A permafrost roadbed pile foundation model test device

Abstract

The application relates to a permafrost roadbed pile foundation model test device, and relates to a model test device for permafrost.The application aims to solve the technical problem that it is difficult to test uneven settlement of a permafrost pile foundation under the action of uniform load by means of indoor test at present.The device can simulate the action of a pile unit under the action of uniform load in the case of triangular pile arrangement in actual roadbed engineering through a hexagonal foundation model barrel and a uniform load sliding block;displacement of multiple loading blocks is independent, and uneven settlement in a permafrost foundation can be directly reflected; the application further increases a broken ice layer on the basis of artificial compaction of frozen soil, and the distribution of an ice layer in an actual permafrost foundation can be reflected; the application uses wet soil and broken pure ice chips to configure foundation soil, so that the ice content of the frozen soil is uniform, and the permafrost roadbed pile foundation model can well simulate actual engineering conditions.

Description

Technical Field

[0001] This invention relates to a model test device for permafrost. Background Technology

[0002] In my country, permafrost is mainly distributed in the Qinghai-Tibet Plateau and the Greater and Lesser Khingan Mountains in Northeast China. When constructing infrastructure such as highways and railways in permafrost areas, it is essential to address the uneven settlement of the roadbed caused by permafrost degradation. Pile foundations are a commonly used method for reinforcing permafrost roadbeds, significantly enhancing the bearing capacity of the permafrost foundation. When the roadbed and pavement structure are built on a permafrost foundation, a uniformly distributed load can be applied. Under these conditions, the uneven deformation of the permafrost pile foundation composite foundation will be transmitted to the roadbed and pavement structure, leading to uneven settlement of the roadbed and longitudinal cracks in the pavement. To ensure the safe and stable operation of highways and railways in permafrost areas, targeted research on the uneven settlement of pile foundations is necessary. Indoor model testing is a common method for testing the physical and mechanical properties of pile foundations. Numerous related experimental studies have been conducted, primarily based on scaled-down test designs. This involves constructing the pile foundation within an indoor model test chamber and embedding stress, temperature, hydrological, and pore water pressure sensors in the ground. Simultaneously, dynamic and static loads are applied to the pile top using actuators and reaction devices to obtain the stress-displacement development patterns of the foundation. Placing the entire setup in a controlled-temperature chamber can simulate the mechanical characteristics of pile foundations in cold regions.

[0003] However, while current experimental methods can conduct model tests on pile foundations for permafrost subgrades, they struggle to analyze the most crucial engineering characteristic of permafrost foundations—uniform settlement. Furthermore, the geological strata in permafrost regions are often complex, and field investigations reveal the presence of ice layers beneath the foundation, which significantly impacts uneven settlement. Therefore, it is necessary to design the experimental setup to account for different layers of permafrost to effectively simulate uneven settlement. Finally, since pile foundations in permafrost regions are often arranged in an equilateral triangle configuration, under uniformly distributed loads on the subgrade, the pile unit is essentially a hexagonal foundation. Therefore, applying uniformly distributed loads to these hexagonal foundation units and recording the occurrence of uneven settlement is paramount in permafrost subgrade pile foundation model tests.

[0004] Currently, there are few reports on the study of uneven settlement of roadbeds based on roadbed pile foundation model tests, especially regarding the uneven settlement of pile foundations under roadbed loads in permafrost with special underlying conditions. Patent CN2023116662241 discloses a loading device for a scaled-down model of a pile group foundation, but its loading method is difficult to test the uneven settlement of the top surface under simulated uniformly distributed loads. Patent CN2019100471407 discloses a monitoring device and its usage method for permafrost model tests, which mainly focuses on the migration of temperature, moisture, and salt in permafrost foundations, but does not test for uneven settlement. Patent CN2022212354492 discloses a temperature-controlled pile foundation model test device, which uses a structural loading system to load the model, but this also makes it difficult to monitor uneven settlement in real time. Patent CN2022109257523 proposes a hot-pipe roadbed frost heave test device, which can test the uneven frost heave deformation of the top surface of a model under small-scale conditions. However, it cannot apply uniformly distributed loading to the top surface of the model, and therefore cannot simulate the actual stress state of the frozen soil foundation. In summary, there is a need to develop a test device and supporting test methods that can simulate the actual stress and deformation state of frozen soil roadbed pile foundations, and to study the uneven settlement of frozen soil roadbed pile foundations under uniformly distributed loads. Summary of the Invention

[0005] The present invention aims to solve the technical problem that it is currently difficult to test the uneven settlement of pile foundations in permafrost containing ice layers under uniformly distributed loads through indoor tests, and provides a model test device for pile foundations in permafrost subgrades.

[0006] The permafrost roadbed pile foundation model test device of the present invention consists of a controlled room 1, four industrial cameras 2, a uniformly distributed loading slider 3, a sand cushion layer 4, a temperature sensor 5, a model pile 6, a crushed ice layer 7, artificially compacted frozen soil 8, a hexagonal foundation model barrel 9, a hexagonal temperature-controlled cold plate 10, a temperature-controlled cold bath box 11, a hoop 15, steel bars 16, and an irregularly shaped chassis compaction hammer;

[0007] The hexagonal foundation model barrel 9 is a hollow regular hexagonal prism structure with an open top and a closed bottom;

[0008] The hexagonal temperature-controlled cold plate 10 is a thin plate with a regular hexagonal prism structure, and a serpentine water-cooling pipe 10-1 is evenly arranged inside it. The two ends of the serpentine water-cooling pipe 10-1 are respectively provided with liquid inlet and liquid outlet. The hexagonal temperature-controlled cold plate 10 is placed on the bottom surface of the inner cavity of the hexagonal foundation model barrel 9 and the two are tightly attached. The liquid inlet and liquid outlet of the hexagonal temperature-controlled cold plate 10 are connected to the liquid outlet and liquid inlet of the temperature-controlled cold bath box 11, respectively.

[0009] A layer of crushed ice 7 is also set in the hexagonal foundation model barrel 9 to simulate the ice layer that exists in the permafrost foundation; artificially compacted frozen soil 8 is set above and below the crushed ice layer 7, and multiple temperature sensors 5 are evenly distributed in the artificially compacted frozen soil 8.

[0010] A model pile 6 is vertically set on the central axis of the hexagonal foundation model barrel 9. The top of the model pile 6 is at the same height as the artificially compacted frozen soil 8. A sand cushion layer 4 and a uniformly distributed loading slider 3 are set above the model pile 6. The uniformly distributed loading slider 3 is above the sand cushion layer 4. Both the sand cushion layer 4 and the uniformly distributed loading slider 3 are set in the hexagonal foundation model barrel 9.

[0011] The uniformly distributed loading slider 3 is a regular hexagonal prism structure, specifically composed of multiple cuboid sliders 3-3 and two isosceles triangular sliders 3-2. The multiple cuboid sliders 3-3 are positioned in the middle, closely fitted together to form a cuboid structure. An isosceles triangular slider 3-2 is set on each side, with the two sides of the isosceles triangular slider 3-2 set on the outer edge. Each of the cuboid sliders 3-3 and the isosceles triangular sliders 3-2 is equipped with a pull ring 3-1, and multiple steel bars are inserted into the pull rings 3-1 located in the same row. A sleeve 15 is set around the uniformly distributed loading slider 3, and the two are slidably connected. The sleeve 15 is a hollow regular hexagonal prism structure with open structures at both the top and bottom. The sleeve 15 rests on the side wall of the hexagonal foundation model barrel 9.

[0012] The chassis 14 of the irregular chassis hammer has an obtuse-angled pointed structure 14-1 with an included angle of 120° at one end and an inwardly concave arc structure 14-2 with an arc of 60° at the other end.

[0013] The hexagonal foundation model barrel 9 and four industrial cameras 2 are all installed in the control room 1. Two industrial cameras 2 are arranged at the top of the inner cavity of the control room 1 to monitor the deformation of the uniformly distributed loading slider 3 at the top of the model in real time. The other two industrial cameras 2 are arranged in the middle of the side wall of the control room 1 to monitor the deformation of the soil inside the hexagonal foundation model barrel 9 in real time.

[0014] The method of using the permafrost subgrade pile foundation model test device of the present invention is as follows:

[0015] Step 1: Dry the soil for the test, pass it through a 5mm geotextile sieve, add water and mix evenly to a moisture content of 12% to ensure that the soil particles are moist but do not clump together in large quantities, put it in a refrigerator at 2℃ to cool down, seal and let it stand for 24 hours for later use.

[0016] Step 2: Adjust the temperature of the temperature control chamber 1 to -5℃, crush the pure ice into ice chips and keep them warm in the temperature control chamber 1; assemble the hexagonal foundation model barrel 9 and the hexagonal temperature control cold plate 10 in the temperature control chamber 1, connect the hexagonal temperature control cold plate 10 to the temperature control cold bath box 11, and fill the temperature control cold bath box 11 with alcohol as a refrigerant.

[0017] Step 3: Adjust the temperature of the controlled chamber 1 to -2℃. Under this temperature environment, add the crushed ice prepared in step 2 to the cooled soil sample with 12% moisture content prepared in step 1 to the target ice content of the model test, and stir quickly and evenly.

[0018] Step 4: Experimental Model Construction

[0019] Scenario 1: Model test of precast pile foundation for permafrost roadbed:

[0020] Prefabricated model piles 6 are placed into the hexagonal foundation model barrel 9, ensuring that model piles 6 are centered within the hexagonal foundation model barrel 9. Soil samples with the target ice content are prepared and layered into the hexagonal foundation model barrel 9 according to the target compaction density. A compaction hammer with an irregularly shaped base is used to compact the soil, with the obtuse-angled pointed structure 14-1 and the rounded arc structure 14-2 used to compact the inner corners of the foundation model barrel 9 and around the model piles 6. The thickness of each compacted layer is set to 5cm. The soil is then laid in the lower middle part of the model piles 6. A 10cm thick layer of crushed ice 7 is laid and compacted to simulate the ice layer in a permafrost foundation; then, soil samples are filled to the same height as the top of the model pile 6, and temperature sensors 5 are evenly distributed in the soil samples; then, a 10cm sand cushion layer 4 is laid on top and compacted; the entire model is temperature controlled in a -2℃ controlled chamber 1, and the temperature controlled cold bath box 11 is turned on to ensure that the hexagonal temperature controlled cold plate 10 is also at -2℃; the temperature is controlled until the temperature range of all temperature sensors 5 is between -2℃ and 0℃;

[0021] Scenario 2: Model test of reinforced thermomelting pile foundation for permafrost roadbed

[0022] Install an acrylic tube at the target hole position of the reinforced hot-melt pile in the hexagonal foundation model bucket 9 to reserve the pile hole position; similar to case one, fill the hexagonal foundation model bucket 9 and pay attention to laying the ice crush layer 7, but after each layer is compacted, gently rotate the acrylic tube to avoid it freezing tightly with the frozen soil; when filling to 10cm away from the top surface of the hexagonal foundation model bucket 9, rotate and pull out the acrylic tube, put the geotextile sleeve into the reserved hole, and control the temperature until the temperature range of all temperature sensors 5 is between -2℃ and 0℃; then fill the geotextile sleeve with hot-melt pile material as model pile 6, and then set a 10cm thick sand cushion layer 4 on top of the foundation model;

[0023] Step 5: Using a small crane, the evenly distributed loading sliders 3 are smoothly installed on top of the sand cushion layer 4 using multiple steel bars 16. The hoop 15 overlaps with the side wall of the hexagonal foundation model barrel 9. All the cuboid sliders 3-3 and the two isosceles triangular sliders 3-2 are completely pressed on top of the sand cushion layer 4. The steel bars 16 are removed to allow the loading sliders to move freely again. Then, the whole thing is statically loaded with gravity at a controlled temperature of -2℃ to 0℃ for 48 hours. The temperature is monitored in real time using a temperature sensor 5. The vertical displacement of each loading slider is monitored in real time using two industrial cameras 2. The deformation of the ice layer is monitored in real time from the side using two industrial cameras 2.

[0024] Step Six: After the loading test is completed, insert the steel bar 16 into the pull ring 3-1 again to restore its integrity. Use a small crane to remove the uniformly distributed loading slider 3 from the hexagonal foundation model bucket 9. Raise the temperature control box 1 to room temperature. After the model has fully recovered to room temperature, remove the soil around the pile and observe the damage to the pile.

[0025] The beneficial effects of this invention are:

[0026] 1. The device of the present invention can conduct indoor model tests on various permafrost model piles. Through the hexagonal foundation model bucket 9, the hexagonal temperature-controlled cold plate 10 and the uniformly distributed loading slider 3, it can simulate the effect of the pile unit under the uniformly distributed load in the case of equilateral triangular pile arrangement in actual roadbed engineering, and simulate the effect of group piles with single pile test.

[0027] 2. The uniformly distributed loading slider 3 of the present invention is evenly distributed on the top of the model pile 6 to apply a uniformly distributed load to the foundation. It eliminates the traditional loading method of setting up reaction frames, actuators and loading disks. Compared with the traditional reaction frame loading, it is closer to the roadbed filling load. At the same time, multiple loading blocks generate displacements independently, which can intuitively reflect the uneven settlement in the permafrost foundation. The test range of uneven settlement is accurate to the size of a single loading block. The settlement displacement of the loading blocks can be captured in real time by an industrial camera 2, eliminating the influence of conventional embedded displacement sensors on the foundation. It achieves multiple benefits.

[0028] 3. The present invention adds a layer of crushed ice 7 to the artificially compacted frozen soil 8, which can reflect the distribution of ice layers in the actual permafrost foundation. The hexagonal foundation model barrel 9 is made of transparent plexiglass, and the deformation of the crushed ice layer 7 can be monitored in real time by an industrial camera 2.

[0029] 4. This invention uses moist soil and crushed pure ice chips to prepare the foundation soil, which can ensure that the ice content of the frozen soil is uniform. The hexagonal temperature-controlled cold plate 10 used can effectively simulate the temperature boundary of the frozen bedrock under the permafrost pile foundation. The irregularly shaped chassis compaction hammer used has both an obtuse-angled tip structure 14-1 and a circular arc structure 14-2, which can compact the soil around the pile and at the corners of the model box. The roadbed pile foundation model made by this test method can well simulate the actual engineering situation. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall test device for the pile foundation model of permafrost roadbed according to specific implementation method one.

[0031] Figure 2 for Figure 1 Top view of barrel 9 in the hexagonal foundation model;

[0032] Figure 3 This is a front view of the uniformly loaded slider 3 in the first specific implementation method;

[0033] Figure 4 for Figure 3 Top view;

[0034] Figure 5 The front view of the hammer impact test on an irregularly shaped chassis;

[0035] Figure 6 for Figure 5 A bottom view;

[0036] Figure 7 for Figure 1 Top view of the hexagonal temperature-controlled cold plate 10. Detailed Implementation

[0037] Specific Implementation Method 1: This implementation method is a test device for pile foundation model of permafrost roadbed, such as... Figures 1-7 As shown, it is specifically composed of a controlled temperature chamber 1, four industrial cameras 2, a uniformly distributed loading slider 3, a sand cushion layer 4, a temperature sensor 5, a model pile 6, a crushed ice layer 7, artificially compacted frozen soil 8, a hexagonal foundation model barrel 9, a hexagonal temperature-controlled cold plate 10, a temperature-controlled cold bath box 11, a hoop 15, steel bars 16, and an irregularly shaped chassis compaction hammer.

[0038] The hexagonal foundation model barrel 9 is a hollow regular hexagonal prism structure with an open top and a closed bottom;

[0039] The hexagonal temperature-controlled cold plate 10 is a thin plate with a regular hexagonal prism structure, and a serpentine water-cooling pipe 10-1 is evenly arranged inside it. The two ends of the serpentine water-cooling pipe 10-1 are respectively provided with liquid inlet and liquid outlet. The hexagonal temperature-controlled cold plate 10 is placed on the bottom surface of the inner cavity of the hexagonal foundation model barrel 9 and the two are tightly attached. The liquid inlet and liquid outlet of the hexagonal temperature-controlled cold plate 10 are connected to the liquid outlet and liquid inlet of the temperature-controlled cold bath box 11, respectively.

[0040] A layer of crushed ice 7 is also set in the hexagonal foundation model barrel 9 to simulate the ice layer that exists in the permafrost foundation; artificially compacted frozen soil 8 is set above and below the crushed ice layer 7, and multiple temperature sensors 5 are evenly distributed in the artificially compacted frozen soil 8.

[0041] A model pile 6 is vertically set on the central axis of the hexagonal foundation model barrel 9. The top of the model pile 6 is at the same height as the artificially compacted frozen soil 8. A sand cushion layer 4 and a uniformly distributed loading slider 3 are set above the model pile 6. The uniformly distributed loading slider 3 is above the sand cushion layer 4. Both the sand cushion layer 4 and the uniformly distributed loading slider 3 are set in the hexagonal foundation model barrel 9.

[0042] The uniformly distributed loading slider 3 is a regular hexagonal prism structure, specifically composed of multiple cuboid sliders 3-3 and two isosceles triangular sliders 3-2. The multiple cuboid sliders 3-3 are positioned in the middle, closely fitted together to form a cuboid structure. An isosceles triangular slider 3-2 is set on each side, with the two sides of the isosceles triangular slider 3-2 set on the outer edge. Each of the cuboid sliders 3-3 and the isosceles triangular sliders 3-2 is equipped with a pull ring 3-1, and multiple steel bars are inserted into the pull rings 3-1 located in the same row. A sleeve 15 is set around the uniformly distributed loading slider 3, and the two are slidably connected. The sleeve 15 is a hollow regular hexagonal prism structure with open structures at both the top and bottom. The sleeve 15 rests on the side wall of the hexagonal foundation model barrel 9.

[0043] The chassis 14 of the irregular chassis hammer has an obtuse-angled pointed structure 14-1 with an included angle of 120° at one end and an inwardly concave arc structure 14-2 with an arc of 60° at the other end.

[0044] The hexagonal foundation model barrel 9 and four industrial cameras 2 are all installed in the control room 1. Two industrial cameras 2 are arranged at the top of the inner cavity of the control room 1 to monitor the deformation of the uniformly distributed loading slider 3 at the top of the model in real time. The other two industrial cameras 2 are arranged in the middle of the side wall of the control room 1 to monitor the deformation of the soil inside the hexagonal foundation model barrel 9 in real time.

[0045] The method of using the permafrost subgrade pile foundation model test device in this embodiment is as follows:

[0046] Step 1: Dry the soil for the test, pass it through a 5mm geotextile sieve, add water and mix evenly to a moisture content of 12% to ensure that the soil particles are moist but do not clump together in large quantities, put it in a refrigerator at 2℃ to cool down, seal and let it stand for 24 hours for later use.

[0047] Step 2: Adjust the temperature of the temperature control chamber 1 to -5℃, crush the pure ice into ice chips and keep them warm in the temperature control chamber 1; assemble the hexagonal foundation model barrel 9 and the hexagonal temperature control cold plate 10 in the temperature control chamber 1, connect the hexagonal temperature control cold plate 10 to the temperature control cold bath box 11, and fill the temperature control cold bath box 11 with alcohol as a refrigerant.

[0048] Step 3: Adjust the temperature of the controlled chamber 1 to -2℃. Under this temperature environment, add the crushed ice prepared in step 2 to the cooled soil sample with 12% moisture content prepared in step 1 to the target ice content of the model test, and stir quickly and evenly.

[0049] Step 4: Experimental Model Construction

[0050] Scenario 1: Model test of precast pile foundation for permafrost roadbed:

[0051] Prefabricated model piles 6 are placed into the hexagonal foundation model barrel 9, ensuring that model piles 6 are centered within the hexagonal foundation model barrel 9. Soil samples with the target ice content are prepared and layered into the hexagonal foundation model barrel 9 according to the target compaction density. A compaction hammer with an irregularly shaped base is used to compact the soil, with the obtuse-angled pointed structure 14-1 and the rounded arc structure 14-2 used to compact the inner corners of the foundation model barrel 9 and around the model piles 6. The thickness of each compacted layer is set to 5cm. The soil is then laid in the lower middle part of the model piles 6. A 10cm thick layer of crushed ice 7 is laid and compacted to simulate the ice layer in a permafrost foundation; then, soil samples are filled to the same height as the top of the model pile 6, and temperature sensors 5 are evenly distributed in the soil samples; then, a 10cm sand cushion layer 4 is laid on top and compacted; the entire model is temperature controlled in a -2℃ controlled chamber 1, and the temperature controlled cold bath box 11 is turned on to ensure that the hexagonal temperature controlled cold plate 10 is also at -2℃; the temperature is controlled until the temperature range of all temperature sensors 5 is between -2℃ and 0℃;

[0052] Scenario 2: Model test of reinforced thermomelting pile foundation for permafrost roadbed

[0053] Install an acrylic tube at the target hole position of the reinforced hot-melt pile in the hexagonal foundation model bucket 9 to reserve the pile hole position; similar to case one, fill the hexagonal foundation model bucket 9 and pay attention to laying the ice crush layer 7, but after each layer is compacted, gently rotate the acrylic tube to avoid it freezing tightly with the frozen soil; when filling to 10cm away from the top surface of the hexagonal foundation model bucket 9, rotate and pull out the acrylic tube, put the geotextile sleeve into the reserved hole, and control the temperature until the temperature range of all temperature sensors 5 is between -2℃ and 0℃; then fill the geotextile sleeve with hot-melt pile material as model pile 6, and then set a 10cm thick sand cushion layer 4 on top of the foundation model;

[0054] Step 5: Using a small crane, the evenly distributed loading sliders 3 are smoothly installed on top of the sand cushion layer 4 using multiple steel bars 16. The hoop 15 overlaps with the side wall of the hexagonal foundation model barrel 9. All the cuboid sliders 3-3 and the two isosceles triangular sliders 3-2 are completely pressed on top of the sand cushion layer 4. The steel bars 16 are removed to allow the loading sliders to move freely again. Then, the whole thing is statically loaded with gravity at a controlled temperature of -2℃ to 0℃ for 48 hours. The temperature is monitored in real time using a temperature sensor 5. The vertical displacement of each loading slider is monitored in real time using two industrial cameras 2. The deformation of the ice layer is monitored in real time from the side using two industrial cameras 2.

[0055] Step Six: After the loading test is completed, insert the steel bar 16 into the pull ring 3-1 again to restore its integrity. Use a small crane to remove the uniformly distributed loading slider 3 from the hexagonal foundation model bucket 9. Raise the temperature control box 1 to room temperature. After the model has fully recovered to room temperature, remove the soil around the pile and observe the damage to the pile.

[0056] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the temperature-controlled cold bath 11 is filled with alcohol as a refrigerant, with a temperature control range of -20℃ to 20℃ and a temperature control accuracy of ±0.1℃. Everything else is the same as in Specific Implementation Method One.

[0057] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the hexagonal foundation model barrel 9 is made of transparent plexiglass panels, each 20mm thick. A 10mm opening is provided at the bottom of each of the two opposing plexiglass panels to facilitate connection of the piping to the temperature-controlled cold bath chamber 11. Everything else is the same as in Specific Implementation Method One or Two.

[0058] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the hexagonal temperature-controlled cold plate 10 is made of aluminum plate with a thickness of 10mm. Everything else is the same as in Specific Implementation Methods One to Three.

[0059] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that the artificially compacted frozen soil 8 is made from silty clay taken from permafrost regions, with a maximum particle size of 5mm. After drying, crushed pure ice chips are added, mixed evenly, and compacted to form a compacted density of 1.5g / cm³. 3 The ice content is 20% to 40% by mass. Everything else is the same as in Specific Implementation Method Four.

[0060] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that the ice crushed layer 7 is made of compacted ice crushed chips with a compaction density of 0.9 g / cm³. 3 A 5cm thick layer is used to simulate the ice layer present in permafrost foundations. Everything else is the same as in Specific Implementation Method Five.

[0061] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that the model pile 6 is a precast cement concrete pile or a reinforced thermoplastic pile used in permafrost regions, with a pile height of 1m. When using a precast cement concrete pile, the outer diameter is 50mm, and when using a reinforced thermoplastic pile, the outer diameter is 100mm. Everything else is the same as in Specific Implementation Method Six.

[0062] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that the thickness of the sand cushion layer 4 is 100mm. Everything else is the same as in Specific Implementation Method Seven.

[0063] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that the temperature sensor 5 is a T-type Teflon thermocouple with a test temperature range of -20~150℃ and an accuracy of ±0.01℃. Everything else is the same as in Specific Implementation Method Eight.

[0064] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that the cross-sectional dimensions of the cuboid slider 3-3 are 30mm × 30mm; and the uniformly distributed loading slider 3 is a solid stainless steel body. Everything else is the same as in Specific Implementation Method Nine.

[0065] The invention was verified using the following experiments:

[0066] Experiment 1: This experiment is a model test device for pile foundations in permafrost subgrade, such as... Figures 1-7 As shown, it is specifically composed of a controlled temperature chamber 1, four industrial cameras 2, a uniformly distributed loading slider 3, a sand cushion layer 4, a temperature sensor 5, a model pile 6, a crushed ice layer 7, artificially compacted frozen soil 8, a hexagonal foundation model barrel 9, a hexagonal temperature-controlled cold plate 10, a temperature-controlled cold bath box 11, a hoop 15, steel bars 16, and an irregularly shaped chassis compaction hammer.

[0067] The internal dimensions of the temperature control chamber 1 are 3m×3m×3m, the temperature control accuracy is ±1℃, and the temperature control range is -20℃~20℃, which can control the molding temperature of the permafrost foundation model.

[0068] The thickness of the sand cushion layer 4 is 100 mm;

[0069] The temperature sensor 5 is a T-type Teflon thermocouple with a test temperature range of -20~150℃ and an accuracy of ±0.01℃.

[0070] The hexagonal foundation model barrel 9 is a hollow regular hexagonal prism structure with an open top and a closed bottom. It is 1.2m high and 30cm long on each side, and can simulate a single pile foundation unit with triangular pile arrangement in the foundation. The hexagonal foundation model barrel 9 is made of transparent plexiglass panels. The thickness of the plexiglass panels is 20mm, the inner side length is 30cm, and the included angle between the panels is 120°. Two opposite side panels have 10mm openings at the bottom to facilitate the connection of the pipeline of the temperature-controlled cold bath box 11.

[0071] The hexagonal temperature-controlled cold plate 10 is a thin plate with a regular hexagonal prism structure, and a serpentine water-cooling pipe 10-1 is evenly arranged inside it. The two ends of the serpentine water-cooling pipe 10-1 are respectively provided with liquid inlet and liquid outlet. The hexagonal temperature-controlled cold plate 10 is placed on the bottom surface of the inner cavity of the hexagonal foundation model barrel 9 and the two are tightly attached. The liquid inlet and liquid outlet of the hexagonal temperature-controlled cold plate 10 are connected to the liquid outlet and liquid inlet of the temperature-controlled cold bath box 11, respectively. The hexagonal temperature-controlled cold plate 10 is made of aluminum plate with a thickness of 10mm and a side length of 297mm to facilitate embedding into the bottom of the hexagonal foundation model barrel 9.

[0072] The model pile 6 is a precast cement concrete pile or a reinforced thermoplastic pile commonly used in permafrost areas. The pile height is 1m. When using a precast cement concrete pile, the outer diameter is 50mm, and when using a reinforced thermoplastic pile, the outer diameter is 100mm.

[0073] A layer of crushed ice 7 is also set in the hexagonal foundation model barrel 9 to simulate the ice layer that exists in the permafrost foundation; artificially compacted frozen soil 8 is set above and below the crushed ice layer 7, and multiple temperature sensors 5 are evenly distributed in the artificially compacted frozen soil 8.

[0074] The ice layer 7 is made of compacted ice chips with a compaction density of 0.9 g / cm³. 3 The thickness is 5cm, used to simulate the ice layer present in permafrost foundations;

[0075] The artificially compacted frozen soil 8 is made from silty clay taken from permafrost regions, with a maximum particle size of 5mm. After drying, crushed pure ice chips are added, mixed evenly, and compacted to achieve a compaction density of 1.5g / cm³. 3The mass fraction of ice is 20% to 40%;

[0076] A model pile 6 is vertically set on the central axis of the hexagonal foundation model barrel 9. The top of the model pile 6 is at the same height as the artificially compacted frozen soil 8. A sand cushion layer 4 and a uniformly distributed loading slider 3 are set above the model pile 6. The uniformly distributed loading slider 3 is above the sand cushion layer 4. Both the sand cushion layer 4 and the uniformly distributed loading slider 3 are set in the hexagonal foundation model barrel 9.

[0077] The uniformly distributed loading slider 3 has a regular hexagonal prism structure, specifically composed of multiple cuboid sliders 3-3 and two isosceles triangular sliders 3-2. The cuboid sliders 3-3 are positioned in the center, tightly fitted together to form a cuboid structure. An isosceles triangular slider 3-2 is positioned on each side, with its two legs located along the outer edge. Each slider is 50cm high. The cross-section of the cuboid slider 3-3 is 30mm × 30mm, and the leg length of the isosceles triangular slider 3-2 is 297mm, with an included angle of 1° between the two legs. 20°; the sliders are thoroughly ground and polished, and lubricated to ensure free relative sliding; each of the cuboid sliders 3-3 and isosceles triangular sliders 3-2 is equipped with a pull ring 3-1, and multiple steel bars are inserted into the pull rings 3-1 in the same row; a sleeve 15 is set around the uniformly loaded slider 3 and the two are slidably connected. The sleeve 15 is a hollow regular hexagonal prism structure with open structures at the top and bottom. The sleeve 15 rests on the side wall of the hexagonal foundation model barrel 9; the height of the sleeve 15 is 10cm, which is used to limit the lateral tilt of the uniformly loaded slider 3;

[0078] The irregularly shaped chassis hammer has a chassis 14 with one end being an obtuse-angled pointed structure 14-1 with an included angle of 120°, and the other end being an inwardly concave arc structure 14-2 with an arc of 60°. The irregularly shaped chassis hammer also includes a vertical rod 12 and a load-bearing part 13, with the load-bearing part 13 fitted onto the vertical rod 12 and the two being in a sliding connection relationship.

[0079] The hexagonal foundation model barrel 9 and four industrial cameras 2 are all installed in the control room 1. Two industrial cameras 2 are arranged at the top of the inner cavity of the control room 1 to monitor the deformation of the uniformly distributed loading slider 3 at the top of the model in real time. The other two industrial cameras 2 are arranged in the middle of the side wall of the control room 1 to monitor the deformation of the soil inside the hexagonal foundation model barrel 9 in real time.

[0080] The method of using the permafrost subgrade pile foundation model test apparatus in this experiment is as follows:

[0081] Step 1: Dry the soil for the test, pass it through a 5mm geotextile sieve, add water and mix evenly to a moisture content of 12% to ensure that the soil particles are moist but do not clump together in large quantities, put it in a refrigerator at 2℃ to cool down, seal and let it stand for 24 hours for later use.

[0082] Step 2: Adjust the temperature of the temperature control chamber 1 to -5℃, crush the pure ice into ice chips and keep them warm in the temperature control chamber 1; assemble the hexagonal foundation model barrel 9 and the hexagonal temperature-controlled cold plate 10 in the temperature control chamber 1, connect the hexagonal temperature-controlled cold plate 10 to the temperature-controlled cold bath box 11, fill the temperature-controlled cold bath box 11 with alcohol as a refrigerant, the temperature control range is -20℃~20℃, and the temperature control accuracy is ±0.1℃;

[0083] Step 3: Adjust the temperature of the controlled chamber 1 to -2℃. Under this temperature environment, add the crushed ice prepared in step 2 to the cooled soil sample with 12% moisture content prepared in step 1 to the target ice content of the model test, and stir quickly and evenly.

[0084] Step 4: Experimental Model Construction

[0085] Scenario 1: Model test of precast pile foundation for permafrost roadbed:

[0086] Prefabricated model piles 6 are placed into the hexagonal foundation model barrel 9, ensuring that model piles 6 are centered within the hexagonal foundation model barrel 9. Soil samples with the target ice content are prepared and layered into the hexagonal foundation model barrel 9 according to the target compaction density. A compaction hammer with an irregularly shaped base is used to compact the soil, with the obtuse-angled pointed structure 14-1 and the rounded arc structure 14-2 used to compact the inner corners of the foundation model barrel 9 and around the model piles 6. The thickness of each compacted layer is set to 5cm. The soil is then laid in the lower middle part of the model piles 6. A 10cm thick layer of crushed ice 7 is laid and compacted to simulate the ice layer in a permafrost foundation; then, soil samples are filled to the same height as the top of the model pile 6, and temperature sensors 5 are evenly distributed in the soil samples; then, a 10cm sand cushion layer 4 is laid on top and compacted; the entire model is temperature controlled in a -2℃ controlled chamber 1, and the temperature controlled cold bath box 11 is turned on to ensure that the hexagonal temperature controlled cold plate 10 is also at -2℃; the temperature is controlled until the temperature range of all temperature sensors 5 is between -2℃ and 0℃;

[0087] Scenario 2: Model test of reinforced thermomelting pile foundation for permafrost roadbed

[0088] Install an acrylic tube at the target hole position of the reinforced hot-melt pile in the hexagonal foundation model bucket 9 to reserve the pile hole position; similar to case one, fill the hexagonal foundation model bucket 9 and pay attention to laying the ice crush layer 7, but after each layer is compacted, gently rotate the acrylic tube to avoid it freezing tightly with the frozen soil; when filling to 10cm away from the top surface of the hexagonal foundation model bucket 9, rotate and pull out the acrylic tube, put the geotextile sleeve into the reserved hole, and control the temperature until the temperature range of all temperature sensors 5 is between -2℃ and 0℃; then fill the geotextile sleeve with hot-melt pile material as model pile 6, and then set a 10cm thick sand cushion layer 4 on top of the foundation model;

[0089] Step 5: Using a small crane, the evenly distributed loading sliders 3 are smoothly installed on top of the sand cushion layer 4 using multiple steel bars 16. The hoop 15 overlaps with the side wall of the hexagonal foundation model barrel 9. All the cuboid sliders 3-3 and the two isosceles triangular sliders 3-2 are completely pressed on top of the sand cushion layer 4. The steel bars 16 are removed to allow the loading sliders to move freely again. Then, the whole thing is statically loaded with gravity at a controlled temperature of -2℃ to 0℃ for 48 hours. The temperature is monitored in real time using a temperature sensor 5. The vertical displacement of each loading slider is monitored in real time using two industrial cameras 2. The deformation of the ice layer is monitored in real time from the side using two industrial cameras 2.

[0090] Step Six: After the loading test is completed, insert the steel bar 16 into the pull ring 3-1 again to restore its integrity. Use a small crane to remove the uniformly distributed loading slider 3 from the hexagonal foundation model bucket 9. Raise the temperature control box 1 to room temperature. After the model has fully recovered to room temperature, remove the soil around the pile and observe the damage to the pile.

[0091] The beneficial effects of this experiment are:

[0092] 1. The apparatus of this experiment can conduct indoor model tests on various permafrost model piles. The hexagonal foundation model bucket 9, the hexagonal temperature-controlled cold plate 10 and the uniformly distributed loading slider 3 can simulate the effect of the pile unit under the uniformly distributed load in the case of equilateral triangular pile arrangement in actual roadbed engineering. The single pile test can simulate the effect of pile group.

[0093] 2. In this experiment, the uniformly distributed loading slider 3 is evenly distributed on the top of the model pile 6 to apply a uniformly distributed load to the foundation. This eliminates the need for traditional reaction frames, actuators, and loading discs. Compared with traditional reaction frame loading, this method is closer to the load of roadbed fill. At the same time, multiple loading blocks generate displacements independently, which can intuitively reflect the uneven settlement in permafrost foundations. The test range of uneven settlement is accurate to the size of a single loading block, and the settlement displacement of the loading blocks can be captured in real time by an industrial camera 2. This eliminates the influence of conventional embedded displacement sensors on the foundation, achieving multiple benefits.

[0094] 3. This experiment added a layer of crushed ice 7 to the artificially compacted frozen soil 8, which can reflect the distribution of ice layers in the actual permafrost foundation. The hexagonal foundation model barrel 9 is made of transparent plexiglass, and the deformation of the crushed ice layer 7 can be monitored in real time by an industrial camera 2.

[0095] 4. This experiment uses moist soil and crushed pure ice chips to prepare the foundation soil, which can ensure that the ice content of the frozen soil is uniform. The hexagonal temperature-controlled cold plate 10 used can effectively simulate the temperature boundary of the frozen bedrock under the permafrost pile foundation. The irregularly shaped chassis compaction hammer used has both an obtuse-angled pointed structure 14-1 and a circular arc structure 14-2, which can compact the soil around the pile and at the corners of the model box. The roadbed pile foundation model made by this experimental method can well simulate the actual engineering situation.

Claims

1. A test device for pile foundation model of permafrost roadbed, characterized in that... The permafrost roadbed pile foundation model test device consists of a controlled room (1), 4 industrial cameras (2), a uniformly distributed loading slider (3), a sand cushion layer (4), a temperature sensor (5), a model pile (6), a crushed ice layer (7), artificially compacted frozen soil (8), a hexagonal foundation model bucket (9), a hexagonal temperature-controlled cold plate (10), a temperature-controlled cold bath box (11), a hoop (15), steel bars (16), and a special-shaped chassis compaction hammer; The hexagonal foundation model barrel (9) is a hollow regular hexagonal prism structure with an open top and a closed bottom; The hexagonal temperature-controlled cold plate (10) is a thin plate with a regular hexagonal prism structure, and a serpentine water-cooling pipe (10-1) is evenly arranged inside it. The two ends of the serpentine water-cooling pipe (10-1) are respectively provided with liquid inlet and liquid outlet. The hexagonal temperature-controlled cold plate (10) is placed on the bottom surface of the inner cavity of the hexagonal foundation model barrel (9) and the two are tightly attached. The liquid inlet and liquid outlet of the hexagonal temperature-controlled cold plate (10) are respectively connected to the liquid outlet and liquid inlet of the temperature-controlled cold bath box (11). A layer of crushed ice (7) is also set in the hexagonal foundation model bucket (9) to simulate the ice layer that exists in the permafrost foundation; artificially compacted frozen soil (8) is set above and below the crushed ice layer (7), and multiple temperature sensors (5) are evenly distributed in the artificially compacted frozen soil (8); A model pile (6) is vertically set on the central axis of the hexagonal foundation model barrel (9). The top of the model pile (6) is at the same height as the artificially compacted frozen soil (8). A sand cushion layer (4) and a uniformly distributed loading slider (3) are set above the model pile (6). The uniformly distributed loading slider (3) is above the sand cushion layer (4). Both the sand cushion layer (4) and the uniformly distributed loading slider (3) are set in the hexagonal foundation model barrel (9). The uniformly distributed loading slider (3) is a regular hexagonal prism structure, specifically composed of multiple cuboid sliders (3-3) and two isosceles triangular sliders (3-2); multiple cuboid sliders (3-3) are set in the middle position, closely fitting together to form a cuboid structure, and an isosceles triangular slider (3-2) is set on each side, with the two sides of the isosceles triangular slider (3-2) set on the outer edge; all cuboid sliders (3-3) and isosceles triangular sliders (3-2) are provided with a pull ring (3-1), and multiple steel bars are inserted into the pull rings (3-1) located in the same row; a sleeve (15) is set on the periphery of the uniformly distributed loading slider (3) and the two are in a sliding connection relationship. The sleeve (15) is a hollow regular hexagonal prism structure with open structures at the top and bottom, and the sleeve (15) rests on the side wall of the hexagonal foundation model barrel (9); The chassis (14) of the irregular chassis hammer has an obtuse angle pointed structure (14-1) with an included angle of 120° at one end and an inwardly concave arc structure (14-2) at the other end, with an arc of 60°. The hexagonal foundation model barrel (9) and four industrial cameras (2) are all installed in the control room (1). Two industrial cameras (2) are arranged at the top of the inner cavity of the control room (1) to monitor the deformation of the uniformly distributed loading slider (3) at the top of the model in real time. The other two industrial cameras (2) are arranged in the middle of the side wall of the control room (1) to monitor the deformation of the soil inside the hexagonal foundation model barrel (9) in real time.

2. The experimental device for pile foundation model of permafrost subgrade according to claim 1, characterized in that... The temperature-controlled cold bath (11) is filled with alcohol as a refrigerant, and the temperature control range is -20℃ to 20℃, with a temperature control accuracy of ±0.1℃.

3. The experimental device for pile foundation model of permafrost subgrade according to claim 1, characterized in that... The hexagonal foundation model barrel (9) is made of transparent plexiglass panels. The thickness of the plexiglass panels is 20mm. There are 10mm openings at the bottom of the two opposite plexiglass panels to facilitate the connection of the pipelines of the temperature-controlled cold bath box (11).

4. The experimental device for pile foundation model of permafrost subgrade according to claim 1, characterized in that... The hexagonal temperature-controlled cold plate (10) is made of aluminum plate with a thickness of 10mm.

5. The experimental device for pile foundation model of permafrost subgrade according to claim 1, characterized in that... The artificially compacted frozen soil (8) is made from silty clay taken from permafrost regions, with a maximum particle size of 5 mm. After drying, crushed pure ice chips are added, mixed evenly, and compacted to form a compacted density of 1.5 g / cm³. 3 The mass fraction of ice is 20% to 40%.

6. The experimental device for pile foundation model of permafrost subgrade according to claim 1, characterized in that... The ice layer (7) is made of compacted ice chips with a compaction density of 0.9 g / cm³. 3 It is 5cm thick and is used to simulate the ice layer that exists in permafrost foundations.

7. The experimental device for pile foundation model of permafrost subgrade according to claim 1, characterized in that... The model pile (6) is a precast cement concrete pile or a reinforced thermomelted pile used in permafrost areas. The pile height is 1m. When using a precast cement concrete pile, the outer diameter is 50mm. When using a reinforced thermomelted pile, the outer diameter is 100mm.

8. The experimental device for pile foundation model of permafrost subgrade according to claim 1, characterized in that... The thickness of the sand cushion layer (4) is 100 mm.

9. The experimental device for pile foundation model of permafrost subgrade according to claim 1, characterized in that... The temperature sensor (5) is a T-type Teflon thermocouple with a test temperature range of -20~150℃ and an accuracy of ±0.01℃.

10. The experimental device for pile foundation model of permafrost subgrade according to claim 1, characterized in that... The rectangular slider (3-3) has a cross-sectional dimension of 30mm×30mm; the uniformly distributed loading slider (3) is a solid stainless steel body.

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