JP2022036294A - Underground impervious water wall and underground impervious water wall construction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an underground impervious water wall realizing both of enough impervious performance and deformation followability, and an underground impervious water wall construction method allowing quality stability of the underground impervious water wall to be kept and environmental load to be suppressed under construction.

SOLUTION: An underground impervious water wall of the present invention is an underground impervious water wall constructed in the ground through solidification of soil cement produced by mixing and stirring cement milk with solidification material including hydrogen carbonate. An area of a region in which there is C-S-H gel in a cross section of the soil cement after the solidification is 15% or more of the total area of the cross section.

SELECTED DRAWING: Figure 5

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to an underground impermeable wall and a method for constructing an underground impermeable wall.

There is a method of constructing a continuous impermeable wall in the ground for the purpose of adjusting the groundwater level, containing contaminated water and contaminated soil, and preventing water leakage from the embankment and the regulating pond.

In particular, the groundwater level lowering method has been adopted as a measure against liquefaction caused by earthquakes. In the groundwater level lowering method, a continuous impermeable wall is constructed in the ground around the area where liquefaction measures are taken in the ground, and then the groundwater level in the ground surrounded by the continuous impermeable wall using a well or the like. To reduce.

As a method for constructing such a continuous impermeable wall in the ground, a slurry using a cement-based solidifying material or a cement / bentonite slurry as shown in Patent Document 1 is injected into the ground and stirred and mixed to continuously shield the slurry. There is a way to build a water wall underground. Further, as shown in Patent Document 2, there is a method of constructing an underground impermeable wall by bentonite without using a cement-based solidifying material.

JP-A-2015-172319 Japanese Unexamined Patent Publication No. 2006-291703

The underground impermeable wall made of the slurry using the cement-based solidifying material of Patent Document 1 or the cement / bentonite slurry is vulnerable to bending and tension, and has extremely low flexibility. In addition, it is difficult to adjust the required amount of cement-based solidifying material and cement / bentonite, and there is also a problem that the quality of the underground impermeable wall is not stable. There is also the problem that a large amount of water is required to knead the slurry in the ground.

The underground impermeable wall made of bentonite of Patent Document 2 has a problem that the viscosity development and the water swelling property are poor and sufficient impermeable performance may not be obtained. There is also a problem that it is difficult to adjust the required amount of bentonite and the quality of the underground impermeable wall is not stable. In addition, there is a problem that a large amount of soil is discharged.

Therefore, from the above points, the present invention stabilizes the quality of the underground impermeable wall and the underground impermeable wall that achieve both sufficient impermeable performance and deformation followability, and suppresses the environmental load by construction. The purpose is to provide a method for constructing an underground impermeable wall that can be constructed.

The underground impermeable wall according to claim 1 is an underground impermeable wall constructed in the ground by solidifying soil cement obtained by mixing and stirring cement milk containing a solidifying material containing hydrogen carbonate and ground earth and sand. As an average of the values in all cross sections of the solidified soil cement, the area of the region where the CSH gel is present is 15% or more of the area of the entire cross section.

According to the underground impermeable wall of claim 1, the area of the region where the CSH gel is present is 15% or more of the area of the entire cross section as an average of the values in all the cross sections of the solidified soil cement. As a result, the CSH gel existing in the underground impermeable wall can make the impermeable coefficient of the underground impermeable wall virtually impermeable, and sufficient impermeable performance can be realized. .. Further, in the cross section of the solidified soil cement, the area of the region where the CSH gel exists is 15% or more of the area of the entire cross section, so that the C present in the underground impermeable wall -The SH gel makes the fracture strain 2% or more, the flexibility of the impermeable wall is obtained, and sufficient deformation follow-up performance and self-repairing performance can be realized.

The method for constructing an underground impermeable wall according to claim 1 is to construct the impermeable wall according to claim 1 by mixing and stirring cement milk containing a solidifying material containing hydrogen carbonate and ground earth and sand in the ground. ..

According to the method for constructing an underground impermeable wall according to claim 2, a hydrogen carbonate whose required amount can be easily adjusted is used. Therefore, it is possible to construct an underground impermeable wall with stable quality. Further, since the solidifying material containing cement milk and bicarbonate and the ground soil are mixed and agitated in the ground, the amount of soil discharged can be suppressed and an impermeable wall can be constructed in the ground.

The method for constructing an underground impermeable wall according to claim 3 is the method for constructing an underground impermeable wall according to claim 2, wherein the hydrogen carbonate is baking soda.

The method for constructing an underground impermeable wall according to claim 3 operates in the same manner as the method for constructing an underground impermeable wall according to claim 2, and even if the baking soda is injected into the ground, it causes harm to animals and plants including humans. Since it is a substance that is clearly not afraid, it is possible to improve the safety of construction.

The method for constructing an underground impermeable wall according to claim 4 is the method for constructing an underground impermeable wall according to claim 2 or 3, after excavating the ground earth and sand in the ground with muddy water, and then using cement milk containing a solidifying material containing hydrogen carbonate. While injecting, mix and stir with the ground earth and sand in the ground to solidify.

The method for constructing an underground impermeable wall according to claim 7 operates in the same manner as the method for constructing an underground impermeable wall according to claim 5 or 6, and also contains hydrogen carbonate after excavating the ground soil in the ground with muddy water. By injecting cement milk containing a solidifying material and mixing and stirring it with the ground soil in the ground to solidify it, it is possible to efficiently mix the ground soil and the solidifying material while suppressing the amount of soil discharged.

The underground impermeable wall according to claim 1 can achieve both sufficient impermeable performance, deformation followability, and self-repairing property. Further, in the method of constructing the underground impermeable wall according to claims 2 to 4, the quality of the underground impermeable wall is stable, and the environmental load can be suppressed by constructing the underground impermeable wall.

It is a stereomicrograph of a fracture surface of a soil cement test piece made of cement milk not mixed with baking soda. It is a stereomicroscopic observation photograph of a fracture surface of a test piece of soil cement made of cement milk mixed with baking soda. It is a secondary electron image of a scanning electron microscope of a test piece of soil cement made of cement milk not mixed with baking soda. It is a secondary electron image of a scanning electron microscope of a test piece of soil cement made of cement milk mixed with baking soda. It is a perspective view of the underground impermeable wall of one Embodiment of this invention. It is sectional drawing which shows the construction of the columnar body which constitutes the underground impermeable wall of FIG.

1.1 Experiment of solidified soil cement specimen A test was conducted for the purpose of confirming that the underground impermeable wall of the present invention has both sufficient impermeable performance, deformation followability and self-repairing property. ..

1.2 Materials of the specimen As shown in Examination Examples 1 to 4 in Table 1 to be described later, the specimen is a mixture of bicarbonate, baking soda, clay, cement and water in the "standard sand" of the ground soil. They were prepared by mixing them under different conditions. As a specimen for comparison, as shown in Comparative Examples 1 and 2 in Table 1 described later, it was prepared by mixing clay, cement and water with "standard sand".
"Standard sand" is a pure natural silica sand that is produced only in limited places even in the Toyoura area of Yamaguchi prefecture. Compared to crushed artificial sand, the nature of natural sand has a shape that exists in nature, so the grains are rounded, and due to that nature, errors that occur in experiments and measurements are reduced and stable. It is a silica sand that can produce results.
Furthermore, as shown in Examination Examples 6 to 10 in Table 2 to be described later, hydrogen carbonate is added to the “Kumamoto City Ward Site Soil (hereinafter referred to as Kumamoto Sand”) where liquefaction actually occurred after the earthquake as the ground soil. It was prepared by mixing the salts of baking soda, clay, cement, and water under different compounding conditions. As a specimen for comparison, as shown in Comparative Example 3 in Table 2 described later, it was prepared by mixing clay, cement and water with "standard sand".
"Kumamoto sand" was collected at the liquefied in-situ in Kumamoto city. Kumamoto sand had a high water content of about 40% and the soil saturation exceeded 100%, so the water content was adjusted to 20% before use.

1.3 Preparation of specimen (1) Put 300 g of tap water in a beaker with a dose of 3000 ml and install it in the disper.
(2) Rotate the mixer at 700 rpm, add an amount of cement that matches the compounding conditions of each study example, and stir for 3 minutes.
(3) In the specimen of the study example, baking soda and clay, which are hydrogen carbonates in an amount suitable for the compounding conditions of each study example, are added to (2) above, and the mixture is stirred for 5 minutes to prepare a solidifying agent. In the specimen of the comparative example, only the amount of clay corresponding to the compounding conditions of each comparative example is added to (2) above, and after stirring for 5 minutes, a solidifying agent is prepared.
(4) Add the solidifying agent of each of the study examples and comparative examples of (3) above to 700 g of standard sand or Kumamoto sand.
(5) Stir with a mortar mixer for 5 minutes to prepare soil cement before solidification by mixing and stirring cement milk containing a solidifying material and ground earth and sand.
(6) Soil cement obtained by mixing and stirring the cement milk containing the solidifying material of (5) above and the ground earth and sand is filled in a hydraulic conductivity test mold to prepare specimens for hydraulic conductivity of each study example and each comparative example. do.
(7) Soil cement obtained by mixing and stirring the solidifying material containing cement milk and bicarbonate of (5) above and the ground earth and sand is put into a uniaxial compression test mold and placed in a constant temperature bath at 20 ° C ± 0.5 ° C for a predetermined period. After curing, specimens for uniaxial compression test of each study example and each comparative example are prepared.

1.4 Permeability test (variable water level method JIS A1218 / JGS 0311)
In the permeability test, the permeability coefficient was measured using the test method of JIS A 1218 / JGS 0311, which is a variable water level method used for cohesive soil and silty soil with relatively low permeability. The target value of the hydraulic conductivity that can achieve sufficient impermeable performance in the underground impermeable wall is set to 10 ^-7 cm / sec or less.

1.5 Uniaxial compression test (JIS A1216 / JGS 0511)
The uniaxial compression test is to determine the uniaxial compressive strength and fracture strain of a cohesive soil specimen. The test was carried out using a uniaxial compressive strength machine with a curing period of 7 days for specimens mixed with a plurality of compounding patterns. In order to ensure safety against unbalanced earth pressure due to the groundwater level lowering method, the target value of sufficient strength in the underground impermeable wall was set to 100 kN / m ² or more. In addition, the target value of fracture strain was set to 2% or more in order to realize deformation followability and self-repairing property in the underground impermeable wall.

2.1 Experiment of soil cement specimen before solidification In addition, when constructing the underground impermeable wall of the present invention, it is sufficient to mix and stir the solidifying material containing cement milk and bicarbonate and the ground earth and sand. An experiment was also conducted to confirm the fluidity. This experiment will be described below.

2.2 Materials of the specimen The specimen is made of standard sand, as in the test for the purpose of confirming that the underground impermeable wall has both sufficient impermeable performance, deformation followability and self-repairing property. Examples 1 to 5, Comparative Examples 1 to 3 of standard sand, and Examples 6 to 11 of Kumamoto sand.

2.3 Preparation of specimen (1) Put 300 g of tap water in a beaker with a dose of 3000 ml and install it in the disper.
(2) Rotate the mixer at 700 rpm, add an amount of cement that matches the compounding conditions of each study example, and stir for 3 minutes.
(3) In the specimen of the study example, baking soda and clay, which are hydrogen carbonates in an amount suitable for the compounding conditions of each study example, are added to (2) above, and the mixture is stirred for 5 minutes to prepare a solidifying agent. In the specimen of the comparative example, only the amount of clay corresponding to the compounding conditions of each comparative example is added to (2) above, and after stirring for 5 minutes, a solidifying agent is prepared.
(4) Add the solidifying agent of each of the study examples and comparative examples of (3) above to 700 g of standard sand or Kumamoto sand.
(5) Stir with a mortar mixer for 5 minutes, and mix and stir the cement milk containing the solidifying material and the ground earth and sand to prepare a specimen for the flow test of the soil cement before solidification.

2.4 Flow test (JIS A313)
The flow test confirmed the fluidity of soil cement specimens mixed in multiple compounding patterns before solidification. The target value of the flow value is 15 cm so that the soil cement before solidification can be filled in a predetermined position while suppressing the unnecessary diffusion of the soil cement before solidification during the construction of the underground impermeable wall. That's all.

3. 3. Test results Table 1 below shows the results of the compounding conditions, water permeability test, uniaxial compression test and flow test of each study example and each comparative example using standard sand.

Among the study examples and comparative examples of standard sand, study example 4 and study example 5 of standard sand have a target value of water permeability coefficient of 10 ^-7 cm / sec or less, a target value of strength of 100 kN / m ² or more, and fracture strain. The target value of 2% or more and the target value of 15 cm or more of the flow value are all satisfied.

Therefore, by using the "standard sand" of the ground earth and sand, baking soda, which is a hydrogen carbonate, clay, cement, and water as appropriate compounding conditions, the underground impermeable wall can have sufficient impermeable performance and deformation followability. Can be compatible with self-healing

In Comparative Example 1 and Comparative Example 2, the target value of the fracture strain cannot be satisfied due to the increase in the amount of cement.

In Study Example 4 and Study Example 5 of standard sand, the target values of hydraulic conductivity, strength, fracture strain and flow value can be satisfied with a smaller amount of cement as compared with Comparative Example 1 and Comparative Example 2. Therefore, by setting appropriate compounding conditions for "standard sand" of ground soil, baking soda, which is a hydrogen carbonate, clay, cement, and water, the underground impermeable wall can suppress the amount of cement used. Economic efficiency can be improved and the environmental load can be suppressed.

Table 2 below shows the compounding conditions, water permeability test, uniaxial compression test, and flow test of each study example and comparative example in Kumamoto sand.

In Kumamoto sand study example 9 and study example 10, the target value of water permeability coefficient is 10 ^-7 cm / sec or less, the target value of strength is 100 kN / m ² or more, the target value of fracture strain is 2% or more, and the target of flow value. Satisfy all values above 15 cm. In Comparative Example 3 and Examination Examples 6 to 8 of Kumamoto sand, the specimens did not stand on their own and naturally did not meet the target value of strength.

Therefore, by using "Kumamoto sand", which is the ground earth and sand, baking soda, which is a hydrogen carbonate, clay, cement, and water as appropriate compounding conditions, the underground impermeable wall can have sufficient impermeable performance and deformation followability. It is possible to achieve both self-healing properties.

The mechanism by which the formation of CSH gel is promoted by mixing baking soda, which is a hydrogen carbonate, in cement milk will be described below.

The chemical reaction between 3CaO · SiO ₂ which is a cement composition and water is as follows.

2CaO · SiO ₂ · 1.17H ₂ O in Chemical Formula 1 is a hydrate of CSH gel.

In addition, when baking soda is mixed with cement milk, a hydrolysis reaction occurs between the baking soda and water.

The sodium ion generated by the hydrolysis reaction of Chemical Formula ₂ promotes the formation of 2CaO · SiO 2.1.17H _2O C—SH gel in Chemical Formula 1.

FIG. 1 shows a stereomicroscopic photograph of a fracture surface of a soil cement test piece made of cement milk not mixed with baking soda. FIG. 2 shows a stereomicroscopic photograph of a fracture surface of a soil cement test piece made of cement milk mixed with baking soda.

A large number of dark white granular dots can be seen on each fracture surface. This dark white granular point is the CSH gel. The ratio of the area of the area of the CSH gel in each fracture surface to the area of the entire fracture surface is about 10% in the test piece of soil cement made of cement milk not mixed with baking soda, and is mixed with baking soda. It is about 15% in the test piece of soil cement consisting of cement milk.

The CSH gel is porous and absorbs water to expand. The CSH gel that has absorbed water to the limit and expanded is impermeable to water. Therefore, the larger the amount of CSH gel in the underground impermeable wall, the better the impermeable performance can be.

Further, when the CSH gel absorbs water and expands, the voids inside the underground impermeable wall are filled, and the self-repairing performance of the underground impermeable wall can be obtained.

In a soil cement test piece made of cement milk not mixed with baking soda, the fracture surface was visually observed, and an observation sample was taken from the place where the CSH gel, which is a white product, could be confirmed. The collected sample is fixed to the sample table so that the observation surface faces up, and in order to have conductivity, gold is vapor-deposited on the surface with an ion sputtering device, and then a scanning electron microscope is used to show FIG. A secondary electron image was obtained in which the end structure of the shown CSH gel could be observed.

Similarly, in the test piece of soil cement made of cement milk mixed with baking soda, a secondary electron image was obtained in which the end structure of the CSH gel shown in FIG. 4 could be observed.

In FIG. 3, the end of the CSH gel of soil cement made of cement milk not mixed with baking soda has a shape in which a large number of fine needles are projected. On the other hand, in FIG. 4, the fine needles at the ends of the CSH gel of the soil cement made of cement milk mixed with baking soda are thicker than those in FIG.

Hereinafter, the construction of the underground impermeable wall 1 of the present invention will be described.

As shown in FIG. 5, the underground impermeable wall 1 of the present invention has a structure in which a plurality of columnar bodies 10 having an impermeable performance are connected in the ground. The plurality of columnar bodies 10 are arranged in a lap.

The construction of the columnar body 10 will be described with reference to FIG. The construction machine used in the construction of the underground impermeable wall of the present invention includes a rod 2 that is supported up and down and rotatably, and a stirring head 3 that is provided under the rod and rotates integrally with the rod 2. Has.

As shown in FIG. 6A, the rotation axis of the rod 2 is set at the pile core position of the columnar body. Then, as shown in FIGS. 6 (b) to 6 (c), the rod 2 is rotated and lowered while injecting muddy water from the stirring head 3, so that the ground sediment and muddy water are reached until the stirring head 3 reaches a predetermined depth. To stir. Next, as shown in FIGS. 6 (d) to 6 (e), the stirring head 3 further stirs the ground soil and muddy water by rotating and raising the rod 2.

Next, as shown in FIGS. 6 (f) to 6 (g), the stirring head 3 is predetermined by rotating and lowering the rod 2 while injecting cement milk containing a solidifying material containing a hydrogen carbonate from the stirring head 3. Stir the cement milk with bicarbonate containing bicarbonate and the ground sediment and muddy water until the depth is reached. Next, as shown in FIGS. 6 (h) to 6 (i), the stirring head 3 further stirs the ground soil and muddy water by rotating and raising the rod 2.

As shown in FIG. 6 (j), when the region where the cement milk containing the solidifying material containing hydrogen carbonate, the ground earth and sand, and the muddy water are agitated is solidified, the columnar body 10 constituting the underground impermeable wall 1 is formed. To.

After the muddy water injection agitation work of FIGS. 6 (a) to 6 (e) is performed at the predetermined plurality of pile core positions, the cement milk injection agitation work of FIGS. 6 (e) to 6 (i) is performed to solidify. , A plurality of columnar bodies 10 are connected in a wall shape, and an underground impermeable wall 1 is constructed. By constructing an underground impermeable wall in which a plurality of columnar bodies 10 having impermeable performance are connected in the ground in the ground around the area for liquefaction countermeasures, the groundwater level can be lowered. The effect can be eliminated.

In the implementation of the present invention, since the underground impermeable wall can be constructed with a relatively small excavation heavy machine, noise and vibration can be suppressed, and the underground impermeable wall in a narrow road or a densely populated residential area can be constructed. Can be built.

Further, in FIG. 6, the case of creating a single columnar body has been described, but the present invention is not limited to this. For example, a plurality of columnar bodies may be created at the same time. Further, a columnar body may be created by a trencher type heavy machine.

1 Underground impermeable wall 2 Rod 3 Stirring head 10 Columnar body

Claims (2)

It is an underground impermeable wall built in the ground by solidifying soil cement that is a mixture of cement milk containing a solidifying material containing bicarbonate and ground earth and sand and stirring.
An underground impermeable wall characterized in that the area of the region where the CSH gel is present is 15% or more of the area of the entire cross section as an average of the values in all the cross sections of the solidified soil cement. The method for constructing an underground impermeable wall according to claim 1, wherein cement milk containing a solidifying material containing a hydrogen carbonate and ground earth and sand are mixed and stirred in the ground to be solidified.

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