JP2656432B2 - Liquefaction prevention method and liquefaction prevention drain hole - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing ground liquefaction caused by an earthquake and a liquefaction prevention drain hole.

[0002]

A loose sandy ground with a high groundwater level is liable to be liquefied by an earthquake and causes the collapse of the structure. Therefore, measures to prevent liquefaction are required, and considerable measures have been proposed. I have. In other words, the groundwater level lowering method that lowers the original groundwater level at the pumping well to prevent liquefaction. Excessive pore water pressure dispersal method in which the excess pore water pressure generated by liquefaction is dissipated in the horizontal direction by installing gravel drains and the like. The AE sensor detects liquefaction or the vibration of an earthquake, and starts pumps to pump up wells, or operates a well pump with vacuum pumps to lower groundwater level and sucks groundwater.

[0003] However, these conventional methods cause problems such as the subsidence of the surrounding ground due to lowering of the groundwater level, a time lag in starting the pump in the event of an earthquake, and anxiety about power supply as a power source during an earthquake. There was a point, and the improvement was required.

The present invention has been made in view of the above problems. An object of the present invention is to propose a liquefaction prevention method and a drain hole capable of preventing liquefaction by high-performance, high-reliability, low-maintenance, and low-cost maintenance.

[0005]

A liquefaction prevention drain hole according to claim 1 is formed of a double pipe consisting of an inner pipe having a lower end opened and an airtight upper part and a water-permeable outer pipe in a ground having a high groundwater level. The inner pipe is provided with an exhaust valve that opens when sensing an earthquake and discharges the compressed air by providing a drain hole, filling the inner pipe with compressed air and lowering the water level in the inner pipe.

The liquefaction prevention drain hole according to claim 2 is provided with a single pipe drain hole having an impermeable upper portion and a lower portion having a water permeable portion on the ground with a high groundwater level, and pressurized air is sealed in the airtight portion. Then, the water level in the airtight part is lowered, and the airtight part is provided with an exhaust valve that opens upon sensing an earthquake and releases compressed air.

[0007] Liquefaction prevention method according to claim 3, ground water level the drain holes provided in the high ground, the land of the bore in the siphon tube
Connects sewage with drainage lower than the water level in the hole,
Closes the drain valve provided on the siphon pipe to drain
The head difference between the tip and the drain water level is maintained,
At the time of birth, open the drain valve to discharge water in the drain and drain holes.
Drain the drain hole with a head gap,
Prevent backflow with a valve provided at the bottom to lower the water level in the drain hole
It is characterized by keeping .

[0008]

FIG. 1 shows an embodiment of a liquefaction prevention method using a drain hole according to the first aspect of the present invention, wherein a vertical ground comprising an inner pipe 3 and an outer pipe 4 is provided on a ground 2 having a high groundwater level 1-1. A drain hole 5 for the tube is provided. The inner tube 3 has an opening surface 6 at a lower end and an airtight portion 7 at an upper portion. The outer tube 4 is water-permeable and has a water-permeable hole formed in the side surface, and a strainer 8 covers the periphery. Usually, the inner tube diameter is 200 to 250 mm and the outer tube diameter is about 300 mm.

At the top of the airtight portion 7 of the drain hole 5,
An air supply pipe 11 extending from the compressor 9 via an air supply valve 10 and an exhaust pipe 13 opened to the atmosphere via an exhaust valve 12 are connected. The exhaust valve 12 is provided on the ground or in the ground. An earthquake sensor 14 is mounted to detect an earthquake and open a valve.

The drain hole 5 is always filled with air having a pressure corresponding to the underground water pressure supplied from the compressor 9 in the hermetic part 7, and the water level 1-2 is maintained near the lower end of the hermetic pipe. At this time, the water level in the gap between the inner and outer pipes 3 and 4 becomes equal to the original groundwater level 1-1.

When an earthquake occurs and the sensor 14 senses this, the exhaust valve 12 is opened and the pressure in the hermetic part 7 is released, so that the pressure in the hermetic part 7 decreases. Therefore, the groundwater in the drain hole 5 (the groundwater in the gap between the inner and outer pipes 3 and 4) rapidly flows into the inner pipe 3, and the original groundwater level 1-
The water level in the hole becomes 1-3 from 1 and the water pressure in the hole falls from the hydrostatic pressure (water level 1-1) to a pressure corresponding to the water level 1-3.

[0012] When an earthquake occurs on the ground with a high groundwater level, a large excess pore water pressure is generated. However, since the water pressure on the hole wall of the drain hole falls, the pore water pressure causes a lateral seepage flow toward the drain hole. Dissipate.

FIGS. 2A and 2B show the distribution of water pressure acting on the drain hole wall and the distribution of water pressure in the horizontal direction around the drain hole. The hydrostatic pressure in the drain hole 5, i.e., the outer pipe 4 in the normal state, corresponds to the original groundwater level 1-1, but decreases rapidly with the occurrence of the earthquake, and changes to a pressure corresponding to the in-hole water level 1-3.
Thus, the difference between the excess pore water pressure u ₀ and downhole pressure generated in the liquid layer of the soil as compared to the difference between the hydrostatic pressure becomes larger by an amount corresponding to a downhole drawdown [Delta] H. This results in a large permeate flow into the holes, the excess pore water pressure of the liquefaction drops rapidly and the residual excess pore water pressure in the surrounding ground decreases.

At the same time, a downward osmotic pressure is also generated to prevent primary liquefaction (rapid dissipation of excess pore water pressure and increase in effective stress) and secondary liquefaction (upward osmotic pressure =
Reduction of upward movement of excess pore water pressure) is achieved.

The primary liquefaction due to the rise of the excess pore water pressure and the dissipation of the excess pore water pressure are phenomena for several minutes, and the effect of preventing liquefaction can be enhanced by lowering the water level in the drain hole for several minutes. it can.

FIG. 3 shows an embodiment of liquefaction prevention using the liquefaction prevention drain hole according to the second aspect . The drain hole 5 ′ is a single pipe 17 having an airtight part 15 at the upper part and a water permeable part 16 at the lower part.
Consists of The water permeable portion 16 has a water permeable hole formed in the periphery, and is covered with a strainer 8 surrounding the periphery. Airtight part 15
Is connected to an intake pipe 11 extending to the compressor 9 via an intake valve 10 and an exhaust pipe 13 opened to the atmosphere via an exhaust valve 12. Is installed to open the valve 12 upon sensing an earthquake.

The drain hole 5 'is always filled with air in the hermetic portion 15 so that the water level 1-2 is maintained near the lower end of the hermetic portion. Upon detecting the earthquake, the valve 12 is opened to release the compressed air. The airtight section necessarily forms an impermeable drain hole wall
The surrounding groundwater rapidly flows into the hermetic part 15 from the lower permeable part , and reaches a water level 1-3 in the hole. The water pressure in the drain hole is from the hydrostatic pressure (water level 1-1) to the water level 1 -3. This drain hole is also the lower permeable section
De The excess pore water pressure as in the drain hole in the peripheral
The dissipation in the horizontal direction toward the lane can be mitigated to prevent liquefaction at the lower part of the ground.

FIG . 4 shows a case where an impermeable airtight portion is provided at the top.
Shows the horizontal water pressure distribution around the upper part of the drain hole when
The solid and dashed lines in the middle and the end of the earthquake respectively
Water pressure distribution during post-dissipation is shown). Around the upper impervious part
In the ground, the downward seepage current is
Occurs and instantaneous downward osmotic pressure almost equal to the water level drop
Occurs. Excess pore water pressure of liquefaction with this downward osmotic pressure
Of soil in the ground due to upward seepage flow
Immediately prevent child jets (damage from secondary liquefaction). Time
The water level in the drain hole gradually rises with
The osmotic pressure also decreases, but the excess pore water pressure also gradually decreases,
The excess pore water pressure remains low.

FIG. 5 shows an embodiment using a drain hole whose water level is lowered by the siphon pipe according to the third aspect .
A vertical drain hole 5 "comprising an outer pipe 4 and a siphon pipe 3 'connected to a drainage destination 18 is provided in the ground 2 having a high height 1. The siphon pipe 3' has an opening surface 6 at the lower end in the drain hole 5". , Has an opening surface 6 ″ at the tip of the drainage destination 18, a drainage valve 19 on the drainage side, and a check valve 2 on the drain hole side.
0, an air valve 21 is provided at the top. Drain valve 19
Is equipped with an earthquake sensor 14 and detects an earthquake to open a valve.

The drain hole 5 "is always filled with water in the siphon tube 3 'and the drain valve 19 is closed.
The water level between the siphon pipe 3 'and the outer pipe 4 on the drain hole 5 "side is equal to the original groundwater level 1-1.

When an earthquake occurs and the sensor 14 senses this, the drain valve 19 is opened, so that a head difference is generated in the siphon pipe 3 'from the open surface 6' to the open surface 6 "at the drainage destination 18. Therefore, groundwater in the drain hole 5 ″ (groundwater in the gap between the siphon pipe 3 ′ and the outer pipe 4)
Rapidly flows out to the drainage destination 18 through the siphon pipe 3 ', and reaches the underground water level 1-3 in a few seconds from the original groundwater level 1-1, and the underground water pressure changes from the hydrostatic pressure (water level 1-1) to the water level 1-3. Drop to the corresponding pressure. At this time, the non-return valve 20 prevents pulsation of the water flow from returning from the siphon pipe 3 'into the drain hole 5 ", and the water level 1-3 is maintained in the drain hole 5".

This drain hole can also be used to prevent liquefaction of the ground by dissipating and relaxing excess pore water pressure, similarly to the drain hole.

[0023]

The present invention has been described above, and the liquefaction preventing method and the drain hole have the following effects.

Since the power source for lowering the water level in the drain hole is stored in advance as compressed air or potential energy at the groundwater level, no power is required during an earthquake, and the safety and reliability are high.

Since the water level is immediately lowered at the time of an earthquake without a time lag, it functions reliably and there is no need to predict and detect an earthquake in advance.

There is no danger of the surrounding ground drop due to a drop in groundwater level.

Compared with other methods of lowering the water level, the equipment is simpler, the operation is simpler, the maintenance is easier, the cost is lower and the cost is lower. Inspection maintenance and re-activation after an aftershock can be achieved by simply closing the exhaust valve and supplying compressed air, or closing the drain valve and evacuating the air valve with a vacuum pump.

In a drain using a double pipe, the inner pipe is sealed.
The water level in the drain hole, which is almost the same as the
And collect the groundwater with a permeable outer pipe, mainly in the horizontal direction.
Liquefaction is promoted by promoting the dissipation of excess pore water pressure.
To prevent.

The upper part of the single tube uses a water-impermeable airtight part.
In the drain, pressure was sealed in the airtight part and lowered in advance.
Obtaining a drop in water pressure in the drain hole approximately equal to the water level
Not only that, the instantaneous downward osmotic pressure
Liquefaction damage can be prevented. For drains using siphon pipes, the water level
Using the difference to lower the water level in the drain hole in a few seconds,
A check valve prevents the water level from dropping above the water level difference.
You.

[Brief description of the drawings]

1 is a longitudinal sectional view of the drain hole in the embodiment of the invention according to claim 1.

FIGS. 2 (a) and 2 (b) are explanatory diagrams respectively showing a water pressure distribution acting on a drain hole wall and a horizontal water pressure distribution around the drain hole.

FIG. 3 is a longitudinal sectional view of a drain hole in the embodiment of the invention according to claim 2 ;

FIG. 4 is an airtight part at the upper part, that is, a drain which is impermeable to water.
Figure showing the horizontal water pressure distribution around the upper part of the hole
is there.

FIG. 5 is a longitudinal sectional view of a drain hole in the embodiment of the invention according to claim 3 ;

[Explanation of symbols]

1-1: Original groundwater level, 1-2: Water level in the hole when air is sealed,
1-3 ... water level in the hole at the time of pressure release, 2 ... ground, 3 ... inner pipe,
3 ': siphon pipe, 4: outer pipe, 5, 5', 5 "... drain hole, 6, 6 ', 6" ... opening surface, 7 ... airtight part, 8 ... strainer, 9 ... compressor, 10 ... air supply Valve, 1
DESCRIPTION OF SYMBOLS 1 ... Air supply pipe, 12 ... Exhaust valve, 13 ... Exhaust pipe, 14 ... Earthquake sensor, 15 ... Airtight part, 16 ... Permeable part, 17 ... Single pipe, 18 ... Drainage destination, 19 ... Drainage valve, 2
0: check valve, 21: air valve.

Claims (3)

(57) [Claims] 1. A drain hole comprising a double pipe of an inner pipe having an open lower end and an airtight upper part and a permeable outer pipe is provided in a ground with a high groundwater level, and compressed air is sealed in the inner pipe. A liquefaction prevention drain hole characterized by lowering the water level in the inner pipe, opening the inner pipe upon sensing an earthquake, and having an exhaust valve for releasing compressed air. 2. The upper part is impermeable to the ground where the groundwater level is high .
The airtight part, the lower part has a drain hole of a single pipe with a water-permeable part, the air pressure is sealed in the airtight part to lower the water level in the airtight part, and the airtight part detects the earthquake and opens and releases the air A liquefaction prevention drain hole comprising an exhaust valve. 3. A drain hole is provided on the ground water level is high ground, connecting the lower drainage destination than groundwater and downhole level surface in the pores in the siphon down tube, is always drain valve provided in the siphon tube the Yes keep the water head difference between the water discharge destination and the drain hole water closed, by opening the drain valve in the event of an earthquake brought draining the drain hole in the water head difference between the water discharge destination and the drain hole, provided in the siphon tube A method for preventing liquefaction, characterized in that backflow is prevented by a valve and the water level in the drain hole is kept low.