JP5997093B2 - Structure to prevent liquefaction of ground due to structural load - Google Patents

Description

  The present invention relates to a liquefaction countermeasure structure for preventing liquefaction of a ground due to a load of a structure constructed on the ground.

  Conventionally, as one of the countermeasures for liquefaction, as shown in FIG. 11, by providing a grid-like underground wall 102 on the ground 103, deformation of the ground 103 surrounded by the grid-like underground wall 102 is suppressed. At the same time, a liquefaction countermeasure technique for blocking liquefaction by blocking the flow of groundwater from the surrounding ground 104 is known (Patent Document 1).

In order to suppress the liquefaction of the ground, it is necessary to create the underground wall with a somewhat narrow lattice interval, which may increase the cost of creating the underground wall and increase the construction period.
In addition, when trying to prevent liquefaction of an existing structure, it is difficult to create an underground wall on the ground directly under the structure, and it can be expensive to create the underground wall. Cannot be created. If the underground wall cannot be created directly under the structure, this liquefaction countermeasure technology cannot be adopted.

Therefore, as shown in FIG. 12, the underground wall 112 made of a ground improvement body surrounding the structure 111 with a predetermined width and thickness in a plan view, which does not require the formation of the underground wall directly under the structure, The first liquefaction that is the foundation ground of the structure that is formed on the liquefied layer 113 that is formed in the vertical direction from at least the bottom lower end surface of the structure 111 to the non-liquefied layer 114 and that may be liquefied. A countermeasure structure 110 has been proposed (Patent Document 2).
However, this liquefaction countermeasure structure has an underground wall made of ground improvement material only around the structure, so that when the structure is large, the gap between the opposing underground walls becomes wide and liquefaction occurs. It cannot prevent itself.

In addition, the horizontal force due to the inertia of the structure during an earthquake is transmitted from the structure 111 to the ground of the liquefied layer 113 that may be liquefied as schematically shown in FIG. However, effective measures are not taken against it.
Furthermore, as shown in FIG. 5B, external force from the structure to the ground is generated by rocking vibration of the structure during an earthquake, but no means for suppressing it is considered.

  In order to solve these problems, as shown in FIG. 14, an underground wall 122 surrounding the ground 125, and a rigid plate disposed on the ground and having higher rigidity than the ground and covering the inside of the underground wall. 123 and a joint member 124 made of a granular material packed in a water-permeable bag for closing the gap between the inner surface of the underground wall 122 and the rigid plate 123. A countermeasure structure 120 has been proposed (Patent Document 3).

This liquefaction countermeasure structure 120 transmits shear force of the ground 124 surrounded by the underground wall by transmitting a horizontal force due to the building inertia force from the rigid plate 123 to the underground wall 122 via the joint member 124 in the event of an earthquake. It can be suppressed and liquefaction can be prevented.
Moreover, the joint member can suppress the vertical movement of both ends of the building by locking the building.

  However, this second liquefaction countermeasure structure has an area for transmitting force to the underground wall 122 when the thickness of the rigid plate 123 is not thick, as shown in FIG. Therefore, it is assumed that the force concentrates on the upper part of the underground wall and the stress on the underground wall becomes severe.

Furthermore, the joint member 124 is assumed to be a granular material packed in a bag (sand, gravel, etc. packed in a sandbag), but restrains the vertical movement by volume expansion of the granular material accompanying shear deformation. However, there is anxiety as to whether or not the effect can be surely obtained depending on the filling state of the granular material and the embedding condition of the bag.
Furthermore, depending on the rigidity of the underground wall 122, it cannot be denied that the effect of suppressing the shear deformation of the ground 125 surrounded by the underground wall and preventing liquefaction cannot be sufficiently obtained.

Japanese Examined Patent Publication No. 04-054004 JP 2005-105602 A JP 2010-216107 A

  An object of the present invention is to provide a liquefaction prevention effect even when a gap between opposing underground walls is wide in a liquefaction countermeasure in which an underground wall is arranged on the outer periphery of a structure, and is arranged on the outer periphery of a structure. By combining the underground wall and the underground wall connected to the structure, the structure inertia force generated during the earthquake is transmitted to the underground wall arranged around the structure through the underground wall connected to the structure, The vertical load of the structure is transmitted to the structure directly under the ground, and the rocking vibration of the structure is prevented, so that sufficient liquefaction prevention effect can be achieved even if the space between the underground walls arranged around the structure is large The purpose is to provide a liquefaction countermeasure structure for soft ground that can be obtained.

  The invention according to claim 1 encloses a structure supported on a foundation of a type in which a vertical load of the structure acts on the upper surface of the ground, and is slightly spaced outward from the outer periphery of the structure and surrounds the structure's direct foundation board. A ground liquefaction countermeasure structure comprising an outer underground wall extending to a non-liquefied ground and an inner underground wall connected in the vicinity of a lower edge of the structure, the inner underground wall and the The vertical ground edge is cut from the outer underground wall, and the structure inertia force in the horizontal direction due to the earthquake is transmitted to the outer underground wall via the inner underground wall, and In addition to reducing the external force due to the inertial force acting on the structure and reducing the shear stress of the ground, the rocking vibration of the structure due to the earthquake is suppressed by the friction between the inner underground wall and the ground, The entire load is applied to the foundation base plate of the structure, so that the effective response of the ground It was liquefaction countermeasure structure of the ground to increase.

  The invention according to claim 2 is characterized in that at least a part of the outer surface upper portion of the outer ground wall made of a cement-based ground improvement body is reinforced by the cement-based ground improvement body.

  The invention according to claim 3 is characterized in that the inner underground wall is provided so as to surround the ground continuously or intermittently in plan view.

  According to the first aspect of the present invention, the structure supported by the foundation of the type in which the vertical load of the structure acts on the upper surface of the ground, and the structure directly grounded board is separated slightly outward from the outer periphery of the structure. Because the outer underground wall extended to the non-liquefied ground at the inside and the inner underground wall connected to the vicinity of the lower edge of the structure are combined, the structure inertia force generated at the time of the earthquake is the inner underground wall. Can be transmitted to the outer underground wall, reducing the external force due to the inertial force of the structure acting on the ground between the inner underground walls and reducing the shear stress of the ground, resulting in a liquefaction suppression effect .

  In addition, although the ground is slightly sandwiched between the inner and outer underground walls, the thickness of the sandwiched ground is very thin, which adversely affects the transmission of structural inertial force between both underground walls. Is negligible without affecting

On the other hand, because the vertical edges of the inner and outer underground walls connected to the structure are cut off, the vertical load of the structure is not transmitted to the outer underground wall as much as possible, but to the structure directly under the ground. I can tell you.
As a result, the effect of suppressing shear deformation by the outer underground wall, increasing the effective stress due to the vertical load of the structure, and reducing the external force to the structure directly under the ground by the inner underground wall are obtained. Compared with the liquefaction countermeasure structure of only the ground, it can exhibit an excellent liquefaction suppression effect.
As a result, it is possible to prevent liquefaction even when the space between the underground walls is wider than before.

  Further, in the present invention, since the force is exchanged with the outer underground wall within the range of the found area of the inner underground wall, the force is larger in the area than when the force is exchanged only with the root portion of the structure. Therefore, stress concentration at the upper part of the underground wall can be prevented. Therefore, the possibility of damage to the underground wall due to the transmission of the structure inertia force to the underground wall can be reduced.

  Furthermore, even with respect to rocking vibration of the structure that occurs during an earthquake, it is possible to suppress the vibration by friction between the inner underground wall and the ground.

  According to the second aspect of the present invention, at least a part of the outer surface upper portion of the outer underground wall made of a cement-based ground improvement body is reinforced by the cement-based ground improvement body to enhance the earthquake resistance of the underground wall. Therefore, it is possible to prevent the underground wall from being damaged by the horizontal structure inertia force due to the earthquake.

According to the invention in which the inner underground wall according to claim 3 is provided so as to surround the ground continuously in plan view, the inner underground wall constructed in different directions integrally resists. Rigidity can be easily obtained, and the structure inertia force can be easily transmitted to the outer underground wall.
On the other hand, according to the invention in which the inner underground wall according to claim 3 is provided so as to surround the ground by interrupting the plan view, the construction amount can be reduced to reduce the cost, and the position of the buried piping etc. can be avoided. An inner underground wall can be constructed.

It is a longitudinal cross-sectional view of the ground liquefaction countermeasure structure of Example 1 of this invention. It is a figure which shows the mechanism in which the inner underground wall of this invention transmits structure inertia force to an outer underground wall in a wide area, and relieve | moderates stress concentration. It is a figure which shows the mechanism in which the inner underground wall of this invention suppresses the rocking vibration of a structure by the friction of a ground. It is a figure which shows the effective stress analysis result which simulated the rise and dissipation of the excess pore water pressure at the time of an earthquake. It is a figure which shows the time history of the excess pore water pressure ratio in the structure base foundation board depth of 2.5 m. It is a top view of the ground liquefaction countermeasure structure of Example 1 of the present invention. It is a top view of the ground liquefaction countermeasure structure of the modification of Example 1. It is a longitudinal cross-sectional view of the ground liquefaction countermeasure structure of Example 2 of the present invention. It is a top view of the ground liquefaction countermeasure structure of Example 2. It is a top view of the ground liquefaction countermeasure structure of the modification of Example 2. It is a longitudinal cross-sectional view which shows typically the 1st liquefaction countermeasure structure described in patent document 1. FIG. It is a longitudinal cross-sectional view which shows typically the 1st liquefaction countermeasure structure described in patent document 2. FIG. (A) is a figure which shows typically the mechanism in which a structure inertia force is transmitted to a structure direct foundation | ground board, (b) is the external force which acts on the ground by rocking vibration with respect to the liquefaction suppression of a ground. It is a figure which shows typically having a negative effect | action. It is a longitudinal cross-sectional view which shows typically the 2nd liquefaction countermeasure structure described in patent document 3. FIG. The second liquefaction countermeasure structure is a longitudinal sectional view schematically showing a mechanism of stress concentration because the area for transmitting the structure inertia force to the outer underground wall is small.

One method for preventing liquefaction is to increase the effective stress of the ground.
When there is a structure directly supported by a foundation, the effective stress increases immediately below the structure, so liquefaction is unlikely to occur. However, if the structure is supported on the ground where no countermeasures are taken, if the surrounding ground liquefies during an earthquake, the ground directly under the structure swells sideways and excessive subsidence occurs.

  Therefore, in order to prevent the ground from squeezing out to the side, as shown in FIG. 12, by providing an underground wall so as to surround the ground directly under the structure, the structure can be prevented from sinking, It is possible to obtain two liquefaction suppression effects, namely, shear deformation suppression by walls and increase of effective stress due to vertical load on the structure.

However, when a vertical load of the structure is applied to the ground, the effective stress increases, but a horizontal force due to the inertial force of the structure generated during the earthquake is transmitted to the ground.
As a result, the shear stress of the ground surrounded by the underground wall increases, and there is a possibility that the effect of suppressing liquefaction cannot be obtained sufficiently.

  Therefore, it is necessary to devise a way to prevent the inertia of the structure from being transmitted to the ground in some way. Therefore, it is conceivable to transmit the inertial force of the structure to the underground wall side through the pierced part.However, if the area where the structure is in contact with the underground wall is small, such as when the piercing is shallow, The force acting on the wall is concentrated on the upper part of the underground wall, and the underground wall may be damaged (see FIG. 15).

The ground liquefaction countermeasure structure of the present invention also has a function of suppressing stress concentration on the upper part of the underground wall.
An embodiment of the liquefaction countermeasure structure according to the present invention will be described in detail.

First, the first embodiment will be described in detail with reference to FIGS. 1 to 3.
As a premise, the foundation 5 of the type on which the structure 2 is loaded and the vertical load of the structure acts is composed of a non-liquefied ground 4 from below the ground and a ground 3 that may be liquefied stacked on the foundation. Has been.
The structure 2 is directly supported by the ground 3 which may be liquefied. When the structure 2 receives a horizontal load due to an earthquake under the condition that the outer underground wall 6 and the structure 2 do not exist, Liquefaction phenomenon occurs.

  The liquefaction countermeasure structure 1 of this embodiment is an outer ground that surrounds the structure 2 supported by the foundation 5 and the structure direct ground board 31 in which the vertical load of the structure acts on the ground 3 that may be liquefied. And a wall 6.

  The present invention is a liquefaction countermeasure structure characterized by combining a structure 2, an outer underground wall 6, and an inner underground wall 7 connected to the structure 2. The outer underground wall 6 is disposed at a slight distance from the structure 2 in a plan view, and is usually a continuous wall having poor permeability, and the lower end of the underground wall 6 is a ground that may be liquefied. 3 is embedded in the non-liquefied layer 4 below 3.

  The outer underground wall 6 is formed of cement-based ground improvement body, reinforced concrete connection wall, steel sheet pile, SMW which is a composite structure of a wall body and steel material formed by mixing and stirring soil and cement slurry in situ. be able to.

The inner underground wall 7 is attached to the lower end of the outer peripheral wall of the structure 2 or the lower surface of the foundation in the vicinity of the outer peripheral wall, and is integrated with the structure 2.
The inner underground wall 7 can be continuously formed of a reinforced concrete continuous wall, a steel sheet pile, H steel, or the like.

  Further, the inner underground wall 7 does not need to reach the non-liquefied ground 4, and the length in the depth direction is such that a horizontal load from the structure is sufficiently transmitted to the outer underground wall 6 surrounding the structure direct foundation 31. As long as it has.

  The distance between the inner underground wall 7 and the outer underground wall 6 is such that the structure inertia force generated during the earthquake is transmitted to the outer underground wall 6 through the inner underground wall 7 integrated with the structure 2. It is set to a distance that can be. For this reason, although the ground is sandwiched between the underground walls 6 and 7, since the thickness is set to an appropriate range, the transmission of the structure inertia force is not adversely affected, It can be ignored.

Since the horizontal force due to the structure inertia force generated at the time of the earthquake can be transmitted to the outer underground wall 6 via the inner underground wall 7, it is caused by the structure inertia force acting on the ground 31 itself directly under the structure 2. Horizontal external force decreases.
Thereby, the liquefaction suppression effect is obtained by reducing the shear stress of the ground 3.

  On the other hand, since the upper and lower edges of the inner underground wall 7 connected to the structure 2 and the outer underground wall 6 surrounding the structure direct ground board are cut, the structure 2 is allowed to move downward, and the structure The vertical load of the object does not flow to the outer underground wall 6, but the entire vertical load of the structure acts on the above-described direct foundation base 31 of the structure, thereby reliably increasing the effective stress of the ground.

As a result, the shear deformation is suppressed by the outer underground wall 6 that surrounds the structure direct foundation board 31, the effective stress is increased by the vertical load of the structure, and the external force to the ground is reduced by the inner underground wall 7 connected to the structure. An effect is acquired and the liquefaction suppression effect superior to the conventional liquefaction countermeasure structure of only the underground wall 112 shown in FIG. 12 can be exhibited.
As a result, liquefaction can be prevented even when the distance between the underground walls facing each other is wider than in the past.

Further, in this embodiment, as shown in FIG. 2, the outer underground wall 6 and the force that surround the structure base ground board are within the range of the found area of the inner underground wall 7 integrated and connected to the structure 2. Exchange.
Accordingly, as shown in FIG. 12, the force is exchanged over a larger area than the liquefaction countermeasure structure that exchanges force only at the root portion of the structure 2, and the stress on the outer underground wall 6 is changed. Concentration can be prevented.
Therefore, the possibility of damage to the underground wall 6 caused by transmitting the structure inertia force to the outer underground wall 6 via the inner underground wall 7 can be greatly reduced.

  Further, as shown in FIG. 3, the present embodiment suppresses the vibration caused by the friction between the inner underground wall 7 connected to the structure 2 and the ground even with respect to the rocking vibration of the structure 2 generated during an earthquake. It is possible.

In this embodiment, a solid foundation (direct foundation) is adopted as the basic form of the structure in which the vertical load of the structure acts on the ground.
The inner underground wall 7 does not necessarily have to be continuous so as to surround the ground in plan view. Therefore, as a modification of this embodiment, as shown in FIG. 7, it is provided in a form that is provided so as to surround the ground intermittently in plan view, that is, in a form divided in plan view. Is also possible.

In order to demonstrate the effects of the present invention described above, effective stress analysis that can simulate the increase / dissipation of excess pore water pressure during an earthquake was conducted, and the effect of suppressing liquefaction caused by the vertical load on the grid underground wall and structure It was investigated.
In this analysis model, the outer underground wall 6 is constructed to a depth of 10 m from the ground surface, the wall thickness is 0.8 m, and the distance between the opposing walls is 15 m.

In the analysis case, when the countermeasure is applied only with the underground wall without the vertical load of the structure, when the vertical load of the structure is 60 kN / m ² , the vertical load of the structure is 60 kN / m ^2. 3 cases in which the inner underground wall 7 connected to the structure is provided.

FIG. 4 shows a contour of excess pore water pressure ratio, and FIG. 5 shows a time history of excess pore water pressure ratio at a depth of 2.5 m. It can be seen that the amount of increase in the excess pore water pressure ratio is smaller when the vertical load of the structure is applied (B) than when the vertical load of the structure is not applied (A).
This is thought to be because the vertical load of the structure acts on the ground surrounded by the outer underground wall 6 to increase the effective stress of the ground and increase the liquefaction strength of the ground.

  Furthermore, in the case where the inner underground wall 7 connected to the structure is provided (C), it can be confirmed that the amount of increase in the excess pore water pressure ratio is smaller and the effect of suppressing liquefaction is increased. When there is no inner underground wall 7 connected to the structure 2, the inertial force of the structure generated by the earthquake motion acts as an external force on the ground 31 surrounded by the outer underground wall 6 to promote liquefaction. However, when a wall connected to the structure is provided, the inertial force of the structure flows to the outer underground wall 6 via the inner underground wall 7 connected to the structure. It can be seen that the external force of the enclosed ground decreased and the liquefaction suppression effect increased.

The time history of the excess pore water pressure ratio of the ground surrounded by the underground wall at a depth of 2.5 m in FIG. 5 will be examined.
According to this, when the vertical load of the structure is not applied (A), the liquid is substantially liquefied approximately 15 seconds after the occurrence of the earthquake, and the liquefaction phenomenon is not dissipated even after 120 seconds.
When the vertical load of the structure is applied (B), liquefaction begins to dissipate after approximately 40 seconds although liquefaction occurs approximately 20 seconds later, and the liquefaction phenomenon dissipates substantially completely after approximately 120 seconds.

  On the other hand, when the inner underground wall 7 connected to the structure is provided in addition to applying the vertical load of the structure (C), the increase amount of the excess pore water pressure ratio becomes significantly smaller. Thus, it can be confirmed that the excessive liquefaction pressure ratio of the ground is restored to the state before the earthquake motion after about 120 seconds without liquefaction, and the effect of suppressing liquefaction is increased.

  In the case where there is no inner underground wall 7 connected to the structure (B), the inertial force of the structure generated by the earthquake motion acts as an external force on the ground surrounded by the underground wall to promote liquefaction. However, in the case where the inner underground wall 7 connected to the structure is provided (C), the inertia force of the structure flows to the outer underground wall 6 through the inner underground wall 7 connected to the structure. It is supported that the external force of the ground 31 surrounded by the outer underground wall 6 is reduced and the effect of suppressing liquefaction is increased.

A second embodiment will be described with reference to FIGS.
As shown in FIGS. 8 and 9, the liquefaction countermeasure structure 1 includes a reinforcing pile 61 in which the entire upper surface of the outer ground wall 6 made of a cement-based ground improvement body is made of a cement-based ground improvement body. It is reinforced by.

  Since the upper part of the outer underground wall 6 receives horizontal structure inertia force from the inner underground wall 7 in the event of an earthquake, the possibility of damage increases as the depth of the inner underground wall 7 is reduced. Become.

And in this Example, the reinforcement pile 61 of the substantially same depth as the inner underground wall 7 is constructed | assembled.
Thereby, since the rigidity of the outer underground wall 6 increases, it becomes easier to transmit the structure inertia force from the inner underground wall 7 to the outer underground wall 6 and further relieve the stress of the outer underground wall 6. Since the seismic resistance of the outer underground wall 6 is improved, it can withstand horizontal vibration caused by an earthquake.

In the second embodiment described above, the reinforcing piles 61 are arranged in a single layer. However, the reinforcing piles 61 can be made thicker by double or triple.
What is shown in FIG. 10 is a modification of the second embodiment, in which the upper outer surface of the outer underground wall 6 made of a cement-based ground improvement body is intermittent, that is, spaced horizontally. A reinforcement pile 61 made of a ground improvement body of the system is partially reinforced.

DESCRIPTION OF SYMBOLS 1 Liquefaction countermeasure structure 2 Structure 3 Ground which may be liquefied 31 Ground directly under structure 4 Non-liquefaction ground 5 Foundation 6 Outer underground wall 61 Reinforcement pile 7 Inner underground wall

Claims (3)

A structure supported by a foundation of a type in which a vertical load of the structure acts on the upper surface of the ground, and slightly extended outward from the outer periphery of the structure to extend directly to the non-liquefied ground surrounding the foundation ground A ground liquefaction countermeasure structure comprising an outer underground wall and an inner underground wall connected in the vicinity of the lower edge of the structure,
The inner underground wall and the outer underground wall have a vertical edge cut,
The horizontal structure inertia force due to the earthquake is transmitted to the outer underground wall through the inner underground wall, reducing the external force due to the structure inertia force acting on the structure directly under the ground, and reducing the shear of the ground. While reducing the stress, rocking vibration of the structure due to the earthquake is suppressed by the friction between the inner underground wall and the ground,
The entire vertical load of the structure is applied to the foundation ground board, increasing the effective stress of the ground.
Ground liquefaction countermeasure structure characterized by that.   The ground liquefaction countermeasure according to claim 1, wherein at least a part of an outer surface upper portion of the outer ground wall made of a cement-based ground improvement body is reinforced by a cement-based ground improvement body. Construction.   The liquefaction countermeasure structure according to any one of claims 1 to 2, wherein the inner underground wall is provided so as to surround the ground continuously or intermittently in plan view. .