Freezing pipe outer annular space filling material performance testing device and testing method thereof

Abstract

The invention relates to the technical field of filling material performance testing, in particular to a freezing pipe outer annular space filling material performance testing device and a testing method thereof.The freezing pipe outer annular space filling material performance testing device is composed of a main freezing pipe, an auxiliary freezing pipe, M20 bolts, a model test box, a square PVC pipe, a ground temperature simulation system and the like; according to the device, the temperature of each soil layer in the model test box is independently and accurately controlled by using the electronic temperature controller and the sectionally pasted heating tape, and the temperature is adjusted according to the actual formation temperature change, so that the formation environment influence is really simulated; the cold energy is continuously and circularly transferred in the freezing pipes through the low-temperature saline water, and different numbers of freezing pipes are supported to be arranged to simulate the cold energy diffusion and superposition influence; the problem that the performance of the filling material in the annular space outside the freezing pipe is difficult to test in a real service environment is solved, the test accuracy is improved, and an important test means is provided for performance evaluation of the filling material in freezing method construction.

Description

Technical Field

[0001] The invention relates to the technical field of filling material performance testing, in particular to a device and a method for testing the performance of a filling material in an annular space outside a freezing pipe. Background Art

[0002] During coal mine shaft construction, water-bearing, unstable strata are often penetrated, especially in western my country, where weakly cemented, water-bearing strata necessitate the use of the freezing method. This method requires drilling a freezing hole, typically a 210mm diameter circular hole, and a 140mm diameter freezing pipe. This creates an annular space 35mm thick between the freezing hole and the freezing pipe. Mud is used to protect the walls during freezing hole drilling. Since well construction in western China typically involves freezing the entire depth in one go, to prevent the formation of vertical water channels along the annular space after the frozen wall thaws, it is necessary to replace the retaining slurry with slow-setting cement slurry within 100m above the bottom chamber. This improves the frost resistance and impermeability of the annular space filling material. This places higher demands on the density, frost resistance, and impermeability of the slow-setting cement slurry.

[0003] However, filling the annular space outside the freezing pipe is a concealed project and is limited by the narrow annular space. On-site performance testing of the retarding cement slurry within the replacement section's annular space is extremely difficult and expensive. The conventional approach is to retain the retarding cement slurry used on-site in a test mold, cure it indoors, and then conduct performance testing in the laboratory. Obviously, the test specimen environment during testing differs significantly from the on-site project, distorting the subsequent performance test results. Similarly, laboratory performance testing of the retarding cement slurry material during development was conducted under normal test conditions, failing to account for the effects of varying ground temperatures, the low temperatures during freezing of the freezing pipe, and the combined effects of cooling at different locations within the freezing pipe. As is well known, failure to account for these factors during performance testing of the retarding cement slurry inevitably results in significant discrepancies between the test results and actual operating conditions. Consequently, it is impossible to effectively evaluate the performance of the retarding cement slurry and determine whether the retarding cement slurry used in the project meets actual requirements.

[0004] Therefore, it is very necessary to provide an improved technical solution for the above-mentioned shortcomings of the prior art. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the prior art by providing a performance testing device and method for filling materials in the annular space outside a freezing pipe. This device can not only simulate on-site ground temperature, but also reproduce the freezing process and the impact of the cold accumulation effect on the performance of the filling material, thereby obtaining performance indicators that are closer to actual working conditions in the laboratory. The present invention can more comprehensively conduct performance testing of filling materials under laboratory simulated ground temperature and freezing pipe freezing, obtain performance evaluation indicators of the filling materials under corresponding conditions, and provide a test method and important reference for performance testing of filling materials in the annular space outside a freezing pipe.

[0006] To achieve the above objectives, the technical solutions of the present invention are as follows: A device for testing the performance of filling materials in the annular space outside a freezing pipe and a testing method thereof include a main freezing pipe, a secondary freezing pipe, an M20 bolt, a square PVC pipe, a first soil layer, a second soil layer, a third soil layer, a fourth soil layer, a fifth soil layer, a steel plate, a model test box, an electronic heating belt, a waterproof lead, an electronic temperature controller, an inlet, an outlet, and a hanging hole. The main freezing pipe and the secondary freezing pipe have a low-temperature brine inlet and a low-temperature brine outlet. The main freezing pipe and the secondary freezing pipe are buried in the soil layer and the lower end is in contact with the bottom of the model test box. The square PVC pipe Arranged near the freezing pipe, the first soil layer, the second soil layer, the third soil layer, the fourth soil layer, and the fifth soil layer are stacked in the model test box, 16 hoisting holes are provided at the bottom of the model test box, the hoisting holes are provided on the lower end surface of the model test box and are equipped with M20 bolts of matching size, the bottom of the steel plate is fixed with the M20 bolts and is placed vertically in the model test box, the electronic heat-generating belt is adhered to the outside of the steel plate, and the electronic temperature controller is connected to the electronic heat-generating belt through a waterproof lead and is placed outside the model test box.

[0007] Preferably, in the above-mentioned freezing pipe outer annular space filling material performance testing device and testing method, the main freezing pipe and auxiliary freezing pipe have a diameter of 140 mm and a height of 2000 mm, and the upper end of the freezing pipe is exposed from the upper part of the fifth soil layer.

[0008] Preferably, in the above-mentioned device for testing the performance of the filling material of the annular space outside the freezing pipe and the testing method thereof, when a single freezing pipe is arranged, a square PVC pipe is arranged every 20 cm and 40 cm in the four directions of top, bottom, left and right with the main freezing pipe as the center, and a total of square PVC pipes are placed.

[0009] Preferably, in the above-mentioned device for testing the performance of the filling material of the annular space outside the freezing pipe and the testing method thereof, the testing method is that when multiple freezing pipes are arranged, the two freezing pipes are 80 cm apart, and a square PVC pipe is arranged every 20 cm and 40 cm in the four directions above, below, left and right of the main freezing pipe and the auxiliary freezing pipe, respectively, for a total of 16 square PVC pipes.

[0010] Preferably, in the above-mentioned device and method for testing the performance of the annular space filling material outside the freezing pipe, the soil stratification is determined according to the project overview. The exemplary soil is divided into 5 layers, and the thickness of each soil layer is 400mm, 600mm, 300mm, 400mm, and 300mm from top to bottom.

[0011] Preferably, in the above-mentioned device for testing the performance of the filling material of the annular space outside the freezing pipe and the testing method thereof, the size of the model test box is 4000mm (length) × 3000mm (width) × 3000mm (height).

[0012] Preferably, in the above-mentioned device for testing the performance of the filling material in the annular space outside the freezing pipe and the testing method thereof, the size of the square PVC pipe is 200mm (length) × 200mm (width) × 2000mm (height).

[0013] Compared with the prior art, the present invention has the following beneficial effects: The device of the present invention circulates low-temperature brine continuously in the freezing pipe to achieve the diffusion of cold energy to the outside of the freezing pipe, so as to simulate the working conditions of the freezing pipe in the actual project. By setting different numbers of freezing pipes, not only the diffusion effect of the cold energy of a single freezing pipe can be simulated, but also the superposition effect of the cold energy of multiple freezing pipes can be simulated, and the test results are closer to the actual working conditions. At the same time, an electronic temperature controller and a multi-section electronic heating belt are used to make the temperature of each soil layer in the model test box independently controllable, and can be adjusted according to the actual formation temperature changes to simulate the actual formation temperature, thereby improving the authenticity of the test environment and ensuring the applicability of the test results to the actual project. In addition, the thickness of the on-site annular space is only 35mm, which cannot meet the requirements for the standard specimen size during performance test evaluation. The present invention pours slow-setting cement slurry in a square PVC pipe, maintains it under a similar environment to the on-site project, and finally obtains a standard specimen for laboratory testing by coring. The model test box of the present invention has a large volume and an adjustable internal space. The soil layered structure can be set to different thicknesses and different soil combinations according to needs. It has good adaptability and versatility. By setting different distances between the PVC pipe and the freezing pipe, the influence of the freezing effect at different positions on the performance of the retarded cement slurry is obtained. The test data is more accurate and comprehensive, and it can provide an ideal test device and test method for the performance test of the filling material outside the freezing pipe during freezing construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the device for testing the performance of the filling material in the annular space outside the freezing pipe according to the present invention; Figure 2 This is a schematic diagram of the steel plate arrangement according to the present invention; Figure 3 This is a schematic diagram of the structural arrangement of Example 1 of the present invention; Figure 4 This is a schematic diagram of the structural arrangement of Example 2 of the present invention; Figure 5 This is a schematic diagram of the structure of the geothermal simulation device of the present invention; Figure 6 This is a schematic diagram of the freezing cooling cycle of the freezing pipe according to the present invention; Figure 7 This is a schematic diagram of the lifting holes at the bottom of the model test box of the present invention.

[0015] Explanation of the numbers in the figure: 1-main freezing pipe, 2-secondary freezing pipe, 3-M20 bolt, 4-square PVC pipe, 5-first soil layer, 6-second soil layer, 7-third soil layer, 8-fourth soil layer, 9-fifth soil layer, 10-steel plate; 11-model test box, 12-electronic heating belt, 13-waterproof lead, 14-electronic temperature controller, 15-inlet, 16-outlet, 17-hanging hole DETAILED DESCRIPTION

[0016] The following is a further detailed description of the present invention in conjunction with the accompanying drawings and specific embodiments. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0017] In the description of the present invention, it should be noted that the orientations or positional relationships indicated by terms such as "outer wall" and "interior" are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not require that the present invention must be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention.

[0018] In the description of the present invention, the terms "install," "connect," and "attach" should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; they may refer to direct or indirect connections through an intermediary; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in the present invention. Example

[0019] This embodiment is carried out under the freezing effect of a single freezing pipe. Figure 3The performance testing device and testing method of the filling material of the annular space outside the freezing pipe shown include a main freezing pipe 1, an M20 bolt 3, a square PVC pipe 4, a first soil layer 5, a second soil layer 6, a third soil layer 7, a fourth soil layer 8, a fifth soil layer 9, a steel plate 10, a model test box 11, an electronic heating belt 12, a waterproof lead 13, an electronic temperature controller 14, an inlet 15, an outlet 16, and a lifting hole 17. The main freezing pipe has a low-temperature brine inlet and a low-temperature brine outlet. The main freezing pipe is buried in the soil layer and its lower end contacts the bottom of the model test box 11. The first soil layer 5, the second soil layer 6, the third soil layer 7, the fourth soil layer 8, and the fifth soil layer 9 are stacked in the model test box 11. The bottom of the model test box 11 is provided with 16 hoisting holes. The hoisting holes 17 are arranged on the lower end surface of the model test box 11 and are equipped with M20 bolts 3 of matching size. The square PVC pipe 4 is arranged near the freezing pipe. The bottom of the steel plate 10 is fixed with the M20 bolts 3 and is placed vertically in the model test box 11. The electronic heat-generating belt 12 is adhered to the outside of the steel plate 10. The electronic temperature controller 14 is connected to the electronic heat-generating belt 12 through a waterproof lead 13 and is placed outside the model test box 11. The main freezing pipe 1 and the auxiliary freezing pipe 3 have a diameter of 140 mm and a height of 2000 mm, and the upper end of the main freezing pipe 1 is exposed from the upper part of the fifth soil layer 9. The soil stratification is determined according to the project overview. The exemplary soil is divided into 5 layers, and the thickness of each soil layer is 400 mm, 600 mm, 300 mm, 400 mm, and 300 mm from top to bottom. The size of the model test box 11 is 4000 mm (length) × 3000 mm (width) × 3000 mm (height), and the size of the square PVC pipe 4 is 200 mm (length) × 200 mm (width) × 2000 mm (height).

[0020] The specific steps are as follows: (a) Mark the outer walls of the model test box 11, steel plate 10, and square PVC pipe 4 with layer markings according to the designed soil layer depths; (b) Adhere the electronic heating tape 12 to the outside of the steel plate 10 in layers according to the depth markings. Then, vertically install the steel plate 10 on the bottom of the model test box using the M20 bolts 3 at the bottom. The steel plate 10 forms a square space with dimensions of 3800 mm (length) × 2600 mm (width) × 2500 mm (height). Connect the waterproof lead 13 to ensure a waterproof seal. (c) Fill the bottom of the model box with a first soil layer 5, place the main freezing pipe 1 in the predetermined position, and then arrange square PVC pipes 4 at intervals of 20 cm and 40 cm in the top, bottom, left, and right directions around the main freezing pipe 1, for a total of eight square PVC pipes 4. Tamp the first soil layer 5 to secure the main freezing pipe 1 and the square PVC pipes 4. Repeat the process for the remaining four soil layers and compact them layer by layer. (d) Turn on each layer of electronic heating tape 12 and activate the electronic temperature controller 14, accurately setting and controlling its temperature to simulate the ground temperature of the target stratum. Exemplary temperature settings, from top to bottom, are: 30°C, 33°C, 35°C, 37°C, and 38°C. After the internal temperature of each layer stabilizes and reaches the set value, inject slow-setting cement slurry into the square PVC pipe 4. After 7 days of normal curing, turn off the electronic heating tape 12. (e) opening the freezing pipe refrigeration cycle system, allowing low-temperature brine to enter from the inlet 15 and be discharged from the outlet 16, thereby freezing the soil layer. For example, after the soil is frozen for 30 days, 45 days, or 60 days, the refrigeration cycle system is closed; (f) After the soil layer thaws, the square PVC tube 4 is removed and cut into sections corresponding to different depths according to the depth marks on the outer wall of the square PVC tube 4. Standard specimens are drilled from the square PVC tube in each section and the density and impermeability performance of the standard specimens are tested. Example

[0021] This embodiment is carried out under the freezing effect of multiple freezing pipes, such as Figure 4The performance testing device and testing method of the filling material of the annular space outside the freezing pipe shown include a main freezing pipe 1, an auxiliary freezing pipe 2, an M20 bolt 3, a square PVC pipe 4, a first soil layer 5, a second soil layer 6, a third soil layer 7, a fourth soil layer 8, a fifth soil layer 9, a steel plate 10, a model test box 11, an electronic heating belt 12, a waterproof lead 13, an electronic temperature controller 14, an inlet 15, an outlet 16, and a lifting hole 17. The main freezing pipe 1 and the auxiliary freezing pipe 2 have a low-temperature brine inlet 15 and a low-temperature brine outlet 16. The main freezing pipe 1 and the auxiliary freezing pipe 2 are buried in the soil layer and the lower ends are in contact with the bottom of the model test box 11. The first soil layer 5, the second soil layer 6, the third soil layer 7, the fourth soil layer 8, and the fifth soil layer 9 are stacked in the model test box 11. The bottom of the model test box 11 is provided with 16 hoisting holes. The hoisting holes 17 are arranged on the lower end surface of the model test box 11 and are equipped with M20 bolts 3 of matching size. The square PVC pipe 4 is arranged near the freezing pipe. The bottom of the steel plate 10 is fixed with the M20 bolts 3 and is placed vertically in the model test box 11. The electronic heat-generating belt is adhered to the outside of the steel plate 10. The electronic temperature controller 14 is connected to the electronic heat-generating belt 12 through a waterproof lead 13 and is placed outside the model test box 11. The main freezing pipe 1 and the auxiliary freezing pipe 2 have a diameter of 140 mm and a height of 2000 mm, and the upper end of the freezing pipe is exposed from the upper part of the fifth soil layer 9. The soil stratification is determined according to the project overview. The exemplary soil is divided into 5 layers, and the thickness of each soil layer is 400 mm, 600 mm, 300 mm, 400 mm, and 300 mm from top to bottom. The size of the model test box 11 is 4000 mm (length) × 3000 mm (width) × 3000 mm (height), and the size of the square PVC pipe 4 is 200 mm (length) × 200 mm (width) × 2000 mm (height).

[0022] The specific steps are as follows: (a) Mark the outer walls of the model test box 11, steel plate 10, and square PVC pipe 4 with layer markings according to the designed soil layer depths; (b) Adhere the electronic heating tape 12 to the outside of the steel plate 10 in layers according to the depth markings. Then, vertically mount the steel plate 10 to the bottom of the model test box using the M20 bolts 3 at the bottom. The steel plate 10 forms a square space with dimensions of 3800 mm (length) × 2600 mm (width) × 2500 mm (height). Connect the waterproof lead 13 to ensure a waterproof seal. (c) Fill the bottom of the model box with a first soil layer 5. Place the main freezing pipe 1 and auxiliary freezing pipe 2 in the predetermined position, with the two freezing pipes 80 cm apart. Next, place square PVC pipes 4 every 20 cm and 40 cm above, below, left, and right of the main freezing pipe 1 and auxiliary freezing pipe 2, respectively, for a total of 16 square PVC pipes 4. Finally, tamp the first soil layer 5 to secure the main freezing pipe 1, auxiliary freezing pipe 3, and square PVC pipes 4. Repeat the process for the remaining four layers of soil and compact them layer by layer. (d) Activate the electronic temperature controller 14, turn on each layer of electronic heating belts 12, and precisely set and control their temperatures to simulate the ground temperature of the target stratum. Exemplary temperature settings, from top to bottom, are: 30°C, 33°C, 35°C, 37°C, and 38°C. Once the internal temperature of each layer stabilizes and reaches the set value, inject slow-setting cement slurry into the square PVC pipe 4. After 7 days of normal curing, turn off the electronic heating belts 12. (e) opening the freezing pipe refrigeration cycle system, allowing low-temperature brine to enter from the inlet 15 and be discharged from the outlet 16, thereby freezing the soil layer. After the soil is frozen for 30 days, 45 days, or 60 days, the refrigeration cycle system is closed; (f) After the soil layer thaws, the square PVC tube 4 is removed and cut into sections corresponding to different depths according to the depth marks on the outer wall of the square PVC tube 4. Standard specimens are drilled from the square PVC tube in each section and the density and impermeability performance of the standard specimens are tested.

[0023] The above is only a preferred specific implementation method of the present application, but the scope of protection of the present application is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes based on the technical solution and concept of the present application within the technical scope disclosed in the present application, and they should be covered by the scope of protection of the present application.

[0024] It is understood from common technical knowledge that the present invention may be implemented by other embodiments that do not depart from its spirit or essential features. Therefore, the embodiments disclosed above are, in all respects, merely illustrative and not exclusive. All modifications within the scope of the present invention or equivalent to the scope of the present invention are intended to be encompassed by the present invention.

Claims

1. A device for testing the performance of a filling material in an annular space outside a freezing pipe and a testing method thereof, comprising a main freezing pipe (1), a secondary freezing pipe (2), an M20 bolt (3), a square PVC pipe (4), a first soil layer (5), a second soil layer (6), a third soil layer (7), a fourth soil layer (8), a fifth soil layer (9), a steel plate (10), a model test box (11), an electronic heating belt (12), a waterproof lead (13), an electronic temperature controller (14), an inlet (15), an outlet (16), and a hanging hole (17), wherein the main freezing pipe (1) and the secondary freezing pipe (2) have a low-temperature brine inlet (15) and a low-temperature brine outlet (16), the main freezing pipe (1) and the secondary freezing pipe (2) are buried in the soil layer and the lower ends thereof are in contact with the bottom of the model test box (11), the square PVC pipe (4) is arranged near the freezing pipe, the first soil layer (5), the second soil layer (6), the third soil layer (8), the fourth soil layer (9), the fifth soil layer (11), the steel plate (10), the model test box (11), an electronic heating belt (12), a waterproof lead (13), an electronic temperature controller (14), an inlet (15), an outlet (16), and a hanging hole (17), wherein the main freezing pipe (1) and the secondary freezing pipe (2) have a low-temperature brine inlet (15) and a low-temperature brine outlet (16), the main freezing pipe (1) and the secondary freezing pipe (2) are buried in the soil layer and the lower ends thereof are in contact with the bottom of the model test box (11), the square PVC pipe (4) is arranged near the freezing pipe, the first soil layer (5), the second soil layer (6), the third soil layer (7), the fourth soil layer (8), and the fifth soil layer (9) are stacked in the model test box (11). The bottom of the model test box (11) is provided with 16 hoisting holes (17). The hoisting holes (17) are provided on the lower end surface of the model test box (11) and are equipped with M20 bolts (3) of matching size. The bottom of the steel plate (10) is fixed with the M20 bolts (3) and is vertically placed in the model test box (11). The electronic heating belt (12) is attached to the outside of the steel plate (10). The electronic temperature controller (14) is connected to the electronic heating belt (12) through a waterproof lead (13) and is placed outside the model test box (11). The main freezing pipe (1) and the auxiliary freezing pipe (2) have a diameter of 140 mm and a height of 2000 mm, and the upper end of the freezing pipe is exposed from the upper part of the fifth soil layer (9). The size of the square PVC pipe (4) is 200 mm. (length) × 200mm(width) × 2000mm(height).

2. The device for testing the performance of the filling material of the annular space outside the freezing pipe according to claim 1, characterized in that: When the test method is to arrange a single freezing pipe, a square PVC pipe (4) is arranged at intervals of 20 cm and 40 cm at the top, bottom, left, and right directions with the main freezing pipe (1) as the center, and a total of 8 square PVC pipes (4) are placed.

3. The device for testing the performance of the filling material of the annular space outside the freezing pipe according to claim 1, characterized in that: The test method is to arrange multiple freezing pipes, wherein the main freezing pipe and the auxiliary freezing pipe are 80 cm apart, and a square PVC pipe (4) is arranged every 20 cm and 40 cm at the top, bottom, left and right of the main freezing pipe (1) and the auxiliary freezing pipe (2), respectively, and a total of 16 square PVC pipes (4) are placed.

4. The method for testing the performance of the filling material of the annular space outside the freezing pipe according to claim 1, characterized in that: (a) Mark the outer walls of the model test box (11), steel plate (10) and square PVC pipe (4) according to the designed soil layer depth; (b) According to the depth mark, the electronic heating tape (12) is layered and pasted on the outside of the steel plate (10), and then the steel plate (10) is vertically installed on the bottom of the model test box through the bottom M20 bolt (3). The steel plate (10) is surrounded by a square space with a space size of 3800mm (length) × 2600mm (width) × 2500mm (height). Then, the waterproof lead (13) is connected to make a waterproof seal. (c) Fill the bottom of the model box with a first soil layer (5), place the main freezing pipe (1) in a predetermined position, and then arrange a square PVC pipe (4) every 20 cm and 40 cm in the four directions of the main freezing pipe (1) at the top, bottom, left, and right, placing a total of 8 square PVC pipes (4), compact the first soil layer (5) to fix the main freezing pipe (1) and the square PVC pipe (4), and repeat the filling of the remaining 4 layers of soil and compacting them layer by layer; (d) turning on the electronic heating belts (12) of each layer, starting the electronic temperature controller (14) and accurately setting and controlling the temperature thereof to simulate the ground temperature of the target stratum. The exemplary temperature settings from top to bottom are: 30°C, 33°C, 35°C, 37°C, 38°C. After the temperature inside each layer of soil stabilizes and reaches the set value, slow-setting cement slurry is injected into the square PVC pipe (4). After 7 days of normal curing, the electronic heating belts (12) are turned off. (e) opening the freezing pipe refrigeration cycle system, allowing low-temperature brine to enter from the inlet 15 and be discharged from the outlet 16, thereby freezing the soil layer. After the soil is frozen for 30 days, 45 days, or 60 days, the refrigeration cycle system is closed; (f) After the soil layer thaws, the square PVC tube (4) is taken out and cut into sections corresponding to different depths according to the depth marks on the outer wall of the square PVC tube (4). Standard specimens are drilled from the square PVC tube (4) in each section and the density and impermeability performance of the standard specimens are tested.

5. The method for testing the performance of the filling material of the annular space outside the freezing pipe according to claim 1, characterized in that: (a) Mark the outer walls of the model test box (11), steel plate (10) and square PVC pipe (4) according to the designed soil layer depth; (b) According to the depth mark, the electronic heating tape (12) is layered and pasted on the outside of the steel plate (10), and then the steel plate (10) is vertically installed on the bottom of the model test box through the bottom M20 bolt (3). The steel plate (10) is surrounded by a square space with a space size of 3800mm (length) × 2600mm (width) × 2500mm (height). Then, the waterproof lead (13) is connected to make a waterproof seal. (c) Filling the bottom of the model box with a first soil layer (5), placing the main freezing pipe (1) and the auxiliary freezing pipe (2) in a predetermined position, wherein the two freezing pipes are 80 cm apart, and then arranging a square PVC pipe (4) every 20 cm and 40 cm on the top, bottom, left and right of the main freezing pipe (1) and the auxiliary freezing pipe (2), respectively, for a total of 16 square PVC pipes (4), and finally tamping the first soil layer (5) to fix the main freezing pipe (1), the auxiliary freezing pipe (2) and the square PVC pipe (4), and repeating the filling of 5 layers of soil and compacting them layer by layer; (d) turning on the electronic heating belts (12) of each layer, starting the electronic temperature controller (14) and accurately setting and controlling the temperature thereof to simulate the ground temperature of the target stratum. The exemplary temperature settings from top to bottom are: 30°C, 33°C, 35°C, 37°C, 38°C. After the temperature inside each layer of soil stabilizes and reaches the set value, slow-setting cement slurry is injected into the square PVC pipe (4). After 7 days of normal curing, the electronic heating belts (12) are turned off. (e) opening the freezing pipe refrigeration cycle system, allowing low-temperature brine to enter from the inlet (15) and be discharged from the outlet (16), thereby freezing the soil layer. After the soil is frozen for 30 days, 45 days, or 60 days, the refrigeration cycle system is closed; (f) After the soil layer thaws, the square PVC tube (4) is taken out and cut into sections corresponding to different depths according to the depth marks on the outer wall of the square PVC tube (4). Standard specimens are drilled from the square PVC tube (4) in each section and the density and impermeability performance of the standard specimens are tested.

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