Single-measuring-surface concrete defect nondestructive testing method capable of eliminating influence of steel lining

Abstract

The invention discloses a single-measuring-surface concrete defect nondestructive testing method capable of eliminating the influence of a steel lining. The method comprises the following steps: calibrating P-wave velocities of a steel plate and concrete in a component; drawing measuring lines and measuring points in the measuring area, and collecting the predominant frequency of each measuring point; if the P-wave velocity of the concrete can be calibrated, the thickness of the measuring point is calculated based on the P-wave velocity of the steel plate and the concrete and the outstanding frequency of the measuring point, a thickness measurement value is obtained, and the internal defect of the component is determined based on the deviation between the thickness measurement value and the thickness standard value; and if the P wave velocity of the concrete cannot be calibrated, determining the internal defect of the component based on the deviation between the predominant frequency measurement value of each measurement point and the standard predominant frequency. According to the method, quantitative detection or defect position detection of the impact echo method can be carried out according to different field conditions in actual engineering, and the influence of the steel lining on a detection result is eliminated.

Description

Technical Field

[0001] The invention belongs to the field related to safety detection of steel-lined concrete structures, and in particular relates to a single-surface concrete defect nondestructive detection method that eliminates the influence of steel lining. Background Art

[0002] In hydraulic tunnels with steel-lined concrete structures, if there is a gap between the steel lining and the concrete or if there are quality defects inside the concrete, the structural bearing capacity will be reduced, which will have an adverse impact on the safety of the tunnel. For steel-lined concrete composite structures, traditional coring detection methods will cause damage to the structure, have low detection efficiency, long detection time, and inconvenient operation, so it is necessary to carry out research on non-destructive testing technology.

[0003] Existing nondestructive testing technologies mainly include ultrasonic method, ground penetrating radar method, thermal imaging method, impact echo method, neutron method, etc. The ultrasonic method requires that the component to be tested has one or two pairs of parallel test surfaces, so that ultrasonic transmitters and signal receivers can be arranged on both sides of the component. This condition is often not met at the construction site. The accuracy of the ground penetrating radar method is greatly reduced due to the shielding effect of the steel lining on electromagnetic waves. The thermal imaging method cannot detect concrete quality defects inside the steel-lined concrete.

[0004] The impact echo method is often used to detect the thickness and defects of a single medium structure, such as plain concrete components. It is a non-destructive testing technology that applies an impact or excitation signal (such as knocking or vibration) to the object being tested, and then records the echo signal to analyze the internal structure and defects of the object. After converting the echo signal in the time domain to the frequency domain, the dominant frequency of the measuring point is obtained, and then the calculation formula is used to convert the dominant frequency into the component thickness measurement value at the measuring point. Finally, the measured value is compared with the component design value to obtain the internal state of the component at the measuring point. When the impact echo method is carried out on steel-lined concrete components, it is necessary to correct the calculation error caused by the steel plate. The article "Research on Internal Defect Detection of Steel-lined Concrete Based on Impact Echo Method" by Xu Ningyuan et al. provides a thickness calculation formula for the impact echo method suitable for steel-lined concrete components, and combined with experiments, it is shown that the corrected formula can more accurately calculate the thickness of steel-lined concrete components and eliminate the influence of steel lining.

[0005] However, the impact echo method still faces difficulties in the engineering application of steel-lined concrete structure defect detection. For example, when testing the quality of the concrete layer of a hydraulic steel-lined concrete tunnel, there is a steel lining on the surface of the tunnel, and the apparent wave velocity of the concrete layer cannot be directly tested, and the P-wave velocity in the concrete cannot be directly calibrated. When the P-wave velocity in the concrete is unknown, the impact echo method detection of the tunnel can only determine the location and nature of the defect, but cannot quantitatively measure the depth of the defect. Summary of the invention

[0006] The purpose of the present invention is to overcome the problems existing in the above-mentioned prior art and provide a single-surface concrete defect nondestructive detection method that eliminates the influence of steel lining.

[0007] To achieve the above object, the present invention adopts the following technical solution: The single-surface nondestructive testing method for concrete defects that eliminates the influence of steel lining includes: Calibrate the P-wave velocity of steel plates and concrete in components; Draw measurement lines and measurement points in the measurement area and collect the outstanding frequency of each measurement point; If the P-wave velocity of concrete can be calibrated, the thickness of the measuring point is calculated based on the P-wave velocity of the steel plate and concrete and the superior frequency of the measuring point to obtain the thickness measurement value. The internal defects of the component are determined based on the deviation between the thickness measurement value and the thickness standard value. If the P-wave velocity of concrete cannot be calibrated, the internal defects of the component are determined based on the deviation between the measured value of the predominant frequency at each measuring point and the standard predominant frequency; The method of calibrating the P wave velocity of concrete is to determine whether the velocity calibration can be performed based on the following methods in sequence according to the engineering requirements until the velocity calibration is completed or all methods are judged: a. Dig out the steel plate in the component and conduct apparent wave velocity test on the internal concrete; b. Conduct apparent wave velocity test on the concrete samples; c. After obtaining the standard superior frequency through the impact echo calibration experiment, the P-wave velocity is inferred based on the designed thickness of the concrete layer; d. Use the concrete grade to search for the corresponding P wave velocity in the concrete P wave velocity database.

[0008] As a preferred implementation, the standard superior frequency is determined as follows: Select a location in the measurement area where concrete voids are less likely to occur to carry out impact echo calibration tests; The survey line whose variance of the dominant frequency of the measuring points in the survey line during the calibration test is within the first preset threshold is selected as the calibration survey line. The dominant frequencies of several measuring points are randomly selected on the survey line, and the average value is taken as the standard dominant frequency of the survey area.

[0009] As a preferred implementation, the thickness standard value is determined as follows: If the site conditions satisfy that the actual thickness of the concrete layer without any defects is consistent with the design value, the design value is taken as the standard value of the component thickness in the measurement area; if not, the standard value of the component thickness is calibrated: A location where concrete voids are less likely to occur is selected in the measuring area, and a calibration test is carried out using the impact echo method. A measuring line whose variance of the calculated thickness values ​​of components at the measuring points in the calibration test is within the second preset threshold is selected as the calibration measuring line. The calculated thickness values ​​of several measuring points are randomly selected on the measuring line, and the average value is taken as the thickness standard value for the measuring area.

[0010] Here, it is judged whether the on-site conditions meet the requirement that the actual thickness of the concrete layer is consistent with the design value when there are no defects. This can be confirmed with the construction party. For example, if the construction process includes pouring concrete behind the steel plate until it is dense after the steel plate is installed, in this case it cannot be guaranteed that the actual thickness of the concrete layer is consistent with the design value.

[0011] For hydraulic tunnels, it can also be confirmed based on the tunnel structure. Specifically, when the axis of the steel cylinder coincides with the axis of the tunnel, the thickness of the concrete layer in the absence of defects is consistent with the design value. When the axis of the steel cylinder coincides with the axis of the tunnel, it cannot be guaranteed that the thickness of the concrete layer in the absence of defects is consistent with the design value, and on-site calibration is required.

[0012] As a preferred implementation manner, the location where concrete voids are less likely to occur is a bottom arch or a side arch.

[0013] As a preferred implementation, the concrete P-wave velocity database is constructed by obtaining concrete of different grades and measuring the P-wave velocity, storing the concrete grade and the corresponding P-wave velocity data in the database, and constructing a concrete P-wave velocity database.

[0014] As a preferred implementation, the method for determining the internal defects of a component based on the deviation between the thickness measurement value and the thickness standard value is as follows: Compare the calculated thickness value of each measuring point with the standard thickness value. If the calculated thickness value of the measuring point is less than (100-a)% of the standard thickness value, there is an internal defect at the measuring point. If the calculated thickness value of the measuring point is greater than (100+a)% of the standard thickness value, there is a void at the measuring point. Otherwise, there is no defect at the measuring point and a is the preset value.

[0015] As a preferred implementation, the method of determining the internal defects of a component based on the deviation between the dominant frequency of each measuring point and the standard dominant frequency is as follows: Compare the measured value of the superior frequency of each measuring point with the standard superior frequency. If the superior frequency of the measuring point is greater than (100+b)% of the standard frequency, there is an internal defect in the measuring point; if the measured value of the superior frequency of the measuring point is less than (100-b)% of the standard superior frequency, there is a gap in the measuring point; otherwise, there is no defect in the measuring point, and b is the preset value.

[0016] As a preferred embodiment, the method further comprises: Draw a defect map of the measuring area with marked measuring lines and measuring points, and assign a value to each measuring point based on the calculated component thickness value or the outstanding frequency value of each measuring point to obtain the defect map of the measuring area.

[0017] Furthermore, the method also includes, for the measurement area defect map, if there are continuous defects at multiple measurement points, marking the total defect area of ​​the continuous defect area.

[0018] Furthermore, the method also includes, based on the range of the component thickness measurement value and the outstanding frequency value at the measuring point, equally dividing the thickness and the outstanding frequency value into several numerical ranges, and marking the measuring points with different colors in the defect map of the measuring area for the values ​​within different numerical ranges.

[0019] The method of the present invention can be used in actual engineering to determine whether quantitative detection by the impact echo method can be carried out according to different on-site conditions. If there are no quantitative detection conditions, defect position detection can be carried out. If quantitative detection by the impact echo method is carried out, the quality of the concrete inside the steel-lined concrete component can be determined, and the defect-free areas, voids, and internal defects can be distinguished; the depth of the internal defects can be quantitatively calculated. If defect position detection is carried out, the quality of the concrete inside the steel-lined concrete component can be determined, and the defect-free areas, voids, and internal defects can be distinguished. The method of the present invention selects quantitative detection or defect position detection according to the on-site conditions to eliminate the influence of the steel lining on the detection results to the greatest extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a flow chart of the method of the present invention.

[0021] Figure 2 It is a cross-sectional view of a shield tunnel (steel pipe lining) in a certain embodiment.

[0022] Figure 3 It is a photograph of the survey area in a certain embodiment.

[0023] Figure 4 It is a schematic diagram of survey lines in four survey areas A, B, C and D in a certain embodiment.

[0024] Figure 5 yes Figure 4 Scatter plot of calculated component thickness in measuring area A.

[0025] Figure 6 yes Figure 4 There are no defects in the measuring area A, and the average value and increase of the thickness of components at each defect are calculated.

[0026] Figure 7 yes Figure 4 Scatter plot of calculated component thickness in the middle B measurement area.

[0027] Figure 8 yes Figure 4 Average value and increase of component thickness measurement in the middle B measuring area.

[0028] Fig. 9 yes Figure 4 Scatter plot of calculated component thickness in the middle C measurement area.

[0029] Fig.10 yes Figure 4 Scatter plot of calculated component thickness in the middle D measurement area. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0031] In the embodiment, the Pearl River Delta water resources allocation project is used as an example to illustrate the technical solution of the present invention. The water supply structures of the project mainly include shield tunnels, drill and blast tunnels, TBM tunnels, box culverts, inverted siphons, and jacking pipes. The four measurement areas involved in the embodiment are located in three different construction sites, covering the double-line shield lined steel pipe solution and the single-line shield lined steel pipe solution. The tunnel cross-section diagram is shown in FIG. Figure 2 The outer lining of the shield tunnel with a steel pipe diameter of 4.8m is supported by segments, and the inner lining is made of DN4800 steel pipe (wall thickness 18mm), and C30 self-compacting concrete (wall thickness 30cm) is backfilled between the inner lining and the segments.

[0032] The method of the present invention is used to perform nondestructive testing of single-surface steel-lined concrete defects. The process is as follows: Figure 1 As shown, the specific steps are as follows: Step 1: Determine the survey area, calibrate the standard parameters of the survey area, draw the survey line, and carry out impact echo detection Before the measurement, the measurement area is selected, the measurement line is arranged, and the instrument parameters are set. In this embodiment, a total of 4 detection areas are set.

[0033] The detection area A is the left-line water diversion tunnel of A7 in Nansha District, with pile numbers of LG38+994.79~LG39+018.79, and the measurement area ranges from LG38+998.39 to LG39+010.39. The longitudinal length of the measurement area is 7.2m, and the circumferential width is 2m. The circumferential measurement line spacing is 20cm, and it is arranged in the direction of the countercurrent, numbered 01-37, with a total of 37 measurement lines. The measurement line layout is as follows: Figure 4 As shown in (a).

[0034] First, the P-wave velocity of the steel plate is calibrated. The P-wave velocity of the steel plate can be directly calibrated using the existing impact echo method or ultrasonic conversion method. In this embodiment, ultrasonic thickness measurement and apparent wave velocity test are carried out on the steel plate in measurement area A. The thickness of the steel plate in the measurement area is 20.02 mm, and the P-wave velocity of the steel plate is 6126 m / s.

[0035] Then, the P wave velocity in the concrete is obtained based on the on-site conditions. The acquisition principle is: ① Determine whether the project allows excavation of steel plates. If so, excavate the steel plates, conduct an apparent wave velocity test on the concrete, and obtain the concrete P wave velocity. If excavation of steel plates is not allowed, proceed to ②; ②Find the concrete samples on site. If there are any samples, conduct the apparent wave velocity test on them to determine the P wave velocity of the concrete in the test area. If there are no samples, proceed to ③. ③Find areas without defects where the thickness of the concrete layer is known, such as the arch waist and bottom arch of hydraulic tunnels, where concrete defects are less likely to occur due to concrete gravity factors, and carry out impact echo detection. The concrete wave velocity value is inferred by the known component thickness and outstanding frequency. If detection is not possible, proceed to ④; ④ If the thickness of the concrete layer is unknown, ask the construction unit for the concrete grade. If the concrete grade is available, find the corresponding P-wave velocity data in the concrete P-wave velocity database to calibrate the concrete P-wave velocity in the measuring area.

[0036] The concrete P-wave velocity database is constructed in the following way: concrete of different grades is obtained in advance and the P-wave velocity is measured, the concrete grade and the corresponding P-wave velocity data are stored in the database, and the concrete P-wave velocity database is constructed.

[0037] In this embodiment, excavation of steel plates is not allowed, but concrete samples are retained. Therefore, an apparent wave velocity test is carried out on the concrete samples retained in measurement area A, and the concrete wave velocity in measurement area A is 3185m / s.

[0038] The test areas B and C are the welds at the junction of the eighth and ninth warehouses of the A6 mark. The B test area is centered on the top of the steel pipe. The starting point of the test area in the circumferential direction is 1.6 meters away from the top and extends 3 meters after crossing the top of the steel pipe in the circumferential direction. The total length is 4.6 meters. The longitudinal direction is centered on the weld and extends 1 meter on both sides. The total length is 2 meters. There are 11 test lines in total. The test line layout is as follows: Figure 4 As shown in (b). The total length of the C measurement area in the longitudinal direction is 3.8 meters. The starting point of the measurement line is located upstream of the weld, 1 meter away from the weld, and the end point of the measurement line is located downstream of the weld, 2.8 meters away from the weld, with a total of 20 measurement lines. Ultrasonic thickness measurement and apparent wave velocity tests were carried out on the steel plates in the B and C measurement areas. The thickness of the steel plates in the measurement area was 20.05mm, and the P wave velocity of the steel plates was 6149m / s; the apparent wave velocity test was carried out on the concrete samples in the B and C measurement areas. The concrete wave velocity in the B and C measurement areas was 3243m / s.

[0039] The detection area D is the lower arch waist on the left side of the steel pipe section DR018 on the right line of A3. The starting point of the measurement area is 3.65m from the weld of the DR019 and DR018 steel pipes, and the lower boundary is 20cm away from the junction of the roadway and the steel pipe. The longitudinal length of the measurement area is 2m, the circumferential width is 2m, the measurement line interval is 20cm, and a total of 11 measurement lines 01~11 are arranged. Ultrasonic thickness measurement and apparent wave velocity test were carried out on the steel plate in the D measurement area. The thickness of the steel plate in the measurement area is 20.01mm, and the P wave velocity of the steel plate is 6098m / s; the apparent wave velocity test was carried out on the concrete sample retained in the D measurement area, and the concrete wave velocity in the D measurement area was 3178m / s.

[0040] Impact echo detection was carried out on the above-mentioned measurement areas respectively: 1. After arriving at the area to be tested, first record the location information of the test area, observe the state of the test surface and find that because it is a newly built water diversion tunnel that has not been put into use yet, the surface of the steel pipe is highly flat, but a lot of dust is attached. In order to prevent dust from affecting the test results, the test personnel clean the surface of the test area and then arrange the test line. Use a laser level with a tape measure and a measuring tape to accurately calibrate the position of the test area, use a marker pen to draw each test line, and number each test line after drawing.

[0041] Figure 3 This is a photo of test area A. It can be seen that the surface of the steel lining is smooth, but there is dust on it.

[0042] 2. After the survey line is drawn, assemble the impact echo detection instrument, set the relevant parameters after turning on the machine, name the test file with the section and warehouse number of the survey area, and record the specific information in a paper notebook to facilitate verification during data post-processing.

[0043] 3. During the test, the construction unit provides a trolley for the inspection personnel to climb. The impact echo method inspection instrument is turned on for test. After the waveform is stable and there are no obvious problems during the test, the formal inspection is carried out. The inspection personnel hold the test trolley with the four wheels close to the surface of the steel plate and maintain a uniform speed of about 0.1m / s during the test.

[0044] 4. Save the data immediately after each measurement line test is completed, and record the number of each measurement line in a paper record book.

[0045] Step 2: Conduct data analysis and draw defect maps In step 1, the thickness of the steel plate and the P wave velocity of the steel plate and the P wave velocity of the concrete are obtained. Different methods need to be used according to the conditions on site to obtain the standard value of the concrete layer thickness, which can be obtained according to the following principles: 1. If the axis of the steel cylinder coincides with the axis of the tunnel, it can ensure that the thickness of the concrete layer is consistent with the design value without defects (or other similar engineering situations). In this case, the design value of the concrete layer is taken as the standard value.

[0046] 2. If the axis of the steel cylinder does not coincide with the axis of the tunnel, it is impossible to ensure that the thickness of the concrete layer is consistent with the design value when there are no defects (or other similar engineering situations). At this time, it is necessary to carry out standard value calibration test, select the bottom arch, side arch and other locations in the survey area where concrete voids are not likely to occur to carry out impact echo method calibration test, select the survey line with the thickness calculated value of the component within 0.1 in the calibration test as the calibration survey line, randomly select the calculated values ​​of 10 measuring points on the survey line, and take the average value as the standard value of the survey area.

[0047] Use the composite structure component thickness calculation formula to calculate the component thickness measurement value of each measuring point. Arrange the component thickness measurement values ​​of each measuring point according to the measuring point position, draw a test area detection result map, and determine the internal state of the component according to the following principles: When the calculated value of the component thickness at the measuring point is within the range of 90%-110% of the standard value of the component thickness at the defect-free location, it means that the component is defect-free.

[0048] When the calculated value of the component thickness at the measuring point is greater than 110% of the standard value of the component thickness at the defect-free location, it indicates that a void defect exists.

[0049] When the calculated value of the component thickness at the measuring point is less than 90% of the standard value of the component thickness at the defect-free location, it means that there are internal concrete defects in the component. At this time, the calculated value of the component thickness is the buried depth of the defect.

[0050] The component thickness measurement values ​​of each measuring point are plotted according to the position of the measuring point on the measuring area to form a measuring area result map. For a patch of defective areas, the defect area should be indicated. If the elastic wave velocity of the concrete is known, the defect depth should also be marked in the defective area. In this embodiment, in order to more intuitively display the severity and range of the defects, the thickness is graded into different ranges, and different color markings are used for measuring point areas in different thickness ranges.

[0051] In this embodiment, step 1 obtains the steel plate thickness, steel plate P wave velocity, concrete P wave velocity, and the superior frequency of each measuring point in each measuring area, and substitutes the parameters into the composite structure member thickness calculation formula: In the formula, Twice the thickness of the steel lining; For the frequency of excellence; is the velocity of P wave in the steel plate; is the velocity of P wave in concrete; is the empirical coefficient.

[0052] This modified formula can calculate the thickness of steel-lined concrete components more accurately and eliminate the influence of the steel lining.

[0053] The component thickness calculation value of each measuring point is obtained, and a component thickness calculation value cloud map is drawn. It can be seen from the component thickness calculation value cloud map that individual measurement points with abnormal data are ignored, and only continuous abnormal data measurement points are selected as the areas calibrated as defects. According to the cloud map, the areas with abnormal component thickness calculation values ​​are calibrated for specific analysis.

[0054] Test results of test area A The steel pipe axis of the section where the measurement area is located does not coincide with the tunnel axis, that is, the actual concrete thickness is unknown when there are no defects in the internal concrete. The calibration test shows that the thickness standard value of the A measurement area is 0.253m. Figure 5 It can be seen that there are 4 highlighted data abnormal areas in the figure, numbered as defects 1, 2, 3, and 4 from left to right. Ten measurement points are randomly selected in each defect area, and the average values ​​of relevant parameters are counted and analyzed. Figure 6 .

[0055] Depend on Figure 6 It can be seen that the average and increase values ​​of the thickness of components without defects and at various defects are shown.

[0056] The average thickness of the center of defect No. 1 is 0.639m, and the area of ​​the abnormal data is 0.235m 2 The average thickness of the center of defect No. 2 is 0.876m, and the area of ​​the abnormal data is 0.315m 2 The average thickness of the center of defect No. 3 is 0.939m, and the area of ​​the abnormal data is 0.140m. 2 The average thickness of the center of defect No. 4 is 0.887m, and the area of ​​the abnormal data is 0.460m. 2 .

[0057] observe Figure 5 , Figure 6 It can be found that all the defects in the A measurement area are void defects, and as the area of ​​the void area increases, the excessive value of the component thickness measurement also changes. This is because when the void area changes, the area of ​​the steel plate that loses the concrete support changes. When excited by the exciter, the resonant vibration mode of the steel plate changes accordingly, resulting in a decrease in its dominant frequency.

[0058] Test results of area B The steel pipe axis of the section where the measurement area is located does not coincide with the tunnel axis, that is, the actual concrete thickness is unknown when there are no defects in the internal concrete. The calibration test shows that the standard value of the B measurement area is 0.342m. Figure 7It can be found that a bright strip-shaped data abnormal area runs through the entire measurement area. This measurement line is measurement line 6, which is the weld of two sections of steel pipes. The weld surface is extremely uneven, which greatly affects the detection results. Excluding measurement line 6, there is one hollow defect and three internal defects in the defects of measurement area B, which are numbered 1, 2, 3, and 4 from top to bottom. Among them, No. 1 is a hollow defect, and No. 2, 3, and 4 are internal defects. Ten measurement points are randomly selected in each defect area, and the average values ​​of relevant parameters are counted and analyzed. Figure 8 .

[0059] Depend on Figure 8 It can be seen that the average and increase values ​​of the thickness of components without defects and at various defects are shown.

[0060] The average thickness of the center of defect No. 1 is 0.997m, and the area of ​​the abnormal data is 1.415m 2 The average thickness of the center of defect No. 2 is 0.281m, and the area of ​​the abnormal data is 0.805m 2 The average thickness of the center of defect No. 3 is 0.291m, and the area of ​​the abnormal data is 1.350m 2 The average thickness of the center of defect No. 4 is 0.280m, and the area of ​​the abnormal data is 0.815m 2 .

[0061] observe Figure 7 , Figure 8 It can be found that there are one void defect and three internal defects in the B measurement area, and the calculated average value of the component thickness of the void defect is significantly increased compared with the defect-free area, while the calculated average value of the component thickness of the other three internal defects is significantly reduced compared with the defect-free area. It is speculated that the internal defects cause the elastic wave propagation distance inside the component to be shortened, the elastic wave propagation time to be shortened, the dominant frequency to increase, and the calculated value of the component thickness to decrease.

[0062] From the rules obtained from numerical simulation and model test, it can be seen that the distance from the upper surface of the defect to the steel lining surface (i.e., the buried depth) of these three internal defects is the calculated value of the component thickness at that location.

[0063] C test area test results The axis of the steel pipe in the section where the measurement area is located does not coincide with the axis of the tunnel. That is, the actual concrete thickness is unknown when there are no defects in the internal concrete. The calibration test shows that the standard value of the C measurement area is 0.255m. Fig. 9It can be found that a bright strip-shaped data abnormal area runs horizontally through the entire measurement area. Ten measurement points are randomly selected in each defect area, and the average values ​​of relevant parameters are counted and analyzed. No area with abnormally small component thickness calculation values ​​was found in measurement area C, and it was determined that there were no internal defects in the measurement area. The average values ​​of component thickness calculations in the horizontal data abnormal area were 0.998m and 0.939m, respectively, which far exceeded the standard value of 0.255m for component thickness in the defect-free measurement area of ​​the measurement area, with the largest increase of 291%. The empty area of ​​the measurement area is 0.54m 2 .

[0064] D test area test results The axis of the steel pipe in the section where the measurement area is located does not coincide with the axis of the tunnel. That is, the actual concrete thickness is unknown when there are no defects in the internal concrete. The calibration test shows that the standard value of the D measurement area is 0.279m. Fig.10 It can be found that a highlighted data anomaly area is at the top of the 4-7 measuring line, which is the concrete pouring hole. There are also sporadic data anomaly areas in the lower half of the measuring area. Ten measuring points were randomly selected in each defective area, and the average values ​​of relevant parameters were calculated and analyzed. No areas with abnormally small calculated component thickness values ​​were found in the D measuring area, and it was determined that there were no internal defects in the measuring area. The calculated average values ​​of component thickness in the lower half of the data anomaly area were 0.506m and 0.477m, respectively, both exceeding the standard value of component thickness of 0.279m in the defect-free measuring area of ​​the measuring area, with the maximum increase of 81%. The hollow area of ​​the measuring area is 0.12m 2 .

[0065] The concrete P wave velocity can be obtained in all four measurement areas of this embodiment, and internal defects can be directly judged based on the thickness value. If the P wave velocity of concrete in the on-site project cannot be calibrated, the internal defects of the component are determined based on the deviation between the superior frequency measurement value of each measurement point and the standard superior frequency. At this time, internal defects can only be judged qualitatively. The specific steps are: The state of concrete in the measurement area is judged by the superior frequency value obtained by the impact echo method. The impact echo method calibration test is carried out in the measurement area, where concrete voids are not likely to occur, such as the bottom arch and side arch. The measurement line with the superior frequency variance of the measurement points within the measurement line within 0.1 in the calibration test is selected as the calibration measurement line. The superior frequencies of 10 measurement points are randomly selected on the measurement line, and the average value is taken as the standard superior frequency of the measurement area.

[0066] In step 1, the superior frequency of each measuring point is obtained and compared with the standard superior frequency of the measuring area. When the superior frequency of the measuring point is within the range of 90%-110% of the standard superior frequency of the measuring area, it means that the component has no defects.

[0067] When the superior frequency of the measuring point is less than 90% of the standard superior frequency of the measuring area, it indicates that there is a void defect.

[0068] When the predominant frequency of the measuring point is greater than 110% of the standard predominant frequency of the measuring area, it indicates that there are internal defects in the concrete of the component.

[0069] The component superior frequency values ​​of each measuring point are plotted into a measuring area result diagram according to the position of the measuring point on the measuring area. For defective areas that are in batches, the defect area can be indicated.

Claims

1. A nondestructive testing method for single-surface concrete defects that eliminates the influence of steel lining, characterized in that: include: Calibrate the P-wave velocity of steel plates and concrete in components; Draw measurement lines and measurement points in the measurement area and collect the outstanding frequency of each measurement point; If the P-wave velocity of concrete can be calibrated, the thickness of the measuring point is calculated based on the P-wave velocity of the steel plate and concrete and the superior frequency of the measuring point to obtain the thickness measurement value. The internal defects of the component are determined based on the deviation between the thickness measurement value and the thickness standard value. If the P-wave velocity of concrete cannot be calibrated, the internal defects of the component are determined based on the deviation between the measured value of the predominant frequency at each measuring point and the standard predominant frequency; The method of calibrating the P wave velocity of concrete is to determine whether the velocity calibration can be performed based on the following methods in sequence according to the engineering requirements until the velocity calibration is completed or all methods are judged: a. Dig out the steel plate in the component and conduct apparent wave velocity test on the internal concrete; b. Conduct apparent wave velocity test on the concrete samples; c. After obtaining the standard superior frequency through the impact echo calibration experiment, the P-wave velocity is inferred based on the designed thickness of the concrete layer; d. Use the concrete grade to search for the corresponding P wave velocity in the concrete P wave velocity database.

2. The method according to claim 1, characterized in that The standard superior frequency is determined as follows: Select a location in the measurement area where concrete voids are less likely to occur to carry out impact echo calibration tests; The survey line whose variance of the dominant frequency of the measuring points in the survey line during the calibration test is within the first preset threshold is selected as the calibration survey line. The dominant frequencies of several measuring points are randomly selected on the survey line, and the average value is taken as the standard dominant frequency of the survey area.

3. The method according to claim 1, characterized in that The thickness standard value is determined as follows: If the site conditions satisfy that the actual thickness of the concrete layer without any defects is consistent with the design value, the design value is taken as the standard value of the component thickness in the measurement area; if not, the standard value of the component thickness is calibrated: A location where concrete voids are less likely to occur is selected in the measuring area, and a calibration test is carried out using the impact echo method. A measuring line whose variance of the calculated thickness values ​​of components at the measuring points in the calibration test is within the second preset threshold is selected as the calibration measuring line. The calculated thickness values ​​of several measuring points are randomly selected on the measuring line, and the average value is taken as the thickness standard value for the measuring area.

4. The method according to claim 2 or 3, characterized in that: The location where concrete voids are less likely to occur is a bottom arch or a side arch.

5. The method according to claim 1, characterized in that The concrete P-wave velocity database is constructed by obtaining concrete of different grades and measuring the P-wave velocity, storing the concrete grades and the corresponding P-wave velocity data in the database, and constructing the concrete P-wave velocity database.

6. The method according to claim 1, characterized in that The method for determining the internal defects of a component based on the deviation between the thickness measurement value and the thickness standard value is as follows: Compare the calculated thickness value of each measuring point with the standard thickness value. If the calculated thickness value of the measuring point is less than (100-a)% of the standard thickness value, there is an internal defect at the measuring point. If the calculated thickness value of the measuring point is greater than (100+a)% of the standard thickness value, there is a void at the measuring point. Otherwise, there is no defect at the measuring point and a is the preset value.

7. The method according to claim 1, characterized in that The method for determining the internal defects of a component based on the deviation between the predominant frequency of each measuring point and the standard predominant frequency is as follows: Compare the measured value of the superior frequency of each measuring point with the standard superior frequency. If the superior frequency of the measuring point is greater than (100+b)% of the standard frequency, there is an internal defect in the measuring point; if the measured value of the superior frequency of the measuring point is less than (100-b)% of the standard superior frequency, there is a gap in the measuring point; otherwise, there is no defect in the measuring point, and b is the preset value.

8. The method according to claim 1, characterized in that Also includes: Draw a defect map of the measuring area with marked measuring lines and measuring points, and assign a value to each measuring point based on the calculated component thickness value or the outstanding frequency value of each measuring point to obtain the defect map of the measuring area.

9. The method according to claim 8, characterized in that It also includes that, for the defect map of the measurement area, if there are continuous defects at multiple measurement points, the total defect area is marked for the continuous defect area.

10. The method according to claim 8, characterized in that It also includes dividing the thickness and the outstanding frequency values ​​equally into several value ranges based on the calculated value of the component thickness and the range of the outstanding frequency value at the measuring point, and marking the measuring points with different colors in the defect map of the measuring area for the values ​​within different value ranges.

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