Permafrost roadbed pile foundation model test device

Abstract

The invention discloses a permafrost roadbed pile foundation model test device, and relates to a permafrost model test device. The invention aims to solve the technical problem that the differential settlement of the permafrost pile foundation containing the ice layer under the action of uniformly distributed load is difficult to test through indoor tests at present. According to the device, through the hexagonal foundation model barrel and the uniformly-distributed loading sliding blocks, the effect that the pile unit bodies bear uniformly-distributed loads under the condition that the piles are distributed in a regular triangle in actual roadbed engineering can be simulated; the plurality of loading blocks are mutually independent to generate displacement, so that the differential settlement in the permafrost foundation can be intuitively reflected; the broken ice layer is additionally arranged on the basis of manually compacted frozen soil, and distribution of ice layers in the actual permafrost foundation can be reflected. According to the permafrost roadbed pile foundation model, the wet soil and the crushed pure ice chips are used for preparing the foundation soil, so that the ice content of the permafrost can be uniform, and the actual engineering condition can be well simulated through the permafrost roadbed pile foundation model.

Description

Technical Field

[0001] The invention relates to a model test device for permafrost. Background Art

[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 roads and railways in permafrost areas, it is necessary to face the uneven settlement of the roadbed caused by permafrost degradation. Pile foundation is currently a commonly used permafrost roadbed reinforcement measure, which can significantly enhance the bearing capacity of permafrost foundation. When the roadbed and pavement structure is filled on the permafrost foundation, it can be considered that a uniformly distributed load is applied to the foundation. In this case, the uneven deformation of the permafrost pile foundation composite foundation will be transmitted to the roadbed and pavement structure, resulting in uneven settlement of the roadbed and longitudinal cracks in the pavement. In order to ensure the safe and stable operation of roads and railways in permafrost areas, it is necessary to conduct targeted research on the uneven settlement of pile foundation foundations. Among them, indoor model test is a common method to test the physical and mechanical properties of pile foundation. At present, there have been a large number of related experimental studies, which are mainly based on scaled test design. The pile foundation is filled in the indoor model test box, and stress, temperature, hydrology and pore water pressure sensors are buried in the foundation. At the same time, the actuator and reaction device are used on the top of the pile to apply dynamic and static loads to it to obtain the stress-displacement development law of the foundation. Placing the entire device in a controlled room can simulate the mechanical properties of the pile foundation in cold regions.

[0003] However, although the current test method can be used to conduct model tests on pile foundations of permafrost roadbeds, it is difficult to analyze the most important engineering characteristic of frozen foundations - uneven settlement. At the same time, the strata in permafrost areas are often complex in engineering geology. Field survey results show that there is often an ice layer under the foundation, which has a great impact on the uneven settlement of the foundation. It is necessary to design different layers of frozen soil in the test design to effectively simulate the occurrence of uneven settlement of frozen foundations. Finally, since the pile foundation layout in permafrost areas is often arranged in an equilateral triangle, under the uniform load of the roadbed, the pile unit is a hexagonal foundation with the idea of ​​axisymmetry. Therefore, how to apply uniform loads to the hexagonal foundation unit and record the occurrence of uneven settlement of the model is the top priority of the permafrost roadbed pile foundation model test.

[0004] At present, there are few reports on the study of uneven settlement of roadbed based on roadbed pile foundation model tests, especially there is no relevant research on the uneven settlement of pile foundations under special bottom conditions of permafrost under roadbed load conditions. Patent CN2023116662241 discloses a loading device for a scaled model of a pile group foundation, and its loading method makes it difficult to test the uneven settlement of the top surface under simulated uniformly distributed loads. Patent CN2019100471407 discloses a monitoring device for frozen soil model tests and its use method, which are mainly aimed at the migration of temperature, moisture, and salt in frozen soil foundations, and do not test uneven settlement. Patent CN2022212354492 discloses a temperature-controlled pile foundation model test device, which uses a structural loading system to load the model, and it is also difficult to monitor uneven settlement in real time. Patent CN2022109257523 proposes a hot rod roadbed frost heave test device, which can test the uneven frost heave deformation of the top surface of the model under small-scale conditions, but cannot load the top surface of the model evenly, and cannot model the actual stress state of the frozen soil foundation. In summary, it is necessary to develop a test device and a matching test method that can simulate the actual stress state and deformation state of the frozen soil roadbed pile foundation, and study the uneven settlement of the frozen soil roadbed pile foundation under uniform load. 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 a permafrost pile foundation containing an ice layer under a uniformly distributed load through indoor tests, and to provide a permafrost roadbed pile foundation model test device.

[0006] The permafrost roadbed pile foundation model test device of the present invention is composed of a control 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 barrel 9, a hexagonal temperature-controlled cold plate 10, a temperature-controlled cold bath box 11, a hoop 15, a steel bar 16 and a special-shaped chassis compacting 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, and a liquid inlet and a liquid outlet are respectively arranged at both ends of the serpentine water-cooling pipe 10-1; 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 fitted, and the liquid inlet and liquid outlet of the hexagonal temperature-controlled cold plate 10 are respectively connected with the liquid outlet and liquid inlet of the temperature-controlled cold bath box 11;

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

[0010] A model pile 6 is vertically arranged 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 arranged above the model pile 6, the uniformly distributed loading slider 3 is above the sand cushion layer 4, and the sand cushion layer 4 and the uniformly distributed loading slider 3 are both arranged in the hexagonal foundation model barrel 9;

[0011] The uniformly distributed loading slider 3 is a regular hexagonal prism structure, specifically composed of a plurality of rectangular sliders 3-3 and two isosceles triangle sliders 3-2; the plurality of rectangular sliders 3-3 are arranged in the middle position, closely fitting each other to form a rectangular structure, an isosceles triangle slider 3-2 is arranged on each side, and the two waists of the isosceles triangle slider 3-2 are arranged on the outer edge; all the rectangular sliders 3-3 and the isosceles triangle sliders 3-2 are provided with a pull ring 3-1, and a plurality of steel bars are respectively inserted into the pull rings 3-1 located in the same row; a hoop 15 is arranged on the periphery of the uniformly distributed loading slider 3 and the two are in a sliding connection relationship, the hoop 15 is a hollow regular hexagonal prism structure and is open at the top and bottom, and the hoop 15 falls on the side wall of the hexagonal foundation model barrel 9;

[0012] One end of the chassis 14 of the special-shaped chassis hammer is a blunt-angled tip structure 14-1 with an angle of 120°, and the other end is an inwardly concave arc structure 14-2, and the arc of the arc structure 14-2 is 60°;

[0013] The hexagonal foundation model barrel 9 and four industrial cameras 2 are all set in the control room 1, two of which are arranged at the top of the inner cavity of the control room 1 to monitor the deformation of the uniformly loaded slider 3 on the top of the model in real time, and 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 in the hexagonal foundation model barrel 9 in real time.

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

[0015] Step 1: Dry the test soil, pass it through a 5mm geotechnical sieve, add water and mix evenly to a moisture content of 12% to ensure that the soil particles are moist and not a large amount of lumps, put it in a refrigerator at 2°C to cool, seal it and let it stand for 24 hours for use;

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

[0017] Step 3: Adjust the temperature of the control room 1 to -2°C, add the crushed ice prepared in step 2 to the cooling soil sample with a water content of 12% prepared in step 1 to the target ice content of the model test under this temperature environment, and stir quickly and evenly;

[0018] Step 4: Test model making:

[0019] Case 1: Model test of precast pile foundation on permafrost roadbed:

[0020] The prefabricated model pile 6 prepared in advance is placed in the hexagonal foundation model barrel 9 to ensure that the model pile 6 is in the center of the hexagonal foundation model barrel 9; the soil sample with the target ice content is filled into the hexagonal foundation model barrel 9 in layers according to the target compaction density, and compacted with a special-shaped chassis compacting hammer, and the inner corners of the foundation model barrel 9 and the surrounding of the model pile 6 are compacted with the blunt-angle tip structure 14-1 and the arc structure 14-2 respectively. The thickness of each layer after compaction is set to 5 cm, and the middle and lower parts of the model pile 6 are paved A layer of crushed ice 7 with a thickness of 10 cm is provided and compacted to simulate the ice layer in the permafrost foundation; then the soil sample is continuously filled to the same height as the top of the model pile 6, and the temperature sensor 5 is evenly arranged in the soil sample; then a 10 cm sand cushion layer 4 is laid on top and compacted; the whole model is temperature-controlled in a -2°C controlled room 1, and the temperature-controlled cold bath box 11 is turned on to ensure that the hexagonal temperature-controlled cold plate 10 is also -2°C; the temperature is controlled until the temperature range of all temperature sensors 5 is between -2°C and 0°C;

[0021] Case 2: Model test of reinforced hot-thaw pile foundation on permafrost roadbed

[0022] A plexiglass tube is installed at the target hole position of the reinforced hot-melt pile in the hexagonal foundation model barrel 9 to reserve the pile body hole position; similar to the first case, the hexagonal foundation model barrel 9 is filled and the crushed ice layer 7 is laid, but the plexiglass tube is gently rotated after each layer is compacted to prevent it from being tightly frozen with the frozen soil; when the filling is 10 cm away from the top surface of the hexagonal foundation model barrel 9, the plexiglass tube is rotated and pulled out, and the geotextile sleeve is placed in the reserved hole, and the temperature is controlled until the temperature range of all temperature sensors 5 is between -2°C and 0°C; then the hot-melt pile body material is filled into the geotextile sleeve as a model pile 6, and then a 10 cm thick sand cushion layer 4 is set above the foundation model;

[0023] Step 5: Use a small crane to steadily install the uniformly distributed loading slider 3 to the top of the sand cushion layer 4 through multiple steel bars 16, the hoop 15 overlaps with the side wall of the hexagonal foundation model barrel 9, all the rectangular sliders 3-3 and the two isosceles triangle sliders 3-2 are completely pressed on the top of the sand cushion layer 4, and the steel bars 16 are pulled out to restore the free movement of the loading slider, and then the whole is placed at -2℃~0℃ temperature controlled static gravity loading for 48h, and the temperature is monitored in real time using a temperature sensor 5, and the vertical displacement of each loading slider is monitored in real time using two industrial cameras 2, and the deformation of the ice layer is monitored in real time from the side using two industrial cameras 2;

[0024] Step 6: After the loading test is completed, the steel bar 16 is inserted into the pull ring 3-1 again to restore its integrity. The uniformly distributed loading slider 3 is removed from the hexagonal foundation model barrel 9 using a small crane, and the temperature control box 1 is raised to room temperature. After the model is completely restored to room temperature, the soil around the pile is excavated to observe the damage of the pile.

[0025] The beneficial effects of the present invention are:

[0026] 1. The device of the present invention can carry out indoor model tests of various permafrost model piles. The hexagonal foundation model barrel 9, the hexagonal temperature-controlled cold plate 10 and the uniformly distributed loading slider 3 can simulate the effect of the pile unit body under the uniformly distributed load in the case of regular triangle pile arrangement in actual roadbed engineering, and use a single pile test to simulate the effect of pile groups;

[0027] 2. The uniformly distributed loading slider 3 of the present invention is evenly arranged on the top of the model pile 6, and a uniformly distributed load is applied to the foundation, eliminating the loading method of setting up the traditional reaction frame, actuator and loading plate. Compared with the traditional reaction frame loading, it is closer to the roadbed fill load. At the same time, multiple loading blocks are independently displaced, which can intuitively reflect the uneven settlement in the permafrost foundation, and the test range of the uneven settlement is accurately determined to the size of a single loading block. The settlement displacement of the loading block can be captured in real time by the industrial camera 2, eliminating the influence of the conventional embedded displacement sensor on the foundation, achieving multiple goals at one stroke;

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

[0029] 4. The present invention uses moist soil and crushed pure ice chips to configure 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 special-shaped chassis compacting hammer used has both a blunt-angle tip structure 14-1 and an 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 produced by this test method can well simulate the actual engineering situation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is an overall schematic diagram of a permafrost roadbed pile foundation model test device according to a specific implementation method 1;

[0031] Figure 2 for Figure 1 A top view of the middle hexagonal foundation model barrel 9;

[0032] Figure 3 It is a front view of the uniformly loaded slider 3 of the first specific implementation mode;

[0033] Figure 4 for Figure 3 A top view of

[0034] Figure 5 This is a front view of the hammer used to strike the special-shaped chassis in Test 1;

[0035] Figure 6 for Figure 5 Bottom view of

[0036] Figure 7 for Figure 1 A top view of the middle hexagonal temperature-controlled cold plate 10. DETAILED DESCRIPTION

[0037] Specific implementation method 1: This implementation method is a permafrost roadbed pile foundation model test device, such as Figure 1-Figure 7 As shown, it is specifically composed 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 barrel 9, a hexagonal temperature-controlled cold plate 10, a temperature-controlled cold bath box 11, a hoop 15, a steel bar 16 and a special-shaped chassis compacting 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, and a liquid inlet and a liquid outlet are respectively arranged at both ends of the serpentine water-cooling pipe 10-1; 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 fitted, and the liquid inlet and liquid outlet of the hexagonal temperature-controlled cold plate 10 are respectively connected with the liquid outlet and liquid inlet of the temperature-controlled cold bath box 11;

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

[0041] A model pile 6 is vertically arranged 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 arranged above the model pile 6, the uniformly distributed loading slider 3 is above the sand cushion layer 4, and the sand cushion layer 4 and the uniformly distributed loading slider 3 are both arranged in the hexagonal foundation model barrel 9;

[0042] The uniformly distributed loading slider 3 is a regular hexagonal prism structure, specifically composed of a plurality of rectangular sliders 3-3 and two isosceles triangle sliders 3-2; the plurality of rectangular sliders 3-3 are arranged in the middle position, closely fitting each other to form a rectangular structure, an isosceles triangle slider 3-2 is arranged on each side, and the two waists of the isosceles triangle slider 3-2 are arranged on the outer edge; all the rectangular sliders 3-3 and the isosceles triangle sliders 3-2 are provided with a pull ring 3-1, and a plurality of steel bars are respectively inserted into the pull rings 3-1 located in the same row; a hoop 15 is arranged on the periphery of the uniformly distributed loading slider 3 and the two are in a sliding connection relationship, the hoop 15 is a hollow regular hexagonal prism structure and is open at the top and bottom, and the hoop 15 falls on the side wall of the hexagonal foundation model barrel 9;

[0043] One end of the chassis 14 of the special-shaped chassis hammer is a blunt-angled tip structure 14-1 with an angle of 120°, and the other end is an inwardly concave arc structure 14-2, and the arc of the arc structure 14-2 is 60°;

[0044] The hexagonal foundation model barrel 9 and four industrial cameras 2 are all set in the control room 1, two of which are arranged at the top of the inner cavity of the control room 1 to monitor the deformation of the uniformly loaded slider 3 on the top of the model in real time, and 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 in the hexagonal foundation model barrel 9 in real time.

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

[0046] Step 1: Dry the test soil, pass it through a 5mm geotechnical sieve, add water and mix evenly to a moisture content of 12% to ensure that the soil particles are moist and not a large amount of lumps, put it in a refrigerator at 2°C to cool, seal it and let it stand for 24 hours for use;

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

[0048] Step 3: Adjust the temperature of the control room 1 to -2°C, add the crushed ice prepared in step 2 to the cooling soil sample with a water content of 12% prepared in step 1 to the target ice content of the model test under this temperature environment, and stir quickly and evenly;

[0049] Step 4: Test model making:

[0050] Case 1: Model test of precast pile foundation on permafrost roadbed:

[0051] The prefabricated model pile 6 prepared in advance is placed in the hexagonal foundation model barrel 9 to ensure that the model pile 6 is in the center of the hexagonal foundation model barrel 9; the soil sample with the target ice content is filled into the hexagonal foundation model barrel 9 in layers according to the target compaction density, and compacted with a special-shaped chassis compacting hammer, and the inner corners of the foundation model barrel 9 and the surrounding of the model pile 6 are compacted with the blunt-angle tip structure 14-1 and the arc structure 14-2 respectively. The thickness of each layer after compaction is set to 5 cm, and the middle and lower parts of the model pile 6 are paved A layer of crushed ice 7 with a thickness of 10 cm is provided and compacted to simulate the ice layer in the permafrost foundation; then the soil sample is continuously filled to the same height as the top of the model pile 6, and the temperature sensor 5 is evenly arranged in the soil sample; then a 10 cm sand cushion layer 4 is laid on top and compacted; the whole model is temperature-controlled in a -2°C controlled room 1, and the temperature-controlled cold bath box 11 is turned on to ensure that the hexagonal temperature-controlled cold plate 10 is also -2°C; the temperature is controlled until the temperature range of all temperature sensors 5 is between -2°C and 0°C;

[0052] Case 2: Model test of reinforced hot-thaw pile foundation on permafrost roadbed

[0053] A plexiglass tube is installed at the target hole position of the reinforced hot-melt pile in the hexagonal foundation model barrel 9 to reserve the pile body hole position; similar to the first case, the hexagonal foundation model barrel 9 is filled and the crushed ice layer 7 is laid, but the plexiglass tube is gently rotated after each layer is compacted to prevent it from being tightly frozen with the frozen soil; when the filling is 10 cm away from the top surface of the hexagonal foundation model barrel 9, the plexiglass tube is rotated and pulled out, and the geotextile sleeve is placed in the reserved hole, and the temperature is controlled until the temperature range of all temperature sensors 5 is between -2°C and 0°C; then the hot-melt pile body material is filled into the geotextile sleeve as a model pile 6, and then a 10 cm thick sand cushion layer 4 is set above the foundation model;

[0054] Step 5: Use a small crane to steadily install the uniformly distributed loading slider 3 to the top of the sand cushion layer 4 through multiple steel bars 16, the hoop 15 overlaps with the side wall of the hexagonal foundation model barrel 9, all the rectangular sliders 3-3 and the two isosceles triangle sliders 3-2 are completely pressed on the top of the sand cushion layer 4, and the steel bars 16 are pulled out to restore the free movement of the loading slider, and then the whole is placed at -2℃~0℃ temperature controlled static gravity loading for 48h, and the temperature is monitored in real time using a temperature sensor 5, and the vertical displacement of each loading slider is monitored in real time using two industrial cameras 2, and the deformation of the ice layer is monitored in real time from the side using two industrial cameras 2;

[0055] Step 6: After the loading test is completed, the steel bar 16 is inserted into the pull ring 3-1 again to restore its integrity. The uniformly distributed loading slider 3 is removed from the hexagonal foundation model barrel 9 using a small crane, and the temperature control box 1 is raised to room temperature. After the model is completely restored to room temperature, the soil around the pile is excavated to observe the damage of the pile.

[0056] Specific embodiment 2: This embodiment is different from specific embodiment 1 in that the temperature-controlled cold bath box 11 is filled with alcohol as a refrigerant, the temperature control range is -20°C to 20°C, and the temperature control accuracy is ±0.1°C. Other aspects are the same as specific embodiment 1.

[0057] Specific embodiment 3: This embodiment is different from specific embodiment 1 or 2 in that the hexagonal model test barrel 9 is made of transparent organic glass plates, the thickness of the organic glass plates is 20 mm, and a 10 mm opening is opened below the two opposite organic glass plates to facilitate the connection of the pipeline of the temperature-controlled cold bath box 11. Others are the same as specific embodiment 1 or 2.

[0058] Specific embodiment 4: This embodiment is different from specific embodiments 1 to 3 in that the hexagonal temperature-controlled cold plate 10 is made of an aluminum plate with a thickness of 10 mm. Other aspects are the same as those of specific embodiments 1 to 3.

[0059] Specific embodiment 5: This embodiment differs from specific embodiment 4 in that the artificially compacted frozen soil 8 is made of silty clay taken from permafrost areas, with a maximum particle size of 5 mm, and after drying, crushed pure ice chips are added thereto and mixed and compacted evenly, with a compaction density of 1.5 g / cm 3 , the mass fraction of ice is 20% to 40%. Other aspects are the same as those of the fourth embodiment.

[0060] Specific embodiment 6: This embodiment is different from the specific embodiment 5 in that the crushed ice layer 7 is made of compacted crushed ice chips with a compacted density of 0.9 g / cm 3 , with a thickness of 5 cm, is used to simulate the ice layer existing in the permafrost foundation. The rest is the same as the specific implementation method five.

[0061] Specific embodiment 7: This embodiment is different from specific embodiment 6 in that the model pile 6 is a cement concrete precast pile or a reinforced hot-melt pile for permafrost areas, the pile height is 1m, the outer diameter is 50mm when the cement concrete precast pile is used, and the outer diameter is 100mm when the reinforced hot-melt pile is used. Others are the same as specific embodiment 6.

[0062] Specific embodiment 8: This embodiment is different from specific embodiment 7 in that the thickness of the sand cushion layer 4 is 100 mm. The rest is the same as specific embodiment 7.

[0063] Specific embodiment 9: This embodiment is different from specific embodiment 8 in that the temperature sensor 5 is a T-type Teflon thermocouple, the test temperature range is -20 to 150°C, and the accuracy is ±0.01°C. Other aspects are the same as specific embodiment 8.

[0064] Specific embodiment 10: This embodiment is different from specific embodiment 9 in that the cross-sectional dimensions of the rectangular parallelepiped slider 3 - 3 are 30 mm×30 mm, and the uniformly loaded slider 3 is a solid stainless steel body. The rest is the same as specific embodiment 9.

[0065] The present invention is verified by the following tests:

[0066] Test 1: This test is a permafrost roadbed pile foundation model test device, such as Figure 1-Figure 7 As shown, it is specifically composed 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 barrel 9, a hexagonal temperature-controlled cold plate 10, a temperature-controlled cold bath box 11, a hoop 15, a steel bar 16 and a special-shaped chassis compacting hammer;

[0067] The internal dimensions of the control room 1 are 3m×3m×3m, the temperature control accuracy is ±1°C, the temperature control range is -20°C to 20°C, and the molding temperature of the permafrost foundation model can be controlled;

[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 to 150°C and an accuracy of ±0.01°C;

[0070] The hexagonal foundation model barrel 9 is a hollow regular hexagonal prism structure with an open top and a closed bottom, a height of 1.2m, and a side length of 30cm, which can simulate a single pile foundation unit with triangular piles in the foundation; the hexagonal model test barrel 9 is spliced ​​by transparent organic glass plates, the thickness of the organic glass plates is 20mm, the inner side length is 30cm, and the angle between the plates is 120°, wherein two opposite side plates have 10mm openings below for easy 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, and a liquid inlet and a liquid outlet are respectively arranged at both ends of the serpentine water-cooling pipe 10-1; 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 fitted, and the liquid inlet and the liquid outlet of the hexagonal temperature-controlled cold plate 10 are respectively connected with the liquid outlet and the liquid inlet of the temperature-controlled cold bath box 11; the hexagonal temperature-controlled cold plate 10 is made of aluminum plate, with a thickness of 10 mm and a side length of 297 mm, which is convenient for embedding into the bottom of the hexagonal model test barrel 9;

[0072] The model pile 6 is a cement concrete precast pile or a reinforced hot-melt pile commonly used in permafrost areas, with a pile height of 1 m, an outer diameter of 50 mm when a cement concrete precast pile is used, and an outer diameter of 100 mm when a reinforced hot-melt pile is used;

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

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

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

[0076] A model pile 6 is vertically arranged 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 arranged above the model pile 6, the uniformly distributed loading slider 3 is above the sand cushion layer 4, and the sand cushion layer 4 and the uniformly distributed loading slider 3 are both arranged in the hexagonal foundation model barrel 9;

[0077] The uniformly distributed loading slider 3 is a regular hexagonal prism structure, specifically composed of a plurality of rectangular sliders 3-3 and two isosceles triangle sliders 3-2; the plurality of rectangular sliders 3-3 are arranged in the middle position, closely fitting each other to form a rectangular structure, an isosceles triangle slider 3-2 is arranged on each side, and the two waists of the isosceles triangle slider 3-2 are arranged on the outer edge; the height of each slider is 50cm, the cross section of the rectangular slider 3-3 is 30mm×30mm, the waist length of the isosceles triangle slider 3-2 is 297mm, and the angle between the two waists is 1 20°; the sliders are fully polished and lubricated to ensure free relative sliding; all rectangular sliders 3-3 and isosceles triangle sliders 3-2 are provided with a pull ring 3-1, and multiple steel bars are respectively inserted into the pull rings 3-1 in the same row; a hoop 15 is provided on the periphery of the uniformly loaded slider 3 and the two are in a sliding connection relationship, the hoop 15 is a hollow regular hexagonal prism structure and has an open structure on the top and bottom, and the hoop 15 falls on the side wall of the hexagonal foundation model barrel 9; the height of the hoop 15 is 10 cm, which is used to limit the lateral tilt of the uniformly loaded slider 3;

[0078] One end of the chassis 14 of the special-shaped chassis hammer is a blunt-angled tip structure 14-1 with an angle of 120°, and the other end is an inwardly concave arc structure 14-2, and the arc of the arc structure 14-2 is 60°; the special-shaped chassis hammer also includes a vertical rod 12 and a weight-bearing part 13, and the weight-bearing part 13 is sleeved on the vertical rod 12 and the two are in a sliding connection relationship;

[0079] The hexagonal foundation model barrel 9 and four industrial cameras 2 are all set in the control room 1, two of which are arranged at the top of the inner cavity of the control room 1 to monitor the deformation of the uniformly loaded slider 3 on the top of the model in real time, and 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 in the hexagonal foundation model barrel 9 in real time.

[0080] The method of using the permafrost roadbed pile foundation model test device in this test is as follows:

[0081] Step 1: Dry the test soil, pass it through a 5mm geotechnical sieve, add water and mix evenly to a moisture content of 12% to ensure that the soil particles are moist and not a large amount of lumps, put it in a refrigerator at 2°C to cool, seal it and let it stand for 24 hours for use;

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

[0083] Step 3: Adjust the temperature of the control room 1 to -2°C, add the crushed ice prepared in step 2 to the cooling soil sample with a water content of 12% prepared in step 1 to the target ice content of the model test under this temperature environment, and stir quickly and evenly;

[0084] Step 4: Test model making:

[0085] Case 1: Model test of precast pile foundation on permafrost roadbed:

[0086] The prefabricated model pile 6 prepared in advance is placed in the hexagonal foundation model barrel 9 to ensure that the model pile 6 is in the center of the hexagonal foundation model barrel 9; the soil sample with the target ice content is filled into the hexagonal foundation model barrel 9 in layers according to the target compaction density, and compacted with a special-shaped chassis compacting hammer, and the inner corners of the foundation model barrel 9 and the surrounding of the model pile 6 are compacted with the blunt-angle tip structure 14-1 and the arc structure 14-2 respectively. The thickness of each layer after compaction is set to 5 cm, and the middle and lower parts of the model pile 6 are paved A layer of crushed ice 7 with a thickness of 10 cm is provided and compacted to simulate the ice layer in the permafrost foundation; then the soil sample is continuously filled to the same height as the top of the model pile 6, and the temperature sensor 5 is evenly arranged in the soil sample; then a 10 cm sand cushion layer 4 is laid on top and compacted; the whole model is temperature-controlled in a -2°C controlled room 1, and the temperature-controlled cold bath box 11 is turned on to ensure that the hexagonal temperature-controlled cold plate 10 is also -2°C; the temperature is controlled until the temperature range of all temperature sensors 5 is between -2°C and 0°C;

[0087] Case 2: Model test of reinforced hot-thaw pile foundation on permafrost roadbed

[0088] A plexiglass tube is installed at the target hole position of the reinforced hot-melt pile in the hexagonal foundation model barrel 9 to reserve the pile body hole position; similar to the first case, the hexagonal foundation model barrel 9 is filled and the crushed ice layer 7 is laid, but the plexiglass tube is gently rotated after each layer is compacted to prevent it from being tightly frozen with the frozen soil; when the filling is 10 cm away from the top surface of the hexagonal foundation model barrel 9, the plexiglass tube is rotated and pulled out, and the geotextile sleeve is placed in the reserved hole, and the temperature is controlled until the temperature range of all temperature sensors 5 is between -2°C and 0°C; then the hot-melt pile body material is filled into the geotextile sleeve as a model pile 6, and then a 10 cm thick sand cushion layer 4 is set above the foundation model;

[0089] Step 5: Use a small crane to steadily install the uniformly distributed loading slider 3 to the top of the sand cushion layer 4 through multiple steel bars 16, the hoop 15 overlaps with the side wall of the hexagonal foundation model barrel 9, all the rectangular sliders 3-3 and the two isosceles triangle sliders 3-2 are completely pressed on the top of the sand cushion layer 4, and the steel bars 16 are pulled out to restore the free movement of the loading slider, and then the whole is placed at -2℃~0℃ temperature controlled static gravity loading for 48h, and the temperature is monitored in real time using a temperature sensor 5, and the vertical displacement of each loading slider is monitored in real time using two industrial cameras 2, and the deformation of the ice layer is monitored in real time from the side using two industrial cameras 2;

[0090] Step 6: After the loading test is completed, the steel bar 16 is inserted into the pull ring 3-1 again to restore its integrity. The uniformly distributed loading slider 3 is removed from the hexagonal foundation model barrel 9 using a small crane, and the temperature control box 1 is raised to room temperature. After the model is completely restored to room temperature, the soil around the pile is excavated to observe the damage of the pile.

[0091] The beneficial effects of this experiment are:

[0092] 1. The test device can carry out indoor model tests of various permafrost model piles. The hexagonal foundation model barrel 9, the hexagonal temperature-controlled cold plate 10 and the uniformly distributed loading slider 3 can simulate the effect of the pile unit body under the uniformly distributed load in the case of regular triangle pile arrangement in actual roadbed engineering, and use a single pile test to simulate the effect of pile groups;

[0093] 2. The uniformly distributed loading slider 3 of this test is evenly arranged on the top of the model pile 6 to apply a uniformly distributed load to the foundation, eliminating the loading method of setting up the traditional reaction frame, actuator and loading plate. Compared with the traditional reaction frame loading, it is closer to the roadbed fill load. At the same time, multiple loading blocks are displaced independently of each other, which can intuitively reflect the uneven settlement in the permafrost foundation, and the test range of uneven settlement is accurately determined to the size of a single loading block. The settlement displacement of the loading block can be captured in real time by the industrial camera 2, eliminating the influence of the conventional embedded displacement sensor on the foundation, achieving multiple goals at one stroke;

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

[0095] 4. This test uses moist soil and crushed pure ice chips to configure 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 special-shaped chassis compacting hammer used has both a blunt-angle tip structure 14-1 and an 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 produced by this test method can well simulate the actual engineering situation.

Claims

1. A permafrost roadbed pile foundation model test device, characterized in that The permafrost roadbed pile foundation model test device is composed of a control 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), a steel bar (16) and a special-shaped chassis 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, and a liquid inlet and a liquid outlet are respectively arranged at both ends of the serpentine water-cooling pipe (10-1); 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 fitted, and 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 crushed ice layer (7) is also arranged in the hexagonal foundation model barrel (9) to simulate the ice layer existing in the permafrost foundation; artificially compacted frozen soil (8) is arranged above and below the crushed ice layer (7), and a plurality of temperature sensors (5) are evenly distributed in the artificially compacted frozen soil (8); A model pile (6) is vertically arranged 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 arranged above the model pile (6), the uniformly distributed loading slider (3) is above the sand cushion layer (4), and the sand cushion layer (4) and the uniformly distributed loading slider (3) are both arranged in the hexagonal foundation model barrel (9); The uniformly distributed loading slider (3) is a regular hexagonal prism structure, specifically composed of a plurality of rectangular sliders (3-3) and two isosceles triangle sliders (3-2); the plurality of rectangular sliders (3-3) are arranged in the middle position, closely fit together to form a rectangular structure, an isosceles triangle slider (3-2) is arranged on each side, and the two waists of the isosceles triangle slider (3-2) are arranged on the outer edge; all the rectangular sliders (3-3) and the isosceles triangle sliders (3-2) are provided with a pull ring (3-1), and a plurality of steel bars are respectively inserted into the pull rings (3-1) located in the same row; a hoop (15) is arranged on the periphery of the uniformly distributed loading slider (3) and the two are in a sliding connection relationship, the hoop (15) is a hollow regular hexagonal prism structure and has an open structure at the top and bottom, and the hoop (15) falls on the side wall of the hexagonal foundation model barrel (9); One end of the chassis (14) of the special-shaped chassis hammer is a blunt-angle tip structure (14-1) with an included angle of 120°, and the other end is an inwardly concave arc structure (14-2), and the arc of the arc structure (14-2) is 60°; The hexagonal foundation model barrel (9) and four industrial cameras (2) are all arranged in a control room (1), wherein two industrial cameras (2) are arranged at the top of the inner cavity of the control room (1) to monitor in real time the deformation of the uniformly distributed loading sliders (3) at the top of the model, and the other two industrial cameras (2) are arranged in the middle of the side wall of the control room (1) to monitor in real time the deformation of the soil in the hexagonal foundation model barrel (9).

2. A permafrost roadbed pile foundation model test device according to claim 1, characterized in that The temperature-controlled cold bath box (11) is filled with alcohol as a refrigerant, the temperature control range is -20°C to 20°C, and the temperature control accuracy is ±0.1°C.

3. A permafrost roadbed pile foundation model test device according to claim 1, characterized in that The hexagonal model test barrel (9) is formed by splicing transparent organic glass plates, the thickness of the organic glass plates is 20 mm, and a 10 mm opening is opened below two opposite organic glass plates to facilitate the connection of the pipeline of the temperature-controlled cold bath box (11).

4. A permafrost roadbed pile foundation model test device according to claim 1, characterized in that The hexagonal temperature-controlled cold plate (10) is made of an aluminum plate and has a thickness of 10 mm.

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

6. The permafrost roadbed pile foundation model test device according to claim 1, characterized in that The crushed ice layer (7) is made of compacted crushed ice, and the compacted density is 0.9 g / cm 3 , with a thickness of 5 cm, is used to simulate the ice layer existing in permafrost foundations.

7. The permafrost roadbed pile foundation model test device according to claim 1, characterized in that The model pile (6) is a cement concrete precast pile or a reinforced hot-melt pile for use in permafrost areas, with a pile height of 1 m. When a cement concrete precast pile is used, the outer diameter is 50 mm, and when a reinforced hot-melt pile is used, the outer diameter is 100 mm.

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

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

10. The permafrost roadbed pile foundation model test device according to claim 1, characterized in that The cross-sectional dimensions of the rectangular parallelepiped slider (3-3) are 30 mm×30 mm; the uniformly loaded slider (3) is a solid stainless steel body.

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