Strength estimation method of chemically improved soil and ground improvement method

Abstract

To provide a strength estimation method of chemically improved soil capable of estimating strength of chemically improved soil using chemical of a chemical feed method to improve the ground and a ground improvement method.SOLUTION: A strength estimation method of chemically improved soil of the present invention is a method for estimating strength of chemically improved soil using chemical of a chemical feed method to improve the ground, comprising: sampling a specimen from an objective ground to be improved (S01); carrying out a soil test using the specimen (S02); and estimating strength of the chemically improved soil where site soil to be improved is mixed with the chemical on the basis of particle surface areas per unit volume acquired through the soil test and homogel strength of the chemical (S04).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for estimating the strength of chemically improved soil using a chemical solution in a chemical solution injection method for ground improvement, and a ground improvement method. [Background technology]

[0002] A known countermeasure against liquefaction caused by earthquakes directly beneath existing structures is the chemical injection method, in which holes are drilled from the ground surface and chemicals are injected to improve the ground (see Non-Patent Document 1). This chemical injection method prevents ground liquefaction by replacing the interstitial water between soil particles in the ground with a chemical solution. By carrying out infiltration injection without destroying the soil particle skeleton that constitutes the ground, it is possible to carry out high-quality ground improvement work while preventing uplift of the ground and runaway of chemicals.

[0003] Patent Document 1 discloses a method for estimating a liquefaction strength ratio, which includes a first step of acquiring a micro-deformation characteristic value (VS or G) of the original ground, a second step of acquiring a micro-deformation characteristic value (VS* or G*) and a liquefaction strength ratio (RL*) for a test sample having a density equivalent to that of the original ground, and a third step of estimating the liquefaction strength ratio (RL) of the original ground from the micro-deformation characteristic value (VS or G) of the original ground, the micro-deformation characteristic value (VS* or G*) of the test sample, and the liquefaction strength ratio (RL*) of the test sample (Claim 1).

[0004] Patent Document 2 aims to accurately estimate the strength of improved ground from the early age after improvement using an active silica-based chemical agent, and installs an oscillator sensor capable of emitting and receiving compression waves and shear waves in the improved ground improved by injecting an active silica-based chemical agent.The method discloses a ground strength estimation method (abstract) that uses the compression wave velocity obtained by this oscillator sensor to estimate the uniaxial compressive strength of the improved ground by fitting it to a regression curve that shows the relationship between compression wave velocity and uniaxial compressive strength obtained in advance from a laboratory test. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-188887 A [Patent Document 2] JP 2011-106843 A [Non-patent literature]

[0006] [Non-Patent Document 1] "Technical Manual for Seepage Solidification Treatment Method (Revised New Edition)" Coastal Technology Center, General Incorporated Foundation, July 2020 [Non-Patent Document 2] Teppei Akimoto, Noriaki Sendo, and Kazuhiko Ueno, "Evaluation of factors affecting the unconfined compressive strength of soil improved by chemical grouting," Journal of the Japan Society of Civil Engineers, Vol. 78, No. 2, I_535-I_540, 2022 Summary of the Invention [Problem to be solved by the invention]

[0007] When carrying out ground improvement work using the liquid grouting method, local soil is sampled and a mix test is carried out before construction. That is, the local soil is mixed with several types of liquids with different silica concentrations (for example, silica concentrations of 7%, 8%, and 9%) to prepare liquid-improved soil, and a uniaxial compression test is carried out on this liquid-improved soil to confirm the strength corresponding to each concentration. The liquid concentration that satisfies the required performance is determined by comparing with the required performance (design standard strength). The higher the liquid concentration, the greater the strength, but the higher the cost, so the liquid with the lowest concentration that satisfies the design standard strength is determined as the liquid to be grouted. Since strength development differs depending on the local soil, such mix tests must be carried out for each construction project.

[0008] However, there are cases where the required performance cannot be met with normal chemical concentrations, and compounding tests must be conducted again with special high-concentration chemicals. If the strength still cannot be secured, the chemical injection method cannot be applied and another method must be used. This requires a lot of rework, the compounding tests are wasted, and it is a heavy burden in terms of costs and processes.

[0009] In view of the problems of the conventional technology as described above, the present invention aims to provide a method for estimating the strength of chemical-improved soil and a ground improvement method that can estimate the strength of chemical-improved soil using a chemical solution in a chemical injection method for ground improvement before a mixing test is conducted. [Means for solving the problem]

[0010] The method for estimating the strength of chemically improved soil to achieve the above object is a method for estimating the strength of chemically improved soil using a chemical solution for a chemical solution injection method for ground improvement, A sample is taken from the site to be improved, and a soil test is conducted using the sample. The strength of the improved soil when the local soil of the site is mixed with the chemical solution is estimated based on the soil particle surface area per unit volume obtained from the soil test and the homogel strength of the chemical solution.

[0011] According to this method for estimating the strength of soil improved with a chemical solution, a soil test is conducted using a sample taken from the target site for ground improvement, the soil particle surface area per unit volume is determined from this soil test, and by taking into account the homogel strength of the chemical solution as well as the particle size and density of the local soil particles using the soil particle surface area per unit volume, it is possible to accurately estimate the strength of the soil improved with a chemical solution when the local soil at the target site is mixed with the chemical solution. This method for estimating the strength of soil improved with a chemical solution is completely different from the strength estimation methods in References 1 and 2.

[0012] By estimating the strength of the liquid-improved soil before a mix test, which is carried out prior to the execution of a chemical injection method for injecting a chemical into the ground for the ground improvement, the strength of the liquid-improved soil can be grasped before the mix test is carried out. For example, when the strength of the estimated liquid-improved soil satisfies the design standard strength, a mix test can be carried out with different types and / or concentrations of the chemical, the type and / or concentration of the chemical can be determined from the mix test results, and the liquid injection method can be carried out with the chemical of the determined type and / or concentration. On the other hand, when the strength of the estimated liquid-improved soil does not satisfy the design standard strength, it is possible to prevent rework such as reviewing the ground improvement method after the mix test, and it is possible to take measures such as changing from the liquid injection method to another method without carrying out a mix test, thereby eliminating the need to carry out unnecessary mix tests, avoiding the waste of costs and time related to the mix test, and causing no adverse effects on the ground improvement process and construction period.

[0013] It is also preferable to set multiple homogel strengths of the chemical solution through experiments and estimate the strength of the chemical-improved soil for each homogel strength of the chemical solution. For this purpose, it is preferable to set multiple homogel strengths through experiments in which the type and / or concentration of the chemical solution is changed.

[0014] In addition, it is preferable to calculate the soil particle surface area per unit volume by taking into consideration the coarse and fine particles of the soil particles obtained in the soil test. In this case, the diameter of the coarse particles is calculated based on the particle size addition curve obtained in the soil test, and the diameter D 50 It is preferable to calculate the soil particle surface area per unit volume from a sphere with a diameter of 0.05 mm and a sphere with a diameter of 0.075 mm for the fine particles.

[0015] It is also preferable to estimate the strength of the chemically improved soil from the following formulas 1 to 4. TIFF2024178540000002.tif46101 However, q u : Unconfined compressive strength of chemically improved soil (kN / m 2 ) q uh : homogel strength of drug solution (kN / m 2 ) a,b,c: constant S * : Soil particle surface area per unit volume (cm 2 / cm 3 ) S Cm : Specific surface area of ​​coarse particles (cm 2 / g) S Fm : Specific surface area of ​​fine particles (cm 2 / g) ρ d :Dry density (g / cm 3 ) F c :Fine particle content (%) S s : Surface area of ​​one soil particle (sphere) (cm 2 ) ρ s :Soil particle density (g / cm 3 ) V s : Volume of one soil particle (sphere) (cm 3 ) The coarse particles are D of the particle size addition curve. 50 The fine particles are spheres with a diameter of 0.075 mm, and the surface area of ​​one soil particle (sphere) is S s and the volume V of the soil particle (sphere) s Calculate the following.

[0016] The ground improvement method for achieving the above-mentioned objective involves, when the strength of the chemically improved soil estimated by the above-mentioned method for estimating the strength of chemically improved soil satisfies the design standard strength, conducting a blending test of the chemically improved soil by mixing local soil collected from the target site with a chemical solution, determining the type and / or concentration of the chemical solution based on the blending test, and carrying out a chemical injection method using the chemical solution of the determined type and / or concentration.

[0017] According to this ground improvement method, when the strength of the chemically improved soil estimated by the above-mentioned method for estimating the strength of chemically improved soil before the mix test satisfies the design standard strength, the mix test can then be conducted by changing the type and / or concentration of the chemical solution, the type and / or concentration of the chemical solution can be determined from the mix test results, and the chemical injection method can be conducted using the determined type and / or concentration of the chemical solution. On the other hand, if the strength of the estimated chemically improved soil does not satisfy the design standard strength, it is possible to prevent rework such as reviewing the ground improvement method after the mix test, and it is possible to take measures such as changing from the chemical injection method to another method without conducting the mix test, thereby eliminating the need to conduct unnecessary mix tests, avoiding the waste of costs and time related to the mix test, and preventing adverse effects on the ground improvement process and construction period. Effect of the Invention

[0018] According to the method for estimating the strength of chemically improved soil and the ground improvement method of the present invention, the strength of soil improved with a chemical solution by a chemical injection method for ground improvement can be estimated before a mix test is carried out. [Brief description of the drawings]

[0019] [Figure 1] 1 is a flowchart for explaining each step of a ground improvement method using a method for estimating strength of chemically improved soil according to this embodiment. [Diagram 2] 1 is a graph showing an example of the relationship between the chemical solution concentration and the unconfined compressive strength of chemical solution-improved soil obtained by a blending test in this embodiment. [Diagram 3] This is the particle size addition curve for Tohoku silica sand No. 6 used in this experimental example. [Figure 4] This is a graph showing the relationship between the soil particle surface area per unit volume S* (cm2 / cm3) obtained in this experimental example and the unconfined compressive strength qu of the chemically improved soil obtained from the experimental results, for each chemical concentration. [Diagram 5] This is a graph showing the relationship between the coefficient a in Equation 2 and the homogel strength quh of the drug solution obtained in this experimental example. [Figure 6] This is a comparison diagram between the unconfined compressive strength qu (horizontal axis) of chemically improved soil estimated from equations 1 to 4 and the unconfined compressive strength qu (vertical axis) of the experimental results. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a flow chart illustrating the steps of a ground improvement method using a method for estimating strength of chemically improved soil according to the present embodiment;

[0021] First, local soil samples are taken from the site to be improved using the chemical grouting method (S01). Soil tests are then conducted on these samples (S02). The following values ​​and data are obtained from the soil tests, including a grain size test (JIS A 1204). ·Dry density ρ d : weight of soil per unit volume ·Soil particle density ρ s : Specific gravity of soil particles ·Fine particle content F c : Weight percentage of soil particles passing through a 0.075 mm sieve (particle size smaller than 0.075 mm) Particle size addition curve

[0022] Meanwhile, the homogel strength of the chemical solution used in the chemical grouting method is determined and set by experiment (S03). Experiments are conducted with chemical solutions of multiple concentrations, and the homogel strength of the chemical solution is set for each concentration. The homogel strength is the strength of the solidified body (without sand) in which only the chemical solution has solidified.

[0023] Next, the strength of the solution-improved soil when the local soil at the target site is mixed with the solution is estimated based on the soil particle surface area per unit volume obtained by the soil test in step S02 and the homogel strength of the solution set in step S03 (S04).

[0024] The method for estimating the strength of the chemically improved soil based on the results of the on-site soil test in step 04 will be described. It is generally said that there is a relationship between the size of soil particles (particle size) and strength (see Non-Patent Document 2). For homogeneous sand such as the sand used in the experiment, the average particle size D 50It is possible to estimate the strength only from the average particle size D. However, local soil usually has a large uniformity coefficient (good grain size distribution) and contains fine grains. 50 It is difficult to estimate the strength of soil by itself. In addition, the strength of soil improved with chemical solution is affected by the density of the soil as well as the homogel strength of the chemical solution, so the density must be taken into consideration. Therefore, the soil particle surface area per unit volume S * (cm 2 / cm 3 ) and homogel strength of the drug solution q uh The strength of the soil improved with chemical solution is estimated based on the above. The soil particle surface area per unit volume is calculated taking into account the coarse and fine particles of the soil particles obtained from the soil test. Estimation formulas 1 to 4 are shown below.

[0025]

number

[0026] However, q u : Unconfined compressive strength of chemically improved soil (kN / m 2 ) q uh : homogel strength of drug solution (kN / m 2 ) a,b,c: constant S Cm : Specific surface area of ​​coarse particles (cm 2 / g) S Fm : Specific surface area of ​​fine particles (cm 2 / g) ρ d :Dry density (g / cm 3 ) F c :Fine particle content (%) S s : Surface area of ​​one soil particle (sphere) (cm 2 ) ρ s :Soil particle density (g / cm 3 ) V s : Volume of one soil particle (sphere) (cm 3 ) The coarse particles are D on the particle size addition curve. 50The fine particles are spheres with a diameter of 0.075 mm, and the fine particles are spheres with a diameter of S s and V s Calculate (S s =4πr 2 ,V s =(4 / 3)πr 3 ,r: radius of the sphere).

[0027] Next, if the strength of the above estimated chemically improved soil satisfies the design standard strength (Yes in S05), a mix test of the chemically improved soil is conducted by mixing the local soil taken from the target site for ground improvement with the chemical solution (S06). Next, the concentration of the chemical solution is determined based on the results of the mix test (S07).

[0028] In the mix test, local soil is mixed with several types of chemical solutions with different silica concentrations (for example, silica concentrations of 7%, 8%, and 9%) to prepare chemically improved soil, and the strength of each concentration is confirmed, for example, by the results of a uniaxial compression test conducted based on JIS A 1216. The chemical solution concentration that satisfies the required performance (design standard strength) is determined by comparing it with the required performance.

[0029] Figure 2 shows an example of the relationship between the concentration of the chemical solution obtained from a mix test and the unconfined compressive strength of the chemically improved soil. 2 Then, the drug concentration is determined to be 8%.

[0030] Next, in the area to be improved, the chemical solution of the determined concentration is used to carry out ground improvement by a chemical injection method (S09).

[0031] Furthermore, if the strength of the chemically improved soil estimated in step S04 does not satisfy the design standard strength (No in S05), the method is changed to another method (S08), and ground improvement is carried out using that method (S09).

[0032] (Experimental Example) Next, the unconfined compressive strength q of the improved soil was measured using five types of sand. u and the soil particle surface area per unit volume S *The following describes an example of an experiment that confirmed the relationship between the strength and the unconfined compressive strength, and the accuracy of the estimation. The sand materials used and their soil properties are shown in Table 1 below. As an example of the grain size test results, the grain size addition curve for Tohoku silica sand No. 6 is shown in Figure 3. In addition, the homogel strength q uh was determined by experiment and is shown in Table 2 for each chemical concentration. The chemical used was Ecosilica (registered trademark), a solution-type activated silica grout.

[0033] [Table 1]

[0034] [Table 2]

[0035] For each sand material, chemically improved soil was prepared using a chemical solution of each concentration, and a uniaxial compression test was carried out for each chemically improved soil based on JIS A 1216. The soil particle surface area per unit volume S calculated from Equations 3 and 4 was * (cm 2 / cm 3 ) and the unconfined compressive strength q of the improved soil u The experimental results are shown in Fig. 4. From Fig. 4, the surface area of ​​soil particles per unit volume S * (cm 2 / cm 3 ) and the unconfined compressive strength q of the improved soil u It can be seen that there is an approximately proportional relationship between the concentration of the chemical and the coefficient a for chemical concentrations of 6%, 8%, and 10% corresponds to the formula 1. The approximation formula for each chemical concentration shown in Fig. 4 corresponds to the formula 1, and the coefficient a is 0.594, 1.040, and 1.406, respectively.

[0036] As shown in Equation 2, the coefficient a is the homogel strength q of the drug solution containing coefficients b and c. uh The coefficient a in Equation 2 and the homogel strength q of the drug solution are shown in Fig. 5. uh The relationship between the coefficient a and homogel strength q of the drug solution shown in Figure 5 is shown. uh The approximation equation for corresponds to equation 2, where b = 0.381 and c = 0.397.

[0037] Figure 6 shows the unconfined compressive strength q of the improved soil estimated from Eqs. 1 to 4. u (horizontal axis) and the experimental result of uniaxial compressive strength q u (vertical axis) in Fig. 6. The root mean square error (RMSE) in Fig. 6 is 37.6 kN / m 2 and the estimated unconfined compressive strength q u The results were relatively close to the experimental results, and it was found that the unconfined compressive strength of the chemically improved soil can be estimated relatively accurately using equations 1 to 4.

[0038] As described above, according to the method for estimating the strength of the chemically improved soil according to the present embodiment, the strength of the chemically improved soil can be estimated from the results of the on-site soil survey before the mix test, which is performed prior to the construction of the chemical injection method. Therefore, it is possible to determine whether the strength of the estimated chemically improved soil satisfies the design standard strength before the mix test, and to determine whether the mix test is necessary or not, thereby realizing the suppression of economical time loss. In other words, if the strength of the estimated chemically improved soil does not satisfy the design standard strength, it is possible to prevent rework such as reviewing the ground improvement method after the mix test, and it is possible to take measures such as changing from the chemical injection method to another method without conducting the mix test. Since it is possible to avoid re-running the mix test, the cost and time related to the mix test are not wasted, and there is no adverse effect on the process and construction period of the ground improvement. In addition, if the strength of the estimated chemically improved soil satisfies the design standard strength, a mix test is performed, the concentration of the chemical solution is determined from the mix test results, and the chemical injection method can be performed using the chemical solution of the determined concentration.

[0039] In addition, in step S03 of Figure 1, experiments are conducted using multiple concentrations of chemical solutions, and the homogel strength of the chemical solution is set for each concentration. This makes it possible to grasp the strength of the chemical-improved soil for each concentration of chemical solution before the blending test and to estimate the required chemical solution concentration, which can be used as a guide for setting the chemical solution concentration in the blending test.

[0040] Although the embodiments for carrying out the present invention have been described above, the present invention is not limited to these, and various modifications are possible within the scope of the technical concept of the present invention. In this embodiment, the present invention is applied to the case where the strength of the chemically improved soil is estimated before the mix test carried out prior to the construction of ground improvement work by the chemical injection method, but the present invention is not limited to this, and it is of course applicable to the case where the strength of the chemically improved soil is estimated for the purpose of an investigation at a stage when the implementation of ground improvement work by the chemical injection method has not been decided.

[0041] 1, experiments were performed with multiple concentrations of drug solutions to set the homogel strength of the drug solution for each concentration, but the present invention is not limited to this, and multiple homogel strengths of the drug solution may be set by experiments with different types and concentrations of drug solutions. Also, the blending test in step S06 may be performed with different types and concentrations of drug solutions, and the type and concentration of the drug solution may be determined based on the blending test results.

[0042] The chemical used in the present embodiment and experimental examples is a solution-type activated silica grout, but is not limited to this, and other chemicals can be used as long as they are solution-type water glass-based. [Industrial Applicability]

[0043] According to the present invention, the strength of soil improved with a chemical solution used in a chemical injection method for ground improvement can be estimated before a mix test is conducted, thereby eliminating the need to conduct mix tests again, eliminating the waste of costs and time associated with mix tests, and preventing adverse effects on the ground improvement process and construction period.

Claims

1. A method for estimating the strength of soil improved by a chemical solution in a chemical solution grouting method for ground improvement, comprising: Collecting samples from the site to be improved and conducting soil tests using the samples; A method for estimating the strength of chemically improved soil, which estimates the strength of the chemically improved soil when the local soil at the target site is mixed with a chemical solution based on the soil particle surface area per unit volume obtained by the soil test and the homogel strength of the chemical solution.

2. A method for estimating the strength of chemically improved soil as described in claim 1, in which the strength of the chemically improved soil is estimated before a mixing test is conducted prior to the construction of a chemical injection method in which a chemical is injected into the ground for ground improvement.

3. 2. A method for estimating the strength of chemical-solution-improved soil as claimed in claim 1, wherein a plurality of homogel strengths of the chemical solution are experimentally determined, and the strength of the chemical-solution-improved soil is estimated for each homogel strength of the chemical solution.

4. 2. A method for estimating the strength of chemically improved soil as claimed in claim 1, wherein the soil particle surface area per unit volume is calculated taking into account the coarse and fine particles of the soil obtained in the soil test.

5. The diameter of the coarse particles is determined as the particle diameter D corresponding to a passing mass percentage of 50% on the particle diameter addition curve obtained in the soil test. ５０ 5. A method for estimating the strength of chemically improved soil as described in claim 4, wherein the soil particle surface area per unit volume is calculated from a sphere having a diameter of 0.05 mm and a sphere having a diameter of 0.075 mm for the fine particles.

6. A method for estimating the strength of chemical-improved soil according to claim 1, in which the strength of the chemical-improved soil is estimated from the following equations 1 to 4. Where, q ｕ : Unconfined compressive strength of chemically improved soil (kN / m ２ ) q ｕｈ : homogel strength of drug solution (kN / m ２ ) a, b, c: constants S ＊ : Soil particle surface area per unit volume (cm ２ / cm ３ ) S Ｃｍ : Specific surface area of ​​coarse particles (cm ２ / g) S Ｆｍ : Specific surface area of ​​fine particles (cm ２ / g) ρ ｄ : Dry density (g / cm ３ ) F ｃ :Fine particle content (%) S ｓ : Surface area of ​​one soil particle (sphere) (cm ２ ) ρ ｓ : Soil particle density (g / cm ３ ) V ｓ : Volume of one soil particle (sphere) (cm ３ ) The coarse particles are D of the particle size addition curve. ５０ The fine particles are spheres with a diameter of 0.075 mm, and the surface area of ​​one soil particle (sphere) is S ｓ and the volume V of one soil particle (sphere) ｓ Calculate the following.

7. A ground improvement method, in which, when the strength of the chemical-improved soil estimated by the method for estimating the strength of chemical-improved soil described in any one of claims 1 to 6 satisfies the design standard strength, a blending test is conducted on the chemical-improved soil by mixing local soil collected from the target site with a chemical solution, the type and / or concentration of the chemical solution is determined based on the blending test, and a chemical injection method is performed using the chemical solution of the determined type and / or concentration.

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