JPH04203014A - Prevention work for liquefaction of sandy ground - Google Patents

Abstract

PURPOSE:To prevent the liquefaction of sandy ground during earthquake by a method in which a pump is operated by a controller to drain void water in the sandy ground, and a compressor is operated to send compressed air into the liquefied ground layer. CONSTITUTION:When earthquake of a sandy ground 31 is detected by a seismometer 49, signal is sent to a controller 46 to operate a pump 42 and a compressor 45. The pump 42 operates to pump up excess void water from a liquefied layer 47 through a water collecting tube 41 and to discharge it into a water storage tank 43, making the liquefaction of the ground 31 impossible. Also, at the same time, the compressor 45 also operates to supply compressed air from the small holes of the bottom 44a of a rubber pack 44 into the layer 47, rasing the water- pumping and draining efficiency of the pump 42. In the layer 47, downward permeation flow is generated to increase effective stress in the ground 31, preventing the liquefaction of the ground effectively. The liquefaction of the sandy ground can thus be easily prevented at low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION Second Industrial Field of Application This invention relates to a construction method that is easy to handle and can prevent liquefaction of sandy ground at low cost during an earthquake.

: Conventional technology j In general, sandy ground that is close to a saturated state is at risk of liquefying during an earthquake, so when building structures on such sandy ground, the ground must be improved using various ground improvement methods. Is it necessary? Typical ground improvement methods are known to include compaction, chemical injection, and cement mixing. However, these ground improvement methods are extremely expensive, so low-cost methods of liquefying sandy ground are known. It is desired to develop a construction method that prevents this. The following methods (a) and (b) are known as conventional construction methods for preventing liquefaction of sandy ground with low vibration and noise that can be applied even in urban areas.

(B) Groundwater level lowering method As shown in Fig. 5, in this construction method, a water stop wall 4 reaching an impermeable layer 3 is formed in the ground 2 around a structure 1, and the inside of the water cutoff wall 4 is Pumping wells consisting of deep wells, well points, etc. 5.5.・ A pumping well 5,
5. ... is activated to lower the underground water level 6 to the water level 7 inside the water stop wall 4, thereby preventing liquefaction of the sandy ground.

Here, a deep well 8 will be explained as an example of the pumping well 5.

In the deep well 8, a strainer-equipped vibrator 10 is inserted into a cylindrical well 9 of a predetermined depth, and a filter material 12 made of coarse gravel is inserted between the strainer-equipped pipe IO and the well wall 11. is filled. A submersible pump 13 is fixed near the bottom of the strainer-equipped pipe IO, and a long drain pipe 14 is connected to the upper tip 13a of the submersible pump 13. The drain pipe 14 has a long cylindrical shape and extends in the vertical direction, and the upper tip thereof is bent in the horizontal direction and placed in the drain groove 15.

Pore water having a water level of 7 flows into the well 9 through the filter material 12 and is stored inside the vibrator 10 with a strainer. The water storage level is lower than the water level 7, and is called the falling water level]6. The two stored water are drained R by the submersible pump 13.
Drained into l5. Therefore, the water stop wall 4 surrounds f
By constantly lowering the water level 7 inside, liquefaction of the sandy ground can be prevented.

(b) Gravel drain construction method As shown in Figure 6, in this construction method, a large number of gravel piles 19 are installed at predetermined positions in the ground 18 around the structure 17, and these gravel piles 19 are drained from liquid. By shortening the horizontal drainage path of the layer 20, the drainage effect is enhanced and the increase in pore water pressure during an earthquake in the sandy ground is reduced. Therefore, pore water pressure can be dissipated quickly and liquefaction of sandy ground can be prevented.

``Problem to be solved by the invention: In the groundwater level lowering method described in (a) above, it is necessary to constantly operate a submersible pump in order to continue pumping up groundwater, and equipment for pumping and processing is indispensable. In addition, problems such as ground subsidence may occur due to a decline in the groundwater level.

Furthermore, the gravel lane construction method described in (b) above has problems such as the fact that the gravel piles 19 need to be constructed at a fine pitch, which increases the construction cost and causes an increase in costs.

This invention was made in view of the above circumstances, and does not require large-scale equipment for water pumping treatment, provides a reliable drainage effect, is easy to handle, and is low-cost, and can liquefy sandy ground. The objective is to provide a construction method that can prevent this.

[Means for Solving the Problems] In order to solve the above problems, the present invention employs the following method for preventing liquefaction of sandy ground. That is, it is a construction method that prevents liquefaction by pumping up pore water in sandy ground using a water collection device installed in a structure, and the water collection device includes:
a water collection pipe penetrating into the sandy ground, a pump connected to the water collection pipe, a compressed air supply member disposed near the top of the liquefaction layer of the sandy ground and feeding compressed air into the liquefaction layer; A pressurizing device connected to the compressed air supply member, and a control device connected to the pump and the pressurizing device to control their operation, and when an earthquake occurs, the control device It is characterized in that the pot is operated to pump up and drain the pore water in the sandy ground, and the control device operates the pressurizing device to send compressed air into the liquefaction layer.

[Operation] In the sand ground liquefaction prevention method of this invention, when constructing a structure on sand ground, or when the sand ground on which a structure has already been built is nearly completely saturated, penetrate a water collection pipe, connect a pump to the water collection pipe, and
A compressed air supply member is disposed near the top of the liquefied layer of the sandy ground, a pressurizing device is connected to the compressed air supplying member, and a control device is connected to each of the pump and the pressurizing device.

When an earthquake occurs, the control device operates the pump to pump up and drain the pore water in the sandy ground, reducing the pore water pressure. This decrease in pore water pressure increases the vertical effective stress in the ground, making it difficult for sandy ground to liquefy. Further, the control device operates the pressurizing device to feed compressed air into the liquefied layer from the compressed air supply member to pressurize the liquefied layer.

This pressurization increases the pressure in the liquefaction layer and increases the pressure difference between the liquefaction layer and the pump. Therefore, the water pumping and drainage efficiency of the pump is improved. In addition, by sending compressed air downward from near the top of the liquefaction layer, a downward seepage flow is generated within the liquefaction layer, increasing the effective stress within the sandy ground, which is effective in preventing liquefaction. done to.

In addition, since water is collected and pressurized during an earthquake, the excess water pressure generated during an earthquake is quickly dissipated while maintaining the increased effective stress within the sandy ground, effectively suppressing the increase in pore water pressure during an earthquake. be done.

Hereinafter, each aspect of the present invention will be explained based on the drawings.

[First Embodiment] FIG. 1 is a diagram showing a first embodiment of the method for preventing liquefaction of sandy ground according to the present invention.

This embodiment is a construction method for preventing liquefaction of sandy ground by providing a water collection device 33 in a structure 32 built on sandy ground 31.

Around the structure 32, there is a ground surface 3 that goes around the outer wall surface.
A vertical water-stop wall 36 is constructed that reaches the impermeable layer 35 from 4. The water-stop wall 36 is a continuous water-impermeable wall that prevents water from seeping into the ground, leaking water, and the like. A water collection device 33 is provided at the bottom 32a of this structure 32.

The water collection device 33 includes a water collection pipe 41, a pump 42, and a water storage tank 43.
, a rubber bag (compressed air supply member) 44, a compressor (pressurizing device) 45, and a control device 46.

The water collection pipe 41 is a long pipe that penetrates the liquefaction layer 47 and extends vertically downward from one end of the bottom 32 a of the structure 32 , with the tip 41 a bent into an L shape and inserted into the bottom of the liquefaction layer 47 . placed horizontally. A large number of pores are formed in this tip 41a to maximize the water collection effect. The other end 41b of this water collection pipe 41 is connected to a water pump 42,
This pot 42 is connected to a water storage tank 43 installed at the bottom 32a of the structure 32 via a drain pipe 48.

The pump 42 pumps up the pore water in the liquefied layer 47 of the sandy ground 31 through the water collection pipe 41, and pumps up the pore water in the liquefaction layer 47 of the sandy ground 31 through the drainage pipe 48.
3.

The rubber bag 44 is a thick bag-like material with some elasticity.
It is arranged horizontally near the top of the liquefaction layer 47 and supplies compressed air into the liquefaction layer 47. The bottom 44a of the rubber bag 44 has a large number of pores formed in the shape most suitable for supplying compressed air. A compressor 46 that compresses air is connected to this rubber bag 44. The pump 42 and compressor 45 are each connected to a control device 46.

The control device 46 is equipped with an earthquake sensor 49 and outputs an appropriate output to the pump 42 based on the signal generated by the earthquake sensor 49.
and is sent to the compressor 45 to control these operations.

The pump 42 can be used in various ways, as shown in FIG. 4, depending on the amount of water that needs to be pumped. That is, if the water pressure drop can be small, the fourth
A vacuum pop 51 as shown in Fig. 4(a) or as shown in Fig. 4(b)
A Hugal pop 52 as shown in FIG. The vacuum pump 51 stores interstitial water pumped from the water collection pipe 41 into a large vacuum tank 54 via a valve 53.

Activation and stopping of the vacuum pump 51 and opening and closing of the valve 53 are as follows:
This is performed in conjunction with the earthquake sensor 49. Further, the Hugal pump 52 pumps water from the water collection pipe 41 and discharges the pore water f2 to the outside. The activation and stopping of the Hugal pump 52 is performed in conjunction with the earthquake sensor 49.

Second, when the drop in water pressure is large as usual, a method is adopted in which the vacuum pump 5I and the Hugal pump 52 are used together, as shown in FIG. 4(c). The vacuum pump 51 and the Hugal pump 52 are directly connected to a large vacuum tank 54, and serve to store the interstitial water pumped up from the water collection pipe 41 in the large vacuum tank 54 and discharge it to the outside. The vacuum pump 51 and the Hugal pump 52 are activated and stopped in conjunction with the earthquake sensor 49.

Next, the effects of the above method will be explained.

Normally, during peacetime, the earthquake sensor 49 does not operate, so there is no output from the control device 46, and the pump 42
The compressor 45 is not operating, and no interstitial water is pumped up.

Here, when an earthquake occurs in the sandy ground 31, the earthquake sensor 4
9 immediately senses an earthquake and promptly sends the signal to the control device 46. The controller 46 sends appropriate output to each of the pump 42 and compressor 45 for operation based on the signals.

The pump 42 starts operating with this output, and the water collection pipe 41
Excess pore water in the liquefaction layer 47 is pumped up and drained into the water storage tank 43. Therefore, the pore water pressure in the liquefaction layer 47 decreases and the effective stress in the sandy ground 31 increases, making it difficult for the sandy ground 3I to liquefy. At the same time, the compressor 45 also starts operating based on this output, and the rubber bag 44
Compressed air is supplied into the liquefied layer 47 from the pores in the bottom 44a of the liquefied layer 47 to pressurize the liquefied layer 47. Due to this pressurization, the pressure in the liquefied layer 47 increases, and the pressure difference between the upper and lower parts of the liquefied layer 47 increases. This will improve the water pumping and drainage efficiency of the pot 42. Further, by sending compressed air downward from near the top of the liquefaction layer 47, a downward permeation flow is generated within the liquefaction layer 47. This increases the effective stress within the sandy ground 31 and effectively prevents liquefaction.

In this way, the pump 42 pumps up and drains the pore water in the sandy ground 31, and the rubber bag 44 and compressor 46
By pressurizing the liquefaction layer 47, the pore water in the sandy ground 31 is rapidly reduced, and liquefaction of the sandy ground 31 can be prevented.

When the earthquake subsides, the earthquake sensor 49 quickly senses the decrease in the shaking of the earthquake and promptly sends the signal to the control device 46. Controller 46 provides appropriate output to pump 42 and compressor 46 to deactivate them based on the signal. The pump 42 stops operating due to this output and stops pumping up the interstitial water from the water collection pipe 41, and the compressor 46 also stops operating and stops pressurizing the liquefaction layer 47.

In addition, since water is collected and pressurized during an earthquake, the effective stress within the sandy ground 31 increases, and while maintaining the f2 state, the excess water pressure generated during an earthquake is quickly dissipated, and the increase in pore water pressure during an earthquake is also effective. is suppressed. The above operations are repeated every time an earthquake occurs, pore water is pumped and drained, and the liquefaction layer 47 is pressurized, so that liquefaction of the sandy ground 31 can be effectively prevented.

As explained in detail above, according to the method for preventing liquefaction of sandy ground according to the first embodiment, the pore water in the sandy ground 31 is pumped and drained by the water collection pipe 41 connected to the pop-up 42. The pore water pressure in the formed layer 47 can be reduced,
The effective stress in the sandy ground 31 can be increased, and liquefaction of the sandy ground 31 can be prevented.

In addition, since the liquefaction layer 47 is pressurized by the rubber bag 44 connected to the compressor 46, the pressure difference between the liquefaction layer 47 and the pump 42 increases, which improves the water pumping and drainage efficiency of the boss 42. I'll come. Mafni, liquefaction layer 4
Since compressed air is sent downward from near the top of 7, a downward seepage flow is generated within the liquefaction layer 47 and the inside of the sandy ground 31 is ○.
The effective stress is increased, and liquefaction can be effectively prevented.

In addition, since the pump 42 and compressor 46 operate only when an earthquake occurs, there is no need for large-scale equipment for pumping water, and a reliable drainage effect can be obtained. There is no risk of problems occurring.

It is easy to handle, equipment and running costs can be kept low, and liquefaction of sandy ground can be reliably prevented.

ESecond Embodiment FIG. 2 is a diagram showing a second embodiment, which is another embodiment of the method for preventing liquefaction of sandy ground according to the present invention.

In the following second embodiment, the same elements as those described in the first embodiment are denoted by the same reference numerals, and a description of these same elements will be omitted.

First, the configuration of this embodiment will be explained with reference to FIG.

A water collection device 61 is provided below the bottom portion 32a of the f-2 structure 32, which is constructed on the sandy ground 31.

The water collection device 61 is substantially composed of a water collection pipe 62, a pump 42, a compressed air pipe (compressed air supply member) 63, a compressor (pressurizing device) 45, and a control device 46.

The water collection pipe 62 is a pipe penetrated into the liquefaction layer 47 below the bottom 32a of the structure 32, and includes a main pipe 64 horizontally disposed below the bottom 32a and above the liquefaction layer 47, and A plurality of branch pipe parts 65 extending vertically downward from the main pipe part 64
．． 65. It is composed of... These branch pipe parts 65. - A large number of pores are formed from the center to the tip 65a to maximize the water collection effect. and,
One end 64a of this main pipe portion 64 is bent vertically upward and connected to a pump 42, which is disposed in a drain groove 66 via a drain pipe 48.

The compressed air pipe 63 is arranged horizontally near the top of the liquefied layer 47 so as to be parallel to the main pipe part 64, and
This is to supply compressed air into the air conditioner 7. The tip 63a of the compressed air pipe 63 has a large number of pores shaped like this, which is most suitable for supplying compressed air.
3b is bent vertically upward and connected to the compressor 45.

The functions, effects, etc. of the second embodiment are almost the same as those of the first embodiment, and only the different points will be listed below.

Since the pump 42 discharges the pumped pore water to the drainage groove 66, the effort and time required for drainage treatment when the water storage tank 43 is full can be saved, and a reliable drainage effect can be obtained. In addition, since a plurality of water collection pipes 65, 65 are arranged below the bottom 32a of the structure 32, the excess pore water in the liquefaction layer 47 can be pumped and drained more quickly, and the Liquefaction of the ground 31 can be prevented.

[Effects of the Invention] As explained in detail above, the present invention provides a construction method for preventing liquefaction by pumping up pore water in sandy ground using a water collection device installed in a structure. The water collection device includes an f-squared water pipe that penetrates into the sandy ground, a pop connected to the water collection pipe, and a pot that is disposed near the top of a liquefaction layer of the sandy ground and that contains water in the liquefaction layer. A compressed air supply member that sends compressed air to the compressed air supply member, a pressurizing device connected to the compressed air supplying member, and a control device connected to each of the pump and the pressurizing device to control their operation, At the time of occurrence, the pump is operated by the control device to pump up and drain the pore water in the sandy ground, so the pore water pressure in the liquefaction layer of the sandy ground can be reduced, and the pore water in the sandy ground can be drained. The effective stress of sandy ground can be increased and liquefaction of sandy ground can be prevented.

In addition, since the control device operates the pressurizing device to send compressed air into the liquefaction layer, the pressure difference between the liquefaction layer and the pump increases, reducing the water pumping and drainage efficiency of the pump. can be improved. In addition, since compressed air is sent into the liquefaction layer from near the top of the liquefaction layer, a seepage flow is generated within the liquefaction layer, increasing the effective stress in the sandy ground.
Liquefaction can be effectively prevented.

The pump, pump, and pressurizing device operate only when an earthquake occurs, so there is no need for large-scale equipment for pumping and processing, and moreover, a reliable drainage effect can be obtained, and it can prevent soil damage caused by a drop in the groundwater level. There is no risk of problems occurring.

In addition, it is easy to handle, equipment and running costs can be kept low, and liquefaction of sandy ground can be reliably prevented.

In this way, it is possible to provide a construction method that does not require large-scale equipment for water pumping treatment, provides a reliable drainage effect, is easy to handle, and can prevent liquefaction of sandy ground at low cost. can.

[Brief explanation of the drawing]

1 to 4 are diagrams showing the method for preventing liquefaction of sandy ground according to the present invention, and FIG. 1 is a sectional view showing the method for preventing liquefaction of sandy ground according to the first embodiment of the present invention. Fig. 2 is a sectional view showing a sand ground liquefaction prevention method according to the second embodiment of the present invention, Fig. 3 is a schematic configuration diagram of a water collection device, and Fig. 4 (a
) to (c) are schematic diagrams of the pumps used in the water collection device of the present invention, and FIGS. 5 and 6 are diagrams showing conventional methods for preventing liquefaction of sandy ground, and FIG. 5(a) 6 is a cross-sectional view of the groundwater level lowering method; FIG. 6(b) is a cross-sectional view of a deep well, which is an example of a pumping well using the groundwater level lowering method; 31...Sand ground, 32...Structure, 33...Water collection device, 41...Water collection pipe, 42...
・Pump, 43...Water tank, 44...Rubber bag (compressed air supply member)
, 45 ... Compressor (pressurizing device), 46 ・
...control device, 47 ...liquefaction layer, 4
8...Drain pipe, 49...Earthquake detector, 51...Vacuum pump, 52...Hyugal pump, 53...Valve, 54...Vacuum tack, 61...Water collection Device, 63 Compressed air pipe (compressed air supply member), 64
・ ・- Main pipe section, 65-- Branch pipe section, 66
...Drainage ditch.

Claims (1)

[Claims] A construction method for preventing liquefaction by pumping up pore water in sandy ground using a water collection device installed in a structure, wherein the water collection device penetrates into the sandy ground. a pump connected to the water collection pipe, a compressed air supply member disposed near the top of the liquefaction layer of the sandy ground and feeding compressed air into the liquefaction layer, and the compressed air supply member. The pump is equipped with a pressurizing device connected thereto, and a control device connected to each of the pump and the pressurizing device to control their operation, and when an earthquake occurs, the control device operates the pump to pump water into the sandy ground. A method for preventing liquefaction of sandy ground, characterized in that pore water is pumped up and drained, and at the same time, the control device operates a pressurizing device to send compressed air into the liquefaction layer.