JP2021046766A - Liquefaction countermeasure structure of underground structure - Google Patents

Abstract

To provide a liquefaction countermeasure structure of an underground structure which can suppress a dynamic water pressure in earthquake even when rigidity of a ground improvement wall is reduced by introducing a technical concept for achieving such a configuration as to intentionally lower a degree of fixation of the ground improvement wall to the underground structure and permit lift, and is excellent in economical efficiency and workability.SOLUTION: Ground improvement bodies 2 having small improvement diameters S are constructed along both sides in an extension direction of an underground structure (existing utility tunnel) 1 until the ground improvement bodies reach a non-liquefaction layer 5 in the shape of the columns, and rod-like reinforcing members (reinforcements) 3 are built in the ground improvement bodies 2 until the reinforcing members do not reach the non-liquefaction layer 5, and thereby a ground improvement wall 4 is constructed; and embedding of the lower end of the ground improvement wall 4 to the non-liquefaction layer 5 is small, on the other hand, the upper end thereof is not constructed to be higher than the middle of the underground structure 1.SELECTED DRAWING: Figure 1

Description

The present invention belongs to the technical field of liquefaction countermeasure structures for linear underground structures (hereinafter abbreviated as underground structures) such as utility tunnels and underground roads buried in the ground. Regarding the technology to prevent liquefaction by using a column-type ground improvement wall for the existing utility tunnel constructed in the ground (soft ground) where there is concern about ground damage due to liquefaction.

Among the underground structures, for example, as a liquefaction countermeasure for an existing utility tunnel, there is a construction method for improving the grid-like ground and suppressing shear deformation due to a continuous underground wall. In addition, there are also construction methods aimed at preventing lifting due to buoyancy, such as a groundwater level lowering method using a deep well and a pore water pressure dissipation method using a steel material with a drainage function.

Specifically, FIG. 9 shows a technique for preventing the existing utility tunnel A from rising by a deep mixing treatment method. In this technique, in order to suppress the floating caused by the wraparound from the surrounding ground, the improved walls a and a are created by the deep mixing treatment method along both sides in the extension direction of the existing utility tunnel A.
According to the technique adopting the deep mixing treatment method according to FIG. 9, since the bottom friction force is required to satisfy the external stability of the created improved body a at the time of an earthquake, it is constructed on both sides of the existing utility tunnel A. A very wide range of improvements are required, such as setting the improvement width of the improved body a to 5.7 m. Therefore, the construction period is prolonged, the cost is high, and there is a problem that it is difficult to implement in a narrow place.

FIG. 10 shows a technique for preventing the existing utility tunnel A from rising by using a steel sheet pile. In this technique, steel sheet piles b and b with drainage drains are placed on both sides of the existing utility tunnel A in order to prevent the existing utility tunnel A from rising due to wraparound from the surrounding ground.
According to the technique using the steel sheet pile b according to FIG. 10, since the steel sheet pile b is continuously constructed, it cannot be carried out (or it is difficult to construct) when underground buried objects other than the utility tunnel A interfere with each other. There are challenges. Further, the lifting due to the buoyancy is dealt with by installing a protrusion or the like on the steel sheet pile b, but there is also a problem that it is troublesome and costly.

Further, in Patent Document 1, as shown in FIG. 11, after retaining the piles with the ready-made steel sheet piles c and c and excavating to the bottom slab of the structure (utility tunnel) A, the back surface of the steel sheet piles c and c is formed. A liquefaction countermeasure construction method for a linear structure is disclosed, which comprises installing drain materials f and f and backfilling the fluidized soil g between the structure A and the steel sheet pile c (a method for preventing liquefaction of a linear structure). (Refer to the description of claim 1).
According to the construction method according to Patent Document 1, since the steel sheet pile c is used, it cannot be carried out (or it is difficult to construct) when underground buried objects other than the structure (utility tunnel) A interfere with each other. There is.

Therefore, the applicant has developed the invention of Patent Document 2 based on the above-mentioned problems.
In this patent document 2, as shown in FIGS. 1 to 3 of the same document 2, the improved body 2 having a small improved diameter is arranged in a column shape along both sides in the extension direction of the underground structure 1 by a high-pressure jet stirring method. By repeating the process of constructing the non-liquefied layer 6 until it reaches the non-liquefied layer 6 and repeatedly building the core material 3 inside the improved body 2, the synthetic pile composed of the improved body 2 and the core material 3 is made continuous. A liquid underground structure characterized in that the ground improvement composite wall 4 is created and the drain material 5 is installed at the trace of boring the tangent portion P near the underground structure 1 of the adjacent synthetic pile. The liquefaction countermeasure construction method is disclosed (see the description of claim 1 etc.).

According to the invention of Patent Document 2, since the improved body 2 having a small improved diameter (for example, about 2 m) is constructed in a columnar shape and carried out, it can be sufficiently carried out even in a narrow place. Therefore, it is possible to solve the problem that arises in the technique that employs the deep mixing treatment method according to FIG. Further, since the improved body 2 is constructed by the high-pressure injection stirring method without using a steel sheet pile, flexible construction without restrictions is possible even when underground buried objects other than the structure (utility tunnel) A interfere with each other. Therefore, it is possible to solve the problem that arises in the technique of adopting the steel sheet pile according to FIGS. 10 and 11.

Japanese Unexamined Patent Publication No. 7-127045 JP-A-2017-96045

In addition to the effects described in the above paragraph [0007], the invention of Patent Document 2 states that "a synthetic pile composed of an improved body and a core material and having excellent strength and rigidity is provided along both sides in the extension direction of the underground structure. Since a continuous ground improvement synthetic wall is created, the adhesive force (binding force) to the underground structure such as the existing common groove can be sufficiently exerted, and the buoyancy to the underground structure at the time of liquefaction causes the floating and the surrounding ground. It is possible to prevent buoyancy caused by wraparound from the ground ”(see paragraph [0016] 1) of the same document 2).
That is, in the invention of Patent Document 2, the underground structure 1 is firmly held (fixed) by the ground improvement composite wall 4, and the improved body 2 is subjected to seismic force due to the passive resistance of the rooted portion. Based on the technical idea of considering it as a resisting pile design, it is highly practical, as it exerts the effect of preventing the floating due to the buoyancy of the underground structure 1 during liquefaction.

In addition, as a design problem, in the above-mentioned continuous underground wall and steel sheet pile with drainage function, it is assumed that the improved body is an immovable body that is embedded in the non-liquefaction layer. It is also necessary to consider the water pressure.

An object of the present invention is a reversal idea of realizing a configuration in which the degree of fixation of a ground improvement wall to an underground structure is intentionally lowered to allow liquefaction with respect to the above-mentioned technical idea according to the above-mentioned Patent Document 2. By introducing the technical idea based on the above, it is possible to suppress the hydrodynamic pressure during an earthquake while reducing the rigidity of the ground improvement wall, and it is an economical and workable measure against liquefaction of underground structures. To provide the structure.

As a means for solving the above-mentioned problems of the background technology, the liquefaction countermeasure structure of the underground structure according to the invention according to claim 1 has a ground having a small improvement diameter along both sides in the extension direction of the underground structure. The ground improvement wall is created by constructing the improved body in a column shape until it reaches the non-liquefaction layer and building a rod-shaped reinforcing member inside the ground improvement body so as not to reach the non-liquefaction layer. It is characterized in that the lower end of the ground improvement wall is less embedded in the non-liquefaction layer, while the upper end is not constructed higher than the middle of the underground structure.

According to the second aspect of the present invention, in the liquefaction countermeasure structure of the underground structure according to the first aspect, the upper end of the ground improvement wall is 1/4 to 2/2 / of the total height of the underground structure. It is characterized in that it is constructed so as to be higher than the lower end of the underground structure by the height of 3.

According to the third aspect of the present invention, in the liquefaction countermeasure structure of the underground structure according to the first or second aspect, the lower end of the ground improvement wall is 1/2 to 1/2 of the effective width of the ground improvement wall. It is characterized in that it is constructed so as to be rooted in the non-liquefied layer by an effective width of 3/2.

According to the liquefaction countermeasure structure of the underground structure according to the present invention, the following effects are obtained.
1) Along both sides of the extension direction of the underground structure, a ground improvement body with a small improvement diameter is constructed in a columnar shape until it reaches the non-liquefaction layer, and a rod-shaped reinforcing member is not formed inside the ground improvement body. Since the ground improvement wall is constructed and implemented so as not to reach the liquefaction layer, it is possible to suppress the floating of the ground structure due to the wraparound of the surrounding ground that occurs when liquefaction occurs.
Further, since liquefaction of the underground structure in the direct basement is allowed, the underground structure and the ground improvement wall are wrapped by a high-pressure jet stirring method, and the ground improvement wall is made into a non-liquefaction layer. By embedding, it is possible to secure the adhesive force generated in each portion and suppress the lifting due to the buoyancy generated in the underground structure when liquefaction occurs.
2) The lower end of the ground improvement wall reduces the penetration into the non-liquefaction layer, while the upper end is not constructed higher than the middle of the underground structure, so that the degree of fixation to the underground structure is reduced. Is intentionally lowered to cause fine locking to the extent that the ground improvement wall does not collapse (destroy) during an earthquake, and as a result, the hydrodynamic pressure generated at the ground improvement wall during an earthquake can be reduced.
3) With the effect of 2) above, the scale (strength / rigidity) of the ground improvement wall can be reduced, and the workability and economy are excellent.
4) When the ground improvement body is constructed by the high-pressure injection stirring method or the high-pressure injection stirring combined mechanical stirring method, it can be flexibly and efficiently constructed even when underground buried objects other than the underground structure interfere with each other or in a narrow place. Therefore, it is excellent in workability.

It is a vertical sectional view schematically showing the case where the liquefaction countermeasure structure of this invention is applied to a common groove (existing common groove). It is an enlarged vertical sectional view showing the peripheral part of the common groove of FIG. It is a plan view corresponding to FIG. It is a vertical sectional view which showed the variation of FIG. It is an enlarged view of the main part of FIG. It is a plan view corresponding to FIG. A to E are tables showing the results of the centrifugal model implementation performed to confirm (comparatively examine) the effect of the present invention. It is a graph which showed the examination result of the bending moment generated by the water pressure difference (the dynamic water pressure at the time of an earthquake). It is a vertical sectional view which showed the prior art. It is a vertical sectional view which showed the prior art. It is a vertical sectional view which showed the prior art.

Hereinafter, examples of the liquefaction countermeasure structure of the underground structure according to the present invention will be described with reference to the drawings. Incidentally, in this embodiment, as an underground structure, a case where lifelines such as electricity, telephone, gas, and water are applied to an existing utility tunnel constructed for burying underground is shown.

FIGS. 1 to 3 show a utility tunnel (underground structure) 1 to which measures against liquefaction have been taken by a column-type ground improvement wall.
In the liquefaction countermeasure structure of the utility tunnel (underground structure) 1, a columnar ground improvement body 2 having a small improvement diameter S is a pillar along both sides of the extension direction of the utility tunnel 1 buried in the ground 6. It is constructed in a row until it reaches the non-liquefaction layer 5, and a rod-shaped reinforcing member (for example, a reinforcing bar) 3 is built inside the ground improvement body 2 so as not to reach the non-liquefaction layer 5. The ground improvement wall 4 is constructed.
Incidentally, the width of the utility tunnel 1 according to the present embodiment is assumed to be about 480 cm, but of course, the width is not limited to this, and can be applied to various forms of underground structures.

The ground improvement body 2 is constructed by the high pressure injection stirring method in this embodiment. This high-pressure injection agitation method is a method of mixing and stirring while excavating (drilling) the ground 6 by injecting a solidifying material at high pressure using a small (efficiency-oriented) or ultra-small (installability-oriented) injection-type ground improvement machine. Is.
In this embodiment, the guide pipe is installed at a position avoiding the utility tunnel 1 when viewed from the plane direction, the rod is penetrated in the vertical direction (not shown), and the extension direction side surface and a part of the adjacent utility tunnel 1 are wrapped. The lower end of the ground improvement body 2 (ground improvement wall 4) is constructed so that the rooting in the non-liquefaction layer 5 is reduced (about 0.5 to 3 m). On the other hand, the upper end of the ground improvement body 2 (ground improvement wall 4) is not constructed higher than the middle of the common groove 1 (created so as to be 1 to 2 m higher than the lower end of the common groove 1). Integrates with the utility tunnel 1 and contributes to suppressing the floating of the underground structure when liquefaction occurs.

It should be noted that the same can be carried out by adopting the high-pressure injection stirring combined mechanical stirring method instead of the high-pressure injection stirring method, and the same effect can be obtained.
In this way, when the ground improvement body 2 is constructed by the high injection stirring method (or the mechanical stirring method combined with high pressure injection stirring), there is a case where an underground buried object other than the utility tunnel (underground structure) 1 exists. However, unlike the case where the steel sheet pile is used, the ground improvement body 2 can be continuously constructed while avoiding the underground buried object, and the construction can be flexibly performed.

The improved ground body 2 has an improved diameter S (outer diameter φ) of about 1.0 to 2.5 m. This is much smaller than the improved width (for example, 5.7 m) in the conventional deep mixing treatment method. Therefore, it can be sufficiently constructed even in a narrow place.
Further, the form of the ground improvement body 2 is not limited to the illustrated example, and the outer diameter, outer shape, number, and the like can be appropriately changed according to the ground improvement machine to be constructed and the like. The ground improvement body 2 may be placed in the order of placing one or a plurality of the ground improving bodies 2 by placing one or a plurality of the ground improving bodies 2 in a timely manner, or by pushing one side. However, the rod-shaped reinforcing member 3 is quickly built in until the improved body 2 in each area develops a predetermined strength.

The ground improvement body 2 according to the present embodiment has an improvement diameter S of about 2.0 m, and the adjacent improvement bodies 2 and 2 have a distance between cores (between cores). It is set to about 1.7 m and wrapped. In this embodiment, the reinforcing bar (or a material equivalent thereto) 3 used as the rod-shaped reinforcing member 3 has one reinforcing bar (φ51 mm) for one ground improving body 2 and the axis of the ground improving body 2. It is implemented in a configuration that is built in the position (approximately the central part).
Thus, on both sides of the utility tunnel 1 shown in the plan view of FIG. 3, the adjacent ground improvement bodies 2 and 2 constructed in a row are not only partially wrapped with each other, but also the adhesive force (binding force) is increased. Therefore, by constructing the joint groove 1 so as to partially wrap it, a ground improvement wall 4 in which the ground improvement body 2 is continuous over the entire length in the extension direction of the underground structure is created.
Incidentally, as shown in FIG. 1, the ground improvement wall 4 according to the present embodiment is formed so as to have a substantially uniform cross-sectional shape from the upper end portion to the lower end portion. Further, the improvement strength of the ground improvement body 2 is 2000 to 3000 kN / m ² , but the improvement strength is not limited to this, and the design can be appropriately changed according to the ground properties and the like.

As described above, the liquefaction countermeasure structure of the utility tunnel (underground structure) 1 has a depth such that the rod-shaped reinforcing member 3 does not reach the non-liquefaction layer 5 in the ground improvement body 2 having the above configuration. (In the illustrated example, the depth is about 1 m shallower than that of the non-liquefied layer 5).
This is because the ground improvement body 2 with a small improvement diameter S alone cannot sufficiently secure stability against lifting and wraparound due to buoyancy generated during an earthquake, and dynamic water pressure during an earthquake, and collapses (destroys). There is a risk, but this is due to the fact that the stability can be ensured by building and reinforcing one rod-shaped reinforcing member (reinforcing bar) 3 (see FIGS. 1 to 3).
When one rod-shaped reinforcing member 3 is built in the center, it effectively acts on the shearing force generated in the ground improvement body 2, but contributes to stability against the bending moment. I can't. Therefore, when there is a concern about destruction due to bending moment in the structural design, for example, as shown in FIGS. 4 to 6, a plurality of well-balanced sizes (small diameter (about φ25 mm) in the illustrated example) are used at equal intervals from the center. (2) Arrangement is being made as appropriate to ensure the stability.

However, it should be noted that simply reinforcing the ground improvement body 2 increases the rigidity of the entire ground improvement wall 4, excessively resists the hydraulic water pressure during an earthquake, and may damage the ground improvement wall 4. There is a need.
That is, in the present invention, the ground improvement wall 4 does not use a highly rigid member such as H-shaped steel for the reinforcing member 3 (core material) or root into the non-liquefaction layer 5, and the ground improvement wall 4 is subjected to an earthquake. A rod-shaped reinforcing member (reinforcing bar) having a lower rigidity than a steel material such as the H-shaped steel, in order to reinforce it to the extent that it can cause locking and to realize a structure in which the hydrodynamic pressure acting on the ground improvement wall 4 is appropriately received. ) 3 is adopted, and the non-liquefied layer 5 is built so shallowly that it does not reach the non-liquefied layer 5.

Therefore, in the above-mentioned liquefaction countermeasure structure of the underground structure 1, the ground improvement body 2 having a small improvement diameter reaches the non-liquefaction layer 5 in a columnar shape along both sides in the extension direction of the underground structure 1. In addition to constructing up to, the ground improvement wall 4 is constructed and implemented by building a rod-shaped reinforcing member 3 inside the ground improvement body 2 so as not to reach the non-liquefaction layer 5. Therefore, the underground structure 1 is constructed. It is possible to suppress the floating caused by the wraparound of the surrounding ground that occurs when liquefaction occurs.
Further, the lower end portion of the ground improvement wall 4 reduces the penetration into the non-liquefaction layer 5, while the upper end portion is not constructed higher than the middle of the underground structure 1, so that the underground structure 1 is not constructed. The degree of fixation to the ground is intentionally lowered to cause fine locking to the extent that the ground improvement wall 4 does not collapse (destroy) during an earthquake, and as a result, the hydraulic water pressure generated at the ground improvement wall 4 during an earthquake is reduced. be able to. Along with this, the scale (strength / rigidity) of the ground improvement wall 4 can be reduced, and the workability and economy are excellent.

Next, regarding the above-mentioned liquefaction countermeasure structure of the underground structure 1, the centrifugal model experiment (effect confirmation test) conducted by the applicant will be described.

FIG. 7A shows a model case of the liquefaction countermeasure structure according to the present invention. In this model case, the lower end of the ground improvement wall 2 has a small rooting in the non-liquefaction layer 5 (about 0.9 m). On the other hand, the upper end of the ground improvement body 2 has a height 1.0 m higher than the lower end of the underground structure 1 (improved strength 3000 kN / m ² , improved length 12.2 m, improved top end GL-3). .8m). The reinforcing bar 3 (core material) built in the ground improvement body 2 adopts a length of 10 m, the upper end thereof is aligned with the upper end of the ground improvement body 2, and the lower end portion is about 1 m shallower than the non-liquefied layer 5. By the way, I'm stopping.
According to the centrifugal model experiment in this model case, the amount of lifting was 55 mm, and the ground improvement body 2 was not broken (collapsed) at all, and the soundness could be confirmed.
This is intended to reduce the rooting in the non-liquefied layer 5 and the degree of fixation to the underground structure 1 as compared with Patent Document 2 previously filed by the applicant described in the above background technology section. It is good that the ground improvement body 2 was able to generate fine locking to the extent that the ground improvement body 2 did not collapse (destroy) during an earthquake, and as a result, the hydraulic water pressure generated in the ground improvement body 2 during an earthquake could be reduced. It is presumed that this is the reason why the results were obtained. As a basis, as shown in FIG. 8, in the calculation measurement (actual measurement) obtained from the centrifugal model experiment, the cross-sectional force (bending moment) was not confirmed in the ground improvement body 2 as much as the theoretical value (hydraulic pressure during an earthquake). Can be mentioned.
Further, as a result of reducing the embedding, the cross-sectional force generated by the decrease in the degree of fixation at the boundary portion between the ground improvement body 2 and the non-liquefaction layer 5 is reduced, and as a result, the lower end portion of the reinforcing bar 3 is not formed. It is highly probable that the ground improvement body 2 did not break (collapse) even if it was stopped at a place shallower than the liquefaction layer 5.

The model case of FIG. 7B is different from that of FIG. 7A in that the lengths of the ground improvement body 2 and the reinforcing bar 3 (core material) are formed higher to the top of the underground structure 1 (improvement length 14). .2m, core material length 12m).
According to the centrifugal model experiment in this model case, the amount of lifting was 37 mm, but the ground improvement body 2 was found to be broken (collapsed). This is because the degree of fixation between the underground structure 1 and the ground improvement body 2 has increased, and as a result, the inertial force generated in the underground structure 1 during an earthquake acts intensively on the ground improvement body 2 as a horizontal load. It is presumed that a break (collapse) occurred.
That is, it was confirmed that the ground improvement body 2 cannot ensure the soundness of the ground improvement body 2 simply by increasing the degree of fixation to the non-liquefied layer 5 and the underground structure 1.

Compared to FIG. 7A, the model case of FIG. 7C adopts a length of 5 m for the reinforcing bar 3 built in the ground improvement body 2, the upper end thereof is aligned with the upper end of the ground improvement body 2, and the lower end portion is not. The difference is that it is stopped at a place about 6 m shallower than the liquefied layer 5.
According to the centrifugal model experiment of this model case, the amount of lifting was 87 mm, and the ground improvement body 2 was found to be broken (collapsed).
That is, in the ground improvement body 2, the hydraulic water pressure during an earthquake that acts is reduced for the reasons shown in the paragraphs [0027] and [0028], but the reinforcing bar 3 (core material) is used for the generated cross-sectional force. It was confirmed that the soundness of the ground improvement body 2 could not be ensured unless reinforcement was performed for an appropriate range. Here, the appropriate range is that the top end of the ground improvement body 2 is the starting point and the ending point is slightly shallower than the non-liquefied layer 5.
As a precaution, as shown in FIGS. 7D and 7E, we conducted an experiment with a model without reinforcing bars (core material) 3, but the amount of lifting was 131 mm and 103 mm, respectively, and the ground improvement body 2 both broke (collapsed). It was confirmed that even if the strength of the ground improvement body 2 is insufficient, the soundness of the ground improvement body 2 cannot be ensured.

In summary, the ground improvement wall 4 has a moderately shallow rooting of the ground improvement body 2 with respect to the underground structure 1, and the fixing to the underground structure 1 is held with an appropriate degree of fixation, and the reinforcing bars are also held. The soundness of the ground improvement wall 4 itself is such that the upper part of the ground improvement body 2 is reinforced by inserting 3 and the reinforcing bar (core material) 3 is also reinforced in an appropriate range so as not to be rooted. It turned out to be very important in maintaining sex.
By the way, when the ground improvement wall 4 is constructed so that the upper end portion thereof is higher than the lower end portion of the underground structure 1 by a height of 1/4 to 2/3 of the total height of the underground structure 1. Good results are obtained. This is derived in consideration of the numerical values obtained by the applicant based on his experiments and his insight. On the other hand, good results are obtained when the ground improvement wall 4 is constructed so that the lower end portion thereof is embedded in the non-liquefaction layer 5 by an effective width of 1/2 to 3/2 of the effective width of the ground improvement wall 4. Is obtained. This is also derived in consideration of experiments and numerical values obtained by the applicant based on his insight.

Although the examples have been described above based on the drawings, the present invention is not limited to the illustrated examples, and includes a range of design changes and application variations normally performed by those skilled in the art within a range that does not deviate from the technical idea thereof. I will mention it just in case.

For example, the form (size, shape, improvement strength) of the ground improvement body 2 and the form (size, shape, number) of the rod-shaped reinforcing member 3 are not limited to the above, and the ground improvement body 3 is not limited to the above. The design can be appropriately changed according to the structural design that can maintain the soundness of the ground improvement wall 4 by causing fine locking so that the 2 does not collapse (break).

Further, the liquefaction countermeasure structure of the underground structure according to the present invention can be similarly implemented for so-called linear underground structures such as underground roads and underground railroads, in addition to utility tunnels.

1 Underground structure (utility tunnel)
2 Ground improvement body 3 Rod-shaped reinforcing member (reinforcing bar)
4 Ground improvement wall 5 Non-liquefied layer 6 Ground (liquefied layer)
S improved diameter

Claims (3)

Along both sides of the extension direction of the underground structure, a ground improvement body having a small improvement diameter is constructed until it reaches the non-liquefaction layer in a columnar shape, and a rod-shaped reinforcing member is non-liquid inside the ground improvement body. The ground improvement wall is created by building so as not to reach the chemical layer, and the lower end of the ground improvement wall has a small rooting in the non-liquefaction layer, while the upper end has the underground structure. A liquefaction countermeasure structure for underground structures, characterized in that it is not constructed higher than the middle of the object. The ground improvement wall is characterized in that the upper end thereof is constructed so as to be higher than the lower end of the underground structure by a height of 1/4 to 2/3 of the total height of the underground structure. The liquefaction countermeasure structure for the underground structure according to claim 1. The ground improvement wall is characterized in that the lower end portion thereof is formed so as to be rooted in the non-liquefaction layer by an effective width of 1/2 to 3/2 of the effective width of the ground improvement wall. The liquefaction countermeasure structure for the underground structure according to claim 1 or 2.

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