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Publication numberUS3841041 A
Publication typeGrant
Publication dateOct 15, 1974
Filing dateMay 21, 1973
Priority dateMay 30, 1972
Also published asDE2327411A1
Publication numberUS 3841041 A, US 3841041A, US-A-3841041, US3841041 A, US3841041A
InventorsFriedland J, Habib P
Original AssigneeFriedland J, Habib P
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Tank for a swimming pool or the like
US 3841041 A
Abstract
A tank of the swimming-pool type formed of rigid plastic material such as polyurethane foam and provided with a fluid-tight lining of small thickness is placed directly in contact with the soil within a pit which has been dug in the ground. The modulus of elasticity of the side wall and preferably of the bottom is close in value to that of the surrounding soil so as to result in a uniform stress distribution and a deformability which removes any danger of crack formation.
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ilite tates atet Friedland et al.

145] Oct. 15, 1974 TANK FOR A SWIMMING POOL OR THE LUKE lnventors: Jacques Friedland, 14, rue

Beautreillis; Pierre Habit), 2, rue Turgot, both of Paris, Seine, France Filed: May 21, 1973 Appl. No.: 362,236

Foreign Application Priority Data May 30, 1972 France 72.19256 US. Cl. 52/1169, 4/172, E04h/3/l6 Field 01 Search 52/169, 309, 265, 167; /172 References Cited UNITED STATES PATENTS Klingberg 52/169 X 3,015,191 1/1962 Lucchesi 52/169 3,031,801 5/1962 Leuthesser 52/169 X 3,429,035 2/1969 Stillman t 52/169 3,610,564 10/1971 Mattingly...; 52/169 X 3,660,957 5/1972 Schankler 52/169 X Primary Examiner-1r. Faw Attorney, Agent, or FirmThomps.on and Thompson [57] ABSTRACT A tank of the swimming-pool type formed of rigid plastic material such as polyurethane foam and provided with a fluid-tight lining of small thickness is placed directly in contact with the soil within a pit which has been dug in the ground. The modulus of elasticity of the side wall and preferably of the bottom is close in value to that of the surrounding soil so as to result in a uniform stress distribution and a deformability which removes any danger of crack formation.

2 Claims, 5 Drawing Figures 1 TANK FOR A SWIMMING POOL OR THE LIKE This invention relates to a swimming-pool tank which is placed in a pit dug in the ground. The word tank as used in the description of the present invention refers preferentially to-swimming-pool's but extends to all types of receptacles for containing liquids, especially for industrial or agricultural purposes.

It is known that a swimming-pool tank has a side wall and a bottom which are adjacent to the soil of the pit and the function of which is to maintain the shape of the tank while affording resistance to the thrust developed by the hydrostatic pressure of the liquid.

Said side wall and tank bottom are usually covered with a fluid-tight lining.

In one known design of swimming-pool tank, the bottom is a concrete raft and the side wall is constructed by means of breeze-blocks or concrete slabs which are bonded together by means of mortar and covered with a fluid-tight lining which is moulded over the subjacent slabs or breeze-blocks.

Swimming-pool tanks of known types are capable of undergoing small deformations at right angles to the surface of the side wall or the bottom without thereby sustaining any damage, under the action of variations which occur in the pressure exerted by the surrounding media, especially at the time of emptying and filling of the tank orduring periods of frost.

The masonry or concrete slabs of which the side wall and the bottom of the tank are formed have the disadvantage of being non-deformable along their own plane, with the result that any possible deformation under the influence of the above-mentioned variations in pressure is liable to take place only at the level of localized zones of lower resistance such as the joints between the slabs or breeze-blocks. In consequence, the fluid-tight lining which is bonded to the slabs is subjected at the level of said joints to tensile stresses which are liable to result in crack formation or tearing. Said fluid-tight lining must therefore be formed of material which is capable of withstanding such stresses without damage.

In the most recent designs, this problem is solved by making use of a composite material which has both.

flexibility and strength but is very costly, such as a laminate of glass fabrics impregnated with polyester resin.

Elements of large size are sometimes employed with a view to limiting the number of joints between the breeze-blocks or slabs since these joints are liable to constitute an equal number of zones of lower strength. However, both labour and handling means are required for the positioning of these elements.

Furthermore, the walls of the above-mentioned swimming-pool tanks provide only limited thermal insulation for the water which is contained in the tank and is usually heated to a temperature above that of the surrounding soil.

This invention is intended to overcome the disadvantages referred-to above by providing a swimming-pool tank of simple and inexpensive construction comprising a wall adjacent to. the soil andhaving a deformability such as to eliminate any risk of crack formation or damaging of the tank as a result of the variations in pressure which were mentioned earlier.

In accordance with the invention, the swimming-pool tank placed in a pit and comprising a wall which is adjacent to the soil of the pit and covered with a fluid tight lining is characterized in that the wall has a modulus of elasticity which is closely related in value to the modulus of elasticity of the soil in the vicinity of the pit.

It is known that the modulus of elasticity E which is also designated as the coefficient of elasticity or Youngs modulus of a material is determined by crushing a cylindrical test specimen of said material between two plates and by measuring the deformation exhibited by the test specimen as a function of the pressure applied.

If I is the initial length of the test specimen and d! is the deformation developed at the pressure P, the modulus of elasticity E is equal to: P-l/dl. V

.The modulus of elasticity of a material is therefore equal to the quotient of the pressure applied on the material by the corresponding relative deformation and consequently has the dimensions of a pressure.

p The modulus of elasticity is a physical quantity which characterizes a material in a very accurate manner. In fact, the modulus of elasticity varies considerably from one material to another as shown by the following list of materials for whichthe moduli of 'elasti city'are given in decanewtons per cm (daN/cm which is a unit corresponding to 1 bar):

. gelatin- 0.1 daN/cm pneumatic type rubber 5O methyl polymethacrylate 30,000 do; tungsten carbide 3,000,000 do.

The modulus of elasticity is also variablefrom one soil to another. A few moduli of elasticity of different soils are given hereunder:

20 to I00 Surface clays daN/cm Silts 40 to I50 do.

Sands to 400 do.

Old alluvia, sands and gravels 400 to 2000 u do. do.

Chalk 10,000 to 20,000 i As contemplated by the invention, the adaptation of the modulus of elasticity of the wall to that of the soil surrounding the pit results in the following technical effect: when the wall of the tank in accordance with the invention is subjected to variations of pressure, which takes place in practice when the tank is emptied and filled, the soil which is adjacent to said wall will be de formed in much the same manner as this latter. In consequence, the tensile stresses which are liable to be set up in the plane of said wall under the action of said variations of pressure can only be very moderate and are not liable to cause crack formation in the wall.

In a preferred embodiment of the invention, the entire wall including the bottom of the tank has a modulus of elasticity which is close in value to that of the soil. In this manner, even the most moderate tensile stresses are distributed throughout the entire tank.

In order to remove any danger of crack formation in the tank wall, the modulus of elasticity of said wall is preferably equal at a maximum to twice themodulus of elasticity of the soil.

For example, when the tank wall is adjacent to a soil having a modulus of elasticity within the range of 50 to daN/cm, which corresponds to a good soil for the installation of a swimming-pooltank, it is preferable to ensure that the modulus of elasticity of said wall is within the range of 50 to 200 daN/cm The aforementioned conditions in regard to the modulus of elasticity of the tank wall make it possible for this latter to undergo deformations in its own plane without any resultant localized concentration of stresses which would be liable to produce cracks.

However, the wall must also be capable of undergoing deformations at right angles to its own plane without cracking.

In point of fact, a soil is never homogeneous and its modulus of elasticity is variable from one point to another.

It can be acknowledged that, by reason of this lack of homogeneity of the soil and under the action of pressures applied at right angles to the wall, this latter must be capable of undergoing a deflection (f) of 1 cm over a distance (2a) of l m.

Given that R is the radius of curvature corresponding to said deflection f and said distance 20, we have:

f R w) that is to say for a small value off:

R=a 2f= 1,250 cm In the case of a wall having a thickness e, failure is obtained when its radius of curvature attains the value defined by the known relation:

e 2,500 s/E In practice, in order to guard against any risk of crack formation, it is preferable to limit the thickness of the wall to a value which is four times smaller than that given by the formula referred-to above, that is to say:

e A 2,500 s/E This relation defines the maximum limit which is set for the thickness of the wall and which must not be exceeded. Fluid-tightness of the swimming-pool tank in accordance with the invention can be obtained by covering the wall with an inexpensive lining which can be of very small thickness since it will practically not be subjected to any tensile stress.

Further properties of the invention will become apparent from the detailed description which is given below, reference being made to the accompanying drawings which are given by way of non-limitative example, and wherein:

FIG. 1 is a perspective view of a swimming-pool tank in accordance with the invention, the side walls of which are rounded;

FIG. 2 is a sectional view of the swimming'pool tank as taken along line II-ll of FIG. 1;

, FIG. 3 is a sectional view of the tank wall which is drawn to a larger scale and shows a particular method of anchoring said wall to the ground;

FIG. 4 is a sectional view of the upper edge of the swimming-pool tank;

FIG. 5 is a sectional view of the tank wall which is drawn to a larger scale and shows in particular the structure of a fluid-tight lining.

Referring now to FIGS. 1 and 2, it is apparent that the swimming-pool tank 1 in accordance with the invention is placed within a pit dug in the ground 2. The tank 1 has a side wall 3 of rounded shape and a bottom 4 which are adjacent to the soil and covered with a fluid-tight lining 5.

In accordance with the invention, the wall 3 and the bottom 4 of the tank I are formed by means of material having a modulus of elasticity which is close in value to that of the ground or soil 2 and preferably equal at a maximum to twice that of the soil. To this end, the value of the modulus of elasticity of the soil is determined by the method indicated earlier, namely by means of test specimens taken from the immediate vicinity of the pit and the mean value of the modulus E is then determined.

Under these conditions, the tensile stresses which are generated within the wall 3 and the bottom 4 under the effect of variations of pressure which occur, for example, at the time of filling or emptying of the tank 1 remain of very moderate value.

These stresses would be practically eliminated if it were found possible to construct a wall 3 and a bottom 4 having a modulus of elasticity which is equal to that of the soil 2 but this condition cannot be fulfilled systematically since the modulus of elasticity of the soil can vary to an appreciable extent from one place to another.

Taking account of the fact that swimming-pool tanks are usually placed in a soil having a modulus of elasticity within the range of 50 to daN/cm it is an advantage to form the wall 3 and the bottom 4 of the tank 1 in a material having a modulus of elasticity which is substantially comprised between 50 and 200 daN/cm As shown in FIG. 2, the side wall 3 and the bottom wall 4 of the tank 1 are formed by a continuous layer of material whichcomplies with the above-mentioned characteristics of elasticity, with the result that the entire wall of the tank 1 has a modulus of elasticity which corresponds substantially to that of the soil.

Accordingly, the low stresses which are liable to be set up as a result of a variation of the pressure applied on the layer aforesaid are uniformly distributed throughout all the tank walls without giving rise to any appreciable stress concentration at a given point of said walls.

Suitable materials corresponding to the characteristics of elasticity aforesaid are selected from the plastics of cellular structure such as the polyurethane foams, expanded polystyrene and polyethylene which additionally ensure good thermal insulation for the water contained in the tank. The foams which usually permit achievement of the best results are the rigid polyurethane foams which have a specific density within the range of 0.03 to 0.15 g/cm and have a modulus of elasticity after hardening which ranges from 50 to 200 daN/cm.

By way of example, it is possible to make use of a polyurethane foam of the type commercialized by Societe Bayer under the trade name of Moltopren. It is also possible to employ coating or sealing compounds of the mastic type containing a polyurethane resin binder and filled with expanded vermiculite, sawdust or fine rubber powder so as to form a material having the requisite characteristics. By suitably selecting the proportions of constituents, it is an easy matter to modify the modulus of elasticity of the product so as to attain the desired value.

In the swimming-pool tank according to the invention, it is unnecessary and even disadvantageous to provide a substantial thickness in the case of either the wall 3 or the bottom 4. A thickness of a few millimetres or a few centimetres at a maximum is sufficient. This particular feature which is a priori contrary to ordinary experience represents one of the essential advantages of the invention.

The thickness of the polyurethane layer 3 has been exaggerated in the drawings, especially in FIG. 4, for the sake of enhanced clarity of illustration. It is readily apparent that the real thickness of the post or beam 6 is distinctly greater than the thickness of the foam layer In point of fact and in accordance with the invention, the maximum thickness of the wall 3 and the bottom 4 as expressed in centimetres is preferably smaller than or equal to: A 2,500 -s/E.

From this it follows that, in the case of material having a modulus of elasticity E equal to 200 daN/cm and a tensile strength s equal to 2 daN/cm the maximum thickness of the wall 3 and the bottom 4 is equal to approximately 6 cm. It is not essential although preferable to ensure that the surface of the soil 2 which is adjacent to the wall 3 or the bottom 4 is perfectly levelled or made smooth since the application of a layer of plastic material such as the above-mentioned polyurethane foams either by spraying or injection behind shuttering serves to compensate for any surface irregularities of the soil as shown in FIG. 3.

However, in order to ensure good seating on the ground or soil 2, the surface of this latter should preferably be as flat as possible. The surface flatness of the bottom of the pit can be obtained simply by means of a surface coating 12 of mortar as indicated in FIG. 2. The surface flatness of the sides of the pit can also be ensured by filling the largest cavities such as the cavi ties 13 (shown in FIG. 2) with a coating compound or with mortar.

As shown in FIG. 2 and more clearly in FIG. 4, the upper end of the wall 3 of the tank 1 is applied against a rigid support such as a post 6 or any suitable material which is fixed in the ground at the edge 7 of the tank. A curbstone 8 which is usually of reinforced concrete covers the post 6 as well as the upper end of the wall 3. The fluid-tight lining 5 partially covers the curbstone 8. A concrete pavement 9 which is placed over said curbstone and over the upper end of the lining 5 plays a contributory part in anchoring this latter.

Adhesion of the end of the wall 3 to the post 6 and to the curbstone 8 is obtained either by bonding or directly when the wall 3 is formed by application of a foam such as a ployurethane foam. Attachment of the curbstone 8 to the post 6 and of the pavement 9 to the curbstone 8 is obtained by means of mortar.

Additional posts (not shown) which are similar to the post 6 can be placed at intervals along the edge 7 and around the pit so as to ensure that the wall 3 is securely amchored to the edge 7 of the swimming-pool tank. A construction of this type is advantageous in the case of a swimming-pool which has a sinuous contour. In the case of a swimming-pool of rectangular or polygonal shape, the posts 6 can be replaced by a string of joists or beams, for example of reinforced concrete.

From FIG. 3 it is apparent that, in order to improve the adhesion of the wall 3 to the soil 2, anchoring rods or pins 10 of metal which is protected against corrosion or of plastic material can be driven into the ground to an appreciable depth, the ends ll of said rods being embedded in the material which forms the wall 3. The pins 10 thus ensure effective anchoring of the wall 3 relatively to the ground.

The continuous layer which forms the wall 3 and the bottom 4 of the tank is covered with a fluid-tight lining 5 made up of one or a number of layers. Said fluid-tight lining does not need to be formed of high-strength material such as glass fabric impregnated with polyester resin. By way of example, a simple coating of polyurethane resin having a thickness of a few millimetres and formed by means of a mixture of products such as those made available by Societe Bayer under the trade names Desmophen" and Desmodur may prove sufficient for this purpose.

Said fluid-tight lining can also be composed of three layers of polyurethane resin having different functions as shown in FIG. 5. In this figure, the first layer 5a which is illustrated is formed by a non-pigmented polyurethane resin which ensures fluid-tightness. The layer 5a is applied against the external surface of the wall 3 and of the bottom 4. The second layer 5b can consist of a polyurethane resin in which there have been incorporated coloured pigments, non slip pigments or simple fillers of silica. The external finishing layer 50 can be of non-pigmented polyurethane resin.

Prior to application of the fluid-tight lining, the surface of the polyurethane foam layer can be trued by sand-papering.

Two examples of composition for a fluid-tight lining layer are given hereunder:

Example I Sealing compound Polyhydroxylated polyester resin Desmophen 850" Castor oil Titanium oxide Pyrogenated silica parts by weight do.

do. do.

Example ll Finishing coat over sealing compound Polyhydroxylated polyester resin Desmophen 850" I5 Castor oil 85 Titanium oxide 75 Pyrogenated silica 15 parts by weight do.

do. do.

Prior to use, there are added to this composition 48 parts by weight of Desmodur L 75", parts by weight of semi-rigid isophthalic unsaturated polyester resin and 0.6 parts by weight of monomer styrene.

Example lll Sealing compound 2 Semi-rigid isophthalic Prior to use, there is added to this composition a hardener formed by a diisocyanate which is dissolved in ethyl acetate such as Desmodur L 75 in a proportion of parts by weight of the composition aforesaid.

Example lV Finishing coat on sealing compound Semirigid isophthalic unsaturated polyester resin 48 parts by weight Polyhydroxylated polyester resin 13 do. Titanium oxide l2 do. Silica passed through a lZO-micron mesh sieve do. Ultra-fine pyrogenated silica 2 do. Styrene 5 do.

Prior to use, there is added to this composition a hardener formed by a diisocyanate which is dissolved in ethyl acetate such as Desmodur N 75 in a proportion of 10 parts by weight of the composition aforesaid.

the walls are formed of a material which affords excellent thermal insulation and said material can readily be placed in position on the soil surface of the pit which is dug in the ground, thus permitting a reduction in costs arising from the use of handling means and in labour costs.

The invention is clearly not limited to the embodiments' which have been described in the foregoing and a large number of alternative forms of construction can accordingly be contemplated without thereby departing either from the scope or the spirit of the invention.

In particular, the shape of the tank, the material or materials constituting said tank, the thickness of the walls, the anchoring of said walls to the ground of the pit in which the tank is placed can be adapted to various uses.

In a particular mode of execution of the invention, it can also be ensured that the constituent material of the tank wall is selected so that, in addition to the requisite values of the modulus of elasticity, said material has a coefficient of expansion which is comparable with that of the soil. This makes it possible to reduce the thermal stresses which arise either from the water or from ambient conditions.

We claim:

1. A swimming-pool tank in a pit in the ground with a wall adjacent to the soil of said pit and having a fluidtight inner lining, wherein the value of the modulus of elasticity of said wall is equal at amaximum value to twice the modulus of elasticity of the soil in the vicinity of said pit, wherein the maximum thickness 2 of the wall in centimeters is about e A- 2,500- s/E of 50 to 200 daN/cm

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2333315 *Aug 25, 1939Nov 2, 1943Svenska Entreprenad AktiebolagConstruction of underground tanks for storing liquid fuels and other fluids
US3015191 *Dec 27, 1956Jan 2, 1962Leo LucchesiSwimming pool and method for erecting same
US3031801 *Dec 14, 1956May 1, 1962Edward G LeuthesserMethod of installing swimming pools
US3429035 *Jun 16, 1965Feb 25, 1969Lynn W NortonMethod of making a heating element
US3610564 *Jan 17, 1969Oct 5, 1971Mattingly IncConstruction means for the construction of a swimming pool
US3660957 *Dec 10, 1968May 9, 1972Schankler Martin MPrefabricated swimming pool construction
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4027442 *Feb 18, 1976Jun 7, 1977Kdi Sylvan Pools, Inc.Method of constructing swimming pools
US4060946 *May 18, 1976Dec 6, 1977L. F. Lang & Son Pools, Inc.In-ground swimming pool construction
US4065893 *Jan 16, 1976Jan 3, 1978Epes Archie CComposite foundation framing assembly
US4217739 *Apr 6, 1978Aug 19, 1980Granger Jim G JrGrain storage bin and method of making and using the same
US4263759 *Mar 15, 1979Apr 28, 1981Bradley Enterprises, Inc.Swimming pool construction and method of making the same
US4335548 *Apr 30, 1980Jun 22, 1982Millcraft Housing Corp.Insulating skirt
US4860916 *Sep 15, 1988Aug 29, 1989Environetics, Inc.Tank and method of making same
US5806252 *Nov 21, 1996Sep 15, 1998Sibelon S.P.A.Waterproofing system for hydraulic structures with rigid sheets in synthetic material
US20100270001 *Aug 5, 2009Oct 28, 2010Parrella Michael JSystem and method of maximizing grout heat conductibility and increasing caustic resistance
Classifications
U.S. Classification52/169.7, 52/169.11
International ClassificationE04H4/00, E04H4/14
Cooperative ClassificationE04H4/142
European ClassificationE04H4/14A1