JPH09158161A - Method and equipment for draining underground drain pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the damage of a distributing pipe even at the time of a large quantity of precipitation at comparatively low cost, and to maintain drainage capacity by a pipeline by installing an air vent device, from which air is not flowed back, on the upper side of a bend. SOLUTION: An air vent device is composed of a top plate 9 in the bend of an underground drain pipe, a box mounted on the upper side of the top plate 9 and made of concrete, a pressure pipe communicating both top plate 9 and box, and a combustion hole 4, etc., drying clay 10 packed into the box made of concrete. When a pipeline is filled with drain by a large quantity of precipitation, air remaining in a bend section is discharged from the air vent device to the outside of the pipeline. Consequently, since an air reservoir is removed in the pipeline, water is drained by a total cross section. The pipeline is worked as a siphon at that time, and drainage discharge is increased suddenly. Accordingly, even when there is a large quantity of precipitation, a back flow and the damage of the pipeline are not generated by the air reservoir, and drainage capacity under the state of a total sectional flow can be maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rainwater drainage facility in a surrounding area such as a house or a cleaning plant site, where rainwater permeates into the ground, and the permeated underground water is trapped to induce drainage. The present invention relates to a drainage method and device using a drainage pipe (underdrain).

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional underground drainage pipe.
In underground drainage pipes that have curved pipes (or bent pipes, the same applies below), the design flow rate of drainage is extremely small and
The tube diameter is empirically designed to be large so that air flows through the upper part of the tube (30 to 50% of the cross-sectional area).

However, when there is a large amount of precipitation, the inside of the pipe is rapidly filled with water, and due to the rapid rise of the water level, the air accumulated at the hydraulic highest point (convex portion) in the pipe is compressed and the flowing water is obstructed. When this compressed air escapes inside the pipe, it causes a backflow, and the running water overflows, which may damage the underground drainage pipe.

Explaining this phenomenon in more detail, the underground drainage pipe in the conventional rainwater drainage system has the following drawbacks when a large amount of precipitation occurs. (1) The drainage pipe at a relatively deep position or the drainage pipe under the slope of the surrounding area such as the site of a cleaning plant has a relatively low velocity, and the flowing water in the curved pipe connected to it has a high velocity. The air is compressed by the piston action into the bent pipe. Since compressed air is light, it bends and accumulates at the highest hydraulic point (convex) in the pipe, causing surging. (2) Furthermore, because compressed air has no escape,
Water with a full cross-sectional flow is caused to flow backward toward the rainwater cell, which is located in a direction with relatively little resistance and shallower than the curved pipe, and overflows from the rainwater cell, damaging underground pipes.

These phenomena will be described in more detail. As a phenomenon, a few air pockets are compressed many times and become extremely high pressure, there is no place to escape, so go back up the bent pipe,
It is a phenomenon that causes the flow to flow backward, and there is a large amount of air mixed into the underground drainage pipe ahead of the rainwater chamber, and the flow is obstructed by the large amount of air, and the reverse flow does not occur.

Whether air is mixed or not is a hydraulic problem that comes from the structural shape of the underground drainage pipe.
Even if there is a high possibility that air will be mixed, the water pressure is very high, so it is only a problem if the structure of the underground drainage pipe is complicated and it can not escape once air enters. Occurs, and in other cases, there is no problem even if the air is in contact with a large area. That is, the underground drainage pipe has a structural shape that cannot escape once it enters, which causes an aeration problem of the underground drainage pipe.

In order to prevent such a problem, there is an example in which the underground drainage pipe is provided with an air vent. FIG.
FIG. 4 is a diagram showing a typical configuration of a manhole having a step connection on an underground drainage pipe or on a steep slope of the ground surface. In this example, the air entrapped at the step junction 32 returns upward through the auxiliary pipe 31, and is discharged from the manhole 30 into the atmosphere.
The manhole 30 is installed only in a special place such as a confluence part or a step part of the pipeline. Since the air is exhausted from the manhole part, the above-mentioned backflow phenomenon does not occur. However, this method causes a large amount of construction work, which causes a problem in terms of cost.

[0008]

In the drainage method using the underground drainage pipe, when there is a large amount of precipitation, the inside of the pipe rapidly fills up, and the water level rises sharply. The air trapped in is compressed and the running water is blocked. When this compressed air escapes in the pipe, it causes a backflow, and the flowing water overflows, which causes a problem of damaging the pipe.

[0009] Although such a problem does not occur in a manhole having a step connection, it requires a large amount of work, which causes a problem in terms of cost.

It is an object of the present invention to provide an underground drainage method / apparatus capable of preventing the drainage pipe from being damaged at a relatively low cost and maintaining the drainage capacity by the pipeline even when there is a large amount of precipitation.

[0011]

[Means for Solving the Problems] The above-mentioned problems consist of a closed underground drainage pipe having at least one bent pipe portion, and an air venting means for discharging the air accumulated in the underground drainage pipe to the outside of the drainage pipe. This is a drainage method, and the air venting means does not allow air to flow backward, and is solved by a drainage method characterized in that the bent pipe portion is a siphon. Also, the drainage method is characterized in that the attachment portion of the air venting means is the highest hydraulic point of the underground drainage pipe.

The apparatus according to the present invention removes air that is trapped in a closed underground drainage pipe having at least one bent pipe portion and the air accumulated in the underground drainage pipe to the outside of the underground drainage pipe. After that, the drainage device is characterized by having an air vent device having a structure that does not allow air to flow backward. Further, the air venting device is a drainage device characterized in that it is composed of a unglazed cup and clay.

When a pipeline is filled with drainage due to a large amount of precipitation, the air remaining in the bent pipe portion hinders the drainage capacity of the pipeline. Since the pressure of the air filled in the pipeline increases, the accumulated air is discharged from the air venting means to the outside of the pipeline. The pipeline will be free of air traps, so drain the entire cross section. At this time, the pipeline works as a siphon, and the drainage flow rate increases rapidly. When the flow of the pipe becomes a siphon flow, and when the pipe becomes a siphon, the pressure head of the pipe does not rise, the pressure balances at the interface between water and air, and the cross-sectional area of the flow decreases, so it is pushed up once. The trapped air tries to flow back into the pipeline. The backflow preventing means does not generate backflow of air to the pipeline, and the siphon flow state is maintained, so that the pipeline has the maximum drainage capacity.
Therefore, even if there is a large amount of precipitation, backflow and damage to the pipeline are not caused by this air pool, and the drainage capacity in the entire cross-sectional flow state can be maintained.

Since the air in the pipe line gathers at the highest hydraulic point of the bent pipe portion, the air trapped is quickly exhausted by providing the air venting means here.

When the air vent is composed of a unglazed cup and clay, the accumulated air rises in the pressure head in the bent pipe, and in the pressure pipe connected to the unglazed cup embedded in the clay, By forming a column of pressure water, it is lifted from inside the bend to the unglazed cup. Immediately after that, the water in the unglazed cup passed through a small gap in the porous material of the unglazed cup and became a capillary.
As it permeates, the lifted air is compressed more and more, and the small gaps in the porous material are very small pores, so the very large capillary forces will entrap the air in a more orderly manner than in clay. And while sucking up, into the very small gaps that are numerous in clay,
It is rapidly taken in together with soil water (it becomes entrapped air in clay). The air in the unglazed cup is aspirated and, through the pressure tube, the compressed air pool that obstructs the running water is eliminated from inside the bend tube. The flow 17 having a low flow velocity in the bent pipe portion constituted by the top plate 9 of the bent pipe is replaced with a siphon flow, and the drainage flow rate is increased at a stretch in response to a large amount of water discharged during abnormal rainfall, and the flow is dropped at a stretch.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a vertical cross-sectional view showing an embodiment of a buried structure of a drainage device according to the present invention, and FIG. 2 is an enlarged cross-sectional view of an air vent device of the drainage device (enlarged view of portion a in FIG. 1).

The buried structure of the drainage device according to this embodiment is
First, rainwater basin 1, U-shaped underdrain (or round underdrain) 8,
And a top plate 9 of a bent tube. Covering layer 3 for covering underground drainage pipes (including perforated drainage pipes), trench-shaped protective filter layer 2 for buried cross-section, underground drainage pipe foundation that withstands sediment outflow and differential settlement and supports underground drainage pipes It is composed of 7 etc.

Further, the air venting device of the drainage device comprises a top plate 9 of the bent pipe of the underground drainage pipe, a concrete box 16 installed on the upper side thereof, and a pressure pipe 1 connecting both of them.
5, a combustion hole 4 for drying the clay 10 packed in a concrete box 16, and a packing 11 for sealing the combustion hole 4 for dropping fuel in an emergency and a sled 13. The clay 10 has a unglazed cup (cross section). Is an arbitrary shape), and a negative pressure (suction) is generated in the negative pressure generating hole 5 in the unglazed cup, and the pressure hole 6 is connected to the air vent hole (with mud guard) 19 of the top plate 9 of the bent tube. It is composed of

Next, the operation and effect of the underground drainage constructed as described above will be described. [Regarding Air Mixing and Air Removal] The present invention can reduce the pipe diameter of the underground drainage pipe 8 only in the portion ahead of the rainwater chamber, but when the abnormal rainfall starts and continues. The incoming air always passes through the rainwater chamber and is blocked and removed in the rainwater chamber space, so the air accumulated in the underground drainage pipe beyond that is accumulated when the abnormal rainfall starts. There is only air in the bend tube, and the amount of air that must be removed by the air bleeding device will be only the volume of a small air pool in the bend tube under atmospheric pressure.

The pressure on the surface of the water flowing through the underground drainage pipe is always atmospheric pressure, but the flow in the curved pipe is obstructed by the compressed air pool, stays, and the flow velocity becomes very high in the process of turning from the forward flow to the reverse flow. It becomes smaller, the pressure of water in the bent pipe increases, the cross-sectional area of flowing water expands, and the air pool is compressed more and more. The pressure head in the bent pipe rises and becomes a pressure water column, and through the air vent hole at the top of the pipe, through the pressure pipe above the bent pipe, the unglazed cup 14 embedded in the clay.
Lift the air inside. Immediately after that, the water in the unglazed cup begins to penetrate into the clay 10 by capillary force through the small gaps of the porous material of the unglazed cup, and the soil water in the clay having a high air entry value that easily contains air. Becomes Since the composition of the unglazed cup is exactly the same as that of soil water, the water in the unglazed cup receives a large negative pressure (suction) and is continuously sucked until a balanced state is reached. Therefore, for a long time, all the compressed air pools are continuously removed from the inside of the bent pipe, and the bent pipe portion of the underground drainage pipe operates as a siphon that uses the flow in the bent pipe as a siphon flow.

[Necessity of the Air Venting Device to Operate Only Once] Since the rainwater chamber is basically a chamber in which rainwater from the ground is collected, air from the ground is mixed, and depending on the amount of air. There is a great possibility that air will be mixed from the rainwater chamber to the underground drainage pipe.

However, in the underground drainage pipe in which the air trap is removed by the air bleeding device and the siphon flow forms a siphon, the water pressure is 1.
The air pressure is very high at about 5 atm, and even if air from the rainwater chamber tries to mix in, due to the fact that it is a full-section flow and the high pressure, the mixing of air is in the state of boil. Boundary lines are limited to those that go in and out of the bottom of the rainwater basin, and air cannot be recreated by mixing air up to the bend pipe.

Therefore, the air mixed in from the rainwater chamber only for a short distance is pushed back again by the high water pressure and does not become an air pool, and it is necessary to consider the mixing of air during the abnormal rainfall continues. There is no. Inevitably, when air is mixed in, abnormal rain has already ended,
Since the water pressure in the bent pipe is 1.0 atm, which is equal to the atmospheric pressure and the flow rate is decreasing, the underground drainage pipe has a space (airway) through which air again passes. Therefore, it is not necessary for the function of sucking / removing the air pool of the air vent device to work, and air may be mixed.

Only when the abnormal rainfall starts and the entire cross-section flow is about to start, it is only necessary for the air venting device to work once, and during the subsequent abnormal rainfall, air is not mixed. Since it does not exist, the air venting device does not need to work, and naturally, even when the abnormal rainfall ends, the air venting device does not need to work.

[Regarding the Action of Clay] Above the curved pipe of the underground drainage pipe, a concrete box having a combustion hole is installed, and the box is filled with clay having a large amount of fine-grained soil. . This clay is kept dry except when it is raining, and when heavy rain is to be warned, fuel is dripped from the combustion holes and burned to dry. It is protected by being distinguished from other covering layers of underground drainage pipes. The water rises due to the rise of the pressure head from the underground drainage pipe, so that the water comes up and comes into contact with it, so that a large negative pressure (suction) works inside the unglazed cup. The bent pipe part is connected to the top of the underground drainage pipe by a pressure pipe, and through the air vent hole at the top of the pipe, the compressed air pool that obstructs the flow in the bent pipe is pushed up and eliminated, so that the bent pipe part Operates as a siphon with flow as siphon flow.

[0026]

【The invention's effect】

(1) The compressed air accumulated in the curved pipe is removed by a simple method of installing an air vent device on the upper side of the curved pipe so that the air does not flow backward, and the flow in the curved pipe is changed to a siphon flow to increase the drainage flow rate all at once. , By draining it all at once, the drainage flow rate of the underground drainage pipe (perforated drainage pipe) is increased, and the water permeability around the drainage pipe is increased. Improve the rainwater drainage function.

(2) By removing the compressed air pool from the inside of the curved pipe, the flow of water is prevented, and there is no escape, and the rainwater basin is located at a position shallower than the curved pipe in a direction with less resistance than that of the curved pipe. As a result, the probability of overflow of running water to the ground (overflow rate) is reduced.

(3) By removing the compressed air accumulated in the curved pipe and obstructing the flowing water, the flowing water is prevented from being disturbed, and the compressed air is extremely violent toward the rain basin located at a position shallower than the curved pipe. Damage to the drain of the underground drainage pipe when escaping (breaking through the entire cross-sectional flow state) is prevented.

(4) For the underground drainage pipe in the rainwater drainage facility, it is necessary to remove the compressed air from the inside of the bent pipe and make the flow into a siphon flow state so that the air always flows in the upper part of the pipe. In general, the cross-sectional area of air is 50 to 70% of the cross-sectional area of the pipe, and thus the cross-sectional area of the pipe can be significantly reduced.
It is economical.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a drainage device according to the present invention.

FIG. 2 is an enlarged cross-sectional view of an air vent portion of the drainage device according to the present invention.

FIG. 3 is a cross-sectional view showing a buried structure of a conventional underground drainage work.

FIG. 4 is a sectional view showing a buried structure of a conventional underground drainage work.

[Explanation of symbols]

 1 Rainwater basin 2 Filter layer 3 Coating layer 4 Combustion hole 5 Negative pressure generation hole 6 Pressure hole 7 Underground drainage pipe foundation 8 U-shaped underdrain (or round underdrain) 9 Bent pipe (or bent pipe) top plate 10 Clay 11 Seal Packing 12 Backfilling Soil 13 Plug 14 Unfired Cup 15 Pressure Tube 16 Concrete Box 17 Bending Pipe (or Bending Pipe) Flow 18 Air Reservoir 19 Air Venting Hole (with Mudguard) 30 Manhole 31 Sub-pipe 32 Step Joint 33 A steep slope with a ground slope

Claims (5)

[Claims] 1. A drainage method comprising a closed underground drainage pipe having at least one bent pipe portion and an air venting means for discharging the air accumulated in the underground drainage pipe to the outside of the underground drainage pipe, A drainage method characterized in that the air bleeding means does not allow air to flow backward, and the bent pipe portion is a siphon. 2. The drainage method according to claim 1, wherein the attachment portion of the air venting means is the highest hydraulic point of the underground drainage pipe. 3. A closed underground drainage pipe having at least one bent pipe portion, and a structure for removing air accumulated in the underground drainage pipe to the outside of the drainage pipe and preventing backflow of air after the air is removed. The drainage device, which has the air vent device. 4. The drainage device according to claim 3, wherein the air venting device is composed of a unglazed cup and clay. 5. The drainage device according to claim 3, which is a closed structure in which the air vent device and the bent pipe portion are integrally formed.