JP6066275B2 - Liquefaction prevention system and method - Google Patents

Description

  The present invention relates to a liquefaction prevention system and method mainly for a liquefied ground spreading directly under an existing structure such as embankment.

  Liquefaction of the ground is caused by the fact that when the vibration due to earthquake acts on the ground, the pore water pressure between the sand particles increases due to the shear deformation of the ground, and as the pore water pressure increases, the effective stress becomes zero. This is a phenomenon in which the stress cannot be transmitted and the fluidity becomes high, and it tends to occur in loose saturated sandy ground (hereinafter, the ground where liquefaction is likely to occur is called liquefied ground).

  As liquefaction progresses, the ground loses its vertical bearing capacity, leading to collapse of the building, and damage to the piles due to lateral flow of the ground occurs. It has come to be clearly recognized.

  Various countermeasures against such liquefaction damage have been researched and developed in the past, such as compacting the liquefied ground, injecting chemicals into the liquefied ground, improving the ground strength, and lowering the groundwater level. In addition to known countermeasures such as reducing the degree of saturation of the liquefied ground, water containing microbubbles (hereinafter simply referred to as microbubble-containing water) is injected into the liquefied ground. A method has also been developed to send fine bubbles into the soil particle gaps of the ground.

  Among these, according to countermeasures using microbubble-containing water, microbubbles absorb the increase in pore water pressure during earthquakes by reducing their volume, resulting in ground subsidence like countermeasures due to water level reduction. In addition, the ground can be prevented from being liquefied at a more reasonable cost than the countermeasure work by the drug injection.

JP 2007-2111537 A JP 2008-002170 A JP 2007-239405 A Japanese Patent No. 3374224

  However, in conventional countermeasures using microbubbles, if existing structures such as embankments exist on the surface of the earth, an injection well cannot be provided immediately below, so if the scale of the existing structures is large to some extent, There was a problem that it was difficult to feed water containing microbubbles appropriately and sufficiently into the liquefied ground directly under the existing structure.

  By the way, if the injection well and the pumping well are spaced apart in the ground and the microbubble-containing water injected from the injection well is recovered from the pumping well, the microbubble-containing water Since it flows horizontally in the ground, the microbubble-containing water can be sent to the lower part of the existing structure by installing the injection well and the pumping well across the existing structure.

  However, when the poorly permeable region or impermeable region is scattered in the ground, these serve as a barrier to block the flow of water containing microbubbles, and the water permeability in the ground varies. When there is water mist, the water containing microbubbles flows in a direction in which the water permeability resistance is smaller, and as a result, it is difficult to uniformly inject the water containing microbubbles under the existing structure.

  This situation is the same when trying to feed microbubble-containing water through a horizontal hole, and if there is a variation in water permeability in the ground or water is present, the water permeability resistance is smaller. Since the microbubble-containing water flows in the direction, it is difficult to uniformly inject the microbubble-containing water below the existing structure.

  The present invention has been made in consideration of the above-described circumstances, and provides a liquefaction prevention system and method that can reliably and evenly supply microbubbles even under an existing structure such as embankment. For the purpose.

In order to achieve the above object, the liquefaction prevention system according to the present invention is the ground as described in claim 1, such that the ground area extending below an existing structure such as embankment is surrounded or sandwiched laterally. An end portion is opened at least at one of the two ground surface positions sandwiching the existing structure in the impermeable wall disposed inside and the treatment area surrounded or sandwiched by the impermeable wall, and from the end portion A microbubble supply hole extending downward in a depth direction toward the lower side of the existing structure and a perforated tube inserted and disposed in the microbubble supply hole or the microbubble supply hole and a microbubble supplying means capable of supplying microbubbles into the processing region through, said microbubble supply means, said one of the microbubble supply holes, micro disposed in a layer is greater permeability The micro supply hole or the perforated tube inserted in the microbubble supply hole or the perforated tube inserted in the microporous supply hole or the perforated tube inserted in the Each bubble is supplied .

Further, the liquefaction prevention system according to the present invention is arranged in the ground so that the ground area extending below the existing structure such as embankment is surrounded or sandwiched laterally as described in claim 2 . At least one of two ground surface positions sandwiching the existing structure in a water-impervious wall, a bubble generating device capable of discharging water containing microbubbles, and a processing region surrounded or sandwiched by the water-impervious wall. A microbubble supply hole extending from the end and extending downward from the end portion to the existing structure, and the microbubble supply hole or a perforated tube inserted into the microbubble supply hole. And the discharge pipe of the bubble generating device communicates with a space partitioned by the two packers in the internal space of the microbubble supply hole or the perforated tube. It forms a sea urchin said discharge exit discharge hole in the pipe, the air bubble generating device, a small supply pressure when the two packers are arranged in a large area of water permeability, large when placed in a small area water permeability The microbubble-containing water is supplied at a supply pressure .

In addition, the liquefaction prevention system according to the present invention is arranged in the ground so that the ground range extending below an existing structure such as embankment is surrounded or sandwiched laterally as described in claim 3 . Among the two ground surface positions sandwiching the existing structure in the treatment area surrounded or sandwiched by the water shielding wall, a bubble generating device provided with a diffuser pipe for ejecting microbubbles, and the water shielding wall A microbubble supply hole that opens at one end and extends from the end toward the lower side of the existing structure, and the microbubble supply hole or a perforated tube that is inserted into the microbubble supply hole And a depth that is equal to or lower than the groundwater level, which is a space partitioned by the two packers among the internal space of the microbubble supply hole or the perforated pipe. It is arranged the diffuser tube, the air bubble generating device, a small supply pressure when the two packers are arranged in a large area of water permeability, a large supply pressure when placed in a small area water permeability, Each of the microbubbles is supplied .

  Further, in the liquefaction prevention system according to the present invention, the microbubble supply hole is configured as a curved hole whose respective ends are opened at the two ground surface positions so as to pass below the existing structure, Alternatively, the two ground surface positions are formed by oblique holes each having an upper end opened and extending downward from the existing structure.

Further, the liquefaction prevention method according to the present invention includes a water-impervious wall as described in claim 5 so that a ground range extending below an existing structure such as embankment is surrounded or sandwiched laterally. And at least one of the two ground surface positions sandwiching the existing structure in the processing region surrounded or sandwiched by the water-impervious wall, and an end is opened at at least one of the existing structures from the end. Extending the microbubble supply hole downward and in a plurality of stages in the depth direction, the microbubble supply hole or the perforated tube inserted in the microbubble supply hole is inserted into the processing region A liquefaction prevention method for injecting microbubble-containing water,
After pumping up groundwater in the treatment area, air is trapped in the soil particle gap in the dewatering area generated in the pumping process, and the microbubbles arranged in the layer with high water permeability among the microbubble supply holes A small supply pressure is applied to the bubble supply hole or the perforated pipe inserted therein, and a high supply pressure is applied to the microbubble supply hole arranged in the layer having a low water permeability or the perforated pipe inserted therein. The microbubble-containing water is poured into the dewatering region.

Moreover, the liquefaction prevention method according to the present invention includes a water-impervious wall as described in claim 6 so that a ground area extending below an existing structure such as embankment is surrounded or sandwiched laterally. And at least one of two ground surface positions sandwiching the existing structure so as to extend below the existing structure in the processing region surrounded or sandwiched by the water shielding wall. A microbubble supply hole is formed so as to open, and the microbubble supply hole or a perforated tube inserted and disposed in the microbubble supply hole is separated from each other by two packers into the processing region. A liquefaction prevention method for injecting microbubble-containing water,
After pumping up the groundwater in the treatment area, a small supply pressure when air is trapped in the soil particle gap in the dewatering area generated in the pumping process and when the two packers are arranged in a highly permeable area Thus, the microbubble-containing water is poured into the dewatering region so that a high supply pressure is obtained when it is disposed in a region having low water permeability .

  Further, in the liquefaction prevention method according to the present invention, the microbubble supply hole is constituted by a curved hole whose respective ends are opened at the two ground surface positions so as to pass under the existing structure, Alternatively, the two ground surface positions are formed by oblique holes each having an upper end opened and extending downward from the existing structure.

  Further, the liquefaction prevention method according to the present invention performs the aeration process on the dehydration area after the pumping process and before the water injection process, or decompression in the dehydration area and the subsequent air supply process Is to do.

[First invention]
In the liquefaction prevention system according to the first aspect of the invention, first, a ground area that extends downward from an existing structure such as embankment is targeted for liquefaction prevention, and the ground area is surrounded or sandwiched laterally. Install impermeable walls in the ground.

  Next, the microbubble supply holes are arranged in the processing region surrounded or sandwiched by the impermeable walls at the same time as or behind the impermeable walls.

  When arranging the microbubble supply holes, at least one of the two ground surface positions sandwiching the existing structure has an end opening at a plurality of stages in the depth direction from the end toward the lower side of the existing structure. Extend so that.

  If a plurality of microbubble supply holes are formed in the processing region, the microbubbles are supplied to the processing region through the microbubble supply hole or a perforated tube inserted and arranged in the microbubble supply hole.

  The supply of microbubbles may be in the form of injecting microbubble-containing water containing microbubbles into the treatment area, or in the form of ejecting microbubbles into the groundwater in the treatment area. Moreover, it is arbitrary whether it supplies simultaneously or sequentially to the microbubble supply hole formed in multiple steps.

  When microbubbles are supplied in this manner, even when the water permeability of the ground varies in the vertical direction, for example, even when a layer with high water permeability and a layer with low water permeability are stacked on each other, The microbubble supply holes or perforated pipes arranged in the layer with high permeability are supplied with a relatively low supply pressure, and the microbubble supply holes or perforated pipes arranged in the layer with low water permeability are supplied with a relatively high supply pressure. Since each microbubble can be supplied, the microbubbles are uniformly supplied to the entire processing region, and after supply, the microbubbles stay in water for a long time and are dispersed by the mutual repulsive force due to electric charges. Diffuses to every corner of the soil particle gap, and then remains in the soil particle gap mainly as normal bubbles or voids, sometimes as microbubbles. Suppress the pore water pressure rise due to the panel shear deformation.

  For this reason, even if there is a poorly water-permeable region, a water-impermeable region, or water pits under the existing structure, the pore water pressure suppression action by microbubbles, normal bubbles, or voids is applied to every corner of the treatment region. As a result, the liquefaction below the existing structure can be reliably prevented.

  Further, by operating the microbubble supply means, it is possible to replenish the processing region with microbubbles at any time, so that it is possible to maintain the initial liquefaction prevention state after taking countermeasures for a long period thereafter. .

  As described above, the microbubble supply hole has an opening at least at one of the two ground surface positions sandwiching the existing structure, and a plurality of steps in the depth direction from the end toward the lower side of the existing structure. It is only necessary to extend so that a plurality of steps are not necessarily meant to mean only a plurality of steps in a horizontal posture, and a plurality of steps in an oblique posture are also included, and existing structures Of the two ground surface positions that sandwich the ground, it is included even if it extends only from one side, but in particular, the curves where each end opens to the two ground surface positions so as to pass under the existing structure. Forms constituted by holes and forms constituted by oblique holes each having an upper end opened at two ground surface positions and extending downward from the existing structure are included.

  When the microbubble supply hole is formed of a curved hole, the curved hole may be drilled using a known drilling technique such as curved boring or curved boring.

  The supply of microbubbles may be performed directly through the microbubble supply hole, but instead, a perforated tube is inserted into the microbubble supply hole and the microbubble is supplied through the perforated tube. You may comprise a microbubble supply means so that. In this case, after passing through the through hole formed in the perforated tube, the microbubble penetrates into the ground from the hole wall of the microbubble supply hole and is supplied to the processing region.

  According to this configuration, the perforated pipe can be used for protecting the wall of the microbubble supply hole. Here, the perforated pipe may be inserted and arranged simultaneously with the drilling when drilling.

  The configuration of the microbubble supply means is arbitrary, but when microbubbles are supplied to the processing region by injecting the microbubble-containing water, the microbubble-containing water can be discharged, and the output side is a microbubble supply hole. When the microbubbles are supplied to the processing region in a form in which the microbubbles are ejected, the air diffuser that ejects the microbubbles can be configured by a bubble generating device connected to one end of the perforated tube or one end of the perforated tube It is possible to adopt a configuration in which the air diffuser is installed at a depth which is the internal space of the microbubble supply hole or the perforated tube and is below the groundwater level.

  Here, in the above specific configuration in the case of injecting microbubble-containing water, the bubble generation device is appropriately selected or combined from known generation methods such as a pressure dissolution method, a high-speed swirling method, and a gas-liquid mixing shear method. In the above-described specific configuration in which microbubbles are ejected, the bubble generating device includes a blower and an air diffuser connected to the blower via a hose, and It is possible to configure the trachea by inserting it into a microbubble supply hole or a perforated tube.

  On the other hand, in the above specific configuration, among a plurality of saturation measuring instruments installed at different depth positions in the processing region, and a microbubble supply hole or a perforated tube inserted and disposed in the microbubble supply hole And a configuration that includes a switching device that connects the bubble generating device to a specific microbubble supply hole or a perforated tube, and a control unit that controls the switching device according to the measurement value output from the saturation meter. The control unit may be configured to control the switch so that the bubble generating device is connected to a microbubble supply hole or a perforated pipe corresponding to a ground depth whose saturation exceeds a predetermined threshold value. Is possible.

  According to such a configuration, when the countermeasure work is performed, the microbubble is formed at a depth position where the saturation does not fall below the predetermined threshold by performing the construction while monitoring the decrease in the saturation in the processing region. Thus, even in the ground where the water permeability varies along the depth direction, the microbubbles are evenly supplied within the treatment area to further ensure liquefaction below the existing structure. After the countermeasures are taken, the microbubbles are processed at a depth where the saturation level exceeds the predetermined threshold by continuously monitoring the increase in the saturation level within the processing area. The region can be replenished, and the liquefaction prevention state can be more reliably maintained.

[Second and third inventions]
In the liquefaction prevention system according to the second and third inventions, the ground area extending below an existing structure such as embankment is targeted for liquefaction prevention, and the ground area is surrounded or sandwiched laterally. A water-impervious wall is disposed in the ground, and an end portion is opened in at least one of two ground surface positions sandwiching the existing structure in the processing region surrounded or sandwiched by the water-impervious wall. A microbubble supply hole is extended from the end toward the lower side of the existing structure, and two packers are arranged apart from each other in the microbubble supply hole or a perforated pipe inserted into the microbubble supply hole. is there.

  Here, a discharge hole is formed in the discharge pipe so that the discharge pipe of the bubble generating device communicates with the space partitioned by the two packers in the internal space of the microbubble supply hole or the perforated tube (the second pipe). (Invention) or a space divided by two packers and a diffuser pipe is disposed at a depth below the groundwater level (third invention).

  When the bubble generating device is operated in these configurations, the microbubbles are in the form of microbubble-containing water discharged into a space partitioned by two packers or ejected into a space partitioned by two packers. However, even if the water permeability of the ground varies along the horizontal direction, when two packers are arranged in a region with high water permeability, the water permeability can be reduced with a relatively low supply pressure. When two packers are arranged in a small area, the microbubbles can be supplied with a relatively high supply pressure, so that the microbubbles are evenly supplied to the entire processing area. Stays in the water for a long time and diffuses to the corners of the soil particles while being dispersed by the repulsive force of each other due to the electric charge. As the bubbles or voids, in some cases remain leaving soil particles gap microbubbles, inhibit pore pressure increase due to soil shear deformation during an earthquake.

  For this reason, even if there is a poorly water-permeable region, a water-impermeable region, or water pits under the existing structure, the pore water pressure suppression action by microbubbles, normal bubbles, or voids is applied to every corner of the treatment region. As a result, the liquefaction below the existing structure can be reliably prevented.

  In addition, by operating the bubble generating device, microbubbles can be replenished to the processing area as needed, so that the initial liquefaction prevention state after taking countermeasures can be maintained for a long period thereafter.

  The bubble generating device in the second invention is the same as the bubble generating device injecting microbubble-containing water among the bubble generating devices in the first invention, and is a pressure dissolution method, a high-speed swirling method, a gas-liquid mixing shear It is possible to appropriately select or combine the known generation methods such as the method, and the bubble generating device in the third invention is the same as the bubble generating device in the first invention that ejects microbubbles. In addition, the blower and the diffuser pipe connected to the blower via a hose can be used, and the diffuser pipe can be arranged between two packers.

  As in the first aspect of the invention, the microbubble supply hole has an end opening at least one of two ground surface positions sandwiching the existing structure, and the depth from the end toward the lower side of the existing structure. It is sufficient to extend so as to have a plurality of stages, and the plurality of stages does not necessarily mean only a plurality of stages arranged in a horizontal posture, but also includes a plurality of stages arranged in an oblique posture. The case where only one of the two ground surface positions sandwiching the structure is included is included, but in particular, each end opens at two ground surface positions so as to pass under the existing structure. A form constituted by a curved hole or a form constituted by a slant hole each having an upper end opened at two ground surface positions and extending downward from an existing structure is included.

  When the microbubble supply hole is formed of a curved hole, the curved hole may be drilled using a known drilling technique such as curved boring or curved boring.

  The two packers may be appropriately arranged at a horizontal position corresponding to the ground range to which microbubbles are to be supplied. In the second invention, the microbubble supply holes or the microbubbles are arranged so that a large number of packers are separated from each other. Containing microbubbles in the section sandwiched between each packer and the discharge pipe of the bubble generating device through each packer arranged in a row in the inner space of the perforated pipe inserted and arranged in the supply hole In addition to providing a discharge hole that can be opened and closed so that water can be discharged, and opening a discharge hole in a section sandwiched between any two packers adjacent to each other, the microbubble-containing water can be discharged in the section. In addition, a discharge hole is provided in the discharge pipe of the bubble generating device, and two packers are attached at positions sandwiching the discharge hole, and the discharge pipe is connected to the microbubble supply hole or After being configured to move forward and backward along the hole axis of the perforated tube inserted and arranged in the microbubble supply hole, the discharge pipe is appropriately advanced and retracted in the microbubble supply hole or perforated tube, and then the discharge hole of the discharge pipe is used. A structure for discharging water containing microbubbles is included, and in the third invention, a plurality of packers are inserted into the microbubble supply holes or the perforated pipes inserted into the microbubble supply holes so that they are separated from each other. Arranged in a row in the space and through each of the packers through the ejection pipe of the bubble generating device, and the diffuser pipes are arranged in such a way that microbubbles are ejected in the section sandwiched between each packer The configuration in which the microbubbles are ejected in the section by operating the air diffuser in the section sandwiched between any two adjacent packers is included.

  The packer may be arranged directly in the microbubble supply hole, but if a perforated tube is inserted into the microbubble supply hole and arranged in the inner space of the perforated tube, the packer Can be arranged smoothly, and there is no need to worry about collapse of the hole wall.

[Fourth Invention]
In the liquefaction prevention method according to the fourth aspect of the invention, when water is injected into the treatment region through the microbubble supply hole, prior to the injection of the microbubble-containing water, the groundwater in the treatment region is pumped, Thereafter, water containing microbubbles is poured into the dewatering region so that air is trapped in the soil particle gaps of the dewatering region generated in the pumping process.

  In this case, in addition to the decrease in the saturation due to the replacement of the existing groundwater with the water containing microbubbles, the decrease in the saturation due to the trapped air in the soil particle gap is added, and thus, due to the microbubbles, the normal bubbles or the voids. The pore water pressure suppressing action is further enhanced, and liquefaction below the existing structure can be more reliably prevented.

  The method for raising the groundwater in the treatment area to lower the groundwater level is arbitrary, but if the so-called vacuum deep well method using gravity drainage and forced drainage by decompression is used, the groundwater level will be shortened. Since it can be reduced in time, the liquefaction prevention work using the present invention can be realized in a short construction period.

  With regard to how much the groundwater level is lowered, typically, a configuration in which the groundwater level is lowered so that the area where the microbubble-containing water is injected, that is, the area where the microbubble supply holes are arranged, becomes the dehydration region as it is. Although the degree of groundwater level drop is assumed, the groundwater level is lowered to the vicinity of the intermediate position in the arrangement range of the microbubble supply holes, for example, and the existing groundwater existing below the intermediate position is lowered. You may make it employ | adopt the structure substituted by the water containing microbubbles without pumping up.

  Even in this configuration, it is possible to enjoy the effect that the saturation lowering action by the trapped air is added to the saturation lowering action by the replacement with the microbubble-containing water from above the intermediate position.

  Note that the microbubble supply hole can be configured by a curved hole or an oblique hole, which is the same as in the first or second invention, and the description thereof is omitted here.

  After pumping up the groundwater in the treatment area, the water containing microbubbles may be poured directly into the dewatering area generated in the pumping process, but after the pumping process and before the water pouring process, dewatering is possible. If the area is ventilated, or if the depressurization in the dehydration area and the subsequent air supply process are performed, the moisture remaining on the soil particle surface and the soil particle gap is also removed, so that more Air is trapped in the soil particle gap as bubbles, and thus the saturation can be further reduced.

  The aeration process can be performed, for example, by sending air through or sucking air through the microbubble supply hole. For example, a process using warm air is effective.

  On the other hand, in the depressurization in the dehydration region and the subsequent air supply process, the water evaporates almost completely due to the lowering of the boiling point of the water due to the reduced pressure, and air enters the corners of the soil particle gap by the air supply process in that state. For this reason, air is more likely to remain in the soil particle gaps after the water injection of the microbubble-containing water.

  Depressurization in the dehydration area is achieved by air-tightening the dehydration area by laying an airtight sheet on the surface of the existing structure or on the ground surface spreading on both sides of the structure, and then vacuuming the air in the space within the dehydration area It can be implemented by pulling out with

  After the microbubble-containing water is poured into the dewatering region, the dewatering region becomes a condensate region filled with water. If it is made to measure, it will become possible to objectively grasp whether the pore water pressure suppression effect is exhibited reliably at the time of an earthquake, and the reliability of the liquefaction prevention work improves.

  The degree of saturation in each of the above-described inventions means the proportion of water in the soil particle gap, that is, the water saturation.

  As long as the groundwater in the treatment area does not flow into or out of the ground in a short period of time due to horizontal movement of groundwater between the treatment area and the surrounding ground, the impermeable wall However, it is not necessary for the lower end to penetrate the impermeable layer, and groundwater wraparound at the lower end due to relatively slow changes in the groundwater level such as seasonal factors is allowed.

  In this case, the groundwater in the treatment area also rises and falls due to the fluctuation of the groundwater level in the surrounding ground, and the groundwater exchange occurs between the treatment area and the surrounding ground, and accordingly, the concentration of microbubbles or normal bubbles in the treatment area It is assumed that the concentration decreases and the degree of saturation increases. In such a case, using the liquefaction prevention system according to the present invention, the supply of microbubbles to the processing region via the microbubble supply holes is performed. It can be done at any time.

  A microbubble corresponds to a microbubble mainly having a bubble diameter of several μm to several tens of μm. In the present invention, a microbubble having a size of about 500 μm or less is also included in the microbubble.

It is a figure of the liquefaction prevention system which concerns on 1st Embodiment, (a) is a general view, (b) is a detailed figure which showed a mode that the perforated pipe | tube 7 is arrange | positioned in the curved hole 6. FIG. Explanatory drawing which showed the effect | action of the liquefaction prevention system which concerns on 1st Embodiment. The whole figure of the liquefaction prevention system concerning a modification. It is a figure of the liquefaction prevention system which concerns on another modification, (a) is a whole figure, (b) is a detailed figure which showed a mode that the diffuser tube 24 is arrange | positioned at the perforated pipe | tube 7. The whole figure of the liquefaction prevention system concerning a 2nd embodiment. It is a figure of the liquefaction prevention system which concerns on a modification, (a) is a general view, (b) is a detailed figure which showed a mode that the diffuser tube 24 is arrange | positioned at the perforated tube 7. FIG. The whole figure of the liquefaction prevention system concerning a 3rd embodiment. The whole figure of the liquefaction prevention system concerning a modification. Explanatory drawing which showed the procedure which implements the liquefaction prevention method which concerns on 4th Embodiment. Explanatory drawing which showed the procedure of implementing the liquefaction prevention method which concerns on 4th Embodiment continuously. Explanatory drawing which showed the liquefaction prevention method which concerns on the modification of 4th Embodiment. Explanatory drawing which showed the procedure which implements the liquefaction prevention method which concerns on 5th Embodiment. Explanatory drawing which showed the procedure of implementing the liquefaction prevention method which concerns on 5th Embodiment continuously.

  Embodiments of a liquefaction prevention system and method according to the present invention will be described below with reference to the accompanying drawings. Note that components that are substantially the same as those of the prior art are assigned the same reference numerals, and descriptions thereof are omitted.

[First Embodiment]
FIG. 1 is a diagram showing a liquefaction prevention system according to the present embodiment. As can be seen in the figure, the liquefaction prevention system 1 according to the present embodiment is intended for liquefaction prevention in the ground area extending below the embankment 3 as an existing structure constructed on the ground surface of the ground 2. The water shielding walls 4 and 4 are arranged in the ground 2 so that the ground area is sandwiched laterally, and the processing region 5 sandwiched by the water shielding walls passes below the embankment 3. The curved hole 6 is formed as a microbubble supply hole so that each end is opened at two ground surface positions sandwiching the embankment and has a plurality of steps in the depth direction. Are provided with perforated tubes 7, respectively.

  The curved hole 6 is formed in the processing region 5 so as to protrude downward and to be horizontal as a whole.

  On the other hand, the liquefaction prevention system 1 according to the present embodiment includes a bubble generation device 8 as a microbubble supply unit whose output side is connected to one end of a perforated tube 7 disposed in the curved hole 6.

  The bubble generating device 8 is connected to the input side of the output side of the vacuum pump 9, and by operating the vacuum pump, the bubble generating device 8 passes through the perforated tube 7 whose other end is connected to the input side. In addition to pumping up the groundwater in 5, microbubbles are contained in the groundwater, and then discharged from the output side as microbubble-containing water, and the microbubble-containing water is injected into the treatment region 5 through the perforated pipe 7. It is like that.

  The bubble generation device 8 can be configured by appropriately selecting from known generation methods such as a pressure dissolution method, a high-speed swirling method, and a gas-liquid mixing and shearing method.

  In order to construct the liquefaction prevention system 1 according to the present embodiment, first, the impermeable walls 4 and 4 are arranged in the ground so that the ground range extending below the embankment 3 is sandwiched laterally.

  The impermeable wall 4 only needs to extend downward to a depth at which it is desired to prevent liquefaction, and it is not necessary for the lower end to penetrate the impermeable layer 10. In addition, the impermeable wall 4 can be comprised by a sheet pile, for example.

  Next, at the same time as the arrangement process of the impermeable walls 4 or before and after, the curved holes 6 are formed in multiple stages in the depth direction in the treatment region 5 sandwiched between the impermeable walls 4 and 4.

  In forming the curved hole 6, as described above, the curved boring, the curved boring, and the curved drilling hole are made so that each end portion opens on the two ground surfaces sandwiching the embankment so as to pass below the embankment 3. It can be formed as appropriate using a known curve drilling technique in the field of chemical solution injection.

  For example, a flexible rod is gripped by a drilling machine installed on the ground, and the ground 2 is bent by a drilling bit attached to the tip of the rod while the rod is sent obliquely downward by the drilling machine. It is only necessary to form the hole 6 and manage the shape of the curved hole 6 by a posture detection sensor such as a gyro or a position detection sensor provided near the tip of the rod.

  Next, a perforated tube 7 is arranged in the curved hole 6, and the perforated tube has a number of through holes and an interval so that a desired amount of microbubble-containing water is injected into the treatment region 5 over a desired range. The opening dimensions or the formation range thereof are appropriately determined. The perforated tube 7 can be inserted and disposed in the curved hole simultaneously with the drilling of the curved hole 6 and also for protecting the hole wall.

  In the liquefaction prevention system 1 according to this embodiment, as shown in FIG. 2, the bubble generating device 8 is connected to one end of the perforated tube 7 and the vacuum pump 9 is connected to the other end. By operating the vacuum pump 9, microbubbles are contained in the groundwater pumped from the processing region 5 to form microbubble-containing water, and the microbubble-containing water is injected into the processing region 5 through the perforated pipe 7.

  In injecting water containing microbubbles, an on-off valve is installed in a hose (not shown) appropriately interposed between the bubble generating device 8 and the plurality of perforated pipes 7 to operate the on-off valve. Or by individually operating the packer inserted on the base end side of each perforated tube 7, the perforated tube 7 corresponding to the depth at which microbubbles are to be supplied is selected from the plurality of perforated tubes 7 To do.

  In this case, when the water permeability of the ground 2 varies in the vertical direction, for example, even when a layer having a high water permeability and a layer having a low water permeability are laminated with each other, the water permeability is high. The microbubbles are supplied to the perforated pipe 7 arranged in the layer with a relatively small discharge pressure and to the perforated pipe 7 arranged in the layer having a low water permeability with a relatively large discharge pressure. The microbubbles stay in water for a long time and are dispersed by the repulsive force of each other due to the electric charge and diffused to every corner of the soil particle gap in the treatment region 5, and after a certain period of time, mainly as normal bubbles or voids It remains in the soil particle gap and suppresses the increase of pore water pressure due to the ground shear deformation at the time of earthquake.

  It should be noted that some of the bubbles remaining in the gap between the soil particles in the treatment region 5 are diffused into the atmosphere over time, or the amount of bubbles is reduced by exchanging with the surrounding groundwater, and the saturation in the treatment region 5 is increased. When it rises, the bubble generation device 8 and the vacuum pump 9 are operated to replenish the treatment region 5 with water containing microbubbles as appropriate.

  As described above, according to the liquefaction prevention system 1 and method according to the present embodiment, the curved holes 6 are formed in multiple stages, and the perforated tubes 7 are inserted and arranged in the curved holes, respectively. Since the microbubble-containing water is individually injected, even if the water permeability of the ground 2 varies in the vertical direction, it is relatively small to the perforated tube 7 arranged in a layer having a high water permeability. It is possible to supply microbubbles to the perforated pipes 7 arranged in a layer having a low water permeability at a discharge pressure, respectively, with a relatively large discharge pressure. As a result, it is possible to reliably prevent liquefaction below the embankment 3 as well as to cover every corner of the treatment region 5.

  Moreover, according to the liquefaction prevention system 1 according to the present embodiment, since the microbubbles can be replenished to the processing region 5 at any time by operating the bubble generating device 8 and the vacuum pump 9, countermeasures have been taken. The initial liquefaction prevention state can be maintained for a long time thereafter.

  In the present embodiment, the perforated tube 7 is inserted and disposed in the curved hole 6 and the bubble generating device 8 is connected to the perforated tube. As long as protection can be achieved, the perforated tube 7 may be omitted, and the bubble generating device 8 may be connected to the inlet opening of the curved hole 6.

  Although not specifically mentioned in the present embodiment, if the microbubble-containing water is individually injected into the plurality of perforated tubes 7, the discharge pressure to each perforated tube 7 can be controlled individually. Instead of injecting the books one by one, they may be injected at the same time.

  In the present embodiment, the curved hole 6 is configured so that the curvature is substantially constant along the hole axis direction. However, if there is no problem during drilling, the curved hole 6 is divided into a portion with a large curvature and a portion with a small curvature. For example, it may be formed in a bent shape.

  Moreover, in this embodiment, since the case where the existing structure was the embankment 3 was taken as an example, the impermeable walls were the impermeable walls 4 and 4 constructed so as to sandwich the embankment, but the existing structures were If it is not extended in one direction, for example, if the plane is rectangular, a water shielding wall may be arranged so as to surround the existing structure.

  Moreover, in this embodiment, in order to produce microbubble containing water using the groundwater in the process area | region 5, this groundwater was pumped up with the vacuum pump 9, but the water used as the raw material of microbubble containing water is It is optional and may be procured separately in place of the groundwater in the treatment area 5. In this case, the vacuum pump 9 can be omitted.

  In the above-described embodiment in which microbubble-containing water is produced using the groundwater pumped from the processing region 5 by the vacuum pump 9 and injected into the processing region 5, as a result, the groundwater in the processing region 5 contains microbubbles. In the case where the vacuum pump 9 is not used, the existing groundwater is discharged from the lower side of the impermeable wall 4 to the periphery while being pushed down by the injected microbubble-containing water.

  Further, in the present embodiment, the microbubble supply holes are opened at two ground surface positions sandwiching the embankment so as to pass below the embankment 3 so that the respective end portions are opened in a plurality of stages in the depth direction. Instead of this, as shown in FIG. 3, instead of this, the microbubble supply holes are opened at two ground surface positions sandwiching the embankment 3 at the upper ends and in the depth direction. It is composed of inclined holes 6a, 6a extending downward from the embankment 3 so as to form a plurality of stages, and the bubble generating device 8 as microbubble supply means is provided in the perforated pipe 7a arranged in the inclined hole. The output side can be connected, and the input side of the vacuum pump 9 connected to the input side of the bubble generating device can be connected to the well 11 installed in the ground 2.

  In this modified example, the microbubble supply holes are not the curved holes 6 formed so as to protrude downward, but the inclined holes 6a and 6a, and the existing groundwater is pumped through the well 11. Although the configuration is different from the above-described embodiment, other configurations and operational effects are substantially the same as those of the above-described embodiment, and thus detailed description thereof is omitted.

  In the present embodiment, the microbubbles are supplied to the treatment area 5 in the form of microbubble-containing water. Instead, as shown in FIG. 4, the microbubbles are jetted into the groundwater in the treatment area 5. Microbubbles may be supplied to the processing area in a form.

  That is, the liquefaction prevention system 21 according to the modified example includes a microbubble supply unit that includes a blower 22 that pumps air and a diffuser pipe 24 that is connected to the output side of the blower via a pumping hose 23. The microbubble is ejected from the trachea into the groundwater, and the bubble generating device 8 ′ is constructed. The diffuser 24 is an internal space of the perforated pipe 7 and has a depth that is equal to or lower than the groundwater level 25 in the treatment region 5. It is installed in.

  In the liquefaction prevention system 21 according to this modification, by operating the blower 22, microbubbles are ejected from the air diffuser tube 24 and the microbubbles are supplied to the processing region 5 through the perforated tube 7. When the water permeability of the ground 2 varies in the vertical direction, for example, even when a layer having a high water permeability and a layer having a low water permeability are laminated to each other, they are arranged in a layer having a high water permeability. Air is supplied from the blower 22 at a relatively low jet pressure to the air diffuser 24 and at a relatively high jet pressure to the air diffuser 24 arranged in a layer having a small water permeability. While staying in the water for a long time, it diffuses to every corner of the soil particle gap in the treatment region 5 in a state of being dispersed by the mutual repulsive force due to the electric charge. Remaining particles gap, suppressing pore pressure increase due to soil shear deformation during an earthquake.

  It should be noted that some of the bubbles remaining in the gap between the soil particles in the treatment region 5 are diffused into the atmosphere over time, or the amount of bubbles is reduced by exchanging with the surrounding groundwater, and the saturation in the treatment region 5 is increased. In the case of rising, the microbubbles may be appropriately ejected to the processing region 5 by operating the blower 22.

  Since the other configurations and operational effects are the same as those of the above-described embodiment, the description thereof is omitted here.

[Second Embodiment]
Next, a second embodiment will be described. Note that components that are substantially the same as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 5 is a diagram showing a liquefaction prevention system according to the present embodiment. As can be seen from the figure, the liquefaction prevention system 31 according to the present embodiment is intended for liquefaction prevention in the ground range extending below the embankment 3 as an existing structure constructed on the ground surface of the ground 2. The water shielding walls 4 and 4 are arranged in the ground 2 so that the ground area is sandwiched laterally, and the processing region 5 sandwiched by the water shielding walls passes below the embankment 3. The curved hole 6 is formed as a microbubble supply hole so that each end is opened at two ground surface positions sandwiching the embankment and has a plurality of steps in the depth direction. Are provided with perforated tubes 7, respectively.

  The liquefaction prevention system 31 according to the present embodiment includes a bubble generating device 8 as a microbubble supply unit, a plurality of saturation measuring meters 33 installed at different depth positions in the processing region 5, and a plurality of perforations. Among the tubes 7, the output side of the bubble generating device 8 is connected to one end of a specific perforated tube, and the switch 32 a and the switch 32 b are connected to the other end, and the saturation measuring meter 33 outputs the same. And a control unit 34 for controlling the switching device 32a and the switching device 32b in accordance with the measured values, and the control unit has bubbles in the perforated tube 7 corresponding to the ground depth at which the saturation exceeds a predetermined threshold value. The switch 32a and the switch 32b are controlled so that the generator 8 and the vacuum pump 9 are connected.

  The bubble generating device 8 is connected to the input side of the output side of the vacuum pump 9, and by operating the vacuum pump 9, the groundwater in the treatment region 5 is pumped through the perforated pipe 7, After the microbubbles are contained in the ground water, the microbubbles-containing water is discharged from the output side, and the microbubbles-containing water can be injected into the treatment region 5 through the perforated pipe 7.

  As shown in FIG. 5, the saturation meter 33 is embedded in the processing region 5 so as to form a line along the depth direction. The saturation meter 33 is saturated based on a time domain measurement method called TDR (Time-Domain Reflectometry) and a frequency domain measurement method called FDR (Frequency-Domain Reflectometry) in addition to the resistivity method and the RI method. It can be set as the structure which measures a degree.

  In the liquefaction prevention system 31 according to the present embodiment, as in the liquefaction prevention system 1 described in the first embodiment, microbubbles are contained in groundwater pumped from the treatment region 5 to obtain microbubble-containing water. By injecting the bubble-containing water into the treatment region 5 through the perforated pipe 7, an increase in the pore water pressure at the time of the earthquake in the treatment region 5 is suppressed. However, in this embodiment, A drop in the saturation level is monitored by the saturation meter 33, and if the saturation level does not fall below a predetermined threshold value, the bubble generating device 8 and the vacuum pump 9 are added to the perforated tube 7 near the depth position. Is controlled by the control unit 34 so that the switch 32a and the switch 32b are driven.

  If it does in this way, microbubbles will be supplied intensively in the ground range with high saturation.

  On the other hand, after taking countermeasures, some of the bubbles remaining in the soil particle gap in the treatment area 5 are diffused into the atmosphere over time, or the amount of bubbles is reduced by exchanging with the surrounding groundwater. Since the saturation in the processing region 5 may increase, the increase in the saturation in the processing region 5 is continuously monitored by the saturation meter 33, and when the saturation exceeds a predetermined threshold value. The switching unit 32a and the switching unit 32b are driven and controlled by the control unit 34 so that the bubble generating device 8 and the vacuum pump 9 are connected to the perforated tube 7 close to the depth position.

  If it does in this way, a microbubble will be replenished intensively to the ground range where the degree of saturation became high.

  As explained above, according to the liquefaction prevention system 31 and method according to the present embodiment, even when a poorly water-permeable region, a water-impermeable region, or water is present below the embankment 3, The pore water pressure suppression action by the microbubbles or the normal bubbles extends evenly to every corner of the treatment region 5 and as a result, it is possible to reliably prevent liquefaction below the embankment 3.

  Further, according to the liquefaction prevention system 31 according to the present embodiment, since the microbubbles can be replenished to the processing region 5 at any time by operating the bubble generating device 8 and the vacuum pump 9, countermeasures have been taken. The initial liquefaction prevention state can be maintained for a long time thereafter.

  Further, according to the liquefaction prevention system 31 according to the present embodiment, the perforated tube 7 is disposed in the curved hole 6 and the microbubbles are supplied to the processing region 5 through the perforated tube. When the hole 6 is drilled, the perforated tube 7 can be made to play a role of protecting the wall of the curved hole.

  In addition, according to the liquefaction prevention system 31 according to the present embodiment, when the countermeasure work is performed, the saturation is set to a predetermined threshold by performing the construction while monitoring the decrease in the saturation in the processing region 5. It is possible to supply microbubbles intensively to a depth position that does not fall below the value, thus evenly supplying microbubbles within the treatment area 5 even in the ground having different water permeability along the depth direction. The liquefaction below the bank embankment 3 can be prevented more reliably, and after the countermeasure work is taken, the saturation is continuously monitored by monitoring the increase in the saturation within the treatment area 5. Microbubbles can be intensively replenished in the processing region 5 at a depth position exceeding the value, and the liquefaction prevention state can be more reliably maintained.

  In the present embodiment, the microbubbles are supplied to the treatment region 5 in the form of microbubble-containing water. Instead, as shown in FIG. 6, the microbubbles are jetted into the ground water in the treatment region 5. Microbubbles may be supplied to the processing area.

  That is, the liquefaction prevention system 41 according to the above modification is connected to the blower 22 for pumping air and the blower hose 23 via the pressure hose 23 and is an internal space of the perforated pipe 7 and has a groundwater level of 25 or less in the treatment region 5. A bubble generating device 8 ′ serving as a microbubble supply means, which is configured to discharge microbubbles from the diffuser pipe to the groundwater, and a different depth in the processing region 5. A plurality of saturation measuring meters 33 installed in the position, and a switcher 32a for connecting the blower 22 to a specific diffuser tube among the diffuser tubes 24 respectively disposed in the internal spaces of the plurality of perforated tubes 7, And a control unit 34 for controlling the switch 32a in accordance with the measurement value output from the saturation meter 33. The control unit is an air diffuser corresponding to the ground depth at which the saturation exceeds a predetermined threshold value. 4 so that the blower 22 is connected, so as to control the switching device 32a.

  In the liquefaction prevention system 41 according to the present modification, when a countermeasure is taken when supplying microbubbles to the processing area 5, the saturation meter 33 monitors a decrease in saturation in the processing area 5. When the saturation does not fall below a predetermined threshold value, the control unit 34 drives and controls the switching device 32a so that the blower 22 is connected to the diffuser tube 24 close to the depth position. After the processing, the increase in the saturation in the processing area 5 is continuously monitored by the saturation meter 33, and when the saturation exceeds a predetermined threshold value, the dispersion near the depth position is measured. The controller 34 drives and controls the switch 32 a so that the blower 22 is connected to the trachea 24.

  According to such a modified example, as in the above-described embodiment, when the countermeasure work is performed, the saturation is lowered below a predetermined threshold by performing the construction while monitoring the decrease in the saturation in the processing region 5. It is possible to supply microbubbles intensively at a depth position that is not deep, and thus even if the ground has different water permeability along the depth direction, the microbubbles are supplied uniformly within the processing region 5 and below the embankment 3 Liquefaction can be further reliably prevented, and after taking countermeasures, the saturation exceeds the predetermined threshold by continuously monitoring the increase in the saturation in the processing region 5. Microbubbles can be intensively replenished in the processing region 5 at the depth position, and the liquefaction prevention state can be maintained more reliably.

  Hereinafter, other modifications described in the first embodiment can also be adopted as modifications in the present embodiment. However, since the contents are the same as the modifications of the first embodiment, here Then, the explanation is omitted.

[Third Embodiment]
Next, a third embodiment will be described. In addition, about the components substantially the same as 1st, 2 embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  FIG. 7 is a diagram showing a liquefaction prevention system according to the present embodiment. As can be seen in the figure, the liquefaction prevention system 61 according to the present embodiment is intended for liquefaction prevention in the ground range extending below the embankment 3 as an existing structure constructed on the ground surface of the ground 2. Then, the water shielding walls 4 and 4 are arranged in the ground 2 so that the ground range is sandwiched laterally, and the processing region 5 sandwiched between the water shielding walls passes below the embankment 3. A curved hole 6 as a microbubble supply hole is formed so that each end is opened at two ground surface positions sandwiching the embankment in the form, and a perforated tube 7 is inserted into the curved hole. .

  Here, the liquefaction prevention system 61 includes a bubble generator 8 that supplies microbubbles to the treatment region 5 in the form of water containing microbubbles, and has a discharge pipe 63 connected to the output side of the bubble generator. The discharge pipe is arranged in the perforated tube 7 so as to be able to advance and retreat along the hole axis direction in the internal space of the hole tube 7.

  Here, packers 62 and 62 that can come into contact with the inner surface of the perforated pipe 7 during expansion are attached to the peripheral surface in the vicinity of the tip of the discharge pipe 63 so as to be separated from each other. A discharge hole 64 is provided in the discharge pipe so that the passage communicates with the internal space of the perforated pipe 7 sandwiched between the packers 62 and 62, and is sent from the output side of the bubble generating device 8 through the discharge hole. The microbubble-containing water thus produced is discharged.

  On the other hand, a vacuum pump 9 is connected to the input side of the bubble generating device 8, and on the side of the perforated tube 7 opposite to the side through which the discharge pipe 63 of the bubble generating device 8 is movably inserted. The pumping hose 65 connected to the vacuum pump 9 is inserted, and by operating the vacuum pump 9, the groundwater in the treatment area 5 collected by the perforated pipe 7 is pumped through the pumping hose 65. At the same time, after the microbubbles are contained in the groundwater by the bubble generating device 8, the microbubble-containing water is discharged from the output side of the bubble generating device.

  In order to construct the liquefaction prevention system 61 according to the present embodiment, the impermeable walls 4 and 4 are arranged in the same manner as in the first embodiment, and the curved hole 6 is formed in the treatment region 5 sandwiched between the impermeable walls. Form.

  The curved hole 6 can be appropriately formed using a curved hole drilling technique as in the first embodiment.

  Next, a perforated tube 7 is arranged in the curved hole 6, and the perforated tube has a number of through holes and an interval so that a desired amount of microbubble-containing water is injected into the treatment region 5 over a desired range. The opening dimensions or the formation range thereof are appropriately determined. The perforated tube 7 can be inserted and disposed in the curved hole simultaneously with the drilling of the curved hole 6 and also for protecting the hole wall.

  In order to perform liquefaction countermeasures using the liquefaction prevention system 61 according to the present embodiment, the packers 62 and 62 attached to the discharge pipe 63 of the bubble generating device 8 are moved forward and backward (not shown) so as to be in a desired horizontal position. The mechanism is driven to advance or retract the discharge pipe.

  When the packers 62 and 62 are positioned at a desired horizontal position, the packer 62 and 62 are then expanded by operating an air compressor (not shown), and the internal space of the perforated tube 7 is partitioned by the packer.

  Next, by operating the bubble generating device 8 and the vacuum pump 9, the groundwater is pumped from the processing region 5, and the microbubble-containing water in which microbubbles are contained in the groundwater is discharged through the discharge holes 64 of the discharge pipe 63. To the processing region 5.

  In this way, even if the water permeability of the ground 2 varies in the horizontal direction, when the packers 62 and 62 are positioned in the area where the water permeability is large, the area where the water permeability is small with a relatively small discharge pressure. When the packers 62 and 62 are positioned, the microbubble-containing water is supplied at a relatively large discharge pressure, and after the supply, the microbubbles stay in the water for a long time and are dispersed by the mutual repulsive force due to electric charges. It diffuses to every corner of the soil particle gap in the treatment region 5 and remains in the soil particle gap mainly as a normal bubble or as a void after a certain period of time, thereby suppressing an increase in pore water pressure due to ground shear deformation during an earthquake.

  It should be noted that some of the bubbles remaining in the gap between the soil particles in the treatment region 5 are diffused into the atmosphere over time, or the amount of bubbles is reduced by exchanging with the surrounding groundwater, and the saturation in the treatment region 5 is increased. When it rises, the bubble generation device 8 and the vacuum pump 9 are operated to replenish the treatment region 5 with water containing microbubbles as appropriate.

  As described above, according to the liquefaction prevention system 61 according to the present embodiment, the discharge pipe 63 of the bubble generating device 8 is inserted through the perforated tube 7 inserted through the curved hole 6 so as to freely advance and retract, The packers 62 and 62 are attached so as to sandwich the discharge hole 64 formed in the discharge pipe, and the discharge pipe 63 is moved forward and backward so that the discharge hole 64 is positioned at a desired horizontal position, and then the packers 62 and 62 are operated. Then, since the bubble generating device 8 is operated after partitioning the inner space of the perforated tube 7, even when the water permeability of the ground 2 varies in the horizontal direction, the area of the water permeability is large. When the packers 62 and 62 are disposed, the microbubbles are contained with a relatively small discharge pressure, and when the packers 62 and 62 are disposed in the region where the water permeability is small, the microbubbles are contained with a relatively large discharge pressure. It becomes possible to discharge water respectively, and thus the pore water pressure suppression action by microbubbles, normal bubbles or voids extends evenly to every corner of the treatment area 5 and as a result, liquefaction below the embankment 3 is surely prevented. It becomes possible to do.

  Further, according to the liquefaction prevention system 61 according to the present embodiment, the microbubbles can be replenished to the processing region 5 at any time by operating the bubble generating device 8 and the vacuum pump 9, so that countermeasures have been taken. The initial liquefaction prevention state can be maintained for a long time thereafter.

  In this embodiment, the perforated tube 7 is inserted into the curved hole 6 and the discharge pipe 63 of the bubble generating device 8 is inserted into the perforated tube. If the hole wall can be protected, the perforated pipe 7 may be omitted, and the discharge pipe 63 of the bubble generating device 8 may be inserted into the curved hole 6.

  Moreover, in this embodiment, since the case where the existing structure was the embankment 3 was taken as an example, the impermeable walls were the impermeable walls 4 and 4 constructed so as to sandwich the embankment, but the existing structures were If it is not extended in one direction, for example, if the plane is rectangular, a water shielding wall may be arranged so as to surround the existing structure.

  Moreover, in this embodiment, in order to produce microbubble containing water using the groundwater in the process area | region 5, this groundwater was pumped up with the vacuum pump 9, but the water used as the raw material of microbubble containing water is It is optional and may be procured separately in place of the groundwater in the treatment area 5. In this case, the vacuum pump 9 can be omitted.

  In the above-described embodiment in which microbubble-containing water is produced using the groundwater pumped from the processing region 5 by the vacuum pump 9 and injected into the processing region 5, as a result, the groundwater in the processing region 5 contains microbubbles. In the case where the vacuum pump 9 is not used, the existing groundwater is discharged from the lower side of the impermeable wall 4 to the periphery while being pushed down by the injected microbubble-containing water.

  In the present embodiment, the microbubbles are supplied to the treatment area 5 in the form of microbubble-containing water. Instead, as shown in FIG. 8, the microbubbles are ejected into the groundwater in the treatment area 5. Microbubbles may be supplied to the processing area in a form.

  That is, the liquefaction prevention system 71 according to the modification includes a blower 22 that pumps air to the bubble generating device 8 ', a pumping hose 23 connected to the output side of the blower, and a plurality of pumps connected to the pumping hose. A plurality of packers 62 that can come into contact with the inner surface of the perforated tube 7 at the time of expansion are attached to the peripheral surface of the pressure feeding hose 23 so as to be separated from each other and arranged in a row. Each air diffuser 24 is arranged between adjacent packers 62, 62, respectively.

  In order to apply the liquefaction countermeasure work using the liquefaction prevention system 71 according to this modification, 2 corresponding to the desired horizontal position among the plurality of packers 62 attached to the pressure feeding hose 23 of the bubble generating device 8 ′. The two packers 62 and 62 are inflated by operating an air compressor (not shown), and the internal space of the perforated tube 7 is partitioned by the packer, and air is only supplied to the diffuser tube 24 installed between the two packers. Each air diffuser 24 is operated so as to be pumped.

  Next, by operating the bubble generating device 8 ′, micro bubbles are ejected from the diffuser tubes 24 arranged in the two packers 62, 62 and supplied to the processing region 5 through the perforated tube 7.

  In this way, even when the water permeability of the ground 2 varies in the horizontal direction, when the packers 62, 62 are positioned in the area where the water permeability is large, the area having a low water permeability is obtained with a relatively small jet pressure. When the packers 62 and 62 are positioned, the microbubbles are respectively supplied with a relatively large jet pressure, and after the supply, the microbubbles stay in the water for a long time and are dispersed by the mutual repulsive force due to the charges. 5 spreads to every corner of the soil particle gap, and after a certain period of time, it remains in the soil particle gap mainly as normal bubbles or as voids, suppressing the increase in pore water pressure due to ground shear deformation during an earthquake.

  It should be noted that some of the bubbles remaining in the gap between the soil particles in the treatment region 5 are diffused into the atmosphere over time, or the amount of bubbles is reduced by exchanging with the surrounding groundwater, and the saturation in the treatment region 5 is increased. In the case of rising, the microbubbles may be appropriately ejected to the processing region 5 by operating the blower 22.

  Since the other configurations and operational effects are the same as those of the above-described embodiment, the description thereof is omitted here.

[Fourth Embodiment]
Next, a fourth embodiment will be described. In addition, about the components substantially the same as each embodiment mentioned above, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  9 and 10 are explanatory views showing a state in which the liquefaction prevention method according to this embodiment is performed. As shown in the figure, in order to carry out the liquefaction prevention method according to the present embodiment, as shown in FIG. 9 (a), the range extending below the embankment 3 of the ground 2 is sandwiched by the side in advance. As shown in FIG. 2, the impermeable walls 4 and 4 are arranged in the ground, and the curved holes 6 are formed in the depth direction in the treatment region 5 sandwiched between the impermeable walls, and the perforated pipe 7 is formed in the curved holes. Further, the pumping wells 11 and 11 are installed in the ground 2 near the impermeable walls 4 and 4 and on the embankment 3 side. In addition, about the construction procedure of the impermeable wall 4, the curved hole 6, and the perforated pipe 7, since it is the same as that of the case where the liquefaction prevention system 1 is constructed | assembled, the detailed description is abbreviate | omitted here.

  In order to implement the liquefaction prevention method according to the present embodiment, first, groundwater in the treatment region 5 is pumped through the pumping wells 11 and 11.

  The pumping of groundwater through the pumping wells 11 and 11 can be performed by using, for example, a so-called vacuum deep well method in which gravity drainage and forced drainage are used in combination. It can be reduced.

  If the groundwater level in the treatment area 5 is lowered to a position below the lowermost curved hole 6 among the curved holes 6 due to the above-described pumping, dehydration in the range from the groundwater level before pumping to the groundwater level after pumping. Aeration treatment is performed on the region 12 while maintaining the water level after pumping.

  In the ventilation process, as shown in FIG. 9 (b), an air compressor 13 is connected to one end of a perforated pipe 7 disposed in the curved hole 6, and the inside of the dehydration region 12 is passed through the perforated pipe 7 from the air compressor. Although air is sent to the water, the aeration treatment can remove moisture remaining on the surface of the soil particles and the soil particle gaps in the dewatering region 12. In addition, in order to volatilize the moisture remaining on the soil particle surface and the soil particle gap, the aeration process may be performed using warm air.

  Here, when the air permeability of the ground 2 varies along the depth direction, a flow valve (not shown) is installed at the open end of each perforated pipe 7, and the flow valve is connected to the ground 2. It is only necessary to operate according to the degree of air permeability and adjust the supply pressure or supply amount of air to each perforated tube 7.

  In this case, for example, even in a case where a layer with high air permeability and a layer with low air permeability are laminated together, the perforated tube 7 arranged in the layer with high air permeability is relatively small. By supplying air to the perforated pipe 7 arranged in a layer having a low air permeability at a supply pressure, a situation where air flows into a flowable path is avoided by feeding air at a relatively large supply pressure, and the entire dehydration region 12 is made uniform. It becomes possible to ventilate.

  Next, as shown in FIG. 10, bubble generating devices 8 and 8 are respectively connected to the respective ends of the perforated pipe 7 disposed in the curved hole 6, and the microbubble-containing water produced by the bubble generating device is used. Water is poured into the dewatering region 12 through the perforated tube 7. What is necessary is just to make it produce microbubble containing water using the groundwater pumped up from the process area | region 5. FIG.

  Here, in injecting the microbubble-containing water, if the water permeability of the ground 2 varies along the depth direction, the microbubble-containing water may flow unevenly into a path that easily flows when the water permeability of the ground 2 varies along the depth direction. However, the flow rate valve (not shown) installed between the bubble generating device 8 and each perforated tube 7 is operated according to the degree of water permeability of the ground 2 to provide a micro to each perforated tube 7. If the supply pressure or supply amount of bubble-containing water is adjusted, for example, even when a layer with high water permeability and a layer with low water permeability are laminated together, the layer with high water permeability Microbubble-containing water is injected by pouring water containing microbubbles into the perforated pipe 7 arranged at a relatively small injection pressure and into the perforated pipe 7 arranged in a layer with low water permeability at a relatively large injection pressure. Water is uniformly distributed in the dewatering region 12 It is possible to spread.

  When the water containing microbubbles is injected as described above, the dehydration region 12 becomes a condensate region filled with the water containing microbubbles. In the condensate region, the microbubbles stay in water for a long time, It diffuses to every corner of the soil particle gap in the processing region 5 in a dispersed state by the repulsive force of each other.

  In addition, in the dehydration region 12 before the water containing microbubbles is injected, water is removed from the soil particle gaps by the above-described aeration treatment, and most of the soil particle gaps are occupied by air. When water is injected, the air occupying the soil particle gap is trapped in the soil particle gap and remains as bubbles or voids.

  In addition, when water is injected into the microbubble-containing water, if the pumping wells 11 and 11 cannot prevent the groundwater from flowing around at the lower ends of the impermeable walls 4 and 4, the lower ends of the impermeable walls 4 and 4 are impermeable to the impermeable layer 10. It is sufficient to prevent the inflow of groundwater into the treatment region 5 by penetrating into the processing area 5 or pumping up the surrounding groundwater on the side opposite to the embankment 3.

  As described above, according to the liquefaction prevention method according to the present embodiment, after the groundwater in the treatment area 5 is pumped up, air is trapped in the soil particle gap in the dewatering area 12 generated in the pumping process. In addition to injecting water containing microbubbles into the dewatering region, in addition to lowering the degree of saturation due to the replacement of existing groundwater with water containing microbubbles, the degree of saturation due to air trapped in the soil particle gaps Thus, the reduction of the pore water pressure due to the microbubbles, bubbles or voids is further enhanced, and liquefaction below the embankment 3 can be more reliably prevented.

  Further, according to the liquefaction prevention method according to the present embodiment, the dehydration region 12 is subjected to the aeration process after the pumping process and before the water injection process. Moisture that remains attached is removed, and more air is trapped in the soil particle gaps as bubbles or voids, thus making it possible to further reduce the degree of saturation.

  In addition, according to the liquefaction prevention method according to the present embodiment, the supply to each perforated pipe 7 in accordance with the degree of variation in the air permeability and water permeability of the ground 2 in the aeration process and the water injection process of the microbubble-containing water. Since the pressure is adjusted, the entire dewatering region 12 can be uniformly ventilated and water can be uniformly injected into the entire dewatering region 12, and thus the above-described saturation lowering effect can be uniformly distributed over the entire processing region 5. It can be exerted.

  In the present embodiment, when water containing microbubbles is injected, aeration treatment is performed so that air is easily trapped in the soil particle gap. On the contrary, if water removal cannot be sufficiently performed by simple aeration processing, decompression in the dehydration region 12 and subsequent air supply processing may be performed instead of the ventilation processing. .

  In this way, water is evaporated almost completely due to a drop in the boiling point of water due to reduced pressure, and air is introduced to the corners of the soil particle gap by performing the air supply treatment in that state. It becomes easier for air to be trapped in the gap between the soil particles after performing the above.

  The depressurization in the dewatering region 12 is performed by air-tightening the dewatering region 12 by laying an airtight sheet on the surface of the embankment 3 or the surface of the ground 2 spreading on both sides of the embankment 3 and then removing the air present in the space in the dewatering region. What is necessary is just to pull out with a vacuum pump.

  In the air supply process following the pressure reduction in the dehydration region 12, the air supply pressure to each perforated tube 7 is changed according to the degree of variation in the air permeability of the ground 2 in the same manner as the air flow process in the above-described embodiment. It is possible to adjust, and according to such a configuration, the entire dehydration region 12 can be supplied uniformly.

  Further, in the present embodiment, the microbubble supply hole is configured by the curved hole 6, but instead of this, it is possible to configure the microbubble supply hole by the oblique holes 6a and 6a shown in FIG.

  Although not specifically mentioned in the present embodiment, as shown in FIG. 11, a plurality of saturation measuring meters 33 are installed at different depth positions in the processing region 5, and the processing region is processed by the saturation measuring meter. It is possible to employ a configuration for monitoring the degree of saturation within 5.

  In the above configuration, when water is injected into the microbubble-containing water, the saturation in the treatment area 5 is monitored by the saturation meter 33, and if the saturation after water injection is higher than planned, Water containing microbubbles is again injected through the perforated pipe 7 close to the depth position.

  In addition, after taking countermeasures, some of the bubbles remaining in the soil particle gap in the treatment area 5 are diffused into the atmosphere over time, or the amount of bubbles is reduced by exchanging with the surrounding groundwater. Since the saturation in the processing region 5 may increase, the increase in the saturation in the processing region 5 is continuously monitored by the saturation meter 33, and when the saturation exceeds a predetermined threshold value. Then, the microbubble-containing water is poured again through the perforated pipe 7 close to the depth position.

  In this way, it is possible to reliably lower the saturation in the processing region 5 when performing the countermeasure work, and also to maintain the initial reduced saturation state for a long period of time even after the countermeasure work is performed. It becomes possible.

  Since the saturation meter 33 has already been described in the second embodiment, a detailed description thereof will be omitted here.

[Fifth Embodiment]
Next, a fifth embodiment will be described. In addition, about the components substantially the same as each embodiment mentioned above, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  12 and 13 are explanatory views showing a state in which the liquefaction prevention method according to this embodiment is performed. As shown in the figure, in order to carry out the liquefaction prevention method according to the present embodiment, as shown in FIG. 12 (a), the range extending below the embankment 3 of the ground 2 is sandwiched by the side beforehand. As shown in FIG. 2, the impermeable walls 4 and 4 are arranged in the ground, the curved hole 6 is arranged in the treatment region 5 sandwiched between the impermeable walls, and the perforated pipe 7 is arranged in the curved hole. In the vicinity of the water walls 4, 4 and on the embankment 3 side, pumping wells 11, 11 are installed in the ground 2. In addition, about the construction procedure of the impermeable wall 4, the curved hole 6, and the perforated pipe 7, since it is the same as that of the case where the liquefaction prevention system 1 is constructed | assembled, the detailed description is abbreviate | omitted here.

  In order to implement the liquefaction prevention method according to the present embodiment, first, groundwater in the treatment region 5 is pumped through the pumping wells 11 and 11.

  The pumping of groundwater through the pumping wells 11 and 11 can be performed by using, for example, a so-called vacuum deep well method in which gravity drainage and forced drainage are used in combination. It can be reduced.

  If the groundwater level in the treatment area 5 is lowered to the position below the curved hole 6 due to the above-described pumping, the water level after pumping is compared with the dewatering area 12 in the range from the groundwater level before pumping to the groundwater level after pumping. The ventilation process is performed through the discharge pipe 63 disposed in the perforated pipe 7 while maintaining the above.

  Here, as described in the third embodiment (FIG. 7B), the discharge pipe 63 is placed in the perforated pipe so that it can advance and retreat along the hole axis direction in the inner space of the perforated pipe 7. Further, packers 62 and 62 that can be brought into contact with the inner surface of the perforated tube 7 during expansion are attached to the peripheral surface near the tip so as to be separated from each other. A discharge hole 64 is provided in the internal space of the tube 7 so that the internal flow path communicates.

  Accordingly, as shown in FIG. 12B, by operating the air compressor 13 connected to the proximal end side of the discharge pipe 63, air is fed from the air compressor into the dehydration region 12 through the discharge pipe 63. The moisture remaining on the surface of the soil particles and the soil particle gap in the dewatering region 12 can be removed. In addition, in order to volatilize the moisture remaining on the soil particle surface and the soil particle gap, the aeration process may be performed using warm air.

  When performing the ventilation process, the packer 62, 62 attached to the discharge pipe 63 is driven to advance or retreat by driving an advancing / retreating mechanism (not shown) so that the packer 62, 62 is desired. Then, the packers 62 and 62 are expanded to partition the inner space of the perforated pipe 7, and the air compressor 13 is operated in such a state so that the discharge holes 64 formed in the discharge pipe 63 can be used. Discharge air.

  A series of operations such as positioning by the forward or backward movement of the discharge pipe 63, partitioning in the perforated pipe 7 due to expansion of the packers 62 and 62, and discharging air from the discharge hole 64 are performed along the perforated pipe 7, for example. What is necessary is just to repeat it for every predetermined interval.

  In this way, even when the air permeability of the ground 2 varies in the horizontal direction, when the packers 62, 62 are positioned in the area where the air permeability is large, the area where the air permeability is small with a relatively small supply pressure. When the packers 62 and 62 are positioned, the air is sent with a relatively large supply pressure, so that the situation where air flows into the flowable path can be avoided and the entire dehydration region 12 can be vented uniformly.

  Next, as shown in FIG. 13, the bubble generating device 8 is connected to the proximal end side of the discharge pipe 63 arranged in the perforated tube 7, and the microbubble-containing water produced by the bubble generating device is perforated. Water is poured into the dewatering region 12 through the pipe 7. What is necessary is just to make it produce microbubble containing water using the groundwater pumped up from the process area | region 5. FIG.

  Here, in injecting the water containing microbubbles, there is a concern that the water containing microbubbles may flow unevenly in a path that easily flows when the water permeability of the ground 2 varies along the horizontal direction, as in the above-described aeration treatment. However, if the supply pressure or supply amount of the microbubble-containing water is adjusted according to the degree of water permeability of the ground 2 where the packers 62 and 62 are positioned, the microbubble-containing water is arranged in a region with high water permeability. The microbubble-containing water is dehydrated by pouring the microbubble-containing water into the discharge pipe 63 with a relatively small injection pressure and into the discharge pipe 63 arranged in a region with low water permeability with a relatively large injection pressure. The region 12 can be evenly distributed.

  When the water containing microbubbles is injected as described above, the dehydration region 12 becomes a condensate region filled with the water containing microbubbles. In the condensate region, the microbubbles stay in water for a long time, It diffuses to every corner of the soil particle gap in the processing region 5 in a dispersed state by the repulsive force of each other.

  In addition, in the dehydration region 12 before the water containing microbubbles is injected, water is removed from the soil particle gaps by the above-described aeration treatment, and most of the soil particle gaps are occupied by air. When water is injected, the air occupying the soil particle gap is trapped in the soil particle gap and remains as bubbles or voids.

  In addition, when water is injected into the microbubble-containing water, if the pumping wells 11 and 11 cannot prevent the groundwater from flowing around at the lower ends of the impermeable walls 4 and 4, the lower ends of the impermeable walls 4 and 4 are impermeable to the impermeable layer 10. It is sufficient to prevent the inflow of groundwater into the treatment region 5 by penetrating into the processing area 5 or pumping up the surrounding groundwater on the side opposite to the embankment 3.

  As described above, according to the liquefaction prevention method according to the present embodiment, after the groundwater in the treatment area 5 is pumped up, air is trapped in the soil particle gap in the dewatering area 12 generated in the pumping process. In addition to injecting water containing microbubbles into the dewatering region, in addition to lowering the degree of saturation due to the replacement of existing groundwater with water containing microbubbles, the degree of saturation due to air trapped in the soil particle gaps Thus, the reduction of the pore water pressure due to the microbubbles, bubbles or voids is further enhanced, and liquefaction below the embankment 3 can be more reliably prevented.

  Further, according to the liquefaction prevention method according to the present embodiment, the dehydration region 12 is subjected to the aeration process after the pumping process and before the water injection process. Moisture that remains attached is removed, and more air is trapped in the soil particle gaps as bubbles or voids, thus making it possible to further reduce the degree of saturation.

  Moreover, according to the liquefaction prevention method according to the present embodiment, in the ventilation process and the water injection process of the microbubble-containing water, according to the degree of the air permeability of the ground 2 where the packers 62 and 62 are positioned, Since the supply pressure to the discharge pipe 63 is adjusted, the entire dehydration region 12 can be uniformly ventilated and water can be uniformly injected into the entire dehydration region 12, thus processing the above-described saturation lowering effect. It can be applied uniformly over the entire region 5.

  In the present embodiment, when water containing microbubbles is injected, aeration treatment is performed so that air is easily trapped in the soil particle gap. On the contrary, if water removal cannot be sufficiently performed by simple aeration processing, decompression in the dehydration region 12 and subsequent air supply processing may be performed instead of the ventilation processing. .

  In this way, water is evaporated almost completely due to a drop in the boiling point of water due to reduced pressure, and air is introduced to the corners of the soil particle gap by performing the air supply treatment in that state. It becomes easier for air to be trapped in the gap between the soil particles after performing the above.

  The depressurization in the dewatering region 12 is performed by air-tightening the dewatering region 12 by laying an airtight sheet on the surface of the embankment 3 or the surface of the ground 2 spreading on both sides of the embankment 3 and then removing the air present in the space in the dewatering region. What is necessary is just to pull out with a vacuum pump.

  In the air supply process following the pressure reduction in the dehydration region 12, the air supply pressure to each perforated tube 7 is changed according to the degree of variation in the air permeability of the ground 2 in the same manner as the air flow process in the above-described embodiment. It is possible to adjust, and according to such a configuration, the entire dehydration region 12 can be supplied uniformly.

  Further, in the present embodiment, the microbubble supply hole is configured by the curved hole 6, but instead of this, it is possible to configure the microbubble supply hole by the oblique holes 6a and 6a shown in FIG.

  Although not specifically mentioned in the present embodiment, a plurality of saturation meter 33 are installed at different depth positions in the processing region 5 as in the modification of the fourth embodiment described in FIG. It is possible to employ a configuration in which the saturation in the processing region 5 is monitored by the saturation meter.

  In addition, since the effect in that case is as substantially the same as the said modification, the description is abbreviate | omitted here.

1, 21, 31, 41, 61, 71
Liquefaction prevention system 2 Ground 3 Embankment (existing structure)
4 Water-impervious wall 5 Treatment area 6 Curved hole (microbubble supply hole)
6a Oblique hole (micro bubble supply hole)
7,7a Perforated tube 8,8 'Bubble generator (microbubble supply means)
11 Pumping Well 12 Dewatering Area 22 Blower (Bubble Generator, Micro Bubble Supply Means)
23 Pressure feed hose (bubble generator, microbubble supply means)
24 Air diffuser (bubble generator, microbubble supply means)
32a Switch 33 Saturation meter 34 Control unit 62 Packer 63 Discharge pipe 64 Discharge hole

Claims (8)

The water shielding wall disposed in the ground so that the ground area extending below the existing structure such as embankment is surrounded or sandwiched by the side, and the treatment area surrounded or sandwiched by the water shielding wall Of the two ground surface positions sandwiching the existing structure, at least one end is open, and the micro is extended from the end toward the lower side of the existing structure so as to have a plurality of steps in the depth direction. bubbles and feed holes, made and a said microbubble supplying hole or the microbubbles microbubble supplying means capable of supplying through the insertion arranged perforated pipe supply hole microbubbles in the processing region, wherein said microbubbles Of the microbubble supply holes, the supply means supplies the microbubble supply holes arranged in the layer with high water permeability or the perforated pipe inserted and arranged in the layer with low water permeability to the layer with low water permeability. Microbubbles supply hole or it large supply pressure to the insert arranged perforated pipe, liquefaction prevention system, characterized in that has said microbubbles to be supplied. A water shielding wall disposed in the ground so that a ground area extending below an existing structure such as embankment is surrounded or sandwiched laterally, a bubble generating device capable of discharging microbubble-containing water, and the shielding. At least one of the two ground surface positions sandwiching the existing structure in a processing region surrounded or sandwiched by a water wall, an end is opened at one end and extends downward from the end to the existing structure. A microbubble supply hole and two packers spaced apart in the microbubble supply hole or a perforated pipe inserted and arranged in the microbubble supply hole, and the microbubble supply hole or the perforated pipe of the internal space, the discharge pipe of the air bubble generating device in a space partitioned by two packers is formed a discharge hole in said discharge output pipe so as to communicate, said bubble generating device, before A small supply pressure when the two packers are arranged in a large area of water permeability, a large supply pressure when placed within a small area of the water permeability, it has become the microbubble-containing water to be supplied Characterized liquefaction prevention system. A bubble generating device provided with a water-impervious wall disposed in the ground so that a ground range extending below an existing structure such as embankment is surrounded or sandwiched laterally, and a diffuser pipe for ejecting microbubbles; Of the two ground surface positions sandwiching the existing structure in the processing region surrounded or sandwiched by the water-impervious wall, at least one end opens to the lower side of the existing structure from the end. An extended microbubble supply hole and two packers spaced apart in the microbubble supply hole or a perforated tube inserted and arranged in the microbubble supply hole, and the microbubble supply hole or the in the internal space of the bore tube, the result by arranging the diffuser tube at a depth partitioned by a spatial becomes less groundwater level in two packers, the bubble generating device, the two packer Liquefaction but that a small supply pressure when placed greater area of water permeability, a large supply pressure when placed within a small area of the water permeability, characterized in that it is the microbubbles to be supplied Prevention system. The microbubble supply hole is configured by a curved hole that opens at each of the two ground surface positions so as to pass below the existing structure, or an upper end opens at each of the two ground surface positions. The liquefaction prevention system according to any one of claims 1 to 3, wherein the liquefaction prevention system is configured by oblique holes respectively extending downward from the existing structure. A water shielding wall is arranged in the ground so that a ground area extending below an existing structure such as embankment is surrounded or sandwiched by the side, and the treatment area surrounded or sandwiched by the water shielding wall is Among the two ground surface positions sandwiching the existing structure, the microbubble supply holes are formed so that at least one end thereof is open, and a plurality of steps are formed in the depth direction from the end toward the lower side of the existing structure. A liquefaction prevention method for injecting microbubble-containing water into the treatment region through a microtube supply hole or a perforated pipe inserted and arranged in the microbubble supply hole,
After pumping up groundwater in the treatment area, air is trapped in the soil particle gap in the dewatering area generated in the pumping process, and the microbubbles arranged in the layer with high water permeability among the microbubble supply holes A small supply pressure is applied to the bubble supply hole or the perforated pipe inserted therein, and a high supply pressure is applied to the microbubble supply hole arranged in the layer having a low water permeability or the perforated pipe inserted therein. A method for preventing liquefaction, comprising pouring the microbubble-containing water into the dewatering region. A water shielding wall is arranged in the ground so that a ground area extending below an existing structure such as embankment is surrounded or sandwiched by the side, and the treatment area surrounded or sandwiched by the water shielding wall is A microbubble supply hole is formed so as to open at least one of two ground surface positions sandwiching the existing structure so as to extend below the existing structure, and inserted into the microbubble supply hole or the microbubble supply hole A liquefaction prevention method for injecting microbubble-containing water into the treatment region from a location partitioned by two packers spaced apart from each other in a perforated tube disposed therein,
After pumping up the groundwater in the treatment area, a small supply pressure when air is trapped in the soil particle gap in the dewatering area generated in the pumping process and when the two packers are arranged in a highly permeable area The liquefaction prevention method is characterized by pouring the microbubble-containing water into the dewatering region so that a high supply pressure is obtained when it is arranged in a region with low water permeability . The microbubble supply hole is configured by a curved hole that opens at each of the two ground surface positions so as to pass below the existing structure, or an upper end opens at each of the two ground surface positions. 7. The liquefaction prevention method according to claim 5 or 6 , wherein the liquefaction prevention method comprises slant holes each extending downward from the existing structure. 8. The method according to claim 5 , wherein after the pumping step and before the water pouring step, the dehydration region is subjected to aeration treatment, or the depressurization in the dehydration region and the subsequent air supply treatment are performed . liquefaction prevention method of one described.

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