JP2017061844A - Reinforcement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly mix soil particles and cement particles together by making air bubbles adhere to surfaces of the cement particles to prevent local coagulation.SOLUTION: In a reinforcement method, soil particles and cement particles are agitated and mixed together to produce soil cement, and the soil cement is hardened to form a reinforced area. The reinforcement method includes a mixing step (step S3) of mixing the soil particles and the cement particles together, and an air bubble adhesion step (step S2) that is performed before the mixing step (step S3) to make air bubbles adhere to surfaces of the cement particles.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a reinforcing method.

  Conventionally, in order to reinforce soft ground such as clay, a reinforcement method has been used in which soil cement generated by injecting and stirring cement milk while excavating the ground is hardened in the soil. . For example, Patent Document 1 discloses an excavator including a bit portion that digs the ground while rotating and a nozzle that injects cement milk into the soil.

JP-A-3-132515

  However, in general, soil particles are negatively charged and cement particles are positively charged. For this reason, in the above-mentioned reinforcement method, soil particles and cement particles are locally aggregated by electrostatic force, and the generated soil cement may not be uniform, and the strength of the cured soil cement may be uneven. is there. Therefore, it has been studied to attach a surfactant to the surface of cement particles. However, it is desirable not to use the surfactant because it increases the burden of arranging and transporting the surfactant separately. In Patent Document 1, bubbles are mixed at the same time when cement milk is poured into the soil. However, in this method, contact between the cement particles and the soil particles cannot be avoided. The adhesion of soil particles cannot be prevented. Therefore, the technique of Patent Document 1 cannot improve local aggregation.

  The present invention has been made in view of the above-described problems, and aims to prevent local aggregation by adhering bubbles to the surface of cement particles and to uniformly mix soil particles and cement particles. To do.

  In order to achieve the above object, in the present invention, as a first solution, a soil cement is generated by stirring and mixing soil particles and cement particles, and a reinforcing region is formed by curing the soil cement. It is a reinforcing method, and adopts a means of having a mixing step of mixing soil particles and cement particles, and a bubble adhering step that is performed before the mixing step and attaches bubbles to the surface of the cement particles.

  As the second solving means, in the first solving means, a means is adopted in which the bubble adhering step is performed at the same work site as the mixing step.

  As the third solving means, in the first or second solving means, a means is adopted in which the bubbles have a particle size of 100 μm or less, preferably 50 μm or less.

  According to the present invention, air bubbles can be attached to the surface of the cement particles before the soil particles and the cement particles are mixed. Thereby, electrical aggregation of cement particles and soil particles can be prevented, and the soil particles and cement particles can be mixed uniformly.

It is the schematic of an excavator and a cement milk supply part used for the reinforcement construction method concerning one embodiment of the present invention. It is the schematic of the cement milk supply part used for the reinforcement construction method which concerns on one Embodiment of this invention. It is a flowchart showing the flow of the reinforcement construction method in this embodiment. 3 is a graph of a coefficient of variation of uniaxial compressive strength of a specimen in Experimental Example 1. 4 is a graph of the average uniaxial compressive strength of a specimen in Experimental Example 1. It is a graph which shows the relationship between the bubble diameter in Experimental example 2, and the volume ratio of a fine bubble. 10 is a table showing conditions for each case in Experimental Example 2. It is a table | surface which shows the conditions of the mixing | blending used in Experimental example 2, and the solidification material. It is a graph which shows the particle size accumulation curve of the soil used in Experimental example 2. 10 is a graph showing variation (coefficient of variation) in uniaxial compression strength for each case in Experimental Example 2.

  Hereinafter, as an embodiment of a reinforcement method according to the present invention, a reinforcement method for curing a soil cement in soil and forming a columnar body (reinforcement region) that reinforces the ground will be described with reference to the drawings. Note that the scale and shape of the drawings are appropriately changed so that they can be recognized. FIG. 1 is a schematic configuration diagram of an excavator 1 and a cement milk supply unit 2 used in the reinforcement method according to the present embodiment.

  The reinforcing method in the present embodiment is performed using the excavator 1 and the cement milk supply unit 2. The excavator 1 is a machine that excavates the ground and injects and stirs bubble-adhered cement milk X2 (cement milk containing cement particles with fine bubbles adhering to the surface) into the excavation hole. At the work site). Such an excavator 1 includes a rotating shaft 10, a rotating device 11, an excavating unit 12, a stirring unit 13, and a support mechanism 14. The excavator 1 may include a vehicle unit and be movable. The rotating shaft 10 has a hollow structure through which the bubble-adhered cement milk X2 can flow, and is rotatably supported by the support mechanism 14 so as to stand upright with respect to the ground. Moreover, the rotating shaft 10 has the discharge outlet 10a for discharging the bubble adhesion cement milk X2 to the surrounding surface of the lower end vicinity which is an edge part by the side of the ground.

  The rotating device 11 is a driving device for rotating the rotating shaft 10 and is supported by the support mechanism 14. The rotating device 11 is connected to an upper end that is the end of the rotating shaft 10 opposite to the ground. The excavation part 12 is a rotating body provided to make a hole for injecting the bubble-attached cement milk X2 into the soil. Such excavation part 12 has base 12a and projection part 12b. The base portion 12a is a flat plate fixed to the lower end of the rotation shaft so that the plane is parallel to the ground, and supports the protruding portion 12b. The protrusion 12b protrudes perpendicularly to the ground from the plane of the base 12a. The protrusion 12b excavates the ground by rotating in contact with the ground. The stirring unit 13 is a blade provided for stirring and mixing the bubble-adhered cement milk X2 injected into the hole formed by the excavation unit 12 and the surrounding soil particles, and a plurality of the stirring unit 13 are attached to the rotary shaft 10. Yes.

  FIG. 2 is a configuration diagram of the cement milk supply unit 2 used in the reinforcement method according to the present embodiment. The cement milk supply unit 2 is installed at the same work site as the excavator 1. The cement milk supply unit 2 includes a fine bubble supply device 20, a cement milk storage tank 21, and a pump 22.

  The fine bubble supply device 20 is a device that takes in air from the outside, refines the taken-in air, and supplies it to the cement milk X1 (cement milk to which fine bubbles are not supplied) as fine bubbles B. The cement milk storage tank 21 It is installed inside. The fine bubbles B generated by the fine bubble supply device 20 are, for example, bubbles having a particle size of 100 μm or less and preferably 50 μm or less. Such a fine bubble B has a small buoyancy due to its small bubble diameter and a long residence time in the liquid. Further, the fine bubbles B are negatively charged and have a characteristic of being attracted to a positive object.

  The cement milk storage tank 21 is a tank for storing the produced cement milk X1 and blowing fine bubbles B therein. The pump 22 pumps the bubble-attached cement milk X2 produced in the cement milk storage tank 21 to the excavator 1.

  In addition, the cement milk X1 used in this embodiment is obtained by dissolving cement particles with water. In the state of cement milk X1, the cement particles are positively charged and are in a state in which particles that are negatively charged are easily attracted. The cement milk supply unit 2 generates a bubble-attached cement milk X2 in which fine bubbles B (bubbles) made of microbubbles or nanobubbles are attached to cement particles, and supplies them to the excavator 1.

  Then, with reference to FIG. 3, the reinforcement construction method in this embodiment is demonstrated. FIG. 3 is a flowchart showing the flow of the reinforcing method in the present embodiment.

  First, a cement milk production process (step S1) is performed. In this cement milk production process (step S1), water is added to the cement and mixed to produce cement milk X1. The cement milk X1 is stored in the cement milk storage tank 21. Next, a bubble adhesion process (step S2) is performed. In this bubble adhering step (step S2), the fine bubbles B are supplied from the fine bubble supply device 20 to the cement milk X1 in the cement milk storage tank 21, and the fine bubbles are attached to the surface of the cement particles. At this time, since the cement particles are positively charged and the fine bubbles B are negatively charged, the cement particles and the fine bubbles B attract each other, and the fine bubbles B adhere to the surface of the cement particles. As a result, the cement milk X1 becomes the bubble-attached cement milk X2 including the cement particles to which the bubbles are attached. This bubble-attached cement milk X2 is supplied to the excavator 1.

  Next, a mixing process (step S3) is performed. In this mixing step (step S3), the excavator 1 makes a drilling hole in the ground forming the columnar body, injects the bubble-attached cement milk X2 into the drilling hole and mixes it with soil particles. At this time, the agitating unit 13 is rotated together with the rotating shaft 10, whereby the excavated soil particles and the bubble-attached cement milk X2 are mixed to form a soil cement. When the excavation part 12 finishes excavation to a predetermined depth, the rotary shaft 10 is lifted. At this time, the stirring unit 13 re-stirs the soil cement in the hole while rising.

  The soil cement in this mixing step (step S3) is in a state in which the negatively charged fine bubbles B adhere to the cement particles, and the negatively charged soil particles and the fine bubbles B repel each other. For this reason, cement particles and soil particles do not aggregate. Therefore, the stirring by the stirring unit 13 is sufficiently performed and mixed uniformly. Finally, a curing process (step S4) is performed. In this curing process (step S4), curing is performed until the soil cement in the mixed holes is completely cured. Through the above steps, a ground improvement body is formed in the soil, and the reinforcement of the ground is completed.

  Here, the experiment conducted in order to verify the performance of the soil cement produced by the reinforcement method according to the present embodiment will be described.

(Experimental example 1)
In this experiment, first, 20 test specimens α were prepared by adhering fine bubbles to cement milk mixed with cement and water, and mixing kaolin clay, silica sand, water and the cement milk. For comparison with this specimen α, specimens A1 to A5 and specimen β were produced under the conditions described later.

  Specimen A1 was prepared under the condition that nothing was added to cement milk. Specimen A2 was prepared by adding 0.1% of a surfactant (sodium gluconate) to cement milk. Specimen A3 was prepared by adding 0.2% of a surfactant (sodium gluconate) to cement milk. Specimen A4 was prepared by adding 0.3% of a surfactant (sodium gluconate) to cement milk. Specimen A5 was prepared by adding 0.6% of a surfactant (sodium gluconate) to cement milk. The specimen β was prepared by attaching bubbles to cement milk and adding 0.2% of a surfactant. The amounts of cement milk, kaolin clay and silica sand in each specimen were all the same.

  FIG. 4 is a graph of the coefficient of variation of the uniaxial compressive strength of the specimen. Note that the coefficient of variation described here indicates variations in the uniaxial compressive strength of the same type of specimen, and it is considered that the coefficient of variation decreases when cement milk, kaolin clay, and silica sand are sufficiently mixed. For soil cement that is actually used for reinforcement work, the coefficient of variation is preferably 30% or less in order to maintain strength.

  However, as shown in the graph of FIG. 4, the specimen A1 to which no surfactant is added has a coefficient of variation exceeding 40%, and it can be seen that there is a large variation in strength between specimens. On the other hand, the specimen α to which fine bubbles are attached has a variation coefficient of 27.1%, which is lower than the upper limit of 30% of the required variation coefficient. This is the same level as the specimen A4 to which 0.3% of the surfactant was added. Further, the coefficient of variation of the specimen β, to which fine bubbles are adhered by adding a surfactant, is approximately the same as that of the specimen α. That is, it can be said that the soil cement to which fine bubbles are attached is sufficiently homogeneous because the variation in strength is suppressed similarly to the soil cement to which the surfactant is added.

  FIG. 5 is a graph of the average uniaxial compressive strength of the specimen. As this graph shows, even when the specimens A2 to A6 to which the surfactant is added are compared with the specimen α to which fine bubbles are attached, there is no significant difference in strength. Moreover, it can be said that it is comparable intensity | strength even if the specimen (alpha) to which only the fine bubble was made to adhere and the specimen (beta) which added surfactant and made the fine bubble adhere. From this, it can be said that the strength of the specimen α and the specimen β to which fine bubbles are attached is comparable to the strength of the specimens A2 to A6 to which the surfactant is added.

  Furthermore, comparing the additive-free specimen A1 with the specimen α to which fine bubbles are attached, it can be seen that the specimen α to which fine bubbles are attached has a higher uniaxial compressive strength. From this, it is considered that the adhering of fine bubbles promoted the mixing of the soil and the cement milk, homogenized the specimen, and increased the uniaxial compressive strength.

(Experimental example 2)
In this experiment, an experiment was conducted using a stirring shear type fine bubble generator. This fine bubble generating device accommodates an impeller inside a cylindrical porous plate, generates fine bubbles in shearing force by rotating the impeller at high speed while supplying air to the impeller containing space, The fine bubbles discharged to the surroundings are configured to stir and diffuse with a stirrer. In this experiment, the amount of air supplied to the fine bubble generator is adjusted by a mass flow controller as necessary.

  FIG. 6 is a graph showing the relationship between the bubble diameter and the volume ratio of the fine bubbles when the impeller is rotated at 4000 rpm in water with natural intake without adjusting the air supply amount by the mass flow controller. . As shown in this figure, when the microbubble generator in this experiment was rotated at 4000 rpm by natural suction, microbubbles having a bubble diameter of 20 μm to 200 μm were generated, and in particular, a bubble diameter of 25 μm to 100 μm was generated. Fine bubbles are generated. The mode bubble diameter is about 50 μm.

  In this experiment, specimens were produced under the conditions of Cases 1 to 5 shown in FIG. 7 below, and the variation in uniaxial compressive strength of each specimen was examined. In Case 1, a specimen was prepared without mixing fine bubbles into cement milk. In Case 2, a specimen was produced by setting the fine bubble generator to natural suction, the impeller rotational speed of 4000 rpm, and the supply time of the fine bubbles to 5 minutes. In case 3, a specimen was prepared with an air supply amount of 50 cc per minute, an impeller rotation speed of 4000 rpm, and a microbubble supply time of 5 minutes. In Case 4, a specimen was prepared with an air supply rate of 25 cc per minute, an impeller rotation speed of 4000 rpm, and a microbubble supply time of 5 minutes. In Case 5, a specimen was prepared with an air supply amount of 50 cc per minute, an impeller rotation speed of 4000 rpm, and a microbubble supply time of 2.5 minutes.

  In each case, a specimen was prepared by the following method. After mixing kaolin clay and silica sand No. 5 in a dry state and adding water content ratio adjusted water (tap water), the mixture is stirred for 5 minutes with a mixer to prepare a sample soil. Cement milk is prepared by adding solidification water (tap water) to the solidification material and stirring and mixing with a hand mixer. When mixing fine bubbles into cement milk, fine bubbles are mixed into the produced cement milk for a predetermined time using a fine bubble generator. After putting cement milk into the sample soil, the mixture is stirred and mixed with a mixer for 1 minute to prepare a soil cement. A soil cement is packed in three layers in a mold having a diameter of 5 cm and a height of 10 cm, and each layer is tapped to obtain a specimen. Twenty specimens were prepared for each case, and these specimens were cured for 7 days at 20 ° C. and 60% constant temperature and humidity.

In this experiment, viscous soil was used as the sample soil. FIG. 8 shows the composition of the sample soil and the conditions of the solidified material, and FIG. 9 shows the particle size accumulation curve of the soil. Sample soil was mixed with kaolin clay (ρ _s = 2.748, I _P = 30.2) and silica sand No. 5 (ρ _s = 2.667) at a dry mass ratio of 7: 3, and then the water content ratio was adjusted. Went. A cement-based solidifying material for general soft soil (hereinafter, solidified material) was used as the solidifying material, and 10% was added to the mass of the sample soil.

As a result of the experiment, the average strength of the specimen of Case 1 was 445 kN / m ² . The average strength of the case 2 specimen was 521 kN / m ² . The average strength of the case 3 specimen was 487 kN / m ² . The average strength of the specimen of Case 4 was 612 kN / m ² . The average strength of the specimen of Case 5 was 619 kN / m ² .

  FIG. 10 is a graph showing variation (coefficient of variation) in uniaxial compression strength for each case. It can be seen that Case 1 in which fine bubbles are not mixed has a large variation in strength. Case 2 containing fine bubbles had a greatly reduced variation in strength compared to Case 1, and the average strength was slightly increased. Case 3 in which the amount of air supplied is 50 cc per minute is even smaller in intensity variation than Case 2. Cases 4 and 5 in which the total amount of microbubbles is half that of case 3 show that the average strength is high although the variation in strength is larger than that in case 3, and the effect of reducing variation is higher as the amount of fine bubbles is larger. It was. It is clear from FIG. 10 that Cases 2 to 5 (particularly Case 3) have a smaller variation reduction than Case 1. That is, as shown in FIG. 6, it was found that variation in strength can be suppressed by mixing fine bubbles having a bubble diameter of 100 μm or less into cement milk.

  In the reinforcing method according to the present embodiment as described above, the bubble adhering step (step S2) is performed before the soil and the cement milk X1 are mixed. Thereby, before making it mix with soil, the fine bubble B can be made to adhere to the surface of a cement particle, and the fluidity | liquidity of the cement milk X1 can be raised. Therefore, local aggregation of soil particles and cement particles can be prevented without using a surfactant, and uniform mixing is possible.

  According to such a reinforcing method according to the present embodiment, the soil particles and the cement particles can be uniformly mixed without using the surfactant, so that the burden of separately arranging and transporting the surfactant or the like is eliminated. . However, sufficient homogeneity and strength can be obtained even when a surfactant is added as shown in the above experiment. For this reason, this invention does not exclude adding a small amount of surfactant to the bubble-attached cement milk X2.

  In the reinforcing method according to the present embodiment, the bubble adhering step (step S2) and the mixing step (step S3) are performed at the same work site. For this reason, it takes a short time from the preparation of the bubble-attached cement milk X2 to the mixing with the soil, and many of the fine bubbles B attached to the cement particles remain. Thereby, local aggregation of soil particles and cement particles can be more effectively prevented. Therefore, it is possible to mix the soil particles and the cement particles uniformly.

  Further, in the reinforcing method according to the present embodiment, fine bubbles B of 50 μm or less are adhered to cement milk X1 using fine bubble supply device 20. For this reason, bubbles can be electrostatically attached to positively charged cement particles. Therefore, the soil particles and the fine bubbles B repel each other, so that the cement particles to which the fine bubbles B adhere can be uniformly mixed with the soil particles without locally agglomerating.

  In addition, the bubble-attached cement milk X2 produced by blowing the fine bubbles B into the cement milk X1 has high fluidity and further increases the volume when the fine bubbles B enter between the cement particles. Therefore, it is possible to reduce the amount of cement milk X1 used in the reinforcing method according to the present embodiment.

  Further, it has been confirmed that when a surfactant is added to cement milk X1, the time required for inhibiting the hardening of the soil cement and increasing the strength is increased. On the other hand, in this embodiment, fine bubbles are adhered to the cement milk X1 without adding a surfactant. Therefore, it does not inhibit the hardening of the soil cement, and hardens in the same setting time as that of the soil cement without addition of the surfactant, so that the strength is developed.

In addition, this invention is not limited to the said embodiment, For example, the following modifications can be considered.
(1) In the present embodiment, the ground is excavated by the excavator 1 and the soil cement is generated in the soil. However, the present invention is not limited to this. It is good also as what mixes previously prepared soil and bubble adhesion cement milk X2 using a concrete mixer etc., without using excavator 1. FIG. When mixing with a concrete mixer, it can be applied to sabo work and reinforcement work to prevent falling.

(2) Moreover, after performing the mixing process (step S3) in this embodiment, it is possible to form a stronger columnar body by curing after embedding H-shaped steel in the soil cement before hardening. It is.

(3) In the present embodiment, the bubble adhering step is performed at the same work site as the mixing step, but the present invention is not limited to this. It is good also as what performs a bubble adhesion process in a place different from a work site. If the bubble adhering step is performed at a place different from the work site, for example, since the bubble adhering cement milk X2 can be generated in a factory or the like, a large amount of the bubble adhering cement milk X2 can be generated.

(4) In the present embodiment, the bubble adhering step is performed after producing the cement milk X1, but the present invention is not limited to this. It is good also as what prepares the bubble adhesion cement milk X2 by mixing the water containing a fine bubble and cement. Since the cement milk X1 has a high viscosity, usable fine bubble supply devices are limited. However, since the viscosity of water is low, more fine bubble supply devices can be used.

(5) In the present embodiment, fine bubbles are attached to the cement milk X1, but the present invention is not limited to this. The fine bubbles B may be adhered to the cement milk X1, and a surfactant may be further added.

(6) In the present embodiment, the fine bubbles having a particle size of 50 μm or less are attached to the cement particles using the fine bubble supply device 20, but the present invention is not limited to this. The bubbles attached to the cement particles may be 50 μm or more.

(7) In the present embodiment, in the mixing step, the bubble adhering cement milk X2 and the soil particles are mixed by rotating the stirring unit 13, but the present invention is not limited to this. In the mixing step, for example, the bubble-attached cement milk X2 is ejected to the soil by high-pressure jetting toward the outer side in the radial direction of the rotary shaft 10, thereby discharging the bubble-attached cement milk X2 to the soil and attaching the soil particles and the bubbles. It is good also as what mixes with cement milk X2.

DESCRIPTION OF SYMBOLS 1 Excavator 10 Rotating shaft 10a Discharge port 11 Rotating device 12 Excavating part 12a Base part 12b Protrusion part 13 Stirring part 2 Cement milk supply part 20 Fine bubble supply apparatus 21 Cement milk storage tank 22 Pump X1 Cement milk X2 Bubble adhesion cement milk B Fine bubbles

Claims (3)

It is a reinforcing method for forming a soil cement by stirring and mixing soil particles and cement particles and forming a reinforcing region by hardening the soil cement,
A mixing step of mixing soil particles and cement particles;
And a bubble adhering step for adhering bubbles to the surface of the cement particles, which is performed before the mixing step.   The reinforcing method according to claim 1, wherein the bubble adhering step is performed at the same site as the work site where the mixing step is performed.   The reinforcing method according to claim 1 or 2, wherein the bubbles have a particle size of 100 µm or less, preferably 50 µm or less.

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