JP7424068B2 - How to manage bentonite mixed soil - Google Patents

Description

The present invention relates to a method for managing bentonite mixed soil using a bentonite mixing ratio.

Conventionally, bentonite mixed soil, which is produced by mixing bentonite with soil and sand in a predetermined ratio, has a high water-blocking performance when compacted and compacted, so it is used in waste disposal sites, contaminated soil, etc. It is widely used in general for containment work and foundation ground work for structures. When using these bentonite mixed soils at construction sites, the base material is locally generated soil or purchased sand, and water is added to this base material by mixing bentonite in an amount designed based on the results of laboratory tests, etc. By doing so, bentonite mixed soil with desired water-blocking performance is produced.

Then, quality control is performed on the manufactured bentonite mixed soil for each manufacturing quantity determined in the specifications. Quality control is mainly to confirm that the amount of bentonite in the mixture satisfies the design and that the bentonite is mixed homogeneously. Generally, a methylene blue adsorption test is often specified as a method for confirmation.

In the methylene blue adsorption amount test, a methylene blue solution is added to a solution in which a bentonite-containing sample is dispersed, and the mixture is stirred.The amount of methylene blue adsorbed to bentonite in the sample is determined.From this amount of methylene blue adsorption, the bentonite mixing ratio or the bentonite mixing ratio is determined. Calculate the amount.

However, the methylene blue adsorption amount test tends to depend on the skill level of the measurer, such as determining the methylene blue adsorption amount based on the visual judgment of the measurer, and the test results tend to vary. For this reason, for example, in Patent Document 1, the amount of methylene blue that is not adsorbed to the sample is measured using an analyzer such as a color difference meter or a spectrophotometer, and the amount of methylene blue adsorbed is calculated based on this measurement value. This eliminates the variation in test results caused by this.

Japanese Patent Application Publication No. 03-237339

It is known that the test results of the methylene blue adsorption amount test are greatly influenced not only by the skill level of the measurer, but also by the condition and particle size distribution of the sample. In particular, if the bentonite mixed soil to be managed contains a large amount of gravel, even if the amount of samples collected from the bentonite mixed soil is the same, the amount of gravel contained in the sample will vary depending on the amount of gravel contained in the sample. The amount of bentonite also increases or decreases. For this reason, if collected samples are used as they are for testing, the amount of methylene blue adsorbed tends to vary from sample to sample, and it is difficult to estimate the bentonite mixing ratio or amount of bentonite that accurately reflects the current situation based on these adsorbed amounts of methylene blue. It can be difficult.

In order to cope with this, it is possible to increase the amount of sample collected and conduct a methylene blue adsorption test, but as the amount of sample increases, a large amount of methylene blue solution is also required for measurement, which poses an economical issue. In addition, the test time tends to be long, making it disadvantageous to carry out at construction sites.

The present invention was developed in view of these problems, and its main purpose is to efficiently increase the bentonite mixing ratio with a small amount of sample even when the bentonite mixed soil to be managed contains a large amount of gravel. It is an object of the present invention to provide a method for managing bentonite mixed soil that can be estimated and managed.

In order to achieve this objective, the bentonite mixed soil management method of the present invention is a method for managing bentonite mixed soil using a bentonite mixing ratio estimated based on the results of a methylene blue adsorption amount test. The method includes sieving the bentonite mixed soil to remove gravel, separating a sample soil from the fine particle mixed soil, and conducting a methylene blue adsorption amount test using the sample soil. , a step of obtaining a methylene blue adsorption amount of the fine particle mixed soil, a step of obtaining a methylene blue adsorption amount of the bentonite mixed soil based on the methylene blue adsorption amount of the fine particle mixed soil, and a step of obtaining a methylene blue adsorption amount of the bentonite mixed soil. The method is characterized in that it includes a step of obtaining the bentonite mixing ratio of the bentonite mixed soil based on the adsorption amount .

Further, the method for managing bentonite mixed soil of the present invention is characterized in that the particle size of the fine particle mixed soil is approximately 2 mm or less.

According to the bentonite mixed soil management method of the present invention, the sample soil used for the methylene blue adsorption amount test is separated from the fine particle mixed soil prepared by removing gravel from the bentonite mixed soil. As a result, it is possible to suppress the variations that tend to occur in the results of methylene blue adsorption amount tests due to the separation of sample soil, and it becomes possible to efficiently estimate the bentonite mixing ratio that accurately reflects the current situation using a small amount of sample soil. .

Therefore, the amount of methylene blue solution used in the test can be reduced, making it possible to conduct the test economically, and the time required for the test can also be shortened, reducing the time and cost of overall quality control of bentonite mixed soil. becomes possible. Along with this, it is also easy to increase the frequency of conducting methylene blue adsorption tests compared to the past, and to adjust the amount of bentonite used when producing bentonite mixed soil as necessary to prevent problems caused by insufficient addition of bentonite. It becomes possible to suppress excessive addition.

The bentonite mixed soil management method of the present invention corrects the methylene blue adsorption amount of the fine-grained soil based on the gravel content and the mass of the fine-grained soil, and corrects the methylene blue adsorption amount of the bentonite-mixed soil. It is characterized by calculating. Further, the bentonite mixing ratio is calculated based on a relational expression between the bentonite mixing ratio and the methylene blue adsorption amount, which is obtained by obtaining the methylene blue adsorption amount from bentonite mixed soil with a known bentonite mixing ratio.

According to the bentonite mixed soil management method of the present invention, the methylene blue adsorption amount of the fine particle mixed soil is appropriately corrected according to the gravel content in the bentonite mixed soil, and the methylene blue adsorption amount of the bentonite mixed soil is calculated. Therefore, it is possible to estimate the bentonite mixing ratio of bentonite mixed soil with high reliability based on this methylene blue adsorption amount.

The method for managing bentonite mixed soil of the present invention is characterized in that the bentonite mixed soil is dried and then sieved.

According to the method for managing bentonite mixed soil of the present invention, it is possible to minimize the phenomenon in which bentonite is adsorbed not only to gravel but also to sieves, so that bentonite contained in bentonite mixed soil can be efficiently removed from fine particles mixed soil. It can be classified as

According to the present invention, by separating the sample soil used for the methylene blue adsorption amount test from the fine-grain mixed soil created by removing gravel from the bentonite mixed soil, the methylene blue adsorption amount due to the collection of the sample soil can be reduced. In order to suppress the variations that tend to occur in test results, even if the bentonite mixed soil to be managed contains a large amount of gravel, the bentonite mixing ratio can be efficiently estimated using a small amount of sample, and the bentonite mixed soil can be managed. becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the outline of the management method of bentonite mixed soil in embodiment of this invention. It is a figure showing the flow of the management method of bentonite mixed soil in an embodiment of the present invention. It is a figure which shows the calculation result of the methylene blue adsorption amount of bentonite mixed soil in embodiment of this invention. FIG. 3 is a diagram showing the relationship between methylene blue mixing ratio and methylene blue adsorption amount in an embodiment of the present invention. It is a figure which shows the calculation result (comparative example) of the methylene blue adsorption amount of the bentonite mixed soil which does not perform sieving in embodiment of this invention. It is a figure which shows the comparative graph of the dispersion|distribution calculated|required from the calculation result of the methylene blue adsorption amount in embodiment of this invention. FIG. 4 is a diagram comparing the relationship between the bentonite mixing ratio and the adsorption amount of methylene blue in the embodiment of the present invention, with and without sieving.

Regarding the management method of bentonite mixed soil of the present invention, an example is given in which the bentonite mixed soil to be managed is used for the bottom and/or slope structure used for water-blocking construction of a waste disposal site among earth structures. The details will be explained below with reference to FIGS. 1 to 7.

As shown in FIG. 1, in the waste disposal site 10, a structure 11 is constructed by compacting bentonite mixed soil 1, and waste 12 is contained inside the structure 11. The bentonite mixed soil 1 used in such water barrier construction is manufactured by adding and mixing bentonite 3 to earth and sand 2 such as locally generated soil at a construction site.

The blending amount of bentonite 3 is designed after confirming in a laboratory test the amount that can achieve the water-blocking performance required for the structure 11 for which bentonite mixed soil 1 is used. When manufacturing, bentonite 3 is added in an amount exceeding this design value.

The bentonite mixed soil 1 produced in this way is managed in specifications, etc. by checking the bentonite mixing ratio and confirming that the amount of bentonite 3 exceeds the design value before it is used at the construction site. This is done according to the specified production quantity. Therefore, the details of the method for managing the bentonite mixed soil 1 will be explained below with reference to the flowchart of FIG. 2.

≪How to manage bentonite mixed soil≫
<Collection of sample preparation material 4: STEP 1>
As shown in FIG. 1, a portion of bentonite mixed soil 1 prepared on site is collected as sample preparation material 4 (for example, about 500 to 1000 g).

<Sample creation: STEP 2>
A sample soil 7 to be used in a methylene blue adsorption amount test to be described later is prepared from the sample preparation material 4 taken through the following steps.

First, the sample preparation material 4 is sufficiently dried. Although any drying method may be used, it is preferable to heat the sample preparation material in a microwave oven (for example, for about 15 minutes) to evaporate water, imitating the microwave method used in soil moisture content tests. Note that the water-containing state is preferably an absolutely dry state.

Next, the dried sample preparation material 4 is sieved. For sieving, a test sieve used in a sieving test is used, and a sieve with a nominal size of 2.0 mm is suitable. Through this sieving, the particles with a particle size of approximately 2 mm or less passing through the sieve are classified as fine grain mixed soil 5, and those with particle diameters exceeding 2 mm are classified as gravel 6, and the mass of fine grain mixed soil 5 (S1) and gravel fraction 6 Measure the mass (S2).

In this way, when preparing the fine-grain mixed soil 5 by removing the gravel 6 from the sample preparation material 4, by sufficiently drying the sample preparation material 4 before sieving, bentonite 3 can be Not only the gravel 6 but also the phenomenon of adsorption to the sieve can be suppressed to a minimum. Therefore, the bentonite 3 contained in the sample preparation material 4 can be efficiently sorted into the fine-grained soil 5.

Thereafter, a predetermined amount (for example, about 5 g) is taken from the fine-grained soil 5 and used as the sample soil 7 for the methylene blue adsorption amount test.

<Acquisition of methylene blue adsorption amount (per 100g) of fine-grained soil 5: STEP 3>
Using the sample soil 7 created in STEP 2, conduct a methylene blue adsorption amount test, and use the test results to calculate the methylene blue adsorption amount (per 100 g) of the fine-grained soil 5 (hereinafter referred to as "MB adsorption amount (MBC (2) ) is calculated. The calculation method is based on the colorimetric method of "Method for measuring the adsorption amount of methylene blue on bentonite, etc. (JIS Z 2451)", and the general flow of the test method will be explained below.

First, a dispersion liquid was prepared by dispersing sample soil 7 in a 2% sodium pyrophosphate solution and stirred sufficiently (STEP 31, STEP 32). After that, a methylene blue solution was added in an amount exceeding the expected MB adsorption amount (MBC(2)). Add and stir again (STEP33, STEP34). In this embodiment, the liquid-solid ratio (L/S) of the methylene blue solution to the sample soil 7 is set to about 15.

Next, remove the supernatant from the mixture of the dispersion of sample soil 7 and the methylene blue solution, filter it (STEP 35), and dilute the filtered supernatant to create a diluted supernatant solution of the filtrate ( STEP 361). In other words, unadsorbed methylene blue that was not adsorbed to the bentonite 3 in the sample soil 7 remains in the supernatant diluted solution.

On the other hand, three types of methylene blue standard solutions (1 μmol/L, 3 μmol/L, 5 μmol/L) and a blank (0 μmol/L) were created to create the calibration curve used to determine the methylene blue concentration. Make adjustments (STEP 362). Then, the absorbance at a wavelength of 664 nm was measured for each of the methylene blue standard solution and the blank, and based on these measurement results, a correlation analysis was performed to obtain a relational expression in which the methylene blue concentration is (X) and the absorbance is (Y), Create a calibration curve (relationship) (STEP 363, STEP 364).

After this, the absorbance of the diluted supernatant solution (created in STEP 361) at a wavelength of 664 nm is measured (STEP 365), and the methylene blue concentration of the diluted supernatant solution is measured based on the absorbance of the diluted supernatant solution and the above calibration curve. (STEP 37).

Based on the methylene blue concentration of the supernatant diluted solution measured in this way, the methylene blue concentration of the filtrate (prepared in STEP 35) is determined. Calculate the amount of unadsorbed methylene blue.

Next, based on the difference between the amount of unadsorbed methylene blue and the amount of methylene blue added to the dispersion of sample soil 7 added in STEP 33, calculate the adsorption amount of methylene blue adsorbed to bentonite 3 contained in sample soil 7. , is calculated by converting it into the MB adsorption amount (MBC(2)) of soil 5 containing fine particles (STEP 38).

<Calculation of MB adsorption amount (per 100g) of bentonite mixed soil: STEP 4>
Based on the MB adsorption amount (MBC(2)) of the fine-grained soil 5 calculated in STEP 3, the estimated adsorption amount of methylene blue that would be adsorbed to the bentonite 3 contained in the bentonite mixed soil 1 is calculated using the bentonite mixed soil 1. It is calculated by converting it into the methylene blue adsorption amount (per 100 g: hereinafter referred to as "MB adsorption amount (MBC)").

The MB adsorption amount (MBC) of bentonite mixed soil 1 is determined by the mass of fine grain mixed soil 5 (S1) measured in STEP 2, the mass of gravel 6 (S2), and the fine grain mixed soil 5 calculated in STEP 3. It is calculated by equation (1) based on the MB adsorption amount (MBC(2)).

In this way, by appropriately correcting the MB adsorption amount (MBC(2)) of the fine grain mixed soil 5 in accordance with the content of gravel 6 in the bentonite mixed soil 1, the MB of the bentonite mixed soil 1 can be adjusted. Adsorption amount (MBC) can be calculated.

<Estimation of bentonite mixing ratio in bentonite mixed soil 1: STEP 5>
Based on the relational expression between the MB adsorption amount (MBC) of bentonite mixed soil 1 calculated in STEP 4 and the bentonite mixing ratio shown in Figure 4, estimate the bentonite mixing ratio corresponding to the MB adsorption amount (MBC) of bentonite mixed soil 1. do.

<Obtaining the relational expression between MB adsorption amount (MBC) and bentonite mixing ratio: STEP 51>
The relational expression between the MB adsorption amount (MBC) of bentonite mixed soil 1 and the bentonite mixing ratio is determined by a correlation analysis performed separately. Specifically, the above-mentioned steps STEP 1 to STEP 4 are performed on multiple bentonite mixed soils 1 with different known bentonite mixing ratios to calculate the MB adsorption amount (MBC), and the bentonite mixing ratio is calculated. (X) and the MB adsorption amount (MBC) as (Y).

The following is an example of a case where six types of bentonite mixed soil 1 with different bentonite mixing ratios are used, and the procedure for determining the relational expression between the bentonite mixing ratio and the MB adsorption amount (MBC) is shown.

First, as shown in Fig. 3, six types of bentonite mixed soil 1 with different bentonite mixing ratios are prepared (about 460 g in this embodiment), and after sufficiently drying them by microwave oven, they are sieved. The soil containing fine particles 5 and gravel 6 were obtained, and the mass (S1, S2) of each was measured. Next, the sample soil 7 was separated from the fine particle mixed soil 5 five times to prepare a total of 30 types of sample soil 7.

Thereafter, for these 30 types of sample soils 7, the MB adsorption amount (MBC(2)) of the fine-grained soil 5 was measured. As a result, five measurement results are obtained for each of the six types of bentonite mixed soil with different bentonite mixing ratios, so calculate the average of the three measurement results excluding the highest and lowest values, and calculate this. This was adopted as the MB adsorption amount (MBC(2)) of soil 5 containing fine particles.

Substituting the thus calculated MB adsorption amount of the fine-grained soil 5 (MBC(2)) and the mass (S1, S2) of the fine-grained soil 5 and gravel 6 into the above equation (1), Figure 3 shows the results of calculating the MB adsorption amount (MBC) of bentonite mixed soil 1, and Figure 4 shows the results of analyzing the correlation between the bentonite mixing ratio and the MB adsorption amount (MBC) of bentonite mixed soil 1. Looking at the graph in FIG. 4, it can be seen that the coefficient of determination R ² is 0.9837, which is close to 1, indicating a good fit.

By substituting the MB adsorption amount (MBC) of bentonite mixed soil 1 calculated in STEP 4 into the relational expression shown in FIG. 4 calculated in this way, it is possible to estimate the bentonite mixing ratio of bentonite mixed soil 1 to be managed. becomes.

According to the bentonite mixed soil management method described above, the sample soil 7 used for the methylene blue adsorption amount test is separated from the fine particle mixed soil 5 prepared by removing the gravel 6 from the sample preparation material 4. The MB adsorption amount (MBC(2)) of the fine-grained soil 5 obtained by this method is less likely to vary due to the separation of the sample soil 7, and the trouble of preparing a large amount of sample soil 7 and conducting the test is reduced. By omitting this, it becomes possible to efficiently estimate the bentonite mixing ratio of the bentonite mixed soil 1 that accurately reflects the current situation using a small amount of sample soil 7.

Therefore, the amount of methylene blue solution used in the test can be reduced, making it possible to conduct the test economically, and the time required for the test can also be shortened, reducing the time and cost of overall quality control of bentonite mixed soil 1. It becomes possible to achieve this goal. Accordingly, it is easy to increase the frequency of conducting the methylene blue adsorption amount test compared to the conventional method, and when producing the bentonite mixed soil 1, it becomes possible to adjust the amount of bentonite 3 used as appropriate.

Therefore, it is possible to avoid problems such as insufficient water-blocking performance that may occur when constructing soil structures such as structure 11 using bentonite mixed soil 1 in which bentonite 3 is insufficiently added. Become. Moreover, when producing the bentonite mixed soil 1, excessive addition of bentonite 3 can be suppressed, making it possible to significantly improve economic efficiency.

≪Comparative experiment to understand the effect≫
Regarding the above management method for bentonite mixed soil 1, the following tests were conducted in order to understand its effects.

As a comparative example, six types of bentonite mixed soil 1 with different bentonite mixing ratios, similar to those used in calculating the relational expression shown in Figure 4, were separated without sieving after drying. The test was performed five times to create a total of 30 types of samples. Then, a methylene blue adsorption amount test was conducted on each of these 30 types of samples, and the amount of methylene blue adsorption (per 100 g: hereinafter referred to as "MB adsorption amount (MBC (no))" in bentonite mixed soil 1 that was not sieved was determined. ) was calculated. In addition, the dispersion of the MB adsorption amount (MBC (absent)) was determined for each of the six types of bentonite mixed soils with different bentonite mixing ratios, and the results are shown in FIGS. 5 and 6.

The graph in Figure 6 shows the MB adsorption amount (MBC(2)) of the fine-grain mixed soil 5 obtained by sifting each of the six types of bentonite mixed soil 1 with different bentonite mixing ratios calculated in STEP 51. From this, the variance was calculated as shown in FIG. 3, and the results are also shown.

Looking at FIG. 6, it can be seen that when no sieving is performed, the dispersion becomes larger as the bentonite mixing ratio increases. Among these, at a bentonite mixing ratio of 12%, the dispersion is large at 2.81, and looking at the details in Figure 5, the minimum value of the MB adsorption amount (MBC (absent)) of bentonite mixed soil 1 is 6.5. The maximum value is 10.2, which is nearly double the difference, and it can be seen that there is variation in the calculation results.

On the other hand, when sieving is performed, the dispersion does not change significantly even if the bentonite mixing ratio increases, and even at its maximum, it is as small as about 0.33 when the bentonite mixing ratio is 15%. Looking at the details of this point in Figure 3, the minimum value of the MB adsorption amount (MBC(2)) of the fine-grained soil 5 is 12.1 and the maximum value is 13.6, and the difference is about 10%. It can be seen that there is little variation in the calculation results.

Further, FIG. 7 shows the results of an analysis of the correlation between the MB adsorption amount (MBC (no)) of bentonite mixed soil 1 that has not been sieved and the bentonite mixing ratio. Looking at the graph in FIG. 7, it can be seen that the coefficient of determination R ² is 0.9751, which indicates that the correlation is inferior to that in the case where sample soil 7 is separated from fine-grained soil 5 and tested.

Therefore, when estimating the bentonite mixing ratio, the MB adsorption amount (MBC(2)) of the bentonite mixed soil 5 is calculated by mass correction according to equation (1) above. It can be seen that by using the MB adsorption amount (MBC), the bentonite mixing ratio that reflects the current situation can be estimated more accurately than when using the MB adsorption amount without sieving (MBC (none)).

The method for managing bentonite mixed soil of the present invention is not limited to the above-described embodiments, and various changes can be made without departing from the spirit of the present invention.

For example, in the present embodiment, when sifting the sample preparation material 4 collected from the bentonite mixed soil 1 into the fine-grained soil 5 and the gravel 6, the threshold value is set at 2 mm, but this is not necessarily limited. It is not something that will be done. The threshold value may be set to any value as long as the sample soil 7 to be separated from the fine particle mixed soil 5 can be prepared to have a particle size suitable for the methylene blue adsorption amount test.

Further, the water content state of the sample preparation material 4 after drying does not necessarily have to be an absolutely dry state as long as the bentonite 3 is in a state where it is difficult to adhere to the gravel 6 or the sieve.

1 Bentonite mixed soil 2 Earth and sand 3 Bentonite 4 Sample preparation material 5 Gravel 6 Fine grain mixed soil 7 Sample soil 10 Waste disposal site 11 Structure 12 Waste

Claims (5)

A method for managing bentonite mixed soil using a bentonite mixing ratio estimated based on the results of a methylene blue adsorption amount test, the method comprising:
Sieving the bentonite mixed soil and removing gravel to separate a sample soil from the fine grain mixed soil,
conducting a methylene blue adsorption amount test using the sample soil to obtain the methylene blue adsorption amount of the soil containing fine particles;
obtaining the methylene blue adsorption amount of the bentonite mixed soil based on the methylene blue adsorption amount of the fine particle mixed soil;
A method for managing bentonite mixed soil, comprising the step of obtaining the bentonite mixing ratio of the bentonite mixed soil based on the methylene blue adsorption amount of the bentonite mixed soil . In the method for managing bentonite mixed soil according to claim 1,
A method for managing bentonite mixed soil, characterized in that the particle size of the fine-grained soil is approximately 2 mm or less. The method for managing bentonite mixed soil according to claim 1 or 2,
The amount of methylene blue adsorbed in the soil mixed with fine particles is corrected based on the mass of the gravel and the soil mixed with fine particles, and the amount of methylene blue adsorbed in the bentonite mixed soil is calculated. Management method. In the method for managing bentonite mixed soil according to any one of claims 1 to 3,
A method for managing bentonite mixed soil, which comprises drying the bentonite mixed soil and then sieving the bentonite mixed soil. In the method for managing bentonite mixed soil according to claim 1,
The bentonite mixing ratio is calculated based on a relational expression between the bentonite mixing ratio and the methylene blue adsorption amount, which is obtained by obtaining the methylene blue adsorption amount from a bentonite mixed soil with a known bentonite mixing ratio. Management method.

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