JP2021080701A - Freezing construction method - Google Patents

Abstract

To provide a freezing construction method capable of freezing the ground even if it is difficult to apply a freezing construction method in accordance with the previous freezing construction method and requiring no large scale construction facilities.SOLUTION: A freezing construction method on the ground where ground water flows comprises: a step of controlling ground water speed or/and flowing direction with liquid nitrogen using a freezing pipe 1; a step of keeping a frozen state of the ground by supplying second refrigerant (for example, liquefied carbon dioxide) to the freezing pipe 1 using circulation means; and a step of supplying the second refrigerant to the freezing pipe 1 after a temperature in the freezing pipe 1 becomes higher than a triple point of the second refrigerant upon measuring the temperature in the freezing pipe 1, wherein a channel of the liquid nitrogen and a channel of the second refrigerant is a common one.SELECTED DRAWING: Figure 1

Description

The present invention relates to a freezing method for freezing the ground.

In the freezing method, it is well known that when groundwater is flowing in the ground, if the groundwater flow velocity is high, the ground does not freeze even if the ground is cooled, or it is difficult to freeze. This is because the groundwater flow supplies heat energy to the ground to be frozen, which slows down the cooling and freezing of the ground.
Here, in order for water to become ice, it must crystallize and align the molecules, but the faster the flow velocity of groundwater, the more difficult it becomes for the water molecules to align. In other words, even if the flow velocity is high, if cold heat that exceeds the cold heat required for water molecules to align is input, even the sea, rivers, and waterfalls will freeze.
In the conventional freezing method that uses brine with a cooling temperature of -20 ° C to -30 ° C or carbon dioxide with a cooling temperature of -30 ° C to -45 ° C as the refrigerant, as an empirical guideline, the flow velocity of groundwater before freezing is 1 to 2 m. / Day was the limit groundwater flow velocity for construction.

When constructing the freezing method, it may be required to reduce the flow velocity of the groundwater or stop the groundwater (make the flow velocity zero).
In order to reduce the flow velocity of groundwater or stop the groundwater, it is conceivable to create an impermeable wall (continuous underground wall, ground improvement). However, there is a problem that the number of construction processes increases due to the construction of the impermeable wall, the construction cost rises, and the construction period becomes long.
It is also conceivable to increase the number of freezing pipes and narrow the interval between the freezing pipes, but there is a problem that the construction cost rises by the amount of the additional freezing pipes and the construction period becomes long.
Further, it is conceivable to use a refrigerant having a low cooling temperature other than brine or carbon dioxide. For example, if liquid nitrogen at an extremely low temperature (boiling point at 1 atm-196 ° C.) is used as a refrigerant, it can be frozen if the flow velocity of groundwater is 10 m / day or less. However, since liquid nitrogen becomes disposable after cooling the ground (it is released to the atmosphere after vaporization), a large amount of liquid nitrogen is required for construction, and the construction equipment becomes large-scale, so long-term freezing work from the viewpoint of cost. The application to is unsuitable and unrealistic.

As another conventional technique, there is a technique for improving the frozen soil formation efficiency, reducing the power consumption, and reducing the cost (see, for example, Patent Document 1).
However, Patent Document 1 cannot meet the request for reducing the flow velocity of groundwater or stopping the groundwater, or the request for not requiring large-scale equipment.

Japanese Unexamined Patent Publication No. 9-41356

The present invention has been proposed in view of the above-mentioned problems of the prior art, and the ground is difficult to construct by the conventional freezing method (freezing method using brine or carbon dioxide as a refrigerant) (for example, the ground). It can be frozen even in the ground where there is a groundwater flow with a flow velocity exceeding the construction limit, when the ground heat is high, when the construction period is very short and / or when the construction area is wide, etc.), and it is large-scale. The purpose is to provide a freezing method that does not require construction equipment.

The freezing method of the present invention is a freezing method for the ground where a groundwater flow exists.
A step of controlling the flow velocity and / and flow direction of groundwater by liquid nitrogen (first refrigerant) using a freezing pipe (1), and
After the step of controlling, a step of supplying a second refrigerant (for example, liquefied carbon dioxide) to the freezing pipe (1) using a circulating operation means to maintain the ground in a frozen state.
The temperature inside the freezing pipe (1) is measured, and after the temperature inside the freezing pipe (1) becomes higher than the triple point of the second refrigerant, the second refrigerant (refrigerant other than liquid nitrogen: first It has a step of supplying a refrigerant different from the refrigerant) to the freezing pipe (1).
The flow path of the liquid nitrogen and the flow path of the second refrigerant are common (the same flow path).
The "triple point" indicates a state in which a gas phase, a liquid phase, and a solid phase of one substance coexist at the same time and are in thermal equilibrium. That is, in the phase diagram of the gas phase, the liquid phase, and the solid phase, the three coexisting lines of the gas phase-liquid phase, the liquid phase-solid phase, and the gas phase-solid phase are concentrated in one. In the case of carbon dioxide, it is −56.4 ° C. (see FIG. 8).

In the present invention, liquefied carbon dioxide or brine can be used as the second refrigerant.
Then, in the present invention, it is preferable that the liquid nitrogen and the second refrigerant are switched by predetermined switching means (first and second switching valves V1, V2). Here, by the switching means (V1, V2), liquid nitrogen flows through a pipe (open type pipe) open to the atmosphere, and a second refrigerant (for example, liquefied carbon dioxide) is a closed type (circulation type) pipe. It is preferable to flow.

Further, in the present invention, the freezing tube (1) is preferably a microchannel or a perforated tube.
The freezing tube (1) is preferably made of a material (for example, copper, aluminum, austenitic stainless steel, glass fiber reinforced resin) that does not cause low temperature brittleness even when in contact with liquid nitrogen.

Alternatively, in the present invention, when switching from liquid nitrogen to a second refrigerant, a step of supplying a temperature adjusting fluid after stopping the supply of liquid nitrogen is provided.
The step of supplying the second refrigerant to the freezing pipe (1) is preferably executed after the step of supplying the temperature adjusting fluid.
Here, the temperature adjusting fluid is preferably nitrogen gas.

In carrying out the present invention, it is preferable to measure the temperature inside the freezing tube using an optical fiber (2).
Further, it is preferable to have a step of creating a poorly permeable region (Q) by improving the ground before the construction of the freezing method.

Then, in carrying out the present invention, it is preferable that the region of the freezing pipe (1) corresponding to the non-freezing section in the construction target ground is composed of a heat insulating structure. As the heat insulating structure, for example, a vacuum double pipe structure can be adopted, or a structure coated with a heat insulating material can be used.

In the freezing method of the present invention
The process of supplying liquid nitrogen (first refrigerant) to the freezing pipe (1) to freeze the ground to be constructed, and
After freezing the ground to be constructed with liquid nitrogen, a second refrigerant (refrigerant other than liquid nitrogen: for example, liquefied carbon dioxide) is supplied to the freezing pipe (1) using a circulating operation means to freeze the ground. The process of maintaining and
A step of measuring the temperature inside the freezing pipe (1) and supplying the second refrigerant to the freezing pipe (1) after the temperature inside the freezing pipe (1) becomes higher than the triple point of the second refrigerant. And have
The flow path of the liquid nitrogen and the flow path of the second refrigerant are common (the same flow path).

In order to carry out the above-mentioned freezing method, in the system (100) for constructing the freezing method of the present invention,
A refrigerant piping system (10) having a freezing pipe (1) is provided.
In the refrigerant piping system (10), a supply source (3) of liquid nitrogen (first refrigerant) and a second refrigerant (refrigerant other than liquid nitrogen which is the first refrigerant: for example, carbon dioxide) are liquefied. Refrigerating equipment (4) is connected
A freezing tube temperature measuring device (2: for example, an optical fiber) arranged in the freezing tube (1) and measuring the temperature inside the freezing tube,
A peripheral ground temperature measuring device (5) that is placed near the freezing pipe (1) and measures the temperature of the ground near the freezing pipe (1).
Has a control unit (CU)
The control device (CU) is
A function to determine whether the ground near the freezing pipe (1) has frozen based on the measurement results of the surrounding ground temperature measuring device (5), and
A function to determine whether or not the temperature inside the freezing pipe (1) has reached a temperature higher than the triple point of the second refrigerant after the ground near the freezing pipe (1) has frozen.
It is characterized by having a function of supplying the second refrigerant to the freezing pipe (1) when the temperature inside the freezing pipe (1) becomes higher than the triple point of the second refrigerant. ..

When liquefied carbon dioxide is selected as the second refrigerant in carrying out the present invention, a microchannel is preferable as the freezing tube (1).
The microchannel is a pipe having a flat shape as a whole (a pipe having a non-flat shape may be used), and a plurality of minute refrigerant flow paths (1δ) are formed therein. The material of the microchannel is preferably aluminum, which is lightweight and has excellent thermal properties involved in heat dissipation and heat absorption. As the material, not only aluminum but also copper, aluminum alloy, copper alloy, austenitic stainless steel, glass fiber reinforced resin and the like can be used. However, the material is not particularly limited.

According to the present invention having the above-mentioned configuration, since the flow velocity and / and the flow direction of the ground water are controlled by liquid nitrogen (first refrigerant) using the freezing pipe (1), the ground to which the freezing method should be applied is used. Even if the flow velocity of groundwater is difficult to freeze with brine or liquefied carbon dioxide (for example, 1 to 2 m / day or more), it can be frozen at an ultra-low temperature of liquid nitrogen (boiling point at 1 atm: -196 ° C). ..
Here, as compared with freezing the construction target ground, less cold heat to be administered may be administered in order to maintain the construction target ground in a frozen state. That is, a second refrigerant (for example, −30 ° C. to −45 ° C.) having a temperature higher than that of liquid nitrogen (for example, −30 ° C. to −45 ° C.) without flowing ultra-low temperature liquid nitrogen (boiling point at 1 atm) through the freezing tube (1). If a degree of liquefied carbon dioxide) is poured into the freezing pipe (1), the frozen state of the ground to be constructed can be sufficiently maintained.
In the present invention, when the groundwater flow velocity becomes or less than a value that can be frozen even with a second refrigerant (for example, 1 to 2 m / day in the case of liquefied carbon dioxide) or when it is estimated as such (for example, the surrounding ground). (When the temperature reaches zero ° C), switch from liquid nitrogen to a second refrigerant (for example, liquefied carbon dioxide) to reduce the amount of ultra-low temperature liquid nitrogen (liquid nitrogen) used for construction. It eliminates the need for large-scale equipment required to supply a large amount of liquid nitrogen, and makes it possible to reduce construction costs even if the freezing period is long.
Therefore, the freezing method of the present invention can be applied even when it is necessary to continue the frozen soil for a long period of time.

In the freezing method of the present invention, since the flow path of the liquid nitrogen and the flow path of the second refrigerant are common (the same flow path), there is no need to make new holes or install pipes.
At that time, switching between liquid nitrogen and the second refrigerant can be easily performed by predetermined switching means (switching valves V1 and V2).

According to the present invention, since the cryogenic characteristics of liquid nitrogen and the circulation utilization characteristics of a second refrigerant (for example, liquefied carbon dioxide) are effectively utilized, the cost in the construction of the freezing method is reduced, and freezing is conventionally performed. Difficult construction target ground can be easily frozen. The construction period is shortened, and there are various cost-saving effects associated with the shortening of the construction period.
It should be noted that the present invention is not applied only to the ground where there is a groundwater flow. For example, when the geothermal heat is high, the construction period is very short and / or the construction area is wide, the present invention can be applied regardless of the presence or absence of groundwater flow.

It is a block diagram which shows the 1st Embodiment of this invention. It is a partial cross-sectional explanatory view which shows the case where the micro channel is used as a freezing tube. It is a flowchart which shows the procedure of 1st Embodiment. It is explanatory drawing which shows the main part of the 2nd Embodiment of this invention. It is a flowchart of the main procedure in 2nd Embodiment. It is explanatory drawing which shows the main part of the 3rd Embodiment of this invention. It is a flowchart of the main procedure in 3rd Embodiment. It is a phase diagram of carbon dioxide.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
In the illustrated embodiment, liquid nitrogen having an ultra-low temperature (boiling point-196 ° C.) is used as the refrigerant (first refrigerant). Then, liquefied carbon dioxide is exemplified as a second refrigerant having a temperature higher than that of liquid nitrogen. Of course, the second refrigerant is not limited to liquefied carbon dioxide, and brine or other refrigerants can be used.
First, the first embodiment of the present invention will be described with reference to FIGS. 1, 2, and 3.
In FIG. 1 showing a system for constructing the freezing method used in the first embodiment, the system 100 for constructing the freezing method (system for the freezing method) includes a refrigerant piping system 10 including a freezing pipe 1. ing. The refrigerant piping system 10 is interposed (communication) with a liquid nitrogen supply device 3 for supplying liquid nitrogen (first refrigerant) and a refrigerating device 4 for supplying liquefied carbon dioxide (second refrigerant). The refrigerating device 4 has a function of freezing carbon dioxide in the gas phase and condensing it into liquefied carbon dioxide. The liquid nitrogen supply device 3 has a function of supplying liquid nitrogen to the refrigerant piping system 10 from a storage means (not shown).
The refrigerant (liquid nitrogen, liquefied carbon dioxide) flowing through the refrigerant piping system 10 is supplied to the freezing pipe 1, flows through the supply side flow path (arrow A) in the freezing pipe 1, and flows through the discharge side flow path (arrow B). , Is discharged from the freezing pipe 1.
The freezing tube 1 is made of a material (for example, aluminum, copper, austenitic stainless steel, glass fiber reinforced resin) that does not cause low temperature brittleness even when it comes into contact with liquid nitrogen.

In the refrigerant piping system 10, a first switching valve V1 is interposed on the upstream side (supply side of liquid nitrogen and liquefied carbon dioxide) of the freezing pipe 1, and the first switching valve V1 is a liquid nitrogen supply device 3. And the carbon dioxide refrigerating device 4. Then, by switching the first switching valve V1, the refrigerant supplied to the refrigerant piping system 10 (freezing pipe 1) can be switched to either liquid nitrogen or liquefied carbon dioxide. Further, the first switching valve V1 can be fully closed so that neither liquid nitrogen nor liquefied carbon dioxide is supplied to the refrigerant pipe system 10 (freezing pipe 1).
In the refrigerant piping system 10, a second switching valve V2 is interposed on the downstream side (nitrogen and carbon dioxide discharge side) of the freezing pipe 1, and the discharge side of the freezing pipe 1 has a second switching valve V2. It communicates with the open side to the atmosphere or communicates with the carbon dioxide refrigerating device 4. Here, the open side to the atmosphere is an open type pipe that is open to the atmosphere (nitrogen is open to the atmosphere) as shown by an arrow O. By switching the switching valve V2, the discharge side of the freezing pipe 1 is switched so as to communicate with either the open side to the atmosphere or the carbon dioxide refrigerating device 4.

When supplying liquid nitrogen to the freezing pipe 1, the refrigerant piping system 10 includes a liquid nitrogen supply device 3, a first switching valve V1 (in a state of being switched to the liquid nitrogen supply device 3 side), a freezing pipe 1, and a second. It is configured to communicate with the switching valve V2 (switched to the open side to the atmosphere), liquid nitrogen is supplied to the freezing pipe 1, cold heat is administered to the ground, and vaporized nitrogen is discharged from the freezing pipe 1. As shown by the arrow O, an open pipe (open to the atmosphere piping system) that is open to the atmosphere is configured.
On the other hand, when supplying liquefied carbon dioxide to the freezing tube 1, the refrigerant piping system 10 includes a carbon dioxide refrigerating device 4, a first switching valve V1 (in a state of being switched to the carbon dioxide refrigerating device 4 side), and a freezing tube 1. , The second switching valve V2 (switched to the carbon dioxide refrigeration device 4 side), is configured to circulate the carbon dioxide refrigeration device 4, supplies liquefied carbon dioxide to the freezing tube 1, and administers cold heat to the ground. The vaporized carbon dioxide is returned from the freezing pipe 1 to the carbon dioxide refrigerating apparatus 4 to form a closed type pipe (circulation pipe system). In this specification, this closed type piping (circulation piping system) may be referred to as "circulation operation means".
In the refrigerant piping system 10, liquid nitrogen and liquefied carbon dioxide commonly flow through the piping (flow path) in the region from the first switching valve V1 to the second switching valve V2 via the freezing pipe 1. Common piping (flow path) or the same piping (flow path).
In the illustrated embodiment, when liquid nitrogen is supplied to the freezing pipe 1, it is nitrogen that constitutes an open type pipe (open to the atmosphere piping system) in which cold heat is administered to the ground to release vaporized nitrogen to the atmosphere. This is to ensure safety against expansion of nitrogen when liquid nitrogen is used as a refrigerant because it expands when vaporized. That is, in the case of nitrogen having a large expansion rate, it is safer to open it to the atmosphere instead of using a closed pipe.
Although not clearly shown, safety means such as a relief valve are provided in the piping system communicating with the open side to the atmosphere in order to further improve the safety against nitrogen expansion.

In FIG. 1, a third switching valve V3 is interposed in a region on the upstream side of the freezing pipe 1 of the refrigerant piping system 10 and on the downstream side of the first switching valve V1. A nitrogen gas supply device 6 communicates with the third switching valve V3, and the nitrogen gas supply device 6 is connected to the refrigerant piping system 10 via the third switching valve V3. Nitrogen gas is supplied from the nitrogen gas supply device 6 to the refrigerant piping system 10, and the nitrogen gas is used as a temperature adjusting fluid. Then, by switching the third switching valve V3 to the side connected to the nitrogen gas supply device 9, nitrogen gas (temperature adjusting fluid) can be supplied to the freezing pipe 1.
In order to measure the temperature inside the freezing tube 1, a temperature measuring device 2 inside the freezing tube using an optical fiber is arranged in the freezing tube 1.
Further, in the peripheral ground near the freezing pipe 1, a peripheral ground temperature measuring device 5 for measuring the temperature of the ground is arranged, and the peripheral ground temperature measuring device 5 is, for example, a type of temperature measurement using an optical fiber. The device is used.

The system 100 has a control device CU, and the control device CU is connected to the temperature measuring device 2 in the freezing pipe by the measurement signal line SL1 and is connected to the surrounding ground temperature measuring device 5 by the measurement signal line SL2.
Further, the control device CU is connected to the first switching valve V1 by the control signal line SL3, connected to the second switching valve V2 by the control signal line SL4, and connected to the third switching valve V3 by the control signal line SL5. To.
Here, the control device CU can be configured by an information processing device (computer or the like), but it is also possible for an operator to configure the control device CU.

The control device CU has a function of acquiring the measurement result of the surrounding ground temperature measuring device 5 via the measurement signal line SL2 and determining whether or not the ground in the vicinity of the freezing pipe 1 is frozen.
Further, after the ground in the vicinity of the freezing tube 1 is frozen, the control device CU acquires the measurement result of the temperature measuring device 2 in the freezing tube via the measurement signal line SL1, and the temperature in the freezing tube 1 is liquefied carbon dioxide ( It has a function of determining whether or not the temperature is higher than the triple point of the second refrigerant).
Further, as will be described later, the control device CU has a first switching valve V1, a second switching valve V2, and a third switching valve V1, based on the measurement results of the freezing tube internal temperature measuring device 2 and the measurement results of the peripheral ground temperature measuring device 5. A control signal is transmitted to the switching valve V3 via the control signal lines SL3, SL4, and SL5, and switching control of the first switching valve V1, the second switching valve V2, and the third switching valve V3 is executed and frozen. The tube 1 has a function of selectively supplying liquid nitrogen (first refrigerant), liquefied carbon dioxide (second refrigerant), or nitrogen gas (temperature adjusting fluid).

In FIG. 1, when the target ground region is frozen by the system 100, the liquid nitrogen supply device 3 side of the first switching valve V1 is opened and the carbon dioxide refrigerating device 4 side is closed, and the second switching valve V2 is used. The air opening side (arrow O side) is opened and the carbon dioxide freezing device 4 side is closed, the upstream side of the third switching valve V3 (first switching valve V1 side) is opened, and the nitrogen gas supply device 6 side. To close. Then, liquid nitrogen is supplied from the liquid nitrogen supply device 3 to the refrigerant piping system 10 (freezing pipe 1).
Even if the flow velocity of the groundwater in the ground where the freezing method should be applied is a flow velocity that is difficult to freeze with liquefied carbon dioxide (for example, 1 to 2 m / day or more), the ultra-low temperature of liquid nitrogen (boiling point at 1 atm) Therefore, if the flow velocity of the groundwater is 10 m / day or less, it can be frozen.
By supplying liquid nitrogen to the freezing pipe 1, the ground to be constructed is frozen to create frozen soil, and the groundwater flow is stopped or the flow velocity of the groundwater flow is reduced (for example, a flow rate of 1 to 2 m / 2 m / which can be frozen even with liquefied carbon dioxide). Sun) or change the direction of groundwater. Here, by changing the flow direction of the groundwater, for example, it is possible to avoid the region where the groundwater flow is desired to be frozen.
Then, liquid nitrogen is supplied to the freezing pipe 1 until the groundwater flow velocity of the target ground becomes equal to or lower than the speed at which it can be frozen by liquefied carbon dioxide (1 to 2 m / day).

Whether or not the groundwater flow velocity in the area to be frozen (target ground) is below the speed at which liquefied carbon dioxide can freeze (1 to 2 m / day) is determined by the peripheral ground temperature measuring device 5 for the ground around the freezing pipe 1. The temperature is measured, and the measurement result is transmitted to the control device CU by the measurement signal line SL2. If the temperature of the ground drops to zero ° C, it is judged that the groundwater has frozen, and the groundwater velocity is frozen by liquefied carbon dioxide. It is determined that the speed is less than the possible speed (1 to 2 m / day).
In the illustrated embodiment, for example, an optical fiber is used as a device for measuring the underground temperature or the surrounding ground temperature. This is because an optical fiber that detects temperature-dependent Raman diffused light and measures the temperature can set the temperature measurement point over the entire region along the optical fiber.
In the illustrated embodiment, it is determined by measuring the underground temperature or the surrounding ground temperature whether or not the flow velocity of the groundwater is below the speed at which it can be frozen by liquefied carbon dioxide (1 to 2 m / day). It is also possible to make a judgment by measuring the flow velocity of the above, or by measuring the water level in the hole.

The amount of cold heat required to keep the construction target ground frozen is smaller than the amount of cold heat required to freeze the construction target ground. Therefore, in order to maintain the frozen state of the ground to be constructed, it is about -30 ° C to -45 ° C without supplying liquid nitrogen at an ultra-low temperature (boiling point of -196 ° C under 1 atm) to the freezing pipe 1. The liquefied carbon dioxide may be allowed to flow in the freezing tube 1.
In the illustrated first embodiment, when the groundwater flow velocity becomes or less than the rate at which it can be frozen by liquefied carbon dioxide (1 to 2 m / day) or when it is determined (estimated) as such (for example, the temperature of the surrounding ground is zero). (When the temperature reaches ° C.), the refrigerant supplied to the refrigerating pipe 1 is switched from liquid nitrogen to liquefied carbon dioxide, and the liquefied carbon dioxide is circulated in the refrigerant piping system 10. As a result, the amount of liquid nitrogen required for the construction of the freezing method is reduced, the large-scale equipment required for supplying a large amount of liquid nitrogen is not required, and the construction cost can be reduced even in the case of long-term freezing.

In FIG. 1, in order to switch the refrigerant supplied to the freezing pipe 1 from liquid nitrogen to liquefied carbon dioxide, the side of the first switching valve V1 communicating with the liquid nitrogen supply device 3 is closed and communicated with the carbon dioxide refrigerating device 4. The side that communicates with the air opening side (arrow O) is closed and the side that communicates with the carbon dioxide refrigerating device 4 (circulation operating means side) is opened while switching so as to open the side to be operated. Switch to.
Therefore, liquefied carbon dioxide is supplied to the refrigerant pipe system 10 (freezing pipe 1) and circulated. At that time, the third switching valve V3 closes the side communicating with the nitrogen gas supply device 6 and opens the upstream side (switching valve V1 side).

Here, when the temperature in the freezing tube 1 is lower than the triple point of carbon dioxide, carbon dioxide becomes a solid (dry ice) in which a large amount of fine solid phase components are mixed. When carbon dioxide becomes solid, it blocks the inside of the freezing pipe, so it is difficult for carbon dioxide to flow in the freezing pipe 1, and it becomes impossible to circulate in the carbon dioxide circulation system (refrigerant piping system 10). Can no longer be kept frozen.
That is, immediately when the groundwater flow velocity becomes less than or equal to the rate at which it can be frozen in liquefied carbon dioxide (1 to 2 m / day) or when it is estimated as such (for example, when the temperature of the surrounding ground becomes zero ° C.). When the refrigerant is switched to liquefied carbon dioxide, the liquefied carbon dioxide becomes solid in the freezing tube 1 cooled to an ultra-low temperature by liquid nitrogen, and cannot flow in the freezing tube 1.

Therefore, in the illustrated first embodiment, when the refrigerant is switched to liquefied carbon dioxide, the liquefied carbon dioxide does not become solid in the freezing tube 1 and flows smoothly in the freezing tube 1 so that the liquefied carbon dioxide flows smoothly in the freezing tube 1. After the temperature of the above reaches a temperature higher than the triple point of carbon dioxide, the refrigerant is switched to liquefied carbon dioxide and supplied to the freezing tube 1.
That is, the temperature is adjusted when the groundwater flow velocity becomes lower than the rate at which it can be frozen by liquefied carbon dioxide (1 to 2 m / day) or when it is estimated as such (for example, when the temperature of the surrounding ground becomes zero ° C.). Nitrogen gas is flowed into the freezing tube 1 as a fluid for use, and the temperature inside the freezing tube 1 is set to a temperature higher than the triple point of carbon dioxide, and then liquefied carbon dioxide is supplied.

In FIG. 1, in order to switch the fluid supplied to the freezing pipe 1 from liquid nitrogen to nitrogen gas (fluid for temperature adjustment), the first switching valve V1 is closed to stop the supply of liquid nitrogen and supply liquefied carbon dioxide. Prevent it from being done. Then, the second switching valve V2 is maintained in a state in which the atmosphere open side (arrow O) is open. Further, the third switching valve V3 closes the upstream side (the first switching valve V1 side) and opens the side communicating with the nitrogen gas supply device 6 to communicate the nitrogen gas supply device 6 and the freezing pipe 1 side. .. As a result, the nitrogen gas supplied from the nitrogen gas supply device 6 flows into the freezing pipe 1 via the third switching valve V3, raises the temperature inside the freezing pipe 1, and enters the atmosphere through the switching valve V2. Be released.
During the above-mentioned switching control of the first to third switching valves V1, V2, and V3, the temperature of the surrounding ground drops to zero ° C., and the groundwater flow velocity is liquefied by the control device CU based on the measurement results of the peripheral ground temperature measuring device 5. It is judged that the speed is lower than the speed at which it can be frozen with carbon dioxide (1-2 m / day). Then, the valve switching control signal is transmitted to the first switching valve V1 via the control signal line SL3, the valve switching control signal is transmitted to the second switching valve V2 via the control signal line SL4, and the control signal line SL5 A valve switching control signal is transmitted to the third switching valve V3 via.

With carbon dioxide, the temperature at which the state changes from liquid to solid differs depending on the pressure. In the illustrated embodiment, it is possible to control the supply pressure and temperature of the refrigerant as parameters. Then, the "triple point" can be selected as the threshold temperature. In other words, if the temperature is controlled with the triple point as the threshold value, the ground can be frozen without causing any inconvenience.
If carbon dioxide, at a pressure of 5.18 × ¹⁰ 5 Pa, the state of the temperature of -56.4 ° C. is a triple point (see FIG. 8).
Therefore, if the temperature inside the freezing tube is higher than the triple point temperature of −56.4 ° C., even if liquefied carbon dioxide is supplied to the freezing tube 1, it does not become a solid, and blockage inside the freezing tube is prevented. Can be done.
Here, the water or ice generated in the freezing tube can be removed by the nitrogen gas which is the temperature adjusting fluid.
The temperature of the temperature adjusting fluid is set to a dew point temperature that does not cause dew condensation that causes the inside of the freezing tube to be blocked. The dew point temperature is the temperature at which dew condensation begins when a gas containing water vapor is cooled.

When nitrogen gas, which is a liquid for temperature adjustment, is passed through the freezing tube 1 and the temperature inside the freezing tube 1 becomes higher than the triple point temperature (-56.4 ° C.), the liquefied carbon dioxide becomes solid in the freezing tube 1. The liquefied carbon dioxide flows smoothly in the freezing pipe 1, and the ground to be constructed can be cooled by the liquefied carbon dioxide and maintained in a frozen state.
It is also possible to apply a fluid other than nitrogen gas as the temperature adjusting fluid, and for example, carbon dioxide gas obtained by vaporizing air or liquefied carbon dioxide may be used. It can be appropriately selected from an inert gas with a low cost or an inert gas.

In FIG. 1, in order to switch the fluid supplied to the freezing tube 1 from nitrogen gas to liquefied carbon dioxide, the first switching valve V1 is switched so as to open the side communicating with the liquefied carbon dioxide refrigerating device 4, and the second switching valve V1 is opened. The switching valve V2 is switched so as to close the side communicating with the atmosphere opening side (arrow O side) and open the side communicating with the carbon dioxide refrigerating device 4 (that is, the circulation operation means side), and the third switching valve V3 is The side communicating with the nitrogen gas supply device 6 is closed (the supply of nitrogen gas is stopped), and the side communicating with the upstream side (switching valve V1 side) is opened. By the switching control, liquefied carbon dioxide is supplied to the freezing tube 1, and the carbon dioxide refrigerant circulating operation means can be circulated.
When the temperature inside the freezing tube 1 becomes higher than the triple point temperature (-56.4 ° C.) of carbon dioxide by the temperature measuring device 2 inside the freezing tube, the above-mentioned first to third switching valves V1 to V3 The switching control is executed.

Although not clearly shown, the region of the freezing pipe 1 corresponding to the non-freezing section in the construction target ground has a heat insulating structure. As the heat insulating structure, for example, a vacuum double pipe structure can be adopted, or a structure coated with a heat insulating material can be used.
Further, as will be described later in the third embodiment, the opening / closing control of the switching valves V1 to V3 also considers whether or not the ground to be constructed is frozen and whether or not the surrounding ground is adversely affected by deformation or the like. May be done.
Further, it is also possible to arrange a plurality of or a plurality of freezing pipes 1 and a refrigerant piping system 10 according to the illustrated embodiment on the construction target ground.

In the illustrated embodiment, the freezing pipe 1 is a pipe having a flat shape as a whole (a pipe having a non-flat shape may be used), and a plurality of minute refrigerant flow paths 1δ are formed therein. You have selected a microchannel that has been selected.
The material of the microchannel is aluminum, which is lightweight and has good thermal properties for heat dissipation and heat absorption. However, the material of the microchannel is not limited to aluminum, and copper, aluminum alloy, copper alloy, austenitic stainless steel, glass fiber reinforced resin and the like can be used.
As shown in FIG. 2, for example, a part of a plurality of minute refrigerant flow paths 1δ (right side in FIG. 2) constitutes a refrigerant supply side flow path 1S, and another minute refrigerant flow path (left side in FIG. 2) forms a refrigerant. The discharge side flow path 1E can be configured.
Further, in FIG. 2, a minute refrigerant flow path 1λ that does not correspond to either the refrigerant supply side flow path 1S or the refrigerant discharge flow path 1E is provided, and the optical fiber OP is arranged in the minute refrigerant flow path 1λ to arrange the temperature inside the freezing pipe. The measuring device 2 can be configured to measure the temperature inside the freezing tube 1 as a whole.
Alternatively, although not shown, the small refrigerant flow path 1λ that does not correspond to any of the refrigerant supply side flow path 1S and the refrigerant discharge flow path 1E is evacuated, and the refrigerant and the refrigerant flow through the refrigerant supply side flow path 1S are discharged. It is also possible to prevent heat exchange with the refrigerant flowing through the flow path 1E.
In FIG. 1, liquid nitrogen and liquefied carbon dioxide are the same pipe and the same in the refrigerant piping system 10 in the region from the first switching valve V1 to the second switching valve V2 via the freezing pipe 1. It is flowing through the freezing pipe of. However, it is also possible to configure the piping system and the freezing pipe through which liquid nitrogen flows and the piping system and the freezing pipe through which liquefied carbon dioxide flows in separate systems (not shown).

The construction procedure of the freezing method according to the first embodiment will be described mainly with reference to FIG.
In FIG. 3, in step S1, liquid nitrogen is supplied to the freezing tube 1 as a refrigerant.
At that time, the side communicating with the liquid nitrogen supply device 3 of the first switching valve V1 is open, and the side communicating with the carbon dioxide refrigerating device 4 is closed. The second switching valve V2 is open on the side communicating with the atmosphere open side (arrow O side) and closed on the side communicating with the carbon dioxide refrigerating device 4. The third switching valve V3 closes the side communicating with the nitrogen gas supply device 6 and opens the side communicating with the upstream side (first switching valve V1 side).
By supplying liquid nitrogen from the liquid nitrogen supply device 3 to the freezing pipe 1, the ground to be constructed is frozen. Then, the process proceeds to step S2.

In step S2, the ground temperature around the freezing pipe 1 is measured by the peripheral ground temperature measuring device 5. Then, the process proceeds to step S3.
In step S3, as a result of the measurement in step S2, it is determined whether or not the temperature of the ground around the freezing pipe 1 is 0 ° C. or lower. The determination is executed by the control device CU based on the measurement result of the ground temperature by the surrounding ground temperature measuring device 5.
As a result of the determination in step S3, if the ground temperature is 0 ° C. or lower (step S3 is “Yes”), the process proceeds to step S4, and if the ground temperature is not 0 ° C. or lower (step S3 is “No”), the step is taken. Return to S1 and continue the supply of liquid nitrogen.

In step S4 (when the temperature of the ground around the freezing pipe 1 is 0 ° C. or lower), the groundwater flow velocity can be frozen by liquefied carbon dioxide (1 to 2 m / day) in response to the ground temperature dropping to 0 ° C. or lower. ) It is determined that the result is as follows, and the fluid supplied to the freezing tube 1 is switched from liquid nitrogen to nitrogen gas (fluid for temperature adjustment).
At the time of the switching, the side communicating with the liquid nitrogen supply device 3 and the side communicating with the carbon dioxide refrigerating device 4 are closed (fully closed) to stop the supply of liquid nitrogen. The second switching valve V2 opens the side communicating with the atmosphere opening side (arrow O) as in step S1. The third switching valve V3 closes the side communicating with the upstream side (the first switching valve V1 side) and opens the side communicating with the nitrogen gas supply device 6. As a result, nitrogen gas is supplied from the nitrogen gas supply device 6 to the freezing tube 1, the temperature inside the freezing tube 1 is raised, and when the liquefied carbon dioxide is supplied to the freezing tube 1, it becomes solid. Is prevented.
Then, the process proceeds to step S5.

In step S5, the temperature inside the freezing tube 1 is measured by the freezing tube temperature measuring device 2, and the process proceeds to step S6.
In step S6, the temperature inside the freezing tube 1 measured by the control device CU by the temperature measuring device 2 inside the freezing tube (step S5) is higher than the triple point temperature (-56.4 ° C.) of carbon dioxide. Judge whether or not.
In step S6, if the temperature inside the freezing tube 1 is higher than the triple point temperature (-56.4 ° C.) of the liquefied carbon dioxide (step S6 is “Yes”), the process proceeds to step S7, and the freezing tube 1 When the temperature inside is not higher than the triple point temperature (-56.4 ° C) of the liquefied carbon dioxide (step S6 is "No"), the process returns to step S4, and the nitrogen gas is supplied (the temperature inside the freezing tube 1 rises). ) Continue.

In step S7 (when the temperature inside the freezing tube 1 is higher than the triple point temperature of the liquefied carbon dioxide), the fluid supplied to the freezing tube 1 is switched from nitrogen gas to liquefied carbon dioxide and supplied.
When switching from nitrogen gas to liquefied carbon dioxide, the side of the first switching valve V1 communicating with the carbon dioxide refrigerating device 4 is opened, and the side communicating with the liquid nitrogen supply device 3 is closed. Then, the side communicating with the atmosphere opening side (arrow O) of the second switching valve V2 is closed, and the side communicating with the carbon dioxide refrigerating apparatus 4 side (that is, the circulation operation means side) is opened. Further, the third switching valve V3 closes the side communicating with the nitrogen gas supply device 6 to stop the supply of nitrogen gas, and opens the side communicating with the upstream side (first switching valve V1 side).
By such switching control, liquefied carbon dioxide is supplied to the freezing pipe 1, carbon dioxide circulates in the refrigerant piping system 10, and the ground around the freezing pipe 1 is maintained in a frozen state.
Then, the process proceeds to step S8.

In step S8, it is determined whether or not the construction is completed (whether or not the ground to be constructed is maintained in a frozen state).
As a result of the determination in step S8, when the maintenance of the frozen state of the construction target ground is completed (step S8 is “Yes”), a predetermined procedure (not shown) to be performed at the end of the freezing method is executed. .. On the other hand, when the frozen state of the ground to be constructed is maintained (step S8 is “No”), the process returns to step S7 and the ground is maintained in the frozen state.
Although not explicitly shown in FIG. 3, if there is a risk that the frozen ground will melt in the loop of steps S7 and S8 for some reason, the process returns to step S1.
Further, although not shown, in step S1 of FIG. 3 or a step before that (for example, step S11 of FIG. 5 described later), fine powder iron powder (metal powder having high thermal conductivity) is applied to the ground to be constructed. It can also be injected and filled to promote the freezing effect. By mixing metal powder with high thermal conductivity into the construction target ground, the cold heat of liquid nitrogen and liquefied carbon dioxide can be efficiently put into the construction target ground (ground to be frozen), and the ground can be frozen efficiently. ..
Alternatively, although not shown, when creating an underground wall, the freezing pipes can be arranged in a single row, a plurality of rows, or in a staggered pattern (staggered structure). By devising the arrangement of the freezing pipes in this way, the flow velocity and flow direction of the groundwater can be controlled.

According to the freezing method of the first embodiment shown in FIGS. 1 to 3, liquid nitrogen is supplied to the freezing pipe 1 to freeze the ground to be constructed to create frozen soil, or the flow velocity of groundwater is reduced or reduced to zero. (For example, even liquefied carbon dioxide is reduced to the flow velocity of groundwater until it can be frozen), or the flow direction of groundwater is changed (for example, the flow direction of groundwater is changed so as to avoid the area to be frozen). Even if the flow velocity is difficult to freeze with brine or liquefied carbon dioxide (for example, 1 to 2 m / day or more), if the flow velocity is ultra-low temperature of liquid nitrogen (boiling point at 1 atm-196 ° C), the flow velocity of groundwater will be high. It can be frozen if it is 10 m / day or less.
Here, compared to freezing the ground to be constructed, in order to maintain the frozen state of the ground to be constructed, less cold heat should be administered, and ultra-low temperature liquid nitrogen (boiling point at 1 atm) is required. Even if -196 ° C.) is not passed through the freezing tube 1, if liquefied carbon dioxide at about −30 ° C. to −45 ° C. is passed through the freezing tube 1, the frozen state of the ground to be constructed can be sufficiently maintained.
In the first embodiment, when the groundwater flow velocity becomes or less than a value that can be frozen even with liquefied carbon dioxide (for example, 1 to 2 m / day for liquefied carbon dioxide) or when it is estimated as such (for example, for example). When the temperature of the surrounding ground becomes 0 ° C.), the refrigerant supplied to the freezing pipe 1 is switched from liquid nitrogen to liquefied carbon dioxide which is a second refrigerant. As a result, the amount of ultra-low temperature liquid nitrogen used for construction is reduced, eliminating the need for large-scale equipment required to supply a large amount of liquid nitrogen, and construction is carried out even if the freezing period is long. The cost can be reduced.
Therefore, even when it is necessary to continue the frozen soil for a long period of time, the first embodiment shown in the figure can prevent the cost from rising.

When supplying liquefied carbon dioxide to the freezing tube 1, if the temperature inside the freezing tube 1 is lower than the triple point of carbon dioxide, the carbon dioxide becomes a solid (dry ice) containing a large amount of solid phase components, and the freezing tube 1 It is difficult to flow inside, and the ground around the freezing pipe 1 (ground to be constructed) cannot be maintained in a frozen state.
In the illustrated first embodiment, the temperature of the surrounding ground becomes zero ° C. when the groundwater flow velocity becomes or less than the rate at which it can be frozen by liquefied carbon dioxide (1 to 2 m / day) or when it is estimated as such (for example, the temperature of the surrounding ground becomes zero ° C.). At that time, nitrogen gas, which is a fluid for temperature adjustment, is flowed into the freezing tube 1 and the temperature inside the freezing tube 1 is heated to a temperature higher than the triple point temperature (-56.4 ° C.) of the liquefied carbon dioxide. .. Then, after raising the temperature inside the freezing pipe 1 to a temperature higher than the triple point temperature (-56.4 ° C.) of the liquefied carbon dioxide, the refrigerant is switched to the liquefied carbon dioxide, and the liquefied carbon dioxide is transferred to the refrigerant piping system 10 (freezing pipe). Since it is supplied to 1), it is prevented that the liquefied carbon dioxide becomes solid in the freezing pipe 1, and the liquefied carbon dioxide flows smoothly in the freezing pipe 1 to maintain the ground to be constructed in a frozen state. Can be done.

Further, in the freezing method of the first embodiment shown in the figure, the flow path of the liquid nitrogen and the flow path of the second refrigerant (liquefied carbon dioxide) are common (the same flow path), and the first of the refrigerant piping systems 10 Since the flow path (piping) from the switching valve V1 of 1 to the second switching valve V2 via the freezing pipe 1 is common, it is not necessary to newly drill a hole in the ground and install a pipe (piping). Or less).
At that time, switching between the liquid nitrogen and the second refrigerant (liquefied carbon dioxide) can be easily performed by switching and controlling the predetermined switching valves V1, V2, and V3.

According to the freezing method of the first embodiment, the cryogenic characteristics of liquid nitrogen and the circulation utilization characteristics of the second refrigerant (liquefied carbon dioxide) are effectively utilized, so that the construction cost is reduced and the conventional method is used. Then, the ground that is difficult to freeze can be easily frozen. It also has the effect of shortening the construction period and reducing various costs.
The freezing method of the first embodiment is not applied only to the ground with a groundwater flow.
When the geothermal heat is high, the construction period is very short, and / or the construction area is wide, the first embodiment can be applied regardless of the presence or absence of groundwater flow.

Next, a second embodiment of the present invention will be described with reference to FIGS. 4 and 5.
The second embodiment is applied when the groundwater flow velocity exceeds the limit groundwater flow velocity (for example, 10 m / day) at which the ground can be frozen by liquid nitrogen.
In FIG. 4, a function such as an impermeable wall is provided on the upstream side (right side in FIG. 4) of the groundwater flow F from the construction target area R (the area where the freezing pipe 1 is arranged to freeze the ground). An underground solidified body Q is created as a water-impermeable region Q. The underground consolidated body Q is formed by a known ground improvement method.
By creating the underground consolidation body Q, the groundwater flow (thick arrow F) is obstructed and flows around the underground consolidation body Q (thin arrow F). As a result, even if the flow velocity exceeds 10 m / day on the upstream side (thick arrow F), it is decelerated to 10 m / day or less in the vicinity of the frozen region R.
If the groundwater flow velocity in the vicinity of the freezing target region R is 10 m / day or less, it can be frozen by supplying liquefied nitrogen to the freezing pipe 1.

In FIG. 5, which shows the main procedure of the second embodiment, steps S11, S12, and S13 are executed prior to step S1 of the flowchart of FIG. 3 according to the first embodiment.
In FIG. 5, in step S11, the flow velocity of groundwater in the vicinity of the frozen region R (FIG. 4) is measured by a groundwater flow velocity measuring device (not shown). Then, the process proceeds to step S12.
In step S12, it is determined whether or not the groundwater flow velocity measured in step S11 is faster than the groundwater flow velocity (10 m / day) that can be frozen in liquid nitrogen. The determination in step S12 is executed by the control device CU (FIG. 1).

In step S12, if the groundwater flow velocity is faster than 10 m / day (step S12 is “Yes”), the process proceeds to step S13. On the other hand, when the groundwater flow velocity is slower than 10 m / day (step S12 is “No”), the process proceeds to step S1 of FIG. 3, and the freezing method is executed according to the procedure of FIG.
In step S13 (when the groundwater flow velocity is faster than 10 m / day), as shown in FIG. 4, an underground consolidation body Q is formed on the upstream side of the groundwater flow F with respect to the frozen region R by conventional ground improvement. When the underground consolidation body Q is formed in step S13 and the groundwater flow velocity in the vicinity of the frozen region R becomes 10 m / day or less, the process proceeds to step 1 of FIG. 3, and the freezing method is executed according to the procedure of FIG. To do.
According to the freezing method according to the second embodiment of FIGS. 4 and 5, the groundwater flow velocity in the vicinity of the frozen region R is large (greater than 10 m / day), and it is difficult to freeze the ground even if liquid nitrogen is used. Even in such a case, since the underground solidified body Q is formed on the upstream side of the groundwater flow from the frozen region R, the groundwater flow velocity in the vicinity of the frozen region R can be reduced to 10 m / day or less. Therefore, it is possible to freeze the ground using liquid nitrogen.
Other configurations and effects of the second embodiment of FIGS. 4 and 5 are the same as those of the first embodiment of FIGS. 1 to 3.

A third embodiment of the present invention will be described with reference to FIGS. 6 and 7.
When constructing the freezing method, it is inconvenient that the surrounding ground is deformed due to freezing of the ground, and it must be avoided.
In the third embodiment, a strain sensor is arranged around the construction target ground on which the freezing pipe is arranged, and when the construction target ground freezes and the surrounding ground expands and deforms, the strain generated by the deformation is generated. Detected by a strain sensor. If the strain is larger than the permissible value, it is judged that the surrounding ground has been deformed, and necessary measures such as stopping the freezing work of the ground are taken.

In FIG. 6, the strain sensor 7 is arranged in the peripheral ground region above the freezing pipe 1.
When liquid nitrogen is supplied to the freezing pipe 1, the ground to be constructed freezes, and the ground above the freezing pipe 1 is deformed and raised, the strain sensor 7 detects the strain. If the strain is larger than the permissible value, the control device CU determines that the uplift (deformation) of the ground above the freezing pipe 1 has exceeded the permissible range, and the construction is stopped. Therefore, it is possible to prevent the ground from rising (deformed) more than necessary in the surrounding ground.
Here, the allowable strain value is determined on a case-by-case basis depending on the conditions of the construction site and various specifications of the freezing method.

In FIG. 7, which shows the procedure of the freezing method of the third embodiment, steps S21, S22, and S23 are executed in parallel with the flowchart of FIG.
In step S21, the strain generated in the surrounding ground is measured by the strain sensor 7 arranged on the ground. Then, the process proceeds to step S22.
In step S22, it is determined whether or not the strain measured in step S21 is larger than the preset allowable value. The determination is executed by the control device CU.
As a result of the determination in step S22, if the strain of the surrounding ground is larger than the permissible value (step S22 is “Yes”), the process proceeds to step S23, and if the strain of the surrounding ground is less than or equal to the permissible value (step S22 is “No”). The process proceeds to step S24.

In step S23 (when the strain of the surrounding ground is larger than the permissible value), the first switching valve V1 (FIG. 1) of the refrigerant piping system 10 communicates with the liquid nitrogen supply device 3 and the carbon dioxide refrigeration device 4. The side is closed (fully closed), and the supply of the refrigerant to the freezing pipe 1 is stopped.
On the other hand, in step S24 (when the strain of the surrounding ground is equal to or less than the permissible value), the freezing work of the ground to be constructed is continued.
According to the third embodiment of FIGS. 6 and 7, when the surrounding ground is deformed due to freezing of the ground to be constructed, the strain sensor arranged on the surrounding ground detects it, and the freezing work of the ground is stopped. You can take the necessary measures.
Other configurations and effects of the third embodiment of FIGS. 6 and 7 are the same as those of the third embodiment of FIGS. 1 to 5.

It should be added that the illustrated embodiment is merely an example and is not a description intended to limit the technical scope of the present invention.
For example, in the illustrated embodiment, the case where “there is a groundwater flow” has been described. However, even if there is no groundwater flow, for example, when the geothermal heat is high, the construction period is very short and / or the construction area is wide, the illustrated embodiment can be applied.

1 ... Freezing pipe 1δ ... Micro refrigerant flow path 2 ... Temperature measuring device inside the freezing pipe (optical fiber)
3 ... Liquid nitrogen supply device (supply source of liquid nitrogen)
4 ... Carbon dioxide refrigeration device 5 ... Peripheral ground temperature measuring device 6 ... Nitrogen gas supply device 10 ... Refrigerant piping system 100 ... Freezing method system CU ... Control devices V1, V2, V3 ・ ・ ・ Switching valve Q ・ ・ ・ Impermeable area (underground solidification)

Claims (8)

In the freezing method of the ground where the groundwater flow exists,
The process of controlling the flow velocity and / and flow direction of groundwater with liquid nitrogen using a freezing pipe, and
After the control step, a step of supplying a second refrigerant to the freezing pipe to maintain the ground in a frozen state by using a circulation operation means, and a step of maintaining the ground in a frozen state.
It has a step of measuring the temperature inside the freezing pipe and supplying the second refrigerant to the freezing pipe after the temperature inside the freezing pipe reaches a temperature higher than the triple point of the second refrigerant.
A freezing method characterized in that the flow path of liquid nitrogen and the flow path of the second refrigerant are common. The freezing method according to claim 1, wherein the second refrigerant is liquefied carbon dioxide or brine. The freezing method according to any one of claims 1 and 2, wherein the liquid nitrogen and the second refrigerant are switched by a predetermined switching means. The freezing method according to any one of claims 1 to 3, wherein the freezing tube is a microchannel or a perforated tube. When switching from liquid nitrogen to a second refrigerant, it has a step of supplying a fluid for temperature adjustment after stopping the supply of liquid nitrogen.
The freezing method according to any one of claims 3 to 4, wherein the step of supplying the second refrigerant to the freezing pipe is executed after the step of supplying the temperature adjusting fluid. The freezing method according to any one of claims 1 to 5, which has a step of creating a water-impermeable region by ground improvement before the construction of the freezing method. The process of supplying liquid nitrogen to the freezing pipe to freeze the ground to be constructed,
After freezing the ground to be constructed with liquid nitrogen, a second refrigerant is supplied to the freezing pipe using a circulating operation means to maintain the ground in a frozen state.
It has a step of measuring the temperature inside the freezing pipe and supplying the second refrigerant to the freezing pipe after the temperature inside the freezing pipe reaches a temperature higher than the triple point of the second refrigerant.
A freezing method characterized in that the flow path of liquid nitrogen and the flow path of the second refrigerant are common. Equipped with a refrigerant piping system with a freezing pipe
A supply source of liquid nitrogen and a refrigerating device for liquefying a second refrigerant communicate with each other in the refrigerant piping system.
A freezing tube temperature measuring device that is placed in the freezing tube and measures the temperature inside the freezing tube.
A peripheral ground temperature measuring device that is located near the freezing pipe and measures the temperature of the ground near the freezing pipe,
Has a control device
The control device
A function to determine whether the ground near the freezing pipe has frozen based on the measurement results of the surrounding ground temperature measuring device, and
A function to determine whether the temperature inside the freezing pipe has reached a temperature higher than the triple point of the second refrigerant after the ground near the freezing pipe has frozen.
A system for constructing a freezing method, which has a function of supplying a second refrigerant to a freezing pipe when the temperature inside the freezing pipe becomes higher than the triple point of the second refrigerant.

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