JP7090386B2 - Content rate measurement method and method for producing improved soil using this - Google Patents

Description

In the present invention, for example, in the ground improvement work of volcanic ash coarse-grained soil containing allophane, allophane in the volcanic ash coarse-grained soil, etc. The present invention relates to a method for measuring a content suitable for use in determining the content of soil, and a method for producing improved soil using the method.

For road earthwork that uses locally generated soil or locally (currently located) ground (hereinafter referred to as "locally generated soil, etc."), improvement of locally generated soil, etc. with solidifying material is carried out in order to obtain the required ground strength. .. The component of the solidifying material is mainly a cement composition, which contains a small amount of hexavalent chromium.

In general ground improvement for locally generated soil, hexavalent chromium is fixed to the hydrate of cement produced in the process of hardening of the solidifying material, so hexavalent chromium is obtained from the obtained improved soil. It does not elute in excess of soil environmental standards.

However, when the locally generated soil is volcanic ash coarse-grained soil, hexavalent chromium is likely to elute from the improved soil. It is considered that this is because allophane contained in the coarse grain soil of volcanic ash inhibits the hydration reaction of cement, and the hydrate cannot sufficiently fix hexavalent chromium. Therefore, there is a risk that hexavalent chromium may elute from the improved soil in excess of the soil environmental standard, or the strength required for the improved soil may not be exhibited.

As a countermeasure, it is conceivable to quantify allophane contained in locally generated soil and add an amount of quicklime according to the quantification result to locally generated soil.

Yasuo Kitagawa, Rapid Quantification Method of Allophane and Amorphous Inorganic Components in Soil, Japanese Society of Soil Science and Technology, April 1977, Vol. 48, No. 4, pp.124-129

However, although conventional methods for quantifying allophane, such as an acid-alkali alternating dissolution method and a 200 ° C. heating weight loss method (see Non-Patent Document 1), many of these quantification methods are required until results are obtained. It takes 5 to 7 days or more for the former and 4 days or more for the latter, and an indoor test environment equipped with test equipment is indispensable. Increase the price.

The above problem is not derived only from allophane, but is caused by an amorphous component (amorphous clay mineral) containing active aluminum as well as allophane (amorphous aluminum silicate clay mineral).

The present invention has been made in consideration of the above-mentioned matters, and an object thereof is to be able to easily and quickly measure the content of a specific component such as allophane including active aluminum, and by extension, the soil environmental standard for hexavalent chromium elution. It is an object of the present invention to provide a method for measuring the content rate, which also contributes to ensuring the suppression of excess soil, and a method for producing improved soil using the method.

In order to achieve the above object, the content rate measuring method according to the present invention is to rub the volcanic ash coarse-grained soil on the phenol phthalaine paper and then remove the volcanic ash coarse-grained soil adhering to the outer surface of the phenol phthalaine paper. After wiping off, a predetermined concentration of sodium fluoride solution was dropped on the place where the volcanic ash coarse-grained soil remained on the phenol phthalaine paper, and the color development state of the place where the dropping was performed was recorded using a color space. It is quantified, and the content of the specific component containing active aluminum in the clay is determined based on this value, and the content in the clay is multiplied by the ratio of the clay to the coarse grain soil of the volcanic ash to obtain the coarse grain soil of the volcanic ash. The content of the specific component in the clay is calculated (claim 1).

On the other hand, in order to achieve the above object, the method for producing improved soil according to the present invention is based on the content rate obtained by the content rate measuring method according to claim 1 , and the volcanic ash coarse grains used for ground improvement. The addition ratio of the fresh lime in the improved material to be mixed with the soil or the addition ratio of the fresh lime to be mixed with the coarse-grained volcanic ash soil is determined (Claim 2 ).

In the present invention, the content rate of a specific component such as allophane containing active aluminum can be easily and quickly measured, and the content rate measuring method that contributes to ensuring the suppression of excess of the soil environmental standard for hexavalent chromium elution, and the like. A method for producing improved soil using the above can be obtained.

That is, in the method for measuring the content of the invention according to each claim of the present application, only a relatively easily available phenolphthalein paper, sodium fluoride solution (NaF reagent), an imaging device, or the like is used, which is a complicated procedure. Since it is not necessary, the content of a specific component can be measured easily and in a short time, and if a phenolphthalein paper or the like is carried, the measurement can be performed on-site. In addition, when requesting a testing institution to quantify allophen in locally generated soil collected as in the past, if the number of samples (number of samples) is reduced in order to reduce the test cost, which tends to be expensive, the number is small. However, in the content rate measuring method of the present invention, it is not necessary to ask the testing institution for quantification as described above, so that the variation in the measurement result and the reliability can be eliminated. It is also easy to increase the number of samples in order to improve.

In addition, only clay contains a specific component in volcanic ash coarse-grained soil, and clay and silt covered with clay adhere to phenolphthalein paper, and the dropping of NaF reagent causes the phenolphthalein paper to have a specific component. Clay containing a specific component is extracted from the remaining clay by, so to speak, coloring. In this way, the proportion of clay in the deposits of phenolphthalein paper is high, and the proportion of clay containing specific components (roughness) can be accurately measured, which in turn allows specific components in volcanic ash coarse-grained soil. The calculation result of the content rate of is also accurate.

The method for producing improved soil according to claim 2 contributes to ensuring that the improved soil is suppressed from exceeding the soil environmental standard for hexavalent chromium elution.

It is explanatory drawing which shows the relationship between the specific component content | content of the simulated soil, and the specific component content obtained from the relational expression. The result obtained by the content rate measuring method according to the embodiment of the present invention (upper 3 steps) and the result obtained by the conventional test method (lower 3 steps) in the actual volcanic ash coarse grain soil. It is explanatory drawing which shows. It is a relational diagram of the above both results which concerns on FIG. Relationship between the amount of fresh lime added and the amount of hexavalent chromium eluted when the addition rate of fresh lime in the cement-based solidifying material mixed with simulated soil having an allofen content of 5% to 20% (in 5% increments) is changed. The horizontal axis shows the allophen content, the vertical axis shows the elution amount of hexavalent chromium, and the broken line shows the addition ratio (%) of fresh lime. It is a bar graph showing the relationship between the amount of quicklime added and the amount of hexavalent chromium eluted according to the amount of cement-based solidifying material added to soil with an allofen content of 2%. The horizontal axis is the quicklime addition rate and the vertical axis is six. The amount of elution of valence chromium and the bar graph show the amount of solidifying material added. It is a graph showing the relationship between the amount of cement-based solidifying material added to soil with a quicklime addition rate of 2% and the uniaxial compressive strength. There is.

Embodiments of the present invention will be described below with reference to the drawings.

The content rate measuring method according to the present embodiment is the content rate of specific components contained in clay in volcanic ash coarse-grained soil (locally generated soil, etc.) in the following steps (1) to (3) (hereinafter, clay). After obtaining the medium content), in the subsequent step (4), the content of the specific component contained in the volcanic ash coarse-grained soil is calculated based on the clay content. Here, the specific component is a component containing active aluminum such as allophane (amorphous clay mineral or amorphous component).

Hereinafter, each step (1) to (4) will be described in detail.

(1) After rubbing a small amount of volcanic ash coarse grain soil strongly on the phenolphthalein paper with a fingertip, tap the phenolphthalein paper to remove the excess volcanic ash coarse grain soil adhering to the outer surface of the phenolphthalein paper. To pay off. As a result, the clay (clay and silt covered with clay) in the volcanic ash coarse-grained soil adheres to and remains on the phenolphthalein paper (the surface of the paper and the gaps in the mesh).

In this example, a filter paper capable of capturing dried clay particles is used as the phenolphthalein paper. Specifically, it is conceivable to use a filter paper having a mesh size of 100 to 200 mesh and an opening of 149 μm to 74 μm. .. For example, a filter paper having fine pores (opening) having a size that allows dry clay particles to pass through and has a larger particle size than the clay particles may be used.

The phenolphthalein paper of this example is obtained by impregnating the filter paper with a phenolphthalein solution having a predetermined concentration (for example, 1 g of phenolphthalein dissolved in 100 mL of methanol) and drying the paper.

(2) A predetermined concentration of sodium fluoride solution is dropped on the phenolphthalein paper where the volcanic ash coarse-grained soil remains.

In this example, a sodium fluoride solution (NaF reagent) in which 42 g of sodium fluoride is dissolved in 1 L of water to make a 1 M solution is used.

(3) After a lapse of a predetermined time, the RGB value of the coloration state of the place where the dropping is performed on the phenolphthalein paper is acquired, and the content rate of the specific component in the clay is obtained based on this RGB value.

That is, when there is a large amount of active aluminum (specific component) in the volcanic ash coarse-grained soil remaining on the phenolphthalein paper, the pH rises and the place where the dropping is performed (dropping point) turns red. The degree of color development varies depending on the amount of clay particles containing active aluminum (specific component). Then, in the present embodiment, the phenolphthalein paper is left to stand until a predetermined time (for example, 3 minutes) has elapsed from the dropping, for the purpose of acquiring the RGB value in a state where the coloration is stable.

To acquire the RGB values, the color development status of the above-mentioned dripping points on the phenolphthalein paper is digitally photographed using a photographing device such as a digital camera, and the RGB values are acquired from the region corresponding to the dripping points in the photographed image (for example, presented). This is done by averaging 5 points in the center of the color.

Then, the acquired RGB value is substituted into the relational expression between the clay content and the RGB value derived in advance from the statistical analysis to obtain the clay content of the specific component.

Here, in the derivation of the above relational expression, a total of 11 types of simulated soils in which the content of the specific component is different from 0% to 100% at 10% intervals are prepared, and for each simulated soil, the above steps (1) and (2) was carried out, the coloration situation after 3 minutes was photographed, and analysis (multiple regression analysis) was performed using the acquired RGB value and the content rate of the specific component, and the content rate of the specific component and the RGB value were obtained. I got the relational expression. The relational expression is shown below, and FIG. 1 shows the relationship between the specific component content of the simulated soil and the specific component content obtained from the relational expression. The 11 points in FIG. 1 are plots of the specific component content of the simulated degree obtained from the relational expression corresponding to the known content (horizontal axis: 10% interval from 0% to 100%). Is.
Specific component content = -0.713 x R value -0.607 x G value -0.388 x B value
+261.833

(4) The above-mentioned clay content is multiplied by the ratio of clay to the volcanic ash coarse grain soil (clay fraction) to calculate the content of the specific component in the volcanic ash coarse grain soil.

Here, the ratio of clay to volcanic ash coarse-grained soil can be obtained by a soil particle size test.

FIG. 2 shows the results of obtaining the specific component content of the actual volcanic ash coarse-grained soil (locally generated soil, etc.) by the method of the present embodiment consisting of the above steps (1) to (4) (upper three stages). And the results (lower 3 steps) obtained by the conventional test method (Gotemba 1-3: acid-alkali alternating dissolution method, Aso and Himeji: 200 ° C. heating weight loss method) are shown. The relationship between the two results is shown in FIG. From this FIG. 3, it can be understood that there is a high correlation between the two results. The five points in FIG. 3 are plots of the content rates obtained from the relational expression corresponding to the content rate (horizontal axis) of the conventional test method, and R ² is the phase relationship of the five points. It is a number, and it can be said that there is a strong correlation between 0.8 and 1.0.

In addition, in order to investigate the variation in the content of specific components due to differences in shooting conditions such as illuminance and lighting, the present inventor has three indoor locations with different illuminance such as under fluorescent lights and near windows, and is not exposed to direct sunlight. RGB obtained from image data by digitally photographing a color chart for evaluation corresponding to the color development situation at 10% intervals from 0% to 100% in the clay content of a specific component at three outdoor locations such as in the shade of a building. When the relational expression between the clay content and the RGB value for each shooting condition was obtained based on the value, the variation in the clay content of the specific component obtained for each shooting condition was within the range where there was no practical problem. It turned out that the influence of the shooting conditions was negligible.

As described above, the content rate measuring method of the present embodiment only uses a relatively easily available phenolphthalein paper, sodium fluoride solution (NaF reagent), imaging equipment, etc., and does not require a complicated procedure. Therefore, the content of a specific component can be measured easily and in a short time, and if a phenolphthalein paper or the like is carried, the measurement can be performed on-site, and the variation in measurement results caused by the limitation of the number of samples collected can be suppressed. Therefore, it is possible to measure multiple points of the target soil on site.

Further, in the volcanic ash coarse-grained soil, only clay contains a specific component, and clay and silt covered with clay adhere to the phenolphthalein paper, and in the present embodiment (step (1)). , The clay containing a specific component is extracted from the clay remaining on the phenolphthalein paper by dropping the NaF reagent, so to speak, by color development. In this way, the proportion of clay in the deposits of phenolphthalein paper is high, and the proportion of clay containing specific components (roughness) can be accurately measured, which in turn allows specific components in volcanic ash coarse-grained soil. The calculation result of the content rate of is also accurate.

Next, in the method for producing the improved soil of the present embodiment, based on the content rate obtained by the above-mentioned content rate measuring method, the addition ratio of quicklime in the improved material to be mixed with the volcanic ash coarse-grained soil used for ground improvement, Alternatively, the ratio of quicklime to be mixed with the coarse grained soil of volcanic ash is determined.

That is, the present inventor has confirmed the following by laboratory tests and field tests.
(A) By adding quicklime to the cement-based solidifying material according to the amount of the specific component, it is possible to suppress the elution of hexavalent chromium exceeding the soil environmental standard.
(B) The amount of hexavalent chromium eluted has nothing to do with the amount of cement-based solidifying material added required for the required strength.
(C) The uniaxial compressive strength when a predetermined amount of quicklime is added to suppress the elution of hexavalent chromium is proportional to the amount of the cement-based solidifying material added.

Regarding (A), when a simulated soil in which the allophane content was adjusted from 5% to 20% in 5% increments was prepared and mixed with a cement-based solidifying agent in which the addition rate of quicklime (CaO) was changed. As a result of investigating the elution of hexavalent chromium, it was confirmed (see FIG. 4).

Regarding (B), 30 kg / m ³ , 50 kg / m ³ , 100 kg / m ³ , 150 kg / m ³ of cement-based solidifying material was added to the soil having an allophane content of 2%, and each cement-based solidifying material was solidified. As a result of changing the addition rate of quicklime in the material, the elution amount of hexavalent chromium does not change significantly even if the amount of cement-based solidifying material added increases, and when 2% or more of quicklime is added, hexavalent chromium elution occurs. Since it was less than the lower limit of quantification, it could be confirmed (see FIG. 5).

Regarding (C), as a result of adding 30 kg / m ³ , 50 kg / m ³ , 100 kg / m ³ , and 150 kg / m ³ of the cement-based solidifying material to the soil with the addition rate of quicklime of 2%, the cement-based solidifying material was added. It was confirmed that the uniaxial compressive strength was obtained in proportion to the amount of addition (see FIG. 6).

Therefore, in the method for producing the improved soil of the present embodiment, the addition ratio of fresh lime to the volcanic ash coarse grain soil (locally generated soil, etc.) is changed depending on the content ratio of the specific component regardless of the addition ratio of the cement-based solidifying material. Specifically, when the content of the specific component is less than 5% (weight ratio), the addition rate of fresh lime is set to 2% (weight ratio) of the volcanic ash coarse grain soil, and 5% or more and 10% (weight ratio). If less than 3% (weight ratio), 10% (weight ratio) or more and less than 15% (weight ratio), 4% (weight ratio), 15% (weight ratio) or more and 20% (weight ratio) If it is less than 5% (weight ratio), if it is 20% (weight ratio) or more and less than 25% (weight ratio), it is 6% (weight ratio). After premixing the cement-based solidifying material of (1), for example, at a factory to obtain an improved material, for example, the improved material is mixed locally with locally generated soil or the like so as to have the above weight ratio to obtain the improved soil.

Of course, it is not limited to those in which the improved material is first manufactured and then mixed with locally generated soil, etc. For example, quicklime with a predetermined weight ratio and a predetermined amount of cement-based solidifying material are mixed with locally generated soil, etc. May be used to produce improved soil.

The method for producing improved soil as described above contributes to ensuring the suppression of excess of the soil environmental standard for hexavalent chromium elution for improved soil.

It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can be variously modified and implemented without departing from the gist of the present invention.

For example, in the above embodiment, RGB is used as a color space for quantifying the coloration situation, but the present invention is not limited to this, and the coloration situation is quantified using another recordable color space such as CMYK. Of course, the present invention can also be carried out.

Claims (2)

After rubbing the volcanic ash coarse-grained soil on the phenolphthalein paper, the volcanic ash coarse-grained soil adhering to the outer surface of the phenolphthalein paper is wiped off, and the volcanic ash coarse-grained soil remains on the phenolphthalein paper. A predetermined concentration of sodium fluoride solution was dropped onto the site, and the color development status of the dropped site was quantified using a recordable color space. Based on this value, the specific component containing active aluminum was contained in the clay. Find the rate ,
A content rate measuring method for calculating the content rate of the specific component in the volcanic ash coarse grain soil by multiplying the clay content rate by the ratio of the clay to the volcanic ash coarse grain soil . Based on the content rate obtained by the content rate measuring method according to claim 1, the addition ratio of quicklime in the improvement material to be mixed with the volcanic ash coarse grain soil used for ground improvement, or the volcanic ash coarse grain soil. A method for producing improved soil, which determines the addition ratio of quicklime to be mixed.

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