JP7814072B2 - Ground improvement method - Google Patents

Description

The present invention relates to a ground improvement method using suspension grout, and more specifically to a ground improvement method for improving soft or leaky ground by simultaneous combined suspension and solution injection, which simultaneously solidifies the ground with suspended particles and infiltrates and solidifies the ground with a silica solution separated from the suspension grout (suspension).

The basics of the conventional composite grouting method are explained below.
(1) The basic principle of the injection method is to allow grout to penetrate between soil particles, replacing the interstitial water with grout and solidifying it.

(2) However, the ground to be injected is usually complex, with coarse, fine, and different soil layers interspersed. Therefore, if a highly permeable solution grout is injected, the injected grout is likely to deviate from the target area. On the other hand, suspension grout cannot penetrate fine soil layers due to its suspended particles. For this reason, suspension grout or instant-setting grout is first injected to fill the coarse layers, homogenizing the ground, and then a highly permeable solution grout is injected.

(3) For these reasons, the double-pipe composite injection method (FIG. 1(a)) and the double-pipe double packer method (FIG. 1(b)) are used as specific injection methods.
In the double-pipe composite grouting method, a quick-setting grout is injected as the primary grout, and a slow-setting grout is injected as the secondary grout (Fig. 1(a)). In the double-pipe double packer method, a suspension-type grout such as cement bentonite (CB) is injected as the primary grout, and a solution-type grout is injected as the secondary grout (Fig. 1(b)). In both of these methods, the primary and secondary grouts are carried out in separate processes.

Japanese Patent Application Laid-Open No. 2022-066686 JP 2024-053139 A

Yurika Tsunoda, Shunsuke Shimada, Tadao Koyama, Takamitsu Sasaki, Ryozo Yonekura, "Demonstration Study on the Permanence and Penetration/Solidification of Ultrafine Composite Silica," 66th Annual Academic Conference of the Japan Society of Civil Engineers, 2011 Takamitsu Sasaki, Ryozo Yonekura, Shunsuke Shimada, "Field Demonstration Test of the Long-Term Consolidation of Consolidated Ground Using Activated Silica and Ultrafine Composite Silica," 54th Geotechnical Engineering Research Conference, 0241, 2019

Generally, to reinforce water-leaking ground such as soft soil or bedrock made of earth and sand, injection of suspension grout is required. However, suspension grout does not penetrate fine-grained soil or tiny cracks, and therefore does not provide a watertight seal. For this reason, the injection process has traditionally been carried out in two steps: first, by injecting suspension grout, and then, second, by injecting solution grout.

Furthermore, in conventional suspension grouts, which are primarily composed of cement and used as injection materials, the specific gravity of cement is large at 3.17, but the specific surface area is small at approximately 3,220 ^cm2 /g, making the cement particles heavy. In addition, penetration between soil particles in fine-grained soil is difficult, resulting in a short penetration distance, making it difficult to form large solidified bodies.

When using the high-pressure jet mixing method, which primarily uses cement, the solidified material immediately after construction is in an unsolidified state because sufficient hydration reactions have not yet occurred. Therefore, when construction is carried out near a structure, a temporary decrease in bearing capacity can impede the function of the structure. Furthermore, with conventional high-pressure jet mixing methods that rely on the energy of the high-pressure jet fluid, the cutting area is limited by the distance of the jet fluid, which restricts the size of the solidified material made from cement.

Furthermore, with the above-mentioned high-pressure injection mixing method, soil is removed and replaced with cement to form a solidified mass, and disposal of this waste mud is now becoming a major environmental issue. Furthermore, when improving soft ground, the bearing capacity of soft ground is low, so the cement solidified mass, which has a high specific gravity, is prone to settling, which can lead to significant displacement of structures.

In light of the above, the present invention aims to achieve the permeability required to form large solidified bodies by expanding the permeability limit of suspension grout to the permeability range of solution grout during construction, while simultaneously achieving high strength and excellent water-stopping properties as improved effects. It also aims to achieve simultaneous combined suspension and solution injection, which enables the permeation and solidification of solution grout while injecting suspension grout in a single process, thereby enabling the permeation and solidification of suspension and solution grout to be carried out simultaneously, and does not encounter the problems associated with high-pressure injection and mixing methods.

Specific means for solving the problems of the present invention will be described below.
(1) The present inventors have already developed a high-strength permanent grout using silica particles such as slag or fly ash as a low-carbon injection material and injection method (Patent Documents 1 and 2). These low-carbon grouts have been proven to have long-term durability and earthquake resistance (Patent Document 1).
(2) In Patent Document 1, the present inventors conducted research focusing on the gelation of a bleeding liquid of ultrafine particle composite silica consisting of silica particles and a silica solution, and as a result, discovered conditions under which the gelation of the bleeding liquid, strength, and ground improvement effects can be obtained.
(3) As a result, the inventors have realized ground improvement by simultaneous combined injection of suspension and solution, a new concept that integrates the entire target ground, with high permeability, high strength, and excellent water-stopping properties, by covering the injectable limit of suspended particles with the gelling function of solution-type silica (bleeding liquid) separated from the suspension-type injection material (Figure 13).

As described above, the present invention makes it possible to carry out a ground improvement construction method using simultaneous combined injection of suspension and solution, which combines the strength, permeability, and water-stopping effect of the suspension by injecting a ground grouting material consisting of a suspension containing silica solution and suspended particles as active ingredients into the ground, solidifying the coarse-grained soil with the suspended particles, and solidifying the fine-grained soil, which the suspended particles cannot penetrate, through the gelation of the silica solution separated from the suspension, thereby forming a solidified body larger than the solidified body of suspended particles (Figure 13).
Here, the "separated silica solution separated from the suspension" that is produced when the suspension is injected into the ground corresponds to the "bleeding liquid of the suspension" in the experiment, so in the actual test, the "bleeding liquid of the suspension" is used as the "separated silica solution separated from the suspension."

That is, the ground improvement method of the present invention is a ground improvement method in which a ground grouting material consisting of a suspension containing a silica solution and suspended particles as active ingredients is injected into the ground,
The separated silica solution separated from the suspension penetrates into an area where the suspended particles cannot penetrate, and then the separated silica solution gels and solidifies the ground, thereby simultaneously solidifying the ground with the suspended particles and the separated silica solution.

In the present invention, it is preferable that the silica solution is silica colloid and/or water glass, that the separated silica solution gels, and that the silica concentration of the separated silica solution is 0.5 w/v% or more.

In the present invention, it is preferable that the suspended particles contain one or more of the following active ingredients: pyrogenic silica, natural pyrogenic silica with pozzolanic activity, and hardenable silica particles.

In the present invention, the pyrogenic silica is preferably made from one or more of slag, fly ash, cement, sewage incineration ash, plant incineration ash, and calcined clay. Furthermore, in the present invention, the natural pyrogenic silica with pozzolanic activity is preferably made from one or more of loam, shirasu, volcanic ash, niwado, and sanwado.

In the present invention, the ground grouting material preferably contains an alkaline agent consisting of one or more of the following (1) to (3):
(1) An alkaline agent containing one or more of gypsum and MgO as active ingredients.
(2) An alkaline agent containing one or more of Ca salts, Mg salts, Al salts, carbonates, and bicarbonates as active ingredients.
(3) An alkaline agent containing one or more of lime, cement, caustic alkali, water glass, and silica colloid as active ingredients.

In the present invention, it is preferable that the suspended particles have a Blaine value of 4,000 to 20,000 cm ² /g, and that the amount of the suspended particles mixed in the ground grouting material is 50 to 200 kg/400 L.

In the present invention, the suspended particles are slag, and the amount of slag mixed in the ground grouting material is preferably 10 to 25 w/v% when cement is not used, and 10 to 30 w/v% when cement is used.

In the present invention, it is preferable that the molar ratio of the water glass is 1.0 to 5.0, and the amount of water glass blended in the ground grouting material is 10 to 150 L/400 L.

In the present invention, it is preferable that the ground grouting material contains one or more of microbubbles, air, a dispersant, and a thickener as active ingredients.

In the present invention, it is preferable that the ground grouting material contains a hardening agent made of a polyvalent metal compound, and that the hardening agent is one or more of the hydroxides, oxides, or salts of Ca, Mg, or Al, and/or gypsum.

In the present invention, because the ground grout has excellent permeability, in conditions where permeable grout is likely to deviate into unintended ground, is likely to be diluted by groundwater, or is extremely permeable, it is preferable to inject a suspension grout or a quick-setting grout as a primary grout into the ground prior to injecting the ground grout.

The ground improvement method of the present invention strengthens underground structures by injecting the above-mentioned ground grouting material into the periphery of an underground structure having an underground space.

The ground improvement method of the present invention is also suitable for reinforcing and waterproofing excavation wall surfaces or bottom injection. Furthermore, the ground improvement method of the present invention is also suitable for reinforcing rock cracks in rock shafts, waterproofing, or containing harmful substances. Furthermore, the ground improvement method of the present invention is also suitable for reinforcing existing foundations or repairing damaged foundations. Furthermore, the ground improvement method of the present invention is also suitable for liquefaction countermeasures or repairing damaged ground.

In the present invention, the improvement effect of the injection of the grouting material can be confirmed by non-destructive testing. In this case, the non-destructive testing is preferably performed by elastic wave velocity logging, acoustic tomography, or surface wave exploration.

In the ground improvement method of the present invention, a ground grouting material consisting of the suspension is injected into the ground through a plurality of injection holes provided in the ground,
The separated silica solution separated from the suspension of the ground grouting material gels, and the homogel has a strength to stand on its own, and the sand gel solidified by the penetration of the separated silica solution has a strength to stand on its own,
The separated silica solution can penetrate into parts of the ground that the suspended particles could not penetrate, expanding the solidification range, or can integrate with the parts of the ground that the suspended particles have penetrated to form a solidified body.

In the present invention, the phrase "the separated silica solution gels and the resulting homogel becomes self-supporting" means that the silica concentration of the separated silica solution is 0.5 w/v % or more, and the homogel does not collapse even when tilted obliquely in a mold and remains self-supporting; the phrase "the sand gel becomes self-supporting" means that the silica concentration of the separated silica solution is 0.5 w/v % or more, and when No. 6 silica sand is used, the sand gel prepared by a mixing method using the separated silica solution to have a diameter of 5 cm and a height of 10 cm so as to have a relative density of 60% becomes self-supporting, and the strength of the sand gel measured in a uniaxial compression test is 2.0 kN/ ^m2 or more.

In the present invention, it is preferable to set a formulation for the ground injection material that results in lightweight, low-alkali, and low-carbon ground improvement.

According to the present invention, the permeability limit of suspension grout is expanded to the permeability range of solution grout, achieving a large solidification range, and simultaneously achieving high strength and excellent water-stopping and permeability. It also makes it possible to infiltrate and solidify solution grout in a single process while injecting suspension grout, allowing for simultaneous infiltration and solidification of suspension and solution grout, thereby achieving simultaneous combined injection of suspension and solution without the problems associated with high-pressure injection and mixing methods.

The present invention is a ground improvement method that involves injecting into the ground a ground grout consisting of a suspension containing silica solution and suspended particles as active ingredients. The separated silica solution, which separates from the suspension, penetrates and solidifies in areas where suspended particles cannot penetrate, thereby simultaneously solidifying the ground with the suspended particles and the separated silica solution. This method essentially expands the injectability limit of conventional suspension-type grout to that of solution-type silica grout, and significantly expands the penetration and solidification range of conventional suspension-type grout. This greatly expands the range of applications of the ground improvement method, enabling it to be used not only for liquefaction countermeasures, increasing the bearing capacity of ground, and constructing water-stopping walls, but also for injection into the periphery of underground structures with underground spaces, strengthening underground structures, water-stopping and strengthening excavated ground, strengthening and water-stopping for bottom injection, reinforcing and water-stopping rock cracks in rock shafts, or containing harmful substances.

1A and 1B are explanatory diagrams relating to a composite injection method, in which (a) shows an example of a double-pipe composite injection method, and (b) shows an example of a double-pipe double packer method. FIG. 10 is a photograph showing the bleeding state of the sample of Example 36. FIG. 1 is a photograph showing the bleeding state of the sample of Comparative Example 1. FIG. 10 is a photograph showing the state of the sample of Example 36 several days after penetration. FIG. 1 is a photograph showing the state of the sample of Comparative Example 1 several days after penetration. 1 is a graph showing the results of a long-length penetration test for Example 36 and Comparative Example 1. 7 is a graph showing an enlarged portion of the permeation distance of 90 cm to 120 cm in FIG. 6. This is a photograph showing the state in which the bleeding liquid has gelled and the gel does not collapse (stands on its own) even when tilted. This is a graph showing particle size accumulation curves for various on-site sands that have been treated with liquefaction countermeasures using solution-type grout. FIG. 10 is a photograph showing the strength measurement status of a test specimen on the 7th day after the mixing method using a bleeding liquid. FIG. 10 is a photograph showing the state of a test specimen after strength measurement using a mixing method using a bleeding liquid. 1 is a graph showing the physical properties of the sand used. FIG. 1 is an explanatory diagram showing one form of permeation consolidation in the ground improvement method of the present invention. FIG. 10 is an explanatory diagram showing another form of permeation consolidation in the ground improvement method of the present invention. FIG. 10 is an explanatory diagram showing yet another form of permeation consolidation in the ground improvement method of the present invention. FIG. 10 is an explanatory diagram showing yet another form of permeation consolidation in the ground improvement method of the present invention. FIG. 1 is an explanatory diagram showing reinforcement injection into the periphery of a tunnel, as an example of application of the ground improvement method of the present invention. FIG. 1 is an explanatory diagram showing an example of application of the ground improvement method of the present invention, in which concrete is repaired from inside an underground structure in service and reinforced and injected into the surrounding ground. FIG. 1 is an explanatory diagram showing an example of strengthening an underground structure, among application examples of the ground improvement method of the present invention. FIG. 1 is an explanatory diagram showing the strengthening and waterproofing of the base plate by base plate injection, as an example of application of the ground improvement method of the present invention. FIG. 1 is an explanatory diagram showing reinforcement of a missing portion of a retaining sheet pile and water-stopping injection in an application example of the ground improvement method of the present invention. FIG. 1 is an explanatory diagram showing the prevention of subsidence of a tunnel foundation and water sealing in an application example of the ground improvement method of the present invention. FIG. 1 is an explanatory diagram showing an example of application of the ground improvement method of the present invention, in which a foundation is reinforced or a damaged foundation is repaired. FIG. 1 is an explanatory diagram showing reinforced filling of rock cracks and water sealing or waste containment in an application example of the ground improvement method of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The ground improvement method of the present invention is a method of injecting into the ground a ground grouting material consisting of a suspension whose active ingredients are a silica solution and suspended particles, and is characterized in that the separated silica solution separated from the suspension penetrates into areas that the suspended particles cannot penetrate, and then gels and solidifies the ground, thereby simultaneously solidifying the ground with the suspended particles and the separated silica solution.

As a result of continuing research into the gelation of bleeding liquid, the inventors discovered that in suspensions containing silica solution, bleeding liquid gels whether the bleeding rate is 50% or less or 50% or more (Figures 2, 4, 6-8, Table 8). They also discovered that the gelation time and strength of the bleeding liquid can be adjusted by adding a curing agent, and they also discovered the relationship between the gelation of the bleeding liquid and the silica concentration sufficient to form self-supporting homogels and sand gels (Table 9, Figures 2, 4, 6-8, 10, and 11).

Figures 13(a) to (d) show the form of permeation consolidation in the ground improvement method of the present invention. Figure 13 shows that by injecting the silica suspension, the suspended particles permeate between the soil particles, and further, the separated silica solution from the suspension permeates and solidifies, creating an integrated permeation consolidation area. Figure 13 corresponds to Figures 6, 7, and Table 8.
Therefore, the suspended particles of the suspension and the separated silica solution from the suspension are injected into the ground from multiple injection holes and solidified, making it possible to improve the ground as a whole (Figure 13).
Furthermore, the present invention has substantially expanded the injection limit of suspension grout (Fig. 12) to include solution grout (Fig. 9), making it possible to carry out ground improvement using suspension grout injection and solution grout in a single process, and has developed into a ground improvement method based on a new technological concept of simultaneous combined injection of suspension and solution.

As mentioned above, the ground grout used in this invention can be described as a permeable suspension grout that, while being a suspension grout, penetrates and solidifies not only coarse-grained soil but also fine-grained soil in a single process. Therefore, in conditions where permeable grout, due to its excellent permeability, is prone to deviation into unintended ground or is prone to dilution with groundwater, as shown in Figure 1, a primary injection of a suspension grout or instant-setting grout such as cement bentonite (CB) can be carried out in advance, followed by a secondary injection of the above-mentioned ground grout. This allows the specified amount to be injected at the specified injection stage without deviation, enabling high-strength ground improvement with excellent permeability and water-stopping properties.

The suspension grout used for the primary injection can be CB or a suspension grout made of silica particles and a binder, such as the above-mentioned slag or fly ash, which does not contain silica solution. Furthermore, if a quick-setting agent such as calcium chloride, gypsum, or water glass is added to a suspension containing silica solution, it will become an instant-setting grout that sets in a few to 10-odd seconds.

The present invention also relates to a ground improvement method for improving soft or liquefied ground around underground structures with high strength and light weight. This method involves infiltrating silica particles, slag-based consolidating materials, or other materials into the surrounding area to form large consolidations, enabling low-carbon ground improvement. By using particles primarily composed of calcined silica, such as slag or fly ash, or silica particles with natural pozzolanic properties, non-cement-based consolidating materials or consolidating materials with reduced cement content, it is possible to provide environmentally friendly ground improvement with reduced _CO2 emissions from a material perspective. Furthermore, by incorporating a silica solution into the suspended particles, the separated silica solution from the suspension penetrates and solidifies, expanding the penetration and solidification range, achieving high-strength improvement effects, water-stopping effects, and the ability to repair deteriorated underground concrete structures.

Therefore, the present invention provides the advantage of reducing the weight of the entire improved area and eliminating settlement caused by the solidified body by forming a solidified body using artificial calcined silica such as slag or fly ash as the main component of suspended particles, or by using silica particles with natural pozzolanic action as the main component, or by using a formulation with a small amount of cement.
This is because the specific gravity of cement is 3.15, whereas that of slag is 2.9, that of fly ash is 2.8, and that of volcanic ash generally ranges from 0.9 to 2.5, which is almost the same as that of sand or clay.

Table 1 below shows an example of a test for the consolidated strength of a mixture with a consolidating agent when the ground is sandy soil or clayey soil.
Bleeding measurements were performed using bleeding bags (JSCE-F 522-2018, JSCE-F 532-2013) in accordance with the test method.
The viscosity was measured using a tuning fork vibration viscometer (SV-10 manufactured by A&D).
Tables 1 through 7 show examples of the consolidation strength of homogeneous gels or their mixtures with in-situ soil. Table 8 shows the uniaxial compressive strength of sand gels prepared using a blending method with a bleeding solution. In this invention, a lightweight suspension based on small, highly fluid particles is selected depending on the ground conditions, allowing penetration and solidification into the surrounding ground. If the suspension contains silica solution, the separated silica solution gels and solidifies. This extends the consolidation range to surrounding areas, even in areas where the suspension alone cannot penetrate. Furthermore, it provides a water-stopping effect and continuous solidification between the consolidations (Figures 2, 4, 6 through 11). Figure 9 shows the particle size distribution curves for solution-type grouts that achieve a permeation consolidation effect. The above-mentioned suspension-type consolidation material containing silica solution can penetrate and solidify ground with the particle size distribution shown in Figure 9. This enables a new ground grouting method based on the concept of "simultaneous combined suspension/solution injection," which combines the advantages of both suspension and solution injection methods. FIG. 12 shows the particle size distribution of the permeable limit of the suspension grout without silica solution.

The grouting material used in the present invention will be described below.
The grouting material used in the present invention is a suspension containing a silica solution and suspended particles as active ingredients. The grouting material used in the present invention may contain suspended particles made of silica particles as the main ingredient, and one or more of a hardener, an alkali agent, and a silica solution.

The ground grouting material used in this invention is primarily composed of calcined silica such as slag or fly ash, which can be mixed with water glass and/or an alkaline agent or hardener to prepare the grouting material. It is preferable that the active ingredient of the suspended particles be one or more of calcined silica, natural calcined silica with pozzolanic action, and hardenable silica particles.

Among these, pyrogenic silica includes slag and fly ash, as well as cement, paper sludge, sludge incineration ash, sewage incineration ash, plant incineration ash, and calcined clay, as well as plant incineration ash rich in silica. Any one or more of these can be used. Furthermore, natural pyrogenic silica with pozzolanic properties includes natural calcined soils such as loam (Kanto loam), shirasu, volcanic ash, and niwado (fine-ground soil) and sanwado (fine-ground soil). Any one or more of these can be used. These pyrogenic silicas are silica particles with pozzolanic properties, containing soluble silica. They form a crystalline structure similar to that of cement through hydration in the presence of alkalis such as slaked lime, gypsum, magnesium hydroxide, water glass, silica colloid, caustic alkali, carbonates, bicarbonates, aluminum salts, calcium salts, and magnesium salts, thereby solidifying firmly. Furthermore, using aggregates such as soil and clay as thickeners or bulking agents enables economical ground improvement. Additionally, on-site soil can be slurried with the hardening agent and used.

The use of silica particles with a Blaine value of 4,000 to 20,000 cm ² /g as the suspended particles enables penetration between soil particles. Furthermore, high strength can be achieved by using artificial or natural calcined silica as the suspended particles and setting the amount of suspended particles in the ground grouting material to 50 to 200 kg per 400 L. The amount of calcined silica such as slag in the ground grouting material according to the present invention is determined depending on the desired strength of the hardened product, but is preferably 50 to 200 kg per 400 L, 10 to 25 w/v % when cement is not used, and 10 to 30 w/v % when cement is used.

The grouting material of the present invention preferably contains a hardening agent made from a polyvalent metal compound. The hardening agent can be one or more of the hydroxides, oxides, or salts of Ca, Mg, or Al, and/or gypsum. Specifically, these include cement, slaked lime, gypsum, and other calcium molten materials, as well as alkaline agents. Slaked lime is particularly preferred for shortening gelation time and improving early strength. The grouting material can also be used in combination with fillers such as slag, bentonite, calcium carbonate, clay, and silica powders such as earth and sand. Plastic grouts can also be made using fly ash, polymers, cement, plasticizers such as aluminum salts, thickeners, and clay.

The alkaline agent used in the ground grouting material according to the present invention may be any one or more of the following (1) to (3):
(1) An alkaline agent containing one or more of gypsum and MgO as active ingredients.
(2) An alkaline agent containing one or more of Ca salts, Mg salts, Al salts, carbonates, and bicarbonates as active ingredients.
(3) An alkaline agent containing one or more of lime, cement, caustic alkali, water glass, and silica colloid as active ingredients.

In the ground grouting material of the present invention, the silica solution is preferably silica colloid and/or water glass, the separated silica solution separated from the suspension of the ground grouting material is gelled, and the silica concentration of this separated silica solution is preferably 0.5 w/v% or more. In this case, it is preferable that the molar ratio of water glass is 1.0 to 5.0, and the amount of water glass mixed in the ground grouting material is 10 to 150 L/400 L.

In the present invention, the slag used is finely pulverized blast furnace slag, and a finer particle size is preferred to enhance reactivity. For example, a slag having a specific surface area (Blaine value) of 4000 cm ² /g or more, preferably 6000 cm ² /g to 20000 cm ² /g, and an average particle size of 10 μm or less is suitable.

In the present invention, the water glass preferably has a high alkali concentration due to its reactivity with slag, and a _SiO / _Na O molar ratio of 1.0 to 2.5 is particularly preferred. This allows for the production of a high-strength solidified body and the adjustment of gelation time. The water glass may be a mixture of anhydrous sodium orthosilicate and sodium hydroxide, crystalline sodium silicate containing sodium metasilicate, a mixture containing a portion of crystalline sodium silicate, sodium silicate glass (cullet), hydrated glass, dehydrated sodium silicate, semi-solid sodium silicate, viscous sodium silicate, a commercially available sodium silicate solution, or a combination of the water glass with a molar ratio of 1.5 to 5.0. Water glass with a molar ratio of 2.5 to 5.5 or a silica solution obtained by mixing silica colloid with water glass to further increase the molar ratio may also be used with different viscosities, molar ratios, and silica concentrations, or may be used as powder. The alkali content of the water glass stimulates the hydraulic properties of the slag. Water glass with a low molar ratio may be a mixture of water glass and caustic alkali. However, when a Ca molten material such as slaked lime or cement is used in combination, water glass with a high SiO ₂ /Na ₂ O molar ratio, such as water glass No. 3 or No. 4, can be used.

In addition to water glass, silica colloid can also be used as the silica solution, and a mixture of silica colloid, calcined silica such as slag, and cement can also be used. Any silica colloid can be used, including colloids obtained by reducing the alkalinity of water glass using ion exchange and then removing and stabilizing it in the weak alkaline range, silica colloids made from metallic silica, silica colloids derived from geothermal water, and silica colloids obtained by removing the alkalinity from water glass with acid.

The salts used in the present invention include aluminum compounds such as aluminum sulfate and polyaluminum chloride, chlorides and sulfates of Ca and Mg, and products obtained by reacting these with caustic alkali. Furthermore, the molar ratio of _Na2O / _Al2O3 is not particularly limited, but due to its reactivity with slag, it is preferable that the _Na2O concentration in the grout be 1 _wt % or higher. Caustic alkali is effective in stimulating the hydraulic properties of slag, and the aluminum reacts with water glass and the silica in the slag to form aluminum silicate and calcium aluminosilicate. Furthermore, the gel time and strength of the suspension and the separated silica solution separated from the suspension can be adjusted by adjusting the amount of these additives. Furthermore, seawater can be used as a blending liquid for the suspension.

The amounts of water glass and aluminum compound in the grout are such that the hardening time of the grout is several hours, usually within one hour, and preferably within 30 minutes, and although this varies depending on the molar ratio of Na ₂ O, Al ₂ O ₃ and SiO ₂ , it is preferable that the grout contains 1 wt % or more of Na ₂ O. However, when solidifying a wide area, amounts are required that will result in a hardening time of several hours.

Furthermore, the grouting material of the present invention can be made lighter by adding a foaming agent or foaming agent to improve its fluidity. Adding clay, bentonite, or polymer-based thickeners, such as polyvinyl alcohol, carboxymethyl cellulose (CMC), or methyl cellulose, can suppress dispersibility in water, reduce precipitation, and improve workability. It can also function as a water-retaining material and a binder for the silica particles of the main material, such as slag, creating a pseudo-gel-like fluid that maintains fluidity while remaining difficult to disperse. This reduces diffusion and dilution in the ground and promotes the expansion of the solidified body.

In the present invention, microbubbles or microbubbles and air can be mixed and injected into the above-mentioned suspensions of slag, fly ash, etc., or into suspensions of cement, etc. In this way, the bearing action of the microbubbles or microbubbles and air that cover the suspended particles makes it possible to create a widespread solidified body of suspended particles, and also makes it possible to reduce the weight and strength of the solidified body by increasing the amount of gas in the solidified body. It has also been found that the presence of air bubbles in the solidified body improves the liquefaction prevention effect even when the amount of suspended particles in the solidified body is small and the strength is low. Furthermore, in addition to microbubbles and air, the injection material of the present invention can also use dispersants and thickeners, and one or more of these can be used as active ingredients.

In the present invention, a formulation can be established for a ground injection material that is lightweight, low-alkali, and low-carbon for ground improvement.

In the present invention, the grouting material may be directly mixed and sent to the injection rod as a single liquid, or the above-mentioned suspension (Liquid B) and water glass and/or alkaline agent (Liquid A) may be transported by pump, mixed, and injected. In this case, Liquid A and Liquid B are preferably mixed in a ratio of approximately 1:1 (by volume), but are usually mixed at any ratio within the range of 10:1 to 1:10.

In the present invention, for extremely permeable ground, it is preferable to inject a suspension grout or a quick-setting grout as a primary grout prior to injecting the above-mentioned ground grouting material.

In the present invention, the improvement effect of injecting grouting material can be confirmed by non-destructive testing. Non-destructive testing can be performed using seismic velocity logging, acoustic tomography, or surface wave exploration.

The ground improvement method of the present invention can be applied to strengthening underground structures by injecting a ground grouting material into the periphery of an underground structure that has an underground space. The ground improvement method of the present invention can also be suitably applied to strengthening and sealing off excavation wall or bottom grouting, reinforcing and sealing off rock cracks in rock shafts or containing harmful substances, reinforcing existing foundations or repairing damaged foundations, and carrying out liquefaction countermeasures or repairing damaged ground.

(test)
Clayey soil and sandy soil were used, and these were mixed and consolidated with the above-mentioned grouting material according to the present invention. The strength of the consolidated body was measured, and the test results are shown in Table 1.

As can be seen below, cement-free injection materials, or injection materials with reduced cement content, that are primarily made from calcined silica or natural silica with pozzolanic properties, have a lower specific gravity than cement-based injection materials, and therefore solidify the ground using a material that has almost the same specific gravity as the original ground, or even a lighter material, thereby achieving the effect of a lightweight solidified body.

[Materials used]
Slag: A silica-based non-hardening powder having a specific gravity of 2.9 and a Blaine value of 8000 cm ² /g.
Fly ash (FA): Coal ash discharged from thermal power plants: a silica-based non-hardening powder. Specific gravity: 1.9-2.3 g/cm ³ , particle size distribution: 90% or more of which is 0.1 mm or less.
Cement: Ordinary Portland cement: PC, specific gravity 3.15, hardening agent.
Aluminum sulfate: Aluminum sulfate, Al ₂ O ₃ =17.2%, gelling agent, specific gravity 1.32.
Slaked lime: Industrial calcium hydroxide, gelling accelerator and hardener.
Gypsum or gypsum hemihydrate: hardening material, specific gravity 2.6.
Bentonite: Water-retaining and thickening agent, specific gravity 2.6.
Magnesium oxide (gelling agent): specific gravity 3.65.
Calcium chloride (gelling agent): specific gravity 1.85.
Baking soda: specific gravity 2.2.
Dispersant: Specific gravity 1.04.
Sulfuric acid: specific gravity 1.67, 75 w/w%.
No. 5 water glass: specific gravity 1.32, silica concentration 25.5%, Na ₂ O 7.03, molar ratio 3.75.
No. 1 water glass: specific gravity 1.35, silica concentration 21.59%, Na ₂ O 10.80%, molar ratio 2.06.
No. 3 water glass: specific gravity 1.41, silica concentration 29.16%, Na ₂ O 9.36, molar ratio 3.22.
Polyaluminum chloride and foam materials can also be used.

[Test method and test results]
The specimens for the uniaxial compression strength tests in Tables 1 to 7 were prepared in accordance with the Japanese Industrial Standards (Draft) (JIS A 1216:2020) uniaxial compression test method for soil, using cylindrical specimens with a height of 100 mm and a diameter of 50 mm. The results of measuring the strength on the 1st, 7th, and 28th days, or on the 28th day, are shown, respectively.
In Tables 1 to 8, the gel time is the time it takes for the suspension to aggregate while being continuously stirred with a stirring rod.

The grouting material of the present invention can penetrate and solidify sandy ground. In particular, when the grouting material of the present invention contains solution-type silica, it penetrates and solidifies fine-grained soil, connecting the solidified bodies together and achieving a water-stopping effect.

Below, we will explain test examples (Figures 2 to 11) that demonstrate the effect of gelling the bleeding liquid in the above suspension containing silica solution, or the separated silica solution separated from the suspension. Figure 8 shows a tilted view of Figure 2 using Example 36 from Table 4. Figures 10 and 11 show the strength test results of a sand specimen solidified with the bleeding liquid from Table 8.

(Permeability test)
(Testing equipment and testing method)
A one-dimensional infiltration device (2 m long) was used to conduct infiltration tests on No. 6 silica sand, and the infiltration length and strength distribution were investigated.

Test conditions: acrylic mold h = 2 m, compound liquid 3 L
After the sample was saturated with water, the suspension was poured into the bottom until no more liquid was discharged.

The specimens were prepared in accordance with the Japanese Industrial Standard (draft) (JIS A 1216:2020) for the unconfined compression test of soil, and cylindrical specimens measuring 100 mm in height and 50 mm in diameter were used for the unconfined compression test.

The test was carried out using the formulations of Example 36 and Comparative Example 1 (Figures 4-7, 10, and 11).

The solid lines in Figures 6 and 7 show the results obtained using the formulation of Example 36. Strength measurements were possible even with a penetration distance of 120 cm. Although there was no discoloration of the sand gel after 90 cm, it is believed that the reason strength measurements were possible is because the silica solution that separated from the suspension solidified after 90 cm. The portion after 90 cm is believed to contain more than 0.5% silica.

The dotted lines in Figures 6 and 7 show the results obtained using the formulation of Comparative Example 1. Strength could be measured up to 90 cm, but there was no discoloration after 90 cm, making it impossible to measure strength, indicating that the silica solution that separated from the suspension had not gelled.

In the penetration test shown in Figure 5, areas where there was no discoloration of the sand are thought to be areas where slag had not penetrated. Because the bleeding liquid was not self-supporting, the areas where the solution that separated from the suspension had penetrated were also not self-supporting and had not solidified. In contrast, in Figure 4, the bleeding liquid had gelled and was self-supporting, so the suspended particles did not penetrate and the sand gel did not discolor, but the separated silica solution that had separated from the suspension penetrated and solidified, allowing it to stand on its own and develop strength.

From the above, under conditions where penetration between soil particles is not possible due to the particle size and density of the soil, and the particle size distribution of the suspended particles, the separated silica solution will penetrate from the suspension (Figures 9 and 12).

Figures 6 and 7 show that even if the penetration distance of the suspended particles in the suspension is 90 cm, the separated silica solution from the suspension penetrates up to 120 cm, and the solution is strong enough to stand on its own, and the sand gel is strong enough to stand on its own. In this case, the silica concentration can be predicted to be 0.5 to 2% or more (Table 9). Therefore, even if the injection hole spacing is long, the homogel of silica solution will connect the solidified bodies penetrated by the suspended particles, which will achieve high strength.

In this way, a unified solidified mass can be formed even in ground conditions where suspended particles cannot penetrate. Furthermore, even if the injection hole spacing is wide, the solidified masses between the holes can be connected by a self-sustaining gel of silica solution, forming a unified solidified ground.

Suspension grout achieves higher strength than solution grout, but its large particle size makes it less permeable to fine-grained soil. However, by including solution silica, a solidification effect can be achieved even in ground that cannot be penetrated by suspended particles, making it possible to achieve integrated ground improvement and watertightness (Figure 13).

As described above, the inventors focused on the gelation of the bleeding liquid in suspension grout and studied the gelation of the bleeding liquid, the self-sustaining properties of the bleeding liquid homogel, and the self-sustaining properties and strength of the bleeding liquid sand gel. By using these conditions, they were able to improve the penetration and consolidation properties of suspension grout in fine-grained soil or ground containing fine-grained soil, which was previously thought to be inapplicable, and completed the present invention. Furthermore, the present invention can achieve improvement effects, allowing the excavated surface to stand up and become waterproof, even in excavated ground. Therefore, the present invention can be applied not only to ground reinforcement as shown in Figure 14, but also to the reinforcement and waterproofing of excavated ground.

In particular, when a suspension grout containing a silica solution is used, the present invention exhibits the following effects due to the gelation of the separated silica solution from the suspension grout. These effects cannot be obtained by conventional high-pressure injection mixing methods.
(1) Penetration and consolidation of suspended particles into fine-grained soil, where penetration and consolidation was previously impossible.
(2) Self-supporting effect and water-stopping effect of the cutting surface.
(3) Expanding the scope of improvement through infiltration and solidification.
(4) Ground improvement in which adjacent solidified bodies are connected and integrated.
(5) Reduction of construction costs by increasing the intervals between holes drilled in the injection pipe.
(6) The short-term solidification effect of the separated silica solution separated from the suspension grout improves resistance to earth pressure from adjacent structures and the back of the retaining wall, thereby improving construction safety, safety for buried objects through infiltration injection, strengthening of the ground surrounding underground structures with spaces, waterproofing, and repair of deterioration.

An example is shown below.
(Strength test)
(Preparation of sand gel specimen)
Using No. 6 silica sand (Figure 12) and a bleeding liquid, specimens measuring 5 cm in diameter and 10 cm in height were prepared using a mixing method to achieve a relative density of 60%, and the unconfined compressive strength was measured after 28 days. The bleeding rate increased with increasing amounts of water glass and decreased amounts of slag. In sand gels using bleeding liquid, the strength development rate increased with increasing amounts of water glass and slag. In addition, in cases where gypsum was used in combination, the bleeding rate decreased and the strength increased when gypsum was added.

The gelation and self-supporting properties of the bleeding solution, as well as the strength and self-supporting properties of the sand solidified by the bleeding solution (sand gel), vary depending on the amount of slag and water glass in the suspension, the ratio of silica (SiO ₂ ) in the water glass to calcium (CaO) in the slag (CaO/SiO ₂ ), gel time, and the particle size and density of the sand solidified by the bleeding solution. Therefore, tests were conducted to confirm the minimum gelation and self-supporting properties of the bleeding solution, as conditions that comprehensively affect these factors (Table 9). The gel time in Table 8 is the stirring gel time; since no bleeding solution was obtained, the static gel time was used. The static gel time was measured by placing 100 mL of the solution in a standard No. 8 bag (0.03 mm thick x 130 mm wide x 250 mm high). The solution was divided into a lower portion containing a high concentration of suspended particles and an upper portion containing fewer suspended particles (bleeding solution). The static gel time was determined when the upper portion of the lower suspended portion no longer tilted two-thirds of the solids when slowly tilted sideways. The static gel time was shorter than the stirring gel time, and in most cases it was half the stirring gel time. When preparing the sand gels shown in Table 8, 2 L or 3 L of the formulation was placed in a 3 L plastic mug, and the bleeding liquid was removed when the static gel time was half the time, and the liquid was used to prepare the sand gels.
As a result, provided that the bleeding liquid gels and becomes self-sustaining, and the sand gel into which the bleeding liquid has penetrated becomes self-sustaining, it has become possible to improve the ground by using a combined suspension/solution injection method to solidify the fine-grained soil parts where it was difficult for suspended particles to penetrate and solidify, or the parts that did not penetrate, using a separated silica solution separated from the suspension, and to integrate the whole.

Whether the bleeding rate was above or below 50%, gelation allowed the silica solution that separated from the suspension during injection to penetrate and solidify. The minimum strength required for the sand gel to stand on its own was 2.0 kN/ ^m² . The strength of a self-supporting sand gel containing only 75 g of slag and 100 mL of No. 1 water glass per 400 mL of sand gel was 15 kN/ ^m² on the 28th day. The strengths were also measured on the 1st and 7th days. The strength at 1 day was 2.0 kN/ ^m² , while the strength at 7 days was 10 kN/ ^m² (Figures 10 and 11). A similar trend was observed with Toyoura sand. Furthermore, the strength of the sand gel is expected to increase further if salts such as Ca, Mg, and Al are included in the bleeding solution.

In this invention, the test specimen is sized to match the size of the specimen used in the uniaxial compression test of soil. The diameter _D0 (mm) is usually 35 mm or 50 mm, and the height _H0 (mm) is 1.8 to 2.5 times the diameter _D0 (mm). As long as the sand gel is self-supporting, it can be evaluated at any age. Figure 10 shows the test conditions. From this, it was found that even in-situ sand can be self-supporting if it achieves a strength of 2.0 kN/ ^m2 with an injection rate of 40%. Furthermore, the injection rate is the ratio of the injection liquid to the volume of the ground to be improved. For example, if the injection rate is 40% for 1 ^m3 of improved ground, the injection volume is 0.4 ^m3 .

The gel time was shortened by increasing the amount of slaked lime added, and the strength increased with increasing the amount of slag.
In Comparative Example 1, the portion containing the suspended particles solidified, but the portion containing the bleeding liquid did not gel.
The bleeding liquid of Example 36 gelled. It was also found that the bleeding liquid gelled when either silica colloid or water glass or both were used in combination.

(Relationship between silica concentration and strength)
A neutral to alkaline solution was placed in an acrylic mold with a removable bottom and allowed to solidify. The homogels were checked for gelation and the self-supporting ability of the gels at different silica concentrations. The same procedure was also performed on sand gels to check the solidification and self-supporting ability of the consolidated sand. The results are shown in Table 9.

At silica concentrations below 0.5%, the homogel and sand gel could not be self-supporting.
Further tests showed that gelation occurred even at a silica concentration of 0.25%, but the gel did not remain self-supporting, and the sand gel did not solidify or remain self-supporting (Table 9).

In other words, simply gelling the bleeding solution can result in neither homogels nor sand gels being self-supporting, and there are also cases where the sand gel is self-supporting even though the homogel is not. This shows that certain conditions are necessary to ensure the homogel and sand gel are self-supporting (Tables 8 and 9).

In addition, penetration tests using a one-dimensional penetration device (2m long) revealed that in water glass-slag systems, the bleeding liquid gels and has the strength to stand on its own, but that when water glass is not included, the bleeding liquid does not gel. Furthermore, whether the bleeding rate is above or below 50%, the bleeding liquid gels, and the separated silica solution that separates from the suspension penetrates and solidifies. In this case, the silica concentration of the silica solution is predicted to be 0.5w/v% or higher (Table 9).

Furthermore, the penetration test confirmed that in the case of the water glass-slag system and the suspension not containing water glass, the separated silica solution separated from the suspension containing water glass penetrates and solidifies into sand which suspended particles cannot penetrate.
Therefore, this separated silica solution can penetrate into the ground in the particle size accumulation curve of the penetration and solidification of solution-type grout, and it was found that the penetration potential of solution-type silica grout can be obtained (Figure 9).

In this way, suspension grout uses fine particle silica such as slag or fly ash and solution-type silica, allowing the separated silica solution from the suspension to penetrate and solidify in areas where suspended particles cannot penetrate. Therefore, by focusing on the gelation of the bleeding liquid, we discovered the following conditions under which the separated silica solution and sand gel become self-sustaining.

From the above, other preferred embodiments of the ground improvement method used in the present invention are as follows.
This is a ground improvement method in which a ground injection material consisting of the above-mentioned suspension is injected into the ground through a plurality of injection holes provided in the ground, and the separated silica solution separated from the suspension of the ground injection material gels, and the resulting homogel has the strength to be self-supporting, and the sand gel formed by the penetration of the separated silica solution and solidification has the strength to be self-supporting, and the separated silica solution penetrates into parts of the ground that the suspended particles could not penetrate, expanding the solidification range, or integrating with the parts of the ground into which the suspended particles have penetrated to form a solidified body.

When the ground grouting material contains solution-type silica, the separated silica solution gels, and the resulting homogel has the strength to stand on its own. The sand gel solidified by the penetration of the separated silica solution also has the strength to stand on its own. The separated silica solution penetrates into areas of the ground that were previously impervious to suspended particles, integrating with the areas of the ground where the suspended particles had penetrated to form a solidified mass. This allows the solidified masses of suspended particles from adjacent injection holes to be linked together, forming a large, integrated mass (Figure 13). Furthermore, adding CMC, MC, polyacrylamide, clay, etc. to this grouting solution makes it less likely to disperse in the ground and less likely to be diluted, even in gravelly ground.

Here, in the above, the phrase "the separated silica solution separated from the suspension gels and the homogel becomes self-supporting" means that the silica concentration of the separated silica solution is 0.5 w/v% or more, and the homogel does not collapse and remains self-supporting even when tilted diagonally in the mold.
Furthermore, the sand gel being self-supporting means that, when the silica concentration of the separated silica solution is 0.5 w/v % or more and No. 6 silica sand is used, a sand gel prepared by a mixing method using the separated silica solution to have a diameter of 5 cm and a height of 10 cm so as to have a relative density of 60% is self-supporting, and the strength of the sand gel measured in a uniaxial compression test is 2.0 kN/ ^m2 or more.

As mentioned above, sand gels made from a bleeding liquid of silica grout consisting of water glass and calcium-containing silica particles increase in strength over time (Table 8). This is thought to be because the calcium ions in the silica particles continue to dissolve into the gel of the bleeding liquid over a long period of time after gelation and react with the silica, forming calcium silicate and contributing to increased strength. Alternatively, the added hardener containing calcium and magnesium reacts with the soluble silica in the silica particles over a long period of time through pozzolanic action, resulting in an increase in strength due to a hydration reaction.

As described above, this invention allows the penetration and consolidation range to be set by the size of the consolidation bodies, suspended particles, and gelation of the separated silica solution separated from the suspension, depending on the ground conditions and the purpose of ground improvement (strength, range of consolidation area, etc.). Furthermore, the penetration and consolidation range of suspended particles and the penetration and consolidation range of the separated silica solution can be set by the type, particle size, and blending amount of silica particles in the suspension, the hardener and alkali agent, the type and amount of solution-type silica, the bleeding rate, the strength of the bleeding liquid, and the gelation time. As a result, as shown in Figure 13, a new concept of simultaneous combined injection of suspension and solution has been created, making ground improvement using suspension-type grout possible.

Furthermore, according to the present invention, by using as the main ingredients of the injection materials natural or artificial silica particles, calcined silica, silica particles with natural pozzolanic action, or fluidized soil made by turning on-site soil into a slurry, it has become possible to provide a ground improvement method that reduces the weight of the solidified body, expands the range of penetration and solidification, and contributes to the global environment by reducing _CO2 emissions.

As described above, the inventors of the present invention have focused on the fact that a silica-rich suspension solidification body forms around the periphery of the injection of a suspension primarily composed of silica particles containing solution-type silica, connecting adjacent solidification bodies. While the frequent bleeding of suspensions has traditionally been considered a drawback, in this invention, we focused on the fact that the separated silica solution from the suspension can penetrate between soil particles that cannot be penetrated by suspended particles, and conducted research into the gelation of the bleeding liquid. As a result, we found that the gelation and strength of the bleeding liquid itself, the permeability of the bleeding liquid into the sand, and the strength of the sand gel have a significant impact on improving the penetration and consolidation properties of suspension-type grout. Based on these findings, we have identified the conditions for the penetration and gelation of the separated silica solution into areas where suspended particles could not penetrate, the homogelation of the separated silica solution, and the strength of the sand gel, and have invented a new ground improvement method based on the concept of simultaneous combined injection of suspension and solution.

Furthermore, the present invention provides a ground consolidation method that uses a non-cement-based ground grouting material containing slag as its main component, thereby making it possible to obtain a solidified body with excellent durability and that is expected to have a _CO2 reduction effect.

The grouting material according to the present invention has the following characteristics in particular:
(1) By setting the composition of the suspension, which is mainly composed of silica particles that are small in particle size, lightweight, and have good fluidity, it is possible to achieve widespread penetration (Figures 5 to 7).
(2) The inclusion of silica solution causes the bleeding liquid to gel, allowing the separated silica solution from the suspension to penetrate into the fine particle areas where suspended particles cannot penetrate (Figure 4, Figures 6-8), solidifying and becoming self-supporting. Since the bleeding liquid or the separated silica solution from the suspension has the same permeability as solution-type silica grout, the fine soil permeability range shown in Figure 9 can be expected. Figure 2 shows the situation in which the suspended matter solidifies and the bleeding liquid gels when a silica suspension containing silica is left standing. Figures 3 and 5 show the situation in which only the suspended matter solidifies and the bleeding liquid does not gel when a suspension containing no silica is left standing.
(3) The self-sustaining properties of homogel, solidification of sand gel and self-sustaining properties of consolidated sand at low silica concentrations of solution-type grout are shown (Table 9).
(4) From the particle size distribution of the sand used in the infiltration test (Fig. 12), it can be seen that the suspended particles used in the present invention infiltrate and solidify into the sandy ground.

The particle size distribution of the sand used in the infiltration tests (Figures 4-7) was No. 6 silica sand, as shown in Figure 12. With this particle size distribution, suspended particles can penetrate between soil particles at a depth of 80 cm (Figures 6 and 7). With Toyoura sand, a finer-grained soil, the penetration distance was roughly half that distance. Furthermore, using the above suspension containing silica solution achieves the same penetration range (Figure 9) as the solution-type particle size range. Although the penetration distance varies depending on the soil conditions, it is possible to form a solidified body like the one shown in Figure 13. Figures 13(c) and (d) are plan views of the infiltration solidified body. The type and size of silica particles in the suspension can be selected depending on the soil conditions. Furthermore, the ability to infiltrate, as shown in Figure 13(d), enables the stabilization of surrounding structures without damaging buried underground objects. Furthermore, by strengthening and waterproofing the surrounding ground, it is possible to strengthen underground structures with open spaces.

As described above, the inventors discovered that when a suspension containing the above-mentioned suspended particles as its main component is injected, the area near the center becomes a high-strength region with a high concentration of suspended particles, while the strength of the suspended particles decreases with distance from the center, resulting in a low-strength region (Figures 6, 7, and 13). However, outside of this, solidified bodies with a high silica content are formed due to gelation of the separated silica solution separated from the suspension, connecting adjacent solidified bodies. While the high level of bleeding in suspensions has traditionally been considered a drawback, in this invention, we focused on the fact that the separated silica solution can penetrate between soil particles that suspended particles cannot penetrate, and conducted research on the gelation of the bleeding liquid. As a result, we found that the gelation and strength of the bleeding liquid itself, the permeability of the separated silica solution into the sand, and the strength of the sand gel significantly affect the improvement of the penetration and consolidation properties of suspension grout. Based on these findings, we investigated the conditions under which the suspension can not only penetrate into the surrounding ground, but also penetrate and gel the separated silica solution into fine-grained soil areas where suspended particles cannot penetrate, enabling the formation of large solidified bodies.

In suspensions that do not contain silica solution, the bleeding liquid does not gel, and the sand that has been infiltrated with the solution that has separated from the suspension does not stand upright, nor does it obtain sufficient strength (Figures 3 and 5). However, sufficient strength cannot be obtained simply by gelling the bleeding liquid (Table 9). After considering these points, we found that the condition for the self-standing strength of the homogel and sand gel of the separated silica solution that has separated from the suspension is a silica concentration of 0.5 w/v% or more (Table 8). Based on this, we considered this to be infiltration and solidification using solution-type silica grout, leading to the invention of the ground improvement method of the present invention.

The present invention also provides a ground improvement method that can obtain a solidified body with excellent durability and is expected to have a _CO2 reduction effect by using a non-cement based ground injection material whose main component is silica particles with natural pozzolanic action, including artificially calcined silica such as slag or fly ash, or soluble silica such as loam soil.

FIG. 14 shows an example of application of the ground improvement method of the present invention.
Figures 14(a)-(c), and (f) show examples of reinforcement of underground structures by ground injection. Figures 14(a), (b), and (f) show examples of ground injection from underground space, and (c) shows an example of injection from the ground surface. The high strength and water-stopping effect protect the underground space from the impact of air raids and other attacks, and prevent water leakage into the underground space (Figure 13(d)). Both methods not only strengthen underground structures, but also enable water stoppage and repair of cracks in deteriorated underground structures.
In the examples shown in Figures 14(d) and (e), conventional suspension grout can strengthen the soil, but it does not penetrate fine-grained soil sufficiently, making it difficult to apply because it does not provide water-stopping properties. However, the suspension of the present invention has a water-stopping effect, making such applications possible.
FIG. 14(f) enables strengthening of the tunnel foundation and waterproofing.
Figure 14(g) shows an example of seismic reinforcement of an existing foundation or repair of a damaged foundation. Even in ground that is impermeable to suspended particles with conventional reinforcement using a suspension alone, the silica solution gels and integrates the solidified parts of the suspended particles, and the solidified area is expanded by the silica solution, thereby increasing the bearing capacity of the foundation.
Figure 14(h) shows an example of reinforced filling of rock cracks and watertight or waste containment. Large rock cracks usually have a series of fine cracks deep inside, which are subject to water pressure. Therefore, suspension grout alone cannot penetrate the fine cracks, and solution grout alone will cause the gel to be pushed out by water pressure. Therefore, injecting either suspension grout or solution grout first will hinder the penetration of the subsequent injection. The present invention automatically enables the infiltration and consolidation shown in Figure 9 in a single process. Therefore, it is expected that the application of this invention will expand beyond rock masses storing nuclear waste or other materials in shafts dug into the rock mass to include the containment of hazardous materials in ordinary soil and sand.
Moreover, FIG. 13(c) can be applied to liquefaction countermeasure works and reinforcement and repair of ground damaged by liquefaction.
According to the ground improvement method of the present invention, the infiltration and solidification of suspended particles and silica solution can be carried out automatically while suppressing ground displacement, without causing ground uplift or ground displacement as occurs in ground strengthening methods in which a low-fluidity suspension is forcibly injected into the ground.

Claims (14)

The following i) to iii)
i) silica particles consisting of one or more of pyrogenic silica and natural pyrogenic silica having pozzolanic activity;
ii) silica particles, wherein the pyrogenic silica is made of any one or more of slag, fly ash, cement, sewage incineration ash, plant incineration ash, and pyrogenic clay;
iii) Silica particles in which the natural pyrogenic silica is composed of any one or more of loam soil, shirasu, volcanic ash, niwado and sanwado;
a ground grouting material comprising a suspension containing suspended particles of any one of the silica particles as a main material and a silica solution as an active ingredient, injected into the ground through a plurality of injection holes provided in the ground,
The separated silica solution separated from the suspension penetrates into an area where the suspended particles cannot penetrate, and then the separated silica solution gels to solidify the ground, thereby solidifying the ground with the suspended particles and the separated silica solution in a single step,
The silica particles have a Blaine value of 4,000 to 20,000 cm ² /g, the amount of the silica particles in the ground grouting material is 50 to 200 kg/400 L, and silica colloid and/or water glass are used as the silica solution,
When the silica solution contains water glass, the water glass has a molar ratio of 1.0 to 5.0, and the amount of water glass in the ground grouting material is 10 to 150 L/400 L,
the silica concentration of the separated silica solution is 0.5 w/v% or more, the homogel formed by gelling the separated silica solution has a strength to be self-supporting, and the sand gel formed by permeating and solidifying the separated silica solution has a strength to be self-supporting,
The phrase "the separated silica solution gels and the resulting homogel is self-supporting" means that the silica concentration of the separated silica solution is 0.5 w/v% or more, and the homogel is self-supporting even when tilted obliquely in a mold without collapsing; the phrase "the sand gel is self-supporting" means that the silica concentration of the separated silica solution is 0.5 w/v% or more, and when No. 6 silica sand is used, the sand gel prepared by a mixing method using the separated silica solution to have a diameter of 5 cm and a height of 10 cm so as to have a relative density of 60% is self-supporting, and the strength of the sand gel measured in a uniaxial compression test is 2.0 kN/m2 or more ^.
The separated silica solution has permeability to fine-grained soil and penetrates into areas of the ground that the suspended particles could not penetrate, connecting the solidified bodies of the suspended particles from adjacent injection holes, and forming a solidified body in one step that consists of, from the center toward the outside, an area solidified with a high concentration suspension, an area solidified with a low concentration suspension, and an area solidified by the gelation of the separated silica solution and having water-stopping properties. The ground improvement method according to claim 1, wherein the ground grouting material contains an alkaline agent consisting of one or more of the following (1) to (3):
(1) An alkaline agent containing one or more of gypsum and MgO as active ingredients.
(2) An alkaline agent containing one or more of Ca salts, Mg salts, Al salts, carbonates, and bicarbonates as active ingredients.
(3) An alkaline agent containing one or more of lime, cement, caustic alkali, water glass, and silica colloid as active ingredients. The ground improvement method according to claim 1, wherein the suspended particles are slag, and the amount of slag mixed in the ground grouting material is 10 to 25 w/v% when cement is not used, and 10 to 30 w/v% when cement is used. 2. The ground improvement method according to claim 1, wherein the ground grouting material contains one or more of microbubbles, air, a dispersant, and a thickener as active ingredients. The ground improvement method according to claim 1, wherein the ground grouting material contains a hardening agent made of a polyvalent metal compound, and the hardening agent is one or more of hydroxides, oxides, or salts of Ca, Mg, or Al, and/or gypsum. A ground improvement method according to claim 1, in which a suspension grout or a quick-setting grout is injected into the ground as a primary grout prior to injecting the ground grout. The ground improvement method according to claim 1, wherein the underground structure is strengthened by injecting the ground grouting material into the periphery of the underground structure having an underground space. The ground improvement method of claim 1 is applied to reinforcement and waterproofing of excavation walls or bottom grouting. The ground improvement method described in claim 1 is applied to reinforcing rock cracks in rock shafts, sealing off water, and containing harmful substances. The ground improvement method described in claim 1 is applied to reinforcing existing foundations or repairing damaged foundations. The ground improvement method according to claim 1, which is applied to liquefaction countermeasures or repair of damaged ground. The ground improvement method according to claim 1, wherein the improvement effect of injecting the ground grouting material is confirmed by non-destructive testing. 13. The ground improvement method according to claim 12 , wherein the non-destructive testing is performed by elastic wave velocity logging, acoustic tomography, or surface wave exploration. The ground improvement method according to claim 1, wherein the separated silica solution penetrates into parts of the ground that the suspended particles could not penetrate, expanding the area of consolidation, or integrating with the parts of the ground into which the suspended particles have penetrated to form a consolidated body.