JP2014001619A - Structure and method for reducing liquefaction damage of structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple construction method which can reduce construction cost and which enables construction in a narrow construction space.SOLUTION: In a structure 1 for reducing liquefaction damage, a gravel layer part 3 having draining function with a coefficient of permeability higher than that of a liquefaction ground G is formed by laying gravel on the outer peripheral side in a foundation of structure 21 of a structure 2, and the gravel layer part 3 is connected with widening part 22 integrally formed with the periphery 21a of the foundation of structure 21. Thus the structure 1 can reduce liquefaction damage without the need for work in the liquefaction ground G immediately therebelow.

Description

  The present invention relates to a liquefaction damage reducing structure and a liquefaction damage reducing method for a structure constructed on a liquefied ground.

  Conventionally, in a ground where a loose sand layer is deposited, liquefaction is likely to occur during an earthquake, and the structure constructed there may cause large settlement or inclination. In order to prevent such liquefaction, sand piles are formed and the ground is compacted to increase the density, or the ground is improved in a grid by improving the cement system, thereby reducing the deformation caused by the earthquake. Construction has been carried out (for example, see Patent Document 1). As another construction method, there is also known a method of preventing settlement or inclination due to liquefaction by supporting a structure with a support pile driven up to a support layer that is not liquefied.

By the way, in the case of existing structures, it is difficult to improve directly under the foundation, and a method that can be handled by oblique boring, such as a chemical injection method, is adopted, or a hole is made in the foundation and then a rod is inserted into the ground, Construction such as solidifying the ground by the jet agitation method is being carried out.
On the other hand, in the case of small-scale existing structures, there is a construction method in which an improved wall is provided around the foundation and the surface layer is replaced with gravel. Things have been done.

JP 2011-127417 A

However, the conventional structure for reducing the damage of liquefaction described above has the following problems.
That is, in the case of improving directly under the existing structure foundation, the construction cost becomes high, and it is necessary to open a large number of holes in the existing structure foundation in the high-pressure jet stirring method.
Moreover, in the case of a construction method in which an improved wall is provided around the foundation, there is a problem that it is limited to a case where a sufficient working space can be secured on the outer circumference of the foundation using a construction machine.
In addition, there are many existing pipes in the ground, and it is necessary to carry out construction methods that do not affect the pipes such as the high-pressure jet agitation method, and the construction costs increase, so there is room for improvement in that respect. there were.

  The present invention has been made in view of the above-mentioned problems, and it is possible to reduce the construction cost by adopting a simple construction method and to liquefy the structure that enables construction in a narrow construction space. An object is to provide a damage reduction structure and a liquefaction damage reduction method.

  In order to achieve the above object, the structure for reducing liquefaction damage of a structure according to the present invention targets a structure constructed on a liquefied ground, and reduces damage to the structure when the liquefied ground is liquefied. A gravel layer having a drainage function that is formed by laying gravel on the outer peripheral side of the structure foundation of the structure and having a hydraulic conductivity larger than that of the liquefied ground, and the structure in the gravel layer It is characterized in that the outer periphery of the foundation is connected.

  Further, in the structure liquefaction damage reducing method according to the present invention, liquefaction damage for reducing the damage to the structure when the liquefied ground is liquefied is intended for the structure constructed on the liquefied ground. A method of reducing a gravel layer part having a drainage function having a larger hydraulic conductivity than liquefied ground by excavating the outer peripheral side of the structure foundation of the structure and laying gravel, And a step of connecting the outer peripheral portion of the structure foundation.

In the present invention, a gravel layer portion is provided on the outer peripheral side of the structure foundation, and the outer periphery of the structure foundation is connected to the gravel layer portion. In the surroundings, when liquefaction occurs in the liquefied ground, which is the original ground immediately below the gravel layer, it is possible to effectively prevent the flow of sand and the occurrence of sandblast.
That is, the gravel layer portion functions as a drainage layer, and excess pore water generated in the liquefied ground due to the earthquake is collected by the gravel layer portion, and further, the water is drained to the ground through the gravel layer portion. And in the liquefied ground, the excessive pore water pressure which arises with liquefaction can be suppressed, and the flow of sand and sand sand can be suppressed. As a result, it is possible to suppress liquefaction damage by effectively suppressing the occurrence of inclination or subsidence in the structure and the occurrence of large unevenness with the surrounding ground. In this way, in the liquefied layer at the time of the earthquake, after the excess pore water pressure ratio reaches 1, the state where the rigidity is restored by shear deformation (this is called “post-liquefaction state”) is maintained and a stable deformation behavior is achieved. It becomes possible to control. Therefore, by stabilizing the liquefaction around the structure foundation at an early stage, even if liquefaction occurs in the ground directly under the structure, it is possible to reduce the slope generated in the structure above it. It is.

  Further, in the present invention, the work on the ground directly under the structure can be reduced, and the gravel layer is constructed only in the vicinity of the surface layer, and the gravel layer needs to be formed so as to reach the deep part of the liquefied ground. Rather, the excavation of the region where the gravel layer portion is provided and the operation of filling the excavation site with gravel material and laying it. Therefore, construction can be performed by a small machine or manpower, and it is not necessary to install a large construction machine as in the conventional ground improvement method, and it is possible to cope even in a narrow area. Therefore, it is suitable for application to a small-scale structure such as a detached house, and is particularly suitable as a liquefaction countermeasure for an existing structure that is difficult to work directly below.

Furthermore, since the present invention is a construction method by laying gravel material, even if there is an existing pipe in the ground, a costly construction method such as a conventional high-pressure jet stirring method is adopted. In addition, there is an advantage that the construction can be performed without affecting the existing piping.
Furthermore, the present invention is not a method for preventing liquefaction, and the structure sinks with the surrounding ground, so that the level difference between the surrounding ground and the ground is reduced. Therefore, even if there is an existing pipe in the ground, the influence on the existing pipe in the ground can be suppressed smaller than in the case where liquefaction is completely prevented.

  In the structure liquefaction damage reducing structure according to the present invention, the outer peripheral portion of the structure foundation may be a widened portion provided integrally with the outer peripheral portion of the structure foundation.

  In the structure liquefaction damage reducing method according to the present invention, a widened portion may be integrally provided on the outer periphery of the structure foundation, and the widened portion may be connected to the gravel layer portion.

  In this case, the widened portion can be provided by post-construction with respect to the existing structure foundation, and the widened portion is connected to the gravel layer portion. Therefore, since difficult construction such as providing a gravel layer portion directly under an existing structure foundation is not required, an increase in construction costs can be suppressed.

  Further, in the structure liquefaction damage reducing structure according to the present invention, the widened portion may be formed with a protruding portion in which the widened distance in the direction away from the structure foundation in the horizontal direction is partially increased. .

  In this case, since the projecting portion and the gravel layer portion can be formed in a fitted state, the direction side orthogonal to the direction in which the projecting portion expands (the direction away from the structure foundation) in plan view. The effect which suppresses the inclination of the structure to a can be heightened. Therefore, for example, when another structure is provided in the vicinity of an existing structure and it is difficult to provide a gravel layer on the other structure side, it protrudes into the widened part on the side other than the structure side. By forming the portion, the inclination of the structure toward the other structure side can be suppressed.

  Moreover, in the structure liquefaction damage reducing structure according to the present invention, the widened portion may be partially arranged along the structure foundation in a plan view.

  In this case, since the construction area of the widened portion can be reduced, the construction cost can be reduced.

  In the structure liquefaction damage reducing structure according to the present invention, the outer peripheral portion of the structure foundation protrudes outward from the outer periphery of the structure foundation and is integrally fixed to the structure foundation. It can also be a part.

  Further, in the structure liquefaction damage reducing method according to the present invention, an overhanging portion protruding outward from the outer peripheral portion of the structure foundation may be provided, and the overhanging portion may be connected to the gravel layer portion.

  In this case, the overhanging portion can be provided by post-construction with respect to the existing structure foundation, and the overhanging portion is connected to the gravel layer portion. Therefore, since difficult construction such as providing a gravel layer portion directly under an existing structure foundation is not required, an increase in construction costs can be suppressed. And compared with the case where a structure foundation is expanded, it becomes the structure which should just provide an overhang | projection part only in the part along a ground surface, and the effort and time concerning construction can be reduced.

  Moreover, in the structure liquefaction damage reducing structure according to the present invention, the overhanging portion may be partially arranged along the structure foundation in a plan view.

  In this case, since the construction area of the overhang portion can be reduced, the construction cost can be reduced.

  Further, in the structure for reducing liquefaction damage of a structure according to the present invention, a vertical drain having water permeability that extends downward in the vertical direction from the gravel layer portion is provided while communicating with the gravel layer portion. it can.

In this case, excess pore water generated in the liquefied ground due to the earthquake is collected by the vertical drain, and the water is pumped from the vertical drain to the gravel layer and drained to the ground through the gravel layer. Therefore, for example, even when excavation at a deeper position than the depth of the bottom surface position of the structure foundation is difficult, the drainage function similar to that of the gravel layer portion can be provided to the vertical drain to a predetermined depth.
In addition, when a vertical drain is placed, it is possible to perform construction while avoiding the existing piping, and it is possible to prevent the existing piping from being affected.

  According to the structure for reducing liquefaction damage and the method for reducing liquefaction damage of the present invention, the construction cost can be reduced by connecting the structure foundation to the gravel layer provided on the surface layer. In addition to being able to achieve reduction, the effect is that construction in a narrow construction space is possible.

It is a longitudinal cross-sectional view which shows the liquefaction damage reduction structure by the 1st Embodiment of this invention. It is a top view of the liquefaction damage reduction structure shown in FIG. It is a figure for demonstrating the principle of this Embodiment. It is a top view which shows the liquefaction damage reduction structure by 2nd Embodiment. It is a top view which shows the liquefaction damage reduction structure by the modification of 2nd Embodiment. It is a top view which shows the liquefaction damage reduction structure by 3rd Embodiment. It is a top view which shows the liquefaction damage reduction structure by 4th Embodiment. It is a longitudinal cross-sectional view which shows the liquefaction damage reduction structure by 5th Embodiment. It is a top view of the liquefaction damage reduction structure shown in FIG. It is a longitudinal cross-sectional view which shows the liquefaction damage reduction structure by 6th Embodiment. It is a longitudinal cross-sectional view which shows the liquefaction damage reduction structure by 7th Embodiment. It is a figure which shows the experimental model by 1st Example, Comprising: (a) is a top view, (b) is a longitudinal cross-sectional view. It is an experimental result of 1st Example, Comprising: It is a figure which shows the relationship between an elapsed time after an earthquake, and a foundation inclination structure. It is an experimental result of 2nd Example, Comprising: It is a figure which shows the relationship between an elapsed time after an earthquake, and a foundation inclination structure. It is an experimental result of 3rd Example, Comprising: It is a figure which shows the relationship between an elapsed time after an earthquake, and a foundation inclination structure.

  Hereinafter, a structure liquefaction damage reducing structure and a liquefaction damage reducing method according to embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
As shown in FIGS. 1 and 2, the structure liquefaction damage reducing structure 1 according to the first embodiment is an existing structure 2 constructed on a site where the original ground is the liquefied ground G (for example, This is an example applied to a case where a liquefaction damage is reduced without requiring work on the underlying ground directly under the target of a detached house. The structure 2 is provided with a structure base 21 in plan view that is slightly larger than the structure 2 in the liquefied ground G, and the structure 2 and the structure base 21 are each rectangular in plan view.

  Specifically, the liquefaction damage reducing structure 1 is provided with a gravel layer portion 3 having a drainage function that is formed by laying gravel all around the outer periphery of the structure foundation 21 and having a hydraulic conductivity larger than that of the liquefied ground G. The gravel layer 3 is connected and configured so that an outer peripheral portion (a widened portion 22 described later) of the structure foundation 21 is placed thereon. A widened portion 22 that extends outward from the structure foundation 2 is integrally provided on the outer peripheral portion 21 a of the structure foundation 21.

  The gravel layer 3 is formed by, for example, burying natural gravel material (gravel) in a place excavated around the structure 2 at a predetermined depth. At this time, it is formed in a state in which a region where the widened portion 22 is provided is opened without covering the ground surface. The depth of the gravel layer 3 is, for example, about 30 cm to 1 m from below the foundation. Note that crushed stones and various artificial water permeable materials can be used as the gravel material as long as equivalent water permeability can be obtained. Moreover, you may make it the gravel layer part 3 spread the sandbag filled with gravel.

  This gravel layer portion 3 is provided in the surface layer portion, and when liquefaction occurs in the liquefied ground G below the structure 2, excess pore water is efficiently drained to the ground surface, and sand is blown to the ground surface. It is for preventing. Therefore, the water permeability coefficient of the gravel layer portion 3 needs to be larger than that of the liquefied ground G that is the original ground, and for example, it is preferably larger than the liquefied ground G by about two digits (100 times) or more.

  In addition, it is preferable to form the gravel layer part 3 in a non-consolidated state so as to have flexibility that can be deformed without breaking during an earthquake. That is, when the gravel layer portion 3 is formed in a solid state and in a rigid state, the gravel layer portion 3 is broken during an earthquake and a gap is formed there, or the entire gravel layer portion 3 is formed in the structure 2. On the other hand, there is a room for generating a relative displacement and a gap between them, and in that case, sand is generated from the gap. On the other hand, by forming the gravel layer part 3 in a non-consolidated state and having flexibility that can absorb deformation during an earthquake, the gravel layer part 3 is broken or a gap is generated. It can prevent, and it can prevent effectively that a sandblast arises from the clearance gap.

Moreover, in order to prevent clogging, the gravel layer portion 3 may be laid with gravel having a small gravel diameter in a range from the bottom to about 5 cm, for example. The gravel diameter can be set to an appropriate dimension based on the design of a deep well filter material or the like.
Further, by interposing a geotextile serving as a filter between the gravel layer portion 3 and the original ground (liquefied ground G), clogging of the gravel layer portion 3 may be prevented and water permeability may be maintained. .

As shown in FIG. 1, the widened portion 22 obtained by enlarging the structure foundation 21 is formed of reinforced concrete, and a connecting material 23 such as an anchor bolt is attached to the side surface (outer peripheral portion 21 a) of the existing structure foundation 21. Are provided integrally. This widened part 22 is arrange | positioned so that it may be located inside the width direction X of the gravel layer part 3 to be laid. And the wide part 22 is arrange | positioned so that it may cover the part by the side of the ground surface of the gravel layer part 3, and the side surface 22a and the bottom face 22b of the wide part 22 are in the state which contacted the gravel layer part 3 without gap. That is, the upper gravel layer portion 3A located on the side surface 22a side of the widened portion 22 communicates with the lower gravel layer portion 3B below in the vertical direction.
In addition, the widening part 22 may be constructed on the outer peripheral part 21a of the structure foundation 21 after the construction of the gravel layer part 3, or the gravel layer part 3 is constructed after being provided integrally with the structure foundation 21 first. It may be a process.

Next, the operation of the liquefaction damage reducing structure 1 having the above-described configuration will be described in detail with reference to the drawings.
As shown in FIGS. 1 and 2, the liquefaction damage reducing structure 1 is provided with a gravel layer portion 3 on the outer peripheral side of a structure foundation 21 and connecting the widened portion 22 of the structure foundation 21 to the gravel layer portion 3. By simple construction with only the surface layer portion, at least around the structure foundation 21, when liquefaction occurs in the liquefied ground G, which is the original ground immediately below the gravel layer portion 3, sand flow and sand discharge occur. This can be effectively prevented.
That is, the gravel layer 3 has a drainage layer function, and the excess pore water generated in the liquefied ground G due to the earthquake is collected by the gravel layer 3, and further, the water passes through the gravel layer 3. To be drained. And in the liquefied ground G, the excess pore water pressure which arises with liquefaction can be suppressed, and the flow of sand and sand sand can be suppressed. Thereby, it is possible to suppress the occurrence of inclination or subsidence in the structure 2 and the occurrence of large unevenness between the surrounding ground and the liquefaction damage can be effectively reduced.

  Thus, in the liquefied ground G at the time of the earthquake, after the excess pore water pressure ratio reaches 1, the state where the rigidity is restored by shear deformation (this is referred to as “post-liquefaction state”) and stable deformation behavior is maintained. It becomes possible to control to do. Therefore, by stabilizing the liquefaction around the structure foundation 21 at an early stage and stabilizing the ground, even if liquefaction occurs in the ground immediately below the structure 2, the inclination generated in the structure 2 thereabove is reduced. Is possible.

Here, in the design method for normal liquefaction, the state where the excess pore water pressure ratio of the ground has reached 1 is not considered as the state after this as a completely liquefied state (a state in which it has become liquid). Focusing on exhibiting the post-liquefaction state, the design philosophy is to maintain and secure the supporting force for the structure 2 by stably continuing the post-liquefaction state.
That is, as shown in FIG. 3, if a shear force continues to act on the ground that has reached the post-liquefaction state without draining, the reversible due to the directivity is applied to the irreversible plastic volume strain (compression side). Plastic volume strain (expansion side) cannot catch up, and the ground becomes completely liquid. This state is the state that reached the destruction of the ground where the undesired subsidence of the sand and structures.
On the other hand, if the above shear force is applied while draining properly, the irreversible plastic volume strain compression side) and the reversible plastic volume strain (expansion side) are always balanced, and the post-liquefaction state continues stably. The present embodiment reduces the liquefaction damage such as subsidence and inclination of the structure based on the technical idea of ensuring the supporting force of the structure by maintaining such a stable post-liquefaction state. .
In addition, about the effectiveness of this Embodiment, this applicant can confirm based on the analysis experiment previously described by Japanese Patent Application No. 2012-18495.

  Further, as shown in FIGS. 1 and 2, in the liquefaction damage reducing structure 1 of the present embodiment, the work on the ground directly under the structure 2 can be reduced, and the gravel layer portion 3 is only near the surface layer. It is not necessary to form the gravel layer part 3 so as to reach the deep part of the liquefied ground G, and the excavation of the area where the gravel layer part 3 is provided and the work of laying the excavation part with the gravel material filled It becomes. Therefore, construction can be performed by a small machine or manpower, and it is not necessary to install a large construction machine as in the conventional ground improvement method, and it is possible to cope even in a narrow area. Therefore, it is suitable for application to a small-scale structure such as a detached house, and is particularly suitable as a liquefaction countermeasure for an existing structure that is difficult to work directly below.

Furthermore, since it becomes a construction method by laying gravel material, even if there are existing pipes in the ground, without adopting costly construction methods such as the conventional high-pressure jet stirring method, It has the advantage that it can be constructed without affecting the existing piping.
Furthermore, the liquefaction damage reducing structure 1 of the present embodiment is not a method for preventing liquefaction, and the structure 2 sinks together with the surrounding ground, so that the level difference between the surrounding ground and the ground becomes small. Therefore, even if there is an existing pipe in the ground, the influence on the existing pipe in the ground can be suppressed smaller than in the case where liquefaction is completely prevented.

  Moreover, the widening part 22 can be provided by post-construction with respect to the existing structure foundation 21, and it becomes the structure which connects the widening part 22 to the gravel layer part 3. FIG. This eliminates the need for difficult construction such as providing the gravel layer portion 3 directly under the existing structure foundation 21, thereby suppressing an increase in construction costs.

  As described above, in the structure liquefaction damage reducing structure and the liquefaction damage reducing method according to the first embodiment, a simple construction in which the structure foundation 21 is connected to the gravel layer portion 3 provided on the surface layer portion. By adopting the method, it is possible to reduce the construction cost and to produce an effect that enables construction in a narrow construction space.

  Next, another embodiment of the structure liquefaction damage reducing structure and liquefaction damage reducing method of the present invention will be described with reference to the accompanying drawings, but the same as or similar to the first embodiment described above. Components and parts that are the same as those in the first embodiment will be described using the same reference numerals and description thereof will be omitted.

(Second Embodiment)
As shown in FIG. 4, the liquefaction damage reducing structure 1 </ b> A according to the second embodiment does not need to be provided with the widened portion 22 over the entire outer periphery of the structure foundation 21, and has a rectangular existing structure 2 in plan view. The widened portion 22 and the gravel layer portion 3 are provided only in two directions opposite to each other. That is, the adjacent structure 4 is constructed in the two opposite directions in which the gravel layer 3 is not provided in the structure foundation 21.
Further, the liquefaction damage reducing structure 1B shown in FIG. 5 has a configuration in which the widened portion 22 and the gravel layer portion 3 are provided in three directions with respect to the existing rectangular structure 2 in plan view. Also in this case, the adjacent structure 4 is constructed in the other direction in which the gravel layer 3 is not provided in the structure foundation 21.

  Thus, the liquefaction damage reducing structure does not require the gravel layer portion 3 to be provided over the entire outer periphery of the structure 2. Therefore, even if the proximity structure 4 is provided in a part of the periphery of the structure 2 that reduces liquefaction damage, the liquefaction damage reduction structure of the present embodiment can be applied. .

(Third embodiment)
Next, as shown in FIG. 6, in the liquefaction damage reducing structure 1 </ b> C according to the third embodiment, the liquefaction damage reducing structure 1 </ b> A in which the gravel layer 3 is provided in two directions according to the second embodiment described above ( In the widened portion 22 of FIG. 4, a protruding portion 24 is formed in which the widened distance in the direction away from the structure foundation 21 in the horizontal direction (arrow E direction) is partially increased.
In this case, since the protrusion 24 and the gravel layer 3 are provided in a fitted state, the structure 2 is inclined toward the direction F perpendicular to the direction E in which the protrusion 24 expands in plan view. The effect which suppresses can be heightened. Therefore, as in the present embodiment, another structure (proximity structure 4) is provided in the vicinity of the existing structure 2, and it is difficult to provide the gravel layer portion 3 on the proximity structure 4 side. In such a case, by forming the protruding portion 24 in the widened portion 22 on the side that is not on the adjacent structure 4 side, the inclination of the structure 2 toward the adjacent structure 4 side can be suppressed.

(Fourth embodiment)
Next, as shown in FIG. 7, in the liquefaction damage reducing structure 1 </ b> D according to the fourth embodiment, a plurality of block-shaped widened portions 22 </ b> A are spaced along the outer peripheral portion 21 a of the structure foundation 21 in plan view. The gravel layer portion 3 is provided only in the portion that is partially opened and surrounded by the widened portion 22A.
In this case, the construction area of the widened portion 22A can be reduced, so that the construction cost can be reduced.

(Fifth embodiment)
As shown in FIGS. 8 and 9, in the liquefaction damage reducing structure 1E according to the fifth embodiment, the liquefaction damage reducing structure 1E communicates with the gravel layer part 3 and from the gravel layer part 3 in the vertical direction within the liquefaction ground G. A plurality of vertical drains 5 having water permeability extending downward are provided at predetermined intervals in a direction along the outer peripheral portion 21 a of the structure foundation 21. Here, the depth of the gravel layer portion 3 of the present embodiment is a position shallower than the structure foundation 21. The vertical drain 5 is made of a material having water permeability such as gravel and gravel similar to that of the gravel layer 3, but may be made of a material having higher water permeability than the vertical drain 5.

In the fifth embodiment, excess pore water generated in the liquefied ground G due to the earthquake is collected by a plurality of vertical drains 5, and the water is further pumped from the vertical drains 5 to the gravel layer portion 3. It becomes possible to drain the ground through the layer portion 3. Therefore, as in the present embodiment, even when excavation at a deeper position than the depth of the bottom surface position of the structure foundation 21 is difficult, the drainage function similar to that of the gravel layer portion 3 is given to the vertical drain 5 to a predetermined depth. Can be given.
In addition, when the vertical drain 5 is placed, it is possible to perform construction while avoiding the existing piping, and it is possible to prevent the existing piping from being affected.

(Sixth embodiment)
Next, as shown in FIG. 10, the liquefaction damage reducing structure 1 </ b> F according to the sixth embodiment protrudes outward from the outer peripheral portion 21 a of the structure foundation 21 instead of the widened portion 22 described above. In addition, a plate-like overhang portion 25 that is integrally fixed to the structure base 21 is provided. The overhang portion 25 is disposed over the entire outer periphery of the structure 2, and the portion 25 a on the structure 2 side is fixed to the upper edge portion of the structure base 21 by a fixing jig 26 such as an anchor bolt, for example. Is arranged so as to be substantially along the ground surface and cover the inner part of the upper end of the gravel layer portion 3, and is connected to the gravel layer portion 3. Here, the overhang portion 25 is not necessarily limited to the same thickness and rigidity as the structure base 21. Moreover, although the overhang | projection part 25 is made into plate shape in this Embodiment, it is not restrict | limited to plate shape, For example, steel materials, such as L-shaped steel and a channel material, are outer peripheral parts 21a of the structure foundation 21. It is also possible to project outward from the outside.

In this case, the overhanging portion 25 can be provided by post-construction on the existing structure foundation 21, and the overhanging portion 25 is connected to the gravel layer portion 3. This eliminates the need for difficult construction such as providing the gravel layer portion 3 directly under the existing structure foundation 21, thereby suppressing an increase in construction costs. And compared with the case where the structure foundation 21 is expanded, it will be the structure which should just provide the overhang | projection part 25 only in the part along a ground surface, and the effort and time concerning construction can be reduced.
In addition, the said overhang | projection part 25 may be partially arrange | positioned along the structure base 21 by planar view. In this case, since the construction area of the overhang part 25 can be reduced, the construction cost can be reduced.

(Seventh embodiment)
Moreover, as shown in FIG. 11, the liquefaction damage reducing structure 1G according to the seventh embodiment does not include the widened portion 22 and the overhang portion 25 as described above in the structure foundation 21, and the structure foundation 21 It is the structure which excavated under the outer peripheral part and laid the gravel layer part 3. FIG. In this case, the present invention can be applied when the structure foundation 21 is large to some extent and has sufficient rigidity.

  Next, examples for supporting the effects of the structure liquefaction damage reducing structure and the liquefaction damage reducing method according to the above-described embodiment will be described below.

(First embodiment)
In the first example, an experiment was conducted using a model of a liquefaction damage reducing structure similar to the first embodiment described above and a model without countermeasures, and the effect was confirmed.
FIGS. 12A and 12B are experimental model diagrams (experimental model 100) having the same configuration as the liquefaction damage reducing structure 1A shown in FIG. That is, the experimental model 100 includes a gravel layer portion 103 having a drainage function that is formed by laying gravel all around the outer periphery of the structure 101 corresponding to the structure foundation and having a water permeability coefficient larger than that of the liquefied layer 102. The outer peripheral part (widened part 104) of the structure 101 is connected to the gravel layer part 103 and connected. A widened portion 104 extending outward from the structure 101 is integrally provided on the outer periphery of the structure 101.

The experimental model 100 shown in FIG. 12B uses a sheared soil layer of 800 mm × 470 mm × 370 mm in the size in the earth tub. The ground is provided with a thickness of 50 mm of a No. 3 silica sand layer having a relative density of 90% or more, which is a non-liquefied layer 105, at the bottom of the soil tank, and a dry weight ratio of 95: 5 was prepared by the air drop method with a relative density of 35% and a thickness of 240 mm. The pore fluid was 30 cs silicon oil, and the groundwater level was the ground surface.
The structure 101 is an aluminum structure having a base thickness of 12 mm and an eccentric load of 80 mm square and an average contact pressure of 34 kN / m ² . The widened portion 104 is formed by fixing an aluminum material having a length of 80 mm, a width of 17 mm, and a thickness of 10 mm to the base of the structure 101 with bolts.
The gravel layer 103, which becomes the drainage layer, was made of No. 3 silica sand, having a width of 33 mm and a relative density of 90% or more.

The experiment is performed under a centrifugal acceleration of 30 g, and since the eccentric load of the structure 101 is large, centrifugal loading is performed in a state where there is no eccentricity by a counterweight so that the structure 101 does not tilt during centrifugal loading. Was unloaded, the counterweight was removed, and centrifugal loading was performed again to perform a vibration experiment. At the start of vibration, the ground directly under the structure 101 is in an overconsolidated state. As the input wave, a 2 Hz sine wave having a maximum acceleration of 300 cm / s ² in actual conversion was used, and gradually increased 100 waves, stationary 60 waves, gradually decreased 5 waves, and the excitation time was 82.5 seconds.

  FIG. 13 shows the experimental results of the first example in which the horizontal axis indicates the elapsed time after the earthquake (minutes) and the vertical axis indicates the basic slope increment (rad). In the case of the model 100 (first countermeasure T1) and the non-measure T0, the slope increment (rad) after the earthquake is compared. According to this, in the case of no countermeasures, the slope gradually increases after the earthquake and finally a residual slope of 30 ° is generated. On the other hand, in the case of the first countermeasure T1 (that is, when liquefaction damage reduction countermeasures are taken), there is almost no increase in inclination.

(Second embodiment)
In the second example, an experiment was performed using a model of a liquefaction damage reducing structure similar to that of the second embodiment described above, and the effect was confirmed. That is, the experimental model 100 of the first embodiment shown in FIG. 12 is provided with the widened portion 104 and the gravel layer portion 103 over the entire circumference on the outer peripheral side of the structure 101. On the other hand, an experiment model (two-direction countermeasure) provided with the widened portion 104 and the gravel layer portion 103 only in two opposite directions was used, and an experiment was performed under the same conditions as in the first example, and the effect was confirmed. Here, as the liquefaction damage reducing structure provided in the two-direction countermeasure, a countermeasure is taken only in the two directions of load eccentricity (second countermeasure T2), and a countermeasure is taken in only two directions orthogonal to the load eccentric direction ( The third countermeasure T3) was tested.

  FIG. 14 shows the experimental results of the second embodiment. The experimental model with the liquefaction damage reducing structure (second countermeasure T2, third countermeasure T3), the first countermeasure by the omnidirectional countermeasure of the first embodiment. In the case of T1 and no countermeasure T0, the slope increment (rad) after the earthquake is compared. According to this, it can be confirmed that the variation in inclination is the smallest in the case of the omnidirectional measure (first measure T1), and even in the case of only the two directions of the second measure T2 and the third measure T3, 1/1500. It can be confirmed that the degree and the inclination increment are small. For this reason, the liquefaction damage reducing structure is not necessarily limited to being provided in all directions, and a two-way countermeasure can obtain the same effect as the omnidirectional countermeasure.

(Third embodiment)
In the third example, an experiment was performed using a model (not shown) of a liquefaction damage reducing structure corresponding to the above-described fifth embodiment, and the effect was confirmed. Specifically, the experimental model used in the experiment of the third embodiment communicates with the gravel layer portion 103 shown in FIG. 12 (b), and the water permeability that extends downward in the vertical direction from the gravel layer portion 103 in the liquefied layer 102. A plurality of vertical drains (not shown) having characteristics are provided at predetermined intervals in the direction along the outer peripheral portion of the structure 101, and the two-way countermeasures are taken as in the second embodiment instead of the entire circumference. (Fourth countermeasure T4). The vertical drain has three outer diameters of 330 mm (actual conversion) for each of the two-way countermeasures on the front and rear surfaces of the foundation (structure 101) (the side with the large load due to the eccentric load is the front surface). The distance from the bottom surface of the structure 101 is 1.2 m (actual conversion). The vertical drain uses No. 3 silica sand.
Using such an experimental model, an experiment was performed under the same conditions as in the first example, and the effect was confirmed.

  FIG. 15 shows the experimental results of the third embodiment. An experimental model (fourth countermeasure T4) using a liquefaction damage reducing structure and a structure without a vertical drain (that is, the two-way countermeasure of the second embodiment). In the case of the second countermeasure T2) and T0 without countermeasure, the slope increment (rad) after the earthquake is compared. According to this, it can be confirmed that even the fourth countermeasure T4 provided with the vertical drain has a small change in the inclination increment, so that the effect of reducing the liquefaction damage can be obtained.

The embodiments of the structure liquefaction damage reducing structure and the liquefaction damage reducing method according to the present invention have been described above. However, the present invention is not limited to the above embodiments, and does not depart from the spirit of the present invention. The range can be changed as appropriate.
For example, the layer thickness and depth of the gravel layer portion 3 of the present embodiment, the length in the depth direction of the vertical drain 5, the amount of widening of the structure foundation 21 (area of the widened portion 22), etc. It is set as appropriate in consideration of size, weight, ground conditions, etc. For example, for the laying area of the gravel layer portion 3 and the design of the vertical drain, the method previously described by the present applicant in Japanese Patent Application No. 2011-166531 can be used.

  Further, in the liquefaction damage reducing structure of the present invention, each component (the widened portions 22, 22A, the projecting portion 24, the overhanging portion 25, the vertical drain 5, etc.) of the liquefaction damage reducing structure of the above-described embodiment is appropriately used. Combinations are also possible. For example, the widened portion 22 is provided in each of two opposing directions of the structure foundation 21 according to the second embodiment shown in FIG. 4 described above, and the other two directions of the structure foundation 21 where the widened portion 22 is not provided. Can be configured to be provided with the block-like widened portion 22A described in the fourth embodiment shown in FIG. Moreover, it is good also as a structure which provides the vertical drain 5 shown in FIG. 8 only in a part of gravel layer part 3 of 1st Embodiment (For example, only the gravel layer part 3 provided in the one side part of the structure base 21).

  As described above, the present invention is preferably applied to a small-scale structure or an existing structure, but is not limited thereto, and can be widely applied to various structures regardless of the scale. Needless to say, the present invention is not limited to existing structures.

  In addition, it is possible to appropriately replace the components in the above-described embodiments with known components without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1, 1A-1G Liquefaction damage reduction structure 2 Structure 3 Gravel layer part 5 Vertical drain 21 Structure foundation 22 Widening part 24 Projection part 25 Overhang part G Liquefaction ground

Claims (10)

A structure for reducing the damage to the structure when the liquefied ground is liquefied, targeting a structure constructed on the liquefied ground,
Provided with a gravel layer portion having a drainage function formed by laying gravel on the outer peripheral side of the structure foundation of the structure and having a larger permeability than the liquefied ground,
A structure for reducing liquefaction damage, wherein an outer peripheral portion of the structure foundation is connected to the gravel layer.   The liquefaction damage reducing structure according to claim 1, wherein the outer peripheral portion of the structure foundation is a widened portion provided integrally with the outer peripheral portion of the structure foundation.   The liquefaction damage reducing structure according to claim 2, wherein the widened portion is formed with a protruding portion having a partially widened widening distance in a direction away from the structure foundation in the horizontal direction.   The liquefaction damage reducing structure according to claim 2 or 3, wherein the widened portion is partially disposed along the structure foundation in a plan view.   The outer peripheral part of the said structure foundation is an overhang | projection part which protrudes toward the outward from the outer peripheral part of the said structure foundation, and is integrally fixed to the said structure foundation. Liquefaction damage reduction structure.   The liquefaction damage reducing structure according to claim 5, wherein the projecting portion is partially disposed along the structure foundation in a plan view.   The liquid according to any one of claims 1 to 6, wherein a vertical drain having water permeability that communicates with the gravel layer portion and extends downward in the vertical direction from the gravel layer portion is provided. Damage reduction structure. A liquefaction damage reducing method for reducing damage to the structure when the liquefied ground is liquefied, targeting a structure constructed on a liquefied ground,
A step of providing a gravel layer portion having a drainage function having a larger permeability than the liquefied ground by digging the outer peripheral side of the structure foundation of the structure and laying gravel;
Connecting the outer periphery of the structure foundation to the gravel layer,
A liquefaction damage reducing method characterized by comprising:   9. The liquefaction damage reducing method according to claim 8, wherein a widened portion is integrally provided on an outer peripheral portion of the structure foundation, and the widened portion is connected to the gravel layer portion.   The method for reducing liquefaction damage according to claim 8, wherein an overhanging portion projecting outward from an outer peripheral portion of the structure foundation is provided, and the overhanging portion is connected to the gravel layer portion. .

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