JP2014136865A - Earth-retaining wall and construction method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an earth-retaining wall capable of shortening a construction term while reducing construction costs.SOLUTION: An earth-retaining wall 1 is constructed surrounding an underground structure 2. The earth-retaining wall 1 comprises: a soil improvement body 10 constructed by ground-improving a ground 3 around the underground structure 2; and steel materials 20 extending substantially in the vertical direction along a wall surface of the soil improvement body 10 on the side opposite to the underground structure 2, and embedded in a ground 3 directly under the soil improvement body 10. Bending tensile force applied to the earth-retaining wall 1 is borne by the steel materials 20. Thus, it is not necessary to enlarge the thickness of the soil improvement body as before and the soil improvement body 10 becomes small in thickness, thereby shortening a construction term while reducing construction costs.

Description

  The present invention relates to a retaining wall and a construction method thereof.

  Conventionally, ground improvement mountain retaining has been proposed as a retaining wall for constructing underground structures such as power plants. This ground improvement mountain retaining is a ground improvement body obtained by improving the ground around the underground structure (see Patent Documents 1 and 2). The thickness of the ground improvement body is set so that the overturning moment, shearing force and bending tensile force acting on the ground improvement body can be calculated and the yield strength against these can be secured.

JP 2002-206239 A Japanese Patent Laid-Open No. 11-81317

  By the way, in the process of determining the thickness of the ground improvement body, the yield strength of the ground improvement body with respect to bending tensile force is often the most severe. In this case, the thickness of the ground improvement body is determined so that the yield strength against the bending tensile force can be secured.

  However, when the thickness of the ground improvement body is increased, the volume of the soil subjected to the ground improvement increases, which causes a problem that the construction cost increases and the construction period is prolonged.

  An object of this invention is to provide the mountain retaining wall which can shorten a construction period, and its construction method, suppressing construction cost.

  The mountain retaining wall according to claim 1 is a mountain retaining wall (for example, a mountain retaining wall 1 to be described later) for constructing an underground structure (for example, an underground structure 2 to be described later), and is provided around the underground structure. A ground improvement body (for example, a ground improvement body 10 to be described later) constructed by improving the ground (for example, the ground 3 to be described later) and a wall surface on the opposite side of the ground improvement body from the underground structure. A tensile material (for example, a steel material 20 described later) that extends in a substantially vertical direction and is embedded in the ground immediately below the ground improvement body.

  The method for constructing a retaining wall according to claim 2 is a method for constructing a retaining wall for constructing an underground structure, the step of constructing a ground improvement body by improving the ground around the underground structure. And a step of driving a tensile material in a substantially vertical direction along a wall surface of the ground improvement body opposite to the underground structure, and setting it to a ground immediately below the ground improvement body. Features.

  According to the present invention, the tensile material bears the bending tensile force acting on the retaining wall. Therefore, it is not necessary to increase the thickness of the ground improvement body as in the conventional case, and the thickness of the ground improvement body is reduced, so that the construction period can be shortened while suppressing the construction cost.

It is the longitudinal cross-sectional view and top view of the mountain retaining wall which concern on one Embodiment of this invention. It is a figure which shows the main working side pressure used for calculation of the external stability of the retaining wall which concerns on the said embodiment. It is a figure for calculating | requiring the falling moment which acts on the retaining wall which concerns on the said embodiment. It is a figure for calculating | requiring the resistance moment by the retaining wall which concerns on the said embodiment. It is a figure which shows the static side pressure and water pressure which are used for calculation of the internal stability of the retaining wall which concerns on the said embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a longitudinal sectional view and a plan view of a mountain retaining wall 1 according to an embodiment of the present invention.
The retaining wall 1 is for constructing the underground structure 2. The retaining wall 1 includes a ground improvement body 10 constructed by improving the ground 3 around the underground structure 2 by a deep mixing treatment method, and the outside of the ground improvement body 10, that is, the side opposite to the underground structure 2. Steel material 20 as a tensile material provided along the wall surface.

Immediately below the underground structure 2, similarly to the ground improvement body 10, a bottom ground improvement body 30 constructed by ground improvement of the ground 3 by a deep mixing treatment method is constructed. It continues to the bottom ground improvement body 30.
The steel material 20 is H steel that extends in a substantially vertical direction, and is provided at predetermined intervals in the horizontal direction. These steel materials 20 are embedded in the ground 3 immediately below the ground improvement body 10.

The retaining wall 1 is constructed in the following procedure.
First, the ground improvement body 10 is constructed by improving the ground around the underground structure 2.
Next, the steel material 20 is driven in a substantially vertical direction along the wall surface of the ground improvement body 10 on the side opposite to the underground structure 2, and is rooted to the ground directly below the ground improvement body 10.

Hereinafter, the thickness required for the retaining wall 1 will be examined.
In the external stability of the retaining wall 1, it is necessary to consider the safety of the retaining wall 1 against sliding, falling, and subsidence, but the ground improvement body 10 of the retaining wall 1 is continuous with the bottom ground improvement body 30, so that it slides. It may be considered that subsidence does not occur, and the examination on sliding and subsidence is omitted.
On the other hand, for the internal stability of the retaining wall 1, it is necessary to examine the safety of the retaining wall against horizontal shearing and bending tension.

First, the ground improvement body 10 and the steel material 20 of the retaining wall 1 are set as follows.
The depth (height) of the ground improvement body 10 is H, and the thickness is D.
Further, the unit volume weight of the ground improvement body 10 is γ, the allowable compressive stress is σca, the allowable shear stress is τa, and the allowable tensile stress is σta. Here, the allowable shear stress level τa and the allowable tensile stress level σta are expressed by the following formulas (1) and (2).

  Further, the section modulus per steel material 20 is Zs, the pitch is L, and the allowable tensile stress is σtas.

[Examination about falls]
In the calculation of overturning, the weight of the ground improvement body of the retaining wall resists the overturning moment due to the side pressure.
Hereinafter, the thickness D1 of the ground improvement body required for the fall is obtained.

In the calculation of external stability, the main working side pressure Pa is used as the side pressure. This main working side pressure Pa is set as shown in FIG. That is, the main working side pressure at the upper end of the ground improvement body is Pa0, the main working side pressure at the lower end of the ground improvement body is PaH, and the main working side pressure Pa is distributed in a trapezoidal shape.
The rotation center O assumed by the overturning moment Mpa is the lower end of the wall surface of the ground improvement body on the underground structure side.
Then, the overturning moment Mpa is represented by the following formula (3). In the expression (3), as shown in FIG. 3, the distribution of the working side pressure Pa is obtained by dividing it into two.

  The resistance moment Mw with respect to overturning is represented by the following equation (4) as shown in FIG.

  For example, when the safety factor is Fs, the thickness D1 of the ground improvement body may be set so as to satisfy the following expression (5) using the overturning moment Mpa and the resistance moment Mw.

[Study on horizontal shearing]
In the calculation for horizontal shear, the ground improvement body of the retaining wall resists the total shear force due to lateral pressure.
Hereinafter, the thickness D2 required for the horizontal shearing of the ground improvement body is obtained.
In calculating internal stability, static side pressure and water pressure are used as side pressures. These static side pressure and water pressure are set as shown in FIG.
That is, when the water level is the depth Hw, the water pressure is distributed in a triangular shape. Then, the water pressure Pw1 at the upper end and the water pressure Pw2 at the lower end are represented by the following equations (6) and (7).

  Therefore, the total shearing force Pw by water pressure is expressed by the following formula (8).

Further, it is assumed that the stationary side pressure at the upper end of the ground improvement body is Pko1, the stationary side pressure at the water level is Pko2, the stationary side pressure at the lower end of the ground improvement body is Pko3, and the stationary side pressure is distributed in a substantially trapezoidal shape.
These static side pressures Pko1, Pko2, and Pko3 are expressed by the following formulas (9) to (11) using the side pressure coefficient ko, the loading weight Ps, and the unit volume weight γ of the ground improvement body described above.

  Therefore, the total shearing force Pko due to static side pressure is expressed by the following equation (12). In Expression (12), as shown in FIG. 5A, the distribution of the static side pressure is obtained by dividing it into four.

  As described above, the total shear stress τh is expressed by the following equation (13). 1.0 in Formula (13) represents the unit width of the ground improvement body.

  Therefore, the thickness D2 of the ground improvement body may be set so that the allowable shear stress level τa of the ground improvement body> the total shear stress level τh.

[Examination of bending tension]
In the calculation for bending tension, the bending moment due to the lateral pressure is resisted only by the tensile force applied to the steel material, and the resistance by the ground improvement body 10 of the retaining wall 1 is not considered.
Hereinafter, the specifications and pitches of steel materials necessary for bending tension of the ground improvement body are obtained.
Regarding bending tension, a bending moment Mpw due to water pressure with respect to the rotation center O is expressed by the following equation (14) using a total shearing force Pw due to water pressure.

  The bending moment Mpko due to the static side pressure with respect to the rotation center O is expressed by the following equation (15) using the total shearing force Pko due to the static side pressure. In Expression (15), as shown in FIG. 5A, the distribution of the static side pressure is obtained by dividing it into four.

  From the above, the total bending moment M is expressed by the following formula (16).

  On the other hand, the section modulus Z per unit width of the steel material is expressed by the following formula (17) using the section modulus Zs of the steel material and the pitch L of the steel material.

  Therefore, the tensile stress degree σhs acting on the steel material is represented by the following formula (18).

  Therefore, the specification and interval of the steel material may be set so that the allowable tensile stress level σtas of the steel material> the tensile stress level σhs acting on the steel material.

  Furthermore, with regard to the tensile force applied to the steel material, the adhesion force between the steel material and the ground improvement body and the friction force between the steel material and the ground improvement body were also examined, and the adhesion force between these steel material and the ground improvement body, and the steel material and the ground improvement material. It is necessary to confirm that the frictional force exceeds the tensile stress σhs acting on the steel material.

[Examination of bending tension when steel is not provided]
For comparison, the bending tension when no steel material is provided is also examined. In this case, it is assumed that the ground improvement body 10 of the retaining wall 1 resists the bending moment due to the side pressure.
Hereinafter, the thickness D3 required for the bending tension of the ground improvement body is obtained.
The section modulus Z per unit width of the ground improvement body is represented by the following formula (19).

  Therefore, the tensile stress degree σha acting on the ground improvement body is expressed by the following formula (20).

  Therefore, D3 may be set so that the allowable tensile stress σta of the ground improvement body> the tensile stress σha acting on the ground improvement body.

Next, the effect of the present invention is verified by applying specific numerical values to the above formula. A case where the steel material is provided is an example, and a case where the steel material is not provided is a comparative example.
[Example]
If H = 6 (m), γ = 19 (kN / m ³ ), and σca = 400 (kN / m ² ), then σta = 60 (kN / m ² ) and τa = 200 (kN / m ² ). .

1. Consideration of falls When Pa0 = 5.30 (kN) and PaH = 65.72 (kN), Mpa = 457.92 (kNm).
Further, Mw = 57.00 (D1) ² .
Therefore, when Fs = 1.2, D1 = 3.10 (m).

2. Study on horizontal shearing Pw = 80.0 (kN).
If ko = 0.5 and Ps = 10.0 (kN), then Pko1 = 5.0 (kN), Pko2 = 24.0 (kN), Pko3 = 42.0 (kN), and Pko = 161 0 (kN).
Therefore, since τh = 241.0 / D2 (kN / m ² ), D2 = 1.21 (m).

3. Study on bending tension Mpw = 106.67 (kNm), Mpko = 378.67 (kNm), and M = 485.34 (kNm).
Moreover, this steel material shall be installed at 1-m intervals using H-400x400 as a steel material. Then, Zs = 0.00295 (m ³ ), L = 1.0 (m), and σtas = 188000 (kN / m ² ).
Furthermore, since σhs = 164522.01 (kN / m2), σhs <σtas, and it can be seen that the strength against bending tension can be ensured by installing H-400 × 400 at intervals of 1 m.

  As mentioned above, in an Example, the thickness of a ground improvement body is not influenced by the yield strength with respect to bending tension, and is set to 3.10 (m).

[Comparative example]
When a steel material is not provided, when bending tension is examined, D3 that satisfies σha = 60 (kN / m ² ) may be obtained, and thus D3 = 7.00 (m).
Therefore, the thickness of the ground improvement body is determined by the yield strength against bending tension and becomes 7.0 m.

  Therefore, in an Example, it turns out that the thickness of a ground improvement body can be reduced to about half compared with a comparative example.

According to this embodiment, there are the following effects.
(1) The steel material 20 bears the bending tensile force acting on the retaining wall 1. Therefore, it is not necessary to increase the thickness of the ground improvement body as in the conventional case, and the thickness of the ground improvement body 10 is reduced, so that the construction period can be shortened while suppressing the construction cost.

  It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.

DESCRIPTION OF SYMBOLS 1 ... Mountain retaining wall 2 ... Underground structure 3 ... Ground 10 ... Ground improvement body 20 ... Steel material (tensile material)
30 ... Bottom ground improvement body H ... Height (depth) of ground improvement body
D, D1, D2, D3: Thickness of ground improvement body γ: Unit volume weight of ground improvement body σca: Permissible compressive stress level of ground improvement body τa: Permissible shear stress level of ground improvement body σta: Permissible tension of ground improvement body Stress Z: Section modulus per unit width of steel material Zs: Section modulus per steel material L: Steel pitch σtas: Permissible tensile stress of steel material O: Center of rotation Mpa: Falling moment Mw: Resistance moment Fs: Safety Rate Pa ... Active side pressure Hw ... Water level depth Pw ... Total shear force due to water pressure ko ... Side pressure coefficient Ps ... Overload Pko ... Total shear force due to static side pressure τh ... Total shear stress level Mpw ... Bending moment due to water pressure Mpko ... Stationary Moment due to lateral pressure M: Total bending moment σhs: Tensile stress acting on steel material σha: Tensile stress acting on ground improvement body

Claims (2)

A retaining wall for building an underground structure,
The ground improvement body constructed by improving the ground around the underground structure, and the ground improvement body extending in a substantially vertical direction along the wall surface of the ground improvement body opposite to the underground structure. A retaining wall comprising: a tension member rooted in the ground immediately below. A method for constructing a retaining wall for constructing an underground structure,
Improving the ground around the underground structure to construct a ground improved body;
A step of driving a tensile material in a substantially vertical direction along a wall surface on the opposite side of the underground structure of the ground improvement body, and rooting to a ground directly below the ground improvement body, How to construct a retaining wall.

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