Evaluation method of anchor bolt quality grade based on amplitude exponential decay algorithm

Abstract

The present invention provides an anchor bolt anchoring quality grade evaluation method based on an amplitude exponential decay algorithm. The method uses the reflection wave principle to obtain anchor bolt detection data, obtains an anchoring section waveform curve by preprocessing the reflection wave signal, and then obtains the ratio of the area of ​​the fitting curve to the waveform curve based on the characteristics of the waveform amplitude decay to determine the anchoring density range, thereby realizing the classification of the anchor bolt anchoring quality grade. The method transforms the qualitative judgment of the anchor bolt anchoring quality classification in the regulations into a quantitative calculation, eliminates the influence of subjective factors on the judgment result, has the characteristics of simple calculation, high calculation efficiency, etc., the judgment result is accurate and reliable, and has a good application effect.

Description

Technical Field

[0001] The invention belongs to the technical field of engineering non-destructive testing and relates to a method for evaluating the anchoring quality grade of an anchor rod by using the amplitude attenuation characteristics of an acoustic wave reflection signal. Background Art

[0002] Anchor support technology is widely used in various support projects. Its principle is to anchor the anchor into the surrounding rock, thereby changing the mechanical state of the surrounding rock itself, improving its circumferential compressive strength, and effectively controlling the deformation of the surrounding rock. The anchoring quality grade of the anchor is an important indicator for evaluating whether the above engineering objectives can be achieved.

[0003] In engineering applications, the acoustic wave reflection method is usually used to achieve non-destructive testing of anchor quality. The acoustic wave reflection method uses an exciting acoustic wave signal and an acceleration or velocity sensor to obtain a reflected acoustic wave signal based on wave theory. According to the provisions of the national industry standard JGJ / T182-2009 "Technical Specifications for Non-destructive Testing of Anchor Quality", the anchor density and grade of the anchor are determined. There are four types of anchor density grades: A, B, C, and D, and four levels of anchor grades: I, II, III, and IV.

[0004] The JGJ / T182-2009 specification provides qualitative evaluation criteria for anchor density, comprehensively evaluating the system based on four aspects: waveform characteristics, time-domain signal characteristics, frequency-domain signal characteristics, and density. Furthermore, each evaluation criterion is primarily qualitative, and the subjective interpretation of the personnel significantly influences the anchor bolt assessment results, increasing the randomness of the anchor bolt's anchoring quality assessment results. Therefore, reducing this randomness in anchor bolt anchoring quality assessment, achieving quantitative identification of anchor bolt anchoring quality grades through computers, and rapidly obtaining anchor density values ​​are challenges in this field. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for evaluating the anchoring quality grade based on an amplitude exponential decay algorithm.

[0006] The object of the present invention is achieved through the following technical solution: a method for evaluating the anchor bolt anchoring quality grade based on an amplitude exponential decay algorithm, comprising the following steps:

[0007] Step 1: Obtain the reflected wave curve of the anchor to be evaluated and preprocess the reflected wave curve. The length and sampling rate of the received reflected signal are determined based on factors such as rod length, rod system wave velocity, and frequency domain resolution. Preferably, preprocessing includes signal consistency verification of the anchor data, normalization of the reflected signal, and one-dimensional digital filtering of the signal. The reflected signal normalization includes normalization in both the x-direction and the y-direction.

[0008] Among them, the signal consistency test is as follows: in one acquisition, there are 6 waveform data of the same anchor rod. The consistency of the 6 acquisition data is verified through the signal consistency test, the correlation between the waveforms is calculated, and the inconsistent waveform reflection signals are eliminated.

[0009] Normalization in the x-direction can be performed using an interpolation algorithm. This involves normalizing the time coordinates of the reflected signal to the new time interval and resampling the signal based on the new normalized time interval. For ease of processing, the x-values ​​after time normalization are expressed in the new time interval units.

[0010] Normalization in the y-direction normalizes the reflected signal's y-axis to a uniform amplitude range to avoid differences in reflected signal strength due to differences in the excitation signal's strength, which can affect signal comparison. The specific method is to first determine the maximum absolute amplitude of the reflected signal on the y-axis, and then scale all amplitude values ​​proportionally based on the ratio of this maximum amplitude to the maximum value in the set interval.

[0011] One-dimensional digital filtering of the signal: using the moving mean filtering method.

[0012] Step 2: Based on the preprocessing results of the reflected wave curve, the waveform starting point is re-determined and used as the new zero point. The specific method includes: starting from the existing zero point of the preprocessed reflected wave curve, calculating the moving average of the absolute value of the waveform in the y direction and calculating the overall average of the absolute value of the waveform in the y direction. If the moving average is greater than the overall average, it is determined as the new zero point, and all data before the new zero point is cleared. Alternatively, the new zero point position can be calculated based on the previously determined exposed length.

[0013] Step 3, calculate the peak value in the y direction and the correction coefficient in the x direction. Taking into account that during the field measurement process, due to the inconsistency of the intensity and duration of the excitation signal, the main frequency and period of the reflected wave signal will be different, which is reflected in the waveform of the signal as the difference in the peak time interval. In order to facilitate subsequent calculations and comparisons, it is necessary to unify them on a benchmark for calculation: take the interval average of the first three peak and trough values ​​as the benchmark for this measurement, calculate the ratio of this value to the preset waveform transformation coefficient as the correction coefficient, and then multiply the x-coordinate of all peak data by this ratio for correction, so that the data at the subsequent peak can participate in the calculation. Preferably, the waveform transformation coefficient takes a value of 10 to 30.

[0014] Step 4: Calculate the rod bottom peak value A, discarding data after the rod bottom with the rod bottom as the boundary, and retaining the waveform data between the new zero point and the rod bottom. Calculating the rod bottom peak value includes: determining the preliminary position of the rod bottom reflection signal based on the preset rod length and exposed end length, combined with the wave velocity; comparing the position of the reflection signal with the lateral distance between the peak values ​​on the left and right sides; and selecting the peak value near the preliminary position as the rod bottom peak value. Specifically, the abscissa on the side with the smaller lateral distance is used as the abscissa of the rod bottom reflection wave.

[0015] Step 5: Determine whether the waveform of the anchor rod reflected wave is a single-peak signal and count the number of non-single-peak signals. Determining whether the waveform of the anchor rod reflected wave is a single-peak signal includes: obtaining the average value of all peak intervals, calculating and counting the ratio range of the intervals between each peak to the average value of the intervals, and determining whether the waveform is single-peaked based on the ratio range: if the ratio of each peak interval to the interval average is within a certain range, the anchor rod reflected waveform is regular and the amplitude-frequency signal is single-peaked; if the ratio of each peak interval to the interval average is not within this range, then, while ensuring that the anchor rod signal is valid, the peak at that location is counted as a non-single-peak signal waveform, indicating that the anchor rod has a defect at that location.

[0016] Step 6, calculate the highest point peak value Amax, as well as the horizontal and vertical coordinates corresponding to the other shaft peak values ​​A1 and A2 used to fit the attenuation curve. Calculating the highest point peak value Amax specifically involves taking the amplitude corresponding to the signal with the largest amplitude among all peak values ​​as the highest point peak value Amax. Calculating the horizontal and vertical coordinates corresponding to the other shaft peak values ​​A1 and A2 includes: calculating all peak values ​​based on the mathematical property that the peak value is greater than or equal to the amplitude values ​​on both sides, selecting the peak value from the attenuation range of the highest point peak value Amax as A1, selecting the peak value from the attenuation range of A1 as A2, and determining the horizontal and vertical coordinates of A1 and A2 respectively, wherein the attenuation range is 0.4 to 0.9.

[0017] Step 7: Fitting an exponential function. According to regulations, the waveform of the Class A anchor density grade has an exponential decay characteristic. The exponential decay function fitting of the reflected wave signal using the peak values ​​at the base, highest point, and shaft obtained in the above steps is used to assess whether this condition is met.

[0018] Step 8: Calculate the area S0 enclosed by the reflected wave curve and the abscissa on the coordinate axis. Since the anchor rod reflected wave curve is composed of a set of discrete data signals, it is impossible to obtain the reflected wave signal function. Therefore, calculating the area S0 enclosed by the reflected wave curve and the abscissa on the coordinate axis includes: using numerical integration to calculate the area between the reflected wave curve and the abscissa. Due to the small sampling interval of the reflected wave signal, the sum of the ordinates is used instead as the area S0 enclosed by the reflected wave signal and the abscissa.

[0019] Step 9: Calculate the area S = Σ(Yy) between the reflected wave curve and the fitted attenuation function. Using the principle of numerical integration, the area S between the reflected wave curve and the attenuation function is replaced by the sum of the difference between the reflected wave amplitude and the ordinate of the attenuation function at that point.

[0020] Step 10: Calculate the ratio β of S / S0 and the result α of 1-β. According to the range of α and the waveform characteristics, the anchor bolt anchoring quality grade is divided into categories I, II, III, and IV. According to the regulations, the anchor density can be calculated using the reflected wave energy method, and 1-β can be used to approximately replace the anchor density α. The classification of the anchor bolt anchoring quality grade according to the α value and waveform characteristics in step 10 includes:

[0021] The anchoring quality level of Class I anchor bolts is: α≥95%, the number of non-single-peak waveform signals ≤2, and the anchoring density is considered to be Class A;

[0022] The anchoring quality level of Class II anchor bolts is as follows: α≥95%, the number of non-single-peak waveform signals>2; or 95%>α≥80%, then the anchoring density is considered to be Class B;

[0023] The anchoring quality level of Class III anchor bolts is: 80%>α≥70%, and the anchoring density is considered to be Class C;

[0024] The anchoring quality grade of Class IV anchor rods is: α<70%, and the anchoring density is considered to be Grade D.

[0025] The beneficial effects of the present invention are:

[0026] The present invention performs simple operations such as interpolation, data fitting, and numerical integration on the anchor rod reflection wave curve data to quickly and efficiently obtain data for determining the anchor rod anchoring quality grade. The invention has good feasibility and can meet the quantitative rating requirements in actual situations. The determination results are accurate and reliable, have good application effects, and meet the requirements of basic regulations. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the evaluation method of the present invention. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work shall fall within the scope of protection of the present invention.

[0029] See Figure 1The present invention provides a technical solution: an anchor bolt anchoring quality grade evaluation method based on an amplitude exponential decay algorithm, comprising the following steps:

[0030] Step 1: Obtain the reflection wave curve of the anchor to be evaluated and preprocess the reflection wave curve.

[0031] The length and sampling rate of the received reflected signal are determined in advance based on factors such as the rod length, the wave velocity of the rod system and the frequency domain resolution. Based on the interpretation of the anchor rod reflection signal data, this embodiment adopts a fixed number of sampling times. A total of 1000 sampling points of the anchor rod signal are collected at one time, with a time interval of 0.0044ms, a rod length of 8.86m, an exposed length of 0.19m, and a wave velocity of 4700m / s.

[0032] Signal consistency test: Use covariance matrix calculation to eliminate curves with correlation coefficients less than 0.9, and average the remaining waveform curves to improve the signal-to-noise ratio of the reflected wave signal.

[0033] Normalization in the y direction, i.e., amplitude signal normalization: normalize the vertical coordinate of the reflected signal to a uniform amplitude range of ±1000.

[0034] Normalization in the x-direction, i.e., time normalization, is performed: the time coordinate of the reflected signal is normalized to a new time interval, and resampling is performed according to the normalized new time interval. In this embodiment, the time interval is 0.0044ms, which can be normalized to 0.005ms. The sampling algorithm can be a simple sampling interpolation algorithm.

[0035] One-dimensional digital filtering of the signal: using the moving mean filtering method.

[0036] Step 2: Based on the preprocessing results of the reflected wave curve, the waveform starting point is re-determined and used as the new zero point. Starting from the existing zero point, a moving average of the absolute value of the waveform in the y direction and the overall average of the absolute value of the waveform in the y direction are calculated. If the moving average is greater than the overall average, it is determined as the new zero point. All data before the new zero point is cleared. In this embodiment, the first approximately 10 sampling points of the normalized data need to be cleared.

[0037] Step 3: Calculate the peak value in the y-direction and the correction coefficient in the x-direction. Considering that during field measurements, the inconsistency of the intensity and duration of the excitation signal will result in different main frequencies and periods of the reflected wave signal, which will be reflected in the signal waveform as different peak time intervals. To facilitate subsequent calculations and comparisons, it is necessary to unify them on a single benchmark: take the interval average of the first three peak and trough values ​​as the benchmark for this measurement, calculate the ratio of this value to the preset waveform transformation coefficient as the correction coefficient, and then multiply the x-coordinate of all peak data by this ratio for correction, so that the data at the subsequent peaks can be included in the calculation.

[0038] The waveform transformation factor can be set to 20, meaning that the standard peak interval is 20 time interval units. In this embodiment, the modified interval is approximately 0.1ms. If the peak interval of a measurement is 30, the waveform needs to be compressed by 1 / 3. If the peak interval of a measurement is 20, no compression or expansion is required.

[0039] Step 4: Calculate the peak value A at the rod base. Data after the rod base is discarded, retaining the waveform data between the new zero point and the rod base. Based on the preset rod length and exposed end length, combined with the wave velocity, the initial position of the rod base reflection signal is determined. The position of the reflection signal is compared with the lateral distance between the peak values ​​on the left and right sides. The abscissa of the side with the smaller lateral distance is used as the abscissa of the rod base reflection wave.

[0040] Step 5, determine whether the waveform of the anchor rod reflection wave is a single-peak signal, and count the number of non-single-peak signals. The average value of all peak intervals is determined, and the ratio range of the interval between each peak and the average value of the interval is calculated and counted. If the ratio of each peak interval to the interval average value is within a certain interval, the anchor rod reflection waveform is regular, and the amplitude-frequency signal is in a single-peak state; if the ratio of each peak interval to the interval average value is not within the interval, then while ensuring that the anchor rod signal is valid, the peak at this location is counted as a non-single-peak signal waveform, and the anchor rod has a defect at this location. The interval of this embodiment is set to 0.5~0.9. If the range of the interval is expanded, the lower limit is less than 0.5, which will lead to the data that is empirically considered to be double-peaked and cannot be distinguished. The upper limit is greater than 0.9, and the single-peak signal judgment is too strict, which will cause the data signal that is empirically considered to be single-peaked to be misjudged as non-single-peaked, thereby increasing the number of defects.

[0041] Step 6, calculate the highest point peak value Amax, as well as the horizontal and vertical coordinates corresponding to other shaft peak values ​​A1 and A2 used to fit the attenuation curve. The amplitude corresponding to the signal with the largest amplitude among all peak values ​​is taken as the highest point peak value Amax. According to the mathematical property that the peak value is greater than or equal to the amplitude values ​​on both sides, all peak values ​​are calculated, and the peak value is selected as A1 from the attenuation range of the highest point peak value Amax, and the peak value is selected as A2 from the attenuation range of A1. The horizontal and vertical coordinates of A1 and A2 are determined respectively. The attenuation range of this embodiment is 0.4 to 0.9, that is, the shaft peak value A1 used for fitting is 50% to 90% of the highest point peak value Amax, and the shaft peak value A2 is 50% to 90% of the shaft peak value A1.

[0042] Step 7: Fitting an exponential function: Based on the partial data of the base peak, highest point peak, and shaft peak obtained in the above steps, an exponential decay function is fitted to the reflected wave signal.

[0043] Step 8: Calculate the area S0 between the reflected wave curve and the abscissa on the coordinate axis. Using the principle of numerical integration, find the area between the reflected wave curve and the abscissa, and use the sum of the ordinates to replace the area S0 between the reflected wave curve and the abscissa.

[0044] Step 9: Calculate the area S = Σ(Yy) between the reflected wave curve and the fitted attenuation function. Using the principle of numerical integration, replace the area S between the reflected wave curve and the attenuation function with the sum of the difference between the reflected wave amplitude and the ordinate of the attenuation function at that point. Specifically, calculate the attenuation function value Y corresponding to each x value and the reflected wave curve amplitude y. When the attenuation function value Y is greater than the reflected wave curve value y, calculate the difference delt between the amplitude differences (Yy). Sum the delta values ​​of all reflected wave signals before the rod bottom to obtain the area S enclosed by the reflected wave function and the attenuation function.

[0045] Step 10: Calculate the ratio β of S / S0 and the result α of 1-β. According to the value range of α and the waveform characteristics, the anchor bolt anchoring quality grade is divided into I, II, III, and IV:

[0046] The anchoring quality grade of Class I anchor rods is: α≥95%, and the number of non-single-peak waveform signals is ≤2, then the anchoring density is considered to be Class A.

[0047] The anchoring quality grade of Class II anchor rods is: α≥95%, the number of non-single-peak waveform signals is >2; or 95%>α≥80%, then the anchoring density is considered to be Class B.

[0048] The anchoring quality grade of Class III anchor rods is: 80%>α≥70%, and the anchoring density is considered to be Class C.

[0049] The anchoring quality grade of Class IV anchor rods is: α<70%, and the anchoring density is considered to be Grade D.

[0050] The foregoing description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein and should not be construed as excluding other embodiments. Rather, the present invention can be used in various other combinations, modifications, and environments and can be modified within the scope of the concept described herein through the above teachings or techniques or knowledge in the relevant field. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention are intended to be protected by the appended claims.

Claims

1. An anchor bolt anchoring quality grade evaluation method based on amplitude exponential decay algorithm, characterized by: The following steps are involved: Step 1, obtaining the reflection wave curve of the anchor to be evaluated and preprocessing the reflection wave curve; Step 2, based on the preprocessing result of the reflected wave curve, re-determine the waveform starting point and use it as a new zero point; Step 3, obtain the peak value in the y direction and the correction coefficient in the x direction; Step 4, obtain the peak value A of the rod bottom, and discard the data after the rod bottom with the rod bottom as the boundary, and retain the waveform data between the new zero point and the rod bottom; Step 5, determining whether the waveform of the anchor rod reflection wave is a single-peak signal, and counting the number of non-single-peak signals; Step 6, calculating the highest point peak value Amax, and the horizontal coordinates and vertical coordinates corresponding to other shaft peak values ​​A1 and A2 used for fitting the attenuation curve; Step 7, fitting exponential function; Step 8, calculating the area S0 enclosed by the reflection wave curve on the coordinate axis and the abscissa; Step 9, calculating the area S=Σ(Yy) between the reflected wave curve and the fitted attenuation function; Step 10, calculating the ratio β of S / S0 and the result α of 1-β, and dividing the anchor bolt anchoring quality grade into Ⅰ, Ⅱ, Ⅲ, Ⅳ according to the value range of α and the waveform characteristics; The re-determining of the waveform starting point in step 2 includes: starting from the zero point of the reflected wave curve pre-processed in step 1, calculating the moving average of the absolute value of the waveform in the y direction and the total average of the absolute value of the waveform in the y direction, and taking the point where the moving average is greater than the total average as the waveform starting point; Obtaining the rod bottom peak value in step 4 includes: obtaining a preliminary position of the rod bottom reflection signal according to a preset rod length and an exposed end length, and taking a peak value near the preliminary position as the rod bottom peak value.

2. The method for evaluating the anchor bolt anchoring quality grade based on the amplitude exponential decay algorithm according to claim 1 is characterized in that: The preprocessing in step 1 includes signal consistency check, reflection signal normalization processing and signal one-dimensional digital filtering processing, and the reflection signal normalization processing includes x-direction normalization processing and y-direction normalization processing.

3. The method for evaluating the anchor bolt anchoring quality grade based on the amplitude exponential decay algorithm according to claim 1 is characterized in that: Determining the correction coefficient in the x-direction in step 3 includes: obtaining the interval average value of the first three wave crest and trough values, and taking the ratio of the interval average value to the waveform transformation coefficient as the correction coefficient in the x-direction.

4. The method for evaluating the anchor bolt anchoring quality grade based on the amplitude exponential decay algorithm according to claim 3 is characterized in that: The waveform transformation coefficient ranges from 10 to 30.

5. The method for evaluating the anchor bolt anchoring quality grade based on the amplitude exponential decay algorithm according to claim 1 is characterized in that: Determining whether the waveform of the anchor rod reflection wave is a single-peak signal in step 5 includes: obtaining the average value of all peak intervals, calculating and counting the ratio range of the intervals between each peak and the average value of the intervals, and determining whether the waveform is in a single-peak state based on the ratio range.

6. The method for evaluating the anchor bolt anchoring quality grade based on the amplitude exponential decay algorithm according to claim 1 is characterized in that: The calculation of the horizontal and vertical coordinates corresponding to other shaft peak values ​​A1 and A2 used to fit the attenuation curve in step 6 includes: selecting a peak value from the attenuation range of the highest peak value Amax as A1, selecting a peak value from the attenuation range of A1 as A2, and determining the horizontal and vertical coordinates of A1 and A2 respectively, and the attenuation range is 0.4 to 0.

9.

7. The method for evaluating the anchor bolt anchoring quality grade based on the amplitude exponential decay algorithm according to claim 1 is characterized in that: Calculating the area S0 enclosed by the reflection wave curve and the horizontal coordinate on the coordinate axis in step 8 includes: calculating the sum of the vertical coordinates as the area enclosed by the reflection wave curve and the horizontal coordinate by numerical integration.

8. The method for evaluating anchor bolt anchoring quality grade based on amplitude exponential decay algorithm according to claim 1 is characterized in that: The step 10 of classifying the anchor bolt anchoring quality level according to the α value and the waveform characteristics includes: The anchoring quality level of Class I anchor bolts is as follows: α≥95%, the number of non-single-peak waveform signals ≤2, and the anchoring density is considered to be Class A; The anchoring quality level of Class II anchor bolts is as follows: α≥95%, the number of non-single-peak waveform signals>2; or 95%>α≥80%, then the anchoring density is considered to be Class B; The anchoring quality level of Class III anchor bolts is: 80%>α≥70%, and the anchoring density is considered to be Class C; The anchoring quality grade of Class IV anchor rods is: α<70%, and the anchoring density is considered to be Grade D.

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