JP7169666B2 - Underground impermeable wall and underground impermeable wall construction method - Google Patents

Description

The present invention relates to an underground impermeable wall and an underground impermeable wall construction method.

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 body and regulating pond.

In particular, as a countermeasure against liquefaction caused by earthquakes, the groundwater level lowering construction method is adopted. In the groundwater level lowering method, a continuous impermeable wall is built in the ground around the area where liquefaction countermeasures are to be taken, and then the underground water level surrounded by the continuous impermeable wall is lowered using a well, etc. lower the

As a method for constructing 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 poured into the ground and stirred and mixed to continuously impermeable walls. There is a method of building a wall of water in the ground. Furthermore, there is a method of constructing an underground impermeable wall with bentonite without using a cement-based solidifying material, as shown in Patent Document 2.

JP 2015-172319 A Japanese Patent Application Laid-Open No. 2006-291703

The underground impermeable wall made of the slurry using the cement-based solidifying material or the cement-bentonite slurry of Patent Document 1 is weak against bending and tension, and has extremely low flexibility. Another problem is that it is difficult to adjust the required amount of cement-based solidifying material and cement-bentonite, and the quality of the underground impermeable wall is not stable. Another problem is that a large amount of water is required to knead the slurry underground.

The underground impermeable wall made of bentonite in Patent Literature 2 has a problem that it is poor in viscosity development and water swelling, and sufficient impermeable performance may not be obtained. Another problem is that it is difficult to adjust the necessary amount of bentonite, and the quality of the underground impermeable wall is unstable. Moreover, there is a problem that a large amount of soil is generated.

Therefore, from the above points, the present invention provides an underground impermeable wall that achieves both sufficient impervious performance and deformation followability, and that the quality of the underground impermeable wall is stable and the environmental load is suppressed during construction. It is an object of the present invention to provide a method for constructing an underground impermeable wall.

The underground impermeable wall of claim 1 is an underground impermeable wall constructed in the ground by solidifying soil cement obtained by mixing and agitating cement milk containing a solidifying agent containing hydrogen carbonate and ground earth and sand. , as the average of the values in all cross sections of the soil cement after solidification, the area of the region where the C—S—H 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 C—S—H gel exists is 15% or more of the area of the entire cross section as the average of the values in all cross sections of the solidified soil cement. As a result, the impermeable coefficient of the underground impermeable wall can be effectively impermeable due to the CSH gel present in the underground impermeable wall, and sufficient impermeable performance can be achieved. . In addition, in the cross section of the soil cement after solidification, 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 has a breaking strain of 2% or more, provides the water impermeable wall with flexibility, and achieves sufficient deformation following performance and self-healing performance.

In the underground impermeable wall construction method of claim 2 , the impermeable wall of claim 1 is constructed by mixing and stirring cement milk containing a solidifying agent containing bicarbonate and ground soil and sand in the ground and solidifying them. .

According to the underground impermeable wall constructing method of claim 2 , the hydrogen carbonate is used because the required amount can be easily adjusted. Therefore, an underground impermeable wall with stable quality can be constructed. In addition, since the solidification material containing cement milk and hydrogen carbonate and the soil and sand are mixed and stirred in the ground, the amount of discharged soil can be suppressed and the 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 sodium bicarbonate .

The method for constructing an underground impermeable wall according to claim 3 works in the same manner as the method for constructing an underground impermeable wall according to claim 2. In addition, even if sodium bicarbonate is injected into the ground, it harms animals and plants including humans. Since it is a material that is clearly fearless, construction safety can be improved.

In the method for constructing an underground impermeable wall according to claim 4 , in the method for constructing an underground impermeable wall according to claim 2 or 3 , cement milk containing a solidifying agent containing hydrogen carbonate is added after muddy excavation of ground soil and sand in the ground. While injecting, it is mixed and stirred with the soil and sand in the ground and solidified.

The method for constructing an underground impermeable wall according to claim 7 functions in the same manner as the method for constructing an underground impermeable wall according to claim 5 or 6, and in addition, after mud excavation of ground soil in the ground, the method contains hydrogen carbonate. While injecting the cement milk containing the solidifying agent, it is mixed with the soil and solidified in the ground to be solidified, so that the amount of discharged soil can be suppressed and the soil and the solidifying agent can be efficiently mixed.

The underground impermeable wall of claim 1 can achieve both sufficient impermeable performance, deformation followability, and self-repairability. In addition, the underground impermeable wall construction method according to claims 2 to 4 stabilizes the quality of the underground impermeable wall and can reduce the environmental load during construction.

1 is a stereomicroscopic photograph of a fracture surface of a test piece of soil cement made of cement milk not mixed with sodium bicarbonate. 1 is a photograph of a fractured surface of a soil cement test piece made of cement milk mixed with sodium bicarbonate and observed with a stereoscopic microscope. 2 is a scanning electron microscope secondary electron image of a specimen of soil cement made of cement milk without sodium bicarbonate. 2 is a scanning electron microscope secondary electron image of a specimen of soil cement made of cement milk mixed with baking soda. 1 is a perspective view of an underground impermeable wall according to one embodiment of the present invention; FIG. FIG. 6 is a cross-sectional view showing construction of a columnar body that constitutes the underground impermeable wall of FIG. 5 ;

1.1 Test of solidified soil cement test specimen A test was conducted to confirm that the underground impermeable wall of the present invention has sufficient impervious performance, deformation followability, and self-repairability. .

1.2 Specimen material As shown in Examination Examples 1 to 4 in Table 1 below, the specimen is a mixture of bicarbonate of sodium bicarbonate, clay, cement, and water in "standard sand" of ground soil. They were prepared by mixing under different conditions. As comparative specimens, as shown in Comparative Examples 1 and 2 in Table 1, which will be described later, clay, cement and water were mixed with "standard sand".
"Standard sand" is a pure natural silica sand produced only in limited areas in the Toyoura area of Yamaguchi Prefecture. Compared to pulverized artificial sand, natural sand has a shape that exists in nature, so the grains are round. It is silica sand that can get results.
Furthermore, as shown in Examination Examples 6 to 10 in Table 2, which will be described later, hydrogen carbonate Baking soda, which is a salt, clay, cement, and water were mixed under different mixing conditions. As a test piece for comparison, as shown in Comparative Example 3 in Table 2, which will be described later, clay, cement, and water were mixed with "standard sand".
"Kumamoto sand" was collected at the liquefied in situ location in Kumamoto City. Kumamoto sand has a high water content of about 40% and the saturation of the soil exceeded 100%, so it was adjusted to a water content of 20% and used.

1.3 Preparation of test piece (1) Put 300g of tap water into a 3000ml beaker and set it in a disper.
(2) Rotate the mixer at 700 rpm, add cement in an amount that matches the blending conditions of each study example, and stir for 3 minutes.
(3) For the specimens of the study examples, sodium bicarbonate, which is a hydrogen carbonate, and clay are added to the above (2) in amounts that match the mixing conditions of each study example, and after stirring for 5 minutes, a solidifying agent is prepared. For the specimens of the comparative examples, only clay in an amount matching the blending conditions of each comparative example was added to the above (2), and after stirring for 5 minutes, a solidifying agent was prepared.
(4) To 700 g of standard sand or Kumamoto sand, add the solidifying agent of each study example and each comparative example in (3) above.
(5) Stir with a mortar mixer for 5 minutes to prepare soil cement before solidification by mixing and stirring cement milk containing a solidifying agent and ground soil.
(6) The soil cement obtained by mixing and stirring the cement milk containing the solidifying agent in (5) above and the ground soil is filled into a variable water level permeability test mold to prepare a specimen for the permeability test of each study example and each comparative example. do.
(7) The soil cement obtained by mixing and stirring the solidifying material containing cement milk and bicarbonate in (5) above and ground soil is put into a mold for uniaxial compression test and placed in a constant temperature bath at 20°C ± 0.5°C for a predetermined period. After curing, specimens for the uniaxial compression test of each study example and each comparative example are produced.

1.4 Permeability test (fluctuation water level method JIS A1218/JGS 0311)
In the permeability test, the permeability coefficient was measured using the test method of JIS A1218/JGS 0311, which is a changing water level method used for clayey soil and silty soil with relatively low permeability. For underground impermeable walls, the target value of hydraulic conductivity that can achieve sufficient impermeable performance is 10 ^-7 cm/sec or less.

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

2.1 Experiment of soil cement specimen before solidification In addition, when constructing the underground impermeable wall of the present invention, the solidification material containing cement milk and hydrogen carbonate and the ground soil and sand were mixed and agitated sufficiently. An experiment was also conducted to confirm that there is fluidity. This experiment is described below.

2.2 Material of test piece Investigation Examples 1 to 5, Comparative Examples 1 to 3 of standard sand, and Investigation Examples 6 to 11 of Kumamoto sand.

2.3 Preparation of test piece (1) Put 300g of tap water into a 3000ml beaker and set it in a disper.
(2) Rotate the mixer at 700 rpm, add cement in an amount that matches the blending conditions of each study example, and stir for 3 minutes.
(3) For the specimens of the study examples, sodium bicarbonate, which is a hydrogen carbonate, and clay are added to the above (2) in amounts that match the mixing conditions of each study example, and after stirring for 5 minutes, a solidifying agent is prepared. For the specimens of the comparative examples, only clay in an amount matching the blending conditions of each comparative example was added to the above (2), and after stirring for 5 minutes, a solidifying agent was prepared.
(4) To 700 g of standard sand or Kumamoto sand, add the solidifying agent of each study example and each comparative example in (3) above.
(5) Stir with a mortar mixer for 5 minutes to mix and stir the cement milk containing the solidifying agent and ground soil to prepare a sample for a flow test of the soil cement before solidification.

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

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

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

Therefore, by properly blending "standard sand" of ground soil, bicarbonate of sodium bicarbonate, clay, cement, and water, the underground impermeable wall has sufficient impervious performance, deformation followability and It can be compatible with self-repairability

Comparative Examples 1 and 2 cannot satisfy the target value of the breaking strain due to the increased amount of cement.

Compared to Comparative Examples 1 and 2, Investigation Examples 4 and 5, which are standard sands, can satisfy the target values for hydraulic conductivity, strength, breaking strain, and flow value with a smaller amount of cement. Therefore, by setting appropriate blending conditions for the "standard sand" of ground soil, bicarbonate of sodium bicarbonate, clay, cement, and water, the underground impermeable wall can reduce the amount of cement used. Economic efficiency is improved, and environmental load can be suppressed.

Table 2 below shows the blending conditions, water permeability test, uniaxial compression test and flow test results for each study example and each comparative example using Kumamoto sand.

Investigation examples 9 and 10 of Kumamoto sand have a hydraulic conductivity target value of 10 ^-7 cm/sec or less, a strength target value of 100 kN/m ² or more, a fracture strain target value of 2% or more, and a flow value target. Satisfies all values of 15 cm or more. In Comparative Example 3 and Investigative Examples 6 to 8 using Kumamoto sand, the specimens did not stand on their own, and naturally did not meet the target value of strength.

Therefore, the ground soil “Kumamoto sand”, bicarbonate of sodium bicarbonate, clay, cement, and water are properly blended to create an underground impermeable wall with sufficient impervious performance, deformation followability, and It is possible to achieve both self-repairability.

The mechanism by which C—S—H gel formation is promoted by mixing sodium bicarbonate, which is a bicarbonate, into cement milk will be described below.

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

2CaO.SiO ₂ .1.17H ₂ O in chemical formula 1 is a hydrate of C—S—H gel.

Also, when sodium bicarbonate is mixed with cement milk, a hydrolysis reaction between sodium bicarbonate and water occurs.

The sodium ions generated by the hydrolysis reaction of Chemical Formula 2 promote the formation of C—S—H gel of 2CaO.SiO ₂ .1.17H ₂ O of 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 sodium bicarbonate. FIG. 2 shows a stereomicroscopic photograph of a fracture surface of a soil cement test piece made of cement milk mixed with sodium bicarbonate.

A large number of granular dots with a deep white color can be seen on each fracture surface. The white, dense, granular dots are the CSH gel. The ratio of the area of the CSH gel region on each fractured surface to the area of the entire fractured surface was about 10% for the soil cement test specimen made of cement milk without sodium bicarbonate mixed with sodium bicarbonate. It is about 15% for soil cement test specimens made from hardened cement milk.

The C—S—H gel is porous and adapted to absorb water and swell. A CSH gel that has absorbed water to its limit and swelled is impervious to water. Therefore, as the amount of C—S—H gel in the underground impermeable wall increases, the impermeable performance can be improved.

In addition, when the CSH gel absorbs water and expands, the voids inside the underground impermeable wall are filled, and the self-healing performance of the underground impermeable wall is obtained.

The broken surface of the soil cement test piece made of cement milk not mixed with sodium bicarbonate was visually observed, and a sample for observation was collected from a portion where CSH gel, which is a white product, was confirmed. The collected sample was fixed on a sample stage so that the observation surface faced up, and in order to make it conductive, gold was vapor-deposited on the surface using an ion sputtering device. A secondary electron image was obtained in which the edge structure of the C—S—H gel shown can be observed.

Similarly, a secondary electron image was obtained in which the end structure of the C—S—H gel shown in FIG.

In FIG. 3, the ends of the soil cement C—S—H gel made of cement milk not mixed with baking soda have a shape in which a large number of fine needles protrude. On the other hand, in FIG. 4, as compared with FIG. 3, the fine needles at the ends of the C—S—H gel of the soil cement made of cement milk mixed with baking soda are thickened.

The construction of the underground impermeable wall 1 of the present invention will be described below.

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 impermeable performance are connected in the ground. The plurality of columnar bodies 10 are arranged in a wrap arrangement.

Construction of the columnar body 10 will be described with reference to FIG. The construction machine used in the construction work of the underground impermeable wall of the present invention comprises a rod 2 supported so as to be vertically and rotatably supported, and a stirring head 3 provided below the rod and rotating integrally with the rod 2. have

As shown in FIG. 6(a), the rotating shaft of the rod 2 is set at the pile core position of the columnar body. Next, as shown in (b) to (c) of FIG. 6, by rotating and lowering the rod 2 while injecting muddy water from the stirring head 3, the soil and muddy water are mixed until the stirring head 3 reaches a predetermined depth. agitate. Next, as shown in (d) to (e) of FIG. 6, by rotating and raising the rod 2, the agitation head 3 further agitates the soil and muddy water.

Next, as shown in (f) to (g) of FIG. 6, the rod 2 is rotated and lowered while injecting cement milk containing a solidifying agent containing hydrogencarbonate from the stirring head 3, so that the stirring head 3 reaches a predetermined level. Cement milk containing a solidifying agent containing bicarbonate, ground sand and mud water are agitated until the depth is reached. Next, as shown in (h) to (i) of FIG. 6, the stirring head 3 further stirs the soil and muddy water by rotating the rod 2 upward.

As shown in (j) of FIG. 6, when the cement milk containing the solidifying agent containing hydrogen carbonate, the ground soil, and the muddy water are stirred, the columnar bodies 10 constituting the underground impermeable wall 1 are formed. be.

At a plurality of predetermined pile core positions, after performing the stirring work for injecting mud water in FIGS. 6A to 6E, the stirring work for injecting cement milk in FIGS. , a plurality of columnar bodies 10 are connected like a wall, and an underground impermeable wall 1 is constructed. By constructing an underground impermeable wall having a structure in which a plurality of columnar bodies 10 having impermeable performance in the ground are arranged in a row in the ground around the area where liquefaction countermeasures are to be taken, it is possible to reduce the groundwater level. influence can be eliminated.

In the practice of the present invention, the underground impermeable wall can be constructed with a relatively small heavy excavator. can be constructed.

In addition, although FIG. 6 describes the case of forming one columnar body, the present invention is not limited to this. For example, a plurality of columnar bodies may be created at the same time. Alternatively, a trencher-type heavy machine may be used to construct the pillars.

1 Underground Water Impermeable Wall 2 Rod 3 Stirring Head 10 Columnar Body

Claims (4)

An underground impermeable wall constructed in the ground by solidifying soil cement obtained by mixing and stirring cement milk containing a solidifying agent containing hydrogen carbonate and ground earth and sand,
An underground impermeable wall, characterized in that the area of the region where the C—S—H gel is present is 15% or more of the area of the entire cross section as an average of the values in all cross sections of the solidified soil cement . 2. A method for constructing an underground impermeable wall, characterized in that the impermeable wall according to claim 1 is constructed by mixing and stirring cement milk containing a solidifying agent containing bicarbonate and ground earth and sand in the ground and solidifying them. 3. The method for constructing an underground impermeable wall according to claim 2 , wherein the bicarbonate is sodium bicarbonate. It is characterized by injecting muddy water into the ground earth and sand, mixing and stirring with the ground earth and sand, and then injecting cement milk containing a solidifying agent containing hydrogen carbonate, mixing and stirring with the ground earth and sand underground and solidifying. The underground impermeable wall construction method according to claim 2 or 3 .

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