Design method of improved earth retention wall with embedded core

Abstract

To provide a design method of an improved earth retention wall with embedded cores capable of reducing a construction cost of an earth retention wall much more than conventional ones while securing the safety in accordance with "earth retention design guide line" of Architectural Institution of Japan.SOLUTION: A design method of an improved earth retention wall with embedded cores is the design method to form a composite wall 10 self-supporting vertically and retaining the earth which is made by installing a plurality of cores 12 vertically buried inside of an improvement body 14. The method has a rigidity analysis step T2 using a beam / spring model or a simple beam model. The rigidity analysis step T2 has a composite wall rigidity calculation step T2a and a composite wall analysis step T2b. At the composite wall rigidity calculation step T2a, composite wall bending rigidity E12I12 of a composite wall is calculated in an applicable range of the composite wall using core bending rigidity E1I1 of the core and improvement body bending rigidity E2I2 of a soil improvement body. At the composite wall analysis step T2b, displacement of the composite wall (for example, the maximum horizontal displacement) and the maximum bending moment are calculated using the composite wall bending rigidity.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for designing an improved earth retaining wall with core materials, in which a composite wall, which is a vertically self-supporting earth retaining wall, is composed of a ground improvement body and a plurality of core materials buried vertically inside the body. [Background technology]

[0002] "Retaining wall" means a structure installed to prevent the collapse of the surrounding ground during excavation. The "improved earth retaining method" is a construction method in which a ground improvement body is created using a deep mixing treatment method and a retaining wall is constructed. The "core-improved earth retaining wall construction method" is a retaining wall construction method in which a ground improvement body is created using a deep mixing treatment method and then core material is quickly installed. As an improved earth retaining method using core material, for example, the TRD method has been known.

[0003] The SMW method involves mixing and stirring cement milk in situ with the soil in a drilled hole, and then gradually overlapping the columns to construct a pile retaining wall. The SMW method is disclosed in, for example, Non-Patent Document 1.

[0004] The TRD method is a construction method that continuously constructs underground continuous walls by pressing a circulating endless cutter bit chain against the ground and moving it horizontally while injecting grout into the ground from a nozzle. The TRD method is disclosed in, for example, Patent Document 1 and Non-Patent Document 2.

[0005] Furthermore, the earth retaining wall design in the SMW construction method has traditionally been based on the "Earth Retaining Wall Design Guidelines" (Architectural Institute of Japan) in Non-Patent Document 3. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] "What is the SMW Method?", April 25, 2024, Internet <URL:http: / / www.smw-kyokai.jp / about / index.html) [Non-patent document 2] "TRD Method Overview," April 25, 2024, Internet <URL:https: / / www.trd.gr.jp / pages / 19 / ) [Non-patent document 3] “Yamadame Design Guidelines”, Architectural Institute of Japan, April 10, 2023, 4th edition [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-309919 Summary of the Invention [Problem to be solved by the invention]

[0008] The Architectural Institute of Japan's "Guidelines for Earth Retaining Wall Design" recommends the following methods for calculating "stress and deformation of earth retaining walls": (1) beam-spring model, (2) free-standing earth retaining beam-spring model, (3) simple beam model, and (4) finite element method. In addition, (1), (3) and (4) are particularly recommended when the root cutting depth (excavation depth) is in the range of approximately 4 to 15 m. Therefore, in conventional earth retaining wall design, simple beam models and finite element methods are mainly used.

[0009] The finite element method (FEM analysis) provides the most accurate calculation of "stress and deformation of earth retaining walls" as long as the calculation model and calculation conditions are appropriate. However, calculations using the finite element method require advanced simulation technology, which is a high hurdle for non-experts, and there are problems with the time and expense required for analysis. On the other hand, the calculation accuracy of the simple beam model is lower than that of the finite element method. However, because it does not require advanced simulation technology, it is widely used in the conventional earth retaining design, which is frequently carried out.

[0010] In addition, the ground improvement material (soil cement) used in the SMW and TRD methods is a mixture of in-situ soil and cement, and its tensile strength is very low compared to its compressive strength and shear strength. Therefore, in conventional retaining wall design, whether using the simple beam model or the finite element method, the bending rigidity of the improved body was set to 0, and only the bending rigidity of the core material (steel) was used. As a result, the calculated displacement of the earth retaining wall was greater than the actual construction cost, which resulted in the cost of constructing the earth retaining wall being higher than necessary.

[0011] The present invention was devised to solve the above-mentioned problems. That is, the object of the present invention is to provide a design method for an improved earth retaining wall with core material, which is in accordance with the "Earth Retaining Wall Design Guidelines" of the Architectural Institute of Japan, and which can reduce the construction costs of earth retaining walls compared to conventional methods while ensuring safety. [Means for solving the problem]

[0012] According to the present invention, a composite wall, which is a vertically self-supporting earth retaining wall, is a design method for a core-containing improved earth retaining wall, which is composed of a ground improvement body and a plurality of core materials buried vertically inside the ground improvement body, It has a stiffness analysis step using a beam-spring model or a simple beam model, The stiffness analysis step includes: A composite wall stiffness calculation step of calculating the composite wall stiffness of the composite wall from the core material stiffness of the core material and the improvement body stiffness of the ground improvement body within the applicable range of the composite wall; A composite wall analysis step is provided in which the displacement and maximum bending moment of the composite wall are calculated using the composite wall bending stiffness. [Effects of the Invention]

[0013] According to the above-described configuration of the present invention, in the composite wall stiffness calculation step, the core material and core material pitch are set within the applicable range of the composite wall, and the composite wall flexural rigidity of the composite wall is calculated from the core material flexural rigidity and the improved body flexural rigidity. Also, in the composite wall analysis step, the calculated composite wall flexural rigidity is used to calculate the displacement (e.g., maximum horizontal displacement) and maximum bending moment of the composite wall. Furthermore, in the design of the retaining wall, it is determined whether the calculated displacement and maximum bending moment of the composite wall are within the appropriate range.

[0014] Therefore, according to the configuration of the present invention, it is possible to set the core material and core material pitch so that the displacement and maximum bending moment of the composite wall are within the appropriate range while ensuring safety in accordance with the "Earth Retaining Wall Design Guidelines" of the Architectural Institute of Japan. This makes it possible to use smaller core materials or wider core material pitches than before, thereby reducing the construction costs of the earth retaining wall. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is an image of an improved earth retaining wall with a core material that is the subject of this invention. [Figure 2] FIG. 1 is an overall flow diagram of an improved earth retaining wall construction method using core material to which the present invention is applied. [Figure 3] This is an overall flow diagram of the design method for an improved earth retaining wall with core material of the present invention. [Figure 4] FIG. 10 is a diagram showing ground conditions of the design model. [Figure 5] This is an outline diagram of the retaining wall. [Figure 6] Schematic diagram of (a) load, (b) displacement, and (c) bending moment in a simple beam model. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In addition, common parts in the drawings are given the same reference numerals, and duplicated explanations will be omitted.

[0017] FIG. 1 is an image diagram of an improved earth retaining wall with core material to which the present invention is applied. Hereinafter, the "improved earth retaining wall with core material" to which the present invention is directed will be referred to simply as the "synthetic wall 10" unless otherwise necessary.

[0018] The composite wall 10 is a vertically self-supporting retaining wall, and is composed of a soil improvement body 14 and a plurality of core materials 12 buried vertically inside the soil improvement body 14. Hereinafter, the ground improvement body 14 will be simply referred to as "improvement body 14" unless necessary. The width B of the improved body in the thickness direction (y direction in the drawing) perpendicular to the composite wall 10 (hereinafter referred to as "improved body width B") is preferably constant.

[0019] The core material 12 is, for example, steel, preferably H-beam. The multiple core materials 12 are positioned vertically at a predetermined pitch P (hereinafter referred to as "core material pitch P") in the horizontal direction (x direction in the figure) along the wall surface of the composite wall 10. The core material pitch P is the distance between the horizontal axes of adjacent core materials 12. The improved body 14 is formed by injecting, for example, a slurry-like solidification material or improvement material, while stirring and mixing the solidification material and the in-situ soil. Hereinafter, the total length L of the improvement body 14 in the vertical direction (z direction in the figure) will be referred to as the "total length of the improvement body", and the depth D in the z direction from the ground surface GL to the excavation bed 16 will be referred to as the "excavation depth D" or "root cutting depth".

[0020] FIG. 2 is an overall flow diagram of the improved earth retaining method with core material (hereinafter referred to as "this method") to which the present invention is applied. In this diagram, this construction method consists of a preliminary excavation process S1, an improved retaining wall process S2, and a core material installation process S3. In the preliminary excavation step S1, preliminary excavation (depth 1.0 m to 1.5 m) is carried out in advance to reduce the amount of sludge to be transported. In the improved earth retaining wall process S2, an improved body 14 is constructed in the same manner as a normal improved earth retaining wall without a core material 12. In the core material installation process S3, a small vibrating hammer is attached, and while checking the position and installation accuracy, the core material 12 is inserted vertically into the improved body 14. The level of the top end (upper end surface) of the core material 12 is checked and adjusted, and the core material installation is completed.

[0021] The above-mentioned method has the following features: 1. It is water-proof and has performance equal to or better than the SMW method (soil cement column wall method). 2. The core pitch P can be set arbitrarily. 3. Compared to the SMW method, cost reduction effects can be expected. 4. Because it is a small machine, the noise and vibration of the improved machine are reduced compared to large three-point machines. 5. Because the slurry is injected at low pressure and stirred vertically, there is little change to the surrounding ground or impact on groundwater, etc.

[0022] In conventional earth retaining wall calculations (SMW method), only the core material 12 (e.g., steel) is considered as a rigid member that resists bending deformation, and the soil cement portion is used as a member that receives soil and water pressure, like a sheet pile. Hereafter, the method based on the rigidity of "only the core material 12" will be referred to as the "conventional method." On the other hand, in the present invention, the improved body 14 is considered as a rigid member that resists bending deformation like a steel member, and the cross-sectional performance of the "core-containing improved earth retaining wall" (composite wall 10) is calculated as a composite wall 10 that combines the core material 12 (steel material) and the improved body 14. Hereinafter, this method will be referred to as the "method of the present invention" or simply "the present invention."

[0023] FIG. 3 is an overall flow diagram of the method for designing an improved earth retaining wall with core material of the present invention ("the method of the present invention"). In the method of the present invention, as shown in FIG. 1, a composite wall 10, which is a vertically self-supporting retaining wall, is made up of an improvement body 14 and a plurality of core members 12 embedded vertically inside the improvement body 14. The width B of the improved body in the thickness direction (y direction in the drawing) perpendicular to the composite wall 10 is preferably constant.

[0024] The method of the present invention includes an FEM analysis step T1 using the finite element method, and a stiffness analysis step T2 using a beam-spring model or a simple beam model.

[0025] In FIG. 3, the FEM analysis step T1 includes an allowable stress setting step T1a, an analytical stress calculation step T1b, and an application range setting step T1c. In the allowable stress setting step T1a, the allowable compressive stress q of the improved body 14 is ca , allowable tensile stress q ta , and allowable shear stress q sa Set. In the analytical stress calculation step T1b, the compressive stress, tensile stress, and shear stress occurring in the improved body 14 are calculated using the finite element method based on the predetermined analytical model, physical property conditions, and load conditions. In the application range setting step T1c, the application range of the composite wall 10 is set based on the calculation results in the analytical stress intensity calculation step T1b.

[0026] In the method of the present invention, the FEM analysis step T1 using the finite element method is used to set the applicable range of the composite wall 10, and in a similar range, only the stiffness analysis step T2 is performed. In other words, in the range of applicability of the composite wall 10, the FEM analysis step T1 can be omitted in the frequently performed earth retaining design. This significantly reduces the need for advanced simulation techniques.

[0027] As a result of carrying out the above-mentioned FEM analysis step T1, the following results were obtained from the analytical model example described below. 1. Comparison of displacement between conventional method and FEM analysis The maximum displacement is calculated when the core pitch P is 1 m and the ground improvement strength q u is 1000kN / m 2 In this case, the displacement amount in the FEM analysis of the composite wall 10, which takes into account the rigidity of the improved body 14, was 36.9 mm using the conventional method and 31.1 mm using the FEM analysis, and it was confirmed that the displacement amount in the FEM analysis of the composite wall 10, which takes into account the rigidity of the improved body 14, is smaller than that in the conventional method, which takes into account the rigidity of only the core material. The amount of displacement obtained by FEM analysis is approximately 84.3% of that obtained by the conventional method. Note that the amount of displacement refers to the amount of horizontal displacement. 2. Strength of ground improvement body q u and core pitch P After comparing the principal stress (compression, tension, shear) with the allowable stress (compression, tension, shear), the strength of the improved body 14 was 1000kN / m 2 The maximum stress was found to be less than the allowable stress by FEM analysis. The FEM analysis step T1 will be described in detail later. Below is the ground improvement body strength q u Unless necessary, "improved body strength q u " is called.

[0028] In FIG. 3, the stiffness analysis step T2 includes a composite wall stiffness calculation step T2a and a composite wall analysis step T2b. In the composite wall stiffness calculation step T2a, the bending stiffness of the composite wall 10 ("composite wall bending stiffness E") is calculated from the bending stiffness of the core material 12 ("core material bending stiffness E1I1") and the bending stiffness of the improved body 14 ("improved body bending stiffness E2I2") within the applicable range of the composite wall 10. 12 I 12 ") is calculated. In the composite wall analysis step T2b, the composite wall bending stiffness E 12 I 12 The displacement and maximum bending moment of the composite wall 10 are calculated using the formula:

[0029] The stiffness analysis step T2 will be described in detail later. In the examples described later, the displacement y at the point of action is calculated using a simple beam model. a , inclination angle θ at the point of application a , maximum bending moment M max , maximum shear force Q ma x, displacement y0 at the head of the earth retaining wall, and displacement y at the bottom of the excavation g We are looking for...

[0030] In addition, a beam-spring model may be used in the stiffness analysis step T2. In this case, the basic equation for the beam-spring model shown in Equation 1 is used, and as a calculation method, for example, the entire length of the earth retaining wall is divided equally or unequal in the depth direction, and a solution to a multi-variable simultaneous equation is found so that the basic equation is satisfied at each division point. This makes it possible to calculate the horizontal displacement of each part of the earth retaining wall.

[0031]

number

[0032] As a result of carrying out the above-mentioned stiffness analysis step T2, the following results were obtained from the examples described below. Table 1 shows the bending rigidity of the core material only, the ground improvement body only, and the composite wall 10. Table 2 shows the displacement (horizontal displacement) of the core material only and the composite wall 10.

[0033] [Table 1]

[0034] [Table 2]

[0035] Core pitch P is 1m, and ground improvement strength q u is 1000kN / m 2 In this case, the displacement amount of the conventional method using only the core material is 36.9 mm in the FEM analysis, whereas it is 31.5 mm in the rigidity analysis step T2, and the two are different from each other. This is because the calculation conditions for the two are different. Therefore, in the present invention, the difference between the FEM analysis and the stiffness analysis step T2 is determined based on the ratio to the displacement of the core material alone under the same conditions.

[0036] From Tables 1 and 2, the bending stiffness of the composite wall 10 (composite wall bending stiffness E 12 I 12 ) as a result of retaining the earth, the displacement in the present invention is approximately 88% of that in the case of only the core material 12 (conventional method). That is, when the core pitch P is 1 m, the ratio of the displacement amount obtained by the "conventional method" based on the rigidity of "only the core material 12", the method of the present invention, and the FEM analysis is as shown in Table 3. The same applies when the core pitch P is different.

[0037] [Table 3]

[0038] As mentioned above, the stress and deformation of retaining walls can be calculated most accurately using the finite element method (FEM analysis) as long as the calculation model and calculation conditions are appropriate, but this requires advanced simulation technology. On the other hand, although the calculation accuracy using the simple beam model is lower than that using the finite element method, it does not require advanced simulation technology.

[0039] According to the present invention, the applicable range of the composite wall 10 is set in advance by FEM analysis, so safety can be ensured. Furthermore, from Table 3, it can be seen that the displacement amount according to the present invention is larger than that of FEM analysis, which has high calculation accuracy, but smaller than that of the conventional method, so that it is possible to obtain displacement results that are closer to FEM analysis and are on the safer side than the conventional method without requiring advanced simulation technology. As a result, the design displacement can be reduced by approximately 12% compared to conventional methods while still ensuring safety.

[0040] In the on-site inspection described below, the strength of the improved structure was set at 1000kN / m, which is sufficient for normal earth retaining calculations, taking safety into consideration. 2 The core pitch was verified to be 0.9m.

[0041] Examples of the present invention will be described below. [Example]

[0042] (FEM analysis step T1) FIG. 1 mentioned above is an image diagram of the composite wall 10. Assuming that the site will be excavated when constructing a building such as an apartment building, a composite wall 10 consisting of a core material and a ground improvement body is used as a retaining wall at a relatively shallow excavation depth (improvement body depth: 13 m). In addition, in this analysis, static earth pressure was applied as an external force equivalent to excavation.

[0043] Table 4 shows the cases under consideration. The ground conditions and excavation conditions are the same for all cases, and the width of the improved body (improvement body width B), the depth of the improved body (improvement body total length L), and the cross-sectional dimensions per core material are all the same.

[0044] [Table 4]

[0045] FIG. 4 is a diagram showing the ground conditions of the design model. The ground to be analyzed is composed of alternating layers of clayey soil and sandy soil, and the static earth pressure is calculated using a surcharge load of 10 kN / m 2 was taken into consideration.

[0046] Table 5 shows the soil properties used in the analysis. The core material (H-shaped steel) used in the composite wall 10 was modeled using beam elements, and the steel type used was SS400, H-500×200×10×16.

[0047] [Table 5]

[0048] Table 6 shows the improved soil properties used in the analysis. The deformation coefficient E0 of the improved soil used in the composite wall 10 is set based on the design strength, and E0 = 200q u q u is the improved body strength. The improved soil (improved body 14) is treated as equivalent to concrete, and the unit weight is 24.0 kN / m 3 , and Poisson's ratio was set to 0.20.

[0049] [Table 6]

[0050] (loading conditions) Before excavation, the static earth pressure and hydrostatic pressure acting at each position on the excavation surface were calculated, and the acting load was calculated taking into account the area of ​​control of the nodes.

[0051] (allowable stress) Equations (1), (2), and (3) are formulas for setting the allowable stress values ​​(compression, tension, and shear) of the improved body 14. The allowable tensile stress was set on the safe side, with reference to the formula in the "Guidelines for Design and Quality Control of Improved Ground for Buildings" (National Institute of Land and Infrastructure Management, Building Research Institute).

[0052] Allowable compressive stress q ca =q u / 2···(1) Allowable tensile stress q ta =q u / 10.4···(2) Allowable shear stress q sa =q u / 6···(3)

[0053] (Analysis results) Table 7 lists the inspection results of the improved structure. In this table, the symbol ◯ means that the maximum stress value is less than the allowable stress value (compression, tension, shear), and the symbol × means that the maximum stress value exceeds the allowable stress value (compression, tension, shear).

[0054] [Table 7]

[0055] From Table 7, in the embedded part of the improved body deeper than the excavation bed 16, failure was observed regardless of the core pitch P in cases where the improved body strength was low. u is 500kN / m 2 In this case, it was found that it cannot be applied because both compressive stress and shear stress exceed the allowable values ​​regardless of the core pitch P. In addition, the improved body strength q u is 750kN / m 2 It was found that when the core pitch P is 1 m, the shear stress exceeds the allowable value and therefore cannot be applied.

[0056] Therefore, the improved strength q u is 1000kN / m2 In the above cases, the compressive, tensile, and shear stresses generated in the improved body 14 are all below the allowable stress, and it can be determined that the improved body 14 is applicable.

[0057] Table 8 shows the horizontal displacement of the wall surface based on the results of three-dimensional analysis.

[0058] [Table 8]

[0059] From Table 8, the core pitch P and the improved body strength q u The reason for this is that the stiffness of the improved body is much greater than the stiffness of the ground. Furthermore, there was almost no difference between the results of the two-dimensional analysis and the three-dimensional analysis, and it was confirmed that the three-dimensionality was very small within the range of the core material pitch P examined.

[0060] From the above-mentioned FEM analysis step T1, it can be determined that in the following cases, the compressive, tensile, and shear stresses generated in the improved body 14 are all below the allowable stress and are therefore applicable. Improved body strength q u is 1000kN / m 2 That's all. The improved body width B must be 1.0 m or more.

[0061] The following also became clear: The allowable stress value of the improved body 14 can be calculated using the following formula: Allowable compressive stress q ca =q u / 2···(1) Allowable tensile stress q ta =q u / 10.4···(2) Allowable shear stress q sa =q u / 6···(3)

[0062] For greater safety, it is advisable to apply the following formula: Allowable compressive stress q ca =(1 / 3~1 / 2)q u (1a) Allowable tensile stress q ta =(1 / 30~1 / 10)q u (2a) Allowable shear stress q sa =(1 / 8~1 / 6)q u (3a)

[0063] In addition, the core pitch P and improved body strength q u There is almost no difference in the horizontal displacement of the wall surface due to the impact. In addition, there is almost no difference between the results of the 2D analysis and the 3D analysis, and the 3D nature is very small within the range of the core pitch P examined. The amount of displacement in the FEM analysis was approximately 84.3% of that in the conventional method. [Example]

[0064] (Stiffness analysis step T2) The earth retaining wall design for this construction method is carried out using the calculation method for parent piles and horizontal sheet piles (taking into account the groundwater level) in the Earth Retaining Wall Design and Construction Guidelines (Architectural Institute of Japan). The bending rigidity of the composite wall 10 is calculated as the bending rigidity of the core material 12 and the ground improvement body 14 combined (composite wall bending rigidity).

[0065] (Ground improvement body specifications) Improved body strength q u The specifications for the ground improvement body shall be as follows: Improved body strength q u :1000kN / m 2 Width of improvement body: 1.1m, 1.3m (width of mixing blade), 1.3m when the improvement body and heavy machinery are installed directly Ground improvement length: 13m or less

[0066] (Bending stiffness of composite wall) Calculate per unit width of 1.0m. (1) Bending rigidity of core material (bending rigidity of core material) The core bending rigidity E1I1 shall be the value of H-shaped steel specified in JIS G3192. E1: Young's modulus 2.05 x 10 8 (kN / m 2 ) I1: Second moment of area of ​​H-shaped steel (m 4 ) (2) Bending rigidity of the improved body 14 (bending rigidity of the improved body) The improved body bending rigidity E2I2 is as follows: E2: Young's modulus 2.0×10 5 (kN / m 2 ) Improved body strength q u =1000kN / m 2 , E=200qu I2: Moment of inertia of the improved body 14 (m 4 ) I2=Wt 3 / 12=0.11092(m 4 ) W: Unit width 1.0m, B: Improved body width 1.1m (3) Bending rigidity of composite wall (bending rigidity of composite wall) Composite wall bending stiffness E 12 I 12 shall be as follows: E 12 I 12 =E1I1+E2I2

[0067] (Example of calculation of bending rigidity of composite wall) (Mount retaining design conditions) Improved body 14: Strength 1000 (kN / m 2 ), improved body width B = 1.1 (m), improved body depth = improved body total length L = 8.0 (m) Core: H500 x 200 x 10 x 16, total length of core = total length of improved body L = 8.0 (m), installation interval 1.0 (m) (bending rigidity) Core: E1 = 2.05 x 10 8 (kN / m 2 ), I1=0.000468(m 4 ) E1I1=95,940(kN m 2 ) Improved body 14:E2=2.0×10 5 (kN / m 2 ), I2=0.11092(m4 ) E2I2=22,184(kN m 2 ) Composite wall:E 12 I 12 =E1I1+E2I2=95,940(kN m 2 ) + 22,184(kN m 2 )=118,124(kN m 2 )

[0068] (Example of calculation for composite wall analysis) This paper presents an example of calculations using a simplified beam-spring model (i.e., simple beam model) that takes into account the bending rigidity of the composite wall for a parent pile horizontal sheet pile wall retaining wall with an excavation depth of 3.5 m.

[0069] (Ground conditions) The ground conditions are shown in Table 9. The groundwater level is set to GL-4.0m below the excavation surface, but this does not affect the calculations.

[0070] [Table 9]

[0071] (Setting of retaining wall) An overview of the earth retaining wall is shown in Figure 5. The specifications for the composite wall for a root cut depth of GL-3.5m are as follows: The unit width for calculations is 1.0m. Type: Composite wall (improved earth retaining wall with core material) Core material: H-300 x 300 x 10 x 15 (SS400) Installation interval: 1.2 m Improved body 14: Strength 1000kN / m 2 , improved body width B=1.1m

[0072] (Calculation of design lateral pressure) Figure 6 is a schematic diagram of (a) load, (b) displacement, and (c) bending moment in a simple beam model. The main part of the excavated ground is the silty clay layer of soil layer No. 2. The design lateral pressure is lateral pressure coefficient K = 0.5, wet unit volume weight of soil γ t =16.0kN / m 3The load is calculated assuming that it is uniform from the ground surface to the bottom of the excavation. q=10kN / m 2 Assuming that slight ground surface loads of this magnitude are included in the lateral pressure coefficient, the design lateral pressure is set as follows: GL±0 Pa=0(kN / m 2 ) GL-3.5m Pa=0.5×16.0×3.5=28.0(kN / m 2 )

[0073] The resultant force of the triangularly distributed lateral pressure set above is calculated and converted into the concentrated load Pa. Pa=(1 / 2)×28.0×3.5=49.0(kN / m) In addition, the point of action of Pa is 3.5 × (2 / 3) = 2.3, so it is at GL-2.3m. (In Figure 6, l = 2.3m, h = 1.2m) In this study, we have considered the main demographics to be uniform, but in actual research, it is necessary to consider each demographic separately.

[0074] (Setting the design constants required for calculation) (a) Bending stiffness of composite wall Composite wall bending stiffness E per unit width 1m 12 I 12 is calculated as follows: Young's modulus of core material: E1 = 2.05 x 10 8 (kN / m 2 ) Moment of inertia in the direction of the core's strong axis: I x =20,200cm 4 =2.02×10 -4 (m 4 ) Spacing between stress members: a = 1.2 (m) Core bending rigidity per unit width of 1 m: E1I1=E1I x ×1 / a=3.45×10 4 (kN m 2 ) Young's modulus of improved body 14: E2 = 2.0 x 10 5 (kN / m 2 ) Moment of inertia of improved body 14: I2 = 0.11092 (m 4 ) Improved body bending rigidity per unit width of 1 m: E2I2 = 22,184 (kN m 2 ) Composite wall:E 12 I 12 =E1I1+E2I2=3.45×10 4 (kN m 2 ) + 22,184(kN m 2 )=56,684(kN m 2 )

[0075] (b) Coefficient of horizontal subgrade reaction The dominant soil layer below the bottom of the excavation is soil layer No. 3, a fine sand layer. The average N value is 7. kh=5.0MN / m 3 (=5,000kN / m 3 ) is set as kh = 7.0MN / m 3 (=7,000kN / m 3 )

[0076] (Calculation of stress and displacement of earth retaining walls) Calculate the stress and displacement of the retaining wall in accordance with the retaining wall design guidelines. characteristic value)β={K h B / (4EI)} 1 / 4 ={5,000×1.0 / (4×56,684)} 1 / 4 =0.385(m -1 ) Displacement y at the point of application a =Pa{(1+βh) 3 +1 / 2} / (3EIβ 3 ) =49.0×{(1+0.385×1.2) 3 +1 / 2} / (3×56,684×0.385 3 ) = 0.0183 (m) = 18.3 (mm) Inclination angle θ at the point of application a =Pa(1+βh) 2 / (2EIβ 2 ) =49.0×(1+0.385×1.2) 2 / (2×56,684×β 2 )=6.22×10 -3(rad) Maximum bending moment M max =Pa{(1+2βh) 2 +1} 1 / 2 / 2βexp[-tan -1 {1 / (1+2βh)}] =49.0×{(1+2×0.385×1.2) 2 +1} 1 / 2 / (2×0.385)×exp[-tan -1 {1 / (1+2×0.385×1.2)}]=85.4(kN m / m) Maximum shear force Q max =Pa=49.0(kN / m) Displacement at the head of the retaining wall y0=y a +θal =0.0183+6.22×10 -3 ×2.3=0.0326(m)=32.6(mm) Displacement y at the bottom of the excavation g =Pa(1+βh) / (2EIβ 3 ) =49.0×(1+0.385×1.2) / (2×56,684×0.385 3 ) = 0.0110 (m) = 11.0 (mm)

[0077] (Determination of pile length) This is the condition for applying this calculation method. The length required to treat the beam as semi-infinite is calculated using the following formula. Df≧2 / β≧2 / 0.385=5.2(m) Based on the above results, Df = 5.5 m and the total length of the parent pile is set to 9.0 m. However, the embedded length requires separate consideration of the balance of forces. [Example]

[0078] (On-site inspection) A composite wall 10 using the core-inserted improved earth retaining method ("this method") to which the present invention is applied and an improved earth retaining wall using the SMW method were actually constructed and compared.

[0079] (Details of improved earth retaining wall with core material) The following were set identically for this method and the SMW method. Excavation depth D=3.5m Improved body: W=1.0m, H=9.0m, L=6.3m, strength 1000kN / m 2 Core material: H500 x 200 x 10 x 16, L=9.0m, installation interval 0.9m

[0080] (On-site inspection results) 1. Horizontal displacement of composite wall measured by inclinometer The maximum horizontal displacement caused by excavation was 12.6 mm with the SMW method, while the maximum displacement with this method was 9.5 mm, resulting in a smaller displacement with this method than with the SMW method.In addition, compared to the design displacement of 30.1 mm (core material only), the displacement was 31.5% of the design value. From the above results, the composite wall 10 of this construction method is more rigid than that of the SMW construction method, and the effectiveness of the composite wall 10 combining the core material 12 and the improved body 14 was confirmed.

[0081] 2. Strength of improved body 14 by core boring Improved body strength q u (Target strength 1000kN / m 2 In order to confirm this, a core boring uniaxial compression test was conducted. Samples were taken every 1.0 m, and the average value for each layer was 2700 to 4600 kN / m 2 The target strength is 1000kN / m 2 The above were the results. Therefore, the applicable condition of the composite wall 10 is "ground improvement body strength 1000 kN / m 2 It was confirmed that the above could be easily achieved. In addition, the strength of the ground improvement body is set to twice the target strength (2000kN / m 2 ) or more, in which case the allowable stress values ​​(compression, tension, shear) according to equations (1), (2), and (3) are doubled, further expanding the range of applicability of the composite wall 10.

[0082] As described above, in the method of the present invention, the FEM analysis step T1 using the finite element method is used to set the applicable range of the composite wall 10, and in a similar range, only the stiffness analysis step T2 is performed. That is, in the applicable range of the composite wall 10, in the frequently performed earth retaining design, the FEM analysis step T1 is usually omitted. This significantly reduces the need for advanced simulation techniques.

[0083] The earth retaining wall design according to the present invention is carried out using the calculation method of the Earth Retaining Wall Design Guidelines (Architectural Institute of Japan), taking into account the cross-sectional performance of the improved body 14. In this case, the FEM analysis results showed that the displacement was about 85% of the conventional method, which only considered the rigidity of the core material, while the method of the present invention showed that the displacement was about 88% of the conventional method. Furthermore, the results of on-site verification showed that the displacement was even smaller, about 32%.

[0084] According to the present invention, the applicable range of the composite wall 10 is set in advance by FEM analysis, so safety can be ensured. Furthermore, the displacement amount obtained by the present invention is larger than that obtained by FEM analysis, which has high calculation accuracy, but smaller than that obtained by conventional methods. Therefore, it is possible to obtain displacement results that are closer to FEM analysis and are on the safe side than conventional methods, without requiring advanced simulation technology. As a result, the design displacement can be reduced by approximately 12% compared to conventional methods while still ensuring safety.

[0085] As described above, according to the present invention, in the composite wall stiffness calculation step T2a, the core material 12 and the core material pitch P are set within the applicable range of the composite wall 10, and the composite wall stiffness E of the composite wall 10 is calculated from the core material stiffness E1I1 and the improved body stiffness E2I2. 12 I 12 In addition, in the composite wall analysis step T2b, the calculated composite wall bending stiffness E 12 I 12Using this, the displacement (for example, maximum horizontal displacement) and maximum bending moment of the composite wall 10 are calculated. Furthermore, in the design of the retaining wall, it is determined whether the calculated displacement and maximum bending moment of the composite wall 10 are within the appropriate range.

[0086] Therefore, according to the configuration of the present invention, it is possible to set the core material 12 and core material pitch P so that the displacement and maximum bending moment of the composite wall 10 are within the appropriate range while ensuring safety in accordance with the "Earth Retaining Wall Design Guidelines" of the Architectural Institute of Japan. This allows the core material 12 to be smaller or the core material pitch P to be wider than before, thereby reducing the construction cost of the earth retaining wall.

[0087] The scope of the present invention is not limited to the above-described embodiments, but is indicated by the claims, and further includes all modifications within the meaning and scope equivalent to the claims. [Explanation of symbols]

[0088] B Improved body width, D Excavation depth (root cutting depth), E1I1 Core material bending rigidity, E2I2 Improved body bending rigidity, E 12 I 12 Composite wall bending rigidity, GL ground surface, L total length of improved body, P core material pitch, S1 advance excavation process, S2 improved earth retaining wall process, S3 core material erection process, T1 FEM analysis step, T1a allowable stress setting step, T1b analytical stress calculation step, T1c application range setting step, T2 rigidity analysis step, T2a composite wall rigidity calculation step, T2b composite wall analysis step, q ca Allowable compressive stress, q ta Allowable tensile stress, q sa Allowable shear stress, q u Strength of ground improvement body (strength of improvement body), 10. Composite wall, 12. Core material, 14. Ground improvement body (improved body), 16. Excavation bed

Claims

1. A design method for a core-improved earth retaining wall, in which a composite wall, which is a vertically self-supporting earth retaining wall, is composed of a ground improvement body and a plurality of core materials embedded vertically inside the body, A stiffness analysis step using a beam-spring model or a simple beam model is included, The stiffness analysis step includes: A composite wall stiffness calculation step of calculating the composite wall stiffness of the composite wall from the core material stiffness of the core material and the improvement body stiffness of the ground improvement body within the applicable range of the composite wall; A design method for an improved earth retaining wall with core material, comprising a composite wall analysis step of calculating the displacement and maximum bending moment of the composite wall using the composite wall bending rigidity.

2. The composite wall bending stiffness is calculated using the following formula: Composite wall bending rigidity E １２ I １２ = bending rigidity of core material E １ I １ + Improved body bending rigidity E ２ I ２ A method for designing an improved earth retaining wall with core material according to claim 1.

3. The applicable range of the composite wall is Strength of ground improvement body: 1000 kN / m ２ That's all, A design method for an improved earth retaining wall with core material as described in claim 1, in which the width of the improved body is set to 1.0 m or more.

4. A FEM analysis step using a finite element method is included, The FEM analysis step includes: an allowable stress setting step of setting an allowable compressive stress, an allowable tensile stress, and an allowable shear stress of the ground improvement body; an analytical stress calculation step of calculating compressive stress, tensile stress, and shear stress generated in the ground improvement body by the finite element method based on a predetermined analytical model, physical property conditions, and loading conditions; 2. The design method for an improved earth retaining wall with core material according to claim 1, further comprising: an application range setting step of setting the applicable range of the composite wall based on the result of the calculation.

5. The allowable tensile stress is calculated using the following formula: Allowable tensile stress q ｔａ = (1 / 30~1 / 10)q ｕ , where q ｕ The design method for an improved earth retaining wall with core material according to claim 4, wherein is the strength of the ground improvement body.

6. A design method for an improved earth retaining wall with core material as described in claim 4, wherein the FEM analysis step using the finite element method is used to set the applicable range of the composite wall, and in a similar range, only the stiffness analysis step is performed.

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