Ground improvement method

Abstract

To provide a ground improvement method allowing uniform mixing of hydraulic powder being a solidification material into soil containing clay.SOLUTION: In a ground improvement method, hydraulic powder (A) and water insoluble solid particles (B) (excluding the (A)) with a grain fineness number AFS of 20 or more and 100 or less are mixed with soil containing clay. The hydraulic powder (A) is powder hardened by a hydration reaction, for example, cement and gypsum.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a ground improvement method. [Background technology]

[0002] As a method for improving ground, a method is known in which the ground and cement-based solidification material are mixed at a specified position to harden the soft ground and improve it to a good ground. For example, the so-called soil cement method is known in which the ground is mixed with a specially shaped kneading auger, and cement milk is injected through the hollow shaft of the mixer while further mixing and stirring to create a soil cement column in the ground. In addition, the so-called replacement column method is known in which the ground soil is replaced with a solidification material.

[0003] Patent Document 1 discloses a filling material for displacement columns, which is made primarily of water and a hydraulic solidification material and is filled into the ground to replace part of the ground soil to build a displacement column as the foundation of a structure, characterized in that the weight ratio of the hydraulic solidification material to magnesium carbonate as a bleeding prevention material is 0.4 to 5%, and the water / cement ratio is 60 to 120%.

[0004] Patent Document 2 discloses a ground improvement method characterized by supplying a ground improvement material consisting of 100 parts by weight of a cement composition having a mineral composition with a C3S content of 35 to 65% by weight, a C3A content of 10 to 20% by weight, an Fe2O3 content of 2% by weight or less, and an Al2O3 / Fe2O3 weight ratio of 3 or more, 10 to 300 parts by weight of gypsum, and 10 to 300 parts by weight of blast furnace slag to ground having at least two layers of soil with different soil components, and performing a deep mixing treatment. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-219502 A [Patent Document 2] JP 2006-144434 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the method of improving soft ground by mixing and stirring soil and solidification material, the properties of the target soil vary, but for example, in soil with a high clay content, the excavated soil may adhere to the excavation and mixing blades of the excavation and mixing device and rotate synchronously with these blades, which is called a co-rotation phenomenon, and the soil and solidification material may not be mixed uniformly. If the clay is not mixed uniformly, clay lumps will be localized in the soil cement column, resulting in a decrease in strength. The present invention provides a ground improvement method capable of uniformly mixing hydraulic powder, which is a solidification material, into soil containing clay. [Means for solving the problem]

[0007] The present invention relates to a ground improvement method in which (A) hydraulic powder (hereinafter referred to as component (A)) and (B) water-insoluble solid particles having a particle size index AFS of 20 or more and 100 or less (excluding component (A)) (hereinafter referred to as component (B)) are mixed into clay-containing soil. Effect of the Invention

[0008] According to the present invention, there is provided a ground improvement method capable of uniformly mixing soil and a solidification material even if the ground contains a large amount of clay. [Brief description of the drawings]

[0009] [Figure 1] Photograph showing the staining state of the soil cement whose mixability was judged in Example 1 [Diagram 2] Photograph showing the staining state of the soil cement whose mixability was judged in Comparative Example 1 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The soil targeted by the present invention is a soil having a ratio of fine particles having a particle size of 0.074 mm or less of 50% by mass or more. The classification standard for soil as a ground material is summarized as the Geotechnical Society Standard (Geotechnical Society of Japan, 2009). According to this, particles having a particle size of 0.005 mm or more and 0.074 mm or less are classified as silt, and particles having a particle size of less than 0.005 mm are classified as clay. These fine particles are components that give the soil viscosity. According to the Geotechnical Society Standard, clay soil, organic soil, and volcanic ash clay soil are known as soils having a ratio of fine particles having a particle size of 0.074 mm or less of 50% by mass or more. Such soils can be targeted by the present invention. An example of a soil targeted by the present invention is a soil having a ratio of fine particles having a particle size of 0.074 mm or less of preferably more than 50% by mass, more preferably 60% by mass or more, more preferably 70% by mass or more, and preferably 100% by mass or less.

[0011] Clay is mainly composed of hydrous silicate minerals (hereinafter referred to as clay minerals) having a layered structure, and examples of clay minerals contained as fine particles in this clay include kaolin (kaolinite, dickite, nacrite, etc.), serpentine (lizardite, antigorite, chrysotile, etc.), mica clay minerals (illite, sericite, glauconite, celadonite, etc.), chlorite, vermiculite, smectite (montmorillonite, beidellite, nontronite, saponite, hectorite, etc.). The types and amounts of clay contained in soil are diverse, but the present invention can target soil containing clay minerals selected from, for example, kaolin and smectite.

[0012] The hydraulic powder of component (A) is a powder having the physical property of hardening through a hydration reaction, and examples thereof include cement, gypsum, etc. The hydraulic powder preferably contains cement. The cement is, for example, Portland cement such as ordinary Portland cement, belite cement, moderate heat cement, high-early strength cement, ultra-high-early strength cement, sulfate-resistant cement, etc. The hydraulic powder contains cement, further Portland cement, preferably 25% by mass or more, more preferably 35% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 70% by mass or more, and preferably 95% by mass or less, more preferably 92% by mass or less, even more preferably 90% by mass or less, even more preferably 85% by mass or less.

[0013] The hydraulic powder may contain powders having pozzolanic action and / or latent hydraulic properties, such as blast furnace slag, fly ash, and silica fume, and stone powder (calcium carbonate powder). These may be added to cement, such as blast furnace slag cement, fly ash cement, and silica fume cement. The hydraulic powder preferably contains blast furnace slag from the viewpoint of an aluminum ion source for ettringite, which is a hydration product. When the hydraulic powder contains blast furnace slag, the content of the slag in the hydraulic powder is preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 60% by mass or less, more preferably less than 50% by mass.

[0014] In the present invention, the amount of hydraulic powder is the amount of powder having the physical property of hardening through a hydration reaction, such as the amount of cement or gypsum. However, in cases where the hydraulic powder includes a powder selected from a powder having pozzolanic action, a powder having latent hydraulic properties, and stone powder (calcium carbonate powder), the amounts of these powders are also included in the amount of hydraulic powder in the present invention.

[0015] Component (B) is a water-insoluble solid particle having a particle size index AFS of 20 or more and 100 or less. Here, the grain size index AFS is a grain size index according to the American Foundry Society standard (AFS1106-00-S). The AFS of component (B) is preferably 30 or more, more preferably 40 or more, and preferably 80 or less, more preferably 90 or less.

[0016] Moreover, the water-insolubility of component (B) means that the amount of the component that dissolves in 100 g of water at 20° C. is 0.2 g or less.

[0017] The average particle size of component (B) may be, for example, 100 μm or more, or even 200 μm or more, and 2 mm or less, or even 1 mm or less. This average particle size may be measured by a microscopic method, a sieving method, a sedimentation method, or a light scattering method.

[0018] From the viewpoint of the stability of the particle shape during mixing, the component (B) preferably has a Mohs hardness of at least 2, more preferably at least 3, and even more preferably at least 4. The upper limit may be, for example, 1600 or less.

[0019] From the viewpoint of suppressing settling during mixing of the slurry, the component (B) preferably has a specific gravity of 1.1 or more, more preferably 1.6 or more, and preferably 3.3 or less, more preferably 2.8 or less.

[0020] The component (B) may be inorganic particles. Furthermore, the component (B) may be particles containing mullite. Furthermore, the sphericity of component (B) may be 0.2 or more and 1 or less. The sphericity can be determined as the quotient of the surface area of ​​the particle and the surface area of ​​a sphere having the same volume as the particle, or by calculating the cube root of the quotient of the volume of the particle and the volume of the circumscribed sphere.

[0021] The component (B) is preferably sand. For example, commercially available casting sand can be used. Commercially available products include mullite-based artificial casting sands Lunamos #080 and Lunamos #050, alumina-based artificial casting sands Espearl #075, Espearl #050, and Espearl #025 (all from Kao Corporation), and standard sand for cement testing (General Incorporated Association Cement Association). For the slag, steel slag, granulated slag, blast furnace slag, and the like can be used. In addition, fine powder components contained in slag aggregates obtained by solidifying slag with cement, and fine powder components contained in other artificial aggregates can be used. In addition, fine powders contained in waste soil, scrap metal, scrap glass, scrap concrete, scrap ceramics, and the like generated from demolition work and construction and civil engineering work, and dry powders obtained by crushing them can be used.

[0022] In the component (B), the proportion of particles containing mullite is preferably 30 mass % or more, more preferably 60 mass % or more, and preferably 100 mass % or less, and may be 100 mass %.

[0023] In the present invention, from the viewpoint of improving the strength of the improved soil and material costs, the (A) component is preferably added to the soil at a rate of 100 kg / m 3 More preferably, 200 kg / m 3 More than 500 kg / m 3 Less than or equal to 400 kg / m 3 The following is mixed.

[0024] In the present invention, from the viewpoint of improving the mixing uniformity of the improved soil and preventing clogging during pumping of the slurry, the (B) component is mixed in an amount of preferably 1 mass % or more, more preferably 5 mass % or more, and preferably 20 mass % or less, more preferably 15 mass % or less, relative to the (A) component.

[0025] In the present invention, it is preferable to mix a composition containing component (A), component (B), and water with soil. The composition may be a so-called cement milk (cement milk containing component (B)). The composition has a water / (A) component mass ratio of preferably 0.3 or more, more preferably 0.5 or more, and preferably 0.8 or less, more preferably 1 or less.

[0026] In the present invention, the components (A) and (B) can also be mixed with the soil separately.

[0027] The ground improvement method of the present invention can be implemented in civil engineering works. Furthermore, it can be implemented in ground improvement methods. Examples of ground improvement methods include surface layer mixing method, mid-layer mixing method, deep layer mixing method, steel pipe pile method, shield method, pile-shaped ground reinforcement method, cement milk injection method, etc. For example, deep layer mixing improvement methods include high pressure injection method, TRD method, SMW method, etc. The method of the present invention is suitable for deep layer mixing method.

[0028] The specific method for injecting the composition into the ground may conform to known ground improvement methods. Examples of methods for injecting the composition into the ground include injection mixing methods (one-phase flow method, two-phase flow method, three-phase flow method), mechanical mixing methods (CDM method, etc.), and underground diaphragm wall methods (SMW method, TRD method, etc.). The mixture of the composition and soil is solidified according to a known ground improvement method.

[0029] In the present invention, a soil cement column can be constructed by injecting the composition into the ground and mixing it with the soil. In the present invention, the composition can be discharged from the tip of a mixing and stirring device while rotating and drilling the ground, and the soil and the composition can be mixed. These methods can be combined. Such a method is suitable for a deep mixing treatment method.

[0030] In the present invention, the mixing and stirring device may be, for example, an earth auger for excavation, which is provided with an auger rod, a nozzle for the solidification material (the composition) provided on the auger rod, an excavation blade provided on the auger rod, an agitation blade provided on the auger rod, and, if necessary, a co-rotation prevention blade provided on the auger rod. Such an earth auger for excavation may be any known one used in the method of constructing a soil cement column. The earth auger for excavation is set at a position in the ground where a soil cement column is to be constructed, and excavated to a specified dry excavation depth while rotating. During this process, the composition is discharged from the auger rod while excavating. When the injection excavation process (mixing and stirring) is completed, the discharge of the composition is stopped, the rotation direction of the auger rod is reversed, and then lifting (mixing and stirring) is started. The auger is pulled out to complete the process. In the present invention, the clay lumps in the soil cement column are reduced, and any clay lumps that are present are also small, so that a decrease in the strength of the soil cement column can be suppressed. EXAMPLES

[0031] <Preparation of soil cement> Soil cement was prepared by mixing clay and cement milk (solidification material slurry) according to the ratio shown in Table 1. The soil cement was prepared by mixing the ingredients for 1 minute in a mortar Hobart mixer. In this ratio, the injection amount of cement milk was 100 kg / 1 m of clay. 3 It becomes. The cement milk was prepared by adding component (B) in the type and amount shown in Table 2. The cement milk was prepared by mixing the components with a hand mixer for 1 minute. The obtained soil cement was subjected to the following evaluations. The results are shown in Table 2.

[0032] [Table 1]

[0033] The ingredients in Table 1 are as follows: Clay: Kasaoka clay (water content 50%) Cement: Tufflock 2000 (Sumitomo Osaka Cement)

[0034] <Evaluation> (1) Mixability A container measuring 10 cm in diameter and 5 cm in height was filled with soil cement, and the container was tapped 10 times to remove any coarse voids. The soil cement was cut at a position 2.5 cm above the container's height, and the cross section was sprayed with 1% phenolphthalein (90% ethanol). The parts containing the cement were stained, so by observing the staining condition, the mixing ability of the cement can be determined. The presence or absence of clay lumps larger than 1 cm was confirmed from the staining condition. Additionally, the diameter of the maximum grain size of the unstained parts was measured vertically at two points, and the average value was taken as the maximum size of the clay lumps.

[0035] (2) Bigger needle strength A container with a diameter of 10 cm and a height of 5 cm was filled with soil cement, and tapped 10 times to remove any coarse voids. The soil cement filled at a height of 2.5 cm was cut, and a Bigger needle tester was used to measure the displacement when a needle was inserted into the cross section at a constant load. The penetration test was performed using the device used in JIS K 2207. The needle weight was 2.5 g, the needle holder was 47.5 g, and the load was 100 g including a weight of 50 g. After cutting the soil cement, the test was performed after curing for 24 hours at room temperature of 25°C. The larger the needle penetration, the lower the strength, and the smaller the needle penetration, the higher the strength. Measurements were performed at five arbitrary points on the cross section, and measurements were performed at a position at a radius of 1 cm or more from each measurement point. The average value, standard deviation, and coefficient of variation of the five measurement points were calculated. The coefficient of variation was large in the areas where cement was not present, as the strength was extremely low. The coefficient of variation is calculated using the following formula: Coefficient of variation = Standard deviation of penetration / Mean value of penetration

[0036] [Table 2]

[0037] Fig. 1 shows the stained state of the soil cement whose mixability was judged in Example 1. Fig. 2 shows the stained state of the soil cement whose mixability was judged in Comparative Example 1. In Figs. 1 and 2, the black parts are the stained areas, and the more of these there are, the more uniform the mixability can be judged to be. In Example 1 of Fig. 1, there are more black parts (stained areas) than in Comparative Example 1, and it can be seen that the mixability is better than in Comparative Example 1.

Claims

1. A ground improvement method comprising mixing a cement milk, which is a composition containing (A) hydraulic powder (hereinafter referred to as component (A)), (B) water-insoluble solid particles (excluding component (A)) (hereinafter referred to as component (B)) having a particle size index AFS of 30 or more and 90 or less, and water, into soil containing clay, Component (A) contains cement, The component (B) is mixed in an amount of 1% by mass to 15% by mass based on the component (A); Ground improvement method.

2. 2. The ground improvement method according to claim 1, wherein component (A) is cement.

3. Component (A) is applied to the soil at a concentration of 100 kg / m ３ More than 500kg / m ３ The ground improvement method according to claim 1 or 2, further comprising the steps of: mixing the above-mentioned materials;

4. The ground improvement method according to any one of claims 1 to 3, wherein the (B) component has a Mohs hardness of 2 or more.

5. The ground improvement method according to any one of claims 1 to 4, wherein the (B) component has a specific gravity of 1.1 or more and 3.3 or less.

6. The ground improvement method according to any one of claims 1 to 5, wherein the component (B) is inorganic particles.

7. The ground improvement method according to any one of claims 1 to 6, wherein the component (B) is a particle containing mullite.

8. The ground improvement method according to any one of claims 1 to 7, wherein the (B) component has a sphericity of 0.2 or more and 1 or less.

9. The ground improvement method according to any one of claims 1 to 8, wherein the composition has a water / (A) component mass ratio of 0.4 to 0.

9.

10. The ground improvement method according to any one of claims 1 to 9, wherein the composition is mixed and stirred with soil while being injected into the ground to construct a soil cement column.

11. The ground improvement method according to any one of claims 1 to 10, wherein the composition is discharged from the tip of a mixing and stirring device while rotary drilling the ground to mix the soil with the composition.

12. The ground improvement method according to any one of claims 1 to 11, which is used in a deep mixing treatment method.

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