Synchronous detection system for anchor rod axial force and anchorage segment damage based on multi-order natural frequency

Abstract

The application discloses a synchronous detection system for anchor rod axial force and anchoring section damage based on multiple order inherent frequencies, and relates to the technical field of nondestructive testing of rock-soil engineering supporting structures.The system comprises an excitation module, a vibration signal acquisition module, a signal processing and analysis module, an intelligent calibration and compensation module, and a data management and early warning module.The application realizes decoupling identification of the anchor rod axial force and anchoring section damage by using the sensitivity difference of different order inherent frequencies to the axial force and damage and combining a multiple frequency characteristic fusion technology, solves the problem that the prior art cannot quantitatively evaluate the two key parameters at the same time, eliminates the influence of system coupling effects and environmental factors by introducing an adaptive weight coefficient and a multi-factor correction algorithm, improves the reliability and environmental adaptability of the detection results, and realizes automation of the detection process and full life cycle health monitoring by integrating the intelligent calibration and compensation module and the data management and early warning module.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing technology for geotechnical engineering support structures, specifically to a synchronous detection system for anchor bolt axial force and anchorage section damage based on multiple natural frequencies. Background Technology

[0002] An anchor bolt is a rod-shaped support component that penetrates deep into the soil or rock mass. Through bonding or mechanical interlocking with the soil or rock mass, it effectively connects unstable soil or rock masses to deep, stable rock masses, actively restrains soil or rock deformation, and significantly improves the self-bearing capacity of the soil or rock mass. It is a core support method for ensuring the safety and stability of underground engineering and slope engineering. Anchor bolt axial force refers to the axial tensile force that the anchor bolt bears during its service life. It is a core parameter directly reflecting the anchor bolt support effectiveness. Insufficient axial force will lead to the failure of the support system, while excessive axial force may cause the anchor bolt to yield and fracture. The anchoring section is the part of the anchor bolt embedded in the soil or rock mass, tightly bonded to the anchoring agent and surrounding rock. It is the key area for transmitting the axial force of the anchor bolt to the surrounding rock. Bond damage, debonding, or deterioration of the anchoring section will directly weaken the anchor bolt's bearing capacity and cause structural instability. Simultaneous detection of anchor bolt axial force and anchorage section damage refers to a detection technology that simultaneously and quantitatively obtains the magnitude of anchor bolt axial force and the degree of damage to the anchorage section. It can comprehensively and accurately assess the service safety status of anchor bolts and is of irreplaceable importance for timely detection of support hazards and prevention of major engineering accidents.

[0003] Anchor bolts are widely used in various geotechnical engineering projects, including mine shafts, traffic tunnels, hydraulic tunnels, foundation pit support, slope reinforcement, and building strengthening. The quality of their support directly affects the long-term safety of the engineering structure. Currently, non-destructive testing of anchor bolts mainly employs the stress wave method and the natural frequency vibration method. The stress wave method struggles to distinguish the signal differences caused by axial force changes and anchorage damage. The natural frequency vibration method is often based on a single-order frequency, failing to fully utilize the sensitivity differences of multiple frequencies to axial force and damage. Furthermore, the theoretical model is oversimplified, neglecting system coupling effects and environmental factors. This makes it impossible to achieve decoupled identification and simultaneous quantitative assessment of axial force and anchorage damage, resulting in low reliability of the test results and failing to meet the needs of large-scale, high-precision on-site testing. Therefore, developing a synchronous detection system for anchor bolt axial force and anchorage damage based on multiple natural frequencies is of great significance. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a synchronous detection system for anchor bolt axial force and anchorage section damage based on multiple natural frequencies. It aims to reveal the interaction mechanism between the multiple natural frequencies of anchor bolts, axial force, and anchorage section damage, overcome the technical difficulty of coupled identification of axial force and anchorage section damage, realize the simultaneous quantitative identification of anchor bolt axial force and anchorage section damage based on natural frequencies, develop a rapid detection system suitable for engineering sites, and provide technical support for the comprehensive, accurate, and efficient assessment of anchor bolt service status.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a synchronous detection system for anchor bolt axial force and anchorage section damage based on multi-order natural frequencies. The system includes: an excitation module, a vibration signal acquisition module, a signal processing and analysis module, an intelligent calibration and compensation module, and a data management and early warning module. The five modules work together to form a complete closed-loop detection process from excitation generation, signal acquisition, environmental calibration, data processing to result output, which can complete non-destructive testing without damaging the anchor bolt structure. The excitation module is used to apply lateral impact excitation to the exposed end of the anchor bolt, record the excitation force time history curve and transmit it to the signal processing and analysis module; The vibration signal acquisition module is used to acquire the vibration response signal of the anchor bolt after it is excited and transmit it to the signal processing and analysis module. The intelligent calibration and compensation module is used to collect environmental parameters at the detection site and transmit them to the signal processing and analysis module; The signal processing and analysis module is used to receive the above signals and parameters, extract multi-order natural frequencies and complete corrections, calculate the comprehensive damage index of the anchorage section and the axial force of the anchor bolt, and transmit the calculation results to the data management and early warning module. The data management and early warning module is used to store the entire process detection data and output the safety status and maintenance suggestions.

[0006] Furthermore, the excitation module employs a controllable force hammer or a miniature vibrator, with a piezoelectric force sensor integrated into the striking end of the excitation module. The excitation direction is perpendicular to the anchor bolt axis. The frequency band of the excitation signal output by the excitation module covers the natural frequency range of all working orders of the anchor bolt. The force sensor uses a level triggering method to collect the force time history data of each excitation in real time. The excitation module and the vibration signal acquisition module are connected through a hardware synchronous trigger line. The time axis error between the excitation signal and the response signal does not exceed one sampling period, ensuring the time synchronization accuracy of the excitation signal and the response signal, eliminating the frequency extraction error caused by time deviation. At the same time, the controllable excitation force and frequency band ensure the consistency and repeatability of each detection.

[0007] Furthermore, the vibration signal acquisition module includes a piezoelectric accelerometer and a high-speed data acquisition instrument. The accelerometer adopts a magnetic fixing structure and is attached to the center of the exposed end of the anchor bolt. The sensitivity of the accelerometer is not less than 100mV / g, and the frequency response range covers the range of multiple natural frequencies of the anchor bolt. The high-speed data acquisition instrument adopts a 24-bit analog-to-digital converter, and the sampling frequency is not less than five times the highest value of the multiple natural frequencies. The high-speed data acquisition instrument converts the acquired analog vibration signal into a digital signal and transmits it to the signal processing and analysis module. It can accurately capture the weak high-frequency vibration response signal of the anchor bolt. The magnetic installation method does not require drilling or bonding, and the installation and disassembly are convenient, which greatly improves the efficiency of on-site testing.

[0008] Furthermore, the signal processing and analysis module performs the following operations when extracting multi-order natural frequencies: The received vibration response signal is subjected to adaptive filtering to separate the environmental noise component from the signal; An improved Hilbert-Huang transform was used to perform time-frequency decomposition on the filtered signal to obtain independent intrinsic mode functions of each order. The spectrum of each natural mode function is smoothed by using a multi-point average power spectral density estimation method. By extracting the natural frequencies of each order through peak picking, and taking the arithmetic mean of the natural frequencies obtained from multiple excitations as the final frequency extraction result, the accuracy of frequency identification in low signal-to-noise ratio environments is effectively improved, and the result deviation caused by the susceptibility of single-order frequencies to interference is avoided, providing reliable basic data for subsequent damage and axial force calculations.

[0009] Furthermore, the intelligent calibration and compensation module performs the following operations when correcting the frequency results: The system collects ambient temperature data at the detection site using a built-in temperature sensor and background vibration acceleration data at the detection site using a built-in vibration sensor. The pre-stored temperature frequency correction model and vibration disturbance compensation model were invoked. Both models were calibrated through laboratory environmental tests of the same batch of anchor bolts. The temperature correction and vibration compensation amounts under the current environment are calculated separately. The temperature correction and vibration compensation amounts are then superimposed on the original frequency extraction results to obtain the corrected multi-order natural frequencies, which are then transmitted to the signal processing and analysis module. This solves the problem of interference between temperature fluctuations and background vibrations at the engineering site and the detection results, and significantly improves the detection stability and accuracy of the system under complex working conditions.

[0010] Furthermore, the signal processing and analysis module performs the following operations when calculating the comprehensive damage index of the anchorage section: The reference frequency data of a single anchor bolt stored in the data management and early warning module is called to obtain the ratio of the reference frequencies of adjacent orders of the second order and the first order, and the third order and the second order, under the condition of being in good condition; Calculate the ratio of the current adjacent order frequencies based on the corrected current multi-order natural frequencies; Based on the anchor bolt specifications and surrounding rock conditions, the corresponding frequency damage sensitivity coefficient is selected, and the comprehensive damage index of the anchorage section is calculated using the following formula: Where DI is the comprehensive damage index of the anchorage section, W1 is the damage weighting coefficient of the ratio of the second-order frequency to the first-order frequency, W2 is the damage weighting coefficient of the ratio of the third-order frequency to the second-order frequency, and r 21 r is the ratio of the second natural frequency to the first natural frequency in the current state.210 r is the ratio of the second natural frequency to the first natural frequency under the reference state. 32 r is the ratio of the third natural frequency to the second natural frequency in the current state. 320 This represents the ratio of the third natural frequency to the second natural frequency under the reference condition. , ,S 21 S is the sensitivity coefficient for comparing the second-order and first-order frequencies to the damage in the anchorage section. 32 The sensitivity coefficient for comparing the third-order and second-order frequencies to assess anchorage section damage is obtained through indoor progressive damage tests on anchor rods from the same batch. The degree of damage to the anchorage section is determined by matching the pre-stored damage level classification standard. The damage index is constructed by fusing multiple-order frequency ratios, eliminating the influence of differences in anchor rod parameters on damage identification. The adaptive weighting coefficient can adapt to different specifications of anchor rods and surrounding rock conditions, ensuring the universality and accuracy of damage assessment.

[0011] Furthermore, the signal processing and analysis module performs axial force inversion based on the corrected first-order natural frequency, second-order natural frequency, and comprehensive damage index of the anchorage section, and calculates the current axial force of the anchor bolt using the following formula: Where N is the current axial force of the anchor bolt, α is the axial force sensitivity coefficient corresponding to the first-order frequency, γ is the axial force sensitivity coefficient corresponding to the second-order frequency, β is the damage correction coefficient, f1 is the corrected current first-order natural frequency, and f 10 f1 is the first natural frequency under the reference state, f2 is the corrected current second natural frequency, and f3 is the second natural frequency. 20 The second-order natural frequency under the baseline condition and DI are the comprehensive damage index of the anchorage section. All three coefficients were obtained through indoor graded pull-out tests of the same batch of anchor rods. For anchor rods in important engineering parts, the signal processing and analysis module uses the particle swarm optimization algorithm for multi-objective optimization inversion. The objective function is the sum of squares of the deviations between the measured frequency and the calculated frequency. The constraint condition is that the axial force is in the range of 0 to the axial force corresponding to the ultimate tensile strength of the anchor rod, and the equivalent damage value is in the range of 0 to 1. This achieves complete decoupling identification of axial force and anchorage section damage, eliminates the coupling interference between the two, and ensures the quantitative evaluation accuracy of the two key parameters. The multi-objective optimization inversion further controls the detection error within 5%, meeting the high-precision detection requirements of important engineering projects.

[0012] Furthermore, the data management and early warning module establishes a frequency fingerprint database for each anchor bolt, employing a storage architecture that combines local and cloud storage. This database stores the anchor bolt's specifications, length, strength grade design parameters, initial benchmark test data, historical test data, and evaluation results. The initial benchmark test data is collected after the anchor bolt is installed and the anchoring agent is fully cured, including multiple natural frequencies in a healthy state and the ratio of adjacent benchmark frequencies. The data management and early warning module assigns a unique digital identification code to each anchor bolt, linking all relevant data for that anchor bolt through this code. This achieves full lifecycle traceability management of the anchor bolt's service status. Local storage ensures that on-site test data is not lost, while cloud storage supports remote access and data sharing from multiple terminals.

[0013] Furthermore, the data management and early warning module performs the following operations when conducting security status assessments and issuing early warnings: The system receives data on the current axial force and the degree of damage to the anchorage section from the signal processing and analysis module, compares the current axial force with the pre-stored upper and lower warning thresholds for axial force, and determines the axial force status. The damage level of the anchorage section is matched with the pre-stored four-level damage level standard to determine the damage status. The overall safety index of the anchor bolt is calculated using the following formula: Where SI is the comprehensive safety index of the anchor bolt, k1 is the axial force deviation weighting coefficient, and k2 is the damage weighting coefficient. N is the current axial force of the anchor bolt. d Design axial force for anchor bolts, N u The ultimate tensile axial force of the anchor bolt is denoted as DI, which is the comprehensive damage index of the anchorage section. The weighting coefficient is determined through the risk level assessment of the engineering structure. The comprehensive safety level is determined based on the comprehensive safety index. Corresponding suggestions for normal monitoring, intensified monitoring, reinforcement treatment or immediate replacement maintenance are generated and output. The automatically generated graded early warning and maintenance suggestions provide a direct decision-making basis for engineering safety management, avoiding the subjectivity and lag of manual assessment.

[0014] Furthermore, the system's testing process is divided into four stages: preliminary preparation and calibration, regular routine testing, emergency rapid testing, and result output and early warning. The preliminary preparation and calibration stage collects anchor bolt design parameters, completes the calibration of the frequency-axial force damage benchmark relationship for anchor bolts in the same batch, and performs initial benchmark testing on a single anchor bolt. The regular routine testing stage involves repeated testing according to a preset cycle, with each test involving three repeated excitations. The emergency rapid testing stage extracts only the first two natural frequencies for rapid evaluation. The result output and early warning stage outputs the final test results and maintenance recommendations. This multi-stage testing process can adapt to different testing scenarios and needs. The emergency rapid testing mode can complete a preliminary safety assessment of a single anchor bolt within one minute, meeting the emergency investigation needs after a sudden disaster.

[0015] Compared with existing technologies, this synchronous detection system for anchor bolt axial force and anchorage section damage based on multi-order natural frequencies has the following advantages: This invention utilizes the differences in sensitivity of different natural frequencies to axial force and damage, combined with multi-order frequency feature fusion technology, to achieve decoupled identification of anchor bolt axial force and anchorage section damage. This solves the problem that existing technologies cannot simultaneously quantitatively assess two key parameters. By introducing adaptive weighting coefficients and multi-factor correction algorithms, the system coupling effect and the influence of environmental factors are eliminated, improving the reliability and environmental adaptability of the test results. By integrating intelligent calibration and compensation modules and data management and early warning modules, the testing process is automated and full life cycle health monitoring is achieved, improving testing efficiency and reducing testing costs. It is suitable for large-scale anchor bolt testing applications in various geotechnical engineering sites.

[0016] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0018] Figure 1 This is a schematic diagram of a system for synchronously detecting anchor bolt axial force and anchorage section damage based on multiple natural frequencies. Figure 2 This is a flowchart of a system for synchronously detecting anchor bolt axial force and anchorage section damage based on multi-order natural frequencies. Figure 3 This is a flowchart of the signal processing and analysis module extracting multiple natural frequencies. Detailed Implementation

[0019] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0020] The present invention provides a synchronous detection system for anchor bolt axial force and anchorage section damage based on multi-order natural frequencies, which consists of five core modules: excitation module, vibration signal acquisition module, signal processing and analysis module, intelligent calibration and compensation module, and data management and early warning module. Each module works in concert according to the data flow to form a complete closed-loop non-destructive testing process from excitation generation, signal acquisition, environmental calibration, data processing to result output.

[0021] The core principle of the system lies in utilizing the differences in sensitivity of different natural frequencies to anchor bolt axial force and anchorage section damage. Through multi-order frequency feature fusion technology, the system achieves decoupled identification of axial force and anchorage section damage. At the same time, it introduces adaptive weighting coefficients and multi-factor correction algorithms to eliminate the system coupling effect and interference from factors such as ambient temperature and background vibration. It integrates intelligent calibration and compensation functions as well as full life cycle data management and hierarchical early warning mechanisms to achieve automation of the detection process and continuous monitoring of the anchor bolt service status.

[0022] This system completely solves the technical challenge of existing non-destructive testing technologies for anchor bolts, which cannot simultaneously and quantitatively assess two key parameters: axial force and anchorage section damage. It significantly improves the reliability of test results and adaptability to complex engineering environments, and can be widely applied to the quality inspection and health monitoring of anchor bolt support in various geotechnical engineering projects such as mine shafts, traffic tunnels, hydraulic tunnels, foundation pit support, and slope reinforcement. A detailed description is provided below with reference to specific embodiments.

[0023] This embodiment is applied to the inspection of anchor bolts in the secondary lining of an underground traffic tunnel. The tunnel uses full-length bonded anchor bolts for active support of weak surrounding rock. The anchor bolts are arranged in a quincunx pattern along the tunnel arch, arch waist, and sidewalls. Regular inspections of the anchor bolts' service condition are required to promptly detect abnormal axial forces and potential damage to the anchoring sections, ensuring the long-term safety and stability of the tunnel structure during operation. The overall structure of the inspection system used in this embodiment is as follows: Figure 1 As shown, the complete workflow of the system is as follows: Figure 2 As shown, the testing process strictly follows the stages of preliminary preparation and calibration, on-site testing implementation, signal processing and analysis, intelligent calibration and compensation, axial force and damage decoupling calculation, and data management and safety early warning to ensure the accuracy and repeatability of the test results.

[0024] The preliminary preparation and calibration phase is the foundation of the entire testing process. Its core objective is to establish a frequency-axial force-damage benchmark relationship and an environmental correction model for anchor bolts in the same batch, while simultaneously completing initial benchmark testing for individual anchor bolts and establishing a frequency fingerprint database. The quality of work in this phase directly determines the reliability of subsequent on-site testing results.

[0025] First, engineering data collection was conducted to comprehensively obtain the design parameters and engineering geological conditions of the anchor bolts to be tested, including the bolt material, nominal diameter, effective length, strength grade, anchoring agent type, anchoring length, and key parameters such as the surrounding rock grade and rock mass integrity coefficient of the corresponding area. Based on the collected parameters, anchor bolt samples of the same batch and specifications as those on-site, along with the same type of anchoring agent, were selected. A dedicated test bench was built in a laboratory environment to simulate the anchoring conditions of the anchor bolts on-site, and a series of calibration tests were carried out.

[0026] The first calibration test was an indoor progressive damage test used to calibrate the frequency damage sensitivity coefficient. The test bench could simulate the bonding state between the anchor bolt and the surrounding rock, and could precisely control the location and degree of damage in the anchoring section. During the test, the anchor bolt sample was first installed on the test bench, ensuring that the anchoring section was completely bonded to the simulated surrounding rock. After the anchoring agent was completely cured, a transverse impact excitation was applied to the intact anchor bolt, and the multi-order natural frequencies at this time were collected as initial reference data. Subsequently, damage to the anchoring section was gradually introduced through a preset artificial damage method. After each level of damage was introduced, while keeping other conditions of the anchor bolt unchanged, the transverse impact excitation was applied again, and the multi-order natural frequency data were collected. The artificial damage was achieved by local debonding. A fixed amount of debonding area was set at different locations in the anchoring section each time to simulate the bonding failure of the anchoring agent with the bolt or surrounding rock in the engineering field. Record the ratio of the second-order natural frequency to the first-order natural frequency and the ratio of the third-order natural frequency to the second-order natural frequency for each damage level. Obtain a large number of data samples through multiple parallel experiments. Use the least squares method to fit the data samples to obtain a linear relationship curve of the frequency ratio as a function of damage level. The slope of the curve is the sensitivity coefficient of the corresponding order frequency ratio to the anchorage section damage. In the specific implementation of this embodiment, the damage weight coefficients of the second-order to first-order frequency ratio and the third-order to second-order frequency ratio are calculated through sensitivity coefficient normalization. The calculation formula is as follows: , Where W1 is the damage weighting coefficient of the ratio of the second-order frequency to the first-order frequency, W2 is the damage weighting coefficient of the ratio of the third-order frequency to the second-order frequency, and S 21 S is the sensitivity coefficient for comparing the second-order and first-order frequencies to the damage in the anchorage section. 32 This is the sensitivity coefficient for comparing the third-order and second-order frequencies to assess anchorage section damage. By calculating the adaptive weighting coefficient, the damage index can be automatically adapted to different anchor bolt specifications and surrounding rock conditions, ensuring the universality and accuracy of the damage assessment results.

[0027] The second calibration test was an indoor graded pull-out test, used to calibrate the axial force sensitivity coefficient and damage correction coefficient. During the test, an axial tensile force was first applied to an intact anchor bolt sample using a graded loading method. After each grade of tensile force was applied, the load was kept stable until the anchor bolt deformation stabilized, and then a lateral impact excitation was applied, collecting the corresponding multi-order natural frequency data. The loading process continued until the anchor bolt reached a certain multiple of the design axial force, ensuring coverage of the normal operating axial force range of the anchor bolt. Subsequently, the above graded pull-out test was repeated on anchor bolt samples with different degrees of damage, covering the entire damage range from intact to severely damaged states, recording the first and second natural frequencies under different combinations of axial force and damage degree. Multiple linear regression analysis was performed on the acquired test data, with axial force as the dependent variable and the relative change rates of the first and second natural frequencies as independent variables, introducing a damage correction term. The regression analysis yielded the axial force sensitivity coefficient corresponding to the first frequency, the axial force sensitivity coefficient corresponding to the second frequency, and the damage correction coefficient.

[0028] The third calibration test is a laboratory environmental test, used to establish a temperature-frequency correction model and a vibration disturbance compensation model. The temperature-frequency correction model is established by placing a healthy anchor bolt sample in a temperature-controlled environmental test chamber, setting different ambient temperature gradients, and maintaining each gradient for a sufficient time to allow the anchor bolt temperature to reach equilibrium with the ambient temperature. Then, a lateral impact excitation is applied, and multi-order natural frequency data are collected. The natural frequency values ​​at different temperatures are recorded, and a polynomial fitting method is used to obtain the functional relationship between frequency and temperature, which is the temperature-frequency correction model. The vibration disturbance compensation model is established by installing the anchor bolt sample on a test platform with controlled background vibration, applying sinusoidal and random background vibrations of different intensities to simulate background disturbances such as mechanical vibration and vehicle vibration at the engineering site. Under each background vibration condition, multi-order natural frequency data of the anchor bolt are collected, and a functional relationship between frequency and background vibration acceleration is fitted, which is the vibration disturbance compensation model. All the sensitivity coefficients, weighting coefficients, correction coefficients, and environmental correction model parameters obtained from the above calibration are pre-stored in the local database of the signal processing and analysis module for use during on-site testing.

[0029] After completing the laboratory calibration, the initial benchmark testing phase for individual anchor bolts begins. This initial benchmark testing is conducted immediately after the anchor bolts are installed and the anchoring agent has fully cured, at which point the anchor bolts are in an intact, unloaded, and unloaded initial state. Testing personnel test each anchor bolt in the order they were installed, first cleaning the exposed ends of the bolts to ensure the sensors can be firmly attached. The accelerometer of the vibration signal acquisition module is magnetically attached to the center of the exposed end of the anchor bolt, ensuring the sensor's sensitive direction aligns with the excitation direction. Three transverse impact excitations are applied to the exposed end of the anchor bolt using the excitation module, each excitation direction strictly perpendicular to the anchor bolt axis, with consistent excitation force to ensure the excitation signal frequency band covers the range of all working orders of the anchor bolt's natural frequencies. The excitation force time history curve and anchor bolt vibration response signal corresponding to each excitation are collected. Simultaneously, the initial ambient temperature and background vibration data of the testing site are collected through the intelligent calibration and compensation module. The collected signals undergo preliminary processing, extracting the multi-order natural frequencies in the intact state, and calculating the ratios of the second-order to the first-order and the third-order to the adjacent second-order benchmark frequencies. The data management and early warning module assigns a unique digital identification code to each anchor bolt, associating and storing the anchor bolt's design parameters, installation location, and initial baseline test data with the corresponding digital identification code to establish a frequency fingerprint database for each anchor bolt. The database employs a combined local and cloud storage architecture. The local storage stores raw test data and processing data to ensure no data loss on-site, while the cloud storage stores the final test results and evaluation reports, supporting remote access and data sharing across multiple terminals.

[0030] During the on-site inspection implementation phase, regular routine inspections are conducted according to the preset inspection cycle. For anchor bolts in important engineering components such as tunnel arches, the inspection cycle is appropriately shortened and the monitoring frequency is increased. For emergency inspections following sudden geological disasters or structural anomalies, an emergency rapid inspection mode is activated to simplify the inspection process and achieve rapid assessment of the anchor bolt condition.

[0031] Before on-site testing, the assembly and debugging of the testing equipment were completed. The excitation module and vibration signal acquisition module were connected via a hardware synchronization trigger line. After powering on the equipment, a synchronization test was performed to ensure that the time axis error between the excitation signal and the response signal did not exceed one sampling period, thus eliminating frequency extraction errors caused by time deviation. The sensitivity and frequency response range of the piezoelectric accelerometer were checked to confirm that it could cover the range of the anchor bolt's multiple natural frequencies. The working status of the high-speed data acquisition instrument was checked. The high-speed data acquisition instrument uses a 24-bit analog-to-digital converter, which can achieve high-precision analog-to-digital signal conversion. The sampling frequency was set to more than five times the highest value of the multiple natural frequencies to ensure accurate capture of the anchor bolt's weak high-frequency vibration response signal.

[0032] After equipment debugging, anchor bolts were inspected one by one according to the preset testing route. Upon reaching the anchor bolt to be tested, the inspectors cleaned the exposed end of the bolt again and firmly attached the accelerometer to the center of the exposed end to prevent signal distortion caused by sensor loosening. Then, the excitation module applied lateral impact excitation to the exposed end of the anchor bolt. The excitation module used a controllable hammer, with a piezoelectric force sensor integrated into the striking end, capable of real-time acquisition and recording of the force-time history curve for each excitation. Each test was repeated three times, with a certain time interval between each excitation to allow the free vibration of the anchor bolt to completely decay before the next excitation. During each excitation, the vibration signal acquisition module simultaneously acquired the lateral vibration response signal of the anchor bolt after excitation, and the intelligent calibration and compensation module simultaneously acquired real-time ambient temperature data and background vibration acceleration data at the testing site. All acquired data was transmitted wirelessly in real-time to the signal processing and analysis module for subsequent processing and analysis.

[0033] For emergency rapid detection following sudden disasters such as tunnel collapses and water inrushes, an emergency rapid detection mode is activated. This mode extracts only the first two natural frequencies of the anchor bolts for rapid evaluation, omitting the extraction and calculation of the third natural frequency. It also simplifies signal processing steps, significantly reducing the detection time for a single anchor bolt. The emergency rapid detection mode can complete preliminary safety checks on a large number of anchor bolts in a short time, quickly identifying anchor bolts with serious safety hazards, and providing timely data support for post-disaster rescue and structural safety assessments.

[0034] The signal processing and analysis module is the core of the entire detection system, undertaking key tasks such as signal preprocessing, extraction of multiple natural frequencies, calculation of damage indicators, and axial force inversion. The specific process for extracting multiple natural frequencies is as follows: Figure 3 As shown, the entire process begins with receiving the original vibration response signal, goes through a series of processing steps, and finally outputs accurate multi-order natural frequency data.

[0035] First, the received raw vibration response signal undergoes adaptive filtering. The engineering site contains significant environmental noise, including vibrations from construction machinery, passing vehicles, and personnel activity, which severely interfere with the actual vibration response signal of the anchor bolt. The adaptive filtering process employs a least mean square adaptive filtering algorithm. This algorithm automatically adjusts the filter coefficients based on the signal's statistical characteristics, tracks noise changes in real time, and effectively separates the environmental noise component from the anchor bolt's actual vibration response component. The signal-to-noise ratio of the filtered signal is significantly improved, laying a solid foundation for subsequent time-frequency decomposition and frequency extraction.

[0036] Subsequently, an improved Hilbert-Huang transform was used to perform time-frequency decomposition on the filtered signal. The vibration response signal of the anchor bolt is a typical non-stationary signal, and traditional Fourier transform methods are insufficient to accurately analyze the time-frequency characteristics of non-stationary signals. The improved Hilbert-Huang transform decomposes the complex non-stationary signal into multiple independent intrinsic mode functions (IMFs) through empirical mode decomposition. Each IMF has a clear physical meaning and corresponds to the first-order vibration mode of the anchor bolt. Compared with traditional empirical mode decomposition, the improved Hilbert-Huang transform effectively suppresses mode aliasing and can more accurately separate the IMFs of each order.

[0037] Next, a multi-point average power spectral density estimation method is used to smooth the spectra of each intrinsic mode function. A Fast Fourier Transform is performed on each intrinsic mode function to obtain its spectrum. Due to random fluctuations in the signal, the spectral curve will have many spikes, affecting the accuracy of peak identification. The multi-point average power spectral density estimation method eliminates random fluctuations in the spectrum by segmenting and averaging the spectrum, making the spectral curve smoother and highlighting the true frequency peaks.

[0038] Finally, the peak frequencies corresponding to each natural mode function are extracted using the peak picking method, which are the natural frequencies of the anchor bolt. The arithmetic mean of the natural frequencies obtained from three repeated excitations is taken as the final frequency extraction result. The method of averaging multiple excitations can effectively reduce the randomness error of a single excitation and further improve the reliability of the frequency extraction result.

[0039] Fluctuations in ambient temperature and background vibrations at the construction site can significantly affect the natural frequency of anchor bolts, leading to deviations in the original frequency extraction results. The intelligent calibration and compensation module introduces a multi-factor correction algorithm to correct the original frequency results for environmental factors, eliminating interference from environmental factors and improving the accuracy and stability of the detection results.

[0040] The intelligent calibration and compensation module first receives the raw multi-order natural frequency data transmitted from the signal processing and analysis module, and simultaneously receives real-time acquired ambient temperature data and background vibration acceleration data. It then calls pre-stored temperature-frequency correction and vibration disturbance compensation models. Substituting the current ambient temperature data into the temperature-frequency correction model, it calculates the temperature correction amount for the current temperature. Substituting the current background vibration acceleration data into the vibration disturbance compensation model, it calculates the vibration compensation amount for the current background vibration. The temperature correction amount and the vibration compensation amount are linearly superimposed onto the original frequency extraction result to obtain the corrected multi-order natural frequencies. The corrected multi-order natural frequencies accurately reflect the vibration characteristics of the anchor bolt itself and are unaffected by ambient temperature and background vibration. The corrected multi-order natural frequencies are transmitted to the signal processing and analysis module for subsequent calculation of the comprehensive damage index of the anchorage section and anchor bolt axial force inversion.

[0041] The core innovation of this invention is the decoupled calculation of axial force and damage. Through multi-order frequency feature fusion technology, the complete decoupled identification of anchor bolt axial force and anchorage section damage is achieved, and two key parameters are quantitatively obtained at the same time.

[0042] First, the comprehensive damage index of the anchorage section is calculated. The signal processing and analysis module calls the reference frequency data of a single anchor bolt stored in the data management and early warning module to obtain the adjacent order reference frequency ratios of the second order and the first order, and the third order and the second order, under the condition that the anchor bolt is intact. Based on the corrected current multi-order natural frequencies, the corresponding current adjacent order frequency ratios are calculated. According to the anchor bolt specifications and the corresponding surrounding rock conditions, the corresponding frequency damage sensitivity coefficient is retrieved from the pre-stored database. In the specific implementation of this embodiment, the comprehensive damage index of the anchorage section is obtained by weighted fusion calculation of multi-order frequency ratios, and the calculation formula is as follows: Where DI is the comprehensive damage index of the anchorage section, r 21 r is the ratio of the second natural frequency to the first natural frequency in the current state. 210 r is the ratio of the second natural frequency to the first natural frequency under the reference state. 32 r is the ratio of the third natural frequency to the second natural frequency in the current state. 320 This represents the ratio of the third natural frequency to the second natural frequency under the baseline condition. Using this frequency ratio to construct a damage index effectively eliminates the influence of differences in parameters such as anchor length and material on damage identification results, improving the accuracy of damage assessment. After calculating the comprehensive damage index of the anchorage section, it is matched with a pre-stored four-level damage classification standard to determine the degree of damage to the anchorage section. The four damage levels correspond to intact condition, minor damage, moderate damage, and severe damage, respectively.

[0043] After calculating the comprehensive damage index of the anchorage section, the axial force of the anchor bolt is inverted. Traditional axial force inversion methods do not consider the influence of anchorage section damage; when damage exists in the anchorage section, the axial force inversion results will show significant deviations. This invention introduces a damage correction term into the axial force inversion formula, using the comprehensive damage index of the anchorage section to correct the frequency, thus decoupling the axial force from the damage. In the specific implementation of this embodiment, the current axial force of the anchor bolt is obtained by jointly inverting the corrected first two natural frequencies with the comprehensive damage index of the anchorage section. The calculation formula is as follows: Where N is the current axial force of the anchor bolt, α is the axial force sensitivity coefficient corresponding to the first-order frequency, γ is the axial force sensitivity coefficient corresponding to the second-order frequency, β is the damage correction coefficient, f1 is the corrected current first-order natural frequency, and f 10 f1 is the first natural frequency under the reference state, f2 is the corrected current second natural frequency, and f3 is the second natural frequency. 20This is the second natural frequency under the reference condition. All three coefficients were obtained through indoor graded pull-out tests on the same batch of anchor bolts.

[0044] For anchor bolts in critical engineering components such as tunnel arches and fault fracture zones, higher detection accuracy is required. The signal processing and analysis module employs a particle swarm optimization algorithm for multi-objective optimization inversion. The objective function is the sum of squared deviations between the measured and calculated frequencies. Constraints are set such that the axial force is between 0 and the axial force corresponding to the anchor bolt's ultimate tensile strength, and the equivalent damage value is between 0 and 1. The position and velocity of the particle swarm are initialized, with each particle representing a set of axial force and damage values. The position and velocity of the particles are continuously updated through iterative optimization until the objective function reaches its minimum or the convergence condition is met. After iteration, the axial force and damage values ​​corresponding to the optimal particle are the final detection results. Multi-objective optimization inversion can further improve the detection accuracy of axial force and damage, meeting the high-precision detection requirements of critical engineering components.

[0045] The signal processing and analysis module transmits the calculated current axial force and anchorage section damage level data to the data management and early warning module. The data management and early warning module first associates the current test data with the anchor's digital identification code and stores it in a frequency fingerprint database. This database includes the original excitation force time history curve, vibration response signal, environmental parameters, corrected multi-order natural frequencies, comprehensive anchorage section damage index, anchor axial force, and safety assessment results—a complete set of data. Through the frequency fingerprint database, all historical test data for any anchor from installation to the present can be queried, enabling full lifecycle traceability management of the anchor's service status.

[0046] Simultaneously, the data management and early warning module performs anchor bolt safety status assessment and graded early warning. First, the current axial force is compared with pre-stored upper and lower axial force warning thresholds. The upper axial force warning threshold is determined based on the anchor bolt's yield strength, and the lower axial force warning threshold is determined based on the anchor bolt's minimum support axial force. If the current axial force exceeds the upper axial force limit, it indicates a risk of yield fracture in the anchor bolt; if the current axial force is below the lower axial force limit, it indicates insufficient support effectiveness of the anchor bolt. The degree of damage to the anchorage section is matched with pre-stored four-level damage standards to determine the anchor bolt's damage status. In the specific implementation of this embodiment, the comprehensive safety index of the anchor bolt is calculated by weighting the axial force deviation and the anchorage section damage index, using the following formula: Where SI is the comprehensive safety index of the anchor bolt, k1 is the axial force deviation weighting coefficient, and k2 is the damage weighting coefficient, and satisfies the following conditions: N d Design axial force for anchor bolts, N uThe ultimate tensile axial force of the anchor bolt. The axial force deviation weighting coefficient and the damage weighting coefficient are determined through the engineering structure risk level assessment. For high-risk engineering parts, the damage weighting coefficient is appropriately increased, focusing on the damage situation of the anchorage section; for axial force controlled support areas, the axial force deviation weighting coefficient is appropriately increased, focusing on the axial force state of the anchor bolt.

[0047] Based on the calculated comprehensive safety index, the overall safety level of anchor bolts is divided into four levels. For Level 1 anchor bolts with the highest comprehensive safety index, maintenance recommendations for normal monitoring are generated, and subsequent inspections are carried out according to the preset cycle. For Level 2 anchor bolts with a comprehensive safety index, maintenance recommendations for intensified monitoring are generated, the inspection cycle is shortened, and close attention is paid to the axial force and damage trends of the anchor bolts. For Level 3 anchor bolts with a comprehensive safety index, maintenance recommendations for reinforcement are generated, and measures such as anchor bolt grouting reinforcement and additional anchor bolts are taken in a timely manner to eliminate safety hazards. For Level 4 anchor bolts with the lowest comprehensive safety index, maintenance recommendations for immediate replacement are generated, and related work in the area is immediately stopped, and personnel are organized to replace the failed anchor bolts. All assessment results and maintenance recommendations are output in the form of visual reports, which include anchor bolt location information, inspection data, safety level, and maintenance recommendations, providing engineering management personnel with direct and clear decision-making basis.

[0048] In summary, this embodiment fully implements the entire process of a synchronous detection system for anchor bolt axial force and anchorage section damage based on multi-order natural frequencies. Accurate benchmark relationships and environmental correction models were established through laboratory calibration, and on-site testing achieved synchronous quantitative detection of anchor bolt axial force and anchorage section damage. The system successfully decouples the identification of axial force and anchorage section damage using multi-order frequency feature fusion technology, completely eliminating coupling interference between the two. The intelligent calibration and compensation module effectively eliminates the influence of ambient temperature and background vibration on the detection results, significantly improving the system's adaptability and stability in complex engineering sites. The data management and early warning module enables full lifecycle traceability management and automatic graded early warning of anchor bolt service status, avoiding the subjectivity and lag of manual assessment. This embodiment fully verifies the feasibility and effectiveness of the technical solution of this invention, meeting the needs of large-scale, high-precision anchor bolt detection in various geotechnical engineering sites. It has significant application value for timely detection of hidden dangers in support structures, prevention of engineering accidents, and ensuring the safety and stability of engineering structures.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A synchronous detection system for anchor bolt axial force and anchorage section damage based on multi-order natural frequencies, characterized in that, The system includes: an excitation module, a vibration signal acquisition module, a signal processing and analysis module, an intelligent calibration and compensation module, and a data management and early warning module; The excitation module is used to apply lateral impact excitation to the exposed end of the anchor bolt, record the excitation force time history curve and transmit it to the signal processing and analysis module; The vibration signal acquisition module is used to acquire the vibration response signal of the anchor bolt after it is excited and transmit it to the signal processing and analysis module. The intelligent calibration and compensation module is used to collect environmental parameters at the detection site and transmit them to the signal processing and analysis module; The signal processing and analysis module is used to receive the above signals and parameters, extract multi-order natural frequencies and complete corrections, calculate the comprehensive damage index of the anchorage section and the axial force of the anchor bolt, and transmit the calculation results to the data management and early warning module. The data management and early warning module is used to store the entire process detection data and output the safety status and maintenance suggestions.

2. The synchronous detection system for anchor bolt axial force and anchorage section damage based on multi-order natural frequencies according to claim 1, characterized in that, The excitation module uses a controllable hammer or a micro exciter. A piezoelectric force sensor is integrated into the striking end of the excitation module. The excitation direction is perpendicular to the anchor bolt axis. The frequency band of the excitation signal output by the excitation module covers the natural frequency range of all working orders of the anchor bolt. The force sensor uses a level triggering method to collect the force time history data of each excitation in real time. The excitation module and the vibration signal acquisition module are connected through a hardware synchronous trigger line. The time axis error between the excitation signal and the response signal does not exceed one sampling period.

3. The synchronous detection system for anchor bolt axial force and anchorage section damage based on multi-order natural frequencies according to claim 1, characterized in that, The vibration signal acquisition module includes a piezoelectric accelerometer and a high-speed data acquisition instrument. The accelerometer adopts a magnetic fixing structure and is attached to the center of the exposed end of the anchor rod. The high-speed data acquisition instrument adopts a 24-bit analog-to-digital converter. The high-speed data acquisition instrument converts the acquired analog vibration signal into a digital signal and transmits it to the signal processing and analysis module.

4. The synchronous detection system for anchor bolt axial force and anchorage section damage based on multi-order natural frequencies according to claim 1, characterized in that, The signal processing and analysis module performs the following operations when extracting multi-order natural frequencies: The received vibration response signal is subjected to adaptive filtering to separate the environmental noise component from the signal; An improved Hilbert-Huang transform was used to perform time-frequency decomposition on the filtered signal to obtain independent intrinsic mode functions of each order. The spectrum of each natural mode function is smoothed by using a multi-point average power spectral density estimation method. The natural frequencies of each order are extracted by peak picking method, and the arithmetic mean of the natural frequencies obtained by multiple excitations is taken as the final frequency extraction result.

5. The synchronous detection system for anchor bolt axial force and anchorage section damage based on multi-order natural frequencies according to claim 1, characterized in that, The intelligent calibration and compensation module performs the following operations when correcting frequency results: The system collects ambient temperature data at the detection site using a built-in temperature sensor and background vibration acceleration data at the detection site using a built-in vibration sensor. The pre-stored temperature frequency correction model and vibration disturbance compensation model were invoked. Both models were calibrated through laboratory environmental tests of the same batch of anchor bolts. The temperature correction and vibration compensation are calculated separately under the current environment. The temperature correction and vibration compensation are then superimposed on the original frequency extraction result to obtain the corrected multi-order natural frequencies, which are then transmitted to the signal processing and analysis module.

6. The synchronous detection system for anchor bolt axial force and anchorage section damage based on multi-order natural frequencies according to claim 1, characterized in that, The signal processing and analysis module performs the following operations when calculating the comprehensive damage index of the anchorage section: The reference frequency data of a single anchor bolt stored in the data management and early warning module is called to obtain the ratio of the reference frequencies of adjacent orders of the second order and the first order, and the third order and the second order, under the condition of being in good condition; Calculate the ratio of the current adjacent order frequencies based on the corrected current multi-order natural frequencies; Based on the anchor bolt specifications and surrounding rock conditions, the corresponding frequency damage sensitivity coefficient is selected, and the comprehensive damage index of the anchorage section is calculated using the following formula: Where DI is the comprehensive damage index of the anchorage section, W1 is the damage weighting coefficient of the ratio of the second-order frequency to the first-order frequency, W2 is the damage weighting coefficient of the ratio of the third-order frequency to the second-order frequency, and r 21 r is the ratio of the second natural frequency to the first natural frequency in the current state. 210 r is the ratio of the second natural frequency to the first natural frequency under the reference state. 32 r is the ratio of the third natural frequency to the second natural frequency in the current state. 320 Let be the ratio of the third natural frequency to the second natural frequency under the reference state. , , is the sensitivity coefficient for comparing the second-order and first-order frequencies to the damage in the anchorage section, S 32 The sensitivity coefficient for comparing the third-order and second-order frequencies to the anchorage segment damage is used to determine the degree of damage to the anchorage segment by matching it with a pre-stored damage level classification standard.

7. The synchronous detection system for anchor bolt axial force and anchorage section damage based on multi-order natural frequencies according to claim 1, characterized in that, The signal processing and analysis module performs axial force inversion based on the corrected first-order natural frequency, second-order natural frequency, and comprehensive damage index of the anchorage section, and calculates the current axial force of the anchor bolt using the following formula: Where N is the current axial force of the anchor bolt, α is the axial force sensitivity coefficient corresponding to the first-order frequency, γ is the axial force sensitivity coefficient corresponding to the second-order frequency, β is the damage correction coefficient, f1 is the corrected current first-order natural frequency, and f 10 f1 is the first natural frequency under the reference state, f2 is the corrected current second natural frequency, and f3 is the second natural frequency. 20 DI is the second natural frequency under the reference state, and DI is the comprehensive damage index of the anchorage section. For anchor bolts in important engineering parts, the signal processing and analysis module uses the particle swarm optimization algorithm to perform multi-objective optimization inversion. The objective function is the sum of squares of the deviations between the measured frequency and the calculated frequency. The constraint is that the axial force is in the range of 0 to the axial force corresponding to the ultimate tensile strength of the anchor bolt, and the equivalent damage value is in the range of 0 to 1.

8. The synchronous detection system for anchor bolt axial force and anchorage section damage based on multi-order natural frequencies according to claim 1, characterized in that, The data management and early warning module establishes a frequency fingerprint database for each anchor bolt, using a storage architecture that combines local and cloud storage. It stores the anchor bolt's specifications, length, strength grade design parameters, initial benchmark test data, previous test data, and evaluation results. The initial benchmark test data is collected after the anchor bolt is installed and the anchoring agent is fully cured. It includes the multi-order natural frequencies and the ratio of adjacent order benchmark frequencies in a good condition. The data management and early warning module assigns a unique digital identification code to each anchor bolt, and associates all relevant data of that anchor bolt through the identification code.

9. The synchronous detection system for anchor bolt axial force and anchorage section damage based on multi-order natural frequencies according to claim 1, characterized in that, The data management and early warning module performs the following operations when conducting security status assessments and early warnings: The system receives data on the current axial force and the degree of damage to the anchorage section from the signal processing and analysis module, compares the current axial force with the pre-stored upper and lower warning thresholds for axial force, and determines the axial force status. The damage level of the anchorage section is matched with the pre-stored four-level damage level standard to determine the damage status. The overall safety index of the anchor bolt is calculated using the following formula: Where SI is the comprehensive safety index of the anchor bolt, k1 is the axial force deviation weighting coefficient, and k2 is the damage weighting coefficient. N is the current axial force of the anchor bolt. d Design axial force for anchor bolts, N u DI represents the ultimate tensile axial force of the anchor bolt, and DI represents the comprehensive damage index of the anchorage section. The comprehensive safety level is determined based on the comprehensive safety index, and corresponding recommendations for normal monitoring, intensified monitoring, reinforcement treatment, or immediate replacement maintenance are generated and output.

10. The synchronous detection system for anchor bolt axial force and anchorage section damage based on multi-order natural frequencies according to claim 1, characterized in that, The system's testing process is divided into four stages: preliminary preparation and calibration, regular routine testing, emergency rapid testing, and result output and early warning. In the preliminary preparation and calibration stage, anchor bolt design parameters are collected, the frequency-axial force damage benchmark relationship of anchor bolts in the same batch is calibrated, and the initial benchmark testing of a single anchor bolt is performed. In the regular routine testing stage, repeated testing is conducted according to a preset cycle, with three repeated excitations for each test. In the emergency rapid testing stage, only the first two natural frequencies are extracted for rapid evaluation. In the result output and early warning stage, the final test results and maintenance recommendations are output.

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