JPH07216909A - Underground vertical type water tank and construction method - Google Patents

Abstract

PURPOSE:To make it possible to construct an underground vertical type water tank at a low cost and facilitate the maintenance of the underground vertical type water tank. CONSTITUTION:A pilot hole excavated on a ground G is expanded with a strong back, thereby forming a hole H. A flexible water storage bas 4 is removably installed inside a tank wall 2. This water storage bag 4 is filled-up with water 5, thereby constructing an underground vertical type water tank 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underground water tank suitable for storing cold water, hot water, etc. for use in cooling and heating of a building, and a construction method thereof.

[0002]

2. Description of the Related Art In recent years, the efficiency and energy saving of building equipment have been remarkably progressing. In particular, as one example thereof, there is a marked increase in the spread of underground heat storage water tanks (hereinafter abbreviated as "heat storage water tanks"). Can be mentioned. Generally, a heat storage water tank stores water in a tank installed in an underground pit of a building, and cools or heats the inside of the building by the heat accumulated by the water. However, if the heat storage water tank is installed in the underground pit of the building, it is necessary to deepen the root cutting depth of the foundation of the building, and the construction of the building itself becomes a large-scale construction, resulting in an increase in construction cost. There is a problem that it causes rise and prolongs the construction period. Naturally, since the heat storage water tank with such a structure must be constructed at the time of new construction of a building, it is very difficult to realize it even if an attempt is made to add a heat storage water tank to increase the heat source capacity after the construction. Has become.

As an effective means for solving such a problem, there is a distributed heat storage water tank. This distributed heat storage water tank is a ground water tank that is formed by drilling a vertically extending hole in the ground at a location other than the underground bit of a building and forming a ground water tank inside this hole. It is used as an aquarium.

[0004]

However, even in the conventional ground neutral heat storage water tank as described above, there are the following problems. First, in order to excavate a hole in the ground, a device for excavating the hole becomes large-scaled, resulting in high construction cost. In addition, there is a problem that disposal of excavated earth and sand is troublesome and costly. Furthermore, noise and vibration are generated during excavation work, especially if there is an existing building in the vicinity, it may interfere with the work there, resulting in a prolonged construction. Become. Further, in order to secure the heat source capacity, the holes to be excavated in the ground may be deep. Then, since the lateral pressure applied from the surrounding ground to the wall surface of the hole becomes large, it is necessary to increase the strength of the tank wall of the heat storage water tank to cope with this, which also causes a problem that the cost is significantly increased. . Furthermore, if the inside of the heat storage water tank is to be cleaned during maintenance, it requires underground work, which requires a large amount of cost and time. The present invention has been made in consideration of the above points, and it is possible to construct a ground-neutral water tank at a low cost, and to easily perform maintenance of the ground-neutral water tank. It is intended to provide a water tank and a construction method thereof.

[0005]

The invention according to claim 1 is
A tank wall made of one or more tubular tank wall members is formed in a hole formed by excavation to a certain depth in the ground, and the inside of the tank wall has flexibility and A removable water storage bag is provided, and the bag is filled with fluid. The bag is provided with an inlet / outlet port communicating with the inside and outside of the bag. Is configured so that it can be injected into and discharged from the inside and outside of the bag.

According to a second aspect of the present invention, in the ground neutral water tank according to the first aspect, a plurality of the ground neutral water tanks are installed at positions separated from each other, and the plurality of ground neutral water tanks are connected to each other. It is characterized by being.

The invention according to claim 3 is a construction method for constructing a ground-neutral water tank in the ground, wherein a communication hole communicating with the inside and outside is formed in the peripheral wall and the outer periphery of the peripheral wall is flexible. A press-fitting tube having a fixed bag body is inserted into the ground, and a step of inserting a fluid into the press-fitting tube to press the fluid into the bag body through the communication hole, A second step of expanding the body in a direction orthogonal to the axial direction of the bag to expand the surrounding ground of the bag to form a hole for constructing the ground-neutral water tank, and a fluid in the bag. A third step of causing the discharged fluid to flow between the bag body and the hole while contracting the bag body by discharging from the press-fitting tube, and then drawing out the press-fitting tube from the hole. , A tubular tank wall material that forms the tank wall of the ground neutral type water tank to be constructed, A fourth step of inserting and installing / fixing in the hole, and inserting a water storage bag having flexibility and detachable inside the tank wall into the tank wall, And a fifth step of filling the water storage bag with the fluid while discharging the fluid.

[0008]

According to the first aspect of the invention, since the water storage bag is arranged inside the tank wall and the bag is filled with the fluid, the ground neutral water tank is formed. It In addition, the water storage bag has flexibility, is detachable from the tank wall, and has an inlet / outlet port. Accordingly, when the fluid in the bag body is discharged, the bag body is narrowed, and by removing this from the tank wall, the bag body can be pulled out from the inside of the tank wall to the outside.

According to the second aspect of the present invention, a plurality of such ground neutral water tanks are installed at positions separated from each other, and the plurality of ground neutral water tanks are connected to each other according to the purpose. As a result, the degree of freedom in arranging the ground-neutral water tank is increased, and it becomes possible to disperse and arrange multiple ground-neutral water tanks on different premises, for example. It becomes possible.

According to the third aspect of the present invention, the press-fitting pipe is inserted into the ground, and the bag body fixed to the outer periphery of the bag is expanded in the radial direction, whereby the surrounding ground is pressed and the ground neutral water tank is constructed. The hole to be formed is formed. Then, the fluid in the bag body is discharged from the press-fitting pipe to reduce the diameter of the bag body, and the discharged fluid is caused to flow between the bag body and the hole, so that the lateral pressure from the surrounding ground is supported by this fluid. be able to.
After that, by installing and fixing the tank wall material in the hole, inserting the water storage bag inside it and filling it with fluid,
An underground water tank has been constructed.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to an embodiment shown in the drawings. FIG. 1 shows an example in which the ground neutral water tank according to the present invention is used as a heat storage water tank for cooling and heating.
Here, for example, an example of constructing a heat storage water tank having a diameter of about 3 m and a depth of about 30 m will be described. Figure 1
As shown in, the heat storage water tank (ground neutral water tank) 1 is the ground G
A tank wall 2 formed in a hole H having a circular cross-section when excavated therein
The grout material 3 filled in the gap between the tank wall 2 and the hole H, the water storage bag 4 arranged inside the tank wall 2, and the water filled in the water storage bag 4. (Fluid) 5 and the general structure.

The tank wall 2 has a structure in which a plurality of cylindrical tank wall members 6 having a length of, for example, 5 to 10 m are vertically connected. In addition, among these, the tank wall member 6a located at the lowermost portion has a bottomed shape. Each tank wall member 6 has a laminated structure in which a heat insulating material is sandwiched and sealed between a plurality of main materials made of, for example, resin, precast concrete, or metal, and has water impermeability and heat insulating properties. ing. The water storage bag body 4 is made of vinyl, rubber or the like as a main material, and is combined with a reinforcing cloth or the like for reinforcement if necessary, and is flexible and watertight and lightweight. ing. An injection / exhaust port 4a communicating with the inside and outside is formed in the upper part of the water storage bag 4, and water 5 is injected into the water storage bag 4 by a pump or the like not shown, or vice versa. The fluid can be discharged.

The heat storage water tank 1 having such a structure is provided in a predetermined number in order to supply a required amount of heat to a building (not shown) including the heat storage water tank 1. The plurality of heat storage water tanks 1 are connected to each other by a communication pipe (not shown). In this case, it is not necessary to install all the heat storage water tanks 1 in the same site, and they may be installed in dispersed sites. In such a heat storage water tank 1, the water 5 filled in the water storage bag 4 stores heat, and the heat is used to cool or heat the building.

Next, prior to explaining a method of constructing such a heat storage water tank 1, a strong bag 10 used when constructing the heat storage water tank 1 will be described with reference to FIGS.
Will be described with reference to. As shown in FIGS. 2 and 3, the strong back 10 is a press-fitting pipe 1 made of resin or steel.
1 and a bag body 12 provided on the outer periphery thereof.

A plurality of communication holes (not shown) are formed on the outer peripheral surface of the press-fitting pipe 11 to communicate the inside and outside of the peripheral wall 11a.
As shown in FIG. 2, the bag body 12 has a tubular shape, and both ends (only one of which is shown) along the axial direction of the press-fitting tube 11 are fixed to the press-fitting tube 11 by metal bands 13. Thus, the bag body 12 has a bag shape between the metal bands 13 and 13 and is kept watertight.

As shown in FIGS. 2 and 3, the bag body 12 includes a plurality of rubber layers 14 arranged concentrically and a tape integrated in the rubber layers 14 in an embedded state. It is composed of 15 and a strip 16. The rubber layer 14 has, for example, (1) an elongation rate of 500 to 600%,
(2) It has properties such as resilience that hardly causes residual strain against repeated expansion and contraction, (3) watertightness or airtightness that does not leak high-pressure fluid, and (4) adhesiveness with reinforcing cloth, As a result, the bag body 12 has flexibility and stretchability. As shown in FIG. 3, the tape 15 is concentric with the rubber layer 14 so that the high-strength yarn 15a made of, for example, aramid fiber, carbon fiber, glass fiber, vinylon fiber, or the like forms a continuous waveform in the circumferential direction. It is configured to be woven on the outer peripheral side of the ground warp (not shown) formed on the. For this ground warp, for example, cotton, etc.
It is composed of fibers woven by yarns of lower strength. The tape 15 is designed to withstand tensile stress in the circumferential direction of the bag body 12. When the bag body 12 expands, the ground warp (not shown) is broken, and the high-strength yarn 15a which is the main material. Is stretched integrally with the rubber layer 14, and when the bag body 12 reaches the limit of expansion, it becomes a tensioned state to regulate the expansion thereof. The band cloth 16 is made of a plurality of fibers arranged in the circumferential direction such that a main material having a high elongation rate such as nylon extends in the length direction of the press-fitting pipe 11, and is mainly a bag body. It is designed to support the stretching force in the longitudinal direction of the twelve.

In the strong bag 10 having such a structure, when a fluid such as water is injected into the press-fitting tube 11 at a high pressure, the fluid enters the bag 12 from the communication hole (not shown) of the peripheral wall 11a of the press-fitting tube 11. And the bag body 12 is inflated by this pressure. At this time, the bag 12
Since both ends of the are fixed by the metal band 13, the expansion direction thereof is the direction orthogonal to the axial direction of the strong back 10, that is, the diameter expanding direction. Also, the press-fitting pipe 11
When the fluid that has been press-fitted is discharged from, the bag body 12 is reduced in diameter due to the elasticity of the rubber layer 14. As shown in FIG. 4, generally, when a pressure P in the direction of expanding the diameter is applied to a hole formed in the ground and the pressure P becomes larger than a certain pressure Py, the hole diameter D rapidly increases. There is a property to do. The strong bag 10 shown in FIG. 2 and FIG. 3 utilizes the above-mentioned properties and expands the bag body 12 in the radial direction as described above, thereby applying pressure from the bag body 12 to the surrounding ground, This pressure effectively expands the diameter of the hole formed in the ground.

Next, a method for constructing the heat storage water tank 1 using the strong bag 10 will be described with reference to FIGS. 1 to 13.

(First Step) First, as shown in FIG.
For example, a pilot hole (hole) 20 with a diameter of about 0.2 m
Drilling is performed at a predetermined position of the ground G to a predetermined depth (for example, 30 m) using a boring machine (not shown).

(Second Step) Next, the pilot hole 20
Expand the diameter. At this time, the pilot hole 2 with a diameter of 0.2 m
0 to a diameter of 3 m of the hole H shown in FIG.
The diameter expansion step is divided into a plurality of times as follows. First,
As shown in FIG. 6, for example, a plurality of strong bags 10 having a diameter expanding ability up to a diameter of 0.6 m are connected and inserted into the pilot hole 20. At this time, the strong backs 10, 10, ... Connected in the vertical direction are configured to be attached to one press-fitting pipe 11 extending in the vertical direction,
When water is pressed into the press-fitting pipe 11, all strong backs 1
0 is expanding. Then, as shown in FIG. 7, the water 5 is press-fitted into the press-fitting pipe 11 of the strong back 10 to expand the bag body 12 in the diameter-expanding direction to expand the pilot hole 20. At this time, if the N value of the surrounding ground G is 30 to 40, the water 5 to be press-fitted is 20 kg /
It is desirable to apply a pressure of about cm ² . in this way,
When the pilot hole 20 is expanded to a hole H having a diameter of, for example, 0.6 m by the strongback 10, the state is maintained for, for example, one day and night to stabilize the ground G around the hole H,
Prevents return deformation due to diameter expansion, hole diameter contraction due to water pressure fluctuation, and hole wall collapse. After this, the hole H
Since the hole wall of is compressed by the diameter expansion, it is in a stable state.

(Third Step) Next, as shown in FIG. 8, the water 5 in the bag body 12 is discharged from the press-fitting pipe 11 and the bag body 1 is discharged.
Shrink 2 In parallel with this, the water 5 discharged from the press-fitting pipe 11 is poured into the gap formed between the bag body 12 and the outside and the hole H. In this way, by constantly filling the hole H with the water 5, the pressure applied to the hole wall of the hole H is resisted. Then, at the time when the water 5 in the bag 12 is completely discharged, the strong bags 10 are made into the holes H.
Pull out from within.

In the second step and the third step, as shown in FIG.
Since there is a recess 10a at the connecting portion of 0, 10, ...
In order to make the hole wall of No. 2 smooth, it is necessary to shift the strong backs 10, 10, ... Up as shown in FIG. Also,
The length of the strong back 10, 10, ... Does not always match the depth of the hole H to be formed, and the diameter is similarly expanded in such a case.

Next, for example, strong bags 10, 10, ... Having a diameter expanding ability of up to 1.5 m are connected and inserted into the hole H, and the second step and the third step are performed in the same manner as above. The above process is repeated to expand the hole H to a diameter of 1.5 m. In the same manner as above, strong backs 10, 10, ...
Finally, the hole H is expanded to a diameter of 3 m.

(Fourth Step) Next, as shown in FIG. 9, the tank wall members 6, 6, ... Are inserted into the expanded hole H while being sequentially connected. At this time, since the bottom wall 6a of the tank has a bottomed shape, when it is inserted, water 5 is poured into it to reduce the buoyancy acting on the wall 6a of the tank. Then, as shown in FIG. 10, the strong bag 10, 10,
... is inserted, and water 5 in the tank wall members 6, 6, ... is injected into the strong bags 10, 10, ... to inflate each bag body 12, and thereby the outer wall surface of each tank wall member 6 is formed. Support work to resist the pressure applied to the ground. Next, as shown in FIG. 11, a grout material 3 such as mortar or cement paste is filled in the gap between the inserted tank wall materials 6, 6, ... And the hole H. At this time, the strong bags 10 are placed in the wall materials 6 of each tank.
Is installed, damage to the tank wall material 6 due to the pressure of the grout material 3 is prevented. , Are fixed to the ground G by the filled grout material 3, and a force is applied between the tank wall 2 and the ground G formed by the tank wall materials 6, 6 ,. Transmission will be ensured. Further, concrete 22 is also placed on the ground surface around the hole H to pave. Then, as shown in FIG. 12, after the grout material 3 hardens, water 5 in the strong bag 10
Is poured into the tank wall 2, the strong back 10 is contracted, and the strong back 10 is pulled up.

(Fifth Step) Next, as shown in FIG. 13, the water storage bag 4 is inserted and installed inside the tank wall 2 in a contracted state. At this time, the water 5 may be injected at the same time when the water storage bag 4 is inserted. By doing so, the insertion work can be easily performed without being hindered by buoyancy. Then, as shown in FIG. 1, while discharging the water 5 in the tank wall 2, the water 5 is filled into the water storage bag 4 through the inlet / outlet port 4a, whereby the heat storage water tank 1 is constructed. It

Thereafter, a pipe (not shown) is connected to the water storage bag 4 and is connected to another heat storage water tank (not shown) or a heat exchanger (not shown).

After that, when the heat storage water tank 1 is maintained, the water 5 in the water storage bag 4 is injected / discharged 4a.
Discharge from. Then, since the water storage bag 4 has flexibility, it gradually narrows. At this time, the injection / discharge port 4
If the water 5 discharged from a is made to flow between the tank wall 2 and the water storage bag 4, it is not necessary to discharge the water 5 in the water storage bag 4 to another and it is reused. be able to.
Of course, the water 5 in the water storage bag 4 is discharged to the other side, and the water 5
Needless to say, it is possible to replace the above. After discharging the water 5 in the water storage bag 4 in this way, the water storage bag 4 is pulled up from the inside of the tank wall 2 to the ground, and maintenance such as cleaning and repair is performed on the ground.
Then, after the maintenance is completed, the water storage bag 4 is again inserted into the tank wall 2. Then, the water 5 in the tank wall 2 is injected into the water storage bag body 4 from the injection / discharge port 4a by a pump (not shown), thereby returning to the original state shown in FIG.

In the heat storage water tank 1 described above, a flexible water storage bag 4 is detachably disposed inside the tank wall 2, and water 5 is filled in the water storage bag 4. , And this water 5
Is configured to be discharged from the filling / discharging port 4a of the water storage bag 4. Accordingly, by discharging the water 5 from the water storage bag 4 and constricting the water 5, the water storage bag 4 can be pulled out from the inside of the tank wall 2 to perform maintenance on the ground. Therefore, the water storage bag 4 can be easily maintained in a short period of time. In addition, the heat storage water tank 1 can be installed not only in the underground pit of the building structure but also in another site such as a surrounding vacant lot. As a result, the underground space of the building structure can be effectively used, and the root cutting depth can be made shallow. As a result, the construction period and construction cost can be significantly reduced. Besides, heat storage water tank 1
The construction can be performed separately from the construction work of the building structure body, which can also shorten the construction period and reduce the cost. Moreover, since the heat storage water tank 1 can be installed even after the construction of the building structure is completed, it is possible to easily cope with the increase in the heat source capacity. Also, by disposing a plurality of heat storage water tanks 1 at positions separated from each other and connecting them to each other, it is possible to effectively utilize the site and even if each site is narrow, it is sufficient. It is possible to configure heat storage equipment having heat storage capacity.

In the method of constructing the heat storage water tank 1 described above, the pilot holes 20 drilled in the ground G are set in the strong back 1
The diameter was increased to 0 to form the holes H. This allows
The remaining soil that is generated is only that generated when the pilot hole 20 is drilled, and the labor and cost required for its disposal can be saved. Further, since the diameter of the strong back 10 is expanded, noise and vibration can be significantly reduced as compared with the conventional case. As a result, even if there is an existing building or the like in the vicinity, it is possible to perform the construction without hindering the work there, and it is possible to prevent the construction period from being extended. Furthermore, when constructing the heat storage water tank 1, always
Since any one of the water 5, the strong bag 10 and the water storage bag 4 is arranged in the hole H or the tank wall 2,
The lateral pressure applied to the hole H or the tank wall 2 can be supported by the water 5. As a result, the tank wall 2 can be made lower in strength than before, and the cost for constructing the tank wall 2 can be significantly reduced. As described above, the construction cost of the heat storage water tank 1 can be significantly reduced as compared with the conventional case.

In the above embodiment, the pilot hole 20 is first drilled, and the diameter of the pilot hole 20 is expanded by the strong back 10. However, the invention is not limited to this. While drilling pilot hole 20 by attaching the device as one unit,
The strong back 10 may be inserted. Also, for example, when the ground is soft or there is an existing hole,
As long as the strong back 10 can be inserted, it is not necessary to drill the pilot hole 20, but the strong back 10 is inserted into the ground and the hole H is formed by expanding the diameter of the surrounding ground as it is. May be. Further, when the grout material 3 is filled between the tank wall material 6 and the hole H, the strong back 10 is installed in the tank wall material 6 to support it. , The structure for improving the strength of the tank wall material 6 itself, the tank wall material 6,
It is also possible to prevent the use of the supporting work by sealing the members 6 and ... And by applying pressure to the inside to thereby resist the external pressure. Further, in the above embodiment, when the pilot hole 20 is expanded in diameter to form the hole H, the diameter expansion process is divided into three stages. Of course, the diameter of the hole H to be formed and the diameter of the strong back 10 are expanded. Depending on ability
It may be divided into only one stage or a plurality of stages. Of course, even in this case, each of the above effects can be obtained. Furthermore, the numerical values used in the above examples do not limit the ground neutral water tank and the construction method thereof according to the present invention, and may be appropriately determined according to various conditions.

[0031]

As described above, according to the neutral type water tank of the first aspect, the flexible water storage bag is disposed inside the tank wall, and the bag body is provided in the bag body. Since the configuration is such that the fluid is filled, the ground neutral type water tank can be configured by this. Moreover, the bag for storing water is detachable from the tank wall, and is provided with an inlet / outlet port. This allows
By discharging the fluid from the water storage bag and constricting it, the water storage bag can be pulled out from the inside of the tank wall for maintenance on the ground. Therefore, it becomes possible to perform maintenance of the ground neutral type water tank easily and in a short period of time. In addition to the underground pit of the building structure, the ground-neutral water tank can be installed in another site such as a vacant land around the building. As a result, the underground space of the building structure can be effectively used, and the root cutting depth can be reduced to shorten the construction period and significantly reduce the construction cost. Moreover, it is possible to perform the construction work of the ground neutral type water tank separately from the construction work of the building structure main body, which can also shorten the construction period and reduce the cost. Moreover, since the ground water tank can be installed even after the construction of the building structure, it is possible to easily cope with the increase in the heat source capacity.

According to the ground neutral water tank of the second aspect, a plurality of ground neutral water tanks are installed at positions separated from each other, and the plurality of ground neutral water tanks are connected to each other. This increases the degree of freedom in arranging the ground-neutral aquarium, and it is possible to place multiple ground-neutral aquariums on different sites, for example. It becomes possible to provide a water tank.

According to the construction method of the ground neutral type water tank according to the third aspect, the hole for constructing the ground neutral type water tank is formed by expanding the ground. As a result, the amount of residual soil that is generated can be significantly reduced, and the labor and cost required for its disposal can be saved. In addition to this, it is possible to significantly reduce noise and vibration compared to the past, so even if there is an existing building in the neighborhood, it is possible to perform construction without hindering the work there. This makes it possible to prevent the construction period from being extended. Furthermore, at the time of construction, always
Since the fluid is arranged inside the hole or the tank wall,
The lateral pressure applied here can be supported by a fluid. As a result, the tank wall can be made lower in strength than before, and the cost for constructing the tank wall can be significantly reduced. As described above, it is possible to significantly reduce the construction cost of the ground neutral type water tank as compared with the conventional method.

[Brief description of drawings]

FIG. 1 is a front cross-sectional view showing an example of a ground neutral type water tank according to the present invention.

FIG. 2 is a front view showing a configuration of a press-fitting pipe having a bag body used when constructing the ground neutral water tank.

FIG. 3 is a plan sectional view showing a part of the press-fitting pipe.

FIG. 4 is a diagram showing the relationship between the pressure when expanding the ground and the amount of increase in the hole diameter.

FIG. 5 is a diagram showing a method of constructing the ground neutral type water tank, and is a front sectional view showing a state in which a hole is drilled in the ground.

FIG. 6 is a front sectional view showing a state in which a press-fitting tube is inserted in the hole.

FIG. 7 is a front sectional view showing a state in which the bag body is expanded in diameter.

FIG. 8 is a front sectional view showing a state where the press-fitting pipe is pulled out.

FIG. 9 is a front sectional view showing a state in which the tank wall material is inserted into the hole.

FIG. 10 is a front sectional view showing a state where the press-fitting pipe is inserted into the tank wall material.

FIG. 11 is a front sectional view showing a state in which the tank wall material is fixed to the ground in the same manner.

FIG. 12 is a front sectional view showing a state in which the press-fitting pipe is pulled out.

FIG. 13 is a front sectional view showing a state where the water storage bag is inserted into the tank wall.

[Explanation of symbols]

 1 Heat Storage Water Tank (Ground Neutral Water Tank) 2 Tank Wall 4 Water Storage Bag 4a Injecting / Discharging Port 5 Water (Fluid) 6 Tank Wall Material 11 Press-fitting Pipe 12 Bag 20 Pilot Hole G Hole H Hole

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Katsuyuki Tamaki 1-3-2 Shibaura, Minato-ku, Tokyo Shimizu Corporation

Claims (3)

[Claims] 1. A tank wall made of one or more tubular tank wall members is formed in a hole excavated to a certain depth in the ground, and the tank wall has flexibility inside. At the same time, a removable water storage bag is disposed on the tank wall so that the bag is filled with a fluid, and the bag has an inlet / outlet port communicating with the inside and outside thereof. The ground water tank is configured so that the fluid can be poured into and discharged from the inside and outside of the bag body. 2. The ground neutral water tank according to claim 1,
The ground neutral water tank, wherein a plurality of the ground neutral water tanks are installed at positions separated from each other, and the plurality of ground neutral water tanks are connected to each other. 3. A construction method for constructing a ground-neutral water tank in the ground, wherein a peripheral wall is formed with a communication hole communicating with the inside and outside thereof, and a flexible bag body is formed on the outer periphery of the peripheral wall. The first step of inserting the fixed press-fitting pipe into the ground, and the fluid is press-fitted into the press-fitting pipe to press-fit the fluid into the bag body through the communication hole so that the bag body moves in the axial direction thereof. A second step of expanding the surrounding ground of the bag body by expanding in a direction orthogonal to form a hole for constructing the ground-neutral water tank, and discharging the fluid in the bag body from the press-fitting pipe. A third step of pulling the press-fitting tube out of the hole after allowing the discharged fluid to flow between the bag body and the hole while contracting the bag body. The tubular tank wall material that forms the tank wall of the neutral water tank is installed by inserting it into the hole. -Fourth step of fixing, inserting a water storage bag having flexibility and detachable inside the tank wall inside the tank wall, while discharging the fluid in the tank wall, A method for constructing a ground-neutral water tank, comprising a fifth step of filling a fluid storage bag with a fluid.