JP5564676B1 - Liquefaction suppression device and liquefaction suppression method - Google Patents

Abstract

The present invention relates to a liquefaction suppression device capable of preventing damage caused by liquefaction during an earthquake, such as the inclination or subsidence of a building built on a ground on which a loose sand layer accumulates, and the floating of a structure embedded in the ground. And a method for inhibiting liquefaction.
It is installed around a manhole A embedded in the liquefied ground. A drainage pipe 1 buried around the manhole A, a drainage adjustment valve 5 attached to the upper end of the drainage pipe 1, a coil spring 6 and a cap 7 are provided. The drainage regulating valve 5 is opened upward by the excess pore water pressure in the ground that has flowed into the drainage pipe 1 to open the drainage port 1b provided at the upper end of the drainage pipe 1 and the excess gap. The drainage port 1b is attached so as to be closed by being pushed down by the coil spring 6 in the downward direction of the pipe axis of the drainage pipe 1 as the water pressure decreases. A plurality of water collecting holes 1B are provided around the drain pipe 1.
[Selection] Figure 2

Description

  The present invention relates to a structure built on a ground that is likely to be liquefied, a liquefaction suppression device and a liquefaction suppression method used for liquefaction countermeasures for buried objects embedded in the ground, and liquefaction during an earthquake Prevents subsidence and inclination of existing structures such as above-ground houses, levitation due to liquefaction of underground structures such as underground water and sewage pipes, telegraph cable ducts, underground pipes such as manholes and common grooves, etc. In addition, ground subsidence around the structure due to excessive groundwater drainage during normal times can be prevented.

  In recent years, it has become clear that ground liquefaction during earthquakes occurs not only in soils with loose sand layers, but also in soils with cohesive soils or with soils with alternating clay and sand layers. .

  In these grounds, when liquefaction occurs during an earthquake, buildings such as houses built on the ground will tilt or sink, and underground pipes such as water and sewage pipes, telegraph and telephone cable ducts buried underground, In some cases, existing underground structures such as manholes and common trenches may be damaged.

  Conventionally, as a method of preventing damage due to this type of liquefaction, a sand pile is formed around the structure on the ground or in the ground, the ground is compacted to increase the density, and the cement-based solidification in the ground A solidification method that suppresses deformation during earthquakes by injecting materials into hard ground, and also burying multiple drain pipes around the structure to drain excess pore water in the ground to the ground level The groundwater level lowering method to reduce

JP2013-155559A JP-A-5-321238 Japanese Patent Laid-Open No. 2007-132061

  However, the methods of compacting the ground by creating sand piles in the ground and improving the ground to hard ground with cement-based improvement materials use dedicated heavy machinery and equipment, so such dedicated heavy machinery and equipment In many cases, a work space that can be used for work is required, and the work itself is large and cannot be performed around existing structures. In the first place, these construction methods are generally applied to lands.

  Moreover, in the known groundwater level lowering method, liquefaction during an earthquake can be prevented by desaturating the groundwater level, but there is a risk of causing ground subsidence as the groundwater level decreases.

  In addition, excessive groundwater drainage may consolidate the ground around the structure and cause unexpected ground subsidence, which may cause unexpected damage such as subsidence and inclination. In addition, it is practically difficult to keep the groundwater level low for earthquakes that do not know when they will strike.

  In recent years, in particular, it has been found that liquefaction occurs not only on loose sandy ground but also on ground where cohesive soil is mixed or ground where a viscous soil layer is interposed. If drain pipes or the like are permanently installed on such ground and groundwater continues to be drained, pore water in the ground may be excessively drained and the ground around the structure may cause consolidation settlement.

  The present invention has been made in order to solve the above-mentioned problems, and the liquidity at the time of an earthquake such as the sinking or tilting of a structure built on the ground where there is a risk of liquefaction, the floating of a structure embedded in the ground, etc. It aims to provide a liquefaction suppression device and a liquefaction suppression method that can prevent damage caused by liquefaction and prevent ground subsidence around existing structures due to excessive drainage of groundwater during normal times It is.

  The present invention suppresses liquefaction by controlling the pore water pressure between soil particles in the ground, so that subsidence and inclination of existing structures accompanying liquefaction during earthquakes, water and sewage pipes, telegraph cable ducts, etc. It is possible to prevent underground structures such as underground pipes, as well as floating structures such as manholes and common ditches, and to prevent ground subsidence around existing structures due to excessive drainage of normal groundwater. It is a thing.

  According to the present invention, normally, the interstitial water in the ground is drained into the drain pipe, and the ground is in an unsaturated state (a state in which groundwater and air are present). Even if it occurs and the soil deposition shrinks, the effective stress between the soil particles is not converted into pore water pressure, so that the occurrence of liquefaction can be prevented.

  In addition, normally, the drainage port provided at the upper end of the drainage pipe is closed by the drainage adjustment valve, so that pore water in the ground is not drained to the ground via the drainage pipe. Abnormal subsidence of the ground due to excessive drainage can be prevented.

  Furthermore, even if the effective stress between the soil particles decreases due to the dilatancy during the earthquake, and the pore water pressure increases accordingly, the drainage adjustment valve is pushed up and opened by the excess pore water pressure flowing into the drain pipe. As a result, the excess pore water is drained from the drain port, so that the increase in the excess pore water pressure in the ground is suppressed, so that the effective stress between the soil particles is prevented from reaching 100% liquefaction. be able to.

  This will prevent the inclination and sinking of existing structures on the ground, underground pipes such as water and sewage pipes in the ground, telegraph cable racks, etc., as well as the floating of existing underground structures such as manholes and common grooves. Can do.

  In this case, under normal conditions, the drainage adjustment valve is pushed down below the pipe axis of the drainage pipe by an elastic member such as a spring or rubber, so that the drainage port is closed. When the water pressure rises and the drainage adjustment valve is pushed up, the drainage port is opened, so that excess pore water pressure can be drained.

  Also, as the excess water pressure in the ground decreases as the earthquake subsides, the drainage adjustment valve is pushed down by the elastic member downwards the pipe axis and automatically returns to its original position. There is no drainage of pore water.

  In the present invention, it is only necessary to drill the hole around the existing structure or in the ground directly below and lay the drain pipe without modifying the existing structure.

  In the present invention, the drainage adjustment valve can be adjusted so as to have a compression amount of an elastic body such as a spring or rubber corresponding to the magnitude of the excess pore water pressure. And by controlling the amount of drainage of pore water in the ground by adjusting the opening of the drain outlet corresponding to the compression amount, to suppress liquefaction during earthquakes and prevent subsidence during normal times Can do.

  The graph shown in FIG. 7 shows the relationship between the change in excess pore water pressure ratio and the liquefaction during an earthquake in the excess pore water pressure dissipation method. The excess pore water pressure ratio in FIG. By adjusting, even if the excess pore water pressure rises, it is not more than 1.0, so it does not reach a 100% liquefaction state where the effective stress between soil particles becomes zero, so subsidence of the ground does not occur Or even if it occurs, it is estimated that it is slight.

  The elastic member can be a compression coil spring, elastic rubber, or the like, and in particular, adjust the resilience of the elastic member (the force that pushes down the drainage adjustment valve) to remove excess pore water drained from the drainage port. By adjusting the amount of drainage, excess pore water pressure in the ground can be adjusted to suppress liquefaction. In addition, a check valve for preventing the backflow of the pore water drained out of the drain pipe may be attached to the drain port (FIGS. 4 (a) and (b)).

  In addition, by installing a water-absorbing mat consisting of a sandproof mat, a water-permeable mat, or a synthetic resin foam such as polyethylene foam on the outer periphery below the drain outlet of the drain pipe, the drain pipe in the event of an earthquake is covered. The ground water in contact with the outer periphery of the ground can be drawn into the drain pipe through the drainage hole over the entire surface, and pore water can be collected evenly and uniformly in the drain pipe from the entire area around the drain pipe. Clogging of the water collecting hole can be prevented by the earth and sand of the hole wall, and thereby a rapid increase in pore water pressure in the ground around the structure can be suppressed.

  In addition, a shielding wall (underground wall) is installed around the structure and drain pipe to block the inflow of groundwater from the outside of the shielding wall, and inflow of groundwater and propagation of seismic force into the shielding wall during an earthquake. The liquefaction suppression function can be enhanced by suppressing the increase in excess pore water pressure.

  In addition, a perforated pipe made of a steel pipe or a vinyl chloride pipe can be used as the drain pipe, and the drainage adjusting valve can be made of hard rubber, hard synthetic resin, soft rubber or the like.

  Further, by providing a drainage channel made of crushed stone or gravel around the upper end of the drainage pipe, excess pore water drained on the ground can be drained quickly. In particular, when a drain pipe is installed around the manhole, a drain pipe can be laid between the drain hole and the manhole, and the interstitial water drained from the drain port can be drained into the manhole.

  Furthermore, the ground subsidence at the normal time around the existing structure can be suppressed by circulating the excess pore water drained to the ground through the drain pipe in the ground. In order to realize this method, there is a reservoir for temporarily storing excess pore water drained to the ground via a drain pipe and an excess gap in the reservoir depending on the degree of excess pore water pressure in the ground. What is necessary is just to provide the circulating pump etc. for circulating water in the ground.

  When this method is implemented around an existing manhole, the manhole and drainage pipe are connected by a horizontal drainage pipe instead of providing a water storage tank, and excess pore water during an earthquake is drained into the manhole. Sometimes, the water in the manhole may be circulated in the ground around the manhole through a horizontal drainage pipe and a drainage pipe.

  According to the present invention, by controlling pore water between soil particles in the ground to suppress liquefaction, the subsidence and inclination of existing structures on the ground accompanying liquefaction during earthquakes, water and sewage pipes, telegraphs, It is possible to prevent underground underground pipes such as telephone cable ducts and the like from floating due to liquefaction of existing underground structures such as manholes and common grooves.

  That is, without adding any work to the existing underground structure, liquefaction can be prevented by simply burying the drain pipe of the present invention by drilling in the surrounding ground of the existing underground structure. Can- Moreover, the drainage pipe can easily stop the original drainage function of the drainage pipe for draining the groundwater to the ground by closing the drainage adjustment valve to be in a sealed state.

  In addition, since the drain outlet provided at the upper end of the drain pipe is normally closed by the drain adjustment valve, the pore water in the ground is not drained to the ground via the drain pipe. Since the drainage pipe does not have a drainage function, it is possible to prevent abnormal subsidence of the ground during normal times. Therefore, even if the ground contains a cohesive soil or includes a cohesive soil layer, the consolidation phenomenon does not occur, so that the structure does not sink.

  On the other hand, in the event of an earthquake, even if the effective stress between soil particles decreases due to dilatancy and the pore water pressure rises, the drainage adjustment valve is pushed up by the excess pore water pressure in the drain pipe, and the drain port opens and the excess gap Since the increase in excess pore water pressure in the ground is suppressed by draining water, it is possible to prevent a 100% liquefaction state in which the effective stress between soil particles becomes zero.

  Furthermore, by adjusting the opening of the drainage regulating valve in response to excess pore water pressure, the superstructure can be adjusted even if a slight ground change occurs by adjusting the effective stress ratio between 0 and 1.0. The displacement can be adjusted to the extent that no coating occurs.

  As a result, liquids such as the tilting and sinking of existing structures on the ground, underground water pipes such as water and sewage pipes in the ground, telegraph and telephone cable racks, and the floating of existing underground structures such as manholes and common grooves The damage caused by the conversion can be prevented.

FIG. 1 (a) is a plan view and FIG. 1 (b) is a side view showing a liquefaction suppression device laid around a manhole. It is a longitudinal cross-sectional view of a liquefaction suppression apparatus. 3 (a) is a cross-sectional view taken along the line II in FIG. 2, and FIG. 3 (b) is a cross-sectional view taken along the line. 4 (a) and 4 (b) are cross-sectional views showing the structure of a check valve provided at the drain port. It is an enlarged vertical sectional view of a drainage pipe explaining the situation where excess pore water in the ground at the time of an earthquake is drained to the ground through the drainage pipe. It is a partial side view of the drain pipe which has the block solid body which consists of solidification materials on the outer periphery. It is a graph which shows the relationship between the change of the excess pore water pressure ratio at the time of an earthquake, and liquefaction in the excess pore water pressure dissipation method. It is explanatory drawing which shows the method of circulating the excess pore water drained on the ground in the ground around an existing structure.

  FIGS. 1-5 is one Embodiment of this invention, and illustrates the liquefaction adjustment apparatus laid around the manhole embed | buried in the ground where a loose sandy layer accumulates.

  In the figure, around the manhole A, a plurality of drain pipes 1 are buried vertically and at regular intervals in the circumferential direction of the manhole A. In particular, in a ground that is liable to be liquefied, such as a soft ground, a plurality of drain pipes 1 are buried around the manhole A concentrically.

  Further, a drainage mat 2 made of crushed stone or gravel is laid in a predetermined thickness around each drainage pipe 1 and on the surface layer portion of the ground between each drainage pipe 1 and 1, and below the drainage mat 2. Around each drain pipe 1, a water collecting mat 3 made of a sandproof mat, a water permeable mat, or a synthetic resin foam such as a polyethylene foam is installed with a certain thickness in the radial direction of the drain pipe 1 (see FIG. 2, see FIG. 3 (b) and FIG.

  The drain pipe 1 is made of a hard synthetic resin pipe such as a steel pipe or a vinyl chloride pipe, and a plurality of water collecting holes 1a are formed in the peripheral wall of the lower end portion and the intermediate portion of each drain pipe 1 in the axial direction and the circumferential direction of the drain pipe 1. Are formed at regular intervals. In addition, a plurality of drain ports 1b are formed on the peripheral wall of the upper end portion (a portion above the middle portion) of each drain pipe 1.

  The drainage port 1b is formed in a side surface in three or four directions of the drainage pipe 1 so as to be slightly larger than the water collecting hole 1a and is open in a drainage mat 2 laid around the drainage pipe 1.

  In the drain port 1b, a drainage regulating valve 4 that regulates the drainage of excess pore water drained to the ground via the drainage pipe 1 and the backflow into the drainage pipe 1 of excess pore water drained to the ground are prevented. Check valves 5 are respectively attached. The check valve 5 is formed by attaching a rubber tube or the like on the outer periphery of the drain pipe 1 so as to cover the drain port 1b.

  The drainage adjustment valve 4 is inserted into the upper end of the drainage pipe 1 so as to move up and down within a certain range in the drainage pipe 1. Further, an elastic member 6 (hereinafter referred to as “spring 6”) that constantly applies a force so as to push down the drainage adjustment valve 4 in the downward direction of the pipe axis of the drainage pipe 1 and the reaction force of the spring 6. Caps 7 to be received are respectively attached. A compression coil spring is used for the spring 6, and elastic rubber may be used instead of the spring 6.

  The drainage adjustment valve 4 is formed in a short cylindrical shape that can be inscribed in the inner peripheral surface of the drainage pipe 1 from hard rubber or hard synthetic resin. Further, the drainage adjustment valve 4 is pushed down to the position of the drainage port 1b by the spring 6, so that the drainage hole 1b is closed by the drainage adjustment valve 4. Normally, the drainage adjustment valve 4 is drained by the spring 6 by the drainage adjustment valve 4b. It is pushed down to position 1b and closed.

  Also, in the event of an earthquake, the drainage regulating valve 4 resists the force of the spring 6 due to the excess pore water pressure flowing into the drainage pipe 1 from each water collecting hole 1 a of the drainage pipe 1. The drain port 1b is opened by being pushed upward in the axial direction, and the excess pore water in the drain pipe 1 is drained from the drain port 1b into the drain mat 2 around the drain pipe 1 by this. It is like that.

  The spring 6 is interposed between the drainage adjustment valve 4 and the cap 7, and acts so as to constantly push down the drainage adjustment valve 4 below the pipe axis of the drainage pipe 1. Thereby, the drain port 1b is normally closed, and the pore water in the ground that has flowed into the drain pipe 1 is prevented from being drained out of the drain pipe 1 through the drain port 1b.

  Also, when the effective stress between soil particles decreases due to dilatancy and the pore water pressure rises during an earthquake, the drainage regulating valve 4 is pushed up by the excess pore water pressure in the drainpipe 1 and the drainage port 1b opens to open the excess porewater. Is drained out of the drain pipe 1 to suppress an increase in excess pore water pressure in the ground.

  The cap 7 is formed in a short cylindrical shape capable of accommodating the drainage adjustment valve 4 and the spring 6, and the upper end surface portion is a reaction force receiver 7 a of the spring 6. The cap 7 has an inner diameter that can be circumscribed to the upper end portion of the drain pipe 1, and is detachably attached to the upper end portion of the drain pipe 1 by a screw type or the like.

  In such a configuration, the drainage adjustment valve 4 attached to the upper end portion of each drainage pipe 1 is normally pushed down by the spring 6 in the downward direction of the pipe axis of the drainage pipe 1, thereby closing the drainage port 1b. Since pore water in the ground that has flowed into the drain pipe 1 is not drained to the ground from the drain port 1b, ground subsidence around the manhole A due to excessive drainage of groundwater during normal times can be prevented.

  On the other hand, in the ground around the manhole A with the occurrence of the earthquake, even if the effective stress between the soil particles decreases due to the ground dilatency, and the pore water pressure increases accordingly, the excess pore water pressure in each drain pipe 1 As the drainage regulating valve 4 is pushed up by this, the drainage port 1b opens and excess pore water is drained from the drainage port 1b (see FIG. 5), so that the increase in excess pore water pressure in the ground is suppressed. It is possible to prevent a 100% liquefaction state in which the effective stress between soil particles is zero, and to prevent the manhole A from rising (see FIG. 7).

  In this case, in particular, a water absorption mat 3 made of a synthetic resin foamed body such as a sandproof mat, a water permeable mat, or a polyethylene foamed body is installed on the outer periphery below the drain port 1a of the drain pipe 1 to cover the water collecting hole 1a. As a result, the groundwater in the ground that is in contact with the outer periphery of the drainage pipe 1 at the time of the earthquake is taken into the drainage pipe 1 from the catchment hole 1a over the entire surface, and pore water is drained from the ground of the entire area around the drainage pipe 1 Water can be collected uniformly in the drain pipe 1 (see FIG. 5).

  Moreover, clogging of the water collecting hole 1a can be prevented by the earth and sand of the hole wall, thereby suppressing a rapid increase in pore water pressure in the ground around the manhole A (see FIG. 5).

  In addition, when the earthquake has passed and the liquefaction has settled, excess pore water in the drain pipe 1 gradually permeates into the surrounding ground through the water collecting hole 1a, and accordingly, the excess pore water pressure in the drain pipe 1 gradually increases. To drop. At the same time, the drainage adjusting valve 5 is pushed back to the original position by the spring 6, and the drainage port 1b is closed.

  When the liquefaction suppression device of the present invention is laid around the manhole A, a horizontal drainage pipe (not shown) that leads from the drainage port 1b of each drainage pipe 1 to the manhole A is laid. If the excess pore water drained to the ground via the drain is drained to the manhole A via the horizontal drainage pipe, the ground drain mat 2 can be omitted.

  4 (a) and 4 (b) illustrate a modification of the check valve provided in the drain hole. In the figure, there are a plurality of short columnar protrusions 8 on the peripheral wall of the upper end of the drain pipe 1. The drainage pipe 1 is formed so as to protrude in three or four directions.

  A circular hole 8a is formed at a predetermined depth in the center of each protrusion 8, and a drain hole 8b is formed in the peripheral wall so as to communicate with the hole 8a. Further, the bottom of the hole 8a is formed in a concave curved surface shape, and a drain hole 1b communicating with the drain pipe 1 is formed at the center thereof.

  In addition, a sphere 9 or a cone 10 inscribed in the bottom of the hole 8a is inserted into the hole 8a, a compression coil spring 11 is inserted thereafter, and a reaction force receiver of the compression coil spring 11 is inserted into the end of the hole 8a. A cap 12 is attached.

  With the above configuration, the sphere 9 and the compression coil spring 11 or the cone 10 and the compression coil spring 11 are accommodated in the hole 8a, and the sphere 9 and the cone 10 are strongly pressed against the bottom of the hole 8a by the compression coil spring 11, respectively. .

  As a result, the drain port 1b does not allow excess pore water drained outside the drain pipe 1 to flow back into the drain pipe 1 from the drain hole 1b. The cap 12 is detachably attached to the end portion of the protruding portion 8 by a screw type or the like, whereby the sphere 9 or the cone 10 and the compression coil spring 11 are detachably attached together with the cap 12.

  FIG. 6 shows the drain pipe 1 and its surroundings by forming one or more solid consolidated bodies 13 made of a solidified material on the outer periphery of each drain pipe 1 at intervals in the pipe axis direction and integrally with the drain pipe 1. The drainage pipe 1 is fixed in the ground and the drainage pipe 1 is fixed in the ground so that the drainage pipe 1 can surely fulfill the function of suppressing liquefaction without tilting or rising in the event of an earthquake.

  The massive consolidated body 13 in this case can be formed by injecting a cement-based solidified material or the like into a bag body attached around the drain pipe 1. Further, the lump gel (solidifying material) can be partially formed in a lump shape without clogging the water collecting port 1a around the drain pipe 1.

  Further, the solidifying material can be injected through a water collecting hole 1 a provided in the peripheral wall of the drain pipe 1 by inserting an injection pipe (not shown) equipped with a double packer into the drain pipe 1.

  FIG. 7 illustrates a method of suppressing ground subsidence around an existing structure by circulating excess pore water drained to the ground through a drain pipe.

  In order to carry out this method, a reservoir 14 for temporarily storing excess pore water drained to the ground via the drain pipe 1 and the inside of the reservoir 14 according to the degree of excess pore water pressure in the ground A recirculation pump 15 or the like may be provided for circulating the excess pore water in the ground.

  In particular, when this method is carried out around the existing manhole A, the manhole and drainage pipe are connected by a horizontal drainage pipe (not shown) instead of providing a water storage tank, and excess pore water during an earthquake is manholed. In addition, the water in the manhole may be circulated in the ground around the manhole through a horizontal drainage pipe and a drainage pipe.

  The present invention is accompanied by liquefaction such as abnormal inclination and subsidence of buildings built on the ground where there is a risk of liquefaction such as ground where a loose sand layer accumulates, and the rise of structures such as manholes embedded in the ground. Damage can be prevented.

A Manhole 1 Drain pipe
1a Water collecting hole
1b Drainage port 2 Drainage mat 3 Catchment mat 4 Check valve 5 Drainage adjustment valve 6 Spring (elastic member)
7 Cap
7a Reaction force receiving plate 8 Projection
8a hole
8b Drain hole 9 Sphere
10 cones
11 Compression coil spring
12 cap
13 Bulk consolidated body
14 Water tank
15 Pore water pressure sensor
16 Circulation pump

Claims (12)

  In a liquefaction suppression device installed around a structure built on liquefied ground or an underground structure built in liquefied ground, a drain pipe buried around the structure and the drain pipe A drainage adjusting valve attached to the upper end, an elastic member and a cap, wherein the drainage pipe has a drainage port at the upper end, and the drainage adjustment valve is drained by excess pore water pressure in the ground flowing into the drainage pipe. A liquefaction suppression device, wherein the liquefaction suppression device is attached so as to open a mouth and close the drainage port by the elastic member as the excess pore water pressure decreases.   2. The liquefaction suppression device according to claim 1, wherein the liquefaction suppression device is configured to adjust an opening degree of the drainage adjustment valve in response to an excessive pore water pressure.   The liquefaction suppression device according to claim 1 or 2, wherein a plurality of water collection holes are provided around the drain pipe.   The liquefaction suppression device according to any one of claims 1 to 3, wherein the elastic member is formed of a coil spring or rubber.   The liquefaction suppression device according to any one of claims 1 to 4, further comprising a check valve for preventing a reverse flow of excess interstitial water discharged to the drain port. apparatus.   The liquefaction suppression apparatus according to any one of claims 1 to 5, wherein a water collection mat is attached to an outer periphery of the drain pipe so as to cover the water collection hole.   The liquefaction suppression device according to any one of claims 1 to 6, wherein a drainage mat made of crushed stone or gravel is laid on a surface layer around the drainage pipe.   The liquefaction suppression device according to any one of claims 1 to 7, wherein a shielding wall is provided around the structure and the drain pipe.   A plurality of the liquefaction suppression devices according to any one of claims 1 to 8 are installed in the ground around the structure at intervals, and a surface layer around each liquefaction suppression device and between the liquefaction suppression devices. A liquefaction suppression method characterized in that a drainage mat made of gravel or crushed stone is laid on the part, and excess pore water in the ground around the structure at the time of an earthquake is drained to the drainage mat.   The liquefaction suppression method according to claim 9, wherein the effective stress ratio of the ground is adjusted between 0 and 1.0 by adjusting the opening of the drainage regulating valve in response to the excess pore water pressure. Suppression method.   11. The liquefaction suppression method according to claim 9 or 10, wherein a plurality of solid aggregates are formed at intervals on the outer periphery of the drain pipe to fix the drain pipe in the ground.   The liquefaction suppression method according to any one of claims 9 to 11, wherein excess pore water drained to the ground is circulated in the ground around the existing structure.

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