US3326001A - Surface proofing arrangement - Google Patents

Description

June 20, 1967 G. STAPELFELD v SURFACE PROOFING ARRANGEMENT Filed Sept. 30, 1964 United States Patent 3,326,001 SURFAtIE PROOFING ARRAVGEMENT Gerhard Stapeifeld, Dortmund, Germany, assignor to Gelsenkirchener Bcrgwerks-Aktien-Gesellschaft, Essen, Germany Filed Sept. 30, 1964, Ser. No. 400,377 Claims priority, application Germany, Oct. 3, 1963, G 38,846 11 Claims. (Cl. 61-1) The present invention relates to a surface proofing arrangement and particularly to an arrangement for preventing the seepage of a water-immiscible liquid below a given surface of a liquid-permeable material, such as the prevention of seepage of leak oil from stationary oil tanks into the ground so that such leak oil cannot reach the ground water level and cannot contaminate the ground water.

In order to maintain the purity of the ground water special measures must be taken to assure with certainty that no leak oil or other harmful liquids will reach the ground water area. It has been proposed to form an impervious barrier for stationary oil tanks and the like of clay or similar material. However, this will give the desired result only if the underlying ground is of suitable structure and it also requires the availability of clay or other suitable loamy material for forming the barrier. Only in relatively few locations can this type of barrier be produced so as to give an effective protection and to be economically feasible. Furthermore, it is not possible to control the effectiveness of the impervious layer or of individual portions thereof once the same have been installed.

It has also been proposed to form the impervious layer of a foil or synthetic material which is resistant against attack by crude oil. Such foil, on the one hand, must be hard and impact resistant and, on the other hand, resilient in order to withstand the stresses to which such foil will be exposed by uneven pressure of particles of the ground against the foil and by the movement of the ground. For these reasons, impervious layers consisting of a synthetic foil have met with only limited success and must be arranged with extraordinary care.

Rigid barriers such as forming a concrete layer in the ground or inserting concrete plates are not suitable because they can follow the movement of the ground layers only upon partial destruction of the concrete or the like structure.

It is therefore an object of the present invention to provide a surface or ground proofing arrangement for preventing seepage of a water-immiscible liquid therethrough which will not be subject to the above discussed difficulties and disadvantages.

It is a further object of the present invention to provide a surface or ground proofing arrangement which can be produced in a simple and economical manner and which will effectively prevent undesirable seepage therethrough.

It is yet a further object of the present invention to provide a surface or ground proofing arrangement which permits easy control of the impermeability of individual portions thereof.

Other objects and advantages of the present invention will become apparent from a further reading of the description and of the appended claims.

With the above and other objects in view, the present invention contemplates a surface proofing arrangement for preventing seepage of a water-immiscible liquid below a given surface of a liquid-permeable material, comprising, in combination, a lower layer consisting of a material impermeable to liquids disposed to cover the surface, and

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an upper layer superimposed on said lower layer and consisting of a water absorbent material, and of water absorbed in the upper layer and retained in the same by the lower layer so that the upper layer is adapted to repel the water-immiscible liquid whereby contact of the same with the lower layer and seepage of the same into the liquid permeable material below the given surface is prevented.

Thus, according to the present invention the barrier is formed of a preferably highly capillary layer of synthetic foam plastic material which layer is superposed upon an impervious foil or layer of synthetic plastic material. The porous capillary layer is capable of absorbing water and has water absorbed in its capillary interstices and the underlying impermeable synthetic foil prevents escape of the water which is located in the porous foam plastic layer.

Preferably another foam plastic layer is arranged underneath the impermeable foil and serves primarily the purpose of protecting the lower face of the impermeable foil against damage by possibly sharp edged particles of sand or other ground material.

In order to reduce the amount of synthetic material required for the foam plastic layers and also to reduce the compressibility of the same, it is sometimes desirable to incorporate a filler material such as bentonite in the foam plastic layers and in such case the diameter of the individual particles of the filler material preferably should be less than 0.9 mm.

Within the two foam plastic layers located above and below the impermeable foil, measuring electrodes may be arranged for the purpose of determining the location of any damaged and thus permeable portion of the impermeable foil. In order to control the water level above the barrier layer, it is advantageous to provide a pumping arrangement at the lowermost point of the trough formed by the barrier layer as will be described in more detail further below.

The surface or ground proofing arrangement of the present invention is particularly suitable for proofing the ground water carrying level against penetration by leak oil from stationary oil tanks. However, the ground proofing arrangement may be advantageously used wherever the problem of preventing penetration of the ground water level by harmful liquids may exist, particularly with respect to harmful liquids which are immiscible with water and which have a lesser specific gravity than water, such as light fuel oil, medium heavy oil, gasoline, benzene, oxylene, p-xylene and similar products.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a diagrammatic cross sectional view through an oil tank installation provided with the ground proofing arrangement of the present invention; and

FIG. 2 is an enlarged cross sectional view through the portion of FIG. 1 indicated by circle A and also includes a diagrammatic showing of a testing device for indicating any leakage through the ground proofing arrangement.

Referring now to the drawing it will be seen that a trough-shaped cavity 14} is formed in the underground 11. The surface of the cavity is then covered with a layer of sand 1 having a particle size of up to 3 mm. Sand layer 1 supports a highly capillary layer 2 of synthetic foam plastic material having a thickness of between about 3 and 5 cm. Layer 2 may consist for instance of two layers, one

of foamed styrene and one of foamed urea formaldehyde resin. Layer 2 supports a continuous, welded, liquid impervious foil 3 of synthetic plastic material and foil 3 is covered by a highly capillary synthetic foam plastic layer 4 which, for instance, may be formed of foamed urea formaldehyde resin. Layer 4 will be of such initial thickness that even when covered by layer 5 and thus compressed the thickness of layer 4 will still be at least about mm. The foamed layers may include filler material having a particle size of less than 0.9 mm., for instance of bentonite. The protective barrier which thus is formed of foamed layers 2 and 4 with interposed impervious foil 3 is then covered with a sand layer 5 having a thickness of about 50' cm. This sand layer 5 is preferably compacted for instance by having a heavy caterpillar vehicle run over the same. The sand of layer 5 preferably will have a particle size of up to 3 mm. and is superposed by a surface layer 6 also consisting of sand. A conventional pumping arrangement 7 is located so as to have suction pipes extending into the area of deepest depression or the lowest point 12 of the cavity or trough 10.

After the sand layers which are superposed upon the plastic barrier layers are compacted, the entire area of the thus filled cavity 10 is watered preferably with about 10 to 15 liters of water per square meter. In this manner an artificial ground water level 9 is formed above the barrier layers 2, 3, 4. The regular, natural ground water level is indicated by reference numeral 13. It will be seen that the regular ground water will be maintained below the barrier layer 2, 3, 4. Oil tank 14 is located above the filled in cavity 10.

Foam plastic layer 2 will protect the superposed impervious foil 3 against penetration and damage by sand particles. It is the purpose of foil3 to prevent downward escape of water from the highly capillary superposed water filled layer 4. Furthermore, porous foam layer 4 will also protect foil 3 against damage by particles of sand or layer 5. Furthermore, due to its water content, layer 4 will serve to prevent migration of softeners from foil 3 and simultaneously also prevent direct contact between any leak oil or seepage from tank 14 and foil 3. Thus, the material which in fact prevents further downward passage of the oil is the water contained in foam plastic layer 4.

Throughout the entire barrier layer arrangement pairs of electrodes such as the electrode pair 8 and theelectrode pair 8 are arranged with the two electrodes of each pair located adjacent each other in layer 2 and layer 4 respectively. By connecting any given pair of electrodes to a source of electric current and to an instrument indicating the passage of current, it can be determined whether current flow takes place between'the two electrodes of the respective pair of electrodes. Such current fiow is an indication of water penetration from layer 4 through foil 3 into layer 2, in other words, an indication of damage or variations in the height of the natural ground water level and that it can also be easily located on sandy ground without risk of damage to the impermeable foil 3 since the adjacent foam plastic layers 2 and4 will protect foil 3 against damage by grains of sand. Since leak oil does not get into direct contact with foil 3, the washing out of softeners from foil 3is also effectively prevented. Due to the capillarity of layer 4, the same will contain absorbed water also in its more elevated portions such as those which are located within embankments 15.

The artificialground water level 9 above the barrier layer will be controlled by operation of pumps 16 and 18 which are connected respectively to suction pipes 17 and 19. Suction pipe 17 reaches somewhat lower so as to be located within the uncontaminated water level, while suction pipe 19 terminates at a somewhat higher point and may deliver a mixture of water and leak oil. Due to its resiliency, the barrier consisting of layers 2, 3 and 4 will easily and without damage adjust to movements of the ground.

Layers 2 and 4 may be formed of the same foam plastic material. However, it is essential that layer 4 consists of a hydrophilic material for instance urea formaldehyde foam since the capillary interstices in layer 4 are to be filled with water. With respect to layer 2 this is not absolutely necessary and thus layer 2 may, for instance, be formed as a composite layer comprising a core portion of styrene foam which is covered on both sides by urea formaldehyde foam, or layer 2 may also consist of a particularly stiff and rigid ureaformaldehyde foam since its main function is the cushioning of foil 3 while, in contrast thereto, layer 4 has the further function of being the carrier of the water which in fact prevents contact between layer 3 and the leak oil or the like.

When foaming urea formaldehyde, closed small bubbles of polyhedric shape are formed which adhere to each other and which form between themselves a system of capillary interstices which serve, as described above, for absorbing and storing water in layer 4. It is the purpose of this microporous layer, due to its high capillarity, to maintain the water in layer 4 even if the artificial ground water level 9 should drop. In thiscase the capillarity of the layer will serve to hold the water therein. The barrier water layer is essential in order to avoid wetting of foil 3 with leak oil which may originate fro-m tank 14. Contact between leak oil and water impermeable foil 3 particularly in conjunction with mechanical stress could lead to destruction of the impermeability of layer 3.

Preferably the diameter of the capillaries forming a network of interstices in layer 4 should not exceed 0.01 mm. in order to assure the desired capillary effect.

Microporous layer 4 and thus also microporous layer 2 may be formed of practically all available hydrophilic synthetic materials which can be foamed so as to form a network of capillary interstices and which will conform to the technical and chemical requirements. The microporous foam layers must be capable to withstand chemical attack by the ground water and should not be decomposed by organic solvents. Very good results are achieved with urea formaldehyde condensation products of which compressible foamed layers can be produced.

It is esseential that after hardening the foam layer can still be compressed and will not break when exposed to the load of the superposed sand layers.

To form porous layer 2 of polystyrene foam, for instance of type commercially available under the tradename Styropor, and urea formaldehyde foam has primarily economic advantages. By using Styropor foil having a thickness of between 8 and 10 mm., it is possible to reduce the thickness of the urea formaldehyde foam layer so that the same will be between 5 and 10 mm. in compressed condition. This will suffice to protect foil 3 from mechanical attack by the underlying sand layer.

Good results were obtained with an arrangement according to which on sandlayer 1 having a particle size of between 1 and 3 mm. is placed a microporous, highly capillary hydrophilic synthetic foam plastic layer having a thickness in uncompressed condition of between about 20 and 25 .mm. and consisting for instance of urea formalhyde foam. The next portion of the layer consists of a Styropor foilor plate having a thickness ofbetween about 8 and 10 mm. and this is followed by a second microporous highly capillary hydrophilic synthetic foam layer of between about 20 and 25 mm. thickness. The compound layer 2 consisting of. two microporous highly capillary hydrophilic synthetic foam layers with an interposed Styropor layer should be so dimensioned that even under the greatest load to which it will be exposed by the superposed sand layers 5 and 6, layer 2 in thus compressed condition will still have a thickness of at least mm. Thereby it is assured that foil 3 will not be exposed to mechanical attach from sand layer 1. Since Styropor possesses greater rigidity than urea formaldehyde foam layers, it is possible to use in this manner a Styropor layer which is thinner than the urea formaldehyde foam layer which would be required to replace it.

The incorporation of a filler material in the foamed layers 2 and 4 serves for reducing the costs of the layers and also to improve the mechanical resistance of the same. The amount of filler material such as bentonite should not exceed 50% of the weight of the layer and the filler material must be evenly distributed throughout the layer with the individual particles of the filler material having a size not exceeding 0.9 mm.

Under operating conditions, i.e., when compressed by the superposed sand layers 5 and 6, the thickness of each of layers 2 and 4 should not be less than 10 mm. respectively. The thickness of the uncompressed layer is best determined experimentally after the maximum height and thus the weight of the combined sand layers 5 and 6 has been established.

Urea formaldehyde foam with a Weight of between about 5 and kg./m possesses the desired degree of plastic deformability. The volume of capillaries within the urea formaldehyde foam increases with increase in weight per volume of the same while simultaneously the size of the closed bubbles decreases. Since a maximum capillary volume is desired, preferably a urea formaldehyde foam having a weight of between 10 and 15 kg./m. will be used.

Plastic foil 3 should consist of a synthetic plastic material which is extensible even after prolonged storage and is capable of resisting chemical attack by the soil. Good results are achieved with foils of polyvinyl chloride, polyethylene and polyisobutylene. It is also possible to use such synthetic plastic foils which are coated with a special bitumen. In this case the synthetic plastic foil may be thinner and thus more economical to use. In any event, it is essential that foil or layer 3 will remain impermeable to water even upon prolonged storage and upon being exposed to the movement of the underground. The thickness of foil 3 should be at least 0.75 mm. and preferably will be about 1 mm.

Referring now again to FIG. 2 of the drawing, it is diagrammatically illustrated therein how the electrode pairs 8 and 8, which are only representative of a large number of such electrode pairs, will serve to control the impermeability of foil 3. As long as foil 3 is impermeable it constitutes an electric insulation between layers 2 and 4. In case of permeability, i.e., if the foil is punctured or torn at some place, water will penetrate from layer 4 through broken foil 3 into layer 2. Each electrode pair, such as electrode pair 8 or 8, consists of one electrode which is located in layer 4 which due to its water content is conductive and another electrode which is located in layer 2 which layer is insulated from layer 4 unless foil 3 is broken in the vicinity of the electrode pair. As illustrated in FIG. 2, the electrical circuit will be closed only when Water has penetrated into layer 2 and thus has made layer 2 conductive. The thus established current flow can then be indicated in conventional manner at 20. Preferably, the electrodes are located close to the adjacent sand layers 1 and '5 respectively. It has been found advantageous to use electrodes of synthetic resinbound carbon which are then connected to the required wiring because in this manner corrosion and the formation of an electric cell is effectively prevented.

Each pair of electrodes is separately connected with the control devices and preferably voltage and current flow will be shown by the indicator.

The distance of the electrode pairs from each other may be between 50 and meters depending on how accurately one wishes to determine the point at which foil 3 has become permeable. If sand layer 6 is relatively thin, the electrode pairs may be spaced further apart since the costs of digging to the foil will be relatively small. On the other hand, if sand layer 6 is very thick, it will be economical to arrange a greater number of electrode pairs so as to determine with greater accuracy the area in which foil 3 will have to be repaired.

As illustrated in FIG. 1, two pumps are arranged with suction pipes extending in a conventionally structured sump to different levels in the vicinity of the lowermost portion of the trough formed by the barrier layers 2, 3 and 4. Preferably water is removed through suction pipes 17 and pump 16 only, until the water level in the sump has been lowered to the vicinity of the outlet end of suction pipe 19 and only then an oil-water mixture is withdrawn through suction pipe 19 and pump 18.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of surface proofing arrangements differing from the types described above.

While the invention has been illustrated and described as embodied in a ground surface proofing arrangement for preventing seepage of a water-immiscible liquid below a given ground surface, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any Way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A ground surface proofing arrangement for preventing seepage of a water-immiscible liquid below a given ground surface, comprising, in combination, a lower layer consisting of a water-impermeable sheet of plastic material disposed to cover said ground surface; and an upper layer superimposed upon and contacting said lower layer and consisting of a water absorbent foam plastic material, and of water absorbed in said upper layer and prevented from escaping downwardly by said lower layer.

2. A ground surface proofing arrangement as defined in claim 1, wherein said water absorbent foam plastic material of said upper layer consists essentially of a urea formaldehyde resin.

3. A ground surface proofing arrangement for preventing seepage of a water-immiscible liquid below a given ground surface, comprising, in combination, a trough-shaped lower layer consisting of a liquid impermeable sheet of plastic material disposed to cover a depressed portion of said ground surface; and an upper trough-shaped layer having a configuration matching said lower layer and superimposed on the same to cover the entire top surface of the same, said upper layer consisting of a water absorbent synthetic foam plastic material, and of water absorbed in said upper layer and retained in the same by said lower layer so'that said upper layer is adapted to repel said water-immiscible liquid whereby contact of the same with said lower layer and seepage of the same into the ground below said given ground surface is prevented.

4. A ground surface proofing arrangement for preventing seepage of a water-immiscible liquid below a given ground surface, comprising, in combination, a trough-shaped lower layer consisting of a liquid impermeable sheet of plastic material disposed to cover a depressed portion of said ground surface; and an upper trough-shaped layer having a configuration matching said lower layer and superimposed on the same to cover the entire top surface of the same forming a cavity open on top, said upper layer consisting of a water absorbent synthetic foam plastic material; a water absorbent material at lease partially filling said cavity; and water absorbed in said water absorbent material in said cavity and in said upper layer and retained in the latter by said lower layer so that said upper layer. is adapted to repel said water-immiscible liquid whereby contact of the same with said lower layer and seepage of the same into the ground below said given ground surface is prevented.

5. A ground surfact proofing arrangement for preventing seepage of a water-immiscible liquid below a given ground surface, comprising, in combination, a bottom layer consisting of a foam plastic material disposed to cover said ground surface; an upper layer superimposed on said bottom layer and consisting of a water absorbent foam plastic material and of water absorbed in said upper layer; and alayer consisting of a waterimpermeable sheet of synthetic plastic material interposed between and contacting said bottom and said upper layer and preventing contact between said water in said upper layer and said lower layer so that said upper watercontaining layer is adapted to repel water-immiscible liquid whereby contact of water-immiscible liquid with said water-impervious sheet and seepage of water-immiscible liquid into said ground surface is prevented.

6. A ground surface proofing arrangement for preventing seepage of a water-immiscible liquid below a given. ground surface, comprising, in combination, a bottom layer consisting of a foam plastic material disposed to cover said ground surface; an upper layer superimposed on said bottom layer and consisting of a water absorbent capillary, filler-containing foam plastic material and of water absorbed in said upper layer; and a layer consisting of a water-impermeable sheet of synthetic plastic material interposed between and contacting said bottom and said upper layer so as to prevent contact between said water in said upper layer and said lower layer so that said upper water-containing layer is adapted to repel water-immiscible liquid.

7. A ground surface proofing arrangement for preventing seepage of a water-immiscible liquid below agiven ground surface, comprising, in combination, a bottom layer consisting of a filler-containing foam plastic ma-- terial disposed to cover said ground surface; an upper layer superimposed on said bottom layer and consisting of a water absorbent foam plastic material and of water absorbed in said upper layer; and a layer consisting of a water-impermeable sheet of synthetic plastic material interposed between and contacting saidbottorn and said upper layer so to prevent contact between said .water in said upper layer and said lower layer so that said upper water-containing layer is adapted to repel waterirnmiscible liquid.

8. A ground surface proofing arrangement for preventing seepage of a water-immiscible liquid below a given ground surface, comprising, in combination, a bottom layer consisting of a foam plastic material containing a particulate filler having a particle size below 0.9 mm. disposed to cover said ground surface; an upper layer superimposed on said bottom layer and consisting of a water absorbent foam plastic material of capillary structure and containing a filler material having a particle size of below 0.9 mm. and of water absorbed in said upper layer; and a layer consisting of a water-impermeable sheet of synthetic plastic material interposed between and contacting said bottom and said upper layer so as to prevent contact between said water in said upper layer and said lower layer so that said upper water-containing layer is adapted to repel water-immiscible liquid.

9. A ground surface proofing arrangement for preventing seepage of a water-immiscible liquid below a given ground surface, comprising, in combination, a

o trough-shaped lower layer consisting of a liquid impermeable sheet of plastic material disposedto cover a depressed portion of said ground surface; and an upper trough-shaped layer having a configuration matching said lower layer and superimposed on the same to cover the entire top surface of the same forming a cavity open on top, said upper layer consisting of a water absorbent synthetic foam plastic material; sand at least partially fill ing said cavity; and water absorbed in said sand in said cavity and in said upper layer and retained in the latter by said lower layer so that said upper layer is adapted to repel said water-immiscible liquid whereby contact of the same with said lower layer and seepage of the same into the ground below said given ground surface is prevented.

10. A surface proofing arrangement for preventing seepage of a water-immiscible liquid below a given surface of a liquid permeable material, comprising, in combination, a bottom layer consisting of a foam plastic material disposed to cover said surface; an upper layer superimposed on said bottom layer and consisting of a water absorbent foam plastic material and of water absorbed in said upper layer; a layer consisting of a liquidimpervious sheet of synthetic plastic material interposed between and contacting said bottom and said upper layer and retaining said water in said upper layer so that said upper layer is adapted to repel said water-immiscible liquid whereby contact of the same with said liquid impervious sheet and seepage of the same into said bottom layer is prevented; and electrode means operatively connected to said bottom layer and said upper layer and including current supply means and indicating means for determining current flow between said upper and said bottom layer indicating rupture of said passage of water through said interposed impervious sheet.

11. A ground surface proofing arrangement for preventing seepage of a water-immiscible liquid below a given ground surface, comprising, in combination a trough-shaped lower layer consisting of a liquid impermeable sheet of plastic material disposed to cover a depressed portion of said ground surface; and an upper trough-shaped layer having a configuration matching said lower layer and superimposed on the same to cover the entire top surface of the same forming a cavity open on top, said upper layer consisting of a water absorbent synthetic foam plastic urea formaldehyde resin; sand at least partially filling said cavity; and water absorbed in said sand in said cavity and in said upper layer and retained in the latter by'said lower layer so that said upper layer is adapted to repel said water-immiscible liquid whereby contact of the same with said lower layer and seepage of the same into the ground below said given ground surface is prevented.

References Cited UNITED STATES PATENTS 2,437,909 3/1948 Cooper 615 X 2,794,756 6/ 1957 Leverenz. 2,806,812 9/1957 Merz. 3,004,293 10/ 1961 Kreidl.

3,142,855 8/1964 Gilchrist 161159 X 3,188,814 6/1965 Rettiug 6131 FOREIGN PATENTS 1,267,566 6/ 1961 France.

789,644 1/1958 Great Britain.

OTHER REFERENCES Abstract 148,996, O.G., vol. 656; page 893; Mar. 18, 1952.

Popular Mechanics; April 1963, page 126.

EARL J. WITMER, Primary Examiner.

Claims (1)

1. A GROUND SURFACE PROOFING ARRANGEMENT FOR PREVENTING SEEPAGE OF A WATER-IMMISCIBLE LIQUID BELOW A GIVEN GROUND SURFACE, COMPRISING, IN COMBINATION, A LOWER LAYER CONSISTING OF A WATER-IMPERMEABLE SHEET OF PLASTIC MATERIAL DISPOSED TO COVER SAID GROUND SURFACE; AND AN UPPER LAYER SUPERIMPOSED UPON AND CONTACTING SAID LOWER LAYER AND CONSISTING OF A WATER ABSORBENT FOAM PLASTIC MATERIAL, AND OF WATER ABSORBED IN SAID UPPER LAYER AND PREVENTED FROM ESCAPING DOWNWARDLY BY SAID LOWER LAYER.

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