JP6665129B2 - Premix composition used for ground strengthening compaction material, ground strengthening compaction material, method for producing the same, and ground strengthening method using the same - Google Patents

Description

  The present invention relates to a compaction material for strengthening ground by increasing the density of the ground, a method of manufacturing the same, and a method of strengthening ground using the same. The present invention also relates to a premix composition before producing the compaction material by mixing water on the ground when producing the compaction material for ground reinforcement.

  In soft sandy ground, when an earthquake occurs, excessive pore water pressure is generated, soil particles are fluidized, and a "liquefaction phenomenon" occurs, in which the bearing capacity of the ground is temporarily lost. Various ground strengthening techniques have been developed as measures to prevent such liquefaction and have been put to practical use (for example, Non-Patent Document 1).

  One of them is called “compaction method” (also called “density increasing method”), and a typical example is “static press-fitting method”. This method is a method of compacting with a static force (static press-fitting by pumping) without applying dynamic energy (hitting or vibration). Specifically, the compacted material is pressed into the ground to form a consolidated mass, the surrounding ground is compressed by the compacting effect of the compacted mass, and the density of the ground is increased (in this specification, simply “ (Also referred to as “density increase”) to reinforce the ground (for example, Patent Document 1).

  As a compaction material used in the static press-fitting compaction method (for example, compaction grouting method), a mixture of a solidified material, an aggregate, and water is used. Therefore, the properties of the compaction material at the time of completion of mixing are in a wet mortar state or a slurry state (cement paste state). The solidified material is a component that imparts compaction performance (self-hardening) to the compacted material, and cement-based and lime-based materials are widely used (for example, Patent Documents 1 and 2). It has also been proposed to use magnesium oxide as a solidifying material (Patent Document 3).

  Various injection methods (chemical injection, cement injection, jet grout, etc.) are known in addition to the static press-fitting method. In the injection of the chemical solution, the injection material permeates between the soil particles and solidifies (permeates and consolidates). In cement-based injection, cement grout solidifies in the ground in the form of veins (pulse consolidation). In the jet grout (discharge half-replacement), the solidified material and the soil particles are forcibly stirred and mixed by high-pressure injection to form a soil mortar-like compact. The ground reinforcement principle of the injection method such as the chemical liquid injection method is “solidification”, which is completely different from the “density increase” of the ground reinforcement principle of the static press-fitting method. Generally, liquefaction countermeasures using `` solidification '' as the principle of ground reinforcement is called `` solidification method '' or `` consolidation method '', `` density increase method '' using `` density increase '' as the ground reinforcement principle or It is technically distinguished from a method called "compaction method" (for example, Non-Patent Document 1). FIG. 1 shows the static press-fitting method (for example, compaction grouting method) in comparison with other methods.

  In addition, there is a "special lime pile method" that uses a dry granular material or powdered material obtained by mixing special lime (hard burnt lime), granulated slag (or cement), gypsum and sand as a compacting material (Patent Reference 4). According to this method, a granular or powdery (dry) compaction material is put into a spiral-fitted casing while rotatingly penetrating the casing, and the compaction material is left in a pile shape in the ground while the casing is pulled out. Things. This compacted material in the dry state absorbs groundwater and expands due to the hydration reaction. In this method, the surrounding ground is compressed by this expansion pressure, and compaction is performed. On the other hand, in the static press-in compaction method, a mortar-like (wet state) compacted material produced by adding water on the ground and kneading the material is pressed into the ground to form a consolidated mass. This is a method of compressing the surrounding ground by the compaction effect of the consolidated mass, increasing the density of the ground, and strengthening the ground. For this reason, the static press-fitting compaction method compacts the ground with static force by pumping the compaction material, whereas the special lime pile method absorbs groundwater and expands due to hydration reaction, There is a difference that the ground is compacted by this expansion pressure. In other words, the special lime pile method is one of the "static compaction methods" in which the density is increased and the surrounding ground is compacted, similar to the static press-fit compaction method, and is classified as the "density increase method". The properties of compaction material and compaction principle are completely different.

  In addition, it has been proposed to use gypsum as a soil conditioner capable of making sludge reusable by adding, mixing, and solidifying sludge containing a large amount of water (Patent Document 5). . This technology is a technology for reforming the sludge itself, in which the water in the sludge is quickly absorbed by gypsum and solidified by mixing with the sludge, and the compaction method represented by the static press-in compaction method It is fundamentally different from the technology using "density increase" as the ground strengthening principle.

"Classification of liquefaction countermeasures construction methods and outline of construction methods", Japan Society of Civil Engineers, Construction Technology Research Committee, Construction Technology Systemization Subcommittee (April 2012)

JP-A-6-108449 JP 2013-159916 A JP 2005-105740 A JP-A-10-280382 JP 2001-335778 A

  Cement-based and lime-based materials, which are solidifying materials generally used in the static press-in compaction method, exhibit strong alkalinity. Therefore, when a compaction material containing such a solidified material as a component is pressed into the ground in a neutral region, the ground around the construction also becomes alkaline, which has a problem of adversely affecting ecosystems such as vegetation and microorganisms. is there. In particular, when construction is performed in or around a water area such as a harbor or coast, or a river or a lake, alkalizing of the surrounding ground or water area exceeding pH 9 has a particularly large adverse effect on ecosystems such as aquatic organisms due to water pollution.

  Magnesium oxide, which is proposed to be used as a solidifying material in Patent Document 3, is a highly alkaline material although the pH value of a saturated aqueous solution is lower than that of cement. Further, the strength of the compacted mass formed by compacting the compacting material is proportional to the amount of magnesium oxide. Therefore, in ground improvement work requiring high strength to some extent, there is a problem that if a sufficient amount of magnesium oxide is used to develop the required strength, the surrounding ground becomes alkalized. Moreover, the price of magnesium oxide is 10 times or more that of a general solidifying material such as cement. In addition, recently, it has been difficult to provide a stable supply of materials, and there is a problem that it takes a lot of time to obtain materials.

In addition, the cement, lime, and magnesium oxide-based solidifying materials described above gradually solidify and develop strength, and the strength continues to increase for one week to one month or more. The compacted material using these also continues to increase in strength from one week to one month or more after being pressed into the ground, and finally reaches a desired strength. That is, the final strength expression is slow. Therefore, there are the following problems, for example.
-It takes a long time to estimate the final strength of the improved body in the preliminary test.
-It is necessary to confirm the soil improvement effect by performing a standard penetration test after the aging period (curing period until the completion of strength development) from the completion of press-in, but it takes a long time to confirm. Therefore, the construction of the superstructure or the like cannot be started.
-It cannot be applied as a measure when re-operation is required as soon as possible during construction (nighttime construction, etc.) when facilities are not used, such as facilities in use (runways, etc.).
・ The time required for fluidity to consolidate is long, and compaction materials and solidified materials may flow out into water or penetrate into groundwater during construction under water or near water.

The present invention has been made in view of such a problem, and it is possible to maintain the surrounding ground in a neutral state even when press-fitting into a neutral ground, press-fit the ground, and quickly press-fit the ground. It is an object of the present invention to provide a compaction material for ground reinforcement which solidifies in a ground and a ground reinforcement method using the same. Here, the term “ground strengthening” as used in the present invention means a method using “density increase” as a ground strengthening principle.
The term "neutral" as used herein means a pH in the range of 5.8 to 8.6 unless otherwise specified. This is a uniform wastewater standard set by the Ministry of the Environment (specifically, a general ordinance (items other than harmful substances) related to the Article 3 (1) of the Water Pollution Prevention Act). Conforms to the Prime Minister's Ordinance No. 35 Separate Table 2) ").

  The present inventors have conducted intensive studies to solve the above-described problems, and as a result, to produce a ground strengthening compaction material by mixing at least a predetermined amount of a premix composition containing gypsum and aggregate with water. A compaction material for strengthening the ground that has a pH of 5.8 or more and 8.6 or less after completion of strength development and completes strength development within 24 hours after completion of the mixing of the gypsum, aggregate and water. And completed the present invention.

That is, the present invention
(1) A premix composition used for a compaction material for ground reinforcement, comprising at least gypsum and an aggregate, and 1 to 30 parts by mass of the gypsum with respect to 100 parts by mass of the aggregate.
(2) The composition according to (1), further comprising 0.1 to 3.0 parts by mass of a solidification retarder with respect to 100 parts by mass of the aggregate.
(3) The composition according to (2), wherein the solidification retarder is neutral.
(4) A soil compaction material containing at least gypsum, aggregate and water, wherein the pH after completion of strength development is 5.8 or more and 8.6 or less, and the strength development is the gypsum, aggregate and water. Is a compaction material for ground reinforcement that is completed within 24 hours from the completion of mixing.
(5) The compaction material according to (4), further including a solidification delay material, wherein the onset of strength development is 30 minutes or more after the completion of the mixing of the gypsum, the aggregate, the water, and the solidification delay material.
(6) The compacted material according to (4) or (5), which has a uniaxial compressive strength of 40 to 500 kN / m ² after the completion of strength development.
(7) An aggregate and a compacting material containing at least 1 to 30 parts by mass of gypsum and 10 to 30 parts by mass of water with respect to 100 parts by mass of the aggregate.
(8) The compaction material according to (7), further including 0.1 to 3.0 parts by mass of a solidification retarder with respect to 100 parts by mass of the aggregate.
(9) The compaction material according to (5) or (8), wherein the solidification delay material is neutral.
(10) The compaction material according to (9), wherein the neutral solidification retardant is a citrate.
(11) The compaction material according to any one of (4) to (10), wherein the compaction material further contains an iron compound.
(12) The compacting material according to (11), wherein the iron compound is contained in gypsum.
(13) A method for producing a compaction material for ground reinforcement by mixing any one of the compositions (1) to (3) with water.
(14) The compacted material according to any of (4) to (12) is pressed into a drilled hole formed in the ground to form a consolidated mass, and the surrounding ground is compressed to increase the density of the ground and strengthen the ground. This is a method of strengthening the ground.

If the compaction material is prepared by mixing with water using the premix composition used for the compaction material for ground reinforcement of the present invention, the compaction material has a pH of 5.8 or more even after the development of strength. Since it is 8.6 or less, the surrounding ground can be maintained neutral even when it is injected into the neutral ground, and alkalizing of the surrounding ground, which adversely affects ecosystems such as vegetation, microorganisms, and aquatic organisms, can be avoided. Therefore, according to the compaction material of the present invention, environmental compatibility in ground reinforcement can be enhanced. Furthermore, when the ground strengthening method by the compaction method such as the static press-fit compaction method is performed using the compaction material of the present invention, a low-strength and neutral used compaction material (waste mud) can be obtained. Therefore, the used compacted material (waste mud) that has been disposed of as industrial waste because it was alkaline in the conventional method can be reused as remaining soil. For this reason, industrial waste disposal costs can be reduced. Further, the cost of the gypsum-based solidifying material is lower than that of the magnesium oxide-based material, and stable supply is possible, so that the material cost can be reduced and the economic effect can be obtained.
In addition, the compacting material of the present invention has its strength manifested within about 24 hours from the completion of the mixing of each material of gypsum, aggregate, and water, and can be pressed into the ground, and It can solidify quickly after press-fitting to exhibit its function.

Further, by mixing the setting retarder, the onset of strength development can be delayed as required (for example, 30 minutes or more after the completion of mixing of gypsum, aggregate, water and the setting retarder).
Further, according to the compacted material of the present invention, the uniaxial compressive strength after completion of strength development can be set to 40 to 500 kN / m ² . Since it has a uniaxial compressive strength of 40 kN / m ² or more, liquefaction of the compacted material itself that has solidified during the earthquake does not occur. Therefore, it can be applied as a liquefaction countermeasure method. Furthermore, since it has a uniaxial compressive strength of 500 kN / m ² or less, an effect that it is suitable for use as a low-strength material can be obtained. Because it is suitable for use as a low-strength material, it can be constructed without adverse effects when driving piles, etc. when rebuilding the upper facilities after ground improvement using the compacted material, Removal costs are not required. Furthermore, when a high-strength material of 500 kN / m ² or more is used, seismic waves concentrate on the compacted material portion solidified during an earthquake, which may have an adverse effect on the upper structure. Can prevent seismic wave concentration.
According to the present invention, for example, the following additional effects can be obtained.
・ Since the final strength can be estimated in a short time in the preliminary test, the design can be performed in a short time.
・ Because the time required for the final strength to appear can be shortened, the time required for the ground improvement effect confirmation test can be shortened, and it is possible to immediately start the superstructure work, thereby shortening the construction period of the entire work.
-Since compaction can be carried out immediately after press-fitting, it is possible to reduce the outflow of compacted material into water during or underwater construction.

Conceptual diagram showing the compaction grouting method in comparison with other methods Particle size distribution diagram of blended aggregate Schematic diagram of the construction mode of the static press-fitting method Particle size distribution diagram of blended aggregate used in the experiment

Hereinafter, embodiments for carrying out the present invention will be described in detail.
One embodiment of the present invention is a premix composition containing at least gypsum and an aggregate, used for a compaction material for ground reinforcement, including 1 to 30 parts by mass of the gypsum with respect to 100 parts by mass of the aggregate. A composition comprising:
Here, the “premix composition” (also referred to as “premix material” in this specification) refers to a method of mixing water on the ground when producing a compaction material for soil reinforcement containing at least gypsum, aggregate and water. Before producing the compacted material, it means a composition containing gypsum and aggregate as the material. The amount of the gypsum is 1 to 30 parts by mass based on 100 parts by mass of the aggregate. This means that, when the compaction material is made by mixing water, if the amount of gypsum is 1 part by mass or more with respect to 100 parts by mass of the aggregate, the compaction material for ground reinforcement shows sufficient strength. When the amount is 30 parts by mass or less, the strength is not increased unnecessarily and it is economical.
The “premix composition” may include a solidification retarder, if necessary. When including a setting retarder, gypsum, aggregate, the order of compounding each material of the setting retarder is not particularly limited, but first, the gypsum and the setting retarder are mixed, and then the aggregate is mixed. It is preferable from the viewpoint of uniform mixing of the solidification retarder. It is preferable that the compounding amount of the solidification retarder is 0.1 to 3.0 parts by mass based on 100 parts by mass of the aggregate. This is because if the solidification delay material for the aggregate is 0.1 parts by mass or more, when the compaction material is made by mixing with each material of the aggregate and the gypsum and adding water, the rapid solidification can be suppressed. Therefore, it is possible to secure a sufficient time for press-into the ground, and when the amount is 3.0 parts by mass or less, it is economical.
Another embodiment of the present invention is a compaction material for ground reinforcement containing at least gypsum, aggregate and water, wherein the pH after completion of strength development is 5.8 or more and 8.6 or less, Is a compaction material for ground reinforcement that is completed within 24 hours after the completion of the mixing of the gypsum, aggregate and water. The gypsum and the aggregate used at this time may be added individually, or may be provided together as the premix composition in which both are previously blended. It is preferable to mix water after mixing gypsum and aggregate. The method of mixing water is not particularly limited, and water may be added to a mixture containing gypsum and aggregate, or a mixture containing gypsum and aggregate may be added to water.

The “compacting material for ground reinforcement” referred to in the present invention has a self-hardening property because it contains a solidifying material, and forms a lump when forcibly pressed into the ground by a pump. It is a material that has the function of increasing the density of the ground by compressing and strengthening the surrounding ground by the compaction effect of the consolidation. Since the density is increased by forcible press-fitting by a pump, the ability of the compaction material itself to expand itself (self-expanding property) is not required. The “ground compaction material” according to the present invention generally refers to a ground compaction material used in the static press-fitting method, but the ground reinforcement compaction material used in the static press-fitting method is used. The hardening material has a slurry-like or mortar-like property and can be pumped by a pump.
On the other hand, the compacted material used in the special lime pile method is a self-expanding material in which hard burnt lime absorbs groundwater and expands due to a hydration reaction. By the compaction effect of this expansion, the surrounding ground is compressed to increase the density. The static press-fitting method and the special lime pile method are both classified as the density increasing method, but the properties of the compacting material and compacting principle are different.
For example, even if the compaction material without self-expansion (the present invention) used in the static press-fitting compaction method is used in the special lime pile method, the ground cannot be compressed and the density cannot be increased, so that the improvement effect is not obtained. Can't expect. Conversely, if the self-expanding material used in the special lime pile method is used in the static press-in compaction method, water will be added and the material will be mixed. And expands due to the hydration reaction. For this reason, the compaction material expands and is clogged in the injection pipe and the injection hose, and cannot be pumped or pressed. Further, when water is added during the production of the compacted material and kneaded until the water absorption and expansion are completed, the compacted material is in a solidified state, and cannot be pumped by the pump. Further, when a dry compaction material to which water is not kneaded is applied, there is no fluidity, so that it cannot be pumped by a pump.
For the reasons described above, the self-expanding material such as hard-burned lime used in the special lime pile method cannot be applied in the construction of the static press-fitting method.
Accordingly, the “ground compaction material” according to the present invention is pressed into the ground in a dry state, such as a powdery or granular form that does not contain water, such as a ground reinforcement compaction material used in a special lime pile method. However, it is different from the compaction material that absorbs groundwater.

  The compacted material of the present invention uses gypsum as a solidifying material component therein, and has a pH of 5.8 or more and 8.6 or less after completion of strength development. This makes it possible to maintain the surrounding ground to be neutral even if it is injected into the neutral ground, and to avoid alkalizing of the surrounding ground, which adversely affects ecosystems such as vegetation, microorganisms and aquatic organisms. Therefore, the compacted material of the present invention has high environmental compatibility.

  In the present specification, the pH test is performed based on JGS 0211-2009 (Soil suspension pH test method) based on the Japanese Geotechnical Society, and the mass ratio of water to the dry mass of the sample is 5 for the non-dry sample. Is added thereto, and the mixture is left standing for 30 minutes or more and 3 hours or less after stirring and suspension. The solution is measured at 25 ° C. with a glass electrode type pH meter.

  Completion of strength development means that, in the strength measured by the uniaxial compression test of the compacted material, the strength increase at a certain point in time after 48 hours from that point is within 20%. . The method of the uniaxial compression test and the calculation of the strength are performed based on JIS A 1216: 2009.

  The compaction of the present invention completes the strength development within 24 hours from the completion of the mixing of all of the gypsum, aggregate and water. Generally, it is preferred to complete all mixing of the materials with stirring. That is, the strength measured 48 hours after the measurement (= 72 hours after the completion of the mixing of all the materials of gypsum, aggregate and water) with respect to the strength measured by the uniaxial compression test 24 hours after the production of the compacted material. Is within 20%. As is clear from the examples described later, the compacted material of the present invention completes the development of strength earlier than a known compacted material. For this reason, the compacting material of the present invention can be press-fitted into the ground, and can be quickly consolidated after press-fitting to exhibit its function. For this reason, as described above, it is possible to obtain the effect that the design can be performed in a short period of time and the construction period of the entire construction can be shortened.

  The compaction material of the present invention is gypsum as a solidification material component therein, and further uses a solidification delay material as a component for delaying the solidification, thereby starting the development of strength with gypsum, aggregate, water and a solidification delay material. It can be 30 minutes or more after the completion of mixing of all the materials. That is, consolidation starts 30 minutes or more after the production of the compacted material, and until that time, the compacted material can maintain sufficient fluidity. Therefore, it is possible to prevent the compaction material from being consolidated in the construction equipment such as a plant, a pressure feeding hose, and a press fitting pipe. The compaction time of the compacted material of the present invention can be adjusted in accordance with the application conditions, and the start of strength development can be set to one hour or more after the completion of the mixing. However, if the start of strength development is delayed, the time required for completion of strength development is also prolonged. Therefore, the start of strength development is preferably within 5 hours from the completion of the mixing.

  The strength onset time can be measured by using a Vicat needle setting time measuring instrument and referring to JIS R 9112. Specifically, it refers to the time until the standard needle of the measuring instrument stops at a height of 1 mm from the bottom of the test specimen by pouring the produced compacted material into a metal cylindrical mold to form a test specimen. The time zero point is when the mixing of gypsum, aggregate, water, and setting retarder is completed. The standard needle of the Vicat needle setting time measuring device is a metal needle having a length of 45 mm / diameter of 2 mm and the head thereof is cut flat.

The compacted material of the present invention can have a uniaxial compressive strength of 40 to 500 kN / m ² after completion of strength development, and is suitable for use as a so-called low-strength material. In the conventional compaction material using a cement material as a solidification material, the uniaxial compressive strength easily exceeds 500 kN / m ² and the strength is too high. At that time, there were problems such as limitations on the construction method due to selection of the pile driving method, and the necessity of removing compaction materials before driving the pile. On the other hand, since the compacted material of the present invention can have a uniaxial compressive strength of 500 kN / m ² or less, there is no restriction on the construction method when rebuilding the upper facilities after ground improvement using the material. be able to. Further, since the compacted material of the present invention can have a uniaxial compressive strength of 40 kN / m ² or more, the compacted material itself does not liquefy and can be suitably used as a low-strength material. . A conventional compacting material used as a cement-based or magnesium oxide-based solidifying material becomes alkaline when trying to develop the strength in the above-described range necessary for the compacting method. Thus, the compacted material of the present invention has sufficient strength to compress the surrounding ground when pressed into the ground as a compacted material to form a consolidated mass, even in the neutral region. It has a high degree of freedom in the formulation design in the neutral pH range. Uniaxial compressive strength after strength development completion of the compaction material according to the present invention can be in the range of 40~500kN / ^{m 2,} when in the range of 40~300kN / ^{m 2} Preferably, 100~300kN / ^{m 2} Is more preferable.

  The compacted material of the present invention includes at least a solidified material, an aggregate, and water, and the solidified material includes gypsum. Moreover, the compacting material of the present invention includes a solidification retarding material as necessary.

  Aggregate is a material that forms a skeleton when formed into a consolidated mass, and also has a function of suppressing overheating and shrinkage during compaction. The aggregate is not particularly limited, and a known aggregate can be used. Any kind and amount can be selected according to the purpose within a range where the effects of the present invention can be obtained. Specific examples include gravel, sand, crushed stone, crushed sand, silt, clay, slag aggregate, artificial lightweight aggregate, recycled aggregate, and the like, and combinations thereof. It is particularly preferable to use silica sand or commercially available Tochiclay (registered trademark) because overheating and shrinkage during consolidation are further suppressed.

  It is preferable that the particle size of the aggregate is not concentrated on a specific particle size. As a result, when the compaction material is pressed into the ground during the construction of the static press-fitting method described later, it is prevented from being penetrated or injected in a pulsating manner. It is easy to tie, and dehydration and blockage in piping such as a pressure feeding hose and an injection pipe are less likely to occur. In particular, the particle size accumulation curve is more preferably between the upper and lower lines in FIG. 2, and even more preferably substantially parallel to the upper and lower lines. The particle size accumulation curve can be obtained according to JIS A 1204 (Soil particle size test method).

The solidified material is a component that imparts compaction performance to the compacted material. In the present invention, the solidified material refers to a material made of gypsum or a material containing gypsum. When the material contains gypsum, it is preferable to use a solidified material containing gypsum as a main component. The phrase "mainly composed of gypsum" means that 80% by mass or more of the solidified material is gypsum. It is preferable that 90% by mass or more is gypsum.
Among the components of the solidification material contained in the composition or compaction material of the present invention, cement, lime, magnesium oxide, an organic absorbent, and the like are optional as long as the purpose other than gypsum can be achieved. They can be used alone or in combination as components.

  Gypsum is itself neutral. Therefore, the surrounding ground can be maintained neutral even if it is injected into the neutral ground, and the ecological system such as vegetation, microorganisms and aquatic organisms is not adversely affected by the alkalinization of the surrounding ground, and the environmental compatibility is high. . In addition, since the neutrality can be maintained regardless of the blending amount, the strength of the consolidation mass can be arbitrarily adjusted by adjusting the blending amount, and the freedom of blending design in a neutral pH range is increased. Can be used for high and wide construction objects.

Gypsum specifically refers to a compound containing calcium sulfate (CaSO ₄ ) as a main component, and among them, calcined gypsum that chemically reacts with water is preferably used. The calcined gypsum refers to a compound represented by hemihydrate gypsum (chemical formula CaSO ₄ .0.5H ₂ O) and / or type III anhydrous gypsum (CaSO ₄ ). Further, gypsum (CaSO ₄ .2H ₂ O) or type II anhydrous gypsum (CaSO ₄ ) may be used. These gypsums may partially contain calcium carbonate (CaCO ₃ ) and the like. Commercially known calcined gypsum includes, for example, Gypsander (registered trademark) manufactured by Ishihara Sangyo Co., Ltd.

There is no particular limitation on the shape and specific surface area of the gypsum, and any material can be used. In particular, calcined gypsum having a flaky particle shape and a BET specific surface area of ² to 70 m ² / g is preferable because the contact area with water can be increased.

  In the case of using a solidified material containing gypsum as a main component in the compaction material of the present invention, it is preferable to use a solidification retardant together. Here, the setting retarder is a material capable of delaying the solidification of gypsum, and by adjusting the compounding amount of the setting retarder, it is possible to control the setting time of the compaction material as already described. is there. Thereby, it has fluidity without being consolidated during the press-fitting operation, and can quickly consolidate after the press-fitting to exhibit its function. For this reason, as described above, it is possible to prevent the compaction of the compacted material in the construction equipment, and it is also possible to obtain the effect that the design in a short period and the construction period of the entire construction can be shortened.

  There is no particular limitation on the solidification retarder, and any known solidification retarder can be used. Specifically, at least one component selected from a metal salt, a carboxylic acid, and a carboxylate is used. Examples of the metal salt include potassium sulfate and aluminum sulfate. Examples of the carboxylic acid and the carboxylate include a carboxylic acid selected from citric acid, sodium gluconate, and L-tartaric acid, or a carboxylate thereof.

  In the present invention, a neutral solidification retarder is particularly preferred. By using gypsum as a solidifying material and a neutral solidification retarding material together, it becomes easy to maintain the compacted material to be neutral. Further, since the neutrality can be maintained irrespective of the compounding amount, the control range of the compaction time of the compacted material can be further expanded. Examples of the neutral solidification retarder include carboxylate. Among them, citrate is preferred, and trisodium citrate is more preferred. As described above, neutral means that the pH is 5.8 or more and 8.6 or less. The pH is measured with a glass electrode type pH meter by adding water to the measurement sample so that the mass ratio of water to the sample becomes 10 and stirring the mixture, and allowing the mixture to stand for 5 minutes after stirring as a sample solution. Go and ask.

In the compacted material of the present invention, the gypsum of the solidified component, the aggregate, and water are contained in an amount of 1 to 30 parts by mass of gypsum and 10 to 30 parts by mass of water with respect to 100 parts by mass of the aggregate. Preferably, when the solidification retardant is further included, the solidification retardant is preferably contained in an amount of 0.1 to 3.0 parts by mass with respect to 100 parts by mass of the aggregate. Therefore, when producing a compaction material of the present invention, when using a premix composition containing gypsum and aggregate, when mixing water, gypsum is 1 to 30 mass parts per 100 mass parts of aggregate. It is preferable to use the above premix composition having a mixing ratio of parts. When using a premix composition also including a solidification retarder, it is preferable to use a premix composition further containing 0.1 to 3.0 parts by mass of the solidification retarder with respect to 100 parts by mass of the aggregate.
The preferred amount of gypsum relative to 100 parts by mass of the aggregate is 1 to 30 parts by mass as described above. When the amount of gypsum is 1 part by mass or more with respect to 100 parts by mass of the aggregate, sufficient strength is exhibited as a compaction material for reinforcing the ground, and when the amount is 30 parts by mass or less, the strength does not become unnecessarily high and economical. It is a target. The amount of gypsum with respect to 100 parts by mass of the aggregate is more preferably 3 to 30 parts by mass, and even more preferably 10 to 30 parts by mass.
Further, the preferable amount of the solidification retarder to 100 parts by mass of the aggregate is 0.1 to 3.0 parts by mass as described above. When the solidification delay material for the aggregate is 0.1 parts by mass or more, rapid solidification can be suppressed when each material is mixed and used as a compaction material, and a sufficient press-in time to the ground can be secured. . There is no problem at most, but it is economical if it is 3.0 parts by mass or less. Further, the solidification retardant is preferably 0.7 to 12 parts by mass with respect to 100 parts by mass of gypsum, and when it is 1 to 12 parts by mass, the press-fitting time and strength of the compacted material into the ground are exhibited. It is more preferable from the viewpoint of speed balance.
In addition, gypsum generally becomes softer with more water and has a slower setting speed. On the other hand, when the amount of water is small, the material becomes hard and the setting speed is high. Therefore, the amount of water affects the strength and the solidification rate. From such a viewpoint, the content of water in the compacted material of the present invention is preferably 10 to 30 parts by mass with respect to 100 parts by mass of the aggregate.

  The compacting material of the present invention can be prepared by mixing the above components. There are no particular restrictions on the mixing order of the gypsum, aggregate, and if necessary, the setting retarder. When the setting retarder is mixed, it is preferable to mix the gypsum and the setting retarder first. By doing so, the gypsum and the setting retarder are more evenly mixed, and unevenness in setting delay is eliminated. The water is preferably mixed with the mixture of gypsum, aggregate and, if necessary, the setting retarder immediately before the press-fitting operation.

  In carrying out the static press-in compaction method as a ground strengthening method using the compaction material of the present invention, gypsum, aggregate, if necessary, may be supplied in the form of a premix material blended with a solidification delay material. It is possible, and it is possible to mix it with water immediately before to prepare a compacting material and to provide it for press-fitting into the ground. This method is similar to a conventional compaction material such as a cement type or a magnesium oxide type, can be easily replaced, and can use the same mechanical equipment as the conventional one. In addition, since the construction can be performed in the same procedure as in the past, it is possible to selectively use each construction area, for example, to apply only to a location close to the water area.

The compacting material of the present invention may contain an iron compound. Since the iron compound can adsorb and fix hydrogen sulfide, when applied to the ground where harmful hydrogen sulfide is generated, the ground can be rendered harmless. Examples of the iron compound contained include various compounds such as iron oxide hydroxide, iron oxide, and iron hydroxide. When the iron compound is contained, when the content is calculated as Fe ₂ O ₃ and is 0.2 to 50% by mass based on the mass of calcined gypsum, the function of immobilizing hydrogen sulfide can be sufficiently exhibited. . From the viewpoint of solidification rate, the content of the iron compound is more preferably 0.6 to 30% by mass, and still more preferably 0.6 to 10% by mass. As a side effect of including an iron compound, good results can be obtained for the growth of organisms in the soil.

  The iron compound is preferably contained in gypsum. This facilitates uniform mixing of the iron component into the compaction material in mixing each material of the compaction material.

  Next, as another embodiment of the present invention, the above-mentioned compaction material is pressed into a drilled hole formed in the ground to form a consolidated compact, and the surrounding ground is compressed to increase the density of the ground. There is a way. The ground strengthening method of the present invention will be described below.

  FIG. 3 schematically shows an example of a construction mode of the ground strengthening method according to the embodiment of the present invention. In this method, a plurality of rod-shaped injection pipes 11 are drilled to a predetermined depth using a boring machine (not shown), and the injection pipes face the holes. After drilling to a predetermined depth, the injection pipe lifting device 13 is set to the injection pipe 11 in the penetrating state, and the injection pipe is connected to the special injection pump 21 via the flow pressure monitoring device 15 and the pressure feeding hose 19. The compacted material of the first invention of the present invention prepared in the special injection plant 23 is forcibly pumped by the special injection pump 21 and pressed into the ground via the pressure feeding hose 19, the flow pressure monitoring device 15, and the injection pipe 11. Is done. In the press-fitting step of the compacted material, the press-feeding of the compacted material and the step-up of the injection pipe 11 are repeated. Typically, the injection tube is stepped up three steps per meter.

  The compacted material pressed into the ground is solidified at a predetermined position without stray or penetrating in the soil due to its low fluidity. Therefore, by repeatedly feeding the compaction material by the above-described special infusion pump and stepping up the injection pipe, the bulb-shaped consolidated body 1 made of the compaction material as shown in the figure is continuously formed. Then, the surrounding ground is compressed by increasing the volume of the consolidated body 1 and the density of the ground is increased, whereby the liquefied ground can be improved to a non-liquefied ground.

  The remaining compacted material that has not been used during the construction can be reused by blending it as aggregate in the compacted material during the next and subsequent constructions. Specifically, the surplus compaction material, aggregate, gypsum, water, and, if necessary, a solidification retardant material can be mixed and used as a compaction material.

  When the static press-fitting method is carried out, a loss (specifically, a compaction material that cannot be used as a pressure feeding hose and remains as a loss) or a used compaction material by cleaning equipment (in this specification, Is referred to as “waste mud”). When a conventional compaction material is used, such waste sludge is alkalinized, and thus is disposed of as industrial waste, which incurs additional costs. The waste mud generated when the compacting material of the present invention is used is neutral and has low strength, so that it can be reused as surplus soil, and is advantageous from the viewpoint of waste reduction and cost reduction. is there.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited by the Examples, and does not depart from the scope of the claims of the present invention and equivalents thereof. The present invention can be arbitrarily changed within the scope.

Experiment 1
Aggregate, solidified material, and solidification retardant were placed in a plastic bag and mixed. This mixture was transferred to a 3 L container, a predetermined amount of water was further added, and the mixture was kneaded with a spatula until the mixture became muddy, thereby producing compacting materials (Examples 1 to 8 and Comparative Examples 1 to 6). As the aggregate, commercially available silica sand and Tocicle (registered trademark) were mixed and used. The particle size distribution of this aggregate was measured according to JIS A 1204, and is as shown in FIG. 4, which was between the upper and lower lines of the particle size accumulation curve of FIG. Any of the solidifying materials shown in Table 1 was used as the solidifying material. The composition of the materials for each sample was as shown in Table 2. Commercially available trisodium citrate (pH = 8.3) was used as the solidification retarder in Examples 1 to 8. Gypsum includes Gypsander (registered trademark) (manufactured by Ishihara Sangyo Co., Ltd., flaky hemihydrate gypsum having a specific surface area of 30 m ² / g, calcium sulfate hemihydrate (CaSO ₄ .1 / 2H ₂ O) content 94% by mass. , Iron oxide content 1.8 mass%). The compaction material was manufactured such that the volume was approximately 2 L. In the tables 2, with respect to the mixing ratio of the solidifying material of Example 1-8, also parentheses value of calcium sulfate hemihydrate _{(CaSO 4 · 1 / 2H 2} O) component terms contained therein It was also described. The compacted material thus produced was packed in a mold having a size of φ50 mm × 100 mm, sealed with a wrap so as not to evaporate water, and cured until an evaluation described later was performed.

(Evaluation 1) Uniaxial Compressive Strength The uniaxial compressive strength of the compacted material was measured at 24 hours, 72 hours, 120 hours, and 168 hours after preparation, and was measured from 24 hours to 72 hours, 120 hours, and Up to 72 hours, 168 hours, and 120 hours after, the rate of increase in strength was calculated, and the time to complete strength development was determined. Specifically, when the calculated rate of increase in strength at each elapsed time was within 20%, it was evaluated that strength development was completed, and when it exceeded 20%, it was evaluated as incomplete. The method of uniaxial compression test and calculation of the strength were performed based on JIS A 1216: 2009. The test machine used was a single-shaft compression tester manufactured by Shinohara Seisakusho. The dimensions of the test piece were φ50 mm × 100 mm. Table 3 shows the results.

The compacted materials of Examples 1 to 8 using gypsum as a solidified material had a strength measured by a uniaxial compression test at 24 hours after the production of the compacted material, which was 72 hours after material mixing (= 48 from the previous measurement). The increase rate of the intensity (after time) is within 20%, and the intensity expression has been completed at 24 hours. On the other hand, in the compacted materials of Comparative Examples 1 to 6, the strength development was not completed in 24 hours. This indicates that the compaction material of the present invention has a short time to complete strength development. In addition, even in Example 1 in which the blending amount of gypsum was as small as 2 parts by mass, 24 hours after the production of the compacted material, the completion of strength development was recognized at 50 kN / m ² , which can be used as a low-strength material. From 2 to 8, during the same period, the completion of strength development was observed in the range of 100 to 500 kN / m ^{2 which} is preferable as a low-strength material. Furthermore, as will be described later, according to the present example, based on the results of the strength measured in the uniaxial compression test at 24 hours after the production of the compacted materials in Examples 15 to 17 (Table 8), according to this example, after 24 hours from the ^formation, it was found that the strength development completion is observed in the range of ^{40kN / m 2 ~500kN / m 2} .

(Evaluation 2) pH
24 hours, 72 hours, 120 hours, and 168 hours after the preparation, the pH of the compacted material was measured according to JGS0211-2009, JGS0211-2009. The sample solution was prepared by adding water to a non-dried sample such that the mass ratio of water to the dry mass of the sample was 5, stirred and suspended, and allowed to stand for 30 minutes or more and 3 hours or less. . A glass electrode type pH meter was used for the measurement. Table 4 shows the results.

  Each of the compacted materials of Examples 1 to 8 using gypsum as a solidifying material shows a neutral pH of about 7.7 after the completion of strength development, and thereafter maintains the same pH in the neutral region. I understood that. It was found that the compacted materials of Comparative Examples 1 to 3 using magnesium oxide as a solidifying material exhibited alkaline of about pH = 10. In addition, it was found that the compacted materials of Comparative Examples 4 to 6 using cement as a solidifying material did not attain the completion of the strength development, and exhibited alkalinity of pH = 11 or more at any measurement. From this, it was found that the compacted material of the present invention can maintain neutrality regardless of the compounding amount.

Experiment 2
Aggregate, solidified material, and solidification retardant were placed in a plastic bag and mixed. A predetermined amount of water was placed in a 500 mL PP (polypropylene) container, and the mixture was poured therein for 1 minute. The mixture was stirred at 110 rpm for 1 minute with a φ15 mm stirring rod to prepare a compacted material. The composition of the material of each sample was as shown in Table 5. The same materials as in Experiment 1 were used for each material. In Table 5, in addition to the compounding ratios of the solidifying materials of Examples 3, 6, 7, and 8 in Table 2, the compounding ratios of the solidifying materials of Examples 9 to 14 also show the calcium sulfate 1 contained therein. The value in terms of a / 2 hydrate (CaSO ₄ .1 / 2H ₂ O) component is also shown in parentheses. In addition, the ratio of the compounding ratio of the solidification retarder to the compounding ratio of the solidifying agent was evaluated by converting the compounding ratio of the solidifying agent into a calcium sulfate 1/2 hydrate (CaSO ₄ • 1 / 2H ₂ O) component. The results are shown in parentheses.

(Evaluation 3) Measurement of Strength Onset Time At the compounding ratio (parts by mass) shown in each example in Table 5, as described above, all the materials were mixed with stirring to complete the production of the compacted material. After that, the compacted material was immediately poured into a metal cylinder (upper base φ75 mm, lower base φ85 mm, height 40 mm), and the upper part was cut off with a spatula to obtain a measurement sample. For each sample, a Vicat needle was inserted at a specific time, and the intensity onset time was measured. A coagulation tester (manufactured by Marubishi Kagaku Seisakusho) is used for the setting time measuring device of the Vicat needle device, and the standard needle is a metal needle having a length of 45 mm / diameter of 2 mm, whose head is cut flat, and descends with this. The total mass of the product was 300 g. The zero point of the intensity onset time is defined as the time when all of the above materials have been mixed while stirring, and the time until the standard needle of the measuring instrument stops at a height of 1 mm from the bottom surface of the specimen is expressed as the intensity onset. Start time. Table 6 shows the results. (In the table, "-" indicates that the appearance was in a slurry state, and no sign of the start of consolidation was observed, and thus no measurement was performed, or no measurement was performed because consolidation was completed.)

It was found that by adjusting the ratio of the amount of the solidification retarder to the solidified material, the strength development start time can be controlled. In general, the incorporation of 1% by mass or more of the solidification retarder with respect to the solidified material can make the strength onset time 30 minutes or more, and the incorporation of 3% by mass or more makes the strength onset time 1 hour or more. We were able to. In addition, the intensity onset time of Examples 1, 2, 4, and 5 was measured by the same method. As a result, it was confirmed that the behavior was similar to that of Example 3 and that the intensity onset started in 2 to 3 hours. In addition, all the compacting materials of Examples 9 to 14 showed neutrality of pH 7.5 to 8.0, and the strength development was 24 hours after the completion of mixing of gypsum, aggregate, water and the solidification retardant. are completed within the time, the uniaxial compressive strength was 200~350kN / ^{m 2.}

Experiment 3
Aggregate, solidified material, and solidification retardant were placed in a plastic bag and mixed. A predetermined amount of water was further added to the mixture, and the mixture was kneaded for 5 minutes to produce compaction materials (Examples 15 to 17). As the aggregate, commercially available silica sand and Tocicle (registered trademark) were mixed and used. The particle size distribution of this aggregate was measured according to JIS A 1204, and is as shown in FIG. 4, which was between the upper and lower lines of the particle size accumulation curve of FIG. Any of the solidifying materials shown in Table 1 was used as the solidifying material. Table 7 shows the composition of the materials for each sample. Commercially available trisodium citrate (pH = 8.3) was used as the solidification retarder in Examples 15 to 17. The gypsum contains Gypsander (registered trademark) (manufactured by Ishihara Sangyo Co., Ltd., flaky hemihydrate gypsum having a specific surface area of 30 m ² / g, content of (calcium sulfate hemihydrate (CaSO ₄ .1 / 2H ₂ O)). 94% by mass and an iron oxide content of 1.8% by mass). The compaction material was manufactured such that the volume was approximately 3 L. In the tables 7, regarding the mixing ratio of the solidifying material of Examples 15 to 17, also parentheses value of calcium sulfate hemihydrate _{(CaSO 4 · 1 / 2H 2} O) component terms contained therein It was also described. The compacted material thus produced was packed in a mold having a size of φ50 mm × 100 mm, sealed with a wrap so as not to evaporate water, and cured until an evaluation described later was performed.

(Evaluation 4) Liquefaction Strength Ratio to Uniaxial Compressive Strength Twenty-four hours after the preparation, the uniaxial compressive strength of the compacted material was calculated. The method of uniaxial compression test and calculation of the strength were performed based on JIS A 1216: 2009. The dimensions of the test piece were φ50 mm × 100 mm.
Further, in order to confirm the liquefaction strength of the solidified compact, the liquefaction strength ratio of the compact was calculated 24 hours after the production. The liquefaction strength ratio was determined based on a repeated undrained triaxial test of the Japan Geotechnical Society standard JGS-0541. The dimensions of the test piece were φ50 mm × 100 mm. Table 8 shows the results. It is generally said that if the N value is 25 or more, it will not liquefy even in a large-scale earthquake. Here, a diagram showing the relationship between the liquefaction intensity ratio, which is known as the liquefaction condition of the saturated soil, and the corrected N value (“Guidelines for Building Basic Structure Design” by the Architectural Institute of Japan (edited), Maruzen Co., Ltd. According to Fig. 4.5.1) on January 25, 1988 (first edition), the liquefaction strength ratio when the corrected N value is 25 in the 5% shear strain amplitude curve of the figure is as follows. It is about 0.44. From this, it was confirmed that all the results in Table 8 have liquefaction strength equal to or higher than that of the ground on which the liquefaction countermeasures were taken by the compaction method.
From the above results, it was confirmed that when the uniaxial compressive strength was about 40 kN / m ² or more, the solidified compacted material itself did not liquefy even when an earthquake occurred.

  According to the present invention, it is a compaction material for ground reinforcement using gypsum as a solidifying material, wherein the pH after completion of strength development is 5.8 or more and 8.6 or less, and strength development is completed within 24 hours. Since the compaction material can be provided, it is possible to press-fit the ground by using a static press-fitting compaction method or the like, and it is possible to quickly compact after the press-fitting. For this reason, there is industrial applicability as a measure for preventing the liquefaction phenomenon of soft sandy ground.

Claims (14)

Includes solidifying material and aggregate consisting mainly of at least hemihydrate gypsum, the relative said aggregate 100 parts by weight comprising the hemihydrate stone plaster 1 - 30 parts by weight, premix for use in soil reinforcing compacting member Composition.   The composition according to claim 1, further comprising 0.1 to 3.0 parts by mass of a solidification retarder with respect to 100 parts by mass of the aggregate.   3. The composition of claim 2, wherein said set retarder is neutral. Solidifying material mainly composed of at least hemihydrate gypsum, comprising aggregates and water, wherein to the aggregate 100 parts by weight comprising the hemihydrate stone plaster 1 - 30 parts by weight, there in soil reinforcing compacting member The pH after completion of the strength development is 5.8 or more and 8.6 or less, and the strength development is completed within 24 hours after the completion of the mixing of the solidified material, the aggregate, and the water containing the hemihydrate gypsum as a main component. Compaction material for ground reinforcement.   The compaction material according to claim 4, further comprising a solidification delay material, wherein the onset of strength starts 30 minutes or more after the completion of the mixing of the solidification material mainly composed of hemihydrate gypsum, aggregate, water, and the solidification delay material. Compaction material according to claim 4 or 5 unconfined compressive strength after strength development completion is 40~500kN / ^{m 2.} A soil reinforcing compacting material aggregate includes solidifying material consisting mainly of hemihydrate gypsum, relative to the aggregate 100 parts by weight of the hemihydrate stone plaster 1 - 30 parts by weight of water 10 to 30 parts by weight Ground compaction material, including at least.   The compaction material for ground reinforcement according to claim 7, further comprising 0.1 to 3.0 parts by mass of a solidification retarder with respect to 100 parts by mass of the aggregate.   The compaction material according to claim 5, wherein the solidification delay material is neutral.   10. The compaction of claim 9, wherein the neutral setting retardant is citrate.   The compaction material according to claim 4, wherein the compaction material further contains an iron compound.   The compaction material according to claim 11, wherein the iron compound is contained in a solidification material containing hemihydrate gypsum as a main component.   A method for producing a compaction material for ground reinforcement by mixing the composition according to claim 1 with water.   A ground strengthening method for press-fitting the compacted material according to any one of claims 4 to 12 into a drilled hole formed in the ground to form a consolidated mass, compressing the surrounding ground, increasing the density of the ground, and strengthening the ground.