JP7187755B2 - High-pressure injection stirring method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high-pressure injection stirring method.

As one of the ground improvement methods, the high-pressure injection stirring method creates a ground improvement body by stirring and mixing the cut ground and cement milk while cutting the ground with cement milk (high-pressure jet) that is injected into the ground at high pressure. It has been known. Compared to the mechanical agitation method, the high-pressure jet agitation method does not require large heavy machinery, so the construction space is small, and construction can be performed in narrow spaces or places with limited headroom.

In addition, the high-pressure injection agitation method uses a small-diameter rod, and the improvement diameter of the soil improvement body can be freely changed by adjusting the injection pressure and flow rate of the cement milk. , can flexibly respond to construction conditions without removal. On the other hand, the high-pressure injection agitation method requires a larger amount of cement milk to be injected (injected) into the ground than the mechanical agitation method.

In order to solve this problem, for example, in Patent Document 1, by using cement milk (cement slurry) with a low water-cement ratio, the amount of cement milk injected into the ground is reduced, and the discharged sludge (slime) is reduced. A high pressure jet agitation process is disclosed which reduces the volume.

Japanese Patent No. 6313697

However, as in the high-pressure injection stirring method shown in Patent Document 1, when the cement milk with a low water-cement ratio is used to reduce the injection amount (injection amount) of cement milk into the ground, the cutting ground and cement milk are mixed. Stirability is reduced, and variations in the strength of the soil improvement material increase.

In view of the above facts, an object of the present invention is to provide a high-pressure injection stirring method that can reduce the variation in strength of the soil improvement body while reducing the amount of cement milk injected into the ground.

In the high-pressure injection stirring method according to the first aspect, the rod inserted into the ground is pulled up while rotating so that the number of rotations for a predetermined amount of pulling is a predetermined number of rotations, and the cement milk with a low water-cement ratio is injected from the rod at high pressure. By doing so, the cement milk and the cut ground are stirred and mixed to perform the first preparation of the soil improvement body, and the rod is pulled down while rotating so that the number of rotations for a predetermined amount of pulling down is greater than the predetermined number of rotations, Alternatively, the rod is reinserted, the rod is pulled up while rotating so that the number of rotations for a predetermined amount of pulling is greater than the predetermined number of rotations, and the cement milk is injected from the rod at high pressure to obtain the cement milk and The ground improvement body is prepared for the second time by stirring and mixing with the cut ground.

According to the above configuration, the soil improvement body can be formed by pulling up the rod inserted into the ground while rotating and injecting cement milk from the rod at high pressure. Here, since the cement milk has a low water-cement ratio, the amount of cement milk to be injected into the ground can be reduced compared to the case of using cement milk with a normal water-cement ratio.

In addition, the soil improvement body is created twice, and the number of rotations for the predetermined pull-down amount or the predetermined pull-up amount of the rod in the second creation is set to be greater than the number of rotations for the predetermined pull-up amount of the rod in the first creation. ing. As a result, the improved diameter of the ground improvement body can be secured in the first creation, and the number of times of stirring and mixing the cut ground and cement milk can be increased while suppressing the expansion of the improved diameter of the ground improvement body in the second creation. . Therefore, even if the amount of cement milk injected into the ground is reduced, variations in the strength of the soil improvement material can be reduced.

The high pressure injection stirring method according to the second aspect is the high pressure injection stirring method according to the first aspect , wherein the rotation speed for the predetermined pulling amount or the predetermined pulling amount of the rod in the second formation is the predetermined It is 1.5 times or more and 3.0 times or less of the rotational speed.

According to the above configuration, the rotation speed for the predetermined pulling amount or the predetermined pulling amount of the rod in the second formation is 1.5 times or more the rotation speed for the predetermined pulling amount of the rod in the first formation. less than double. As a result, compared to the case where the number of revolutions is less than 1.5 times or more than 3.0 times, it is possible to reduce variations in the strength of the soil improvement material while improving workability.

The high pressure injection stirring method according to the third aspect is the high pressure injection stirring method according to the first aspect or the second aspect , wherein the water cement ratio of the cement milk is in the range of 0.7 or more and 1.0 or less. and a fluidizing agent is added to the cement milk.

The water-cement ratio of the cement milk injected into the ground is usually set within the range of about 0.8 to 1.2 by laboratory mixing tests and the like. Here, according to the above configuration, by setting the water-cement ratio to a low cement ratio in the range of 0.7 or more and 1.0 or less, compared to the case where cement milk with a normal water-cement ratio is used, of cement milk can be reduced.

In addition, by adding a fluidizing agent to the cement milk, it is possible to suppress an increase in the viscosity of the sludge even when the cement milk has a low water-cement ratio. As a result, it is possible to suppress the deterioration of workability and the quality of the ground improvement material due to the blockage of the sludge discharge route and the upheaval of the ground, or the sludge spouting from an unexpected location.

According to the high pressure injection stirring method according to the present invention, it is possible to reduce the variation in the strength of the soil improvement material while reducing the amount of cement milk injected into the ground.

1(A) to 1(C) are process diagrams (part 1) showing a procedure for performing a high-pressure injection stirring method according to an example of an embodiment; (A) to (C) are process diagrams (Part 2 following Part 1) showing a procedure for performing a high-pressure injection stirring method according to an example of the embodiment. It is a cross-sectional elevational view showing a rod used in the high-pressure jet stirring construction method according to an example of the embodiment. 4 is a graph showing the amount of sludge generated when creating soil improvement bodies according to Example 1 and Comparative Examples 1 to 4. FIG. (A) is a graph showing the unconfined compressive strength of soil improvement bodies according to Example 1 and Comparative Examples 1 to 4, and (B) is a graph showing the coefficient of variation of the unconfined compressive strength.

A high-pressure jet stirring method according to one embodiment of the present invention will be described below with reference to FIGS. 1 to 3. FIG.

As shown in FIGS. 1 and 2, the high pressure injection stirring method of the present embodiment includes a ground drilling step of forming a guide hole 14 in the ground 10 using a rod 12, and a plurality of times using the rod 12 (this It has a soil improvement body creation step of creating a soil improvement body 16 in two steps).

In this embodiment, the same rod 12 is used in the ground drilling process and the ground improvement body construction process. As shown in FIG. 3, the rod 12 is, for example, a double tube having a first channel 18 formed in the center and a second channel 20 formed outside the first channel 18. there is

An injection device 22 is connected to the lower end of the rod 12 . The injection device 22 has a discharge port 24 formed at the lower end and communicating with the first flow path 18 , and a plurality of injection ports 26 formed on the side surface and communicating with the first flow path 18 and the second flow path 20 . have.

In addition, it is not necessary to use the same rod 12 in the ground drilling process and the ground improvement body construction process. For example, in the ground drilling process, a drilling rod having a discharge port 24 formed at the lower end is used, and in the soil improvement body creation process, another injection rod having a side surface with the injection port 26 may be used.

(Ground drilling process)
First, in the ground drilling process, as shown in FIG. 1A, a rod 12 is used to excavate an improved range of the ground 10 to a target depth.

Specifically, a drilling water supply pipe (not shown) is connected to the first flow path 18 of the rod 12 shown in FIG. do. Then, as shown in FIG. 1A, the rod 12 is inserted into the ground 10 by a drilling machine 28 such as a boring machine while the drilling water P is discharged vertically downward from the discharge port 24 of the injection device 22. Thus, the ground 10 is excavated to form the guide hole 14 .

In addition, before or after the guide hole 14 is formed, a pit 30 (recess) having a larger diameter than the guide hole 14 is grooved at the upper end of the guide hole 14, that is, at the pile center position on the surface of the ground 10. Keep

(First ground improvement body construction process)
After forming the guide hole 14 in the ground 10 in the ground drilling process, as shown in FIGS. Perform the improved body creation process.

Specifically, first, a cement milk supply pipe (not shown) is connected to the first channel 18 of the rod 12 shown in FIG. 3 to supply the cement milk Q to the first channel 18 . A compressed air supply pipe (not shown) is connected to the second flow path 20 of the rod 12 to supply compressed air to the second flow path 20 .

At this time, the discharge port 24 of the injection device 22 is temporarily blocked by, for example, dropping a spherical blocking member (not shown) into the injection device 22 . As a result, the cement milk Q supplied to the first flow path 18 of the rod 12 is injected by the injection device 22 together with the compressed air supplied to the second flow path 20 of the rod 12, as shown in FIG. 1(B). A high-pressure jet is horizontally directed from the port 26 .

Then, as shown in FIG. 1(C), the rod 12 inserted into the ground 10 is pulled up along the guide hole 14 by a predetermined amount by the construction machine 28, and each time the rod 12 is pulled up, the rod 12 is lifted by a predetermined amount. The cement milk Q is injected at a high pressure from the injection port 26 of the injection device 22 by rotating at the number of rotations (hereinafter referred to as "the number of rotations M").

As a result, the cement milk Q cuts the ground 10 around the rod 12 (guide hole 14) to ensure the improved diameter of the soil improvement body 16, and the ground improvement body is stirred and mixed with the cut ground and the cement milk Q. Build 16 for the first time. Sludge R (slime) generated during the construction of the soil improvement body 16 is discharged to the pit 30 through the guide hole 14 and carried out to the outside by a sand pump, a vacuum vehicle, or the like (not shown).

In this embodiment, in the first soil improvement body creation process, as an example, every time the rod 12 is pulled up by 2.5 cm, the rod 12 is rotated once (360 ° rotation) and the cement milk Q is injected into the ground 10. (injecting).

(Second ground improvement body construction process)
After the first construction of the soil improvement body 16, as shown in FIGS. 2(A) to 2(C), the second soil improvement body construction process is performed in the same range as the first time. In addition, the second soil improvement body creation process is performed continuously without leaving time from the first soil improvement body creation process, for example.

Specifically, as shown in FIG. 2A, first, the rod 12 positioned at the upper end of the improvement range of the ground 10 is reinserted to the lower end of the improvement range. Then, as shown in FIG. 2(B), the rod 12 inserted into the ground 10 is pulled up along the guide hole 14 by the construction machine 28 in the same manner as the first soil improvement body construction process, and the rod 12 is pulled up. Each time the rod 12 is pulled up, the cement milk Q is injected at high pressure from the injection port 26 of the injection device 22 by rotating the rod 12 . As a result, the ground improvement body 16 is created by further stirring and mixing the cut ground and the cement milk Q.

Here, in the second soil improvement body construction process, the number of rotations of the rod 12 with respect to a predetermined pulling amount (hereinafter referred to as "rotation number N") is the rotation of the rod 12 in the first soil improvement body construction process number M (number of revolutions for a given amount of pulling).

Specifically, the number of rotations N of the rod 12 in the second formation is preferably 1.5 to 3.0 times the number of rotations M of the rod 12 in the first formation. In this embodiment, in the second soil improvement body creation process, as an example, every time the rod 12 is pulled up by 2.5 cm, the rod 12 is rotated twice (720 ° rotation) and the cement milk Q is injected into the ground 10. (injecting).

In addition, the injection amount (L/min) of the cement milk Q in the second formation of the soil improvement body 16 is the same amount as the injection amount (L/min) in the first formation. Also, the pulling speed of the rod 12 in the second formation of the soil improvement body 16 is set faster than the pulling speed of the rod 12 in the first formation.

After the second preparation of the soil improvement body, as shown in FIG. 2(C), the rod 12 is pulled out from the guide hole 14 and the guide hole 14 is closed with cement milk Q, thereby completing the preparation of the soil improvement body 16. Note that the above procedure is an example, and the procedure may be different or include other procedures.

For example, in the above procedure, in the second soil improvement body creation process, the soil improvement body 16 was created while pulling up after reinserting the rod 12. However, the ground improvement body 16 may be formed by rotating the rod 12 located at the upper end of the improvement range of the ground 10 while pulling it down to inject the cement milk Q into the ground 10 . Also in this case, the number of rotations of the rod 12 for a predetermined pull-down amount is made greater than the number of rotations M of the rod 12 in the first soil improvement body construction step.

Further, in the above procedure, the soil improvement body creation process was performed twice, but the soil improvement body creation process may be performed three times or more. Even when the soil improvement body creation process is performed 3 times or more, the rotation speed N of the rod 12 in at least the second soil improvement body creation process is more than the rotation number M of the rod 12 in the first soil improvement body creation process. It is done a lot.

In addition, when the soil improvement body creation process is performed three times or more, by reducing the injection amount of cement milk Q in each soil improvement body creation process, the total injection amount (injection amount) of cement milk Q is suppressed from increasing. be able to.

(cement milk)
Next, the cement milk Q injected into the ground 10 in the ground improvement body formation step of the high-pressure injection stirring method of the present embodiment will be specifically described.

In this embodiment, the cement milk Q has a low water-cement ratio. In the present invention, "low water-cement ratio" refers to a lower water-to-cement ratio in the cement milk formulation than the normal water-cement (W/C) ratio.

Further, the "usual water-cement ratio" refers to a water-cement ratio determined by, for example, an indoor mixing test. Specifically, the "ordinary water-cement ratio" is obtained by preparing multiple test specimens with different amounts of cement milk added, obtaining the unconfined compressive strength, and determining the indoor compound strength from the relationship between the added amount and the unconfined compressive strength. It is determined by obtaining the amount of cement milk to be added to secure the required amount.

Here, the uniaxial compression test for calculating the "uniaxial compression strength" is carried out, for example, by the method specified in JIS A 1216:2009. In general, the "normal water-cement ratio" of cement milk is set in the range of about 0.8 to 1.2, whereas the cement milk Q of the present embodiment has a water-cement ratio of 0. .7 or more and 1.0 or less.

Further, in this embodiment, the cement milk Q is added with a fluidizing agent. The fluidizing agent is an agent that reduces the viscosity of the cement milk Q. For example, an agent containing a polycarboxylic acid compound or naphthalenesulfonic acid as a main component, or an agent containing a polycarboxylate as a main component and an inorganic compound as an auxiliary agent. etc. As the fluidizing agent, other known agents capable of reducing the viscosity of the cement milk Q can be used in addition to the exemplified agents.

Also, the amount of fluidizing agent to be added to the cement milk Q is determined by, for example, a table flow test. Specifically, the amount of fluidizing agent required to make the table flow value of cement milk Q with a low water-cement ratio of this embodiment comparable to the table flow value of cement milk with a "normal water-cement ratio" Determined by finding the amount to be added.

In addition, in this embodiment, the injection rate of the cement milk Q into the ground 10 is 25% or more and 100% or less of the volume of the soil improvement body 16 . Further, the amount of the fluidizing agent added to the cement milk Q is about 5 kg/m ^{3 or more and 30 kg/m 3 or} less with respect to the volume of the soil improvement body 16 .

(action, effect)
According to the high-pressure injection stirring method of the present embodiment, the rod 12 inserted into the ground 10 is pulled up while rotating, and the cement milk Q is injected from the rod 12 through the injection device 22 at high pressure to create the ground improvement body 16. can do.

Here, according to this embodiment, the cement milk Q injected into the ground 10 has a low water-cement ratio. Specifically, as an example, the water-cement ratio of the cement milk Q is in the range of 0.7 or more and 1.0 or less. As a result, the amount of cement milk Q injected into the ground 10 can be reduced compared to the case of using cement milk with a normal water-cement ratio (approximately 0.8 or more and 1.2 or less), so the construction time is reduced. can be shortened, construction efficiency can be improved, and costs can be reduced.

Further, according to this embodiment, the ground improvement body 16 is created twice, and the rotation speed N (the rotation speed for a predetermined amount of pulling) of the rod 12 in the second creation is set to the rotation speed N of the rod 12 in the first creation The number of revolutions is greater than M (the number of revolutions for a predetermined pulling amount).

Generally, when the injection amount of the cement milk Q is the same, the greater the rotation speed of the rod 12, the shorter the flight distance (injection diameter) of the cement milk Q. For this reason, after securing the improved diameter of the soil improvement body 16 in the first creation, while suppressing the expansion of the improved diameter of the soil improvement body 16 in the second creation, the number of times of stirring and mixing the cutting ground and cement milk Q can be increased. As a result, while reducing the amount of cement milk Q injected into the ground 10, variations in the strength (uniaxial compressive strength) of the soil improvement body 16 can be reduced.

Specifically, as an example, the number of rotations N of the rod 12 in the second formation (the number of rotations for a predetermined amount of pulling) is changed to the number of rotations M of the rod 12 in the first formation (the number of rotations for a predetermined amount of pulling). 1.5 times or more and 3.0 times or less. As a result, compared to the case where the rotation speed N is less than 1.5 times the rotation speed M, the variation in the strength of the soil improvement body 16 can be reduced by increasing the number of times of stirring and mixing, and the rotation speed N is rotated. Workability can be improved as compared with the case of more than 3.0 times the number M.

Further, according to this embodiment, the cement milk Q is added with a fluidizing agent. Therefore, even when the cement milk Q has a low water-cement ratio, it is possible to prevent the viscosity of the sludge R from increasing. As a result, the sludge discharge path (guide hole 14) is blocked and the ground 10 is raised, or the sludge R is spouted from an unexpected place, which suppresses the deterioration of workability and the quality of the soil improvement material. be able to.

(Other embodiments)
Although one example of the embodiment of the present invention has been described above, the present invention is not limited to such an embodiment, and various other embodiments are possible within the scope of the present invention.

For example, in the embodiment described above, the rod 12 is a double tube having the first channel 18 and the second channel 20 . However, the configuration of the rod 12 is not limited to the above embodiment, and may be, for example, a triple tube having three channels, ie, a drilling water channel, a compressed air channel, and a cement milk channel.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. In addition, the present invention is not limited to the following examples.

(Example 1)
In Example 1, cement milk with a water-cement ratio of 0.78 (78%) to which 7.5 kg / m ³ of fluidizing agent was added was used, and the injection rate of cement milk to the volume of the soil improvement body was 32.3. A ground improvement body with an improved diameter of 2.3 m and an improved length of 5 m was created as a %.

In the first preparation of the soil improvement body, the rotation speed M of the rod was set to 1 rotation/2.5 cm, the lifting speed of the rod was set to 4 minutes/m, and the injection amount of cement milk was set to 250 L/minute. In addition, the number of rotations N of the rod in the second preparation of the soil improvement body was set to 2 rotations/2.5 cm, the lifting speed of the rod was set to 2.5 minutes/m, and the injection amount of cement milk was set to 250 L/minute.

(Comparative Examples 1 and 2)
In Comparative Examples 1 and 2, cement milk with a water-cement ratio of 0.89 (89%) to which no fluidizing agent was added was used, and the injection rate of cement milk relative to the volume of the soil improvement body was improved by 50.1%. A ground improvement body with a diameter of 2.3 m and an improved length of 5 m was constructed.

In the first preparation of the soil improvement body, the rotation speed M of the rod was set to 1 rotation/2.5 cm, the lifting speed of the rod was set to 8 minutes/m, and the injection amount of cement milk was set to 180 L/minute. Further, in the second construction of the soil improvement body, the rotation speed N of the rod was set to 1 rotation/2.5 cm, the lifting speed of the rod was set to 6 minutes/m, and the injection amount of cement milk was set to 180 L/minute.

(Comparative Examples 3 and 4)
In Comparative Examples 3 and 4, only the number of rotations N of the rod in the second preparation of the soil improvement body was 1 rotation / 2.5 cm, and the other cement milk water-cement ratio, the improvement diameter of the soil improvement body, the improvement length, The lifting speed of the rod, the injection amount of cement milk, etc. were all the same conditions as in Example 1.

(Comparison of sludge discharge amount between Example 1 and Comparative Examples 1 to 4)
First, the amount of sludge (discharged sludge amount) generated when creating the soil improvement bodies according to Example 1 and Comparative Examples 1 to 4 was measured. The results are shown in the graph of FIG. Note that the vertical axis in FIG. 4 represents the amount of sludge discharged (m ³ ), and the No. on the horizontal axis. 5 is Example 1, No. 1 to 4 represent Comparative Examples 1 to 4, respectively.

As shown in FIG. 4, in Example 1 (No. 5) and Comparative Examples 3 and 4 (No. 3 and 4) using cement milk with a low water-cement ratio to which a fluidizing agent was added, normal Compared to Comparative Examples 1 and 2 (No. 1 and 2) using cement milk with a water-cement ratio, the amount of sludge discharged was small.

Specifically, for example, in Example 1 (No. 5), the amount of sludge discharged was about 32% less than in Comparative Example 1 (No. 1). From the above, it was confirmed that the amount of sludge discharged could be reduced by using cement milk with a low water-cement ratio.

(Comparison of average strength and coefficient of variation of soil improvement bodies of Example 1 and Comparative Examples 1 to 4)
Next, a uniaxial compressive strength test was performed on the soil improvement bodies according to Example 1 and Comparative Examples 1 to 4, and the uniaxial compressive strength of each soil improvement body and the coefficient of variation, which is an evaluation index for the dispersion of the uniaxial compressive strength, were calculated. sought each.

The results are shown in FIGS. 5(A) and 5(B). 5(A) and 5(B), No. on the vertical axis. 5 is Example 1, No. 1 to 4 represent Comparative Examples 1 to 4, respectively. The horizontal axis of FIG. 5(A) represents the uniaxial compressive strength (kN/m ³ ), and the horizontal axis of FIG. 5(B) represents the coefficient of variation.

As shown in FIG. 5(A), for example, in the soil improvement bodies according to Comparative Examples 1 and 2 (No. 1 and 2) created under the same conditions, the unconfined compressive strength (kN/m ³ ) is about 2500 kN/m ² difference (variation) occurred. Similarly, in the soil improvement bodies according to Comparative Examples 3 and 4 (No. 3 and 4) created under the same conditions, a difference (variation) of about 2000 kN/m ² occurred in the unconfined compressive strength (kN/m ³ ). .

Specifically, as shown in FIG. 5(B), Comparative Examples 1 to 4 ( In Nos. 1 to 4), the coefficient of variation was about 30%. On the other hand, in Example 1 (No. 5) in which the number of rotations N of the rod in the second construction of the soil improvement body was greater than the number of rotations M of the rod in the first construction, the coefficient of variation was about 20%.

From the above, by increasing the rotation number N of the rod in the second construction of the soil improvement body more than the rotation number M of the rod in the first construction, the coefficient of variation of the uniaxial compressive strength of the soil improvement body, that is, the variation in strength It was confirmed that it can be made smaller.

10 ground 12 rod 16 soil improvement body Q cement milk

Claims (3)

The rod inserted into the ground is pulled up while being rotated so that the number of rotations for a predetermined amount of pulling up becomes a predetermined number of rotations, and the cement milk with a low water-cement ratio is injected from the rod at high pressure to separate the cement milk and the ground ground. Stir and mix to create the first ground improvement body,
The rod is pulled down into the soil improvement body while rotating so that the number of rotations for a predetermined pull-down amount that is the same as the predetermined pulling amount is greater than the predetermined number of rotations, or the rod is reinserted into the soil improvement body. Then, the rod is pulled up while being rotated so that the number of rotations for the predetermined amount of pulling is greater than the predetermined number of rotations, and the cement milk is jetted from the rod at high pressure, thereby stirring and mixing the cement milk and the ground ground. and create the second soil improvement body,
High-pressure injection stirring method. 2. The number of rotations with respect to the predetermined amount of pull-down or the predetermined amount of pull-up of the rod in the second formation is 1.5 times or more and 3.0 times or less of the predetermined number of rotations, according to claim 1 High-pressure injection stirring method. 3. The high-pressure injection stirring method according to claim 1 or 2, wherein the cement milk has a water-cement ratio in the range of 0.7 or more and 1.0 or less, and a fluidizing agent is added to the cement milk. .

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