JP5975892B2 - Ground liquefaction countermeasure structure by structure load and seismic isolation device - Google Patents

Description

  The present invention relates to a liquefaction countermeasure structure for preventing liquefaction of the ground by a load of a structure constructed on the ground and a seismic isolation device.

  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. In addition, a liquefaction countermeasure technique for blocking liquefaction by blocking the flow of groundwater from the surrounding ground 104 is known.

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 directly under the structure.

  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 plan view, which does not require the formation of the underground wall directly under the structure, First countermeasure against liquefaction of the foundation ground of the structure formed on the liquefied layer 113 which 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 which may be liquefied. A structure 110 has been proposed (see Patent Document 1).

  However, this liquefaction countermeasure structure 110 has the underground wall 112 made of the ground improvement body only around the structure 111. Therefore, when the plane of the structure 111 is large, the wall interval between the underground walls 112 is small. Liquefaction that cannot be prevented from becoming liquefied itself due to its large size, and that the horizontal force due to the inertia of the structure at the time of an earthquake may liquefy from the structure 111 as schematically shown in FIG. Although it is assumed that it is transmitted to the ground of the layer 113 and becomes rather negative with respect to liquefaction suppression, no effective countermeasure has been taken.

  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. An anti-countermeasure structure 120 has been proposed (see Patent Document 2).

  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.

  However, since the second liquefaction countermeasure technique transmits the horizontal force due to the inertial force of the structure to the underground wall 122 via the joint member 124, the second liquefaction countermeasure technique is surely as shown schematically in FIG. There is a possibility that the horizontal force due to the structure inertia force cannot be transmitted to the underground wall, and since this technique originally does not take measures to reduce the structure inertia force itself, a heavy burden is imposed on the underground wall 122. Further, 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.

JP 2005-105602 A JP 2010-216107 A

  The present invention combines the underground wall arranged on the outer periphery of the structure and the seismic isolation device to reduce the structure inertia force in the horizontal direction to the ground between the underground walls without reducing it as much as possible. While transmitting to the inner wall, the structure weight in the vertical direction is transmitted to the ground between the underground walls so that a sufficient liquefaction prevention effect can be obtained even if the distance between the underground walls is large. It aims to provide a liquefaction countermeasure structure.

  The invention according to claim 1 is a liquid in a ground comprising a structure supported by a foundation of a type in which a structure load acts on the upper surface of the ground, and an underground structure constructed by an underground wall surrounding the structure's immediate foundation board. In the anti-seismic structure, the base has a seismic isolation device interposed between the structure and the outer surface of the retaining wall erected on the peripheral edge of the foundation to allow the structure to move downward. The horizontal wall inertia force caused by an earthquake is reduced by the seismic isolation device, and the reduced structure inertia force is formed at the peripheral edge of the foundation. The external force due to the structure inertia force transmitted to the underground wall through the structure and acting directly on the structure base plate is reduced, and the shear stress of the ground is reduced, while the entire structure load in the vertical direction is reduced to the structure. A structure that increases the effective stress of the ground by acting on a straight foundation. And the.

  The invention according to claim 2 is a liquid in a ground comprising a structure supported on a foundation of a type in which a structure load acts on the upper surface of the ground, and an underground structure constructed by an underground wall surrounding the structure's immediate foundation board. In the anti-seismic structure, a seismic isolation device is interposed between the foundation and the structure, and an outer surface of the outer wall of the underground building constructed between the foundation and the seismic isolation device extends downward from the structure. In contact with the inner surface of the underground wall in a state where movement is allowed, the structure inertia force in the horizontal direction due to the earthquake is reduced by the seismic isolation device, and the reduced structure inertia force is reduced through the outer wall of the underground structure. The external force due to the structure inertia force transmitted to the underground wall and acting on the structure directly underlaying ground is reduced, and the shear stress of the ground is reduced, while the entire structure load in the vertical direction is applied to the structure underlaying ground. To increase the effective stress of the ground That is, instead of the retaining wall formed in the foundation peripheral part of the ground liquefaction countermeasure structure according to claim 1, the structure is provided through the outer surface of the outer wall of the underground building constructed between the foundation and the seismic isolation device. It is characterized by transmitting a physical inertia force to the underground wall.

The invention according to claim 3, basic format acts structure load on the ground is directly foundation, and characterized in that either Pas Ile-raft foundation.
The invention according to claim 4 is characterized in that at least a part of the outer surface upper portion of the underground wall made of a cement-based ground improvement body is reinforced by a cement-based ground improvement body.

  According to the invention which concerns on Claim 1, the underground wall which surrounds a structure foundation | substrate ground board suppresses the shear deformation of the ground between underground walls, and a liquefaction suppression effect is acquired. And since the underground wall retaining wall and the underground wall are not connected with steel materials etc. and allow slipping between both, it is possible to apply a structural load to the ground between the underground walls, The effect of suppressing liquefaction by increasing the effective stress of the ground can also be obtained.

Furthermore, because the outer surface of the retaining wall is in contact with the inner surface of the underground wall, the structure inertia force is transmitted to the underground wall through the retaining wall, and the external force due to the structure inertia force acting on the ground between the underground walls is reduced. And the liquefaction suppression effect is acquired because the shear stress of a ground reduces.
In addition, since the structure is seismically isolated, the inertial force of the structure itself is reduced, and the external force acting on the ground is reduced, thereby further enhancing the liquefaction suppression effect.
In addition, since the horizontal force transmitted to the underground wall through the retaining wall is reduced by the seismic isolation of the structure, the present invention can reduce the stress generated in the underground wall and damage the underground wall. It can be prevented.

  According to the invention which concerns on Claim 2, it replaces with the retaining wall formed in the base peripheral part, and a structure inertia force is applied to an underground wall via the outer surface of an underground outer wall constructed between a foundation and a base isolation device. Since it is transmitted, when the seismic isolation layer is on the ground, the effect of reducing the shear stress of the ground can be obtained without providing a separate retaining wall in the basement.

According to the invention of claim 3, foundation, direct foundation, structure load to one of the ground of Pas Ile-raft foundation is the form to act, retaining wall and underground walls are connected by steel or the like However, the outer wall of the retaining wall standing upright at the peripheral edge allows sliding with the inner wall of the underground wall. The stress can be increased.
According to the invention according to claim 4, at least a part of the outer surface of the underground wall made of cement ground improvement body is reinforced by the cement 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.

It is a longitudinal cross-sectional view of the ground liquefaction countermeasure structure of Embodiment 1 of the present invention. It is a figure which shows the mechanism of the structure inertia force by the base isolation of this invention, and the shear stress reduction of a ground. It is a figure which shows the mechanism of the shear stress reduction by the effective stress increase by the structure load of this invention, and the structure inertia force transmission to a underground wall. 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 longitudinal cross-sectional view of the ground liquefaction countermeasure structure of Embodiment 2 of the present invention. It is a longitudinal cross-sectional view of the ground liquefaction countermeasure structure of Embodiment 3 of this invention. It is a longitudinal cross-sectional view of the ground liquefaction countermeasure structure of Embodiment 4 of this invention. It is a top view of the ground liquefaction countermeasure structure of Embodiment 4. It is a top view of the ground liquefaction countermeasure structure of the modification of Embodiment 4. FIG. It is a longitudinal cross-sectional view of the conventional ground liquefaction countermeasure structure. It is a longitudinal cross-sectional view which shows typically the 1st liquefaction countermeasure structure described in patent document 1. FIG. It is a figure which shows typically the mechanism in which a structure inertia force is transmitted to a structure direct foundation | substrate board. It is a longitudinal cross-sectional view which shows typically the 2nd liquefaction countermeasure structure described in patent document 2. FIG. It is a figure which shows typically the fall of the inertial force transmission degree of the liquefaction countermeasure structure through a joint member.

Four embodiments of the liquefaction countermeasure structure of the present invention will be described.
Embodiment 1.3.4 is a structure of a ground comprising a structure supported on a foundation of a type in which a structure load acts on the ground, and an underground structure constructed by an underground wall surrounding the structure's immediate foundation board. In the liquefaction countermeasure structure, a base is installed with a seismic isolation device between the structure and the outer wall of the retaining wall standing on the periphery of the foundation is allowed to slide with the inner surface of the underground wall. While they are in contact with each other and allow the structure to move downward, the foundations and underground structures have different forms.
Moreover, Embodiment 2 replaces the retaining wall outer surface erected on the foundation peripheral edge of Embodiment 1 with the outer surface of the underground outer wall constructed between the foundation and the seismic isolation device.

First, Embodiment 1 will be described in detail with reference to FIGS.
As a premise, the ground 5 on which the structure 2 is loaded is composed of a non-liquefied ground 4 and a ground 3 that may be liquefied stacked on the ground 5 from below the ground.
And this structure 2 is directly supported by the ground 3 which may be liquefied, and when it receives a horizontal load due to an earthquake under the condition that the underground structure 6 and the structure 2 do not exist, Liquefaction phenomenon occurs.

  The liquefaction countermeasure structure 1 of this embodiment is a ground wall surrounding the structure 2 supported by the foundation 7 and the structure direct foundation board 3 in which the structure load acts on the ground 3 that may be liquefied. And a built underground structure 6.

The underground wall of the underground structure 6 is normally a continuous wall that is hardly permeable, and the lower end of the underground wall 6 is rooted in the non-liquefied layer 4 below the ground 3 that may be liquefied. It is put.
The underground wall 6 is made of cement-based ground improvement body, reinforced concrete connection wall, steel sheet pile, SMW, etc., which is a composite structure of a wall body and steel material formed by mixing and stirring soil and cement slurry in situ. Can do.

The foundation 7 is in contact with the inner surface of the underground wall 6 while the outer surface of the retaining wall 71 erected on the peripheral edge thereof is allowed to move downward.
With this configuration, the foundation 7 does not restrict the downward movement of the structure 2 but allows the downward movement of the structure 2 to allow the entire vertical load of the structure to act on the structure direct ground board 3 described above. , Reliably increase the effective stress of the ground.

  On the other hand, most of the horizontal force due to the inertial force of the structure generated during an earthquake is transmitted to the ground 3 where there is a risk of liquefaction. As a result, the shear stress of the ground 3 surrounded by the underground wall 6 increases, and there is a possibility that the effect of suppressing liquefaction cannot be obtained sufficiently.

Therefore, in this embodiment, since the outer surface of the retaining wall 71 is in contact with the inner surface of the underground wall 6 while allowing the structure 2 to move downward, as shown schematically in FIG. The physical inertia force is transmitted to the underground wall 6 through the foundation retaining wall 71, and the horizontal external force due to the structural inertia force acting on the ground 3 itself between the underground walls 6 is reduced.
Thereby, the liquefaction suppression effect is acquired because the shear stress of the ground 3 reduces.

  In addition, since the structure 2 is seismically isolated by the seismic isolation device 8, the inertia force of the structure 2 itself is greatly reduced as shown schematically in FIG. Since the horizontal external force is merely transmitted to the ground 3, the liquefaction suppression effect can be further enhanced.

Moreover, in this embodiment, the seismic isolation device 8 is interposed between the foundation 7 and the structure 2, and the structure 2 is seismically isolated, so that the structure 2 is underground through the retaining wall 71 of the foundation. Since the horizontal force transmitted to the wall 6 is greatly reduced, the stress generated in the underground wall can be reduced, and the underground wall 6 can be prevented from being damaged.
The seismic isolation method may be a single type of laminated rubber, sliding bearing, or rolling bearing, but may be a hybrid type combining these, and the type is not particularly limited.

  In addition, a solid foundation (direct foundation) is adopted in the present embodiment as the basic form of the structure on which the structure load acts on the ground.

  Further, as a method of allowing the outer surface of the retaining wall 71 to contact the inner surface of the underground wall 6 while allowing the structure 2 to move downward, a veneer plate is provided between the outer surface of the retaining wall 71 and the inner surface of the underground wall 6. There is a method of constructing the retaining wall 71 by placing concrete in a state where a sheet-like object such as plywood or vinyl sheet is interposed. Further, when there is an existing retaining wall 71, a ground improvement body or a steel sheet pile is formed close to the retaining wall 71 to the extent that force can be transmitted from the outer surface of the retaining wall 71 to the inner surface of the underground wall 6. There is a method of constructing the underground wall 6 by press-fitting.

In order to verify the above-described effects of the present invention, an effective stress analysis was performed that can simulate the rise and dissipation of excess pore water pressure during an earthquake.
As a result, the liquefaction suppression effect by the underground wall surrounding the structure and the seismic isolation structure load was verified.
In this analysis model, the underground wall 6 is constructed to a depth of 10 m from the ground surface, and has a wall thickness of 0.8 m and a wall interval of 15 m.

Analysis case, when measures liquefied only underground walls without structural load, when allowed to act structure load 60 kN / m ^2, the structure in addition to the action of the structure load 60 kN / m ² There are 3 cases of seismic isolation.

FIG. 4 shows the contour of the excess pore water pressure ratio, and FIG. 5 shows the time history of the excess pore water pressure ratio at a depth of 2.5 m directly under the structure.
In FIG. 4, it can be seen that the amount of increase in the excess pore water pressure ratio is smaller when the structural load is applied (B) than when the structural load is not applied (A).
This is presumably because the effective stress of the ground increased and the liquefaction strength of the ground increased due to the structure load acting on the ground surrounded by the underground wall.

Furthermore, when the structure is seismically isolated in addition to acting on the structure load (C), the increase in excess pore water pressure ratio is significantly smaller, and the effect of suppressing liquefaction is increasing. Can be confirmed.
In the form of a structure that is not seismically isolated, the inertial force of the structure generated by the earthquake motion acts directly as an external force on the ground surrounded by the underground wall, which promotes liquefaction. In the seismic isolation embodiment, the acceleration at the top of the structure is reduced by the seismic isolation and the inertial force of the structure is reduced, so the external force transmitted to the ground surrounded by the underground wall is reduced and liquefaction is suppressed. It is thought that the 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 structural load 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 a structural load is applied (B), the liquefaction phenomenon begins to dissipate after approximately 40 seconds, although the liquefaction phenomenon begins to dissipate after approximately 40 seconds, and the liquefaction phenomenon dissipates substantially completely after approximately 120 seconds.

On the other hand, when the structure is seismically isolated in addition to applying the structure load (C), liquefaction does not occur, and the excess pore water pressure ratio of the ground shows earthquake motion after approximately 120 seconds. It can be confirmed that the state before receiving is restored.
This also confirms that the external force transmitted to the ground surrounded by the underground wall is reduced and the liquefaction suppression effect is enhanced.

Embodiment 2 will be described.
With respect to this embodiment, the liquefaction countermeasure structure 1 is such that the seismic isolation device 8 is interposed between the underground frame 72 and the structure 2, and the outer surface of the outer wall slips from the inner surface of the underground wall 6. Is allowed to move downward in the structure 2.

  In this embodiment, when the seismic isolation layer is on the ground, the structure inertia force can be transmitted to the underground wall in the underground frame without providing a separate retaining wall in the basement, and the external force transmitted to the ground Is reduced, and a liquefaction suppressing effect can be obtained.

Next, Embodiment 3 will be described.
As described above, also in this embodiment, the liquefaction countermeasure structure 1 includes the base 7 and the structure 2 with the seismic isolation device 8 interposed therebetween, and is erected on the periphery thereof. Further, the outer surface of the retaining wall 71 is in contact with the inner surface of the underground wall 6 in a state that allows sliding, and allows the structure 2 to move downward.
And the foundation form that a structure load acts on this ground is regarded as a piled raft foundation.

In this embodiment, as a load transmission means for transmitting the vertical load of the structure 2 to the ground 3 that may be liquefied, a friction pile 9 is provided on the lower surface in addition to the foundation 7.
As a result, the vertical load of the structure 2 is transmitted from the foundation 7 itself to the ground base 3 of the structure and also from the friction pile 9 to the ground 3.
For this reason, the effective stress of the ground can be increased to a deeper layer.

Furthermore, Embodiment 4 has a structure in which the upper portion of the underground wall 6 of Embodiment 1 or Embodiment 2 described above is provided with a reinforcing body 10 made of, for example, a columnar ground improvement body.
Since the upper part of the underground wall 6 receives a structure inertia force in the horizontal direction from the retaining wall 71 of the foundation during an earthquake, there is a high possibility of damage.

For this reason, in this embodiment, the reinforcing body 10 deeper than the depth of the retaining wall 71 is constructed.
Thereby, since the earthquake resistance of the underground wall 6 increases, it can endure the horizontal vibration by an earthquake.

DESCRIPTION OF SYMBOLS 1 Liquefaction countermeasure structure 2 Structure 3 Ground which may be liquefied 4 Non-liquefaction ground 5 Ground 6 Underground wall 7 Foundation 71 Retaining wall 72 Underground structure 8 Seismic isolation device 9 Friction pile 10 Reinforcement body

Claims (4)

In the ground liquefaction countermeasure structure comprising a structure supported by a foundation in which a structure load acts on the ground upper surface and an underground structure constructed by an underground wall surrounding the structure directly underlaying ground,
The base wall is provided with a seismic isolation device between the structure and the outer wall of the retaining wall erected on the periphery thereof to allow the structure to move downward. In contact with the inside,
The structure inertia force in the horizontal direction due to the earthquake is reduced by the seismic isolation device, and the reduced structure inertia force is transmitted to the underground wall through the retaining wall formed at the periphery of the foundation. While reducing the external force due to the inertial force of the structure acting on the foundation floor, reducing the shear stress of the ground,
Causing the entire load of the structure in the vertical direction to act on the structure's direct groundwork, increasing the effective stress of the ground,
Ground liquefaction countermeasure structure characterized by that. In the ground liquefaction countermeasure structure comprising a structure supported by a foundation in which a structure load acts on the ground upper surface and an underground structure constructed by an underground wall surrounding the structure directly underlaying ground,
The foundation has a seismic isolation device interposed between the structure and the outer surface of the outer wall of the underground building constructed between the foundation and the seismic isolation device allows the structure to move downward. In contact with the inner surface of the underground wall,
The structure inertia force in the horizontal direction due to the earthquake is reduced by the seismic isolation device, and the reduced structure inertia force is transmitted to the underground wall through the outer wall of the underground skeleton and acts on the foundation base plate of the structure. While reducing the external force due to the inertia of the structure and reducing the shear stress of the ground,
Causing the entire load of the structure in the vertical direction to act on the structure's direct groundwork, increasing the effective stress of the ground,
Ground liquefaction countermeasure structure characterized by that. Basic format acts structure load on the ground upper surface is directly foundation, Pa Ile--raft foundation of ground according to any of claims 1 to 2, characterized in that either Liquefaction countermeasure structure.   The at least part of the outer surface upper part of the underground wall which consists of a cement-type ground improvement body is reinforced by the cement-type ground improvement body, It is described in any one of Claim 1 thru | or 3 characterized by the above-mentioned. Structure to prevent liquefaction of ground.