JP2008150896A - Method and structure of aseismic reinforcing backfill ground - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of aseismic reinforcing backfill ground, which contributes to reduction of dynamic earth pressure and hydraulic pressure occurring in the backfill ground developed on a rear surface of a structure at the time of an earthquake, and exerts excellent construction efficiency, and to provide a structure of seismically reinforcing the same. <P>SOLUTION: According to the method, a cushioning layer 6 formed of a mixed material 5 consisting of rubber chips 5a and crushed stones 5b having almost the same particle diameter, is arranged along the rear surface of the structure 1. Then the dynamic earth pressure of the backfill ground 3, occurring due to the earthquake is transmitted via a pressure plate 8 to the cushioning layer 6 which then absorbs the dynamic earth pressure by virtue of elastic deformation of the rubber chips 5a while securing suitable voids therein. Further the voids having excellent water permeability function to reduce increased hydraulic pressure of the backfill ground 3, to thereby prevent liquefaction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a seismic reinforcement method and structure for backfill ground, and more specifically, it can reduce the dynamic earth pressure and water pressure generated in the backfill ground created on the back of the structure during an earthquake. It is related to the seismic reinforcement method and structure of the backfill ground which is excellent in

  Examples of seismic reinforcement for existing structures include physical reinforcement of structures and foundation ground, as well as methods of reducing earth pressure during earthquakes in the backfill area and dissipating excess water pressure acting on landfills. It is done. As methods for reducing earth pressure during earthquakes, there are various methods to dissipate excess water pressure using vertical drains that are arranged in a columnar shape with materials with excellent water permeability such as crushed stone, and generally ground improvement by compaction and agitation and mixing of solidified materials. It has been proposed (see, for example, Patent Document 1).

In addition, it is also considered to place a rubber chip on the back of the structure to form a buffer layer, but the rubber chip has a low specific gravity in construction below the groundwater level or at sea, so the rubber chip is stably placed in place. It was difficult to arrange and there was a problem in workability.
JP 2001-11848 A

  The object of the present invention is to reduce the dynamic earth pressure and water pressure generated in the backfill ground created on the back of the structure at the time of an earthquake, and to improve the seismic reinforcement method and structure of the backfill ground with excellent workability. It is to provide.

  In order to achieve the above object, the seismic reinforcement method for backfilled ground according to the present invention is a seismic strengthening method for backfilled ground created on the back of a structure, in which rubber chips having substantially the same particle size and crushed stone are mixed. The buffer material is formed by arranging the mixed material along at least a part of the back surface of the structure in the vertical direction.

  Here, the buffer material may be formed by arranging the mixed material so as to be continuous from the lower end portion to the upper end portion of the structure along the back surface of the structure. A plate can also be arranged. Alternatively, the mixed material may be stored in advance in a plurality of bag-shaped containers having water permeability, and the buffer members may be formed by stacking the containers containing the mixed materials. Further, the back surface of the buffer layer may be inclined so that the thickness of the buffer layer becomes larger on the lower side.

  Further, the seismic reinforcement structure of the backfill ground according to the present invention is a seismic reinforcement structure of the backfill ground formed on the back surface of the structure, and has a particle size along at least a part of the back surface of the structure in the vertical direction. Is provided with a buffer layer made of a mixed material obtained by mixing substantially the same rubber chip and crushed stone.

  Here, the buffer layer may be provided continuously from the lower end to the upper end of the back surface of the structure, or the pressure receiving plate may be provided along the back surface of the buffer layer. In addition, the buffer layer may be formed by stacking a plurality of bag-like containers having water permeability and containing a mixed material. It is also possible to adopt a structure in which the back surface of the buffer layer is inclined so that the thickness of the buffer layer becomes larger on the lower side. The particle size of the rubber chip and crushed stone is, for example, 2 mm or more and 60 mm or less.

  According to the present invention, the backfill ground formed by backfilling earth and sand etc. on the back surface of the structure is mixed with rubber chips and crushed stones of substantially the same particle size formed along the back surface of the structure. The buffer layer made of wood absorbs the dynamic earth pressure generated in the backfill ground by elastic deformation of the rubber chip while having an appropriate gap in the event of an earthquake, and excellent due to the gap between the rubber chip and the crushed stone Since the water pressure rise of the backfill ground is reduced by the water permeability, the liquefaction phenomenon of the backfill ground can be suppressed.

  Moreover, since the crushed stone having a specific gravity larger than that of the rubber chip is mixed with the mixed material, even when the buffer layer is formed below the seawater surface or the groundwater surface, the mixed material can be stably disposed at a predetermined position. The workability is improved.

  Further, by arranging the pressure receiving plate along the back surface of the buffer layer, the back surface earth pressure can be transmitted and absorbed evenly and efficiently. When a structure is newly established, a structure in which this mixed material is filled between the structure and the pressure plate can reduce the cross-section of the structure itself and the ground improvement range of the foundation ground of the structure. It becomes possible and contributes to cost reduction.

  Hereinafter, the seismic reinforcement method and structure of the backfill ground of the present invention will be described based on the embodiments shown in the drawings.

  As illustrated in FIG. 1, a backfill ground 3 formed by backfilling backfill soil 4 such as earth and sand on the back of a structure 1 such as a caisson or a retaining wall is an object of seismic reinforcement of the present invention. The structure 1 is erected on the seabed 2 from above the seabed, and a buffer layer 6 having a substantially constant layer thickness (horizontal length) is formed along the back surface thereof. A gravel mat 6 a is laid on the upper surface of the buffer layer 6, and a pressure receiving plate 8 is installed on the rear surface, and the back side of the pressure receiving plate 8 is the backfill ground 3.

  The buffer layer 6 is formed by storing a mixture 5 of rubber chips 5a and crushed stones 5b having substantially the same particle diameter in a bag-like container 7 having water permeability, and by stacking a plurality of these containers 7. There are voids. As long as the porosity of about 50 to 60% can be ensured, the mixed material 5 may be mixed with rubber chips 5a, crushed stones 5b, and other mixtures having different particle sizes. The preferable particle diameters of the rubber chip 5a and the crushed stone 5b are, for example, 2 mm to 60 mm, and within this range, more appropriate voids and elastic deformation of the rubber chip 5a can be ensured, and an excellent buffering effect can be obtained.

  In addition, the volume mixing ratio of the rubber chip 5a and the crushed stone 5b is measured with the test sample S by preparing the test sample S of the buffer layer 6 using the mixed material 5 in which the mixing ratio is changed in advance, as shown in the examples described later. The buffer effect (earth pressure reduction effect) is grasped and determined based on the measurement result and the required specifications at the construction site.

  As the rubber chip 5a, for example, a crushed used tire (tire chip) can be used, and according to this, the used tire can be effectively used. The crushed stone 5b may be various crushed stones such as concrete recycled crushed stone or the like, and the specific gravity of the rubber chip 5a and the crushed stone 5b is about 1.10 to 1.20 and about 2.60 to 2.80, respectively.

  The container 7 is made of, for example, a woven fabric, a nonwoven fabric, a knitted fabric, or the like made of a polymer material used for civil engineering or the like called geotextile. In addition, the container 7 can be used as long as it has water permeability and can hold the mixed material 5.

  Next, the seismic reinforcement method of the present invention for constructing the seismic reinforcement structure of the backfill ground 3 will be exemplified.

  First, when the structure 1 is newly established and the backfill ground 3 is newly created on the back surface thereof, the pressure receiving plate is previously spaced from the back surface of the structure body 1 at the factory or construction site as illustrated in FIG. 8, a partition wall is provided at both ends in the width direction between the back surface of the structure 1 and the pressure receiving plate 8, and a box-like space for arranging the mixed material 5 is provided. The partition wall is assumed to have low rigidity so as not to hinder the buffering effect of the buffer layer 6.

  And the buffer layer 6 is formed by stacking up and down and filling the container 7 which previously accommodated the mixed material 5 of the rubber chip 5a and the crushed stone 5b between the back surface of the structure 1 and the pressure receiving plate 8. FIG. In the present invention, the mixed material 5 may be charged directly between the back surface of the structure 1 and the pressure receiving plate 8 without being accommodated in the accommodating body 7.

  As illustrated in FIG. 3, the pressure receiving plate 8 can be constructed in such a manner that a plurality of the pressure receiving plates 8 that are divided into upper and lower portions are sequentially connected upward.

  As described above, after the mixed material 5 is arranged along the back surface of the structure 1 so as to be continuous from the lower end portion to the upper end portion of the structure 1 to form the buffer layer 6, the backfilling soil is formed on the back surface of the pressure receiving plate 8. 4 is backed up and back ground 3 is created.

  In this seismic strengthening method, the mixed material 5 is mixed with the crushed stone 5b having a specific gravity larger than that of the rubber chip 5a. Therefore, even when the buffer layer 6 is formed below the seawater surface or the groundwater surface, the mixed material is stably provided. 5 can be arrange | positioned in a predetermined position, and workability improves remarkably.

  The mixed material 5 may be stored in the container 7 at the construction site. However, if the mixed material 5 is stored in advance in a factory or the like, the mixed material 5 is not scattered around and the construction time can be shortened. Further, when the mixed material 5 is accommodated in the accommodating body 7 and the accommodating bodies 7 are stacked to form the buffer layer 6, the work can be quickly performed without diffusing the mixed material 5 around. Moreover, if the mixed material 5 is accommodated in the accommodating body 7, it will not spread carelessly in the ground after construction, and the buffering effect of dynamic earth pressure and water pressure during an earthquake will not be easily impaired.

  When the backfill ground 3 is vibrated by an earthquake, the water pressure between the particles of the backfill soil (backfill sand) 4 of the backfill ground 3 rises rapidly and a liquefaction phenomenon is likely to occur. Moreover, although dynamic earth pressure acts on the structure 1 and an excessive load is applied to the structure 1, according to the earthquake-proof reinforcement structure of the present invention, the structure 1 and the backfill ground 3 In the buffer layer 6 sandwiched between the rubber chips 5a, the rubber chips 5a are elastically deformed while securing an appropriate gap between the rubber chips 5a and the crushed stones 5b. Due to this elastic deformation, the dynamic horizontal earth pressure is absorbed and reduced, and the water pressure rise of the backfill ground 3 is reduced due to the excellent water permeability due to the moderate gap of the buffer layer 6, thereby suppressing the liquefaction phenomenon. can do. Furthermore, the earth pressure acting on the structure 1 is also reduced.

Since the pressure receiving plate 8 provided on the back surface of the buffer layer 6 transmits the earth pressure caused by the shaking at the time of the earthquake dispersed to the buffer layer 6, it is possible to absorb the dynamic earth pressure in a wide range of the buffer layer 6. become. That is, by providing the pressure receiving plate 8, the earth pressure on the back surface can be transmitted and absorbed to the buffer layer 6 evenly and efficiently to obtain a more excellent buffering effect. The pressure receiving plate 8 is not particularly limited as long as the earth pressure can be distributed and transmitted to the buffer layer 6. For example, an iron plate or a sheet pile steel plate can be used. The pressure receiving plate 8 can have a perforated structure in order to provide water permeability.
In addition, by using a structure in which the mixed material 5 is filled between the back surface of the new structure 1 and the pressure plate 8 as described above, the horizontal earth pressure acting on the structure 1 during an earthquake is reduced and the backfill ground Sectional structure including the foundation ground, such as dissipating the excess pore water pressure of 3 and reducing the falling moment and edge pressure resulting from these, reducing the bottom width and wall thickness of the structure 1, and reducing the ground improvement width of the foundation ground By reducing the overall size, it is possible to reduce the manufacturing cost of the structural member such as the structure 1 and the cost required for construction.

  In the present invention, a seismic reinforcement structure in which the pressure receiving plate 8 is not provided on the back surface of the buffer layer 6 can be provided. The moisture contained in the backfill ground 3 can pass between the particles of the mixed material 5 of the buffer layer 6 having an appropriate gap and flow out to the surface. Thus, when the buffer layer 6 functions as a drain, the effect of preventing the liquefaction phenomenon by suppressing the increase in water pressure of the backfill ground 3 can be obtained.

  Next, the case where the backfill ground 3 on the back surface of the existing structure 1 is seismically reinforced will be described.

  As illustrated in FIG. 4, when there is a backfill stone 4 a on the back surface of the structure 1 or when there is a construction work, first, the back surface of the structure 1 is excavated with a stable gradient to form the buffer layer 6. To secure space. Next, as illustrated in FIG. 5, the pressure receiving plate 8 is erected at a predetermined interval from the back surface of the structure 1, and the container 7 containing the mixed material 5 is sequentially placed between the back surface of the structure 1 and the pressure receiving plate 8. The buffer layer 6 is formed by stacking. After the buffer layer 6 is formed, the backfill soil 4 is backfilled on the back side of the pressure receiving plate 8 to construct an earthquake resistant reinforcement structure.

  As illustrated in FIG. 6, when there is no backfilling stone 4 a or a guard on the back surface of the structure 1, the pressure receiving plate 8 and the mountain stopper 18 are driven at a predetermined interval from the back surface of the structure 1, The backfill soil 4 between the structure 1 and the pile 18 is excavated and removed to secure a space for forming the buffer layer 6. Next, the buffer material 6 is formed by charging and filling the mixed material 6 into the space between the structure 1 and the pile 18. Even when there are no backfill stones 4a and no back work on the back surface of the structure 1, the back surface of the structure 1 is excavated with a stable gradient to secure a space for forming the buffer layer 6, and from the back surface of the structure 1 to a predetermined value. The buffer plate 6 can also be formed by standing up the pressure receiving plate 8 at intervals and sequentially stacking the accommodating bodies 7 containing the mixed material 5 between the back surface of the structure 1 and the pressure receiving plate 8.

  The buffer layer 6 may not only be formed continuously from the lower end portion to the upper end portion of the structure 1 along the back surface of the structure 1 as in the various embodiments described above, but the necessary buffer performance may be obtained. For example, it can also be formed along a part in the vertical direction of the back surface of the structure 1.

  For example, when the maximum earth pressure when a reduced model of backfill ground with backfill soil backed on the back of the caisson is vibrated with a shaking table tester is measured, data as shown in FIGS. The reduced model used for this measurement is model A (no buffer layer) backed with crushed stone as backfilling soil along the backside of the caisson (600mm) in the vertical direction, and the overall length (600mm) along the back of the caisson. Model B (with a buffer layer) with only a rubber chip with a particle size of about 20 mm as the back-filling soil and a buffer layer provided on the back side of the caisson, and a rubber chip with a particle size of about 20 mm. The model C (with the upper half buffer layer) is provided with a buffer layer made of

  Measurements using this shaking table tester were carried out by installing a earth pressure gauge on the back of the caisson of each model and applying vibration at an acceleration of about 680 gal in the horizontal direction. The maximum earth pressure measured at that time is shown in FIGS. ing. The plots in FIG. 15 indicate the data of model A, the diamonds are model B, and the plots in FIG. 16 indicate the data of model A in the circles and model C in the triangles.

  From the result of FIG. 15, in the model B provided with the buffer layer, the maximum earth pressure can be reduced by about 50% as compared with the model A. From the result of FIG. In (300 to 600 mm from the bottom of the caisson), it can be seen that the maximum earth pressure can be reduced by about 50% compared to the model A. In addition, it can be seen that the maximum earth pressure can be reduced by about 10% in comparison with the model A even in the lower half range where the buffer layer of the model C is not provided. It is considered that the earth pressure reduction in the lower half of the model C is due to weight reduction by replacing the upper half with crushed stones and rubber chips.

  Thus, it can be seen that even if the buffer layer 6 is provided on a part of the rear surface of the structure 1 in the vertical direction, a considerable earth pressure reduction effect can be obtained, and this data includes the rubber chip 5a and the crushed stone 5b as in the present invention. It is considered that this also applies to the buffer layer 6 made of the mixed material 5. Therefore, the buffer layer 6 can be formed along a part of the back surface of the structure 1 in the vertical direction so that the required buffer performance can be obtained.

  In order to form the buffer layer 6 along a part of the back surface of the structure 1, for example, as shown in FIG. 7, the back surface of the existing structure 1 is formed with a stable gradient to a required depth halfway in the vertical direction of the structure 1 A space for excavating and forming the buffer layer 6 is secured. Next, a first-stage pressure plate 8 is installed at a predetermined distance from the back of the structure 1 at the bottom of the space secured by excavation, and the mixed material 5 is charged between the pressure plate 8 and the back of the structure 1 and filled. After that, the backfill soil 4 is backfilled on the back side of the pressure receiving plate 8 to complete the first stage construction. Thereafter, the second and third steps are repeated in the same manner. In this way, the buffer material 6 is formed along the upper half of the back surface of the structure 1 as illustrated in FIG. Can do.

  In this embodiment, since the formation range of the buffer layer 6 can be set to a minimum range necessary for obtaining a predetermined buffer performance, the construction can be performed in a short construction period with a reduced cost. The formation range of the buffer layer 6 is not limited to the upper half range of the back surface of the structure 1, and the buffer layer 6 may be placed in an arbitrary range as necessary, such as a lower half range or a partial range in the vertical center. Can be formed. Further, the buffer layer 6 can be formed by using the pressure receiving plate 8 that is integrated without being divided into a plurality of parts, and the buffer layer 6 is formed by charging and filling the mixed material 5 without providing the pressure receiving plate 8. You can also

  Moreover, regardless of the new structure or the existing structure 1, as illustrated in FIG. 9, the seismic reinforcement structure in which the back surface of the buffer layer 6 is inclined so that the layer thickness of the buffer layer 6 becomes larger on the lower side. You can also Since the buffer layer 6 has a larger layer thickness on the lower side in accordance with the pressure distribution of the backfill ground 3 where a greater earth pressure is generated on the lower side, the buffer effect can be obtained efficiently without waste. .

  This seismic reinforcement structure can also be constructed by the construction methods of the various embodiments exemplified above. A pressure receiving plate 8 can be provided along the back surface of the buffer layer 6, and the buffer layer 6 can also be formed by sequentially stacking a plurality of containers 7 containing the mixed material 5.

  As shown in Table 1 using rubber chips (specific gravity of about 1.15) and crushed stones (specific gravity of about 2.70) having the same particle size (average particle size of 10 mm), only the volume mixing ratio of rubber chips and crushed stones 4 types of test samples S (Examples 1 and 2 and Comparative Examples 1 and 2) were prepared, and the earth pressure measurement was performed on each test sample S to confirm the earth pressure reduction effect. . The results are shown in FIGS. The rubber chip mixing ratio in Table 1 is the volume ratio of rubber chips to the total volume of rubber chips and crushed stone.

[Measure earth pressure]
As shown in FIG. 10, the earth pressure measuring device 9 includes a load meter 13 on a rigid loading plate 12 (diameter 19.5 cm), and a pole 15 is erected on the load meter 13. (Weight 294N (30 kg)) is inserted, and the upper end of the pole 15 is provided with a dropping device 17 for dropping the weight 14. As shown in FIG. 11, a soil pressure gauge 11 is installed at the bottom of a mold 10 made of an acrylic resin cylinder having an inner diameter of 20 mm and a height of 60 cm and a steel frame, and a test sample S that has been mixed uniformly in advance is placed on a predetermined layer. The thickness (9 cm, 18.5 cm, 37 cm, 50 cm) is set, the loading plate 12 of the earth pressure measuring device 9 is placed on the upper surface of the test sample S, and the measurement data is input to the load gauge 13 and the earth pressure gauge 11 The control device 16 to be connected is connected. Next, the weight 14 was dropped freely with a drop height of 60 cm with respect to the load meter 13, and the load was measured with the load meter 13 and earth pressure gauge 11. The load measured by the load meter 13 is the earth pressure (reaction force) on the upper surface of the test sample S, and the load measured by the earth pressure meter 11 is the earth pressure (transmitting force) on the lower surface of the test sample S.

  The test sample S is prepared by dropping and filling the mold 10 with a mixture of rubber chips and crushed stone under a constant condition of 80 cm in height and leveling the surface. Table 1 shows the air density and porosity measured and calculated at that time. Also, silicon grease was applied to the inner wall of the acrylic resin cylinder to reduce friction.

  FIG. 12 shows the relationship between the layer thickness of each test sample S and the earth pressure reduction rate on the upper surface of the test sample S with reference to Comparative Example 1 (test sample consisting only of crushed stone). FIG. 13 shows the relationship between the layer thickness of each test sample S and the earth pressure reduction rate on the lower surface of the test sample S with reference to Comparative Example 1. FIG. 14 is a rewrite of FIG. 13 with the horizontal axis as the rubber chip mixing rate, and shows the relationship between the rubber chip mixing rate of each test sample S and the earth pressure reduction rate on the lower surface of the test sample S based on Comparative Example 1. ing. The plots in FIGS. 12 and 13 are a round shape for Example 1 (rubber chip mixing rate of 25%), a triangle for Example 2 (rubber chip mixing rate of 50%), a square for Comparative Example 1 (rubber chip mixing rate of 0%), and a rhombus. Comparative Example 2 (rubber chip mixing ratio 100%) is shown, and the plot in FIG. 14 shows that the round shape has a layer thickness of 50 cm, the triangle has a layer thickness of 37 cm, the square has a layer thickness of 18.5 cm, and the rhombus has a layer thickness of 9 cm. Shows the case.

  From the results of FIGS. 12 to 14, Examples 1 and 2 in which rubber chips and crushed stone were mixed did not reach Comparative Example 2 consisting only of rubber chips, but had a certain earth pressure reduction effect and changed the mixing ratio of rubber chips. It can be seen that the desired earth pressure reduction effect can be obtained.

It is side surface sectional drawing which illustrates the seismic reinforcement structure of the backfill ground of this invention. It is explanatory drawing which illustrates the earthquake-proof reinforcement construction method which constructs the earthquake-proof reinforcement structure of the backfill ground of FIG. It is explanatory drawing which shows another example of the earthquake-proof reinforcement construction method of FIG. It is explanatory drawing which illustrates the construction method at the time of carrying out earthquake-proof reinforcement of the back-filling ground of the back of the existing structure in which the back-filling stone was installed. FIG. 5 is an explanatory diagram illustrating the next process of FIG. 4. It is explanatory drawing which illustrates the construction method at the time of carrying out earthquake-proof reinforcement of the back-filling ground of the back of the existing structure without a back-filling stone and a back-up work. It is explanatory drawing which illustrates the construction method which forms a buffer layer along the up-down direction part of the back surface of a structure. It is side surface sectional drawing which illustrates the earthquake-proof reinforcement structure completed by the construction method of FIG. It is side surface sectional drawing which illustrates another embodiment of the seismic reinforcement structure of the backfill ground of this invention. It is a perspective view which illustrates an earth pressure measuring device. It is explanatory drawing which shows the earth pressure measuring method by an earth pressure measuring apparatus. It is a graph which shows the relationship between the layer thickness of the test sample by earth pressure measurement, and the earth pressure reduction rate of the test sample upper surface. It is a graph which shows the relationship between the layer thickness of the test sample by earth pressure measurement, and the earth pressure reduction rate of the test sample lower surface. It is a graph which shows the relationship between the rubber chip mixing rate by earth pressure measurement, and the earth pressure reduction rate of a test sample lower surface. It is a graph which illustrates the earth pressure reduction effect of the buffer layer (model B) by a shaking table experiment. It is a graph which illustrates the earth pressure reduction effect of the buffer layer (model C) by a shaking table experiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Structure 2 Mound 3 Backfill ground 4 Backfill soil 4a Backfill stone 5 Mixed material
5a Rubber chip 5b Crushed stone 6 Buffer layer
6a Gravel mat 7 Container 8 Pressure receiving plate 9 Earth pressure measuring device 10 Mold 11 Earth pressure meter 12 Loading plate 13 Load meter 14 Weight 15 Pole 16 Control device 17 Drop device

Claims (11)

  A seismic reinforcement method for backfill ground created on the back side of a structure, wherein a mixed material in which rubber chips and crushed stones having substantially the same particle size are mixed is disposed along at least a part of the back side of the structure in the vertical direction. Seismic reinforcement method for backfill ground that is placed to form a buffer layer.   The seismic reinforcement method for a backfill ground according to claim 1, wherein the mixed material is arranged so as to be continuous from the lower end portion to the upper end portion of the structure along the back surface of the structure.   The seismic reinforcement method for a backfill ground according to claim 1 or 2, wherein a pressure receiving plate is disposed along the back surface of the buffer layer.   The said mixed material is previously accommodated in the bag-shaped accommodating body which has several water permeability, The said accommodating body was accommodated, and the said buffer layer is formed in any one of Claims 1-3. Seismic reinforcement method for backfill ground.   The seismic reinforcement method for a backfill ground according to any one of claims 1 to 4, wherein the back surface of the buffer layer is inclined so that the layer thickness of the buffer layer becomes larger on the lower side.   A seismic reinforcement structure for backfill ground created on the back surface of a structure, comprising a mixture of rubber chips and crushed stone having substantially the same particle size along at least a part of the back surface of the structure in the vertical direction Seismic reinforcement structure for backfill ground with a buffer layer.   The seismic reinforcement structure for a backfill ground according to claim 6, wherein the buffer layer is provided so as to be continuous from the lower end portion to the upper end portion of the back surface of the structure.   The seismic reinforcement structure for backfilled ground according to claim 6 or 7, wherein a pressure receiving plate is provided along the back surface of the buffer layer.   The seismic reinforcement structure for a backfill ground according to any one of claims 6 to 8, wherein the buffer layer is formed by stacking a plurality of bag-like containers having water permeability that contain the mixed material.   The seismic reinforcement structure for a backfill ground according to any one of claims 6 to 9, wherein the back surface of the buffer layer is inclined so that the thickness of the buffer layer becomes larger on the lower side.   The seismic reinforcement structure for backfilled ground according to any one of claims 6 to 10, wherein the rubber chips and crushed stone have a particle size of 2 mm or more and 60 mm or less.

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