Method for Evaluating Ground Improvement Effect by Chemical Solution Injection Method

Abstract

To provide a method for evaluating the effect of ground improvement by a chemical injection method using electrical logging, which enables evaluation of a uniaxial compressive strength of an improved body by measuring electrical resistivity before and after improvement.SOLUTION: In advance, a correlation diagram is obtained in which the vertical axis is a uniaxial compressive strength (qu) and the horizontal axis is a ratio of electrical resistivity (Rimp) of the improved ground and electrical resistivity (Runimp) of the unimproved ground (Rimp / Runimp). Based on the correlation diagram, a threshold value is set for the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground and the electrical resistivity (Runimp) of the unimproved ground under the condition that target uniaxial compressive strength (quck) can be secured. Before and after the ground improvement, the electrical resistivity is measured by electrical logging using a penetration hole vertically formed in the ground, and the ratio of the electrical resistivity (Rimp / Runimp) is obtained. Depending on whether this is greater or less than the threshold, it is determined whether the target uniaxial compressive strength (quck) is secured.SELECTED DRAWING: Figure 22

Description

Technical Field

[0001] The present invention relates to a method for evaluating the ground improvement effect by a chemical injection method using electrical logging.

Background Art

[0002] Conventionally, for ground strengthening of soft ground such as landfill sites, ground improvement work has been carried out by a chemical injection method in which a chemical solution composed of water glass (sodium silicate) or the like is injected into the ground. In the ground improvement work by the chemical injection method, after the implementation, a construction confirmation survey is conducted to confirm whether the chemical solution is evenly distributed in the target ground.

[0003] The most common method for the construction confirmation survey of the chemical injection method is a method of evaluating the improved soil by the uniaxial compression strength (qu). However, the uniaxial compression strength of the improved soil by chemical injection is as small as about qu = 50 to 100 kPa, and depending on the target ground, there may be variations in strength and it may not be properly evaluated. That is, in the evaluation by the uniaxial compression strength qu, in the case of a small ground with qu of about 50 to 100 kPa, disturbance leading to a strength decrease is likely to occur during sample collection or specimen preparation in the post - investigation. Also, depending on the target ground, shells, wood chips, silt, organic soil, etc. may be mixed into the specimen, resulting in variations in strength and inability to properly evaluate.

[0004] As a method for directly evaluating the quality of improved ground by means other than such uniaxial compression strength tests, in a study committee etc. regarding ground improvement work by chemical injection methods in landfill sites etc. of the Ministry of Land, Infrastructure, Transport and Tourism, a dynamic cone penetration test capable of measuring pore water pressure, such as a piezodrive cone (PDC), has been proposed. The said piezodrive cone penetrates the ground by hitting a cone with a built-in pressure sensor with a hammer, and measures the penetration amount per blow and the response value of the pore water pressure during penetration. From the penetration amount, the dynamic penetration resistance value (Nd value) of the ground corresponding to the N value of the standard penetration test is calculated for each blow. Also, from the pore water pressure in the ground generated by impact penetration, the fine particle content ratio Fc is estimated, and it has been proposed in the said study committee etc. that the cumulative excess pore water pressure ratio obtained using this pore water pressure can be an index for evaluating the penetration of the chemical into the ground.

[0005] Also, as another method for construction confirmation surveys of chemical injection methods, electric logging is cited. Electric logging utilizes the fact that in chemical injection methods, the pore water in the ground is replaced by the chemical, the compressibility of the ground changes, and the strength of the ground increases due to the solidification of the chemical, so the characteristics of the electrical conductivity of the improved ground change. In this electric logging, a qualitative judgment of the improvement effect can be made based on the decrease in the electrical resistivity value before and after construction. The measurement procedure of the said electric logging is to insert a measurement probe equipped with a plurality of electrodes at predetermined intervals in the vertical direction into a boring hole, then energize the current electrodes, and obtain the resistivity from the potential difference between the electrodes.

[0006] As a method for quality confirmation of ground improvement work by such electric logging, in Patent Document 1 below, an electrode attachment body with an annular electrode attached to the outer surface is inserted into the improvement body, the improvement body formed around the electrode attachment body is energized, and a method for obtaining the resistivity using the current between the current electrodes and the potential difference between the potential electrodes measured in such a state is disclosed. Also, in Non-Patent Document 1, a method for obtaining the chemical filling rate from the change in electrical resistivity before and after chemical injection is disclosed.

[0007] Even the present applicants have proposed, in Patent Document 2 below, a method for confirming the ground improvement effect with little variation and allowing direct confirmation of the quality of the improved ground. This is a method for confirming the ground improvement effect by the chemical solution injection method. After ground improvement, a depth distribution diagram of the Nd value showing the relationship between the depth and the Nd value is obtained by a small dynamic cone penetration test, and a primary effect confirmation for confirming the ground improvement effect is performed based on the increase amount of the Nd value before and after ground improvement. When the ground improvement effect is not recognized by the primary effect confirmation, an electrical logging is performed by inserting a measurement probe equipped with an electrode into the penetration hole of the small dynamic cone penetration test to measure the specific resistance, and a depth distribution diagram of the specific resistance showing the relationship between the depth and the specific resistance is obtained. A secondary effect confirmation for confirming the ground improvement effect is performed based on the decrease amount of the specific resistance before and after ground improvement.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0009]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] However, the method according to Patent Document 1 calculates the output of the improved body, i.e., the cross-sectional area, size, diameter, etc., from the measured specific resistance. The method according to Non-Patent Document 1 calculates the chemical solution filling rate from the electrical specific resistance. The method according to Patent Document 2 enables confirmation of the existence of the ground improvement consolidation body from the reduction in specific resistance even when the ground improvement effect cannot be judged only from the increase amount of the Nd value.

[0011] As described above, although the primary evaluation method of the ground improvement effect by the chemical solution injection method is the method of evaluating by the uniaxial compression strength qu, none of the above-mentioned conventional techniques directly evaluates the strength of the consolidation body.

[0012] In addition, when evaluating the ground improvement effect by measuring the electrical specific resistance, it has also been pointed out that in the case where the salinity concentration of the interstitial water is high and the electrical specific resistance is low, such as in the reclaimed land in the coastal area, the possibility of applying it to the discrimination of chemical solution penetration is low (Non-Patent Document 2).

[0013] Therefore, the main object of the present invention is to provide a method for evaluating the ground improvement effect by the chemical solution injection method using an electrical logging that enables evaluation of the uniaxial compression strength of the improved body by measuring the electrical specific resistance before and after improvement.

[0014] The second object is to clarify the applicable range (salinity concentration range of interstitial water) of the method for evaluating the ground improvement effect by the chemical solution injection method according to the present invention.

Means for Solving the Problems

[0015] As the present invention according to claim 1 for solving the above problems, in advance, a correlation diagram is obtained with one axis being the uniaxial compression strength (qu) and the other axis being the ratio (Rimp / Runimp) of the electrical specific resistance (Rimp) of the improved ground to the electrical specific resistance (Runimp) of the unimproved ground. Based on the correlation diagram, a threshold value of the ratio (Rimp / Runimp) of the electrical specific resistance (Rimp) of the improved ground to the electrical specific resistance (Runimp) of the unimproved ground under the condition that the target uniaxial compression strength (quck) can be ensured is set. Before and after ground improvement, the electrical resistivity is measured by electrical logging using the penetration holes formed vertically in the ground, and the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground is obtained. Whether the target uniaxial compression strength (quck) is ensured is determined based on whether this ratio of electrical resistivity (Rimp / Runimp) is greater than or less than the threshold value. medicine Method for evaluating ground improvement effect by liquid injection method which is Before recording phase The related diagram is for grasping the electrical resistivity characteristics of the silica solution used for ground improvement. For the first step, the silica solution is diluted with water to measure the electrical resistivity for each silica concentration, and a correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rc) is obtained. For the second step, a correlation diagram between the electrical resistivity (Rs·Rimp) of the unimproved / improved ground and the electrical resistivity (Rpw·Rc) of the pore water / chemical solution is obtained. Based on the correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rc) obtained in the first step and the correlation diagram between the electrical resistivity (Rs·Rimp) of the unimproved / improved ground and the electrical resistivity (Rpw·Rc) of the pore water / chemical solution obtained in the second step, for the third step, a correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rimp) of the improved ground is obtained. For the purpose of setting the chemical solution silica concentration corresponding to the target uniaxial compression strength (quck), for the fourth step, using the specimens prepared indoors, a correlation diagram between the silica concentration (SiO2) and the uniaxial compression strength (qu) is obtained. For the fifth step, the correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rimp) of the improved ground obtained in the third step is arranged, with one axis being the ratio (c / co) of the diluted silica concentration (c) to the expected silica concentration (co), and the other axis being the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground, to obtain a correlation diagram. For the sixth step, the correlation diagram between the silica concentration (SiO2) and the uniaxial compression strength (qu) obtained in the fourth step is arranged, with one axis being the ratio (c / co) of the diluted silica concentration (c) to the expected silica concentration (co), and the other axis being the uniaxial compression strength (qu), to obtain a correlation diagram. Based on the correlation diagram obtained in the fifth procedure and the correlation diagram obtained in the sixth procedure, obtain a correlation diagram with the one axis as the uniaxial compression strength (qu) and the other axis as the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground in the seventh procedure. characterized by A method for evaluating the ground improvement effect by the chemical solution injection method is provided.

[0016] In the invention described in claim 1 above, when evaluating the ground improvement effect (uniaxial compression strength) by the chemical solution injection method, in advance, obtain a correlation diagram with one axis as the uniaxial compression strength (qu) and the other axis as the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground, and based on this correlation diagram, set a threshold value of the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground for the conditions under which the target uniaxial compression strength (quck) can be ensured. Regarding the specific method for obtaining the correlation diagram the following first step to seventh step as follows.

[0017] Then, on-site, before and after ground improvement, measure the electrical resistivity by electrical logging using the penetration holes formed vertically in the ground respectively, obtain the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground, and determine whether the target uniaxial compression strength (quck) is ensured based on whether this ratio (Rimp / Runimp) of the electrical resistivity is greater than or less than the threshold value.

[0018] Therefore, it becomes possible to evaluate the uniaxial compression strength of the improved body by measuring the electrical resistivity before and after improvement. That is, conventionally, it was a qualitative evaluation of whether the chemical solution was filled by comparing the electrical resistivity before and after improvement, but according to the present invention, it becomes possible to simply grasp the uniaxial compression strength after improvement numerically from the electrical resistivity before and after improvement, and it becomes possible to quantitatively evaluate the improvement effect.

[0019] Before recording phaseThe related diagram is obtained by diluting the silica solution with water to measure the electrical resistivity for each silica concentration in order to grasp the electrical resistivity characteristics of the silica solution used for ground improvement, and obtaining a correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rc) in the first step, and a second step of obtaining a correlation diagram between the electrical resistivity (Rs·Rimp) of the unimproved / improved ground and the electrical resistivity (Rpw·Rc) of the pore water / chemical solution, and Based on the correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rc) obtained in the first step and the correlation diagram between the electrical resistivity (Rs·Rimp) of the unimproved / improved ground and the electrical resistivity (Rpw·Rc) of the pore water / chemical solution obtained in the second step, a third step of obtaining a correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rimp) of the improved ground, and a fourth step of obtaining a correlation diagram between the silica concentration (SiO2) and the uniaxial compressive strength (qu) using a specimen prepared indoors for the purpose of setting the chemical solution silica concentration corresponding to the target uniaxial compressive strength (quck), and a fifth step of organizing the correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rimp) of the improved ground obtained in the third step, with one axis being the ratio (c / co) of the diluted silica concentration (c) to the expected silica concentration (co), and the other axis being the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground, and a sixth step of organizing the correlation diagram between the silica concentration (SiO2) and the uniaxial compressive strength (qu) obtained in the fourth step, with one axis being the ratio (c / co) of the diluted silica concentration (c) to the expected silica concentration (co), and the other axis being the uniaxial compressive strength (qu), and Based on the correlation diagram obtained in the fifth step and the correlation diagram obtained in the sixth step, a seventh step of obtaining a correlation diagram with one axis being the uniaxial compressive strength (qu) and the other axis being the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground is obtained 。

[0020] Claim 2 As the present invention according to the claim, the ground with a pore water salt concentration of 5,000 to 10,000 ppm is targeted for ground improvement. Claim one recordA method for evaluating the ground improvement effect by the chemical solution injection method described above is provided.

[0021] The above claim 2 The invention described in the above claim clarifies the applicable range (salt concentration range of interstitial water) of the method for evaluating the ground improvement effect by the chemical solution injection method according to the present invention. Even in coastal areas where evaluation by the electrical resistivity method has been considered unsuitable, reliable evaluation becomes possible by clarifying its applicable range.

[0022] Claim 3 As the present invention according to the claim Instead of the correlation diagram with one axis being the uniaxial compression strength (qu) and the other axis being the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground, based on the conversion formula between the uniaxial compression strength (qu) and the liquefaction strength ratio (RL) or the conversion formula between the uniaxial compression strength (qu) and the adhesion (c), corrected, using a correlation diagram with one axis being the liquefaction strength ratio (RL) or the adhesion (c) and the other axis being the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground, according to any one of claims 1 and 2 A method for evaluating the ground improvement effect by the chemical solution injection method is provided.

[0023] The above claim 3 In view of the fact that the uniaxial compressive strength (qu) and the liquefaction strength ratio (RL) can be converted by a certain conversion formula, and the uniaxial compressive strength (qu) and the cohesion (c) can be converted by a certain conversion formula, in the correlation diagram with the one axis being the uniaxial compressive strength (qu) and the other axis being the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground instead Based on the uniaxial compressive strength (qu) of the one axis being the liquefaction strength ratio (RL) or the cohesion (c) set as Correlation in the figure The ground improvement effect is determined.

[0024] Claim 4 As the present invention according to the claim Instead of the correlation diagram with one axis being the uniaxial compression strength (qu) and the other axis being the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground, based on the conversion formula (R(Ω·m)=1 / σ(S / m)) between the electrical resistivity (R) and the conductivity (σ), corrected, using a correlation diagram with one axis being the uniaxial compression strength (qu) and the other axis being the ratio (σunimp / σimp) of the conductivity (σunimp) of the unimproved ground to the conductivity (σimp) of the improved ground, according to any one of claims 1 and 2 A method for evaluating the ground improvement effect by the chemical solution injection method is provided.

[0025] The above claim 4 In view of the fact that the electrical resistivity (R) and the conductivity (σ) can be converted by a conversion formula (R = 1 / σ), in the correlation diagram with the one axis being the uniaxial compressive strength (qu) and the other axis being the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground instead of, the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground of the other axis to the electrical resistivity (Runimp) of the unimproved ground is the ratio (σunimp / σimp) of the conductivity (σunimp) of the unimproved ground to the conductivity (σimp) of the improved ground set as Correlation in the figure Based on this, the ground improvement effect is determined.

Effect of the Invention

[0026] As described in detail above, according to the present invention, it becomes possible to provide a method for evaluating the ground improvement effect by a chemical injection method using an electrical logging method capable of evaluating the uniaxial compressive strength of the improved body by measuring the electrical resistivity before and after improvement.

[0027] In addition, the applicable range (salt concentration range of interstitial water) of the method for evaluating the ground improvement effect by the chemical injection method according to the present invention becomes clear.

Brief Description of the Drawings

[0028]

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Embodiments for Carrying Out the Invention

[0029] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0030] The present invention is a method for evaluating the ground improvement effect by a chemical injection method in which a chemical solution composed of water glass (sodium silicate) or the like is injected into the ground for strengthening the ground of soft ground such as landfill sites, and specifically, it is carried out according to the following procedure.

[0031] In advance, obtain a correlation diagram with the uniaxial compression strength (qu) on the vertical axis and the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground and the electrical resistivity (Runimp) of the unimproved ground on the horizontal axis, and based on this correlation diagram, set the threshold value of the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground and the electrical resistivity (Runimp) of the unimproved ground under the conditions that can ensure the target uniaxial compression strength (quck). Before and after ground improvement, measure the electrical resistivity by electrical logging using the penetration holes formed vertically in the ground, obtain the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground and the electrical resistivity (Runimp) of the unimproved ground, and determine whether the target uniaxial compression strength (quck) is ensured based on whether this ratio (Rimp / Runimp) of the electrical resistivity is greater than or less than the threshold value.

[0032] That is, in the present invention, prior to ground improvement by the chemical solution injection method, through an indoor experiment using the in-situ soil of the improved ground, a correlation diagram (hereinafter also referred to as the uniaxial compression strength correlation diagram) is obtained with the vertical axis being the uniaxial compression strength (qu) and the horizontal axis being the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground. At this time, based on the uniaxial compression strength correlation diagram, a threshold value of the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground under the condition that the target uniaxial compression strength (quck) can be ensured is set.

[0033] Then, an electrical sounding probe is inserted into the penetration hole formed in the ground before ground improvement, and the electrical resistivity (Runimp) is measured at each predetermined depth. Also, after ground improvement, an electrical sounding probe is inserted into the penetration hole formed in the ground, and the electrical resistivity (Rimp) is measured at each predetermined depth.

[0034] After that, it becomes possible to determine whether the target uniaxial compression strength (quck) is ensured by obtaining the ratio (Rimp / Runimp) of the electrical resistivity before and after ground improvement and checking whether this ratio (Rimp / Runimp) of electrical resistance is greater than or less than the threshold value. In addition, not only can it be determined whether the target uniaxial compression strength (quck) is ensured, but it is also possible to specifically know the numerical value of the uniaxial compression strength qu of the ground after improvement from the intersection point with the correlation line by fitting the ratio (Rimp / Runimp) of the actual electrical resistivity before and after ground improvement to the horizontal axis of the uniaxial compression strength correlation diagram.

[0035] Next, the procedure for obtaining the uniaxial compression strength correlation diagram will be described in detail.

[0036] (First step) First of all, in order to grasp the electrical resistivity characteristics of the silica solution used for ground improvement, the silica solution is diluted with water, and the electrical resistivity for each silica concentration is measured to obtain a correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rc). That is, it is to quantitatively grasp how much the electrical resistivity decreases when a certain amount of water glass (silica solution) is injected into the ground for ground improvement. An example of this correlation diagram is shown in FIG. 4 described later.

[0037] (Second step) A correlation diagram between the electrical resistivity (Rs·Rimp) of the unimproved / improved ground and the electrical resistivity (Rpw·Rc) of the interstitial water / chemical solution is obtained. That is, the electrical resistivity (Rs·Rimp) of the unimproved / improved ground is dominated by the electrical resistivity (Rpw·Rc) of the interstitial water / chemical solution, and the relationship between the electrical resistivity (Rs·Rimp) of the unimproved / improved ground and the electrical resistivity (Rpw·Rc) of the interstitial water / chemical solution is extremely highly correlated. An example of this correlation diagram is shown in FIG. 6 described later.

[0038] (Third step) Based on the correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rc) obtained in the first step and the correlation diagram between the electrical resistivity (Rs·Rimp) of the unimproved / improved ground and the electrical resistivity (Rpw·Rc) of the interstitial water / chemical solution obtained in the second step, a correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rimp) of the improved ground is obtained. That is, the silica concentration (SiO2) in the correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rc) obtained in the first step remains unchanged, and the electrical resistivity (Rc) is converted using the correlation diagram between the electrical resistivity (Rs·Rimp) of the unimproved / improved ground and the electrical resistivity (Rpw·Rc) obtained in the second step to obtain a correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rimp) of the improved ground. This correlation diagram becomes the correlation diagram data (electrical resistivity data) on one side required to obtain the target uniaxial compression strength correlation diagram. An example of this correlation diagram is shown in FIG. 7 described later.

[0039] (Step 4) Next, for the purpose of setting the chemical solution silica concentration corresponding to the target uniaxial compressive strength (quck), a correlation diagram between the silica concentration (SiO2) and the uniaxial compressive strength (qu) is obtained using the specimens prepared indoors. That is, corresponding to the correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rc) obtained in the first step, a correlation diagram between the silica concentration (SiO2) and the uniaxial compressive strength (qu) is obtained. An example of this correlation diagram is shown in FIG. 8 described later.

[0040] (Step 5) The correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rimp) of the improved ground obtained in the third step is organized, and a correlation diagram is obtained with the ratio (c / co) of the diluted silica concentration (c) to the desired silica concentration (co) on the horizontal axis and the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground on the vertical axis.

[0041] That is, in order to obtain a correlation diagram with the uniaxial compressive strength (qu) as the final desired vertical axis and the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground as the horizontal axis, the correlation diagram between the silica concentration (SiO2) and the electrical resistivity (Rimp) of the improved ground obtained in the third step is converted. Since the silica concentration (SiO2) is the concentration as an absolute value, it is generalized as a relative value. That is, the horizontal axis is set as the ratio (c / co) of the diluted silica concentration (c) to the desired silica concentration (co). Thereby, the parameter of the silica concentration on the horizontal axis can be generalized regardless of the value of the desired concentration. Also, the electrical resistivity (Rimp) of the improved ground on the vertical axis is set as the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground to generalize the parameter. An example of this converted correlation diagram is shown in FIGS. 19 and 20 described later.

[0042] (Step 6) Arrange the correlation diagram between the silica concentration (SiO2) and the uniaxial compressive strength (qu) obtained in the fourth step, and obtain a correlation diagram with the ratio (c / co) of the silica concentration (c) after dilution to the desired silica concentration (co) on the horizontal axis and the uniaxial compressive strength (qu) on the vertical axis.

[0043] That is, convert the correlation diagram between the silica concentration (SiO2) and the uniaxial compressive strength (qu) obtained in the fourth step. Since the silica concentration (SiO2) is a concentration as an absolute value, it is generalized as a relative value. That is, the horizontal axis is the ratio (c / co) of the silica concentration (c) after dilution to the desired silica concentration (co). Thereby, the parameter of the silica concentration on the horizontal axis can be generalized regardless of the value of the desired concentration. Examples of this converted correlation diagram are shown in FIGS. 21(A) and 21(B).

[0044] (Step 7) Based on the correlation diagram obtained in the fifth step and the correlation diagram obtained in the sixth step, obtain the uniaxial compressive strength correlation diagram.

[0045] That is, when the horizontal axis is the ratio (c / co) of the silica concentration (c) after dilution to the desired silica concentration (co) in the fifth step, a correlation diagram between the electrical resistivity (Rimp) of the improved ground and the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground is obtained, and in the sixth step, a correlation diagram between the uniaxial compressive strength (qu) when the horizontal axis is also the ratio (c / co) of the silica concentration (c) after dilution to the desired silica concentration (co) is obtained.

[0046] Since these correlation diagrams are common in that the horizontal axis is the ratio (c / co) of the silica concentration (c) after dilution to the desired silica concentration (co), it is possible to draw a correlation diagram based on the relationship between the vertical axes. This graph is the aforementioned uniaxial compressive strength correlation diagram that is finally desired. An example of this correlation diagram is shown in FIG. 22.

[0047] In the uniaxial compression strength correlation diagram, if a threshold value of the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground is set for the condition that can ensure the pre-targeted uniaxial compression strength (quck) in advance, the electrical resistivity is measured before and after improvement, the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground is obtained, and it can be determined whether the targeted uniaxial compression strength (quck) is ensured based on whether the ratio (Rimp / Runimp) of the electrical resistivity is greater than or less than the threshold value.

[0048] By the way, the method of the present invention requires that the electrical resistivity (Rimp) of the improved ground and the electrical resistivity (Runimp) of the unimproved ground be clearly different before and after improvement. Therefore, as revealed in the experiments described later, the ground that satisfies this condition is the ground with the salt concentration of the interstitial water ranging from 5,000 to 10,000 ppm. Therefore, the method of the present invention is preferably applicable to the ground with the salt concentration of the interstitial water ranging from 5,000 to 10,000 ppm.

Example

[0049] 1. Small soil tank experiment First, a small soil tank experiment was conducted for the purpose of clarifying the electrical resistivity characteristics of the improved sand and the applicable range of this method.

[0050] (1) Experiment overview This experiment confirmed the influence of the salt concentration (electrical resistivity) of the interstitial water on the resistivity of the ground, and verified whether the improved area could be discriminated from the resistivity changes before and after improvement. In the experiment, a small cylindrical soil tank shown in Fig. 1 was used to prepare an unimproved ground made with interstitial water having different salt concentrations and a chemical improved ground obtained by injecting a special silica solution into the same ground for improvement, and the electrical resistivity of each ground was measured.

[0051] (2) Experiment method The unimproved ground was prepared by filling dry sand into the soil tank by the air-drop method to a predetermined density. fillAfter that, carbon dioxide gas was injected from the lower part of the soil tank to replace the air in the gaps with carbon dioxide gas. Then, degassed water with a predetermined salt concentration was infiltrated from the lower part of the soil tank with a hydraulic head difference below the critical hydrodynamic gradient. In addition, the improved ground was prepared by infiltrating and injecting a special silica solution with a predetermined silica concentration from the lower part of the soil tank after preparing the unimproved ground. The sands used in the experiment were silica sand No. 7 (produced in Seto) and Enshu silica sand. The physical properties and particle size accumulation curves of the sands used are shown in Table 1 and Figure 2 below, and the preparation conditions of the soil tank ground are shown in Table 2 below. [Table 1] [Table 2]

[0052] The measurement of electrical resistivity was carried out using an electrical logging probe. The probe has an electrode configuration of point electrodes (four-electrode method) with an electrode interval of 25 mm. Also, since the ratio of the measurement pore diameter to the electrode diameter of the previously arranged circular electrodes has a very large influence on the measured electrical resistivity, point electrodes without such influence are adopted.

[0053] The measurement was carried out at the plane positions shown in Figure 3 with the lower end depth of the probe at depths of 14 cm, 15 cm, 16 cm, and 17 cm from the ground surface. Therefore, the number of measurement points per soil tank is 20 points for the unimproved ground and 8 points for the improved ground. For the improved ground, after the resistivity measurement, uniaxial compression tests and silica content tests were carried out on the samples collected by pushing a Shinwall liner with an inner diameter of 75 mm × height of 150 mm into the improved ground.

[0054] (3) Electrical Resistivity of Special Silica Solution During the experiment, in order to grasp the electrical resistivity characteristics of the special silica solution, the chemical solution was diluted with water and the electrical resistivity for each chemical solution silica concentration was measured. The relationship between the electrical resistivity of the special silica solution used in the experiment and the chemical solution silica concentration is shown in Figure 4. The electrical resistivity increases rapidly when the silica concentration is lower than 1.5 wt%, but when it exceeds 2.0 wt%, the electrical resistivity decreases with the increase of the silica concentration and is in the range of 0.4 - 1.3 Ω·m.

[0055] (4) Experimental results Fig. 5 shows the relationship between the electrical resistivity and the interstitial water salt concentration of the unimproved ground and the improved ground of silica sand No. 7 (produced in Setouchi) and Enshu silica sand. Fig. 6 shows the relationship between the electrical resistivity Runimp and Rimp of the unimproved and improved ground and the electrical resistivity Rpw and Rc of the interstitial water and the chemical solution. The electrical resistivity is the average value of each measurement point shown in Fig. 3 based on the measurement results with an electrode interval of 25 mm. The coefficient of variation of the measured electrical resistivity is small, about 0.04 for the unimproved ground and about 0.02 for the improved ground of silica sand No. 7 (produced in Setouchi), and about 0.06 for the unimproved ground and about 0.02 for the improved ground of Enshu silica sand.

[0056] The electrical resistivity of the unimproved ground and the improved ground is dominated by the electrical resistivity of the interstitial water and the chemical solution, and the relationship between the electrical resistivity of the unimproved ground and the improved ground and the electrical resistivity of the interstitial water and the chemical solution is highly correlated. Also, from the same figure, in the unimproved ground, the resistivity decreases as the salt concentration of the interstitial water increases.

[0057] On the other hand, in the improved ground, it is almost constant regardless of the salt concentration of the interstitial water. The electrical resistivity of the unimproved ground and the improved ground becomes the same when the salt concentration of the interstitial water is about 10,000 ppm, and when it exceeds this concentration, the electrical resistivity of the interstitial water becomes smaller than that of the chemical solution.

[0058] From the above, the difference in the electrical resistivity between the unimproved and improved cases depends on the type of ground, but it is considered possible to distinguish until the salt concentration of the interstitial water is about 5,000 to 10,000 ppm.

[0059] Fig. 7 shows the relationship between the electrical resistivity of the improved ground and the silica concentration of the chemical solution calculated from the relationship between the electrical resistivity of the unimproved and improved ground - interstitial water - chemical solution shown in Fig. 6 and the relationship between the electrical resistivity of the chemical solution - silica concentration shown in Fig. 4. The electrical resistivity of the chemical solution is also shown in the same figure. When the silica concentration of the chemical solution is 2 wt% or more, the range of the electrical resistivity of the improved ground becomes wider, from 1.0 to 3.3 Ω·m, compared to the range of 0.4 to 1.3 Ω·m for the electrical resistivity of the chemical solution.

[0060] In the experimental results using the electrical logging, there is almost no variation in the electrical resistivity values, and the electrical resistivity ratio Rimp / Runimp between the improved ground and the unimproved ground is proportional to the electrical resistivity ratio Rc / Rpw of the chemical solution and the interstitial water.

[0061] From the above experimental results, (a) There is a very high correlation between the electrical resistivity of the unimproved ground / improved ground and the electrical resistivity of the interstitial water / chemical solution. (b) The difference in electrical resistivity between the unimproved and improved cases depends on the type of ground, but it is possible to distinguish until the salt concentration of the interstitial water is about 5,000 - 10,000 ppm. (c) The electrical resistivity of the special silica solution increases rapidly when the silica concentration is lower than 1.5 wt%. On the other hand, when it exceeds 2.0 wt%, the electrical resistivity of the chemical solution does not change much and is in the range of 0.4 - 1.3 Ω·m, but in the improved ground, the range width becomes larger, being 1.0 - 3.3 Ω·m. (d) The measurement of the electrical resistivity by this electrical logging can obtain values with little variation regardless of the value of Rc / Rpw.

[0062] Next, it is the evaluation of the improvement effect using the electrical resistivity. From the relationship between the electrical resistivity Rimp of the improved ground and the silica concentration shown in Fig. 7, Rimp for each silica concentration can be obtained. Also, in actual construction, for the purpose of setting the chemical solution silica concentration corresponding to the design reference strength quck, uniaxial compression tests for each silica concentration are carried out using specimens prepared indoors. Fig. 8 shows the relationship between the uniaxial compressive strength qu of silica sand No. 7 (produced in Setouchi) and the silica concentration (SiO2).

[0063] (5) Summary In this experiment, it was verified whether it is possible to distinguish the improved area from the influence of the salt concentration (electrical resistivity) of the interstitial water on the resistivity of the ground and the change in resistivity before and after improvement. As a result of the experiment, the results shown in the following (1) - (3) were obtained. (a) The difference in electrical resistivity between the unimproved / improved ground depends on the type of ground, but it is possible to distinguish until the salt concentration of the interstitial water is about 5,000 - 10,000 ppm. Also, the applicability of this method can be judged by conducting this experiment in advance using in-situ soil and sand. (b) Measurement of electrical resistivity by electrical logging using a point electrode can obtain values with little variation regardless of the value of Rc / Rpw. Therefore, fine changes in resistivity can be captured. (c) Evaluation of the improvement effect using electrical resistivity can be performed using the relationship between the electrical resistivity of the ground and the silica concentration and the relationship between the improvement strength and the silica concentration.

[0064] 2. In-situ verification experiment (1) Experiment overview In this experiment, after conducting a small-scale dynamic cone penetration test on the ground before and after improvement for the chemically improved ground by improvement test construction, the electrical resistivity was measured by electrical logging using the same penetration hole, and the improvement effect of the improved area was evaluated. Also, the Nd value obtained from the small-scale dynamic cone penetration test was compared with the results of uniaxial compression tests and cyclic triaxial tests conducted on undisturbed samples taken, and the effectiveness of this method was verified. In the measurement of electrical resistivity, the push-in type micro-electrical logging method was adopted.

[0065] (2) Overview of the push-in type micro-electrical logging method The push-in type micro-electrical logging method is different from the general electrical logging measured by electrodes inserted into a boring hole. After conducting a dynamic cone penetration test or the like, the measurement is carried out using the same penetration hole. The probe of the push-in type micro-electrical logging method has electrode spacings of 2.5 cm and 5.0 cm in the electrode arrangement of a point electrode (two-electrode method). The diameter of the probe was set to 32 mm assuming it would be pressed into the penetration hole of the small-scale dynamic cone penetration test. Also, 3-mm protrusions are provided on the sleeve side to press the probe electrode against the wall surface of the penetration hole. Fig. 9 shows the pressing device 1 of the probe into the penetration hole.

[0066] The pressing-in device 1 has pistons 10, 10 that are arranged on the ground surface directly above the penetration hole 3 and are stretchable along the vertical direction on both sides of the penetration hole 3. A chuck 12 that clamps a penetration rod 4 with a measurement probe 2 connected to its lower end is provided at the center of a gantry 11 that straddles the upper ends of these pistons 10, 10. A control unit 13 that controls the operation of the pistons 10, 10 is also provided. Further, a hydraulic unit 14 composed of an engine and a hydraulic pump is connected to the control unit 13.

[0067] In the pressing-in device 1, the pistons 10, 10 on both sides expand and contract in synchronization, and the gantry 11 moves in the vertical direction, so that the penetration rod 4 clamped by the chuck 12 moves in the vertical direction, and the measurement probe 2 is pushed into and pulled out of the penetration hole 3.

[0068] (3) Outline of the experimental site Figures 10 and 11 show the soil columnar diagram, N value, and particle size accumulation curve of the experimental site, and Table 3 below shows the physical properties. The stratum consists of fill, silt mixed with sand from the ground surface, and silt mixed with sand continues below it. The silt mixed with sand, which is the layer to be improved with chemical solution, contains organic soil from GL - 2m to - 4m and contains silt in layers at depths below GL - 5m. The groundwater level is at GL - 1.1m, the electrical resistivity of the groundwater is in the range of 4 to 12 Ω·m, and the salt concentration is in the range of 400 to 1,300 ppm.

Table 3

[0069] Figure 12 shows the plan view of the chemical solution improved body, Figure 13 shows its cross-sectional view, and the improvement specifications are shown in Table 4 below. Both Improvement A and Improvement B satisfy the planned improvement diameter of 2.5 m, and no unconsolidated part is seen on the surface of the improved body.

Table 4

[0070] (4) Experimental method After backfilling the improved body, a small dynamic cone penetration test (Penny) was carried out, and a push-in type micro electrical logging was carried out using the same penetration hole. The measurements were carried out at one unimproved location, two improved A locations, and two improved B locations as shown in Fig. 12. The measurement depths were GL - 10m for unimproved, GL - 8m for improved A, and GL - 5m for improved B. The age of the improved body material at the time of measurement was about 23 months. Also, a small - scale model ground similar to the above was made using in - situ soil and sand, and the electrical resistivity of the unimproved and improved ground was measured.

[0071] (5) Experimental results Figs. 14 and 15 respectively show the depth distributions of the uniaxial compressive strength qu, the N - equivalent N obtained from the small dynamic cone penetration test, the electrical resistivity R obtained from the push - in type micro electrical logging (electrode interval 2.5 cm), and the ratio of the electrical resistivity of the improved ground to that of the unimproved ground (Rimp / Runimp) for improved A and improved B. d value, the electrical resistivity R obtained from the push - in type micro electrical logging (electrode interval 2.5 cm), and the ratio of the electrical resistivity of the improved ground to that of the unimproved ground (Rimp / Runimp).

[0072] (a) Uniaxial compressive strength qu The uniaxial compressive strength test was carried out on the improved sand samples (age 28 days) collected by block sampling with a rotary triple - tube sampler during the improved test construction. Since the strength of the improved body is evaluated using the samples collected at the 1 / 2 position of the improved body radius, Figs. 14 and 15 show the test results of the samples collected at the same position. Also, when organic soil, humus soil, etc. are present in the collected test specimens, cracks occur along the same location, resulting in significantly low values. Therefore, the specimens were sorted according to the presence or absence of organic soil and humus soil.

[0073] The uniaxial compressive strength qu has a particularly large variation in improved A. This is mainly due to the occurrence of cracks caused by the presence of organic soil and humus soil in the collected test specimens. Similar test specimens were frequently found in the samples collected by the triple - tube sampler. It was a difficult result to quantitatively grasp the change in characteristics before and after improvement based on the uniaxial compressive strength in the natural ground.

[0074] (b) N d value In improved A, the N after improvementd The value generally increases. N due to improvement d The average value increment was about 16 at the position 10 cm from the improvement center and about 6 at the position 60 cm from the improvement center in the upper improvement body of GL - 2m to - 4m, about 6 at the position 10 cm from the improvement center and about 6 at the position 60 cm from the improvement center in the lower improvement body of GL - 4m to - 6m. On the other hand, in improvement B where the target improvement strength is 1 / 2 compared to improvement A, although an increase in the N value was observed in the upper half of the improvement body, no increase was observed in the lower half. d Although an increase in the N value was observed, no increase was observed in the lower half.

[0075] (c) Electrical resistivity R The electrical resistivity R shows a high value of about 90 - 130 Ω·m in the vicinity of GL - 3.0m to - 4.0m in the unimproved ground, while it is generally 30 - 60 Ω·m at other depths. On the other hand, in the improved ground, improvement A shows a low value of about R = 1 - 3 Ω·m at all improvement depths from GL - 2.0m to GL - 6.0m, and improvement B shows values of 2 - 10 Ω·m at GL - 2.0m to - 3.5m and 20 - 70 Ω·m at GL - 3.5m to 4.0m. It can be seen that the electrical resistivity has decreased significantly due to the improvement.

[0076] (d) Evaluation of improvement effect To evaluate the improvement effect based on the electrical resistivity measured in the field, a model ground was prepared using the on - site soil in the same way as the above - mentioned small - scale soil tank experiment, and the electrical resistivities of the unimproved and improved grounds were measured. The production conditions of the soil tank are: ground density: D r = 50% (e = 0.911), salinity concentration of interstitial water: 400, 1,300, 20,000 ppm, chemical solution used: 8 wt% special silica solution. Also, the improved ground was prepared by infiltrating and injecting the special silica solution into the same ground.

[0077] Therefore, it is considered that the electrical resistivity of the improved ground measured in the same experiment is under conditions close to a chemical solution filling rate of 100%.

[0078] Fig. 16 shows the relationship between the resistivity of unimproved / improved ground and pore water / chemical solution. Fig. 17 shows the relationship between the resistivity of the improved ground Rimp and the silica concentration (SiO2) of the chemical solution, calculated from the relationship between the resistivity of the chemical solution and the silica concentration shown in this figure and Fig. 4. Fig. 18 shows the relationship between the uniaxial compressive strength qu and the silica concentration (SiO2) obtained from the mixing test. Fig. 22 shows the relationship between the uniaxial compressive strength qu and the ratio of the resistivity of the improved ground to that of the unimproved ground Rimp / Runimp, organized based on Fig. 18 and Fig. 17.

[0079] Specifically, the following procedure is used to obtain the correlation diagram in Fig. 22 (the relationship between the uniaxial compressive strength qu and the ratio of the resistivity of the improved ground to that of the unimproved ground Rimp / Runimp).

[0080] The correlation diagram between the silica concentration (SiO2) and the resistivity of the improved ground (Rimp) shown in Fig. 17 is organized (converted) so that, as shown in Fig. 19 and Fig. 20, the horizontal axis is the ratio (c / co) of the silica concentration (c) after dilution to the desired silica concentration (co), and the vertical axis is the ratio (Rimp / Runimp) of the resistivity of the improved ground (Rimp) to the resistivity of the unimproved ground (Runimp), to obtain a correlation diagram.

[0081] Fig. 19 is the converted graph for the case of Improvement A. In this case, it is assumed that Runimp = 15 Ω·m (groundwater salinity concentration of 1,300 ppm). The desired silica concentration is co = 8 wt%. In this figure, the left side of the drawing is a graph with the horizontal axis being the ratio (c / co) of the silica concentration (c) after dilution to the desired silica concentration (co), and the right side of the drawing is a graph with the vertical axis further being the ratio of the resistivity of the improved ground (Rimp) to the ratio of the resistivity of the improved ground (Rimp) to the resistivity of the unimproved ground (Runimp).

[0082] Figure 20 shows the converted graph for Improvement B. In this case, it is assumed that Runimp = 15 Ω·m (groundwater salinity concentration of 1,300 ppm). The desired silica concentration is co = 5 wt%. In the figure, on the left side of the drawing, the horizontal axis is a graph with the ratio (c / co) of the silica concentration (c) after dilution to the desired silica concentration (co), and on the right side of the drawing, the vertical axis is further a graph with the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground with respect to the electrical resistivity (Rimp) of the improved ground.

[0083] Next, by organizing the correlation diagram between the silica concentration (SiO2) and the uniaxial compressive strength (qu) shown in Figure 18, as shown in Figure 21, a correlation diagram is obtained with the horizontal axis being the ratio (c / co) of the silica concentration (c) after dilution to the desired silica concentration (co) and the vertical axis being the uniaxial compressive strength (qu). Note that Figure 21(A) is for Improvement A and Figure 21(B) is for Improvement B.

[0084] Since the horizontal axes of the correlation diagrams in Figures 19 and 20 and the correlation diagram in Figure 21 are common in the ratio (c / co) of the silica concentration (c) after dilution to the desired silica concentration (co), by organizing the relationships of the vertical axes of the two, a correlation diagram of the uniaxial compressive strength qu and the ratio Rimp / Runimp of the electrical resistivity of the improved ground to the unimproved ground as shown in Figure 22 can be obtained.

[0085] Then, in Figure 22, when an approximate straight line is drawn by the least squares method and a threshold value for judging the improvement effects of Improvement A (target improvement strength quck ≧ 100 kPa) and Improvement B (target improvement strength quck ≧ 50 kPa) is set, for Improvement A, Rimp / Runimp ≦ 0.13, and for Improvement B, Rimp / Runimp ≦ 0.16. (e) Discussion Looking at the depth distribution of Rimp / Runimp shown in Figures 14 and 15, in Improvement A, Rimp / Runimp is generally 0.1 or less at a depth of GL - 2.0 m to - 6.0 m. On the other hand, in Improvement B, Rimp / Runimp is 0.1 or less at GL - 2.0 m to - 3.5 m and is 0.25 to 0.8 at GL - 3.5 m to - 4.0 m.

[0086] From Figure 22, the threshold values for judging the improvement effect are set as follows: for Improvement A, Rimp / Runimp ≤ 0.13; for Improvement B, Rimp / Runimp ≤ 0.16. Therefore, for Improvement A, the filling of the chemical solution is recognized at GL - 2.0 m to - 6.0 m, fill while for Improvement B, the filling of the chemical solution is recognized at GL - 2.0 m to - 3.5 m. However, sufficient filling is not recognized at GL - 3.5 m to - 4.0 m, fill resulting in a situation where no sufficient filling is recognized. fill

[0087] (6) Summary In this experiment, the electromagnetic resistivity of the in - situ improved ground was measured by electrical logging (pushed - in type micro - logging) using point electrodes, and an attempt was made to evaluate the improvement effect. As a result of the experiment, the results shown in the following (a) and (b) were obtained. (a) The resistivity measured by the newly developed pushed - in type micro - logging can sensitively represent the difference before and after chemical solution improvement. (b) The evaluation of the improvement effect using the electrical resistivity measured by the same method is reasonable compared with the increment of the N - value, uniaxial compression strength, and liquefaction strength ratio in the improvement range. d

[0088] 3. Conclusion In this experiment, paying attention to the change in electrical resistivity before and after improvement as a confirmation of the output of the chemical solution injection method, small - scale soil tank experiments and in - site verification experiments were carried out by electrical logging using point electrodes. From this experiment, the following conclusions (1) - (4) were obtained. (1) The electrical resistivity of the special silica solution increases rapidly when the silica concentration is lower than 1.5 wt%, and when it exceeds 2.0 wt%, the electrical resistivity of the chemical solution does not change much and is in a narrow range of 0.4 - 1.3 Ω·m. However, in the improved ground, in the range exceeding 2.0 wt%, the range width becomes larger, from 1.0 - 3.3 Ω·m. (2) The difference in electrical resistivity between the unimproved and improved ground depends on the type of ground, but it is possible to distinguish up to a salt concentration of the interstitial water of about 5,000 - 10,000 ppm. Also, the applicability of this method can be judged by conducting this experiment in advance using in - site soil and sand. ​​(3) The measurement of electrical resistivity by electrical logging using a point electrode can obtain values with less variation regardless of the value of Rc / Rpw, as compared with the measurement by resistivity tomography. That is, even in a ground where the electrical resistivity of interstitial water is low, highly accurate values can be obtained. (4) The evaluation of the improvement effect using electrical resistivity can be performed using the relationship between the electrical resistivity of the ground and the silica concentration and the relationship between the improvement strength and the silica concentration. However, it is necessary to clarify the influence such as dilution of the silica concentration when setting the threshold value of the electrical resistivity for judging the improvement effect.

[0089] 〔Other Embodiment Examples〕 (1) In the above embodiment, a correlation diagram (uniaxial compression strength correlation diagram) with the vertical axis being the uniaxial compression strength (qu) and the horizontal axis being the ratio (Rimp / Runimp) of the electrical resistivity of the improved ground (Rimp) to the electrical resistivity of the unimproved ground (Runimp) was used to judge the ground improvement effect. However, the uniaxial compression strength (qu) and the liquefaction strength ratio (RL) can be converted by a fixed conversion formula. Also, the uniaxial compression strength (qu) and the cohesion (c) can be converted by a fixed conversion formula. Specifically, the correlation formula between the uniaxial compression strength (qu) and the liquefaction strength ratio (RL) is shown in Fig. 23 (Source: Penetration Solidification Treatment Method Technical Manual Revised Edition July R2 year, Coastal Technology Research Center, Incorporated Administrative Agency), and the correlation formula between the uniaxial compression strength (qu) and the cohesion (c) is shown in Fig. 24 (Source: Penetration Solidification Treatment Method Technical Manual Revised Edition July R2 year, Coastal Technology Research Center, Incorporated Administrative Agency). Therefore, in the correlation diagram (uniaxial compression strength correlation diagram) with the vertical axis being the uniaxial compression strength (qu) and the horizontal axis being the ratio (Rimp / Runimp) of the electrical resistivity of the improved ground (Rimp) to the electrical resistivity of the unimproved ground (Runimp), it is also possible to use a correlation diagram with the vertical axis of the uniaxial compression strength (qu) replaced by the liquefaction strength ratio (RL) or the cohesion (c), and perform the determination of the ground improvement effect using this.

[0090] (2) In the above-described embodiment, a correlation diagram (uniaxial compression strength correlation diagram) was used to determine the ground improvement effect, with the vertical axis being the uniaxial compression strength (qu) and the horizontal axis being the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground. However, the electrical resistivity and the conductivity can be converted by a conversion formula. Specifically, the electrical resistivity (R) and the conductivity (σ) are related by R (Ω·m) = 1 / σ (S / m). Therefore, when the conversion formula is applied, the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground can be converted to the ratio (σunimp / σimp) of the conductivity (σunimp) of the unimproved ground to the conductivity (σimp) of the improved ground. Therefore, in the correlation diagram (uniaxial compression strength correlation diagram) with the one axis being the uniaxial compression strength (qu) and the other axis being the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground, it is also possible to use, as a correlation diagram, the one in which the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground on the other axis is replaced by the ratio (σunimp / σimp) of the conductivity (σunimp) of the unimproved ground to the conductivity (σimp) of the improved ground, and to determine the ground improvement effect using this.

[0091] (3) In the above-described embodiment, in the uniaxial compression strength correlation diagram, the vertical axis was the uniaxial compression strength (qu) and the horizontal axis was the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground. However, it is also possible to set the vertical axis as the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground and the horizontal axis as the uniaxial compression strength (qu). Also, regarding the correlation diagram with the horizontal axis in the fifth step being the ratio (c / co) of the silica concentration (c) after dilution to the desired silica concentration (co) and the vertical axis being the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground, and the correlation diagram with the horizontal axis in the sixth step being the ratio (c / co) of the silica concentration (c) after dilution to the desired silica concentration (co) and the vertical axis being the uniaxial compressive strength (qu), it is similarly possible to interchange the horizontal axis and the vertical axis.

Explanation of Signs

[0092] 1…Press-in device, 2…Measurement probe, 3…Penetration hole, 4…Penetration rod, 10…Piston, 11…Gantry, 12…Chuck, 13…Control unit, 14…Hydraulic unit

Claims

1. In advance, a correlation diagram is obtained with one axis as the uniaxial compression strength (qu) and the other axis as the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground. Based on this correlation diagram, a threshold value of the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground is set under the condition that the target uniaxial compression strength (quck) can be ensured. Before and after ground improvement, the electrical resistivity is measured by electrical logging using the penetration holes formed vertically in the ground, and the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground is obtained. A method for evaluating the ground improvement effect by a chemical solution injection method is provided, which determines whether the target uniaxial compression strength (quck) is ensured based on whether the ratio (Rimp / Runimp) of this electrical resistivity is greater than or less than the threshold value. In order to grasp the electrical resistivity characteristics of the silica solution used for ground improvement, the silica solution is diluted with water to measure the electrical resistivity for each silica concentration, and the first step of obtaining a correlation diagram between the silica concentration (SiO 2 ) and the electrical resistivity (Rc); The second step of obtaining a correlation diagram between the electrical resistivities (Rs·Rimp) of the unimproved / improved ground and the electrical resistivities (Rpw·Rc) of the pore water / chemical solution; Based on the correlation diagram between the silica concentration (SiO 2 ) and the electrical resistivity (Rc) obtained in the first step, and the correlation diagram between the electrical resistivities (Rs·Rimp) of the unimproved / improved ground and the electrical resistivities (Rpw·Rc) of the pore water / chemical solution obtained in the second step, the third step of obtaining a correlation diagram between the silica concentration (SiO 2 ) and the electrical resistivity (Rimp) of the improved ground; For the purpose of setting the chemical solution silica concentration corresponding to the target uniaxial compression strength (quck), using specimens prepared indoors, the fourth step of obtaining a correlation diagram between the silica concentration (SiO 2 ) and the uniaxial compression strength (qu); The silica concentration (SiO 2a fifth step of arranging a correlation diagram between the diluted silica concentration (c) and the electrical resistivity (Rimp) of the improved ground, to obtain a correlation diagram in which one axis is the ratio (c / co) of the silica concentration after dilution (c) to the intended silica concentration (co), and the other axis is the ratio (Rimp / Runimp) of the electrical resistivity of the improved ground to the electrical resistivity of the unimproved ground (Runimp); The silica concentration (SiO 2 and the sixth step of arranging the correlation diagram between the silica concentration after dilution (c) and the unconfined compressive strength (q) to obtain a correlation diagram in which one axis is the ratio (c / co) of the silica concentration after dilution (c) to the desired silica concentration (co) and the unconfined compressive strength (q) on the other axis. A method for evaluating the effect of ground improvement using a chemical injection method, characterized in that a correlation diagram is obtained by a seventh step, based on the correlation diagram obtained in the fifth step and the correlation diagram obtained in the sixth step, in which one axis is the uniaxial compressive strength (qu) and the other axis is the ratio (Rimp / Runimp) of the electrical resistivity of the improved ground (Rimp) to the electrical resistivity of the unimproved ground (Runimp).

2. 2. A method for evaluating the effect of ground improvement using the liquid grouting method according to claim 1, in which the target of ground improvement is ground having a salinity of pore water of 5,000 to 10,000 ppm.

3. A method for evaluating the effect of ground improvement using the chemical injection method described in either claim 1 or 2, in which a correlation diagram in which one axis is the uniaxial compressive strength (qu) and the other axis is the ratio (Rimp / Runimp) of the electrical resistivity of improved ground (Rimp) to the electrical resistivity of unimproved ground (Runimp) is used, which is modified based on the conversion formula between uniaxial compressive strength (qu) and liquefaction resistance ratio (RL) or the conversion formula between uniaxial compressive strength (qu) and cohesion strength (c), and in which one axis is the liquefaction resistance ratio (RL) or cohesion strength (c) and the other axis is the ratio (Rimp / Runimp) of the electrical resistivity of improved ground (Rimp) to the electrical resistivity of unimproved ground (Runimp), modified based on the conversion formula between uniaxial compressive strength (qu) and liquefaction resistance ratio (RL) or the conversion formula between uniaxial compressive strength (qu) and cohesion strength (c).

4. Instead of the correlation diagram with one axis being the uniaxial compressive strength (qu) and the other axis being the ratio (Rimp / Runimp) of the electrical resistivity (Rimp) of the improved ground to the electrical resistivity (Runimp) of the unimproved ground, based on the conversion formula between the electrical resistivity (R) and the conductivity (σ) (R (Ω·m) = 1 / σ (S / m)), a correlation diagram with one axis being the uniaxial compressive strength (qu) and the other axis being the ratio (σunimp / σimp) of the conductivity (σunimp) of the unimproved ground to the conductivity (σimp) of the improved ground, which is corrected, is used. The method for evaluating the ground improvement effect by the chemical solution injection method according to any one of Claims 1 and 2.

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