which extends beyond said water discharging aperture, characterised in that the drainage valves are provided on a wall of the body of the hydraulic structure, said drainage valves being arranged to drainage the seepage water downwardly, by gravity.
According to several embodiments, the discharge valve device can extend over part or the entire width of opposite edges of sheet materials of the waterproof geomembrane.
The drainage valve device can be provided and carried out during the construction and installation of the waterproof geomembrane, for example by overlapping a certain length of the cross edges of two consecutive sheets of the sheathing, without sealing them; it is also possible to form the drainage valve device after the waterproof sheathing has been installed, for example by making a cut or an aperture for the outflow of the water in the waterproof sheathing, and subsequently covering the cut or aperture with a valving sheet of an elastically deformable synthetic or bituminous material, which is sealed on three consecutive edges more precisely the rear edge and two lateral edges of the cut or aperture; the fore edge of the valving sheet is consequently left free to flex and lift up and down under the effect of the differential pressure of the water acting on the fore and rear faces of the same valving sheet, to enable the outflow of the seeped water, preventing water inflow.
Other features of the method and the waterproofing and drainage device according to the invention are defined by the dependent claims.
These and further features of the method and the drainage device according to this invention, and several of its possible embodiments, are illustrated hereunder with reference to the accompanying drawings, in which:
With reference to the figures from 1 to 5 a description is given hereunder of the general features of the method and of the waterproofing and drainage system according to the invention.
The sheets 11 can be secured by any known means, for example by providing suitable structural steel sections which enable them to be tensioned or stretched, as described for example in U.S. Pat. No. 5,720,576; or by means of a plurality of pins 14 (
Depending upon requirements or the type of hydraulic structure, the sheets 11 of synthetic material can be placed in direct contact with the surface to be waterproofed. Conversely, a layer 15 of draining material can be disposed between the sheets 11 and the front surface of the hydraulic structure, for example a geonet, a geospacer or the like, as shown in
The sheets 11 of waterproof material can in turn be in the form of a geocomposite, comprising a layer of waterproof material, coupled to a geotextile, in a per se known way, provided they are suitable for the intended use.
A one-way drainage valve 13, in a waterproofing and draining device according to the invention, and its working are explained in greater detail hereunder, with reference to
According to a preferential embodiment, the one-way drainage valve device 13 is obtained directly during the formation of the waterproof sheathing. In this configuration, during the installation of the waterproofing sheet material 11, as indicated in
During the installation of the sheets 11.1 and 11.2, the overlapped side edges 12 of the juxtaposed sheets will be sealed together, and subsequently secured by means of pins 14, or in any other way.
During the sealing and fastening of the sheets 11, care must be taken to ensure that the overlapped transversal edge 11a of the overlying sheet 11.1 must be free, that is to say, the edge of the upper sheet 11.1, is free to flex, and/or move up and down with respect to the underlying sheet 11.2, and to extend beyond the transversal edge 11b of the latter in the direction of the natural downflow of the water, by gravity; in this way a one-way valve device is obtained directly by the waterproof sheathing, which is capable of being operated by the differential pressure of the water acting on a flexible flat valving member M, provided by a portion of the sheet 11.1 overlapping the sheet 11.2; the outflow aperture thus provided will be oriented in the natural downflow direction of the water which seeps, from the main body 10 of the hydraulic structure, between the latter and the waterproof sheathing, allowing a natural discharge of the water simply by gravity.
More precisely, the overlapped transversal edges 11a and 11b of the two sheets 11.1 and 11.2 which define a one-way drainage valve of the geomembrane type, in a drainage device according to this invention can extend along part or along the entire width of the sheets, as shown.
In general terms, the length “d” of the edges overlapped between two adjacent sheets, and the width of the geomembrane valve device 13 must be such as to enable the efficient operation of the valve thus formed. In particular, the surface freely in contact of the two superposed sheets which constitute the valve device 13, must be of such kind as to provide a seal exclusively by means of the pressure P1 of the water existing upstream or inside the hydraulic structure, as shown in
In particular, as can be seen in
Conversely, when the level of the water drops below the valve device 13, for example as indicated by reference L2 in
The valve device 13 will operate in the same way, each time the differential pressure P1-P2 is negative, that is to say, each time the pressure P2 is higher than the hydrostatic pressure P1 existing at the level L3 of the valve 13, as schematically indicated in
In this way it is possible to obtain a waterproof sheathing provided with water drainage device which uses flexible one way valves, automatically operated, both to open and to close, by the differential pressure of the water existing on the two sides of the waterproof sheathing itself.
A drainage device which uses a geomembrane-type single-acting water discharge valve according to the invention, in addition to being simple and inexpensive, is operatively extremely reliable over time, without requiring any substantial maintenance.
Although in principle the invention is applicable to any type of waterproof sheathing of elastically deformable synthetic or bituminous material, best results are obtained by using highly flexible plastic materials in sheets.
The material used for the geomembrane constituting the waterproof sheathing and/or the drainage valve device can be of any kind whatsoever, provided it is suitable for the intended purpose; in particular, it can be chosen from among synthetic and bituminous materials in the following table, taken either individually or in combination.
The geomembranes may be of a thickness ranging from 0.2 to 60 mm, with a modulus of elasticity ranging from 10 to 5,000 MPa.
According to this embodiment, a cross-cut or elongated aperture 20 is made in one sheet 11 of the waterproof sheathing, in a direction transversal to the downflow direction of the seeped water, indicated by the arrow W.
A sheet M of elastically deformable synthetic or bituminous material defining a flat valving member is superimposed to the cut 20; the sheet M is sealingly connected, i.e. thermally sealed to the waterproof sheet 11, along three edges 21, leaving the fore edge 22 of the sheet M parallel to the cut 20, extending downstream with respect to the downflow direction W, to freely flex and rise under the thrust of the water which tends to flow downwards by gravity, as shown by the broken line indicated by reference M′ in
Furthermore, when the dam, hydraulic tunnel or hydraulic structure is emptied, or when the pressure of the water that has seeped behind the waterproof sheathing tends to increase, exceeding the pressure of the water on the front side of the valve device 13, the differential pressure will open the valve 13 allowing the natural downflow of the seeped water. This prevents the accumulation of seeped water behind the waterproof sheathing from damaging or causing the latter to explode, due to an excessive deformation.
As mentioned previously, the waterproof sheathing provided by sheets 11 of flexible synthetic material, can be installed directly in contact with the surface of the hydraulic structure to be waterproofed; conversely, a drainage layer can be positioned between the facing surfaces of the hydraulic structure and the sheets 11 of the waterproof sheathing, consisting for example of a geonet, or in any case by a draining element as indicated by reference 23 in
Also in this case, the waterproof sheathing 30 comprises a plurality of sheets 11 of elastically deformable synthetic material, disposed in a transversal or longitudinal direction to the tunnel, always taking care to overlap the edges as shown in
At the bottom, on the two opposite sides of the tunnel 31, or in pre-established positions of the waterproof sheathing 30, one-way drainage valve devices 13 are provided, in the way described previously, as schematically shown in the enlarged detail of
Lastly, the example of
Likewise, in
Also in this case, the opposite transversal edges 11a and 11b of the two sheets 11.1 and 11.2 are overlapped for a space of a pre-established length, leaving the edge 11a of the upper sheet 11.1 free to flex, to open and close the flat valving member M of the valve device 13 under the differential pressure of the water, in the way previously described; obviously, other modifications and/or applications of the waterproofing and drainage system by means of one-way valve devices are possible, compared to those shown.
For example, as show in
According to a further embodiment, the overlap “d” of the previous cases can be avoided by creating a simple cut along a line transversal to the moving or outflow direction of the water, as in
From what has been described and shown in the accompanying drawings, it will be clear that what is provided is a method and a waterproofing and drainage device for draining off the seeped water in hydraulic structures, which makes use of a special drainage valve device, of the geomembrane type, oriented in the natural downflow direction of the water. The presence of a drainage device of this kind substantially reduces the loads supported by the anchorage points, thereby increasing the safety factor for the entire waterproof sheathing.
It is understood however that what has been described and shown should not be construed in a limitative sense with regard to any possible applications and ways of performing the one-way valve device, by the use of geomembrane sheets; therefore, other modifications or variations may be made both to the drainage device itself, and to the method without thereby departing from the scope of the claims.
Number | Date | Country | Kind |
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05025533.0 | Nov 2005 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2006/011163 | 11/22/2006 | WO | 00 | 5/22/2008 |