Magnetic type testing device suitable for pile foundation quality detection and testing method thereof

Abstract

The invention discloses a magnetic type testing device and method for pile foundation quality detection, and belongs to the technical field of pile foundation quality monitoring in the field of geotechnical engineering and foundation engineering. According to the scheme, based on the magnetic medium action principle, an excitation magnetic field is generated through the permanent magnets and the magnetic cores, the magnetic cores and the in-pile longitudinal steel bars form a closed magnetic loop, and reliable connection is achieved through magnetic force among the permanent magnets, the magnetic cores and the in-pile longitudinal steel bars. On the basis, the quality of the steel bars in the pile foundation can be effectively and remotely monitored by transmitting signals to the master control end through the wireless signal transmission module by means of the magnetic conductivity difference of iron rust, air and the steel bars in the steel bars, and meanwhile, the monitoring range can be effectively adjusted by means of specific stretching and retracting. The testing device is adsorbed on the surface of a pile body through strong magnetism and can move along the pile body to synchronously monitor the corrosion degree of longitudinal bars and stirrups; a wireless transmission function is integrated, data can be remotely sent to a monitoring center, long-term and dynamic automatic monitoring is achieved, and detection is accurate and efficient.

Description

Technical Field

[0001] This invention belongs to the technical field of pile foundation quality monitoring in geotechnical engineering and foundation engineering, and specifically relates to a magnetic suction testing device and its testing method suitable for pile foundation quality testing. Background Technology

[0002] In the field of civil engineering, pile foundations, as critical underground load-bearing components, are of paramount importance for their long-term durability and structural safety. However, pile foundations embedded in complex environments often face severe corrosion threats to their internal steel reinforcement, mainly due to two reasons: First, the harsh service environment. Pile foundations are constantly exposed to media containing chloride ions, moisture, and oxygen, which can damage the passivation film on the steel reinforcement and accelerate electrochemical corrosion, particularly in coastal areas, bridges and roads with de-icing salt deposits, and areas with fluctuating groundwater levels. Second, the concealment and difficulty in detection. Steel reinforcement corrosion is a hidden process within the concrete, and traditional methods (such as visual inspection and grooving) suffer from problems such as lag, destructiveness, or insufficient accuracy, making early, rapid, and non-destructive diagnosis difficult. The consequences of steel reinforcement corrosion are severe: the volume expansion of corrosion products can lead to cracking and spalling of the concrete cover, weakening the effective cross-sectional area of ​​the steel reinforcement and the bond strength of the concrete, directly reducing the bearing capacity of the pile foundation and endangering structural safety.

[0003] Therefore, developing a non-destructive testing technology and device that can diagnose the corrosion status of pile foundation steel bars in an early, rapid, and reliable manner is of great practical significance for ensuring the long-term safety of infrastructure, preventing catastrophic accidents, and scientifically guiding maintenance decisions.

[0004] Patent publication number CN208420791U, entitled "An Electromagnetic Field Variation Response Device for Steel Reinforcement Corrosion," provides a steel reinforcement corrosion monitoring sensor embedded in concrete. This type of sensor can accurately determine the uniform corrosion of steel reinforcement, but it still has the following shortcomings: Built-in monitoring sensors, by clamping the reinforcing bars, restrict the corrosion expansion of the reinforcing bars, affecting the natural corrosion pattern of the reinforcing bars. In addition, in real-world engineering, pile foundations are all precast piles, and it is not practical to insert built-in sensors during the prefabrication process. Furthermore, sensors embedded in concrete can only be used once, resulting in higher costs. The patent document with publication number CN108469514A, entitled "A Monitoring Device and Method for Corrosion Behavior of Steel Reinforcing Bars in Concrete," involves an external sensor. Its corrosion measurement is limited to single-point monitoring and cannot monitor a wide area. At the same time, its magnetic circuit passes through relatively few steel bars, and the magnetic attraction is insufficient to support and fix it to the concrete structure. Furthermore, it can only monitor via wired connection and does not consider wireless remote data collection and detection, thus lacking specificity for pile foundation monitoring. Therefore, none of the above patents can effectively monitor steel reinforcing bars in pile foundations and all have certain limitations.

[0005] In actual foundation engineering, there is still no testing device or method to accurately determine the quality of steel reinforcement in such pile foundations. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, the present invention aims to provide a magnetic suction testing device and its testing method suitable for pile foundation quality testing. The testing method is highly stable, easy to operate, and can monitor steel corrosion of longitudinal reinforcement and stirrups in pile foundations, enabling both in-situ and dynamic movement testing.

[0007] This invention provides the following technical solution: a magnetic attraction testing device suitable for pile foundation quality inspection, comprising a testing system and a data processing system. The testing system includes a split-structure 3-shaped magnetic core, a permanent magnet, at least one Hall sensor, and a signal acquisition module. The permanent magnet is fixed to one end of the magnetic core to provide magnetic attraction, causing the device to adhere to the pile foundation surface and establish a magnetic circuit passing through the reinforcing steel bars inside the pile. The Hall sensor is disposed on the magnetic core to detect changes in the magnetic flux of the magnetic circuit. The signal acquisition module is electrically connected to the Hall sensor to acquire the sensor's signal. The split structures of the magnetic core are connected by a telescopic module, which drives the testing system to move relative to the pile foundation surface to adjust the monitoring range. The data processing system is communicatively connected to the signal acquisition module to receive and process the signals sent by the signal acquisition module to evaluate the corrosion status of the reinforcing steel bars.

[0008] Furthermore, the telescopic module includes a cylindrical outer shell, with a sleeve slidably disposed at one end of the cylindrical outer shell. An inner rod and a telescopic mechanism are disposed inside the sleeve. One end of the inner rod is fixedly connected to the sleeve, and the other end is fixedly connected to one end of the telescopic mechanism. The other end of the telescopic mechanism is connected to the cylindrical outer shell through an end cap. The sleeve is separately connected to one side of the magnetic core, and the end cap is separately connected to the other side of the magnetic core. The sleeve and the inner rod are made of ferromagnetic material.

[0009] Furthermore, the number of Hall sensors is two, and the two Hall sensors are symmetrically arranged along the center line of the magnetic core.

[0010] Furthermore, the testing system also includes a housing, in which the magnetic core, permanent magnet and Hall sensor are housed; the housing is made of non-magnetic insulating material.

[0011] Furthermore, the bottom of the encapsulation shell is provided with a bayonet structure for fitting the surface of the pile foundation; the bayonet structure is an arc-shaped bayonet for fitting the pipe pile or a trapezoidal bayonet for fitting the square pile.

[0012] Furthermore, the encapsulation shell is provided with fixing holes, which are equipped with brass fasteners for auxiliary fixing between the device and the pile foundation surface.

[0013] Furthermore, the data processing system includes a signal processor and a central controller. The signal acquisition module communicates wirelessly with the signal processor via a wireless transmission module, and the signal processor is electrically connected to the central controller.

[0014] A detection method using a magnetic suction testing device suitable for pile foundation quality testing as described in any one of claims 1-7, comprising the following steps: S1. Attach the testing device to the surface of the pile foundation, so that the magnetic path of the magnetic core is parallel to the direction of the longitudinal reinforcement or stirrups in the pile to be tested. S2. Adjust the monitoring range of the testing device using the telescopic module; S3. Establish a magnetic circuit passing through the reinforcing steel bars inside the pile using a permanent magnet; S5. Detect the change signal of magnetic flux in the magnetic circuit caused by steel corrosion using a Hall sensor; S6. Acquire the magnetic flux change signal of the magnetic circuit in S5 through the signal acquisition module and send it to the data processing system; process the signal through the data processing system to evaluate the degree of corrosion of the steel reinforcement.

[0015] By employing the above-described technology, the beneficial effects of the present invention compared to the prior art are as follows: 1) The testing device of the present invention can be attached to the surface of the pile body by strong magnetic attraction, without causing any damage to the pile foundation, thus achieving non-destructive testing; 2) This invention is based on the physical principle of changes in magnetic permeability caused by steel corrosion. Through calibration, a quantitative relationship between magnetic signals and the degree of corrosion can be established, and the evaluation results are accurate and reliable. 3) In this invention, the design based on the telescopic module enables the device to move along the pile body, expanding the coverage of single-point monitoring and improving detection efficiency; 4) The device design of this invention takes into account the monitoring of longitudinal reinforcement and stirrups in the pile. The shell bayonet design allows the testing device to fit pipe piles and square piles, making it highly targeted in the field of pile foundation testing. 5) The testing device of this invention integrates wireless transmission function, and data can be remotely sent to the monitoring center, which facilitates long-term, dynamic and automated monitoring. Attached Figure Description

[0016] Figure 1 This is a left-view structural schematic diagram of the testing system of the present invention applied to the quality testing of longitudinal reinforcement in pile foundations; Figure 2 This is a top view schematic diagram of the test system of the present invention applied to the quality testing of longitudinal reinforcement in pile foundations; Figure 3 This is a top view schematic diagram of the test system of the present invention applied to the quality testing of pile foundation stirrups.

[0017] Figure 4This is a schematic diagram of the magnetic core structure of the present invention; Figure 5 This is a three-dimensional structural schematic diagram of the telescopic module of the present invention; Figure 6 This is an exploded view of the telescopic module of the present invention.

[0018] The attached diagram is labeled as follows: 1. Hall sensor; 2. Encapsulation shell; 3. Magnetic core; 4. Permanent magnet; 5. Signal acquisition module; 6. Longitudinal reinforcement to be measured inside the pile; 7. Stirrup to be measured inside the pile; 8. Pile body concrete; 9. Pile body concrete protective layer; 10. Wireless transmission module; 11. Signal indicator light; 12. Signal processor; 13. Central controller; 14. Telescopic module; 14-1. Fixed end cap; 14-2. Sleeve; 14-3. Inner rod; 14-4. Telescopic spring. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] Conversely, this invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined in the claims. Furthermore, to provide a better understanding of the invention, certain specific details are described in detail below. However, those skilled in the art will fully understand the invention even without these detailed descriptions. Example

[0021] Device structure as follows Figure 1 , Figure 2 , Figure 4 , Figure 5 and Figure 6 As shown, the magnetic testing device in this embodiment mainly consists of a testing system, a telescopic module 14, and a data processing system.

[0022] The testing system includes a "3"-shaped magnetic core 3 made of a high-permeability iron-cobalt-vanadium alloy. A neodymium iron-boron permanent magnet 4 is fixed to one end of the magnetic core 3, and two high-sensitivity Hall sensors 1 (i.e., the first Hall sensor and the second Hall sensor) are symmetrically mounted on the magnetic core 3; the parts of the magnetic core 3 are connected by a telescopic module 14.

[0023] The permanent magnet 4 is used to provide a stable bias magnetic field and generate sufficient magnetic attraction force so that the entire device can be firmly attached to the surface of the pile concrete 8.

[0024] In this embodiment, two Hall sensors 1 (i.e., the first Hall sensor and the second Hall sensor) are symmetrically installed on both sides of the magnetic core 3 to detect changes in magnetic flux in the magnetic circuit flowing through the magnetic core and the reinforcing bar.

[0025] The entire magnetic core, permanent magnet, and sensor assembly are encapsulated within a housing 2 made of engineering plastic. The housing 2 is made of non-magnetic, insulating engineering plastic to protect the internal core, permanent magnet, and Hall sensor, and also provides insulation and moisture protection. The housing 2 has a first and a second fixing hole, which can be secured using matching brass screws and nuts. The brass material avoids interference with the measured magnetic field. The housing 2 employs two types of adapter bayonets: an arc-shaped bayonet is used for monitoring pipe piles, while a trapezoidal bayonet is used for monitoring square piles, ensuring a tight fit between the testing device and the pile surface, thus improving the accuracy and reliability of the monitoring data.

[0026] The signal acquisition module 5 is integrated inside or connected to the housing 2. Its input terminal is electrically connected to the signal output terminals of two Hall sensors for acquiring sensor signals. This module has signal conditioning (such as amplification and filtering), analog-to-digital conversion functions, and integrates a wireless transmission unit (such as a 4G / 5G, LoRa, or Wi-Fi module), which can wirelessly transmit the acquired data to a remote data processing center.

[0027] The telescopic module 14 includes a cylindrical outer shell. A sleeve 14-2 is slidably disposed at one end of the cylindrical outer shell. An inner rod 14-3 and a telescopic mechanism 14-4 are disposed inside the sleeve 14-2. One end of the inner rod 14-3 is fixedly connected to the sleeve 14-2 (by means of end cap snapping, welding, thread fastening, etc.), and the other end is fixedly connected to one end of the telescopic mechanism 14-4. The other end of the telescopic mechanism 14-4 is connected to the cylindrical outer shell through an end cap 14-1. The sleeve 14-2 is separately connected to one side of the magnetic core 3, and the end cap 14-1 is separately connected to the other side of the magnetic core 3. The sleeve 14-2 is made of a ferromagnetic metal tube, and the inner rod 14-3 is a solid ferromagnetic metal rod. The telescopic mechanism 14-4 uses a telescopic spring 14-4 to achieve bidirectional movement. The end of the telescopic spring is equipped with an end cap 14-1, which has a corresponding snapping structure. All components must be rust-proofed to avoid affecting the magnetic permeability. The telescopic module 14 allows the testing device to flexibly adjust the monitoring range, thereby effectively covering the reinforcing bars in different areas of the pile.

[0028] The data processing system can be located remotely and includes a signal processor 12 and a central controller 13 (such as a computer or cloud server). The signal acquisition module 5 sends data to the signal processor 12 via a wireless network. The signal processor 12 further analyzes and processes the data (such as calculating the change in magnetic induction intensity and its corresponding degree of corrosion). The processing results are finally transmitted to the central controller 13 for display, storage, early warning, or decision support. Signal indicator lights 11 can be installed on the signal acquisition module 5 to indicate the working status of the module and sensors (such as whether the power supply, signal acquisition, and communication are normal).

[0029] Example 2: Corrosion Monitoring of Longitudinal Reinforcing Bars in Pile Foundations S1. Installation: The testing device is directly attached to the pile surface using magnetic attraction, ensuring that the bottom of the device (the open end of the magnetic core 3) is directly facing and in close contact with the pile surface outside the concrete protective layer 9, and that its magnetic path is parallel to the axis of the longitudinal reinforcement 6 to be tested inside the pile. For more secure fixing, brass screws can be used to pass through the fixing holes in the outer casing for auxiliary mechanical fixation. After determining the monitoring range, the telescopic spring 14-4 in the telescopic module 14 extends outward from the sleeve under driving force, thereby extending the length of the entire testing device. End caps are used for fixation, expanding the monitoring range to cover a larger area of ​​steel reinforcement corrosion within the pile body.

[0030] S2. Measurement: The magnetic field generated by the permanent magnet 4 forms a loop through the "3"-shaped magnetic core 3. This loop passes through the concrete protective layer 9 and couples to the longitudinal reinforcement 6 to be measured inside the pile. When the reinforcement corrodes, the permeability of the corrosion products changes, which in turn causes a change in the magnetic induction intensity throughout the magnetic loop. Two symmetrically arranged Hall sensors 1 detect this change and transmit the signal to the signal acquisition module 5.

[0031] S3. Data Processing and Corrosion Assessment: The signal acquisition module 5 wirelessly transmits the signal to the data processing system. By analyzing changes in the magnetic flux signal, the system can quantitatively assess the degree of corrosion of the reinforcing steel. Simultaneously, by comparing the readings of two symmetrically arranged Hall sensors 1, the system can determine the non-uniformity of corrosion along the circumference or both sides of the reinforcing steel.

[0032] Example 3: Monitoring Corrosion of Pile Foundation Stirrups S1. Installation: Determine the monitoring range and adopt the following methods... Figure 3 As shown, the testing device is placed horizontally so that its magnetic path is parallel to the direction of the stirrup 7 to be tested inside the pile, and is then attached and fixed to the corresponding position on the pile foundation surface.

[0033] S2. Measurement and Evaluation: Its working principle is similar to that of longitudinal reinforcement monitoring. The magnetic field circuit is mainly coupled with the stirrups, and the Hall sensor detects the change in magnetic induction intensity caused by stirrup corrosion, thereby realizing the monitoring of the stirrup corrosion status.

[0034] Example 4: Indoor Calibration Test for Steel Corrosion Rate Based on Changes in Magnetic Induction Intensity I. Purpose of the calibration test: This experiment aims to simulate different corrosion states of longitudinal reinforcement in pile foundations through a controlled, accelerated indoor corrosion process, and to measure these states using the aforementioned magnetic suction testing device. The ultimate goal is to establish a reliable mathematical model (calibration curve) to clarify the quantitative relationship between the corrosion rate (η) of the reinforcement and the change in magnetic induction intensity (ΔB) measured by the testing device, providing a scientific basis for the non-destructive and quantitative assessment of reinforcement corrosion in on-site pile foundations.

[0035] II. Experimental Materials and Equipment: 1) Specimen: Prepare 10 sets (or more to increase data reliability) of precast concrete pile specimens.

[0036] Each specimen has longitudinal steel bars of a specified material and diameter pre-embedded around its perimeter to simulate the longitudinal reinforcement of a pile foundation.

[0037] Strictly control the concrete mix proportions and protective layer thickness (e.g., 40mm) to ensure consistency of all specimens and eliminate the influence of other variables.

[0038] 2) Testing apparatus: The magnetic testing device includes: a "3"-shaped iron-cobalt-vanadium alloy magnetic core, a permanent magnet, two symmetrically arranged Hall sensors, a packaged housing, and an integrated signal acquisition and wireless transmission module.

[0039] 3) Auxiliary and calibration equipment: Electrochemical accelerated corrosion system: DC regulated power supply, electrolytic cell (can be replaced by brine soaking), wires, sodium salt solution.

[0040] Precision electronic balance: measuring range ≥1000g, accuracy 0.01g, used to accurately weigh the initial and post-corrosion mass of steel bars, which is the benchmark for calculating the true corrosion rate.

[0041] Data acquisition system: Used to receive and record magnetic induction intensity signals from the test device.

[0042] Vernier calipers: used for precise control of the placement of devices.

[0043] III. Experimental Procedure: Step 1: Initial State Reference Measurement All concrete specimens with embedded steel bars were numbered (1# to 10#).

[0044] Using a magnetic testing device, the magnetic circuit is attached to the surface of each specimen in a uniform position and orientation (the magnetic circuit is parallel to the reinforcing bar).

[0045] Record the initial magnetic flux density values ​​B10 and B20 output by the two Hall sensors at this time. Calculate the initial average magnetic flux density B0 = (B10 + B20) / 2. This value is the "health baseline value" for the specimen.

[0046] Step 2: Accelerated Corrosion Grading and Process Measurement Develop a corrosion plan: Design different target corrosion rates for 10 specimens (e.g., 0%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 25%).

[0047] Accelerated corrosion: Electrochemical methods or brine immersion methods were used to grade and accelerate corrosion of the specimens (except for #1, which served as a blank control). The degree of corrosion was roughly controlled by adjusting the energizing time or the brine concentration / time.

[0048] Process monitoring: During the corrosion process, the testing device is periodically reinstalled to the initial measurement position, and the magnetic induction intensity value Bi (i is the number of measurements) of each specimen at different corrosion stages is measured and recorded.

[0049] Step 3: Final Value Measurement and Rebar Removal Once a specimen is deemed to have reached the target level of corrosion, the final magnetic induction intensity Bf is measured.

[0050] Subsequently, the concrete specimen was broken, and the internal reinforcing steel was removed.

[0051] In accordance with the "Technical Standard for Testing Building Structures" (GB / T 50344) and other relevant standards, the extracted reinforcing bars were treated as follows: Remove all rust products by soaking in hydrochloric acid solution. Rinse with water and neutralize with sodium hydroxide solution. Dry to constant weight. Weigh the rusted material using a precision electronic balance.

[0052] Step 4: Data processing and relationship establishment.

[0053] Calculate the actual corrosion rate η: η = m0 - ms / m0 x 100%; Calculate the change in magnetic flux density ΔB: ΔB = B0 − Bf; Where B0 is the initial magnetic flux density, and Bf is the final magnetic flux density after corrosion. As the steel bar corrodes (the magnetic permeability decreases), the magnetic reluctance of the magnetic circuit increases, and the value of Bf measured by the Hall sensor decreases. Therefore, ΔB is a positive value and increases with the intensification of corrosion.

[0054] Plot the calibration curve and fit the model: With the change in magnetic induction intensity ΔB as the abscissa and the actual corrosion rate η as the ordinate, the data points (ΔB, η) of all specimens were plotted on a scatter plot.

[0055] Regression analysis was performed on the data points to fit the optimal curve. Based on electromagnetic principles and previous research, this relationship is typically linear, so a linear relationship fitting was performed.

[0056] Example mathematical model: η = α*ΔB; Where α is the fitting parameter determined through linear regression analysis.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A magnetic suction testing device suitable for pile foundation quality inspection, characterized in that, The test system includes a test system and a data processing system. The test system includes a 3-shaped magnetic core (3) with a split structure, a permanent magnet (4), at least one Hall sensor (1), and a signal acquisition module (5). The permanent magnet (4) is fixed to one end of the magnetic core (3) to provide magnetic attraction so that the device is attracted to the surface of the pile foundation and establishes a magnetic circuit through the steel reinforcement inside the pile. The Hall sensor (1) is set on the magnetic core (3) to detect the change in magnetic flux of the magnetic circuit. The signal acquisition module (5) is electrically connected to the Hall sensor (1) to acquire the sensor signal. The split structures of the magnetic core (3) are connected to each other through a telescopic module (14), which is used to drive the test system to move relative to the pile foundation surface to adjust the monitoring range. The data processing system is communicatively connected to the signal acquisition module (5) to receive and process the signal sent by the signal acquisition module (5) to evaluate the corrosion status of the steel reinforcement.

2. The magnetic suction testing device for pile foundation quality testing according to claim 1, characterized in that, The telescopic module (14) includes a cylindrical shell, with a sleeve (14-2) slidably disposed at one end of the cylindrical shell. An inner rod (14-3) and a telescopic mechanism (14-4) are disposed inside the sleeve (14-2). One end of the inner rod (14-3) is fixedly connected to the sleeve (14-2), and the other end is fixedly connected to one end of the telescopic mechanism (14-4). The other end of the telescopic mechanism (14-4) is connected to the cylindrical shell through an end cap (14-1). The sleeve (14-2) is separately connected to one side of the magnetic core (3), and the end cap (14-1) is separately connected to the other side of the magnetic core (3). The sleeve (14-2) and the inner rod (14-3) are made of ferromagnetic material.

3. The magnetic suction testing device for pile foundation quality testing according to claim 1, characterized in that, The number of Hall sensors (1) is two, and the two Hall sensors (1) are arranged symmetrically along the center line of the magnetic core (3).

4. A magnetic suction testing device suitable for pile foundation quality testing according to claim 1, characterized in that, The test system also includes a package shell (2), in which the magnetic core (3), permanent magnet (4) and Hall sensor (1) are housed; the package shell (2) is made of non-magnetic insulating material.

5. A magnetic suction testing device for pile foundation quality testing according to claim 4, characterized in that, The bottom of the encapsulation shell (2) is provided with a bayonet structure for fitting the surface of the pile foundation; the bayonet structure is an arc-shaped bayonet for fitting the pipe pile or a trapezoidal bayonet for fitting the square pile.

6. A magnetic suction testing device suitable for pile foundation quality testing according to claim 4, characterized in that, The encapsulation shell (2) is provided with fixing holes, and the fixing holes are equipped with brass fasteners for auxiliary fixing between the device and the pile foundation surface.

7. A magnetic suction testing device suitable for pile foundation quality testing according to claim 1, characterized in that, The data processing system includes a signal processor (12) and a central controller (13). The signal acquisition module (5) communicates wirelessly with the signal processor (12) through the wireless transmission module (10), and the signal processor (12) is electrically connected to the central controller (13).

8. A testing method using a magnetic suction testing device suitable for pile foundation quality testing as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Attach the testing device to the surface of the pile foundation so that the magnetic path of the magnetic core (3) is parallel to the direction of the longitudinal reinforcement (6) or stirrup (7) in the pile to be tested. S2. Adjust the monitoring range of the test device using the telescopic module (14); S3. Establish a magnetic circuit through the reinforcing steel bars inside the pile using a permanent magnet (4); S5. The change signal of magnetic flux in the magnetic circuit caused by steel corrosion is detected by Hall sensor (1); S6. The magnetic flux change signal of the magnetic circuit in S5 is acquired by the signal acquisition module (5) and sent to the data processing system; the signal is processed by the data processing system to evaluate the degree of corrosion of the steel bars.

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