Ground improvement method

Abstract

To provide a ground improvement method that is easy to construct and can create an improved body with a sufficient improvement diameter.SOLUTION: In a method for improving the ground by discharging a solidification material, a particle size distribution of the solidification material suspension has 5% by volume or more of particles with a diameter of 3 μm or less and 20% by volume or more of particles with a diameter of 30 μm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a ground improvement method. [Background technology]

[0002] To date, many methods have been developed for ground improvement using high-pressure jet mixing with solidifying materials. The classic example is the so-called CCP method, but in recent years, improvements have been made to the methods, such as using air, cutting with water, or special solidifying materials, as well as the rods and fluid supply devices used.

[0003] High-pressure injection methods that use air, such as the so-called jet grouting method, offer the advantage of being able to increase the diameter of the improved soil using air. However, the strength of the improved soil is not necessarily sufficiently high. In the so-called CCP method, which does not use air, the normal improved soil diameter is 1000 mmφ or less, and it never reaches 1500 mmφ. On the other hand, the CCP method has the advantage of requiring small-scale equipment, being extremely simple to implement, and being able to create an improved soil that exhibits sufficient strength. There have also been proposals for a ground improvement method that is easy to implement and can create an improved soil with a sufficient diameter (see, for example, Patent Document 1). However, demand for ground improvement is insatiable, and further improvements are required. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-36768 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a ground improvement method that is easy to carry out and that can create an improved body with a sufficient improvement diameter. [Means for solving the problem]

[0006] The means for solving the above problems are as follows. (Means described in claim 1) This is a method of improving the ground by discharging solidifying material. The particle size distribution of the solidification material suspension is such that particles with a diameter of 3 μm or less are 5% by volume or more and particles with a diameter of 30 μm or more are 20% by volume or more. A ground improvement method characterized by:

[0007] (Means described in claim 2) The rod installed in the ground is rotated around its axis and moved in the axis direction, and the solidification material is discharged from the rod to improve the ground. The ground improvement method according to claim 1.

[0008] (Means described in claim 3) The solidifying material contains a dispersant, As the dispersant, a comb polymer having a polyoxyalkylene chain in the graft chain is used. The ground improvement method according to claim 1.

[0009] (Means described in claim 4) The solidification material has a discharge rate of 5 L / min to 50 L / min and a discharge pressure of 1 to 8 MPa, The rod intermittently rotates and stops around its axis. The ground improvement method according to claim 2.

[0010] (Means described in claim 5) The concentration of the solidification material is 200 to 600 kg / m 3 That is, The ground improvement method according to claim 2.

[0011] (Means described in claim 6) The injection rate of the solidification material suspension into the ground is 30 to 80%; The ground improvement method according to claim 2. [Effects of the Invention]

[0012] According to the present invention, a ground improvement method is provided which is easy to carry out and can create an improved body with a sufficient improvement diameter. [Brief explanation of the drawings]

[0013] [Figure 1] This is an explanatory diagram of the ground improvement method. [Figure 2] (a) is an explanatory diagram of the ground improvement method, and (b) is an explanatory cross-sectional view of the construction of the improved body. [Figure 3] FIG. 1 is a schematic diagram of the flow of solidification material. DETAILED DESCRIPTION OF THE INVENTION

[0014] Next, a description will be given of an embodiment of the invention. Note that this embodiment is an example of the present invention. The scope of the present invention is not limited to the scope of this embodiment. Furthermore, the present invention can also be applied to high-pressure mixing methods, simple injection methods, etc., but the effects of the present invention are most pronounced in the following methods.

[0015] 1 is used to explain the outline of the present invention, and shows a boring machine 1 used to penetrate and pull up a drilling rod 2. The boring machine 1 is equipped with a pump 3, and the drilling rod 2 is equipped with a swivel and the like.

[0016] As shown in (a) and (b) of Figure 1, the boring machine 1 rotates the drilling rod 2 to apply a penetration force, while supplying drilling water W through the drilling rod 2 and allowing it to flow out from the lower end opening, thereby drilling to the specified depth.

[0017] Then, as shown in Figure 1 (c) and Figure 2, solidification material M is supplied into the drilling rod 2 by a pump 3, and is ejected in one direction from a nozzle 2a provided on the wall of the drilling rod 2, and the drilling rod 2 is pulled up, finally creating a cylindrical improvement body 10 of a predetermined length in the ground as shown in Figure 1 (d).

[0018] The above method is essentially the same as the conventional CCP method. CCP methods are broadly divided into two types: those that do not use water cutting and those that do. This embodiment is related to the CCP method that does not use water cutting by water injection during the process of pulling up the drilling rod 2. Furthermore, this embodiment does not use air to increase the reach of the solidification material, as is used in some high-pressure injection methods, but only ejects the solidification material. As mentioned above, it should be noted that the above does not mean that the present invention cannot be applied to the CCP method or high-pressure injection method.

[0019] In the CCP method, the drilling rod is rotated continuously around its axis at a predetermined speed at each step-up position, while continuously discharging solidification material. In contrast, in this embodiment, the drilling rod 2 is not rotated continuously around its axis, but is rotated around its axis at a certain swing angle θ (see Figure 2(b)), stopped at that position for a short time, and then rotated at the next swing angle θ, repeating this rotation and stopping intermittently. In general, the cross-sectional shape of the outer periphery of the improved body obtained often resembles the outer periphery shape indicated by a group of adjacent petals, the number of which corresponds to the number of swings at the swing angle θ.

[0020] The discharge rate of the solidification material is preferably 5 to 50 L / min, especially 15 to 30 L / min. If the discharge rate is too low, a sufficiently large improved diameter cannot be obtained, and if the discharge rate is too high, there is a limit to the improved diameter.

[0021] The discharge pressure should be 1 to 8 MPa, and especially 3 to 6 MPa. If the discharge pressure is low, sufficient shear force cannot be obtained, and a sufficiently large improved diameter cannot be obtained. If the discharge pressure is too high, the nozzle diameter must be reduced at low flow rates, and the nozzle is likely to become clogged with the solidification material.

[0022] In this regard, when the discharge rate of the solidification material is 5 L / min to 50 L / min and the discharge pressure is 1 to 8 MPa, the following effects can be obtained by intermittently rotating and stopping the rod 2 around its axis. In conventional jet grouting, the rod is continuously rotated while ascending. This method involves finely cutting the ground with a jet, and the turbulence of a large flow rate mixes the grout material and the fragmented soil particles. When this method is performed with a small flow rate, as in the present embodiment, the jet cuts the ground to some extent, but subsequent agitation by the liquid flow is difficult. Large particles of solidification material clog the surface of the excavated ground, leaving a film-like coating on the excavated ground. This inhibits the penetration effect of the small particles of solidification material contained in the subsequent excavation suspension. In contrast, in the present embodiment, the rod rotation is stopped for a certain period of time before the grout material is sprayed and a certain amount of return fluid is discharged to the surface. Therefore, the flow of the solidification material in the ground reaches its limit in one go from the drilling rod 2, as shown in Figure 3. The remaining return fluid then flows around the rod and is discharged to the surface as sludge, creating a flow of return fluid on the surface of the pipe-like drilled hole. This flow washes away the large particles deposited on the surface that hinder infiltration, allowing the fine particles to infiltrate more easily into the ground. In Figure 3, the flow of large particles is indicated by solid arrows, and the flow of fine particles is indicated by dashed arrows. This is the same mechanism as cross-flow filtration in filtration methods.

[0023] From the above viewpoints, the rotational swing angle θ around the axial direction of the drilling rod is preferably 5 to 50 degrees, more preferably 10 to 40 degrees, and even more preferably 15 to 30 degrees. If the swing angle θ is small, it becomes similar to continuous rotation and the effect of increasing the improved diameter is insufficient, while if the swing angle θ is large, unevenness is likely to occur in the improved body, especially on the outer periphery, and variations in the density of the solidification material filling are likely to occur on the outer periphery and in the area close to the drilling rod.

[0024] The rest time after rotation is preferably 1 to 30 seconds, more preferably 3 to 20 seconds, and even more preferably 5 to 10 seconds. A short rest time results in a similar effect to continuous rotation, resulting in insufficient increase in the improved diameter. On the other hand, a long rest time increases the swing angle θ when the injection rate is constant, which makes the improved body more likely to become uneven, especially at the periphery. Furthermore, more soil particles than necessary are discharged to the surface, which tends to cause variations in the solidification material filling density at the periphery and in the area near the drill rod, resulting in variations in the strength of the improved body. A constant swing angle θ increases the injection volume of the solidification material suspension, which limits the effect of increasing the improved diameter, but extends the construction work time and reduces construction efficiency.

[0025] The injection rate of the solidification material suspension into the ground is preferably 30 to 80%, more preferably 30 to 70%, and particularly preferably 30 to 60%. If the injection rate is low, the diameter of the improved body will be small, or the improved body generated by intermittent discharge will not be able to wrap sufficiently, resulting in a loss of continuity of the improved body. If the injection rate is high, a large amount of waste mud will be discharged, as with conventional high-pressure injection mixing methods, making it uneconomical. Note that the injection rate refers to the percentage of the amount of solidification material suspension injected / the volume of the ground to be improved.

[0026] The step-up length after one rotation of the drilling rod should be 15 to 250 mm, and preferably 50 to 200 mm. If the step-up length is too short, construction efficiency will be low, and if the step-up length is too long, strength variations and discontinuities will occur along the height of the improved body.

[0027] To obtain the desired improvement, the discharge volume and discharge pressure are strongly correlated, so it is desirable to select them as the first factor, and then select the swing angle and dwell time as the second (supplementary) factor.

[0028] The solidification material used is typically cement-based, such as blast furnace cement B. However, it is preferable that the particle size distribution of the solidification material suspension contains 5% by volume or more of particles with a diameter of 3 μm or less (preferably 7% by volume or more of particles with a diameter of 3 μm or less) and 20% by volume or more of particles with a diameter of 30 μm or more (preferably 25% by volume or more of particles with a diameter of 30 μm or more).

[0029] The shear force of high pressure jet of suspension is given by the equation of motion E=mV 2 / 2, it is proportional to the injection velocity, i.e., the square of the injection pressure, and the weight of the particles contained, i.e., the particle diameter. In other words, the shear force increases when a large amount of large particles (30 μm or more in diameter) is included. On the other hand, small particles are essential for penetration into the sand layer, and sufficient penetration cannot be expected for fine sand unless the particles are small, i.e., 3 μm or less. Therefore, by mixing a certain amount of large particles with small particles that can penetrate sufficiently, it is possible to effectively form a columnar improved body.

[0030] The solidifying agent preferably contains a dispersant, which adsorbs to the surfaces of agglomerated particles and imparts an electric charge, thereby breaking up the agglomerates and producing particles with smaller diameters.

[0031] Furthermore, it is more preferable that the dispersant is a comb polymer having a polyoxyalkylene chain in the graft chain, since this type of dispersant has the effect of inhibiting re-agglomeration of the solidifying material, and this dispersant fully exhibits the effect of hybridizing the large particle size solidifying material and the small particle size solidifying material.

[0032] As a dispersant made of a comb polymer having a polyoxyalkylene chain in the graft chain, for example, the Marialim (registered trademark) series manufactured by NOF Corp. can be used.

[0033] The solidification material suspension should have a concentration of 200 to 600 kg / m3 for efficient cutting and penetration. 3 It is preferable to use the cement slurry to which a dispersant has been added. The concentration means the amount of solidification material mixed / unit volume of solidification material suspension.

[0034] The viscosity of the solidification agent suspension is preferably 1 to 30 mPa·s, more preferably 1 to 10 mPa·s. The lower the viscosity of the solidification agent suspension, the smaller the pressure loss at the nozzle, and the less the shear force caused by spraying. However, since the viscosity of water is 1 mPa·s, the solidification agent suspension theoretically cannot be lowered below this. High viscosity increases the pressure loss at the nozzle, resulting in a decrease in flow rate at the same pressure or an increase in pressure at the same flow rate, which ultimately leads to a decrease in shear force. The above viscosity adjustments can be made by adding the dispersant, adjusting the amount of cement added, or by using a cement hardening retarder. [Example]

[0035] Next, an embodiment of the present invention will be described. Test solutions were prepared by blending blast furnace B cement, dispersant, and water in the proportions shown in Table 1. A bleeding test (20 cm long) was then conducted on each test solution. In this test, the test solution placed in a beaker was sampled 5 cm from the top, and the absorbance was measured at each elapsed time. Marialim (registered trademark) HKM-50A (manufactured by NOF Corp.) was used as the dispersant for test solutions 2 and 5. Furthermore, Floric R (manufactured by Floric Corp.), a lignin-based cement dispersant, was used as the dispersant for test solutions 3 and 4. The results are shown in Table 2.

[0036] [Table 1]

[0037] [Table 2]

[0038] Table 2 shows that the top 5 cm of test liquid 2 and test liquid 5 remained cloudy even after 6 hours, while the top 5 cm of the other liquids became almost transparent after 1 hour. From this, and according to Stokes' theorem, it can be seen that test liquids 2 and 5 contain more fine particles than the other liquids.

[0039] Next, the materials for Test Solutions 1 to 5 were weighed out to a total volume of 200 ml and mixed in a mixer for 3 minutes. Test Solutions 1D and 5D had the same material composition as Test Solutions 1 and 5, and were mixed in a homogenizer at 20,000 rpm for 2 minutes. This mixture was diluted 50 times with pure water, and particle size distribution was measured by centrifugal sedimentation. The results are shown in Table 3.

[0040] [Table 3]

[0041] Table 3 shows that when the solidification material contains a dispersant, and a comb polymer with a polyoxyalkylene chain in the graft chain is used as the dispersant, a large particle size is maintained while a large number of fine particles are present. Therefore, when a return flow parallel to the cutting surface is generated as in this case, it can be said that the suspension has high penetration performance while maintaining shear force. Furthermore, it can be seen that using a high-shear mixer can further reduce the particle size of small-particle solidification materials while maintaining the particle size of large-particle solidification materials. To achieve the desired particle size of the solidification material, it is preferable to mix the solidification material suspension with a high-shear mixer.

[0042] Next, the particle size volume percentages were measured for test solutions 1 to 5, 1D, and 5D by the light transmission centrifugal sedimentation method. The results are shown in Table 4.

[0043] [Table 4]

[0044] Table 4 shows that Test Solution 2, Test Solution 5, and Test Solution 5D contain 5% by volume or more of particles with a diameter of 3 μm or less and 20% by volume or more of particles with a diameter of 30 μm or more. This shows that Test Solution 2, Test Solution 5, and Test Solution 5D have an increased proportion of fine particles with high permeability, while the proportion of large particles with high shear force remains almost unchanged compared to the other liquids. [Industrial Applicability]

[0045] The present invention can be used as a ground improvement method. [Explanation of symbols]

[0046] 1...boring machine, 2...boring rod, 2a...nozzle, 10, 10A...improved body, 10B...second improved body.

Claims

1. This is a method of improving the ground by discharging solidifying material. The particle size distribution of the solidification material suspension is such that particles with a diameter of 3 μm or less are 5% by volume or more and particles with a diameter of 30 μm or more are 20% by volume or more. A ground improvement method characterized by:

2. The rod installed in the ground is rotated around its axis and moved in the axis direction, and the solidification material is discharged from the rod to improve the ground. The ground improvement method according to claim 1.

3. The solidifying material contains a dispersant, As the dispersant, a comb polymer having a polyoxyalkylene chain in the graft chain is used. The ground improvement method according to claim 1.

4. The solidification material has a discharge rate of 5 L / min to 50 L / min and a discharge pressure of 1 to 8 MPa, The rod intermittently rotates and stops around its axis. The ground improvement method according to claim 2.

5. The concentration of the solidifying agent is 200 to 600 kg / m ３ That is, The ground improvement method according to claim 2.

6. The injection rate of the solidification material suspension into the ground is 30 to 80%; The ground improvement method according to claim 2.

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