JP7846581B2 - Water supply unit and underground water pressure release structure - Google Patents

Description

This invention relates to a water passage unit and a structure for releasing underground water pressure that can efficiently release underground water pressure through drainage without causing clogging by suspended soil particles.

Traditionally, the Granbell Drain method, which aims to reduce pore water pressure, has been known as a liquefaction countermeasure, for example, in sandy soil.

This construction method involves using heavy machinery to form drain columns in the ground. By allowing these drain columns to absorb groundwater, the rise in pore water pressure in the surrounding soil is suppressed, thereby preventing soil liquefaction.

However, there were challenges to the construction process, such as the need to use a large number of heavy machines and the requirement for a vast construction area.

Patent Document 1 is known as a technology that considers ease of construction, such as eliminating the need for the use of large heavy machinery.

Patent Document 1, "Drainage Pipe for Liquefaction Countermeasures," aims to provide a drainage pipe for liquefaction countermeasures that ensures good workability without the need for numerous large heavy machines, prevents soil particles from the surrounding ground from flowing into the pipe, and minimizes changes in liquefaction prevention effectiveness over time after construction. This is achieved by providing linear slits penetrating the inner and outer walls of the pipe in a predetermined pattern on the pipe surface, either in the approximately axial direction or approximately circumferentially.

Japanese Patent Publication No. 2000-144705

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 the inflow of soil particles into the pipe simultaneously with drainage through the slits, making it challenging to ensure sufficient liquefaction prevention.

This invention was conceived in view of the above-mentioned conventional problems, and aims to provide a water passage unit and a groundwater pressure release structure that can efficiently release underground water pressure through drainage without causing clogging by suspended soil particles.

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. On the other end of the 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 multiple water passages on the outer surface of the lower water passage pipe. The gap between the upper and lower water passage pipes forms a communication space that connects the multiple water passages to the hollow interiors of these upper and lower water passage pipes.

The aforementioned joint pipe is characterized by comprising an upper pipe section constituting one end, a lower pipe section constituting the other end, and a recess constituting the communication space; being positioned between the upper and lower pipe sections, and being plate-shaped in which 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 and lower water pipes; and comprising an annular boundary section that connects the hollow interiors of the upper and lower water pipes.

The upper pipe section is formed with the same wall thickness as the lower pipe section at the groove formation location. A hollow cylindrical coupler, formed with a wall thickness matching the radial dimension of the groove, is provided inside the upper pipe section. The upper water pipe is inserted by sliding against the inner surface of the coupler, rather than sliding against the inner surface of the joint pipe.

The lower water pipe is characterized by having water passages appropriately provided facing the groove, which connect the water passage to the hollow interior of the lower water pipe.

The underground water pressure release structure according to the present invention is characterized in that the above-mentioned water passage unit is installed underground.

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.

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, preventing clogging and allowing for efficient release of underground water pressure through drainage.

This is a cross-sectional view illustrating a first embodiment of the water supply unit according to the present invention. Figure 1 shows a cross-sectional view taken along the line A-A. Figure 1 shows a cross-sectional view taken along the line B-B. 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. This is a cross-sectional view illustrating a modified example of the water supply unit shown in Figure 1. This is a cross-sectional view illustrating a second embodiment of the water supply unit according to the present invention. Figure 6 shows a top-down view of the boundary section of the water supply unit. Figure 6 shows a view from below of the boundary section of the water supply unit. Figure 6 shows a cross-sectional view taken along the line D-D. This is a cross-sectional view illustrating a third embodiment of the water supply unit according to the present invention. This is a cross-sectional view illustrating a modified example of a joint pipe provided in a water supply unit according to the present invention. This is an explanatory diagram illustrating a modified example of the underground water pressure release structure according to the present invention.

Preferred embodiments of the water supply unit and underground water pressure release structure according to the present invention will be described in detail below with reference to the accompanying drawings.

Figures 1 to 3 show a water passage unit 1 according to the first embodiment. Figure 1 is a cross-sectional view of the water passage unit 1 according to the first embodiment, Figure 2 is a cross-sectional view taken along the line A-A in Figure 1, and Figure 3 is a cross-sectional view taken along the line B-B in Figure 1. Note that Figure 1 is a cross-sectional view taken along the line C-C in Figure 3.

Figure 4 shows the underground water pressure release structure 2, which is constructed by installing the water passage unit 1.

First, regarding the water supply unit 1, it mainly consists of a joint pipe 3, an upper water supply pipe 4, and a lower water supply pipe 5.

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 hollow interiors with openings at both ends in the longitudinal direction.

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

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

The 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 at one end of the joint pipe 3.

The 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 at the other end of the joint pipe 3.

Inside the joint pipe 3, the upper end 5a of the lower water pipe 5 is positioned to leave a gap with 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.

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.

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.

On the other end of the joint pipe 3 where the lower water pipe 5 is located, a linear 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 to the gap G.

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

On the other end of the joint pipe 3, multiple water passages 7 are formed, separated by the outer surface 5b of the lower water passage pipe 5, which 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. These passages communicate with each other from the opening 3a at the other end of the joint pipe 3 in the longitudinal direction, across the gap G.

Therefore, the water passage 7 has an inlet 7a formed at the opening 3a at the other end of the joint pipe 3 in the longitudinal direction, and is connected to the outside of the joint pipe 3 through this inlet 7a.

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.

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

The grooves 6 are not limited to being formed at equal intervals in the circumferential direction of the joint pipe 3; they may be formed at appropriate intervals.

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.

The groove 6 may also be formed in a spiral 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.

Based on the shape of the groove 6 described above, it is preferable to form the joint pipe 3 by a molding method such as casting.

The gap G formed between the upper water passage 4 and the lower water passage 5 inside the joint pipe 3, and reached by multiple water passages 7, 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.

Therefore, the hollow interiors of the upper water pipe 4 and the lower water pipe 5 are connected to the outside of the joint pipe 3 via the communication space 8 and the water passage 7 and its inlet 7a.

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.

The underground water pressure release structure 2 according to this embodiment is constructed by burying multiple water passages 9, each consisting of two or more water passage units 1 connected in series to form a multi-stage structure, in the ground U of the liquefaction countermeasure area, vertically oriented in the vertical direction and spaced apart from one another.

Each water-conducting body 9, when explained using one of the water-conducting units 1 as a reference, has its upper water-conducting pipe 4 inserted from below into the other end of another joint pipe 3 that also has an upper water-conducting pipe 4, and its lower water-conducting pipe 5 inserted from above into one end of yet another joint pipe 3 that also has a lower water-conducting pipe 5.

As a result, the upper water pipe 4 of the reference water supply unit 1 is provided as the lower water supply pipe 5 in another joint pipe 3 that has another upper water supply pipe 4, thereby forming another water supply unit 1.

Similarly, in 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.

In this way, for each water-conducting unit 1, the upper and lower water-conducting pipes 4 and 5 are shared with a single connecting pipe 3, thereby forming a water-conducting body 9 in which multiple water-conducting units 1 are connected in series in the vertical direction.

The water-conducting body 9 may be a single water-conducting unit 1, and multiple such single water-conducting units 1 may be buried and installed vertically in the ground U of the liquefaction countermeasure area, spaced apart from each other, thereby forming a groundwater pressure release structure 2.

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.

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 structure 10a of the structure 10.

Next, the operation of the water-conducting unit 1 and the underground water pressure release structure 2 using the same, according to the first embodiment, will be explained.

When liquefaction of the soil increases the pore water pressure within the ground U, 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 approximately 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.

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 into these voids.

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 vertically oriented, groundwater f containing particles such as soil and sand, attempting to flow from the inlet 7a into the water passage 7, has difficulty with the heavier soil and sand due to gravity, and remains outside the joint pipe 3. However, the groundwater f, although containing suspended matter, flows into the water passage 7 as supernatant, and through the connecting space 8, flows into the hollow interiors of the upper and lower water passages 4 and 5.

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

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, causing clogging. This allows for efficient release of underground water pressure by guiding and discharging the groundwater f to the ground surface.

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.

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 provides excellent workability and allows for easy installation without requiring a large space.

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

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, connecting 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.

By providing the water passage hole 5c, the groundwater f flowing into the water passage 7 can be efficiently directed into the hollow interior of the lower water pipe 5, thereby efficiently releasing the water pressure within the ground U.

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

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 positioned between the lower pipe section 13 and the upper pipe section 12.

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

Figure 6 is a cross-sectional view of the water passage 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 D-D in Figure 6.

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

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 area).

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 8.

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

Furthermore, 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 area).

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.

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.

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.

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.

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

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

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. This may result in the upper pipe section 12 being unnecessarily thick and heavy.

In the third embodiment, the wall thickness of the upper pipe section 12 is made thinner by subtracting the dimension of the groove 6 of the lower pipe section 13. Therefore, the wall thickness of the lower pipe section 13 at the location where the groove 6 is formed is the same as the wall thickness of the lower pipe section 13.

By thinning the upper pipe section 12, it is possible to ensure a lighter joint pipe 3, reduced material costs, and improved workability.

A hollow cylindrical coupler 15 is provided between the thinned upper pipe section 12 and the upper water passage pipe 4, with dimensions matching the thinned portion, i.e., the radial dimension of the groove section 6. The coupler 15 may be made of metal or a resin such as FRP.

When the coupler 15 is installed, the opening 3a at one end of the joint pipe 3 is formed by the opening 15a of the coupler 15.

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

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.

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.

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.

In the above embodiment of the joint pipe 3, the tip surface of the projection 3c that extends along the longitudinal direction 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 circumferential surface 5b of the lower water passage pipe 5 (see Figure 3).

In this modification, the tip surface of the projection 3c is formed as a convex surface 3e instead of a concave surface 3d.

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

Even with such modifications, it is naturally possible to achieve the same effects and advantages as the water passage unit 1 of the above embodiment.

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 increases, it may be installed at an angle to the slope 16a of the sloping ground 16.

In this case, the water-conducting body 9, which is angled diagonally downward relative to the horizontal, is installed such that the inlet 7a of the water passage 7 is also angled diagonally downward.

Even with such modifications, it is naturally possible to achieve the same effects and benefits as the underground water pressure release structure 2 of the above embodiment.

1 Water supply unit 2 Underground water pressure release structure 3 Joint pipe 3b Inner surface of joint pipe 4 Upper water supply pipe 4a Lower end of upper water supply pipe 5 Lower water supply pipe 5a Upper end of lower water supply pipe 5b Outer surface of lower water supply pipe 5c Water supply hole 6 Groove 7 Water supply passage 8 Communication space 12 Upper pipe section 13 Lower pipe section 14 Boundary section 14b Recess 15 Coupler 15b Inner surface of coupler G Gap U Underground

Claims (6)

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. The water supply unit according to claim 1, characterized in that the joint pipe comprises an upper pipe portion constituting one end, a lower pipe portion constituting the other end, and a recess constituting 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 supply pipe and the upper end of the lower water supply pipe abut against each other to form the gap between the upper water supply pipe and the lower water supply pipe, and is composed of an annular boundary portion that connects the hollow interiors of the upper water supply pipe and the lower water supply pipe. The water supply unit according to claim 2, characterized in that the upper pipe section is formed with the same wall thickness as the lower pipe section at the groove formation position, a hollow cylindrical coupler is provided inside the upper pipe section 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. 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. A subterranean water pressure release structure characterized in that the water passage unit described in any one of claims 1 to 3 is installed underground. 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.