JPH07268856A - Freezing method wherein break of freezing pipe can be prevented - Google Patents

Abstract

PURPOSE:To prevent freezing pipe from being broken due to tensile forces of frozen soil caused by freeze-expansion of the ground, in a freezing method wherein refrigerant is passed through a freezing pipe buried under the ground to form frozen soil. CONSTITUTION:In a freezing method wherein refrigerant is passed through a freezing pipe 1 buried under the ground to form a frozen soil wall, in an appropriate period while a frozen soil is being formed, a heating medium of high temperature, in place of refrigerant, is passed, temporarily, proper number of times through the pipe 1, whereby the frozen interface between the outer periphery of the pipe 1 and frozen soil 3 is melted, so that a tensile force, which is caused by freeze-expansion of the frozen soil 3 due to the formation thereof and which acts on the pipe 1 in the longitudinal direction, is removed, and thereafter refrigerant is passed through the pipe 1 to form a frozen soil in succession.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a freezing method used in a ground improvement method, which can prevent a freezing pipe buried in the ground from being damaged by a tensile force due to expansion of frozen soil. .

[0002]

2. Description of the Related Art The freezing method is a method in which a refrigerant such as calcium chloride solution is circulated at a low temperature of approximately -20 ° C. or less in a steel freezing pipe buried in the ground at regular intervals to freeze each freezing pipe. This is a method of creating a frozen soil wall with a specified thickness by advancing the creation of frozen soil while creating cylindrical frozen soil from the periphery of the pipe and connecting the frozen soil around each frozen pipe as a whole. Generally, a unit length of 5.5 m, for example, is buried while being connected by welding.

When frozen soil is formed around the freezing tube, the frozen soil expands and a tensile force is exerted in the longitudinal direction of the freezing tube and a compressive force is exerted in the diameter direction of the freezing tube. Works. In particular, excessive tensile force applied in the longitudinal direction may cause cutting damage to the freezing pipe, but this cutting damage often occurs at the joints of the freezing pipe, and when the cutting damage occurs, the refrigerant inside the freezing pipe will enter the ground. Leakage and outflow may cause adverse effects such as melting and eroding frozen soil and degrading the ground, hindering normal frozen soil formation, and cutting damage of the freezing pipe is more likely to occur as the depth increases.

As a prominent example thereof, as shown in FIGS. 3 and 4, there is a case where a block-shaped frozen soil 3 is formed by surrounding it with a freezing tube 1. In this case, the unfrozen soil portion 52 closed in the middle portion of the freezing pipe 1 has no escape area for the amount of freezing expansion due to the progress of freezing, so that the generated excessive internal pressure is applied to the surrounding frozen soil wall, and the structure is compared. 6 at a weak point
At the same time, the pulling force acts on the freezing tube 1 in the longitudinal direction of the freezing tube 1, causing cutting damage of the freezing tube 1.

In particular, as in the soil structure shown in FIG. 3, a silt layer 43 and a viscosity layer 44 are provided in the middle of the buried freezing pipe, and a buried soil layer 41 and a fine sand layer 42 are provided at the upper end of the freezing pipe 1. Similarly, when the sand layer 45 and the gravel layer 46 are present at the lower end, the buried soil layer 41, the fine sand layer 42, the sand layer 45, and the gravel layer 46 grow frozen soil faster than the silt layer 43 or the viscosity layer 44. It has been confirmed in the implementation work that it progresses, and as a result, the boundary surface 51 between the created frozen soil portion 3 and the unfrozen soil portion 5 has a recessed middle portion, and an upper end portion and a lower end portion as shown in FIG. Since the closed unfrozen soil portion 52 is formed in the central portion in a swelled shape, the degree of cutting damage to the freezing tube 1 is further increased.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional techniques, the present invention is a freezing method in which a refrigerant is circulated through a freezing pipe buried in the ground to create frozen soil. It is an object of the present invention to provide a freezing method capable of preventing the freezing tube from being cut and damaged by force.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and its constitution is a freezing method in which a refrigerant is circulated through a freezing pipe buried in the ground to form a frozen soil wall. In, at an appropriate time during the frozen soil formation, an appropriate number of times, the refrigerant in the freezing tube is temporarily changed to a high-temperature heat transfer medium and circulated, and the freezing surface of the freezing tube and the frozen surface are thawed, After removing the tensile force applied to the freezing tube in the longitudinal direction by freezing and expanding the frozen soil with the creation of the frozen soil, the refrigerant is passed through the freezing tube again to continue the creation of the frozen soil. To do.

[0008]

According to the method of the present invention, during the formation of frozen soil, the refrigerant in the freezing tube is temporarily changed to a high-temperature heat transfer fluid and circulated, and the freezing surface between the outer periphery of the freezing tube and the frozen soil is thawed to freeze the freezing tube. At this stage, since the pulling force applied to the freezing pipe in the longitudinal direction of the freezing pipe does not act directly, the freezing pipe is not damaged at all at this stage. Therefore, the subsequent frozen ground can be safely created.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of carrying out the method of the present invention will be described below with reference to the drawings. FIG. 1 is a vertical cross-sectional view showing a state where an example of the method of the present invention is being carried out, FIG. 2 is a plan view showing a state where an example of the method of the present invention is being carried out, and FIG. FIG. 4 is a plan view showing a state where the conventional method is carried out.

In FIGS. 1 and 2, 1 and 2 are the same as in FIGS. 3 and 4 described above, 1 is a freezing pipe, 2 is an inner pipe, and this inner pipe 2 only supplies a refrigerant in the conventional method. However, in the method of the present invention, a heat transfer liquid for temporarily thawing frozen soil is also supplied. Reference numeral 3 denotes a formed frozen soil portion, and reference numeral 31 is a thaw for releasing freezing and adhesion between the outer periphery of the freezing pipe 1 formed by supplying the heating medium liquid to the inner pipe 2 and circulating the heating medium liquid to the freezing pipe 1 and the frozen soil 3. Surface, 41-46
Is the same as that shown in FIG. 3, and is the application target ground structure whose effect is remarkable by the method of the present invention.

Thus, in the method of the present invention, in the freezing method, the refrigerant is circulated in the freezing tube 1 to form the frozen soil 3 around the freezing tube 1, and the calcium chloride solution flowing in the freezing tube 1 is formed. By temporarily increasing the temperature of the refrigerant represented by 1 to obtain a high-temperature heat transfer liquid of preferably 40 to 60 ° C. and circulating it for about 1 to 2 hours to thaw the frozen soil 3 around the freezing tube 1. , Forming a thawing surface 31 for releasing freezing and adhesion of the freezing tube 1 and the frozen soil 3.

By doing so, the freezing tube 1 can be freely shrunk and restored to its original shape without being bound by the frozen soil 3. That is, when the frozen soil 3 around the freezing tube 1 is formed, the frozen soil expands and a tensile force acts in the longitudinal direction of the freezing tube 1, and a compressive force acts in the diametrical direction of the freezing tube 1. In particular, an excessive tensile force applied in the longitudinal direction causes the freezing tube 1
However, the formation of the thawing surface 31 eliminates the influence of the external force of the frozen soil 3 on the freezing tube 1,
The freezing tube 1 freely contracts and returns to its original shape before the start of freezing, and then the refrigerant is circulated again in the freezing tube 1 to complete the predetermined ground freezing without causing cutting damage of the freezing tube 1. Can be done.

When the method of the present invention is applied,
That is, the time to switch to the heat transfer liquid is the initial stage 7 to 10 days after the start of the circulation of the refrigerant in the freezing tube 1, and about 3 weeks when the wall of the frozen soil 3 is formed by the row of the freezing tubes. In the case where the closed unfrozen soil portion 52 is formed due to the progress of the intermediate stage and the block-like frozen soil as in the present embodiment, it is suitable during the period from the start of the closing of the frozen soil 3 to the end of the closing. Therefore, it is extremely effective to circulate the heat transfer liquid through the freezing tube 1 at these times to form the thawing surface 31 a proper number of times.

[0014]

The present invention is as described above, and according to the freezing method of the present invention, it is possible to avoid a tensile force applied to a frozen pipe buried in the ground due to freezing expansion of the ground at the time of creating frozen soil. It is possible to create a safe and reliable frozen soil without damaging the freezing tube.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a state in which an example of a freezing method of the present invention is being carried out.

FIG. 2 is a plan view showing a state in which an example of the freezing method of the present invention is being carried out.

FIG. 3 is a vertical cross-sectional view of a state in which a conventional freezing method is being performed.

FIG. 4 is a plan view showing a state where a conventional freezing method is being performed.

[Explanation of symbols]

 1 Frozen tube 2 Inner tube 3 Frozen soil 31 Thaw surface for releasing freezing and adhesion of frozen tube and frozen soil 5 Unfrozen soil portion 51 Boundary between frozen soil portion and unfrozen soil portion 52 Blocked unfrozen soil portion in the center 6 Frozen soil portion Stress crack

Claims (1)

[Claims] 1. In a freezing method for creating a frozen soil wall by circulating a refrigerant in a frozen tube buried in the ground, the refrigerant in the frozen tube is temporarily heated to a high temperature at an appropriate time during the frozen soil creation. The heat transfer liquid is changed to a heat transfer liquid, and the frozen surface between the outer circumference of the freezing pipe and the frozen soil is thawed, and the tensile force applied to the freezing pipe in the longitudinal direction by freezing and expansion of the frozen soil along with the formation of the frozen soil is applied. After the removal, the freezing method is characterized in that the refrigerant is circulated through the freezing tube again to continue the creation of frozen soil.