JP7112242B2 - Impermeability and Permeability Restoration Method in the Ground - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act (1) GeoKanto 2017 Program and Abstracts of the 14th Geotechnical Society Kanto Branch Presentation (pages 371-374, Geotechnical Society Kanto Branch, Date of Distribution: November 2017 (2) Announced at the 14th Geotechnical Society Kanto Branch Presentation GeoKanto 2017 (Tochigi Prefectural Cultural Center) on November 17, 2017

TECHNICAL FIELD The present invention is one of ground improvement methods for constructing a structure in the ground, and relates to a method for imperviousness and restoration of water permeability in the ground.

When constructing a structure in the ground, it is necessary to improve the water impermeability of the ground to inhibit the upstream and downstream flow of groundwater. Conventionally, there are several methods to improve the water impermeability of the ground: 1) water impermeability method by injecting water glass chemical solution or fine cement into the ground; 3) Jet grouting method, in which a liquid solidified material is sprayed into the ground at high pressure and mixed with the soil in the ground to create a solidified body; 4) Target Various construction methods such as a ground freezing method are employed, in which a frozen pipe is piped into a drilled hole drilled in the ground, and a cooling liquid sent through the frozen pipe is circulated to create frozen soil.

However, each of the methods 1) to 4) has the following problems. For example, in each of the construction methods 1) to 3), since the impermeability is secured by the solidification method, it is difficult to restore the permeability of the ground mixed or injected with the solidification material to the same level as the original ground after construction. rice field. Therefore, on the upstream side of the ground mixed or injected with solidifying material, the groundwater level may rise, and buoyancy may act on underground structures, causing them to float up. There is a risk that the groundwater level will drop and ground subsidence will occur, and there is concern that the problem of groundwater flow inhibition will occur. In particular, when the temporary seepage control method such as the soil cement diaphragm wall in 2) is applied to a large-scale construction work, the problem of groundwater flow inhibition is conspicuous due to the wide range of water interception. On the other hand, in the ground freezing method of 4), although it is possible to restore the permeability to that of the original ground after construction, it is necessary to maintain the frozen state of the frozen soil by consuming electricity during the construction period, resulting in running costs. There was a problem of high In addition, if there is groundwater flow in the ground to be constructed and the groundwater flow velocity is high, it is difficult to freeze the ground, and it is necessary to use auxiliary construction methods such as chemical injection method. There was a problem that the ground could not be restored to its original state later.

Therefore, until now, various methods have been examined as countermeasures for preserving groundwater flow. For example, a construction method that installs a water pipe that can flow from the upstream side of the groundwater flow to the downstream side in the ground deeper than the construction site, and a pumping well that is installed upstream and downstream of the construction site to pump up groundwater from the upstream side. , a method of discharging downstream, and the like have been proposed.

However, the method of installing a water pipe is not widely used because maintenance of the water pipe requires a huge amount of cost and effort. In addition, in the method of installing a pumping well, it was necessary to constantly pump up groundwater from the pumping well using a pump or the like during the construction period. Therefore, there is a problem that running costs, such as electricity costs for operating the pump, increase when the construction takes a long period of time.

In view of such problems, the present inventors have so far proposed an earth retaining wall construction method capable of quickly restoring the water permeability of the earth retaining wall after construction (Patent Document 1).

In the proposal of Patent Document 1, excavation and mixing are performed while adding the superabsorbent polymer particle-containing liquid, or after excavating without adding the superabsorbent polymer particle-containing liquid, superabsorbent polymer particle-containing It is characterized by constructing a retaining wall made of a mixed soil of excavated soil and a liquid containing superabsorbent polymer particles underground by adding and mixing the liquids. In addition, after constructing the earth retaining wall underground, the earth retaining wall having a water stoppage by soil cement is constructed underground on the upper part thereof. According to these proposals, when it becomes necessary to restore the permeability after construction due to the stoppage of groundwater, the water level on the downstream side of the groundwater can be restored by restoring the permeability of a part of the retaining wall. This indicates that it is possible to reduce social impacts such as ground subsidence, subsidence of structures, depletion of well water, etc., and adverse effects on the natural environment such as vegetation caused by a decrease in water.

Patent No. 6141660

However, as a result of subsequent studies, the present inventors focused on the physical properties of the soil. Since the skeleton of the original ground is not maintained, the ground may loosen slightly after mixing and stirring compared to the original ground, and there is still room for further improvement.

The present invention has been made in view of the above circumstances, and maintains sufficient water stoppage during construction while maintaining the skeleton and strength of the original ground, and easily restores water permeability after construction. It is an object to provide a construction method excellent in environmental remediation that enables

In order to solve the above-described problems, the method for impermeability and restoration of permeability in ground according to the present invention has the following features.

First, the method for impermeability and restoration of permeability in the ground of the present invention is characterized by including at least the following steps <1> and <2>.

<1> A step of injecting a superabsorbent polymer particle-containing liquid into the surrounding ground through an injection pipe inserted into the excavated hole in the ground to form a superabsorbent polymer injection layer to impermeable water;
<2> A step of injecting a separating agent into the superabsorbent polymer-injected layer to release the moisture taken in by the superabsorbent polymer particles to restore water permeability.

Second, in the first method for impermeability and water permeability restoration in the ground, before or after the step <1>, an earth retaining wall is installed at the upper, lower or intermediate part of the superabsorbent polymer injection layer. It is preferably considered to include the step of creating.

Thirdly, in the method for impermeability and permeability recovery in the first or second ground, it is preferably considered that the ground is gravel ground.

Fourth, in the first to third ground impermeable and permeable restoration methods, the superabsorbent polymer particles are at least one selected from the group consisting of starch-based, cellulose-based and synthetic polymer-based particles. One is preferably considered.

Fifth, in the first to fourth ground impermeable and permeable restoration methods, it is preferable that the superabsorbent polymer particle-containing liquid contains a swelling degree adjusting agent.

Sixthly, in the fifth method for impermeability and restoration of water permeability in ground, it is preferably considered that the swelling degree adjusting agent contains a first electrolyte.

Seventhly, in the sixth method for impermeability and restoration of permeability in ground, it is preferably considered that the first electrolyte is a monovalent metal salt.

Eighth, in the first to seventh ground impermeable and permeable restoration methods, it is preferably considered that the separating agent contains a second electrolyte.

Ninthly, in the eighth method for impermeability and restoration of permeability in ground, it is preferably considered that the second electrolyte is a polyvalent metal salt having a valence of two or more.

According to the present invention, there is a construction method excellent in environmental remediation that maintains sufficient water stoppage during construction while maintaining the skeleton and strength of the original ground, and enables easy recovery of water permeability after construction. Realized.

(a) is a schematic diagram schematically showing step <1> in the method for impermeability and restoration of permeability in the ground of the present invention. The lower part shows the aa section of the schematic process cross-sectional view shown in the upper part. (b) is a schematic diagram schematically showing step <2>. The bb cross section of the schematic process cross-sectional view shown in the upper part is shown in the lower part. (1), (2), (3), and (4) are schematic process cross-sectional views schematically showing another embodiment of the method for imperviousness and water permeability restoration in the ground of the present invention. 1(a) and 1(b) are schematic process cross-sectional views schematically showing still another embodiment of the method for impermeability and restoration of permeability in ground according to the present invention. 4 is a graph showing the relationship between the electrical conductivity of a liquid containing superabsorbent polymer particles and the water absorption capacity of the superabsorbent polymer particles. 4 is a graph showing the relationship between the concentration (% by mass) of NaCl, which is a swelling degree adjusting agent, and the electrical conductivity of a liquid containing superabsorbent polymer particles. 1 is a schematic diagram showing a test apparatus used for impermeable layer formation by one-dimensional injection and a water permeability recovery test; FIG. (a) is a photograph showing a test apparatus used for impermeable layer formation by two-dimensional injection and a water permeability recovery test. (b) is a schematic cross-sectional view of (a). FIG. 8 is a diagram schematically showing the flow of a two-dimensional injection test using the device of FIG. 7; It is a graph showing the relationship between the injection time (elapsed time) and the injection amount of the superabsorbent polymer particle-containing liquid. (a) is a photograph showing the upper surface of the two-dimensional model ground after the completion of the injection of the liquid containing superabsorbent polymer particles. (b) is a photograph showing a cross section of (a). It is the graph which showed the hardness distribution of the two-dimensional model ground upper surface. It is a photograph showing the state of specimen sampling to be subjected to a permeability test from the two-dimensional model ground.

The method for impermeability and restoration of water permeability in the ground according to the present invention will be described below in detail.

In this specification, the term "injection of polymer particles" means to inject a liquid containing swollen polymer particles into the gaps in the soil skeleton without mixing or stirring the original soil. ing.

The term "superabsorbent polymer particles" as used herein means that individual particles retain their granular form even after they absorb water and swell. Therefore, the term superabsorbent polymer particles does not include and excludes particles in which a plurality of water-absorbent polymer molecules cannot maintain independent particle morphology and form a pasty polymer.

The ground impermeability and permeability restoration method of the present invention includes at least the following steps <1> and <2>.

That is, <1> a step of injecting a superabsorbent polymer particle-containing liquid into the surrounding ground through an injection pipe inserted into the excavated hole in the ground to form a superabsorbent polymer injection layer to block water; <2> Including a step of injecting a separating agent into the superabsorbent polymer injection layer to release the moisture taken in by the superabsorbent polymer particles to recover the water permeability.

FIG. 1(a) is a schematic diagram schematically showing step <1> in the method for impermeability and restoration of permeability in ground according to the present invention. The lower part shows the aa section of the schematic process cross-sectional view shown in the upper part. (b) is a schematic diagram schematically showing step <2>. The bb cross section of the schematic process cross-sectional view shown in the upper part is shown in the lower part.

As shown in FIG. 1(a), in step <1> of the method for impermeability and water permeability restoration in the ground, in order to impermeable the ground G, which is the ground to be constructed, in the excavation hole 1 of the ground G, A superabsorbent polymer particle-containing liquid 3 is injected into the surrounding ground through an injection pipe 2 inserted into a borehole 1 . Thereby, the superabsorbent polymer injection layer 4 can be formed.

The ground G to which the ground impermeability and permeability recovery method of the present invention can be applied is not particularly limited. In particular, it is considered preferable that the ground G is gravel ground.

The hole diameter of the excavation hole 1 is, for example, about φ100 mm to φ600 mm, but it can be changed as appropriate according to the diameter of the shaft used for excavation and the diameter of the injection pipe 2. As for the material of the shaft (excavation shaft) used for excavation, for example, a corrosion-resistant stainless steel pipe is exemplified.

The injection pipe 2 has a plurality of through-holes 21 in its side wall surface, and the superabsorbent polymer particle-containing liquid 3 fed into the injection pipe 2 forms the hole wall of the excavation hole 1 through the through-holes 21. It is supposed to be able to be injected into the interstices in the soil skeleton of the ground. The through-hole 21 of the injection tube 2 may be in an open state at all times, covered with an openable and closable lid, or opened and closed by rotating the double-structured cylindrical body. It may be a mode that can be switched to and from the closed state. It is also taken into account that the gap between the injection tube 2 and the borehole 1 is plugged. By plugging the gap between the injection pipe 2 and the excavated hole 1 , it is possible to prevent the superabsorbent polymer particle-containing liquid 3 from flowing back in the excavated hole 1 .

The diameter of the injection pipe 2 is, for example, about φ100 mm, but it can be changed as appropriate according to the diameter of the excavation shaft. The material of the injection tube 2 is not particularly limited, but for example, a corrosion-resistant stainless steel tube, a plastic resin tube, or the like can be used as appropriate.

The injection pipe 2 may be a separate pipe from the excavation shaft as described above, or may be the same pipe as the excavation shaft and the injection pipe, such as an injection pipe used in a known jet grouting method. good too. Furthermore, the structure of the injection pipe 2 may be a double pipe structure in which the injection pipe is arranged in the inner space of the excavation shaft, which is used in a known chemical injection method.

In the method for imperviousness and water permeability restoration in the ground of the present invention, in step <1>, soil particles in the ground G and a liquid 3 containing superabsorbent polymer particles are mixed at the time of forming the superabsorbent polymer injection layer 4, It is characterized by injecting the superabsorbent polymer particle-containing liquid 3 into the gaps in the soil skeleton of the ground constituting the hole wall of the drilled hole 1 to form the superabsorbent polymer injection layer 4 without stirring.

The superabsorbent polymer particle-containing liquid 3 contains at least water and superabsorbent polymer particles swollen by absorbing water. The present inventors have so far proposed a stable composition containing a liquid containing superabsorbent polymer particles for ground excavation and a construction method using the same, and the superabsorbent polymer particles used in this proposal can be applied (see, for example, Japanese Patent Application Laid-Open No. 2013-57061).

Specifically, the superabsorbent polymer particles are hydrophilic polymers having a crosslinked structure, have a water absorbency of about 10 to 500 times their own weight, and are less likely to release water even when pressure is applied. It has the characteristics of The water absorbing action of such a polymer is exhibited by the osmotic pressure caused by the ion concentration difference between the inside and outside of the polymer. Therefore, the electrical conductivity of the solvent to be mixed and stirred with the polymer can be adjusted, for example, by adding an electrolyte such as sodium chloride, and the mass ratio of absorbed water to the mass of the polymer (hereinafter referred to as water absorption ratio) is changed. be able to. As the solvent, for example, water, especially tap water can be suitably used at construction sites.

The particle size of superabsorbent polymer particles after water absorption is determined by the particle size and water absorption ratio of the polymer particles before water absorption. Desired.

D _a =(Q+1) 1/ ³ ·D _b (1)
(In the formula, Q: water absorption capacity, D _a : polymer particle size after water absorption, D _b : polymer particle size before water absorption)
The product of the mass of the polymer particles and the water absorption capacity represents the maximum amount of water that the polymer particles can absorb under the liquid contained therein. occur. This is defined as free water, and the ratio of free water to the total amount of water is defined as the free water ratio by equation (2).

Free water rate: η (%) = (mass of free water) / (total water volume) x 100 (2)
The amount of water absorption of the superabsorbent polymer particles is defined in JIS K 7223, and the method for measuring the amount of water absorption is also based on the description of JIS K 7223.

The type of superabsorbent polymer particles can be used without particular limitation as long as they satisfy the above conditions. For example, at least one selected from the group consisting of starch, cellulose, and synthetic polymer One type is preferably considered.

Among the superabsorbent polymer particles described above, synthetic polymer-based sodium polyacrylate superabsorbent polymer particles are excellent in terms of both performance and cost, and thus can be particularly preferably used.

Sodium polyacrylate superabsorbent polymer particles are sodium acrylate (CH2=CH-COONa) added with a cross-linking agent, and lightly cross-linked acrylic acid polymer partial sodium salt cross-linked product having a three-dimensional network structure. is a gel. A conventionally well-known thing can be used as a crosslinking agent.

It is known that when the sodium polyacrylate superabsorbent polymer particles absorb water, the carboxyl groups dissociate sodium ions in the gel, and if pure water is used, the degree of swelling reaches 100 to 1000 times its own weight. there is

Examples of such sodium polyacrylate superabsorbent polymer particles include GEOSAP (registered trademark, hereinafter the same). In the case of GEOSAP, the water absorption capacity is about 450 times its own weight, the fluidity of the liquid 3 containing superabsorbent polymer particles is good, and the gaps in the gravel layer can be reliably filled.

In addition, by blending a large amount of a cross-linking agent with sodium polyacrylate, the resulting gel becomes hard and its water absorption is reduced. Also, when the amount of the cross-linking agent is reduced, the resulting gel becomes softer and its water absorption increases.

Furthermore, as a special sodium polyacrylate superabsorbent polymer particle, the surface of the superabsorbent polymer particle polymerized with a cross-linking agent is further crosslinked, and the sodium polyacrylate superabsorbent polymer has a double structure of shell and core. The use of polymer particles is exemplified.

In the sodium polyacrylate superabsorbent polymer particles having a double structure of shell and core, the thicker the shell, which is the outer shell, the harder the gel becomes, and the water absorption decreases. On the other hand, if the thickness of the shell is reduced, it becomes a soft gel and its water absorption increases.

The above shell and core are usually crosslinked by ester bonds, but the shell and core are crosslinked by ether bonds that are excellent in alkali resistance and electrolyte resistance Sodium polyacrylate high water absorption There are also polymeric particles. In the present invention, it is more preferable to use sodium polyacrylate superabsorbent polymer particles in which the shell and core are crosslinked by ether bonds.

In addition to the above properties, the dissociation of sodium ions in sodium polyacrylate superabsorbent polymer particles also depends on conditions such as pH and electrolyte concentration where the gel is placed, so other superabsorbent polymers may be used depending on the conditions of use. Particles can be appropriately selected and used.

The superabsorbent polymer particle-containing liquid 3 is also assumed to be used at a great depth such as underground tunnel construction, and is pressurized and sent to the construction site. In this case, since the superabsorbent polymer particles in the superabsorbent polymer particle-containing liquid 3 are exposed to high pressure, there is little reduction in water retention due to pressurization, and the polymer particles themselves have a crosslinked structure that is difficult to deform. It is necessary to select superabsorbent polymer particles with Moreover, in order to close the gaps of the water _- permeable layer G1, it is desirable that the particle size of the superabsorbent polymer particles after swelling is 3 mm or less and the particle size distribution is better.

In addition, when the ground G is gravel ground, it is exemplified that the amount of gaps between soil skeletons of the ground is 45 to 50%.

In the present invention, when sodium polyacrylate superabsorbent polymer particles are used as the superabsorbent polymer particles, they can be used without particular limitation as long as they satisfy the above conditions. , sodium polyacrylate superabsorbent polymer particles having a double structure of shell and core adjusted to the above conditions can be preferably used.

In addition, in the present invention, it is preferably considered that the superabsorbent polymer particle-containing liquid 3 contains a swelling degree adjusting agent. Furthermore, it is considered preferable that this swelling degree modifier contains an electrolyte, and that this electrolyte is a monovalent metal salt. The degree of swelling of the superabsorbent polymer particles is maximized in pure water, but the degree of swelling decreases in an aqueous solution containing the swelling degree adjusting agent. Based on such characteristics of the superabsorbent polymer particles, by adding a swelling degree adjusting agent to the superabsorbent polymer particle-containing liquid 3 in advance, the swelling of the superabsorbent polymer particles is suppressed and the particle size is controlled to be small. In addition, the content of the superabsorbent polymer particles contained per unit volume of the superabsorbent polymer particle-containing liquid 3 can be increased. As a result, the superabsorbent polymer particle-containing liquid 3 having a high superabsorbent polymer particle content can be delivered to the construction target ground G without clogging the injection pipe or the liquid delivery system. Then, in the construction target ground G, the superabsorbent polymer particle-containing liquid 3 comes into contact with groundwater, so that the electrolyte concentration in the superabsorbent polymer particle-containing liquid 3 is diluted, and the superabsorbent polymer particles are reduced to the desired level. It becomes possible to swell to a particle size of 100 to exhibit the effect of filling the gaps between soil particles.

As the swelling degree adjusting agent that can be added to the superabsorbent polymer particle-containing liquid 3, it is preferable to use an electrolyte that has a small environmental load and is less likely to deteriorate the superabsorbent polymer particles, such as sodium chloride and potassium chloride. Monovalent metal salts such as , potassium hydroxide are preferably considered. Considering environmental load and economic efficiency, it is particularly preferable that the electrolyte is sodium chloride. By using such a swelling degree adjusting agent, it becomes possible to appropriately adjust the swelling degree of the superabsorbent polymer particles.

As the superabsorbent polymer particle-containing liquid 3, for example, in a state in which the superabsorbent polymer particles are swollen with pure water, the specific gravity is 1.20 or less, preferably in the range of 0.95 to 1.20. An adjusted one is exemplified.

Moreover, the viscosity of the superabsorbent polymer particle-containing liquid 3 can be adjusted based on the free water content (%) in the superabsorbent polymer particle-containing liquid 3 .

Further, an auxiliary agent can be added to the superabsorbent polymer particle-containing liquid 3 for the purpose of improving the hole wall stability of the drilled hole 1 and adjusting the viscosity of the superabsorbent polymer particle-containing liquid 3 .

Examples of the auxiliary agent include bentonite, sawdust, pulp, rock wool, and fibers, or water-soluble polymers. These can be used singly or in combination of two or more.

Furthermore, when the superabsorbent polymer particle-containing liquid 3 is mixed with electrolytes such as acidic substances, basic substances and salts, it is possible to suppress and recover the deterioration of the properties and quality of the superabsorbent polymer particle-containing liquid 3. Stabilizers can be added to

Examples of the stabilizer include dilute sulfuric acid, aluminum sulfate, aluminum hydroxide, magnesium hydroxide, polyacrylamide, polyvinyl alcohol, sodium polyacrylate, polyethylene oxide and the like. Examples of the stabilizer include hydrogencarbonates such as sodium hydrogencarbonate, calcium hydrogencarbonate, potassium hydrogencarbonate and ammonium hydrogencarbonate. Furthermore, examples of the stabilizer include carbonates such as sodium carbonate, calcium carbonate, potassium carbonate and ammonium carbonate. These can be used singly or in combination of two or more.

When injecting the superabsorbent polymer particle-containing liquid 3 having such a composition into the excavation hole 1, first, as shown in FIG. After excavation, an injection pipe 2 is laid in the excavated hole 1 . Then, the superabsorbent polymer particle-containing liquid 3 is supplied to the injection pipe 2, and the superabsorbent polymer particle-containing liquid 3 in a fluid state is transferred from the through hole 21 of the injection pipe 2 to the soil skeleton of the ground G. Inject into the gap between

When a monovalent metal salt is added as a swelling degree adjusting agent to the superabsorbent polymer particle-containing liquid 3 to suppress the degree of swelling of the superabsorbent polymer particles, in the ground G, the superabsorbent polymer particles When the contained liquid 3 and the groundwater W come into contact with each other, the electrolyte concentration in the contained liquid decreases, and the superabsorbent polymer particles swell to 100 times or more of their own weight. The particle diameter of the superabsorbent polymer particles after swelling reaches about 0.5 mm to 3 mm.

The highly swollen superabsorbent polymer particles injected into the ground G in this way fill the gaps between the soil particles in the ground G while maintaining the soil skeleton. By forming a superabsorbent polymer injection layer 4 in which the gaps between soil particles are filled with the superabsorbent polymer particles, and reducing the permeability of the ground G, the flow of groundwater W in the ground G is impermeable. can do.

As described above, in the method of impermeability and water permeability restoration in the ground of the present invention, the superabsorbent polymer By injecting the particle-containing liquid 3, the water impermeability of the ground G is improved, so the improvement range of the water impermeability can be reduced compared to the conventional method of injecting the chemical solution upstream of the construction site. Therefore, compared with the conventional construction method, the environmental load is small, and it is possible to suppress the construction cost.

Following step <1> as described above, in the impermeable and permeable restoration construction method by injecting a polymer into the ground of the present invention, a separating agent 81 is injected into the superabsorbent polymer injection layer 4, and the superabsorbent polymer is injected. The water trapped in the superabsorbent polymer particles in the layer 4 is released. That is, as shown in FIG. 1(b), the separation agent 81 is injected by embedding the perforated pipe 8 in the superabsorbent polymer injection layer 4, and through the through hole 82 provided in the perforated pipe 8. A method of injecting into the flexible polymer injection layer 4 is exemplified.

As shown in FIG. 1(b), by injecting the separating agent 81, the water of the superabsorbent polymer particles that filled the gaps between the soil particles is released, and the water permeability in the ground G is reduced. can be recovered.

Separating agent 81 is preferably considered to contain a second electrolyte. The second electrolyte referred to here is an electrolyte different from the first electrolyte contained in the superabsorbent polymer particle-containing liquid 3 as a swelling degree adjusting agent.

When a second electrolyte is injected as a separating agent 81 into the superabsorbent polymer injection layer 4, the superabsorbent polymer particles in the superabsorbent polymer injection layer 4 are dispersed depending on the type of electrolyte and the electrolyte concentration of each electrolyte. , releases the entrapped water and reduces its volume.

The second electrolyte is not particularly limited as long as it is different from the first electrolyte and can release water when injected into the superabsorbent polymer injection layer 4. be able to. Examples include basic substances such as calcium hydroxide, salts such as calcium chloride, acidic substances such as hydrochloric acid, sulfuric acid, nitric acid and citric acid, and salts of these acidic substances. These electrolytes can be used singly or in combination of two or more. Among them, it is preferable that the second electrolyte is a divalent metal salt such as calcium hydroxide or calcium chloride. Considering environmental load and economic efficiency, it is particularly preferable that the second electrolyte is calcium chloride.

As for the addition of the separating agent 81, for example, the component composition of the superabsorbent polymer particle-containing liquid 3 is 0.2% by mass of the superabsorbent polymer particles, 4.8% by mass of the weighting material, and 95.0% by mass of water. In this case, it is exemplified that 0.2% by mass or more of the normal superabsorbent polymer particle-containing liquid, and 0.3 to 0.4% by mass of calcium chloride is added in the case of a high specific gravity superabsorbent polymer particle-containing liquid. be. If the amount of the separating agent 81 added is within the above range, the separating agent 81 converts the superabsorbent polymer particle-containing liquid 3 into 5% by mass of solid matter containing the weighting material and superabsorbent polymer particles that have released moisture. and an aqueous calcium chloride solution that accounts for 95% by mass. In addition, 95 mass % here does not mean the mass % density|concentration of calcium chloride aqueous solution.

By injecting the separating agent 81 into the superabsorbent polymer injection layer 4 by the mechanism described above, water is released from the superabsorbent polymer particles in the superabsorbent polymer injection layer 4, and the superabsorbent polymer is injected. The volume and degree of swelling of the polymeric particles are greatly reduced. Therefore, the effect of filling the gaps between the soil particles by the superabsorbent polymer particles is reduced, and the water permeability in the ground G is restored.

In addition, since the superabsorbent polymer particle-containing liquid 3 does not contain heavy metal elements and the like that have a large environmental impact, even if the superabsorbent polymer particles that have released moisture are left in the ground as they are, they will not affect the environment. There is little risk of contaminating the Further, the superabsorbent polymer particles deteriorate over time by coming into contact with the separating agent 81 and eventually decompose in the ground. As described above, according to the method of blocking and restoring water permeability by injecting the polymer into the ground of the present invention, which can separate the liquid 3 containing superabsorbent polymer particles into solid matter and liquid and dispose of it, construction materials can be reduced. Not only is disposal easier, but processing costs can be kept very low.

In the case of the mode in which the perforated pipe 82 for injecting the separating agent 81 is installed in the ground G, the perforated pipe 82 is finally removed from the excavation hole 1 provided in the ground G. After the perforated pipe 82 is removed, the excavated hole 1 is backfilled with earth and sand from the excavated hole 1 to complete the restoration of the ground G, which is the construction target, to its original state.

In this way, according to the method of imperviousness and permeation restoration by injecting polymer into the ground of the present invention, which can separate the superabsorbent polymer particle-containing liquid 3 into solids and liquids and restore it to its original state, environmental restoration In addition to being highly efficient, processing costs can be kept very low. In addition, since the polymer injection into the ground is performed while maintaining the skeleton and strength of the original ground, even if the superabsorbent polymer particles release moisture and the gaps in the soil skeleton of the original ground are restored, construction The strength of the original ground does not decrease compared to before.

In addition, in the method for impermeability and water permeability recovery in the ground of the present invention, before or after the step <1>, a step of creating an earth retaining wall on the upper, lower or intermediate portion of the superabsorbent polymer injection layer. It is preferably considered to include.

FIGS. 2(1), (2), (3), and (4) are schematic process cross-sectional views schematically showing another embodiment of the method for impermeability and restoration of permeability in ground according to the present invention. In this embodiment, after the construction of the superabsorbent polymer injection layer 4 is completed, an earth retaining wall 6 is constructed above it (above the construction depth D from the ground surface).

In this way, by coexisting the superabsorbent polymer injection layer 4 and the retaining wall 6 in the ground G, the superabsorbent polymer injection layer 4 can be reinforced, and not only is it excellent in water impermeability, but also in terms of strength. It is possible to construct a water stop structure in the ground G which is also excellent.

As shown in FIG. 2(1), in the present embodiment, first, in order to impermeably treat the ground G, which is the ground to be constructed, drill holes 1 are drilled in the permeable layer G ₁ and the impermeable layer G ₂ , An injection pipe 2 is connected to this excavation hole ₁ , and a liquid 3 containing superabsorbent polymer particles is injected through the injection pipe ₂ into the soil of the permeable layer G1 and the impermeable layer G2.

Examples of the permeable layer G1 include sandy _ground (sand layer), gravel ground (gravel layer), and the like, and gravel ground is particularly preferred.

Moreover, as the impermeable layer G2, for example, a clayey ground ₍ clay layer) is exemplified.

Subsequently, as shown in FIG. 2(2), after the construction of the superabsorbent polymer injection layer 4 is completed, an earth retaining wall 6 is constructed above it (above the construction depth D from the ground surface).

The earth retaining wall 6 can be formed using a conventionally known hardening material. Claywall and the like are exemplified.

When constructing a soil cement layer as the earth retaining wall 6, the excavated soil 7a is mixed with cement milk 7b. In this way, the earth retaining wall 6 made of the soil cement layer can be constructed while pulling up the excavator 5 to the ground.

The superabsorbent polymer injection layer 4 and the earth retaining wall 6 may be constructed so that the upper end surface and the lower end surface of each are in direct contact, or the superabsorbent polymer injection layer 4 and the earth retaining wall 6 may be constructed. An intermediate layer may be provided between them.

Furthermore, in order to reinforce the strength of the earth retaining wall 6, as shown in FIG.

Then, in the present embodiment, after constructing the impermeable structure and constructing underground structures and the like, the separating agent 81 is injected into the superabsorbent polymer injection layer 4, and the superabsorbent polymer in the superabsorbent polymer injection layer 4 release the water trapped in the polymeric particles. That is, as shown in FIG. 2(4), by injecting the separating agent 81, the water of the superabsorbent polymer particles that have clogged the gaps between the soil particles is released, and the construction in the ground G is performed. _Permeability in permeable layer G1 below depth D can be restored. Since the soil skeleton in the original ground G ₀ is maintained, the strength of the original ground G ₀ is maintained even after the water of the superabsorbent polymer particles filling the gaps between the soil particles is released. maintained.

The method of injecting the separating agent 81 is not particularly limited. For example, as shown in FIG. 8 are buried and injected into the superabsorbent polymer injection layer 4 through through holes 82 provided in the perforated pipe 8, and the like.

FIGS. 3(a) and 3(b) are schematic process cross-sectional views schematically showing still another embodiment of the method for impermeability and restoration of permeability in ground according to the present invention.

In the embodiment of FIG. 3( a ), the retaining wall 6 is not constructed on the same axis of the superabsorbent polymer injection layer 4 , but the upper end portion of the superabsorbent polymer injection layer 4 and the lower end portion of the retaining wall 6 . are adjacent so as to partially overlap each other.

In the embodiment shown in FIG. 3(b), a portion of the earth retaining wall 6 such as a continuous soil cement wall is provided with a portion having a shorter overall length than other portions in advance, and the earth retaining wall 6 having a shorter overall length is provided. This is an embodiment in which a superabsorbent polymer injection layer 4 is formed below. When the superabsorbent polymer injection layer 4 is still intact, it is possible to block the flow of groundwater W from the front side toward the depth direction, which is indicated by the dashed arrow in the figure, and after the separation agent 81 is injected, the ground G When the water permeability is restored, the groundwater W can flow down the portion of the earth retaining wall 6 where the overall length is short.

Examples are shown below, but the method for impermeability and water permeability restoration in the ground of the present invention is not limited by the examples.

<1. Basic Experiment of Liquid Containing Super Absorbent Polymer Particles>
Basic experiments have confirmed the following properties of the liquid containing superabsorbent polymer particles used in the ground impermeability and permeability recovery method of the present invention.

(1) Relationship between electrical conductivity and water absorption capacity of liquid containing superabsorbent polymer particles As shown in FIG. , the following relational expression holds.

y=3×10 ⁻⁶ x+0.0016 (3)
Here, x: the electrical conductivity of the liquid containing the superabsorbent polymer particles (μS/cm)
y: reciprocal of water absorption ratio (1/fold)
From the above formula (3), it was confirmed that the water absorption rate of the superabsorbent polymer particles can be controlled by adjusting the electrical conductivity of the superabsorbent polymer particle-containing liquid.

(2) Relationship between electrolyte concentration and electrical conductivity of swelling degree modifier When sodium chloride NaCl is used as the swelling degree modifier, the relationship between NaCl concentration (mass% concentration) and electrical conductivity is shown in FIG. As such, there is an almost proportional relationship. The following relational expression holds between the NaCl concentration (mass % concentration) x and the electrical conductivity y of the superabsorbent polymer particle-containing liquid.

y=1.75×10 ⁴ x+43.8 (4)
Here, x: NaCl concentration (mass% concentration)
y: electrical conductivity of liquid containing superabsorbent polymer particles (μS/cm)
From the above formula (4), it was confirmed that the electrical conductivity of the superabsorbent polymer particles can be controlled by adjusting the amount of NaCl added.

From the results of (3) and (4) above, the electrical conductivity of the water used to pre-absorb water into the superabsorbent polymer particles or the liquid containing superabsorbent polymer particles is adjusted to increase the free water content of the liquid containing superabsorbent polymer particles. By adjusting, it becomes possible to adjust the viscosity (fluidity) according to the pumping machine and pump the superabsorbent polymer particles with a predetermined residual water absorption capacity.

<2. Impermeable Layer Formation Test and Permeability Recovery Test on One-Dimensional Model Ground>
With regard to the formation of the impermeable layer, it was confirmed in the following experiments that the liquid containing the superabsorbent polymer particles forms the impermeable layer around the wall surface of the borehole.

FIG. 6 is a schematic diagram of an apparatus for measuring impermeable layer formation. In FIG. 6, the simulated ground 11 has a thickness of 200 mm, a gravel ground is assumed from the sand layer, and two types of silica sand (Tohoku silica sand No. 4 with a medium grain size) are used as the sample soil. In addition, as superabsorbent polymer particles (sodium polyacrylate: trade name GEOSAP, manufactured by Sanyo Chemical Industries, Ltd.), two types with different particle sizes (coarse particles in dry state: particle size 150 to 710 μm, fine particles: 20 to 50 μm) It was used.

First, in order to confirm the formation of the impermeable layer in the ground, a confining pressure of 300 kN/m ² was applied to the first cylinder 13 and the second cylinder 14 by the compressor 9, and further the first cylinder 13 added 20 kN/m ² as a pressure head and a total of 320 kN/m ² was added by the compressor 9 . The permeated water 10 that permeates the simulated ground 11 moves into the second cylinder 14 via the communication passage that connects the first cylinder 13 and the second cylinder 14 . In this way, the mass of the permeated water 10 moved into the second cylinder 14 and stored was weighed by the electronic balance 12, and the hydraulic conductivity was calculated based on the mass of the stored permeated water 10.

As a result of the water permeability test, the permeability coefficient of Tohoku Silica Sand No. 4 is 2.0 to 4.75×10 ⁻² cm/s. It was as small as 83×10 ⁻⁸ cm/s, confirming the formation of a waterproof layer.

Next, when a 1% by mass solution of calcium chloride CaCl ₂ is permeated into the simulated ground 11 as the infiltrating water 10, the hydraulic conductivity of the simulated ground 11 increases to 2.67×10 ⁻⁴ cm/s, which is equivalent to that of the original silica sand. It will be within the range of hydraulic conductivity. This indicates that the superabsorbent polymer particles released water by the action of calcium chloride CaCl ₂ and the volume decreased, so that the gaps in the soil skeleton could not be clogged and water could pass through. ing.

<3. Impermeable layer formation test and permeability recovery test on two-dimensional model ground>
2. above. Based on the results of the one-dimensional injection experiment, the formation test of the impermeable layer on the two-dimensional model ground and the A water permeability recovery test was performed.

FIG. 7 shows a schematic cross-sectional view of a two-dimensional soil tank (inner diameter of the soil tank of 90 cm, height of 10 cm) and a two-dimensional model ground, which are experimental devices.

First, a two-dimensional model ground was prepared by an underwater drop method in which a water depth of 6 cm was maintained in a two-dimensional soil tank and sample sand was dropped from a height of 20 cm above the water surface. The height of the surplus was set to 3 cm, and the surplus sand sample was removed.

The upper surface of the two-dimensional model ground prepared in this manner was covered, and a pore water pressure of 10 kPa was applied. compacted.

After the consolidation, as shown in FIG. 8, the water in the injection pipe was replaced with the liquid containing superabsorbent polymer particles, and the liquid containing superabsorbent polymer particles was pumped from the injection tank at an effective injection pressure of 300 kPa. The interstitial water that was pushed out was discharged into the drainage tank. As the superabsorbent polymer particles, GEOSAP was used and prepared with a formulation that gave good injectability in a one-dimensional injection experiment. A containing liquid was prepared.

After confirming the convergence of the injection amount of the liquid containing superabsorbent polymer particles, the two-dimensional soil tank was dismantled, and the injection amount was estimated and the injection diameter was measured. In addition, penetration resistance was measured on the upper surface of the two-dimensional model ground, and sampling was performed from the injection area to conduct a permeability test.

[Estimation of Polymer Injection Amount]
FIG. 9 shows the relationship between injection time (elapsed time) and injection amount. From FIG. 9, it was presumed that the superabsorbent polymer particle-containing liquid was injected to a diameter of about 47 cm in about 65 hours. In addition, FIG. 9 also shows numerical values calculated from the injection amount assuming that the gaps in the two-dimensional model ground are filled with the superabsorbent polymer particle-containing liquid as the estimated injection diameter.

FIGS. 10(a) and 10(b) are photographs showing the two-dimensional model ground after completion of pouring. When the injection diameter was actually measured on the upper surface shown in FIG. 10(a), it was about 45 cm on average. It was confirmed that the values of the above estimated injection diameters and the measured values are very close.

[Hardness measurement]
The penetration resistance of the top surface of the two-dimensional model ground was measured using a Yamanaka soil hardness tester.

Fig. 11 shows the penetration resistance distribution on the top surface of the two-dimensional model ground. The measurement position is No. in FIG. 10(a). 6 and No. It is on the straight line connecting 12. Note that the central portion was not measured due to the existence of the injection pipe.

As shown in FIG. 11, it was confirmed that the penetration resistance was about 1.5 to 2 times higher in the region near the injection pipe where the liquid containing superabsorbent polymer particles was injected than in the non-injected region. From this result, it is considered that superabsorbent polymer particles are filled in the liquid injection region containing superabsorbent polymer particles.

[Permeability test]
From the superabsorbent polymer particle-containing liquid injection area in the two-dimensional model ground, as shown in FIG. (Specimen Nos. 3 and 4) Samples were collected and subjected to a constant water level triaxial permeability test. The test conditions were a confining pressure of 310 kPa, a back pressure of 0 kPa, and a water head difference of 100 kPa in terms of pressure.

Table 1 shows the results.

As shown in Table 1, almost the same hydraulic conductivity of 3.60 × 10 ^-9 to 8.98 × 10 ^-9 (cm/s) was obtained both in the inner part and the outer part of the injection zone. , it was confirmed that sufficient imperviousness can be obtained in the entire injection area.

D construction depth G _ground G0 ground surface G1 permeable layer G2 impermeable layer G3 original ground W groundwater ₁ drilling hole ₂ injection pipe 21 through hole ₃ liquid containing super absorbent polymer particles 4 super absorbent polymer injection layer 5 construction machine 6 retaining wall 7 mixed soil 7a excavated soil 7b cement milk 71 core material 8 perforated pipe 81 separating agent 82 through-hole 9 compressor 10 seepage water 11 simulated ground 12 electronic balance 13 first cylinder 14 second cylinder

Claims (4)

A method for impermeability and restoration of permeability in the ground, characterized by including at least the following steps <1> and <2>.
<1> Injection of a liquid containing superabsorbent polymer particles having a specific gravity in the range of 0.95 to 1.20 and containing a swelling degree adjusting agent made of a monovalent metal salt inserted into the drilled hole in the ground. A step of injecting into the surrounding ground from the pipe to form a superabsorbent polymer injection layer to impermeable water;
<2> In the superabsorbent polymer injection layer, 0.2 to 0.4% by mass of a separating agent composed of a polyvalent metal salt having a valence of 2 or more is added to 100% by mass of the superabsorbent polymer particle-containing liquid. A step of injecting water in a range to release the water taken in by the superabsorbent polymer particles to recover the water permeability. In the method for impermeability and water permeability recovery in the ground according to claim 1, before or after the step <1>, an earth retaining wall is formed in the upper, lower or intermediate part of the superabsorbent polymer injection layer. A method for impermeability and restoration of permeability in the ground, characterized by including steps. 3. The method of repairing water impermeability and permeability in the ground according to claim 1 or 2, wherein the ground is gravel ground. In the ground according to any one of claims 1 to 3, wherein the superabsorbent polymer particles are at least one selected from the group consisting of starch-based, cellulose-based and synthetic polymer-based particles. Impermeable and permeable restoration method.

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