JP7150656B2 - Ground Displacement Control Method for Slurry Agitation Deep Mixing Method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a ground displacement control method for a slurry agitation deep mixing treatment method that prevents displacement of existing structures and ground on adjacent ground during foundation work and ground improvement.

The slurry agitating deep layer mixing method is a ground improvement method that creates solidified columnar piles by adding solidified slurry (fluid matter) to the ground and agitating and mixing it with in-situ soil such as cohesive soil using agitating blades. Construction method. As a slurry agitation type deep mixing treatment method, Fig. 5 shows ground displacement when the solidified slurry is pumped and discharged without using compressed air, and Fig. 6 shows the solidified slurry being atomized using compressed air. It schematically shows the generation of ground displacement when discharged. Here, the method of FIG. 5 is called a slurry agitating deep mixing treatment method, and penetrates into the ground in the improvement zone while rotating a rotating shaft equipped with a stirring blade, and the rotating shaft or the stirring blade is provided The solidified slurry is discharged to the in-situ soil at a low pressure from the discharge port. The discharged slurry is dispersed along the rotational trajectory as the stirring blade rotates, and is stirred and mixed with the in-situ soil. At that time, when the slurry is discharged into the ground, it stays in the unmelted ground and the pressure in the ground rises, pushing the ground laterally as indicated by the arrows in the figure, causing ground displacement. do.

On the other hand, the method of FIG. 6 is called the CI-CMC method (registered trademark), and as disclosed in Patent Document 1, it penetrates while rotating a rotating shaft equipped with a stirring blade into the ground in the improved area. Then, a solidified slurry mixed with compressed air is ejected in the form of a mist from an ejector provided on at least one of the rotating shaft and the stirring blade. The ejected misty slurry subdivides the in-situ soil and increases the fluidity of loosened soil particles. Since the mud in the stirring area rises to the ground surface and is discharged according to the amount of slurry charged, the effect of reducing the peripheral displacement can be obtained.

In addition, the main part of Patent Document 1 is a configuration that improves low displacement performance without increasing the water-cement ratio (W / C) by adding a delayed water-reducing material to cement slurry, which is a solidifying slurry. .

Japanese Patent No. 5759151

The construction method shown in FIG. 6 can greatly suppress ground displacement compared to the construction method shown in FIG. Moreover, in order to achieve more effective low-displacement construction, it is preferable to increase the fluidity of the soil in the stirring area and discharge it smoothly, in addition to the application of an ejector. In order to realize this, the present applicants, for example, variously change the table flow value of the slurry or the agitated soil, set the water-cement ratio (W/C) of the slurry higher than usual, and add We have examined this while conducting test construction, such as adding a fluidization accelerator. However, it is difficult to predict the table flow value of mixed or agitated soil in advance, and there are problems such as economic considerations when using additives. was there.

From the above background, the object of the present invention is to make the ground displacement close to zero as a low displacement construction of the slurry agitating deep layer mixing method, that is, to easily and accurately implement minimal low displacement construction, for example, test construction. To provide a configuration suitable as an index for managing a mixing plan in a site or situation where implementation is impossible. Other purposes will be made clear in the following description.

In order to achieve the above object, the invention of claim 1 penetrates into the ground in the improvement zone while rotating a rotating shaft equipped with a stirring blade, and from a discharge port provided on at least one of the rotating shaft and the stirring blade. The solidified slurry mixed with compressed air is discharged, and according to the supply amount of the discharged solidified slurry, excess mud in the agitation zone in the ground is pushed up to the ground together with the compressed air and discharged. In the ground displacement control method of the slurry agitation type deep mixing treatment method that reduces the displacement around the area, the slurry injection rate, which is the slurry injection amount per unit improved soil volume improved by the discharged solidification system slurry, is about 30%. , the discharge rate of the surplus mud is set to 90% or more, and the ground displacement is brought close to zero.

According to a second aspect of the present invention, there is provided an ejector that mixes cement slurry as the solidifying slurry with the compressed air and discharges it from the discharge port in the form of a mist. Here, the target ejector includes at least the configuration disclosed in Japanese Patent No. 3416774 and the configuration disclosed in Japanese Patent No. 3389527, which will be described later. Further, the sludge discharge rate is calculated from the formula of (sludge discharge amount/slurry injection amount)×100. As illustrated in Patent Document 1, a retarding water-reducing agent and other modifiers may be added to the cement slurry, which is a solidifying slurry.

In the present invention as described above, if the mud removal rate is about 100%, it can be estimated that the pressure increase due to the injected slurry does not occur in the ground, and the actual construction hardly causes ground displacement. The method of evaluating the ground displacement by the sludge discharge rate is an effective means because it can be determined with a smaller number of works than the method of directly measuring the displacement with a displacement meter. However, as an exception, in the case of loose sandy ground that causes negative dilatancy due to agitation or highly permeable gravel ground that causes slurry to escape, even if the sludge removal rate is < 100% , there are also cases where ground displacement does not occur.

In addition, the present invention was completed with motivation such as examination and evaluation of test construction results as exemplified below. That is, the inventors of the present invention, in the above-mentioned CI-CMC construction method, from the viewpoint that it is important to increase the fluidity of the stirring zone in order to achieve extremely low displacement, that is, almost zero displacement, especially cement slurry water The effect of cement ratio (W/C) has been investigated through test construction. Figures 1 to 3 show representative examples of the test construction. Figure 1 shows the outline of the ground on which the test construction was performed. In this construction, the soft layer thickness is about 18 m, and the ground is composed mainly of silty clay with w _n ≈ 50 to 60%, sandwiching high organic soil with w _n ≈ 120% in the middle. The amount of solidifying material added was set to 3 MN/m ² , which is three times the design strength of 1 MN/m ² , based on an indoor blending test. m ³ (injection rate 25%), and W/C=1.0, slurry addition amount is 290 to 240 kg/m ³ (injection rate 32%). In each case, 4 sets of improved piles (8 in total, consisting of 2 rotating shafts) were constructed. 2 and 3 show the distance from the improved body and the horizontal and vertical displacements as the results of this test. Each figure also shows a case of W/C=0.9 (separately determined by an indoor mixing test, injection rate of 23%) performed in an adjacent construction section.

2 and 3, in the case of W/C=1.0, the maximum horizontal displacement and vertical displacement are both 6 mm, and almost no ground displacement occurs. However, in the cases of W/C=0.8 and W/C=0.9, considerable ground displacement occurs. In addition, in this test, the amount of raised soil or the amount of sludge discharged due to construction is measured. The measurement results show that when W/C = 1.0, the sludge removal rate is 98%, when W/C = 0.8, the sludge removal rate is 67%, and when W/C = 0.9, the sludge removal rate is 98%. was 60%. For this reason, in the case of W/C = 1.0, the fluidity in the stirring area was secured, but in the cases of W/C = 0.8 and W/C = 0.9, the fluidity in the stirring area was not secured. It is considered that it was insufficient.

In other words, in order to realize low-displacement construction by the CI-CMC construction method, the displacement generally decreases as the water-cement ratio W/C increases. However, this way of thinking cannot explain the phenomenon that the displacement is larger at W/C=0.9 than at W/C=0.8 in FIGS. Also, as construction conditions, when the target strength is high, or when the cement addition amount must be increased due to high organic soil with low strength development, etc., there are cases where the W/C must be set low. Based on these test results and recognition, the present inventors reexamined the test construction data at each site that was performed by changing the W/C that had been performed by their company so far, and the results are shown in FIG. From the relationship between the slurry injection rate and the sludge discharge rate, which is the condition for realizing almost zero displacement, that is, the extremely low displacement construction, the slurry It was found that the injection rate should be about 30%, which led to the present invention. In the present invention, it is essential to adjust the slurry injection rate to about 30%. About 30% refers to 28% or more as a guideline, and the upper limit is set to 32% in order to avoid excessive increase in material cost, which is economical.

In the invention of claim 1, it is necessary to ensure a mud discharge rate of 90% or more as a condition for realizing almost zero displacement, that is, extremely low displacement construction as a ground displacement control method for the slurry agitating deep layer mixing method. In order to achieve this, it is essential to set the slurry injection rate, which is the amount of slurry injected per unit amount of improved soil, to about 30%. It can be effectively used as an index for managing the mixing plan in the field or situation where it is impossible.

In the invention of claim 2, since the ejector used in the existing CI-CMC construction method is used, more accurate construction can be performed and zero ground displacement can be reliably achieved.

In the CI-CMC construction method, in realizing almost zero ground displacement, it is a schematic diagram showing the outline of the ground that was tested when examining the influence of the water-cement ratio. FIG. 2 is a schematic diagram showing the results of examining the distance from the improved body and the horizontal displacement by driving a plurality of improved piles by the CI-CMC construction method in the ground of FIG. 1 . FIG. 2 is a schematic diagram showing the results of examining the distance from the improved body and the vertical displacement by driving a plurality of improved piles by the CI-CMC method in the ground of FIG. 1 . FIG. 4 is a diagram showing the relationship between the slurry injection rate and the mud discharge rate measured at many construction sites to which the CI-CMC construction method is applied. Fig. 2 conceptually shows the behavior of the slurry discharged by the slurry agitating deep layer mixing method, (a) is a schematic view from above, and (b) is a schematic view of the ground cross-sectioned in the vertical direction. 1 conceptually shows the behavior of the slurry discharged by the CI-CMC construction method, (a) is a schematic view from above, and (b) is a schematic view of the ground in a longitudinal section.

Table 1 below shows the construction history data of many construction sites where the applicants have applied the CI-CMC construction method as ground improvement. FIG. 4 is a diagram showing the relationship between the slurry injection rate and the mud discharge rate performed at each construction site A to E based on Table 1. As shown in FIG. Hereinafter, using these, the ground displacement control method of the slurry agitating deep layer mixing method of the present invention will be clarified.

(Table 1)

In Table 1, W/C is the water-cement ratio, that is, the ratio of water and cement expressed as a percentage. The magnitude of the water-cement ratio affects the quality (strength, durability, etc.) of improved piles. In general, too large a water-cement ratio leads to insufficient strength and durability, and too small a drop in workability. The amount added is the amount of cement slurry added (kg/m ³ ). A unit injection amount is a slurry injection amount per unit volume (liter/m ³ ). The sludge discharge rate is calculated by measuring the amount of soil discharged to the ground during pile construction and calculating it as a ratio to the amount of slurry injected, that is, (amount of discharged soil discharged to the ground during pile construction/per unit volume slurry injection amount)×100. The injection rate is the slurry injection rate, and the slurry injection amount per unit improved soil volume improved with the discharged solidification slurry. /1,000)×100. The unit injection amount in Table 1 is rounded off to the nearest whole number.

The CI-CMC construction method is not shown because it is substantially the same as that disclosed in Patent Document 1, but it penetrates the ground in the improved area while rotating a rotating shaft equipped with a stirring blade, and stirs with the rotating shaft. The solidified slurry mixed with compressed air is discharged from the discharge port provided on at least one of the blades, and the surplus mud in the agitation zone in the ground is discharged to the ground together with the compressed air in accordance with the supply amount of the discharged solidified slurry. It pushes up and discharges to make it possible to reduce the displacement around the improvement area.

More specifically, in this construction method, the construction equipment includes a rotating shaft and a stirring blade that rotates integrally with the rotating shaft, a drive mechanism that drives the rotating shaft up and down, a solidification system slurry supply means and a compressed air supply means. , and an ejector provided on the rotary shaft and/or the stirring blade side and connected to the slurry supply means and the compressed air supply means through pipes corresponding to the slurry supply means and the compressed air supply means. And, the construction procedure is that slurry such as cement slurry sent from the slurry supply means through the corresponding pipe by the ejector is sent from the compressed air supply means through the corresponding pipe in the process of penetrating the rotary shaft into the ground or pulling it out. It is mixed with air and discharged forward in the direction of rotation of the stirring blade from the discharge port of the ejector or the nozzle connected to the ejector, mixed and stirred with the in-situ soil, and the discharged slurry is supplied. Depending on the amount, surplus mud in the agitation zone in the ground is pushed up to the ground together with compressed air and discharged, making it possible to reduce the displacement around the improvement zone.

As a construction procedure, first, the construction machine is set at a predetermined position. Secondly, while the rotating shaft is continuously inserted, the mixing ejector accompanies the slurry with the compressed air, mixes it, and discharges it from the discharge port in the direction of rotation of the stirring blade in the form of mist. Third, after confirming that the tip of the rotary shaft has reached the support layer, the discharge of the slurry is stopped, and the tip is processed by moving the rotary shaft up and down by a predetermined distance. Fourthly, withdraw while rotating the stirring blade in the reverse direction. Fifth, after building the improved body up to the design position on the ground surface, move to the next construction position. However, the slurry may be discharged by both inserting and withdrawing the rotary shaft.

In the ground improvement at each construction site A to E, the amount of discharged soil accompanying the formation of improved piles is measured. The method for measuring the amount of discharged soil was obtained by putting the discharged soil per construction set into a truncated square pyramid, shaping it, and measuring the length of each side. The ground at each construction site A to E was mainly made of cohesive soil, and the water content (natural water content) was generally in the range of 40 to 75% w ⁿ as shown in the same table.

As for the ground displacement control method, from FIG. It can be seen that the slurry injection rate needs to be about 30% in order to achieve a rate of 90% or more. In other words, regarding the ground displacement control method by the slurry stirring deep mixing method, especially the CI-CMC method, it is necessary to ensure the fluidity of the stirring blade in order to realize almost zero displacement, that is, extremely low displacement construction. As a result, it is important to set the slurry injection rate to about 30% or more. In other words, about 30% refers to 28% or more as a guideline, and the upper limit is set to 32% in order to avoid excessive increase in material cost.

The above advantages can be effectively used as an index for managing the mixing plan in a site or situation where the mixing plan and test construction cannot be carried out, for example, when planning the test construction of ground improvement. In addition, in the case of extreme soil properties, etc., even if the slurry injection rate is lower than 25%, the sludge discharge rate will be ≈ 100% or the sludge discharge rate will be 90%. However, such exceptional cases are excluded from the present invention.

In the CI-CMC construction method described above, the rotating shaft is not limited to a single shaft, and may be two or more shafts as disclosed in Patent Document 1. The stirring blades may have a single-stage structure instead of providing a plurality of stages. As an ejector, as shown in FIG. 6(c), a discharge port is formed on the tip side, and a solidified slurry mixed with compressed air is discharged from the discharge port (for example, Japanese Patent No. 3416774 (see Japanese Patent No. 3389527), and a configuration in which the discharge port is composed of a dedicated nozzle, and a solidified slurry mixed with compressed air by an ejector is discharged from the nozzle through a supply pipeline (see, for example, Japanese Patent No. 3389527). , can be of any configuration. Also, the ejector can be provided on the rotating shaft instead of the stirring blade.

Moreover, the above embodiment does not limit the present invention. The present invention only needs to have the technical elements specified in the claims, and the details can be changed in various ways as necessary.

DESCRIPTION OF SYMBOLS 1... Rotating shaft 2... Stirring blade 3... Ejector 4... Piping 5... Piping 6... Piping 7... Discharge port

Claims (2)

A rotating shaft equipped with agitating blades is penetrated into the ground in the improved zone while rotating, and a solidified slurry mixed with compressed air is discharged from a discharge port provided on at least one of the rotating shaft and the agitating blades, and this Slurry agitation type deep mixing process for reducing displacement around the improvement zone by pushing up and discharging surplus mud in the agitation zone in the ground together with the compressed air according to the amount of solidified slurry discharged. In the ground displacement control method of the construction method,
By adjusting the slurry injection rate, which is the amount of slurry injected per unit improved soil volume improved with the discharged solidified slurry, to about 30%, the discharge rate of the excess mud is 90% or more and ground displacement A ground displacement control method for a slurry agitating deep layer mixing method, characterized by bringing the ground displacement closer to zero. The ground displacement of the deep mixing treatment method according to claim 1, characterized in that it has an ejector that mixes cement slurry as the solidification system slurry with the compressed air and allows it to be discharged in the form of a mist from the discharge port. control method.

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