Soil improvement method

Abstract

To provide a ground improvement method capable of maintaining the effect of reducing ground displacement even when the ground to be improved is composed of, in particular, highly adhesive cohesive soil.SOLUTION: To standardize a range of a water content in which an earth removal rate becomes appropriate from a water content of soil of a ground in consideration of an amount of drilling water at the time of drilling in a ground improvement construction method for constructing a cylindrical improvement body in a ground to be improved, and to set the amount of drilling water. The water content ratio of the ground in consideration of the amount of drilling water at the time of drilling can be normalized by the liquid limit of the soil of the ground, and the range of the normalized water content ratio (W / WL) = 0.7 to 1.3, preferably, the range of the normalized water content ratio (W / WL) = 0.8 to 1.2 can be set as the range of the reference water content ratio.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a ground improvement method, and more particularly to a ground improvement method for creating a cylindrical improved body in ground to be improved. [Background technology]

[0002] Conventionally, there has been a ground improvement method (see, for example, Patent Document 1) in which a drilling blade at the tip of a single-tube injection rod is used to drill a hole in the ground to a predetermined depth, and the outside of the stirring blades is cut and mixed with the energy of the solidification material slurry that is injected into the ground through the injection rod at high pressure, while a soil pushing-up disk installed close to the top of the solidification material slurry injection part of the injection rod pushes up the disturbed soil near the solidification material slurry injection port, forming a void below the soil pushing-up disk, which absorbs the mixed soil mixed with the solidification material slurry into the void, creating a cylindrical improvement body in the ground to be improved and preventing displacement and movement into the surrounding ground. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-120819 Summary of the Invention [Problem to be solved by the invention]

[0004] In ground improvement methods, drilling water is added during drilling. However, if too much water is added during drilling, the soil will exceed its liquid limit, turning into muddy water. This reduces the effectiveness of the soil push-up disks in pushing up the disturbed soil when creating an improved body. Conversely, if too little water is added during drilling, the soil will be less disturbed and the pull-out resistance will increase. This reduces both the effect of the increase in internal pressure in the ground due to the increase in ground volume caused by the injection of solidification slurry, and the effect of the soil push-up disks in pushing up the disturbed soil when creating an improved body. Therefore, if water is not added appropriately during drilling, the soil removal rate will decrease, and the effectiveness of reducing ground displacement will be reduced.

[0005] With conventional ground improvement methods, when the ground to be improved is composed of highly cohesive clay, in particular, the resistance of the agitator blades increases when drilling and penetrating the ground to be improved. This causes the agitator blades to rotate insufficiently, resulting in less disturbance of the ground. Alternatively, more water than necessary may be added to reduce resistance during penetration, causing the ground to turn into muddy water, which reduces the upward pushing effect of the blade, lowers the soil removal rate, and reduces the effectiveness of reducing ground displacement.

[0006] Therefore, the present invention aims to provide a ground improvement method that can maintain the effect of reducing ground displacement even when the ground to be improved is composed of particularly high-cohesion clayey soil. [Means for solving the problem]

[0007] This invention is a ground improvement method in which a drilling blade at the tip of a single-tube injection rod is used to drill a hole in the ground to the planned depth, and the energy of the solidification material slurry injected into the ground through the injection rod at high pressure cuts and mixes the outside of the agitator blade, while a soil push-up disk installed adjacent to the top of the solidification material slurry injection part of the injection rod pushes up the disturbed soil near the solidification material slurry injection port, forming a void below the soil push-up disk, and the mixed soil mixed with the solidification material slurry is absorbed into the void, thereby creating a cylindrical improved body in the ground to be improved.In this method, drilling to the planned improvement depth is performed in multiple steps using an agitator equipped with a soil push-up disk adjacent to the top of the agitator blade installed above the drilling blade at the tip of the injection rod, and the step length in the depth direction corresponding to the amount of soil that can be drilled and extracted in one drilling is set appropriately according to the soil quality during drilling. This is a ground improvement method in which drilling is performed up to the set first step depth while injecting drilling water at low pressure, then the soil is withdrawn and discharged by a length equivalent to that step depth, drilling is performed again down to the bottom of the next second step depth while injecting drilling water at low pressure, then the soil is withdrawn and discharged by a length equivalent to that step depth, and this process is repeated for each step to drill and discharge soil up to the planned improvement depth, then the rod is temporarily withdrawn to the ground, and drilling is performed again to the planned improvement depth, after which a slurry-like solidification material is withdrawn while being sprayed sideways at high pressure from a mixing blade nozzle installed near the tip of the rod that has reached the planned depth, thereby creating a cylindrical improved body.This ground improvement method is characterized by the fact that the range of moisture content at which the soil removal rate is appropriate is standardized based on the moisture content of the soil of the ground, taking into account the amount of drilling water used during drilling, and the amount of drilling water can be set.

[0008] Furthermore, the present invention can standardize the range of water content where the soil discharge rate is 80% or more. Also, the present invention can standardize the range of water content where the soil discharge rate is 90% or more. Also, the present invention can normalize the water content of the ground, taking into account the amount of drilling water, by the liquid limit of the soil of the ground. Also, the present invention can normalize the normalized water content (W / W L The drilling water can be injected at such a rate that the normalized water content ratio (W / W) is 0.7 to 1.3. LThe drilling water can be injected at a rate such that the ratio of the water content of the drilling water to the total water content is 0.8 to 1.2. [Effects of the Invention]

[0009] The present invention standardizes the range of moisture content at which the soil discharge rate is appropriate based on the moisture content of the soil of the ground, taking into account the amount of drilling water used during drilling, and makes it possible to set the amount of drilling water.This makes it possible to provide a ground improvement method that can maintain the effect of reducing ground displacement even when the ground to be improved is mainly composed of highly cohesive clay soil. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing an embodiment of the present invention, and is a diagram schematically showing a graph used when standardizing the range of moisture content in which the soil discharge rate is appropriate. [Figure 2] FIG. 1 is a diagram showing an embodiment of the present invention, and is a diagram schematically showing the trajectory of the drilling depth position of the rod tip in a ground drilling method using an improved device. [Figure 3] 1 is a diagram showing an embodiment of the present invention, and is a cross-sectional view showing an apparatus used in the construction method of this embodiment and a state of soil removal. FIG. [Figure 4] FIG. 4 is a view taken along the line IV-IV in FIG. 3. [Figure 5] 1 is a diagram showing an embodiment of the present invention, and is a cross-sectional view showing an apparatus used in the construction method of this embodiment and an improved state. FIG. [Figure 6] 6 is a cross-sectional view corresponding to the VI-VI cross-sectional view of FIG. 5. DETAILED DESCRIPTION OF THE INVENTION

[0011] In order to achieve the above object, the inventor of the present invention has conducted an intensive analysis of construction data from various ground improvement work sites accumulated over many years, and has found that it is possible to standardize the range of water content of the ground soil, taking into account the amount of drilling water during drilling that results in an appropriate soil discharge rate. The present invention is based on this finding.

[0012] An embodiment of the present invention will be described with reference to Figs. 1 to 6. First, a ground improvement device used in the ground improvement method of this embodiment will be described. The ground improvement device 1 (hereinafter abbreviated as device 1) comprises a rotating and vertical movement mechanism 2 and a single-pipe injection rod 3 (hereinafter referred to as injection rod 3). The rotating and vertical movement mechanism 2 supports the injection rod 3 by a support 4 so that it can rotate and move up and down.

[0013] The upper end of the injection rod 3 is connected to a solidification material slurry pressure-transport hose 6 via a swivel 5. The lower end of the injection rod 3 is provided with an excavation fang (also called an earth auger) 7, which is a type of excavation blade that constitutes the agitation device, and an agitation blade 8, and the shaft and the agitation blade 8 are provided with an injection nozzle 9 for the solidification material slurry S, which is a type of solidification material slurry injection part. The solidification material slurry S is, for example, a mixture of a solidification material and water.

[0014] A soil pushing-up disk 10 is provided near the top of the mixing blade 8 and close to the top of the injection nozzle 9 for pushing up the soil disturbed by the mixing blade 8 when the injection rod 3 is raised in steps. The soil pushing-up disk 10 pushes up the disturbed soil near the injection port (not shown) of the injection nozzle 9, forming a void below the soil pushing-up disk 10, and absorbs the mixed soil mixed with the solidification material slurry S into the void, thereby creating a cylindrical improved body in the soft ground G (hereinafter abbreviated as ground G), which is the ground to be improved.

[0015] In order to maximize the efficiency of soil removal when the injection rod 3 is pulled up after being inserted into the ground, the radius of the soil push-up disk 10 is set to the same dimension as the radius of the agitator blade 8 or to be 10 cm or less, preferably 5 cm smaller than the radius of the agitator blade 8, and the slope of the soil push-up disk 10 in a projected planar shape is preferably 10 to 20 degrees, preferably 15 degrees.

[0016] The injection rod 3 rotates and penetrates the ground G while injecting drilling water at low pressure, so that a disturbed area G1 is formed by the stirring blades 8. In this disturbed area G1, a roughly cylindrical muddy water film G2 is formed by the disturbed soil and drilling water.

[0017] Next, the ground improvement method of this embodiment will be described. (0) First, when carrying out the ground improvement method, the range of water content that will result in an appropriate soil removal rate is standardized. Figure 1 shows a graph for standardizing the range of water content that will result in an appropriate soil removal rate. The graph shows the relationship between the water content, taking into account the amount of water used for drilling the soil, and the soil removal rate. In this embodiment, in order to minimize the influence of the soil quality at each site, the actual water content W is set as the water content, which is the liquid limit W. L Normalized water content (W / W L ) is used.

[0018] The soil discharge rate is calculated using the following formula:

[0019]

number

[0020] At least when the soil of ground G is clayey, such as highly cohesive clay, it has been found through experience that the relationship between the water content of the soil, taking into account the amount of drilling water, and the soil discharge rate can be approximated to the estimated line shown in the graph, although there will be some deviation depending on the soil quality of each site. Therefore, it is possible to standardize the range of water content for which the soil discharge rate is appropriate, based on the water content of the soil of ground G, taking into account the amount of drilling water used during drilling.

[0021] For example, if the soil discharge rate is 80% or more, that is, the normalized moisture content (W / W L ) = 0.7 to 1.3, preferably, the soil removal rate is 90% or more, that is, the normalized water content (W / W L It is possible to standardize the range of moisture content where )=0.8 to 1.2.

[0022] (1) Next, a soil survey of the ground G is carried out. In this soil survey, at least the natural water content (Wn : unit %), liquid limit (W L : Unit % Investigate the liquid limit W L is evaluated, for example, by the Casagrande method.

[0023] And the standardized water content (W / W L ) and the liquid limit W of the soil L The soil moisture content W is calculated by taking into account the amount of drilling water required to achieve an appropriate soil removal rate, and the moisture content W and the natural moisture content W of the soil are then calculated. n Using the standardized water content ratio W / W L The amount of water to be added during drilling, i.e., the amount of drilling water and drilling speed, is determined so that the above equation is satisfied.

[0024] (2) After that, the actual construction is carried out. In this construction, first, for example, as shown in Figure 2, the ground G is excavated to the planned depth using the excavation fangs 7 in a multiple step method. Specifically, the step length in the depth direction corresponding to the amount of soil that can be excavated and extracted in one step is appropriately set according to the soil quality of the ground G, and the ground G is excavated to the first step depth using the equipment 1 until the standardized water content (W / W L ) while injecting drilling water at low pressure with the amount of water determined in step (1) so that the depth becomes equal to the depth of one step, the hole is drilled at the same drilling speed, and then the soil is pulled out and removed by a length equivalent to the depth of one step (hereinafter, the removed soil will be referred to as removal soil G3).

[0025] Next, drilling is performed again at the same drilling speed while injecting drilling water at a low pressure with the amount of water determined in step (1) to the bottom of the second step depth, and then the soil is extracted and removed for a length equivalent to that one step depth (second step depth). This process is repeated for each step until the hole is drilled to the planned improvement depth.

[0026] In this embodiment, when the injection rod 3 penetrates the ground G while rotating, the stirring blades 8 press against the injection rod 3 to form a disturbed section G1 in the ground G. At this time, gaps are formed on the outer circumferential surface of the disturbed section G1, and drilling water enters the gaps, mixing the disturbed soil and drilling water. In particular, the disturbed soil in the gaps is converted into a muddy state, forming a thin, approximately cylindrical muddy water film G2. This separates the disturbed soil located within the diameter of the soil push-up disk 10 from the area outside the diameter, and the rotation of the soil push-up disk 10 causes the disturbed soil within the diameter to be pushed upward and removed.

[0027] Next, the injection rod 3 is temporarily withdrawn to the ground, and the hole is again excavated to the planned improvement depth, after which the solidification material slurry S is ejected sideways at high pressure from the injection nozzle 9 of the injection rod 3 while being pulled out, forming an improved area G4. During this process, the energy of the solidification material slurry S ejected at high pressure into the ground G through the injection rod 3 cuts and mixes the outside of the agitator blades 8, while the soil push-up disk 10 pushes up the disturbed soil near the solidification material slurry ejection port, forming a void below the soil push-up disk 10, and the mixed soil mixed with the solidification material slurry S is absorbed into this void, creating an improved column in the ground G and completing the improvement of the ground G.

[0028] Therefore, in the ground improvement method of this embodiment, the range of water content W of the ground G taking into account the amount of drilling water during drilling is standardized to provide an appropriate soil discharge rate, and the amount of drilling water can be set, making it possible to drill the ground G with an appropriate amount of drilling water and drilling speed, and providing a ground improvement method that can maintain the effect of reducing ground displacement even when the ground G is composed of particularly high-cohesion clay soil.

[0029] Although the present invention has been described above based on the above embodiment, the present invention is not limited to the above embodiment and can be modified as appropriate within the scope of the invention. For example, in the above embodiment, the water content is standardized from the graph and used as the standard, but since there is a possibility that some deviation will occur depending on the soil quality of each site, a test construction may be carried out before the actual construction and the standardized water content may be corrected. [Explanation of symbols]

[0030] 1 Ground improvement device 2 Rotating and vertical mechanism 3 Single pipe injection rod 4 Support 5 Swivel 6 Solidification material slurry pressure hose 7 Excavation fang 8 Mixing blade 9 Injection nozzle 10 Soil push-up disk G Ground G1 disturbance part G2 Mud film G3 Earth removal G4 Improvement section S Solidification material slurry

Claims

1. This is a ground improvement method in which a drilling blade at the tip of a single-tube injection rod is used to drill a hole in the ground to a predetermined depth, and the outside of the agitator blade is cut and mixed with the energy of the solidification material slurry that is injected into the ground through the injection rod at high pressure. At the same time, a soil pushing-up disk installed close to the top of the solidification material slurry injection part of the injection rod pushes up the disturbed soil near the solidification material slurry injection port, forming a void below the soil pushing-up disk, and the mixed soil mixed with the solidification material slurry is absorbed into the void, creating a cylindrical improved body in the ground to be improved. a mixing device equipped with a soil pushing-up disk adjacent to the top of the excavation blade at the tip of the injection rod is used to drill holes up to the planned improvement depth in multiple steps, and the step length in the depth direction corresponding to the amount of soil that can be drilled and extracted in one drilling is appropriately set according to the soil quality during the drilling; drilling is performed while injecting drilling water at low pressure to the set first step depth, and then the soil is extracted and removed by the length equivalent to the depth of that one step; drilling is performed again while injecting drilling water at low pressure to the bottom of the next second step depth, and then the soil is extracted and removed by the length equivalent to the depth of that one step; this is repeated for each step to drill and remove the soil up to the planned improvement depth; next, the rod is temporarily withdrawn to the ground, and after drilling again to the planned improvement depth, a slurry-like solidification material is extracted while being sprayed at high pressure sideways from the nozzle of the mixing blade installed near the tip of the rod that has reached the planned depth, creating a cylindrical improved body; This is a ground improvement method characterized by standardizing the range of moisture content at which the soil discharge rate is appropriate based on the moisture content of the soil of the ground, taking into account the amount of drilling water used during drilling, and making it possible to set the amount of drilling water.

2. 2. The ground improvement method according to claim 1, wherein the range of water content at which the soil discharge rate is 80% or more is standardized.

3. 2. The ground improvement method according to claim 1, wherein the range of water content at which the soil discharge rate is 90% or more is standardized.

4. 4. The ground improvement method according to claim 1, wherein the water content of the ground taking into account the amount of drilling water is normalized by the liquid limit of the soil of the ground.

5. Normalized water content ratio (W / W Ｌ 5. The ground improvement method according to claim 4, which cites claim 1 or 2, characterized in that the amount of drilling water injected is such that the ratio of the water content of the drilling water to the total water content is 0.7 to 1.

3.

6. Normalized water content ratio (W / W Ｌ 5. The ground improvement method according to claim 4, which cites claim 1 or 3, characterized in that the amount of drilling water injected is such that the ratio of the total surface area to the total surface area is 0.8 to 1.2.

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