JP4437481B2 - Ground improvement method - Google Patents

Description

  The present invention relates to the injection of silica grout in a non-alkaline region, particularly an acidic region, and is related to a ground injection method in which the gelation time of the injection solution is set from the injection time and the gelation time in the soil, and reliably infiltrates a wide range of injection regions. And equalizing the strength.

  Conventionally, the injection method using a silica solution has an injection hole interval (≈ permeation diameter) of about 0.8 to 1.0 m in diameter, a discharge rate of 8 to 20 l / min, and an injection stage pitch of 0.30 to 0.5 m. I took the way. If the interval between the injection holes is larger than this, consolidation is uncertain, and uniform consolidation cannot be expected. Therefore, it was necessary to improve the ground by shortening the injection hole interval.

  However, an injection method can be used to prevent liquefaction by using a silica solution having excellent long-term durability. Therefore, in order to obtain economy, it is necessary to increase the injection hole interval and obtain a large injection consolidation diameter. became. For this purpose, it is necessary to carry out large permeation consolidation with an injection hole interval of 1 m or more to 4 m, that is, a consolidation diameter of 1.5 m or more, for example 2 to 4 m, by infiltration between soil particles.

  In this case, the injection volume per injection stage is several hundred l or more, usually 400 l or more, or 1000 l or more, and it takes several to ten or more hours of injection time per injection stage. Since the gelation time of the liquid needs to be longer than the injection time for permeation between the soil particles, a long gelation time of several hours to several tens of hours is required.

  In addition, the liquefaction prevention injection naturally requires permanent and economical ground solidification. In order to obtain a permanent injection effect, it is necessary to infiltrate between soil particles at a low injection rate using a durable silica injection solution. This is because, in order to obtain economic efficiency, injection is performed at a high injection rate, or when the gelation time is short, pulse injection occurs and an unconsolidated portion is generated, and a permanent consolidated ground is not formed.

  However, low speed injections require longer injection times and therefore gelation times will naturally require longer time, which not only dilutes and disperses with groundwater, but also the injection ground and injections in between. It was found that the reaction time of the liquid becomes longer, which has a great influence on the gelation behavior such as the gelation time and the permeation solidification. In fact, for such new ground injection, a compounding design corresponding to the injection design for obtaining a reliable injection effect has not yet been established.

Japanese Patent No. 3509744

  The chemical solution in the ground is often neutral to alkaline in the planned injection ground, and when acidic silica grout is used, it moves in the neutral direction in the ground, or the acidic silica grout and the alkaline substance in the ground It will react and gel time will become short. The sandy ground near the coast, which is sometimes subject to liquefaction prevention methods, has a problem that there is a lot of ground with weak alkalinity mixed with shells, and the acidic silica grout rapidly increases in pH and gelation time is shortened rapidly.

  Therefore, in the past, excessive acidic reactants were mixed as acidic silica grout to be injected into the ground, and grout material having a long gel time was injected. In the conventional acidic silica grout, in order to increase the permeation distance, a long gelation time was obtained by setting the silica concentration low or setting the grout itself near pH 1 using a large amount of acid.

  In the actual injection, the in-air gelation time (Ta) of the injection solution is set by sand collected in the field ground, mixed with silica grout in the laboratory test, and the gelation time (Ts) of the sand gel, that is, the gelation time in the soil Is measured, and the amount of acid to obtain the gel time (Ts) in the soil corresponding to the time (H) for injecting the injection amount calculated from the necessary consolidation range is set, and the gelation time in the air of silica grout ( The method of determining the formulation with Ta) was taken.

  As described above, in order to form a ground having excellent durability, it is necessary to form a homogeneous consolidated body by infiltration between soil particles. For this reason, in order to obtain a consolidated diameter having a large diameter with a low discharge amount, a long gelling time (Ta) of several tens of hours is required. However, it has been found that when the acidic silica injection solution having such a long gelation time is injected, if the solidification system is large as 1.5 to 4.0 m, the solidification becomes insufficient as the distance from the injection hole increases. In addition, it was found that the strength development of the improved ground could be slow, deviated without consolidating, or diluted with groundwater and insufficiently consolidated.

  That is, in the conventional temporary injection, the injection hole interval is about 1.0 m, that is, the consolidation diameter is about 1.0 m, and the injection amount of one stage is about several tens of liters. The effect of was able to be obtained. On the other hand, when the injection hole interval is 1 to 4 m, the injection per stage is an injection of several hundred to several thousand l, and the injection time must be continuously injected for several hours to several tens of hours. It was found that it was necessary to be based on a completely different idea from the conventional way of thinking.

  Therefore, the present inventor, in permanent ground improvement such as liquefaction countermeasure work that continuously injects between soil particles for such a long time, the characteristics of the grout in the ground are in contact with the soil particles during penetration and penetrated into the ground. In view of the fact that the process changes every moment, the present invention was completed with the idea that it is necessary to adopt a blending setting and injection method corresponding to such changes and behaviors of the characteristics of the injection material. .

  In large-scale ground improvement work with large intervals between injection holes, appropriate inclusion design and injection design must be performed in response to different ground conditions and design strength at each site. For this reason, laboratory experiments are carried out using on-site collected soil, and the composition suitable for the pouring time and the target strength is determined.

For example, in the case of the conventional temporary injection, it is sufficient if the individual diameter is about 1 m in diameter. However, when a solidified diameter of 2 to 4 m is infiltrated between soil particles with a low-pressure infiltrator, continuous injection for 10 or more hours per stage is required. As during the time of injection, since it is not going to penetrate while contacting the soil, by reaction with components contained in the soil, also fluctuates soil gel time, and also affected by dilution of soil water The strength also changes.

Note During gelatinizing of the incoming material, it can while gelatinizing the grout itself range and local Release soil properties, related to the continuous infusion time per stage. The injection time is related to the discharge amount per minute, and the discharge amount per minute is determined by the injection method applied, the ground conditions, and the permeation limit injection pressure between soil particles. Therefore, it is necessary to conduct inclusion design such as silica concentration and gelation time by confirming experiments using the current excavated soil.

  The present invention performs an injection design to obtain the target strength based on these data, and a series of designs to obtain a reliable ground improvement effect, especially in a ground injection construction with a large durable injection hole gap. A method is provided.

  Therefore, the present applicant has elucidated the factors affecting the change in properties of the non-alkaline silica solution in the ground and the gelation behavior in the case of ground improvement with a large consolidated diameter. The ratio of the gelation time to the injection time in the soil (A) determines the formulation of the infusion solution that solidifies evenly in the ground without using any gelation modifier (acid or inorganic salt) and quickly develops strength. Thus, the problems were solved and the present invention was completed. Further, it has been found that if the interval between the injection holes is increased, the caking property near the boundary of the caking range per one is poor, but the present invention can also solve this problem.

Since the present inventors have for the solution of the above-described problems, (1) Blend the pH of the acidic silica solution in the beaker (aerial pH: pHa) and gel time (aerial gelation time: Ta) relations, (2 ) The pH of the in-situ sand mixed with the acidic silica solution in the small mold (diameter 5 cm x length 10 cm) and the gelation time (with soil gelation time: Ts) I investigated the relationship.

(3) Further, the pH of the consolidated soil permeated into a cylindrical mold having a diameter of 10 cm and a length of 2 m (soil infiltrate pH: pH _sf ), soil permeate gelation time (Ts _f ), and permeation length L The relationship between the strength of sand and the strength (qu _L ) of the consolidated sand at penetration length L was investigated. (4) From the relationship between the results and the strength and pH of the sampling specimens in the actual consolidated ground, the change and behavior of the characteristics when the acidic silica solution penetrated in the injection ground for a long distance was clarified. The inventors have found that the above-mentioned problems occur for the following reasons, and have solved the above problems and completed the present invention.

If a non-alkaline silica solution, such as an acidic silica solution, is continuously injected into an almost neutral or weakly alkaline ground that is normal ground, the neutralization reaction proceeds in the ground, or shells in the ground, etc. The silica solution reacts with alkali components or reacts with polyvalent metal ions such as Ca, Mg, Fe, etc. contained in the ground, and the pH of the silica solution shifts from acidic to neutral (soaking solution in soil (during infiltration) PHs _f ) of the injection solution) and the gelation time of the silica solution penetrating into the soil (gelation time in the penetrating soil: Ts _f ) is shortened.

In the initial stage of the injection, the silica solution in the initial stage always reacts with the new ground, so the above reaction proceeds rapidly, but the subsequent silica solution penetrates into the ground after the reaction, so there is little reaction with the ground. Therefore, the degree of increase in pH is reduced, and the pH of the soil osmotic solution (pHs _f ) is close to the pH (pHa) of the infusion solution formulated in the air, thus reducing the gelation time in the osmotic soil. The tendency decreases and approaches the air gelation time (Ta). For this reason, it was found that the longer the permeation distance, the longer the permeation region closer to the injection hole, the longer the permeation time, and the longer the permeation, the longer the permeation time.

  As the injection hole interval becomes larger than that of the conventional injection hole interval of 1 m, the permeation area of the injection solution rapidly increases although the pH of the tip of the injection solution that has infiltrated increases due to reaction with new soil. Since the pressure gradient of the injection pressure is greatly reduced, the permeation area is expanded, the permeation rate per unit area of the infusion liquid is reduced, the infusion liquid is diffused, and diluted with ground water to reduce the caking property.

  For this reason, the injection solution in the soil in which the subsequent gelation time remains long dilutes and disperses and loses its caking property. For this reason, as it is separated from the central portion of the injection region, not only is the strength significantly reduced and an unconsolidated portion is generated, but also the injection solution deviates from the injection range or deviates to the ground part during the injection. Once it deviates, it must stop and wait for consolidation without stopping, in which case it takes a long time to wait for consolidation, and even after reinjection, the consolidated state is uneven, so injection It was found that the target ground could not be injected as planned, and the consolidation inside the injection area was uneven.

  The present inventor who found the above characteristics solved the above-mentioned problems by the following method.

The present inventors investigated the improved ground in advance, calculated the injection time H from the injection hole interval, injection stage, injection rate, injection amount Q, and injection speed q, and the gelation time of the in-situ sand of the chemical solution to be injected By setting the ratio A of (Ts) and injection time H to a range of 0.01 to 1, preferably 0.03 to 0.5, the amount of acidic reactant used is small and the gel time in soil is shorter than the injection time (H). Even if it was a chemical | medical solution, the ground of the wide improvement range could be improved, the ground could be solidified reliably, and said subject was able to be solved by setting the following mixing | blending settings.

1. A ground injection method for injecting non-alkaline silica injection solution into the ground, and in the ground to improve the ground, the composition of the injection solution is set by the following methods (1) to (8) Improvement method.

(1) Check the relationship between the composition of the injection solution (silica concentration and reactant concentration), air pHa, and air gelation time (Ta).
(2) Using the soil collected from the ground to be improved and the injection solution, check the composition of the injection solution and the relationship between the gelation time (Ts) in the soil and the pH in the soil.
(3) Using the collected soil and the injected solution, check the relationship between the composition of the injected solution and the strength (qu) of the consolidated collected soil.
(4) Determine the silica concentration of the injection solution from the required ground improvement strength.
(5) Calculate the injection volume per unit volume of improved soil in the soil layer to be injected.
(6) The injection hole interval and the injection stage length are determined, and the injection amount (Ql) per stage is calculated from the amount of soil per unit stage.
(7) Set the discharge amount (ql) per minute and set the injection time (H) per injection stage.
(8) to set the reactant concentration of the infusate from the relationship between the injection time (H) and soil gelation time (Ts).

2. 2. The ground improvement method according to claim 1, wherein the strength (qu) of the consolidated soil is confirmed by applying an overpressure in (3).

3. 3. The ground improvement method according to claim 2, wherein the discharge rate (ql) per minute in (7) is from an initial linear gradient region in which the injection speed and the injection pressure are proportional to each other and a transition region from the initial linear gradient to the fracture gradient region. Ground improvement method characterized by injecting at an injection rate of.

4). The ground improvement construction method according to claim 1, 2 or 3, wherein the injection time (H) and the gelation time (Ts) of the injection solution are set so as to satisfy the following conditions.

(1) 0.01 ≦ A < 1
(2) Ts <H <Ta
(3) 15 minutes <H <1500 minutes (4) pHa is 1.5-8
here,
A: Ratio of soil gelation time Ts ( min ) to injection time H ( min ) (= Ts / H)
Ta: In-air gelation time of injection solution (20 ° C)
Ts: Gelation time (min) of mixed soil of in-situ collected soil and injected solution
H: Injection time per stage (minutes)
pHa: Air pH

5. The ground improvement construction method according to claim 4, wherein the ground improvement construction method is set so as to satisfy the following conditions.
(1) 0.01 ≦ A <1
(2) 10 minutes <Ts <H <Ta <4000 minutes
(3) 15 minutes <H <1500 minutes
(4) 2 <pHa <8
(5) 3 <pHs <9
here,
pHs: pH in soil

6). The ground improvement construction method according to claim 4 or 5 , wherein 0.03≤A≤0.5.

7). The ground improvement construction method according to claim 4 or 5 , wherein a different combination of A in a range of 0.01 to 1 is used during injection.

In 8.5, a ground improvement method using a combination of Ts of 10 minutes or less during injection.

In 9.1-5, the ground injection method with an injection interval of 1-4m.

10. Ground injection method in which the injection amount (Q) and injection time (H) per stage satisfy the following injection conditions in 10.1 to 5.
(1) Q ≧ 400l
(2) H ≧ 60 minutes

11. A ground injection method using an injection solution containing a metal ion sequestering agent as a silica injection solution in 11.1 to 5 or a silica injection solution not containing a metal ion sequestering agent.

In 12.1-5, the ground injection construction method in which the silica injection liquid contains Al ions.

13. The ground improvement construction method in which silica injection liquid is simultaneously injected from a columnar infiltration source or a plurality of injection points in 1-5.

In 14.1-5, the ground injection construction method inject | poured in order to prevent liquefaction of the ground directly under or near the structure.

In 15.1-5, the ground improvement construction method inject | poured into the structure directly under or near the structure, or the structure directly under or near the structure.

1. Because even if shortened Lido in gelation time by the present invention, may periphery near also ensure a homogeneous consolidation also injected consolidation diameter injection hole periphery by setting a sufficient penetration distance longer, osmotic diameter 1 Reliable injection of a large consolidated area of 4m has become possible.

2. It is not necessary to use an excessive amount of acidic reactant in the injected chemical solution, thereby reducing the reaction product and making the pH of the chemical solution higher than before, which is economical and makes the ground near neutrality. It is environmentally friendly by holding and has the effect of little impact on the groundwater and surrounding environment after construction.

3. Since an excessive gelation modifier is not used for the injected drug solution, the ground becomes strongly acidic and the strength development is not delayed as in the past. Improvement effect tends to appear.

4. Simultaneous injection or continuous injection from a plurality of discharge holes restrains each other by consolidation by adjacent injection holes, so that the injection solution at the tip is difficult to dilute and disperse normally and gels normally. For this reason, even if the handling consolidation area per one is large, it is not necessary to reduce the consolidation of the boundary portion between the adjacent injection holes.

  As described above, the main construction work such as a liquefaction countermeasure work must be performed with an appropriate blending design and injection design corresponding to the ground conditions and design strengths that differ from site to site. For this reason, laboratory experiments are performed using on-site collected soil, and the composition suitable for the injection time and target strength is determined.

  For example, in the conventional temporary injection, a consolidated diameter of about 1 m in diameter can be used. However, when solidified with a diameter of 2 to 4 m is infiltrated between soil particles by low-pressure osmotic injection, continuous injection for several tens of hours per stage is required. During the injection time, it permeates while in contact with the soil, so the gelation time in the soil fluctuates due to the reaction with the components contained in the soil, and the strength is also affected by the dilution of the soil water. Also changes.

  The gelation time of the injection material is related to the possible range of gelation time of the injection material itself, the soil properties of the local board, and the continuous injection time per stage. The injection time is related to the discharge amount per minute, and the discharge amount per minute is determined by the injection method applied, the ground conditions, and the permeation limit injection pressure between soil particles. Therefore, in addition to the past experience and accumulated data and know-how, it is necessary to carry out blending design such as silica concentration and gelation time through confirmation experiments using on-site collected soil.

  In the liquefaction countermeasure work, the era of the injection hole interval (osmosis consolidation diameter) is aiming for 1.5 to 4.0 m in the rapid penetration injection method from the conventional 0.5 to 1 m. Along with the expansion of the injection hole interval, the injection volume per stage is conventionally 100 to 200 l at a diameter of 1 m, and the injection time is from several tens of minutes to several tens of minutes. It is becoming a completely different content of setting a gel time corresponding to continuous injection of 10 to several hours from time.

  When such chemical injection is used in this injection method, the inventor introduced the concept of gelation time in the soil to introduce the uncertainty of the injection effect caused by the widening of the injection hole interval. It was solved by setting the conditions in consideration of the factors that affect it.

  The silica grout used in the present invention is a grout made from water glass and is an acid water glass solution obtained by mixing water glass and acid to dealkali, or obtained by dealkalizing water glass. Silica grout with active silicic acid or silica based on colloidal silica concentrated and granulated as an active ingredient. Add acid to this to make acidic silica solution, or add water glass or alkali. PH is adjusted to be stabilized with alkali, and acid silica grout with acid added, or colloidal silica or active silica mixed with acid or water glass, or acid silica grout mixed with acid water glass, etc. .

  More specifically, the water glass is completely or partially removed with an ion exchange resin or an ion exchange membrane, or the water glass is mixed with an acid to neutralize the alkali in the water glass. Acidic active silica obtained by removing all or part of the acid or salt in the acidic water glass with an ion exchange resin or ion exchange membrane, or a colloidal stabilized by weak polymerization by concentration polymerization Add silica to silica, activated silica or colloidal silica with water glass, acid silica grout with acid added, or a mixture of the above silica or water with glass or alkali, adjust and bring to site. Examples thereof include silica grout using an acidic silica solution as a raw material after pH adjustment.

  Alternatively, these acidic silica grouts can be rapidly added by adding a poorly soluble alkaline agent such as calcium carbonate, magnesium carbonate, calcium hydroxide, magnesium hydroxide, calcium silicate, etc., and gradually moving in the neutral direction by the neutralization reaction. It is also possible to suppress the shortening of the gelation time due to an increase in pH and to reach the pH range close to neutral after gelation to suppress the acidification of groundwater.

  In general, alkaline silica grout using water glass as a silica source has a large gel shrinkage, and unreacted water glass is eluted to reduce durability. On the other hand, acidic water glass grout has little shrinkage of silica but large shrinkage. On the other hand, the active silica exhibiting acidity obtained by ion exchange of water glass has high strength and is stable with little shrinkage even at a low concentration.

  In addition, colloidal silica grout with increased active silica has large silica particles and the gel itself is stable. Is so small that it can be almost ignored, the gel is structurally and chemically stable and has excellent long-term durability. These are preferably used alone or in combination according to the application.

  The water glass used in the present invention may have any molar ratio, but is practically a water glass from JIS No. 3 water glass to a molar ratio of 5. In addition, water-soluble silicates such as potassium silicate and aluminum silicate can be used in place of the water glass.

  Examples of the curing agent used in the present invention include mineral acids such as phosphoric acid and sulfuric acid, sodium hydrogen sulfate, aluminum sulfate, aluminum chloride and the like, salts that dissolve in water and exhibit relatively strong acidity, carbon dioxide, carbonates, and the like. Inorganic salts, metal organic acids, and the like.

  Among them, in particular, sequestering agents such as phosphoric acid and phosphoric acid compounds, chelating agents, and further reactive agents mainly used in combination with sulfuric acid, etc. mask the concrete structures in the ground together with silica. Since the coating film of the hardly soluble silica compound is formed by the action, it is preferable because it has an effect of protecting the concrete.

  In addition, silica containing sequestering agents such as phosphate ions reacts with trace metals in the soil and calcium components such as shells to produce insoluble or poorly soluble silica compounds, thus passivating alkaline components in the ground, It is presumed that the shortening of gelation due to a sudden increase in pH of the silica in the soil during infiltration can be suppressed.

  Reactive agents include water-soluble sodium chloride, potassium chloride, calcium chloride and other mineral acid alkali metal salts, alkaline earth metal salts, or aluminum salts such as sulfate bands, aluminum chloride, polyaluminum chloride, and alum. In addition, a small amount of these may be added or used together to increase the buffering capacity and maintain the function as a gelling time adjusting agent.

  Furthermore, in the present invention, a metal ion sequestering agent other than the phosphoric acid compound can be used to expect metal ion masking. Such sequestering agents include tetrapolyphosphates, hexametaphosphates (especially sodium salts are good), tripolyphosphates, pyrophosphates, acidic hexametaphosphates, acidic pyrophosphates and other condensed phosphates, ethylenediaminetetraacetic acid Nitrilotriacetic acid, gluconic acid, tartaric acid, or salts thereof.

  Typical silica solutions used in the present invention include acidic silica solutions (silica liquid I) obtained by mixing water glass and acid to neutralize alkalis in water glass, colloidal silica (or active silica), and the like. An active silica colloidal silica solution (silica liquid II) obtained by mixing water glass and an acid is preferred. Among these, the difference between the acidic silica solution and the active silica-based colloidal silica solution is that, as shown in FIG. 1, the silica liquid I becomes an instantaneous setting region in the neutral region, so it is necessary to make it strongly acidic to obtain a long gel time. There is. Further, since the gelation time and pH curve are steep, it is difficult to adjust the gelation time.

  On the other hand, in the silica solution II, the gelation time is shortened in the neutral region, but it does not lead to instantaneous setting, so a long gelation time can be obtained in the weakly acidic region, However, since the gelation time is not rapidly shortened, it is suitable for obtaining gelation in the soil for a long time.

  These differences are due to the fact that silica liquid II is colloidal and has a large silica particle diameter, and silica liquid I is small in colloidal silica particle diameter. A silica liquid containing both silica liquid II and silica as active ingredients has these intermediate characteristics.

  Table 1 shows the relationship between the pH (pHa) and the gelation time (Ta) in the air of the phosphoric acid and sulfuric acid injection solutions. As can be seen, when using phosphoric acid as the acid, the gradient of pH and air gelation time is gentler than when sulfuric acid is used as the acid, making it easy to adjust the pH. Easy.

  In contrast, in the case of sulfuric acid alone, the relationship between pH and gelation time changes rapidly, and it is easy to set whether the gelation time is short or very long, but the intermediate gelation time is adjusted. It is more difficult to do than with phosphoric acid. However, if an aluminum salt is used in combination or a phosphate compound is used in combination, pH and gelation time can be easily changed.

  Therefore, it is easier to adjust both pH and gelation time by using phosphoric acid alone as the acid or using phosphoric acid and sulfuric acid in combination. When phosphoric acid and sulfuric acid are used in combination, the intermediate values in Table 1 are obtained.

  It is also effective to use an aluminum salt such as sulfuric acid band, aluminum chloride, polyaluminum chloride, and alum in combination with an acid. That is, phosphoric acid and a sulfuric acid band, sulfuric acid and a sulfuric acid band, etc. are used together. In this case, since the rapid change in pH is suppressed by the buffering action of Al ions and the rapid change in gelation time is suppressed, the gelation time can be easily adjusted.

  Hereinafter, the principle, configuration, and effect of the present invention will be described by way of examples. However, the present invention is not limited to these examples.

[Experiment 1]
1) Change in pH and strength In order to demonstrate that the consolidation strength of silica grout changes with pH, a sand gel specimen was prepared by a mixing method using Toyoura standard sand (or an infiltration method) (Dr = 60%). The uniaxial compressive strength was measured.
(1) Mold inner diameter about 50mm, length about 100mm
(2) Sample sand Toyoura standard sand
(3) Silica injection solution

  An acidic silica liquid obtained by adding an acid to an alkaline silica sol stabilized by adding water glass (or alkali) to active silica is taken as an example.

[Active silica]
The activated silica is silica having a pH of 2.8, a specific gravity of 1.03, and SiO ₂ = 4.5% obtained by passing a solution obtained by diluting No. 3 water glass with water through a cation exchange resin.

  In the above, colloidal silica obtained by increasing the active silica may be used instead of active silica. Or even if it uses the acidic silica liquid which consists of acidic silica sol obtained by adding water glass and an acid and removing the alkali of water glass, the substantially same effect is acquired. When the colloid is large, it has the characteristics of the active silica colloidal silica (silica-II) shown in FIG. 1, and when the colloid is a small acidic silica sol, it has the characteristics of the water glass acidic silica liquid (silica-I) shown in FIG. .

  In the acidic silica solution, 75% phosphoric acid was used as the acid, and the silica concentration was adjusted to 5%. Moreover, the addition amount of phosphoric acid was changed and pH of the chemical | medical solution was adjusted to 2-7.

  Changes in pH and uniaxial compressive strength are shown in Table 2.

  Silica grout expresses higher uniaxial compressive strength as it is closer to neutrality in the acidic region, and lower uniaxial compressive strength as it becomes acidic.

2) Silica concentration and gelation time The gelation time of silica grout in the ground depends not only on the amount of curing agent in the chemical solution but also on the silica concentration and the environment in the ground. When the silica concentration in the chemical solution is high, the gelation time is shortened. In addition, when the silica grout is consolidated by a table test (gel time of homogel, that is, air gelation time Ta) and when the silica grout is mixed with the sand collected in the field and gelled. The gelation time (sand gelation time-soil gelation time: Ts) differs depending on the pH of the sand and the components in the sand. Therefore, the gelation time (Ta) at a silica concentration of 6% and the gelation time in soil (Ts) (Kobe field sampling sand) were measured (Table 4).

  Mix colloidal silica, water glass (molar ratio 3.75), 75% phosphoric acid, adjust the silica concentration to 4, 5 and 6%, and measure the gelation time (gelation time in the air) of the chemical only did.

  Moreover, 30g of chemical | medical solution 10ml sample sand (Kobe field collection sand) was mixed, and the gelation time (Ts) in soil was measured. The results are shown in (Table 4).

  Further, FIG. 2 shows the relationship between the gelation time (Ta) in the air with a silica concentration of 5% and the gelation time in the soil (Ts) and pH (pHs) when mixed in the in-situ sand.

  The pH test of the sample sand at this time is Toyoura standard sand pH 7.26 and on-site collected sand pH 7.20.

  Table 3 shows the results of a calcium and Cl content test of the sand collected on site.

  As shown in Table 2, in the case of the acidic solution type silica grout, the silica grout becomes higher in the uniaxial compressive strength of the consolidated body as it is closer to neutrality. However, the more neutral the region, the shorter the gel time and the easier it is to consolidate.

  Further, when the silica concentration is low, the gelation time is long, and when the silica concentration is high, the gelation time is short.

  However, in the ground that is actually injected, the injected solution reacts with calcium content of shells and the like in the ground, and a small amount of alkali metal salt or alkaline earth metal salt (Table 3), and the gelation time in the soil (Ts ) Becomes shorter than the air gelation time (Ta) of the chemical solution (Table 4, FIG. 2).

  In Table 4, the pH and gelation time of silica injection liquid and injection liquid mixed sand were compared.

  The gelation time in the soil in the field sand is shorter than the gelation time in the air of the silica injection solution. This is due to the fact that the sand in the field is near neutral and the calcium content (Table 3).

[Experiment 2]
Changes in pH (pHs _f ) of silica grout in the ground, changes in infiltration distance (L) and infusion ground pH (pHs _f ), infiltration distance (L) and strength (qu) In order to do so, a penetration experiment was conducted.
(1) Sample sand
(2) Chemical solution

The active silica was processed by passing a solution obtained by diluting No. 3 water glass with water through a cation exchange resin, and active silica having a pH of 2.8, a specific gravity of 1.03, and SiO ₂ = 4.5% was obtained.

  Further, water glass (molar ratio 3.75) and 75% phosphoric acid were mixed to adjust the silica concentration to 4, 5, and 6%.

〔Experimental device〕
As an advance preparation, using the apparatus of FIG. 3, the sample sand 12 was dropped from the upper part of the acrylic mold 11 having a length of 2 m and filled (Dr = 60%), and saturated with water prior to injection of the chemical solution. .

  A mixed solution of an active silica solution and water glass, a curing agent, and water are put into tanks 4, 5, and 6, and are put into a water tank 9 by a pump 7.

  The input amount at this time is managed by the flow meter 8. The chemical solution introduced into the water tank 9 is stirred by the stirrer 10, pushed out by the compressor 1, and permeated into the sample sand 12 in the acrylic mold 11. The chemical liquid is injected at a constant pressure of 0.03 MPa from the lower part of the acrylic mold 11, and the chemical liquid that has passed through the sample sand 12 is discharged from the upper part of the acrylic mold 11 and collected in the measuring cylinder 13.

  The sand gel (penetration consolidated sand gel) specimen prepared after the infiltration was allowed to stand for 4 weeks, then cut, and the uniaxial compressive strength and the pH of the specimen were measured every 10 cm of the infiltration distance.

〔result〕
1) Change in pH of effluent The change in pH of the chemical solution flowing out from the upper part of the acrylic mold was observed in the penetration test (FIG. 4).

First, saturated water overflowed, and then the injection liquid overflowed. The gap in the mold is about 1500 cm ³ . After the overflow corresponding to the gap amount is over, the pH of the overflowing solution gradually changes from neutral to acidic, so that the injected solution injected into the ground becomes more neutral as the permeation distance becomes longer (the larger the amount of overflowing). The amount of overflow until it changed to acidic was large. This indicates that the longer the permeation distance of the preceding silica liquid is, the easier it is to be diluted, which means that the solidification by the preceding silica is insufficient.

At the same time, since the chemical solution in the initial stage of injection reacts with the sample sand of the acrylic mold and is neutralized, the pH of the preceding silica solution (pHs _f ) is close to neutral. However, as the injection amount increases, the neutralization reaction ends, the sample sand itself is saturated with the acidic silica liquid, and the pH (pHs _f ) of the overflowing silica liquid approaches the pH (pHa) of the silica liquid and the pH decreases.

2) Penetration distance and pH change due to pH test of osmotic solids After one week of chemical injection of sand collected on site, the acrylic mold was cut at 10cm intervals, and the osmotic solids in the acrylic mold were scraped and a 50g sample was taken. Then, 125 g (mass ratio 2.5) of distilled water was mixed and stirred. The pH was measured after standing for 2 hours (FIG. 5). From this, it can be seen that the non-alkaline silica itself is acidic, but the final consolidated soil is almost medieval. However, the present invention solves the problem caused by the soil particles being filled with the preceding acidic silica during the injecting step and the subsequent acidic silica permeating therethrough.

3) Penetration distance and strength change Fig. 6 shows the relationship between the penetration distance and uniaxial compressive strength in the sand when the silica concentration in the chemical solution is 4,5,6%.

[Experiment 3]
Changes in soil pH (pHs _f ) and infiltration soil gelation time (Ts _f ) of infiltrated sand after passing through silica solution In the actual ground, the initial infusate solution (Table 6), mid-term infusate solution, late phase The pH of the soil in the soil (pHs _f ), the pH of the chemical solution (pHa), and the gelation time (Ta) of the chemical solution after passing through the injected chemical solution were examined by the following methods.

〔experimental method〕
・ In-situ sand pH6.46
・ Combination of chemicals

  Prepare 20 pieces of sand with 200ml of sand on the filter paper laid in the funnel, and number them No.1 to No.20. This is the amount of sand on site corresponding to a penetration distance of 10 cm for a penetration test of 2 m. No. 1 is the closest to the injection hole and No. 20 is the farthest.

Add about 100 ml of the injected drug solution to No. 1 on-site sand, take 100 ml of passing solution, and pass it through No. 2 on-site sand. The same operation is repeated up to No. 20, and the pH of the in-situ sand after passing through each chemical solution, that is, the pH in the soil (pH of the permeation chemical solution: pHs _f ) is measured. The same operation was repeated 15 times.

〔result〕
Table 7 shows the pH of the chemical solution after passing through the sand in the field (pH of the penetrating chemical solution: pHs _f ) and the gelation time of the chemical solution after passing (gelation time of the penetrating chemical solution in the osmotic soil: Ts _f ). Show.

From the relationship between the pH of each site sand flow rate in Table 7, No. 1 is greatly affected by the chemical solution, and after penetration of the chemical solution, it is almost the same infiltration soil pH (pHs _f ) as the chemical solution (pHa). I found out that On the other hand, in No. 20, although the pH increased greatly at the first liquid passage, it did not harden. Therefore, the pH increased due to the progress of the neutralization reaction, but the dilution was large and the silica concentration was decreased, so that it did not solidify. I found out. In the subsequent flow, the pH in the infiltrated soil (pHs _f ) decreased due to the influence of the chemical solution, but the pH after the flow became closer to the pHa value as the inside and as the number of passages increased.

As a cause of this, it can be seen that the pH of the ground decreases as the amount of the chemical solution passed increases, and that the shorter the permeation distance, the more affected by the initial penetrating chemical solution, the pHs _f approaches the pH of pHa. For this reason, in the actual ground, the ground closer to the injection hole is filled with the chemical solution equivalent to the injection solution to the ground that has reacted with the chemical solution, and its pHs _f exhibits a value close to pHa and penetrates. As the distance is longer, the acidic content of the pH of the previous penetrant solution is neutralized and lost, and the pHs _f is also more acidic toward the inside.

In addition, the longer the permeation distance, the greater the dilution and the insufficient consolidation. Then, since the subsequent silica solution passes through the acidic ground, the pH (pHs _f ) of the chemical solution during infiltration approaches the pH (pHa) of the infusion solution, and the inside, the longer the permeation distance, the longer the infusion time. The larger the injection amount, the stronger the acidity, and thus the gelation time of the osmotic drug solution remains long.

Next, the relationship between the flow rate of the chemical solution after penetrating the ground and the gelation time is as follows. For the chemical solution at the initial stage of the injection (penetration chemical solution), the gelation time after 2 m penetration is long, and the previous injection solution is 300 ml or less. Then, it did not gel. This is probably because the initial infusion solution was diluted with soil water. When the flow rate increases (subsequent injection solution in the later stage of injection), the gelation time (gelation time of the osmotic injection solution: pHs _f ) is as short as 400 minutes due to the reaction with the ground due to the reaction with the ground. The gelation time (Ta) was shorter than about 1000 minutes.

FIG. 7 shows the relationship between the pH (pHa) of the injection solution of 4 to 6% and the air gelation time (Ta). No. 20 in the case of silica concentration of 5% in Table 7, that is, the relationship between the pH (pHs _f ) and the gelation time (Ts) of the injected solution having passed through 6 to 12 times at the end is shown. .

  From this, it can be seen that the drug solution that passed through the initial liquid passage has a higher pH, but the gelation time becomes longer due to dilution, and the pH of the injection solution that passed in the latter period is the air gelation time (Ta). It can be seen that it almost overlaps the graph of the pH and gelation time of the injection solution with 5% silica concentration and pH, and it is a passing solution close to the mixture solution of the injection solution itself.

  From the above, the following can be understood. In order to increase the penetration distance and expand the improved ground in the ground, it is necessary to inject the silica solution into the ground extensively. However, when the normal injection pressure is used, the pressure gradient is generated at the outer periphery of the consolidated ground. Therefore, when the injection range is widened, the injection becomes insufficient, and a sufficient pressure gradient cannot be obtained, which is close to penetration by diffusion. For this reason, the strength of the solidified body decreases as it goes to the outer periphery due to dilution.

  In order to prevent this, conventionally, a method of setting the silica concentration of the chemical solution high has been used. In addition, if the injection speed is reduced to infiltrate between the soil particles for a large amount of soil supported by setting the injection hole interval, such as liquefaction prevention, to 1 to 4 m, the injection time will become very long. A silica solution has been used in which the pH is lowered by increasing the amount of acidic reactant in the injection so that the time is longer than the injection time.

  This is because, conventionally, it has been considered that when the gelation time in the soil is shorter than the gelation time in the air, the chemical solution injected into the ground does not penetrate between the soil particles. Therefore, the injection solution was set to be equal to or longer than the soil gelation time corresponding to the injection time. For this reason, the above-mentioned problem occurred. Alternatively, when the acid value of the injection solution is increased to increase the gelation time, a large amount of acid radicals as reaction products are left in the ground. This is not preferable in terms of groundwater quality, and is not preferable for underground structures.

  The present invention uses a silica grout having a non-alkaline pH range to obtain a permeation-consolidated diameter of 1 to 4 m, preferably 1.5 to 4 m, with a uniform pH of the consolidated body without deviating. Thus, the present invention was completed by elucidating the relationship between the injection time per stage (H), the in-air gelation time (Ta), and the soil gelation time (Ts).

[Example 2]
Based on the results of Example 1, an actual ground penetration test was conducted.

(1) Injection method The composition of the chemical solution to be injected according to the present invention is designed within the range of the ratio formula (1) between the gelation time and the injection time in the soil and the ground is improved, and Comparative Example 1 outside the range set by the present invention. Compared with the case of improving the ground in the method of 2.
The injection rate was 40%.
The injection rate was determined by performing an in-situ injection rate test.

○ In-situ injection rate test An experiment was conducted to determine the injection rate at which the chemical solution was injected by infiltration in the ground where injection was performed. First, the relationship between the injection rate of the chemical solution and the injection pressure on the ground where injection is performed was measured, and the case where no injection was performed in FIG. 8 was zero, the injection pressure was recorded on the vertical axis, and the injection speed was recorded on the horizontal axis.

  When the injection speed is increased, the injection pressure also increases, and in the initial linear gradient region shown in FIG. 8 in the proportional relationship and in the range of the injection speed in the transition region from the initial linear gradient to the fracture gradient region, the voids in the ground are replaced with the chemical solution. It is thought that. However, it can be seen that when the injection speed and the injection pressure deviate from this region, turbulence occurs in the ground, and the osmotic injection is not performed due to injection in a pulse shape or cracks. From this, the initial linear gradient based on the injection pressure and the injection speed is obtained, the injection speed deviating from the proportional relationship is the limit injection speed 11 (l / min), and the transition region is q = 11 to 16 (l / min). .

  From this result, the injection rate q in this experiment was 10 (l / min) which is lower than the limit injection rate.

  The present invention and Comparative Examples 1 and 2 are compared in Table 8.

Calculation method of Table 8 1) Ground improvement method of the present invention Volume of improved ground = (4 m / 2) ³ × 3/4 × π = 18.840 m ³ = 18840 l
* The volume of the improved ground is considered to produce a consolidated body with a diameter of 4m from the injection hole interval.
Injection quantity Q = Volume of improved ground x Injection rate = 18840 x 0.4 = 7536 l
Injection time H = Injection amount Q / Injection speed q = 7536/10 = 753.6 minutes Injection time ratio A = Soil gelation time Ts / Injection time H = 14.5 / 251.2 = 0.058
Thus, the ground improvement method of the present invention falls within the range of 0.01 ≦ A <1 in the formula (1), and therefore is within the scope of the present invention.

2) Comparative Example 1: An example is shown in which the gel time Ts of the chemical solution is long and the injection time ratio is A> 1.
Injection time ratio A = Soil gelation time Ts / Injection time H = 1000 / 753.6 = 1.327

3) Comparative Example 2: An example is shown in which the gel time Ts in the soil of the chemical solution is short and the injection time ratio is A <0.01.
Injection time ratio A = Soil gelation time Ts / Injection time H = 7 / 753.6 = 0.09

(2) Results After injection under the injection conditions set in Table 8, samples were taken from each consolidated ground, and the pH in the soil and the gelation time in the soil were measured. Moreover, the uniaxial compressive strength after one week was measured. In FIG. 9 of the improved ground, sample 1 is the ground in contact with the adjacent injected consolidated body, sample 2 is the ground near the injection liquid discharge port, and sample 3 is the ground at the outer periphery of the consolidated body. . Similarly, in Comparative Examples 1 and 2, samples were collected to compare the improved ground. The results are shown in Table 9. Data are average values of three sources.

  The consolidated ground using the present invention is one day at all sample positions of the ground near the discharge port (sample 2), the outer periphery of the consolidated ground (sample 3), and the contact portion of the adjacent consolidated ground (sample 1). Later gelation was observed. Moreover, it turned out that uniaxial compressive strength also expresses substantially constant.

  In Comparative Example 1, gelation after 1 day was confirmed at the outer peripheral portion of the consolidated ground (Sample 3) and the contact portion of the adjacent consolidated ground (Sample 2), and sufficient uniaxial compressive strength was expressed. In the ground near the discharge port (sample 2), the pH was low, and it took about 4 days for gelation, and the uniaxial compressive strength was also low. This is because it reacts with the initial injection solution near the discharge port, and the latter injection solution is injected into the ground and the ground after the reaction, so the injection solution shows the same behavior as the gelation of the homogel, and the gelation time is It seems to be long. Moreover, since gelation time becomes long, strength expression becomes slow and it seems that sufficient uniaxial compressive strength was not obtained.

  In Comparative Example 2, the ground near the discharge port (Sample 2) showed gelation after 1 day and sufficient uniaxial compressive strength was obtained, but the outer periphery of the consolidated ground (Sample 3) and adjacent consolidated Since the ground contact portion (Sample 1) was partially consolidated and gelled in a vein shape, a uniform consolidated ground could not be obtained, and the uniaxial compressive strength decreased. This is because the amount of acid in the homogel is small and reacts when it comes into contact with the alkaline component in the ground, and the infused solution is solidified without sufficiently penetrating before forming the solid ground, and a solid ground is obtained. It seems to be impossible.

  From this, when injecting at the actual construction site, if the present invention is used, it can be fed into the ground longer than the gelation time in the soil, and even if the distance between the injection holes of the ground improved ground is long and the chemical penetration distance is long enough It was confirmed that it penetrated and consolidated uniformly.

  Under the conditions of the present invention, even if the gelation time in the soil is shorter than the injection time, the initial chemical solution gels at a short penetration distance and cannot be delivered in the ground. As the gel becomes gelled, the pH is lowered by the chemical solution sent from one to the next, and it penetrates without solidifying in the ground, the penetration distance is long and the injection diameter of 1 to 4 m is possible, and the injection time is gel The present invention was found because the injection pressure hardly increased even after the control time was exceeded.

  It was found that even when the gelation time in the soil is shorter than the injection time, by setting the permeation conditions, it is possible to perform injection that solidifies uniformly even if the injection hole interval is long. Even if the gelation time in the air is longer than the injection time, the chemical solution penetrating the ground after injection is affected by the reaction with the ground, so the effect depends on the gelation time in the soil and the injection time. It is necessary that the gelation time is shorter than the injection time, but if the gelation time is too short, it does not penetrate and the ratio needs to be greater than 0.001.

  Further, the air pH is 1.5 to 8, the air gel time Ts is preferably within 4000 minutes, and the soil gel time Ts is preferably 10 minutes or more. Of course, when it deviates to the ground surface, the gel time in the soil (Ts) can be rapidly gelled by using a combination having a gel time (Ts) within 10 minutes to prevent the deviation.

  The injection time in the present invention is preferably between 1500 minutes and 15 minutes. When the time is 1500 minutes or longer, the injection solution is easily dispersed into the injection target range. Also, if it is less than 15 minutes, the desired penetration distance cannot be obtained, and the injected solution will gel in the soil, the subsequent injected solution will deviate and solidify in a vein shape, and a uniform improved ground can be obtained. I found that there was no.

Example 3
Example in which the gelation time (Ta) in the air of the injection solution is set longer than the injection time of the injection solution in the injection stage and the gelation time (Ts) in the soil is set shorter than the injection time. Will be described below.

The following chemical solutions were used in this example (chemical solution with a pH of 1.51 and a silica concentration of 8%).
Water glass: Specific gravity (20 ° C) 1.32, SiO2 concentration 25.5%, Na2O concentration 7.23%, molar ratio 3.75, pH 11.5.
Colloidal silica: A colloidal silica solution that has been condensed and stabilized by adding alkali to a water glass aqueous solution treated with a cation exchange resin. It has a SiO ₂ concentration of about 30% and a Na ₂ O concentration of 0.7%. Hereinafter, colloidal silica having physical properties of specific gravity (20 ° C.) of 1.21 to 1.22 and pH of 9 to 10.
75% phosphoric acid:

(1) Ground conditions In the present invention, it is necessary to measure the soil quality of the improved ground, the Fc value, the amount of calcium in the ground, and the pH of the soil suspension. The ground that contains a lot of calcium as the soil has a tendency that gelation of the chemical solution is accelerated and the permeation time is shortened. The ground having a high Fc value tends to delay the penetration time of the chemical solution relative to the amount of consolidated soil. Further, when the pH of the soil suspension is high, gelation of the chemical solution may be accelerated.

〔Measuring method〕
Fc value: Determined according to JIS A 1223 “Soil fine grain content test method”. In this example, Fc = 4.5 to 8.6.
Calcium content in the ground: In-situ sand was extracted with alkali or water and analyzed by ICP method.

  PH of the soil suspension: The sample is a soil from which soil particles having a particle size of 10 mm or more are removed. Use the consolidated sand after loosening it. An appropriate amount of sample is placed in a beaker, and distilled water is added so that the mass ratio of water (including water in the sample) to the dry mass of the sample is 5. The sample is stirred with a stir bar and allowed to stand for 30 minutes or longer and within 3 hours to obtain a sample solution for measurement. Measure with a pH meter. In this example, the soil was sand mixed with shells, the amount of water-soluble calcium was 105 mg / kg, and the pH of the soil suspension was 10.61.

(2) In-air gelation time (Ta) measurement of chemicals and in-soil gelation time (Ts) using in-situ sand
1) Air gelation time (Ta)
The time from when the chemical solution is blended until the viscosity of the chemical solution exceeds 100 Mpa · s is defined as the air gelation time (by B-type viscometer). In this example, it was about 3000 minutes.
2) Gelation time in soil (Ts)
A representative soil of the ground to be injected is collected and dried (air-dried) as necessary. Weigh 100 g of this soil (consolidate) into a cup for gelation time measurement. Add 25-30 ml of the drug solution to this and mix well. The penetration tester's needle or something similar to this is used, and when it is pulled out, the time when the hole is not blocked is taken as the gel time in the soil. In this example, it was 24 minutes.

(3) Strength test of consolidated sand using on-site sand Using the sand collected at the construction site in the laboratory test, a specimen was prepared with the same composition as the chemical solution to be actually injected, and the strength test was performed. A specimen was prepared by mixing in-situ sand and a chemical solution in a mold having a diameter of 5 cm and a length of 10 cm.

In-situ sand contains a lot of shells and the amount of calcium in the sand is large, so when mixed with the chemical solution, it reacts with the curing agent in the chemical solution and foams, and the created specimen has many cavities and exhibits strength. The strength was 0.13 MN / m ² .

Therefore, a specimen was prepared under the same conditions as the construction ground by applying a pressure on the sample (on-site sand) and infiltrating the chemical from the chemical tank into the in-situ sand. In the prepared specimen, the generation of cavities inside the specimen was suppressed by the mounting pressure, and the strength was observed in the uniaxial compression test. The strength was 0.36 MN / m ² .

  Therefore, in the case where a chemical solution is blended in the present invention, when a lot of calcium such as shells is included in the on-site sand, it is necessary to apply a top pressure and prepare a specimen under the same conditions as the actual ground to confirm the strength.

(4) The ratio of the gelation time in the soil and the injection time is determined from the injection conditions.
Injection hole interval = 2.0m
Injection stage length = 0.5m
Improved ground volume = (2.0m ÷ 2) ² x π x 0.5 = 1.57m ³
* The improved ground was calculated as a diameter of 2.0m in diameter and 0.5m in depth.
Injection rate = 40%
Injection volume = 1.57m ³ × 0.4 = 628l
Injection rate = 5 l / min Injection time = injection amount / injection rate = 125.6 minutes Injection time coefficient A = Soil gelation time / injection time = 24 / 125.6 = 0.19, so that it falls within the range of (Equation 1).

(5) Construction results Swedish ground penetration test was conducted on the ground after construction, and the results of the improved uniaxial compression test were examined and compared with the laboratory test. As a result, 0.38 MN / m ² was obtained, which was the same strength as the laboratory test. It was.

  Under the same conditions, Comparative Example 3 has an air gelation time (Ta) of 5000 minutes, soil gelation time (Ts) of 1800 minutes, A = 14.33, and Comparative Example 4 air gelation time (Ta). 1000 minutes, soil gelation time (Ts) 7 minutes, and A = 0.055 were injected and compared.

  In Comparative Example 3, a decrease in strength was observed in the vicinity of the injection hole in the ground after injection, and a ground that was not partially consolidated was observed when the ground was excavated after one day. In Comparative Example 4, it was injected in a vein shape in the ground, and the ground could not be improved uniformly.

  Therefore, in the present invention, in particular, when excavation work is performed after ground improvement, or in order to speed up the development of the strength of the chemical solution, 15 minutes to (3) of claim 1 of the present invention, The injection time of 1500 minutes is preferable, and the soil gel time (Ts) is set between 10 minutes and 1500 minutes as described in (2) of claim 1 and (2) of claim 5 to improve the ground. It was found that the strength development later was quick and the improvement range could be improved uniformly.

Example 4
The ground improvement of the present invention was performed by a columnar infiltration method under the following conditions.

  Columnar infiltration method improves the ground by creating a solid body in the ground by injecting the chemical solution shown in Patent Document 1 (Patent No. 3509744) by the applicant, and stacking the solid body in the ground by performing several stages. It is a method to do.

The chemical solution used in this example was one having a pH of 3.3 and a silica concentration of 6%.
Water glass: Same as Example 3.
Colloidal silica: Same as Example 3.
75% phosphoric acid:

(1) Ground conditions Soil was mixed with shells, Fc value 4.2-9.2, water-soluble calcium content 40900mg / kg, and pH of soil suspension was 9.3.

(2) Measurement of gel time of chemicals and measurement of gel time in soil using in-situ sand
The gelation time was about 2000 minutes, and the gelation time in soil was 30 minutes.

(3) From the injection conditions, find the ratio between the gelation time in the soil and the injection time.
Injection hole interval = 3m
Injection stage length = 1.5m
Improved ground volume = 10.6m ³
Injection rate = 55%
Injection volume = 5829 l
Injection rate = 10 l / min Injection time = injection amount / injection rate = 582.9 minutes Injection time factor A = soil gelation time / injection time = 30 / 582.9 = 0.051 Is possible.

(4) Construction results The hydraulic conductivity decreased to 1/100 compared to before construction.

Example 5
The ground improvement of the present invention was performed by the multi-point infiltration method under the following conditions.

Since the chemical used in this example is adjacent to the construction ground and there is a concrete structure, 75% phosphoric acid is used as a metal ion sequestering agent, and colloidal silica is used to set the pH to 3.3. A silica having a silica concentration of 6% was used.
Water glass: Same as Example 3.
Colloidal silica: Same as Example 3.
75% phosphoric acid:

(1) Ground conditions The soil was sand, soil suspension pH 7.5.

(2) Measurement of chemical solution gelation time and soil gelation time using in-situ sand.

  The gel time was about 1000 minutes and the gel time in soil was 97 minutes.

(3) A strength of 0.25 MN / m ² was confirmed by a mixing method in laboratory tests.

(4) The ratio of the gelation time in the soil and the injection time is determined from the injection conditions.
Injection hole interval = 3m
Injection stage length = 0.5m
Improved ground volume = 3.53m ³
Injection rate = 40%
Injection volume = 1412 l
Injection rate = 5 l / min Injection time = Injection amount / Injection rate = 282.4 minutes Injection time factor A = Soil gelation time / Injection time = 97 / 282.4 = 0.34 Is possible.

(5) Construction results A Swedish penetration test was conducted on the ground after construction, and the results of the improved uniaxial compression test were examined. A strength of 0.28 MN / m ² was obtained, similar to the laboratory test. Moreover, the pH in the soil near the injection hole of the ground after construction was 5.1, and the pH in the ground in contact with the structure was 7.6. From this, the influence on the structure could be suppressed.

4 is a graph showing the relationship between the pH of a silica solution and air gelation time in Experiment 1. It is a graph which shows the relationship between the air gelatinization time of the injection liquid in Experiment 1, and the gelation time in soil. 6 is a schematic diagram of an experimental apparatus used in Experiment 2. FIG. 6 is a graph showing a change in pH of a chemical solution that has flowed out in a penetration test in Experiment 2. FIG. 6 is a graph showing changes in permeation distance and pH of an osmotic solid body in Experiment 2. It is a graph which shows the relationship between the penetration distance and the uniaxial compressive strength in Experiment 2. It is a graph which shows the relationship between pH of the injection liquid in experiment 3, and air gelation time. It is a graph which shows the relationship between the injection | pouring speed | rate in the in-situ injection | pouring speed | rate test of Example 2, and injection | pouring pressure. It is a figure which shows the sample collection position in the penetration test of the actual ground of Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Compressor 2 Pressure gauge 3 Pressure gauge 4 Activated silica solution tank 5 Hardener tank 6 Water tank 7 Pump 8 Flow meter 9 Water tank
10 Stirrer
11 Acrylic mode
12 Sample sand
13 Measuring cylinder

Claims (15)

A ground injection method for injecting silica injection solution into the ground, and the ground improvement method is characterized in that the composition of the injection solution is set according to the following methods (1) to (8) on the ground to be improved. .
(1) Check the relationship between Blend and aerial pH of the infusate (pHa) and aerial gelation time (Ta).
(2) Using the soil collected from the ground to be improved and the injection solution, check the composition of the injection solution and the relationship between the gel time in the soil (Ts) and the pH in the soil (pHs).
(3) Using the collected soil and the injected solution, check the relationship between the composition of the injected solution and the strength (qu) of the consolidated collected soil.
(4) Determine the silica concentration of the injection solution from the required ground improvement strength.
(5) Calculate the injection volume per unit volume of improved soil in the soil layer to be injected.
(6) The injection hole interval and the injection stage length are determined, and the injection amount (Ql) per stage is calculated from the amount of soil per unit stage.
(7) Set the discharge amount (ql) per minute and set the injection time (H) per injection stage.
(8) to set the reactant concentration of the infusate from the relationship between the injection time (H) and soil gelation time (Ts).   2. The ground improvement method according to claim 1, wherein the strength (qu) of the consolidated soil is confirmed by applying an overpressure in (3).   In the ground improvement method according to claim 1, in (7), the discharge amount per minute (ql) is an initial linear gradient region in which the injection speed and the injection pressure are proportional to each other and a transition region from the initial linear gradient to the fracture gradient region. Ground improvement method characterized by injecting at an injection rate of. The ground improvement construction method according to claim 1, 2 or 3, wherein the injection time (H) and the gelation time (Ts) of the injection solution are set so as to satisfy the following conditions.
(1) 0.01 ≦ A <1
(2) Ts <H <Ta
(3) 15 minutes <H <1500 minutes (4) pHa is 1.5-8
here,
A: Ratio of soil gelation time Ts (min) to injection time H (min) (= Ts / H)
Ta: In-air gelation time of injection solution (20 ° C)
Ts: Gelation time (min) of mixed soil of in-situ collected soil and injected solution
H: Injection time per stage (minutes)
pHa: Air pH The ground improvement construction method according to claim 4, wherein the ground improvement construction method is set so as to satisfy the following conditions.
(1) 0.01 ≦ A <1
(2) 10 minutes <Ts <H <Ta <4000 minutes
(3) 15 minutes <H <1500 minutes
(4) 2 <pHa <8
(5) 3 <pHs <9
here,
pHs: pH in soil   The ground improvement construction method according to claim 4 or 5, wherein 0.03≤A≤0.5. In ground improvement method according to claim 4 or 5 Symbol mounting, ground improvement method used in combination with different formulations in a range width of 0.01 to A during the injection.   The ground improvement construction method according to claim 5, wherein a combination of Ts of 10 minutes or less is used during the injection.   The ground improvement construction method according to any one of claims 1 to 5, wherein the ground injection construction method has an injection interval of 1 to 4 m. The ground improvement construction method according to any one of claims 1 to 5, wherein the injection amount (Q) and the injection time (H) per stage satisfy the following injection conditions.
(1) Q ≧ 400l
(2) H ≧ 60 minutes   The ground improvement construction method according to any one of claims 1 to 5, wherein an injection solution containing a metal ion sequestering agent is used as a silica injection solution, or a silica injection solution not containing a metal ion sequestering agent is used in combination. .   The ground improvement construction method according to any one of claims 1 to 5, wherein the silica injection solution contains Al ions.   The ground improvement construction method according to any one of claims 1 to 5, wherein the silica injection solution is simultaneously injected from a columnar penetration source or a plurality of injection points.   The ground improvement construction method according to any one of claims 1 to 5, wherein the ground is injected to prevent liquefaction of the ground directly under or near the structure.   The ground improvement construction method according to any one of claims 1 to 5, wherein the ground improvement construction method is to inject directly into or near the ground of the structure, or directly under or near the ground where the structure is to be built.

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