JP4510325B2 - Rainwater infiltration facility with mud tank - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a rainwater facility that is excellent in workability and that can ensure rainwater penetration capability over a long period of time.
[0002]
[Prior art]
In recent years, urban areas covered with buildings and asphalt have expanded rapidly, resulting in a decrease in the surface of the water that has been functioning for water retention and recreation. The risk of urban flooding has also increased. In addition, a decrease in the amount of rainwater or the like penetrating into the ground disturbs the water cycle in nature, such as lowering the water level in urban shallow land, leading to a decrease in river normal flow and evapotranspiration. Yes. In such a background, it is required to effectively infiltrate rainwater underground.
[0003]
As the infiltration facility for rainwater, products such as various infiltration troughs, infiltration trenches, and infiltration side grooves have been proposed, and products made of concrete products, plastic products, or porous concrete having holes and slits have already been used. And while embedding said product in the ground, the circumference | surroundings are filled with crushed stone No. 4 (20-30 mm) etc., for example, and the rainwater which collected is infiltrated from the bottom part or the side surface, and it is set as the infiltration facility. However, in the above infiltration facility, when sediment that flows in along with rainwater accumulates, there is a disadvantage that the infiltration capacity is lowered and the function as the infiltration facility is not achieved.
[0004]
For this reason, a water collecting tank is sometimes provided to remove dust and mud before rainwater flows into the infiltration facility. For example, Japanese Utility Model Publication No. 63-20547 discloses a cage for catching fallen leaves, garbage, or earth and sand inside a rainwater catchment for collecting water. In addition, a filter made of a wire mesh or the like is provided at the pipe port connecting the rainwater tank and the infiltration facility.
[0005]
[Problems to be solved by the invention]
Even if a basket is provided in a water collecting basin, that is, a mud storage basin, if the basket is made fine, the cage will be clogged in a short period of time, preventing rainwater from flowing into the basin. It needs to be rough. For this reason, large garbage such as fallen leaves and plastic bags can be captured, but most of the inflowing earth and sand cannot be prevented from flowing into the mud pool. It is also possible to make the rainwater permeate at the bottom of the dredging so that the rainwater does not stay in the mud pool. However, as time passes, the sediment deposited on the bottom prevents the rainwater from penetrating. Accordingly, the rainwater is likely to stay gradually, and the earth and sand softened by the rain are agitated by the inflowing rainwater and flow into the seepage trough connected to the mud reservoir. In order to maintain the function as an infiltration facility, it is sufficient to remove the sediment deposited on the mud pool dredging, but there are problems such as difficult maintenance.
Even if a basket is provided in a water collecting basin, that is, a mud storage basin, if the basket is made fine, the cage will be clogged in a short period of time, preventing rainwater from flowing into the basin. It needs to be rough. For this reason, large garbage such as fallen leaves and plastic bags can be captured, but most of the inflowing earth and sand cannot be prevented from flowing into the mud pool. Moreover, the earth and sand which flowed into the mud pool dredged and settles with time. Since the rainwater stays in the mud pool, it is stirred by the rainwater that flows in again, and flows into the seepage tank connected to the mud pool.
[0006]
It is also possible to make the rainwater permeate at the bottom of the dredging so that the rainwater does not stay in the mud pool. However, as time passes, the sediment deposited on the bottom prevents the rainwater from penetrating. Accordingly, the rainwater is likely to stay gradually, and the earth and sand softened by the rain are agitated by the inflowing rainwater and flow into the seepage trough connected to the mud reservoir. In order to maintain the function as an infiltration facility, it is sufficient to remove the sediment deposited on the mud pool dredging, but there are problems such as difficult maintenance.
[0007]
[Means for Solving the Problems]
The present invention has been proposed in view of the above, and the infiltration facility according to claim 1 constructs a rainwater infiltration facility with a crushed stone layer, and disposes a plurality of mud reservoirs in the same crushed stone layer. The storage tank is made of porous concrete, and a plurality of mud storage tanks are connected by pipes to allow rainwater to communicate with each other.
[0008]
Infiltration facilities aimed at controlling runoff have excessive infiltration capacity for normal rainfall, and it is rare that the facilities are filled with rainwater. Therefore, by installing a mud storage tank with high water permeability in the infiltration facility, rainwater will not stay in the mud tank during normal rainfall, and solid-liquid separation of mud in rainwater is ensured in the mud tank. Can be performed.
In addition, by installing mud pool tanks made of multiple porous concrete in the infiltration facility, the mud pool is blocked due to earth and sand and the safety against accidents that prevent the inflow of rainwater into the infiltration facility is improved. It becomes possible.
Furthermore, even with respect to rainfall intensity that may cause flooding, by arranging a plurality of mud storage tanks made of porous concrete in the infiltration facility, it is difficult for the inflowing earth and sand to diffuse.
[0009]
In the case where a concrete product or plastic product mud reservoir is provided in the crushed stone layer of the seepage facility, the size of the hole or slit is approximately 20 mm or more. It flows out to the crushed stone layer. The hole or slit may be sized so that earth and sand do not pass through, but it is not practical. In addition, measures such as covering the holes and slits with filter material are also conceivable, but the number and area of the permeated soot holes and slits are limited mainly due to strength restrictions, and the permeability of the soot is reduced by the installation of the filter material. However, rainwater tends to stay in the mud pool and the problem cannot be solved.
[0010]
According to the infiltration facility according to the present invention, the mud reservoir tank made of porous concrete holds earth and sand having a particle size of approximately 0.3 mm or more in the tank, so that most of the inflowing earth and sand remains in the tank. Become. And the upper surface of the accumulated sediment is always in contact with the porous concrete, and rainwater is difficult to stay at normal rainfall intensity, so it flows in unless the accumulated sediment volume exceeds the design sediment volume of the mud tank. There is no risk of stirring into the rainwater and flowing into another tank connected to the mud tank.
On the other hand, for rainfall intensity that may cause flooding, rainwater stays in the crushed stone layer, so rainwater also stays in the mud tank. Also in this case, since a plurality of mud storage tanks are connected by a pipe and communicated with each other, rainwater usually flows into a tank in which no sediment has accumulated, so that the accumulated sediment does not agitate. Accordingly, it is possible to prevent the rainwater penetration capacity of the seepage facility from being reduced due to the outflow of earth and sand.
[0011]
Although it is the amount of rain to be infiltrated, if Tokyo is taken as an example, there is about 1400 mm of rainfall per year, and the number of rain days is around 100 days. The average daily rainfall is around 15 mm, the average rainfall over 50 mm is around 4 days per year, and the average rainfall over 100 mm is about one day per year. However, a general infiltration facility is designed with a rainfall intensity of 50 mm / h, which is once a few years. This is a design to prevent flooding, and it is considered sufficient to study mud storage facilities usually assuming a rainfall of about 15 mm / day.
[0012]
Further, the infiltration facility according to claim 2 constructs a rainwater infiltration facility with a crushed stone layer, and a mud reservoir is disposed in the same crushed stone layer, the mud reservoir is made of porous concrete, and the mud reservoir is The rainwater infiltration facility is divided into a plurality of partitions by the partition walls, the partition walls are porous concrete, and rainwater overflowing the partition walls flows into the adjacent mud pools.
[0013]
Similar to the infiltration facility described in claim 1, even when there is rainfall intensity that may cause a flood, the mud storage tank is divided into a plurality of areas and communicated with each other, so that normal rainwater flows in. Rainwater overflowing from the mud reservoir flows into the adjacent mud reservoir where normally no sediment is deposited. Accordingly, it is possible to prevent the accumulated sediment from flowing out due to stirring, and to prevent the rainwater penetration ability of the seepage facility from being lowered.
[0014]
Further, the means of the present invention is a permeation facility in which a permeation trench is communicated with the mud reservoir, wherein a porous concrete lid or an impermeable lid is fitted to the permeation trench port. The infiltration facility according to claim 1 or 2.
[0015]
Even if rainfall intensity that may cause flooding occurs and rainwater stays in the mud tank, the trench port connected to the mud tank is fitted with a porous concrete lid or an impervious lid. Since they are combined, the earth and sand are substantially blocked, so there is no possibility that the earth and sand will flow backward. Since the crushed stone layer of the infiltration trench is in contact with the porous concrete, the movement of rainwater is not hindered even if the pipe opening is closed with an impermeable lid.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the rainwater infiltration facility according to the present invention will be described in more detail.
[0017]
As shown in FIG. 1, a rainwater infiltration facility 1 according to the present invention includes a crushed stone layer 2, a plurality of mud reservoirs 3, and a pipe 4.
As the crushed stone layer 2, conventionally known crushed stones such as No. 4 crushed stone, No. 5 crushed stone, No. 6 crushed stone, 2005 crushed stone and the like can be applied, and not limited to virgin aggregate, recycled aggregate may be used.
[0018]
The mud storage tank 3 is composed of a porous concrete side wall 3a and a bottom block 3b. The bottom block is preferably formed by dropping a bottom plate made of porous concrete into a frame made of ordinary concrete. It may be fitted into the side wall. Although the side lump in the figure is shown in a cylindrical shape, it may be a rectangular tube shape, and the shape is not particularly limited.
[0019]
Porous concrete is concrete that has been hardened and hardened so that the porosity of the hardened concrete body is approximately 5 to 30%. Generally, coarse aggregate is mixed with a binder such as cement and water. / Mixed and mixed with water so as to obtain an appropriate consistency when the cement ratio is 20 to 40%. As the coarse aggregate to be used, No. 5 crushed stone, No. 6 crushed stone, No. 7 crushed stone and 2005 crushed stone can be used.
At this time, the water permeability coefficient of the cured body is approximately in the range of 1 × 10 ⁰ to 1 × 10 ⁻³ cm / s, and the bending strength is approximately in the range of 1.5 to 6 N / mm ² .
[0020]
The pipe 4 connects a plurality of mud reservoirs and communicates with each other. Such a pipe may be any of general concrete, porous concrete, and plastic, and the material is not particularly limited as long as a predetermined strength is satisfied.
[0021]
The rainwater infiltration facility 1 ′ according to the present invention shown in FIG. 2 includes a crushed stone layer 2 and a mud reservoir 3 ′. Moreover, in this figure, it is an infiltration facility with which an infiltration trench is communicated, an infiltration trench tube 4 'is communicated with a mud reservoir 3', and a lid 5 is fitted to the mouth of the infiltration trench tube.
[0022]
The mud reservoir 3 'is composed of a plurality of mud reservoir portions 3'a and a bottom lump 3'b partitioned by a porous concrete partition wall 3'c, and the bottom lump is made of porous concrete in a frame made of ordinary concrete. It is preferable that the bottom plate is dropped, but a porous concrete plate may be directly fitted into the mud reservoir.
[0023]
A trench pipe has a perforated or water-permeable gap, and a facility that allows rainwater collected through crushed stone to penetrate into the ground is called an infiltration trench. The lid of the trench pipe is a porous concrete lid or a water-impervious lid, but the material of the water-impervious lid may be any of plastics, rubber, ordinary concrete, etc. The material is not particularly limited as long as it is present.
[0024]
According to the rainwater infiltration facility having such a configuration, most of the earth and sand flowing into the mud storage tank made of porous concrete remains. The top surface of the sediment is always in contact with the porous concrete, and it is difficult for rainwater to stay at normal rainfall intensity. Therefore, as long as the sediment volume does not exceed the tank's designed sediment volume, There is no risk of stirring and flowing into another tank connected to the mud tank.
On the other hand, even when the rainfall intensity is such that there is a risk of flooding, the rainwater usually flows into a tank in which no sediment has accumulated, so the accumulated sediment does not agitate. Therefore, it is possible to prevent the rainwater penetration ability of the facility from being reduced due to the outflow of earth and sand.
[0025]
In addition, when the infiltration trench is communicated, there is no possibility that the earth and sand will flow backward. Therefore, the frequency of maintenance can be reduced, the rainwater penetration capability can be maintained over a long period of time, and a larger amount of rainwater penetration can be ensured.
[0026]
【Example】
A rainwater infiltration facility having a mud reservoir shown in FIG. 1 was implemented. First, after excavating the Kanto loam layer into a tetrahedron shape with a width of 4m x 4m and a height of 1.5m, an in-situ penetration test was conducted, and the permeability coefficient of the local board was 2 x 10 ^-4 cm. / S.
Next, it was backfilled with No. 4 crushed stone to a height of 40 cm from the bottom, and four side lumps made of cylindrical porous concrete having an inner diameter of 50 cm and a height of 60 cm were appropriately disposed on the upper surface of the crushed stone. The side lumps were drilled around a point 30 cm below the top, and four side lumps were connected by a pipe having an inner diameter of 100 mm. Further, a bottom lump made of porous concrete was fitted into the side lump to form a mud reservoir.
Again, between the outer periphery of the side lump and the excavation layer was backfilled with No. 4 crushed stone to the top of the side lump to make an infiltration facility.
[0027]
The material and composition of porous concrete are shown.
Cement: normal Portland cement, density = 3.16 g / cm ³
Coarse aggregate: No. 6 crushed stone, density = 2.64 kg / L
Target porosity: 25%, W / C: 28%
Unit amount (kg / m ³ ) = water: 84, cement: 300, coarse aggregate: 1507
[0028]
Separately from the above facility, 1 m ³ of muddy water containing 5 kg of mud (maximum particle size 5 mm) was injected over 1 hour from above the mud reservoir made of porous concrete. The turbid water that soaked out from the side and bottom masses was received in the water tank, and the amount and particle size of the mud flowing into the crushed stone layer from the mud reservoir were investigated.
As a result, it was estimated that about 5% of the mud flowed out of the mud reservoir made of porous concrete, and the maximum particle size was approximately 0.3 mm.
[0029]
Based on the Rainwater Infiltration Facility Technical Guidelines (Draft) Survey and Planning, find the unit design infiltration amount for the above infiltration facilities. Here, the design head H is set to 0.9 m.
Unit design penetration amount Q = 0.81 × 3600/100 × 2 × 10 ⁻⁴ × 26.68 = 0.156 m ³ / hr.
Also, assuming that the gap of crushed stone is 40%, the amount of storage Q 'of the facility is roughly 40% of the facility volume.
That is, the amount of storage in the facility is Q ′ = 16 × 0.4 = 6.4 m ³ .
Therefore, the stored infiltration amount Qt of the infiltration facility is Qt = Q + Q ′ = 6.556 m ³ / hr.
The present facility, it is possible to stormwater area of approximately 130m ^2. (Rain strength i = 50mm / hr)
[0030]
Rainwater Infiltration Facility Technical Association (Rainwater Infiltration Facility Technical Guidelines (Draft) Survey and Plan) From rainwater turbidity concentration of 74.8mg / L (Housing and Urban Development Corporation document) 1400mm / year in Tokyo area It is necessary to expect the amount of sedimentation of × 130 m ² × 7.48 mg / L = 13.6 kg / year.
[0031]
2 m ³ of muddy water containing 15 kg of mud (maximum particle size 5 mm) (15 mm / day equivalent to rainfall) was injected from above the mud reservoir 31 over 24 hours. During this test, turbid water was retained in the crushed stone without turbid water remaining in the tub and without flowing turbid water from the mud tank 31 into another mud tank.
Further, after about 1 day, 6.6 m ³ of turbid water (turbidity concentration was adjusted to about 100 mg / L) was poured into the mud tank over about 1 hour. The water level of the tank rose on the way, and muddy water began to flow from the mud reservoir 31 into another tank 32.
[0032]
The day after the test, the turbid water in the infiltration facility was infiltrated, and after the water level was not confirmed in the tub, the mud deposited in each tank was visually observed. As a result, accumulation of earth and sand was observed in the tank 32, but there was almost no accumulation of earth and sand in the tanks 33 and 34.
[0033]
[Comparative example]
As in Example 1, the Kanto loam layer was excavated into a tetrahedron shape so as to have a size of 4 m × 4 m and a height of 1.8 m. In addition, the hydraulic conductivity of the local board was estimated to be equivalent.
Next, it was backfilled with No. 4 crushed stone to a height of 40 cm from the bottom, and one cylindrical permeable perforated rod having an inner diameter of 50 cm and a height of 120 cm was disposed. Again, the space between the outer periphery of the fence and the excavation layer was back-filled so as to have the same crushed stone height (1 m) as in Example 1 to obtain an infiltration facility. Further, a bottom punch having an inner diameter of 50 cm and a height of 60 cm was installed on the upper surface of the crushed stone, drilled around a point 30 cm lower than the top, and connected to a perforated hole with a PVC pipe having an inner diameter of 100 mm. The upper surface of the crushed stone was covered with a water-permeable sheet and backfilled with generated soil, which was used as an infiltration facility.
[0034]
In the same manner as in Example 1, 2 m ³ of muddy water (15 mm / day equivalent to rainfall) containing 15 kg of mud (maximum particle size 5 mm) was injected over 24 hours from the top surface of the bottom pit. During this test, in the bottom pit, it could not be infiltrated, and after flowing into the permeable perforated pit, it was stored and infiltrated in the crushed stone. At this point, about half of the amount of earth and sand of the example was observed in the bottom pit. There was almost no sediment accumulation in the perforated pits.
Further, after about 1 day, 6.6 m ³ of turbid water (turbidity concentration was adjusted to about 100 mg / L) was poured into the above bottom culm over about 1 hour. In the bottom pit, it was not possible to perform the permeation treatment, and the water level of the perforated trough also rose after flowing into the permeable perforated trough.
[0035]
The day after the test, the turbid water in the infiltration facility was infiltrated, and after the water level was not confirmed in the tub, the mud deposited in each tub was visually observed. As a result, most of the earth and sand accumulated in the bottom-through pit flowed out into the perforated pit, and the earth and sand in the osmotic and perforated pit was about ½ of that in Example 1 and the rest flowed into the crushed stone. it is conceivable that.
[0036]
As a result of flowing about 1 year's worth of earth and sand into the mud reservoir Example 5 About 5% of the earth and sand flowed into the crushed stone layer.
Comparative Example About half of the earth and sand flowed into the crushed stone layer.
In this test, no decrease in infiltration capacity has been confirmed, but due to the difference in the amount of sediment that has flowed in, it is expected that the infiltration capacity will be significantly decreased in the comparative example over the long term.
In the rainwater infiltration facility of the embodiment, the permeation capacity is maintained in the long term by discharging earth and sand about once a year.
[0037]
As mentioned above, although this invention was demonstrated based on the Example, this invention is not limited to an Example, It can implement in any way, unless the structure described in the claim is changed.
[0038]
【The invention's effect】
As described above, according to the rainwater infiltration facility having the mud reservoir according to the present invention, it is possible to prevent sediment from flowing into the crushed stone layer of the infiltration facility, and to prevent a decrease in rainwater infiltration capability. It becomes possible. Therefore, rainwater can be infiltrated for a long time without increasing the frequency of maintenance.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a configuration of an embodiment of a rainwater infiltration facility according to the present invention.
FIG. 2 is a perspective view showing a configuration of an embodiment of a rainwater infiltration facility according to the present invention.
[Explanation of symbols]
1 Rainwater infiltration facility 2 Crushed stone layer 3 Mud reservoir layer 3a Side wall 3b Bottom lump 4 Tube 1 'Rainwater infiltration facility 2' Crushed stone layer 3 'Mud reservoir layer 3'a Mud reservoir 3'b Bottom mass 3'c Bulkhead 4 'seepage trench tube 5 lid 31 one of a plurality of mud reservoir layers 32 one of a plurality of mud reservoir layers one of a plurality of mud reservoir layers 34 one of a plurality of mud reservoir layers

Claims (3)

A storm water infiltration facility is constructed with a crushed stone layer, and a plurality of mud reservoirs are arranged in the same crushed stone layer, and the mud reservoir is made of porous concrete. A rainwater infiltration facility characterized by the communication of water. A rainwater infiltration facility is constructed with a crushed stone layer, and a mud reservoir is installed in the same crushed stone layer. The mud reservoir is composed of porous concrete, and the mud reservoir is divided into a plurality of partitions. The rainwater infiltration facility is characterized in that rainwater overflowing the partition wall flows into the adjacent mud reservoir. 3. A permeation facility in which a permeation trench is communicated with the mud reservoir, wherein a porous concrete lid or a water-impermeable lid is fitted to the permeation trench port. Infiltration facility.

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