JP2008019650A - Ground freezing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ground freezing method which dispenses with the preparation of stainless steel as freezing pipes and the use of brine that is durable for use at extremely low temperatures, and brings about the early freezing of the ground without causing the upsizing of freezing machine facilities. <P>SOLUTION: The brine is supplied to shield machines for freezing the natural ground around a contact portion of first and second shield tunnels excavated by the shield machines 1, 2. The brine is cooled by a freezing device 5 arranged in the shield machines 1, 2. The freezing device 5 cools the brine to temperatures between -60°C and -50°C, and supplies the brine to pasted freezing pipes 31 of the shield machine 1, to thereby freeze the ground. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method of freezing the ground to improve the strength of the ground by freezing the ground to prevent the ground from collapsing, or to prevent the ground from collapsing during tunnel construction. It is related with the freezing method of the ground suitable for doing.

  When starting and reaching a shield machine, non-cutting widening from a tunnel, underground connection of a tunnel or a shaft, etc., a ground freezing method for freezing the ground may be used. In this ground freezing method, for example, brine having a temperature of about −30 ° C. is circulated and supplied to a freezing pipe disposed on the ground, and the ground is frozen to form frozen soil. If it takes a long time to form frozen soil, it will cause adverse effects such as prolonging the construction period. Therefore, it is required to shorten the time (number of days) required to form frozen soil.

  As a method for freezing the ground at an early stage, for example, there is a water stopping method disclosed in Japanese Patent Application Laid-Open No. 11-2087. This water stop method is to prevent groundwater from leaking into the excavation hole when introducing the pipe from the excavation hole to the ground by pipe roof construction method, etc., but by inserting liquid nitrogen into the freezing pipe, A frozen region is formed around the jig. According to this water stopping method, since liquid nitrogen is used, it can be rapidly frozen.

In addition, liquid nitrogen is not directly introduced into a freezing pipe embedded in the ground in this way, but the cold heat of liquefied nitrogen is absorbed into brine, or cooled to about −80 ° C. with a large capacity refrigerator, and the brine is A method of freezing the ground by introducing it into a freezing pipe buried in the ground is also conceivable.
Japanese Patent Laid-Open No. 11-2087

  However, in the water stop method disclosed in Patent Document 1, liquid nitrogen is introduced into the freezing tube, but the liquid nitrogen is cooled to a very low temperature, for example, about -196 ° C. For this reason, there has been a problem that, for example, a stainless steel tube that can withstand the introduction of liquid nitrogen must be used as the freezing tube.

  Further, in the method in which the cold heat of liquid nitrogen is absorbed into the brine and the cooled brine is circulated in the freezing tube, the brine can be cooled to a low temperature of about −80 ° C., for example. The kind of brine that can absorb heat is limited. For this reason, only the special thing which can be used at a very low temperature can be used as a brine.

  Therefore, the problem of the present invention is that it is not necessary to use a stainless steel tube as a freezing tube or a special brine that can withstand use at a very low temperature. An object of the present invention is to provide a ground freezing method that can be frozen at an early stage.

  The ground freezing method according to the present invention that has solved the above problems is a ground freezing method for freezing an area to be frozen in the ground, and is a refrigerant compressed by a compressor with respect to the inside of a freezing pipe disposed in the area to be frozen. Is supplied to the heat exchanger, and the brine cooled to the range of −60 ° C. to −35 ° C. is circulated and supplied by the refrigerator that cools the brine by exchanging heat between the brine and the refrigerant by the heat exchanger. The freezing target area is frozen.

  In the ground freezing method according to the present invention, brine cooled to a range of −60 ° C. to −35 ° C. is circulated and supplied to the inside of the freezing pipe disposed in the freezing target region to freeze the ground. If the brine is cooled to a temperature of about −60 ° C. to −35 ° C., a very low temperature refrigerant such as liquid nitrogen is not required. Further, there is no need to use a stainless steel tube as a freezing tube or a brine that can withstand use at a very low temperature. Moreover, in the range of −60 ° C. to −35 ° C., particularly in the range of −60 ° C. to −50 ° C., the ground can be frozen earlier than the conventional ground freezing method.

  Here, it can be set as the aspect by which the two-stage type compressor which compresses a refrigerant | coolant two steps is used as a compressor.

  Thus, the refrigerant | coolant for cooling a brine to -60 degreeC--35 degreeC can be easily cooled by using the two-stage type compressor as a compressor.

  In addition, the refrigerator includes an expansion valve that supplies the refrigerant supplied from the compressor while expanding it to the heat exchanger, and detects an intake temperature and an evaporation pressure of the refrigerant into the compressor as the expansion valve, A linear valve that adjusts the temperature by linearly changing the opening degree based on the suction temperature and the evaporation pressure can be used.

  Thus, by using a linear valve as an expansion valve that supplies the refrigerant to the heat exchanger, the refrigerant for cooling the brine to −60 ° C. to −35 ° C. can be appropriately supplied to the heat exchanger.

  Furthermore, it can be set as the aspect by which the viscosity of brine is 150 (mPa * s) or less.

  Thus, by using a brine having a viscosity of 150 (mPa · s) or less, the brine can be smoothly supplied into the freezing tube.

  In addition, after freezing the area to be frozen by the freezing method of the ground, a brine having a temperature exceeding −35 ° C. is supplied into the freezing pipe arranged in the area to be frozen, so that the frozen ground is thawed and the frozen ground is overproduced. It can be set as the aspect which prevents.

  Thus, after freezing the freezing target area, it is desired to prevent overproduction of frozen soil in the freezing target area. In addition, it is desirable to thaw frozen soil at an early stage after the role of water stoppage by forming frozen soil in the freezing target region is completed. In order to prevent such over-generation and thaw of frozen soil, in the present invention, brine having a temperature exceeding −35 ° C. is supplied into a freezing tube disposed in the freezing target region. For this reason, since the freezing area can be heated to a high temperature, it is possible to suitably prevent overproduction of frozen soil, and to thaw frozen soil early. In order to thaw the frozen soil, it is preferable to circulate brine having a higher temperature, for example, a temperature of about 0 ° C. to 90 ° C.

  According to the ground freezing method according to the present invention, there is no need to use a stainless steel tube as a freezing tube or a special brine that can be used at a very low temperature, so that the size of the refrigerator equipment is not increased. However, the ground can be frozen at an early stage.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each embodiment, portions having the same function are denoted by the same reference numerals, and redundant description may be omitted. This embodiment demonstrates the example which freezes the surrounding ground in the junction part at the time of joining two shield tunnels.

  FIG. 1 is a cross-sectional view of a joint portion between a first shield tunnel and a second shield tunnel to which a freezing method according to an embodiment of the present invention is applied. In this embodiment, the first shield tunnel 1 and the second shield tunnel 2 are respectively excavated from both directions of the tunnel by the first shield machine 1 and the second shield machine 2, and both tunnels are joined at a predetermined joining position. As a pre-stage for joining the two tunnels, the ground around the joining portion is frozen. By freezing the ground, the strength of the ground is increased to prevent the ground from collapsing, and the water stoppage is enhanced. Here, before describing the ground freezing device, a shield machine for excavating the first shield tunnel and the second shield tunnel will be described.

  The first shield machine 1 includes a first outer cylinder portion 10, and a first cutter device 11 is provided in front of the first outer cylinder portion 10. The first cutter device 11 includes a first cutter unit 11A having a disk shape. A plurality of bits 11B are attached to the surface of the first cutter unit 11A, and the ground is excavated by the bits 11B when the first cutter unit 11A rotates. Moreover, the expansion-contraction spoke 11C is provided in the side edge part of 11 A of 1st cutter parts, and this expansion-contraction spoke 11C expands-contracts in the radial direction with respect to 11 A of 1st cutter parts. Thus, the first cutter device 11 can be reduced in diameter in the radial direction.

  The first cutter portion 11A has the same diameter as that of the first outer cylinder portion 10 while the telescopic spoke 11C is extended during excavation. When the telescopic spoke 11C contracts, the diameter of the first cutter part 11A is smaller than the inner diameter of the first outer cylinder part 10, and the first cutter part 11A can be pulled into the first outer cylinder part 10. Become.

  A first inner cylinder portion 12 is provided behind the first cutter device 11. The first inner cylinder part 12 has an outer peripheral part along the inner surface of the first outer cylinder part 10, and is movable along the inner surface of the first outer cylinder part 10. The first inner cylinder portion 12 is provided with a partition wall 13. The partition wall 13 is provided with a drive motor 11D, and the drive motor 11D rotates the first cutter portion 11A. Further, the first inner cylinder portion 12 is fixed to the first outer cylinder portion 10 during excavation work, and the first cutter device 11 moves forward and backward together with the first outer cylinder portion 10.

  A middle folded jack 14 is attached to the first inner tubular portion 12, and the first outer tubular portion 10 can be folded by the middle folded jack 14. Further, a shield jack 15 is attached to the first outer cylinder portion 10 to press the assembled segment. By pressing the segment with the shield jack 15, the first shield machine 1 moves forward with reaction force applied to the segment. Further, the first outer cylinder portion 10 is provided with an erector (not shown). The erector sequentially assembles the segments in the holes formed by the first cutter device 11.

  The first shield machine 1 is provided with a mud pipe 16 and a mud pipe (not shown). The mud feed pipe 16 and the mud discharge pipe are both disposed between the first cutter unit 11 </ b> A and the partition wall 13 in the first cutter device 11. From the mud pipe 16, high-concentration mud water is supplied between the first cutter unit 11A and the partition wall 13 to increase the pressure of the first cutter unit 11A. Further, the mud discharge pipe discharges high-concentration mud supplied from the mud feed pipe 16 between the first cutter unit 11A and the partition wall 13 and mud made of excavated soil. Thus, the pressure of the first cutter device 11 is adjusted by the amount of water supplied from the mud pipe 16 and the amount of muddy water discharged from the mud pipe. Further, a tail seal is provided at the rear end portion of the first outer cylinder portion 10. The tail seal stops water between the segment and the first shield machine 1 at the rear end portion of the first shield machine 1.

  Moreover, the first shield machine 1 is provided with a first water stop device 3 as shown in FIG. The first water stop device 3 includes a plurality of pasted freeze tubes 31 provided in the first outer cylinder portion 10 and communicating with each other. Brine is circulated and supplied from the freezing device 5 to the pasted freezing pipe 31 to freeze the ground at the joining site of the shield machines 1 and 2. The configuration of the freezing device 5 will be described later.

  The brine to be circulated and supplied from the freezing device 5 flows through the sticking freezing tube 31, thereby freezing the soil water contained in the freezing target region X in the natural ground outside the first outer cylindrical portion 10, thereby freezing the target region. Frozen soil (frozen ground) can be formed on X. Further, after the frozen soil is formed in the freezing target region X, when the low-temperature brine flows through the attached freezing tube 31, the frozen soil is maintained without thawing. In the present embodiment, potassium formate-based brine (manufactured by Showa Co., Ltd .: cold brine) is used as the brine.

  Further, as shown in FIG. 1, the first water stop device 3 has an injection pipe 32 provided in the first inner cylinder portion 12, and the filler F <b> 1 is ejected from the injection pipe 32. As the filler F1, a mixture of a soil-based inorganic material and water can be used. Further, the first water stop device 3 has an annular seal member 33 provided on the slide hood 12 </ b> A located at the tip of the first inner cylinder portion 12. The annular seal member 33 is made of a wire brush, the base end is attached to the slide hood 12A, the tip is in contact with the inner surface of the first outer cylinder 10, and the slide hood 12A and the first outer cylinder 10 are in contact with each other. A space is formed between them.

  When the first tunnel is dug in the first shield machine 1, this space is filled with the filler F1 ejected from the injection pipe 32. A cooling member 34 is provided on the inner surface side of the first inner cylinder portion 12. The cooling member 34 transmits cold heat through the slide hood 12A so that the filler F1 can be frozen.

  The second shield machine 2 has the same configuration as the first shield machine 1 and includes a second outer cylinder portion 20 and a second cutter device 21. A second inner cylinder portion 22 that is a movable inner cylinder portion is provided behind the second cutter portion 21A, and a partition wall 23 is provided in the second inner cylinder portion 22. Further, a bent jack is attached to the rear part of the second inner cylinder part 22.

  Further, a shield jack is attached to the rear portion of the second outer cylinder portion 20, and by pressing the segment, a reaction force is applied to the segment to advance the second shield machine 2. An erector is provided at a position above the rear portion of the second outer cylinder portion 20, and the segments are sequentially assembled. The second shield machine 2 is provided with a mud pipe and a mud pipe, and supplies or discharges mud water between the second cutter part 21A and the partition wall 23. A tail seal is provided at the rear portion of the second outer cylinder portion 20.

  The second shield machine 2 is provided with a second water stop device 4. Similar to the first water stop device 3 provided in the first shield machine 1, the second water stop device 4 includes a plurality of communicating with each other provided in the slide hood 22 </ b> A located at the tip of the second inner cylindrical portion 22. An attached freezing tube 41 is provided. As with the first shield machine 1, the freezing device 5 circulates and supplies brine to the pasted frozen tube 41. In addition, the 2nd water stop apparatus 4 has the same injection pipe as the 1st water stop apparatus 3, an annular seal member, and a cooling member.

  The freezing device 5 is provided in each of the first shield machine 1 and the second shield machine 2 and has the same structure. Hereinafter, the configuration of the freezing device 5 will be described with reference to the freezing device 5 connected to the first shield machine 1.

  The freezing apparatus 5 shown in FIG. 1 includes a brine cooler 50, a condenser 55, and a cooling tower 58, which are heat exchangers, as shown in FIG. The brine cooler 50 includes a brine circulation chamber 51 and a refrigerant circulation pipe 52. The brine stays in the brine circulation chamber 51, and the refrigerant circulates in the refrigerant circulation pipe 52. The brine cooler 50 is provided with a linear valve 53 as an expansion valve. Further, the brine cooler 50 is provided with a temperature sensor (not shown) that measures the temperature when the refrigerant is a liquid and a pressure sensor (not shown) that measures the evaporation pressure when the refrigerant evaporates into a gas. . The refrigerant temperature measured by the temperature sensor and the evaporation pressure measured by the pressure sensor are output to the linear valve 53. The condenser 55 has a refrigerant circulation chamber 56 and a cooling water circulation pipe 57, the refrigerant circulation chamber 56 is filled with vaporized refrigerant, and the cooling water circulates in the cooling water circulation pipe 57. Further, the cooling water stays in the cooling tower 58.

  A brine pipe 61 is connected to the brine circulation chamber 51 in the brine cooler 50, and this brine pipe 61 is connected to the pasted freezing pipe 31 via a brine header 62. Further, a brine circulation pump 63 is provided in the brine pipe 61. The brine that freezes the ground is circulated and supplied from the brine circulation chamber 51 to the pasting freeze tube 31 via the brine piping 61 by operating the brine circulation pump 63.

  The refrigerant circulation pipe 52 is disposed in the brine circulation chamber 51, and the refrigerant circulates through the refrigerant circulation pipe 52 so that the refrigerant flows between the refrigerant circulation pipe 52 and the brine in the brine circulation chamber 51. Heat exchange is performed, the cold heat of the refrigerant is transferred to the brine, and the brine is cooled.

  One end side of the refrigerant flow pipe 52 is connected to the gas refrigerant pipe 64, and the other end side is connected to the liquid refrigerant pipe 65 via the linear valve 53. The gas refrigerant pipe 64 is connected to the refrigerant circulation chamber 56 in the condenser 55, and a refrigerator compressor 66 is provided in the gas refrigerant pipe 64. The liquid refrigerant pipe 65 is connected to the refrigerant circulation chamber 56 in the condenser 55 separately from the gas refrigerant pipe 64. By operating the refrigerator compressor 66, the refrigerant vaporized in the refrigerant circulation pipe 52 circulates in the refrigerant circulation chamber 56 in the condenser 55 through the gas refrigerant pipe 64. As the refrigerator compressor 66, a two-stage compressor having a two-stage compression structure in which a high stage portion and a low stage portion are provided is used, and the refrigerant is compressed in two stages. For this reason, the refrigerant which became gas can be compressed more suitably.

  Further, the refrigerant liquefied in the refrigerant flow pipe 52 in the capacitor 55 flows through the liquid refrigerant pipe 65 and is supplied to the refrigerant flow pipe 52 via the linear valve 53. The linear valve 53 adjusts its opening degree based on the temperature of the liquid refrigerant measured by a temperature sensor and a pressure sensor (not shown) and the pressure of the vaporized refrigerant. Further, in the condenser 55, the cooling water flows through the cooling water flow pipe 57, whereby the refrigerant in the gaseous state absorbs the cold heat and liquefies.

  A cooling water pipe 67 is connected to the cooling water circulation pipe 57 in the condenser 55, and the cooling water pipe 67 is connected to the cooling tower 58. The cooling water pipe 67 is provided with a cooling water circulation pump 68. By operating the cooling water circulation pump 68, the cooling water in the cooling tower 58 is circulated and supplied to the cooling water circulation pipe 57 in the condenser 55. In the cooling tower 58, the heat of the cooling water heated by liquefying the refrigerant in the condenser 55 is released into the atmosphere, and the cooling water is cooled.

  In this freezing apparatus 5, potassium formate-based brine is used as the brine, but in addition, calcium chloride-based, glycol-based, alcohol-based, chlorine-based, silicone-based, and fluorine-based brines shown in Table 1 can also be used. . Among these brines, those having a freezing point of −50 ° C. or less are preferably used, and therefore, a brine other than calcium chloride is suitable from this viewpoint.

  In order to circulate the brine, the viscosity of the brine is preferably 150 (mPa · s) or less. From this point of view, brines other than glycols are suitable. Further, brine used in civil engineering work is required to be free from decomposition due to welding heat or the like. For this reason, brines that cause flammability and toxicity are not suitable. From this point of view, alcohol-based and chlorine-based brines are unsuitable, and fluorine-based brines are not suitable in terms of toxicity because they may generate toxic gases when heated. Therefore, calcium chloride, glycol and potassium formate are preferred.

  As a result of studying based on each of these conditions, a brine that can be most suitably used is a potassium formate-based brine. For these reasons, potassium formate-based brine is used in this embodiment, but other brines shown in Table 1 can also be used. In particular, fluorine-based brine is unsuitable from the viewpoint that it can withstand use at a level of −80 ° C. and tends to be expensive, and may cause toxicity. If it considers the use in the condition which cannot produce toxicity except, it can use suitably.

  In addition, as an expansion valve in a conventional brine cooler, there are many that use an automatic valve, and a refrigeration apparatus using such a brine cooler can usually cool the brine only to about −30 ° C. In contrast, in the brine cooler 50 according to the present embodiment, the linear valve 53 is used. In the linear valve 53, the opening degree is changed based on the refrigerant suction temperature output from the temperature sensor and the refrigerant evaporation pressure output from the pressure sensor, and the brine cooler 50 is heated at a superheat degree separately set by the temperature controller. The heat exchange is performed with high efficiency.

  Here, the degree of superheat refers to the temperature difference between the evaporation temperature of the refrigerant and the suction temperature of the compressor. When the degree of superheat becomes 0, it means that the refrigerant has not completely evaporated in the evaporator, and the refrigerator compressor 66 performs liquid compression. When the refrigerator compressor performs liquid compression, it may cause a failure of the refrigerator compressor. Therefore, in order to prevent liquid compression, it is required to set the superheat degree to be greatly different. . However, when the degree of superheat is set to be large, for example, about 15 ° C., the capacity of the capacitor cannot be fully exhibited, resulting in inefficient operation.

  When an automatic valve is used as an expansion valve, the device cannot always be operated with a constant degree of superheat, so it is required to set a large degree of superheat to prevent damage to the refrigerator compressor. The In this regard, in the present embodiment, since the linear valve 53 is used as the expansion valve, the temperature can be set without greatly changing the degree of superheat. Specifically, the degree of superheat can be about 5 ° C. For this reason, since the capacity | capacitance of a capacitor | condenser can be exhibited efficiently, preventing damage to a refrigerator compressor, a brine can be cooled to temperature ranges, such as -35 degreeC--60 degreeC. Therefore, it is possible to freeze the ground at an early stage without increasing the size of the refrigerator equipment.

Further, in the method of flowing LN ₂ (liquid nitrogen) directly into the freezing tube, it is required to use a stainless steel tube as the freezing tube, but in this embodiment, the freezing tube has a temperature of about −60 ° C. to −35 ° C. Bring in brine. For this reason, an ordinary steel pipe can be used without requiring a high-temperature metal pipe that does not cause low-temperature brittleness, such as a stainless steel pipe. In addition, since the temperature is not lowered to a very low temperature such as -80 ° C., a simple cooling facility can be used. Therefore, the apparatus can be simplified correspondingly.

  This point will be further described. If the brine temperature is set low, the ground can be frozen at an early stage, but the resistance of the freezing tube becomes a problem. In general, carbon steel widely used as a steel pipe has a property of becoming brittle as the temperature decreases. FIG. 4 shows the result of an example of the Charpy test performed using SM490A as a test piece to support this property. FIG. 4A shows the relationship between the test piece temperature and impact absorption energy, and FIG. 4B shows the relationship between the test piece temperature and the brittle fracture surface ratio.

  As can be seen from FIG. 4 (a), even when the specimen has an impact absorption energy of 200 J or more at room temperature, the impact absorption energy is reduced to 10 J or less when the temperature is lower than −80 ° C. Further, as can be seen from FIG. 4B, when the temperature is -80 ° C. or lower, the brittle fracture surface ratio is almost 100%. On the other hand, when the temperature is about −60 ° C., the impact absorption energy can be maintained at about 50 J, and the brittle fracture surface rate can be suppressed to about 85%. From this, it can be seen that if the temperature of the brine is −60 ° C. or higher, the steel pipe can be prevented from being damaged even if a steel pipe using ordinary carbon steel or the like is used as a freezing pipe instead of stainless steel. . Therefore, by setting the temperature of the brine to −60 ° C. or higher and as low as possible, the ground can be frozen at an early stage while using a normal steel pipe as a freezing pipe.

  Next, a ground freezing method using the freezing apparatus according to the present embodiment will be described.

  In the freezing device 5 according to the present embodiment, when the ground is frozen when joining the shield tunnel, the brine circulation pump 63 is operated to circulate and supply the brine to the pasted frozen tube 31. The brine circulated by the brine circulation pump 63 passes through the brine cooler 50. At the same time, the refrigerator compressor 66 is operated to supply the refrigerant to the brine cooler 50.

  In the brine cooler 50, heat exchange is performed between the refrigerant supplied by the refrigerator compressor 66 and the brine supplied by the brine circulation pump 63. By this heat exchange, the refrigerant absorbs heat from the brine, vaporizes with the heat absorbed by the refrigerant, and the brine is cooled. By this heat exchange, the brine is cooled to about −60 ° C. to −50 ° C.

  The cooled low-temperature brine is circulated and supplied to the stick freezing tube 31 through the brine pipe 61. The low temperature brine is circulated and supplied to the affixed freezing pipe 31, so that the heat of the surrounding natural ground at the junction of the shield machine 1 and 2 is absorbed by the brine, the temperature of the brine rises, and the natural ground freezes. Be made. The brine whose temperature has risen flows into the brine cooler 50 via the brine pipe 61. The refrigerant vaporized in the brine cooler 50 is sent to the condenser 55 via the gas refrigerant pipe 64.

  Cooling water is circulated and supplied to the condenser 55 by operating the cooling water circulation pump 68. In the condenser 55, heat exchange is performed between the cooling water and the evaporated refrigerant, and the refrigerant is cooled and liquefied. The liquefied refrigerant is circulated and supplied to the brine cooler 50 to cool the brine.

  In this embodiment, when freezing natural ground and creating frozen soil, the temperature of the brine is in the range of −60 ° C. to −35 ° C., more preferably in the range of −60 ° C. to −50 ° C. Conventionally, in the creation of frozen soil using brine, the brine was set to about −30 ° C. to −25 ° C., but in this embodiment, the temperature is lower than this temperature, for example, −60 ° C. to −50 ° C. Frozen soil is being created. Thus, by creating frozen soil with low-temperature brine, it is possible to quickly create frozen soil and to suppress the occurrence of freezing expansion. In addition, it is possible to create frozen soil at a low temperature, and furthermore, the influence of the inhibition of frozen soil growth by the groundwater can be reduced.

  In this embodiment, the frozen soil is maintained while the shield tunnel is joined, and the frozen soil is thawed after the joining work is completed. In addition, while maintaining frozen soil, an excessively thick frozen soil thickness is not required, and if the frozen soil thickness becomes too large, there is a concern that it adversely affects the environment. Therefore, after circulating brine on the ground to grow frozen soil to a predetermined thickness, in order to prevent overproduction of frozen soil, the temperature is higher than the brine temperature at this time, specifically to a temperature exceeding -35 ° C. Circulate the adjusted brine to the frozen soil. As described above, after the frozen soil having a predetermined thickness is formed, the brine having a high temperature is circulated and supplied, thereby suppressing the excessive growth of the frozen soil and preventing the frozen soil from being thawed.

  Furthermore, after the shield tunnels are combined and the frozen soil is used, the frozen soil can be thawed by circulating a brine at a higher temperature, for example, about 0 ° C. to 30 ° C., to the region to be frozen. Moreover, frozen soil can be thawed at an early stage by circulating and supplying brine at a higher temperature, for example, about 90 ° C., to the ground. At this time, since the brine temperature is adjusted using the brine cooler 50, the brine temperature can be easily adjusted by adjusting the supply amount of the refrigerant supplied to the brine cooler 50, and the like. . Alternatively, the brine can be heated by an electric heater.

  Next, the results of numerical analysis (numerical simulation) performed by the present inventors on the relationship between the temperature of the brine and the thickness of the frozen soil to be created will be described. The results are shown in FIG. In the numerical analysis, the volumetric water content of the ground is set to 60%, the ground temperature is set to 20 ° C., and the brine is adjusted to −30 ° C., −50 ° C., −60 ° C., and −90 ° C. The freezing radius was predicted. In this simulation, the simulation was performed based on the single control theory when the thickness of one-sided frozen soil shown by a broken line in FIG.

  As can be seen from FIG. 5 and Table 2, when −30 ° C. brine was used, the period of 68 days was required for the frozen soil formation period to form 1.5 m of frozen soil, whereas −50 It took 39 days for the brine at 0 ° C, 33 days for the -60 ° C brine, and 25 days for the -80 ° C brine. From this result, it can be seen that the lower the temperature of the brine, the shorter the frozen soil preparation period is. At the same time, when -30 ° C brine is used, it takes 29 days longer than when -50 ° C brine is used, whereas when -50 ° C brine is used, it takes -80 ° C brine. The result was that there was a period that took only about 14 days longer than when using brine. Furthermore, when -60 ° C brine was used, there was a period that took only 8 days longer than when -80 ° C brine was used.

  On the other hand, in order to supply brine cooled to −80 ° C. to the ground, there has been a restriction that a tube that can withstand extremely low temperatures such as a stainless steel tube must be used as a freezing tube. . If it is about this point and about -60 degreeC--35 degreeC, normal steel pipes, such as SM490A and SGP (steel gas pipe, carbon steel pipe for piping) which used the steel pipe by said Charpy test, can be used.

  Further, in order to cool the brine to about −80 ° C., the equipment burden is imposed such as using a binary refrigerator as a large facility or using liquefied nitrogen as a refrigerant, but −60 ° C. to −35. If it is cooled to about 0 ° C., a simple two-stage compressor refrigerator can adequately cope with it. For this reason, it is possible to prevent an increase in the size of the refrigerator equipment.

  As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to the said embodiment. For example, in the above embodiment, frozen soil is created at the junction of the shield tunnel, but it can also be used when frozen soil is formed around the shield tunnel and other tunnels. It can also be used when creating frozen soil when constructing structures.

  Furthermore, in the said embodiment, although the sticking freezing tube is used as a freezing tube, it can also be set as another freezing tube. For example, a single pipe, double pipe, or triple pipe that is drilled and buried in the ground, a frozen pipe that is embedded inside a shield segment or steel pipe, or any other type of freezing pipe may be used. it can.

It is sectional drawing of the junction part of the 1st shield tunnel to which the freezing method is applied, and a 2nd shield tunnel. It is sectional drawing of the water stop apparatus provided in the shield machine. It is a figure explaining the flow of the refrigerant | coolant containing a brine cooler and a brine. It is a graph which shows the result in a Charpy test, (a) shows the relationship between test piece temperature and impact absorption energy, (b) shows the relationship between test piece temperature and a brittle fracture surface ratio, respectively. It is a graph which shows the relationship between the elapsed days before and after frozen soil creation, and frozen soil thickness.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st shield machine 2 ... 2nd shield machine 3 ... 1st water stop apparatus 4 ... 2nd water stop apparatus 5 ... Freezing apparatus 31 ... Adhesion freezing pipe 32 ... Injection pipe 33 ... Annular seal member 34 ... Cooling member 41 ... Adhesion freezing pipe 50 ... Brine cooler 51 ... Brine circulation chamber 52 ... Refrigerant circulation pipe 53 ... Linear valve 55 ... Condenser 56 ... Refrigerant circulation chamber 57 ... Cooling water circulation pipe 58 ... Cooling tower 61 ... Brine piping 62 ... Brine Header 62 ... Brine pipe 63 ... Brine circulation pump 64 ... Gas refrigerant pipe 65 ... Liquid refrigerant pipe 66 ... Refrigerator compressor 67 ... Cooling water pipe 68 ... Cooling water circulation pump X ... Freezing area

Claims (5)

A ground freezing method for freezing a freezing target area in the ground,
The refrigerant compressed by the compressor is supplied to the heat exchanger in the freezing pipe arranged in the freezing area, and the brine is cooled by exchanging heat between the brine and the refrigerant by the heat exchanger. A ground freezing method characterized in that a brine cooled in a range of −60 ° C. to −35 ° C. is circulated and supplied by a freezer to freeze the region to be frozen.   The ground freezing method according to claim 1, wherein a two-stage compressor that compresses the refrigerant in two stages is used as the compressor. The refrigerator includes an expansion valve that supplies the refrigerant supplied from the compressor while expanding the refrigerant to the heat exchanger.
The expansion valve is a linear valve that detects a suction temperature and an evaporation pressure of the refrigerant into the compressor, and linearly changes an opening degree based on the suction temperature and the evaporation pressure. The ground freezing method according to claim 1 or 2.   The ground freezing method according to any one of claims 1 to 3, wherein the brine has a viscosity of 150 (mPa · s) or less. After freezing the region to be frozen by the ground freezing method according to claim 1 to claim 4,
A ground freezing method, wherein brine having a temperature exceeding -35 ° C is supplied into a freezing pipe disposed in the freezing target region to prevent the frozen ground from being thawed and the frozen ground being excessively generated.

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