JPH0343515A - Foundation improvement method - Google Patents

Abstract

PURPOSE:To prevent a sand-like foundation from being fluidized, by arranging injecting means and draining means in a foundation around a structure building so that a liquid mixed with a slight quantity of air-bubbles is charged under pressure from the top ends of the injecting means while underground water is drained. CONSTITUTION:An innumerous number of small blind air-permeable holes are formed in side walls and block plates which block the front ends of an injection pipes 3. Then, an air-bubble mixing device 4 is composed of a closed pressure container 10, a compressor 11, a means for feeding water 12 into the container 10 and an agitator 13. Further, the injection pipes 3 are intruded into a sand-like foundation having a condition nearly equal to a substantially complete saturation, perpendicularly thereto, surrounding around a building 2 and well points 5 are also intruded thereinto. Liquid mixed with air-bubbles produced from the air-bubble mixing unit is charged under pressure from the top ends of the injection pipes 3, and underground water is drained from the well points 5. With this arrangement it is possible to promptly and simply inject air-bubbles into the foundation, thereby a rise of the foundation caused by an increase in underground water and the like can be restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method of improving ground by injecting microbubbles into the ground.

"Conventional technology and its issues" In general, saturated sandy ground may liquefy during an earthquake, so when building on such sandy ground, various ground improvement methods are used to improve the ground. needs to be improved. However, since such ground improvement requires extremely high costs, there is a desire to develop a low-cost method of preventing liquefaction. In addition, if the above-mentioned ground improvement is carried out on sandy ground on which buildings have already been constructed, it may have a negative impact on surrounding buildings, so it is important to avoid sandy ground on which buildings have already been constructed. It is considered impossible to prevent liquefaction with ground improvement methods such as those described above in rough ground.

Therefore, the present applicant penetrated a pipe having a large number of minute air holes into the sandy ground that was almost completely saturated, and injected air from the upper end of the vibrator into the inside of the vibrator through an air injection device. We proposed a method of injecting minute air bubbles into the ground through permeable holes, thereby suppressing the rise in pore water pressure during earthquakes and preventing liquefaction (Japanese Patent Application No. 1983).
-276999 specification).

At this time, it is thought that the air bubbles injected into the ground will gradually spread from around the pipe to the entire ground to be improved.
There was a demand for ensuring that air bubbles were mixed into the ground in a specific area, and further improvements were awaited.

This invention has been made in view of the above circumstances, and aims to provide a soil improvement method that can reliably mix air bubbles in the area of the ground to be improved.

``Means to solve the problem'' Recent research on elastic wave exploration has shown that even in the ground below the groundwater level, if there are minute bubbles in the pore water of the ground, the P wave velocity in the ground is 1500ffi/ s
It was revealed that the velocity decreases below ec (P-wave velocity of water).

On the other hand, it has already been studied that in sandy ground that is close to a completely saturated state, a slight decrease in the degree of saturation causes an increase in strength. If it can be artificially created, it is considered to be a promising new method for preventing liquefaction.

Therefore, the invention according to the first claim of the present invention is to dispose an injection means and a drainage means in the ground on which the structure is built so as to surround the structure, and to inject a liquid into which air bubbles are mixed. A ground improvement method in which microbubbles are injected into the ground from the injection means by pressing into the inside of the means from the upper end of the means, and the ground is improved by draining groundwater using the drainage means. This is an attempt to solve the above problem.

Further, the invention according to the second claim is such that in the ground improvement method according to the first claim, the injection means and the drainage means are arranged as a set so as to sandwich the structure and face each other. We are trying to solve the above problems by using ground improvement methods.

"Operation" In the ground improvement method of this invention, when the ground on which a structure has already been built is to be improved, injection means and drainage means are arranged in the ground so as to surround this structure. . Next, by injecting the liquid mixed with air bubbles into the injection means from the upper end thereof, the water pressure within the means is made higher than the groundwater pressure of the surrounding ground, and from this means the liquid is poured into the ground together with the liquid. Inject minute air bubbles. Also,
Correspondingly, draining groundwater by the drainage means,
To facilitate injection of bubble injection water using an injection means. In this way, the degree of saturation of the ground can be reduced, and an increase in pore water pressure during an earthquake can be suppressed.

Embodiment 1 Hereinafter, the first embodiment of the present invention will be described with reference to FIGS. 1 to 4.
This will be explained with reference to the figures.

This example is an example in which the ground improvement method according to the present invention is applied to a liquefaction prevention method implemented when a building 2 has already been constructed on sandy ground 1 that is nearly completely saturated. , an injection vibe (injection means) 3 having a large number of minute air permeable holes is vertically penetrated into the sandy ground l, and a well point (drainage means) 5 is similarly penetrated into the sandy ground l to remove air bubbles. Liquefaction of the sandy ground 1 is prevented by producing a liquid mixed with air bubbles by the mixing device 4 and pressurizing it into the interior from the upper end of the injection pipe 3, and draining groundwater from the well point 5. I'm trying to prevent it.

The injection pipe 3 is a tube made of stainless steel or synthetic resin, whose tip is closed with a closing plate, and countless minute air permeable holes (not shown) are formed in the side wall and the closing plate. The sandy ground 1 is penetrated into the sandy ground 1 with the shaft facing downward. However, the structure of the injection means is not limited to this, and it is of course possible to use an injection means in which only the lower end is opened and no air permeable holes are provided in the side wall.

The air bubble mixing device 4 is provided corresponding to the injection pipe 3, and as shown in FIG. By doing so, a compressor 11 that makes the pressure inside this pressure vessel IO equal to or higher than atmospheric pressure, and a pressure vessel I
It is generally composed of a supply means (not shown) that supplies water 12 into the inside of the pressure capacity IO, and a stirring device 13 that stirs the inside of the pressure capacity IO. The stirring device 13 includes a stirring shaft 14 protruding from the top of the pressure volume 2W I O, stirring blades 15 installed on the side surface of the stirring shaft 14, and rotationally driving the stirring shaft 14. It is composed of a motor 16.

Further, a closed pressure reducing vessel 18 is connected to the pressure vessel IO via a pressure hose 17, and a switching valve 19 is connected to each of the pressure vessels 110 and the pressure hose 17 in front of the pressure reducing vessel 18.
．． 19 is attached. This pressure reducing vessel 18 is provided with a pressure valve 20 communicating with the atmosphere.

The reduced pressure container 18 and the upper ends of each injection vibrator 3, . . . are connected by hoses 2+, .

On the other hand, the well point 5 also perpendicularly penetrates into the sandy ground 1 in the same way as the injection vibe 3, and is arranged in the sandy ground 1 so that at least its tip reaches below the groundwater level of the sandy ground 1. There is. This well point 5 has a well-known structure used for normal ground improvement, and as shown in Figure 4, a nozzle part (not shown) for penetrating into the ground is formed at the tip of the cylindrical body. In addition, many drainage holes (not shown) for draining underground water are drilled on the sides of the trench. Further, a riser pipe 30 is connected to the upper end of the well point 5, and a drain pump 31 is connected to the riser pipe 30, so that groundwater around the well point 5 is drained.

In addition, the groundwater drained at the well point 5 in this way is first stored in the sedimentation tank 32, whereupon the soil mixed in the groundwater is characterized, and as shown in FIG. 33, and is returned to the pressure chamber 10 of the bubble mixing device 4 via the pump 33 as needed. The water pressure provided by this pump 33 must be higher than the pressure provided by the compressor.

At this time, it is preferable that a partition plate 34 having a certain height is provided inside the sand settling tank 32 to serve as a guide for the amount of groundwater drainage. Further, the earth and sand stored at the bottom of the pillow sand 1'J32 may be discharged from the sand discharge hole 35.35 bored at the lower side of the sand settling tank 32. Naturally, these sand discharge holes 35 are fitted with plugs 36, 36 in a normal state.

As shown in FIG. 2, the injection vibrator 3 and the well point 5 are arranged in pairs to surround the building 2 in a plan view at the boundary of the area A of the ground to be improved. A large number of them are provided along line B. However, the placement positions of the injection vibrator 3 and the well point 5 are not limited to this, and may be determined as appropriate depending on the properties of the ground to be improved, the underground water level, etc.

In order to prevent liquefaction of the sandy ground 1 using such a ground improvement method, first, the injection vibrator 3 and the well point 5 are paired and placed in the sandy ground 1 on which the building 2 is constructed. Placed by penetrating perpendicularly to the position. In particular, the well point 5 has a nozzle section at its tip as described above, and by sending high-pressure water to the well point 5, the water is jetted from the nozzle tip and penetrates into the ground. .

Next, connect the bubble mixing device 4 to the upper end of the injection vibe 3,
After connecting the fn water pump 31 to the well point 5 via the riser pipe 30, water 12 is injected into the pressure/force vessel 10 of the bubble handling device 4 via a supply means (not shown). After storing a predetermined amount of water in the pressure vessel 10, the compressor 11 pressurizes air into the pressure vessel 10, thereby increasing the pressure inside the pressure vessel IO to a predetermined pressure higher than atmospheric pressure. , drives the motor 16 and stirs the stirring blades 15.
, . . . by rotating the stirring shaft 14, the water 12 in the pressure vessel 10 is stirred. As a result, the pressure vessel 10
This air dissolves in the water 12 at a level exceeding its saturation level at atmospheric pressure. The pressure inside the pressure vessel 10 may be determined as appropriate depending on the required air bubbles and the atmospheric pressure at that time.

After continuing stirring in this state for a while, pressurization by the compressed rock 11 and stirring by the stirring 115, etc. are stopped, and the switching valve 19.19 is opened, so that the water in the pressure vessel IO is
2 is introduced into the vacuum container 18. Next, the switching valve 19.1
9 is opened, and then the pressure reducing valve 20 of the pressure reducing container 18 is opened, thereby communicating the inside thereof with the atmosphere. As a result, among the air dissolved in the water 12 in the reduced pressure volume 2318, the air at a saturation fnffi or higher under atmospheric pressure is eluted and becomes minute bubbles, and water 12 mixed with bubbles can be obtained. .

Then, by force-feeding this bubbly water 12 with the pump 22 and pressurizing it into the inside of the injection vibrator 3 from the upper end, the water pressure inside the injection vibrator 3,... The pressure is raised higher than the pressure, thereby causing the bubbly water 12 in the injection vibrator 3,...
The air is released from countless air permeable pores, and minute air bubbles are injected into the sandy ground 1 along with water 12.

On the other hand, in response to the pressure feeding of the bubbled water 12 to the injection vibrator 3, the drain pump 31 is operated to drain the groundwater around the well point 5. The timing of the operation of the drain pump 131 is also arbitrary, and may be performed prior to the injection of the bubbly water 12 by the injection vibrator 3, or may be performed slightly after the bubbly water 12 is pressurized. In short, it is only necessary to drain the surplus underground water by using the well point 5 due to the injection of the aerated water 12 by the injection vibrator 3, and this may be determined as appropriate in consideration of the construction process and the like. Furthermore, if you want to further ensure the ground improvement effect by lowering the groundwater level of the ground 1 along with injecting the aerated water 12 into the ground 1, the amount of groundwater drained should be reduced from the large volume of the aerated water 12 to the drainage range. It is also possible to expand the injection range to the outside and inject the aerated water 12.

In this case, the injection of bubble-mixed water 12 by the injection vibrator 3 may be performed at the same time by all the vibrators 3 penetrated into the sandy ground l, but as described above, the injection vibrator 3 and the well point 5 may be injected in pairs. Since the injection vibrator 3 and the well point 5 are arranged so as to surround the building 2, the aerated water 12 can be injected in a more efficient manner. It is also possible.

That is, as shown in FIG. 2, among the many injection vibrators 3 disposed in the sandy ground, the injection vibrator 3 located at point a is selected and the aerated water 12 is pressurized into it. next,
A well point 5 located at point b, which is a position facing the selected injection vibrator 3 across the building 2, is selected, and groundwater is drained only from this well point 5. Then, after a certain period of time, after the injection of bubble-mixed water 12 and the drainage of ground water are finished, the injection vibrator 3 is placed at point b.
Bubbly water 12 is injected from the well point 5, and groundwater is drained from the well point 5 located at point a.

In other words, in the area connecting the injection vibrator 3 and the well point 5 that face each other across the building 2 (the area surrounded by the dotted line in the middle of Fig. 2), first, the flow of air-containing water from point a to point b is controlled by a sandy layer. Microbubbles are generated in the ground 1, through which minute air bubbles are injected into the sandy ground 1, and then a flow of air-containing water in the opposite direction from point b to point a is generated in the ground 1, as indicated by the dotted line. This ensures bubble injection within the enclosed area.

Then, the injection vibrator 3 into which the bubbly water 12 is press-injected and the well point 5 which drains the groundwater are sequentially moved,
Bubbles may be injected over the entire region A of the ground to be improved.

Injecting countless minute air bubbles into the sandy ground 1 in this way will reduce the saturation level (liquefaction strength) of the sandy ground 1. By installing a sensor to detect the saturation level of the sandy ground 1 or by installing an appropriate measuring device on the sandy ground 1, the saturation level of the sandy ground 1 and its temporal changes can be grasped. Leave it there. This degree of saturation may be detected by measuring the P-wave velocity through elastic wave exploration or the like, based on the relationship between the decrease in the P-wave velocity of the ground and the saturation degree, as described above.

Then, by reducing the degree of saturation of the sandy ground 1 while monitoring the improvement range and improvement effect of the sandy ground 1, the liquefaction strength of the sandy ground 1 is increased to a desired strength. In this way, the increase in pore water pressure during an earthquake in the sandy ground 1 can be reduced and suppressed to an appropriate level, and as a result, even in the sandy ground 1 that is nearly completely saturated, the increase in pore water pressure during an earthquake can be reduced. Liquefaction will be prevented.

In particular, in the ground improvement method of this embodiment, the well point 5 is used to drain the groundwater in response to the injection of 12 bubbles of water by the injection vibrator 3, so it is said that the conventional groundwater is not contaminated with bubbles. Compared to the case where groundwater is not drained using the well point 5, the aerated water 12 can be easily injected into the ground quickly and at low pressure, and the ground directly under the building 2 can be replaced with water 12. Injection of the bubble-injected water 12 is also carried out reliably. Furthermore, since the aerated water 12 can be injected at low pressure, it is possible to prevent the occurrence of inconvenient phenomena such as swelling of the ground and lifting of structures due to water pressure associated with high-pressure injection.

Furthermore, since the injection vibrator 3 and the well point 5 are arranged as a pair in the sandy ground l so as to surround the building 2, the injection vibrator 3 and the well point 5 face each other with the building in between. By injecting the aerated water 12 and draining the ground water, a flow of water can be generated in the sandy ground in the direction that penetrates the building 2, and the aerated water 1 is injected into the ground directly below the building 2. becomes even more certain.

Moreover, by managing the amount of air bubbles in the drained groundwater in this way, it is possible to determine whether the amount of air bubbles in the groundwater in the ground to be improved has reached a predetermined value.
As a ground improvement method, construction management is easy and highly reliable construction is possible.

In addition, in this embodiment, when injecting minute air bubbles into the sandy ground l, the air bubbles are mixed into the water 1 by the air bubble mixing device 4.
Since air bubbles are injected into the ground by making 2 and pressurizing it into the ground 1 through the injection vibrator 3, the amount and injection pressure of the bubbly water 12 to be injected into the sandy ground 1 can be adjusted appropriately. By controlling the amount of air bubbles injected into the ground l, it is possible to easily control the amount of air bubbles injected into the ground l, and moreover, in cases where air bubbles are injected from the air permeable hole of the injection vibe 3 by simply sending compressed air into the injection vibe 3. In comparison, bubble injection into sandy ground can be performed reliably and easily.

That is, according to conventional research, it has been reported that the air permeability of sand decreases as the degree of saturation increases, and that sand becomes clogged at a degree of saturation of about 50%. This means that if only air bubbles are injected into the sand, the saturation of the sand will not reach 50% or less. Therefore, it has been considered difficult to pump air into saturated ground without disturbing the soil's skeletal structure. but,
By mixing minute air bubbles into the water 12 and injecting the minute air bubbles into the ground together with the water 12, air can be pumped into the sand without causing blockages, which can improve sandy ground. can be set to a desired saturation level.

Furthermore, if the bubble mixing device 4 equipped with the pressure vessel 10 and the vacuum vessel 18 is used, the pressure difference between these volumes 1sI0 and 18 makes it possible to easily form bubbles with a uniform particle size and minute distribution in the water 12. Moreover, it can be produced quickly.

Next, regarding the second actual example of this invention, FIGS.
This will be explained with reference to the figures.

In this example, the ground improvement method according to the present invention is applied to the first method described above.
Similar to the embodiment, this embodiment is applied to a method for preventing R1 formation, which is carried out when a building 2 has already been constructed on the sandy ground 1-1, which is nearly completely saturated.

In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

The difference between this embodiment and the first embodiment is the location of the three-person means and the drainage means. That is, as shown in Figures 5 and 6, in the sandy ground l on which the building 2 is constructed, there are deep wells 40, 40, 40, 40, 40, 40, 40, 40, 40, adjacent to the four corners of the building 2. have been excavated, and the injection vibrator 3 and submersible pump 41 are appropriately inserted into these deep wells 40° to serve as injection means and drainage means, respectively.

Therefore, with this method as well, the same effects as in the first embodiment can be obtained. The procedure for arranging the infusion vibrator 3 and the submersible pump 41 is, for example, selecting one deep well 40 and inserting the injecting vibrator 3 into it, and placing the submersible pump 41 in the other deep wells 40, . . . ... is inserted to inject the bubbly water 12 and drain the groundwater, and by sequentially moving the locations of the deep well 40 into which the injection vibrator 3 is inserted, the bubbly water is injected into the sandy ground 1 directly under the building 2. Examples include procedures such as injecting 12.

On the other hand, as shown in FIGS. 7(a) and 7(b), it is of course possible to excavate deep wells 40, . . . so as to surround the building 2.

Note that the details of the ground improvement method of the present invention are not limited to the embodiments described above, and various modifications are possible.

As an example, in the embodiment described above, a well point was used as a means for draining groundwater, but the invention is not limited to this. For example, if the groundwater level is particularly low, a deep well may be installed and the underground water drained using a submersible pump or the like. Drainage methods such as draining water may be adopted.

Furthermore, mixing air bubbles into the water is optional.
For example, water mixed with air bubbles may be prepared by blowing nitrogen gas, carbon dioxide gas, etc. into the water, or may be prepared by introducing a solid foaming agent into the water, and there are no limitations on the countable means.

On the other hand, the ground improvement method of this invention is not only applicable to preventing liquefaction of sandy ground, but also, for example, when anaerobic bacteria breed abnormally in a landfill, it can be used to prevent bacteria by injecting air bubbles into the reclaimed ground. It can also be suitably applied as a soil improvement injection to suppress the proliferation of.

``Experiment Example'' This example experiment is based on a study carried out on liquefaction countermeasures, which involves injecting microbubbles into saturated sand ground to lower the saturation level of the ground and reduce the pore water pressure that occurs during earthquakes. Based on the measurement results of the elastic wave velocity of the specimen during the saturation process, we considered the relationship between the degree of saturation, that is, the B value, and the elastic wave velocity, and investigated the soil saturation state by elastic wave velocity for the purpose of monitoring the effectiveness of countermeasures. This study examines the possibility of estimation methods.

■ Samples and test methods Two types of samples were used: Toyoura sand and gravel.

The physical properties of Trial 11 are shown in Table 1.

Table 1 *: Measurement results for a mold with a diameter of 150++x and height of 150xx.

The test was conducted using a large triaxial testing device (gI-specimen, diameter 300Rx).
.

The measurement of elastic waves was carried out using a height of 6QOzz).
The test was carried out while maintaining the effective confining pressure at 49 kPa and saturating the specimen. The degree of saturation is determined by measuring the change in the volume of pore water caused by the loading of a pressure-resistant billet (capacity 10
00c+y') and calculated from Boyle's law.

■ Using poroelastic body theory for saturation, B value, and elastic wave velocity, and considering the bulk elastic constant of pore water containing bubbles, the relationship between saturation (Sr) and P wave velocity (Yp) is It is given by the following formula.

o ・Vp2−o ・vpd'=
(] )n(Sr/Kw+ (1-3r)/K
a'1 where, ρ ・Density (warm density) ρd: Density of Dokuriku (dry density) Vpd: P-wave velocity of main skeleton Kw: Bulk elastic constant of water that does not contain any air bubbles (2,2X 1okPa ) Ka: Bulk elastic constant of air (pore water pressure expressed in absolute pressure) n: Porosity Figure 8 shows Vp due to the degree of saturation estimated using equation (1).
It shows the change in Proportion of air bubbles in pore water (1
-3r) is 10'' to 1O-3 (99 in terms of saturation)
, 999 to 999%) is extremely large.

On the other hand, if the compressibility of soil particles is ignored, the B value is expressed by the following equation.

FIG. 9 shows changes in the B value depending on the degree of saturation determined from equation (2). It can be seen that the B value is also significantly affected by the degree of saturation, particularly in the region where (1-Sr) changes from 10-' to 10-1.

■ Measurement results and discussion Figure 10 shows the relationship between the elastic velocity measured during the saturation process and the degree of saturation. Vp is significantly affected by saturation,
While the change corresponds well to the estimated value shown in FIG. 8, the change in shear breakwater velocity (Vs) is extremely small. According to calculations, even considering the increase in density due to increase in saturation,
The shear ballistic constant showed almost constant value during the saturation process.

Using the actually measured Vpd (Vp measured on a dry specimen) and Vp, (1-Sr)cal calculated from formula (1),
(1-5r) was determined from the measurement of the volume change of pore water.
5eas, the comparison results are shown in FIG. (1-Sr
Although there are variations in the small area of ) that are thought to be due to measurement accuracy, it can be judged that there is a good correlation overall.

FIG. 12 shows the relationship between the bulk elastic constant (K) determined from the elastic wave velocity and the actually measured B value at each saturation stage. The curve in FIG. 12 represents the following equation obtained by applying poroelastic body theory to equation (2).

B=1-Kd/K (3) It can be seen that the calculated curve closely approximates the measured data. Figure 13 shows K from the elastic wave velocity measured on the dry specimen.
d and calculated the B value (Bcal,
) and the actually measured B value (Bmeas, ). A good correlation is observed over a wide range between the two.

■ Conclusion We measured changes in elastic wave velocity during the saturation process of sand and gravel specimens, and showed that the P-wave velocity significantly decreases when the degree of saturation decreases even slightly from a completely saturated state. In addition, this can be explained by the theory of poroelastic bodies by considering the bulk elastic constant of pore water containing many bubbles, and the degree of saturation, that is, the B value, can be estimated from the elastic wave velocity. revealed.

From the above results, in liquefaction countermeasures by bubble injection,
The effectiveness of the method of measuring the elastic wave velocity in the ground and monitoring the effectiveness of countermeasures was suggested.

``Effects of the Invention'' As explained in detail above, according to the present invention, the injection means and the drainage means are disposed in the ground on which the structure is constructed,
By injecting a liquid mixed with air bubbles into the inside of the means from the upper end of the means, fine air bubbles are injected from the injection means into the ground, and at the same time, underground water is drained by the drainage means to improve the ground. In other words, the existing groundwater is replaced with a liquid containing air bubbles.
Compared to the case where groundwater is not drained by drainage means,
Injection of air bubbles into the ground is performed quickly and easily.

It is also possible to suppress the occurrence of phenomena such as swelling of the ground due to addition of groundwater.

Further, in this invention, since the injection means and the drainage means are arranged so as to surround the structure, if liquid injection and groundwater drainage are performed by these injection means and drainage means,
It is possible to generate a flow of water in the ground in the direction that penetrates the structure, ensuring that air bubbles are injected into the ground directly below the structure.

[Brief explanation of drawings]

1 to 4 are diagrams showing a ground improvement method according to a first embodiment of the present invention, in which FIG. 1 is a perspective view showing a state in which an injection means and a well point are penetrated into the ground, and FIG. Figures 2 (a) and (b) are a plan view and side view schematically showing the injection means and well point, respectively, Figure 3 is a schematic diagram showing an example of a bubble injection device, and Figure 4 is an example of a well point. 5 and 6 are diagrams showing a ground improvement method according to a second embodiment of the present invention, and FIG. 5 shows a state in which the injection means and well point have been penetrated into the ground. 6 is a plan view of the same, and FIG. 7 is a sectional view showing the ground improvement method according to the third embodiment of the present invention.
A) is a plan view, FIG. 8 is a graph showing the relationship between saturation and P wave velocity, FIG. 9 is a graph showing the relationship between saturation and B value, Figure 10 is a graph showing the change in elastic wave velocity due to saturation, Figure 11 is a graph showing the relationship between the measured value and estimated value of saturation, and Figure 12 is a graph showing the relationship between bulk elastic constant and B@. , FIG. 13 is a graph showing the relationship between the calculated value and the measured value of the B value. l...Sandy ground, 2...Buildings (+ll
! structure), 3... Injection pipe (injection means), 4.
... Air bubble mixing device, 5... Well point (drainage means), 12... Water (liquid).

Claims (2)

[Claims] (1) By arranging an injection means and a drainage means in the ground on which the structure is built so as to surround the structure, and pressurizing the liquid mixed with air bubbles into the inside of the said means from the upper end. A ground improvement method that improves the ground by injecting minute air bubbles into the ground from the injection means and draining groundwater by the drainage means. (2) The ground improvement method according to claim 1, wherein the injection means and the drainage means are arranged as a set so as to sandwich the structure and face each other.