Method for measuring height of soil plug in spiral pipe pile model test through air pressure

Abstract

The invention discloses a method for measuring the height of a spiral pipe pile model test soil plug through air pressure, and relates to the technical field of pipe pile soil plug height measurement. The method comprises the following steps: assembling an air pressure method spiral pipe pile soil plug height measurement system; formulating a spiral pipe pile soil plug height measurement scheme in a formal test; obtaining basic parameters of air pressure measurement soil plug height; constructing a spiral pipe pile soil plug height measurement algorithm; and determining the volume coefficient A of the air storage tank and the connection volume coefficient B of the airflow guide pipe, and operating according to a spiral pile pipe pile soil plug height measurement scheme in a formal test to obtain the soil plug height of the installed spiral pipe pile. According to the method, the air pressure method is adopted, measurement operation is completed outside the spiral pipe pile, the problems that multiple measurement results are inconsistent, the perpendicularity of the measuring scale deviates, and the visual angle reading error exists are effectively solved, the measurement precision is greatly improved, and remarkable practical value and practical significance are achieved.

Description

Technical Field

[0001] The present application relates to the technical field of measuring the height of the soil plug in a spiral pipe pile in a model test model box, and particularly relates to a method for measuring the height of the soil plug in a spiral pipe pile model test by air pressure measurement. Background Art

[0002] The technology for measuring the height of the soil plug in a spiral pipe pile is an important means for studying the bearing performance of pile foundations and soil-structure interaction. Although traditional methods such as mechanical measurement and optical measurement are simple to operate, their accuracy and applicability are limited; modern sensing technologies achieve high-precision real-time monitoring through displacement sensors and pressure sensors, but have high requirements for the devices; image processing technologies use high-resolution cameras and video tracking methods to record the changes of the soil plug, which can intuitively reflect the test process, but rely on light conditions and algorithm support. However, the current measurement technologies still face problems such as equipment stability, high cost, complex data processing, and lack of standardization. Measuring the height of the soil plug in a spiral pipe pile by the air pressure method is a non-contact measurement technology, which can be operated outside the spiral pile, will not disturb the soil body, and can solve problems such as the verticality error of the measuring scale and the error caused by the measuring reading angle. It is a simple and reliable measurement method, but no reasonable solution has been proposed yet. Summary of the Invention

[0003] The present application provides a method for measuring the height of the soil plug in a spiral pipe pile model test by air pressure measurement. This method can complete the measurement operation outside the spiral pipe pile, avoiding the limitations brought by the need to extend the measurement equipment into the pipe pile in traditional measurement methods, such as the size and structure limitations of the spiral pipe pile, the verticality error of the measuring scale, the uncertainty of the measurement result, and the deviation caused by the perspective. This technology provides a simple and reliable solution for measuring the height of the soil plug in a spiral pipe pile model test.

[0004] A method for measuring the height of the soil plug in a spiral pipe pile model test by air pressure measurement includes the following steps:

[0005] S1. Assemble the measuring system for the height of the soil plug in the spiral pipe pile by the air pressure method;

[0006] S2. Formulate the measurement plan for the height of the soil plug in the spiral pipe pile during the formal test;

[0007] S3. Obtain the basic parameters for measuring the height of the soil plug by air pressure, and construct the algorithm for measuring the height of the soil plug in the spiral pipe pile;

[0008] S4. Calibrate the algorithm for measuring the height of the soil plug in the spiral pipe pile before the experiment to determine the volume coefficient A of the gas storage tank and the volume coefficient B of the air flow conduit connection;

[0009] S5. Operate according to the measurement plan for the height of the soil plug in the spiral pipe pile during the formal test in step S2 to obtain the height of the soil plug of the installed spiral pipe pile.

[0010] Preferably, step S1 includes the following steps:

[0011] S11. Prepare an air compressor, a double - connectable gas storage tank, two pressure gauges, two thermometers, and two air ducts; wherein, the two air ducts are respectively a first air duct and a second air duct;

[0012] S12. Connect the first air duct between the air compressor and the gas storage tank;

[0013] S13. Install a pressure gauge to measure the pressure in the gas storage tank;

[0014] S14. Install a thermometer to measure the gas temperature in the gas storage tank;

[0015] S15. Connect the gas storage tank with the second air duct, and the second air duct is in a state of waiting to be connected with the screw pile;

[0016] S16. Install a pressure gauge to measure the pressure at the connection between the second air duct and the screw pile in step S15;

[0017] S17. Install a thermometer to measure the temperature at the connection between the second air duct and the screw pile in step S15.

[0018] Preferably, step S2 includes the following steps:

[0019] S21. During the formal test, after the screw pile is installed into the soil and its top is exposed outside the soil mass, under the atmospheric pressure, read the pressure P when the second air duct and the screw pile are in a state of waiting to be connected in step S15 0 ;

[0020] S22. Connect the second air duct in step S15 with the screw pile;

[0021] S23. Check to ensure that the air - pressure - method screw - pile soil - plug height measurement system is in a sealed state after being connected with the screw pile;

[0022] S24. Close the connection between the gas storage tank and the second air duct, start the air compressor, and convey high - pressure gas into the gas storage tank;

[0023] S25. Turn off the air compressor, close the double - connection of the gas storage tank, keep the gas storage tank in a sealed state, measure the air pressure P in the gas storage tank through the pressure gauge installed in step S13 1 , measure the temperature T in the gas storage tank through the thermometer installed in step S14 1 ;

[0024] S26. Open the connection between the gas storage tank and the second gas flow conduit to ensure that gas can be stably transported into the screw pipe pile through the second gas flow conduit;

[0025] S27. Observe whether the pressure gauges in the gas storage tank and at the connection between the second gas flow conduit and the screw pipe pile show equal readings at this time. If the readings are equal, it indicates that the air pressure has reached equilibrium, and record the equilibrium pressure P 2 , and record the reading T of the thermometer in step S17 at equilibrium 2 , and record the reading T of the thermometer in step S14 at equilibrium 3 .

[0026] Preferably, step S3 includes the following steps:

[0027] S31. Obtain the inner cavity diameter R of the screw pipe pile 1 ;

[0028] S32. Obtain the internal volume V of the gas storage tank in step S11 1 ;

[0029] S33. Obtain the atmospheric pressure value P in step S21 during the experiment 0 ;

[0030] S34. Obtain the pressure P in the gas storage tank in step S25 1 ;

[0031] S35. Obtain the temperature T of the gas in the gas storage tank in step S25 1 ;

[0032] S36. Obtain the volume V of the second gas flow conduit in step S15 0 ;

[0033] S37. Obtain the pressure P of the gas at the connection between the second gas flow conduit and the screw pipe pile in step S27 2 , the temperature T of the gas at the connection between the second gas flow conduit and the screw pipe pile 2 , the temperature T of the gas in the gas storage tank at equilibrium 3 ;

[0034] S38. According to the basic parameters obtained in S31 - S37, construct an algorithm for measuring the height of the soil plug in the screw pipe pile, expressed as:

[0035]

[0036] In the formula, h is the height of the soil plug in the screw pipe pile, and H is the height of the inner cavity of the screw pipe pile;

[0037] Preferably, step S4 includes the following steps:

[0038] S41. Based on the basic parameters of the air pressure for measuring the height of the soil plug obtained in steps S31 to S37, further adjust the determination algorithm for the height of the soil plug of the spiral pipe pile constructed in step S29 to obtain:

[0039]

[0040] Among them, A is the volume coefficient of the gas storage tank, and B is the connection volume coefficient of the air flow conduit;

[0041] S42. In the calibration link of the air pressure method for measuring the height of the soil plug of the spiral pile pipe pile, assemble the air pressure method for measuring the height of the soil plug of the spiral pile pipe pile. The air pressure method for measuring the height of the soil plug of the spiral pile pipe pile is in a state of waiting to be connected to the spiral pipe pile. Under the atmospheric pressure, measure the pressure P when the second air flow conduit and the spiral pipe pile are in a state of waiting to be connected 01 ;

[0042] S43. Seal the connection between the second air flow conduit in step S15 and the spiral pipe pile with a sealing flat plate without connecting to the spiral pipe pile, and check to ensure that the air pressure method for measuring the height of the soil plug of the spiral pile pipe pile is in a sealed state;

[0043] S44. Close the connection between the gas storage tank and the second air flow conduit, start the air compressor, and send high-pressure gas into the gas storage tank;

[0044] S45. Turn off the air compressor, close the double-way connection of the gas storage tank, keep the gas storage tank in a sealed state, measure the air pressure P in the gas storage tank through the pressure gauge installed in step S13 11 , measure the temperature T in the gas storage tank through the thermometer installed in step S14 11 ;

[0045] S46. Open the connection between the gas storage tank and the second air flow conduit, and observe whether the readings of the pressure gauges in the gas storage tank and at the connection between the second air flow conduit and the spiral pipe pile are equal at this time. If the readings are equal, it means that the air pressure has reached equilibrium. Record the equilibrium pressure P 21 , record the reading T of the thermometer in step S17 at equilibrium 21 , record the reading T of the thermometer in step S14 at equilibrium 31 ;

[0046] S47. Release the gas in the air pressure method for measuring the height of the soil plug of the spiral pile pipe pile, and open all the connections in the air pressure method for measuring the height of the soil plug of the spiral pile pipe pile; the second air flow conduit is connected to the atmosphere, and read the atmospheric pressure P at this time 02 ;

[0047] S48. Obtain the height H of the internal cavity of the screw pipe pile, connect the second air duct to the screw pipe pile, seal the opening with a plugging flat plate that can cover the opening at the pile end of the screw pipe pile, and check to ensure that the pneumatic screw pile plug height measurement system is in a sealed state after being connected to the screw pipe pile;

[0048] S49. Close the connection between the gas storage tank and the second air duct, start the air compressor, and convey high-pressure gas into the gas storage tank;

[0049] S410. Turn off the air compressor, close the two-way connection of the gas storage tank, keep the gas storage tank in a sealed state, measure the air pressure P in the gas storage tank through the pressure gauge installed in step S13 13 , and measure the temperature T in the gas storage tank through the thermometer installed in step S14 13 ;

[0050] S411. Open the connection between the gas storage tank and the second air duct, observe whether the readings of the pressure gauge in the gas storage tank and the pressure gauge at the connection of the second air duct and the screw pipe pile are equal at this time. If the readings are equal, it means that the air pressure has reached equilibrium, record the equilibrium pressure P 22 , record the reading T of the thermometer in step S17 at equilibrium 22 , record the reading T of the thermometer in step S14 at equilibrium 32 ;

[0051] S412. Obtain the parameters of steps S41 - S42, and construct a calibration equation system:

[0052]

[0053] S413. Solve for the gas storage tank volume coefficient A and the air duct connection volume coefficient B.

[0054] Preferably, the plug height of the screw pipe pile in step S5 is expressed as:

[0055]

[0056] where A is the gas storage tank volume coefficient obtained by solving in the calibration process of step S4, and B is the air duct connection volume coefficient obtained by solving in the calibration process of step S4.

[0057] Preferably, the method further includes: during the preparation of the model test, the screw pipe pile has a connection port at the pile head position or within a set area range from the pile head, and the connection port is connected to the second air duct in step S15.

[0058] Preferably, the air compressor can compress air to a pressure higher than the atmospheric pressure.

[0059] Preferably, the gas storage tank is connected to the first air duct and the second air duct in a two-way manner, and the switch for cutting off the connection is close to the outer wall of the gas storage tank.

[0060] A method for measuring the plug height of a spiral pipe pile model test by air pressure provided by this application has the following beneficial effects:

[0061] (1) By measuring the plug height of the spiral pipe pile by the air pressure method in this application, the entire operation process is completed outside the spiral pipe pile, avoiding the disturbance of the soil body and being not limited by the internal dimensions and structure of the spiral pipe pile at the same time.

[0062] (2) This application effectively solves the problem of measurement deviation of the plug height caused by the non-vertical measuring ruler or the reading error of the measuring ruler in the traditional method.

[0063] (3) This application overcomes the defect that the results of multiple measurements in the traditional measurement method are inconsistent, and provides a measurement technology with high precision and strong reliability. Description of the Drawings

[0064] The drawings here are incorporated into the specification and form a part of this specification, showing the embodiments in line with this application, and are used together with the specification to explain the principle of this application.

[0065] Figure 1 It is a schematic flow chart of a method for measuring the plug height of a spiral pipe pile model test by air pressure;

[0066] Figure 2 It is a two-dimensional schematic diagram of the connection between the assembled air pressure method spiral pile pipe plug height measuring system and the model test spiral pipe pile;

[0067] Figure 3 It is a two-dimensional schematic diagram of plugging the second air duct in the air pressure method spiral pile pipe plug height measuring system during the calibration process;

[0068] Figure 4 It is a schematic diagram of connecting the air pressure method spiral pile pipe plug height measuring system to the spiral pipe pile and plugging the pile end opening during the calibration process.

[0069] Description of the Reference Numerals in the Drawings:

[0070] 1. Air compressor; 2. First air duct; 3. Thermometer; 4. Pressure gauge; 5. Second air duct; 6. Gas storage tank; 7. Spiral pipe pile; 8. Soil body; 9. Model box; 10. Gas storage tank connection switch; 11. Sealing plate.

[0071] Through the above drawings, the clear embodiments of this application have been shown, and there will be more detailed descriptions later. These drawings and text descriptions are not intended to limit the scope of the concept of this application in any way, but to explain the concept of this application to those skilled in the art by referring to specific embodiments. Detailed implementation manners

[0072] Here, the exemplary embodiments will be described in detail, and the examples are shown in the drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementation manners described in the following exemplary embodiments do not represent all implementation manners consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0073] Next, the technical solutions of the present application and how the technical solutions of the present application solve the above technical problems will be described in detail with specific embodiments. The following several specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. Next, the embodiments of the present application will be described with reference to the drawings.

[0074] The embodiment of the present application provides a method for measuring the height of the soil plug in a pneumatic measurement spiral pipe pile model test, as Figure 1 shown, including steps S1 - S5, specifically as follows:

[0075] S1. Assemble the measurement system for the height of the soil plug in the pneumatic spiral pile pipe pile;

[0076] In an alternative embodiment of the present application, as Figure 2 shown, prepare an air compressor 1, a gas storage tank 6, a pressure gauge 4, a thermometer 3, a first air duct 2, and a second air duct 5 in advance. A two-way connection switch 10 is provided on the gas storage tank, and the position of the two-way connection switch 10 is close to the outer wall of the gas storage tank. The gas storage tank 6 is equipped with a thermometer 3 and a pressure gauge 4, and the measurement system for the height of the soil plug in the pneumatic spiral pile pipe pile is assembled.

[0077] In an alternative embodiment of the present application, step S1 includes the following sub - steps:

[0078] S11. Prepare an air compressor, a gas storage tank with double - way connection, two pressure gauges, two thermometers, and two air ducts;

[0079] S12. Connect the first air duct between the air compressor and the gas storage tank;

[0080] S13. Install a pressure gauge to measure the pressure in the gas storage tank;

[0081] S14. Install a thermometer to measure the gas temperature in the gas storage tank;

[0082] S15. Connect the gas storage tank with the second air duct, and the second air duct is in a state to be connected with the spiral pipe pile;

[0083] S16. Install one pressure gauge to measure the pressure at the connection between the second air duct and the screw pile pipe in step S15;

[0084] S17. Install one thermometer to measure the temperature at the connection between the second air duct and the screw pile pipe in step S15.

[0085] S2. Develop a measurement plan for the soil plug height of the screw pile pipe during the formal test;

[0086] In an optional embodiment of the present application, all the steps in the measurement process of the air pressure method screw pile pipe soil plug height measurement system are sorted out. As Figure 2 shown, after the formal test, the model box 9 is filled with soil mass 8, the screw pipe pile 7 is in a semi-buried state, there is a connection port at the pile head position and is in a state to be connected with the second air duct 5, and a thermometer 3 and a pressure gauge 4 are arranged at the connection between the second air duct 5 and the screw pipe pile 7.

[0087] In an optional embodiment of the present application, step S2 includes the following sub-steps:

[0088] S21. During the formal test, after the screw pipe pile is installed and buried, the top is exposed outside the soil mass. Under the atmospheric pressure, read the pressure P when the second air duct and the screw pipe pile are in a state to be connected in step S15 0 ;

[0089] S22. Connect the second air duct in step S15 to the screw pipe pile;

[0090] S23. Check to ensure that the air pressure method screw pile pipe soil plug height measurement system is in a sealed state after being connected to the screw pipe pile;

[0091] S24. Close the connection between the gas storage tank and the second air duct, start the air compressor, and deliver high-pressure gas into the gas storage tank;

[0092] S25. Turn off the air compressor, close the double-pass connection of the gas storage tank, keep the gas storage tank in a sealed state, measure the air pressure P in the gas storage tank through the pressure gauge installed in step S13 1 , measure the temperature T in the gas storage tank through the thermometer installed in step S14 1 ;

[0093] S26. Open the connection between the gas storage tank and the second air duct to ensure that the gas can be stably delivered into the screw pipe pile through the second air duct;

[0094] S27. Observe whether the readings of the pressure gauges in the gas storage tank and at the connection between the second air duct and the screw pipe pile are equal. If the readings are equal, it means that the air pressure has reached equilibrium, and record the equilibrium pressure P 2, record the reading T of the thermometer in step S17 at equilibrium 2 , record the reading T of the thermometer in step S14 at equilibrium 3 .

[0095] S3. Obtain the basic parameters for measuring the height of the soil plug by air pressure, and construct an algorithm for measuring the height of the soil plug of the spiral pipe pile.

[0096] In an alternative embodiment of the present application, as Figure 2 shown, it is necessary to measure in advance the inner diameter of the internal cavity of the spiral pipe pile 7, the volume of the gas storage tank 10, and the volume of the second gas flow conduit 5.

[0097] In an alternative embodiment of the present application, step S3 includes the following sub-steps:

[0098] S31. Obtain the inner diameter R of the internal cavity of the spiral pipe pile 1 ;

[0099] S32. Obtain the internal volume V of the gas storage tank in step S11 1 ;

[0100] S33. Obtain the atmospheric pressure value P in step S21 during the test 0 ;

[0101] S34. Obtain the pressure in the gas storage tank in step S25 as P 1 ;

[0102] S35. Obtain the temperature of the gas in the gas storage tank in step S25 as T 1 ;

[0103] S36. Obtain the volume V of the second gas flow conduit in step S15 0 ;

[0104] S37. Obtain the pressure P of the gas at the connection between the second gas flow conduit and the spiral pipe pile in step S27 2 , the temperature T of the gas at the connection between the second gas flow conduit and the spiral pipe pile 2 , the temperature T of the gas in the gas storage tank at equilibrium 3 ;

[0105] S38. According to the basic parameters obtained in S31 - S37, construct an algorithm for measuring the height of the soil plug of the spiral pipe pile, expressed as:

[0106]

[0107] In the formula, h is the height of the soil plug of the spiral pipe pile, and H is the height of the internal cavity of the spiral pipe pile.

[0108] S4. Conduct pre - experiment calibration on the algorithm for measuring the height of the soil plug in the spiral pipe pile to determine the volume coefficient A of the gas storage tank and the connection volume coefficient B of the air flow conduit.

[0109] In an alternative embodiment of the present application, the calibration process is not carried out in the model box 9, and the air - pressure - method spiral pile pipe pile soil plug height measurement system needs to be operated twice. As Figure 1 shown, for the first time, the air - pressure - method spiral pile pipe pile soil plug height measurement system needs to use a sealing flat plate to block the outlet of the second air flow conduit 5. As Figure 4 shown, for the second time, the second air flow conduit 5 of the air - pressure - method spiral pile pipe pile soil plug height measurement system needs to be connected to the spiral pipe pile and the pile end opening of the spiral pile pipe needs to be blocked with a sealing flat plate.

[0110] In an alternative embodiment of the present application, step S4 includes the following sub - steps:

[0111] S41. According to the basic parameters of measuring the soil plug height by air pressure obtained in steps S31 - S37, further adjust the algorithm for measuring the height of the soil plug in the spiral pipe pile constructed in step S29 to obtain:

[0112]

[0113] where A is the volume coefficient of the gas storage tank, and B is the connection volume coefficient of the air flow conduit.

[0114] S42. In the calibration link of the air - pressure - method spiral pile pipe pile soil plug height measurement system, assemble the air - pressure - method spiral pile pipe pile soil plug height measurement system. The spiral pile pipe pile soil plug height measurement system and the spiral pipe pile are in a state to be connected. Under atmospheric pressure, measure the pressure P when the second air flow conduit and the spiral pipe pile are in a state to be connected. 01 ;

[0115] S43. Seal the connection between the second air flow conduit and the spiral pipe pile in step S15 with a sealing flat plate and do not connect it to the spiral pipe pile. Check to ensure that the air - pressure - method spiral pile pipe pile soil plug height measurement system is in a sealed state;

[0116] S44. Close the connection between the gas storage tank and the second air flow conduit, start the air compressor, and transport high - pressure gas into the gas storage tank;

[0117] S45. Turn off the air compressor, close the double - connection of the gas storage tank, keep the gas storage tank in a sealed state, measure the air pressure P in the gas storage tank through the pressure gauge installed in step S13 11 , measure the temperature T in the gas storage tank through the thermometer installed in step S14 11 ;

[0118] S46. Open the connection between the gas storage tank and the second gas flow conduit, and observe whether the pressure gauges in the gas storage tank and at the connection between the second gas flow conduit and the spiral pipe pile show equal readings at this time. If the readings are equal, it indicates that the air pressure has reached equilibrium, and record the pressure P at equilibrium. 21 , and record the reading T of the thermometer in step S17 at equilibrium. 21 , and record the reading T of the thermometer in step S14 at equilibrium. 31 ;

[0119] S47. Release the gas in the gas pressure method spiral pile pipe plug height measurement system, and open all connections in the gas pressure method spiral pile pipe plug height measurement system; connect the second gas flow conduit to the atmosphere, and read the atmospheric pressure P at this time. 02 ;

[0120] S48. Obtain the height H of the internal cavity of the spiral pipe pile, connect the second gas flow conduit to the spiral pipe pile, and use a sealing plate that can cover the opening at the pile end of the spiral pipe pile to seal the opening. Check to ensure that the gas pressure method spiral pile pipe plug height measurement system is in a sealed state after being connected to the spiral pipe pile;

[0121] S49. Close the connection between the gas storage tank and the second gas flow conduit, start the air compressor, and supply high-pressure gas to the gas storage tank;

[0122] S410. Turn off the air compressor, close the double-way connection of the gas storage tank, keep the gas storage tank in a sealed state, and measure the air pressure P in the gas storage tank through the pressure gauge installed in step S13 13 , and measure the temperature T in the gas storage tank through the thermometer installed in step S14 13 ;

[0123] S411. Open the connection between the gas storage tank and the second gas flow conduit, and observe whether the pressure gauges in the gas storage tank and at the connection between the second gas flow conduit and the spiral pipe pile show equal readings at this time. If the readings are equal, it indicates that the air pressure has reached equilibrium, and record the pressure P at equilibrium. 22 , and record the reading T of the thermometer in step S17 at equilibrium. 22 , and record the reading T of the thermometer in step S14 at equilibrium. 32 ;

[0124] S412. Obtain the parameters in steps S41 - S42, and construct a calibration equation system:

[0125]

[0126] S413. Solve for the volume coefficient A of the gas storage tank and the volume coefficient B of the gas flow conduit connection.

[0127] S5. Operate according to the determination scheme of the soil plug height of the screw pipe pile during the formal test in step S2 to obtain the soil plug height of the installed screw pipe pile.

[0128] In an alternative embodiment of the present application, as Figure 2 shown, during the formal test, the screw pile is located in the model box 9, and the second air duct 5 in the air pressure method screw pipe pile soil plug height measurement system is connected to the screw pipe pile 7

[0129] In an alternative embodiment of the present application, the soil plug height of the screw pipe pile in step S5 can be expressed as:

[0130]

[0131] where A is the volume coefficient of the gas storage tank obtained by solving during the calibration process in step S4, and B is the volume coefficient of the air duct connection obtained by solving during the calibration process in step S4.

[0132] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for measuring the height of soil plugs in a spiral pipe pile model test by air pressure, characterized in that: The following steps are involved: S1. Assemble the air pressure method spiral pile soil plug height measurement system; S2. Develop a plan for measuring the soil plug height of the screw pile during formal testing; S3, obtaining basic parameters for measuring soil plug height by air pressure, and constructing a spiral pipe pile soil plug height measurement algorithm; S4. Calibrate the spiral pile soil plug height determination algorithm before the experiment to determine the air storage tank volume coefficient A and the air flow duct connection volume coefficient B; S5. Operate according to the method for measuring the soil plug height of the spiral pipe pile during the formal test in step S2 to obtain the soil plug height of the installed spiral pipe pile.

2. The method for measuring the soil plug height by air pressure in a spiral pipe pile model test according to claim 1, characterized in that: Step S1 includes the following steps: S11, prepare an air compressor, a double-connectable air storage tank, two pressure gauges, two thermometers and two air flow ducts; wherein the two air flow ducts are respectively a first air flow duct and a second air flow duct; S12, connecting a first air flow conduit between the air compressor and the air storage tank; S13. Install a pressure gauge to measure the pressure in the gas tank; S14. Install a thermometer to measure the temperature of the gas in the gas tank; S15, connecting the gas storage tank to the second air flow conduit, and the second air flow conduit and the spiral pipe pile are in a waiting state; S16, placing a pressure gauge to measure the pressure at the connection between the second air flow conduit and the spiral pile in step S15; S17, placing a thermometer to measure the temperature of the connection between the second airflow duct and the spiral pile in step S15.

3. The method for measuring the soil plug height by air pressure in a spiral pipe pile model test according to claim 2, characterized in that: Step S2 includes the following steps: S21. During the formal test, after the spiral pipe pile is installed into the soil, the top is exposed to the soil. Under atmospheric pressure, the pressure P0 when the airflow duct and the spiral pipe pile are in a state to be connected on the second day in step S15 is read; S22, connecting the second airflow conduit in step S15 to the spiral pipe pile; S23. Check and ensure that the air pressure method spiral pile soil plug height measuring system is in a closed state after being connected to the spiral pile; S24, closing the connection between the gas storage tank and the second air flow conduit, starting the air compressor, and delivering high-pressure gas to the gas storage tank; S25, turn off the air compressor, close the two-way connection of the gas storage tank, keep the gas storage tank in a closed state, measure the air pressure P1 in the gas storage tank by the pressure gauge installed in step S13, and measure the temperature T1 in the gas storage tank by the thermometer installed in step S14; S26, opening the connection between the gas storage tank and the second air flow conduit to ensure that the gas can be stably transported into the spiral pipe pile through the second air flow conduit; S27. Observe whether the readings of the pressure gauge in the gas storage tank and the pressure gauge at the connection point between the second air flow duct and the spiral pipe pile are equal. If the readings are equal, it means that the air pressure has reached equilibrium. Record the pressure P2 at equilibrium, record the reading T2 of the thermometer in step S17 at equilibrium, and record the reading T3 of the thermometer in step S14 at equilibrium.

4. The method for measuring the soil plug height by air pressure in a spiral pipe pile model test according to claim 3, characterized in that: Step S3 includes the following steps: S31, obtaining the inner diameter R1 of the inner cavity of the spiral pipe pile; S32, obtaining the internal volume V1 of the gas storage tank in step S11; S33, obtaining the atmospheric pressure value P0 in step S21 during the test; S34, obtaining the pressure P1 in the gas storage tank in step S25; S35, obtaining the temperature T1 of the gas in the gas storage tank in step S25; S36, obtaining the volume V0 of the second air flow duct in step S15; S37, obtaining the pressure P2 of the gas in the connection between the second gas flow conduit and the spiral pipe pile, the temperature T2 of the gas in the connection between the second gas flow conduit and the spiral pipe pile, and the temperature T3 of the gas in the gas storage tank at equilibrium in step S27; S38. According to the basic parameters obtained in S31 to S37, an algorithm for determining the height of the soil plug of the spiral pipe pile is constructed, which is expressed as: Where h is the height of the soil plug of the spiral pipe pile, and H is the height of the cavity inside the spiral pipe pile.

5. The method for measuring the soil plug height by air pressure in a spiral pipe pile model test according to claim 4, characterized in that: Step S4 includes the following steps: S41, based on the basic parameters of the soil plug height measured by air pressure obtained in steps S31 to S37, the determination algorithm of the soil plug height of the spiral pipe pile constructed in step S29 is further adjusted to obtain: in, A is the volume coefficient of the gas storage tank, and B is the volume coefficient of the air flow duct connection; S42. In the calibration phase of the air pressure method spiral pile soil plug height measuring system, the air pressure method spiral pile soil plug height measuring system is assembled, the spiral pile soil plug height measuring system and the spiral pile are in a waiting state to be connected, and the pressure P when the second air flow duct and the spiral pile are in the waiting state to be connected is measured under atmospheric pressure. 01 ; S43, the connection between the second airflow conduit and the spiral pipe pile in step S15 is blocked with a blocking plate and is not connected to the spiral pipe pile, and the air pressure method spiral pile soil plug height measurement system is checked to ensure that it is in a closed state; S44, closing the connection between the gas storage tank and the second air flow conduit, starting the air compressor, and delivering high-pressure gas to the gas storage tank; S45, turn off the air compressor, close the two-way connection of the gas storage tank, keep the gas storage tank in a closed state, and measure the air pressure P in the gas storage tank by the pressure gauge installed in step S13. 11 The temperature T in the gas storage tank is measured by the thermometer installed in step S14. 11 ; S46, open the connection between the gas storage tank and the second air flow conduit, and observe whether the readings of the pressure gauge in the gas storage tank and the pressure gauge at the connection between the second air flow conduit and the spiral pipe pile are equal. If the readings are equal, it means that the air pressure has reached equilibrium. Record the pressure P at equilibrium. 21 , record the thermometer reading T in step S17 during equilibrium 21 , record the thermometer reading T in step S14 at equilibrium 31 ; S47, release the gas in the system for measuring the height of the screw pile pipe soil plug by air pressure method, open all connections in the system for measuring the height of the screw pile pipe soil plug by air pressure method; connect the second air flow conduit to the atmosphere, and read the atmospheric pressure P at this time. 02 ; S48, obtaining the height H of the internal cavity of the spiral pipe pile, connecting the second airflow conduit to the spiral pipe pile, sealing the opening with a sealing plate capable of covering the opening of the end of the spiral pipe pile, and checking to ensure that the air pressure method spiral pile soil plug height measurement system is in a closed state after being connected to the spiral pipe pile; S49, closing the connection between the gas storage tank and the second air flow conduit, starting the air compressor, and delivering high-pressure gas to the gas storage tank; S410, turn off the air compressor, close the two-way connection of the gas storage tank, keep the gas storage tank in a closed state, and measure the air pressure P in the gas storage tank by the pressure gauge installed in step S13. 13 The temperature T in the gas storage tank is measured by the thermometer installed in step S14. 13 ; S411. Open the connection between the gas storage tank and the second air flow conduit, and observe whether the pressure gauge in the gas storage tank and the pressure gauge at the connection between the second air flow conduit and the spiral pipe pile have the same readings. If the readings are equal, it means that the air pressure has reached equilibrium. Record the pressure P at equilibrium. 22 , record the thermometer reading T in step S17 during equilibrium 22 , record the thermometer reading T in step S14 at equilibrium 32 ; S412, obtaining the parameters of steps S41 to S42, and constructing a calibration equation group: S413, solving the volume coefficient A of the gas storage tank and the volume coefficient B of the air flow duct connection.

6. The method for measuring the soil plug height by air pressure in a spiral pipe pile model test according to claim 4, characterized in that: The height of the spiral pipe pile soil plug in step S5 is expressed as: Wherein, A is the volume coefficient of the gas storage tank obtained by the calibration process of step S4, and B is the volume coefficient of the air flow duct connection obtained by the calibration process of step S4.

7. The method for measuring the soil plug height by air pressure in a spiral pipe pile model test according to claim 2, characterized in that: The method further includes: during the model test preparation, the spiral pipe pile has a connection port at the pile head position or within a set area from the pile head, and the connection port is connected to the second air flow conduit in step S15.

8. The method for measuring the soil plug height by air pressure in a spiral pipe pile model test according to claim 5, characterized in that: The air compressor is capable of compressing air to a pressure higher than atmospheric pressure.

9. The method for measuring the soil plug height by air pressure in a spiral pipe pile model test according to claim 2, characterized in that: The gas storage tank is connected with the first air flow conduit and the second air flow conduit in a two-way manner, and a switch for cutting off the connection is close to the outer wall of the gas storage tank.

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