JP6163173B2 - Construction method of underground impermeable walls - Google Patents

Description

The present invention is constructed how the underground impervious wall, in particular about the building how the clay underground impervious wall.

  Conventionally, slurry containing cement-based solidification material or cement / bentonite slurry, etc. are injected into the ground and mixed with the ground soil and sand as countermeasures such as containment of contaminated soil, prevention of water leakage from the dam body, and water shielding of the regulating pond. There has been a method of constructing a water-impervious wall in the ground (for example, see Patent Document 1). In addition, there has been a construction in which a clay impermeable wall is constructed by feeding and mixing powdered clay such as bentonite into the ground without using a cement-based solidifying material (for example, see Patent Documents 2 and 3).

JP 2009-68331 A JP 2006-291703 A JP 2003-129466 A

A water-impervious wall using a cement-based solidified material is weak against bending and pulling, has extremely low flexibility, and has problems in durability and earthquake resistance. That is, it is difficult to maintain a high water-blocking property for a long period of time due to poor ground following ability and self-repairability.
Moreover, about the water-impervious wall which does not use a cement-type solidification material, when using clay which has water swelling property and viscosity, such as bentonite, there exists a difficulty of handling in a construction process. For example, when sodium-type bentonite is used as muddy water, a considerable degree of dilution is required to avoid an increase in viscosity due to water swelling. Therefore, it is difficult to adjust the required amount of bentonite for making a water-impervious wall having sufficient water-imperviousness and durability. In particular, in order to send a necessary amount of sodium-type bentonite into the ground, a large amount of muddy water must be used, so the amount of waste soil increases and it must be disposed of as industrial waste. Moreover, in the case of powder, there is a problem in homogenous mixing with the ground soil and sand in the construction of the impermeable wall. In addition, when powder is fed, clay dust such as bentonite may be generated.
On the other hand, when calcium-type bentonite is used, the viscosity of muddy water does not increase and it can be handled at a high concentration. However, sufficient water barrier properties cannot be obtained due to poor viscosity expression and water swellability.
In recent years, from the viewpoint of strict countermeasure standards against soil contamination and seismic resistance, an underground impermeable wall is strongly desired that has a higher impermeable effect than the conventional one and stably for a long period of time.

  In view of the above problems, the present invention has an object to provide a method for constructing an underground impermeable wall having better water-impervious properties and having seismic resistance due to ground followability and self-repairing properties, and an underground impermeable wall And The present invention also provides an underground impermeable wall construction method and an underground impermeable wall that are less likely to generate mud when constructing an underground impermeable wall and that are excellent in safety and economy.

The above-described problems of the present invention have been solved by the following means.
(1) A clay mud (A) mainly composed of a layered silicate mineral having a polyvalent cation between layers is injected to a predetermined depth of the ground soil and mixed with the ground soil and sand . A step of forming a precursor, and an ion exchanger liquid (B) for exchanging the polyvalent cation with a monovalent cation are injected and mixed with the precursor of the water-impervious wall to prevent underground water shielding A method for constructing an underground impermeable wall having a step of constructing a wall.
(2) The construction method of the underground impermeable wall according to (1), wherein the polyvalent cation is calcium ion.
(3) The construction method of the underground impermeable wall according to (1) or (2), wherein the monovalent cation is a sodium ion.
(4) The construction method of the underground impermeable wall according to any one of (1) to (3), wherein the clay concentration in the muddy water (A) is 50% or more.
(5) The construction method of the underground impermeable wall according to any one of (1) to (4), wherein an injection rate of the muddy water (A) with respect to the ground soil is 10% to 50%.
(6) Any of (1) to (5) above, wherein an injection rate of the liquid (B) of the ion exchange agent is 5% or more and 25% or less with respect to the mixture of the ground soil and the mud (A). The construction method of the underground water-impervious wall according to Item 1.
(7) A clay composed mainly of a lamellar silicate mineral having a monovalent cation between layers, obtained by injection of the liquid (B) of the ion exchanger into the underground impermeable wall 1m ³ The construction method of an underground impermeable wall according to any one of (1) to (6), wherein the content is 50 kg / m ³ or more.
(8) Contains a mixture of a clay mainly composed of a layered silicate mineral having a monovalent cation between the layers, obtained by ion exchange, and a soil permeability, and has a hydraulic conductivity of less than 1 × 10 ⁻⁹ m / sec. An underground impermeable wall.
(9) The underground impermeable wall according to (8), wherein the monovalent cation is a sodium ion.
(10) to said underground impervious wall 1 m ^3, the content of clay mainly composed of layered silicate mineral having a monovalent cation in the interlayer is 50 kg / m ³ or more the (8) or (9) The underground impermeable wall as described.
(11) The underground impermeable wall according to any one of (8) to (10), wherein the vane shearing force is 0.5 kN / m ² or more and 50 kN / m ² or less.

In the present specification, “a clay mainly composed of a layered silicate mineral having a polyvalent cation between layers” is referred to as a “multivalent cation type clay”. In addition, “monovalent cation exchange” obtained by ion exchange using the “polyvalent cation clay” as an initial raw material is made of “a clay mainly composed of a layered silicate mineral having a monovalent cation between layers”. It is called “clay”.
As a specific example, clay and bentonite having an alkaline earth metal ion between layers are referred to as “alkaline earth metal type clay” and “alkaline earth metal type bentonite”, respectively. Are called “calcium-type clay” and “calcium-type bentonite”, respectively. In addition, these “alkaline earth metal type clay” and “alkaline earth metal type bentonite” were obtained by ion exchange using an initial raw material, respectively, and clay and bentonite having an alkali metal ion between the layers were referred to as “alkali metal exchange clay”, It is called `` alkali metal exchange bentonite '', and the above-mentioned `` calcium type clay '' and `` calcium type bentonite '' are obtained by ion exchange as an initial raw material, and clay and bentonite having sodium ions between layers are referred to as `` sodium exchange clay '', `` It is called “sodium exchange bentonite”. In the present specification, “sodium bentonite” and “monovalent cation type clay” are different from those obtained by the ion exchange and mean natural ones.

  According to the construction method of the underground water-impervious wall of the present invention, the generation of mud during construction is suppressed, it has better water-imperviousness, and is seismic resistant due to the ground following ability and the self-repairing property accompanying the occurrence of cracks, etc. It is possible to safely and economically construct underground underground water barriers. Moreover, the underground water-impervious wall according to the present invention has more excellent water-impervious properties and has earthquake resistance due to ground followability and self-repairability.

It is the graph which showed the viscosity expression in distilled water of each of a sodium type bentonite and a calcium type bentonite. The results in Table 5 shown in the examples, is a graph showing the relationship between the sodium exchanged bentonite content in the ground impervious wall 1 m ³ and permeability.

In the construction method of the underground impermeable wall according to the present invention, the polycation cation clay mud (A) is injected into the ground to a predetermined depth (primary injection) and mixed with the ground soil (original soil). Make it homogeneous. In this way, the front body of the impermeable wall is formed. Next, in order to provide water shielding, an ion exchange agent liquid (B) for exchanging the polyvalent cation of the polyvalent cation type clay with a monovalent cation is injected (secondary injection), and in front of the water shielding wall. Mix with the frame to construct a clay-based underground impermeable wall. In addition, the mixing after the primary injection and the secondary injection can be performed by, for example, stirring in the ground.
In this step, as described later, a highly concentrated mud water (A) can be fed by using a polyvalent cation type clay. That is, a large amount of clay can be injected, and the accuracy of homogeneous mixing with the ground soil and sand is improved. Moreover, when it is completed as an underground impermeable wall, it is replaced with a highly water-swelling monovalent cation exchange clay, which can maintain high water impermeability and plasticity as an underground impermeable wall for a long time. .

  The “multivalent cation type” means a kind of clay determined by the charge of a cation taken in between layers of the layered silicate mineral of the clay. Depending on the charge of the cation between the layers, the water dispersibility and water swellability of the clay differ, and the viscosity varies accordingly. The polyvalent cation type clay has lower water swellability and lower viscosity expression than the monovalent cation type clay. If this polyvalent cation type clay is used, a clay mud (A) having a high concentration of fluidity can be prepared.

The polyvalent cation is not particularly limited, and examples of the divalent ion include alkaline earth metal ions. Specific examples include divalent or higher cation such as calcium ion (Ca ²⁺ ) and magnesium ion (Mg ²⁺ ). In particular, from the viewpoint of ion exchange rate, alkaline earth metal ions are preferred, and calcium ions are preferred. That is, as the polyvalent cation type clay of the mud water (A) to be secondarily injected, alkaline earth metal type clay is preferable, calcium type clay is more preferable, and calcium type bentonite is particularly preferable.

The monovalent cation is not particularly limited, and examples thereof include alkali metal ions. Specifically, sodium ion (Na ⁺ ), lithium ion (Li ⁺ ), etc. are mentioned. Among them, alkali metal ions are preferable and sodium ions (Na ⁺ ) are preferable from the viewpoint of cost effectiveness and safety. That is, the clay contained in the underground impermeable wall obtained by secondary injection is preferably an alkali metal exchange clay, more preferably a sodium exchange clay, and particularly preferably a sodium exchange bentonite. Moreover, the underground impermeable wall in the present invention is not limited to containing only sodium ions (Na ⁺ ), and may contain sodium ions (Na ⁺ ) and other monovalent cations. Good.

In the present invention, the primary injected polyvalent cation type clay means a material satisfying at least one of the following four criteria. Therefore, even if a monovalent cation is contained together with a polyvalent cation between layers, it is defined as a polyvalent cation type clay as long as it has the following properties.
(I) Methylene blue adsorption amount is 100 mmol / 100 g or more.
This methylene blue adsorption amount is a numerical value measured according to the former Japan Bentonite Industry Association Standard Test Method (JBAS) “Measurement Method of Methylene Blue Adsorption Amount of Bentonite (Powder)”.
(Ii) The cation exchange capacity is 70 meq / 100 g or more.
This cation exchange capacity is a numerical value measured according to the former Japan Bentonite Industry Association Standard Test Method (JBAS) “Method for Measuring Cation Exchange Capacity of Bentonite (Powder)”.
(Iii) The ratio of the amount of polyvalent ions in the interlayer cation of the layered silicate mineral that is the main component mineral is 60% or more of the total amount of ions.
This is a numerical value derived from the measured value of leached ions in accordance with the test method “Testing method for leaching cations of bentonite (powder) for green mold” by the Japan Foundry Association, Tokai Branch, Inorganic Sand Research Group.
(Iv) It should be 10 ml / 2g or less in the swelling power test.
This is a numerical value measured according to the former Japan Bentonite Industry Association Standard Test Method (JBAS) “Bentonite (Powder) Swelling Test Method”.

Next, each step of primary injection and secondary injection will be described in detail.
In the primary injection, since the low-viscosity polyvalent cation clay has low swelling and low viscosity, it can be injected as a high concentration mud (A). For example, muddy water can be prepared up to about 65 parts by mass of calcium bentonite, which is a polyvalent ion, per 100 parts by mass of water.
A specific example is the graph shown in FIG. In FIG. 1, calcium-type bentonite (“Kunibond” (registered trademark), manufactured by Kunimine Kogyo Co., Ltd.), which is a polyvalent cation-type clay, and sodium-type bentonite (“Kunigel”, which is a monovalent cation-type clay, are used. (Registered trademark V1; manufactured by Kunimine Kogyo Co., Ltd.) shows the relationship between the concentration at room temperature and the apparent viscosity (cp). To make muddy water with an apparent viscosity of about 45 cp (measured with a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) as measured by a rotary viscometer) with sodium-type bentonite. While the concentration is only about 10%, the concentration can be set to 55% or more in order to obtain a muddy water having the same apparent viscosity with calcium-type bentonite. As described above, the muddy water using the polyvalent cation type clay can have a much lower viscosity and higher concentration than the muddy water using the monovalent cation type clay. In other words, it is possible to send a large amount of clay that is easy to stir together with the underground soil and earth in the ground to a high concentration.
Moreover, since high concentration mud water (A) can be inject | poured, it is not necessary to set it as a large amount of dilution liquid like sodium-type bentonite, the waste mud at the time of construction can be suppressed, and it is excellent in safety and economy.

  The mud water (A) used for the primary injection can be prepared by various methods that can be usually taken. In the specific example shown in FIG. 1, a prescribed amount of bentonite is introduced into a prescribed amount of tap water, and muddy water is prepared using DESPA (700 rpm) (trade name, manufactured by Asada Tekko Co., Ltd.). The apparent viscosity is measured after stirring the mud with a Hamilton Beach mixer (12,000 rpm) for 15 minutes. The apparent viscosity here is measured at room temperature using a Fann Viscometer Model 35SA (trade name, manufactured by Fann Instrument).

The concentration of the muddy water (A) used for the primary injection is preferably 50% or more, and more preferably 55% or more, from the viewpoint of the relationship between the fluidity and the injection amount. If the concentration is too low, the required amount of injection will increase, making it difficult to mix the clay and underground soil. The upper limit of the concentration is not particularly limited as long as it can be produced as muddy water and has fluidity. From the viewpoint of controlling the amount of discharged soil and mud, it is practical to set it to 60% or less.
The apparent viscosity in this case is preferably 60 cp or less, more preferably 55 cp or less, and still more preferably 50 cp or less at room temperature. If it is too high, mixing with earth and sand by machines and devices becomes difficult. The lower limit is not particularly limited as long as it can be handled as muddy water. The apparent viscosity is appropriately determined from the viewpoint of the required amount of clay to be injected, homogeneous mixing property after primary injection, and equipment used.

The injection rate of the muddy water (A) with respect to the ground soil to be injected is preferably 10% to 50%, more preferably 20% to 50%, and still more preferably 20% to 30%. If the injection rate is too low, the required amount of bentonite will be insufficient and the homogeneity will deteriorate, and if it is too high, the amount of soil and mud will be extremely large. Incidentally, the injection rate of the mud (A) here indicates injection capacity ^{(m 3)} with respect to the soil volume 1 m ³ of soil sediment.

Furthermore, the content of the injected clay is preferably 50 kg / m ³ or more, more preferably 60 kg / m ³ or more, and even more preferably 65 kg / m ³ or more with respect to 1 m ³ of the mixed soil of clay and ground soil after primary injection. . If the content is too small, sufficient water shielding and plasticity cannot be obtained. Moreover, there is no upper limit in particular, and it is suitably determined according to the required water-impervious properties and characteristics of the ground soil.

  Thus, since the high concentration mud water (A) is used in the primary injection, a necessary amount of clay can be sent to the ground with a relatively small amount of mud water (A) when injected into the ground. Moreover, the muddy water (A) has an appropriate viscosity and has maintained fluidity for a long time, can be easily injected into the ground soil, and can be efficiently constructed without applying a load during diffusion and mixing. Thereby, the content ratio of the polyvalent cation type clay with respect to the ground soil can be controlled with high accuracy, and the ground soil and the polyvalent cation type clay can be homogeneously mixed. In addition, since there is no injection of clay powder, there is no dust generation and the working environment can be improved.

In the primary injection, the muddy water (A) described above is directly injected to a predetermined depth where it is desired to construct an underground impermeable wall. The “predetermined depth” here means the range of the location where the impermeable wall is constructed, one point at a certain depth from the ground surface, a region from the ground surface to a certain depth, and a certain depth from the ground surface. It is meant to include any region from a point to a certain depth. Moreover, primary injection can be performed with respect to the predetermined volume in the ground so that the water blocking wall precursor and the water blocking wall completed thereafter have a predetermined length and a predetermined thickness at the predetermined depth. For example, it can be performed in accordance with the range of the formation having a coarse grainy sandy content. In that case, any method of injection from one place on the ground surface and injection from a plurality of places may be used.
In this way, the above-described steps can form a water shielding wall precursor with a high concentration and homogeneity of clay.

  In addition, mixing with the said muddy water (A) and underground ground earth and sand can be performed simultaneously with said primary injection | pouring, or after that.

  Next, in the secondary injection, the polyvalent cation type clay is replaced with a monovalent cation exchange clay with an ion exchange agent. At that time, the property of the clay can be changed to a highly water-swellable and plastic material while maintaining homogenization of the clay and the ground soil and sand. That is, through the steps of primary injection and secondary injection, a plastic impermeable wall with flexibility and integrity is built in the ground, in which monovalent cation exchange clay and ground soil and sand are homogeneously mixed. Is done.

  The ion exchange agent is secondarily injected as a liquid (B). This liquid may have any form as long as it can ion-exchange the polyvalent cation in the precursor of the impermeable wall. Examples thereof include various liquid materials such as solutions, mixtures, and slurries. As the medium to be liquefied, those usually used can be employed without any particular limitation, and usually water (tap water, ground water, etc.) is used.

In the secondary injection, the injection rate of the ion exchange agent liquid (B) with respect to the total volume of the ground earth and sand to be injected and the temporarily injected mud water (A) is preferably 5% or more and 25% or less on an external basis. 5% or more and 15% or less are more preferable, and 5% or more and 12% or less are still more preferable. If the implantation rate is too low, the sodium cannot be completely replaced. If the implantation rate is too high, surplus ions are formed and useless. Incidentally, the injection of the ion-exchange agent referred to herein indicates the injection volume (m ³⁾ for the total volume 1 m ³ of the subject of the ground sand and mud (A).

  In addition, for the ion exchange agent liquid (B), the amount of monovalent cations required for completely exchanging the cations of clay in the mud water (A) injected into the monovalent cations to 100 ( The ratio of the ion exchange agent is preferably 100 or more, more preferably 110 or more and 150 or less, and still more preferably 115 or more and 120 or less.

Therefore, the content of the monovalent cation exchange clay in the underground impermeable wall obtained by the method of the present invention is preferably 50 kg / m ³ or more with respect to 1 m ^{3 of the} underground impermeable wall, and 60 kg / m. ³ or more is more preferable, and 65 kg / m ³ or more is still more preferable. If the content is too small, sufficient water shielding and plasticity cannot be obtained. Moreover, there is no upper limit in particular, and it is suitably determined according to the required water-impervious properties and characteristics of the ground soil.

  Mixing of the ion-exchange agent with the ground soil and polyvalent cation-type clay mixture (precursor of the water-impervious wall) can be performed simultaneously with or after the secondary injection.

The underground impervious wall thus obtained is a clay-based impervious impervious wall, which modifies the earth and sand in the ground (particularly, earth and sand having a large amount of grainy sand) and has a permeability coefficient of 1 × 10 ^−9. It can be set to less than m / second, and can have a high level of water shielding compared with the conventional method that does not use the construction method of the present invention. Moreover, as described above, the homogenization at the time of primary injection using the mud water (A) having a high concentration and low viscosity makes the water imperviousness of clay after the secondary injection uniform. The “water permeability coefficient” can be measured according to JIS A 1218: 2009 “Soil permeability test method”.
The permeability coefficient less than 1 × 10 ⁻⁹ m / sec that the underground impermeable wall of the present invention may have is shown in the following Table 1 (edited by the Geotechnical Society Indoor Testing Standards / Standards Committee “Ground Material Testing Method and As described in "Explanation"-2-Volume 1-, Geotechnical Society of Japan, November 25, 2009, page 450 "Part 4-Applicability of water permeability and test method" It is a region of “substantially impervious” and exhibits extremely high impermeability.

  Furthermore, due to the plasticity of the monovalent cation exchange clay that exists uniformly in the ground soil, the entire underground impervious wall is hardly cracked and has earthquake resistance due to ground followability and self-repairability. In addition, since inorganic clay containing no organic material is used, there is no deterioration due to decay. Thus, the underground water-impervious wall obtained is excellent in durability and can maintain high water-impervious properties for a long period of time.

The above characteristics are specifically explained as follows.
That is, the underground water-impervious wall keeps a soft state while maintaining the unity (integration) as a wall over time due to the plasticity and high water swellability of monovalent cation exchange clay. . Further, even after the construction, the high water swellability of the monovalent cation exchange clay stably maintains the integrity and flexibility as the water shielding wall. That is, the plasticity of the impermeable wall can develop over time. Thereby, the underground impervious wall of the present invention has a ground followability (following property) against an underground change due to an external pressure such as an earthquake, and the wall such as a crack is difficult to break. High performance stability.

The degree of plasticity of the underground impermeable walls is indicated by the relationship between soil type, softness and non-shear strength. Table 2 (Geotechnical Society Standard (draft) “In-situ Vane Shear Test Method” JGS1411, “Table B .3 Excerpt from “Vane blade width” (partial excerpt)) is useful for reference.
As the vane shear strength, more preferably 50 kPa (50kN / ^{m 2)} or less, more preferably 20 kPa (20kN / ^{m 2)} or less, still more preferably less than ^{10 kPa (10kN / m 2)} . The lower limit is preferably 0.5 kN / m ² from the viewpoint of the integrity of the underground impermeable wall. The vane shear strength can be measured in accordance with the Geotechnical Society standard (draft) in-situ vane shear test method.

  Moreover, according to the construction method of the underground impermeable wall of the present invention, the depth of the underground to be constructed and the size (width, thickness, depth) of the underground impermeable wall can be arbitrarily determined. Even in this case, it is possible to construct an underground water-impervious wall that maintains a uniform water-impervious property for a long period of time. As a result, the contaminated soil and contaminated water can be enclosed, and the inflow and outflow of groundwater can be effectively blocked over a long period of time.

  In the construction method of the underground impermeable wall according to the present invention, the primary injection method and the secondary injection method, the mixing method, and the machines and devices used in these methods are the normal source for constructing the underground impermeable wall. The method, machine and apparatus used for the position soil agitation method can be employed without any particular limitation.

Next, the clay and ion exchanger used for construction of the underground impermeable wall of the present invention will be described.
The polyvalent cation type clay used in the primary injection can be used without any particular limitation as long as it is suitable for the construction method of the underground impermeable wall of the present invention. In particular, clay having a smectite of a layered silicate mineral is preferable in that it has swelling property or dispersibility in a solvent.
As the smectite, for example, one selected from montmorillonite, beidellite, saponite and the like can be used. Examples of the clay having such a layered silicate mineral include bentonite.

  The dispersion medium used for the preparation of the polyvalent cation clay mud (A) is not particularly limited, and a commonly used one can be employed. For example, water, methanol, ethanol, etc. are mentioned. Usually water (tap water, groundwater, etc.) is used.

  Furthermore, you may use a dispersing agent for preparation of the said muddy water (A). Thereby, a more stable viscosity characteristic is ensured. The dispersant is not particularly limited, and those commonly used can be used regardless of inorganic or organic. Examples include sodium polyacrylate, sodium hexametaphosphate, sodium silicate, sodium pyrophosphate and the like. In particular, sodium polyacrylate is more preferable in terms of stability, mass availability, low cost (economic efficiency), and effects.

  The ion exchange agent used in the secondary implantation can be employed without particular limitation as that used for ion exchange. For example, sodium carbonate, sodium hydrogencarbonate, sodium percarbonate, sodium hydroxide, sodium citrate, sodium silicate and the like can be used as ion exchangers to be substituted with sodium ions. Among these, sodium carbonate is more preferable in terms of cost, safety, and versatility.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these. In the examples, “part” and “%” indicating the composition are based on mass unless otherwise specified.

<Example 1, Comparative Examples 1 and 2>
(1) Preparation of simulated ground A Sandy part: No. 6 silica sand was mixed by 95% by mass and No. 4 silica sand was mixed by 5% by mass.
Clay / silt: “Tochi clay” (trade name, manufactured by Otake Industrial Co., Ltd.) was prepared. The liquid limit of tocicle was 36.0%, the plastic limit was 18.9%, and the plastic index was 17.1. Further, the water content of the Tochi clay was 1.9%.
Next, the sandy content is mixed with 80% by mass of the total amount and the clay / silt content is mixed with 20% by mass of the total amount, and further adjusted to a moisture content of 14.2% (moisture content of 12.4%). 20% simulated soil).
The prepared simulated soil was put in an acrylic cylindrical container to form a simulated ground A having a diameter of 150 mm and a height of 60 mm. This simulated ground A had a wet density of 2.046 g / cm ³ and a dry density of 1.792 g / cm ³ . The wet density and the dry density were measured with a dimensional measurement and a weight scale.

(2) Preparation of mud (A) Calcium-type bentonite (trade name “Kunibond”, registered trademark, manufactured by Kunimine Kogyo Co., Ltd.) and tap water, large-scale DESPA (700 rpm) (trade name, Asada) (Steel Co., Ltd.) and stirred for 15 minutes.

(3) Preparation of ion exchanger liquid (B) An aqueous solution was prepared using sodium carbonate.

(Sample of Example 1)
The muddy water (A) having a concentration of 60% was injected into the earth and sand (anhydrous weight) of the simulated ground A, and the mixture was stirred and mixed to obtain a mixture of the simulated ground A and the muddy water (prelude of the impermeable wall). . The injection rate of muddy water having a concentration of 60% was 92%. As a result, the calcium-type bentonite accounted for 20% by mass with respect to the earth and sand (anhydrous weight) of the simulated ground A. The water content at this time was 32.2%, and the water content ratio was 47.5%. The wet density was 1.736 g / cm ³ and the dry density was 1.177 g / cm ³ . The wet density and the dry density were measured by the same method as the measurement method at the time of preparing the simulated ground described above.
Next, the ion exchange agent aqueous solution (B) was injected at a rate of 10% with respect to the total volume of the muddy water and the simulated ground A, and stirred and mixed. At this time, the water content was 33.3%, and the water content was 49.9%. The wet density was 1.562 g / cm ³ and the dry density was 1.042 g / cm ³ .
In addition, the wet density and dry density at this time were measured by the method similar to the measurement method at the time of the simulation ground preparation mentioned above. Further, the “injection rate” of muddy water indicates the injection capacity (m ³ ) with respect to the soil volume 1 m ³ of the simulated ground A as described above. As described above, the “injection rate” of the ion exchange agent aqueous solution indicates the injection capacity (m ³ ) with respect to the total capacity 1 m ³ of the simulated ground A and mud water.
The sample obtained in this manner was used as the sample of Example 1.

(Sample of Comparative Example 1)
The simulated ground A obtained in (1) was used as a sample of Comparative Example 1.

(Sample of Comparative Example 2)
The sample of Comparative Example 2 that was not subjected to the secondary injection of Example 1 was used.

(Water permeability test (water-impervious test))
About each sample of said Example 1 and the comparative examples 1 and 2, the water permeability test was done at the head water 500cm constant water level using tap water. Each sample was performed three times, and the third measured value was taken as the water permeability coefficient of the sample. The water permeability coefficient was measured according to JIS A 1218: 2009 “Soil permeability test method”.
The results of the water permeability test were as shown in Table 3 below.

As Table 3 shows, in Example 1, the water permeability coefficient was less than 1 × 10 ⁻⁹ m / sec. The water permeability coefficient was two orders of magnitude smaller than those of Comparative Example 1 and Comparative Example 2 on the order of 1 × 10 ⁻⁸ m / sec, indicating a high level of water shielding.

<Example 2>
(1) Production of Simulated Ground B As follows, sand content (coarse grain size) than simulated ground A used in Example 1, Comparative Examples 1 and 2 (hereinafter also referred to as Example 1). ), And a simulated ground B set up with extremely few clays and silts (fine particles) was produced.
Sand content: No. 6 silica sand 50% by mass, No. 4 silica sand 50% by mass were mixed.
Clay / silt: “Tochi clay” (trade name, manufactured by Otake Industrial Co., Ltd.) was prepared. The liquid limit of tocicle was 36.0%, the plastic limit was 18.9%, and the plastic index was 17.1. Further, the water content of the Tochi clay was 1.9%.
Next, the sandy content is mixed with 95% by mass of the total amount and the viscosity / silt content is mixed with 5% by mass of the total amount, and further adjusted to a water content ratio of 9.9% (water content 9.0%) to simulate soil ( 5% simulated soil). The water permeability coefficient of the sample produced in the same manner as Example 1 except for the above conditions was 6.43 × 10 ⁻⁵ m / sec.
(2) Preparation of Muddy Water (A) and Ion Exchanger Liquid (B) Prepared in the same manner as Example 1 and the like.

(Sample of Example 2)
The muddy water (A) having a concentration of 60% was injected into the soil of the simulated ground B, and the mixture was stirred and mixed to obtain a mixture of the simulated ground B and the muddy water (an impervious wall precursor). The injection rate of muddy water having a concentration of 60% was 40%. The water content at this time was 20.9%, and the water content ratio was 24.6%. The wet density was 1.536 g / cm ³ and the dry density was 1.383 g / cm ³ .
Next, the ion exchange agent aqueous solution (B) was injected at an injection rate of 10% with respect to the total volume of the muddy water and the simulated ground B, and stirred and mixed. The water content at this time was 24.6%, and the water content ratio was 32.6%. The wet density was 1.891 g / cm ³ and the dry density was 1.426 g / cm ³ .
In Example 2, injection, stirring / mixing, wet density and dry density were measured by the same method as in Example 1 and the like.
The sample obtained in this manner was used as the sample of Example 2.

(Water permeability test (water-impervious test))
The produced sample of Example 2 was subjected to a water permeability test (water-impervious test) in the same manner as in Example 1, and the third measured value was taken as the water permeability coefficient of the sample. The results were as shown in Table 4 below.

  As shown in Table 4, in the sample of Example 2, the simulated ground B did not change even though the sandy part of coarser grain size was larger than the simulated ground A used in Example 1 etc. It was a value that was two orders of magnitude smaller than the hydraulic conductivity of 1 and 2, and showed a high level of water shielding.

<Examples 3 to 7>
Example 1 except that the simulated ground A used in Example 1 was subjected to primary injection by changing the injection rate of mud water (A) having a concentration of 60% used in Example 1 as shown in Table 5 below. Similarly, each sample of Examples 3 to 7 was produced. The injection rate of the ion exchange aqueous solution (B) in the secondary injection was fixed at 10%.
However, at the time of secondary injection, the calcium-type bentonite is contained so that 1.5 times the amount of ion-exchange agent is added to the “equivalent amount necessary for replacing calcium ions in calcium-type bentonite with sodium ions”. Depending on the amount, the concentration of the aqueous ion exchanger solution was changed as shown in Table 5 below.

(Water permeability test (water-impervious test))
About the produced sample of Examples 3-7, the water-permeation test (water-imperviousness test) was performed like Example 1, and the measured value of the 3rd time was made into the water-permeability coefficient of the sample. The results were as shown in Table 5 below. Moreover, when the relationship between this measured value and bentonite content is shown in a graph, it is as shown in FIG.

As Table 5 shows, in Examples 3-7, the water-permeability coefficient was one or two orders of magnitude smaller than that of Comparative Examples 1 and 2 described above, indicating a high level of water shielding. In particular, as can be seen from Table 5 and FIG. 2, it is found that the content of the primary injected calcium type bentonite is 60 kg / m ³ or more and that all is replaced with sodium type bentonite, thereby showing extremely high water shielding properties. It was.

<Examples 8 to 12>
For the simulated ground A used in Example 1, the injection rate of mud water (A) having a concentration of 60% used in Example 1 is fixed at 30%, and primary injection is performed, and ion exchange agent (sodium carbonate) is injected. Samples of Examples 8 to 12 were prepared in the same manner as in Example 1 except that the amount was changed as shown in Table 6 and secondary injection was performed. However, the injection amount of the ion exchanger was adjusted by fixing the injection rate of the ion exchanger aqueous solution (B) at 10% and changing the concentration.

(Water permeability test (water-impervious test))
About the produced sample of Examples 8-12, the water-permeation test (water-imperviousness test) was performed like Example 1, and the measured value of the 3rd time was made into the water-permeability coefficient of the sample. The results were as shown in Table 6 below.

As Table 6 shows, in Examples 8-12, the water-permeability coefficient was lower than Comparative Examples 1 and 2 described above, indicating high water shielding. In particular, for a calcium type bentonite content of 69.3 kg / m ³ , 75 or more equivalent injections of sodium carbonate required for ion exchange, that is, an ion exchange rate of 75% or more (about 51.9 kg / m ³ or more It was found that calcium-type bentonite was replaced with sodium-type bentonite), which showed extremely high water and water barrier properties.

<Examples 13 to 17>
(Plasticization test)
About Examples 13-16, the sample similar to said Examples 8-11 was prepared.
Moreover, as a sample of Example 17, a dispersant “KS flow” (trade name, manufactured by Kunimine Kogyo Co., Ltd.) was added to the muddy water at an addition rate of 0.75%, and the same as Example 12 was carried out. Made.
About the produced Examples 13-17, the measurement test of vane shear strength was done immediately after preparation, 90 minutes, 2 hours, 4 hours, and 24 hours later. The vane shear strength was measured in accordance with the Geotechnical Society Standard (draft) in-situ vane shear test method.
The results were as shown in Table 7 below.

As Table 7 shows, the samples of Examples 13 to 17 were slowly developed (developed) slowly after the secondary injection mixture was prepared, and values lower than 50 kN / m ² after 24 hours. It was stable in an equilibrium state. As a result, the underground water-impervious wall obtained from each sample was a flexible plastic body while maintaining unity. The temporary decrease in vane shear strength immediately after the preparation of the secondary injection mixture is due to the water content of the sodium carbonate aqueous solution. By subsequent ion exchange, the value of the vane shear strength is gradually increased by the action of sodium exchange clay. Seems to have risen.

<Examples 18 to 24>
(Plasticization test)
As a sample of Examples 18 and 19, Example 10 was carried out except that a dispersant “AK Flow” (trade name, manufactured by TG Corporation) was added to the muddy water at an addition rate of 1.0% and the primary injection was performed. And 12, respectively.
Samples of Examples 20 and 21 were prepared in the same manner as in Examples 10 and 12, respectively, except that the addition rate of the dispersant “AK flow” was 1.2%.
As samples of Examples 22 to 24, samples were prepared in the same manner as in Examples 10 to 12 except that the dispersant “KS flow” was added to the muddy water at an addition rate of 0.85% and the primary injection was performed.
About the produced Examples 18-24, the measurement test of the said vane shear strength was done immediately after preparation, 90 minutes, 2 hours, and 24 hours after.
The results were as shown in Table 8 below.

As Table 8 shows, the samples of Examples 18 to 24 were slowly developed (developed) after the secondary injection mixture was prepared, and values lower than 50 kN / m ² after 24 hours. It was stable in an equilibrium state. As a result, the underground water-impervious wall obtained from each sample was a flexible plastic body while maintaining unity. The temporary decrease in vane shear strength immediately after the preparation of the secondary injection mixture is due to the water content of the sodium carbonate aqueous solution. By subsequent ion exchange, the value of the vane shear strength is gradually increased by the action of sodium exchange clay. Seems to have risen.
In addition, by selecting the type of dispersant used in the muddy water, the fluidity of the muddy water can be adjusted, and the ease of mixing by the machine and device before and after the secondary injection can be controlled. I understood.

Claims (7)

  A clay muddy water (A) mainly composed of a layered silicate mineral having a multivalent cation between layers is injected to a predetermined depth of the ground soil and mixed with the ground soil and the precursor of the impermeable wall is obtained. And forming an underground impermeable wall by injecting a liquid (B) of an ion exchange agent for exchanging the polyvalent cation with a monovalent cation and mixing with the precursor of the impermeable wall A method for constructing an underground impermeable wall.   The method for constructing an underground impermeable wall according to claim 1, wherein the polyvalent cation is a calcium ion.   The construction method of an underground impermeable wall according to claim 1 or 2, wherein the monovalent cation is a sodium ion.   The construction method of the underground impermeable wall according to any one of claims 1 to 3, wherein the clay concentration in the muddy water (A) is 50% or more.   The construction method of the underground impermeable wall according to any one of claims 1 to 4, wherein an injection rate of the muddy water (A) to the ground soil is 10% or more and 50% or less.   The ground according to any one of claims 1 to 5, wherein an injection rate of the liquid (B) of the ion exchange agent is 5% or more and 25% or less with respect to the mixture of the ground soil and the muddy water (A). Construction method of middle impermeable wall. The content of clay mainly composed of a layered silicate mineral having a monovalent cation between layers obtained by injecting the liquid (A) of the ion exchanger to the underground impermeable wall 1m ^{3 is} as follows. It is 50 kg / m < ³ > or more, The construction method of the underground impermeable wall of any one of Claims 1-6 .

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