An ultrasonic guided wave-based quantitative detection method for BFRP anchor rod anchoring defects

Abstract

The present application relates to the technical field of nondestructive testing of anchoring structure in geotechnical engineering, and discloses a BFRP anchor rod anchoring defect quantitative detection method based on ultrasonic guided waves, a plurality of BFRP anchor rod anchoring models with different anchoring conditions are prepared, the anchoring models include a defect-free anchoring model and a defective anchoring model; an ultrasonic guided wave detection system is used to respectively emit ultrasonic guided wave excitation signals to each anchoring model and receive returned ultrasonic guided wave receiving signals; guided wave attenuation values of each anchoring model are extracted according to the excitation signals and the receiving signals; the attenuation difference ratio of the defective anchoring model relative to the defect-free anchoring model is calculated; the attenuation difference ratio is fitted with the corresponding defect position and defect degree to establish a quantitative function relationship; for a BFRP anchor rod to be detected, the attenuation difference ratio is obtained according to the same method and substituted into the quantitative function relationship, and the anchoring defect position and degree are calculated. Nondestructive and accurate quantitative detection of BFRP anchor rod anchoring defects is realized.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing technology for anchorage structures in geotechnical engineering, and in particular to a quantitative detection method for BFRP anchorage defects based on ultrasonic guided waves. Background Technology

[0002] Traditional steel anchor bolts have poor corrosion resistance in humid environments and groundwater erosion, leading to an increasing number of engineering failures caused by corrosion each year. In contrast, BFRP (basalt fiber reinforced polymer) anchor bolts, due to their lightweight, high strength, and superior corrosion resistance, are increasingly being used in geotechnical anchoring projects. Currently, commonly used anchor bolt quality testing methods in engineering mainly include pull-out testing and core sampling. While these two methods provide relatively reliable test data, they are both destructive tests that can damage the anchoring structure, resulting in high testing costs, low efficiency, and the inability to conduct large-scale surveys and non-destructive retesting of in-service anchor bolts.

[0003] To address the aforementioned issues, ultrasonic guided wave-based non-destructive testing technology has been increasingly adopted in evaluating anchor bolt anchorage quality due to its advantages such as high sensitivity, long-distance propagation, and non-destructive nature. This technology determines the anchorage status by analyzing the propagation and reflection characteristics of guided waves within the anchorage structure. It does not require damage to the anchorage system, offering high testing efficiency and low cost, and can meet the practical needs of periodic testing of in-service anchor bolts.

[0004] However, existing ultrasonic guided wave testing technologies are mostly developed for isotropic steel anchors. The guided wave propagation model and attenuation law are not applicable to anisotropic BFRP anchors. Furthermore, the elastic modulus of BFRP anchors is much lower than that of steel, making guided wave velocity, attenuation, and mode transitions more complex. In addition, most existing methods focus on qualitative identification or location of defects, making it difficult to establish a quantitative relationship between guided wave attenuation characteristics and defect location and severity, thus failing to meet the actual needs of engineering projects for accurate assessment of anchorage defect severity. Summary of the Invention

[0005] The purpose of this invention is to provide a quantitative detection method for BFRP anchor bolt anchorage defects based on ultrasonic guided waves, which solves the problem that existing ultrasonic guided wave detection technology is difficult to establish a quantitative relationship between guided wave attenuation characteristics and the location and degree of BFRP anchor bolt anchorage defects.

[0006] To achieve the above objectives, this invention provides a quantitative detection method for BFRP anchor bolt anchorage defects based on ultrasonic guided waves, comprising the following steps: Various BFRP anchor bolt anchorage models with different anchorage conditions were prepared. The anchorage models included a defect-free anchorage model and a defective anchorage model with different locations and degrees of anchorage defects. An ultrasonic guided wave detection system is used to transmit ultrasonic guided wave excitation signals to each anchoring model and to receive ultrasonic guided wave reception signals that have been propagated through each anchoring model. Based on the excitation and reception signals corresponding to each anchoring model, the guided wave attenuation value of each anchoring model is extracted; Calculate the ratio of the waveguide attenuation difference between the defective anchorage model and the defect-free anchorage model. The attenuation difference ratio of each defective anchoring model is fitted with the corresponding defect location and defect degree to establish a quantitative functional relationship between the attenuation difference ratio and the defect location and defect degree. For the BFRP anchor bolt to be tested, the ultrasonic guided wave excitation signal and the received signal are obtained in the same way, and the attenuation difference ratio is calculated. The calculated attenuation difference ratio is substituted into the quantitative function relationship to calculate the location and degree of anchorage defect of the BFRP anchor bolt to be tested.

[0007] In the process of preparing the defective anchoring model, a de-anchoring defect is set at the interface between the anchor rod and the grouting body or at the interface between the grouting body and the soil.

[0008] Wherein, the waveguide attenuation value is the ratio of the amplitude of the received signal to the amplitude of the excitation signal.

[0009] Specifically, before extracting the waveguide attenuation values ​​for each anchoring model, the process includes: The ultrasonic guided wave received signal is first processed using an adaptive noise complete set empirical mode decomposition method. The arrival time of the defect reflection wave is obtained based on the peak value of the intrinsic mode function obtained after decomposition, and the preliminary location of the anchoring defect is determined using the arrival time.

[0010] The process, after calculating the location and severity of the anchorage defect in the BFRP anchor bolt to be inspected, specifically includes: The anchorage quality of the BFRP anchor rod under test is graded and evaluated according to the degree of anchorage defect: when the degree of anchorage defect is lower than the first threshold, the anchorage quality is judged to be excellent; when the degree of anchorage defect is between the first threshold and the second threshold, the anchorage quality is judged to be qualified; and when the degree of anchorage defect is higher than the second threshold, the anchorage quality is judged to be unqualified.

[0011] The ultrasonic guided wave excitation signal is a sinusoidal signal modulated by a Hanning window.

[0012] The degree of defect is defined as the ratio of the defect length to the anchorage length.

[0013] The BFRP anchor bolt anchoring model with various anchoring conditions includes combinations of different anchor bolt diameters and different anchoring lengths.

[0014] This invention discloses a quantitative detection method for BFRP anchor bolt anchoring defects based on ultrasonic guided waves. The method involves pre-preparing multiple BFRP anchor bolt anchoring models, including a defect-free model and defective models with anchoring defects at different locations and degrees. Ultrasonic guided wave signals are emitted and received to each model to extract guided wave attenuation values. The attenuation difference ratio between the defective and defect-free models is then calculated, and this ratio is fitted with the corresponding defect location and degree to establish a quantitative functional relationship. During actual detection, guided wave signals are acquired in the same manner for the BFRP anchor bolt to be tested, and the attenuation difference ratio is calculated. This value is then substituted into the quantitative functional relationship to calculate the location and degree of the anchoring defect. This method effectively solves the problem in existing technologies where it is difficult to establish a quantitative relationship between guided wave attenuation characteristics and anchoring defects in anisotropic BFRP materials. It achieves non-destructive and accurate quantitative assessment of the location and degree of anchoring defects, significantly improving detection efficiency and reliability. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0016] Figure 1 This is a flowchart of the steps of the quantitative detection method for BFRP anchor bolt anchorage defects based on ultrasonic guided waves according to the present invention. Detailed Implementation

[0017] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0018] Please refer to Figure 1 This invention provides a quantitative detection method for BFRP anchor bolt anchorage defects based on ultrasonic guided waves, comprising the following steps: S101: Prepare BFRP anchor bolt anchoring models with different anchoring conditions. The anchoring models include defect-free anchoring models and defective anchoring models with different locations and degrees of anchorage defects. Specifically, firstly, various BFRP anchor bolt anchoring models with different anchoring conditions are prepared. These anchoring models include defect-free anchoring models and defective anchoring models with different locations and degrees of anchorage defects. When preparing the defective anchoring model, the anchorage defects are placed at the first interface where the anchor bolt contacts the grout, or at the second interface where the grout contacts the surrounding soil and rock. Multiple gradients are set for defect locations along the anchoring depth direction; for example, anchorage defects can be placed at distances of 0.5m, 1.0m, 1.5m, 2.0m, and 2.5m from the anchor bolt end. Multiple gradients are also set for defect degrees, which are the proportions of the defect length to the anchoring length; for example, gradients can be set for defect lengths of 5%, 10%, 20%, 30%, 40%, and 50% of the anchoring length. At least five anchoring models are required to cover combinations of different anchor bolt diameters and anchoring lengths. For example, anchor bolt diameters can be selected as 16mm, 20mm, 25mm, and 32mm, and anchoring lengths can be selected as 2.0m, 2.5m, 3.0m, 3.5m, and 4.0m. When preparing the models, the borehole diameter is determined based on the anchor bolt diameter, typically 3 to 4 times the anchor bolt diameter. The borehole inclination angle is set according to the actual project requirements, generally around 15°. After inserting the BFRP anchor bolt into the borehole, full-length grouting is performed using a bottom-groove grouting method. The grouting material is ordinary Portland cement with a grade of 42.5R, and the water-cement ratio is controlled between 0.45 and 0.5. After grouting, curing is required for at least 28 days to allow the grout to reach its design strength.

[0019] S102: An ultrasonic guided wave detection system is used to transmit ultrasonic guided wave excitation signals to each anchoring model and to receive ultrasonic guided wave reception signals that have been propagated through each anchoring model. Specifically, after the anchoring models are prepared and cured to the specified age, an ultrasonic guided wave testing system is used to transmit ultrasonic guided wave excitation signals to each anchoring model and receive the ultrasonic guided wave reception signals returned after propagation through each anchoring model. The ultrasonic guided wave excitation signal is a sinusoidal signal modulated by a Hanning window. The sinusoidal signal modulated by a Hanning window has good narrowband characteristics, which can effectively suppress sidelobe leakage in the signal spectrum, concentrating the energy of the excitation signal near the center frequency, thereby improving the signal-to-noise ratio and resolution of the guided wave detection. The frequency range of the excitation signal can be selected according to the diameter and anchoring length of the BFRP anchor, typically from 20kHz to 100kHz. During testing, the ultrasonic guided wave transducer is installed at the exposed end of the BFRP anchor, and a coupling agent is applied between the transducer and the anchor end face to ensure good acoustic coupling. The ultrasonic guided wave testing system adopts a self-transmitting and self-receiving working mode, that is, the same transducer sequentially completes the transmission of the excitation signal and the acquisition of the received signal. The excitation signal is converted into an ultrasonic guided wave by the transducer and then propagates along the anchor rod axis. When the guided wave encounters the anchoring interface or defect location during propagation, it will be reflected, transmitted and scattered. The echo signal carrying the anchoring structure status information returns along the anchor rod and is received by the same transducer and converted into an electrical signal, which is then collected and stored by the detection system.

[0020] S103: Extract the waveguide attenuation value of each anchoring model based on the excitation and reception signals corresponding to each anchoring model; Specifically, after obtaining the excitation and reception signals, the guided wave attenuation value of each anchoring model is extracted based on the corresponding excitation and reception signals. The guided wave attenuation value is the ratio of the amplitude of the received signal to the amplitude of the excitation signal. In practice, the amplitude of the main wave packet of the guided wave is first extracted from the acquired received signal, and then this amplitude is divided by the amplitude of the excitation signal to obtain the amplitude ratio. The smaller the amplitude ratio, the greater the energy attenuation of the guided wave propagating in the anchoring structure. The amplitude ratio is a dimensionless relative value that effectively reflects the changes in the medium and interface state encountered by the guided wave along its propagation path.

[0021] Before extracting the guided wave attenuation values ​​for each anchoring model, the ultrasonic guided wave received signal can be processed using an adaptive noise-complete ensemble empirical mode decomposition method. This method decomposes the received signal into a series of intrinsic mode functions and a residual component. Based on the peak values ​​of the intrinsic mode functions obtained after decomposition, the arrival time of the defect reflection wave can be identified, and then the preliminary location of the anchoring defect can be determined using this arrival time. This preprocessing step can effectively suppress environmental noise and random interference in the received signal, improving the accuracy of subsequent attenuation feature extraction.

[0022] S104: Calculate the ratio of the attenuation difference between the waveguide attenuation value of each defective anchoring model and the waveguide attenuation value of the defect-free anchoring model. Specifically, after extracting the guided wave attenuation value of each anchoring model, the attenuation difference ratio between the guided wave attenuation value of each defective anchoring model and the guided wave attenuation value of the defect-free anchoring model is calculated. The attenuation difference ratio is calculated by subtracting the guided wave attenuation value of the defect-free anchoring model from the guided wave attenuation value of the defective anchoring model, and then dividing by the guided wave attenuation value of the defect-free anchoring model. This ratio eliminates the influence of non-defect factors such as the inherent characteristics of the BFRP anchor material, the characteristics of the grout material, the anchoring medium conditions, and the ambient temperature on guided wave attenuation, allowing the attenuation difference ratio to accurately reflect the degree of influence of the anchoring defect itself on guided wave propagation. For anchoring models with the same defect location but different defect degrees, the attenuation difference ratio increases with the increase of the defect degree; for anchoring models with the same defect degree but different defect locations, the attenuation difference ratio shows a regular change as the defect location moves further away from the anchor end.

[0023] S105: Fit the attenuation difference ratio of each defective anchoring model with the corresponding defect location and defect degree to establish a quantitative functional relationship between the attenuation difference ratio and the defect location and defect degree; Specifically, after obtaining the attenuation difference ratio of each anchoring model, the attenuation difference ratio of each defective anchoring model is fitted with the corresponding defect location and degree to establish a quantitative functional relationship between the attenuation difference ratio and the defect location and degree. During fitting, the defect location and degree are used as independent variables, and the attenuation difference ratio is used as the dependent variable. A nonlinear regression analysis method is employed to establish the mathematical function relationship. This quantitative functional relationship reflects the mapping law between the parameters (location and degree) of BFRP anchoring defects and the attenuation characteristics of ultrasonic guided waves. Since the data used for fitting comes from various anchoring models under different anchoring conditions (different anchor diameters, different anchoring lengths, different defect locations, and different defect degrees), the established quantitative functional relationship has good representativeness and universality, and can cover various anchoring conditions that may be encountered in actual engineering. This quantitative functional relationship can be stored in the database of the detection system for subsequent actual testing.

[0024] S106: For the BFRP anchor rod to be tested, the ultrasonic guided wave excitation signal and the received signal are obtained in the same way, and the attenuation difference ratio is calculated. The calculated attenuation difference ratio is substituted into the quantitative function relationship to calculate the anchorage defect location and the degree of anchorage defect of the BFRP anchor rod to be tested.

[0025] Specifically, in actual engineering testing, for the BFRP anchor bolt under test, ultrasonic guided wave excitation and reception signals are acquired using the same method as for anchorage model testing, and the attenuation difference ratio is calculated. In practice, the transducer of the ultrasonic guided wave testing system is installed at the exposed end of the BFRP anchor bolt under test. The same excitation signal parameters (including center frequency, number of periods, amplitude, etc.) as when establishing the quantitative function relationship are set. The excitation signal is emitted and the reception signal is acquired, and then the guided wave attenuation value is extracted. The attenuation value of the BFRP anchor bolt under test is subtracted from the attenuation value of the same batch of defect-free anchorage models or standard reference values, and then divided by the reference value to obtain the attenuation difference ratio of the anchor bolt under test. Substituting the calculated attenuation difference ratio into the pre-established quantitative function relationship, the location and degree of anchorage defects in the BFRP anchor bolt under test can be calculated. During the calculation, the location of the defect and the proportion of the defect length to the anchorage length are deduced based on the magnitude and direction of the attenuation difference ratio.

[0026] After calculating the location and severity of anchorage defects in the BFRP anchors to be tested, the anchorage quality can be graded based on the severity of the defects. During the grading evaluation, a first threshold and a second threshold are pre-set. When the degree of anchorage defect is below the first threshold, the anchorage quality is considered excellent, indicating that the anchorage structure is intact and its load-bearing capacity meets design requirements. When the degree of anchorage defect is between the first and second thresholds, the anchorage quality is considered acceptable, indicating that the anchorage structure has certain defects but is still within the allowable range and can be used normally. When the degree of anchorage defect is above the second threshold, the anchorage quality is considered unacceptable, indicating that the anchorage defect is relatively serious and the anchorage load-bearing capacity no longer meets design requirements, suggesting reinforcement measures or reconstruction. The specific values ​​of the first and second thresholds are determined according to the engineering safety level and design specifications. For example, for general slope engineering, the first threshold can be set to 10%, and the second threshold can be set to 30%. The grading evaluation results can serve as a quantitative basis for project acceptance, in-service anchorage safety assessment, and maintenance decisions.

[0027] This invention pre-prepares multiple BFRP anchor bolt anchoring models, including a defect-free model and defective models with varying locations and degrees of anchorage defects. Ultrasonic guided wave signals are emitted and received to each model to extract guided wave attenuation values. The attenuation difference ratio between the defective model and the defect-free model is then calculated. This ratio is fitted with the corresponding defect location and degree to establish a quantitative functional relationship. During actual testing, the attenuation difference ratio of the anchor bolt to be tested is obtained in the same way and substituted into the quantitative functional relationship to calculate the location and degree of anchorage defects. This effectively solves the problem of existing ultrasonic guided wave testing techniques struggling to establish a quantitative relationship between guided wave attenuation characteristics and anchorage defects in anisotropic BFRP materials. It achieves non-destructive, accurate, and quantitative assessment of the location and degree of anchorage defects in BFRP anchor bolts, significantly improving testing efficiency and reliability. This provides a reliable basis for evaluating the anchorage quality and optimizing the structural design of BFRP anchor bolts.

[0028] The above-disclosed embodiments are merely one or more preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art can understand that all or part of the processes for implementing the above embodiments and equivalent changes made in accordance with the claims of this application still fall within the scope of this application.

Claims

1. A quantitative detection method for BFRP anchor bolt anchorage defects based on ultrasonic guided waves, characterized in that, Includes the following steps: Various BFRP anchor bolt anchorage models with different anchorage conditions were prepared. The anchorage models included a defect-free anchorage model and a defective anchorage model with different locations and degrees of anchorage defects. An ultrasonic guided wave detection system is used to transmit ultrasonic guided wave excitation signals to each anchoring model and to receive ultrasonic guided wave reception signals that have been propagated through each anchoring model. Based on the excitation and reception signals corresponding to each anchoring model, the guided wave attenuation value of each anchoring model is extracted; Calculate the ratio of the waveguide attenuation difference between the defective anchorage model and the defect-free anchorage model. The attenuation difference ratio of each defective anchoring model is fitted with the corresponding defect location and defect degree to establish a quantitative functional relationship between the attenuation difference ratio and the defect location and defect degree. For the BFRP anchor bolt to be tested, the ultrasonic guided wave excitation signal and the received signal are obtained in the same way, and the attenuation difference ratio is calculated. The calculated attenuation difference ratio is substituted into the quantitative function relationship to calculate the location and degree of anchorage defect of the BFRP anchor bolt to be tested.

2. The quantitative detection method for BFRP anchorage defects based on ultrasonic guided waves as described in claim 1, characterized in that, When preparing the defective anchoring model, a de-anchoring defect is set at the interface between the anchor rod and the grout or at the interface between the grout and the soil.

3. The quantitative detection method for BFRP anchor bolt anchorage defects based on ultrasonic guided waves as described in claim 2, characterized in that, The waveguide attenuation value is the ratio of the amplitude of the received signal to the amplitude of the excitation signal.

4. The quantitative detection method for BFRP anchor bolt anchorage defects based on ultrasonic guided waves as described in claim 3, characterized in that, Before extracting the guided wave attenuation values ​​for each anchoring model, the specific steps include: The ultrasonic guided wave received signal is first processed using an adaptive noise complete set empirical mode decomposition method. The arrival time of the defect reflection wave is obtained based on the peak value of the intrinsic mode function obtained after decomposition, and the preliminary location of the anchoring defect is determined using the arrival time.

5. The quantitative detection method for BFRP anchor bolt anchorage defects based on ultrasonic guided waves as described in claim 4, characterized in that, After calculating the location and severity of the anchorage defects in the BFRP anchor bolt to be inspected, the specific steps include: The anchorage quality of the BFRP anchor rod under test is graded and evaluated according to the degree of anchorage defect: when the degree of anchorage defect is lower than the first threshold, the anchorage quality is judged to be excellent; when the degree of anchorage defect is between the first threshold and the second threshold, the anchorage quality is judged to be qualified; and when the degree of anchorage defect is higher than the second threshold, the anchorage quality is judged to be unqualified.

6. The quantitative detection method for BFRP anchorage defects based on ultrasonic guided waves as described in claim 5, characterized in that, The ultrasonic guided wave excitation signal is a sinusoidal signal modulated by a Hanning window.

7. The quantitative detection method for BFRP anchor bolt anchorage defects based on ultrasonic guided waves as described in claim 6, characterized in that, The degree of defect is the ratio of the defect length to the anchorage length.

8. The quantitative detection method for BFRP anchor bolt anchorage defects based on ultrasonic guided waves as described in claim 7, characterized in that, The BFRP anchor bolt anchoring models with various anchoring conditions include combinations of different anchor bolt diameters and different anchoring lengths.

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