JP5309384B2 - Ground improvement method - Google Patents

Description

  The present invention relates to seismic reinforcement in the vicinity of concrete structures and underground structures, and to ground improvement methods for constructing concrete structures by excavation after injection, and more specifically, semipermanently durable such as liquefaction countermeasures It is related with the ground improvement which is requested | required and it is requested | required that it does not have a bad influence on an underground structure in order to contact a concrete structure and a buried object permanently. In particular, by reducing the influence of the reaction product of the silica injection material in the entire ground improvement area, and reducing the sulfate ions in contact with the concrete structure or buried in the soil, the concrete structure and the like are protected, and in the groundwater The present invention relates to a ground improvement method capable of preserving water quality by keeping a small amount of reaction products and is excellent in liquefaction countermeasure work and ground injection near a river.

  In ground improvement work by injecting chemicals with silica as the main agent, when performing ground improvement over a wide area, mainly in the vicinity of structures, such as liquefaction countermeasures, it is necessary to obtain long-term durability with a long gelation time It becomes. For this purpose, it is necessary to use an acidic silica solution from which alkali, which is a deterioration factor of the water glass injection material (water glass grout), is removed with an acid. For this reason, sulfuric acid is used as a curing agent for removing the alkali in the water glass and solidifying the silica. Sulfuric acid can change the pH even if the amount of sulfuric acid added is small compared to other acids and salts. For this reason, since ground improvement with a small amount of water-soluble reaction by-products other than silica can be achieved, there is an advantage that it is difficult to affect the surrounding environment in view of the amount of reaction products.

  However, when injecting chemicals to prevent liquefaction of buildings, when performing ground improvement using non-alkaline injection materials, sodium sulfate, which is a water-soluble reaction by-product in gelled products, and sulfate radicals associated with excess sulfuric acid are eluted. Then, it may come into contact with a concrete structure or a buried object in the soil, or may elute into groundwater and contact the concrete structure or the buried object in the soil, thereby adversely affecting the concrete structure or the water quality. Here, in the present invention, the concrete structure is a structure made of concrete, such as an underground structure such as a tunnel, a retaining wall of a slope, a revetment structure, a structure such as a house, a road, a tank, a manhole, etc. Examples include underground concrete such as underground.

  FIG. 10 shows the relationship between the silica-based solution and pH. Conventionally, in order to obtain a silica solution in a non-alkali region, an active silica injection material obtained by removing alkali by ion exchange treatment, a silica colloid injection material obtained by increasing the active silica, or a silica colloid, water glass and an acid. Non-alkaline silica injecting material mixed with water, acidic silica injecting material mixed with water glass and acid, and non-alkaline silica that adjusts gelation time neutrally by adding pH buffering agent or alkaline agent to acidic silica Implants have been proposed.

  This silica injection material has a long gelation time, excellent in a wide range of permeability, and has long gelation time and excellent long-term durability because the alkali that causes deterioration of the water glass injection material is removed with an acid. In terms of obtaining a consolidated region having excellent durability over a wide range, it has unique characteristics that cannot be obtained with water glass injection materials in other alkaline regions.

  As the acid, sulfuric acid, phosphoric acid, or a mixture thereof is used in order to efficiently neutralize the alkali of the water glass, or an acidic salt such as a sulfate, phosphate, or aluminum salt is used. In this case, sulfuric acid is a divalent acid, and in the acidic region, the pH can be adjusted by adding a small amount compared to phosphoric acid that reacts monovalently, so that it is excellent in convenience as a pH adjuster for the injection material.

  In addition to these, as a ground improvement technique using a water glass-based injecting material, Patent Document 1 discloses a technique for containing a water ion sequestering agent or a phosphate compound in water glass. According to this, it is said that the elution of the alkali from the concrete structure or the like can be prevented, and the gelled product of the water glass can be prevented from being dissolved by the alkali.

Japanese Patent No. 2552612

  However, sulfate ion reacts with calcium hydroxide in the hardened cement to produce gypsum, and the gypsum that is produced generates ettringite by hydration of calcium aluminate and tricalcium aluminate (C3A) in the hardened cement. It is already known that the ettringite produced and shows a large volume expansion when producing crystals, and the concrete is damaged by the expansion pressure.

  Accordingly, an object of the present invention is to reduce the sulfate ion in contact with the concrete structure or the buried object in the concrete while reducing the influence of the reaction product of the silica injection material in the entire ground improvement region while using sulfuric acid. An object of the present invention is to provide a ground improvement method capable of protecting structures and the like.

In order to solve the above-mentioned problems, the present inventors have intensively studied the following points.
That is, the ground improvement method of the present invention uses sulfuric acid to inject non-alkaline silica-based injecting material containing sulfate ions into the vicinity of the concrete structure or the vicinity of the planned portion for constructing the concrete structure after excavation. However, it is related to the ground improvement method that forms the ground improvement region by not adversely affecting the concrete.

  Conventionally, acid-to-neutral water glass grout obtained by removing alkali in water glass by using sulfuric acid and phosphoric acid or sulfuric acid and phosphoric acid together as acid when gelling water glass in acidic region The method of injecting the material into the ground has already been invented by the present applicant. The present applicant has also reported that acidic water glass grout containing a sequestering material such as phosphoric acid and phosphate forms a coating layer on the concrete surface to prevent elution of concrete alkali.

  In addition, in the ground to be injected, the present inventor paid attention to the fact that sulfuric acid is the most efficient and economical as the acid used for the non-alkaline silica solution and has few reaction products. It is important to adjust the concentration of sulfate ions in the lower injection ground so that the concrete structure is not adversely affected.

  For this reason, as a result of various studies over many years, the present applicant has clarified the influence of sulfate ions on the concrete, the limit of sulfate ions in consolidated soil solidified with a non-alkaline silica solution, and the influence on the concrete. The concentration of sulfate ion in concrete and the concentration of sulfate ion in the whole ground to be injected was clarified. The effect of the injection material containing sulfate ions on the concrete is different from the effect of simply curing in sulfuric acid or sodium sulfate aqueous solution. The effect of sulfate ions on the concrete is not determined by the sulfate ions contained in the injection material but is solid. It is determined by the sulfate ion concentration eluted from the soil (sand gel). Furthermore, the sulfate, which is a reaction product when solid soil with non-alkaline silica-based injection material using sulfuric acid is cured in water, is cured sooner or later. It was found that almost all of the water was dissolved in water, and the speed was related to the ground conditions, groundwater conditions, the position of the concrete structure and the structure.

  In other words, the present inventors changed the way of thinking about the influence of the conventional acidic water glass grout on the concrete structure from the fact that only the composition of the acidic water glass grout, that is, the concentration and mixing ratio of water glass and sulfuric acid and phosphoric acid. The effect on the concrete is due to the concentration of sulfate ions in the consolidated soil (sand gel) by the acid water glass, and further due to the concentration of the water-soluble reaction product eluted from the sand gel into the groundwater in the ground improvement region, In addition, the concentration was related to the pouring conditions, soil conditions, groundwater conditions, and the positional relationship with the concrete structure, and it was noted that the concentration changed over time based on these relationships. Then, the present invention was completed in consideration of the sulfate ion concentration of the consolidated soil under the groundwater surface and the influence on the concrete structure, and the change of the sulfate ion concentration in the groundwater in the entire ground improvement region. Based on these research results, injecting non-alkaline silica-based injection containing sulfate ions, the inventors have invented an injection design method and an injection method that do not adversely affect concrete.

Based on the above idea, the present applicant has found the following method to prevent the sulfate ion concentration in the ground from affecting concrete. That is,
(1) In formulating a non-alkaline silica solution, use an acid other than sulfuric acid to reduce the amount of sulfuric acid used. For example, non-sulfuric acid salts such as aluminum chloride, phosphoric acid, phosphates, etc. were used as sulfuric acid alone. In this case, a part of the amount of sulfuric acid necessary for obtaining a predetermined gel time at the water glass concentration is replaced with sulfuric acid.
(2) A non-alkaline silica grout containing a sufficient amount of sulfuric acid as an active ingredient is injected into the ground so that the concentration of sulfate ions in the groundwater in the ground to be injected does not affect the concrete as a whole.

  Specifically, (i) It is partially injected into the ground improvement region. That is, a non-consolidated part is interposed between the consolidated parts. Thereafter, sulfate ions, which are water-soluble reaction products, elute over time in the portions not injected from the consolidated sand, and are diffused and diluted by the groundwater throughout the ground improvement region. As a result, the concentration of sulfate ions in the entire ground improvement region is lower than the concentration of sulfate ions in the consolidated portion at the time of injection. As a result, even if the sulfuric acid ion concentration of the injected liquid itself is high, the sulfuric acid ion concentration of the groundwater in the entire ground is reduced to a concentration that does not adversely affect the concrete.

  (Ii) Ground improvement region by injecting non-sulfuric silica grout or low-concentration sulfuric acid silica grout or alkaline silica grout having a lower sulfuric acid content into the portion where the sulfuric silica grout of (i) is not injected. As a whole, the sulfate ion concentration does not adversely affect the concrete, and the injection consolidation effect of the entire ground improvement area is ensured.

  In this case, the alkaline silica-based injection material cannot obtain durability because excessive alkali or unreacted water glass remains in the gel, but the excess acid eluted from the sulfuric acid-based acidic silica injection material consolidation region Durability can be improved by intruding into the injection region of the alkaline silica injection material to neutralize excess alkali. As a result, the entire ground improvement region can be a durable consolidated region. In addition, examples of the silica-based injection material that does not contain sulfate ions include phosphoric acid silica-type injection materials in which alkali in water glass is removed with phosphoric acid, Is an acidic silica injection material in which a part of sulfuric acid necessary for obtaining a predetermined gel time only with sulfuric acid at that silica concentration is replaced with phosphoric acid, or an acidic salt such as aluminum chloride or acidic sodium phosphate , Etc. can be used.

  If the ground improvement region is a ground with a lot of calcareous material such as shells and coral sand, the calcium content reacts with sulfate ions to become calcium sulfate and fixes sulfate ions. In addition, a reactive agent that fixes sulfate ions is added to an acidic silica-based injection material that contains sulfate ions, or an aqueous solution of a reagent that fixes sulfate ions in advance or after injection is injected into the ground before injection. To do. In this case, if a calcium salt is present in the ground, it reacts with sulfuric acid to fix sulfate ions, and sulfate ions can be reduced. Examples of the reactant include carbonates and hydroxides of calcium and magnesium.

  In particular, the concrete vicinity or contact area where the cemented soil with sulfuric non-alkaline silica may be in contact for a long time is in a state where it is constrained by the impermeable consolidation region, so that groundwater contains the sand gel. Sulfate ions are difficult to elute and difficult to dilute. For this reason, the region sandwiched between the concrete structure and the improved portion is a consolidated region of a non-alkaline silica-based injection material having a protective function for concrete or a silica-based injection material that does not contain sulfate ions. The method of blocking the influence of sulfate ions can be taken. In particular, in the case of hollow concrete structures such as tunnels and joint grooves, when the elution water of gelled material penetrates into the hollow part through concrete or cracks, the internal elution water evaporates from the concrete even if the sulfate ion concentration of the injected solution is low. Since there is a danger that the sulfate ion concentration is concentrated, it is preferable to inject a phosphoric acid-based non-alkaline silica-based injection material into the outer peripheral portion.

  The verification test results by the applicant will be described below. Usually, when water glass is used as an active ingredient and the alkali in the water glass is removed only with sulfuric acid, the water glass has a molar ratio of 2.8 to 5.0 and the silica concentration caused by the water glass is 2 to 15% by mass. When the time is 1 hour to 20 hours, the concentration of sulfate ions is 160000 ppm to 8500 ppm. So, concrete specimens (diameter 5cm x 10cm) were immersed in curing water of sodium sulfate aqueous solution with the concentration of 50000ppm, 10000ppm, 8000ppm, 5000ppm, 3000ppm, 0ppm (blank) with sulfate ion, and after curing for a certain period, cut with diamond cutter The erosion depth was measured with phenolphthalein. As a result, the erosion depth was clearly recognized in the case of 50000 to 10000 ppm, whereas almost no penetration was observed at 5000 ppm or less. The 8000 ppm was somewhat eroded after one year.

FIG. 1 shows the results of immersing a concrete specimen in an aqueous sodium sulfate solution and observing the influence of the concrete due to the concentration of sulfate ions. As a result, the concentration of sulfate ions affecting concrete structures within one year is remarkably 10,000 or more, and the concentration of sulfate ions affecting concrete after one year is 10000 ppm to less than 5000 ppm. It was found to be between 5000 ppm. For this reason, the applicant further. After confirming the condition of the concrete specimen surface of each concentration after 3 months, 6 months, and 1 year, if the sulfate ion concentration is 5000 ppm or less, there is no change even after 1 year. When the sulfate ion concentration is 10000 ppm, there is no change until 3 months, but expansion peeling appears after 6 months and becomes remarkable after 1 year (Table 1).

○: No abnormality in appearance shape △: Surface is expanded and part of the surface is peeled ×: Surface is expanded and surface peeling is remarkable

  Further, the applicant of the present invention is 300 mL of a sand gel specimen (a porosity of 0.4, a filling ratio) solidified with an acidic sulfuric acid silica grout of the same volume embedded in a mortar specimen having a diameter of 5 cm and a height of 10 cm (sulfate ion concentration 50000 ppm). 1) was prepared, and this was cured 10 times in the curing water, and the concentration of sulfate ion eluted in the curing water was measured. FIG. 2 shows the sulfate ion concentration in the sand gel calculated from the eluted sulfate ions. From this, it was found that almost all sulfate ions in the sand gel were eluted within 3 months under the size and curing conditions of the sand gel.

  Based on the above results, sulfate ions are eluted from the solidified body (sand gel) into the groundwater, and finally the sulfate ion concentration in the entire ground improvement region is lower than the sulfate ion concentration contained in the solidified body at the time of injection. I understood that. In actual sites, the rate of sulfate ion reduction in the consolidated body depends on the size of the consolidated body, soil permeability, groundwater flow speed, positional relationship with the building, etc. It can be seen that the entire region is diffused and uniformized. On the other hand, a decrease in the concentration of sulfate ions remaining in the solid (sand gel) gel means an increase in the concentration of sulfate ions in the groundwater. Finally, the sulfate ion concentration in the ground improvement area is averaged. Therefore, the sulfuric acid concentration of the groundwater of the whole injection target ground and the influence of concrete become a problem.

In the immediate vicinity of the contact part of the concrete structure and the like, it is restrained by the impervious solidified part by injection between the concrete structure and the peripheral part, so the sulfate ion in the gel is less diluted and remains in the gel for a long time It seems that sulfate ions are gradually eluted into the surrounding groundwater from the outer periphery of the ground improvement area, and the concentration of sulfate ions in the entire ground improvement area decreases, and attached to the solid structure in the immediate vicinity of the concrete structure. Sulfate ions are reduced. However, the rate of reduction of the sulfate ion concentration in the immediate vicinity of the concrete is unclear because it varies depending on the aforementioned requirements. For this reason, it is preferable to interpose the consolidation part by the phosphoric acid type non-alkaline silica grout in the region between the solidification part of the sulfuric acid type non-alkaline silica grout and the concrete structure in the concrete nearest part and the contact part. In this case, before the sulfate ions attack the concrete, the phosphate ions reach the concrete and react with the calcium content of the concrete to form a protective film with a chelate effect on the concrete surface together with the silica content to block the sulfate ions. Based on the above, if the sulfate ion of the entire injected ground at the time of construction is set to 10000 ppm or less, the applicant will reduce the sulfate ion concentration in the ground improvement region to almost ½ over a year due to various factors of Formula 1. did. And since the adverse effect of sulfate ions on concrete appears in half a year to one year, it was speculated that if the average sulfate ion concentration of the entire ground improvement region is reduced to a concentration of 5000 ppm within one year, it will not have an adverse effect on concrete.
In addition, the sulfate ion concentration in the ground improvement region shown in the invention is the sulfate ion concentration X (ppm) in the unit volume of the ground = sulfate ion amount (mg) / the unit volume of the ground 10 cm ³ (1 L).
It is represented by

  Based on this knowledge, the present inventors have conducted further intensive studies. As a result, the inventors have found that the above-described problems can be solved by adopting the following configuration, and have completed the present invention.

In the ground improvement method of the present invention, a ground improvement region is formed by injecting a non-alkaline silica-based injecting material containing sulfate ions into the vicinity of a concrete structure or the vicinity of a planned portion for constructing a concrete structure after excavation. In the ground improvement method,
A ground improvement method for the entire ground improvement region by a non-alkaline silica injection material containing sulfate ions under the groundwater surface, wherein the soil is solidified by the non-alkaline silica injection material containing sulfate ions under the groundwater surface or the entire ground improvement region. The injection is performed so that the average of the sulfate ion concentration is 10000 ppm or less. Here, non-alkali means pH of 8 or less.

  In this invention, it is preferable that the average of the sulfate ion concentration contained in the said ground improvement area | region is 8000 ppm or less.

  Based on the above research results, the present inventors have intensively studied in order to solve the above problems, and as a result, a non-alkaline silica-based injecting material containing sulfate ions in the vicinity of the portion where the concrete structure is to be constructed is as follows. In the ground injection construction method that forms the ground consolidation region by injecting with the injection design, it was possible to protect the concrete protection structure by reducing the sulfate ion in contact with the concrete.

The effect of sulfate ions in the gelation of the injected solution injected into the ground on the concrete is different from the relationship between concrete and sulfate ions in the container. As a result of research over many years, the present applicant studied the behavior of sulfate ions in the gel in the ground. Based on the influence of sulfate ions on the concrete in the container, the inventors have found that it is possible to design and inject the ground in consideration of the following factors, and completed the present invention. That is, the present applicant has found that the influence of sulfate ions on the concrete is the solidified soil in the ground to be injected, or the sulfate ion concentration of the entire ground improvement region, and the concentration is X of the following formula (1), The factors for concrete were clarified. As a result, the ground improvement design method satisfying the following formula for the sulfate ion concentration X (ppm) in the improved ground after injection of solidified soil with the sulfuric non-alkaline silica injection material, and the non-alkaline silica-based injection material using the same Practical use of the injection method has become possible.
X1 = n × A × a (1)
X1: Sulfate ion concentration (ppm) in the entire ground improvement area
n: Soil porosity (%) / 100
Α: Filling ratio of filling material (%) / 100
a: Sulfate ion content of homogel (ppm)
X1 ≦ W1 Formula (2)

When considering the fluctuation Y of sulfate ion X2 = n × A × a × Y (3)
X2: Sulfate ion concentration (ppm) in the entire ground improvement area
n: Soil porosity (%) / 100
Α: Filling ratio of filling material (%) / 100
a: Sulfate ion content of homogel (ppm)
Y is one or more of the following parameters: Δ1: Ratio of injected portion in improved region (%)
Δ2: Rate of change with time due to elution of sulfate ions into groundwater (= α) Δ2 = 1−α
Δ3: Rate of sulfate ion fixation in the ground (= β) Δ3 = 1−β
Δ4: Substitution rate of sulfate ions by non-sulfuric reactant in the injection material X ≦ W2 Formula (4)
W1 and W2 are determined by the importance of the structure, the ground condition, the groundwater condition, the positional relationship with the underground structure, and the structure of the underground structure.

Further, in formulas (2) and (4), W1, 2 ≦ 10000 ppm is set.
In Expressions 1 to 4, nxA may be the injection rate B (injection amount per unit soil volume). For example, when the injection amount used to improve 1 m ³ of soil is 0.4 m ³ , the injection rate B = 0.4.

<Specific example>
The sulfate ion concentration X (ppm) in the improved ground after the injection of the sulfuric acid-based non-alkaline silica injection material can be obtained from the formula (1).
X1 = n × A × a
Here, n is the porosity (%) / 100 of the soil, A is the gap filling rate (%) / 100 by the injection material, and a is the sulfate ion content (ppm) of the homogel (corresponding to the injection solution).
For example, if n = 0.4, A = 1, and a = 25000 ppm,
X1 = 0.4 × 1 × 25000 (ppm)
= 10000 (ppm)

Further, the sulfate ion concentration X (ppm) in the ground improvement region is obtained by the following formula.
X2 = n * A * a * Y Formula (3)
In, for example, when Δ1 = 40% and the above-described sulfate-based silica injection material is used, sulfate ions in the improved ground region are
Y = 0.4 × 1 × 25000 × 0.4
= 4000ppm

From this, the sulfate ion concentration of the consolidated soil in the improved ground is 10000 ppm. Usually, when the silica concentration of water glass is 4-5 mass%, when using sulfuric acid alone, a sulfate ion concentration of 50000-30000 ppm is necessary. Therefore, it can be seen that in order to make a = 25,000 ppm, the deficiency of sulfuric acid can be replaced with phosphoric acid, AlCl ₃ or the like.
a = 20000 ppm, n = 0.4, A = 1.01.0
X1 = 20000 × 0.4 × 0.1 = 8000 ppm
One year later, when sulfate ion is reduced by 40%,
Δ2 = 1−0.4 = 0.4
X2 = 20000 × 0.4 × 1.0 × 0.6 = 4800 ppm <5000 ppm
And less than 5000ppm, and does not affect the concrete structure.
When A = 30000 ppm, n = 0.4, A = 1.0, Δ2 = 1−0.4 (phosphoric acid or aluminum chloride is replaced with sulfate ion 40%),
X2 = 30000 × 0.4 × 1.0 × (1-0.4) = 7200 ppm
If Δ2 = 1−0.6 in the above equation (60% phosphoric acid or aluminum chloride is replaced with sulfate ion),
X2 = 30000 × 0.4 × 1.0 × (1-0.6) = 4800 ppm ≦ 5000 ppm

That is, the ground improvement design method of the present invention is a ground improvement design method used in the ground improvement construction method of the present invention.
The sulfate ion concentration X of the consolidated soil below the groundwater surface in the ground improvement region represented by the following formula (1) is evaluated by the following formula (2).
X = n × A × a (1)
X ≦ W (2)
n: Soil porosity (%) / 100
Α: Filling ratio of filling material (%) / 100
a: Sulfate ion content of homogel (ppm)
nxA may be an injection rate B (injection amount per unit soil volume) W: Average concentration of sulfate ions in the target ground improvement region.

When considering the fluctuation Y of sulfate ion, a ground improvement design method characterized by evaluating the sulfate ion concentration X (ppm) in the improved ground represented by the following formula (3) by the following formula (4).
X = n × A × a × Y (3)
X ≦ W (4)
n: Soil porosity (%) / 100
Α: Filling ratio of filling material (%) / 100
a: Sulfate ion content of homogel (ppm)
Y is one or more of the following parameters Δ1 to Δ4,
Δ1: Ratio of improved ground in the ground improvement area (%) / 100
Δ2: 1-time change rate α (%) / 100 due to elution of sulfate ions into groundwater
Δ3: 1-sulfate ion fixation ratio β (%) / 100 in the ground
Δ4: Rate of exchange of sulfate ion (%) / 100 by non-sulfuric reactant in non-alkaline silica-based injection
nxA may be an injection rate B (injection amount per unit soil volume) W: Average concentration of sulfate ions in the target ground improvement region.

  Specifically, as shown in FIG. 3, by dividing the ground improvement region 2 so that the unimproved region 3 and the improved region 4 are equal, sulfate ions can be diffused to 5000 ppm or less. Further, a non-sulfuric silica solution may be injected into the unimproved region 3 of FIG. For example, water glass-heavy-sodium alkaline water glass grout, other water glass-inorganic salts, inorganic acids, organic reaction goods, and the like may be injected into the unmodified region. In this case, alkaline water glass grout is not durable because unreacted water glass or alkali remains in the alkaline region, but excess acid in the periphery penetrates into the gel to neutralize the alkali and is durable. Can be improved.

  In the present invention, if the average X value of the sulfate ion concentration of the entire ground improvement region that does not affect the concrete is W or less, W is 10000 ppm or less, preferably 8000 ppm or less, more preferably 5000 ppm or less. is there. The value of X can be determined by ground conditions, groundwater conditions, the structure and positional relationship of the concrete structure, water quality conditions, soil conditions, and the like. Further, in the ground improvement region, the non-sulfuric non-alkaline silica injecting material is injected into the non-sulfuric non-alkaline silica injecting material or the phosphoric acid injecting material containing the metal ion sequestering material or the alkaline silica. Preferably, the injection material is injected, and the sulfuric acid-based non-alkaline silica injection material may contain a phosphoric acid compound or a metal sequestering agent, and the silica compound used for the sulfuric acid-based non-alkaline silica injection material is: It is preferably at least one selected from the group consisting of water glass, activated silica or colloidal silica.

  Further, the non-alkaline silica-based injection material injection method of the present invention is designed to inject the non-alkaline silica-based injection material so that the X calculated using the ground improvement design method satisfies the above W. It is characterized by this.

  According to the present invention, the influence of the reaction product of the silica injection material in the entire ground improvement region is reduced, and the sulfate ions that come into contact with the concrete structure or the underground structure are reduced. It is possible to provide a ground improvement method with excellent water quality by protecting the water and reducing the number of reaction products.

It is a graph which shows the relationship between a sulfate ion concentration and the erosion depth of concrete. It is a graph which shows the density | concentration change of the sulfate ion from a sand gel. It is sectional drawing which shows one suitable embodiment of this invention. It is sectional drawing which shows other suitable embodiment of this invention. It is a graph showing the relationship between the gel time and pH of a silica injection material. It is explanatory drawing of the movement of a sulfate ion. It is explanatory drawing of the movement of a sulfate ion. It is explanatory drawing of the movement of a sulfate ion. It is a graph which shows the change of a sand gel sulfate ion concentration. It is a graph which shows the relationship between the pH range of a silica grout, a water glass density | concentration, and gelation time.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 3 is a cross-sectional view showing a preferred embodiment of the present invention. As shown in the figure, the ground improvement region 2 in the vicinity of the concrete structure 1 is divided into an unimproved ground 3 and an improved ground 4 having a predetermined width. In the illustrated example, the section in contact with the concrete structure 1 is the unimproved ground 3, and the improved ground 4 is provided outside the unimproved ground 3. Thereafter, the unimproved ground 3 and the improved ground 4 are alternately provided. ing. In the ground improvement method of the present invention, the sulfuric acid-based non-alkaline silica injection material is injected only into the improved ground 4. The widths of the unmodified ground 3 and the improved ground 4 can be set as appropriate in consideration of the concentration of sulfate ions in the sulfate-based non-alkaline silica injection material, the amount of injection, and the degree of diffusion of sulfate ions in the soil. it can. The unimproved region 3 can be consolidated using a non-sulfuric acid type grout.

  FIG. 4 is a cross-sectional view showing another preferred embodiment of the present invention. In FIG. 3, the unimproved ground 3 and the improved ground 4 are divided only in the depth direction. However, as shown in FIG. 4, the ground improved region 12 near the concrete structure 11 is further divided in the vertical direction. The unmodified ground 13 and the improved ground 14 may be used. The vertical width of the unmodified ground 13 and the improved ground 14 is also in consideration of the concentration of sulfate ions in the sulfate-based non-alkaline silica injection material, the injection amount, and the degree of diffusion of sulfate ions in the soil. These may be set as appropriate.

  As shown in FIG. 10, the non-alkaline silica-based injection material containing sulfate ions penetrates a wide range in the ground due to a long gelation time, and in order to obtain high strength in the improved ground, water glass and sulfuric acid are used. It is preferable that the silica content resulting from water glass is 2 to 15% by mass and the pH is 1 to 8.

  Conventionally, the influence of the injection solution on concrete has been mainly the sulfate ion and compounding recipe of the injection material itself. On the other hand, as a result of many years of research, the present inventors have found that (1) the composition of sulfuric acid-based injection material, (2) positional relationship with concrete, and ground improvement. It has been found that there is a relationship with the ratio of the non-injected portion in the entire region, the behavior of sulfate ions in the groundwater, and the groundwater situation, and the present invention has been completed. That is, the present inventor is that the water-soluble reaction product in the gel elutes into the groundwater, the concentration increases or decreases with time depending on the ground conditions and construction conditions, and the deterioration of the concrete also changes with time. Specifically, as shown in FIG. 4, by dividing the ground improvement region 2 so that the unimproved region 3 and the improved region 4 are equal, sulfate ions can be diffused to 5000 ppm or less.

  Moreover, in this invention, an alkaline silica injection material can be inject | poured into the unimproved grounds 3 and 13 in FIG. In FIG. 5, the graph showing the relationship between the gel time of a silica injection material and pH is shown. As shown in FIG. 5, the silica injecting material can obtain a long gel time in the acidic and alkaline regions, but the gelation in the alkaline region exhibits low strength because unreacted silica remains. In contrast, in the neutral region, the gel time is short, but there are few reaction by-products and the expression of strength is high. Baking soda type (non-sulfuric acid type) silica injection material, which is an alkaline silica injection material, gels silica by the coagulation effect of salt, gels in the alkaline region, and does not contain sulfate ions, so it is applied to concrete It is an injection material with little influence. However, since gelation occurs in the alkaline region, silica leaching occurs over a long period of time, resulting in a decrease in gel strength.

  Therefore, by injecting an alkaline silica injecting material into the unimproved grounds 3 and 13 in FIGS. 3 and 4, sulfate ions can be reduced and the entire improved ground can be consolidated. Furthermore, the excess acid in the gelation product of the sulfuric acid-based silica injection material enters the gelation product of the alkali-based silica injection material, and neutralization with the excess alkali in the gelation product of the alkali silica grout occurs, and the pH is changed over time. Will move to the neutral region and gelation of unreacted silica will proceed, resulting in an increase in strength.

  The sulfuric acid-based non-alkaline silica injection material according to the present invention may be adjusted to a predetermined gelation time by adding a reactive agent (curing agent) thereto. The water glass injection material thus manufactured is injected into the ground and solidifies the ground. At this time, this water glass injection material forms a protective coating on the surface of the concrete structure and cement hardened material (hereinafter referred to as concrete, etc.) existing in the ground at the same time. As well as the above-mentioned reactants, the intrusion of seawater and the like is blocked, and the elution of alkali from the inside of the concrete and the like to the outside is blocked. As a result, deterioration and neutralization of concrete and the like due to the reactant contained in the above-mentioned water glass-based injecting material is prevented, and the water glass-based injecting material gelled material also prevents the influence of alkali from cement and the like. Is done. Furthermore, since cement etc. and the said water glass type injection material gelatinized substance are couple | bonded firmly in the contact surface, neutralization of cement etc. is also prevented.

  Examples of the above-mentioned reactants include acidic salts, carbonates, bicarbonates, carbon dioxide, carbonated water, chlorides, aluminates, glyoxals, carbonates such as ethylene carbonate, polyvalent acetates, and the like. In addition, cement, lime, slag, and the like can be used alone as a reactive agent or in combination with the reactive agent.

  Furthermore, in this invention, it is preferable that a sulfuric acid type non-alkaline silica injection material contains a phosphoric acid compound or a metal sequestering agent. Phosphoric acid compound or sequestering agent mainly takes in calcium and magnesium such as concrete structures existing in the ground, and the protective coating composed of silica and phosphorus in silica solution, magnesium and calcium on the surface of the concrete structure (Masking silica) is formed. Thereby, the penetration | invasion of the sulfate ion to the inside of a concrete structure can be prevented, and the outflow of the alkali from the inside of concrete to the exterior can be prevented. As a result, deterioration of concrete can be suppressed.

  The phosphate compound or metal sequestering agent used in the present invention has a chelating effect, and examples thereof include phosphoric acid, various acidic phosphates, neutral phosphates, and basic phosphates. Examples thereof include condensed phosphates such as tetrapolyphosphate, hexametaphosphate, tripolyphosphate, pyrophosphate, acidic hexametaphosphate, and acidic pyrophosphate, and the condensed phosphates are sodium salts. As a phosphoric acid compound that forms a non-alkaline silica solution, sodium hexametaphosphate is particularly preferable because it forms a strong masking silica on the concrete surface. Examples of the sequestering agent include ethylenediaminetetraacetic acid, nitrilotriacetic acid, gluconic acid, tartaric acid or salts thereof. In the present invention, the phosphoric acid compound is most effective on the concrete surface in the presence of a silica solution. Masking silica is formed.

  Furthermore, in the present invention, the silica compound used for the sulfuric acid-based non-alkaline silica injecting material is preferably at least one selected from the group consisting of water glass, activated silica and colloidal silica. Here, the water glass is a water glass aqueous solution, and an aqueous solution containing an acid, a salt or an organic reactant, for example, an aldehyde compound such as glyoxal, an ester such as acetate, diester, triester and carbonate. Or neutral to non-alkaline silica solutions obtained by neutralizing the alkali of water glass with acid, activated silica, silica colloid, white carbon aqueous solution, and the like.

  In the present invention, as a method of reducing sulfate ions contained in the injection material, by using active silica from which Na ions have been removed from water glass by an ion exchange method, or colloidal silica obtained by concentrating active silica, The amount of sulfuric acid used to neutralize the pH can be reduced by reducing Na ions, which are alkali components derived from silica. Colloidal silica is charged and colloidally aggregated by removing Na ions, so it has a pH of around 9, and its molecular weight is large, so even if the pH is adjusted to near neutral with a small amount of acid, it is compared with water glass. Long gel time can be maintained.

  The activated silica is obtained by treating water glass with an ion exchange resin or an ion exchange membrane to remove a part or all of the alkali in the water glass. Further, an acid water glass obtained by mixing water glass and an acid may be passed through an ion exchange resin or an ion exchange membrane, and a part or all of the salt in the water glass may be obtained by desalting. Good. Furthermore, when the silica concentration of the active silica is low, it can be heated and concentrated, or colloidal silica, water glass or the like can be added as appropriate to increase the silica concentration. The silica concentration of the active silica is 1 to 8% by mass, and the pH is 2 to 4.

  Such activated silica grows to a silica particle size of 1 to 5 nm and gels after several days, but is stabilized by adding an alkali such as caustic alkali or water glass to a pH on the alkali side. To this stabilized activated silica, acid or salt is added on site to adjust pH and gelation time, and then used. Further, an acid can be added to the active silica to increase the pot life and the gelation time can be adjusted. This type of activated silica not only can adjust the gelation time long, but also gels at low concentrations and is excellent in durability after consolidation. The viscosity is almost the same as that of water and is 2 cps or less.

  In addition, colloidal silica is colloidalized, and activated silica is concentrated and polymerized by adding alkali or water glass to be stabilized in a weak alkali region. Accordingly, since the Na content is small, even at a pH near neutral, it is stable for a long time without gelation, and it is suitable for the present invention because it gels even with a small amount of reactant.

  Such colloidal silica is obtained by concentrating and increasing the particle size by heating the active silica and adjusting the pH to 9 to 10 and stabilizing, but the pH may be acidic to neutral. The colloidal silica thus obtained has a silica concentration of 5% by mass or more, usually about 30% by mass, and the particle size is 5 to 20 nm, but it should be increased to more than, for example, about 100 nm. Can do.

  In addition, as the sulfate ion fixing agent in the present invention, one or a plurality of magnesium salts or calcium salts are used, preferably magnesium or calcium hydroxide salts or calcium salts.

Hereinafter, the present invention will be described in detail with reference to examples.
<Example 1>
In the ground, the movement of sulfate ion was measured on the model ground when unimproved ground and improved ground were installed side by side. As shown in FIG. 6, a mortar specimen (diameter 5 cm × height 10 cm) cured for a long time in water is set as a region A in a sealed container having a diameter of 11 cm, and the non-alkaline silica-based injection material shown in Table 2 is used as Toyoura sand. And the gap filling rate with a non-alkaline silica-based injection material was adjusted to 1 and surrounded by a thickness of mcm. Further, the surrounding area was defined as a region B, surrounded by wet sand with a thickness of ncm, adjusted to a gap of 0.4, and then cured at room temperature for 1 year. No. 3 water glass was used as the silica solution of the non-alkaline silica-based injection material. The thickness m of the region A and the thickness n of the region B were performed in the combinations shown in Table 3.

  Results of comparing concrete test specimens with concrete specimens that had been subjected to uniaxial compression test after a year and then subjected to uniaxial compression test. In Examples 1-1 to 1-3 shown in Table 3, the same strength was expressed. In Example 1-4, although the strength was slightly reduced, the appearance of the concrete specimen was not changed. In Comparative Examples 1-1 and 1-2, cracks were observed on the concrete surface, and a low result was obtained as compared with a concrete specimen subjected to water curing. When the sulfate ions contained in each of the regions A and B were measured, they showed almost the same amount of sulfate ions, so that the diffusion of sulfate ions occurred in the regions A and B in contact with each other. It can be seen that the sulfate ion concentration became uniform.

When this result is applied to the following formula (1),
X = n × α × a × A × Y (1)
Y = Δ1
Then, in the case of Example 1-1, n = 1, A = 1, a = 26150 ppm, Δ1 = 34.5%,
X = 0.4 × 1 × 26150 × 0.345 = 3608.7 ppm.
Similarly, the results are shown in Table 3 for Examples 1-2 to 1-4 and Comparative Examples 1-1 and 1-2.

  From this result, even if the sulfuric acid-based injection material is partially injected into the ground improvement area, the diffusion of sulfate ions occurs over time, and the sulfate ion concentration is made uniform throughout the area, reducing the influence on concrete. I understand.

<Example 2>
Furthermore, as a result of conducting a similar experiment using the non-alkaline silica-based injecting material shown in Table 4 below in Example B, the strength decreased in Examples 2-1 to 2-3 as in Example 1-1. In Example 2-4, there was no change in appearance, but a decrease in strength was observed. In Comparative Examples 2-1 and 2-2, cracks were observed and a decrease in strength was observed. By this experiment, it is possible to improve the entire ground improvement region by using a part of the ground improvement region as the sulfuric acid-based injection material and the other non-alkaline silica-based injection material, and to reduce the influence of sulfate ions. .

  Moreover, from the results of FIG. 6 and Examples 1 and 2, it can be seen that the influence of the specimen on the concrete can be reduced by the sulfate ions diffusing to 5000 ppm or less by the ground contacting the concrete specimen after one year. For this purpose, by providing a solidification zone such as non-alkaline silica-based injection material containing a phosphate compound in the vicinity of the concrete, it is necessary that the concrete specimen touches a large amount of sulfate ions in the process until the sulfate ions diffuse. Can be avoided.

<Example 3>
A block of sand gel using a non-alkaline silica-based injection material (compound 2) formed into a 10 cm diameter cube so as to contact a concrete specimen having a thickness of 10 cm, a height of 30 cm and a depth of 30 cm, and a silica-based injection material containing no sulfate ions As shown in FIG. 7, a total of 27 blocks of 3 in the vertical direction, 3 in the horizontal direction, and 3 in the depth direction were used as the sand gel blocks using (Formulation 3) and combined in a grid pattern. There are 14 blocks using non-alkaline silica-based injection material, 13 blocks using silica-based injection material that does not contain sulfate ions, the area of non-alkaline silica-based injection material is 140 cm ³ , and silica that does not contain sulfate ions The area of the system injection material is 130 cm ³ . Table 5 shows the composition of each injection material. At this time, the porosity of the block was 0.4, and the injection rate was 100%.

* 1: Non-alkaline silica injection material containing sulfate ions * 2: Silica injection material containing no sulfate ions

One year later, concrete was formed into a cylinder with a diameter of 5 cm and a height of 10 cm at a position where the concrete was in contact with the ground improvement area and at a position away from the ground improvement area. The concrete specimen at the contacted position showed a slight decrease in strength compared to the water-cured concrete, but the specimen away from the ground improvement area showed no decrease in strength. When Y is Δ1, and the obtained result is applied to the equation (1),
Since n = 1, A = 1, a = 35379.4 ppm and Δ1 = 51.9%,
X = 0.4 × 1 × 35379.4 × 0.519 = 7344.8 ppm.
Furthermore, in order to reduce the influence on the concrete, 16 ml of 75% phosphoric acid was added to the non-sulfuric acid-based injection material and the pH was adjusted to 3. As a result, the influence on the concrete was as strong as that of the water curing. From this, it can be seen that the concrete protective effect of phosphoric acid can reduce the influence on concrete.

<Example 4>
As shown in FIG. 8, the experimental apparatus of Example 1 was installed in a water tank 60 cm wide and 30 cm deep, as shown in FIG. 8, and was 20 cm thick, 30 cm deep, 30 cm deep as an open area far from the concrete. 0.4 unmodified ground wet sand was provided. At this time, the region of the non-alkaline silica-based injecting material is 140 cm ³ , the region of the silica-based injecting material not containing sulfate ions is 130 cm ³ , and the unmodified ground is 180 cm ³ . Moreover, the result of having measured the change of the sulfate ion in the non-alkaline silica injection material block A surrounded by the sand gel block around concrete and the circumference | surroundings is shown in FIG.

From FIG. 9, the sulfate ion of block A is reduced to about 14100 ppm in the initial value and about 10450 ppm in the first month, the reduction rate is 74.1%, and the reduction rate is reduced to about 5100 ppm in the sixth month, and the reduction rate is 36.2%, 12 In the month, it decreased to about 4400 ppm and the reduction rate was 31.2%. One year after the sufficient diffusion of sulfuric acid,
Since n = 1, A = 1, a = 35379.4 ppm, Δ1 = 140 / (140 + 130 + 180) = 31.1%,
X = 0.4 × 1 × 35379.4 × 0.311 = 4401.2 ppm.

In addition, when Y = Δ2 is calculated using the reduction rate of the first month and the sixth month and applied to the equation (1), in the first month,
Δ2 = 74.1%,
X = 0.4 × 1 × 35379.4 × 0.741 = 10486.5 ppm.
Δ2 = 36.2% 6 months after the start of curing,
X == 0.4 × 1 × 35379.4 × 0.362 = 5122.9 ppm.

  One year later, the concrete was formed into a cylinder with a diameter of 5 cm and a height of 10 cm at a position where the concrete was in contact with the improved ground and a position away from the improved ground. The concrete specimen and the specimen away from the improved ground showed the same strength and no decrease in strength compared to the water-cured same concrete.

<Example 5>
Method of reducing sulfate ion by using sulfate ion fixing material Calcium carbonate does not affect the reaction in silica-based injection material that does not contain sulfate ion, but by combining with sulfate ion, calcium sulfate is generated and converted into a concrete structure To reduce the impact. In FIG. 7, 10 g of calcium carbonate as a sulfate ion fixing material was mixed with a silica-based injection material not containing sulfate ions. The formulation is shown in Table 6.

* 2: Non-alkaline silica-based injection material that does not contain sulfate ions * 3: Calcium carbonate

In the laboratory test, when an equivalent amount of calcium carbonate and sulfate ions react, an experimental result in which about 50 to 70% of sulfate ions are immobilized is obtained.
Y = Δ1 × Δ3
Δ1: Ratio of improved ground in the ground improvement area (%) / 100
Δ3: 1-sulfate ion fixation ratio β (%) / 100 in the ground
Since n = 1, A = 1, a = 35379.4 ppm, Δ1 = 51.9%, Δ3 = 50 to 70%,
X = 0.4 × 1 × 35379.4 × 0.519 × 0.5 to 0.7 = 3672.4 to 5141.3 ppm.

  In this example, the concrete was formed into a cylinder with a diameter of 5 cm and a height of 10 cm at a position where the concrete comes into contact with the improved ground one year later and at a position away from the improved ground. The concrete specimens in contact with each other and the specimens away from the improved ground showed the same strength as those obtained by water curing the same concrete, and no decrease in strength was observed.

<Example 6>
Method of reducing sulfate ions by exchanging sulfate ions with a silica-based implant containing no sulfate ions in the implant In the non-alkaline silica-based implant of Table 4, the non-alkaline silica-based implant is 50 % Was reduced to 5.75 mL, and the same pH and gel time were adjusted using 10 ml of 75% phosphoric acid as a non-sulfuric acid-based reactant. The formulation is as shown in Table 7 below.

* 1: Non-alkaline silica-based injection material that does not contain sulfate ions

When applied to equation (1),
Y = Δ1 × Δ4
Δ1: Ratio of improved ground in the ground improvement area (%) / 100
Δ4 :: Exchange rate (%) of sulfate ion by non-sulfuric reactant in non-alkaline silica-based injection material / 100
Since n = 1, A = 1, a = 35379.4 ppm, Δ1 = 51.9%, Δ3 = 50%,
X = 0.4 × 1 × 35379.4 × 0.519 × 0.5 = 3672.4.

  In this example, the concrete was formed into a cylinder with a diameter of 5 cm and a height of 10 cm at a position where the concrete was brought into contact with the improved area after one year and at a position away from the improved ground. The concrete specimens in contact with each other and the specimens away from the improved ground showed the same strength as those obtained by water curing the same concrete, and no decrease in strength was observed.

  From the above results, according to the present invention, the influence of the reaction product of the non-alkaline silica-based injection material in the entire ground improvement region is reduced, and by reducing sulfate ions in contact with the concrete structure or the buried object in the soil, It was confirmed that it is possible to provide a ground improvement method that protects concrete structures and the like and enables consolidation with better gel durability of silica.

1,11 Concrete structure 2,12 Ground improvement area 3,13 Unimproved ground 4,14 Improved ground

Claims (5)

In the ground improvement method of forming a ground improvement region by injecting a non-alkaline silica-based injection material containing sulfate ions into the vicinity of the concrete structure or the vicinity of the part to be constructed after the excavation of the concrete structure,
A ground improvement method of the whole land Release improvement area that by the non-alkaline silica injection material containing sulfate ions under the water table, caking earth or soil improvement by non-alkaline silica injection material containing sulfate ions under the water table A ground improvement method characterized by injecting so that the average sulfate ion concentration in the entire region is 10,000 ppm or less.   The ground improvement construction method according to claim 1, wherein an average concentration of sulfate ions contained in the ground improvement region is 8000 ppm or less. In the ground improvement design method used for the ground improvement construction method according to claim 1 or 2,
The ground improvement design method characterized by evaluating sulfate ion concentration X of the consolidated soil under the groundwater surface of the ground improvement area represented by the following formula (1) by the following formula (2).
X = n × A × a (1)
X ≦ W (2)
n: Soil porosity (%) / 100
Α: Filling ratio of filling material (%) / 100
a: Sulfate ion content of homogel (ppm)
nxA may be an injection rate B (injection amount per unit soil volume) W: Average concentration of sulfate ions in the target ground improvement region. In the ground improvement design method used for the ground improvement construction method according to claim 1 or 2,
The ground improvement design method characterized by evaluating sulfate ion concentration X (ppm) in the improved ground represented by the following formula (3) by the following formula (4).
X = n × A × a × Y (3)
X ≦ W (4)
n: Soil porosity (%) / 100
Α: Filling ratio of filling material (%) / 100
a: Sulfate ion content of homogel (ppm)
Y is one or more of the following parameters Δ1 to Δ4,
Δ1: Ratio of improved ground in the ground improvement area (%) / 100
Δ2: 1-time change rate α (%) / 100 due to elution of sulfate ions into groundwater
Δ3: 1-sulfate ion fixation ratio β (%) / 100 in the ground
Δ4: Rate of exchange of sulfate ion (%) / 100 by non-sulfuric reactant in non-alkaline silica-based injection
nxA may be an injection rate B (injection amount per unit soil volume) W: Average concentration of sulfate ions in the target ground improvement region. A non-alkaline silica-based injection material in which an injection condition is designed so that the X calculated using the ground improvement design method according to claim 3 or 4 satisfies the W, and a non-alkaline silica-based injection material is injected. Injection method of injection material.