JP7798685B2 - Mountain retaining wall structure - Google Patents

Description

The present invention relates to an earth retaining wall structure .

During excavation work, retaining walls are generally installed to prevent ground collapse. Methods for suppressing displacement of retaining walls include increasing the rigidity of the wall and increasing the number of strut support steps. However, when the excavated ground is a thick, soft layer, the retaining wall displacement below the bottom of the excavation is large, and these measures alone are not sufficient to suppress displacement of the retaining wall. For this reason, in excavation work on soft ground, a method of improving the ground on the excavation side adjacent to the retaining wall into a buttress-type (buttress-type) ground improvement method has become common to suppress displacement of the retaining wall (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 7-127064

Buttress-type improved bodies often move and rotate almost like rigid bodies, so in order to achieve sufficient deformation prevention, it is necessary to drive the improved ground down to the hard ground, increasing the bearing capacity of the bottom of the improved body and preventing rotation. However, when the thickness of the soft ground is greater than the excavation depth, the ground improvement depth becomes very large, and because the bottom area of a single row of buttress-type improved bodies is relatively small, in order to achieve sufficient deformation prevention, it is necessary to carry out improvement in multiple rows, increasing the improvement width or length considerably, which poses challenges such as an increase in the improved volume and the cost of the measure.

The present invention has been made in consideration of the above-mentioned problems, and aims to provide a retaining wall structure that can shorten the depth of the buttress-type improved body and suppress the increase in the improved volume.

To achieve the above objective, the earth retaining wall structure of the present invention is constructed around an excavation area in the ground, and is characterized by comprising: an earth retaining wall constructed at the boundary between the ground and the excavation area; a buttress-type improvement body extending on the excavation area side of the earth retaining wall in a direction approximately perpendicular to the earth retaining wall in a plan view; and a base improvement body connected to the lower end of the buttress-type improvement body.

According to this invention, by providing a base improvement body connected to the lower end of the buttress-type improvement body, the same effect as increasing the bottom area of the buttress-type improvement body can be achieved. As a result, the reaction force at the bottom surface can be increased, which increases the effect of suppressing deformation of the retaining wall, making it possible to shorten the depth of the buttress-type improvement body and suppress an increase in the improvement volume.

Furthermore, in the earth retaining wall structure of the present invention, the base improvement body may be formed in a circular shape or a series of circles that encompasses the buttress-type improvement body in a plan view.

According to this invention, by improving the base improvement body to a position further away from the retaining wall than the buttress-type improvement body, the effect of preventing rotational deformation can be increased without increasing the area of the base improvement body.

The construction method for an earth retaining wall structure according to the present invention is a method for constructing an earth retaining wall structure around an excavation area in the ground, and comprises the steps of: constructing an earth retaining wall at the boundary between the ground and the excavation area; constructing a buttress-type improvement body on the excavation area side of the earth retaining wall, the buttress-type improvement body extending in a direction approximately perpendicular to the earth retaining wall in a plan view; and constructing a base improvement body connected to the lower end of the buttress-type improvement body, wherein the base improvement body is constructed using a high-pressure jet mixing method.

According to this invention, the bottom surface area can be increased by providing a bottom improvement body constructed using the high-pressure jet mixing method at the tip depth of the buttress-type improvement body. As a result, the bottom reaction force can be increased, and since a large bottom reaction force can be secured even in non-hard ground, the depth of the buttress-type improvement body can be shortened and the increase in the improvement volume can be suppressed. Furthermore, the bottom improvement body can be constructed efficiently using the high-pressure jet mixing method.

According to the present invention, it is possible to provide a retaining wall structure that can shorten the depth of the buttress-type improved body and suppress the increase in the improved volume.

FIG. 2 is a side view of the retaining wall structure according to the present embodiment. FIG. 2 is a plan view of the retaining wall structure according to the present embodiment. FIG. 10 is a side view of a retaining wall structure according to a modified example 1 of this embodiment. FIG. 10 is a plan view of a retaining wall structure according to a modified example 1 of this embodiment. FIG. 10 is a side view of a retaining wall structure according to a modified example 2 of this embodiment. FIG. 10 is a plan view of a retaining wall structure according to a modified example 2 of this embodiment. FIG. 10 is a side view of another aspect of the retaining wall structure of this embodiment. FIG. 10 is a plan view of another aspect of the retaining wall structure of this embodiment.

Below, an earth retaining wall structure and a construction method for an earth retaining wall structure according to an embodiment of the present invention will be described with reference to Figures 1 to 6.

As shown in Figures 1 and 2, the earth retaining wall structure 1 of this embodiment comprises an earth retaining wall 11 located within ground A at the boundary between ground A and excavation area B, a buttress-type improvement body 12 extending on the excavation area B side of the earth retaining wall 11 in a direction approximately perpendicular to the earth retaining wall 11 in a plan view, and a base improvement body 13 connected to the lower end 12a of the buttress-type improvement body 12 and located at a depth sufficient to stably support the buttress-type improvement body 12.

The retaining wall 11 was constructed using a conventional construction method, such as the soil cement column wall method, steel pipe sheet pile method, diaphragm wall method, parent pile horizontal sheet pile method, and steel sheet pile method. The retaining wall 11 is installed around the entire boundary between ground A and excavation area B.

The buttress-type improved body 12 is a plate-shaped member installed within excavation area B. It is formed, for example, using the soil cement column wall construction method. It may also be formed using a deep mixing method or a high-pressure jet mixing method, which can also improve the buttress-type improved body 12 into a plate-like shape. The buttress-type improved body 12 is formed over a predetermined range in a direction approximately perpendicular to the retaining wall 11 in a plan view. The buttress-type improved body 12 is constructed from near the surface of the ground A to a depth where, upon completion of excavation of excavation area B, the buttress-type improvement with a base plate can be expected to be sufficiently effective in preventing displacement of the retaining wall.

The bottom improvement body 13 is connected to the lower end 12a of the buttress-type improvement body 12. The bottom improvement body 13 is formed in a roughly circular shape in plan view. As shown in Figures 7 and 8, the bottom improvement body 13 may be formed by connecting multiple bottom improvement bodies that are roughly circular in plan view. The top surface of the bottom improvement body 13 is arranged so that it faces vertically upward. The bottom improvement body 13 is also connected to the retaining wall 11. The bottom improvement body 13 is formed to be large enough to encompass the buttress-type improvement body 12 in plan view. The bottom improvement body 13 is formed using a high-pressure jet mixing method.

The construction method for the buttress-type improved body 12 and the bedrock improved body 13 of this embodiment will be described below. Prior to construction of the buttress-type improved body 12, ground improvement (bedrock improvement) is carried out on the ground near the planned bottom depth of the buttress-type improved body 12 using a high-pressure jet mixing method with a diameter larger than the bottom width of the buttress-type improved body 12, and the bedrock improved body 13 is then constructed. After construction of the bedrock improved body 13, the buttress-type improved body 12 is constructed so that it is supported by the bedrock improved body 13.

The retaining wall structure 1 of this embodiment comprises a retaining wall 11 installed at the boundary between ground A and excavation area B, a buttress-type improvement body 12 extending on the excavation area B side of the retaining wall 11 in a direction approximately perpendicular to the retaining wall 11 in a plan view, and a base improvement body 13 connected to the lower end 12a of the buttress-type improvement body 12.

In this way, by providing a base improvement body 13 at the lower end of the buttress-type improvement body 12, the bottom surface area can be increased. As a result, the bottom reaction force can be increased. By increasing the bottom surface area, a bottom reaction force similar to that of hard ground can be ensured even in relatively soft ground, making it possible to shorten the depth of the buttress-type improvement body 12 and suppress an increase in the improvement volume.

In addition, the base improvement body 13 increases the bottom support force of the buttress-type improvement body 12, preventing rotation, and the bottom friction of the base improvement body 13 is expected to have a deterrent effect on horizontal movement, so even in relatively soft ground or with a small number of rows of buttress-type improvement bodies 12, a significant effect can be achieved in preventing deformation of the retaining wall 11.

The size of the bedrock improvement body 13 is calculated based on the ground conditions and the bottom bearing capacity required to prevent deformation. The thickness and strength of the bedrock improvement body 13 are determined to ensure safety against the load acting on the bedrock improvement body 13.

(Variation 1)
3 and 4 show a first modified example of the above embodiment. The first modified example differs from the above embodiment in the construction position of the bottom improvement body 13 in plan view.

The bottom improvement body 13A of variant 1 is connected to the lower end 12a of the buttress-type improvement body 12. The bottom improvement body 13A is formed in a roughly circular shape in plan view. The top surface of the bottom improvement body 13 is arranged so that it faces vertically upward. The bottom improvement body 13 is provided at a distance from the retaining wall 11. The bottom improvement body 13 is formed to a size that encompasses the end 12b of the buttress-type improvement body 12 opposite the retaining wall 11 in plan view. The bottom improvement body 13 is formed using a high-pressure jet mixing method. Note that the bottom improvement body 13A may also be formed by connecting multiple roughly circular shapes in plan view.

In the configuration of variant 1, the base improvement body 13A is located away from the retaining wall 11 and encompasses the end 12b of the buttress-type improvement body 12, which allows the buttress-type improvement body 12 to more efficiently exert its rotation-deterrent effect.

(Variation 2)
5 and 6 show a second modification of the above embodiment. The second modification is further different from the first modification in the configuration of the buttress-type improved body 12.

The buttress-type improved body 12A of Variation 2 is composed of multiple plate-shaped members placed within the excavation area B. The buttress-type improved body 12A is formed, for example, using the soil cement column wall construction method. The buttress-type improved body 12A is formed over a predetermined range in a direction approximately perpendicular to the retaining wall 11 in a plan view. As shown in Figure 6, the buttress-type improved body 12A is composed of three plate-shaped members. The middle buttress-type improved body 21 is formed with a longer improved length than the buttress-type improved bodies 22 and 23 on either side. In other words, the improved length from the retaining wall 11 to the end 12b of the middle buttress-type improved body 21 is longer than the improved length from the retaining wall 11 to the end 12b of the buttress-type improved bodies 22 and 23 on either side. The buttress-type improved bodies 22 and 23 on either side are formed with approximately the same improved length. The buttress-type improved body 12 is constructed from near the surface of the ground A to a depth at least sufficient to ensure that the buttress-type improved body 12A can remain stable without collapsing when excavation of excavation area B is completed.

The bottom improvement body 13A is connected to the lower end 12a of the buttress-type improvement body 12A. The bottom improvement body 13A is formed in a roughly circular shape in plan view. The top surface of the bottom improvement body 13 is arranged so that it faces vertically upward. The bottom improvement body 13 is spaced apart from the retaining wall 11. The bottom improvement body 13 is formed to a size that, in plan view, encompasses all of the end portions 12b of the buttress-type improvement bodies 21, 22, and 23 on the side opposite the retaining wall 11. The bottom improvement body 13 is formed using a high-pressure jet mixing method.

With the configuration of variant 2, the load acting on the bottom improvement body 13A is greatest at the end 12b of the buttress-type improvement body. Therefore, by varying the width (length) of the buttress-type improvement bodies 21, 22, and 23, the load acting on the bottom improvement body 13A from the buttress-type improvement body 12A can be distributed, making it harder for the bottom improvement body 13A to rotate, further enhancing the effect.

The above describes embodiments of the earth retaining wall structure and construction method for the earth retaining wall structure according to the present invention, but the present invention is not limited to the above embodiments and can be modified as appropriate without departing from the spirit of the invention.

For example, the arrangement of the bottom improvement bodies 13, 13A in the above embodiment is merely an example, and the size and position of the bottom improvement bodies that have the greatest deformation suppression effect can be determined depending on the conditions.

In addition, in the above embodiment, the buttress-type improvement body 12 was constructed using the same mechanically mixed soil cement column wall construction method as the retaining wall 11, but the base improvement body 13 and buttress-type improvement body 12 may also be constructed (ground improvement) consecutively using, for example, a high-pressure jet mixing method that can be used to improve the ground into a wall shape.

Furthermore, in the above embodiment, the bottom improvement body 13 was described as being formed with a circular shape when viewed from above, but the shape when viewed from above may be other than circular.

1... Mountain retaining wall structure 11... Mountain retaining wall 12, 12A... Buttress type improved body 12a... Lower end 13, 13A... Bottom base improved body 21, 22, 23... Buttress type improved body A... Ground B... Excavation area

Claims (4)

In a retaining wall structure installed around an excavation area of the ground,
A retaining wall provided at the boundary between the ground and the excavation area;
A buttress-type improvement body extending in a direction substantially perpendicular to the retaining wall in a plan view on the excavation area side of the retaining wall;
a bottom improvement body connected to the lower end of the buttress-type improvement body ,
A retaining wall structure in which the bottom area of the base improvement body is larger than the bottom area of the buttress-type improvement body . 2. The earth retaining wall structure according to claim 1, wherein the bottom improvement body is formed in a circular shape or a shape consisting of a series of circles that encompasses at least a portion of the buttress-type improvement body in a plan view. The earth retaining wall structure according to claim 1, wherein the bottom improvement body is provided at a distance from the earth retaining wall. The buttress-type improved body is configured by a plurality of plate-like members arranged in parallel in a plan view,
4. The retaining wall structure according to claim 1, wherein the buttress-type improvement body in the middle is formed with a longer improvement length than the buttress-type improvements on both sides.