JP6941556B2 - Liquefaction countermeasure method - Google Patents

Description

The present invention relates to a liquefaction countermeasure method.

Conventionally, as measures against liquefaction of the ground, a method of improving the ground by a power blender method, a high-pressure injection method by vertical boring, a chemical solution injection method, or the like has been used. In addition, as a method of reinforcing the ground below the existing structure, a ground improvement part is created around the boring hole while boring the ground almost horizontally with respect to the ground below the existing structure, and the ground improvement part is vertically crossed. A method has been proposed in which the ground is provided so as to surround the ground to be reinforced (see, for example, Patent Document 1).

Japanese Patent No. 3714395

In recent years, liquefaction countermeasures have been required even for grounds having a depth and particle size that were unthinkable in the past. However, the power blender method could not be applied to the deep ground. In addition, the high-pressure injection method and the chemical injection method by vertical boring require a large number of constructions, and if there is a non-liquefied layer in between, there is a lot of waste and it is not economical. Further, in the chemical solution injection method, there is a problem that the chemical solution does not reach when the cohesive soil layer is present in the liquefied layer or when alternating layers are present.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to efficiently improve only the liquefied layer of the supporting ground of the above-ground structure by using the freezing method. It is to provide a liquefaction countermeasure method.

In order to achieve the above-mentioned object, the present invention comprises a step a of starting a drilling rod from the ground to drill a curved boring hole toward the liquefaction layer of the supporting ground of the ground structure, and the liquefaction layer. A step b of further drilling a curved boring hole so as to pass through the inside in a substantially horizontal direction, a freezing tube is arranged in the curved boring hole in the liquefaction layer, and a frozen refrigerant is circulated in the freezing tube. A liquid characterized by comprising a step c of forming a frozen beam, and repeating the steps a and b so that the curved boring holes are drilled at predetermined intervals in the liquefaction layer. It is a countermeasure against liquefaction.

In the present invention, a curved boring hole is drilled so as to reach the liquefaction layer from the ground and pass through the liquefaction layer in a substantially horizontal direction, and a freezing tube is arranged in the curved boring hole in the liquefaction layer. , A frozen beam can be formed only in the liquefied layer. If the freezing method is used, the ground can be reliably improved even when there are cohesive soil layers or alternating layers to which the chemical injection method is difficult to apply. In addition, by using a frozen beam temporarily and melting it when it is no longer needed, it can be easily returned to the original ground, so it can be applied to liquefaction countermeasures for a limited time.

The above-ground structure is, for example, embankment, railway embankment, road embankment, embankment, revetment, or viaduct.
When the above-ground structure is a linear structure as described above, a frozen beam can be efficiently formed by drilling a boring hole along the extension direction of the linear structure.

It is desirable to install the first temperature measuring tube in the direction along the curved boring hole so as to pass between the groups of freezing tubes.
Further, a second temperature measuring tube may be installed in the vertical direction so as to pass between the groups of the freezing tubes.
If the temperature of the ground is measured by installing the first temperature measuring tube and / and the second temperature measuring tube, the freezing state of the liquefied layer can be appropriately grasped in the step c.

When installing the first temperature measuring tube, after completion of the freeze beam, based on the temperature measurement result by the first temperature measuring tube, it is desirable to control the operation of the freezing tube.
Further, when installing the second temperature measuring tube, it is desirable to control the operation of the freezing tube based on the temperature measurement result by the second temperature measuring tube after the completion of the freezing beam.
In this way, if the operation of the freezing tube is controlled based on the temperature measurement results of the first temperature measuring tube and the second temperature measuring tube, it is possible to prevent the freezing beam from thawing and frost heaving, and freezing. The possibility that expansion will affect the structure can be reduced.

According to the present invention, it is possible to provide a liquefaction countermeasure method capable of efficiently improving only the liquefaction layer of the supporting ground of the above-ground structure by using the freezing method.

The figure which shows the process of drilling a curved boring hole 11. The figure which shows the process of arranging the freezing tube 13 in a curved boring hole 11. The figure which shows the process of forming a frozen beam 23 Diagram showing changes in underground temperature The figure which shows the example which circulates the frozen refrigerant 21 only in the freezing pipe 13 of both side part of the embankment 3. The figure which shows the example which maintains the frozen beam 23 together with a heat pipe. The figure which shows the example which frozen a part of the liquefaction layer 5. The figure which shows the example which formed the grid-like frozen beam 39 in the liquefaction layer 5.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a step of drilling a curved boring hole 11. FIG. 1A is a diagram showing a step of drilling a curved boring hole 11 from the ground toward the liquefaction layer 5. 1 (b) and 1 (c) are views showing a step of drilling a curved boring hole 11 in the liquefaction layer 5. FIG. 1 (c) is a cross-sectional view taken along the line AA shown in FIG. 1 (b).

As shown in FIG. 1, an embankment 3 which is a ground structure is installed on the ground 1. A liquefaction layer 5 exists on the supporting ground of the embankment 3. The position of the liquefaction layer 5 in the ground 1 is grasped in advance by a boring survey. A boring machine 7 for driving the drilling rod 9 is arranged on the ground 1 on the extension line of the embankment 3.

In the step shown in FIG. 1 (a), the drilling rod 9 is started from the ground by using the boring machine 7, and the boring hole 11 is bent toward the liquefaction layer 5 of the ground 1 which is the supporting ground of the embankment 3. Drill holes.

In the step shown in FIG. 1B, the curved boring hole 11 is further drilled so as to pass through the liquefaction layer 5 in a substantially horizontal direction. The curved boring hole 11 is drilled in the extension direction of the embankment 3. The curved boring hole 11 is drilled so as to pass through the freezing pipe installation range 15 set in the liquefaction layer 5 below the embankment 3.

In the step shown in FIG. 1, the step shown in FIG. 1 (a) and the step shown in FIG. 1 (b) are repeated to form a curved boring hole 11 in the liquefaction layer 5 as shown in FIG. 1 (c). Holes are drilled at predetermined intervals 17.

Note that FIG. 1C shows an example in which the curved boring holes 11 are drilled at regular intervals 17, but the drilling intervals 17 are not limited to constant. The drilling interval of the curved boring hole 11 is appropriately set according to the conditions of the liquefaction layer 5, for example, the portion that is expected to be hard to freeze is made dense.

Further, FIG. 1C shows an example in which the curved boring holes 11 are drilled in one step at intervals 17 in the horizontal direction, but the number of drilling steps of the curved boring holes 11 is not limited to one. For example, when the liquefaction layer 5 is thick, the curved boring holes 11 are drilled at intervals in the vertical direction, and a group of curved boring holes 11 as shown in FIG. 1C is arranged in two or more stages above and below. You may.

FIG. 2 is a diagram showing a step of arranging the freezing tube 13 in the curved boring hole 11. FIG. 2B is a cross-sectional view taken along the line BB shown in FIG. 2A. In the step shown in FIG. 2, as shown in FIG. 2A, the freezing tube 13 is arranged in the curved boring hole 11 in the liquefaction layer 5. The freezing pipe 13 is installed in the freezing pipe installation range 15.

Then, as shown in FIG. 2B, the first temperature measuring tube 19a is installed in the direction along the curved boring hole 11, that is, in the horizontal direction so as to pass between the groups of the freezing tubes 13. In addition, a second temperature measuring tube 19b is installed in the vertical direction so as to pass between the groups of the freezing tubes 13. A temperature measuring meter such as an optical fiber sensor is arranged in the temperature measuring tube 19 (hereinafter, the temperature measuring tubes 19a and 19b are collectively referred to as the temperature measuring tube 19).

Note that FIG. 2B shows an example in which the temperature measuring tube 19 is installed near the center of the group of the freezing tubes 13, but the installation position of the temperature measuring tube 19 is not limited to this.

FIG. 3 is a diagram showing a process of forming the frozen beam 23. FIG. 4 is a diagram showing changes in underground temperature. The vertical axis of FIG. 4 is the underground temperature at the position of the temperature measuring tube 19, and the horizontal axis is time.

In the step shown in FIG. 3, the frozen refrigerant 21 is circulated in the frozen pipe 13 by using a feed header pipe, a return header pipe, or the like (not shown) for supplying and recovering the frozen refrigerant 21. In the step shown in FIG. 3, the frozen refrigerant 21 is circulated in all the freezing pipes 13 to form the frozen beam 23 having a thickness substantially equal to that of the liquefaction layer 5.

In the step shown in FIG. 3, the underground temperature of the ground 1 is measured at a temperature measuring point set every 1 m, for example, by using a temperature measuring meter (not shown) arranged on the temperature measuring tube 19a and the temperature measuring tube 19b. Then, the frozen state of the frozen beam 23 is determined using the underground temperature at a specific depth or the average underground temperature at all depths.

In the example shown in FIG. 4, for example, −5 ° C. is set as a control value that serves as a reference for stopping the circulation of the frozen refrigerant 21. This is because the formation of frozen soil is promoted at low temperatures, and not only the liquefaction layer 5 but also the nearby clay layer freezes, increasing the risk of frost heaving. Further, −0.5 ° C. is set as a control value that serves as a reference for starting the recirculation of the frozen refrigerant 21. This is because it has been confirmed by experiments that the strength is maintained as long as the frozen soil temperature rises to near 0 ° C. as long as it is not thawed.

In the process shown in FIG. 3, when the circulation of the frozen refrigerant 21 to all the freezing tubes 13 is started as a normal operation, as shown by the solid line 31 in FIG. 4, the temperature measuring tube 19 is in the ground with the passage of time. The temperature drops. After the start of the normal operation, when the underground temperature at the predetermined position measured by the temperature measuring tube 19 falls below −5 ° C., it is determined that the formation of the frozen beam 23 is completed, and the normal operation implementation period 25 ends.

As shown in FIG. 4, after the formation of the frozen beam 23 is completed and the normal operation period 25 is completed, the frozen refrigerant in the freezing pipe 13 is not allowed to grow and thaw more than necessary. The transition to the intermittent operation implementation period 27 in which the circulation and stop of 21 are repeated. The measurement of the underground temperature using the temperature measuring tube 19 is continued during the intermittent operation implementation period 27.

During the intermittent operation implementation period 27, the operation of the freezing pipe 13 is controlled based on the measurement result of the underground temperature by the temperature measuring pipe 19. For example, when the underground temperature measured by the temperature measuring tube 19 becomes −5 ° C. or lower, which is a control value that serves as a reference for stopping the circulation, the circulation of the frozen refrigerant to the freezing tube 13 is stopped. Further, when the underground temperature measured by the temperature measuring tube 19 exceeds the control value of −0.5 ° C., which is a reference for starting recirculation, the circulation of the frozen refrigerant to the freezing tube 13 is restarted.

During the intermittent operation implementation period 27, the underground temperature is maintained in an appropriate range by repeating the stop period 27a and the operation period 27b of the frozen refrigerant, and the freezing beam 23 is prevented from being thawed or excessively formed. Maintain a moderate thickness. The number of repetitions of the stop period 27a and the operation period 27b is not limited to two.

When the frozen beam 23 is temporarily installed, the intermittent operation implementation period 27 is ended at an appropriate time before and after the frozen beam 23 is no longer needed, and the natural melting period 29 is started. In the natural thawing period 29, the circulation of the frozen refrigerant 21 to the freezing pipe 13 is terminated. When the circulation of the frozen refrigerant 21 is completed, the frozen beam 23 is gradually thawed and the ground 1 returns to the original state.

As described above, according to the present embodiment, the curved boring hole 11 is drilled so as to reach the liquefaction layer 5 from the ground and pass through the liquefaction layer 5 in a substantially horizontal direction, and the inside of the liquefaction layer 5 is formed. By arranging the freezing pipe 13 in the curved boring hole 11, the frozen beam 23 can be formed only in the liquefaction layer 5. If the freezing method is used, the ground can be reliably improved even when there are cohesive soil layers or alternating layers to which the chemical injection method is difficult to apply.

In the present embodiment, the frozen beam 23 is efficiently provided so that unnecessary ground improvement points are not generated by drilling the curved boring hole 11 along the extension direction of the embankment 3 which is a linear structure. Can be formed.

In the present embodiment, the first temperature measuring tube 19a is installed in the direction along the curved boring hole 11 and the second temperature measuring tube 19b is installed in the vertical direction so as to pass between the groups of the freezing tubes 13. By measuring the underground temperature, the freezing state of the liquefied layer 5 can be appropriately grasped when the frozen beam 23 is formed. Further, after the completion of the freezing beam 23, if the operation of the freezing tube 13 is controlled based on the temperature measurement results by the first temperature measuring tube 19a and the second temperature measuring tube 19b, the freezing beam 23 can be prevented from melting or freezing. It is possible to reduce the possibility that the above-ground structure such as the filling 3 will be affected by freezing and expansion.

In the present embodiment, the frozen beam 23 is temporarily used during the intermittent operation implementation period 27 shown in FIG. 4, and then the ground 1 is returned to the original state by shifting to the natural thawing period 29 and thawing the frozen beam 23. It can be easily returned. The frozen beam 23 can also be applied to liquefaction countermeasures for a limited time.

The present invention is not limited to the above-described embodiment. In the following examples, points different from the above-described embodiment will be described, and the same points will be omitted by adding the same reference numerals in figures and the like.

In the present embodiment, when the operation of the freezing pipe 13 is controlled based on the temperature measurement result by the temperature measuring pipe 19, the freezing refrigerant 21 is intermittently switched between circulation and stopping in all the freezing pipes 13. The operation was performed, but the control method is not limited to this.

FIG. 5 is a diagram showing an example in which the frozen refrigerant 21 is circulated only in the freezing pipes 13 on both sides of the embankment 3. In the example shown in FIG. 5, after the freezing beam 23 is completed, the frozen refrigerant 21 is circulated only in the freezing pipes 13 on both sides of the embankment 3, and the freezing refrigerant 21 is thinned out to end the circulation to the other freezing pipes 13. Drive. In the completed state of the frozen beam 23, the transfer of cold heat in the liquefaction layer 5 is better than in the unformed state. Therefore, if the frozen refrigerant 21 is circulated only in the freezing pipes 13 on both sides of the embankment 3, the frozen refrigerant 21 can be circulated. The entire frozen beam 23 can be maintained.

FIG. 6 is a diagram showing an example of maintaining the frozen beam 23 in combination with a heat pipe. FIG. 6A is a diagram showing an example in which the heat pipe 33 is installed in the vertical direction. In the figure shown in FIG. 6A, the heat pipe 33 is installed in the vertical direction. In the example shown in FIG. 8A, the frozen beam 23 is maintained by the intermittent operation (FIG. 4) and the thinning operation (FIG. 5) of the freezing pipe 13 in the summer, and the heat pipe 33 is used in the ground 1 in the subzero environment in the winter. Dissipate heat.

FIG. 6B is a diagram showing an example in which the heat pipe 35 is installed in the horizontal direction. In the example shown in FIG. 6B, the heat pipe 35 is horizontally installed in the liquefaction layer 5. Both ends of the heat pipe 35 are connected to a chamber 37 installed on the ground. In the example shown in FIG. 8 (b), the frozen beam 23 is maintained by the intermittent operation (FIG. 4) and the thinning operation (FIG. 5) of the freezing pipe 13 in the summer, and the cold heat in the chamber 37 is heated in the subzero environment in the winter. Supply to pipe 35.

In the example shown in FIG. 6, the freezing pipe 13 and the heat pipe are used in combination, but instead of using the heat pipe, a pipe may be installed in the ground 1 and cold water or liquid nitrogen may be injected into the pipe in winter. Intermittent operation (FIG. 4) and thinning operation (FIG. 5) of the freezing pipe 13 are performed in the summer, and in winter, the use of equipment for circulating the frozen refrigerant 21 is completely stopped and the means as described above. By using the above, the frozen beam 23 can be maintained with a small amount of electric power.

In the above-described embodiment, the entire surface of the liquefaction layer 5 is frozen to form the frozen beam 23, but the entire surface of the liquefaction layer 5 may not be frozen. FIG. 7 is a diagram showing an example in which a part of the liquefaction layer 5 is frozen. In the example shown in FIG. 7, the frozen beam 23a is formed in a part of the liquefaction layer 5 of the supporting ground of the embankment 3. Even if the liquefaction layer 5 is not completely frozen, it may not be liquefied if a part of the liquefaction layer 5 is frozen.

FIG. 8 is a diagram showing an example in which a grid-like frozen beam 39 is formed on the liquefaction layer 5. FIG. 8A is a diagram showing a state in which the freezing tubes 13a and 13b are arranged, and FIG. 8B is a diagram showing a state in which the lattice-shaped freezing beam 39 is formed.

Also in the example shown in FIG. 8, similarly to the above-described embodiment, a curved boring hole is drilled toward the liquefaction layer 5 of the supporting ground of the embankment 3 and passes through the liquefaction layer 5 in a substantially horizontal direction. As shown in FIG. 8A, the curved boring hole 11a is drilled in the longitudinal direction of the embankment 3 and the curved boring hole 11b is drilled in the lateral direction. Then, the freezing tube 13a is arranged in the curved boring hole 11a, and the freezing tube 13b is arranged in the curved boring hole 11b.

After that, the frozen refrigerant is circulated through the freezing pipe 13a and the freezing pipe 13b, and as shown in FIG. The frozen beam 39 is formed. When forming the lattice-shaped freezing beam 39, a temperature measuring tube is installed in the vertical direction to freeze the entire layer thickness of the liquefaction layer 5. When frozen in a grid pattern, liquefaction does not occur in the portion surrounded by the grid-shaped freezing beam 39. When the lattice-shaped frozen beam 39 is used, the amount of frozen soil formed can be reduced as compared with the case where the entire surface of the liquefaction layer 5 is frozen.

In FIGS. 1 to 8, the embankment 3 is shown as an example of the above-ground structure, but the above-ground structure is not limited to the embankment 3. The above-ground structure may be, for example, a linear structure such as a railway embankment, a road embankment, an embankment, a revetment, or a viaduct, or a non-linear structure such as a circular low-temperature tank. Further, the above-ground structure may be a new structure or an existing structure. In the examples shown in FIGS. 1 to 7, the freezing pipe 13 is installed in the extension direction, that is, the longitudinal direction of the linear above-ground structure, but the freezing pipe may be installed in the lateral direction to form the frozen beam.

In the present embodiment, as shown in FIG. 4, a natural thawing period 29 is provided and the frozen beam 23 is used as a temporary liquefaction countermeasure for a limited period, but the natural thawing period 29 is not provided and the main liquefaction is performed. It may be used as a countermeasure.

Although preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person skilled in the art can come up with various modified examples or modified examples within the scope of the technical idea disclosed in the present application, and these also naturally belong to the technical scope of the present invention. Understood.

1 ………… Ground 3 ………… Fill 5 ………… Liquefied layer 7 ………… Boring machine 9 ………… Drilling rods 11, 11a, 11b ………… Bent boring holes 13, 13a, 13b ………… Freezing Pipe 15 ………… Freezing pipe installation range 17 ………… Interval 19, 19a, 19b ………… Temperature measuring pipe 21 ………… Frozen refrigerant 23, 23a, 39a, 39b ………… Frozen beam 25 ………… Normal operation Period 27 ………… Intermittent operation period 27a ………… Stop period 27b ………… Operation period 29 ………… Spontaneous melting period 31 ………… Solid line 33, 35 ………… Heat pipe 37 ………… Chamber 39 ………… Lattice frozen beam

Claims (6)

Step a of starting a drilling rod from the ground and drilling a curved boring hole toward the liquefied layer of the supporting ground of the ground structure.
A step b of further drilling a curved boring hole so as to pass through the liquefaction layer in a substantially horizontal direction.
A step c of arranging a freezing pipe in the curved boring hole in the liquefaction layer and circulating a frozen refrigerant through the freezing pipe to form a frozen beam.
Equipped with
A liquefaction countermeasure method, wherein the step a and the step b are repeated so that the curved boring holes are drilled at predetermined intervals in the liquefaction layer. The liquefaction countermeasure method according to claim 1, wherein the above-ground structure is any one of embankment, railway embankment, road embankment, embankment, revetment, and viaduct. The liquefaction countermeasure method according to claim 1 or 2, wherein the first temperature measuring tube is installed in a direction along the curved boring hole so as to pass between the groups of freezing tubes. The liquefaction countermeasure method according to any one of claims 1 to 3, wherein a second temperature measuring tube is installed in the vertical direction so as to pass between the groups of freezing tubes. Wherein after completion of the freezing beam, the first based on the temperature measurement result by the temperature measuring tube, liquefaction countermeasure method according to claim 3 Symbol mounting and controlling the operation of the freezing tube. Wherein after completion of the freezing beam, before SL on the basis of the temperature measurement result by the second temperature measuring tube,請Motomeko 4 liquefaction countermeasure method according you and controls the operation of the freezing tube.

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