JP7256156B2 - Soil improvement method - Google Patents

Description

The present invention relates to a ground improvement method.

Soil improvement means capable of forming a soil improvement body having excellent uniformity in improved diameter have been known. For example, in Patent Document 1, a high-pressure injection stirrer for soil improvement having a rod equipped with an upper injection nozzle and a lower injection nozzle arranged at intervals in the vertical direction at the tip portion, wherein the upper injection nozzle and the distance between the lower injection nozzle is equal to an integer multiple of one or more times the lifting step length of the rod.

In addition, Patent Document 1 discloses a ground improvement method using the above-described high-pressure injection stirrer for ground improvement, in which the cutting fluid is injected from the upper injection nozzle, and the solidifying material slurry is injected from the lower injection nozzle. A ground improvement method characterized by spraying is described.

In ground improvement work, if the strength of the ground to be improved (e.g., shear strength, N value, etc.) varies depending on the depth (degree of depth), solidification material slurry in ground improvement means (e.g., high-pressure jet stirrer) When the injection pressure (unit: MPa) and the injection amount per unit time (unit: liter / minute) are maintained constant, for example, the ground strength increases vertically upward. , the diameter of the ground improvement decreases as the injection nozzle rises. As a result, there is a problem that the size of the improvement diameter of the ground in the vertical direction (depth direction) does not become constant (in other words, it does not become the design improvement diameter).

In view of such problems, in Patent Document 2, in advance, at various strengths of the ground, the product of the injection pressure and the injection amount per unit time of the solidification material slurry injected from the soil improvement means, and the soil improvement diameter In the actual ground improvement work, using the relationship between the above product and the ground improvement diameter, when the strength of the ground to be improved changes, the planned design improvement diameter will be achieved. , by changing the value of the above product and injecting the solidifying material slurry at the injection pressure and the injection amount per unit time corresponding to the changed product, the size of the ground improvement diameter can be adjusted to the desired value. is disclosed.

JP 2017-172279 A Patent No. 6391876

However, the multi-pipe construction method has the problem that it is expensive and the sludge disposal process is troublesome. Therefore, it has been desired to improve the ground using a low-cost and simple construction method.

An object of the present invention is to provide a novel method that enables ground improvement to be performed easily and inexpensively.

In order to achieve the above object, the present invention
(1) A method for improving ground having a hard layer and a soft layer with different strengths in the depth direction,
The hard layer has three channels of a compressed air channel, a cutting fluid channel and a solidifying material slurry channel, and at least one of the cutting fluid jet and the solidifying material slurry jet is surrounded by compressed air. A step of improving with a stirring method to form a first improved body;
A step of improving the soft layer by a single tube high pressure jet stirring method to form a second improved body,
The first improved body and the second improved body are continuously arranged along the depth direction,
The triple pipe high pressure injection stirring method and the single pipe high pressure injection stirring method are performed using the same triple pipe high pressure injection stirring device. By adjusting the improvement diameter of the first improvement body and the second improvement body, characterized by controlling the ground improvement method.
(2) The ground improvement method according to (1), characterized in that the improved diameter of the first improved body and the improved diameter of the second improved body are substantially the same.

In the present invention, "adjusting the air" means controlling the air to such an extent that sand and soil in the ground do not enter the device during ground improvement work. The term "substantially the same" as used in the present invention means that errors due to equipment and construction methods are included in the complete sameness.

According to the present invention, the triple-pipe high-pressure injection stirring method and the single-pipe high-pressure injection-stirring method are performed using the same triple-pipe high-pressure injection-stirring device, and the single-pipe high-pressure injection stirring method is performed by the triple-pipe high-pressure injection stirring device. The air is adjusted and replaced, so that the single pipe construction method is used in addition to the triple pipe construction method. Therefore, ground improvement can be performed at a low cost, and the work of sludge disposal can be reduced.

It is a soil column diagram in the depth direction of the ground in embodiment.

(First embodiment)
In general, the improved diameter of the multiple pipe high pressure injection stirring method (hereinafter sometimes referred to as "multiple pipe construction method") is about Φ: 1.2 to 5.0 m, and the single pipe high pressure injection stirring method (hereinafter, "single pipe construction method" ) is about Φ: 0.5 to 2.2 m. Therefore, in the ground improvement plan, in order to put the multiple pipe construction method and the single pipe construction method in the same process, it is necessary to control the improvement diameter of the multiple pipe construction method and the improvement diameter of the single pipe construction method to be equal. There is a need.

On the other hand, when comparing the improved diameter of the multi-pipe construction method and the improved diameter of the single-pipe construction method, the multi-pipe construction method encloses the solidification agent slurry jet with compressed air, and the Since the ground cutting distance can be increased, the improved diameter can be increased. Therefore, in this embodiment, in the ground improvement plan, the multiple pipe construction method is used for hard ground, and the single pipe construction method is used for soft ground, so that the improvement diameters of both grounds are equal. .

FIG. 1 is a soil histogram showing an example of the hardness of a stratum in the depth direction from the ground surface to the inside of the ground. In this embodiment, the ground is composed of soft layers N1, N2, hard layer H1, soft layer N3, and hard layer H2 in this order from the surface. The soft layer N1 is, for example, an embankment, and the soft layer N2 is, for example, cohesive soil. The hard layer H1 is, for example, a sand layer, and the soft layer N3 is, for example, cohesive soil. The hard layer H2 is a mixed layer (gravel layer) of sand and stone. In this embodiment, the N value of the soft layers N1 to N3 is about 0, the N value of the hard layer H1 is 30, and the N value of the hard layer H2 is 50.

Such ground improvement can be carried out as follows. First, using a double-pipe high-pressure jet stirring device (hereinafter sometimes referred to as "double-pipe device"), the rod of the device is penetrated into the ground shown in FIG. The hole is drilled up to the hard layer H2. Here, air and solidifying material slurry are injected at an ultrahigh pressure to form an improved body having an improved diameter M1 (eg, 1.6 to 2.2 m). The rod of the double-tube device is composed of an inner tube and an outer tube. Generally, the solidifying material slurry flows through the inner tube and the compressed air flows through the outer tube, but the reverse is also possible.

Next, the rod of the device is pulled up to reach the lower end of the hard layer H1, and is pulled up to the upper end of the hard layer H1 while injecting air and solidifying material slurry at an ultrahigh pressure, thereby similarly forming an improved body having an improved diameter M1. do.

The relationship between the injection pressure of the solidifying material slurry of the double-pipe device, the injection amount per unit time, the improvement time, and the improvement diameters of the hard layers H1 and H2 is derived in advance by carrying out tests.

Next, pull out the double-tube device to the ground surface, replace the double-tube monitor at the tip of the rod with a single-tube monitor, and make a pseudo single-tube high-pressure jet stirring device (hereinafter sometimes referred to as "single-tube device"). . Then, the rod of the device is penetrated into the ground shown in FIG. 1 and drilled to the lower end of the soft layer N3. Then, an ultrahigh-pressure slurry is injected to form an improved body having an improved diameter M1.

Next, the single tube device is pulled up to reach the lower end of the soft layer N2 and the lower end of N1 in sequence, and is pulled up to the upper end of these layers while injecting ultrahigh pressure slurry to form an improved body with an improved diameter M1. .

The relationship between the injection pressure of the solidifying material slurry of the single-pipe device, the injection amount per unit time, the improvement time, and the improvement diameters of the soft layers N1, N2, and N3 is derived by carrying out tests in advance.

Through the steps described above, the ground shown in FIG. 1 can be formed with the improved body having the improved diameter M1, and the ground can be improved.

When replacing the double-tube monitor at the tip of the rod with a single-tube monitor, the air flow path at the joint between the newly installed single-tube monitor and the double-tube monitor (in the case of triple-tube, the air flow path and cutting fluid The double tube monitor can be used as a pseudo single tube monitor by closing the channel) with a special annular packing or the like and allowing only the solidifying material slurry channel to flow. The rod of the triple tube device consists of an inner tube, an intermediate tube, and an outer tube. In general, the solidifying material slurry flows through the inner tube, the compressed air flows through the intermediate tube, and the cutting fluid flows through the outer tube. ing.

As is clear from the above embodiment, the multi-pipe construction method is suitable when the hard layer has an N value of 30 or more, particularly 50 or more.

According to this embodiment, conventionally, two construction methods, a single pipe construction method and a multiple pipe construction method, were required. target.

(Second embodiment)
In the first embodiment, the ground improvement shown in FIG. 1 was performed using a double pipe device or a triple pipe device and a single pipe device, but in this embodiment, only the double pipe device or the triple pipe device is used. Improve the ground.

As described above, the rod of the double-pipe device consists of an inner tube and an outer tube, and generally, the solidifying material slurry flows through the inner tube and the compressed air flows through the outer tube. In addition, the rod of the triple tube device consists of an inner tube, a middle tube, and an outer tube. In general, the solidifying material slurry flows through the inner tube, the compressed air flows through the middle tube, and the cutting fluid flows through the outer tube. ing. However, the solidifying material slurry may flow through the inner tube, the cutting fluid may flow through the intermediate tube, and the compressed air may flow through the outer tube. Alternatively, cutting fluid may flow through the inner tube, compressed air may flow through the intermediate tube, and solidifying material slurry may flow through the outer tube.

First, using a double-pipe system or triple-pipe system, the rod of the device is penetrated into the ground shown in FIG. 1, and drilling is performed up to the hard layer H2 while ensuring a clearance for sludge discharge. Here, air and solidifying material slurry are injected at an ultrahigh pressure to form an improved body having an improved diameter M2 (eg, 1.4 to 1.8 m).

Next, the rod of the device is pulled up to reach the lower end of the hard layer H1. In the case of a pipe, while injecting compressed air at about 0.5 to 1.5 MPa and cutting fluid and solidifying material slurry at an ultrahigh pressure, the hard layer H1 is pulled up to the upper end to form an improved body with an improved diameter M2. .

The relationship between the injection pressure of the solidification material slurry in the double-pipe device and the triple-pipe device, the injection amount per unit time, the improvement time, and the improved diameter of the hard layers H1 and H2 was derived by carrying out tests in advance. Keep

Next, the air in the double-pipe device is adjusted to make the double-pipe device a pseudo single-pipe device, and the single-pipe construction method is performed using the double-pipe device. Alternatively, by adjusting the air in the triple pipe device and stopping the supply of cutting fluid, the triple pipe device is used as a pseudo single pipe device, and the single pipe construction method is performed using the triple pipe device.

Adjust the air pressure by adjusting the compressor of the double-tube or triple-tube system so that at least the air pressure that prevents the inflow of muddy water from the air nozzle is secured. Since the mud water pressure is not constant depending on the depth of the ground being improved, air is discharged while maintaining the air pressure so that the mud water does not flow into the rod through the air nozzle. Then, in that state, the rod of the device is made to reach the lower end of the soft layer N3. Then, an ultrahigh-pressure slurry is injected to form an improved body having an improved diameter M2.

Next, the quasi-single tube device is pulled up to reach the lower end of the soft layer N2 and the lower end of N1 in sequence, and is pulled up to the upper end of these layers while injecting the ultrahigh pressure slurry to form an improved body with an improved diameter M2. .

In addition, the relationship between the injection pressure of the solidifying material slurry of the pseudo single pipe device, the injection amount per unit time, the improvement time, and the improvement diameter of the soft layers N1, N2, and N3 is derived by conducting a test in advance. .

Through the steps described above, the ground shown in FIG. 1 can be formed with the improved body having the improved diameter M2, and the ground can be improved.

Further, in this embodiment, substantially only the double-tube device or the triple-tube device is used, and the single-tube device is not substantially used. That is, it is possible to improve the ground with the complicated layer structure shown in FIG. 1 using only a single device, and to reduce the time and cost required for the improvement.

Although several embodiments of the invention have been described above, these embodiments are provided by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

For example, in the above embodiment, the improved diameters of the soft layers N1, N2, N3 and the hard layers H1, H2 are substantially the same, but the improved diameters of the soft layers and the hard layers can be different. Specifically, the modified diameter of the soft layer can be increased and the modified diameter of the hard layer can be decreased, and vice versa.

Further, it is also possible to increase the improved diameter of any of the soft layers and hard layers, for example, the soft layers N1, N2 and hard layer H1, and reduce the improved diameter of the soft layer N3 and hard layer H2.

Claims (2)

A method for improving ground having a hard layer and a soft layer with different strengths in the depth direction,
The hard layer has three channels of a compressed air channel, a cutting fluid channel and a solidifying material slurry channel, and at least one of the cutting fluid jet and the solidifying material slurry jet is surrounded by compressed air. A step of improving with a stirring method to form a first improved body;
A step of improving the soft layer by a single tube high pressure jet stirring method to form a second improved body,
The first improved body and the second improved body are continuously arranged along the depth direction,
The triple pipe high pressure injection stirring method and the single pipe high pressure injection stirring method are performed using the same triple pipe high pressure injection stirring device. A ground improvement method, characterized in that the improvement diameters of the first improved body and the second improved body are controlled by adjusting the. The ground improvement method according to claim 1, wherein the improved diameter of the first improved body and the improved diameter of the second improved body are substantially the same.

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