Rapid nondestructive detection method for defects of high-speed rail slab ballastless track filling layer

Abstract

The invention discloses a rapid nondestructive detection method for high-speed rail plate-type ballastless track filling layer defects. According to the method, a mechanical impedance method and an impact echo method are organically combined for the first time aiming at internal defects such as void, open joint and cavity of a self-compacting concrete filling layer, and a two-stage detection mode of'rapid screening and positioning 'and'accurate quantitative diagnosis' is formed. In the first stage, mechanical impedance method rapid screening is conducted, specifically, 0.5-1.0 m grids are divided on the surface of a track plate, response signals are collected through polymer energy hammer excitation and a speed sensor, and a suspected defect area is positioned based on a statistical threshold value; in the second stage, accurate quantification is conducted through an impact echo method, grids are encrypted to 0.1-0.2 m in a suspected area, a response signal is excited and collected through an excitation and receiving integrated device trolley, and the defect type is judged according to a defect recognition function. Through the method, the detection efficiency can be improved by more than 5 times, the detection time of a single track plate is shortened to be within 10 minutes, and the method is suitable for short-time detection requirements of a skylight period of a high-speed rail.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-speed railway engineering detection, and in particular relates to a method for rapid non-destructive detection of defects in a filling layer of a slab ballastless track of a high-speed railway. Background Art

[0002] Slab track, due to its high smoothness and stability, has become the predominant track structure for high-speed railways. From top to bottom, a high-speed rail slab track consists of the track slab, self-compacting concrete, geotextile, and base plate. The self-compacting concrete infill layer is a critical force-transmitting, leveling, and buffering layer, and its quality directly impacts the overall stiffness and durability of the track structure, as well as the smoothness and safety of train operation. During construction and operation, the self-compacting concrete infill layer is prone to internal defects such as voids, gaps, cavities, delamination, and looseness. These defects can lead to localized support failure in the track slab, stress concentration, accelerated damage to the track slab and self-compacting concrete, deterioration of track geometry, abnormal vibration and noise, and even threats to train safety. Currently, the more established nondestructive testing methods include mechanical impedance spectroscopy, ground-penetrating radar (GPR), impact echo, infrared thermography, and ultrasonic waveguide. However, these methods all have limitations due to the limited testing conditions and the unique characteristics of the track structure. For example, the uncertainty of the magnitude of the exciting force and the contact time in the mechanical impedance method will affect the accuracy of the measurement, and it is difficult to accurately locate the boundary of the defect; the ground penetrating radar is easily interfered by the steel mesh inside the track plate, resulting in signal mixing; the infrared thermal imaging method is significantly affected by the ambient temperature; in the ultrasonic wave guide method, the ultrasonic wave attenuates rapidly when propagating in the track plate, the received signal is weak, and the signal-to-noise ratio is low; the impact echo method has high detection accuracy, but the single detection area is small, and large-area detection is very time-consuming.

[0003] Given the advantages and disadvantages of different nondestructive testing technologies, research reports have focused on integrating different NDT methods and leveraging their respective strengths. For example, Zhang Bang et al. combined geological radar with ultrasonic array technology to conduct a large-scale rapid survey of ballastless track settlement and detailed detection of key sections. Zhang Guangyuan et al. quantified the characteristics of elastic waves and ground-penetrating radar signals, fused the results using a feature stack, and ultimately used a support vector machine to classify and detect subsurface structural defects. Shu Zhile et al. used ground-penetrating radar to scan a large area of ​​ballastless track, marking suspected defect areas. They then used the impact echo method to re-inspect the areas beneath the rebar and suspected defect areas to identify the defect areas, significantly improving detection efficiency and accuracy. However, the large-area defect screening methods mentioned above are all susceptible to significant environmental interference, resulting in unclear results. Furthermore, the impact echo method used does not establish a correlation between characteristic parameters and defect types. Therefore, the efficiency, accuracy, and precision of their application in real-world scenarios with complex track structures and external environmental interference need to be further improved. Summary of the Invention

[0004] Building on existing technologies, this invention provides a rapid, nondestructive method for detecting defects in the filling layer of high-speed rail slab track. This method, for the first time, organically combines mechanical impedance and impact echo methods. Through a two-stage detection model of "rapid screening and positioning" and "precise quantitative diagnosis," this method achieves efficient synergy between the mechanical impedance and impact echo methods, reconstructing defect identification characteristic parameters and optimizing grid parameters. This significantly improves the efficiency and reliability of large-area track slab filling layer defect detection, meeting the short-term detection requirements during high-speed rail's "window period."

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A method for rapid nondestructive detection of defects in a high-speed railway slab track filling layer comprises the following steps:

[0007] Step 1: Primary grid division: Divide the surface of the high-speed railway slab track to be inspected into rectangular or square grids with a grid side length of 0.5 to 1.0 meters;

[0008] Step 2: Mechanical impedance rapid screening:

[0009] Testing is performed at grid points using a mechanical impedance test device comprising a velocity sensor, a force hammer, and a detection host, the detection host including a switchable mechanical impedance test module and an impact echo test module. The force hammer strikes the track plate, simultaneously collecting the hammer input signal and the velocity sensor response signal. The detection host obtains an impedance spectrum, calculates the dynamic stiffness of each measuring point, and identifies abnormal areas based on statistical thresholds.

[0010] Step 3: Fine mesh division: Divide the abnormal area into fine meshes with a side length of 0.1 to 0.2 meters;

[0011] Step 4: Accurate quantification by impact echo method:

[0012] Testing is performed using a shock echo test device comprising a test trolley; the detection host is switched to a shock echo test module; the test trolley is driven to excite stress waves and collect reflection signals, and the detection host performs a fast Fourier transform to obtain a spectrum; a defect recognition function is calculated based on the main peak and secondary peak characteristics in the spectrum, and the defect type and level are determined based on the defect recognition threshold;

[0013] The defect identification function is implemented in the following way: there are two dominant frequencies in the spectrum, and the amplitude corresponding to the smaller dominant frequency is defined as y1, and the amplitude corresponding to the larger dominant frequency is defined as y2; let F(y) be equal to the ratio of y2 to y1, as the quantitative identification function of the interlayer interface defect, as shown in formula (6)

[0014]

[0015] The defect recognition threshold is as follows:

[0016] When F(y) < 1.0, there are no defects at the interface of the self-compacting concrete filling layer;

[0017] When 1.0 < F(y) ≤ 1.44, there are small bubble pores at the interface of the self-compacting concrete filling layer;

[0018] When 1.44 < F(y) ≤ 2.14, there are large bubble pores at the interface of the self-compacting concrete filling layer;

[0019] When 2.14 < F(y) ≤ 2.71, there are separation joints at the interface of the self-compacting concrete filling layer;

[0020] When F(y) > 2.71, there is voiding at the interface of the self-compacting concrete filling layer;

[0021] Step 5: Evaluate the overall quality of the slab track according to the defect type.

[0022] Furthermore, in the said Step 2, the impedance spectrum is calculated according to Equation (1):

[0023]

[0024] In the formula, V(f) is the velocity spectrum after fast Fourier transform, F(f) is the force spectrum obtained after fast Fourier transform, and H(w) is the impedance spectrum;

[0025] Furthermore, in the said Step 2, the dynamic stiffness of the measured slab track is calculated according to Equation (2):

[0026]

[0027] In the formula, k 50 is the slope at the 50 Hz position in the impedance spectrum, and K d is the dynamic stiffness;

[0028] Furthermore, in the said Step 2, the statistical threshold is calculated as follows:

[0029] Taking the mean value of the dynamic stiffness of all measurement points minus 2 times the standard deviation as the threshold, the measurement points with dynamic stiffness values lower than the lower limit of the threshold are judged as abnormal; the dynamic stiffness threshold is as follows according to Equations (3) to (5):

[0030]

[0031] T L = u-2σ (5)

[0032] In the formula: n is the number of all measurement points, x iis the dynamic stiffness value of the i-th measuring point, u is the mean value of the dynamic stiffness, σ is the standard deviation, T L is the lower threshold.

[0033] Furthermore, the test trolley in step 3 is a mobile scanning device, and the bottom of the trolley includes an impact rod and a signal receiving sensor. In the process of pushing the trolley forward, the impact rod is automatically excited and the sensor automatically receives the signal.

[0034] Furthermore, the method for evaluating the overall quality of the slab track according to the defect type in step 5 is:

[0035] If there are no abnormal areas, the overall quality of the self-compacting concrete filling layer of the slab track is Class A, indicating good quality;

[0036] If only small bubbles exist, the overall quality of the self-compacting concrete filling layer of the slab track is Class B, indicating average quality.

[0037] If only large cells exist or small cells and large cells coexist, the overall quality of the self-compacting concrete filling layer of the slab track is Class C, indicating poor quality;

[0038] If there are gaps or voids, the overall quality of the self-compacting concrete filling layer of the ballastless track is grade D, indicating extremely poor quality and unqualified.

[0039] Compared with the prior art, the present invention has the following significant advantages:

[0040] (1) Strong complementarity: The mechanical impedance method in the present invention is sensitive to changes in dynamic stiffness (suitable for screening defects such as voids and gaps), and the impact echo method is sensitive to changes in internal wave impedance interfaces (suitable for accurately locating the defect range and determining the defect type). The combination of the two forms an effective complement based on physical principles.

[0041] (2) Significantly improve detection efficiency: The present invention uses the mechanical impedance method to quickly complete the preliminary scanning of large-area track plates (few grid points, fast test speed), and further increase the grid size and reduce the number of measurement points while ensuring that no defects are missed, thereby improving detection efficiency. Only in suspicious areas where the dynamic stiffness exceeds the threshold, the more time-consuming impact echo method is used for fine detection, which can increase the detection efficiency by more than 5 times, and the detection time of a single track plate is shortened to within 10 minutes. It is particularly suitable for application scenarios such as high-speed rail slab ballastless tracks that require rapid and large-area screening of key hidden defects, and meets the needs of efficient detection within the "skylight" points of high-speed rail at night.

[0042] (3) Improve detection reliability and accuracy: The impact echo method in the present invention establishes a mapping relationship between characteristic parameters and defect types, which can accurately locate the position, size and type of defects, improve the defect recognition accuracy to 4cm, provide high-precision and quantitative diagnostic results in key areas, and significantly reduce the missed detection and false detection rates.

[0043] (4) High cost-effectiveness: The present invention reduces the large number of test points and test time required for point-by-point intensive testing, thereby reducing labor and equipment loss costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the high-speed railway slab ballastless track structure of the present invention.

[0045] Figure 2 This is a flow chart of the method for rapid nondestructive detection of defects in the filling layer of high-speed railway slab ballastless track according to the present invention.

[0046] Figure 3 It is a schematic diagram of the primary grid division of the high-speed railway slab ballastless track of the present invention.

[0047] Figure 4 It is a schematic diagram of the refined grid division of the high-speed railway slab ballastless track according to the present invention.

[0048] Figure 5 This is the impedance spectrum obtained by the mechanical impedance method at the #11 measuring point in the present invention.

[0049] Figure 6 This is the spectrum obtained by the J8 measuring point based on the impact echo method test in the present invention. DETAILED DESCRIPTION

[0050] The technical solutions of the present invention are clearly and completely described below in conjunction with the embodiments and drawings. The following embodiments are only for illustrating the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

[0051] Example 1

[0052] This embodiment takes the high-speed railway slab ballastless track structure as an example ( Figure 1 ), the structure from top to bottom is track plate, self-compacting concrete, geotextile and base plate; this embodiment adopts the method for rapid non-destructive detection of defects in the filling layer of high-speed iron plate ballastless track of the present invention for inspection, and the detection method process is as follows Figure 2 As shown, the method includes the following steps:

[0053] Step 1: Primary grid division:

[0054] In this embodiment, the track plate size is 5600mm×2500mm, the primary grid size is controlled within the range of 0.5 to 1.0 meters, and the grid division is performed avoiding the sleeper position, and a total of 24 measurement points are obtained, such as Figure 3 shown.

[0055] Step 2: Mechanical impedance rapid screening:

[0056] The detection host is switched to the mechanical impedance method test module. The mechanical impedance method test equipment includes a force hammer, a velocity sensor and a detection host. The detection host includes a switchable mechanical impedance method test module and an impact echo method test module. The sensor is placed at the intersection of the grid. The force hammer is used to strike the track plate near the sensor. Taking the #11 measuring point on the track plate as an example, the detection host obtains the velocity time history curve and the impact force time history curve of the #11 measuring point. According to formula (1), the velocity spectrum after fast Fourier transformation is divided by the force spectrum to obtain the impedance spectrum of the #11 measuring point as follows: Figure 5 shown.

[0057]

[0058] Where V(f) is the velocity spectrum after fast Fourier transform, F(f) is the force spectrum after fast Fourier transform, and H(w) is the impedance spectrum.

[0059] The dynamic stiffness of the ballastless track slab under test is calculated according to formula (2):

[0060]

[0061] Where k 50 is the slope at 50Hz in the impedance spectrum, K d is the dynamic stiffness;

[0062] The statistical threshold is calculated as follows:

[0063] The threshold is the mean of the dynamic stiffness of all measuring points minus 2 times the standard deviation. The measuring points with dynamic stiffness values ​​below the lower limit of the threshold are judged as abnormal. The dynamic stiffness threshold is as follows according to formulas (3) to (5):

[0064]

[0065] T L =u-2σ (5)

[0066] Where: n is the number of all measuring points, x i is the dynamic stiffness value of the i-th measuring point, u is the mean value of the dynamic stiffness, σ is the standard deviation, T L is the lower threshold.

[0067] In this embodiment, the dynamic stiffness of all measuring points of the ballastless track is shown in Table 1:

[0068] Table 1 Dynamic stiffness of all measuring points of the track slab

[0069]

[0070] According to Table 1, the average dynamic stiffness μ of the ballastless track slab is calculated to be 3.30, the standard deviation σ is 0.19, and the lower limit T of the dynamic stiffness threshold L is 2.92. Among all the above measurement points, only the #11 measurement point exceeds the lower limit of the dynamic stiffness threshold. Therefore, this measurement point is an abnormal area and the impact echo method needs to be used for precise quantification.

[0071] Step 3: Refined grid division:

[0072] Divide a refined grid of 0.1 - 0.2 meters within the abnormal area, as Figure 4 shown;

[0073] Step 4: Precise quantification by the impact echo method:

[0074] Based on the impact echo method testing equipment for testing. The impact echo method testing equipment includes a testing trolley; the testing trolley is a mobile scanning device, and the bottom of the trolley contains an impact rod and a signal receiving sensor. During the process of pushing the trolley forward, the impact rod is automatically excited and the sensor automatically receives signals.

[0075] Switch the detection host to the impact echo method testing module; push the testing trolley to generate stress waves and collect reflection signals, and the detection host performs a fast Fourier transform to obtain a spectrum; calculate the defect recognition function according to the peaks corresponding to the two dominant frequencies in the spectrum. The defect recognition function is constructed in the following way:

[0076] As Figure 6 shown, there are two dominant frequencies in the spectrum. The smaller frequency f1 represents a longer reflection time, and the corresponding amplitude is y1. The larger frequency f2 represents a shorter reflection time, and the corresponding amplitude is y2. The generation of the first dominant frequency is due to the stress wave reflecting back from the geotextile interface, and the second dominant frequency is due to the stress wave reflecting back from the interface between the track slab and the self-compacting concrete filling layer. The magnitudes of y1 and y2 reflect the quality of the self-compacting concrete filling layer interface. The larger y1 is, the stronger the reflection degree at the geotextile interface, and the better the quality of the self-compacting concrete filling layer interface; the larger y2 is, the stronger the reflection degree at the self-compacting concrete filling layer interface, and the worse the quality of the self-compacting concrete filling layer interface, indicating the existence of defects. According to this characteristic, let F(y) be equal to the ratio of y2 to y1, as shown in Equation (6), as the interlayer interface defect quantification and recognition function.

[0077]

[0078] The judgment criteria for defect recognition are:

[0079] When F(y) < 1.0, there are no defects in the self-compacting concrete filling layer interface;

[0080] When 1.0 < F(y) ≤ 1.44, there are small bubble holes in the self-compacting concrete filling layer interface;

[0081] When 1.44 < F(y) ≤ 2.14, there are large bubble holes at the interface of the self-compacting concrete filling layer, which is a secondary defect.

[0082] When 2.14 < F(y) ≤ 2.71, there are separation joints at the interface of the self-compacting concrete filling layer.

[0083] When F(y) > 2.71, there is voiding at the interface of the self-compacting concrete filling layer.

[0084] Step 5, Overall quality assessment of the self-compacting concrete filling layer of the slab track:

[0085] If there are no defects, the overall quality of the self-compacting concrete filling layer of this slab ballastless track is grade A, indicating good quality.

[0086] If there are only small bubble holes, the overall quality of the self-compacting concrete filling layer of this slab ballastless track is grade B, indicating average quality. [[ID=1,9]]

[0087] If there are only large bubble holes or both small and large bubble holes coexist, the overall quality of the self-compacting concrete filling layer of this slab ballastless track is grade C, indicating poor quality.

[0088] If there are separation joints or voiding, the overall quality of the self-compacting concrete filling layer of this slab ballastless track is grade D, indicating extremely poor quality and unqualified.

[0089] In this embodiment, the defect identification function values of all measurement points in the abnormal area are shown in Table 2.

[0090] Table 2 Defect identification function values of all measurement points in the abnormal area

[0091] Measuring point J1 J2 J3 J4 J5 F(y) 0.98 0.85 0.97 0.88 0.83 Measuring point J6 J7 J8 J9 J10 F(y) 0.86 0.97 1.29 0.95 0.92 Measuring point J11 J12 J13 J14 J15 F(y) 0.96 1.15 0.85 0.82 0.88 Measuring point J16 J17 J18 J19 J20 F(y) 0.84 0.90 0.93 0.89 0.94 Measuring point J21 J22 J23 J24 J25 F(y) 0.92 0.83 0.86 0.92 0.84

[0092] As can be seen from Table 2, there are small bubble holes at measurement points J8 and J12, and there are no defects at the remaining measurement points. The overall quality of the self-compacting concrete filling layer of this slab ballastless track is grade B.

[0093] The above is only the preferred implementation manner of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments. Instead, it can be used in various other combinations, modifications, and environments, and can be changed within the scope of the concept described herein through the above teachings or the technology or knowledge in related fields. As long as the changes and variations made by those skilled in the art do not depart from the spirit and scope of the present invention, they should all be within the protection scope of the appended claims of the present invention.

Claims

1. A method for rapid nondestructive detection of defects in the filling layer of a high-speed railway slab ballastless track, characterized in that: The method includes the following steps: Step 1, primary grid division: perform rectangular or square grid division on the surface of the ballastless slab track of the high-speed railway to be detected, and the side length of the grid is 0.5 - 1.0 meters; Step 2, rapid screening by mechanical impedance method: Use the mechanical impedance method testing equipment to test at the grid points. The mechanical impedance method testing equipment includes a velocity sensor, a force hammer, and a detection host. The detection host includes a switchable mechanical impedance method testing module and an impact echo method testing module; strike the track slab with the force hammer, and simultaneously collect the force hammer input signal and the velocity sensor response signal; obtain the impedance spectrum through the detection host, calculate the dynamic stiffness of each measurement point, and determine the abnormal area based on the statistical threshold; Step 3, refined grid division: divide refined grids with a side length of 0.1 - 0.2 meters within the abnormal area; Step 4, precise quantification by impact echo method: Perform testing based on the impact echo method testing equipment. The impact echo method testing equipment includes a testing trolley; switch the detection host to the impact echo testing module; push the testing trolley to excite stress waves and collect reflection signals, and the detection host performs fast Fourier transform to obtain the spectrum; calculate the defect recognition function according to the characteristics of the main peak and the secondary peak in the spectrum, and determine the defect type and grade according to the defect recognition threshold; The defect recognition function is realized in the following way: there are two dominant frequencies in the spectrum. Define the amplitude corresponding to the smaller dominant frequency as y1, and the amplitude corresponding to the larger dominant frequency as y2; let F(y) be equal to the ratio of y2 to y1, which is used as the layer interface defect quantification recognition function, as shown in Equation (6) The defect recognition threshold is: When F(y) < 1.0, there is no defect at the interface of the self-compacting concrete filling layer; When 1.0 < F(y) ≤ 1.44, there are small bubble holes at the interface of the self-compacting concrete filling layer; When 1.44 < F(y) ≤ 2.14, there are large bubble holes at the interface of the self-compacting concrete filling layer; When 2.14 < F(y) ≤ 2.71, there is a separation seam at the interface of the self-compacting concrete filling layer; When F(y) > 2.71, there is a void at the interface of the self-compacting concrete filling layer; 2. The method according to claim 1, wherein: Step 5, evaluate the overall quality of the ballastless slab track according to the defect type. The impedance spectrum in Step 2 is calculated according to Equation (1):

3. The method according to claim 1, characterized in that In the formula, V(f) is the velocity spectrum after fast Fourier transform, F(f) is the force spectrum obtained after fast Fourier transform, and H(w) is the impedance spectrum. Where k 50 is the slope at 50Hz in the impedance spectrum, K d is the dynamic stiffness.

4. The method according to claim 1, wherein: In Step 2, the dynamic stiffness of the measured ballastless track slab is calculated according to Equation (2): In Step 2, the statistical threshold is calculated according to the following formula: T L =u-2σ (5) Where: n is the number of all measuring points, x i is the dynamic stiffness value of the i-th measuring point, u is the mean value of the dynamic stiffness, σ is the standard deviation, T L is the lower threshold.

5. The method according to claim 1, wherein: Use the mean value of the dynamic stiffness of all measurement points minus 2 times the standard deviation as the threshold, and the measurement points with dynamic stiffness values lower than the threshold lower limit are determined as abnormal; the dynamic stiffness threshold is calculated according to Equations (3) - (5):

6. The method according to claim 1, wherein: The testing trolley in Step 3 is a mobile scanning device. The bottom of the trolley includes an impact rod and a signal receiving sensor. During the process of pushing the trolley forward, the impact rod is automatically excited and the sensor automatically receives signals. The method for evaluating the overall quality of the ballastless slab track according to the defect type in Step 5 is: If there are no abnormal areas, the overall quality of the self-compacting concrete filling layer of the slab track is Class A, indicating good quality; If only small bubbles exist, the overall quality of the self-compacting concrete filling layer of the slab track is Class B, indicating average quality. If only large cells exist or small cells and large cells coexist, the overall quality of the self-compacting concrete filling layer of the slab track is Class C, indicating poor quality; If there are gaps or voids, the overall quality of the self-compacting concrete filling layer of the ballastless track is grade D, indicating extremely poor quality and unqualified.

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