JPH09324414A - Drain hole for preventing ground liquefaction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a percolation tube against clogging due to the penetration of water in a normal case, or prevent the drop of a ground water level, regarding measures against the liquefaction of the poor subsoil G using the percolation tube. SOLUTION: A percolation tube 11 as well as a water storage pit 13 thereunder is provided in the poor subsoil G, and a water stop tube 16 to stop water from the internal surface of the percolation tube 11 is held on a support plate 14 positioned so as to close the upper end opening of the water storage pit 13, and a weight pendulum 18 is suspended from a cover 12 via a suspending member 17 above the support plate 14. When an earthquake takes place and the vibration angle of the pendulum weight 18 resonating therewith exceeds the preset angle, a suspension state with the suspending member 17 is released and the pendulum weight 18 drops, thereby braking the support plate 14. As a result, the water stop tube 16 drops as well and a water stoppage state around the internal surface of the percolation tube 11 is released. Then, excessive gap water in the poor subsoil G is introduced to the water storage pit 13 through the percolation tube 11, thereby preventing the liquefaction of the poor subsoil G.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drainage hole for draining excess pore water generated in the ground in order to prevent a disaster caused by liquefaction of soft ground when an earthquake occurs.

[0002]

2. Description of the Related Art A large earthquake occurs because the ground of a landfill and the soft ground with a relatively high groundwater level consisting of a sandy soil layer containing a large amount of sand and clay have a small shear resistance against horizontal displacement. Occasionally, excessive pore water pressure is generated between soil particles below the groundwater level, causing groundwater liquefaction such as groundwater being blown up to the surface along with sediment, which may lead to disasters such as collapse of structures such as buildings. There is. As a conventional technique for preventing the liquefaction of soft ground due to such an earthquake, as shown in FIGS. 7 and 8, a permeable water composed of porous concrete in the soft ground G where liquefaction may occur. There is a method in which a vertical shaft-shaped drainage hole 1 is formed by burying the pipe 1a to prevent the excessive pore water pressure from being generated by draining the soft ground G.

Of these, the so-called water permeable manhole method shown in FIG. 7 is used to drain excess pore water in the ground G caused by an earthquake or the like through a large number of minute water permeable holes formed in the water permeable pipe 1a. To the sewage pipe or the rainwater pipe 2 from there. The so-called groundwater level lowering method shown in FIG.
The excess pore water flowing into the drainage hole 1 via a is collected in a pit 1b provided at the lower end of the drainage hole 1,
This is pumped up by the pump 3 and drained.

[0004]

According to the above-mentioned prior art, since groundwater and rainwater at the time of rainfall always flow into the drainage hole 1, the drainage hole 1 is connected to the sewer pipe or the rainwater pipe as shown in FIG. 2 or by installing the pump 3 as shown in FIG.
There is a problem that it is not effective and its maintenance is expensive. Moreover, the minute water permeation holes of the water permeation pipe 1a are clogged with time due to a small amount of earth and sand contained in the groundwater or rainwater that constantly intrudes, and excess pore water can be quickly taken in when an earthquake actually occurs. You may not be able to. Further, in any of the methods, since the groundwater level GWL in normal times is lowered, there is a problem that the water level of this well is lowered when there is a well nearby.

The present invention has been made under the circumstances as described above, and its technical problem is to provide a permeable pipe by permeable under normal conditions as a countermeasure against liquefaction of soft ground using a permeable pipe. It is to prevent the clogging of the groundwater and prevent the groundwater level during normal times from being unnecessarily lowered.

[0006]

The above-mentioned technical problems are as follows.
The present invention can effectively solve the problem. The liquefaction prevention drainage hole of the ground according to the present invention, in the soft ground,
A water-permeable pipe whose upper end is sealed with a lid and a water storage pit located below it are installed, and a support plate is arranged so as to close the upper end opening of this water storage pit, and the inner circumference of the water-permeable pipe is placed on this support plate. It has a structure in which a water-stop pipe for stopping water is supported, and a weight pendulum is suspended and supported by a suspension member in a space above the support plate. Then, when an earthquake occurs, when the vibration angle of the pendulum swinging by this exceeds a predetermined magnitude, the suspended state of the pendulum by the suspension member is released and the pendulum falls, Destroy the support plate. For this reason,
When the water stop pipe supported on the support plate falls, the water stop state of the inner circumference of the water permeable pipe is released, and the pore water in the ground is drained to the water storage pit through this water permeable pipe. In addition,
A water permeable pipe is a drainage pipe made of a porous material in which an extremely large number of fine water permeable holes are formed by open cells or the like, or a material in which a large number of small holes are formed to give water permeability in the thickness direction. Say.

That is, according to the present invention, since the inner circumference of the water permeable pipe is normally stopped by the water stop pipe, groundwater and rainwater do not constantly flow from the surrounding soft ground through the water permeable pipe. Therefore, the water permeation hole of the water permeation pipe is not clogged, and it is not necessary to constantly drain the drainage hole. In the event of a large earthquake, the weight pendulum, which detects this, drops the water-stopping state of the inner circumference of the water-permeable pipe due to the water-stopping pipe, so excess pore water generated in the ground due to the earthquake It is possible to effectively prevent the liquefaction of the ground by draining it into the water storage pit through the water permeable pipe.

More preferably, in the present invention, the suspension weight length of the weight pendulum is set so as to resonate in the frequency band in which the maximum vibration acceleration of an earthquake occurs. In addition, a breaking guide groove is formed on the support plate and the water shutoff pipe to facilitate breaking.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a drainage hole 10 according to the present invention, which is considered to be the best. Reference numeral G indicates that shear resistance against horizontal displacement is small and liquefaction may occur during an earthquake. A soft ground, GWL, is the groundwater level in this soft ground G. The drainage hole 10 is installed in such a soft ground G in a buried state, and has a cylindrical water permeable pipe 11 and an iron lid 12 for sealing the upper end opening thereof.
And a bottomed cylindrical water storage pit 13 installed below the water permeation pipe 11, and the outer peripheral portion is sandwiched between the upper edge of the water storage pit 13 and the lower end edge of the water permeation pipe 11.
The disk-shaped support plate 14 arranged so as to close the upper end opening of No. 3, and the disk-shaped support plate 14 inserted into the inner periphery of the water permeable pipe 11 and supported on the support plate 14 through the annular packing 15 made of an elastomer such as rubber. A cylindrical water stop pipe 16 and a weight pendulum 18 suspended above the support plate 14 via a suspension support member 17 are provided on the lid 12. Further, a filter layer 19 made of pebbles or crushed stone is formed around the water permeable pipe 11, and preferably an annular packing (not shown) is interposed between the upper end edge of the water permeable pipe 11 and the lid 12. To be done.

The water permeable pipe 11 is made of porous concrete having an extremely large number of fine water permeable holes made of open cells, and the water storage pit 13 is made of water impermeable concrete. The support plate 14 is made of unreinforced concrete, and the required number of ventilation holes 14a are opened,
As shown in FIG. 2 (A), an X-shaped destruction guide groove 14b is provided on the upper surface, and on the lower surface in the circumferential direction along the upper inner circumferential surface of the water storage pit 13 as shown in FIG. 2 (B). A continuous fracture guide groove 14c is formed in the groove, and when the weight 182 to be described later is dropped, it is easily broken along the fracture guide grooves 14b and 14c when it is hit in the thickness direction (downward). Has become. The water shutoff pipe 16 is formed of non-permeable concrete and has a large number of fracture guide grooves 16a intersecting in a lattice pattern on its inner peripheral surface, as shown in FIG.
This destruction guide groove 1 when it receives a predetermined impact from falling
It is designed to be easily broken along 6a.

As shown in FIG. 4 (A), the suspension support member 17 is
The case 171 and the cover 171 of the water permeable pipe 11
2, a bolt 172 for fixing the lower surface of the case 2, a ball bearing 173 housed in the case 171, and a shaft portion at an upper end thereof is inserted into the lower surface of the case 171 substantially vertically and horizontally rotated by the ball bearing 173. And a suspension ring 174 that is supported as much as possible. Further, the weight pendulum 18 has a hook 181 that engages with the suspension ring 174 at the upper end.
The hanging rod 181 having a formed therein and a spherical weight 182 attached to the lower end of the hanging rod 181.

The suspension length L from the hook 181a of the weight pendulum 18 to the center of gravity is set so that the weight pendulum 18 resonates in the frequency band in which the maximum acceleration of seismic waves occurs. Here, the cycle of the seismic wave acceleration on the soft ground G is T (second), and the gravity acceleration is g (= 9.8 m / T).
² ) and the pi is π, the suspension length L is calculated by the following formula: L = g · T ² / (4π ² ). Since the period T of the maximum acceleration of the seismic wave in the usual soft ground is about 1 second, the suspension length L is typically set to about 25 cm from the above formula. In addition, the weight of the weight 182 is determined by the height of the suspension support from the supporting plate 14
It is determined in consideration of the destructive force on the support plate 14 when it is allowed to fall freely, and is set to, for example, about 2 kgf.

FIG. 4 viewed from the direction of arrow B in FIG.
As shown in FIG. 4B, the hooks 181a have a doubled shape in parallel. Therefore, the vibration direction of the weight pendulum 18 relative to the suspension ring 174 is in a direction orthogonal to the cross section shown in FIG. 4B. Although stipulated, since the suspension ring 174 itself can be horizontally swung by the ball bearing 173, the weight pendulum 18 can vibrate in any direction corresponding to the input direction of the acceleration of the seismic wave. Also, the hanging ring 17
An interference portion 174a with which the lower portion of the hook 181a is brought into contact with the vibration movement of the weight pendulum 18 is formed in the lower portion of 4, and in the half cycle in which the lower portion of the hook 181a and the interference portion 181b come into contact with each other. , As shown by the one-dot chain line in FIG.
When the hook 181a and the suspension ring 174 slide on each other with the interference portion 174a as a fulcrum, and the vibration angle θ of the weight pendulum 18 becomes a predetermined value or more (for example, θ> 10 °), the hook 181a moves from the suspension ring 174 by the sliding. It comes off, and the weight pendulum 18 falls.

According to the drainage hole 10 for preventing liquefaction having the above-mentioned embodiment, since the inner circumference of the water permeable pipe 11 is normally stopped by the packing 15 and the water stop pipe 16, the surrounding soft ground G. Groundwater and rainwater do not constantly flow in through the permeable pipe 11 from the
It is blocked by the lid 12. Therefore, the filter layer 19
The fine water-permeable holes of the water-permeable pipe 11 do not become clogged due to the intrusion of earth and sand, and the drain hole 10 does not need to be constantly drained by a pump or the like. Further, since the groundwater level GWL is maintained, even if there is a well nearby, the water level of this well will not drop.

When an earthquake occurs, the weight pendulum 18 in the drainage hole 10 resonates with the input seismic wave and makes a pendulum motion around the engaging portion of the suspension ring 174 of the suspension support member 17 and the hook 181a. The vibrating surface of the weight pendulum 18 in this case follows the seismic wave input direction by the turning of the suspension ring 174 by the ball bearing 173.

When the seismic acceleration of the soft ground G due to the seismic wave has a magnitude that may cause a liquefaction phenomenon, the vibration angle θ of the weight pendulum 18 increases accordingly.
As described above, the hook 181 a disengages from the hanging ring 174 due to the large sliding of the hook 181 a and the hanging ring 174 with the interference portion 174 a as a fulcrum. Therefore, the weight pendulum 18 falls and the support plate 1 below the weight pendulum 18 falls.
6, a portion other than the outer peripheral portion sandwiched between the upper edge of the water storage pit 13 and the lower edge of the water permeable pipe 11 is broken along the breaking guide grooves 14b and 14c by the collision of the weight 182, and FIG. As shown in FIG. 3, the fan-shaped fragments 14 ′ fall into the water storage pit 13 together with the weight pendulum 18. Then
The water stop pipe 16 supported on the support plate 14 through the packing 15 also loses the support means due to the breakage of the support plate 14, and therefore falls into the water storage pit 13, and due to the impact at this time,
The pieces are broken along the lattice-shaped breaking guide grooves 16a to form a large number of pieces 16 '.

When the water stop pipe 16 falls, the water stop state of the inner circumference of the water permeate pipe 11 is released, so that the seismic energy is given between the soil particles of the soft ground G, and the pore water whose water pressure rises is generated. From the filter layer 19 made of gravel or crushed stone, the water flows into the drainage hole 10 through a large number of minute water permeation holes in the water permeation pipe 11 and is stored in the water storage pit 13. Since the filter layer 19 and the water-permeable holes are not clogged at all, this inflow is performed quickly. Therefore, the groundwater level GWL around the drainage hole 10 is lowered, and the pore water pressure generated between the soil particles in the soft ground G due to the earthquake is absorbed by the drainage of the pore water to the drainage hole 10 and is caused by the excessive pore water pressure. It is possible to effectively prevent the liquefaction phenomenon of the soft ground G in which groundwater is blown up to the ground surface together with the earth and sand.

The present invention is not construed as being limited to the illustrated embodiment. For example, the structure in which the suspension state of the weight pendulum 18 by the suspension support member 17 is released when the vibration angle θ of the weight pendulum 18 that shakes due to the input of a seismic wave exceeds a predetermined magnitude is shown in FIG. In addition to the one shown in FIG. 5, various combinations such as a combination of hooks are conceivable. Further, as the water permeable pipe 11, other than the above-mentioned porous concrete, any drainage pipe having good water permeability such as a concrete pipe or a metal pipe having a large number of small holes is adopted. be able to.

[0019]

According to the drainage hole for preventing liquefaction of the ground according to the present invention, the following effects are realized. (1) Since groundwater is not taken in during normal times, there is no possibility that excess pore water will not be taken in smoothly when an actual earthquake occurs due to clogging of the permeable pipe. (2) Since groundwater is not taken in during normal operation, it is not necessary to connect to a sewer pipe or rainwater pipe unlike the conventional permeable manhole. (3) Since groundwater is not taken in during normal times, there is no need to constantly pump up the taken-in water. (4) Since groundwater is not taken in during normal times, the water level in the surrounding wells will not always be low. (5) When a large seismic wave acceleration that may cause liquefaction to soft ground is input, the weight pendulum accurately detects it and takes in excess pore water generated in soft ground to lower the groundwater level. Therefore, a disaster caused by liquefaction can be effectively prevented.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a drainage hole for preventing liquefaction according to the present invention, which is considered to be the best embodiment, in a normal state.

FIG. 2 shows the support plate in the above embodiment,
(A) is a perspective view seen from the upper surface side, and (B) is a perspective view seen from the lower surface side.

FIG. 3 is a perspective view showing a part of the water shutoff pipe in the embodiment.

4A and 4B show the suspension support member and the weight pendulum according to the above-described embodiment, FIG. 4A is a schematic configuration explanatory view seen from a direction orthogonal to a vibration surface of the weight pendulum, and FIG. It is a schematic structure explanatory view seen from a B direction, ie, a direction parallel to the vibrating surface.

FIG. 5 is an explanatory diagram showing a lifting support state releasing operation of the weight pendulum in the embodiment.

FIG. 6 is a cross-sectional view showing a situation in which pore water in the surrounding ground flows in when an earthquake occurs in the embodiment.

FIG. 7 is a sectional view of an installed state showing a drainage hole for preventing liquefaction according to a conventional technique using a water permeable pipe.

FIG. 8 is a sectional view of an installed state showing a drainage hole for preventing liquefaction according to another conventional technique using a water permeable pipe.

[Explanation of symbols]

 10 Drainage Hole 11 Water-permeable Pipe 12 Lid 13 Water Storage Pit 14 Support Plates 14b, 14c, 16a Destruction Guide Groove 16 Water Stop Pipe 17 Suspension Support Member 18 Weight Pendulum 182 Weight Weight G Soft Ground

Claims (3)

[Claims] 1. A water-permeable pipe installed in soft ground, the upper end of which is sealed with a lid, and a water storage pit under the water storage pipe, and a support plate arranged so as to close the upper end opening of the water storage pit, and the support plate. A water stop pipe supported above to stop water on the inner circumference of the water permeable pipe; and a weight pendulum suspended by a suspension support member in an upper space of the support plate, wherein the suspension support member is the weight. When the vibration angle of the pendulum exceeds a predetermined size, the suspension for the weight pendulum is released, and the support plate is destroyed by the collision with the weight pendulum dropped from the suspension position. A drainage hole to prevent liquefaction of the ground. 2. The ground liquefaction prevention according to claim 1, wherein the weight pendulum has a suspension support length set so as to resonate in a frequency band in which a maximum vibration acceleration of an earthquake occurs. Drainage hole for. 3. The drainage hole for preventing liquefaction of the ground according to claim 1 or 2, wherein the support plate and the water stop pipe are formed with a breakage guide groove for facilitating breakage. .