JP6512472B2 - Method of predicting strength of improved soil and method of producing improved soil - Google Patents

Description

  The present invention relates to a method of predicting strength of improved soil and a method of producing the improved soil.

  Heretofore, as a method of ground improvement, it has been practiced to manufacture an improved soil in which the strength of the ground is improved by mixing a hardened material such as cement with the excavated soil and hardening it (Patent Document 1). .

  However, with such a method of using a solidifying material, as in Kanto Loam, in the case of a volcanic ash clay soil containing a large amount of volcanic ash and pumice, solidification failure may occur and the strength may not be improved.

Such poor solidification is considered to be caused by allophane, which is a kind of amorphous inorganic component derived from volcanic ash-like viscous soil. Specifically, the volcanic ash clay contains a large amount of allophane (Al ₂ O ₃ · (1-2) SiO ₂ · nH ₂ O), and in the process of hydration of cement in the solidified material It is thought that the hydration reaction of cement is inhibited by the adsorption of calcium by the allophane, and as a result, solidification is inhibited.

  Therefore, if the content of allophane contained in the volcanic ash clay soil is known, it becomes possible to design the mixing amount of the above-mentioned solidifying material according to the content, so the content of allophane is measured, It is performed to determine the mixing amount of the above-mentioned solidifying material based on the obtained allophane content. As the measurement of allophane, for example, using the Kitagawa method, allophane in the volcanic ash clay soil is alternately eluted with hydrochloric acid and sodium hydroxide, and the mass loss due to elution is calculated as the allophane content. ing.

Japanese Patent Application Laid-Open No. 2003-301451

However, such a measurement method requires time for dissolving allophane alternately with an acid and a base, and thus it is difficult to say that the workability is good.
In addition, even if the mixing amount of the solidifying material is set by measuring the allophane content, solidification failure may still occur.

  In view of the above circumstances, the present invention is a method of predicting the strength of improved soil capable of predicting strength more appropriately and with higher workability than in the prior art, and improvement capable of suppressing reduction in strength due to poor solidification. It is an issue to provide a method of producing soil.

The strength prediction method for improved soil according to the present invention is
A method for predicting the strength of an improved soil, which predicts the strength of an improved soil obtained by mixing and solidifying a cement-containing solidifying material and a volcanic ash clay soil, comprising:
Based on the correlation between the amount of aluminum eluted from the volcanic ash cohesive soil and the strength of the improved soil comprising the volcanic ash cohesive soil and the solidifying material,
The strength of the modified soil is predicted from the amount of aluminum eluted from the volcanic ash clay.

According to this configuration, the amount of aluminum eluted from the volcanic clay soil (the amount of dissolved aluminum) and the amount of the aluminum soil improved rather than the amount of allophane contained in the volcanic clay soil (the content of allophane) and the strength of the modified soil Since the relationship between the strength of the soil and the strength of the soil shows a better correlation, the strength of the improved soil can be predicted more appropriately than in the past.
In addition, since it is easier to measure the amount of aluminum released from volcanic clay soil than to measure allophane content in volcanic clay soil, predict the strength of the improved soil with better workability than before. Can.
Therefore, the strength can be predicted more appropriately and with better workability than before.

Moreover, the method for producing the improved soil according to the present invention is
A method for producing an improved soil, which comprises producing an improved soil by mixing and solidifying a cement-containing solidifying material and a volcanic ash-like sticky soil,
Based on the correlation between the amount of aluminum eluted from the volcanic ash cohesive soil and the strength of the improved soil comprising the volcanic ash cohesive soil and the solidifying material, the strength of the improved soil is equal to or greater than a predetermined value, Determine the mixing ratio of the volcanic ash clay soil and the solidification agent, and mix the solidification agent and the volcanic ash clay soil.

According to this configuration, the allophane content is determined by determining the mixing ratio of the volcanic ash-like viscous soil and the solidifying material so that the strength of the improved soil becomes equal to or greater than the predetermined value based on the method of predicting the strength of the improved soil. The mixing ratio can be determined more appropriately and with good workability than when the mixing ratio between the volcanic ash-like viscous soil and the solidifying material is determined based on that.
Therefore, it is possible to suppress a decrease in strength due to poor solidification.

  As described above, according to the present invention, a method of predicting the strength of an improved soil capable of predicting strength with a higher degree of workability and workability than in the prior art, and suppressing a decrease in strength due to solidification failure can be suppressed. Method of producing the improved soil is provided.

Graph showing the relationship between the amount of aluminum elution and the strength of the soil used in Experimental Example 2 of the present invention Graph showing the relationship between aluminum content and strength for soil used in Experimental Example 2 of the present invention Graph showing the relationship between aluminum elution amount and allophane content for the soil used in Experimental Example 2 of the present invention Graph showing the relationship between the aluminum content and the allophane content for the soil used in Experimental Example 2 of the present invention Graph showing the relationship between aluminum elution amount and allophane content for the soil used in Experimental Example 2 of the present invention Graph showing the relationship between the allophane content and the strength of the soil used in Experimental Example 2 of the present invention

  Hereinafter, the strength prediction method of the improvement soil of one embodiment of the present invention and the method of producing the improvement soil will be described.

  The method of predicting the strength of the improved soil according to the present embodiment is a method of predicting the strength of the improved soil, which predicts the strength of the improved soil obtained by mixing and solidifying a cement-containing solidifying material and the volcanic ash cohesion soil. Based on the correlation between the amount of aluminum eluted from the clayey soil and the strength of the improved soil comprising the volcanic clayy soil and the solidifying material, the amount of aluminum eluted from the clayey clay is improved from the amount of aluminum eluted from the clay. Predict the strength of

First, as the volcanic ash clay soil to be improved in the present embodiment, for example, Kanto Loam, Hachinohe Loam, Akaboku etc. may be mentioned.
This volcanic ash cohesion soil contains allophane (Al ₂ O ₃ · (1-2) SiO ₂ · nH ₂ O).
In addition, the volcanic ash clay soil contains allophane at 10% by mass or more, preferably 20% by mass or more. In addition, the volcanic ash clay soil contains allophane at 100% by mass or less, preferably 90% by mass or less.

In the present embodiment, specifically, first, the amount of aluminum eluted from the volcanic ash clay is measured.
Specifically, the volcanic ash clay is mixed with water to prepare a suspension. On the other hand, an aqueous solution of sodium hydroxide is prepared to be 20% by mass. An aqueous solution of sodium hydroxide is added to the obtained suspension to adjust the pH of the suspension to 12, and then the suspension is adjusted so that the mass ratio of the volcanic ash clay soil (dry mass): water = 1: 5. Water is added to the suspension to adjust, and aluminum is eluted in the aqueous solution by stirring for 30 minutes, and the amount of eluted aluminum is measured using inductively coupled plasma emission spectrometry (ICP-AES) Do. In the measurement using ICP-AES, a yttrium solution is added as an internal standard substance.
In addition, dry mass means a mass when drying volcanic ash clay soil at 105 ° C. and the water content (the mass of the dry residue) is in an equilibrium state.

On the other hand, mixed with volcanic ash-like sticky soil, solidifying material and water, put into a cylindrical form with an inner diameter (diameter) of 5 cm and a height of 10 cm, flatten the surface, and make a modified soil at 20 ° C. After curing and sealing in, the uniaxial compressive strength (kN / m ² ) of the obtained modified soil is measured. In this embodiment, uniaxial strong compressive strength at 28 days of material age is measured.

Next, the correlation between the obtained strength and the amount of eluted aluminum is determined.
And, for example, when the amount of aluminum of the volcanic clay clay soil used is measured at the time of manufacture of the modified soil, for example, the strength of the modified soil produced using this volcanic clay clay soil is calculated from the above correlation at 28 days of age. It can be predicted.

  Further, the method for producing the improved soil according to the present embodiment is a method for producing the improved soil, which produces the improved soil obtained by mixing and solidifying a cement-containing solidifying material and the volcanic ash clay soil, which comprises the volcanic ash viscosity Based on the correlation between the amount of aluminum eluted from the soil and the strength of the improved soil comprising the volcanic ash viscous soil and the solidifying material, the volcanic ash viscosity is adjusted so that the strength of the improved soil becomes a predetermined value or more. Determine the mixing ratio between soil and solidifying material, and mix the solidifying material with volcanic ash clay soil

Specifically, from the correlation obtained as described above, it is preferable that the amount of leached aluminum eluted in the above aqueous solution corresponds to the target strength, such as volcanic ash-like viscous soil Calculate the mixing ratio of the solidifying material.
More specifically, for example, the mixing ratio of the volcanic ash clay soil and the solidifying material was changed to prepare an improved soil, and the strength of each modified soil at the age of 28 days and the leached from the volcanic ash clay soil used The correlation with the amount of aluminum is determined respectively. Then, from the obtained correlation, the mixing ratio of the volcanic ash-like viscous soil and the solidifying material is determined so that the strength becomes a predetermined value or more.

Then, an improved soil is produced by mixing and curing the volcanic ash-like viscous soil and the solidifying material so as to obtain the mixing ratio thus determined.
More specifically, water is further added to the volcanic ash-like viscous soil and the solidifying material, and the mixture is mixed and solidified to produce an improved soil.

  The solidifying material used in the present embodiment can be appropriately selected and used from cement-based solidifying materials used for ordinary ground improvement, but various types such as normal, early strong, ultra early strong, etc. Common cements such as portland cement, various mixed cements obtained by mixing blast furnace slag, silica, and fly ash with the portland cement, white cement, super rapid-hardening cement, alumina cement, etc. can be used.

The mixing (blending) amount of the solidifying material is not particularly limited, but is preferably 30 to 160 parts by mass, and more preferably 45 to 70 parts by mass with respect to 100 parts by mass of the volcanic ash clay soil (dry mass) .
In addition, the amount of water (including water contained in the soil) at the time of kneading is preferably 120 to 280 parts by mass, and 160 to 180 parts by mass with respect to 100 parts by mass of the volcanic ash clay soil (dry mass). Is more preferred.

As described above, according to the method for predicting the strength of the improved soil of the present embodiment, the amount of aluminum eluted from the volcanic cohesion soil rather than the amount of allophane contained in the volcanic cohesion soil and the strength of the improved soil Since the direction between the strength of the improved soil and the strength of the improved soil shows a better correlation, the strength of the improved soil can be predicted more appropriately than before.
In addition, since it is easier to measure the amount of aluminum released from volcanic clay soil than to measure allophane content in volcanic clay soil, predict the strength of the improved soil with better workability than before. Can.
Therefore, the strength can be predicted more appropriately and with better workability than before.

Moreover, according to the method for producing improved soil of the present embodiment, the mixing ratio of the volcanic ash-based cohesive soil and the solidifying material so that the strength of the improved soil becomes a predetermined value or more based on the method of predicting the strength of the improved soil. By determining the mixing ratio, the mixing ratio can be determined more appropriately and with good workability than in the case of determining the mixing ratio between the volcanic ash-like viscous soil and the solidifying material based on the allophane content.
Therefore, it is possible to suppress a decrease in strength due to poor solidification.

The method of predicting the strength of the improved soil of the present embodiment and the method of producing the improved soil are as described above, but the present invention is not particularly limited to the above embodiment.
For example, in the above embodiment, a strength of 28 days of material age is adopted as the strength of the improved soil, but in the present invention, strengths of other material ages may be adopted.

  EXAMPLES The present invention will next be described in more detail by way of examples, which should not be construed as limiting the invention thereto.

(Experimental example 1) Measurement of physical properties of soil

-Measurement of aluminum elution amount in soil Kanto loam 1 to 5 collected from five places was used as the volcanic ash clay.
Sandy clay was used for comparison.
These volcanic ash clay soil and sandy clay are mixed with water, 20% sodium hydroxide is further added, pH is 12, soil (dry mass): water (including water contained in soil) = The suspension was prepared by mixing to 1: 5.
The suspension is stirred for 30 minutes, the aluminum is eluted, the amount of aluminum eluted in water is added as an internal standard substance of yttrium solution, inductively coupled plasma emission spectrometry (ICP-AES, CIROS-120 EOP) The amount of eluted aluminum per 1 kg of soil was measured using SPECTRO, Inc.).
The results are shown in Table 1.

-Measurement of allophane content in soil As a comparison object, the content of allophane contained in each soil was measured based on the Kitagawa method. Specifically, after measuring the dry mass of each soil, 8N aqueous solution of hydrochloric acid and 0.5N aqueous solution of sodium hydroxide are alternately added to each soil to elute allophane. The dry mass is measured, and the treatment loss (amount of allophane) is calculated by subtracting the dry mass of each soil after elution from the dry mass of each soil before elution, and the ratio of the treatment loss to the dry mass of each soil before elution (%) Was calculated.
The results are shown in Table 1.

-Measurement of the wet density of soil The wet density of each soil was prepared in accordance with JCAS L-01-2006, and was measured by unit volume mass determined from the mass of the specimen.
The results are shown in Table 2.

Measurement of Natural Water Content of Soil The natural water content of each soil was measured in accordance with JIS A 1203: 2009.
The results are shown in Table 2.

Aluminum Content The aluminum content of each soil was measured by the alkaline melting method using lithium tetraborate.
The results are shown in Table 2. In addition, in Table 2, it shows collectively about the result of allophane content described in Table 1, and the amount of aluminum elution.

(Experimental example 2) The relationship between the amount of aluminum and the strength The above-mentioned Kanto loams 1 to 4 were used as the volcanic ash clay.
In addition, cement-based solidifying material Tough Lock 3E (manufactured by Sumitomo Osaka Cement Co., Ltd.) is used as the solidifying material, and each soil, the solidifying material and water are mixed, and the mixture is a circle having an inner diameter (diameter) of 5 cm and a height of 10 cm. The soil was placed in a columnar mold, the surface was smoothed to prepare an improved soil, and sealed and cured at 20 ° C. to prepare an improved soil.
Regarding the mixing ratio of each component, 100 parts by mass of each soil, 50 parts by mass of the solidifying material, and 165 parts by mass of water (including the amount of water contained in each soil), 100 parts by mass of each soil, 67 parts by mass of solidifying material, and 173 parts by mass of water (including the amount of water contained in each soil) were set.
After mixing and placing at the above mixing ratio, the uniaxial compressive strength after 28 days of material age was measured according to JIS A 1216: 2009. The results are shown in Table 3.
In addition, from Table 2 and Table 3, a graph showing the relationship between the amount of aluminum elution and the strength is created, and is shown in FIG. 1 together with a regression line showing the correlation.
Further, a graph showing the relationship between the aluminum content and the strength is shown in FIG. 2 together with a regression line showing the correlation.

As shown in FIG. 1, in the case of the volcanic ash-like viscous soil, the strength tends to decrease as the amount of elution of aluminum increases regardless of the mixing ratio with the solidifying material. As a result, in the case of the volcanic ash clay soil, if the correlation between the amount of aluminum elution and the strength is determined, the strength of the improved soil is determined based on the above correlation by measuring the amount of aluminum elution of the clay volcanic soil. It turned out that it was predictable.
Moreover, when the compounding ratio of the volcanic ash viscous soil and the solidifying material changed, the correlation between the amount of dissolved aluminum and the strength tended to change. As a result, by changing the mixing ratio between the volcanic ash-like viscous soil and the solidifying material, and determining the correlation between the amount of dissolved aluminum and the strength for each mixing ratio, the mixing ratio which can obtain the strength of a predetermined value or more It turned out that it was asked.
In addition, according to the result of FIG. 1, the mixing ratio of the volcanic ash clay soil and the solidifying material is set so that the strength of the improved soil is 1000 kN / m ² or more, the volcanic clay viscous soil (dry mass): solidifying material = 100 mass It has been found that, by setting the amount to 40 to 70 parts by mass, poor solidification is suppressed, and it is possible to produce an improved soil excellent in strength.

  On the other hand, as shown in FIG. 2, even if the aluminum content was not largely different, the strength of the modified soil tended to be largely different. That is, it was found that even with the same aluminum content, significantly different strengths could be obtained. In addition, the same tendency was observed even if the mixing ratio of the volcanic ash clay soil and the solidifying material was different. As a result, it was found that it is difficult to predict the strength even if the aluminum content contained in Kanto loam is measured.

  In addition, as shown in FIGS. 1 and 2, in sandy clay, the content of allophane is significantly lower than that of volcanic clay, so the relationship between the amount of aluminum elution and the strength is completely different from that of volcanic clay clay soil. I found that.

In order to show the difference in tendency between FIG. 1 and FIG. 2 described above, the following relationships are shown in FIGS.
That is, the relationship between the aluminum elution amount and the allophane content is shown in FIG. 3, the relationship between the aluminum content and the allophane content is shown in FIG. 4, and the relationship between the aluminum elution amount and the aluminum content is shown in FIG.
Further, the relationship between the allophane content and the strength is shown in FIG.

  As shown in FIG. 4, a correlation was observed between the aluminum content and the allophane content. However, as shown in FIG. 3, no correlation was found between the aluminum elution amount and the allophane content. Further, as shown in FIG. 5, it was found that the aluminum content does not change even if the aluminum elution amount changes, and the aluminum elution amount can provide information that can not be understood by the change in the aluminum content.

  On the other hand, as shown in FIG. 6, no correlation was found between the allophane content and the strength than between the aluminum elution amount and the strength (FIGS. 1 to 4), and the strength can be sufficiently predicted. I found it not.

Claims (2)

A method for predicting the strength of an improved soil, which predicts the strength of an improved soil obtained by mixing and solidifying a cement-containing solidifying material and a volcanic ash clay soil, comprising:
The amount of aluminum eluted from the volcanic clay clay soil by adding a sodium hydroxide aqueous solution to the volcanic clay clay soil so that the suspension containing the volcanic clay clay soil has a pH of 12, and the amount of volcanic ash clay On the basis of the correlation between the strength of the improved soil comprising the cohesive soil and the solidifying material,
An aqueous solution of sodium hydroxide is added to the volcanic clay clay soil so that the suspension containing the volcanic clay clay soil has a pH of 12 to obtain a suspension, thereby improving the amount of aluminum eluted from the volcanic clay clay soil Method of predicting the strength of improved soil to predict the strength of A method for producing an improved soil, which comprises producing an improved soil by mixing and solidifying a cement-containing solidifying material and a volcanic ash-like sticky soil,
The amount of aluminum eluted from the volcanic clay clay soil by adding a sodium hydroxide aqueous solution to the volcanic clay clay soil so that the suspension containing the volcanic clay clay soil has a pH of 12, and the amount of volcanic ash clay Based on the correlation between the strength of the improved soil including the cohesive soil and the solidifying material, the mixing ratio of the volcanic ash cohesive soil to the solidifying material is determined so that the strength of the improved soil is equal to or greater than a predetermined value. , A method of producing improved soil, mixing solidifying material and volcanic clay soil.

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