Water supply unit and underground water pressure release structure

Abstract

To provide a water flow unit and an underground water pressure release structure capable of efficiently releasing underground water pressure by drainage without causing clogging due to floating soil particles.SOLUTION: A water flow unit 1 installed underground comprises: a hollow cylindrical joint pipe 3; a hollow cylindrical upper water flow pipe 4 inserted into one end of the joint pipe; and a hollow cylindrical lower water flow pipe 5 inserted into the other end of the joint pipe across a gap G from the upper water flow pipe. At the other end of the joint pipe, a plurality of grooves 6 are formed by recessing an inner circumferential surface of the joint pipe radially outward with respect to the joint pipe at intervals in a circumferential direction of the joint pipe so as to form a plurality of water flow passages 7 by partitioning with an outer circumferential surface 5b of the lower water flow pipe. The gap between the upper water flow pipe and the lower water flow pipe forms a communication space 8 making the plurality of water flow passages communicate with hollow inside of the upper and lower water flow pipes.SELECTED DRAWING: Figure 1

Description

Technical Field

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[0001] The present invention relates to a water-permeable unit and a structure for releasing in-ground water pressure that can efficiently release in-ground water pressure by drainage without clogging due to floating soil particles.

Background Art

[0002] Conventionally, for example, as a countermeasure against liquefaction of sandy soil ground, a sand drain method aimed at reducing pore water pressure is known.

[0003] This method forms drain columns in the ground using large heavy machinery, and by absorbing groundwater into these drain columns, it suppresses the increase in pore water pressure generated in the surrounding soil and prevents ground liquefaction.

[0004] However, there were problems in workability, such as the need to use a large number of large heavy machinery and the requirement of a large construction area.

[0005] As a technology considering workability, such as not requiring the use of large heavy machinery, Patent Document 1 is known.

[0006] The "drainage pipe for liquefaction countermeasure" of Patent Document 1 aims to provide a drainage pipe for liquefaction countermeasure that can ensure good workability without the need to use a large number of large heavy machinery, and moreover, the soil particles of the surrounding ground do not flow into the pipe interior and the change over time of the liquefaction prevention effect after construction is small. The linear slits penetrating the inner and outer walls of the pipe are provided in a predetermined pattern in a substantially axial direction or a substantially circumferential direction of the pipe on the pipe surface.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

[0008] Patent Document 1 describes a method of draining water from the ground through linear slits. However, when the groundwater level rises or the effects of an earthquake increase the pore water pressure and reach the critical hydraulic gradient, the effective stress in the soil decreases and soil particles become suspended. Therefore, it is difficult to prevent soil particles from flowing into the pipe at the same time as draining water through the slits, and it is difficult to ensure a sufficient liquefaction prevention effect.

[0009] The present invention was devised in view of the above-mentioned conventional problems, and aims to provide a water passage unit and an underground water pressure release structure that can efficiently release underground water pressure by drainage without causing clogging by suspended soil particles. [Means for solving the problem]

[0010] The water passage unit according to the present invention is a water passage unit installed underground, comprising a hollow cylindrical joint pipe, a hollow cylindrical upper water passage pipe inserted into one end of the joint pipe, and a hollow cylindrical lower water passage pipe inserted into the other end of the joint pipe, separated from the upper water passage pipe by a gap, wherein a plurality of grooves are formed on the other end of the joint pipe by recessing the inner surface of the joint pipe radially outward at intervals in the circumferential direction of the joint pipe, so as to form a plurality of water passages partitioned by the outer surface of the lower water passage pipe, and the gap between the upper water passage pipe and the lower water passage pipe forms a communication space that connects the plurality of water passages to the hollow interior of these upper and lower water passage pipes.

[0011] The aforementioned joint pipe is characterized by having an upper pipe portion that constitutes one end, a lower pipe portion that constitutes the other end, and a recess that constitutes the communication space, and is positioned between the upper pipe portion and the lower pipe portion, and is plate-shaped in that the lower end of the upper water pipe and the upper end of the lower water pipe abut against each other to form the gap between the upper water pipe and the lower water pipe, and is composed of an annular boundary portion that connects the hollow interiors of the upper water pipe and the lower water pipe.

[0012] The upper pipe section is formed with the same wall thickness as the lower pipe section at the groove formation position, and a hollow cylindrical coupler is provided inside the upper pipe section, formed with a wall thickness matching the radial dimension of the groove, and the upper water pipe is inserted by sliding against the inner circumferential surface of the coupler instead of sliding against the inner circumferential surface of the joint pipe.

[0013] The lower water pipe is characterized in that it is provided with water passages facing the groove, which are appropriately provided to connect the water passage to the hollow interior of the lower water pipe.

[0014] The underground water pressure release structure according to the present invention is characterized in that the water passage unit is installed underground.

[0015] Furthermore, the underground water pressure release structure according to the present invention is characterized in that two or more of the above-mentioned water passage units are installed underground, connected in series by using the above-mentioned water passage units, inserting the upper water passage pipe as a lower water passage pipe into the other end of another joint pipe equipped with an upper water passage pipe, and inserting the lower water passage pipe as an upper water passage pipe into one end of yet another joint pipe equipped with a lower water passage pipe. [Effects of the Invention]

[0016] In the water passage unit and underground water pressure release structure according to the present invention, the inflow of soil particles into the water passage unit can be suppressed, and underground water pressure can be efficiently released by drainage without causing clogging. [Brief explanation of the drawing]

[0017] [Figure 1] This is a cross-sectional view illustrating a first embodiment of the water supply unit according to the present invention. [Figure 2] Figure 1 shows a cross-sectional view taken along the line AA. [Figure 3] Figure 1 shows a cross-sectional view taken along the line BB. [Figure 4] Figure 1 is an explanatory diagram illustrating a preferred embodiment of the underground water pressure release structure according to the present invention, using the water passage unit shown in Figure 1. [Figure 5] It is a cross-sectional view for explaining a modified example of the water flow unit shown in FIG. 1. [Figure 6] It is a cross-sectional view for explaining a second embodiment of the water flow unit according to the present invention. [Figure 7] It is a view looking down from above on a boundary portion included in the water flow unit shown in FIG. 6. [Figure 8] It is a view looking up from below on a boundary portion included in the water flow unit shown in FIG. 6. [Figure 9] In FIG. 6, it is a cross-sectional view taken along the line D-D. [Figure 10] It is a cross-sectional view for explaining a third embodiment of the water flow unit according to the present invention. [Figure 11] It is a cross-sectional view for explaining a modified example of a joint pipe provided in the water flow unit according to the present invention. [Figure 12] It is an explanatory view for explaining a modified example of the underground internal water pressure release structure according to the present invention.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, preferred embodiments of the water flow unit and the underground internal water pressure release structure according to the present invention will be described in detail with reference to the accompanying drawings.

[0019] In FIGS. 1 to 3, a water flow unit 1 according to the first embodiment is shown. FIG. 1 is a cross-sectional view of the water flow unit 1 according to the first embodiment, FIG. 2 is a cross-sectional view taken along the line A-A in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line B-B in FIG. 1. Note that FIG. 1 is a cross-sectional view taken along the line C-C in FIG. 3.

[0020] In FIG. 4, an underground internal water pressure release structure 2 configured by disposing the water flow unit 1 is shown.

[0021] First, regarding the water flow unit 1, the water flow unit 1 is mainly composed of a joint pipe 3, an upper water pipe 4, and a lower water pipe 5.

[0022] The upper water pipe 4 and the lower water pipe 5 are made of a straight cylindrical metal pipe material having a predetermined length, identical inner and outer diameters, and with openings at both ends in the longitudinal direction and a hollow interior.

[0023] The joint pipe 3 is made of a straight cylindrical metal pipe material that has a predetermined length dimension and has openings 3a at both ends in the longitudinal direction, with a hollow interior.

[0024] The inner diameter dimension defining the inner circumferential surface 3b of the joint pipe 3 is set to match the outer diameter dimension of the upper water pipe 4 and the lower water pipe 5 so that the upper water pipe 4 and the lower water pipe 5 are inserted into the inner circumferential surface 3b of the joint pipe 3 with as little gap as possible.

[0025] An upper water pipe 4 is inserted into the joint pipe 3 from one end in the longitudinal direction, and the upper water pipe 4 is positioned on the one end side of the joint pipe 3.

[0026] A lower water pipe 5 is inserted into the joint pipe 3 from the other end in the longitudinal direction, and the lower water pipe 5 is positioned on the other end side of the joint pipe 3.

[0027] Inside the joint pipe 3, the upper end 5a of the lower water pipe 5 is positioned to leave a gap with respect to the lower end 4a of the upper water pipe 4, thereby positioning the lower water pipe 5 apart from the upper water pipe 4 by a gap G.

[0028] In other words, the hollow interior of the upper water pipe 4 and the hollow interior of the lower water pipe 5 are connected via a gap G.

[0029] The upper water pipe 4 and the joint pipe 3 are joined by welding w at the opening 3a at one end of the joint pipe 3 in the longitudinal direction. The lower water pipe 5 and the joint pipe 3 are joined by welding w at the opening 3a at the other end of the joint pipe 3 in the longitudinal direction.

[0030] On the other end of the joint pipe 3 where the lower water pipe 5 is located, a straight groove 6 is formed along the length of the joint pipe 3, extending from the opening 3a at the other end of the joint pipe 3 in the longitudinal direction to the gap G.

[0031] The groove 6 is formed by recessing the inner circumferential surface 3b of the joint pipe 3, with which the lower water pipe 5 slides, radially outward from the joint pipe 3. Multiple grooves 6 are also formed at equal intervals in the circumferential direction of the joint pipe 3.

[0032] On the other end of the joint pipe 3, a plurality of water passages 7 are formed, which are separated by the outer surface 5b of the lower water passage pipe 5 that slides against the inner surface 3b of the joint pipe 3, and a groove 6 formed by recessing from the inner surface 3b of the joint pipe 3, and which communicate from the opening 3a at the other end of the joint pipe 3 in the longitudinal direction through the gap G.

[0033] Therefore, the water passage 7 has an inlet 7a formed at the position of the opening 3a at the other end of the joint pipe 3 in the longitudinal direction, and is in communication with the outside of the joint pipe 3 through the inlet 7a.

[0034] In the illustrated example, four grooves 6 are provided, resulting in four water passages 7. However, any number of grooves 6 and water passages 7 can be provided.

[0035] Furthermore, by setting the length dimension of the water passage 7, and therefore the groove 6, along the longitudinal direction of the joint pipe 3 to an appropriate dimension corresponding to the density of the soil and the particle size of the soil particles suspended by the pore water pressure, it is possible to suppress the inflow of soil particles into the water passage unit 1.

[0036] The grooves 6 are not limited to being formed at equal intervals in the circumferential direction of the joint pipe 3, but may be formed at appropriate intervals.

[0037] In the illustrated example, the cross-section of the groove 6 is formed in a fan shape that gradually widens radially outward from the joint pipe 3, but the cross-sectional shape of the groove 6 can be any shape.

[0038] The groove 6 may also be spiral in shape along the length of the joint pipe 3, instead of being formed in a straight line along the length of the joint pipe 3.

[0039] Based on the shape of the groove 6 described above, it is preferable that the joint pipe 3 be formed by a molding method such as casting.

[0040] The gap G formed inside the joint pipe 3 between the upper water passage 4 and the lower water passage 5, to which multiple water passages 7 reach, forms a communication space 8 that connects these water passages 7 to the hollow interiors of the upper water passage 4 and the lower water passage 5.

[0041] Therefore, the hollow interiors of the upper water pipe 4 and the lower water pipe 5 are in communication with the outside of the joint pipe 3 via the communication space 8 and the water passage 7 and its inlet 7a.

[0042] Next, a preferred embodiment of the underground water pressure release structure 2 using the water passage unit 1 according to the first embodiment will be described with reference to Figure 4.

[0043] The underground water pressure release structure 2 according to this embodiment is constructed by burying multiple water passages 9, which are formed by connecting two or more of the above-described water passage units 1 in series to create a multi-stage configuration, in the ground U of the liquefaction countermeasure area, in a vertical orientation in the vertical direction, spaced apart from one another, so as to form a forest-like structure.

[0044] Each water-conducting body 9 can be described using one of the water-conducting units 1 as a reference. Specifically, the upper water-conducting pipe 4 of the water-conducting unit 1 is inserted from below into the other end of another joint pipe 3 that has another upper water-conducting pipe 4, and the lower water-conducting pipe 5 of the water-conducting unit 1 is inserted from above into one end of yet another joint pipe 3 that has another lower water-conducting pipe 5.

[0045] As a result, in other joint pipes 3 that have other upper water pipes 4, the upper water pipe 4 of the reference water supply unit 1 is provided as a lower water pipe 5, and another water supply unit 1 is formed.

[0046] Similarly, in yet another joint pipe 3 having another lower water pipe 5, the lower water pipe 5 of the reference water supply unit 1 is provided as an upper water pipe 4, and yet another water supply unit 1 is formed.

[0047] In this way, for each water supply unit 1, the upper and lower water supply pipes 4 and 5 are shared with one joint pipe 3, and a water supply body 9 is formed in which multiple water supply units 1 are connected in series in the vertical direction.

[0048] The water-conducting body 9 may be a single water-conducting unit 1, and a structure for releasing underground water pressure 2 may be constructed by burying and installing multiple such single water-conducting units 1 in the ground U of the liquefaction countermeasure area, vertically in the vertical direction, spaced apart from one another.

[0049] Of the upper and lower ends of the water-conducting body 9, it is desirable that the lower end (the lower end of the lower water-conducting pipe 5 located at the very bottom) be closed.

[0050] In the example shown in Figure 4, the underground water pressure release structure 2 is installed in the ground U beneath the gravel mat 11 around the underground frame 10a of the structure 10.

[0051] Next, the operation of the water supply unit 1 according to the first embodiment and the underground water pressure release structure 2 using the same will be described.

[0052] When the pore water pressure within the ground U increases due to soil liquefaction, the water f inside the ground (hereinafter referred to as groundwater) accompanied by particles such as soil and sand flows towards the water-conducting body 9, which is at nearly atmospheric pressure, and then towards the water-conducting units 1 that make up the water-conducting body 9. Specifically, the groundwater f flows towards the inlet 7a of the water-conducting passage 7 inside the joint pipe 3.

[0053] In other words, the hollow interiors of the water passage 7 of the water passage unit 1 and the upper and lower water pipes 4 and 5 become underground voids U, and groundwater f, accompanied by particles such as soil, flows towards these voids.

[0054] The water passage unit 1 is installed vertically in the ground U, with the inlet 7a of the water passage 7 facing downwards. Since the water passage 7 is also oriented vertically, groundwater f containing particles such as soil and sand that attempt to flow into the water passage 7 from the inlet 7a is difficult to flow into the water passage 7 of the joint pipe 3 due to gravity, and the soil and sand, which are denser than water, remain outside the joint pipe 3. On the other hand, the groundwater f, although containing suspended matter, flows into the water passage 7 as supernatant and flows through the connecting space 8 into the hollow interior of the upper and lower water passages 4 and 5.

[0055] The groundwater f that flows into the water supply unit 1 due to the pore water pressure within the underground U rises through the hollow interior of the upper and lower water supply pipes 4 and 5, which are under near atmospheric pressure, and overflows from the top of the water supply body 9, releasing the water pressure within the underground U.

[0056] In the water passage unit 1 and the underground water pressure release structure 2 using the same according to the first embodiment, granular material such as soil and sand does not flow into the water passage unit 1 or the water passage body 9 and cause clogging, allowing the underground water f to be guided to the ground surface and discharged, thereby efficiently releasing the underground water pressure.

[0057] The water supply unit 1 is extremely simple in structure, as it only requires inserting the joint pipe 3, which is a hollow, straight cylindrical metal pipe, and the upper and lower water supply pipes 4 and 5 together, and then joining the joint pipe 3 and the water supply pipes 4 and 5 by welding w.

[0058] The underground water pressure release structure 2 simply involves installing a single water passage unit 1, or a water passage body 9 formed by connecting water passage units 1 in series, vertically in the ground U. This structure offers good workability and can be easily installed without requiring a large space.

[0059] When the water passage 7 is formed with spiral grooves 6, the water resistance (pressure loss) can more effectively prevent granular material such as soil from flowing into the water passage unit 1.

[0060] Figure 5 shows a modified example of the water passage unit 1 of the first embodiment. In this modified example, the lower water passage 5 is appropriately provided with water passage holes 5c facing the groove 6, which connect the water passage 7 to the hollow interior of the lower water passage 5. Each water passage hole 5c is formed through the pipe wall of the lower water passage 5.

[0061] By providing the water passage hole 5c, the groundwater f that flows into the water passage 7 can be efficiently directed into the hollow interior of the lower water passage pipe 5, thereby efficiently releasing the water pressure inside the ground U.

[0062] Figures 6 to 9 show the water supply unit 1 according to the second embodiment.

[0063] In the second embodiment, the joint pipe 3 of the water supply unit 1 is constructed by integrally joining an upper pipe section 12 which constitutes one end into which the upper water supply pipe 4 is inserted, a lower pipe section 13 which constitutes the other end into which the lower water supply pipe 5 is inserted, and a plate-shaped boundary section 14 which is arranged between the lower pipe section 13 and the upper pipe section 12.

[0064] The lower pipe section 13, like the other end of the joint pipe 3 in the first embodiment, has a water passage 7 formed by the groove section 6.

[0065] Figure 6 is a cross-sectional view of the water supply unit 1 according to the second embodiment, Figure 7 is a view of the boundary portion 14 from above, Figure 8 is a view of the boundary portion 14 from below, and Figure 9 is a cross-sectional view taken along the line DD in Figure 6.

[0066] The boundary portion 14 is an annular shape having a central hole 14a, with an outer diameter equal to the outer diameter of the upper pipe portion 12 and the lower pipe portion 13, and the inner diameter of the central hole 14a equal to the inner diameter of the upper water pipe 4 and the lower water pipe 5.

[0067] As shown in Figure 7, the lower end 4a of the upper water pipe 4 abuts against the upper surface of the boundary portion 14 around the central hole 14a (in the figure, the textured portion x is the abutment portion).

[0068] As shown in Figure 8, a recess 14b is formed on the lower surface of the boundary portion 14, corresponding to the arrangement and shape of the water passage 7 of the lower pipe portion 13, and constituting the aforementioned communication space portion 8.

[0069] In the illustrated example, following the first embodiment, four fan-shaped recesses 14b are formed around the central hole 14a.

[0070] Then, the upper end 5a of the lower water pipe 5 abuts against the lower surface of the boundary portion 14 at a position sandwiched between the recess 14b around the central hole 14a (in the figure, the textured portion x is the abutment portion).

[0071] The upper water pipe 4 and the lower water pipe 5 are joined to the upper pipe section 12 and the lower pipe section 13, respectively, by welding w, in the same manner as they are joined to the joint pipe 3 in the first embodiment.

[0072] A predetermined gap G can be formed between the upper water pipe 4 and the lower water pipe 5 by positioning them according to the thickness of the plate-shaped boundary portion 14.

[0073] Furthermore, at the boundary section 14, the hollow interiors of the upper water pipe 4 and the lower water pipe 5 are connected through the central hole 14a, and the hollow interiors of these upper and lower water pipes 4 and 5 are connected to the water passage 7 of the lower pipe section 13 by the recess 14b.

[0074] Even with the water passage unit 1 of the second embodiment, the same effects and advantages as the water passage unit 1 of the first embodiment can be obtained, and the underground water pressure release structure 2 can be the same as in the above embodiment.

[0075] In the second embodiment, the joint pipe 3 is composed of three parts with different structures: an upper pipe section 12, a lower pipe section 13, and a boundary section 14, which simplifies the structure of each part.

[0076] Figure 10 shows a water supply unit 1 according to the third embodiment.

[0077] In the second embodiment of the water supply unit 1, the wall thickness of the upper pipe section 12 into which the upper water supply pipe 4 is inserted is matched to the wall thickness of the lower pipe section 13 into which the water supply passage 7 is formed. However, this may result in the upper pipe section 12 being unnecessarily thick and heavy.

[0078] In the third embodiment, the wall thickness of the upper pipe section 12 is made to be the same as the wall thickness of the lower pipe section 13 at the location where the groove 6 is formed, in order to make it thinner by subtracting the dimension of the groove 6 of the lower pipe section 13.

[0079] By making the upper pipe section 12 thinner, it is possible to ensure a lighter joint pipe 3, reduced material costs, and improved workability.

[0080] Between the thinned upper pipe section 12 and the upper water pipe 4, a hollow cylindrical coupler 15 is provided, formed to a size that matches the dimensions of the thinned section, i.e., the radial dimension of the groove section 6. The coupler 15 may be made of metal or a resin such as FRP.

[0081] When the coupler 15 is installed, the opening 3a on one end of the joint pipe 3 is formed by the opening 15a of the coupler 15.

[0082] If the coupler 15 is made of metal, female threads may be formed on the inner circumferential surface 3b of the joint pipe 3 and male threads on the outer circumferential surface of the coupler 15, and the coupler may be attached by screwing them together. On the other hand, if it is made of resin, the upper water pipe 4 is joined to the coupler 15 with an adhesive or the like.

[0083] In the third embodiment, unlike the second embodiment, the upper water pipe 4 may be inserted by sliding it against the inner circumferential surface 15b of the coupler 15.

[0084] Even with the water passage unit 1 of the third embodiment, the same effects and advantages as those of the water passage unit 1 of the first and second embodiments can be obtained, and the underground water pressure release structure 2 can be the same as that of the above embodiments.

[0085] Figure 11 shows a modified example of the structure of the joint pipe 3 that constitutes the water supply unit 1 described in the first to third embodiments. Figure 11 is a cross-sectional view corresponding to Figure 3.

[0086] In the above embodiment of the joint pipe 3, the tip surface of the projection 3c that extends along the length of the joint pipe 3 and appears between the grooves 6 (between the water passages 7) is formed as a concave surface 3d that is aligned with the outer surface 5b of the lower water pipe 5 (see Figure 3).

[0087] In this modified example, the tip surface of the protrusion 3c is formed as a convex surface 3e instead of a concave surface 3d.

[0088] In this configuration, the outer surface 5b of the lower water pipe 5 may be brought into sliding contact with the convex surface 3e, and the lower water pipe 5 may be inserted into the joint pipe 3.

[0089] Even with such modifications, it is a given that the same effects and advantages as the water supply unit 1 of the above embodiment will be achieved.

[0090] Figure 12 shows a modified example of the underground water pressure release structure 2. In the above embodiment, the water passage 9 was installed vertically in the ground U of the liquefaction countermeasure area. However, as shown in the figure, if the sloping ground 16 is an area where pore water pressure rises, it may be installed at an angle to the slope 16a of the sloping ground 16.

[0091] In this case, the water-conducting body 9, which is angled downwards relative to the horizontal, is installed such that the inlet 7a of the water passage 7 is angled downwards.

[0092] Even with such modifications, it is a given that they will produce the same effects and benefits as the underground water pressure release structure 2 of the above embodiment. [Explanation of symbols]

[0093] 1. Water supply unit 2. Underground water pressure release structure 3. Joint pipes 3b Inner surface of the joint pipe 4 Upper water pipe 4a Lower end of upper water pipe 5 Sewer pipe 5a Upper end of the lower water pipe 5b Outer surface of the lower water pipe 5c Water hole 6 grooves 7 Water passage 8 Communication space 12 Upper tube section 13 Lower section 14 Boundary 14b recess 15 Couplers 15b Inner surface of the coupler G Gap U underground

Claims

1. A water supply unit installed underground, A hollow cylindrical joint pipe, with one end positioned above the other end, A hollow cylindrical upper water pipe is inserted into one end of the joint pipe, The other end of the above-mentioned joint pipe is provided with a hollow cylindrical lower water pipe that is inserted from the above-mentioned upper water pipe, separated by a gap. On the other end of the above-mentioned joint pipe, multiple grooves are formed by recessing the inner surface of the joint pipe radially outward, at intervals in the circumferential direction of the joint pipe, so as to partition the outer surface of the lower water passage and form multiple water passages. The gap between the upper water passage and the lower water passage forms a communication space that connects multiple water passages to the hollow interior of these upper and lower water passages. The outer surface of the lower water passage pipe slides against the inner surface of the other end of the above-mentioned joint pipe, and the water passage is demarcated by the outer surface of the lower water passage pipe and the groove. The above-mentioned water passage extends in the longitudinal direction from the opening at the other end of the joint pipe to the gap, A downward-facing inlet for the water passage is formed at the position of the opening at the other end of the joint pipe in the longitudinal direction. A water supply unit characterized by the following features.

2. The water supply unit according to claim 1, characterized in that the joint pipe has an upper pipe portion that constitutes one end, a lower pipe portion that constitutes the other end, and a recess that constitutes the communication space, is disposed between the upper pipe portion and the lower pipe portion, is in the shape of a plate that abuts the lower end of the upper water supply pipe and the upper end of the lower water supply pipe to form the gap between the upper water supply pipe and the lower water supply pipe, and has an annular boundary portion that connects the hollow interiors of the upper water supply pipe and the lower water supply pipe.

3. The water supply unit according to claim 2, characterized in that the upper pipe portion is formed with the same wall thickness as the lower pipe portion at the groove formation position, a hollow cylindrical coupler is provided inside the upper pipe portion with a wall thickness matching the radial dimension of the groove, and the upper water supply pipe is inserted by sliding against the inner circumferential surface of the coupler instead of sliding against the inner circumferential surface of the joint pipe.

4. The water supply unit according to any one of claims 1 to 3, characterized in that the lower water supply pipe is appropriately provided with water supply holes facing the groove portion, which connect the water supply passage to the hollow interior of the lower water supply pipe.

5. A subterranean water pressure release structure characterized in that the water supply unit described in any one of claims 1 to 3 is installed underground.

6. Using the water supply unit described in any one of claims 1 to 3, An underground water pressure release structure characterized in that two or more of the water supply units, connected in series by inserting the upper water supply pipe as a lower water supply pipe into the other end of another joint pipe equipped with an upper water supply pipe, and inserting the lower water supply pipe as an upper water supply pipe into one end of yet another joint pipe equipped with a lower water supply pipe, are installed underground.

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