Drain structure

Abstract

To provide a drain structure which can sufficiently lower turbidity of drain from a fill-up ground.SOLUTION: A drain structure 1A includes: a water collecting perforated pipe 4 extending in a vertical direction in a fill-up ground 3; a first filtration layer 5 which contains a granular first filtration material and surrounds the water collecting perforated pipe 4; a second filtration layer 6 which contains a granular second filtration material and surrounds the first filtration layer 5; and a drain pipe 7 which is connected to the lower part of the water collecting perforated pipe 4 and extends in substantially a horizontal direction. The first filtration material has a particle diameter smaller than that of the second filtration material. The drain from the fill-up ground 3 enters into the water collecting perforated pipe 4 through two-stage filtration between the second filtration layer 6 and the first filtration layer 5.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a drainage structure. [Background technology]

[0002] Conventionally, culverts such as perforated pipes have been installed to drain rainwater that has seeped into the constructed banked land and groundwater whose water level has risen. At the same time, in order to increase the efficiency of water collection, vertical shafts have been installed in the banked land, and water is drained into a balancing pond or river through the vertical shafts and culverts. In this case, the banking material may flow into the vertical shaft, causing the ground surface to collapse, so measures to prevent this have been devised (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6830042 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional drainage structures, the turbidity of the drainage water is high and there is a risk that the required turbidity standard is not met. Therefore, the object of the present invention is to provide a drainage structure that can sufficiently reduce the turbidity of the drainage water from the embankment ground. [Means for solving the problem]

[0005] The present invention provides a drainage structure comprising a perforated collection pipe extending vertically within an embankment ground, a first filtration layer including a granular first filtration material and surrounding the perforated collection pipe, a second filtration layer including a granular second filtration material and surrounding the first filtration layer, and a drainage pipe connected to the lower part of the perforated collection pipe and extending in a substantially horizontal direction, wherein the first filtration material has a smaller particle size than the second filtration material.

[0006] In this drainage structure, rainwater that has infiltrated into the embankment and groundwater whose water level has risen are drained into the drainage pipe through the perforated water collection pipe. In this process, the water in the embankment must pass through the second filter layer and the first filter layer in order to enter the perforated water collection pipe. In other words, the water in the embankment reaches the perforated water collection pipe after passing through two stages of filtration. In this two-stage filtration, the particle size of the granular first filter material contained in the first filter layer is smaller than the particle size of the granular second filter material contained in the second filter layer, so that among the soil particles that move with the water in the embankment, the soil particles with larger particle size are first captured by the second filter layer, and the soil particles with smaller particle size that pass through the second filter layer are then captured by the first filter layer. The water that reaches the perforated water collection pipe after passing through this has a sufficiently low turbidity.

[0007] In the drainage structure of the present invention, the permeability coefficient of the first filter layer is 1×10 -3 cm / s~1×10 -1 It is preferable that the flow rate is 100 cm / s, which allows most of the small soil particles that make up the banking ground to be captured.

[0008] In the drainage structure of the present invention, it is preferable that the first filtration layer consists essentially of sand, and the second filtration layer consists of single-grain crushed stone having a grain size in the range of 10 mm to 60 mm.

[0009] In the drainage structure of the present invention, it is preferable to provide a suction prevention material at least in one of the following locations: between the perforated water collection pipe and the first filtration layer, between the first filtration layer and the second filtration layer, and between the second filtration layer and the banking ground. This prevents the respective components from mixing with each other, and stabilizes the structure of each part.

[0010] The drain pipe is preferably a perforated pipe, so that when the groundwater level rises, the groundwater is drained directly into the drain pipe without passing through a perforated collection pipe, thereby improving drainage efficiency.

[0011] The perforated water collection pipe, the first filter layer, and the second filter layer may all have their upper portions protruding above the ground surface of the embankment ground. The drainage structure of the present invention functions even during embankment construction.

[0012] The upper end of the perforated collection pipe may be closed with a lid, and the perforated collection pipe, the first filtration layer, and the second filtration layer may all be entirely buried in the banked land. Alternatively, the perforated collection pipe, the first filtration layer, and the second filtration layer may all be entirely buried in the banked land, and the upper end of the perforated collection pipe may be connected to a collection basin buried near the ground surface of the banked land. The drainage structure of the present invention continues to function even after the banking work is completed and the drainage structure of the present invention is buried in the banked land. Effect of the Invention

[0013] According to the present invention, it is possible to provide a drainage structure capable of sufficiently reducing the turbidity of drainage water from a banked land. [Brief description of the drawings]

[0014] [Figure 1] A side cross-sectional view of the drainage structure during embankment construction. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II of FIG. [Diagram 3] A side cross-sectional view of the drainage structure after completion of embankment work. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] When constructing an embankment on the original ground (natural bedrock), over time water accumulates in the embankment due to infiltration of rainwater and rising groundwater levels. To ensure the stability of the embankment, it is desirable to drain the accumulated water. Particularly on slopes, if accumulated water undermines the stability of the embankment, it can cause landslides. Similarly, even after construction of the embankment is complete, there is a demand to continue draining the water from the embankment.

[0016] From the banking land, soil particles that compose the banking land flow out together with the water. If the wastewater is highly turbid, it becomes necessary to treat it in a separate treatment facility (e.g., a turbid water treatment plant) before discharging it, in consideration of the environment. Therefore, it is desirable to sufficiently reduce the turbidity of the wastewater from the banking land. The present invention aims to solve this problem. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Note that the same or corresponding parts in each drawing are given the same reference numerals, and duplicate explanations will be omitted.

[0017] <In the middle of embankment construction> As shown in FIG. 1 and FIG. 2, the drainage structure 1A of this embodiment is a structure that is installed while building a banked land 3 on the original ground 2. The banked land 3 is compacted to have an optimal water content to appropriately suppress the infiltration of rainwater and the rise of groundwater. The properties of the bank that forms the banked land 3 include various types such as sandy soil and clayey soil. The grain size of the banked soil may be, for example, 75 μm to 75 mm, or 7.5 mm to 100 mm. The grain size here is a value measured according to the "Engineering Classification Method for Ground Materials" of the Geotechnical Society Standard (JGS 0051-2020).

[0018] The drainage structure 1A is installed starting from the original ground 2. The drainage structure 1A includes a perforated water collection pipe 4 extending vertically in the banking land 3, a first filtration layer 5 surrounding the perforated water collection pipe 4 in a cylindrical shape, a second filtration layer 6 surrounding the first filtration layer 5 in a cylindrical shape, and a drainage pipe 7 connected to the lower part of the perforated water collection pipe 4 and extending in a substantially horizontal direction. The perforated water collection pipe 4, the first filtration layer 5, and the second filtration layer 6 together form a cylindrical body, the upper part of which protrudes above the ground surface of the banking land 3. As the construction of the banking land 3 progresses, the height of the banking land 3 is increased and the drainage structure 1A is also extended upward.

[0019] The perforated collection pipe 4 and the drainage pipe 7 are both perforated pipes with many holes on the side circumferential surface. The drainage pipe 7 is buried as a culvert in the original ground 2. The drainage pipe 7 and the perforated collection pipe 4 are connected by a T-shaped joint 7A. The drainage pipe 7 may extend horizontally or with a slope. The perforated collection pipe 4 and the drainage pipe 7 both have an inner diameter of about 10 cm to 30 cm. The perforated collection pipe 4 and the drainage pipe 7 may be made of resin or metal. An example of the resin is high-density polyethylene.

[0020] The first filtration layer 5 includes a granular first filtration material. Specifically, the first filtration material is substantially composed of sand. The first filtration material may be composed only of sand. The sand may be lime sand. The particle size of the first filtration material is preferably 75 μm to 4.75 mm, more preferably 75 μm to 425 μm. The particle size here is a value measured by the above-mentioned "Engineering Classification Method of Ground Materials". Also, those belonging to sand to gravel, particularly those belonging to fine sand to fine gravel, in the "Engineering Classification Method of Ground Materials" are suitable. If the particle size of the first filtration material is within these ranges, it is advantageous to capture the coarse particles among the soil particles constituting the banking ground 3 and reduce the turbidity of the drainage water.

[0021] Since the soil particles constituting the banking ground 3 are also blocked by the suction prevention material 8, the particle size of the first filtering material does not necessarily have to be smaller than the particle size of the soil particles constituting the banking ground 3.

[0022] The permeability of the first filtration layer 5 is 1×10 -3 cm / s~1×10 -1 cm / s, preferably 5×10 -3 cm / s~5×10 -2 cm / s is more preferable, and 8×10 -3 cm / s~3×10 -2 It is more preferable that the permeability coefficient of the first filtration layer 5 is within this range, the wastewater that has passed through the second filtration layer 6 can be appropriately filtered.

[0023] The second filtration layer 6 includes a granular second filtration material. Specifically, the second filtration material may be gravel soil or stone. The second filtration material may be made of single-grained crushed stone having a particle size in the range of 10 mm to 60 mm. The particle size of the single-grained crushed stone is more preferably 15 mm to 50 mm, and even more preferably 20 mm to 40 mm. The particle size here is a value measured according to the "Engineering Classification Method for Ground Materials" of the Geotechnical Society Standard (JGS 0051-2020). If the particle size of the second filtration material is within these ranges, it is possible to capture coarse particles among the soil particles constituting the banking land 3, which is advantageous in reducing the burden of filtration by the first filtration material.

[0024] The horizontal thickness of each of the first filtration layer 5 and the second filtration layer 6 may be 50 cm to 120 cm, 60 cm to 100 cm, or 70 cm to 90 cm. The horizontal thicknesses of both filtration layers may be the same or different.

[0025] In this embodiment, the particle size of the first filtering material is smaller than that of the second filtering material, where "smaller" means that the mode diameter is smaller when comparing the two filtering materials.

[0026] The particle size of the first filter material is the 10% particle size (D1 10 )but, 0.01mm <D1 10 <0.03mm D1 10 It may be ≦0.01 mm. The particle size of the second filter material is the 10% particle size (D2 10 ) is the first filter material D1 10 A value greater than D1 10 <D2 10 ). For example, 0.03mm <D2 10 <0.05mm 0.05mm≦D2 10 may be also possible.

[0027] Suction prevention materials 8 are provided between the perforated collection pipe 4 and the first filtration layer 5, between the first filtration layer 5 and the second filtration layer 6, and between the second filtration layer 6 and the banking ground 3. Suction prevention materials 8 are also provided on the upper surfaces of the first filtration layer 5 and the second filtration layer 6, and between the upper surfaces of the first filtration layer 5 and the second filtration layer 6 and the original ground 2.

[0028] The suction prevention material 8 used should be appropriate depending on the particle size. The suction prevention material 8 is preferably a nonwoven fabric made of resin such as polyester, or a metal or resin mesh. In particular, the suction prevention material 8 provided between the second filtration layer 6 and the banking land base 3 is preferably a rigid resin mesh in order to ensure self-supporting in the aerial portion of the banking land base 3 protruding from the ground surface. The thickness of the suction prevention material 8 may be 5 mm to 50 mm, or may be 10 mm to 15 mm.

[0029] Although not shown in Figure 1, multiple drainage structures 1A are provided at predetermined distances from each other on the site of the embankment land 3, and each drainage structure 1A is connected by a drainage pipe 7.

[0030] According to the drainage structure 1A of this embodiment, rainwater that has infiltrated into the banking land 3 and groundwater whose water level has risen are drained into the drainage pipe through the perforated water collection pipe 4. In this process, the water in the banking land 3 needs to pass through the second filtration layer 6 and the first filtration layer 5 in order to enter the perforated water collection pipe 4. In other words, the water in the banking land 3 reaches the perforated water collection pipe 4 after passing through two stages of filtration. In this two-stage filtration, the particle size of the granular first filtration material contained in the first filtration layer 5 is smaller than the particle size of the granular second filtration material contained in the second filtration layer 6, so that among the soil particles moving with the water in the banking land 3, the soil particles with a large particle size (coarse particles) are first captured by the second filtration layer 6, and the soil particles with a small particle size (fine particles) that have passed through the second filtration layer are then captured by the first filtration layer 5. The water that reaches the perforated water collection pipe through this has a sufficiently low turbidity. The turbidity is reduced to, for example, 200 ppm or less, and the outflow of soil particles is sufficiently suppressed even when the water is discharged outside the banking area (for example, into a river or sea area). Even if the banking land 3 is made of red soil, the turbidity can be reduced to a level where the drainage does not take on a reddish color (for example, transparency of 4.5 cm or more).

[0031] Conventional drainage structures often do not have a layer that can be called a filtration layer, or if they have a filtration layer, it is either a single layer with a coarse mesh or a single layer with a fine mesh. For this reason, the turbid water is discharged with high turbidity, or the filtration layer becomes clogged quickly. In contrast, according to the drainage structure 1A of this embodiment, the turbidity of the drainage water can be sufficiently reduced as described above. In addition, since the drainage to the perforated water collection pipe 4 is efficiently advanced, water is prevented from accumulating on the banking ground 3, and the banking ground 3 is prevented from becoming unstable.

[0032] If the second filtration layer 6 did not exist, the coarse particles in the banking land 3 would stick to the periphery of the first filtration layer 5, narrowing the drainage path and increasing the risk of early clogging. In contrast, in the drainage structure 1A of this embodiment, the coarse particles in the banking land 3 are captured in advance by the second filtration layer 6 containing the second filtration material with a large particle size, reducing the burden on the first filtration layer 5 and making clogging less likely to occur.

[0033] Furthermore, in the drainage structure 1A of this embodiment, the permeability coefficient of the first filtration layer 5 is neither too large nor too small, so that an appropriate amount of drainage can be ensured and many of the small soil particles that make up the fill land can be captured.

[0034] Furthermore, in the drainage structure 1A of this embodiment, suction prevention materials 8 are provided between the perforated water collection pipe 4 and the first filtration layer 5, between the first filtration layer 5 and the second filtration layer 6, and between the second filtration layer 6 and the banking land 3. This prevents the respective components from mixing with each other, and the structure of each part is stable.

[0035] In addition, in the drainage structure 1A of this embodiment, the drainage pipe 7 is a perforated pipe. With this, when the groundwater level rises, the groundwater is drained directly to the drainage pipe without passing through the perforated water collection pipe 4, so that the drainage efficiency is improved. Therefore, water is prevented from accumulating in the banking land 3, and the banking land 3 can be stabilized.

[0036] <After completion of embankment work> The drainage structure 1A shown in FIG. 1 is extended upward as the construction of the banking land 3 is advanced and the height of the banking land 3 is increased. As shown in FIG. 3, when the construction of the banking land 3 is completed, the drainage structure 1A of this embodiment becomes a drainage structure 1B or 1C in which the upper end of the perforated water collection pipe 4 is closed with a lid 9 and the perforated water collection pipe 4, the first filtration layer 5, and the second filtration layer 6 are all buried in the banking land 3 in their entirety. In the drainage structure 1B depicted on the left side of FIG. 3, the upper end of the perforated water collection pipe 4 is closed with a lid 9. The lid 9 is located at a depth of about 0.5 m to 1.0 m from the ground surface of the banking land 3. In the drainage structure 1C depicted on the right side of FIG. 3, the upper end of the perforated water collection pipe 4 is not closed with a lid and is connected to a catch basin 10 buried near the ground surface of the banking land 3.

[0037] Even after the embankment work is completed, the drainage structure 1B and the drainage structure 1C function as drainage structures and can drain water derived from rainwater or groundwater. The drainage structure 1C has a stronger function of actively collecting and draining water than the drainage structure 1B.

[0038] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, in the above embodiment, the drainage pipe 7 is installed in the original ground 2, but the drainage pipe 7 may be installed in the banking ground 3.

[0039] In addition, in the above embodiment, the first filtration layer 5 and the second filtration layer 6 surrounding the perforated water collection pipe 4 are cylindrical in shape and have the same thickness in the vertical direction, but this thickness does not necessarily have to be the same, and the thickness (the horizontal thickness of the first filtration layer 5 and the second filtration layer) may be changed depending on the vertical position.

[0040] Furthermore, in the above embodiment, suction prevention material 8 is provided between the perforated collection pipe 4 and the first filtration layer 5, between the first filtration layer 5 and the second filtration layer 6, and between the second filtration layer 6 and the banking land 3. However, if there is little risk of the respective components mixing with each other, it is also possible to adopt an embodiment in which suction prevention material 8 is not provided. [Industrial Applicability]

[0041] The present invention can be used in embankment construction. [Explanation of symbols]

[0042] 1A, 1B, 1C...drainage structure, 2...original ground, 3...filled ground, 4...perforated collection pipe, 5...first filtration layer, 6...second filtration layer, 7...drainage pipe, 7A...T-joint, 8...suction prevention material, 9...cover, 10...collection manhole.

Claims

1. A perforated water collection pipe extending vertically in the embankment ground; a first filter layer including a granular first filter material and surrounding the perforated water collection tube; a second filtration layer including a granular second filtration material surrounding the first filtration layer; A drainage pipe connected to a lower portion of the perforated water collection pipe and extending in a substantially horizontal direction, The drainage structure, wherein the first filtration material has a smaller particle size than the second filtration material.

2. The first filtration layer has a water permeability coefficient of 1×10 －３ cm / s to 1×10 －１ The drainage structure of claim 1, wherein the flow rate is 100 rpm.

3. the first filtration layer consists essentially of sand; The drainage structure according to claim 1, wherein the second filter layer is made of single-grain crushed stone having a particle size in the range of 10 mm to 60 mm.

4. The drainage structure according to claim 1, further comprising a suction prevention material at least in one of the following locations: between the perforated collection pipe and the first filtration layer, between the first filtration layer and the second filtration layer, and between the second filtration layer and the fill land.

5. The drainage structure of claim 1 , wherein the drainage pipe is a perforated pipe.

6. The drainage structure according to claim 1 , wherein the upper portions of the perforated water collection pipe, the first filter layer, and the second filter layer all protrude above the ground surface of the banking land.

7. The upper end of the perforated water collection pipe is closed with a lid, The drainage structure according to claim 1 , wherein the perforated water collection pipe, the first filter layer, and the second filter layer are all entirely buried in the banked land.

8. The perforated water collection pipe, the first filtration layer, and the second filtration layer are all entirely buried in the embankment ground, 2. The drainage structure according to claim 1, wherein the upper end of the perforated water collection pipe is connected to a water collection basin buried near the ground surface of the fill land.

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