JP7474686B2 - Soft ground improvement body and construction method of soft ground improvement body - Google Patents

Description

The present invention relates to a soft ground improvement body and a construction method for the soft ground improvement body.

In recent years, methods of casting pile foundations and columnar ground improvement work, such as that shown in Patent Document 1, have become known as a measure to prevent sliding failure and subsidence in embankments, developed land, reinforced embankments, and retaining wall structures.

Patent Document 1 describes a liquefaction prevention structure that includes an underground wall constructed in the target ground directly below a specified area, and a construction section piled on top of the target ground, with a pile foundation made of multiple piles in the construction section, and these piles are arranged in a space surrounded by a lattice-shaped underground wall, reaching all the way to the supporting ground at the bottom of the target ground.

JP 2015-161093 A

However, in the conventional construction methods described above for driving pile foundations and columnar ground improvement works to prevent sliding failure and subsidence in structures, it was necessary to drive the pile foundations and columnar ground improvement works until they reached solid supporting ground. This required driving the piles deep, which took time for construction and made the piles themselves large. There was also the problem of increased construction costs.

Furthermore, in order to construct piles at great depths, it was necessary to install tall pile driving equipment, and it was necessary to secure a large and tall space in which to install such large-scale construction equipment, so there was room for improvement in this regard.

The present invention was made in consideration of the above-mentioned problems, and aims to provide a soft ground improvement body and a construction method for a soft ground improvement body that can minimize the construction depth, can be easily constructed in a small space, and can reduce construction costs.

In order to achieve the above-mentioned object, the soft ground improvement body of the present invention is a soft ground improvement body that supports a ground end located at the lateral lower end of a structure that is placed on soft ground and receives biased earth pressure, and is formed by excavating the target ground that supports the ground end from below and mixing and stirring a ground improvement material. The soft ground improvement body is characterized by comprising a forward continuous improvement wall that extends continuously along the extension direction of the ground end and receives the ground that supports the load of the structure on the rear side, and a plurality of orthogonal improvement walls that are perpendicular to the rear face of the forward continuous improvement wall in a top view and partition the extension direction, and at least a part of the improvement area consisting of the forward continuous improvement wall and the orthogonal improvement wall is provided in a position that overlaps the ground end of the structure, and the forward continuous improvement wall is located forward of the structure in a top view, and is improved to a depth that reaches the slide surface of the soft ground caused by the biased earth pressure of the structure.

The construction method of the soft ground improvement body according to the present invention is the above-mentioned construction method of the soft ground improvement body, and includes the steps of extending the front continuous improvement wall continuously in the extension direction of the ground end and improving the ground to a depth that reaches the slip surface, ahead of the structure, and providing a plurality of orthogonal improvement walls that are orthogonal to the rear surface of the front continuous improvement wall in a top view, and is characterized in that at least a part of the improvement area consisting of the front continuous improvement wall and the orthogonal improvement walls is provided in a position that overlaps with the ground end of the structure.

In the present invention, the forward continuous improvement wall of the soft ground improvement body is provided in a state in which it intersects with the sliding surface, and part of the improvement area is provided in a position overlapping with the ground edge of the structure when viewed from above, so that it is possible to prevent sliding failure and subsidence of the soft ground caused by the uneven earth pressure of the soil structure. In other words, the soft ground improvement body provides horizontal resistance to the horizontal force acting on the ground surrounded by the improvement area consisting of the forward continuous improvement wall and the orthogonal improvement wall. Therefore, it is possible to suppress deformation of the ground below the structure, and it is possible to provide a ground improvement body with a high improvement effect, and it is possible to reliably support the ground edge of the structure on which uneven earth pressure acts from below.

In addition, in the present invention, since the forward continuous improvement wall is arranged continuously along the extension direction, the forward movement of the ground behind the forward continuous improvement wall can be restricted, and the soft ground partitioned by the forward continuous improvement wall and the orthogonal improvement wall can be made into a restraint area.
Therefore, in the present invention, the improvement area includes the area surrounded by the forward continuous improvement wall and the orthogonal improvement wall, and effective ground improvement can be performed with minimal improvement. Moreover, the soft ground improvement wall only needs to be deep enough to intersect with the slide surface, and the construction depth can be shallower than that of conventional pile foundations, which require deep and long piles that reach the supporting ground. Therefore, the construction depth can be minimized, the height of the construction equipment from the ground can be reduced, and construction can be performed easily in a small space, reducing the cost of construction. For example, a ground improvement device with a reduced height can be used without using a high-height leader-type pile driver, making it possible to carry out construction in areas with overhead restrictions and improving the efficiency of the construction space.

In addition, the present invention provides a wall-type improvement that can minimize the installation area and depth, and the weight of the improvement body itself can be reduced compared to block-type ground improvement works, preventing the soft ground improvement body itself from sinking and reducing the load on the ground below the soft ground improvement body.

The soft ground improvement body according to the present invention may also be characterized in that a rear lateral improvement wall is integrally provided on the rear side of the front continuous improvement wall, extending along the extension direction at a distance from the front continuous improvement wall, and the front continuous improvement wall, the rear lateral improvement wall, and the orthogonal improvement wall form a lattice pattern.

In the present invention, the area surrounded by the front continuous improvement wall, the orthogonal improvement wall, and the rear horizontal improvement wall is restrained in the entire circumferential direction, so more effective ground improvement can be achieved with minimal improvement.

In addition, the soft ground improvement structure according to the present invention has an embankment and a reinforcing wall that reinforces the side of the embankment, and it is preferable that the centroid of the improvement structure having the forward continuous improvement wall and the orthogonal improvement wall coincides with the center of gravity of the load of the reinforcing wall when viewed from the side.

In the present invention, by aligning the centroid of the soft ground improvement body with the center of gravity of the load of the reinforcing wall when viewed from the side, it is possible to create a well-balanced improvement body that can efficiently support the uneven earth pressure of the structure, and also to minimize the size of the soft ground improvement body.

The soft ground improvement body and construction method for the soft ground improvement body of the present invention allow the construction depth to be minimized, making construction easy and requiring a small space, and reducing construction costs.

FIG. 1 is a partially broken vertical cross-sectional view showing the overall configuration of a soft ground improvement body according to an embodiment of the present invention. FIG. 2 is a plan view of the soft ground improvement body shown in FIG. 1 viewed from above. This is a cross-sectional view of the line AA shown in Figure 2, and is a vertical cross-sectional view of the first improved body. This is a cross-sectional view of the line BB shown in Figure 2, and is a vertical cross-sectional view of the second improved body. FIG. 1 is a plan view of the first improved body. FIG. 13 is a plan view of the second improved body. FIG. 13 is a diagram for explaining a method of installing a soft ground improvement body. FIG. 11 is a partially broken vertical cross-sectional view showing the overall configuration of a modified soft ground improvement body.

Below, the soft ground improvement body according to an embodiment of the present invention and the construction method of the soft ground improvement body will be explained with reference to the drawings.

As shown in FIG. 1, the soft ground improvement body 1 of this embodiment supports a ground end 2a located at the lower lateral end of an embankment 2 (structure) that is placed on soft ground G and is subjected to uneven earth pressure, and is formed by excavating the target ground that supports this ground end 2a from below and mixing and stirring the ground improvement material.

In the following description, the direction in which the ground-contact end 2a of the embankment 2 extends is referred to as the extension direction X1, and the direction perpendicular to the extension direction X1 in a top view is referred to as the front-to-rear direction X2. In the front-to-rear direction X2, the direction away from the embankment 2 is referred to as the front or front side, and the opposite side is referred to as the rear or rear side.

The embankment 2 is reinforced by driving multiple anchor bolts 22 into the slope 21 that forms the outer periphery.

As shown in FIG. 2, the soft ground improvement body 1 is improved in an L-shape along the ground edge 2a of the embankment 2 when viewed from above.
The soft ground improvement body 1 is selected depending on the construction conditions as either a first improvement body 1A having a rear lateral improvement wall 13 described later, as shown in Figure 3, or a second improvement body 1B not having a rear lateral improvement wall 13, as shown in Figure 4.

In addition, in Figures 3 and 4, the part of the embankment 2 where the anchor bolts 22 are installed in Figure 1 is shown as a concrete retaining wall 23 (reinforcement wall). In other words, the embankment 2 is a structure that receives uneven earth pressure, with the retaining wall 23 provided on the side of the embankment body 20.

As shown in Figures 2 and 3, the first improvement body 1A comprises a forward continuous improvement wall 11 that extends continuously along the extension direction X1 of the ground end 2a and receives the soft ground G supporting the embankment 2 on the rear surface 11a side, a plurality of orthogonal improvement walls 12 that partition the forward continuous improvement wall 11 in the extension direction X1 perpendicular to the rear surface 11a of the forward continuous improvement wall 11 in a top view, and a rear lateral improvement wall 13 that extends along the extension direction X1 at a distance from the forward continuous improvement wall 11 on the rear surface 11a side of the forward continuous improvement wall 11. The forward continuous improvement wall 11, the plurality of orthogonal improvement walls 12, and the rear lateral improvement wall 13 are integrally formed in a lattice shape.

As shown in Figures 2 and 4, the second improvement body 1B has a configuration in which the rear lateral improvement wall 13 of the first improvement body 1A is omitted, and is provided with a front continuous improvement wall 11 and multiple orthogonal improvement walls 12.

The soft ground improvement body 1 is provided at a position where at least a part of the improvement area 10 surrounded by the forward continuous improvement wall 11 and the orthogonal improvement wall 12 overlaps with the ground end 2a of the embankment 2.
The front continuous improvement wall 11 is disposed in front of the embankment 2 in top view, and is cast to a depth that reaches at least the slip surface R that intersects with the ground contact end 2a of the embankment 2. In other words, the lower end 11c of the front continuous improvement wall 11 and the lower end 13a of the rear lateral improvement wall 13 of the first improvement body 1A are located below the slip surface R.

The symbol P in FIG. 7 indicates the load position passing through the center of gravity of the retaining wall 23 for the load F2 of the retaining wall 23 in side view. This load position P is the center of gravity. Here, the symbol F1 in FIG. 7 indicates the earth pressure of the embankment 2, and the symbol F2 indicates the load F2 of the retaining wall 23. The soft ground improvement body 1 having the forward continuous improvement wall 11 and the orthogonal improvement wall 12 is formed so that the centroid C (dotted line in FIG. 7) of the soft ground improvement body 1 coincides with the center of gravity P of the load F2 of the retaining wall 23 in side view. In other words, the position of the soft ground improvement body 1 is determined so that the centroid C of the soft ground improvement body 1 coincides with the center of gravity P of the retaining wall 23 in the front-to-rear direction X2 in side view.

The soft ground improvement body 1 is formed using a ground improvement device (not shown) by mixing and stirring the ground improvement material into the excavated ground in a specified target ground G. With the above-mentioned ground improvement device, multiple rectangular parts that are elongated horizontally when viewed from above are arranged at equal intervals vertically and horizontally in the ground to be constructed.

The ground improvement device for constructing the soft ground improvement body 1 is used by being attached as an attachment to the arm tip of a working machine such as a 0.5 m ³ class or 0.8 m ³ class backhoe, and excavates the soft ground G by rotating the excavation blades provided at the lower ends of the rods arranged in a plurality of rows, and by adding a ground improvement material to the excavated soil, mixing it, and stirring it, the soft ground improvement body 1 is constructed. For example, a device equipped with a three-axis excavation blade described in JP 2011-226254 A can be used as such a ground improvement device.
Here, as the ground improvement material to be added to the excavated soil, appropriate agents such as liquid materials such as cement milk or powder materials can be used depending on the purpose of the ground improvement.

The construction method of the above-mentioned soft ground improvement body 1 includes the steps of extending the front continuous improvement wall 11 continuously along the extension direction X1 of the ground contact end 2a in front of the embankment 2 and improving the ground to a depth that reaches the slip surface R, providing a plurality of orthogonal improvement walls 12 in the soft ground G that are perpendicular to the rear surface 11a of the front continuous improvement wall 11 when viewed from above, and providing rear lateral improvement walls 13 at intervals behind the front continuous improvement wall 11.
The soft ground improvement body 1 can be provided by constructing the improvement area surrounded by the forward continuous improvement wall 11 and the orthogonal improvement wall 12 so that at least a portion of the improvement area overlaps with the ground end 2a of the embankment 2.

Next, the operation of the above-mentioned soft ground improvement body 1 and the construction method of the soft ground improvement body 1 will be described in detail with reference to the drawings.
In this embodiment, as shown in Figs. 1 to 6, the front continuous improvement wall 11 of the soft ground improvement body 1 is provided in a state in which it crosses the slide surface R, and a part of the improvement area is provided at a position overlapping the ground end 2a of the embankment 2 in a top view, so that it is possible to prevent the sliding failure and subsidence of the soft ground caused by the uneven earth pressure of the embankment 2. In other words, the soft ground improvement body 1 acts as a horizontal resistance against the horizontal force acting on the ground surrounded by the improvement area consisting of the front continuous improvement wall 11 and the orthogonal improvement wall 12. Therefore, it is possible to suppress the deformation of the soft ground G below the embankment 2, and it is possible to provide a ground improvement body with a high improvement effect, and it is possible to reliably support the ground end 2a of the embankment 2 on which the uneven earth pressure acts from below.

In addition, in this embodiment, since the forward continuous improvement wall 11 is arranged continuously along the extension direction X1, the forward movement of the soft ground G behind the forward continuous improvement wall 11 can be restricted, and the soft ground partitioned by the forward continuous improvement wall 11 and the orthogonal improvement wall 12 can be made into a restraint area.
Therefore, in this embodiment, the improvement area includes the area surrounded by the forward continuous improvement wall 11 and the orthogonal improvement wall 12, and effective ground improvement can be performed with minimal improvement. Moreover, the soft ground improvement wall 1 only needs to be deep enough to intersect with the slide surface R, and the construction depth can be made shallower than that of conventional pile foundations that have deep and long piles that reach the supporting ground. Therefore, the construction depth can be made the minimum depth, the height of the construction equipment and the like from the ground can be reduced, and construction can be performed easily in a small space, reducing the cost of construction. For example, a ground improvement device with a reduced height can be used without using a high-height leader-type pile driver, making it possible to carry out construction in areas with overhead restrictions and improving the efficiency of the construction space.

In addition, this embodiment is a wall-type improvement that can minimize the installation area and depth, and the weight of the improvement body itself can be reduced compared to block-type ground improvement, so subsidence of the soft ground improvement body 1 itself can be prevented and the load on the ground below the soft ground improvement body 1 can be suppressed.

In addition, in the soft ground improvement body 1 of this embodiment, the front continuous improvement wall 11, the orthogonal improvement wall 12, and the rear horizontal improvement wall 13 form a lattice pattern, and the ground G in the area surrounded by these is restrained in the entire circumferential direction, so that more effective ground improvement can be performed with minimal improvement.

In addition, in this embodiment, as shown in Figure 7, by aligning the centroid C of the soft ground improvement body 1 with the center of gravity P of the load of the retaining wall 23 in a side view, a well-balanced improvement body can be created that can efficiently support the uneven earth pressure of the embankment 2, and the size of the soft ground improvement body 1 can be minimized.

As described above, the soft ground improvement body 1 and the construction method for the soft ground improvement body 1 according to this embodiment can minimize the construction depth, allowing for simple construction in a small space and reducing construction costs.

The above describes the embodiment of the soft ground improvement body and the construction method of the soft ground improvement body according to the present invention, but the present invention is not limited to the above embodiment and can be modified as appropriate without departing from the spirit of the invention.

For example, in the above-described embodiment, the structure is an embankment 2 provided with a reinforcing wall such as a retaining wall 23, but the structure is not limited to having such a retaining wall 23, and it is also possible to apply the structure to one in which the entire structure is an embankment 2A, for example, as in the modified example shown in Figure 8.
Furthermore, as structures, the soft ground improvement body of the present invention can be applied to embankments with reinforced earth walls or retaining walls reinforced with the above-mentioned anchors, embankments without reinforced walls, and the toes of reclaimed land.

In addition, in this embodiment, the soft ground improvement body 1 is provided directly below the ground end 2a of the embankment 2, but a surface improvement body may also be provided on the surface of the soft ground. In other words, in this case, the soft ground improvement body is provided below the surface improvement body.

In addition, in this embodiment, the centroid C of the improvement body having the forward continuous improvement wall 11 and the orthogonal improvement wall 12 is configured to coincide with the center of gravity P of the load of the retaining wall 23 when viewed from above, but this is not limited to coinciding the centroid C with the center of gravity P.

In addition, there are no particular limitations on the specific configuration of the ground improvement device for constructing the soft ground improvement body 1. In other words, the position, number, shape, etc. of the rotating shaft, drilling blade, mixing blade, etc. can be set arbitrarily.

In addition, the components in the above-described embodiments may be replaced with well-known components as appropriate without departing from the spirit of the present invention.

1 soft ground improvement body 11a rear surface 12 orthogonal improvement wall 13 rear lateral improvement wall 21 slope 22 anchor bolt 23 retaining wall (reinforced wall)
C: centroid of the soft ground improvement body 1 G: soft ground P: center of gravity of the retaining wall 23 R: slip surface X1: extension direction X2: front-rear direction

Claims (4)

A soft ground improvement body is formed by supporting a ground end located at the lateral lower end of a structure that is installed on soft ground and is subjected to uneven earth pressure, excavating the target ground that supports the ground end from below, and mixing and stirring a ground improvement material,
a front continuous improvement wall that extends continuously along the extending direction of the ground contact end and receives, on its rear side, the ground that supports the load of the structure;
a plurality of orthogonal improvement walls that are orthogonal to the rear surface of the front continuous improvement wall in the extending direction when viewed from above;
At least a part of the improved area consisting of the forward continuous improvement wall and the orthogonal improvement wall is provided at a position overlapping the ground edge of the structure,
A soft ground improvement body for a structure, characterized in that the forward continuous improvement wall is positioned forward of the structure when viewed from above and has been improved to a depth that reaches the slide surface of the soft ground caused by the uneven earth pressure of the structure. A rear lateral improvement wall is integrally provided on the rear surface side of the front continuous improvement wall, the rear lateral improvement wall extending along the extension direction at a distance from the front continuous improvement wall,
2. The soft ground improvement body according to claim 1, characterized in that the front continuous improvement wall, the rear horizontal improvement wall, and the orthogonal improvement wall are formed in a lattice pattern. The structure has an embankment and a reinforcing wall that reinforces a side surface of the embankment,
A soft ground improvement body as described in claim 1 or 2, characterized in that the centroid of the improvement body having the forward continuous improvement wall and the orthogonal improvement wall coincides with the center of gravity of the load of the reinforcing wall in a side view. A method for constructing a soft ground improvement body according to any one of claims 1 to 3,
a step of extending the front continuous improvement wall continuously in the extension direction of the ground contact end in front of the structure and improving the ground to a depth reaching the slide surface;
providing a plurality of orthogonal improvement walls perpendicular to the rear surface of the front continuous improvement wall when viewed from above;
having
A construction method for a soft ground improvement body, characterized in that at least a part of the improvement area consisting of the front continuous improvement wall and the orthogonal improvement wall is provided in a position overlapping with the ground end of the structure.

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