JP4368884B2 - Ground improvement method - Google Patents

Description

  The present invention relates to a ground improvement method for compacting a surrounding ground by forming a consolidated body on the ground.

  In recent years, along with the development of urbanization, development of coastal areas in rivers, lakes, coasts, etc. has been promoted. In such areas, the groundwater level is generally high and the ground is loosely deposited, so liquefaction associated with earthquakes is likely to occur.

  Such liquefaction countermeasures that improve the liquefaction resistance of the ground include a dynamic compaction method such as a sand compaction pile method, and a ground improvement method such as a deep mixing treatment method.

  However, dynamic compaction methods such as sand compaction piles are difficult to adopt in urban areas such as urban areas because noise and vibration are generated during construction and affect surrounding areas. Moreover, since the construction machine used at the time of construction is large-scale, there is a problem that construction is difficult when only a narrow work space can be secured, such as directly under a facility in use or an existing structure.

  In addition, the latter ground improvement method is also difficult to construct directly under the facilities and existing structures that are in service, and because construction machines are large, it is difficult to construct in places where only a limited construction space can be secured. Met.

  Therefore, as shown in Patent Document 1, the present applicants have disclosed a static press-fit compaction method that enables construction on the ground immediately under the facility or existing structure in service, and has been put to practical use. .

  In this static press-fit compaction method, holes with a predetermined diameter are drilled at a predetermined interval in the ground to be improved, and a solidified body is continuously formed on the ground by statically pressing a low-fluidity solidified material with a pump. Thus, by increasing the volume due to the consolidated body, the surrounding ground is compressed and the density is increased, thereby improving the liquefied ground to the non-liquefied ground.

JP 2005-105740 A

  However, the conventional static press-fit compaction method has a problem in that excessive pore water pressure may be generated due to the injection of the solidified material into the ground, and the ground may be raised.

  The present invention has been made in order to solve such problems, and relates to a ground improvement method capable of suppressing a ground uplift and ensuring a desired improvement effect.

In order to solve the above-mentioned problem , the ground improvement method according to the first invention includes a drilling step of drilling a boring hole to a predetermined depth , and injecting air bubbles into the ground via the boring hole. Place the air bubbles in the ground, desaturate the ground to be improved beforehand, and inject the solidified material from the borehole to form a consolidated body in the ground to form the surrounding ground of the consolidated body And a solid body forming step for compacting the ground , wherein the solidified material is injected in a state where the ground is desaturated to suppress ground uplift.

  According to such a ground improvement method, it is possible to suppress the bulge of the ground that occurs due to the injection of the solidifying material into the ground by previously desaturating the ground. In other words, by presaturating the saturated ground in advance, it is possible to suppress the occurrence of excess pore water pressure in the surrounding ground due to the injection of the solidified material, thereby suppressing the ground uplift. Furthermore, since the ground is desaturated, the possibility of liquefaction can be reduced.

Further, in the desaturation step, bubbles may be generated by disturbing the water and air in the borehole with an ultrasonic oscillator, a high-frequency vibrator or the like.

Further, the ground improvement method according to the second invention includes a drilling step of drilling a borehole to a predetermined depth, a bubble injection tube insertion step of inserting a bubble injection tube into the borehole, The air bubbles are placed in the ground by injecting the air bubbles from the tip, and the desaturation step of previously desaturating the ground to be improved, and the solidified material is injected into the ground by injecting a solidifying material from the borehole. A solid body forming method for compacting a surrounding ground of the consolidated body by forming a ground, wherein the ground is raised by injecting the solidifying material in a state where the ground is desaturated It is characterized by suppressing.

Further, the ground improvement method according to the third invention includes a drilling step of drilling a borehole to a predetermined depth, an oscillator insertion step of inserting an ultrasonic oscillator, a high-frequency vibrator, etc. into the borehole, An unsaturation step in which the ground is disturbed by ultrasonic waves of a sound wave oscillator or vibration of a high-frequency vibrator to generate bubbles to place the bubbles in the ground, and the ground to be improved is desaturated in advance, and the boring A solid body forming step of compacting a surrounding ground of the solidified body by injecting a solidifying material from a hole to form a solidified body on the ground, wherein the ground is unsaturated In this state, the solidified material is injected to suppress the ground uplift.
Thus, by injecting air bubbles into the ground, the air bubbles can be arranged in the gaps between the soil particles, and the ground can be desaturated. In addition, regarding the injection of bubbles into the ground, it is possible to omit the trouble of performing the boring for piping the bubble injection tube separately by using the boring hole for injecting the solidifying material.

  Furthermore, if a material that weakens the bonding force between the soil particles is injected into the ground together with the injection of bubbles in the desaturation step or before the desaturation step, bubbles are mixed into the soil particles. This makes it possible to satisfactorily desaturate the ground, which is preferable.

  According to the ground improvement method of the present invention, it is possible to prevent the ground from being raised and to secure a desired improvement effect.

Preferred embodiments of the present invention will be described with reference to the drawings. In the description, the same reference numerals are used for the same elements, and duplicate descriptions are omitted.
Here, FIG. 1 is a flowchart showing the procedure of the ground improvement method according to the first embodiment. Moreover, (a)-(c) of FIG. 2 is a side view which shows each construction step by the ground improvement method which concerns on 1st Embodiment. FIG. 3 is a cross-sectional view showing the compaction effect by the ground improvement method according to the first embodiment. Moreover, (a)-(c) of FIG. 4 is sectional drawing which shows the condition of the ground at the time of construction by the ground improvement method which concerns on 1st Embodiment.

<First Embodiment>
As shown in FIG. 1, the ground improvement method according to the first embodiment includes a drilling step S1 for drilling a borehole to a predetermined depth, and a capillary tube for inserting a capillary tube (bubble injection tube) into the borehole. (Bubble injection tube) Insertion step S2, desaturation step S3 for injecting bubbles from the tip of the thin tube into the ground, and solidified body formation by injecting a solidifying material from the boring holes to form a solidified body on the ground Step S4.

As shown in FIG. 2A, the drilling step S1 is a step of drilling the boring hole 1 with a boring machine BM. Here, the diameter of the boring hole 1 is not limited, but in the first embodiment, the hole is drilled through the casing pipe 2 having an outer diameter of 70 mm.
After drilling the boring hole 1, the casing pipe 2 is left in the boring hole 1. In the first embodiment, the boring hole 1 is formed vertically, but it goes without saying that the drilling direction (angle) of the boring hole 1 is not limited.

  As shown in FIG. 2B, the thin tube insertion step S2 is a step of inserting the thin tube 3 into the casing pipe 2 left in the boring hole 1 in the drilling step S1. The thin tube 3 is inserted so that the tip reaches the vicinity of the lower end of the boring hole 1. The narrow tube 3 is not limited as long as it can be inserted into the casing pipe 2 and can transport gas, and can be appropriately selected from known materials and used. is there. For example, a steel seamless tube having an inner diameter of less than 10 mm can be used. Moreover, the number of the thin tubes 3 to be inserted into the casing pipe 2 is not limited, and may be set as appropriate according to the condition of the ground G or the like.

In the desaturation step S3, as shown in FIG. 2 (b), the bubbles 4 are injected into the ground G around the borehole 1 by using the thin tubes 3 inserted into the casing pipe 2 in the thin tube insertion step S2. It is a process.
Here, in the first embodiment, air is used as the gas injected into the ground G in order to generate the bubbles 4, but it is needless to say that the gas is not limited and is appropriately known gas. You can choose from among them.

The bubbles 4 are injected into the ground G by discharging the gas transported through the narrow tube 3 into the ground G from the tip of the narrow tube 3 disposed at the lower end of the boring hole 1.
At this time, since the bubbles 4 are discharged from the lower end of the boring hole 1, the bubbles 4 are replaced with pore water (ground water) W between the soil particles 7, 7,. Then, the ground G is desaturated (see FIGS. 4A and 4B).

  In the desaturation of the ground G by the desaturation step S3 according to the first embodiment, the saturation Sr of the ground G after improvement is preferably 60% so that the saturation Sr satisfies Equation 1. Set to be ~ 90%.

Here, when the volume does not change before and after the improvement, the gap ratio e ₁ after the improvement is as follows by compacting the ground G.
_{e 1 = e 0 - (1} + e 0) a s
e ₀ : Gaps ratio before improvement e ₁ : Gaps ratio after improvement a _s : Improvement rate Since the degree of saturation decreases after bubble injection, the degree of saturation Sr after bubble injection is set to satisfy Equation 1. To do.
Sr <e ₁ / e ₀ = {e ₀ − (1 + e ₀ ) a _s } / e ₀ (Equation 1)

In the first embodiment, in the desaturation step S3, the unsaturated auxiliary material having a function of weakening the bonding force between the soil particles 7 is injected into the ground G together with the injection of the bubbles 4 into the ground G. To do. Thereby, since the bonding force between the soil particles 7 in the ground G is reduced, the bubbles 4 are more effectively injected into the gaps between the soil particles 7. Here, the material used as the desaturation auxiliary material is not limited, but a dispersant is used in the first embodiment. In addition, as an auxiliary material for desaturation other than the dispersant, for example, a surfactant that has an effect of weakening the bonding force between the soil particles and exhibits a function of retaining bubbles may be used.
Here, the injection of the desaturation auxiliary material into the ground G is not necessarily performed together with the injection of the bubbles 4, and only the desaturation auxiliary material may be injected into the ground G before the injection of the bubbles 4.

  In the consolidated body forming step S4, as shown in FIG. 2C, the solidified body 5 is formed by press-fitting the solidified material into the ground G using the casing pipe 2 left in the boring hole 1. It is a process to do. The solidification material is injected by injecting a predetermined amount through the casing pipe 2 to form a solidified body 5 having a predetermined shape, then raising the casing pipe 2 by a predetermined length and injecting it again. Thereby, it becomes possible to form the solidified body 5 continuous in the vertical direction in a columnar shape.

The solidifying material is injected with low vibration and low noise by using a grout machine GM including an injection pump. At this time, a pipe 6 piped from the grout machine GM is connected to the upper end of the casing pipe 2.
Here, the consolidated body 5 may be divided according to the formation of the ground G. For example, when the ground G is a ground having a sand layer and a viscous soil layer, the solidified body 5 may be formed only on the sand layer. In addition, if the formation is confirmed at the time of drilling the borehole 1 in the drilling step S1, an accurate formation status can be grasped, so that a solidified material can be injected according to the formation.

  In the first embodiment, mortar having a slump of 5 cm or less is used as the solidifying material. The grout machine GM allows the solidified material to be injected into the ground G with almost no vibration or impact. Needless to say, the solidifying material is not limited to mortar, and may be appropriately selected from known materials.

  By injecting the mortar (solidifying material) having extremely low fluidity into the ground G, as shown in FIG. 3, a bulb-like solidified body 5 is formed on the ground G. And the volume increase in the ground by this solidified body 5 compresses the surrounding ground G and increases its density, thereby compacting the ground G.

  As described above, according to the ground improvement method according to the first embodiment, since the bubbles 4 are injected into the ground G in the desaturation step S3, the ground water W is saturated as shown in FIG. For the ground G, as shown in FIG. 4B, the bubbles 4 are disposed in the gaps between the soil particles 7, 7,. And by the desaturation of the ground G, the liquefaction of the ground G can be suppressed.

  Moreover, even if the density of the ground G increases when forming the consolidated body 5 in the consolidated body forming step S4 by arranging the bubbles 4 in the gaps between the soil particles 7, 7,. It becomes possible for 4 to shrink and to suppress the generation of excess pore water pressure. Thereby, it becomes possible to suppress the protrusion of the ground G accompanying the formation of the consolidated body 5.

  Further, since the desaturation aid is injected into the ground G together with the injection of the bubbles 4 into the ground G, the bonding force between the soil particles 7 is weakened, and the arrangement of the bubbles 4 in the gap between the soil particles 7 is reduced. This is done more effectively (see FIG. 4).

  Further, the ground improvement method can be constructed by drilling with a boring machine BM and injection of a solidified material with a grout machine GM, so that the facilities are relatively simple and easy to move and install. Therefore, it is possible to suitably perform construction for a limited time, such as construction at a facility in service. Moreover, since construction with simple equipment is possible, construction is possible even when only a narrow work space can be secured, which is preferable. Furthermore, since construction with low vibration and low noise is possible, even if construction is performed on the foundation ground of a structure in service, it will not adversely affect the user, and the ground will be improved to increase the strength of the ground. Making it possible.

<Second Embodiment>
Next, a second embodiment will be described. Here, FIG. 5 is a flowchart showing the procedure of the ground improvement method according to the second embodiment.

  As shown in FIG. 5, the ground improvement method according to the second embodiment includes a drilling step S1 for drilling a borehole to a predetermined depth, and an oscillator insertion step S2 for inserting an ultrasonic oscillator into the borehole. ', An unsaturation step S3 for generating bubbles in the ground via the ultrasonic oscillator, a solid forming step S4 for injecting a solidifying material from the boring holes to form a solid on the ground, It is composed of

  Since the drilling step S1 is the same as the contents shown in the first embodiment, a detailed description thereof is omitted.

  The oscillator insertion step S2 'is a step of inserting an ultrasonic oscillator into the casing pipe 2 left in the boring hole 1 in the drilling step S1. The ultrasonic oscillator is not limited as long as it can be inserted into the casing pipe 2 and can generate the bubbles 4 by ultrasonic waves in the ground G. The ultrasonic oscillator is appropriately selected from known materials. It is possible to use. In the second embodiment, an ultrasonic oscillator is disposed at the lower end of the boring hole 1, but it is possible to generate (inject) bubbles 4 in the ground G and to desaturate the ground G. If so, the installation location of the ultrasonic oscillator is not limited.

The desaturation step S3 ′ is a step of generating (injecting) bubbles 4 in the ground G around the borehole 1 via the ultrasonic oscillator inserted into the casing pipe 2 in the oscillator insertion step S2 ′.
That is, the ultrasonic oscillator generates bubbles 4 in the ground G by disturbing the underground water and air in the borehole 1. The injection of the bubbles 4 into the ground G by the ultrasonic oscillator may generate the bubbles 4 in the ground G by oscillating ultrasonic waves in the ground G.

  At this time, since the bubbles 4 are injected (generated) from the lower end of the borehole 1, the pore water (ground water W) between the soil particles 7, 7,. And the ground is desaturated (see FIGS. 4A and 4B).

In addition, since the matters related to the desaturation step S3 are the same as the contents shown in the first embodiment, detailed description thereof is omitted.
Further, since the consolidated body forming step S4 is the same as the contents shown in the first embodiment, detailed description thereof is omitted.

According to the ground improvement method according to the second embodiment, since the bubbles 4 are generated via the ultrasonic oscillator, the bubbles are injected into the ground G without requiring piping or the like for transporting the gas. Is possible.
Further, since the bubbles 4 are generated by the ultrasonic oscillator, the bubbles 4 having a desired bubble diameter can be arranged in the ground G.

  Since the effects of the ground improvement method according to the other second embodiment are the same as the contents shown in the ground improvement method according to the first embodiment, detailed description thereof is omitted.

  In the second embodiment, the bubbles are generated via the ultrasonic oscillator. However, the same effect can be obtained by using a high-frequency vibrator instead of the ultrasonic oscillator.

<Third Embodiment>
Next, a third embodiment will be described.
The ground improvement method according to the third embodiment includes a drilling step S1 for drilling a borehole to a predetermined depth, an oscillator insertion step S2 ′ for inserting an ultrasonic oscillator into the borehole, and the ultrasonic oscillator. Is formed from a desaturation step S3 ′ for generating air bubbles in the ground and a solid forming step S4 for injecting a solidifying material from the boring holes to form a solid on the ground (FIG. 5).

  Since the drilling step S1 and the oscillator insertion step S2 'are the same as the contents shown in the second embodiment, detailed description thereof is omitted. The ultrasonic oscillator is connected to a vibrating body that vibrates in accordance with the operation of the ultrasonic oscillator. In the oscillator insertion step S2 ', the vibrating body is disposed so as to be in contact with the ground.

In the desaturation step S3 ′, the ground is disturbed by a vibrating body interlocked with the ultrasonic oscillator inserted in the casing pipe 2 in the oscillator insertion step S2 ′, so that bubbles 4 are generated in the ground G around the borehole 1. Is a step of generating
That is, when the ultrasonic oscillator is operated, the vibrating body vibrates, and the ground G is disturbed (vibrated) to generate (inject) the bubbles 4 into the ground G.

  At this time, the bubbles 4 are replaced with pore water (ground water W) between the soil particles 7, 7,... In the ground G, and the ground is desaturated (see FIGS. 4A and 4B). .

In addition, since the matters related to the desaturation step S3 are the same as the contents shown in the second embodiment, detailed description thereof is omitted.
Further, since the consolidated body forming step S4 is the same as the contents shown in the first embodiment, detailed description thereof is omitted.

According to the ground improvement method according to the third embodiment, since the bubbles 4 are generated via the ultrasonic oscillator, the bubbles are injected into the ground G without requiring piping or the like for transporting the gas. Is possible.
Further, since the bubbles 4 are generated by the ultrasonic oscillator, the bubbles 4 having a desired bubble diameter can be arranged in the ground G.

  The operational effects of the ground improvement method according to the other third embodiment are the same as the contents shown in the ground improvement methods shown in the first embodiment and the second embodiment. Omitted.

  In the third embodiment, the bubbles are generated via the ultrasonic oscillator. However, even if a high frequency vibrator is used instead of the ultrasonic oscillator, the same effect can be obtained by the same method. Is possible.

<Fourth embodiment>
Next, a fourth embodiment will be described. Here, FIG. 6 is sectional drawing which shows the construction example of the ground improvement method which concerns on 4th Embodiment.

As shown in FIG. 6, in the fourth embodiment, the ground improvement method of the present invention is applied to the existing structure A in service from the left and right sides of the existing structure A diagonally downward. The construction is done in the shape. Thus, the foundation ground Ga of the existing structure A is compacted by forming the aggregate of the V-shaped solidified bodies 5 on the ground G immediately below the existing structure A.
In addition, since each procedure of the ground improvement method which concerns on 4th Embodiment is the same as the content shown in 1st Embodiment or 2nd Embodiment, detailed description is abbreviate | omitted.

  In the ground G, when the aggregate of the V-shaped solid bodies 5 is formed, a portion (basic ground Ga) surrounded by the aggregate of the solid bodies 5 immediately below the existing structure A is solidified body 5. Compressed by increasing the volume of the material, the density is increased and compacted. At this time, since the ground G is desaturated before the solidified body 5 is formed, the ground G is not raised, and the existing structure A is not adversely affected.

  Furthermore, since the foundation ground Ga is surrounded by the aggregate of the V-shaped solidified bodies 5, the unsaturated state of the foundation ground Ga is maintained for a long time. Therefore, since the state which is hard to liquefy is maintained, the earthquake resistance of the existing structure is further improved. In addition, the code | symbol B in FIG. 6 is an underground continuous wall.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and it goes without saying that the above-described constituent elements can be appropriately changed in design without departing from the spirit of the present invention.

Bubble injection into the earth board (generation) method, the present invention is not limited to the method shown in the embodiments, it may be performed by a suitable known method.
For example, in the desaturation step, liquefaction may be prevented by injecting (generating) air bubbles into the ground through the borehole without using a thin tube. As a method for injecting (generating) air bubbles into the ground through the borehole, for example, there is a method of generating air bubbles in the ground by generating air bubbles in the borehole by disturbing water in the borehole. Here, the method for disturbing the underground water is not limited, and may be appropriately performed by known means.

Moreover, in each said embodiment, although the material which weakens the bond strength between soil particles shall be inject | poured into the ground, such a material does not necessarily need to be inject | poured.
In addition, if a surfactant is used as the desaturation auxiliary material instead of the dispersant, the bubbles arranged in the gap are prevented from dissolving in the gap water, and the bubbles arranged in the gap are prevented for a long time. Therefore, liquefaction can be suppressed while maintaining the unsaturated state of the ground.

  In addition, for the purpose of obtaining a more excellent improvement effect, in the consolidated body forming process, along with the injection of the solidifying material, the surrounding ground is disturbed by using other boring holes formed around the boring hole. Also good. Thereby, since the surrounding ground is desaturated, the injection of the solidified material is performed more effectively, the formation of the desired solidified body is performed more effectively, and the rise of the ground is suppressed. . In addition, arrangement | positioning of the surrounding boring hole with respect to the boring hole which forms a solidified body is not limited. It should be noted that the desaturation of the surrounding ground is not limited to ground disturbance using other boring holes, and the same effect can be obtained even if it is performed by injecting bubbles or the like.

  The application place of the ground improvement method of the present invention is not limited, and can be applied to various places such as a foundation ground of a structure and a surrounding ground of an embedded object. Further, it goes without saying that these structures (buried objects) may be existing or newly established.

It is a flowchart which shows the procedure of the ground improvement method which concerns on 1st Embodiment. (A)-(c) is a side view which shows each construction step by the ground improvement method which concerns on a 1st form. It is a cross-sectional view which shows the compaction effect by the ground improvement method which concerns on a 1st form. (A)-(c) is sectional drawing which shows the condition of the ground at the time of construction by the ground improvement method which concerns on 1st Embodiment. It is a flowchart which shows the procedure of the ground improvement method which concerns on 2nd Embodiment and 3rd Embodiment. It is sectional drawing which shows the construction example of the ground improvement method which concerns on 4th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Boring hole 2 Casing pipe 3 Narrow tube 4 Air bubbles 5 Solid body G Ground W Groundwater S1 Drilling process S2 Narrow tube insertion process S2 'Oscillator insertion process S3, S3' Desaturation process S4 Solid body formation process

Claims (5)

A drilling step of drilling a boring hole to a predetermined depth;
An unsaturation step of placing bubbles in the ground by injecting bubbles into the ground through the boring hole, and desaturating the ground to be improved in advance,
A solid body forming step of compacting a surrounding ground of the consolidated body by injecting a solidifying material from the boring hole to form a consolidated body on the ground, and a ground improvement method comprising:
The ground improvement method characterized by suppressing ground upheaval by inject | pouring the said solidification material in the state which desaturated the said ground . Wherein the desaturase step, and generating bubbles by disrupting the borehole water and air of the borehole by the ultrasonic oscillator and a high frequency vibrator or the like, soil improvement process according to claim 1. A drilling step of drilling a boring hole to a predetermined depth;
A bubble injection tube insertion step of inserting a bubble injection tube into the boring hole;
An unsaturation step of placing bubbles in the ground by injecting bubbles into the ground from the tip of the bubble injection tube, and desaturating the ground to be improved in advance,
A solid body forming step of compacting a surrounding ground of the consolidated body by injecting a solidifying material from the boring hole to form a consolidated body on the ground, and a ground improvement method comprising:
The ground improvement method characterized by suppressing ground upheaval by inject | pouring the said solidification material in the state which desaturated the said ground . A drilling step of drilling a boring hole to a predetermined depth;
An oscillator insertion step of inserting an ultrasonic oscillator, a high-frequency vibrator or the like into the boring hole;
An unsaturation step in which the ground is disturbed by ultrasonic waves of the ultrasonic oscillator or vibration of a high-frequency vibrator, etc. to generate bubbles to place the bubbles in the ground, and the ground to be improved is previously unsaturated.
A solid body forming step of compacting a surrounding ground of the consolidated body by injecting a solidifying material from the boring hole to form a consolidated body on the ground, and a ground improvement method comprising:
The ground improvement method characterized by suppressing ground upheaval by inject | pouring the said solidification material in the state which desaturated the said ground . With bubble injection in the desaturation step, or before performing the desaturation process, characterized by injecting the material to weaken the binding forces between soil particles to the ground, according to claim 1 wherein Item 5. The ground improvement method according to any one of items 4 .

Images