Ground stiffness evaluation method and ground stiffness evaluation device

Abstract

To provide a ground stiffness evaluation method and a ground stiffness evaluation device which can easily evaluate stiffness of the ground.SOLUTION: A ground stiffness evaluation method in which the ground has a backfilled portion obtained by pulling out existing piles and backfilling with a backfill material comprises steps of: setting an evaluation target range in the ground S1; obtaining a ratio of a horizontal area of the backfilled portion to a horizontal area of the evaluation target range and setting this ratio as a backfilling rate S2; setting a stiffness of the backfilled portion S3; and obtaining an equivalent stiffness of the ground in the evaluation target range by applying the set backfilling ratio and stiffness of the backfilled portion to the relation between the backfilling ratio, stiffness of the backfilled portion, and the equivalent stiffness of the ground in the evaluation target range determined in advance by numerical analysis using a homogenization method S4.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and device for evaluating the stiffness of ground, for example, ground in which existing piles have been pulled out and backfilled. [Background technology]

[0002] Conventionally, when constructing a new structure on the ground, the existing piles of the old building buried in the ground are pulled out and backfilled (see, for example, Patent Document 1). All existing piles are pulled out unless they are considered useful. The principle is that the area where the existing piles are pulled out and backfilled should have a rigidity equivalent to that of the original ground so that the design of the horizontal resistance of the new piles and construction such as excavation are not hindered. However, in reality, it is difficult to completely reproduce the rigidity of the original ground in the backfilled area, and there are cases where the backfill material cannot be sufficiently filled in the space where the existing piles were pulled out due to the collapse of the hole wall, and conversely, there are cases where the backfilled area becomes harder than the original ground. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-76648 A Summary of the Invention [Problem to be solved by the invention]

[0004] It is possible to investigate the condition of each backfilled area by taking boring core samples, etc. However, there is a problem in that a method for evaluating the rigidity of the entire affected area that takes into account the investigation results has not yet been established. In addition, while it is possible to precisely reproduce the backfilled areas using the finite element method, etc., there is a problem in that it is not practical due to the enormous amount of work required to create the finite element mesh. For this reason, a simple method for evaluating the rigidity of the ground was required.

[0005] The present invention has been made in consideration of the above, and has an object to provide a method and device for evaluating ground stiffness that can easily evaluate the stiffness of the ground. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the method for evaluating ground stiffness according to the present invention is a method for evaluating the stiffness of ground having a backfilled section obtained by pulling out existing piles and backfilling with backfill material, and is characterized by having the steps of: setting an evaluation range in the ground; determining a ratio of the horizontal area of ​​the backfilled section to the horizontal area of ​​the evaluation range and setting this ratio as a backfilling rate; setting the stiffness of the backfilled section; and applying the set backfilling rate and the stiffness of the backfilled section to a relationship between the backfilling rate, the stiffness of the backfilled section, and the equivalent stiffness of the ground in the evaluation range that has been previously determined by numerical analysis using a homogenization method, to determine the equivalent stiffness of the ground in the evaluation range.

[0007] In addition, the ground stiffness evaluation device of the present invention is a device for evaluating the stiffness of ground having a backfilled section obtained by pulling out existing piles and backfilling with backfilling material, and is characterized in having: a means for setting an evaluation range in the ground; a means for determining the ratio of the horizontal area of ​​the backfilled section to the horizontal area of ​​the evaluation range and setting this ratio as a backfilling rate; a means for setting the stiffness of the backfilled section; and a means for calculating the equivalent stiffness of the ground in the evaluation range by applying the set backfilling rate and the stiffness of the backfilled section to the relationship between the backfilling rate, the stiffness of the backfilled section, and the equivalent stiffness of the ground in the evaluation range that has been determined in advance by numerical analysis using a homogenization method. Effect of the Invention

[0008] According to the ground stiffness evaluation method of the present invention, there is provided a method for evaluating the stiffness of ground having a backfilled section obtained by pulling out existing piles and backfilling with backfill material, the method comprising the steps of: setting an evaluation range in the ground; determining the ratio of the horizontal area of ​​the backfilled section to the horizontal area of ​​the evaluation range and setting this ratio as a backfilling rate; setting the stiffness of the backfilled section; and applying the set backfilling rate and stiffness of the backfilled section to the relationship between the backfilling rate, stiffness of the backfilled section, and equivalent stiffness of the ground in the evaluation range that has been determined in advance by numerical analysis using a homogenization method, thereby determining the equivalent stiffness of the ground in the evaluation range. Thus, the stiffness of the ground can be easily evaluated.

[0009] In addition, according to the ground stiffness evaluation device of the present invention, there is provided a device for evaluating the stiffness of ground having a backfilled section obtained by pulling out existing piles and backfilling with backfill material, and the device includes a means for setting an evaluation range in the ground, a means for determining the ratio of the horizontal area of ​​the backfilled section to the horizontal area of ​​the evaluation range and setting this ratio as a backfilling rate, a means for setting the stiffness of the backfilled section, and a means for calculating the equivalent stiffness of the ground in the evaluation range by applying the set backfilling rate and the stiffness of the backfilled section to the relationship between the backfilling rate, the stiffness of the backfilled section, and the equivalent stiffness of the ground in the evaluation range that has been determined in advance by numerical analysis using a homogenization method, thereby achieving the effect of being able to easily evaluate the stiffness of the ground. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic flow diagram showing an embodiment of a method and device for evaluating stiffness of ground according to the present invention. [Diagram 2] FIG. 2 is a schematic plan view showing an example of ground having a backfilled portion. [Diagram 3] FIG. 3 is a perspective view showing an example of a periodic structure model of the original ground and the backfilled part. [Figure 4]Figure 4 is a chart showing an example of the relationship between the backfilling rate, the stiffness of the backfilled section, and the equivalent stiffness, where (a) is the shear stiffness (XZ direction), (b) is the stiffness in the vertical direction (Z direction), and (c) is the stiffness in the horizontal direction (X direction). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of a method and apparatus for evaluating stiffness of ground according to the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to these preferred embodiments.

[0012] (Method of evaluating ground stiffness) As shown in Fig. 1, the method for evaluating ground stiffness according to the embodiment of the present invention is a method for evaluating the stiffness of ground having a backfilled area where existing piles have been pulled out and backfilled with backfilling material, and includes step S1 for setting an evaluation target range in the ground, step S2 for setting a backfilling rate R, step S3 for setting the stiffness of the backfilled area, and step S4 for calculating the equivalent stiffness of the ground. The processing contents of each of steps S1 to S4 will be specifically described below.

[0013] First, in step S1, the evaluation range for evaluating the ground rigidity is set. For example, assuming the positional relationship between the existing pile 1 and the new pile 2 as shown in Figure 2, the part of the existing pile 1 is the backfilled part that is pulled out of the original ground and backfilled with backfill material. In such ground, a predetermined influence range is set as the evaluation range. Then, the number of existing piles 1 to be pulled out and backfilled within the set influence range is extracted. For example, if the rigidity of the ground is to be evaluated to calculate the horizontal resistance of four new piles within the influence range A in the figure, the number of existing piles 1 within this influence range A is extracted. Also, if the rigidity of the ground is to be evaluated to calculate the passive resistance of the retaining wall at the left end of the figure, the number of existing piles 1 within the influence range B is extracted.

[0014] In the next step S2, the ratio of the horizontal area of ​​the backfilled part to the horizontal area of ​​the evaluation range is calculated, and this ratio is set as the backfilling rate R. The horizontal area of ​​the backfilled part is equal to the horizontal area of ​​the extracted existing piles. If the existing piles have the same dimensions and shape, the horizontal area of ​​the backfilled part can be calculated by multiplying the horizontal area of ​​each existing pile by the number of piles extracted.

[0015] In the next step S3, the stiffness of the backfilled portion is set. This stiffness can be appropriately set depending on the backfilling material, construction conditions, etc. The results of an investigation of boring core samples of the backfilled portion may be used.

[0016] In the next step S4, the equivalent stiffness of the ground is calculated. Specifically, the equivalent shear stiffness, horizontal stiffness, and vertical stiffness of the composite ground consisting of the original ground and the backfilled part are calculated by a well-known mathematical homogenization method. An example of calculating the equivalent stiffness using the mathematical homogenization method is described below.

[0017] First, the extracted existing piles are aggregated and modeled as a "periodic structure with the backfilled part at the center and the original ground around it" as shown in Figure 3. The example in the figure shows a rectangular parallelepiped micro-periodic structure model made of finite element mesh, where the backfilled part is modeled by minute elements of an approximately cylindrical part extending downward with the center of the upper surface as the column axis, and the original ground is modeled by minute elements around the backfilled part.

[0018] The elastic modulus of an equivalent homogeneous body can be calculated by numerical analysis based on the following equations (1) to (3).

[0019]

number

[0020] Here, C is the elastic matrix of the micro-periodic structure (in this case, the unit periodic structure of the backfilled area and the original ground), and X is the response displacement when unit macro-strain I is applied to the micro-periodic structure. In the three-dimensional case, it consists of six components as shown in equation (2).

[0021]

number

[0022] If the inverse matrix of equation (1) is expressed as specific components, it becomes equation (3).

[0023]

number

[0024] Here, E x H , E y H , E z H are the homogenized elastic moduli in the x, y, and z directions. G xy H , G yz H , G xz H are the homogenized shear moduli in the xy, yz, and xz directions. μ is the rigidity modulus, and the subscripts xy etc. denote directions.

[0025] By solving equation (3) by numerical analysis such as the finite element method, a chart like that shown in Figure 4 can be obtained. This chart shows the relationship between the backfilling rate R, the stiffness of the backfilled part, and the equivalent stiffness of the composite ground in the evaluation range (shear stiffness (XZ direction), stiffness in the vertical direction (Z direction), and stiffness in the horizontal direction (X direction)). Here, Gs and Es are the stiffness of the original ground, and Gp and Ep are the stiffness of the backfilled part. Geq, Ev_eq, and Eh_eq are the equivalent stiffness of the composite ground in the evaluation range, respectively. By making a chart like Figure 4 in advance, it is possible to easily obtain the equivalent stiffness of the composite ground according to the backfilling rate R and the stiffness of the backfilled part. When the vertical axis is normalized by the stiffness of the original ground as in Figure 4, if the stiffness of the backfilled part is larger than that of the original ground, the equivalent stiffness will be larger than 1, but if it is smaller, it will be smaller than 1. In addition, since this homogeneous body is evaluated as an orthogonal anisotropic body, the elastic modulus differs depending on the shear direction and the vertical and horizontal directions.

[0026] The equivalent stiffness of the composite ground within the evaluation range is calculated by applying the backfilling rate R and stiffness of the backfilled area set in steps S2 and S3 to a chart like that shown in Figure 4. The calculated equivalent stiffness is evaluated as the stiffness of the ground within the evaluation range. The calculated equivalent stiffness can be used in the design of new structures (in the case of pile foundations: calculation of the horizontal resistance of new piles and earthquake response analysis, in the case of spread foundations: calculation of settlement and earthquake response analysis), calculation of passive embedment resistance when the new structure has an underground, and as the stiffness of the earth retaining wall embedment ground during structure construction (underground excavation) (steps S5 to S7).

[0027] According to this embodiment, since the equivalent stiffness obtained by the homogenization method is used to evaluate the stiffness of the ground, the stiffness of the ground including the backfilled portion can be easily evaluated. Also, by reflecting the effect of the loosening of the ground caused by pulling out the existing piles and backfilling in the design of the earth retaining wall, it is possible to prevent the excessive deformation of the earth retaining wall during excavation.

[0028] (Ground stiffness evaluation device) Next, an embodiment of the ground stiffness evaluation device according to the present invention will be described. The ground stiffness evaluation device of this embodiment is a device for evaluating the stiffness of ground having a backfilled area obtained by pulling out existing piles and backfilling with backfill material, and has a first means for setting an evaluation range in the ground, a second means for determining the ratio of the horizontal area of ​​the backfilled area to the horizontal area of ​​the evaluation range and setting this ratio as the backfilling rate, a third means for setting the stiffness of the backfilled area, and a fourth means for determining the equivalent stiffness of the ground.

[0029] The detailed processing contents of the first means, second means, third means, and fourth means are the same as the processing contents of steps S1 to S4 above, so the explanation will be omitted. The first means, second means, third means, and fourth means can be configured using, for example, a computer device capable of arithmetic processing, a database in which the positional relationship between the existing piles, the new piles, and the original ground, the rigidity of the backfilled part, etc. are stored, and the like.

[0030] According to this embodiment, since the equivalent stiffness obtained by the homogenization method is used to evaluate the stiffness of the ground, the stiffness of the ground including the backfilled portion can be easily evaluated. Also, by reflecting the effect of the loosening of the ground caused by pulling out the existing piles and backfilling in the design of the earth retaining wall, it is possible to prevent the excessive deformation of the earth retaining wall during excavation.

[0031] As described above, according to the ground stiffness evaluation method of the present invention, there is provided a method for evaluating the stiffness of ground having a backfilled section obtained by pulling out existing piles and backfilling with backfill material, the method comprising the steps of: setting an evaluation range in the ground; determining the ratio of the horizontal area of ​​the backfilled section to the horizontal area of ​​the evaluation range and setting this ratio as a backfilling rate; setting the stiffness of the backfilled section; and applying the set backfilling rate and the stiffness of the backfilled section to the relationship between the backfilling rate, the stiffness of the backfilled section, and the equivalent stiffness of the ground in the evaluation range that has been determined in advance by numerical analysis using a homogenization method, to determine the equivalent stiffness of the ground in the evaluation range, thereby enabling the stiffness of the ground to be easily evaluated.

[0032] In addition, according to the ground stiffness evaluation device of the present invention, there is provided a device for evaluating the stiffness of ground having a backfilled section obtained by pulling out existing piles and backfilling with backfill material, and the device includes a means for setting an evaluation range in the ground, a means for determining the ratio of the horizontal area of ​​the backfilled section to the horizontal area of ​​the evaluation range and setting this ratio as a backfilling rate, a means for setting the stiffness of the backfilled section, and a means for calculating the equivalent stiffness of the ground in the evaluation range by applying the set backfilling rate and the stiffness of the backfilled section to the relationship between the backfilling rate, the stiffness of the backfilled section, and the equivalent stiffness of the ground in the evaluation range that has been determined in advance by numerical analysis using a homogenization method, thereby enabling the stiffness of the ground to be easily evaluated.

[0033] The "Sustainable Development Goals (SDGs)" are 17 international goals that were adopted at the United Nations Summit in September 2015. The ground stiffness evaluation method and stiffness evaluation device according to the present embodiment can contribute to the achievement of, for example, "11. Sustainable cities and towns" among the 17 SDGs. [Industrial Applicability]

[0034] INDUSTRIAL APPLICABILITY As described above, the method and device for evaluating ground stiffness according to the present invention are useful for evaluating ground where existing piles have been pulled out and backfilled, and are particularly suitable for easily evaluating the stiffness of ground. [Explanation of symbols]

[0035] 1 Existing piles 2 New piles A,B Scope of impact (scope of evaluation)

Claims

1. A method for evaluating the rigidity of ground having a backfilled portion in which an existing pile is pulled out and backfilled with backfill material, comprising: Setting an evaluation range in the ground; A step of determining a ratio of a horizontal area of ​​the backfilled portion to a horizontal area of ​​the evaluation target range, and setting this ratio as a backfilling rate; Setting the stiffness of the backfilled portion; a step of calculating an equivalent stiffness of the ground in the evaluation range by applying the set backfilling rate and stiffness of the backfilling portion to the relationship between the backfilling rate, stiffness of the backfilling portion, and equivalent stiffness of the ground in the evaluation range that has been previously calculated by numerical analysis using a homogenization method.

2. An apparatus for evaluating the rigidity of ground having a backfilled portion in which an existing pile is pulled out and backfilled with backfill material, A means for setting an evaluation target range in the ground; A means for calculating a ratio of a horizontal area of ​​the backfilled portion to a horizontal area of ​​the evaluation target range and setting this ratio as a backfilling rate; A means for setting the stiffness of the backfilled portion; and a means for calculating the equivalent stiffness of the ground in the evaluation range by applying the set backfilling rate and stiffness of the backfilling portion to the relationship between the backfilling rate, stiffness of the backfilling portion, and equivalent stiffness of the ground in the evaluation range that has been previously determined by numerical analysis using a homogenization method.

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