Ground improvement structure and method for constructing the same

Abstract

To provide a ground improvement structure capable of reducing the range of ground improvement by obliquely providing a highly strong ground improvement body having a core material disposed therein.SOLUTION: The ground improvement structure within a range held between earth walls provided in the ground in which there is an artesian ground water layer below a low-permeable layer comprises: a first ground improvement body 2A having a core material disposed therein and obliquely provided from the ground surface toward the artesian ground water layer; and a second ground improvement body 2B having a core material disposed therein and obliquely provided from the ground surface spaced apart in the plan-view extension direction of the earth walls toward the lower end of the first ground improvement body of the artesian ground water layer. The first and second ground improvement bodies are continuously provided to cross the earth walls, and the lower ends thereof are connected to each other by a connection part 23 in the artesian ground water layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a ground improvement structure and a method for constructing a ground improvement structure in an area sandwiched between retaining walls installed in ground where a confined groundwater layer exists below a low-permeability layer. [Background technology]

[0002] As described in Patent Documents 1 and 2, when a confined groundwater layer exists where confined groundwater is expected to exist below a low-permeability layer, measures must be taken to prevent ground swelling. The consideration of ground swelling is carried out by taking into account the weight of the soil mass below the confined surface, the frictional resistance of the retaining wall, and the load balance between the shear resistance of the ground and the water pressure.

[0003] Therefore, in Patent Documents 1 and 2, measures are taken such as improving the ground over the entire area that will be the bottom of the excavation of the impermeable layer, and resisting the uplift pressure by the friction of the pile circumference or by the tensile force of the tensile anchorage material.

[0004] On the other hand, Patent Document 3 describes a method of constructing a ground improvement body in which H-shaped steel beams are inserted as a core material after the construction of the ground improvement body, and describes how by mixing a solidification retarder into the ground improvement body, the core material can be inserted even a long time after the construction of the ground improvement body. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-144742 A [Patent Document 2] JP 2003-171949 A [Patent Document 3] JP 2011-153449 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, if a method of ground improvement is adopted to prevent ground swelling by completely improving the ground around the bottom of the excavation, the improvement area will become wider, and the construction period and cost will increase. On the other hand, when inserting a core material into the ground improvement body later, it is difficult to insert the core material into the center of the ground improvement body even if the ground improvement body is installed vertically.

[0007] Therefore, the present invention aims to provide a ground improvement structure and a method for constructing a ground improvement structure that can reduce the area of ​​ground improvement by slanting a high-strength ground improvement body in which a core material is arranged. [Means for solving the problem]

[0008] In order to achieve the above-mentioned objective, the ground improvement structure of the present invention is a ground improvement structure in an area sandwiched between retaining walls constructed in ground where a confined groundwater layer exists below a low-permeability layer, and comprises a first ground improvement body having a core material arranged inside and arranged diagonally from the ground surface toward the confined groundwater layer, and a second ground improvement body having a core material arranged inside and arranged diagonally from the ground surface to the lower end of the first ground improvement body in the confined groundwater layer, spaced apart in the planar extension direction of the retaining walls, and is characterized in that the first ground improvement body and the second ground improvement body are continuously constructed so as to cross between the retaining walls, and their lower ends are connected to each other in the confined groundwater layer.

[0009] Here, the first ground improvement body and the second ground improvement body can be cylindrical and multiple bodies can be arranged overlapping each other so as to cross between the retaining walls, and the core material can be configured to be positioned at the center of the cylinders.

[0010] In addition, a third ground improvement body having a core material arranged inside and adjacent to the first ground improvement body in the planar extension direction can be arranged diagonally toward the pressurized groundwater layer on the opposite side of the first ground improvement body, and the lower ends of this third ground improvement body and a fourth ground improvement body having a core material arranged inside and arranged diagonally can be connected to each other in the pressurized groundwater layer.

[0011] Furthermore, the invention of a method for constructing a ground improvement structure is a method for constructing a ground improvement structure provided on ground where a pressurized groundwater layer exists below a low-permeability layer, and includes the steps of: constructing an earth retaining wall facing the ground before excavation; boring a hole using an agitating blade while carrying a core material from the ground surface between the earth retaining walls to the pressurized groundwater layer at a predetermined inclination angle; rotating the agitating blade while spraying a cement-based solidification material, and constructing a first ground improvement body by raising the agitating blade with the core material left behind; and forming a first ground improvement body by continuously cutting the earth retaining walls so as to cross the earth retaining walls. The method includes the steps of constructing the first ground improvement body in a similar manner, drilling holes using an agitator with a core material from the ground surface spaced in the planar extension direction of the retaining wall to the pressurized groundwater layer at a predetermined inclination angle toward the lower end of the first ground improvement body, constructing a second ground improvement body in a similar manner to the first ground improvement body, and constructing the second ground improvement body in a similar manner with the core material continuously extending across the retaining walls, wherein the first ground improvement body and the second ground improvement body are connected at their lower ends in the pressurized groundwater layer.

[0012] Here, the method may be configured to include a step of pumping groundwater from the pressurized groundwater layer surrounded by the first soil improvement body and the second soil improvement body. Effect of the Invention

[0013] In the ground improvement structure of the present invention configured in this manner, a first ground improvement body and a second ground improvement body, each having a core material disposed inside and located in the area sandwiched between the retaining walls, have their lower ends connected to each other in the pressurized groundwater layer.

[0014] Therefore, with a small amount of construction work, it is possible to reduce the range of uplift pressure caused by pressurized groundwater, and the range of ground improvement work can be reduced. In addition, since core materials are placed in the first and second ground improvement bodies, the strength of the ground improvement bodies can be increased.

[0015] In addition, in the invention of a method for constructing a ground improvement structure, a hole is drilled at a predetermined inclination angle using an agitator while carrying a core material, and then the agitator is rotated while spraying a cement-based solidification material, and the agitator is raised while leaving the core material in place to construct a first ground improvement body and a second ground improvement body.

[0016] Therefore, the core material can be easily placed in the center of the inclined ground improvement body. Furthermore, by pumping up groundwater from the confined groundwater layer surrounded by the first and second ground improvement bodies, the area of ​​action of the uplift pressure can be reduced. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is an explanatory diagram showing an overview of the ground improvement structure of this embodiment. [Diagram 2] FIG. 2 is an explanatory diagram showing a schematic configuration of the ground improvement body of this embodiment. [Diagram 3] FIG. 2 is a plan view illustrating the configuration of the ground improvement structure of this embodiment. [Figure 4] 2 is a flowchart illustrating a method for constructing a ground improvement structure according to the present embodiment. [Diagram 5] FIG. 2 is an explanatory diagram showing a schematic configuration of a ground improvement machine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Figures 1 and 3 are diagrams for explaining an outline of a ground improvement structure according to the present embodiment. Also, Figure 2 is an explanatory diagram showing a schematic configuration of a ground improvement body 2 according to the present embodiment.

[0019] The ground improvement structure of this embodiment is constructed between opposing earth retaining walls 1, 1, as shown in the plan view of Fig. 3. The earth retaining wall 1 is provided to protect the vertical excavation surface that appears when the ground is excavated as is. The earth retaining wall 1 can be configured in a variety of forms, including steel sheet piles, parent pile horizontal sheet piles, steel pipe sheet piles, soil cement column walls, diaphragm walls, and mud water solidification walls.

[0020] The ground improvement structure of this embodiment is provided in ground where a confined groundwater layer exists below an aquifer, as shown in Fig. 1. For ease of explanation, the upper half of Fig. 1 is entirely an aquifer and the lower half is entirely a confined groundwater layer, but this is not limiting. In short, if the ground is one in which there is a risk of swelling occurring when excavating between the retaining walls 1, 1, providing the ground improvement structure of this embodiment makes it possible to suppress such swelling.

[0021] The ground improvement structure of this embodiment includes a ground improvement body (2A-2D) that is installed obliquely from the ground surface toward the confined groundwater layer between the retaining walls 1, 1, as shown in Figures 1 and 3. Since the configurations of the ground improvement bodies (2A-2D) are all the same, the configuration of the ground improvement body 2 will be described with reference to Figure 2.

[0022] The ground improvement body 2 is constructed by mixing and stirring, for example, a cement-based solidification material into the ground. For example, a cylindrical improvement body can be provided by using soil cement 20, which is created by injecting a solidification material such as cement slurry while stirring the ground with a stirring blade or auger. Also, a cylindrical column of soil cement 20 that becomes the ground improvement body 2 can be provided by using a high-pressure jet stirring and mixing processing method in which a solidification material is mixed with the ground while being jet-sprayed at high pressure.

[0023] A core material 21 is placed in the center of the cylinder of soil cement 20. A steel wire, steel rod, or the like can be used as the core material 21. Also, an anchor material 22 can be provided at the tip of the core material 21, as shown diagrammatically in FIG.

[0024] In this embodiment, the ground improvement body 2 having such a configuration will be described by assigning symbols to the first ground improvement body 2A, the second ground improvement body 2B, the third ground improvement body 2C, and the fourth ground improvement body 2D, as shown in Figures 1 and 3.

[0025] The first ground improvement body 2A is installed at an angle from the ground surface toward the pressurized groundwater layer at a predetermined inclination angle θ. On the other hand, the second ground improvement body 2B is installed from the ground surface spaced apart from the ground surface of the first ground improvement body 2A in the extension direction of the retaining wall 1 in a plan view to the pressurized groundwater layer at a predetermined inclination angle θ toward the lower end of the first ground improvement body 2A.

[0026] That is, the first soil improvement body 2A and the second soil improvement body 2B are formed in a V-shape in side view as shown in Fig. 1. The lower ends of the first soil improvement body 2A and the lower ends of the second soil improvement body 2B are connected to each other to form a connecting portion 23.

[0027] On the other hand, the third ground improvement body 2C is provided obliquely from a position adjacent to the first ground improvement body 2A in the plan view extension direction of the retaining wall 1 toward the pressurized groundwater layer on the opposite side to the first ground improvement body 2A. The relationship between this third ground improvement body 2C and the fourth ground improvement body 2D is similar to the relationship between the first ground improvement body 2A and the second ground improvement body 2B, so a detailed explanation will be omitted.

[0028] The ground improvement bodies (2A-2D) are installed continuously so as to cross the space between the earth retaining walls 1, 1. For example, as shown in the plan view of Fig. 3, a plurality of cylindrical ground improvement bodies (2A-2D) are installed in an overlapping manner so as to cross the space between the earth retaining walls 1, 1 so as to separate them.

[0029] In this way, by separating the retaining walls 1,1 with a column-shaped, inclined ground improvement body (2A-2D), the ground existing between the retaining walls 1,1 can be captured as a triangular pillar-shaped mass of earth.

[0030] Since peripheral frictional resistance occurs between the ground improvement body (2A-2D) and the surrounding ground, this, together with the frictional resistance between the retaining wall 1 and the ground improvement body (2A-2D) and the ground, as well as the weight of the impermeable layer and the ground improvement body (2A-2D), can be used to resist the uplift pressure U, thereby preventing ground swelling.

[0031] Next, a method for constructing a ground improvement structure according to this embodiment will be described with reference to the flow chart of FIG.

[0032] First, in step S1, the retaining wall 1 is constructed from the surface of the ground before excavation. For example, if the retaining wall 1 is to be constructed with steel sheet piles, the steel sheet piles are driven into the ground, and if the retaining wall 1 is to be constructed as a soil cement column wall, it is constructed by injecting cement slurry while excavating the ground with an auger. The retaining walls 1 are set up so as to face each other on both sides of the excavated ground, as shown in Figure 3.

[0033] In step S2, a ground improvement machine 3 is installed at a position adjacent to the retaining wall 1 on the ground surface, and drilling is performed to create an inclined columnar ground improvement body 2 toward the confined groundwater layer, which is the ground below the bottom of the excavation formed when a trench is excavated between the retaining walls 1, 1.

[0034] 5 is an explanatory diagram showing a schematic configuration of a ground improvement machine 3 that performs drilling and ground improvement. In this figure, the base machine is omitted, and the configuration around the rod 31 and the mixing blade 32 is shown.

[0035] The rod 31 has a double tube structure, and the core material 21 is passed through the inner tube. If the core material 21 is a wire, it can be bent, so it can be easily passed through even a long rod 31. Agitating blades 32 are provided at the tip of the rod 31, and anchor material 22 is provided at the tip of the core material 21 that passes through the inner tube of the rod 31 and protrudes from the agitating blades 32. In other words, the anchor material 22 acts as a catch, preventing the core material 21 from slipping out upward.

[0036] The gap between the inner and outer tubes of the rod 31 serves as a space through which the cement slurry passes, and the cement slurry supplied from the ground passes through the gap between the inner and outer tubes of the rod 31 and is sprayed from the nozzle 33 of the discharge pipe connected above the mixing blade 32.

[0037] The drilling by the soil improvement machine 3 configured in this manner is performed from the ground surface between the retaining walls 1, 1 to the pressurized groundwater layer at a predetermined inclination angle θ with the core material 21 passing through the inner tube of the rod 31. That is, the drilling is performed by rotating the stirring blade 32 together with the core material 21 and forcing the rod 31 into the ground while cutting the ground.

[0038] The impeller 32 is pushed into the impermeable layer at a predetermined inclination angle θ from the ground surface to a predetermined depth in the confined groundwater layer. Then, the impeller 32 is rotated while the cement slurry is sprayed from the nozzle 33 at high pressure, and the impeller 32 is gradually raised while leaving the core material 21 behind, thereby constructing the first ground improvement body 2A (step S3).

[0039] As shown in Figure 3, the first ground improvement body 2A needs to be continuous across the space between the retaining walls 1,1 by placing multiple overlapping cylindrical bodies.Therefore, in step S4, a decision is made to continue construction of the first ground improvement body 2A.

[0040] After separating the retaining walls 1,1 with the column-shaped first ground improvement body 2A, the column row of the adjacent third ground improvement body 2C, or the column row of the second ground improvement body 2B or the fourth ground improvement body 2D is constructed in the same manner as the construction of the column row of the first ground improvement body 2A.

[0041] When the construction of all the ground improvement bodies (2A-2D) is completed in this manner, the ground of the confined groundwater layer will be separated by the ground improvement bodies (2A-2D) as shown in Figure 1. Therefore, in step S5, groundwater is pumped up from the confined groundwater layer surrounded by the ground improvement bodies (2A-2D).

[0042] To explain in detail with reference to Figure 1, the supply of groundwater to the area of ​​the pressurized groundwater layer on the inner corner between the first ground improvement body 2A and the second ground improvement body 2B, whose lower ends are connected by a connecting part 23 (the area surrounded by a dotted line) is blocked by the ground improvement bodies (2A, 2B), so the uplift pressure U can be reduced by pumping groundwater from this enclosed triangular prism-shaped area.

[0043] The uplift pressure U can also be reduced by pumping groundwater in the area of ​​the pressurized groundwater layer (the area surrounded by a dotted line) on the inner corner side of the third ground improvement body 2C and the fourth ground improvement body 2D, whose lower ends are connected by a connecting part 23.

[0044] On the other hand, the confined groundwater layer below the ground improvement bodies (2A-2D) does not become a closed space partitioned by the improvement bodies, so the supply of groundwater from below cannot be stopped, but each inclined ground improvement body (2A-2D) covers the confined groundwater layer as if holding it down, so it can be expected to provide resistance to the uplift pressure U. In other words, when the soil mass of the confined groundwater layer, which is trapezoidal and columnar and narrows at the top, rises, the tapered shape and the peripheral friction with the ground improvement bodies (2A-2D) provide resistance, suppressing ground swelling.

[0045] Next, the operation of the ground improvement structure and the method for constructing a ground improvement structure of this embodiment will be described. In the ground improvement structure and the method for constructing a ground improvement structure of this embodiment configured as described above, a first ground improvement body 2A (third ground improvement body 2C) and a second ground improvement body 2B (fourth ground improvement body 2D), each having a core material 21 arranged inside and provided in the area sandwiched between the retaining walls 1, 1, have their lower ends connected by a connecting part 23 in the pressurized groundwater layer.

[0046] Therefore, the range of action of the uplift pressure U due to pressurized groundwater can be reduced with fewer construction works compared to the construction method of performing ground improvement on the entire area around the bottom of the excavation. For example, when performing ground improvement on the entire area around the bottom of the excavation, it is necessary to repeatedly move and set up the construction machine many times, but with the construction method of the ground improvement structure of this embodiment, it is only necessary to set up the ground improvement machine 3 at a position adjacent to the ground surface of each ground improvement body (2A-2D), which is excellent in workability and allows the range of ground improvement to be reduced.

[0047] In addition, since the core material 21 is arranged in the ground improvement body (2A-2D), the strength of the ground improvement body can be increased. That is, the core material 21 such as a wire adheres to and becomes one with the soil cement 20, and can increase the tensile resistance of the ground improvement body (2A-2D).

[0048] In addition, in the method of constructing a ground improvement structure in this embodiment, a hole is drilled at a predetermined inclination angle θ using the agitator 32 while carrying the core material 21, and then the agitator 32 is rotated while spraying cement slurry from the nozzle 33, and the agitator 32 is raised while leaving the core material 21 behind to construct the ground improvement body (2A-2D).

[0049] In this way, by using a method in which a core material 21 is placed when drilling the ground and a cylindrical soil cement 20 is constructed around the core material 21, the core material 21 can be easily placed in the center even if the ground improvement body (2A-2D) is inclined.

[0050] Furthermore, by pumping groundwater from the pressurized groundwater layer surrounded by the first ground improvement body 2A (third ground improvement body 2C) and the second ground improvement body 2B (fourth ground improvement body 2D), the range of action of the uplift pressure U at the bottom of the excavation can be reduced.

[0051] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes that do not deviate from the gist of the present invention are included in the present invention.

[0052] For example, in the above embodiment, an example was described in which multiple cylindrical ground improvement bodies 2 are arranged in a column row to form a wall to separate the retaining walls 1,1, but this is not limited to this, and other forms of ground improvement bodies may be used as long as they are formed in a wall shape to cross the retaining walls 1,1. [Explanation of symbols]

[0053] 1: Earth retaining wall 2A: 1st ground improvement body 2B: 2nd ground improvement body 2C: Third ground improvement body 2D: Fourth ground improvement body 21: Core material 22: Anchor material 23: Connection part 3: Ground improvement machine 32: Agitation blade 33: Injection port θ: Inclination angle

Claims

1. A ground improvement structure in an area sandwiched between retaining walls installed in a ground where a confined groundwater layer exists below a low-permeability layer, A first ground improvement body having a core material disposed therein and obliquely provided from the ground surface toward the pressurized groundwater layer; a second ground improvement body having a core material disposed therein and obliquely provided from the ground surface at an interval in the plan view extension direction of the earth retaining wall toward the lower end of the first ground improvement body of the pressurized groundwater layer; A ground improvement structure characterized in that the first ground improvement body and the second ground improvement body are arranged continuously across the retaining walls and their lower ends are connected to each other in the pressurized groundwater layer.

2. The ground improvement structure described in claim 1, characterized in that the first ground improvement body and the second ground improvement body are cylindrical and multiple bodies are overlapped and arranged to cross between the retaining walls, and the core material is positioned at the center of the cylinder.

3. A ground improvement structure as described in claim 1 or 2, characterized in that a third ground improvement body having a core material arranged inside and adjacent to the first ground improvement body in the planar extension direction is arranged diagonally toward the pressurized groundwater layer on the opposite side of the first ground improvement body, and the lower ends of this third ground improvement body and a fourth ground improvement body arranged diagonally and having a core material arranged inside are connected to each other in the pressurized groundwater layer.

4. A method for constructing a ground improvement structure provided on ground where a confined groundwater layer exists below a low-permeability layer, comprising the steps of: constructing an earth retaining wall facing the ground before excavation; A step of drilling a hole using an agitator while carrying a core material from the ground surface between the retaining walls to the pressurized groundwater layer at a predetermined inclination angle; A step of rotating the mixing blade while spraying a cement-based solidification material, and raising the mixing blade while leaving the core material in place, thereby constructing a first ground improvement body; A step of similarly constructing the first ground improvement body having the core material continuously so as to cross between the retaining walls; A step of drilling holes using an agitator while carrying a core material from the ground surface at intervals in the plan view extension direction of the retaining wall to the pressurized groundwater layer at a predetermined inclination angle toward the lower end of the first ground improvement body; A step of constructing a second soil improvement body similar to the first soil improvement body; and a step of similarly constructing the second ground improvement body having the core material continuously so as to cross between the retaining walls, A method for constructing a ground improvement structure, characterized in that the first ground improvement body and the second ground improvement body are connected at their lower ends in the pressurized groundwater layer.

5. A method for constructing a ground improvement structure as described in claim 4, characterized in that it includes a step of pumping groundwater from the pressurized groundwater layer surrounded by the first ground improvement body and the second ground improvement body.

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