Novel artificial stratum rapid freezing device and method for pre-improving freezing area

Abstract

The invention discloses a novel artificial stratum rapid freezing device for a pre-improved freezing area, which comprises a storage tank (1) used for containing a sodium sulfate decahydrate solution, a stirring shaft (2), a driving motor (3), a double-layer three-blade propeller blade (21) and a liquid level sensor (4) are arranged in the storage tank (1), a discharge port (1b) is connected with a grouting pump (6) through a first conveying pipe (5), and a second conveying pipe (6) is arranged at the discharge port (1b). The grouting pump (6) is connected with a grouting pipe (8) with a double-layer sleeve structure through a second conveying pipe (7); a pressure sensor (9) is arranged in the grouting pipe (8), the freezing pipe (10) is connected with a freezing station (12) through a refrigerating medium circulating pipeline (11), a temperature sensor (13) is arranged at the lower end of the freezing pipe (10), and a refrigerating unit (121) is arranged in the freezing station (12). The method has the advantages that the soil layer in the freezing area is pre-improved, the freezing speed of the soil layer is increased, the quick freezing cost is reduced, the freezing uniformity is guaranteed, meanwhile, pollution to the surrounding environment is avoided, and the method is efficient and environmentally friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel freezing construction, and in particular relates to a novel artificial stratum rapid freezing device and method for a pre-improved freezing zone. Background Art

[0002] With the continuous occurrence of underground tunnel construction accidents, the application scenarios of tunnel freezing construction are becoming more and more extensive, and often involve various types of engineering repairs. However, the traditional freezing method has the problems of slow construction speed, long time and high cost. Taking the complex underground tunnel repair project in the city as an example, when using the traditional freezing method, it takes several days to prepare the refrigeration equipment and lay the refrigerant circulation pipeline in the early stage. Then the freezing procedure is officially started. The temperature of each inch of soil drops extremely slowly, with only a few centimeters per day. It takes at least more than a month and up to several months to build a stable frozen wall that can support subsequent construction.

[0003] The slow freezing problem of traditional freezing methods has always been a close concern of shield tunnel construction workers. Although there are solutions such as liquid nitrogen freezing and dry ice freezing, although their freezing speed is fast, the freezing is uneven and the cost is high, this problem has never been effectively solved. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that the existing freezing cannot take into account both speed and cost and the freezing is uneven. A new artificial stratum rapid freezing device with pre-improved freezing zone is provided, which can pre-improve the soil layer in the freezing zone, speed up the freezing speed of the soil layer, reduce the cost of rapid freezing, ensure the uniformity of freezing, and at the same time will not cause pollution to the surrounding environment, which is efficient and environmentally friendly.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A novel artificial stratum rapid freezing device for pre-improved freezing zone comprises a storage tank for containing sodium sulfate decahydrate solution, a vertical stirring shaft is arranged in the storage tank, the upper end of the stirring shaft extends out of the storage tank from a feed inlet and is connected to a drive motor, and the lower end is connected to a double-layer three-blade propeller blade, a liquid level sensor is also connected in the storage tank, and the discharge port at the lower end is connected to a grouting pump through a first delivery pipe; The outlet of the grouting pump is connected to the upper end of the grouting pipe through the second delivery pipe. The grouting pipe is a double-layer casing structure, which includes an inner pipe and an outer pipe nested with each other. The axes of the inner and outer pipes coincide with each other, and the inner pipe is evenly distributed with inner grouting holes, and the outer pipe is evenly distributed with outer grouting holes. The inner grouting holes and the outer grouting holes at the same horizontal height are staggered to ensure the uniformity of grouting. A pressure sensor is provided at the upper end of the grouting pipe and the grouting pipe cooperates with the borehole to be grouted. The borehole after grouting cooperates with the freezing pipe. The upper end of the freezing pipe is connected to the freezing station through a refrigeration medium circulation pipeline, and a temperature sensor is also provided at the lower end. The freezing station is provided with a refrigeration unit and refrigeration medium that cooperate with each other. The liquid level sensor, grouting pump, pressure sensor, temperature sensor and freezing station respectively connect their respective liquid level signals, grouting signals, pressure signals, temperature signals and refrigeration signals to the external PLC through the communication network for intelligent control of various parameter values.

[0006] Furthermore, the storage tank is a stainless steel cylindrical tank body, and the sodium sulfate decahydrate solution is stored in the stainless steel storage tank, which has certain corrosion resistance and pressure resistance. The PLC is a control system including a human-machine interface HMI. The operator sets various parameters such as grouting volume, grouting speed, and freezing temperature through the PLC, and checks the operating status of the device, sensor data and other information in real time.

[0007] Furthermore, the grouting pump is a plunger pump that accurately controls the flow rate, and its flow rate adjustment range is 0~100L / min, which is adjusted according to the actual needs of the project. The pump body is connected to the discharge port of the storage tank through a corrosion-resistant first delivery pipe, and the first delivery pipe is connected to a first regulating check valve, and the second delivery pipe is also connected to a second regulating check valve to prevent the solution from flowing back.

[0008] Furthermore, the freezing pipe is made of a copper pipe with high thermal conductivity and a diameter of 50 to 100 mm. The circulating refrigerant medium inside the freezing pipe is ethylene glycol solution or brine. The freezing pipes are arranged in the formation at intervals, generally with a spacing of 0.5 to 1.5 m. Each freezing pipe is connected to a refrigeration unit, which cools the refrigerant medium to the required temperature.

[0009] Furthermore, the temperature sensor is arranged at different depths and positions in the formation to monitor the changes in the formation temperature in real time. The temperature sensor adopts high-precision thermocouples or thermistors with a measurement accuracy of ±0.1°C, and transmits the collected temperature data to the PLC. The PLC determines the freezing effect based on the temperature data and adjusts the grouting speed and refrigeration power accordingly.

[0010] In order to further achieve the purpose of the present invention, a novel artificial stratum rapid freezing method for pre-improved frozen areas is also provided, using the above-mentioned device, and the specific steps are as follows: (1) After the drilling rig drills the hole, prepare a sodium sulfate decahydrate solution of appropriate concentration in a storage tank, and start the drive motor to drive the double-layer three-blade propeller to mix it evenly; (2) Insert the grouting pipe into the borehole. The operator sets the grouting volume, grouting speed and freezing temperature through the PLC HMI, and then starts the grouting pump. The sodium sulfate decahydrate solution is injected from the storage tank into the formation through the double-casing grouting pipe. During the grouting process, the pressure sensor monitors the grouting pressure in real time. When the pressure exceeds the set value, the PLC automatically adjusts the flow rate of the grouting pump or stops grouting. (3) After grouting is completed, the grouting pipe is pulled out and the freezing pipe is inserted into the original borehole. The refrigeration unit is started to cool the refrigerant and circulate it in the freezing pipe to cool the soil layer. The temperature sensor monitors the formation temperature in real time. When the temperature reaches below the crystallization temperature of sodium sulfate decahydrate, 32.4°C, sodium sulfate decahydrate begins to crystallize, and the released latent heat of crystallization is taken away by the refrigerant in the freezing pipe. (4) The PLC continuously adjusts the cooling power of the refrigeration unit based on the temperature data fed back by the temperature sensor to ensure that the ground is frozen according to the set requirements; (5) When the preset freezing time is reached or the ground temperature reaches the set minimum freezing temperature and remains stable for a period of time, the device stops running. At this time, a stable frozen soil structure is formed in the ground, and subsequent engineering construction can be carried out.

[0011] Furthermore, in the step (1), different concentrations of sodium sulfate decahydrate solution are selected according to the type of soil. For coarse sandy soil, the concentration of the sodium sulfate decahydrate solution is 20%-30%; for fine sandy soil and sandy loam, the concentration of the sodium sulfate decahydrate solution is 30%-40%; for clay loam, the concentration of the sodium sulfate decahydrate solution is 40%-50%; for ordinary clay, the concentration of the sodium sulfate decahydrate solution is 50%-60%; for hard clay, the concentration of the sodium sulfate decahydrate solution is 60%-70%.

[0012] Furthermore, in step (2), the grouting amount is calculated according to the pore volume of the formation: first, the porosity of the formation is determined by geological survey, and the total volume of the formation to be grouted is calculated. The grouting amount is generally 80% to 120% of the pore volume of the formation; the grouting rate is determined according to the permeability of the formation. For formations with good permeability, the grouting rate is controlled at 50 to 100 L / min; for formations with poor permeability, the grouting rate is controlled at 10 to 30 L / min to avoid excessive pressure that damages the formation structure; the freezing temperature needs to be set within a range that can meet the stability of the formation during excavation, generally -10°C to -20°C; for long-term water stopping, the freezing temperature is set at -20°C to -40°C; for formations with a water content of more than 30%, the freezing temperature is set below -20°C.

[0013] Furthermore, in step (4), when freezing begins, the ground temperature is relatively high, and the difference between the temperature feedback from the temperature sensor and the set temperature is large. The refrigeration unit operates at a relatively high power to rapidly reduce the ground temperature. As the ground temperature approaches the set value, the difference in the temperature sensor feedback decreases, and the power of the refrigeration unit also gradually decreases, so that the temperature stabilizes near the set value.

[0014] Furthermore, in step (4), the temperature sensor and the refrigeration unit power are adjusted using a PID control algorithm, and the refrigerator power is adjusted according to the temperature deviation, i.e., the ratio P, integral I and differential D of the difference between the actual temperature and the set temperature. The formula is expressed as follows: , in, u ( t ) is the output control quantity, which is related to the refrigerator power. k p is the proportionality coefficient, e ( t ) is the temperature deviation, T i is the integration time constant, T d is the differential time constant, and the control quantity calculated by this algorithm is used to indirectly adjust the refrigerator power.

[0015] Compared with the prior art, the advantages of the technical solution of the present invention are: (1) Compared with the traditional freezing method, the present invention makes full use of the high thermal conductivity of sodium sulfate decahydrate after crystallization. By replacing the freezing medium of the soil layer, the sodium sulfate decahydrate solution is injected into the soil by grouting. After the solution crystallizes, the high thermal conductivity of sodium sulfate decahydrate is used to accelerate the freezing of the soil. (2) The sodium sulfate decahydrate used in the present invention is a relatively stable compound. Under normal freezing process conditions, it will not undergo violent chemical reactions with minerals in the soil. It does not require the addition of other chemical materials or special processes, and will not cause pollution to the surrounding environment. It is green and environmentally friendly. (3) The present invention has a complete control system, has certain flexibility, is easy to operate, and has a clear project progress; (4) The sodium sulfate decahydrate of the present invention has a relatively compact crystal structure, which is conducive to heat conduction. At the same time, during the crystallization process, the volume change is relatively stable, and the frost heave problem will basically not occur; (5) The method of the present invention has a wide range of applications. In addition to being applicable to the field of shield tunnel construction, it can also be applied to other engineering construction fields that require solving the problem of frozen soil layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1It is a combined diagram of a novel artificial stratum rapid freezing device for pre-improved freezing zone of the present invention; Figure 2 It is a schematic diagram of the internal structure of the storage tank of the present invention; Figure 3 It is a schematic diagram of the structure of the first delivery pipe and the first regulating check valve of the present invention; Figure 4 It is a schematic diagram of the opening and closing of the cross section of the first and second regulating check valves of the present invention; Figure 5 It is a schematic diagram of the connection structure between the grouting pump and the grouting pipe of the present invention; Figure 6 It is a schematic diagram of the distribution of grouting holes on the cross section of the grouting pipe of the present invention; Figure 7 It is a schematic diagram of the connection structure between the freezing station and the freezing pipe of the present invention. DETAILED DESCRIPTION Example

[0017] To make the present invention more clearly understood, a novel artificial stratum rapid freezing device and method for pre-improved freezing zone of the present invention are further described below in conjunction with the accompanying drawings. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] A novel artificial stratum rapid freezing device for pre-improved freezing zone, characterized by: See also Figure 1 and Figure 2 , comprising a storage tank 1 for containing sodium sulfate decahydrate solution, a vertical stirring shaft 2 is arranged in the storage tank 1, the upper end of the stirring shaft 2 extends out of the storage tank 1 through a feed port 1a and is connected to a drive motor 3, and the lower end is connected to a double-layer three-blade propeller blade 21, a liquid level sensor 4 is also connected in the storage tank 1, and a discharge port 1b at the lower end thereof is connected to a grouting pump 6 through a first delivery pipe 5; See also Figure 1 , Figure 5 and Figure 6 The outlet of the grouting pump 6 is connected to the upper end of the grouting pipe 8 through the second delivery pipe 7. The grouting pipe 8 is a double-layer casing structure, which includes an inner pipe 81 and an outer pipe 82 nested with each other. The axes of the inner and outer pipes coincide with each other, and the inner pipe 81 is evenly distributed with inner grouting holes 83a, and the outer pipe 82 is evenly distributed with outer grouting holes 83b, and the inner grouting holes 83a and the outer grouting holes 83b located at the same horizontal height are staggered to ensure the uniformity of grouting; See also Figure 1 , Figure 3 and Figure 4The first delivery pipe 5 and the second delivery pipe 7 are respectively connected with a first regulating check valve 51 and a second regulating check valve 71, and the pointer 0° grouting pipe is in a closed state, and the grouting holes 83 of the 6 vertical grouting pipes are opened by turning right by 15°, and the grouting holes 83 of the 12 vertical grouting pipes are opened by turning right by 30°; See also Figure 1 and Figure 7 The upper end of the grouting pipe 8 is provided with a pressure sensor 9 and the grouting pipe 8 cooperates with the borehole to be grouted, and the borehole after grouting cooperates with the freezing pipe 10. The upper end of the freezing pipe 10 is connected to the freezing station 12 through the refrigeration medium circulation pipeline 11, and the lower end is also provided with a temperature sensor 13. The freezing station 12 is provided with a refrigeration unit 121 and a refrigeration medium that cooperate with each other; The liquid level sensor 4, grouting pump 6, pressure sensor 9, temperature sensor 13 and freezing station 12 respectively connect their respective liquid level signals, grouting signals, pressure signals, temperature signals and refrigeration signals to the external PLC 14 through a communication network for intelligent control of various parameter values.

[0019] In actual operation, the novel artificial ground rapid freezing method using the above device to pre-improve the freezing zone is as follows, including: (1) Drilling is performed on site. After drilling, the feed port 1a is opened, and a sodium sulfate decahydrate solution of appropriate concentration is poured into a stainless steel storage tank with a liquid level sensor 4. The drive motor 3 is started to drive the double-layer three-blade propeller 21 to mix the solution evenly. (2) Connect the discharge port 1b of the storage tank 1 and the grouting pump 6 with a corrosion-resistant pipe with a first regulating check valve 51, and then connect the grouting pump 6 and the grouting pipe 8 of a double-layer casing structure with a pressure sensor 9 with a corrosion-resistant pipe with a second regulating check valve 71; (3) The grouting pipe 8 is inserted into the borehole. The operator sets the grouting amount, grouting speed, freezing temperature and other parameters through the human-machine interface 141 of the PLC 14, and starts the grouting pump 6. The sodium sulfate decahydrate solution is injected into the formation through the grouting hole by grouting. During the grouting process, the pressure sensor 9 monitors the grouting pressure in real time. When the pressure exceeds the set value, the control system automatically adjusts the flow rate of the grouting pump or stops grouting. (4) After grouting is completed, the freezing pipe 10 with the temperature sensor 13 is inserted into the ground, the refrigeration unit 121 of the freezing station 12 is started, and the refrigerant circulates through the refrigerant circulation pipeline 11 to cool the soil layer. The temperature sensor 13 monitors the ground temperature in real time, and sodium sulfate decahydrate begins to crystallize. The released latent heat of crystallization is taken away by the refrigerant in the freezing pipe 10; (5) PLC 14 continuously adjusts the cooling power of the refrigeration unit 121 of the freezing station 12 according to the temperature data fed back by the temperature sensor 13 to ensure that the ground is frozen according to the set requirements. If the temperature in a certain area drops too slowly, PLC 14 will increase the cooling power. If the temperature drops too quickly, the cooling power may be appropriately reduced to achieve uniform and stable freezing. (6) When the preset freezing time is reached or the ground temperature reaches the set minimum freezing temperature and remains stable for a period of time, the device stops running. At this time, a stable frozen soil structure is formed in the ground, and subsequent engineering construction can be carried out, such as tunnel excavation and foundation construction.

[0020] The working principle adopted by the present invention is as follows: Since sodium sulfate decahydrate crystals have high thermal conductivity and phase change freezing forms an overall cold source, it prevents the intrusion of external heat and the loss of heat inside the soil, thereby ensuring that the soil freezing conditions required by the freezing process are maintained. When the expected freezing area and temperature are reached, the low temperature state maintained by the sodium sulfate decahydrate crystal solid can effectively prevent the migration of water and heat exchange in the soil. When the ambient temperature is lowered by freezing pipes and other means, the sodium sulfate decahydrate solution will begin to crystallize when it reaches its crystallization temperature below 32.4°C. During the crystallization process, the sodium sulfate decahydrate molecules will be arranged according to a certain lattice structure and change from liquid to solid. This crystallization process is an exothermic process, but because the low-temperature medium in the freezing pipe will take away the heat, the overall ambient temperature will still drop. The crystallization of sodium sulfate decahydrate is like forming tiny "cold sources" in the pores of the soil. Due to its compact crystal structure and good thermal conductivity, it can continuously transfer cold to areas that may heat up and keep the soil in a frozen state. This ensures that the soil freezing conditions required by the freezing process are maintained, such as during the construction of underground projects, ensuring the stability of the soil in the construction area. Its crystallization process is relatively orderly, and it generally does not over-expand the soil pores like some expansive substances, causing the pore structure to be destroyed. In addition, sodium sulfate decahydrate itself is a relatively stable compound. Under normal freezing process conditions, it will not undergo violent chemical reactions with minerals in the soil.

[0021] In this embodiment, the concentration of the sodium sulfate decahydrate solution is generally determined according to the type of soil, as follows: (1) For coarse sand, since lower concentration solutions can flow smoothly in the pores of coarse sand and when the temperature drops, there will be enough solute crystallization to form an effective heat conduction and freezing structure, thus enhancing the strength and stability of the sand, the concentration of sodium sulfate decahydrate solution is 20%~30%.

[0022] (2) For fine sand, since a higher concentration of solution can overcome the resistance to diffusion caused by the small pores of fine sand, a continuous heat conduction path can be formed in the fine sand. When the temperature changes, heat transfer and phase change processes can be better achieved. Therefore, the concentration of sodium sulfate decahydrate solution is 30%~40%.

[0023] (3) For sandy loam, the concentration of sodium sulfate decahydrate solution is 30%~40%. This concentration range can not only ensure that the solution has good permeability in sandy loam, but also provide sufficient phase change materials when the temperature changes, so that the solution can crystallize smoothly in the pores, enhance the integrity and stability of the soil, and at the same time use its thermal conductivity to regulate the soil temperature.

[0024] (4) For clay loam, a higher concentration can overcome the adsorption of solutes by clay and the obstruction of small pores, ensuring that the solution is evenly distributed in the soil layer and effectively crystallizes when the temperature drops, forming a stable thermal conductive and supporting structure. Therefore, the concentration of sodium sulfate decahydrate solution is 40%~50%.

[0025] (5) For ordinary clay, the concentration of sodium sulfate decahydrate solution is 50%~60%. This concentration can ensure that there is enough solute to overcome the adsorption and obstruction of the clay, form an effective heat conduction network in the pores, and crystallize in large quantities when the temperature drops, changing the mechanical properties of the clay and improving its strength and deformation resistance.

[0026] (6) For hard clay, a high concentration is required to ensure that the solution can penetrate into the pores of the hard clay and form sufficient crystalline phases when cooled, thereby effectively enhancing the hardness and stability of the soil. Therefore, the concentration of sodium sulfate decahydrate solution is 60%~70%.

[0027] In this embodiment, the setting method and reference basis for setting the grouting amount, grouting speed and freezing temperature are as follows: (1) Regarding the grouting volume, it is calculated according to the pore volume of the formation: first determine the porosity of the formation through geological exploration, and calculate the total volume of the formation that needs grouting. Generally speaking, the grouting volume should be 80% to 120% of the pore volume of the formation. Loose formations with large pores, such as sand and gravel, require a larger grouting volume to achieve a better filling and reinforcement effect; while dense formations such as clay require a relatively small grouting volume.

[0028] (2) Regarding the grouting speed, the grouting speed should be set in combination with the project requirements. For example, if the flow adjustment range of the plunger pump is 0~100L / min, the appropriate speed can be selected within this range according to the actual situation. Generally, the initial grouting speed can be set to 30~50L / min. After starting grouting, observe the grouting absorption of the formation. If the grouting absorption is fast, the grouting speed can be appropriately increased; if the grouting pressure rises rapidly, it means that the grouting capacity of the formation is limited, and the grouting speed should be reduced. Formations with good permeability, such as sand layers, can absorb slurry quickly, and a higher grouting speed can be used, generally 50~100L / min; for formations with poor permeability, such as clay layers, the grouting speed should be controlled at 10~30L / min to avoid excessive pressure that damages the formation structure.

[0029] (3) Regarding freezing temperature, if the purpose is to strengthen the ground in the short term for excavation, the freezing temperature can be set within the range that can ensure the stability of the ground during excavation, generally -10℃ to -20℃; if the purpose is to stop water for a long time, a lower freezing temperature may be required, such as -20℃ to -40℃. Ground with high water content requires a lower freezing temperature to achieve effective freezing. For ground with a water content of more than 30%, the freezing temperature needs to be set below -20℃; while for ground with low water content, the freezing temperature can be appropriately increased.

[0030] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A novel artificial stratum rapid freezing device for pre-improved freezing zone, characterized in that: The invention comprises a storage tank (1) for containing sodium sulfate decahydrate solution, wherein a vertical stirring shaft (2) is arranged in the storage tank (1), wherein the upper end of the stirring shaft (2) extends out of the storage tank (1) through a feed port (1a) and is connected to a drive motor (3), and the lower end is connected to a double-layer three-blade propeller blade (21), and the storage tank (1) is also connected to a liquid level sensor (4), and the discharge port (1b) at the lower end is connected to a grouting pump (6) through a first delivery pipe (5); The outlet of the grouting pump (6) is connected to the upper end of the grouting pipe (8) through the second delivery pipe (7). The grouting pipe (8) is a double-layer casing structure, comprising an inner pipe (81) and an outer pipe (82) which are nested with each other. The axes of the inner and outer pipes coincide with each other. The inner pipe (81) is evenly distributed with inner grouting holes (83a), and the outer pipe (82) is evenly distributed with outer grouting holes (83b). The inner grouting holes (83a) and the outer grouting holes (83b) which are located at the same horizontal height are staggered. A pressure sensor (9) is provided at the upper end of the grouting pipe (8), and the grouting pipe (8) cooperates with the borehole to be grouted. The borehole after grouting cooperates with the freezing pipe (10). The upper end of the freezing pipe (10) is connected to the freezing station (12) via a refrigeration medium circulation pipeline (11), and a temperature sensor (13) is provided at the lower end. A refrigeration unit (121) and a refrigeration medium that cooperate with each other are provided in the freezing station (12); The liquid level sensor (4), the grouting pump (6), the pressure sensor (9), the temperature sensor (13) and the freezing station (12) respectively connect their respective liquid level signals, grouting signals, pressure signals, temperature signals and refrigeration signals to an external PLC (14) via a communication network.

2. The novel artificial stratum rapid freezing device for pre-improved freezing zone according to claim 1 is characterized by: The storage tank (1) is a stainless steel cylindrical tank body. The sodium sulfate decahydrate solution is stored in the stainless steel storage tank (1). The PLC (14) is a control system including a human-machine interface (141). An operator sets various parameters such as grouting volume, grouting speed, and freezing temperature through the PLC (14) and checks the operating status and data of the device in real time.

3. The novel artificial stratum rapid freezing device for pre-improved frozen areas according to claim 1 or 2, characterized in that: The grouting pump (6) is a plunger pump with precise flow control, and its flow adjustment range is 0-100 L / min, which is adjusted according to the actual needs of the project. The pump body is connected to the discharge port (1b) of the storage tank (1) through a corrosion-resistant first delivery pipe (5), and the first delivery pipe (5) is connected to a first regulating check valve (51), and the second delivery pipe (7) is also connected to a second regulating check valve (71).

4. The novel artificial stratum rapid freezing device for pre-improved frozen areas according to claim 1 or 2, characterized in that: The freezing pipe (10) is made of a copper pipe with high thermal conductivity and has a diameter of 50 to 100 mm. The circulating refrigerant medium inside the freezing pipe (10) is an ethylene glycol solution or brine. The freezing pipes (10) are arranged in the formation at intervals, generally with a spacing of 0.5 to 1.5 m. Each freezing pipe (10) is connected to a refrigeration unit (121), and the refrigeration unit (121) cools the refrigerant medium to a desired temperature.

5. The novel artificial stratum rapid freezing device for pre-improved frozen areas according to claim 1 or 2, characterized in that: The temperature sensor (13) is arranged at different depths and positions in the formation to monitor changes in the formation temperature in real time. The temperature sensor (13) uses a high-precision thermocouple or thermistor with a measurement accuracy of ±0.1°C, and transmits the collected temperature data to the PLC (14). The PLC (14) determines the freezing effect based on the temperature data and adjusts the grouting speed and cooling power accordingly.

6. A novel method for rapid freezing of artificial strata using the device as claimed in claim 1, comprising the following specific steps, characterized in that: Step 1: After the drilling rig drills the hole, a sodium sulfate decahydrate solution of appropriate concentration is prepared in a storage tank (1), and a driving motor (3) is started to drive a double-layer three-blade propeller (21) to mix the solution evenly; Step 2: insert the grouting pipe (8) into the borehole, and the operator sets the grouting amount, grouting speed and freezing temperature through the HMI of the PLC (14), and then starts the grouting pump (6). The sodium sulfate decahydrate solution is injected into the formation from the storage tank (1) through the double-casing grouting pipe. During the grouting process, the pressure sensor (9) monitors the grouting pressure in real time. When the pressure exceeds the set value, the PLC (14) automatically adjusts the flow rate of the grouting pump (6) or stops grouting. Step 3: After the grouting is completed, the grouting pipe (8) is pulled out and the freezing pipe (10) is inserted into the original borehole, and the refrigeration unit (121) is started to cool the refrigerant and circulate it in the freezing pipe (10) to cool the soil layer. The temperature sensor (13) monitors the stratum temperature in real time. When the temperature reaches below the crystallization temperature of sodium sulfate decahydrate 32.4° C., the sodium sulfate decahydrate begins to crystallize, and the released latent heat of crystallization is taken away by the refrigerant in the freezing pipe (10); Step 4: The PLC (14) continuously adjusts the refrigeration power of the refrigeration unit (121) according to the temperature data fed back by the temperature sensor (13) to ensure that the ground is frozen according to the set requirements; Step 5: When the preset freezing time is reached or the ground temperature reaches the set minimum freezing temperature and remains stable for a period of time, the device stops running. At this time, a stable frozen soil structure is formed in the ground, and subsequent engineering construction can be carried out.

7. The novel artificial stratum rapid freezing method for pre-modified frozen zone according to claim 6, characterized in that: In the step 1, different concentrations of sodium sulfate decahydrate solution are selected according to the type of soil. For coarse sandy soil, the concentration of the sodium sulfate decahydrate solution is 20%-30%; for fine sandy soil and sandy loam, the concentration of the sodium sulfate decahydrate solution is 30%-40%; for clay loam, the concentration of the sodium sulfate decahydrate solution is 40%-50%; for ordinary clay, the concentration of the sodium sulfate decahydrate solution is 50%-60%; for hard clay, the concentration of the sodium sulfate decahydrate solution is 60%-70%.

8. The novel artificial stratum rapid freezing method for pre-improved frozen zone according to claim 6, characterized in that: In the step 2, the grouting amount is calculated according to the pore volume of the formation: first determine the porosity of the formation through geological exploration, and calculate the total volume of the formation that needs grouting. The grouting amount is generally 80% to 120% of the pore volume of the formation; the grouting speed is determined according to the permeability of the formation. For formations with good permeability, the grouting speed is controlled at 50 to 100 L / min; for formations with poor permeability, the grouting speed is controlled at 10 to 30 L / min to avoid excessive pressure that damages the formation structure; the freezing temperature needs to be set within a range that can meet the stability of the formation during excavation, generally -10°C to -20°C; for long-term water stopping, the freezing temperature is set at -20°C to -40°C; for formations with a water content of more than 30%, the freezing temperature is set below -20°C.

9. The novel artificial stratum rapid freezing method for pre-improved frozen zone according to claim 6, characterized in that: In step 4, when freezing begins, the formation temperature is high, the temperature feedback from the temperature sensor has a large difference with the set temperature, and the refrigeration unit operates at a higher power to quickly reduce the formation temperature; as the formation temperature approaches the set value, the difference in temperature sensor feedback decreases, and the power of the refrigeration unit gradually decreases, so that the temperature stabilizes near the set value.

10. The novel artificial stratum rapid freezing method for pre-modified frozen areas according to claim 9, characterized in that: In step 4, the temperature sensor and the refrigeration unit power are adjusted using a PID control algorithm, and the refrigerator power is adjusted according to the temperature deviation, i.e., the ratio P, integral I and differential D of the difference between the actual temperature and the set temperature. The formula is expressed as follows: ， in, u ( t ) is the output control quantity, which is related to the refrigerator power. k p is the proportionality coefficient, e ( t ) is the temperature deviation, T i is the integration time constant, T d is the differential time constant, and the control quantity calculated by this algorithm is used to indirectly adjust the refrigerator power.

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