Test device and test method for ultimate pull-out bearing capacity of pull-out piles under seepage conditions

Abstract

The invention discloses an ultimate pull-out bearing capacity test device and a test method for pull-out piles under seepage conditions, comprising a test box, a model pile, a water circulation system, a loading system and a test system; the test box is provided with test soil, and the test soil comprises two soil layers; the water circulation system comprises a water tank, the bottom of which is at the same height as the bottom of the test box and is connected to the bottom water outlet through a bottom water pipe; the loading system comprises a fixed pulley, a cable, a tray and a weight, one end of the cable is connected to the model pile, and the other end is connected to the tray, the middle position of the cable is slidably connected to the fixed pulley, and the weight is placed on the tray; the test system comprises a tension sensor and a dial indicator, the tension sensor is connected to the cable, and the dial indicator is placed on the top of the model pile. The invention can respectively measure the ultimate pull-out bearing capacity of pull-out piles under different head difference upward seepage and different head difference downward seepage conditions, and provide a reference basis for the design of pull-out piles for anti-floating of actual engineering basements.

Description

Technical Field

[0001] The invention belongs to the field of geotechnical engineering research, and in particular relates to an ultimate pull-out bearing capacity test device and a test method for pull-out piles under seepage conditions. Background Art

[0002] Pull-out piles are widely used in large basement anti-floating, high-rise building anti-pulling, offshore dock platforms, anchor pile foundations of suspension bridges and cable-stayed bridges, pile foundations of large dock bottom plates, and anchor pile foundations in static load test piles. When pull-out piles pass through multiple layers of strata, if there is pressurized water and highly permeable soil layers in the soil, seepage will occur in the soil, which will have a certain impact on the ultimate bearing capacity of the pull-out piles.

[0003] At present, there are many pull-out bearing capacity test devices for pull-out piles, such as the device with patent number CN201710942103.3, named "A pull-out bearing capacity test device for fiber reinforced micro pull-out piles", which relates to a pull-out bearing capacity test device for fiber reinforced micro pull-out piles, wherein the upper part of the first steel pad is connected to the high-strength nut, and the lower end is connected to the load sensor, the lower part of the load sensor is connected to the second steel pad, and the bottom of the second steel pad is connected to the reaction beam; the jack pads are placed on both sides of the pile hole, the bottom of the jack is installed in the center of the jack pad, and the top is close to the third steel pad, the beam bench is placed on the jack pad, and the stirrups in the pile hole are connected to the fiber reinforcement to form a pull-out pile fiber reinforcement cage; the fiber reinforcement lock head and the fiber reinforcement are anchored on the enlarged head high-strength pulling screw, the displacement sensors are symmetrically installed on both sides of the pile top of the fiber reinforced micro pull-out pile, and the displacement sensors are fixedly installed on the reference beam; the two ends of the reference beam are respectively supported on the piers.

[0004] Another example is the test device named "Pile Pullout Test Device" with patent number CN201520257518.3, which mainly involves a pile pullout test device, including a pullout pile, a crossbeam and a jack. The pile pullout test device also includes a clamp and a support frame. The clamp is mounted on the outer surface of the pullout pile and is fixedly connected to the pullout pile. The support frame includes a first support plate and a connecting rod. The upper end of the connecting rod is fixed on the first support plate, and the lower end of the connecting rod is fixed on the outer surface of the clamp. The cylinder of the jack is fixed on the crossbeam, and the free end of the jack is upwardly pressed against the lower surface of the first support plate. In the pile pullout test device, the free end of the jack can lift the first support plate during the rising process to pull out the pullout pile, completing the entire pullout test.

[0005] The above-mentioned pull-out pile test device only considers the stress analysis of the pull-out pile itself and the study of the pile-soil interface during the test process, and does not consider the change of the ultimate pull-out bearing capacity of the pull-out pile when seepage occurs in the soil. The research on the action mechanism of the pile-soil interface and the ultimate pull-out bearing capacity of the pull-out pile when seepage occurs in the soil is not enough. In actual engineering, to determine the ultimate pull-out bearing capacity of the pull-out pile under seepage conditions, due to the limitations of the site geological conditions, expensive on-site tests and experience are required, and there is a lack of sufficient theoretical basis.

[0006] In summary, the current research theory on the ultimate pull-out bearing capacity of pull-out piles under seepage conditions lacks data support from experimental devices. Therefore, model tests are needed to provide theoretical analysis of the influence of soil seepage on the ultimate pull-out bearing capacity of pull-out piles. Summary of the invention

[0007] Aiming at the problem that the influence of seepage on the ultimate pullout bearing capacity of pullout piles is not considered during the pullout bearing capacity test of pullout piles in the prior art, the present invention proposes an ultimate pullout bearing capacity test device and a test method for pullout piles under seepage conditions simulating seepage.

[0008] In order to achieve the purpose, the technical solution provided by the present invention is:

[0009] The present invention relates to an ultimate pull-out bearing capacity test device for pull-out piles under seepage conditions, comprising a test box, a model pile, a water circulation system, a loading system and a testing system; the test box is provided with test soil, the side wall of the test box is provided with a test box water inlet and a test box water outlet at an upper opening position, and the bottom is provided with a bottom water outlet; the model pile is inserted into the test soil; the water circulation system comprises a water tank, the bottom of the water tank is at the same height as the bottom of the test box and is connected to the bottom water outlet through a bottom water pipe; the loading system comprises a fixed pulley , cables, trays and weights, one end of the cables is connected to the model pile, the other end is connected to the tray, the middle position of the cables is slidably connected to the fixed pulley, and the weights are placed on the tray; the testing system comprises a tension sensor and a dial indicator, the tension sensor is connected to the cables, and the dial indicator is placed on the top of the model pile; when the water filling height in the water tank is higher than the test soil height, the ultimate pull-out bearing capacity of the pull-out pile under the upward seepage condition is measured; when the water filling height in the water tank is lower than the test soil height, the ultimate pull-out bearing capacity of the pull-out pile under the downward seepage condition is measured.

[0010] Preferably, the test soil is divided into two layers, the lower layer is a pebble layer, the upper layer is a medium sand layer, a geotextile is arranged between the pebble layer and the medium sand layer, and the model pile is inserted into the medium sand layer.

[0011] Preferably, the test system comprises a pressure measuring tube connected to the bottom water outlet, the pressure measuring tube is used to measure the stability of the water level, and observe the degree of the dial indicator when the water level is stable to ensure the accuracy of the data.

[0012] Preferably, both ends of the bottom water pipe are provided with a first control valve, and the first control valve is used to control the connection between the test box and the water tank.

[0013] Preferably, a water tank inlet is provided on the top of the water tank, and a plurality of water tank outlets are provided on the side wall of the water tank. The water tank outlets are arranged at equal intervals in the height direction, and a second control valve is installed corresponding to each water tank outlet.

[0014] Preferably, the test box is arranged inside a steel frame, and the fixed pulley is fixed to the top surface of the steel frame, and the steel frame plays a fixing role.

[0015] The present invention also relates to a test method for the ultimate pull-out bearing capacity test device of the pull-out pile under the above-mentioned seepage condition, comprising the following steps:

[0016] 1) Assemble the test chamber and water circulation system, and install the loading system and test system;

[0017] 2) Place the model pile in the center of the test box, lay test soil in the test box, and inject water into the test soil to make it saturated;

[0018] 3) Set the water head difference of this test, close all the first control valves and the second control valves, and fill the water tank to the corresponding height according to the water head difference of this test;

[0019] 4) Use a cable to hold the model pile and adjust the dial indicator to zero;

[0020] 5) Open the first control valves at both ends of the bottom water pipe, wait for the water level to stabilize and observe the dial indicator reading;

[0021] 6) Load weights on the tray in stages, record the corresponding data on the dial indicator in sequence, and perform data analysis;

[0022] 7) Change the water head difference, repeat steps 2) to 6), and analyze the ultimate pull-out bearing capacity of the pull-out pile under different water head differences.

[0023] Preferably, the method of laying the test soil in the test box in step 2) comprises:

[0024] 2.1) Lay a 9cm thick pebble layer on the bottom of the test box;

[0025] 2.2) Lay a layer of geotextile with a thickness of 1 cm on the pebble layer;

[0026] 2.3) Lay sandy soil layers on the geotextile, each layer is 5 cm thick and water is injected to submerge the soil;

[0027] 2.4) Repeat step 2.3) and repeatedly lay the sand layer to the designed height;

[0028] 2.5) Leave the test soil in the test box to stand for 24 hours to form a saturated sand layer.

[0029] When the water filling height in the water tank in step 3) is higher than the test soil height, the ultimate pull-out bearing capacity of the pull-out pile under the upward seepage condition is measured. During the test process of steps 4) to 6), the second control valve of the corresponding height is opened, and water is continuously injected from the water inlet of the water tank. The water enters the test box through the bottom water pipe and forms an upward seepage in the test box. The water finally overflows from the water outlet of the test box.

[0030] When the water filling height in the water tank in step 3) is lower than the test soil height, the ultimate pull-out bearing capacity of the pull-out pile under the downward seepage condition is measured. During the test process of steps 4) to 6), the second control valve of the corresponding height is opened, and water is continuously injected from the water inlet of the test box. Water enters the water tank through the bottom water pipe, forming a downward seepage in the test box, and the water finally overflows from the water outlet of the water tank.

[0031] The design simulates the ultimate pull-out bearing capacity of the pull-out pile under the conditions of upward seepage with different head differences and downward seepage with different head differences.

[0032] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0033] 1. The ultimate pull-out bearing capacity test device and test method of pull-out piles under seepage conditions of the present invention are equipped with a water circulation system for the test box, that is, a water tank is set next to the test box, and the bottom water pipe of the water tank is connected to the bottom of the test box. The water circulation system simulates the upward seepage under different water head differences and the downward seepage under different water head differences, which more realistically simulates the basement soil environment and makes the pull-out bearing capacity test more accurate.

[0034] 2. The water head height in the test box of the present invention is controlled by the water outlet and the water inlet of the test box. The water head height of the water in the water tank is controlled by the water inlet of the water tank and the second control valve at the water outlet of the water tank at the corresponding height. The water head height control at the two places is accurate and easy to operate, which is convenient for simulating upward seepage or downward seepage. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a structural diagram of the ultimate pull-out bearing capacity test device of the pull-out pile under seepage conditions of the present invention;

[0036] Figure 2 It is a structural schematic diagram of the model pile inserted into the test box;

[0037] Figure 3 It is a schematic diagram of the structure of the water tank;

[0038] Figure 4 It is a flow chart of the test method for the ultimate pull-out bearing capacity of pull-out piles under seepage conditions.

[0039] Label instructions: 1. Test box, 2. Model pile, 3. Bolt, 4. Dial indicator, 5. Tension sensor, 6. Cable, 7. Tray, 8. Weight, 9. Steel frame, 10. Bottom water pipe, 11. Water tank, 12. First control valve, 13. Second control valve, 14. Test box water outlet, 15. Test box water inlet, 16. Water tank water inlet, 17. Pressure measuring tube, 18. Middle sand layer, 19. Pebble layer, 20. Fixed pulley, 21. Geotextile. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] Embodiment 1

[0042] Combined with Figure 1 As shown, the present invention relates to an ultimate pull-out bearing capacity test device for pull-out piles under seepage conditions, comprising a test box 1, a model pile 2, a water circulation system, a loading system and a test system; wherein the test box 1 adopts a plexiglass test box, and the model pile 2 adopts an aluminum tube model pile.

[0043] Combined with Figure 1 and 2 As shown, the test box 1 has a height of 1 m and an inner diameter of 540 mm, which meets the range size required for the boundary effect; the wall thickness of the test box 1 is 8 mm, which meets the rigidity and strength requirements of being filled with sand. The bottom of the test box 1 is supported by a steel frame 19, and the periphery is also supported by a steel frame 19 for installing a loading system and a test system. Test soil is arranged in the test box 1. The test soil is divided into two layers, the lower layer is a pebble layer 19, and the upper layer is a medium sand layer 18. A geotextile 21 is arranged between the pebble layer 19 and the medium sand layer 18. The geotextile 21 only allows water to pass through but prevents the sand particles in the medium sand layer 18 from entering the pebble layer 19. The side wall of the test box 1 is provided with a test box water inlet 15 and a test box water outlet 14 at the upper opening position, and a bottom water outlet (not marked in the figure) is arranged at the bottom. In order to prevent water from overflowing during the test, a water bucket is arranged at the test box water outlet 14 for collecting water; the model pile 1 is inserted into the middle position of the medium sand layer 18 in the test soil, the model pile 2 is opened on both sides 6 cm away from the top and a bolt 3 is inserted, and a layer of standard sand is pasted on the side wall of the aluminum tube with epoxy resin.

[0044] Combined with Figure 1 As shown, the water circulation system comprises a water tank 11, the bottom of the water tank 11 is supported by a steel frame 9, the bottom of the water tank 11 is at the same height as the bottom of the test box 1 and is connected to the bottom water outlet through a bottom water pipe 10, and both ends of the bottom water pipe 10 are provided with a first control valve 12, and the first control valve 12 is used to control the connection between the test box 1 and the water tank 11; Figure 1 and 3 As shown, a water tank inlet 16 is provided on the top of the water tank 11, and a plurality of water tank outlets (not marked in the figure) are provided on the side wall of the water tank 11. The water tank outlets are arranged at equal intervals in the height direction. In this embodiment, the water tank has water tank outlets at intervals of 10 cm on the side wall, and each water tank outlet is respectively installed with a second control valve 13, which is used to control the corresponding water tank outlet switch. In order to prevent water from overflowing during the test, a bucket is provided below the corresponding water tank outlet of the water tank 11 to catch the overflowed water.

[0045] The loading system includes a fixed pulley 20, a cable 6, a tray 7 and a weight 8. Two fixed pulleys 20 are provided and are fixed to the top surface of the steel frame 9, and one of the fixed pulleys 20 is located directly above the model pile 2; one end of the cable 5 is connected to the model pile 2, and the other end is connected to the tray 7, and the middle position of the cable 6 is slidably connected to the fixed pulley 20. A plurality of weights 8 are provided, and the weight of each weight 8 is the same. During the experiment, the weight 8 is placed on the tray 7 to simulate the upward force of the pull-out pile;

[0046] The test system includes a tension sensor 5, a dial indicator 4 and a pressure measuring tube 17. The tension sensor 5 is connected to the cable 6. The tension sensor 5 has a range of 0-500kg and is used to measure the tension of the weight 8 on the model pile 2. The tension sensor 5 is connected to a data display instrument (not shown) and a 220V power supply, and can directly read the tension on the model pile 2; the dial indicator 4 is placed above the model pile 2, and the dial indicator has a range of 0-100mm, and is used to measure the displacement of the model pile 2 pulled upward; the pressure measuring tube 17 is composed of a plexiglass tube with a smaller inner diameter, and a scale is attached to the side wall. The pressure measuring tube has the same diameter as the water outlet at the bottom of the test box, and the pressure measuring tube 17 is connected to the bottom water outlet to measure whether the water level is stable, and observe the degree of the dial indicator when the water level is stable to ensure the accuracy of the data.

[0047] Combined with Figure 4 As shown, the test method for testing the ultimate pull-out bearing capacity of the pull-out pile under the conditions of upward seepage with different water head differences using the above test device includes the following steps:

[0048] 1) Assemble the test box and water circulation system, install the loading system and the test system: set and calibrate the tension sensor 5 and the dial indicator 4 and other components used in the test to ensure correct use and reading; connect the organic glass tube and the pressure measuring tube to the openings of the test box 1 and the water tank 11, and assemble them with glue. The glue used must be a special glue for organic glass, which can play a water-sealing role; symmetrically drill holes in the aluminum tube model pile 2 6 cm away from the top, and insert bolts 3;

[0049] 2) placing the model pile in the center of the test box, laying test soil in the test box, and injecting water into the test soil to make the test soil saturated. The steps of laying the test soil in the test box include:

[0050] 2.1) Lay a 9 cm thick pebble layer 19 on the bottom of the test box;

[0051] 2.2) Laying a layer of geotextile 21 with a thickness of 1 cm on the pebble layer 19;

[0052] 2.3) Laying sandy soil layers 18 on the geotextile 21, each layer is 5 cm thick and water is injected to submerge the soil;

[0053] 2.4) Repeat step 2.3) to repeatedly lay the sand layer 18 to the designed height;

[0054] 2.5) The test soil in the test box 1 is left to stand for 24 hours to form a saturated sand layer 18;

[0055] 3) Set the water head difference of this test. Since this embodiment simulates the upward seepage, the water head height in the water tank 11 is greater than the water head height in the test box 1. Close all the first control valves 12 and the second control valves 13. According to the water head difference of this test, water is poured into the water tank to the corresponding height;

[0056] 4) Use the cable 6 to pull the bolt 3 at the top of the model pile 2 and adjust the dial indicator to zero;

[0057] 5) Open the first control valves 12 at both ends of the bottom water pipe, open the second control valve 13 at the corresponding height, and continue to inject water from the water inlet 16 of the water tank. The water enters the test box 1 through the bottom water pipe 10 and forms an upward seepage in the test box. The water eventually overflows from the water outlet 14 of the test box, simulating the upward seepage. Observe the changes in the pressure measuring tube 17, wait for the water level to stabilize, and then observe the reading of the dial gauge 4. After the reading of the dial gauge 4 stabilizes, read the reading and record the data;

[0058] 6) Load weights 8 on the tray 7 in stages, record the corresponding data on the dial gauge 4 in sequence, and perform data analysis;

[0059] 7) Change the water head difference, repeat steps 2) to 6), and analyze the ultimate pull-out bearing capacity of the pull-out pile under the conditions of upward seepage with different water head differences.

[0060] Embodiment 2:

[0061] The test method for testing the ultimate pull-out bearing capacity of the pull-out pile under downward seepage conditions with different water head differences using the test device described in Example 1 comprises the following steps:

[0062] 1) Assemble the test box and water circulation system, install the loading system and the test system: set and calibrate the tension sensor 5 and the dial indicator 4 and other components used in the test to ensure correct use and reading; connect the organic glass tube and the pressure measuring tube to the openings of the test box 1 and the water tank 11, and assemble them with glue. The glue used must be a special glue for organic glass, which can play a water-sealing role; symmetrically drill holes in the aluminum tube model pile 2 6 cm away from the top, and insert bolts 3;

[0063] 2) placing the model pile in the center of the test box, laying test soil in the test box, and injecting water into the test soil to make the test soil saturated. The steps of laying the test soil in the test box include:

[0064] 2.1) Lay a 9 cm thick pebble layer 19 on the bottom of the test box;

[0065] 2.2) Laying a layer of geotextile 21 with a thickness of 1 cm on the pebble layer 19;

[0066] 2.3) Laying sandy soil layers 18 on the geotextile 21, each layer is 5 cm thick and water is injected to submerge the soil;

[0067] 2.4) Repeat step 2.3) to repeatedly lay the sand layer 18 to the designed height;

[0068] 2.5) The test soil in the test box 1 is left to stand for 24 hours to form a saturated sand layer 18;

[0069] 3) Setting the water head difference of this test. Since this embodiment simulates the downward seepage, the water head height in the water tank 11 is less than the water head height in the test box 1. Close all the first control valves 12 and the second control valves 13. According to the water head difference of this test, water is poured into the water tank 11 to the corresponding height.

[0070] 4) Use the cable 6 to pull the bolt 3 at the top of the model pile 2 and adjust the dial indicator 4 to zero;

[0071] 5) Open the first control valves 12 at both ends of the bottom water pipe, open the second control valve 13 at the corresponding height, and continue to inject water from the water inlet 15 of the test box to maintain the water head height in the test box 1. Water enters the water tank 11 through the bottom water pipe 10, forming an upward seepage in the test box 1. The water eventually overflows from the water outlet of the water tank to simulate the downward seepage. Observe the changes in the pressure measuring tube 17, wait for the water level to stabilize, and then observe the reading of the dial gauge 4. After the reading of the dial gauge 4 stabilizes, read the reading and record the data;

[0072] 6) Load weights 8 on the tray 7 in stages, record the corresponding data on the dial gauge 4 in sequence, and perform data analysis;

[0073] 7) Change the water head difference, repeat steps 2) to 6), and analyze the ultimate pull-out bearing capacity of the pull-out pile under the condition of downward seepage with different water head differences.

[0074] In summary, the above design can simulate the ultimate pull-out bearing capacity of the pull-out pile under the conditions of upward seepage with different head differences and downward seepage with different head differences.

[0075] The present invention is described in detail above in conjunction with the embodiments, but the contents described are only preferred embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of application of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A device for testing the ultimate pull-out bearing capacity of pull-out piles under seepage conditions, characterized in that: The invention comprises a test box, a model pile, a water circulation system, a loading system and a testing system; the test box is provided with test soil, the side wall of the test box is provided with a test box water inlet and a test box water outlet at the upper opening position, and the bottom is provided with a bottom water outlet; the model pile is inserted into the test soil; the water circulation system comprises a water tank, the bottom of which is at the same height as the bottom of the test box and is connected to the bottom water outlet through a bottom water pipe; the loading system comprises a fixed pulley, a cable, a tray and a weight, one end of the cable is connected to the model pile, the other end is connected to the tray, and the middle position of the cable is slidably connected to the fixed pulley, and the weight is placed on the tray; the testing system comprises a tension sensor and a dial indicator, the tension sensor is connected to the cable, and the dial indicator is placed on the top of the model pile; when the water filling height in the water tank is higher than the test soil height, the ultimate pull-out bearing capacity of the pull-out pile under the upward seepage condition is measured; when the water filling height in the water tank is lower than the test soil height, the ultimate pull-out bearing capacity of the pull-out pile under the downward seepage condition is measured.

2. The ultimate pull-out bearing capacity test device of pull-out piles under seepage conditions according to claim 1, characterized in that: The test soil is divided into two layers, the lower layer is a pebble layer, the upper layer is a medium sand layer, a geotextile is arranged between the pebble layer and the medium sand layer, and the model pile is inserted into the medium sand layer.

3. The ultimate pull-out bearing capacity test device of pull-out piles under seepage conditions according to claim 1, characterized in that: The testing system comprises a pressure measuring tube connected to the bottom water outlet and used for measuring whether the water level is stable.

4. The ultimate pull-out bearing capacity test device of pull-out piles under seepage conditions according to claim 1, characterized in that: Both ends of the bottom water pipe are provided with first control valves.

5. The ultimate pull-out bearing capacity test device of pull-out piles under seepage conditions according to claim 1, characterized in that: The top of the water tank is provided with a water inlet, and the side wall of the water tank is provided with a plurality of water outlets. The water outlets are arranged at equal intervals in the height direction, and each water outlet is respectively installed with a second control valve.

6. The ultimate pull-out bearing capacity test device of pull-out piles under seepage conditions according to claim 1, characterized in that: The test box is arranged inside a steel frame, and the fixed pulley is fixed on the top surface of the steel frame.

7. A test method for the ultimate pull-out bearing capacity test device of pull-out piles under seepage conditions based on any one of claims 1 to 6, characterized in that: It includes the following steps: 1) Assemble the test chamber and water circulation system, and install the loading system and test system; 2) Place the model pile in the center of the test box, lay test soil in the test box, and inject water into the test soil to make it saturated; 3) Set the water head difference of this test, close the first control valves at both ends of the bottom water pipe and the second control valve at the water outlet of each water tank, and fill water into the water tank to the corresponding height according to the water head difference of this test; 4) Use a cable to hold the model pile and adjust the dial indicator to zero; 5) Open the first control valves at both ends of the bottom water pipe, wait for the water level to stabilize and observe the dial indicator reading; 6) Load weights on the tray in stages, record the corresponding data on the dial indicator in sequence, and perform data analysis; 7) Change the water head difference and repeat steps 2) to 6) to analyze the ultimate pull-out bearing capacity of the pull-out pile under different water head differences.

8. The test method of the ultimate pull-out bearing capacity test device of pull-out piles under seepage conditions according to claim 7, characterized in that: The method of step 2) laying the test soil in the test box comprises: 2.1) Lay a 9cm thick pebble layer on the bottom of the test box; 2.2) Lay a layer of geotextile with a thickness of 1 cm on the pebble layer; 2.3) Lay sandy soil layers on the geotextile in layers, with each layer being 5 cm thick and inject water to submerge the soil; 2.4) Repeat step 2.3) and repeatedly lay the sand layer to the designed height; 2.5) Allow the test soil in the test chamber to stand for 24 hours to form a saturated sand layer.

9. The test method of the ultimate pull-out bearing capacity test device of pull-out piles under seepage conditions according to claim 7, characterized in that: When the water filling height in the water tank in step 3) is higher than the test soil height, measure the ultimate pull-out bearing capacity of the pull-out pile under the upward seepage condition. During the test of steps 4) to 6), open the second control valve at the corresponding height and continue to inject water from the water inlet of the water tank. The water enters the test box through the bottom water pipe and forms an upward seepage in the test box. The water eventually overflows from the water outlet of the test box.

10. The test method of the ultimate pull-out bearing capacity test device of pull-out piles under seepage conditions according to claim 7, characterized in that: When the water filling height in the water tank in step 3) is lower than the test soil height, measure the ultimate pull-out bearing capacity of the pull-out pile under the downward seepage condition. During the test of steps 4) to 6), open the second control valve at the corresponding height, and continue to inject water from the water inlet of the test box. Water enters the water tank through the bottom water pipe, forming a downward seepage in the test box, and the water eventually overflows from the water outlet of the water tank.

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