JP2024004251A - Ground reinforcement structure and design method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground reinforcement structure and a design method thereof capable of acquiring excellent reinforcement effect.

SOLUTION: A reinforcement structure 1 reinforcing a retain wall rear side ground 10 positioned at a rear side of the retain wall 20 is provided with a plurality of pipes 2 buried in the retain wall rear side ground 10, of which a lower end part is installed deeper than a slip plane 12 of the retain wall rear side ground 10, wherein the plurality of pipes 2 is placed in a row in an installation direction (in a left and right direction) of the retain wall 20 with intervals W meeting at least one of a first condition where the maximum bending moment (bending edge stress σb) of the pipes 2 is lower than an allowed bending moment (allowed bending stress σa), a second condition where the maximum shear stress (shear stress τs) of the pipes 2 is lower than an allowed shear stress (allowed shear stress τs), and a third condition where passive earth pressure of a front surface ground at a root insertion part of the pipe 2 is more than an acted horizontal force (loaded horizontal force H' of the pipe 2.

SELECTED DRAWING: Figure 25

COPYRIGHT: (C)2024,JPO&INPIT

Description

Application for exception to loss of novelty applied

The present invention relates to a ground reinforcement structure for reinforcing the ground behind a retaining wall and a method for designing the same.

Generally, a retaining wall is sometimes provided on a cut or embanked slope in order to stabilize the slope. Because the ground behind the retaining wall, which is located behind the retaining wall, is excavated and backfilled during construction, uneven settlement of buildings due to ground subsidence often becomes a problem. In addition, the ground behind the retaining wall has been excavated and backfilled in the past, so it has low resistance to earthquake forces.
Therefore, for example, Patent Document 1 discloses a reinforcing structure and a reinforcing method for reinforcing the ground behind a retaining wall. The reinforcement structure of Patent Document 1 includes a pile main body made of a steel pipe and a spiral blade provided in a spiral shape at the tip and circumferential surface of the pile main body. The first pile is provided with a first pile, a second pile, and a connecting part that connects the pile cap of the first pile and the pile cap of the second pile in the upper part of the ground, and the first pile is arranged vertically or The tip of the pile main body is installed in the ground in a diagonal direction toward the existing retaining wall, and the second pile is installed in the ground in the diagonal direction along the existing retaining wall. The interval between the two reinforcing structures, that is, the interval between the first piles, is, for example, 5 to 10 times the diameter of the pile.

Patent No. 5455869

The appropriate spacing between piles also varies depending on the characteristics of the piles and the characteristics of the ground. That is, unless the spacing between the piles is determined in consideration of the characteristics of the piles and the characteristics of the ground, there is a risk that a sufficient reinforcing effect cannot be obtained.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a ground reinforcement structure and a method for designing the same that can obtain an excellent reinforcement effect.

The invention according to claim 1, for example, as shown in FIGS. 1 to 6 and 25 to 41,
A ground reinforcement structure 1 for reinforcing a retaining wall back ground 10 located on the back side of a retaining wall 20,
A plurality of pipes 2 are embedded in the retaining wall back ground 10, and the lower end portions are installed deeper than the sliding surface 12 of the retaining wall back ground 10,
The plurality of pipes 2 meet the first condition that the maximum bending moment (bending edge stress σb) of the pipes 2 is less than the allowable bending moment (allowable bending stress σa), and the maximum shear force (shear stress σa) of the pipes 2. The second condition is that the shear stress (degree τs) is lower than the allowable shear stress (allowable shear stress τa), and the passive earth pressure Qp of the ground in front of the embedded part of the pipe 2 is ) are arranged side by side in the installation direction (horizontal direction) of the retaining wall 20 at an interval W that satisfies at least one of the following.

According to the invention set forth in claim 1, the ground reinforcement structure 1 includes a plurality of pipes 2 that are buried in the ground 10 behind the retaining wall and whose lower ends are installed deeper than the sliding surface 12 of the ground 10 behind the retaining wall. The pipe 2 has a first condition that the maximum bending moment (bending edge stress σb) of the pipe 2 is less than the allowable bending moment (allowable bending stress σa), and the maximum shear force (shear stress τs) of the pipe 2. ) is below the allowable shear force (allowable shear stress degree τa), and the passive earth pressure Qp of the ground in front of the embedded part of the pipe 2 exceeds the acting horizontal force of the pipe 2 (burden horizontal force H'). The retaining walls 20 are arranged side by side in the installation direction (horizontal direction) with an interval W that satisfies at least one of the third condition, so that the bending resistance of the pipe 2, the shear resistance of the pipe 2, and the passive resistance of the ground are reduced. Landslide deterrence can be enhanced by at least one of the following. In other words, the spacing between the pipes 2 (the spacing in the installation direction of the retaining wall 20) is set to the spacing W that takes into account the characteristics of the pipes 2 and the characteristics of the ground, so it is possible to exhibit an excellent reinforcing effect. .

The invention according to claim 2, for example, as shown in FIGS. 1 to 6,
In the ground reinforcement structure 1 according to claim 1,
A connecting member 3 that is buried in the ground 10 behind the retaining wall and connects the plurality of pipes 2 arranged in the installation direction (left and right direction) of the retaining wall 20,
The connecting member 3 is installed substantially horizontally, is a long member along the installation direction, and is connected to the upper end of the pipe 2 by a connecting member (clamp (or wire, etc.)). shall be.

According to the invention set forth in claim 2, the ground reinforcement structure 1 includes a connecting member 3 that is buried in the ground 10 behind the retaining wall and that connects a plurality of pipes 2 that are lined up in the installation direction (left-right direction) of the retaining wall 20. Therefore, a sense of unity is enhanced compared to a case where the plurality of pipes 2 lined up in the installation direction of the retaining wall 20 are not connected, and it becomes possible to efficiently resist landslides.
In addition, by simply joining the upper ends of the pipes 2 to the connecting member 3 installed substantially horizontally along the installation direction (left-right direction) of the retaining wall 20, a plurality of pipes 2 lined up in the installation direction of the retaining wall 20 can be connected. Since they can be combined, workability can be improved.
Furthermore, in the ground reinforcement structure 1, not only the pipe 2 but also the coupling member 3 are buried in the ground 10 behind the retaining wall. That is, since the entire ground reinforcement structure 1 is underground, it does not become an obstacle to land use, and the top drainage facility of the retaining wall 20 can be easily installed.

The invention according to claim 3, for example, as shown in FIGS. 1, 4, 5, and 25 to 41,
In the ground reinforcement structure 1 according to claim 1,
It has a plurality of reinforcing units 4A and 4B each including a plurality of the pipes 2 arranged in a row along the installation direction (left-right direction) of the retaining wall 20,
The plurality of reinforcing units 4A, 4B are arranged side by side in a direction (front-back direction) orthogonal to the installation direction,
The number of reinforcement units 4A, 4B that the ground reinforcement structure 1 has and the spacing of the pipes 2 in the installation direction are a combination that satisfies at least one of the first condition, the second condition, and the third condition. It is characterized in that the number n and the interval W are set.

According to the invention described in claim 3, the ground reinforcement structure 1 includes a plurality of reinforcement units 4A and 4B each including a plurality of pipes 2 arranged in a row along the installation direction (left-right direction) of the retaining wall 20. , the number of reinforcement units 4A, 4B that the ground reinforcement structure 1 has, and the spacing between the pipes 2 (the spacing in the installation direction of the retaining wall 20) satisfy at least one of the first condition, the second condition, and the third condition. The number of combinations n and the interval W are set. Therefore, for example, when the number of reinforcing units 4A, 4B is one, even if the interval W that satisfies at least one of the first condition, second condition, and third condition becomes a value that is difficult to realize, the reinforcing units 4A, 4B By increasing the number of reinforcing units 4A, 4B and the spacing between the pipes 2 to satisfy at least one of the first condition, the second condition, and the third condition, the spacing between the pipes 2 can be increased. It becomes possible to set the distance W to be an easily realized distance W, and it becomes possible to reliably exhibit an excellent reinforcing effect.

The invention according to claim 4, for example, as shown in FIGS. 2, 5, and 6,
In the ground reinforcement structure 1 according to claim 1,
The pipe 2 includes a first pipe (valley side pipe) and a second pipe (mountain side pipe) that are not parallel to each other,
The first pipe and the second pipe have upper end portions connected to each other and lower end portions separated from each other in a front-back direction perpendicular to the installation direction (left-right direction),
The angle of the second pipe with respect to the first pipe and the distance between the pipes 2 in the installation direction are such that the angle 2α and the distance of the combination satisfy at least one of the first condition, the second condition, and the third condition. The feature is set to W.

According to the invention described in claim 4, the ground reinforcement structure 1 includes the first pipe (valley side pipe) and the second pipe (mountain side pipe) which are not parallel to each other as the pipes 2, and the first pipe and the second pipe are not parallel to each other. The upper ends of the two pipes are joined together, and the lower ends are separated from each other in the front-rear direction perpendicular to the installation direction (left-right direction) of the retaining wall 20. The pull-out resistance Rt of the other pipe (the mountain-side pipe) (specifically, the perpendicular component R _H of the pull-out resistance R _t with respect to the valley-side pipe) acts on the upper end portion of the valley-side pipe. That is, since the upper end of one pipe can be held down by the other pipe, it becomes possible to reinforce the retaining wall rear ground 10 more effectively.
Furthermore, the angle of the second pipe with respect to the first pipe and the interval between the pipes 2 (the interval in the installation direction of the retaining wall 20) are the angle 2α of the combination satisfying at least one of the first condition, the second condition, and the third condition. and the interval W. Therefore, for example, even if the distance W that satisfies at least one of the first, second, and third conditions is difficult to achieve when the first pipe and the second pipe are parallel, the first pipe and the second pipe By making the two pipes not parallel to each other, the combination of the angle of the second pipe with respect to the first pipe and the interval between the pipes 2 satisfies at least one of the first condition, the second condition, and the third condition. , it becomes possible to set the interval between the pipes 2 to an easily realized interval W, and it becomes possible to reliably exhibit an excellent reinforcing effect.

The invention according to claim 5, for example, as shown in FIGS. 2, 5, and 6,
In the ground reinforcement structure 1 according to claim 4,
The first pipe (valley side pipe) is installed with the lower end located in front (on the retaining wall 20 side) of an imaginary vertical line passing through the upper end,
The second pipe (mountain side pipe) is characterized in that the lower end is located on the rear side (on the building 30 side) of the imaginary vertical line passing through the upper end.

According to the invention set forth in claim 5, the first pipe and the second pipe are installed diagonally toward each other, that is, the first pipe and the second pipe are connected in a Λ shape, so that ground reinforcement is achieved. Even if the installation location of the structure 1 is small, the angle 2α of the second pipe with respect to the first pipe can be increased. The larger the angle 2α of the second pipe with respect to the first pipe (closer to 90 degrees), the greater the force (right angle component R _H (=R _t・sin2α)) that presses the upper end of the first pipe. It becomes possible to reinforce the back ground 10 more effectively.

The invention according to claim 6, for example, as shown in FIGS. 1 to 6 and 25 to 41,
In the ground reinforcement structure 1 according to claim 1,
The length of the pipe 2 and the interval of the pipe 2 in the installation direction (horizontal direction) are set to a length L ₀ and an interval W that satisfy the third condition.

According to the invention set forth in claim 6, the length of the pipes 2 and the interval between the pipes 2 (the interval in the installation direction (horizontal direction) of the retaining wall 20) are the length L ₀ and the interval of the combination satisfying the third condition. It is set to W. Therefore, for example, if the length of the pipe 2 is La, even if the interval W that satisfies the third condition becomes a value that is difficult to achieve, the length of the pipe 2 is made longer than La, and the length of the pipe 2 and By satisfying the third condition by combining the spacings of the pipes 2, it becomes possible to set the spacing between the pipes 2 to an easily realized spacing W, and it becomes possible to reliably exhibit an excellent reinforcing effect. .

The invention according to claim 7, for example, as shown in FIGS. 25 to 41,
A method for designing a ground reinforcement structure 1 for reinforcing a retaining wall back ground 10 located on the back side of a retaining wall 20, comprising:
The ground reinforcement structure 1 includes a plurality of pipes 2 whose lower ends are installed deeper than the sliding surface 12 of the retaining wall rear ground 10,
The plurality of pipes 2 are arranged side by side at predetermined intervals in the installation direction (horizontal direction) of the retaining wall 20,
The predetermined interval is
A first condition that the maximum bending moment (bending edge stress σb) of the pipe 2 is less than the allowable bending moment (allowable bending stress σa);
A second condition that the maximum shear force (shear stress degree τs) of the pipe 2 is less than the allowable shear force (allowable shear stress degree τa);
The spacing W satisfies at least one of the third condition that the passive earth pressure Qp of the ground in front of the embedded part of the pipe 2 exceeds the acting horizontal force (burden horizontal force H') of the pipe 2. shall be.

According to the invention described in claim 7, the interval between the pipes 2 included in the ground reinforcement structure 1 (the interval in the installation direction (left and right direction) of the retaining wall 20) is determined by the maximum bending moment (bending edge stress σb) of the pipe 2. is less than the allowable bending moment (allowable bending stress degree σa), and a second condition that the maximum shear force (shear stress degree τs) of the pipe 2 is less than the allowable shear force (allowable shear stress degree τa), It is possible to set the interval W to satisfy at least one of the third condition that the passive earth pressure Qp of the ground in front of the embedded part of the pipe 2 exceeds the acting horizontal force (bearing horizontal force H') of the pipe 2. Therefore, the landslide prevention force can be increased by at least one of the bending resistance of the pipe 2, the shear resistance of the pipe 2, and the passive resistance of the ground. That is, since it is possible to set the interval between the pipes 2 (the interval in the installation direction of the retaining wall 20) to the interval W that takes into account the characteristics of the pipes 2 and the characteristics of the ground, it is possible to exhibit an excellent reinforcing effect. .

According to the present invention, an excellent reinforcing effect can be obtained.

It is a figure which shows an example of the ground reinforcement structure (Type II type) installed in the ground behind a retaining wall, Comprising: (a) is an elevation view, (b) is a top view. It is a figure which shows an example of the ground reinforcement structure (Λ type) installed in the ground behind a retaining wall, Comprising: (a) is an elevation view, (b) is a figure which shows a top view. It is a figure which shows the modification of the ground reinforcement structure (Type II) installed in the ground behind a retaining wall. It is a figure which shows the modification of the ground reinforcement structure (Type II) installed in the ground behind a retaining wall. It is a figure which shows the modification of the ground reinforcement structure (Λ type) installed in the ground behind a retaining wall. It is a figure which shows the modification of the ground reinforcement structure (Λ type) installed in the ground behind a retaining wall. (a) is a diagram showing a model soil tank experimental device and a list of used equipment/equipment, and (b) is a diagram showing experiment cases and measurement methods. FIG. 3 is a diagram showing reinforcement specifications. (a) is a diagram showing a pull-out test device, and (b) is a diagram showing the pull-out test results. (a) and (b) are diagrams showing the relationship between the vertical load and the displacement amount of the retaining wall, and (c) is a diagram showing the relationship between the maximum load and the displacement amount of the retaining wall. It is a figure which shows the relationship between a vertical load and a retaining wall inclination angle. (a) is a diagram showing an outline of the measuring device, and (b) is a diagram showing the measurement principle of image analysis. It is a figure showing the horizontal displacement of the ground and retaining wall by image analysis at the time of loading (vertical load Mv = 231.9N, horizontal load Mh = 48.8N) just before the unreinforced retaining wall collapses. It is a figure showing the horizontal displacement of the ground and retaining wall by image analysis at the time of maximum load. FIG. 3 is a diagram showing the transition of the fracture area. FIG. 3 is a diagram showing the amount of soil displacement when the maximum load is applied as seen from the side of the model soil tank. FIG. 3 is a diagram showing the amount of soil displacement when the maximum load is applied as seen from the top of the model soil tank. FIG. 3 is a diagram showing the amount of displacement of soil and reinforcement material at the time of maximum load. It is a figure showing the relationship between vertical load and loading plate settlement amount. (a) is a diagram showing analysis parameters, (b) is a diagram showing joint element parameters between a retaining wall, a loading plate, and the ground, and (c) is a diagram showing joint element parameters between a reinforcing material and the ground. . It is a figure showing the relationship between vertical load and retaining wall displacement. It is a displacement contour diagram. It is a plastic zone diagram. (a) is a diagram showing a type II type landslide resistance mechanism, and (b) is a diagram showing a Λ type type landslide resistance mechanism. It is a flowchart which shows an example of the design method of a ground reinforcement structure. It is a figure explaining an example of "setting of a ground constant." FIG. 3 is a diagram illustrating an example of "arc slip calculation for normal conditions and during earthquakes." FIG. 3 is a diagram illustrating an example of "arc slip calculation for normal conditions and during earthquakes." FIG. 3 is a diagram illustrating an example of "setting of material, dimensions, and strength characteristics of a pipe." It is a figure explaining an example of "assumptions, such as pipe arrangement." It is a figure explaining an example of "assumptions, such as pipe arrangement." It is a figure explaining an example of "calculation of a horizontal ground reaction force coefficient and a characteristic value." It is a figure explaining an example of "calculation of maximum bending moment and shear force." It is a figure explaining an example of "calculation of maximum bending moment and shear force." It is a figure explaining an example of "verification of bending stress and shear stress." It is a figure explaining an example of "verification of bending stress and shear stress." FIG. 3 is a diagram illustrating an example of "calculating the penetration length and total length of the pipe." It is a figure explaining an example of "calculation of horizontal displacement." It is a figure explaining an example of "calculation of horizontal displacement." It is a figure explaining an example of "inspection of yield failure of the ground where a pipe is embedded." It is a figure showing an example of reinforcement specifications. It is a figure showing an example of a construction procedure of a ground reinforcement structure. It is a figure showing an example of a construction procedure of a ground reinforcement structure. It is a figure showing an example of a construction procedure of a ground reinforcement structure. It is a diagram explaining the difference between the restraining pile design method and the shear pile design method. It is a calculation condition diagram. (a) is a diagram showing back ground conditions, (b) is a diagram showing retaining wall conditions, (c) is a diagram showing load conditions, and (d) is a diagram showing ground conditions of immobile layer. , and (e) is a diagram showing the pipe pulling resistance force. It is an exploded view of a slip range. FIG. 3 is a diagram showing details of slip calculation results. It is a figure which shows an example of the comparison result of a restraining pile design method and a shear pile design method. It is a figure which shows an example of the comparison result of the model earth tank experiment and the calculation by the restraining pile design method. It is a figure which shows an example of the comparison result of a reinforcement type. It is a figure which shows an example of calculation conditions when comparing linear slip calculation and circular arc slip calculation. It is a figure which shows an example of the comparison result of a linear slip calculation and a circular arc slip calculation.

Embodiments of the present invention will be described below with reference to the drawings. However, although the embodiments described below have various limitations that are technically preferable for implementing the present invention, the technical scope of the present invention is not limited to the embodiments and illustrated examples below. do not have.
Note that the directions in the following embodiments and illustrated examples are set for convenience of explanation only. In this embodiment, the installation direction of the retaining wall 20 is the left-right direction, the height direction of the retaining wall 20 is the up-down direction, and the direction perpendicular to both the left-right direction and the up-down direction is the front-back direction.

《Ground reinforcement structure》
In FIGS. 1 and 2, reference numeral 1 indicates a ground reinforcement structure. This ground reinforcement structure 1 is installed underground on the retaining wall back ground 10 in order to reinforce the retaining wall back ground 10.
The retaining wall back ground 10 is ground (for example, embankment ground) located on the back side (rear side) of the retaining wall 20. That is, the retaining wall rear ground 10 is a ground on which the retaining wall 20 is provided on the slope (front surface). A building 30 is provided on the retaining wall rear ground 10 in close proximity to the retaining wall 20. Although the retaining wall 20 in this embodiment is a block retaining wall, it is not limited to this, and the retaining wall 20 may have a leaning type retaining wall, an inverted T-shaped retaining wall, an L-shaped retaining wall, etc. There may be.

The ground reinforcement structure 1 includes a plurality of pipes 2 and a connecting member 3 that connects the pipes 2 to each other. The ground reinforcement structure 1 of this embodiment has a pipe 2 as a reinforcing material vertically or The required safety factor (resistance) against landslides is achieved by diagonally rotating and penetrating, and by the strength of pipe 2 (bending strength and shear strength) and the passive resistance of the ground (immobile layer) below the landslide line (slip surface 12). This is what we are trying to secure. It also serves as a repose response (angle of repose response) for the building 30.

The pipe 2 is installed at a position avoiding the bottom slab 21 of the retaining wall 20 so as to vertically penetrate the sliding surface 12 that is the boundary between the moving layer and the immobile layer. In this embodiment, a small diameter steel pipe (commonly known as a "single pipe") with a diameter of 48.6 mm is used as the pipe 2, but the pipe 2 is not limited to this. Further, in this embodiment, the wall thickness (thickness dimension) of the pipe 2 is 2.4 mm, but it is not limited to this.
The connecting member 3 is, for example, a long member longer than the width dimension (horizontal dimension) of the building 30, and is installed between the retaining wall 20 and the building 30 approximately along the installation direction (horizontal direction) of the retaining wall 20. Installed approximately horizontally. In this embodiment, a steel pipe (for example, a single pipe) is used as the coupling member 3, but it is not limited to this.

The ground reinforcement structure 1 includes a II-type ground reinforcement structure 1 shown in FIG. 1 and a Λ-type ground reinforcement structure 1 shown in FIG. 2. In the II-type ground reinforcement structure 1, the pipe 2 is installed approximately parallel to the vertical direction (up-down direction), and in the Λ-type ground reinforcement structure 1, the pipe 2 is installed in the vertical direction (up-down direction). It is installed diagonally.

The type II type ground reinforcement structure 1 includes two reinforcement units 4A lined up in the front-rear direction and a connecting member 5 that connects the reinforcement units 4A to each other. The reinforcing unit 4A includes a plurality of pipes 2 installed substantially vertically, one connecting member 3 that connects the upper ends of the plurality of pipes 2, and the upper ends of the pipes 2 and the connecting member 3. It consists of a joining member (clamp (or wire, etc.)) to be joined.
The connecting member 5 has one end connected to the connecting member 3 in the front reinforcing unit 4A with a clamp (or a wire, etc.), and the other end connected to the connecting member 3 in the rear reinforcing unit 4A with a clamp (or a wire, etc.). etc.). In this embodiment, a steel pipe (for example, a single pipe) is used as the connecting member 5, but it is not limited to this.

In the type II ground reinforcement structure 1, the pipes 2 are arranged in a staggered manner. That is, of the two adjacent reinforcement units 4A, the pipe 2 in one reinforcement unit 4A (for example, the front reinforcement unit 4A) and the pipe 2 in the other reinforcement unit 4A (for example, the rear reinforcement unit 4A) are They are arranged so that they do not overlap when viewed from the retaining wall 20 side (when viewed from the front and rear directions).
Note that the number of reinforcement units 4A included in the type II ground reinforcement structure 1 is not limited to two. The type II type ground reinforcement structure 1 may have one reinforcement unit 4A as shown in FIG. 3, or may have three reinforcement units 4A as shown in FIG. Alternatively, it may have four or more reinforcing units 4A. Of course, if the type II type ground reinforcement structure 1 has one reinforcement unit 4A, the ground reinforcement structure 1 does not include the connecting member 5, as shown in FIG. 3.

Here, in one reinforcing unit 4A, a plurality of pipes 2 lined up at predetermined intervals in the installation direction (horizontal direction) of the retaining wall 20 are coupled by one coupling member 3. This predetermined interval is set to a value (pipe interval W) determined by a design method (FIGS. 25 to 41) described later. Specifically, the interval between the pipes 2 constituting one reinforcing unit 4A is determined based on the first condition (the bending edge stress σb calculated in step S9 (specifically, based on the maximum bending moment Mmax calculated in step S8). The condition that the calculated bending edge stress degree σb) is smaller than the allowable bending stress degree σa set in step S5) and the second condition (the shear stress degree τs calculated in step S9 (specifically, the condition that the shear stress degree τs calculated in step S8) The condition that the shear stress degree τs calculated based on the maximum shear force Smax) is smaller than the allowable shear stress degree τa set in step S5) and the third condition (the passive earth pressure Qp calculated in step S13 is calculated in step S6) The interval W is set to satisfy both of the following conditions: (1) the horizontal force H' to be borne by each pipe is greater than the horizontal force H' applied to each pipe;
Note that the pipe spacing (pile spacing) W is not limited to the spacing that satisfies all of the first, second, and third conditions, but may satisfy at least one of the first, second, and third conditions. Any interval that satisfies the requirement is sufficient.

Further, the type II type ground reinforcement structure 1 has a predetermined number of reinforcement units 4A. This predetermined number is set to a value (number of pipe rows n) determined by a design method (FIGS. 25 to 41) described later. Specifically, the number of reinforcement units 4A included in the II type ground reinforcement structure 1 is determined based on the first condition (the bending edge stress degree σb calculated in step S9 (specifically, the maximum bending moment Mmax calculated in step S8). The second condition (the condition that the bending edge stress degree σb calculated based on The condition that the shear stress degree τs calculated based on the calculated maximum shear force Smax) is smaller than the allowable shear stress degree τa set in step S5) and the third condition (the passive earth pressure Qp calculated in step S13 is satisfied in step S6 The number n is set to satisfy both of the condition that the horizontal force H' is larger than the horizontal force H' per pipe calculated in .
Note that the number of pipe rows (pile rows) n is not limited to the number that satisfies all of the first, second, and third conditions, but at least one of the first, second, and third conditions. Any number that satisfies this is sufficient.

Further, in the type II type ground reinforcement structure 1, the length of the pipe 2 is longer than a predetermined length. This predetermined length is set to a value (pipe design length L ₀ ) determined by a design method (FIGS. 25 to 41) described later. Specifically, the length of the pipe 2 constituting the type II ground reinforcement structure 1 is determined based on the third condition (the passive earth pressure Qp calculated in step S13 is the horizontal force borne per pipe calculated in step S6). The length L is set to be greater than or equal to ₀ , which satisfies the condition that the length L is greater than H'.

The Λ type ground reinforcement structure 1 includes one reinforcement unit 4B. The reinforcing unit 4B includes a plurality of pipes 2, one joining member 3 that joins the upper ends of the plurality of pipes 2, and a joining member (clamp) that joins the upper ends of the pipes 2 and the joining member 3. (or wire, etc.)). The reinforcing unit 4B is a pipe 2 (hereinafter referred to as a "valley side pipe") installed with its lower end located closer to the retaining wall 20 (front side) than an imaginary vertical line passing through its upper end. Pipe 2 (hereinafter referred to as "mountain side pipe") is equipped with a plurality of pipes (hereinafter referred to as "mountain side pipe"), and is installed with the lower end located on the building 30 side (rear side) than the imaginary vertical line passing through the upper end. It has multiple books.

In this embodiment, the angle between the imaginary vertical line and the valley side pipe is set to be approximately equal to the angle between the imaginary vertical line and the mountain side pipe, but the angle is not limited to this. If the upper ends of the valley side pipe and the mountain side pipe are connected via the coupling member 3 and the lower ends are separated from each other in the front-rear direction, the angle between the imaginary vertical line and the valley side pipe is , the angle between the virtual vertical line and the pipe on the mountain side may be larger, or conversely, the angle between the virtual vertical line and the pipe on the mountain side may be larger than the angle between the virtual vertical line and the pipe on the valley side. may be small. Specifically, for example, the mountain side pipe may be installed approximately parallel to the vertical direction, and the valley side pipe may be installed obliquely to the vertical direction, or conversely, the mountain side pipe may be installed approximately parallel to the vertical direction. The valley side pipe may be installed substantially parallel to the vertical direction.
Further, the number of reinforcement units 4B included in the Λ type ground reinforcement structure 1 is not limited to one. The Λ type ground reinforcement structure 1 may have two reinforcing units 4B, for example, as shown in FIG. 5, or may have three or more reinforcing units 4B. Furthermore, when the number of reinforcing units 4B included in the Λ-type ground reinforcing structure 1 is plural, the ground reinforcing structure 1 includes a connecting member 5 that connects the reinforcing units 4B to each other, as shown in FIG. You may be prepared.
Furthermore, the numbers of the valley side pipes and the mountain side pipes that constitute one reinforcing unit 4B may not be the same. For example, as shown in FIG. 6, the number of mountain side pipes may be smaller than the number of valley side pipes.

Here, in one reinforcement unit 4B, a plurality of mountain side pipes are lined up in the installation direction (left and right direction) of the retaining wall 20, and a plurality of valley side pipes are lined up at predetermined intervals in the installation direction (left and right direction) of the retaining wall 20. The pipes are connected by one connecting member 3. This predetermined interval is set to a value (pipe interval W) determined by a design method (FIGS. 25 to 41) described later. Specifically, the interval between the valley side pipes constituting one reinforcing unit 4B is determined based on the first condition (the bending edge stress σb calculated in step S9 (specifically, the maximum bending moment Mmax calculated in step S8). The bending edge stress degree σb calculated based on the condition is smaller than the allowable bending stress degree σa set in step S5) and the second condition (the shear stress degree τs calculated in step S9 (specifically, The condition that the shear stress degree τs calculated based on the maximum shear force Smax) is smaller than the allowable shear stress degree τa set in step S5) and the third condition (the passive earth pressure Qp calculated in step S13 is The interval W is set to satisfy both of the condition that the horizontal force H' is larger than the calculated horizontal force H' per pipe.
Note that the pipe spacing (pile spacing) W is not limited to the spacing that satisfies all of the first, second, and third conditions, but may satisfy at least one of the first, second, and third conditions. Any interval that satisfies the requirement is sufficient.

Further, the Λ type ground reinforcement structure 1 has a predetermined number of reinforcement units 4B. This predetermined number is set to a value (number of pipe rows n) determined by a design method (FIGS. 25 to 41) described later. Specifically, the number of reinforcement units 4B included in the Λ type ground reinforcement structure 1 is determined based on the first condition (the bending edge stress degree σb calculated in step S9 (specifically, the maximum bending moment Mmax calculated in step S8). The second condition (the condition that the bending edge stress degree σb calculated based on The condition that the shear stress degree τs calculated based on the calculated maximum shear force Smax) is smaller than the allowable shear stress degree τa set in step S5) and the third condition (the passive earth pressure Qp calculated in step S13 is set in step S6 It is set to a number n that satisfies both the condition that the horizontal force H' is larger than the horizontal force H' per pipe calculated in .
Note that the number of pipe rows (pile rows) n is not limited to the number that satisfies all of the first, second, and third conditions, but at least one of the first, second, and third conditions. Any number that satisfies this is sufficient.

Further, in one reinforcing unit 4B, the predetermined angle is the sum of the angle between the imaginary vertical line and the valley side pipe, and the angle between the imaginary vertical line and the mountain side pipe. This predetermined angle is set to a value (pipe mutual angle 2α) determined by a design method (FIGS. 25 to 41) described later. Specifically, the angle formed by the valley side pipe and the mountain side pipe constituting one reinforcement unit 4B (the angle of the mountain side pipe with respect to the valley side pipe) is based on the first condition (the bending edge stress degree σb (specifically Specifically, the bending edge stress σb calculated based on the maximum bending moment Mmax calculated in step S8 is smaller than the allowable bending stress σa set in step S5), and the second condition (calculated in step S9). The condition that the shear stress degree τs (specifically, the shear stress degree τs calculated based on the maximum shear force Smax calculated in step S8) is smaller than the allowable shear stress degree τa set in step S5), and the third condition ( The angle 2α is set to satisfy both of the condition that the passive earth pressure Qp calculated in step S13 is larger than the horizontal force H' per pipe calculated in step S6.
Note that the pipe mutual angle 2α is not limited to an angle that satisfies all of the first, second, and third conditions, but may be an angle that satisfies at least one of the first, second, and third conditions. Good to have.

Furthermore, in the Λ type ground reinforcement structure 1, the length of the pipe 2 is longer than a predetermined length. This predetermined length is set to a value (pipe design length L ₀ ) determined by a design method (FIGS. 25 to 41) described later. Specifically, the length of the pipe 2 (at least the valley side pipe) constituting the Λ-type ground reinforcement structure 1 is determined based on the third condition (the passive earth pressure Qp calculated in step S13 is the pipe 1 calculated in step S6). The length L is set to be greater than or equal to ₀ , which satisfies the condition that the horizontal force borne per book is greater than the horizontal force H'.

As shown in FIGS. 1 to 6, the ground reinforcing structure 1 is installed so as to be completely buried inside the ground 10 behind the retaining wall. Therefore, since the entire ground reinforcement structure 1 is underground, it does not become an obstacle to land use, and the top drainage facility of the retaining wall 20 can be easily installed. For example, there is a root pile construction method (reinforced earth construction method) using cement milk as a construction method similar to the reinforcement construction method of this embodiment, but when reinforcing the retaining wall rear ground 10 located on the rear side of the existing retaining wall 20, In the construction method using cement milk, there is a risk that the existing retaining wall 20 will be affected due to expansion during solidification. Furthermore, the construction method using cement milk requires capping of the head on the ground surface, which poses a restriction on land use in narrow residential areas. Furthermore, if cement milk is used close to the retaining wall 20, it is possible that the function of the drainage holes in the retaining wall 20 will be affected. On the other hand, the reinforcement method of the present embodiment (method using the ground reinforcement structure 1 (II type ground reinforcement structure 1, Λ type ground reinforcement structure 1)) has the feature of being able to solve these problems.
The ground reinforcement structure 1 can be installed on the ground 10 behind the retaining wall before building the building 30, or can be installed after the building 30 is built. Moreover, when installing the ground reinforcement structure 1 before building the building 30, it is also possible to construct the building 30 directly above the ground reinforcement structure 1.

《Study of ground reinforcement structure》
[1 Introduction]
In the past, such as the Kumamoto Earthquake in April 2016, major earthquakes with a seismic intensity of 6 or higher have caused damage to retaining walls less than 3 meters in height, as well as significant damage to houses located behind retaining walls. Regarding retaining wall structure types, the damage rate is high for existing unsuitable retaining walls that require attention other than RC retaining walls. The safety of these existing unqualified retaining walls has not necessarily been sufficiently studied, and it is predicted that similar damage will occur if an earthquake of the same magnitude or greater occurs again, so it is necessary to reinforce such retaining walls. However, there is an urgent need to ensure the safety of existing housing.

Methods for reinforcing existing retaining walls include the restraining pile method, the ground reinforcement earth method, and the ground anchor method, but due to site restrictions, there are few examples where these methods can be applied to reinforcing retaining walls in detached houses. Another construction method that can be carried out even if there is not enough space on the site involves inserting mortar and reinforcing bars into holes drilled radially from the back of the retaining wall using a relatively small machine. However, when reinforcing the back of an existing retaining wall, the construction method using cement milk has the risk of affecting the existing retaining wall due to expansion during solidification. In addition, if capping of the head is required on the ground surface, it becomes a restriction on land use in narrow residential areas. Furthermore, if the ownership of a residential property changes, underground structures may be required to be removed or returned to vacant land. Therefore, the present inventors have been working on the development of a method for reinforcing retaining walls using small-diameter steel pipes (single pipes) with a diameter of 48.6 mm, as a method that is simpler and can be constructed using small machines. .
Here, we will explain the results of a study on the reinforcing effects of retaining walls using three different reinforcement specifications. Specifically, (1) Measurement results of the displacement of the retaining wall when a ``vertical load'' equivalent to the building load and a ``horizontal load'' assuming an earthquake force were loaded in a 1/10 model experimental soil tank. We will explain the reinforcement effects of each arrangement method, (2) the behavior of the soil on the back of the retaining wall measured and analyzed from the side of the earthen tank using the 2D image correlation method, and (3) the FEM trial analysis.

[2 Overview of model loading experiment]
[2.1 Experiment overview]
An experimental model was created assuming a residential area where a house is being constructed 1.5 m away from an existing unsuitable masonry retaining wall with a height of 3 m, width of 400 mm, slope of 70 degrees, and no backfill material. The comparative experiment was conducted as a 1/10 model of the above-mentioned hypothetical residential area, using an aluminum pipe with a diameter of 5 mm and a length of 600 mm as a reinforcing material to serve as pipe 2, and eight 40 mm x 40 mm x 195 mm aluminum rods stacked at an inclination angle of 70°. The wood was likened to a retaining wall 20. Further, a 140 mm x 195 mm x 12 mm iron plate (hereinafter referred to as a loading plate) was assumed to be the foundation of the building 30, and a vertical load and a horizontal load were loaded thereon.

[2.2 Experimental equipment]
Figure 7(a) shows an outline of the experimental soil tank used in the experiment. It consists of a soil tank made of 30 mm thick acrylic plates on five sides, 1500 mm wide x 1000 mm deep x 200 mm deep, a loading device, a measuring device, and a pedestal for fixing these. Loading was applied in stages in the vertical direction by installing loading plates on the ground behind the retaining wall and stacking weights, and at the same time in the horizontal direction to facilitate the generation of slip surfaces. Specifically, vertical loading is done by sequentially stacking iron plates with a constant load (approximately 22N) on top of the loading plate, and horizontal loading is adjusted horizontally to a load that is 0.2 times the vertical load using a piano wire on the loading plate. The material was loaded by pulling it with a steel plate. The displacement of the retaining wall was measured using laser displacement gauges installed in front of the retaining wall at two locations, the upper and lower. In addition, since a horizontal force was applied and the loading plate gradually moved horizontally, it was difficult to measure the displacement with a dial gauge, so the displacement of the loading plate was measured using image analysis. For the retaining wall, aluminum rods were fixed to the formwork, and after the retaining wall was filled with ground material at the back, it was removed from the formwork and grounded to the ground.

[2.3 Ground materials]
Air-dried Toyoura sand (ρdmax=1.652g/cm ³ , ρdmin=1.369g/cm ³ ) was used as the ground material. The upper part of the experimental soil tank had a relative density of Dr = 30% (ρd = 1.443 g/cm ³ ), and the lower part had a relative density of Dr = 50% (ρdmax = 1.497 g/cm ³ ) using the air drop method. The ground was prepared. This assumes that the original ground has been embanked to construct a retaining wall. To adjust the relative density, Toyoura sand was allowed to fall freely from a height of 40 cm for Dr = 30% and from a height of 70 cm for Dr = 50% while moving the V-shaped funnel horizontally. In order to eliminate as much as possible the effects of friction between the ground material and the acrylic plates, silicone oil is applied to the acrylic plates on the bottom and sides.

[2.4 Experimental case]
The experimental case (quantity/reinforcement specifications) and its measurement method are shown in Figure 7(b).
To ensure that the reinforcing material (aluminum tube) had a completely rough circumferential surface, double-sided tape was wrapped in advance and the reinforcing material (aluminum tube) was statically press-fitted into place. In addition, as an experimental case Case 0, an experiment without a reinforcing material, that is, without horizontal loading was added.

[2.5 Reinforcement material arrangement conditions and loading method]
To compare the reinforcement effects, (i) no reinforcement and (ii) reinforcement with 600 mm long reinforcement placed in a row parallel to the retaining wall at 40 mm intervals at the midpoint between the retaining wall and the building. method (hereinafter referred to as Type I reinforcement, see Figure 8(a)); (iii) reinforcement method in which reinforcing materials are arranged in two rows in a staggered manner at 20 mm intervals (hereinafter referred to as Type II staggered reinforcement; Figure 8 ( (see b)), (iv) a reinforcement method in which two reinforcing members are joined in a Λ-shape using a flexible clamp and arranged at 40 mm intervals (hereinafter referred to as Λ-shape reinforcement; see Fig. 8(c)). We considered reinforcement methods. These specifications are 1/10 of the expected construction size. Figure 8 shows the positional relationship of each experimental specification. Loading is a staged loading method.
In addition, type I reinforcement corresponds to type II type ground reinforcement structure 1 (for example, FIG. 3) that includes one reinforcement unit 4A, and type II staggered reinforcement corresponds to type II type ground reinforcement structure that includes a plurality of reinforcement units 4A. It can be said that it corresponds to the reinforcement structure 1 (for example, FIGS. 1 and 4), and the Λ type reinforcement corresponds to the Λ type ground reinforcement structure 1 (for example, FIGS. 2, 5, and 6).

[3 Reinforcement pull-out test]
In order to confirm the shear resistance of the reinforcing material and the prepared soil tank ground, and the pull-out resistance of the reinforcing material that plays the role of the second pipe (mountain side pipe), the pull-out test shown in Fig. 9(a) was carried out twice with the same specifications. Conducted twice. The results are shown in FIG. 9(b). The frictional force estimated from the pull-out load was 1.45 to 1.75 kN/m ² .

[4 Model soil tank loading test results]
[4.1 Displacement of model earthen tank retaining wall]
At the start of the experiment, the laser displacement meter was installed perpendicular to the retaining wall and fixed to the earthen tank, but the angle gradually changed as the retaining wall was displaced. Therefore, assuming that the retaining wall maintains a straight line, Figure 10 (a) and (b) show the horizontal displacement corrected from the displacement of the upper and lower retaining walls, taking into account the angle between the laser displacement meter and the retaining wall. , summarized in Figure 10(c). FIG. 10(a) shows the displacement 5 mm below the upper end of the retaining wall, and FIG. 10(b) shows the displacement 5 mm above the lower end of the retaining wall. In this experiment, the retaining wall was displaced as the vertical load equivalent to the building load and the horizontal load assuming an earthquake force increased, and measurements were continued until the retaining wall finally collapsed and could no longer be measured with a laser displacement meter. Figures 10(a) and 10(b) show the results up to the stage where measurements were possible and the points beyond that with arrows and x marks, except for the Λ-type reinforcement in which the retaining wall did not collapse until the maximum load was applied to the equipment. Note that the load up to the point where it could be measured is hereinafter referred to as "maximum load."

As shown in FIGS. 10(a) and 10(b), the displacement of the retaining wall at the maximum load stage is larger in the upper stage than in the lower stage for all reinforcement types. The horizontal displacement of the upper stage of Type I reinforcement and Type II staggered reinforcement was about four times larger than that of the lower stage, and it was observed that the retaining wall as a whole moved horizontally and rotated around the lower end of the retaining wall. On the other hand, with Λ-type reinforcement, the horizontal displacement of the upper stage is approximately twice that of the lower stage, and the movement during rotation is also small. In addition, in type I reinforcement and type II staggered reinforcement, the displacement of the retaining wall increases rapidly from around a vertical load of 300 N, and both reach the maximum load when the displacement of the upper level of the retaining wall is around 30 mm, and the displacement of the lower level is approximately 8 mm, and then It collapsed. Looking at the relationship between the vertical load and the horizontal displacement of the retaining wall in the Λ-type reinforcement, the retaining wall displacement increased almost linearly until the vertical load was around 300N. When compared at the same loading stage, Λ-type reinforcement had smaller displacements in both the upper and lower stages than I-type reinforcement and II-type staggered reinforcement. In addition, although an experiment (experimental case Case 0) was conducted in which only a vertical load was applied without applying any force in the horizontal direction, the retaining wall collapsed at the stage of a vertical load of 426.6N. The difference in displacement between the upper and lower retaining walls immediately before collapse was 2.74 mm, and the angle before collapse was approximately 70.3 degrees. This is considered to be the threshold for retaining wall collapse in this experiment.

[4.2 Inclination angle of model earthen tank retaining wall]
Figure 11 shows the relationship between the vertical load and the inclination angle of the retaining wall. At around a vertical load of 231.9N, Type I reinforcement and Type II staggered reinforcement exceeded the threshold of 70.3 degrees for the retaining wall inclination angle without horizontal force applied previously. However, without reinforcement, the retaining wall collapsed before reaching the threshold. As the vertical load increased, Type I reinforcement and Type II staggered reinforcement exceeded the threshold of 70.3 degrees for the retaining wall inclination angle, and collapsed after reaching 74.6 degrees. Since reinforcing materials were placed in Type I reinforcement and Type II staggered reinforcement, it is thought that the retaining wall did not collapse even if the threshold of 70.3 degrees was exceeded due to the effect of the reinforcement.

The relationship between vertical load and retaining wall inclination angle in Figure 11 showed a different tendency only for the Λ type reinforcement. With a vertical load of 341.1 N, the retaining wall inclination angle reached approximately 70.3 degrees, and the subsequent progression of the retaining wall inclination was gradual compared to other cases. At the stage of 875N, which is the vertical loading limit of the experimental equipment, the retaining wall inclination angle was 71.5 degrees. On the other hand, the displacement of the lower level of the retaining wall reached approximately 9 mm, exceeding the 8 mm displacement of the lower level where Type I reinforcement and Type II staggered reinforcement collapsed, and it is thought that although it slid, it did not collapse. As with type I reinforcement and type II staggered reinforcement, the reinforcement material is thought to resist the movement of the soil in particular in addition to resisting the sliding soil mass.

[4.3 Model soil tank loading experiment consideration]
The maximum vertical load is in the order of Λ-type reinforcement > II-type staggered reinforcement > I-type reinforcement > no reinforcement, and it is considered that the Λ-type reinforcement has a large reinforcing effect in terms of load.
From the relationship between vertical load and retaining wall displacement shown in Figures 10(a) and (b), type I reinforcement and type II staggered reinforcement both appear to have sticky behavior, but there is no clear difference between them. Not yet. In addition, in the Λ type reinforcement, the displacement was suppressed more than in the other experimental cases, and the soil behind the retaining wall appeared to be integrated, and only the Λ type reinforcement behaved differently.
It is thought that the experiment involved a combination of bearing capacity and earth pressure issues, but if the reinforcing material is used as a restraining pile, this experiment is considered to have confirmed the effectiveness of the reinforcing material.

[5 Behavior analysis of the soil inside the earth tank using 2D image correlation method]
[5.1 Measurement overview]
The 2D image correlation method is a method of directly detecting displacement and strain over the entire measurement range by analyzing an image of the surface of the object to be measured taken with a digital camera as shown in FIG. 12(a). Digital cameras were installed at two locations: 1.5 m from the front of the acrylic and 0.5 m directly above the retaining wall and loading plate. Digital images were taken simultaneously from the front and directly above at each level of vertical load (approximately 22 kN) until the retaining wall collapsed or until the maximum load of the experimental equipment. Note that "X" and "Y" in the figure indicate the direction of displacement of the analysis image shown later.
The basic principle is to compare images taken of the surface of an object to be measured before and after deformation, and to find the location where a point on the object surface before deformation has moved after deformation, thereby determining displacement. A conceptual diagram thereof is shown in FIG. 12(b). To find out where the object has moved, first, the way colored particles such as sandy mica are scattered on the surface of the acrylic board is preserved as a characteristic before and after deformation. Therefore, the brightness value distribution (light intensity distribution) before deformation of a calculation area consisting of a plurality of pixels called a subset is determined, and an area having a brightness value distribution highly correlated with the subset is searched from the deformed image. Determine the displacement of the subset and the direction in which it moved. The search result outputs a color-coded contour map superimposed on the actual image, but in order to clearly compare each reinforcement method, the contour map is extracted and displayed here.

[5.2 Accuracy of image analysis]
To confirm the accuracy of image analysis, we compared the amount of displacement determined by image analysis with the value measured by a laser displacement meter. Specifically, a 40 mm square pipe with a black and white mottled pattern drawn thereon for image analysis was pushed out approximately 0.4 mm at a time by rotating a bolt, and was displaced to approximately 5 mm. The amount of displacement was determined with the first point of interest near the tip of the square pipe and the second point of interest near the base, and compared with the measured value of the laser displacement meter. We conducted two experiments to confirm the results, and although the amount of displacement determined from image analysis was slightly larger than the value measured by the laser displacement meter, the results were generally correlated. It is thought that the amount of displacement determined by image analysis can be used for qualitative comparison of test results.

[5.3 Measurement results by image analysis]
Figure 13 shows an image taken from the side of the earthen tank when the unreinforced retaining wall was loaded just before it collapsed (vertical load 231.9N, horizontal load 48.8N), analyzed using the 2D image correlation method shown earlier. This figure shows a horizontal displacement contour diagram. The installation positions of each reinforcing material are indicated by broken lines.

Looking at the displacement contour diagrams for the unreinforced and each reinforcement type, there is an area that shows the amount of displacement from just below the loading plate to the retaining wall side, and it can be seen that the amount of displacement tends to decrease as it goes underground. In the case of no reinforcement, the displacement is distributed in a relatively evenly spaced stripe pattern, but on the other hand, when the reinforcement is placed, the angle of the contour becomes almost horizontal with the reinforcement as a boundary. In addition, the displacement distribution changes across the reinforcement material. In addition, when comparing the areas with horizontal displacement of 3.75 mm or more, the difference in displacement between type I reinforcement and type II staggered reinforcement is not large, but in the case of Λ type reinforcement, even though the vertical load is the same, The maximum horizontal displacement was 2.25 mm, indicating that the Λ type reinforcement suppressed the movement of the soil behind the retaining wall the most. In addition, when comparing the horizontal displacement of the retaining wall at the apex of the retaining wall, the amount of displacement is in the order of no reinforcement > I type reinforcement ≒ type II staggered reinforcement > Λ type reinforcement.

Figure 14 shows contour diagrams of horizontal displacement immediately before the retaining wall collapses in the case of no reinforcement, type I reinforcement, and type II staggered reinforcement, and at the time of maximum load in the case of Λ type reinforcement. Here, there is a part directly below the loading plate where the analysis contour is missing, but this part indicates a region (plastic region) where the deformation between soil particles is large and the soil particles lose their bonds and are destroyed. Furthermore, the reinforcing material shown by the broken line in FIG. 14 was added to connect it to the final position of the reinforcing material head, assuming that the tip of the reinforcing material was unchanged from the initial stage of loading. In addition, the assumed slip line has been added as a solid line.
In the case of no reinforcement, the fractured area traced an arc with a large curvature and reached near the bottom end of the retaining wall, indicating an arcuate sliding failure. On the other hand, when reinforcing materials were installed, the destroyed area stopped at the location of the reinforcing materials, and a triangular clod of earth was formed between the reinforcing materials and the retaining wall. Comparing the sizes of these earth clods, it is clear that the relationship is I-type reinforcement < II-type staggered reinforcement < Λ-type reinforcement, which is consistent with the reinforcing effect of the retaining wall shown in Figure 10.

FIG. 15 is a trace of the range where the bond between the soil particles described above is thought to have been lost, from the output image, and shows the transition each time a vertical load is applied.
The slope of the slip line is almost the same in all cases, and the failure area starts from the mountain side edge of the loading plate, and as the vertical load increases, this failure area progresses downward, but stops at the reinforcement material. . In addition, the soil mass between the reinforcement material and the retaining wall shown above has shrunk as if being scraped away from the top of the triangle, and the area of destruction has further expanded. This shows that the reinforcing material forms soil clods, and these soil clods serve as an element of resistance to sliding failure. Note that the loading plate of the Λ-type reinforcement is tilted in the opposite direction to the arrangement method of other reinforcements at the time of final load. This suggests that the supporting capacity of the retaining wall had been destroyed by the vertical force (31.3 kN/m ² ) before it collapsed.

Figure 16 shows the trajectory of the displacement and direction of a certain point in the earthen tank until the retaining wall collapses (up to the maximum load for Λ type reinforcement), as seen from the side of the earthen tank. In the case of no reinforcement, the horizontal displacement was greatest at the diagonal bottom of the retaining wall until just before the retaining wall collapsed. After that, when the retaining wall collapsed, there was a large displacement along the line from the mountain side end of the loading plate to the lower end of the retaining wall, resulting in a large difference from the surrounding area. Therefore, it is thought that this location was the boundary and the retaining wall slipped and collapsed from near the bottom end.
On the other hand, when looking at the trajectory directly under the loading plate when the reinforcing material is installed, the Λ type reinforcement moves deeper at an acute angle compared to the I type reinforcement and the II type staggered reinforcement. This appears to be caused by the diagonally installed reinforcement material acting as resistance and causing the soil particles to move downward. However, for both Type I reinforcement and Type II staggered reinforcement, it is observed that soil particles move from the loading plate to the retaining wall side, but no change in displacement is observed even after passing through the reinforcement material. . In other words, it seems that the reinforcement material did not act as a resistance to the movement of soil due to the applied load, and horizontal force acted directly on the retaining wall. In addition, in the case of I-type reinforcement and II-type staggered reinforcement, the amount of soil movement is larger as it gets closer to the soil tank surface, but in the case of Λ-type reinforcement, the movement is almost the same from the soil tank surface to just over 1/2 of the retaining wall height. The quantity is large. From the above, due to the effect of the reinforcing material, in the case of I-type reinforcement and II-type staggered reinforcement, the soil mass formed near the bottom of the retaining wall, and in the case of Λ-type reinforcement, the soil mass formed at the back of the retaining wall acts as resistance. It is assumed that the movement of the

Furthermore, FIG. 17 shows the displacement and its direction in I-type reinforcement, II-type staggered reinforcement, and Λ-type reinforcement as loci of movement of soil particles and reinforcing material as seen from above the soil tank. Here, the movement of the reinforcement is shown by dashed lines. Further, FIG. 18 shows the average values at each measurement position.
The movement of soil particles and reinforcement seen from above is the same as when viewed from the side, and there is no big difference between type I and type II staggered reinforcement, but in Λ type reinforcement, there is a difference between type I and type II staggered reinforcement. It is about 1/2. In addition, the movement of soil particles between reinforcements is smaller than the displacement of the reinforcement in I-type reinforcement and II-type staggered reinforcement, but it is larger than the displacement of the reinforcement in Λ-type reinforcement. This shows that the Λ-type reinforcement resists the horizontal movement of soil particles, that is, the horizontal force on the retaining wall.

As mentioned above, from the behavior analysis of the ground inside the earth tank using the 2D image correlation method, when a vertical load and a horizontal load of 0.2 times the vertical load are applied at a distance of 1/2 of the height of the retaining wall, the retaining wall can stand on its own without reinforcement. The retaining wall used in this experiment will undergo sliding failure even with a relatively small vertical force of 8.2 kN/m ² under this experimental specification. On the other hand, if the reinforcing material is placed between the loading plate and the retaining wall, the reinforcing material will act as resistance and no sliding failure will occur. However, with type I and type II staggered reinforcement, when the vertical and horizontal forces become larger, the upper end of the reinforcement does not resist the movement of the surrounding soil, and the horizontal force is applied to the retaining wall according to the deflection of the reinforcement. It is thought that it collapsed due to On the other hand, in Λ-type reinforcement, the deflection of the reinforcing material is small, so the force resisting horizontal force is larger than that of other reinforcement methods, and since there is little difference in soil displacement up to the depths, horizontal force is It is considered that the load on the retaining wall was dispersed and did not cause it to collapse.

Since one of the purposes of the present invention is to prevent damage to buildings, the load-settlement curve of a loading plate imitating a foundation was determined by image analysis. FIG. 19 shows the relationship between the vertical load and the amount of subsidence at the center of the loading plate measured by image analysis. Similar to the experimental measurement results of the upper and lower retaining wall displacements, the displacement of I-type reinforcement and II-type staggered reinforcement increases significantly when it exceeds a peak around 300N, and the inflection point of Λ-type reinforcement cannot be confirmed even as loading progresses. There wasn't. In other words, Type I reinforcement and Type II staggered reinforcement showed a clear inflection point, and after exceeding the peak, they sank significantly. On the other hand, the settlement with Λ type reinforcement is linear. The results showed that Λ-type reinforcement is particularly effective in reducing the impact on retaining walls and in reducing foundation (loading plate) subsidence.

[6 FEM trial analysis]
[6.1 FEM analysis model]
Using a three-dimensional elastic-plastic FEM analysis model, we created a model that reproduced the model soil tank experiment. The model ground, an aluminum block imitating a retaining wall, and a loading plate (18 cm x 14 cm x 1 cm) were modeled as solid elements, and the reinforcement material (diameter 5 mm, length 60 cm) was modeled as a beam element. Joint elements are created as friction between the retaining wall, loading plate, and the ground. The boundary conditions are that the bottom is completely fixed and the sides are frictionless roller boundaries.

The analysis parameters were determined based on the soil test results of the Toyoura standard sand used in the experiment, and the value of Dr = 30% was used for the soil behind the retaining wall, and Dr = 50% for the lower ground. The loading plate is made of steel, and the retaining wall and reinforcement materials are made of aluminum. Figure 20(a) shows the material parameters used in the analysis, and Figure 20(b) shows the parameters of the joint elements between the retaining wall, the loading plate, and the ground. Similarly, a joint element with the parameters shown in FIG. 20(c) was created between the reinforcement material and the ground. The normal stiffness K _n was the horizontal ground reaction force coefficient K _h , and the shear stiffness K _t and the maximum shear force were calculated from the results of the pull-out test of the reinforcing material.

[6.2 Analysis method]
A vertical load of 504 N (20 kN/m ² ) and a horizontal load of about 100 N, which are equivalent to those in the model experiment, were applied to the loading plate in 20 steps, and the relationship between the load and the displacement of the retaining wall in each case was compared. The reinforcement arrangement was the same as in the experiment, and analysis was conducted for four cases: no reinforcement, type I reinforcement, type II staggered reinforcement, and Λ type reinforcement.

[6.3 Analysis results]
FIG. 21 shows a graph showing the displacement of the upper and lower parts of the retaining wall. When compared under the same load, similar to the experimental results, when the reinforcing materials were arranged in a Λ-shape, the amount of displacement was smaller and the effect on the retaining wall was reduced. Although type I reinforcement and type II staggered reinforcement had a slight reinforcing effect, there was not much difference in the amount of displacement.
For each analysis case, FIG. 22 shows the composite displacement contour at the final load stage of a cross section of the earthen tank cut at the center in the Y direction. Comparing the Λ type reinforcement with other cases, it can be seen that the influence on the retaining wall direction is smaller.

FIG. 23 shows the plastic zone diagram of each reinforcement type when viewed from the same cross section as the displacement contour diagram. The areas plotted with circles indicate plasticized elements. In the plastic region, the plasticized elements reached the retaining wall without reinforcement, and this was also the case with type I reinforcement and type II staggered reinforcement. On the other hand, in the case of Λ-type reinforcement, the strength remains within the range along the diagonally placed reinforcement. In addition, the unreinforced specimen exhibited a sliding behavior from the loading plate toward the retaining wall, and this was also the case with the I-type reinforcement and the II-type staggered reinforcement. In the case of Λ-type reinforcement, the plastic region extends from just below the loading plate to the lower part of the ground along the reinforcing material, so it can be inferred that the effect on the retaining wall direction is reduced.

[6.4 Summary]
FEM analysis revealed that Λ-type reinforcement was the most effective reinforcement, similar to the experimental results and image analysis results.

[7 Design method]
[7.1 Conventional retaining wall measures]
[7.1.1 Measures against angle of repose]
When constructing a house near an existing retaining wall, it is necessary to investigate and diagnose the retaining wall, back ground, and supporting ground to confirm that there is no problem with the safety of the retaining wall even when the load of the house is applied. There is. However, since this work requires a considerable amount of cost and effort, we gave up on the safety confirmation work and took measures to prevent damage to the building even if the retaining wall collapses or deforms, so-called "angle of repose measures". is often applied.
Examples of angle of repose countermeasures include transmitting the building load to the ground below the angle of repose line using deep foundations, partial surface improvements, columnar improvements, steel pipe piles, etc. so that the building load does not act on (affect) the retaining wall. method is adopted.
However, even if angle of repose measures can prevent building collapse due to retaining wall collapse, it does not necessarily guarantee that there will be no negative effects.

[7.1.2 Measures to ensure the safety of residential land retaining walls and buildings]
Examples of reinforcement measures to increase the safety of existing retaining walls include (1) replacing or solidifying the back ground with lightweight soil, (2) using landslide prevention piles and reinforced earthwork methods, and (3) soil nailing + slope framework. There are various construction methods such as (4) root pile.
However, with conventional construction methods, there are issues such as safety of the retaining wall during construction, securing construction space, restrictions on construction machinery, and construction costs, making it quite difficult to apply it to retaining walls on small-scale residential lots.
As a result, there is currently no progress in making existing residential retaining walls earthquake resistant.

[7.2 Proposal for reinforcement measures for existing residential property retaining walls]
[7.2.1 Concept of reinforcement measures]
The reinforcement method of this embodiment is mainly aimed at block retaining walls, and applies the concept of landslide prevention piles, as will be described later. The principle is that a single pipe treated with anti-corrosion treatment by special plating is rotated vertically or diagonally penetrated into the back ground of a block retaining wall to a predetermined depth, and the bending strength and shear strength of the single pipe and the ground below the landslide line are measured. The objective is to increase the safety factor (resistance) against landslides by using the passive resistance of the ground in front of the single pipe, which is deeply embedded, and to ensure safety (required safety factor) both at all times and during earthquakes.
It goes without saying that this reinforcement increases the safety of the retaining wall, but even if a building is constructed on the ground behind the retaining wall (even if the building load is applied), it is possible to ensure the necessary safety factor at all times and during earthquakes. It also serves as a kind of angle of repose measure.
Figures 1 to 6 show conceptual diagrams of the proposed reinforcement measures, and the pipe 2 (single pipe) is installed vertically with type II type ground reinforcement structure 1 (Figures 1, 3, and 4) facing toward each other. Two types of ground reinforcement structure 1 (Fig. 2, Fig. 5, Fig. 6) can be considered: the Λ type ground reinforcement structure 1 (Fig. 2, Fig. 5, and Fig. 6), which is installed diagonally on the ground. The respective landslide resistance mechanisms are shown in Figure 24.

Type II ground reinforcement structure 1 has a pipe 2 (single pipe) installed vertically, and bends and shears the pipe 2 against the earth pressure (sliding force) above the assumed landslide line (moving layer). Landslide prevention is enhanced by the resistance and passive resistance of the ground in front of the single pipe, which is embedded below the slip line (immobile layer). At this time, the resistance of the moving layer in front of the pipe is not considered.
Type II type ground reinforcement structure 1 has a simple shape and is easy to design and construct, but the pipe 2 (single pipe) has an extremely small diameter of 48.6 mm, so its bending strength is not high, and the finding height is It is difficult to apply to retaining walls exceeding 2 m (pipe spacing W and number of pipe rows n are unrealistic).

The Λ type ground reinforcement structure 1 was devised to compensate for the weaknesses of the type II type, and among the pipes 2 installed diagonally toward each other, the valley side pipe and the mountain side pipe each have the following roles. shall be shared.
Valley side pipe: Acts as a bending/shearing resistance element against sliding force.
Mountain side pipe: The perpendicular component _RH of the pull-out resistance _Rt with respect to the valley side pipe acts as a slip resistance element for the valley side pipe.
Since this arrangement reduces the horizontal force acting on the valley side pipe, it is possible to reduce the bending moment and shear force generated on the valley side pipe.
Although the construction of the Λ type ground reinforcement structure 1 is slightly more complicated than that of the II type, it has the advantage of being able to rationalize the pipe spacing W and the number of pipe rows n.

[7.2.2 Concept of landslide prevention piles]
There are two ways of thinking about landslide prevention piles: ``shear piles'' and ``retaining piles.'' The reinforcement measures proposed this time apply the concept and design method of "holding piles" in consideration of safety.
Shear piles are designed based on the concept of stabilizing against landslides using only the pile's shear resistance on the sliding surface. The use of shear piles is only possible if a sufficient passive area of the ground in front of the piles can be secured. They are often designed on the more dangerous side than restraint piles, which take into account the bending moment generated in the piles.
The restraining piles are designed based on the idea that the pile above the sliding surface is treated as a cantilever beam. In other words, it is designed so that no resistance is expected from the moving layer on the Kuilei side. It is generally adopted as a design method for landslide prevention piles. Although they are safer than shear piles, even if the shear strength of the piles is satisfactory, the bending strength becomes a bottleneck, so it is necessary to increase the bending strength of the piles or narrow the installation interval.

[7.2.3 Design method for restraining piles]
In the design method of this embodiment, the following four items are checked and considered.
(1) Checking the bending moment (stress degree)...Is the maximum bending moment (stress degree) of the pile less than the allowable bending moment (stress degree)?(2) Checking the shear (stress degree)...The maximum shear force (stress degree) of the pile (3) Calculation of required embedment length ... Calculation of embedment depth into immovable layer that can resist horizontal force as a pile (4) Yield failure of embedment ground Consider whether the passive earth pressure in the ground in front of the pile penetration exceeds the acting horizontal force of the pile. In addition to the above four items, check the amount of horizontal displacement (whether the amount of horizontal displacement generated at the head of the pile is allowable). (below the amount of displacement).

[7.2.4 Design flow of reinforcement measures]
FIG. 25 shows a design flow for the reinforcement measures of this embodiment. That is, an example of the design method of the ground reinforcement structure 1 in this embodiment will be explained using FIG. 25.
First, a ground investigation and a soil test are performed on the ground 10 behind the retaining wall (step S1). Specifically, as a ground investigation, for example, an SPT test (standard penetration test) or an SWS test (screw weight penetration test) is performed. In addition, as a soil test, for example, a uniaxial compression test or a triaxial compression test is performed.
Next, the current safety factor is set to 0.95 to 1.00 (step S2). Specifically, for example, the current safety factor is set to 0.95 to 1.00, and then, among the slip surface strengths (c, φ), the adhesion forces C ₁ and C ₂ are calculated using the test results in step S1 ( For example, the internal friction angles φ ₁ and φ ₂ are calculated by inverse calculation based on the average layer thickness of slip. Alternatively, the internal friction angles φ ₁ and φ ₂ may be estimated from the empirical values and the N value, and the adhesive forces C ₁ and C ₂ may be back calculated.

Next, as shown in FIG. 26, for example, a ground constant is set (step S3). Specifically, for example, based on the test results in step S1 (and the calculation results in step S2), the adhesive force C ₁ , the internal friction angle φ ₁ , and the unit volume weight γ ₁ are set as the ground constants of the moving layer ( At the same time, the adhesive force C ₂ , internal friction angle φ ₂ , unit volume weight γ ₂ , N value, and Young's modulus E ₀ are set (input) as ground constants of the immobile layer.
That is, step S1 (and step S2) is a process for determining the ground constant set in step S3. Therefore, the test (ground investigation, soil test) performed in step S1 is not limited to the above-mentioned test as long as it can determine the ground constant set in step S3.

Next, as shown in FIG. 27, for example, circular arc slip calculations are performed for normal conditions and during earthquakes (step S4). Specifically, for example, based on the ground constant etc. set in step S3, a circular arc slip calculation is performed for the constant state, and the constant minimum safety factor (current safety factor) Fs _min and the constant minimum safety factor Fs _min are obtained. Find the arc radius r, the sliding moment M _S that gives the constant minimum safety factor Fs _min , etc. In addition, based on the ground constant etc. set in step S3, arc slip calculation for earthquakes is performed, and the minimum safety factor (current safety factor) Fs _min for earthquakes and the arc radius that provides the minimum safety factor for earthquakes Fs _min are calculated. r, the sliding moment M _S that gives the minimum safety factor Fs _min during an earthquake, etc. are determined. In addition, in this embodiment, the horizontal seismic intensity kh at the time of an earthquake is set to kh=0.25, but it is not limited to this.

Thereafter, as shown in FIG. 28, for example, the necessary deterrent force P _r is calculated.
Specifically, the sliding force (sliding force) that provides the minimum safety factor Fs _min at all times is calculated based on the sliding moment _MS that provides the minimum safety factor Fs _min at all times, and the arc radius r that provides the minimum safety factor Fs _min at all times. Power) After calculating T _S , the always required deterrent force is calculated based on the always required safety factor Fs _n , the always minimum safety factor Fs _min , and the slip force T _S that makes the always minimum safety factor Fs _min . (Insufficient resistance force) P _r is calculated. In addition, in this embodiment, the constant required safety factor Fs _n is set to Fs _n =1.50, but it is not limited to this.

In addition, the sliding force (sliding force) that provides the minimum safety factor Fs _min during an earthquake is calculated based on the sliding moment M _S that provides the minimum safety factor Fs _min during an earthquake, and the arc radius r that provides the minimum safety factor Fs _min during an earthquake. After calculating the power) _TS , calculate the required safety factor during an earthquake based on the required safety factor Fs _n , the minimum safety factor Fs _min during an earthquake, and the slip force T _S that makes the minimum safety factor Fs _min during an earthquake. Calculate the necessary deterrent force (insufficient resistance force) P _r . In addition, in this embodiment, the required safety factor Fs _n in the event of an earthquake is set to Fs _n =1.00, but it is not limited to this.
In addition, in the present embodiment, in step S4, circular arc slip calculations are performed both at normal times and during earthquakes to obtain the required deterrent force P _r ; however, the present invention is not limited to this, and in step S4, linear slip calculations are performed at all times and during earthquakes. The necessary deterrent force P _r may also be obtained by performing the following.

Next, as shown in FIG. 29, for example, the material, dimensions, and strength characteristics of the pipe 2 are set (step S5). Specifically, for example, the material of the pipe 2, the diameter (pile diameter) D, wall thickness t, and cross-sectional area A as the dimensions of the pipe 2, the reference strength F, the allowable bending stress degree σa, and the strength specification of the pipe 2, The allowable shear stress degree τa, the second moment of area I, the section modulus Z, and the Young's modulus E are set (input).
In this embodiment, a general structural carbon steel pipe (JIS G 3444 STK500) is used as the pipe 2, so as shown in FIG. 29, in step S5, the material, dimensions, and strength characteristics of the general structural carbon steel pipe are determined. Set. Note that the pipe 2 is not limited to a general structural carbon steel pipe.

Next, as shown in FIGS. 30 and 31, for example, the arrangement of the pipes 2 is assumed (step S6). Specifically, for example, it is assumed that the pipe interval (pile interval) W, the number of pipe rows (pile rows) n, and the mutual pipe angle 2α. In the case of type II, the pipe mutual angle 2α is assumed (set) to be 2α=0.
In addition, in this embodiment, in the type II type ground reinforcement structure 1, when a plurality of reinforcement units 4A are provided (that is, when the number n of pipe rows is 2 or more), the interval J (m) between the reinforcement units 4A is J=0.25, but is not limited to this.
Furthermore, in this embodiment, in the Λ type ground reinforcement structure 1, when a plurality of reinforcement units 4B are provided (that is, when the number n of pipe rows is 2 or more), the interval J (m) between the reinforcement units 4B is J=0.25, but is not limited to this.

After that, as shown in FIGS. 30 and 31, for example, the assumed pipe spacing W, the number of pipe rows n, and the pipe mutual angle 2α, the allowable pull-out resistance Rt of the pipe 2, and the required deterrent force P _r calculated in step S4 are determined. , the inclination angle θ of the slip surface 12 obtained by the slip calculation in step S4, and the load condition of the pipe 2 is calculated. In the present embodiment, the allowable pulling resistance Rt of the pipe 2 is set to Rt=Ru/3 (Ru: ultimate tensile force of the pipe 2), but is not limited to this.
Specifically, as the load conditions for the pipe 2, a horizontal force H' to be borne by each pipe and a vertical force V' to be borne by each pipe are calculated. That is, after calculating the burden horizontal force Hu per unit width based on the required deterrent force Pr, the inclination angle θ, and the pipe mutual angle 2α, the calculated burden horizontal force Hu per unit width and the pipe interval are calculated. The burden horizontal force H' per pipe is calculated based on W, the number n of pipe rows, the allowable pulling resistance Rt of the pipe 2, and the mutual pipe angle 2α. In addition, the vertical force to be borne per pipe is determined based on the required deterrent force Pr, the inclination angle θ, the pipe mutual angle 2α, the pipe interval W, the number of pipe rows n, and the allowable pulling resistance Rt of the pipe 2. Calculate V'.

Further, in step S6, the effective length Le of the pipe 2 is calculated based on the apparent height h of the retaining wall 20 set in step S4 and the embedded length Ld (m) of the pipe 2. In this embodiment, the embedding length (dry casting depth) Ld of the pipe 2, which is the distance from the upper surface (top) of the retaining wall rear ground 10 to the upper end of the pipe 2, is set to Ld=0.5. It is not limited.
In addition, in step S6, the allowable pulling resistance Rt of the pipe 2, the mutual pipe angle 2α, the effective length Le of the pipe 2, the burden horizontal force Hu per unit width, the pipe interval W, the number n of pipe rows, The height Ls' of the point of application of the resultant force is calculated based on the horizontal force H' per pipe. In this embodiment, if the value of the calculated height Ls' of the point of application of the resultant force is less than 0, a substitute value (for example, 0.01) is used instead of the calculated value as the height Ls' of the point of application of the resultant force. However, it is not limited to this.

Next, as shown in FIG. 32, for example, the horizontal ground reaction force coefficient _kh and the characteristic value β of the pipe 2 are calculated (step S7).
Specifically, the horizontal ground reaction force coefficient k _h is calculated based on the coefficient α, the Young's modulus E ₀ of the immobile layer set in step S3, and the diameter D of the pipe 2 set in step S5. In this embodiment, when the immovable layer is clayey soil, the coefficient α is set to α=60, and when the immobile layer is sandy soil, the coefficient α is set to α=80, but it is not limited to this. do not have.
Further, the characteristic value β of the pipe 2 is calculated based on the calculated horizontal ground reaction force coefficient _kh and the diameter D, Young's modulus E, and second moment of area I of the pipe 2 set in step S5.

Next, as shown in FIGS. 33 and 34, for example, the maximum bending moment Mmax and the maximum shearing force Smax are calculated (step S8).
Specifically, after calculating the maximum bending moment generation depth Lm based on the characteristic value β of the pipe 2 calculated in step S7 and the height Ls' of the point of application of the resultant force calculated in step S6, the maximum bending moment generation depth Lm, the horizontal force H' to be borne per pipe calculated in step S6, the characteristic value β of pipe 2 calculated in step S7, and the height of the point of application of the resultant force calculated in step S6. The maximum bending moment Mmax is calculated based on Ls'. In the case of the Λ type, in step S8, in addition to the maximum bending moment Mmax (maximum bending moment Mmax in the stationary layer part), the maximum bending moment Mmax1 in the moving layer part is also determined.
Further, after calculating the maximum shear force generation depth Ls2 in the immovable layer based on the characteristic value β of the pipe 2 calculated in step S7 and the height Ls' of the point of application of the resultant force calculated in step S6, The calculated maximum shear force generation depth Ls2, the horizontal force H' per pipe calculated in step S6, the characteristic value β of the pipe 2 calculated in step S7, and the point of action of the resultant force calculated in step S6. The maximum shear force Smax2 in the immovable layer portion is calculated based on the height Ls'. Then, the maximum shear force Smax1 in the moving layer section (that is, the horizontal force H' borne per pipe calculated in step S6) and the maximum shear force Smax2 in the stationary layer section are compared, and the larger one is determined as the maximum shear. Set as the force Smax.

Next, as shown in FIGS. 35 and 36, for example, bending stress and shear stress are checked (step S9).
Specifically, the maximum bending moment Mmax calculated in step S8, the section modulus Z of the pipe 2 set in step S5, the burden vertical force V' per pipe calculated in step S6, and the set in step S5. The bending edge stress degree σb is calculated based on the cross-sectional area A of the pipe 2, and the first condition that the calculated bending edge stress degree σb is smaller than the allowable bending stress degree σa of the pipe 2 set in step S5. Determine whether the following is satisfied. In the case of the Λ type, the bending edge stress degree σb1 in the moving layer part is calculated using the maximum bending moment Mmax1 in the moving layer part, and the maximum bending moment Mmax (maximum bending moment Mmax in the stationary layer part) is used to calculate the bending edge stress degree σb1 in the moving layer part. The bending edge stress degree σb2 in the layered portion is calculated, and it is determined whether the larger of the calculated bending edge stress degrees σb1 and σb2 is smaller than the allowable bending stress degree σa of the pipe 2.
Further, the shear stress degree τs is calculated based on the stress concentration coefficient κ, the maximum shear force Smax set in step S8, and the cross-sectional area A of the pipe 2 set in step S5, and the calculated shear stress degree τs It is determined whether or not the second condition that is smaller than the allowable shear stress degree τa of the pipe 2 set in step S5 is satisfied. In this embodiment, the stress concentration coefficient κ is set to κ=2, but the present invention is not limited to this.

Then, if both the first condition and the second condition are not satisfied, or if one of the first condition and the second condition is not satisfied (step S10; No), the process moves to step S6, and the pipe interval W is Assume (review) the number of pipe rows n and the pipe mutual angle 2α (2α=0 in the case of Type II type).
On the other hand, if both the first condition and the second condition are satisfied (step S10; Yes), the process moves to step S11.

In step S11, as shown in FIG. 37, for example, the penetration length Lr and the total length L of the pipe 2 are calculated (step S11).
Specifically, the required penetration length Lr of the pipe 2 is calculated based on the characteristic value β of the pipe 2 calculated in step S7. In the example shown in FIG. 37, the required penetration length Lr of the pipe 2 is set to a value calculated by Lr=1.5×π/β, but the required penetration length Lr is Lr≧1.5× Any value that satisfies π/β may be used.
Further, the total length L of the pipe 2 is calculated based on the calculated required penetration length Lr and the effective length Le of the pipe 2 calculated in step S6. In the example shown in FIG. 37, the total length L of the pipe 2 is set to a value calculated by L=Le+Lr, but the total length L may be any value that satisfies L≧Le+Lr.
Furthermore, in step S11, the pipe design length _L0 is also calculated. In this embodiment, a value obtained by rounding up the whole length L to the nearest whole number is set as the pipe design length _L0 , but the pipe design length L0 is not limited to this.

Next, as shown in FIGS. 38 and 39, for example, horizontal displacement is calculated (step S12).
Specifically, the characteristic value β of the pipe 2 calculated in step S7, the height Ls' of the point of application of the resultant force calculated in step S6, the Young's modulus E and the second moment of area I of the pipe 2 set in step S5. The amount of displacement δ1 on the slip surface is calculated based on the horizontal force H' per pipe calculated in step S6.
Furthermore, the characteristic value β of the pipe 2 calculated in step S7, the height Ls' of the point of application of the resultant force calculated in step S6, the Young's modulus E and the second moment of area I of the pipe 2 set in step S5, and the step The amount of displacement δ2 due to the deflection angle on the sliding surface is calculated based on the horizontal force H' per pipe calculated in S6 and the effective length Le of the pipe 2.
In addition, the horizontal force H' per pipe calculated in step S6, the load degree P at the bottom calculated from the effective length Le, the effective length Le, the Young's modulus E and the cross section of the pipe 2 set in step S5. The deflection displacement amount δ3 of the moving layer portion is calculated based on the second moment I.

Next, as shown in FIG. 40, for example, the yield failure of the ground in which the pipe is embedded is checked (step S13).
Specifically, the safety factor Fs, the diameter D of the pipe 2 set in step S5, the adhesive force C ₂ of the immobile layer set in step S3, the internal friction angle φ ₂ and the unit volume weight γ ₂ , and step S3 The passive earth pressure in front of the pipe is calculated based on the unit volume weight γ ₁ of the moving bed set in step S11, the required penetration length Lr of the pipe 2 calculated in step S11, and the effective length Le of the pipe 2 calculated in step S6. Qp is calculated, and it is determined whether the third condition that the calculated passive earth pressure Qp is larger than the burden horizontal force H' per pipe calculated in step S6 is satisfied. In this embodiment, the safety factor Fs is set to Fs=1.5, but is not limited to this.
If the third condition is not satisfied (step S14; No), the process moves to step S6, and the pipe interval W, the number of pipe rows n, and the mutual pipe angle 2α (2α=0 in the case of type II type) are determined. Make assumptions (review) again. In addition to (or instead of) reviewing the pipe interval W, the number of pipe rows n, and the pipe mutual angle 2α, the penetration length Lr (Lr≧1.5×π/β) of the pipe 2 is set again in step S11. (review).

On the other hand, if the third condition is satisfied (step S14; Yes), the pipe interval W, the number n of pipe rows, and the pipe mutual angle 2α assumed (set) in the latest step S6 are acquired. Furthermore, the pipe design length L ₀ calculated (set) in the latest step S11 is acquired.
As a result, the first condition that the maximum bending moment of the pipe 2 is less than the allowable bending moment, the second condition that the maximum shear force of the pipe 2 is less than the allowable shear force, and the passive soil of the ground in front of the insertion part of the pipe 2 are satisfied. It is possible to obtain the pipe interval W, the number n of pipe rows, the mutual pipe angle 2α, and the pipe design length _L0 that satisfy all of the third condition that the pressure exceeds the horizontal force acting on the pipe 2.
FIG. 41 shows the pipe design length L ₀ , pipe interval W, number of pipe rows n, and pipe mutual angle 2α obtained in the examples shown in FIGS. 26 to 40.

[7.2.5 Construction example of ground reinforcement structure]
The pipe 2 having the pipe design length L ₀ obtained as described above is connected to the retaining wall rear ground 10 using the obtained pipe interval W, number of pipe rows n, and pipe mutual angle 2α (2α=0 for type II type). The ground reinforcement structure 1 is constructed by installing the ground reinforcement structure within the ground.
For example, as in the case of the _Λ type shown in FIG. may be adopted, or the value at the time of the earthquake may be adopted. For example, if the pipe spacing W at normal times is different from the pipe spacing W during an earthquake, either pipe spacing W may be adopted, but the safer (narrower) pipe spacing W (Λ in FIG. 41) may be adopted. In the case of mold type, it is preferable to use the regular pipe spacing W). In addition, if the pipe design length L ₀ at normal times and the pipe design length L ₀ during an earthquake are different, either pipe design length L ₀ may be adopted, but the safer (longer) pipe design It is preferable to adopt a length L ₀ . In addition, if the number n of pipe rows at normal times is different from the number n of pipe rows at the time of an earthquake, either number n of pipe rows may be adopted, but the number n of pipe rows on the safer side (the one with more) is It is preferable to adopt it. In addition, if the pipe mutual angle 2α at normal times and the pipe mutual angle 2α during an earthquake are different, either pipe mutual angle 2α may be adopted, but the safer (larger) pipe mutual angle 2α may be adopted. It is preferable to adopt it.

When constructing the ground reinforcement structure 1, first, a pipe 2 having a length equal to or greater than the acquired pipe design length _L0 is prepared.
Next, as shown in FIG. 42, the top of the retaining wall rear ground 10 is dug to form a hole 14 (empty part).

Next, as shown in FIG. 43, after the coupling member 3 is placed in the hole 14, the prepared pipe 2 is pushed through the hole 14. This pushing operation is performed according to the obtained pipe mutual angle 2α, pipe interval W, and number of pipe rows n. Note that the order in which the coupling members 3 are installed does not matter.
Specifically, for example, a pouring machine is installed parallel to the retaining wall 20, and the leader is tilted at a predetermined angle. In the case of this embodiment, in the Λ type, the angle between the imaginary vertical line and the valley side pipe is approximately equal to the angle between the imaginary vertical line and the mountain side pipe, so the angle at which the leader is tilted is set at an angle α ( = pipe mutual angle 2α/2). Then, (1) insert the prepared pipe 2 into the center of the drifter and move the drifter to the top of the leader. (2) Attach the pipe 2 to the drifter, and push the pipe 2 in by press-fitting, impact, vibro, etc. Thereafter, the leader is tilted at a predetermined angle (angle α in the case of the present embodiment) in the opposite direction to the pushed-in pipe 2, and the pipe 2 is pushed in in the same manner as in (1) and (2).

Next, as shown in FIG. 44, the pipe 2 is joined to the joining member 3 using a joining member (clamp (or wire, etc.)). Although FIGS. 43 and 44 illustrate the case of the Λ type, the same applies to the case of the II type.
Finally, as shown in FIGS. 1 to 6, the hole 14 is backfilled. Thereby, the ground reinforcing structure 1 is installed in the ground of the retaining wall rear ground 10.
In addition, in the Λ type, the valley side pipe and the mountain side pipe were installed symmetrically, that is, the angle of the valley side pipe with respect to the vertical direction and the angle of the mountain side pipe with respect to the vertical direction were made the same, but this is not limited to this. . In other words, as long as the obtained pipe mutual angle 2α is satisfied, for example, instead of installing both diagonally, the valley side pipe may be installed diagonally and the mountain side pipe vertically, or the mountain side pipe may be installed diagonally, and the mountain side pipe may be installed vertically. The pipes may be installed diagonally and the valley side pipes may be installed vertically.

[7.3 Comparison of design methods (retaining piles and shear piles)]
We verified how much the difference in design methods such as restraining piles and shear piles affects the arrangement of pipes 2 (number of pipe rows n, pipe spacing W) between reinforcement type II type staggered reinforcement and Λ type reinforcement. The design flow (FIG. 25) of this embodiment is a design flow of the "holding pile design method". Further, FIG. 45 shows an example of the design flow of the "shear pile design method".
In the shear pile design method, for example, the process of calculating the maximum bending moment Mmax and the maximum shear force Smax (step S8) and the process of calculating the horizontal displacement (step S12) are not performed. Furthermore, instead of the process of checking the bending stress and the shear stress (step S9), the process of checking the shear stress τs (here, τs=H'/A) (step S15) is performed, and the second condition is If (the condition that the shear stress degree τs is smaller than the allowable shear stress degree τa) is satisfied (step S16; Yes), the process moves to step S11. That is, in the shear pile design method, since the bending stress is not verified, the first condition (the condition that the bending edge stress degree σb is smaller than the allowable bending stress degree σa) may not be satisfied.

[7.3.1 Calculation of slip safety factor Fs and required deterrent force Pr using the straight line slip method]
(1) Calculation conditions Figures 47(a) to (e) show the back ground conditions, retaining wall conditions, load conditions, immobile layer ground conditions, and pipe pull-out resistance in the calculation conditions diagram (Figure 46).
(2) Straight-line slip calculation results Straight-line slip calculations were performed by dividing the slip range into two types: 4 parts and 3 parts, as shown in FIG. In addition, the slip angle θ was varied from 5° to 60° as shown in FIG. 46, and the sliding force, resistance force, safety factor, required safety factor, and necessary deterrent force were calculated at normal times and during earthquakes. The slip calculation results are shown in FIG. 49.

[7.3.2 Summary]
Slip calculation results shown in FIG. 49 (always: sliding force Ts = 66.5 kN, resistance force R = 80.1 kN, safety factor Fs = 1.20, required safety factor Fsn = 1.50, required deterrent force Pr = 19. 7kN, inclination angle θ = 30°, earthquake: sliding force Ts = 95.3kN, resistance force R = 75.4kN, safety factor Fs = 0.79, required safety factor Fsn = 1.00, required deterrent force Pr = 19.9 kN, inclination angle θ = 30°), the number n of pipe rows and pipe spacing W in the restraining pile design method, and the number n of pipe rows and pipe spacing W in the shear pile design method are shown in Figure 50. Shown below. Comparing the arrangement of the pipes 2, it is clear that the design method using holding piles allows for a safer design because the pitch of the pipes 2 (pipe interval W) is narrower.
For the above reasons, in this embodiment, the "holding pile design method" is adopted as the design method.
In addition, the "shear pile design method" may be adopted as the design method. That is, the number n of pipe rows and the pipe interval W (in the case of the Λ type, the number n of pipe rows, the pipe interval W, and the mutual pipe angle 2α) satisfy at least the second condition among the first condition, the second condition, and the third condition. It may be one that satisfies the following.
In addition, the number of pipe rows n and the pipe spacing W (in the case of the Λ type, the number of pipe rows n, the pipe spacing W, and the pipe mutual angle 2α) are determined by at least the first condition among the first condition, the second condition, and the third condition. It may be one that satisfies the following.
In addition, the number of pipe rows n and the pipe spacing W (in the case of the Λ type, the number of pipe rows n, the pipe spacing W, and the pipe mutual angle 2α) are determined by at least the third condition among the first condition, the second condition, and the third condition. It may be one that satisfies the following.

[7.4 Verification of reinforcement effect by restraining pile design method]
[7.4.1 Verification of model soil tank experiment using restraining pile design method]
Figure 51 shows a comparison of the reinforcement pitch at maximum load in model earth tank experiments Cases 2 to 4, the number of reinforcement rows n, and the reinforcement pitch W determined by the restraining pile design method.
The soil constants (c, φ) used in the calculation were determined by inverse calculation assuming that the safety factor Fs at the maximum load in Case 1 without reinforcement is Fs=1.00. As a result of back calculation, the internal friction angle φ1 of the moving layer was 33°, and the adhesive force C1 was 1.25 kN/m ² . Calculations were performed using this soil constant, and the reinforcement pitch W in the model soil tank experiment was compared with the reinforcement pitch W calculated by the restraining pile design method.

As shown in FIG. 51, it was confirmed that the reinforcement body pitches W calculated by the model soil tank experiment and the restraining pile design method almost matched in type I reinforcement and type II staggered reinforcement. In addition, in the case of Λ-type reinforcement, it was confirmed that the reinforcing body pitch W calculated using the restraining pile design method was narrower, and that the restraining pile design method could be designed on the safer side.
From the above, it can be said that the design of the reinforcement method of this embodiment is possible by finding the required safety factor by linear slip calculation and using the "holding pile design method".

[7.4.2 Comparison of reinforcement effects under the same load condition]
Reinforcement arrays for each reinforcement method at the maximum load stage (vertical load: P = Mv = 405.3N, horizontal load: H = Mh = 85.6N) of soil tank model experiment type I reinforcement (experiment case Case 2) The number n and the reinforcement pitch W are shown in FIG.
As shown in Fig. 52, the reinforcement pitch W of type II staggered reinforcement is 80 mm and the number of reinforcement rows n is 2 rows, and the reinforcement pitch W of type I reinforcement is 40 mm and the number n of reinforcement rows is 1 row. be. Therefore, it can be said that the reinforcement body pitch W of type II staggered reinforcement and type I reinforcement is the same. Further, in the Λ type reinforcement, the reinforcement body pitch W (arrangement interval) is 2.0 times that of the I type reinforcement.
From the above, it can be said that if the load conditions are the same, the reinforcing effect can be expected in the order of Λ type reinforcement > II type staggered reinforcement = I type reinforcement. The reason why the Λ-type reinforcement has a large reinforcing effect is largely related to the pull-out resistance Rt of the mountain side pipe (here, Rt=0.015×resistance efficiency η=0.010 kN: η=0.682).

[7.5 Comparison of safety factors between linear slip and circular arc slip]
In the restraining pile design method, there are two possible methods for calculating the necessary restraining force: "straight line sliding" and "circular sliding". Here, we will examine how much variation there is in the safety factors between the two. Specifically, the safety factors were compared under one calculation condition.

[7.5.1 Calculation conditions]
Figure 53 shows the calculation conditions for linear slip and circular arc slip. Regarding the ground conditions, the ground was divided into two layers, and the soil texture was changed to ``sandy'', ``viscous'', and ``intermediate soil'' for the upper and lower layers, respectively, and calculations were performed both at normal times and during an earthquake.

[7.5.2 Safety factor comparison]
A comparison chart of safety factors is shown in FIG. The safety factors for straight-line slips and circular arc slips were generally correlated. Specifically, when the upper layer is clay and the lower layer is sandy (square plot), arc slip has a higher safety factor, whereas when the upper layer is sandy and the lower layer is clay (round plot), linear slip has a higher safety factor. It tends to get bigger. We believe that this can be explained to some extent by the length of the slip surface and the angle of the slip surface. In addition, the intermediate soil (star plot) is relatively scattered.

"effect"
According to this embodiment, the ground reinforcement structure 1 for reinforcing the retaining wall back ground 10 located on the back side of the retaining wall 20 is a ground reinforcing structure for increasing the resistance of the retaining wall back ground 10 against sliding failure. , a plurality of pipes 2 are buried in the ground 10 behind the retaining wall, and the lower end portions are installed deeper than the sliding surface 12 of the ground 10 behind the retaining wall. The first condition is that the stress degree σb) is less than the allowable bending moment (allowable bending stress degree σa), and the second condition is that the maximum shear force of the pipe 2 (shear stress degree τs) is less than the allowable shear force (allowable shear stress degree τa). The spacing W satisfies at least one of the following two conditions and the third condition that the passive earth pressure Qp of the ground in front of the embedded part of the pipe 2 exceeds the acting horizontal force (burden horizontal force H') of the pipe 2. Since they are arranged side by side in the installation direction (horizontal direction) of the wall 20, the landslide prevention force can be increased by at least one of the bending resistance of the pipe 2, the shearing resistance of the pipe 2, and the passive resistance of the ground. In other words, the interval between the pipes 2 (the interval in the installation direction of the retaining wall 20) is set to the interval W that takes into account the characteristics of the pipes 2 and the characteristics of the ground, so the pipe is simple and can be constructed using a small machine. 2 (small diameter steel pipe), it becomes possible to exhibit an excellent reinforcing effect.
Construction methods for reinforcing existing retaining walls include the restraining pile method, the ground reinforcement earth method, and the ground anchor method. There are few examples where it can be applied to reinforcement.
In addition, there is a construction method that can be carried out without an existing house, in which cement milk and reinforcing bars are inserted into holes drilled radially from the back of the retaining wall using a relatively small machine, but when reinforcing an existing retaining wall, In construction methods that use cement milk, there is a risk that the existing retaining wall will be affected by expansion of the cement milk and blockage of drainage holes.
Furthermore, there are construction methods that require capping of the head of the reinforcing body on the ground surface, but capping becomes an obstacle and restricts land use in narrow residential areas.
On the other hand, the construction method using the ground reinforcement structure 1 of this embodiment has the feature of being able to solve these problems.

Further, according to the present embodiment, the ground reinforcement structure 1 includes a connecting member 3 that is buried in the ground 10 behind the retaining wall and connects a plurality of pipes 2 arranged in the installation direction (left-right direction) of the retaining wall 20. Therefore, a sense of unity is enhanced compared to the case where the plurality of pipes 2 lined up in the installation direction of the retaining wall 20 are not connected, and it becomes possible to efficiently resist landslides.
Moreover, by simply joining the upper end portions of the pipes 2 to the coupling member 3 installed substantially horizontally along the installation direction (left-right direction) of the retaining wall 20, a plurality of pipes 2 aligned in the installation direction of the retaining wall 20 can be connected. Since they can be combined, workability can be improved.
Furthermore, in the ground reinforcement structure 1, not only the pipe 2 but also the coupling member 3 are buried in the ground 10 behind the retaining wall. That is, since the entire ground reinforcement structure 1 is underground, it does not become an obstacle to land use, and the top drainage facility of the retaining wall 20 can be easily installed.
Note that in this embodiment, one coupling member 3 is provided for one reinforcing unit 4A, 4B, but the present invention is not limited to this. For example, if the upper end portions of a plurality of pipes 2 are to be connected to each other using the connecting members 3, a plurality of connecting members 3 may be provided for one reinforcing unit 4A, 4B.
Further, the ground reinforcement structure 1 only needs to include at least a plurality of pipes 2. That is, the reinforcing structure 1 may not include the coupling member 3.

Further, according to the present embodiment, the ground reinforcement structure 1 includes a plurality of reinforcement units 4A and 4B each including a plurality of pipes 2 arranged in a row along the installation direction (left-right direction) of the retaining wall 20, and The number of reinforcement units 4A, 4B that the ground reinforcement structure 1 has and the spacing between the pipes 2 (the spacing in the installation direction of the retaining wall 20) are a combination that satisfies at least one of the first condition, the second condition, and the third condition. It is possible to set the number n and the interval W. Therefore, for example, when the number of reinforcing units 4A, 4B is one, even if the interval W that satisfies at least one of the first condition, second condition, and third condition becomes a value that is difficult to realize, the reinforcing units 4A, 4B By increasing the number of reinforcing units 4A, 4B and the spacing between the pipes 2 to satisfy at least one of the first condition, the second condition, and the third condition, the spacing between the pipes 2 can be increased. It becomes possible to set the distance W to be an easily realized distance W, and it becomes possible to reliably exhibit an excellent reinforcing effect.

Further, according to the present embodiment, the ground reinforcement structure 1 (Λ type ground reinforcement structure 1) includes a first pipe (valley side pipe) and a second pipe (mountain side pipe) as the pipes 2, which are not parallel to each other. The upper ends of the first pipe and the second pipe are connected to each other, and the lower ends of the first pipe and the second pipe are separated from each other in the front-rear direction perpendicular to the installation direction (left-right direction) of the retaining wall 20. Of the two pipes, at the upper end of one pipe (the valley side pipe), the pulling resistance Rt of the other pipe (the mountain side pipe) (specifically, the perpendicular component R _H of the pulling resistance R _t with respect to the valley side pipe) It will work. That is, since the upper end of one pipe can be held down by the other pipe, it becomes possible to reinforce the retaining wall rear ground 10 more effectively.
Furthermore, the angle of the second pipe with respect to the first pipe and the interval between the pipes 2 (the interval in the installation direction of the retaining wall 20) are set to an angle 2α of a combination that satisfies at least one of the first condition, the second condition, and the third condition. and the interval W can be set. Therefore, for example, even if the distance W that satisfies at least one of the first, second, and third conditions is difficult to achieve when the first pipe and the second pipe are parallel, the first pipe and the second pipe By making the two pipes not parallel to each other, the combination of the angle of the second pipe with respect to the first pipe and the interval between the pipes 2 satisfies at least one of the first condition, the second condition, and the third condition. , it becomes possible to set the interval between the pipes 2 to an easily realized interval W, and it becomes possible to reliably exhibit an excellent reinforcing effect.
In addition, in this embodiment, the first pipe (valley side pipe) and the second pipe (mountain side pipe) are connected at their upper ends via the connecting member 3, but this is not limited to this. For example, the upper ends of the first pipe and the second pipe may be directly connected to each other. As a method for directly coupling the upper ends of the first pipe and the second pipe, for example, they may be directly coupled using a clamp (or a wire, etc.), or may be directly coupled by welding or the like. Further, when the upper end portions of the first pipe and the second pipe are directly connected to each other, the connecting member 3 may not be provided. When the upper ends of the first pipe and the second pipe are directly connected to each other and a connecting member 3 is provided, the connecting member 3 may connect a plurality of first pipes to each other. However, a plurality of second pipes may be connected to each other.

Further, according to the present embodiment, in the Λ type ground reinforcement structure 1, the lower end of the first pipe (valley side pipe) is on the front side (retaining wall 20 side) than the imaginary vertical line passing through the upper end. In addition, it is possible to install the second pipe (mountain side pipe) with the lower end located on the rear side (building 30 side) of the imaginary vertical line passing through the upper end. be. Therefore, since the first pipe and the second pipe are installed diagonally toward each other, that is, the first pipe and the second pipe are connected in a Λ shape, even if the installation location of the ground reinforcement structure 1 is narrow. , the angle 2α of the second pipe with respect to the first pipe can be increased. The larger the angle 2α of the second pipe with respect to the first pipe (closer to 90 degrees), the greater the force (right angle component R _H (=R _t・sin2α)) that presses the upper end of the first pipe, so It becomes possible to reinforce the back ground 10 more effectively.

Further, according to the present embodiment, in the ground reinforcement structure 1, the length of the pipes 2 and the interval between the pipes 2 (the interval in the installation direction (horizontal direction) of the retaining wall 20) are set to the length of the combination satisfying the third condition. It is possible to set it to L ₀ and the interval W. Therefore, for example, if the length of the pipe 2 is La, even if the interval W that satisfies the third condition becomes a value that is difficult to achieve, the length of the pipe 2 is made longer than La, and the length of the pipe 2 and By satisfying the third condition by combining the spacings of the pipes 2, it becomes possible to set the spacing between the pipes 2 to an easily realized spacing W, and it becomes possible to reliably exhibit an excellent reinforcing effect. .

In addition, the design method of the present embodiment is a design method of a ground reinforcement structure 1 that reinforces the retaining wall back ground 10 located on the back side of the retaining wall 20, specifically, the retaining wall 20 and the retaining wall back ground 10 are designed to prevent slippage of the retaining wall 20 and the retaining wall back ground 10. This is a ground reinforcement design method to ensure a predetermined safety factor or more against destruction, and the ground reinforcement structure 1 includes a pipe 2 whose lower end is installed deeper than the slip surface 12 of the retaining wall back ground 10. A plurality of pipes 2 are provided, and the plurality of pipes 2 are arranged side by side at predetermined intervals in the installation direction (horizontal direction) of the retaining wall 20. The predetermined interval is defined by the first condition that the maximum bending moment (bending edge stress σb) of the pipe 2 is less than the allowable bending moment (allowable bending stress σa), and the maximum shear force (shear stress τs) of the pipe 2. ) is below the allowable shear force (allowable shear stress degree τa), and the passive earth pressure Qp of the ground in front of the embedded part of the pipe 2 exceeds the acting horizontal force of the pipe 2 (burden horizontal force H'). Since it is possible to set the interval W to satisfy at least one of the third condition, the landslide deterrent force can be increased by at least one of the bending resistance of the pipe 2, the shear resistance of the pipe 2, and the passive resistance of the ground. can. That is, since it is possible to set the interval between the pipes 2 (the interval in the installation direction of the retaining wall 20) to the interval W that takes into account the characteristics of the pipes 2 and the characteristics of the ground, it is possible to exhibit an excellent reinforcing effect. .
Furthermore, in the case of the Λ type, the bending strength and shear strength of the first pipe (trough side pipe) and the passive resistance of the front surface of the pipe deeper than the sliding surface, and the passive resistance of the second pipe (mountain side pipe) against the sliding force. can be expected to play a role in suppressing the horizontal displacement of the head of the first pipe and reducing the maximum bending moment and maximum shearing force generated in the first pipe by the pipe's pull-out resistance.

Further, according to the present embodiment, there is provided a method for designing a ground reinforcement structure 1 including a plurality of pipes 2 buried in the ground 10 behind a retaining wall, in which the required deterrent force of the ground 10 behind the retaining wall is calculated. a calculation step (step S4), a pipe condition setting step (step S5) for setting the pipe conditions of the pipe 2, a ground condition setting step (step S3) for setting the ground conditions for the ground 10 behind the retaining wall, and a An assumption step (step S6) of setting assumed values regarding the installation interval W and the number of installation rows n, and a stress calculation of stress degrees σ _b and τ _s based on the necessary deterrent force, pipe conditions, ground conditions, and assumed values. and an installation length determination step (step S11) that determines the installation length _L0 of the pipe 2 based on the pipe conditions and ground conditions, and the installation length determination step (step S11) that determines the installation length L0 of the pipe 2 based on the pipe conditions and ground conditions. The allowable stress degrees σ _a , τ _a included in the pipe conditions calculated with the stress degrees σ _b , τ _s calculated in the stress calculation step are compared by changing the assumed values, and the installation interval of pipe 2 is determined based on the comparison result. Determine W and the number of installed rows n (see FIG. 25).

That is, since the installation interval W, the number of installation rows n, and the installation length _L0 of the pipes 2 are determined based on the ground conditions and pipe conditions, the ground conditions of the target retaining wall rear ground 10 and the pipe 2 to be used It becomes possible to design the ground reinforcing structure 1 according to the pipe conditions, and it is possible to construct a highly reliable ground reinforcing structure 1. Therefore, by reinforcing the ground 10 behind the retaining wall with the ground reinforcement structure 1 designed using the design method of this embodiment, the safety factor (resistance) against landslides is increased by the bending strength and shear strength of the pipe 2, and It is possible to secure a safety factor (required safety factor) at the time. This makes it possible to prevent uneven settling of the building 30 on the back side of the retaining wall 20 at all times and during earthquakes.

In addition, when building a building on the ground behind a retaining wall, (1) ensure a sufficient distance between the retaining wall and the building, (2) deeply embed the foundation of the building, and (3) directly under the building. It will be necessary to take measures to deal with the nearby retaining wall (angle of repose), such as driving piles into the wall. On the other hand, by installing and reinforcing the ground reinforcement structure 1 designed by the design method of this embodiment on the ground 10 behind the retaining wall, it is possible to reduce the earth pressure acting on the retaining wall 20 due to the resistance of the pipe 2 passing through. Therefore, the same effect as the above-mentioned ``measure against adjacent retaining walls'' can be expected. In other words, in the ground 10 behind the retaining wall where the ground reinforcement structure 1 is installed, piles are installed directly under the building without ensuring a sufficient distance between the retaining wall and the building and without deepening the foundation of the building. It becomes possible to construct a building without striking the ground, and the site (the top of the ground 10 behind the retaining wall) can be effectively utilized.

Further, according to the present embodiment, in the design method of the ground reinforcement structure 1, the burden horizontal force calculation step (step S6 ), and a passive earth pressure calculation step (step S13) that calculates the passive earth pressure Q _p of the pipe 2 based on the pipe conditions, ground conditions, and assumed values, and a passive earth pressure calculation step (step S13) that calculates the passive earth pressure Q p of the pipe 2, which is The burden horizontal force H' and the passive earth pressure _Qp calculated in the passive earth pressure calculation step are compared with different assumed values, and the installation interval W and the number of installation rows n of the pipes 2 are determined based on the comparison results ( (See Figure 25).
That is, since the installation interval W of the pipes 2 and the number of installation rows n are determined by considering not only the stress level but also the burden horizontal force and the passive earth pressure, it is possible to construct a more reliable ground reinforcement structure 1. Become.

Further, according to the present embodiment, in the design method of the ground reinforcement structure 1, in the assumption step (step S6), a value satisfying W≦8D (D: diameter of the pipe 2) is assumed as the installation interval W of the pipe 2. It is possible to configure it to do so.
With this configuration, the determined installation interval W of the pipes 2 satisfies W≦8D (D: the diameter of the pipes 2), so that there is no gap between the soil masses where the soil masses slip between adjacent pipes 2. This makes it possible to prevent

According to the present embodiment, the ground reinforcement structure 1 includes a first type (II type) in which the pipe 2 is installed vertically, and a second type (Λ type) in which the pipe 2 is installed diagonally. The type can be determined based on the height of the retaining wall rear ground 10 (height h of the retaining wall 20). Specifically, for example, if h≦2.0m, type II is selected, and if 2.0m<h<3.0m, type II or Λ type is selected depending on the conditions. , 3.0m≦h, the Λ type can be selected.
By configuring in this way, it becomes possible to construct a more reliable ground reinforcement structure 1.

Further, according to the present embodiment, in the method for designing the ground reinforcement structure 1, when the ground reinforcement structure 1 is of the second type (Λ type), the installation angle of the pipe 2 is determined in the assumption step (step S6). 2α, the installation interval W, and the number n of installation rows are set, and the installation angle 2α of the pipe 2, the installation interval W, and the number n of installation rows are determined based on the comparison results.
In other words, when the ground reinforcement structure 1 is the second type (Λ type), the installation angle 2α of the pipe 2 is also determined based on the ground conditions and pipe conditions, so a more reliable ground reinforcement structure 1 can be created. It becomes possible to construct.

Further, according to this embodiment, the pipe 2 is a single pipe.
Therefore, since a single pipe having a small diameter is used as the pipe 2, the construction is easy and the resistance force (circumferential surface friction force) of the pipe can be ensured without disturbing the ground.
Furthermore, since a single pipe with a small diameter is used, construction can be carried out without using large-scale construction machinery. In other words, construction can be carried out in narrow spaces. Therefore, even if the building 30 is already erected on the site (the top of the retaining wall rear ground 10), construction can be carried out on the site, so the ground reinforcement structure 1 can be constructed without using the adjacent land.

1 Ground reinforcement structure 2 Pipe 3 Connection members 4A, 4B Reinforcement unit 10 Retaining wall back ground 12 Sliding surface 20 Retaining wall

Claims (7)

A ground reinforcement structure for reinforcing the ground behind the retaining wall located on the back side of the retaining wall,
A plurality of pipes are buried in the ground behind the retaining wall, and the lower ends thereof are installed deeper than the sliding surface of the ground behind the retaining wall,
The plurality of pipes meet a first condition that the maximum bending moment of the pipes is less than the allowable bending moment, a second condition that the maximum shearing force of the pipes is less than the allowable shearing force, and a ground surface in front of the embedded part of the pipes. A ground reinforcing structure characterized in that the retaining walls are arranged side by side in the installation direction at intervals that satisfy at least one of the third condition that the passive earth pressure of the pipe exceeds the acting horizontal force of the pipe. In the ground reinforcement structure according to claim 1,
a connecting member that is buried in the ground behind the retaining wall and connects the plurality of pipes that are lined up in the installation direction of the retaining wall;
The ground reinforcement structure is characterized in that the connecting member is installed substantially horizontally, is a long member along the installation direction, and is joined to the upper end of the pipe by a joining member. In the ground reinforcement structure according to claim 1,
A plurality of reinforcing units each including a plurality of the pipes arranged in a row along the installation direction of the retaining wall,
The plurality of reinforcing units are arranged side by side in a direction perpendicular to the installation direction,
The number of reinforcement units that the ground reinforcement structure has and the spacing in the installation direction of the pipes are set to the number and spacing of a combination that satisfies at least one of the first condition, the second condition, and the third condition. A ground reinforcement structure characterized by: In the ground reinforcement structure according to claim 1,
The pipes include a first pipe and a second pipe that are not parallel to each other,
The first pipe and the second pipe have upper end portions connected to each other and lower end portions separated from each other in a front-back direction perpendicular to the installation direction,
The angle of the second pipe with respect to the first pipe and the interval between the pipes in the installation direction are set to a combination of angle and interval that satisfies at least one of the first condition, the second condition, and the third condition. The ground reinforcement structure is characterized by In the ground reinforcement structure according to claim 4,
The first pipe is installed with a lower end located in front of an imaginary vertical line passing through the upper end,
The ground reinforcing structure is characterized in that the second pipe is installed such that a lower end thereof is located on the rear side of an imaginary vertical line passing through the upper end. In the ground reinforcement structure according to claim 1,
A ground reinforcement structure, wherein the length of the pipe and the interval between the pipes in the installation direction are set to a combination of length and interval that satisfies the third condition. A method for designing a ground reinforcement structure for reinforcing the ground behind a retaining wall located on the back side of a retaining wall, the method comprising:
The ground reinforcement structure includes a plurality of pipes whose lower ends are installed deeper than the slip surface of the ground behind the retaining wall,
The plurality of pipes are arranged side by side at predetermined intervals in the installation direction of the retaining wall,
The predetermined interval is
a first condition that the maximum bending moment of the pipe is less than an allowable bending moment;
a second condition that the maximum shear force of the pipe is less than an allowable shear force;
A design method characterized in that the distance is set to satisfy at least one of the third condition that the passive earth pressure in the ground in front of the penetration part of the pipe exceeds the acting horizontal force of the pipe.

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