Pile-soil interface shear stress test device and pile side friction resistance calculation method thereof

Abstract

The invention discloses a pile-soil interface shear stress testing device and a pile side frictional resistance calculation method thereof, and relates to the technical field of geotechnical engineering. Comprising a loading device, a force measuring device, a signal processing circuit and a signal conversion and numerical value display system, the force measuring device comprises an electromagnet, a shell, a flexible beam, a coil, a coil framework, a differential capacitor, an upper fixing body, a lower fixing body, an electric wire and a loading rod, and the pile friction resistance is solved according to a simulation test pile; the soil body applies pressure to the loading rod, so that the movable polar plate on the flexible beam moves, the capacitance of the differential capacitor is changed, the capacitance variable quantity is output as the current variable quantity through adjustment of the bridge circuit and the V / I conversion circuit, and then the pile body axial force is measured through an electromagnetic structure and a closed-loop circuit according to the electromagnetic balance principle. And further calculating to obtain the pile side friction resistance. The device is simple in measurement principle, high in measurement precision, capable of being repeatedly used, economical, practical and wide in application range.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering technology, and in particular to a pile-soil interface shear stress testing device and a method for calculating pile side friction. Background Technology

[0002] In the field of geotechnical engineering, the accurate calculation of the vertical bearing capacity of a single pile is crucial to the rationality and economy of the pile design. Static load tests are generally conducted using the surcharge method. For large-tonnage piles, a massive reaction platform needs to be built, which is time-consuming, labor-intensive, and extremely costly. Moreover, it is impossible to conduct such tests in areas with limited space.

[0003] To address the shortcomings of the aforementioned pile side friction testing methods, which involve bulky equipment and high costs, this invention utilizes the principle of electromagnetic balance. By layering soil with the same physical and mechanical properties as a certain layer of undisturbed soil at the proposed site in a pile-soil interface shear stress testing device, and further measuring the pile side friction between this soil layer and the pile using an electromagnetic balance force sensor box, the pile side friction can be obtained by repeating the above test. This allows the pile side friction to be obtained over the entire length of the pile. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned problems by providing a pile-soil interface shear stress testing device and a method for calculating pile side friction.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] According to one aspect of the present invention, a pile-soil interface shear stress testing device and a method for calculating pile side friction are provided, comprising a force measuring device, a signal processing circuit and a signal conversion and numerical display system, wherein the force measuring device comprises an electromagnet, a shell, a flexible beam, a coil, a coil frame, a differential capacitor, an upper fixing body, a lower fixing body, an electric wire and a loading rod;

[0007] The electromagnet is fixed above the housing, one end of the flexible beam is fixed inside the housing, the coil is wound on the coil frame, the coil frame is connected to the upper part of the flexible beam, the housing is provided with a support through hole, one end of the loading rod passes through the support through hole and is connected to the flexible beam, the other end of the loading rod 28 is used to load the pressure transmitted by the soil, and the upper and lower fixing bodies are fixed inside the other end of the housing.

[0008] The flexible beam is made of beryllium bronze, and the coil frame is made of stacked silicon steel sheets.

[0009] Furthermore, the signal processing circuit includes a bridge circuit, a differential amplifier circuit, a phase-sensitive detector circuit, a low-pass filter circuit, a power amplifier circuit, and a V / I conversion circuit connected in sequence. One end of the signal processing circuit is connected to a differential capacitor, and the other end is connected to a coil.

[0010] The signal conversion and numerical display system includes a sampling resistor, a signal conditioning circuit, a data acquisition circuit, and a microprocessor system.

[0011] Furthermore, in the signal processing circuit and the signal conversion and numerical display system, the signal processing circuit outputs a current corresponding to the measured force. After the current passes through the sampling resistor, an output voltage is obtained across the sampling resistor. The output voltage is proportional to the measured force, and finally the measured force value is displayed by the signal conversion and numerical display system.

[0012] The data display processor includes sampling resistors and a signal conversion and numerical display system.

[0013] Furthermore, the differential capacitance sensor includes an upper fixed electrode plate, an upper movable electrode plate, a lower movable electrode plate, and a lower fixed electrode plate. The upper fixed electrode plate and the lower fixed electrode plate are respectively mounted on an upper fixed body and a lower fixed body; the upper movable electrode plate and the lower movable electrode plate are respectively mounted on the other end of the flexible beam.

[0014] Furthermore, one end of the flexible beam is fixed to the housing, and the middle part is fixed with a loading rod, a coil, and a coil frame. The upper and lower fixed electrodes fixed to the housing, together with the upper and lower movable electrodes on the flexible beam, serve as electrodes to form a differential capacitance sensor.

[0015] Furthermore, the loading device includes an anchoring top plate, an anchoring bottom plate, a connecting nut, a force transmission frame, a pressure sensor, a hydraulic jack, a reaction frame, bolts, a dial indicator, angle steel, an electromagnetic balance force sensor box, and spring clips.

[0016] Furthermore, the spring clip includes a clip hole, a clip, a spring, and a sliding groove.

[0017] Furthermore, the clamping head is made of high-strength metal, which can slide freely in the sliding groove and clamp the housing onto the pile.

[0018] First, a clamping hole is dug at the height of the pile where the frictional resistance needs to be measured. The spring inside the housing is pressed into the sliding groove to the initial position. The housing is then lowered to the clamping hole, the outlet of the sliding groove is aligned with the clamping hole, the spring pops out, and the housing is fixed to the pile.

[0019] The data conversion method for the pile-soil interface shear stress test device includes the following steps:

[0020] S1. Dig a hole for the clamp at the height where the frictional resistance of pile 1 needs to be measured.

[0021] S2. Based on the physical properties of the soil layer on site, a model box is set up in the laboratory. First, a certain thickness of fine sand is filled into the model box and compacted as a bearing layer and drainage channel. The model soil is filled into the model box in layers, with each layer not exceeding 150mm, to ensure the uniformity and compaction of the soil layer. During the filling process, the soil layers and installation plates are arranged according to the height of the pile to be measured for frictional resistance.

[0022] S3. Place the pile into the model box, arrange the soil layers and mounting plate;

[0023] S4. Press the spring back to its initial position in the sliding groove, lay a layer of soil according to the soil conditions on site, and then lower the shell to the height where the frictional resistance needs to be measured. The spring will automatically pop out and lock into the clip hole on the pile body. Fix the shell on the pile body, and then lay the next layer of soil as before.

[0024] S5. After the pile is ready for testing, install the anchoring base plate, hydraulic jack, pressure sensor, anchoring top plate, force transmission frame, electronic dial indicator, reaction frame, bolts, dial indicator, and angle steel in sequence.

[0025] S6. After the hydraulic jack is activated to apply pressure to the pile, the loading rod is subjected to pressure, causing the upper and lower movable plates on the flexible beam to move, changing the distance between the plates and thus altering the capacitance. The bridge circuit converts the capacitance into a voltage change and outputs a voltage value. This voltage signal, through a V / I converter circuit, provides a current proportional to the applied pressure to the coil. Under the influence of the electromagnet's magnetic field, the coil generates a downward force, causing the flexible beam to move downward. After the flexible beam moves downward, the output voltage of the bridge circuit decreases, while the current continues to increase until the flexible beam returns to its initial equilibrium position. The frictional resistance measured by the three sets of electromagnetic balance force sensing boxes is read through the signal conversion and numerical display system.

[0026] Furthermore, the calculation method in S6 is as follows:

[0027] S1, Capacitive sensor capacitance:

[0028]

[0029] S2. Calculation of the free end of the flexible beam:

[0030] The maximum deflection is considered in terms of the force F acting on the flexible beam and the beam's own weight:

[0031]

[0032] The corner is:

[0033] S3, Bridge circuit calculation:

[0034]

[0035] in For output voltage, The input voltage of the bridge circuit. Angular frequency, bridge resistance k=

[0036] S4. Magnitude of electromagnetic force:

[0037]

[0038] Where I is the current intensity flowing through the coil, B is the magnetic field strength, and L is the total length of the copper wire perpendicular to the magnetic field lines in the coil. The angle between the direction of the current and the direction of the magnetic field;

[0039]

[0040] Where R is the resistance value of the sampling resistor;

[0041] S5. Calculation of the average value of pile side friction:

[0042] Axial force at a certain section of the pile:

[0043] Calculated using the iterative method value

[0044] Average value of pile side friction:

[0045]

[0046] in This represents the average side friction resistance of the i-th segment of the model pile. Let i be the axial force of the i-th segment of the model pile. Let be the thickness of the i-th segment of the pile body.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] This invention includes a loading device, a force measuring device, a signal processing circuit, and a signal conversion and numerical display system. The force measuring device includes an electromagnet, a housing, a flexible beam, a coil and coil frame, a differential capacitor, an upper fixed body, a lower fixed body, wires, and a loading rod. It provides a method for calculating pile skin friction based on simulated test piles. After the pile is subjected to force, the soil exerts pressure on the loading rod, causing a movable plate on the flexible beam to move, changing the capacitance of the differential capacitor. This change is adjusted via a bridge circuit and a V / I conversion circuit, resulting in a current change output from the capacitance change. Based on the principle of electromagnetic balance, the axial force of the pile is measured through an electromagnetic structure and a closed-loop circuit, further calculating the pile skin friction. This invention addresses the shortcomings of existing static load testing methods for pile skin friction, such as large equipment size and high cost, and can further reduce the error in determining the pile skin friction value in pile design.

[0049] The device of this invention has a simple measurement principle, high measurement accuracy, is reusable, economical and practical, and has a wide range of applications. The calculation method of pile side friction has been verified by model test and field static load test results. It can replace the cumbersome field static load test method for testing pile side friction and has good promotion value. Attached Figure Description

[0050] Figure 1 This is a schematic plan view of the pile-soil interface shear stress test device according to the present invention.

[0051] Figure 2 This is a schematic diagram of the loading device structure of the pile-soil interface shear stress test device according to the present invention.

[0052] Figure 3 This is a schematic diagram of the sliding groove structure of the pile-soil interface shear stress testing device according to the present invention.

[0053] Figure 4 This is a schematic diagram of the electromagnetic balance force sensor box structure of the pile-soil interface shear stress testing device according to the present invention.

[0054] Figure 5 This is a three-dimensional schematic diagram of the electromagnetic balance force sensor box structure of the pile-soil interface shear stress test device according to the present invention.

[0055] Figure 6 This is a schematic diagram of the electromagnetic balance force sensor box circuit structure of the pile-soil interface shear stress test device according to the present invention.

[0056] Figure 7 This is a three-dimensional schematic diagram of the pile-soil interface shear stress testing device according to the present invention.

[0057] Figure 8 This is a bridge circuit diagram in S3 of this invention.

[0058] In the diagram: 1. Pile; 2. Model box; 3. Soil; 4. Anchoring top plate; 5. Connecting nut; 6. Force transmission frame; 7. Pressure sensor; 8. Hydraulic jack; 9. Reaction frame; 10. Bolt; 11. Anchoring bottom plate; 12. Dial indicator; 13. Angle steel; 14. Electromagnetic balance force sensor box; 15. Spring clip; 16. Clip hole; 17. Clip; 18. Housing; 19. Spring; 20. Sliding groove; 21. Coil frame 21. Frame; 22. Coil; 23. Electromagnet; 24. Differential capacitor; 25. Lower fixed body; 26. Upper fixed body; 27. Flexible beam; 28. Loading rod; 29. ​​Wire; 30. Upper fixed plate; 31. Upper movable plate; 32. Lower movable plate; 33. Lower fixed plate; 34. Through hole of bracket; 35. Sampling resistor; 36. Signal conversion and numerical display system; 37. Signal processing circuit; 38. Data display processor. Detailed Implementation

[0059] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0060] Benru Figure 1-7 As shown, the present invention provides a pile-soil interface shear stress test device and a method for calculating pile side friction resistance, including a force measuring device, a signal processing circuit and a signal conversion and numerical display system. The force measuring device consists of an electromagnet 23, a shell 18, a flexible beam 27, a coil 22, a coil frame 21, a differential capacitor 24, an upper fixing body 26, a lower fixing body 25, an electric wire 29 and a loading rod 28.

[0061] The electromagnet 23 is fixed above the housing 18, one end of the flexible beam 27 is fixed inside one end of the housing 18, the coil 22 is wound around the coil frame 21, the coil frame 21 is connected to the upper part of the flexible beam 27, the housing (18) is provided with a support through hole (34), one end of the loading rod (11) passes through the support through hole (34) and is connected to the flexible beam (27), the other end of the loading rod 28 is used to load the pressure transmitted by the soil, and the upper fixing body 26 and the lower fixing body 25 are fixed inside the other end of the housing 18.

[0062] One end of the signal processing circuit is connected to the differential capacitor 24, and the other end is connected to the coil 22.

[0063] The signal processing circuit includes a bridge circuit, a differential amplifier circuit, a phase-sensitive detector circuit, a low-pass filter circuit, a power amplifier circuit, and a V / I conversion circuit connected in sequence.

[0064] The signal conversion and numerical display system includes a sampling resistor 35, a signal conditioning circuit, a data acquisition circuit, and a microprocessor system.

[0065] The signal processing circuit 37 and the signal conversion and numerical display system 36 are described. The signal processing circuit 37 outputs a current corresponding to the measured force. After the current passes through the sampling resistor 35, an output voltage is obtained across the sampling resistor 35. The output voltage is proportional to the measured force. Finally, the signal conversion and numerical display system 36 displays the measured force value.

[0066] The data display processor 38 includes a sampling resistor 35 and a signal conversion and numerical display system 36.

[0067] The differential capacitance sensor 24 includes an upper fixed electrode plate 30, an upper movable electrode plate 31, a lower movable electrode plate 32, and a lower fixed electrode plate 33. The upper fixed electrode plate 30 and the lower fixed electrode plate 33 are respectively mounted on the upper fixed body 26 and the lower fixed body 25; the upper movable electrode plate 31 and the lower movable electrode plate 32 are respectively mounted on the other end of the flexible beam 27.

[0068] Flexible beam 27 is made of beryllium bronze.

[0069] The coil frame 21 is made of stacked silicon steel sheets.

[0070] One end of the flexible beam 27 is fixed to the housing 18, and the middle part is fixed to the loading rod 11, the coil 22 and the coil frame 21. The upper fixed electrode plate 30 and the lower fixed electrode plate 33 fixed to the housing 18, together with the upper movable electrode plate 31 and the lower movable electrode plate 32 on the flexible beam 27, serve as electrodes to form a differential capacitance sensor.

[0071] The loading device includes an anchoring top plate 4, an anchoring bottom plate 11, a connecting nut 5, a force transmission frame 6, a pressure sensor 7, a hydraulic jack 8, a reaction frame 9, a bolt 10, a dial indicator 12, an angle steel 13, an electromagnetic balance force sensor box 14, and a spring clip 15.

[0072] The spring clip 15 includes a clip hole 16, a clip 17, a spring 19, and a sliding groove 20.

[0073] The clamp 17 is made of high-strength metal, which can slide freely in the sliding groove 20 and can clamp the housing 18 onto the pile body 1.

[0074] First, a clamping hole 17 is dug at the height where the frictional resistance needs to be measured on the pile body 1. The spring 19 inside the housing 18 is pressed into the sliding groove 20 to the initial position. The housing 18 is then lowered to the clamping hole 17. The outlet of the sliding groove 20 is aligned with the clamping hole 17. The spring 19 pops out and fixes the housing 18 on the pile body 1.

[0075] Geological surveys are conducted to collect local geological data, and appropriate sampling tools such as drilling equipment are prepared. The names and basic properties of the soil and rock are correctly identified. The types of soil samples at the test site are understood. A soil sample with similar physical properties and state indicators to a certain layer of undisturbed soil is filled into the model box. Each soil sample is then placed into the model box to conduct the test, which is used to test the side friction resistance of the soil layer.

[0076] The data conversion method for the pile-soil interface shear stress test device includes the following steps:

[0077] S1. Dig a hole 16 at the height where the frictional resistance of pile 1 needs to be measured.

[0078] S2. Based on the physical properties of the soil layers at the site, model box 2 is set up in the laboratory. First, a certain thickness of fine sand is filled into the model box and compacted to serve as the bearing layer and drainage channel. The model soil is filled into the model box in layers, with each layer not exceeding 150mm, to ensure the uniformity and compaction of the soil layers. During the filling process, the soil layers and installation plate 2 are arranged according to the height at which the skin friction of pile 1 needs to be measured.

[0079] S3. Place pile 1 into model box 2, and arrange the soil layer and installation plate 2.

[0080] S4. Press the spring 19 back into the initial position in the sliding groove 20, lay a layer of soil according to the soil conditions on site, and then lower the shell 18 to the height where the frictional resistance needs to be measured. The spring 19 will automatically pop out and lock into the clip hole 16 on the pile body. Fix the shell 18 on the pile body 1, and then lay the next layer of soil as usual.

[0081] S5. After the pile is ready for testing, install the following components in sequence: anchor base plate 11, hydraulic jack 8, pressure sensor 7, anchor top plate 4, force transmission frame 6, electronic dial indicator 5, reaction frame 9, bolt 10, dial indicator 12, and angle steel 13.

[0082] S6. Loading is performed using hydraulic jacks 8 and pressure sensors 7, in multiple stages, with each stage applying a certain pressure, until half of the single pile's ultimate bearing capacity is reached. Settlement is recorded before and after loading until the maximum load value is reached. During loading, the soil settlement is observed. When the settlement is less than 0.1 mm within one hour, the settlement is considered stable, and the next stage of load is applied.

[0083] S7. After the hydraulic jack 8 is activated to apply pressure to the pile 1, the loading rod 28 is subjected to pressure, causing the upper movable plate 31 and the lower movable plate 32 on the flexible beam 27 to move, changing the distance between the plates and thus changing the capacitance. The bridge circuit converts the capacitance into a voltage change and outputs a voltage value. The voltage signal, through the V / I conversion circuit, provides a current proportional to the applied pressure to the coil 22. Under the magnetic field of the electromagnet 23, the coil 22 generates a downward force, causing the flexible beam 27 to move downward. After the flexible beam 27 moves downward, the output voltage of the bridge circuit decreases, and the current flowing through 22 continues to increase until the flexible beam 27 returns to its initial equilibrium position. The frictional resistance measured by the three sets of electromagnetic balance force sensing boxes 14 is read through the signal conversion and numerical display system.

[0084] The calculation method in S6 is as follows:

[0085] S1, Capacitive sensor capacitance:

[0086]

[0087] S2. Calculation of the free end of the flexible beam:

[0088] The maximum deflection is considered in terms of the force F acting on the flexible beam and the beam's own weight:

[0089]

[0090] The corner is:

[0091] S3, Bridge circuit as follows Figure 8 As shown:

[0092]

[0093] in For output voltage, The input voltage of the bridge circuit. Angular frequency, bridge resistance k=

[0094] S4. Magnitude of electromagnetic force:

[0095]

[0096] Where I is the current intensity flowing through the coil, B is the magnetic field strength, and L is the total length of the copper wire perpendicular to the magnetic field lines in the coil. It is the angle between the direction of the current and the direction of the magnetic field.

[0097]

[0098] Where R is the resistance value of the sampling resistor.

[0099] S5. Calculation of the average value of pile side friction:

[0100] Axial force at a certain section of the pile:

[0101] Calculated using the iterative method value

[0102] Average value of pile side friction:

[0103]

[0104] in This represents the average side friction resistance of the i-th segment of the model pile. Let i be the axial force of the i-th segment of the model pile. Let be the thickness of the i-th segment of the pile body.

[0105] This invention addresses the shortcomings of existing static load testing methods for pile side friction resistance, such as the large size and high cost of the equipment, and can further reduce the error in determining the pile side friction resistance value in pile design.

[0106] The device of this invention has a simple measurement principle, high measurement accuracy, is reusable, economical and practical, and has a wide range of applications. The calculation method of pile side friction has been verified by model test and field static load test results. It can replace the cumbersome field static load test method for testing pile side friction and has good promotion value.

[0107] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0108] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A pile-soil interface shear stress testing device, characterized in that: It includes a force measuring device, a signal processing circuit and a signal conversion and numerical display system. The force measuring device consists of an electromagnet (23), a housing (18), a flexible beam (27), a coil (22), a coil frame (21), a differential capacitor (24), an upper fixing body (26), a lower fixing body (25), a wire (29) and a loading rod (28). Among them, the electromagnet (23) is fixed above the shell (18), one end of the flexible beam (27) is fixed inside one end of the shell (18), the coil (22) is wound on the coil frame (21), the coil frame (21) is connected to the upper part of the flexible beam (27), the shell (18) is provided with a support through hole (34), one end of the loading rod (11) passes through the support through hole (34) and is connected to the flexible beam (27), the other end of the loading rod (28) is used to load the pressure transmitted by the soil, and the upper fixing body (26) and the lower fixing body (25) are fixed inside the other end of the shell (18); The flexible beam (27) is made of beryllium bronze, and the coil frame (21) is made of stacked silicon steel sheets.

2. The pile-soil interface shear stress testing device according to claim 1, characterized in that: The signal processing circuit includes a bridge circuit, a differential amplifier circuit, a phase-sensitive detector circuit, a low-pass filter circuit, a power amplifier circuit, and a V / I conversion circuit connected in sequence. One end of the signal processing circuit is connected to the differential capacitor (24), and the other end is connected to the coil (22). The signal conversion and numerical display system includes a sampling resistor (35), a signal conditioning circuit, a data acquisition circuit, and a microprocessor system.

3. The pile-soil interface shear stress testing device according to claim 2, characterized in that: The signal processing circuit (37) and the signal conversion and numerical display system (36) are described. The signal processing circuit (37) outputs a current corresponding to the measured force. After the current passes through the sampling resistor (35), an output voltage is obtained across the sampling resistor (35). The output voltage is proportional to the measured force. Finally, the measured force value is displayed by the signal conversion and numerical display system (36). The data display processor (38) includes a sampling resistor (35) and a signal conversion and numerical display system (36).

4. The pile-soil interface shear stress testing device according to claim 3, characterized in that: The differential capacitance sensor (24) includes an upper fixed electrode plate (30), an upper movable electrode plate (31), a lower movable electrode plate (32), and a lower fixed electrode plate (33). The upper fixed electrode plate (30) and the lower fixed electrode plate (33) are respectively mounted on the upper fixed body (26) and the lower fixed body (25); the upper movable electrode plate (31) and the lower movable electrode plate (32) are respectively mounted on the other end of the flexible beam (27).

5. The pile-soil interface shear stress testing device according to claim 4, characterized in that: One end of the flexible beam (27) is fixed to the housing (18), and the middle part is fixed to the loading rod (11), coil (22) and coil frame (21). The upper fixed plate (30) and lower fixed plate (33) fixed to the housing (18) and the upper movable plate (31) and lower movable plate (32) on the flexible beam (27) serve as electrodes to form a differential capacitance sensor.

6. The pile-soil interface shear stress testing device according to claim 5, characterized in that: The loading device includes an anchoring top plate (4), an anchoring bottom plate (11), a connecting nut (5), a force transmission frame (6), a pressure sensor (7), a hydraulic jack (8), a reaction frame (9), a bolt (10), a dial indicator (12), an angle steel (13), an electromagnetic balance force sensor box (14), and a spring clip (15).

7. The pile-soil interface shear stress testing device according to claim 6, characterized in that: The spring clip (15) includes a clip hole (16), a clip (17), a spring (19), and a sliding groove (20).

8. The pile-soil interface shear stress testing device according to claim 7, characterized in that: The clamp head (17) is made of high-strength metal, which can slide freely in the sliding groove (20) and can clamp the shell (18) onto the pile body (1); First, a head hole (17) is dug at the height where the frictional resistance is to be measured on the pile body (1). By pressing the spring (19) inside the shell (18) into the sliding groove (20) to the initial position, the shell (18) is lowered to the head hole (17). The outlet of the sliding groove (20) is aligned with the head hole (17), the spring (19) pops out, and the shell (18) is fixed on the pile body (1).

9. The data conversion method of the pile-soil interface shear stress test device according to claim 8, characterized in that, Includes the following steps: S1. Dig a hole (16) at the height where the frictional resistance of the pile (1) needs to be measured. S2. Based on the physical properties of the soil layer on site, a model box (2) is set up in the laboratory. First, a certain thickness of fine sand is filled into the model box and compacted as a bearing layer and drainage channel. The model soil is filled into the model box in layers, with each layer not exceeding 150mm, to ensure the uniformity and compaction of the soil layer. During the filling process, the soil layer and the installation plate (2) are arranged according to the height of the frictional resistance to be measured for the pile (1). S3. Place the pile (1) into the model box (2), and arrange the soil layer and the mounting plate (2). S4. Press the spring (19) back into the initial position in the sliding groove (20), lay a layer of soil according to the soil conditions on site, and then lower the shell (18) to the height where the frictional resistance is to be measured. The spring (19) will automatically pop out and get stuck in the head hole (16) on the pile body. Fix the shell (18) on the pile body (1), and then lay the next layer of soil as usual. S5. After the pile is ready for testing, install the anchoring base plate (11), hydraulic jack (8), pressure sensor (7), anchoring top plate (4), force transmission frame (6), electronic dial indicator (5), reaction frame (9), bolt (10), dial indicator (12), and angle steel (13) in sequence. S6. After the hydraulic jack (8) is turned on to apply pressure to the pile (1), the loading rod (28) is subjected to pressure, which causes the upper movable plate (31) and the lower movable plate (32) on the flexible beam (27) to move, changing the distance between the plates, thereby causing the capacitance to change. The bridge circuit converts the capacitance into a voltage change and outputs a voltage value. The voltage signal is transmitted to the coil (22) through the V / I conversion circuit, providing a current proportional to the pressure. The coil (22) generates a downward force under the magnetic field of the electromagnet (23), causing the flexible beam (27) to move downward. After the flexible beam (27) moves downward, the output voltage of the bridge circuit decreases, and the current flowing through (22) continues to increase until the flexible beam (27) returns to the initial equilibrium position. The frictional resistance measured by the three sets of electromagnetic balance force sensing boxes (14) is read through the signal conversion and numerical display system.

10. The data conversion method for a pile-soil interface shear stress testing device according to claim 9, characterized in that, The calculation method in S6 is as follows: S1, Capacitive sensor capacitance: S2. Calculation of the free end of the flexible beam: The maximum deflection is considered in terms of the force F acting on the flexible beam and the beam's own weight: The corner is: S3. Bridge circuit calculation: in For output voltage, The input voltage of the bridge circuit. Angular frequency, bridge resistance k= S4. Magnitude of electromagnetic force: Where I is the current intensity flowing through the coil, B is the magnetic field strength, and L is the total length of the copper wire perpendicular to the magnetic field lines in the coil. The angle between the direction of the current and the direction of the magnetic field; Where R is the resistance value of the sampling resistor; S5. Calculation of the average value of pile side friction: Axial force at a certain section of the pile: Calculated using the iterative method value Average value of pile side friction: in This represents the average side friction resistance of the i-th segment of the model pile. Let i be the axial force of the i-th segment of the model pile. Let be the thickness of the i-th segment of the pile body.

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