JP6783554B2 - Construction method of waterproof sheet for rainwater storage system and rainwater storage system - Google Patents

Description

The present invention provides a waterproof sheet for a rainwater storage system and a method for constructing a rainwater storage system.

In urban areas, if a large amount of rain falls in a short period of time, rainwater will overflow from the drainage ditch and cause flood damage. As one of the measures against flood damage, a technique is known in which a storage material or a permeation basin is installed underground to guide rainwater underground and temporarily store it so that it gradually permeates underground. This technology is called a rainwater storage / infiltration system, and by installing storage materials or infiltration basins in the basement of parks, playgrounds, parking lots, etc., it is possible to take measures against flood damage while making effective use of the ground. It has become. Among them, rainwater storage systems using storage materials have been installed in recent years because they can store rainwater underground and can use the stored rainwater for fountains, fire prevention water, and the like. In the case of a rainwater storage system, for example, as described in Patent Documents 1 and 2, a storage material for maintaining space is installed in a storage tank provided in the ground, and the storage material is used as a water-impervious sheet. Need to wrap in. Further, as described in Patent Document 2, it is common practice to arrange a protective sheet on one side or both sides of the impermeable sheet.

At present, in the construction of a rainwater storage system, a protective sheet is laid on the excavated surface (storage tank) of the excavated tank space, a water-impervious sheet is laid on it, and a water-impervious sheet is laid on it. At the same time, a plurality of impermeable sheets and protective sheets are joined together according to the size of the storage tank, which causes a problem that the process is complicated.

JP-A-2010-83558 JP-A-2015-224450

In order to solve the above-mentioned conventional problems, the present invention provides a waterproof sheet for a rainwater storage system and a method for constructing a rainwater storage system, which can shorten the process at a construction site of the rainwater storage system.

The present invention is a tarpaulin for a rainwater storage system that prevents the outflow of rainwater from a rainwater storage system, and the tarpaulin for the rainwater storage system is arranged on one or both surfaces of the tarpaulin and the tarpaulin. The water-impervious sheet and the protective sheet are separated from each other at the peripheral portion of the tarpaulin for the rainwater storage system, and the water-impervious sheet and the protective sheet are adhered to each other at other parts. It relates to a tarpaulin for a rainwater storage system, which is characterized by being used.

In the peripheral portion of the waterproof sheet for the rainwater storage system, the width of the portion of the water-impervious sheet and the protective sheet separated from each other is preferably 5 cm or more.

In the present invention, the above-mentioned tarpaulin for rainwater storage system is laid so that the protective sheet side is in contact with the excavated surface of the excavated storage tank, and the peripheral edges of the plurality of tarpaulins for rainwater storage system are heat-sealed. It relates to the construction method of the rainwater storage system including the process of connecting with each other.

The present invention provides a waterproof sheet for a rainwater storage system (hereinafter, also simply referred to as a waterproof sheet) and a construction method of the rainwater storage system, which can shorten the process at the construction site of the rainwater storage system.

FIG. 1 is a schematic cross-sectional view of a rainwater storage waterproof sheet according to an embodiment of the present invention. FIG. 2 is a schematic partial plan view illustrating the arrangement of adhesive points in the rainwater storage waterproof sheet according to the embodiment of the present invention. FIG. 3 is a schematic cross-sectional view of a rainwater storage waterproof sheet according to an embodiment of the present invention.

The present inventor considered shortening the process at the construction site of the rainwater storage system, and found that the water-impervious sheet and the protective sheet should be integrated in order to reduce the number of times the water-impervious sheet and the protective sheet are laid. On the other hand, at the construction site of the rainwater storage system, it is necessary to connect multiple impermeable sheets and protective sheets according to the size of the storage tank, making it easy to connect multiple waterproof sheets. I realized that I was also required to do it. Therefore, if the impermeable sheet and the protective sheet are not joined at the peripheral portion and the other parts are adhered and used as a waterproof sheet, the number of times the impermeable sheet and the protective sheet are laid can be reduced at the construction site of the rainwater storage system. In addition, they have found that the fusing of a plurality of waterproof sheets can be facilitated and the process can be shortened, leading to the present invention. Of course, by using the impermeable sheet and the protective sheet in an integrated manner, the number of times the impermeable sheet and the protective sheet are laid can be reduced, but since the construction site of the rainwater storage system is outdoors, there are strong winds inside. Construction underneath is also possible. In that case, as a matter of course, it was necessary to place weights such as sandbags on the protective sheet and the impermeable sheet so that they would not be turned up. When the waterproof sheet for the rainwater storage system of the present invention is used, for example, in a factory or the like, since the protective sheet and the water-impervious sheet are adhered to each other, the sandbags and the like that have been carried to the construction site until now are eliminated. The preparation of the weight can be eliminated.

The tarpaulin for a rainwater storage system of the present invention is composed of a water-impervious sheet and a protective sheet arranged on one or both surfaces of the water-impervious sheet. At the peripheral edge of the waterproof sheet for the rainwater storage system, the impermeable sheet and the protective sheet are separated from each other (that is, not joined) to form a free end, and the free end provides another waterproof. It can be joined to the free end of the sheet at the required location by heat fusion or the like.

In the peripheral portion of the waterproof sheet for the rainwater storage system, the width of the portion of the water-impervious sheet and the protective sheet separated from each other is preferably 3 cm or more, and more preferably 5 cm or more. When the width of the portion of the water-impervious sheet and the protective sheet separated from each other is 5 cm or more, fusion with another waterproof sheet for a rainwater storage system becomes easy. Further, in the peripheral portion of the waterproof sheet for the rainwater storage system, the width of the portion of the waterproof sheet and the protective sheet separated from each other is preferably 10 cm or less, more preferably 7 cm or less. When the width of the portion of the water-impervious sheet and the protective sheet separated from each other is 10 cm or less, the integrity of the water-impervious sheet and the protective sheet is good, and the waterproof sheet for the rainwater storage system becomes flexible. It is easy to lay because it is excellent. In the present invention, in the peripheral edge of the waterproof sheet for a rainwater storage system, the widths of the portions of the impermeable sheet and the protective sheet that are separated from each other are the edges of the peripheral edge (4 places) and the edges of the peripheral edge. The distance from to the nearest adhesive part.

(Water shield sheet)
The impermeable sheet may be any sheet that does not allow water to permeate, and is not particularly limited. For example, the impermeable sheet preferably contains 20% by mass to 80% by mass of an ethylene-vinyl acetate copolymer and 20% by mass to 80% by mass of polyethylene with respect to the total mass of the impermeable sheet. When the content of the ethylene-vinyl acetate copolymer in the water-impervious sheet is 20% by mass or more, it has good water-impervious property due to the resin properties of the ethylene-vinyl acetate copolymer. From the viewpoint of obtaining such an effect more remarkably, the impermeable sheet more preferably contains 30% by mass or more of the ethylene-vinyl acetate copolymer, and further preferably 40% by mass or more. Furthermore, due to the resin properties of the ethylene-vinyl acetate copolymer, the impermeable sheet does not become hard even in a low temperature environment of, for example, 10 ° C. or lower, and it is easy to lay it. When the content of polyethylene in the water-impervious sheet is 20% by mass or more, a water-impervious sheet having excellent adhesive strength to the protective sheet can be obtained. Further, from the viewpoint of not lowering the suppleness and tensile strength of the impermeable sheet, the impermeable sheet preferably contains 60% by mass or less of polyethylene.

The ethylene-vinyl acetate copolymer preferably has a vinyl acetate content of 3 mol% to 50 mol%. When the vinyl acetate content in the ethylene-vinyl acetate copolymer is 3 mol% or more, a sheet having excellent flexibility can be obtained. Further, when the vinyl acetate content is 50 mol% or less, even when the waterproof sheet is stored in an environment of 30 ° C. or higher, the water-impervious sheets are less likely to stick to each other and become integrated (blocking). .. From the viewpoint of obtaining such an effect more remarkably, the vinyl acetate content is more preferably 5 mol% to 40 mol%, further preferably 10 mol% to 30 mol%.

The polyethylene may be high-density polyethylene or low-density polyethylene. When high-density polyethylene is used, a water-impervious sheet having excellent impact resistance can be obtained due to its resin properties. Further, when low-density polyethylene is used, a water-impervious sheet having excellent heat-weldability can be obtained due to its resin properties. Among them, polyethylene is preferably linear low-density polyethylene. Impermeable sheets containing linear low density polyethylene have particularly good tensile strength. If the impermeable sheet has excellent tensile strength, the impermeable sheet is less likely to break.

The linear low density polyethylene is preferably a density of ^{0.86g / cm 3 ~0.93g / cm 3} . The linear low-density polyethylene having such a density is inexpensive and has excellent workability.

The polyethylene preferably has a melt flow rate (also referred to as "MFR") at 230 ° C. of 1 g / 10 min to 10 g / 10 min. When the MFR of polyethylene is 1 g / 10 minutes or more, it is easy to produce an impermeable sheet. When the MFR of polyethylene is 10 g / 10 minutes or less, there is little possibility that the strength of the impermeable sheet is reduced. From the viewpoint of obtaining such an effect more remarkably, the MFR of polyethylene is more preferably 1.5 g / 10 minutes to 7 g / 10 minutes.

The impermeable sheet may contain other resin components in addition to the ethylene-vinyl acetate copolymer and polyethylene. The content of the other resin component is preferably in the range of 30% by mass or less, and more preferably in the range of 10% by mass or less, based on the total mass of the impermeable sheet. Other resins are not particularly limited, and for example, polyolefin resins such as polypropylene, polybutene, ethylene-propylene copolymer, and ethylene-vinyl alcohol copolymer can be used. Further, the impermeable sheet may contain an antioxidant, a heat stabilizer, or the like in an amount of 10% by mass or less with respect to the total mass of the impermeable sheet, if necessary.

The water-impervious sheet preferably has a thickness of 0.1 mm to 3 mm, more preferably 0.3 mm to 2 mm. When the thickness of the impermeable sheet is 0.1 mm to 3 mm, the handleability of the waterproof sheet for the rainwater storage system at the time of construction is improved. The thickness of the impermeable sheet is measured according to JIS K 6250 8.1 (method A).

It said water barrier sheet tensile strength at 20 ° C. as measured in accordance with JIS K 6773, is preferably 10 N / mm ² or more, more preferably 16N / mm ² or more. When the tensile strength is 10 N / mm ² or more, the impermeable sheet is unlikely to break. The preferable upper limit of the tensile strength is 100 N / mm ² or less.

The water-impervious sheet preferably has an elongation at 20 ° C. measured according to JIS K 6773 of 500% or more, and more preferably 600% or more. When the elongation is 500% or more, laying becomes easy. The preferred upper limit of elongation is 1000% or less.

The water-impervious sheet preferably has a tear strength measured according to JIS K 6301 of 400 N / cm or more, and more preferably 500 N / cm or more. When the tear strength is 400 N / cm or more, the impermeable sheet is hard to tear. The preferable upper limit of the tear strength is 2000 N / cm or less.

(Protective sheet)
As the protective sheet, a non-woven fabric can be used. The non-woven fabric may be a long-fiber non-woven fabric such as a spunbond non-woven fabric or a melt blown non-woven fabric, or a short-fiber non-woven fabric such as a needle punch non-woven fabric, a spunlace non-woven fabric or a thermal bond non-woven fabric. Among them, from the viewpoint of low cost, the non-woven fabric is preferably a non-woven fabric in which spunbonded non-woven fabric is entangled by needle punching.

The non-woven fabric may be composed of one kind of fiber, or may be a non-woven fabric in which two or more fibers are mixed. Further, the non-woven fabric may be a single-layer non-woven fabric composed of one layer of webs, or may be a laminated non-woven fabric in which two or more layers of webs are laminated. Further, the nonwoven fabric may be composed of fibers made of a single component resin, or may be made of composite fibers using two or more resins. The cross-sectional shape of the fiber is not particularly limited, and may be a round cross section, and is a modified cross section such as a concentric circle type, a wedge-shaped divided type, a slit-shaped divided type, a hollow type, a triangular type, a Y type, or a square type. You may.

The fibers constituting the non-woven fabric are not particularly limited, and may be, for example, a polyolefin resin such as polyethylene, polypropylene or polybutene, a polyester resin such as polyethylene terephthalate or polybutylene terephthalate, or a synthetic resin such as a polyamide resin such as nylon 6 or nylon 66. Examples include the constituent fibers. Above all, the fibers constituting the above-mentioned non-woven fabric preferably contain a polyolefin resin from the viewpoint of excellent alkali resistance and weather resistance. Further, by using a non-woven fabric made of aramid fiber or carbon fiber, it is possible to impart tear strength to the tarpaulin for the rainwater storage system.

Non-woven fabric is preferably the basis weight is ^{80g / m 2 ~500g / m 2} . When the basis weight of the non-woven fabric is 80 g / m ² or more, the tensile strength is high and it is difficult to break. Further, when the basis weight of the non-woven fabric is 500 g / m ² or less, it does not become too heavy and the construction is easy. More preferably the basis weight of the nonwoven fabric is ^{200g / m 2 ~400g / m 2} .

The non-woven fabric preferably has a thickness of 0.5 mm to 20 mm. When the thickness of the non-woven fabric is 0.5 mm or more, the effect of preventing the impermeable sheet from being damaged is high. When the thickness of the non-woven fabric is 20 mm or less, the non-woven fabric is unlikely to break or peel off in the thickness direction. The thickness of the non-woven fabric is more preferably 1 mm to 10 mm, still more preferably 2 mm to 8 mm. The thickness of the non-woven fabric is measured in a state where a load of 2.94 cN per 1 cm ² is applied according to JIS L 1096 8.5.

The fibers constituting the non-woven fabric are not particularly limited, but the single fiber fineness may be 1 dtex to 100 dtex. When fibers having a fineness of 1 dtex to 100 dtex are used, the tensile strength and tear strength of the non-woven fabric can be increased.

When the non-woven fabric is a short-fiber non-woven fabric, the fibers constituting the non-woven fabric are not particularly limited, but the fiber length is preferably 10 mm to 200 mm. When the fiber length is 10 mm to 200 mm, the tensile strength and tear strength of the non-woven fabric can be increased.

The non-woven fabric has a tensile strength of 500 N / 5 cm or more, more preferably 700 N / 5 cm or more, as measured according to JIS L 1096. When the tensile strength is 500 N / 5 cm or more, the non-woven fabric is unlikely to break. The preferable upper limit of the tensile strength is 3000 N / 5 cm or less.

The non-woven fabric has an elongation of 20% or more, more preferably 50% or more, as measured according to JIS L 1096. When the elongation is 20% or more, it becomes easy to follow the elongation of the impermeable sheet.

The non-woven fabric has a tear strength of 80 N or more, more preferably 140 N or more, as measured according to JIS L 1096 (single tank method). When the tear strength is 80 N or more, the non-woven fabric is hard to tear. The preferable upper limit of the tear strength is 500 N or less.

(Waterproof sheet)
The water-impervious sheet and the protective sheet (for example, non-woven fabric) are adhered in dots and / or lines in other parts above the peripheral edge from the viewpoint of achieving both the integrity and flexibility of the waterproof sheet for the rainwater storage system. It is preferably state-bonded. The bonding interval between the point bonding or the linear bonding is preferably 2 to 70 cm. Here, the bonding interval means the distance between an arbitrary bonding point and the closest bonding point in the case of point bonding, and in the case of linear bonding, an arbitrary linear bonding portion and the linear bonding portion. The distance between the other linear adhesives closest to the vertical direction. When the bonding interval is 2 cm or more, the flexibility becomes good. When the bonding interval is 70 cm or less, the integrity is good. More preferably, the water-impervious sheet and the protective sheet (for example, non-woven fabric) are point-bonded at other portions above the peripheral edge, and the bonding interval is 10 to 50 cm.

The water-impervious sheet, the protective sheet (for example, non-woven fabric), and other parts other than the peripheral portion may be adhered via an adhesive, or the water-impervious sheet or the protective sheet (for example, non-woven fabric). It may be adhered by heat welding of the constituent components. It is preferable that the water-impervious sheet and the protective sheet (for example, non-woven fabric) are adhered to each other via a hot-melt adhesive. Alternatively, it is preferable that the water-impervious sheet or the protective sheet (for example, a non-woven fabric) is bonded by heat welding of the constituents. Alternatively, the water-impervious sheet and the protective sheet, for example, a non-woven fabric, are bonded to each other at the linear adhesive portion by hot-sealing the components constituting the water-impervious sheet or the protective sheet (for example, non-woven fabric), and are point-bonded. In the portion, it is preferable that the portion is adhered via a hot melt adhesive. With these configurations, no organic solvent is contained, and substances caused by the organic solvent do not volatilize from the waterproof sheet for the rainwater storage system.

At the place where the water-impervious sheet and the protective sheet are adhered, it is preferable that the water-impervious sheet and the protective sheet are punctately bonded via a hot melt adhesive. The size of the bonding point is preferably 1 cm ² or more. When the size of the adhesive point is 1 cm ² or more, the protective sheet and the impermeable sheet can be firmly adhered to each other. More preferably the size of the point of attachment is 5 cm ² to 50 cm ^2.

The waterproof sheet preferably has a weight per unit area is 2 kg / m ² or less, more preferably 1.5 kg / m ² or less. When the mass of the waterproof sheet per unit area is 2 kg / m ² or less, the waterproof sheet is light and easy to install. Although not particularly limited, the preferable lower limit is 0.5 kg / m ² .

Next, it will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a waterproof sheet for a rainwater storage system according to an embodiment of the present invention. The waterproof sheet 10 for a rainwater storage system of the embodiment is composed of a water-impervious sheet 1 and a protective sheet 2 arranged on one surface of the water-impervious sheet 1, and is formed at a peripheral edge of the waterproof sheet 10 for a rainwater storage system. , The water-impervious sheet 1 and the protective sheet 2 are separated from each other (that is, they are not adhered to each other), and in other parts, the impermeable sheet 1 and the protective sheet 2 are point-bonded by the adhesive point 3. That is, the waterproof sheet 10 for the rainwater storage system is composed of the water-impervious sheet 1 and the protective sheet 2 arranged on one surface of the water-impervious sheet 1, and the non-adhesive portion 21a of the water-impervious sheet 1 and the protective sheet 2 And 21b, and a point-like adhesive portion 22. In the rainwater storage system waterproof sheet 10, the portions of the impermeable sheet 1 and the protective sheet 2 that are separated from each other, that is, the non-adhesive portions 21a and 21b of the impermeable sheet 1 and the protective sheet 2 are free ends.

FIG. 2 is a schematic explanatory view illustrating the arrangement of the adhesion points between the impermeable sheet and the protective sheet in the waterproof sheet for the rainwater storage system according to the embodiment of the present invention. The width of the impermeable sheet and the protective sheet separated from each other, that is, the distance La from the adhesive point 13 adhering the impermeable sheet 11 and the protective sheet (not shown) to the end of the peripheral edge is 3 to 10 cm. It is preferably, more preferably 3 to 7 cm. The bonding interval of the point-like bonding, that is, the distance Lb between the two closest bonding points 3 (center points) is preferably 10 to 50 cm, more preferably 10 to 40 cm.

FIG. 3 is a schematic cross-sectional view of a waterproof sheet for a rainwater storage system according to another embodiment of the present invention. The waterproof sheet 100 for a rainwater storage system of the embodiment is composed of a water-impervious sheet 101 and a protective sheet 102 arranged on both surfaces of the water-impervious sheet 101, and is formed at a peripheral edge of the waterproof sheet 100 for a rainwater storage system. , The impermeable sheet 101 and the protective sheet 102 are separated from each other (that is, they are not adhered to each other), and in other parts, the impermeable sheet 101 and the protective sheet 102 are adhered by the adhesive point 103. That is, the waterproof sheet 100 for the rainwater storage system is composed of the water-impervious sheet 101 and the protective sheet 102 arranged on the surfaces of both the water-impervious sheet 1 and the non-adhesive portion 121a of the water-impervious sheet 101 and the protective sheet 102. And 121b, and a point-like adhesive portion 122. In the rainwater storage system waterproof sheet 100, the non-adhesive portions 121a and 121b of the impermeable sheet 101 and the protective sheet 102 are free ends.

In the construction of the rainwater storage system, the waterproof sheet for the rainwater storage system is laid so that the protective sheet side is in contact with the excavated surface of the excavated storage tank, and the peripheral edges of the plurality of waterproof sheets are heat-sealed and joined. Can be done. By using the waterproof sheet for the rainwater storage system of the present invention in which the peripheral portion is not joined and the other parts are bonded, preferably point-like adhesion and / or linear adhesion, the construction site of the rainwater storage system is used. In addition to reducing the number of times the water-impervious sheet and the protective sheet are laid, the bonding of a plurality of waterproof sheets can be facilitated, and the process can be shortened.

This will be described below with reference to Examples. The present invention is not limited to the following examples.

(Tensile strength, elongation and tear strength of impermeable sheet)
The tensile strength and elongation of the impermeable sheet were measured at a measurement temperature of 20 ° C. according to JIS K 6773. The tear strength of the impermeable sheet was measured at a measurement temperature of 20 ° C. according to JIS K 6301.

(EVA resin 1)
As an ethylene-vinyl acetate copolymer, trade name: Ultrasen 626, manufactured by Tosoh Corporation was prepared.

(EVA resin 2)
As an ethylene-vinyl acetate copolymer, trade name: Ultrasen 751, manufactured by Tosoh Corporation was prepared.

(LLDPE resin 1)
As a linear low-density polyethylene, trade name: SP2040, manufactured by Prime Polymer Co., Ltd. was prepared.

Table 1 shows the vinyl acetate content, density, and melt flow rate (MFR) at 230 ° C. of EVA resins 1 and 2 and LLDPE resin 1.

EVA resins 1 and 2 and LLDPE resin 1 were mixed and melted at the ratios shown in Table 2, extruded from a T die, and rolled to a predetermined thickness with a metal roll to obtain impermeable sheets 1 and 2. Table 2 shows the thickness, tensile strength, elongation, and tear strength of the impermeable sheets 1 and 2.

(Example 1)
On the surface of a spunbonded non-woven fabric made of polypropylene fiber and having a thickness of 3.0 mm, a hot melt adhesive made of an ethylene-vinyl acetate copolymer is applied in a dot shape with a bonding point size of 5 cm ² in the width direction of the waterproof sheet. Adhere at intervals of 40 cm in the (CD direction) and at intervals of 30 cm in the length direction (MD direction) of the non-woven fabric, and bond the non-woven fabric and the impermeable sheet 1 except for all peripheral parts (peripheral parts) of the non-woven fabric (5 cm). The waterproof sheet of Example 1 was obtained. The peeling strength of the waterproof sheet of Example 1 was 230 N between the non-woven fabric and the impermeable sheet in the T-shaped peeling test measured according to JIS K 6854-3.

(Example 2)
On the surface of a spunbonded non-woven fabric made of polypropylene fiber and having a thickness of 3.0 mm, a hot melt adhesive made of an ethylene-vinyl acetate copolymer is applied in a dot shape with a bonding point size of 5 cm ² in the width direction of the waterproof sheet. Adhesion is performed at intervals of 40 cm in the (CD direction) and at intervals of 30 cm in the length direction (MD direction) of the non-woven fabric, and the non-woven fabric is adhered to both sides of the water-impervious sheet 1 except for all peripheral parts of the non-woven fabric of 5 cm. The waterproof sheet of Example 2 was obtained. The peeling strength of the waterproof sheet of Example 2 was the same as that of the waterproof sheet of Example 1.

(Example 3)
A hot melt adhesive made of an ethylene-vinyl acetate copolymer is applied to the surface of a spunbonded non-woven fabric made of polypropylene fiber and having a thickness of 3.0 mm at intervals of 50 cm in the width direction (CD direction) of the tarpaulin. The waterproof sheet of Example 3 was obtained by adhering the non-woven fabric linearly in the longitudinal direction (MD direction) and adhering the non-woven fabric and the impermeable sheet 2 except for all peripheral portions of the non-woven fabric of 10 cm. The peeling strength of the waterproof sheet of Example 3 was 250 N between the non-woven fabric and the impermeable sheet in the T-shaped peeling test measured according to JIS K 6854-3.

(Example 4)
Using the waterproof sheet of Example 2, at the construction site of the rainwater storage system, the non-woven fabric was laid so as to come into contact with the excavated surface of the excavated storage tank, and the peripheral edge of the waterproof sheet was laid using a hot air heater. The heat was fused and joined together.

1,101 Water-impervious sheet 2,102 Protective sheet 3,103 Adhesive point 10,100 Waterproof sheet 21a, 21b, 121a, 121b Non-adhesive part

Claims (3)

A tarpaulin for a rainwater storage system that prevents the outflow of rainwater from a rainwater storage system, wherein the tarpaulin for the rainwater storage system is provided on one or both surfaces of the water-impervious sheet and the water-impervious sheet. The water-impervious sheet and the protective sheet are separated from each other at the peripheral portion of the waterproof sheet for the rainwater storage system, and the water-impervious sheet and the protective sheet are point-bonded and / or at other parts. Alternatively , a tarpaulin for a rainwater storage system , which is linearly bonded and has a bonding interval of 2 to 70 cm . The waterproof sheet for a rainwater storage system according to claim 1, wherein the width of the portion of the waterproof sheet for the rainwater storage system that is separated from each other by the water-impervious sheet and the protective sheet is 5 cm or more. A step of laying the waterproof sheet for a rainwater storage system according to claim 1 or 2 so that the protective sheet side is in contact with the excavated surface of the excavated storage tank, and heat-sealing and joining the peripheral portions of the plurality of waterproof sheets. Construction method of rainwater storage system including.

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