A non-destructive testing method for defects in the self-compacting concrete filling layer of subway slab track

Abstract

The present application relates to a non-destructive testing method for defects in the self-compacting concrete filling layer of subway slab tracks, belonging to the technical field of subway railway construction inspection. This method uses an excitation device to strike the ballastless track slab, causing minute vibrations on the surface of the track slab. By establishing the mapping relationship between the admittance characteristic parameters and the defects, the quality status of the self-compacting concrete filling layer at each position can be determined, and a rapid evaluation method for defects in the self-compacting concrete filling layer of subway slab tracks is proposed. It avoids the disadvantages of traditional testing methods such as low efficiency, strong subjectivity, generalization from point to surface, time-consuming and laborious, and can achieve rapid and efficient detection of the self-compacting concrete filling layer; constructs the mapping relationship between the admittance spectrum characteristic signal parameters and the quality defects of the filling layer, proposes the defect recognition threshold for the filling layer, and provides refined evaluation indicators and methods for defects, providing an efficient and reliable testing method for project acceptance.

Description

Technical Field

[0001] The present invention relates to the technical field of subway and railway construction inspection, and particularly relates to a non-destructive inspection method for defects in the self-compacting concrete filling layer of a subway slab track. Background Art

[0002] The slab track cancels the sleepers and ballast beds of the traditional ballasted track, uses precast concrete slabs to support the rails, and fills CA mortar or self-compacting concrete between the track slabs and the concrete base. It is a brand-new fully supported slab track structure. It has the following advantages: good stability and smoothness; low construction height and light self-weight, which can reduce the secondary load of the bridge and lower the tunnel clearance; slow track deformation, good durability, requiring little or no maintenance and having low maintenance costs, etc. Therefore, the adoption of the slab ballastless track structure in urban rail transit has become the mainstream mode and an inevitable trend of the current subway and railway structures. Among them, self-compacting concrete, as a material with high cost performance, self-leveling and high durability, has been widely used as the filling layer material in the slab ballastless track structure, and it has a key influence on the smoothness, safety, durability, etc. of the track structure. Therefore, the construction quality of self-compacting concrete is particularly important, and it is necessary to quickly and effectively monitor the construction quality of self-compacting concrete in a timely manner.

[0003] Since the filling layer of the subway slab ballastless track is constructed using a closed mold cavity, during the pouring process of the filling layer, due to reasons such as the obstruction of the steel mesh, poor exhaust, and dust accumulation, different types and degrees of construction defects often easily occur in the self-compacting concrete filling layer under the slab, such as bubble holes, separation joints, voids, and cavities. These filling layer defects are extremely concealed and are often difficult to detect. If not located and treated in a timely manner, they will seriously affect the safety and durability of the track structure and cause great difficulties to operation and maintenance.

[0004] At present, the on-site detection methods for the defects of the self-compacting concrete filling layer of the subway slab ballastless track mainly include manual visual inspection, measurement by inserting a steel ruler, and on-site plate uncovering test. These methods have disadvantages such as low efficiency, strong subjectivity, generalization from points, time-consuming and laborious, which are not conducive to the rapid and efficient detection of defects. Regarding the non-destructive testing methods for the slab ballastless track structure, there are mainly non-destructive testing methods such as ultrasonic method, ground penetrating radar method, infrared thermal imaging method, and impact echo method. When using the ultrasonic method to detect internal defects of concrete, the opposite side method and the inclined side method are generally adopted, and transducers need to be placed on two test surfaces. However, the subway slab ballastless track can only provide one test surface and cannot be tested; for the ground penetrating radar method, due to the large interference of the steel bar mesh inside the concrete on high-frequency pulsed electromagnetic waves, it is difficult to obtain accurate signals; the infrared thermal imaging method can only test surface defects, and it is difficult to test the internal defects of the self-compacting concrete filling layer, and it is greatly affected by the environment; the impact echo method is currently an emerging method for non-destructive testing of the self-compacting concrete filling layer of the high-speed rail CRTS III slab ballastless track. However, the excitation device it uses is a trolley with a small metal rod, and a shock wave is generated by instantaneously hitting the surface of the track slab through the small metal rod. This impact energy is relatively low. For the slab ballastless track with geotextile or vibration damping pad adhered between the track slab and the filling layer, the shock wave is difficult to penetrate and the signal of the filling layer cannot be obtained.

[0005] Based on the limitations of the above technical means, the present invention adopts the admittance method non-destructive testing technology. Its excitation device uses a polycapability hammer, and the shock wave can effectively penetrate the geotextile or vibration damping pad, and obtain the signal response of the self-compacting concrete filling layer under the slab. Then, the defects of the self-compacting concrete filling layer are detected and identified through the admittance spectrum. Summary of the Invention

[0006] Aiming at the limitations of the existing detection methods for the defects of the self-compacting concrete filling layer of the subway slab track with a laminated composite structure, the present invention provides a non-destructive testing method for the defects of the self-compacting concrete filling layer of the subway slab track. This method uses a polycapability hammer to strike the track slab and obtain the vibration response signal, obtains the admittance spectrum curve according to the measured force time history curve and velocity time history curve, then establishes the mapping relationship between the quality defects of the filling layer and the admittance spectrum characteristic signal parameter (i.e., admittance rate), and further detects and identifies the defects of the self-compacting concrete filling layer through this signal parameter.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A non-destructive testing method for the defects of the self-compacting concrete filling layer of the subway slab track includes the following steps:

[0009] Step 1, Detection preparation:

[0010] Divide the upper surface of the ballastless track slab to be measured into grids, and a total of 4 corner measuring points and multiple in-slab measuring points are obtained; arrange a velocity sensor as a measuring point at the intersection position of each grid, and connect the velocity sensor, the excitation device with a stress sensor, and the detection host located outside the track slab to be measured;

[0011] Preferably, in step 1, the detection grid and the velocity sensor are arranged according to the following scheme:

[0012] Both the grid length and width are less than or equal to 600 mm; the velocity sensor should avoid the sleeper position on the track slab to be measured, and the distance from the edge of the track slab to be measured is greater than or equal to 30 cm;

[0013] Preferably, the excitation device is a polycapability hammer.

[0014] Step 2, Non-destructive testing and data processing:

[0015] Use the excitation device to perform a knocking test within any grid described in step 1. The distance between the knocking point and the velocity sensor is 10 ± 2.5 cm. The detection host obtains the force time history curve and the corresponding velocity time history curve of the measuring point according to the time history data measured by the stress sensor and the velocity sensor, and compares the velocity spectrum and the force spectrum obtained after performing the fast Fourier transform on these two time history curves, that is, obtain the admittance frequency spectrum curve of the measuring point; perform standard knocking tests in other grids in the same way to obtain the admittance frequency spectrum curves of all measuring points on the track slab to be measured;

[0016] Preferably, the admittance of the ballastless track slab to be measured is calculated according to formula (1):

[0017]

[0018] In the formula, V(f) is the velocity spectrum after the fast Fourier transform, F(f) is the force spectrum obtained after the fast Fourier transform, and H(ω) is the admittance spectrum;

[0019] Step 3, Preliminary determination of the quality of the filling layer:

[0020] According to the admittance frequency spectrum curve obtained in step 2, calculate the admittance rate R of each measuring point to obtain the in-slab admittance rate R I and the corner admittance rate R C , and according to the in-slab admittance rate threshold R IT and the corner admittance rate threshold R CT , preliminarily determine whether the quality of the self-compacting concrete filling layer is qualified;

[0021] Preferably, in step 3, the admittance rate R is calculated according to formulas (2) to (4):

[0022] H S = f(x)max , 0 ≤ x ≤ 100 (2)

[0023]

[0024]

[0025] Wherein, x is the frequency, H S is the admittance peak value within the frequency range of 0 - 100 Hz in the admittance spectrum; H is the average admittance value within the frequency range of x1 - x2 Hz in the admittance spectrum, taking x1 = 100 and x2 = 1200; R is the admittance rate, that is, the ratio of the admittance peak value to the average admittance value within a specific frequency range in the admittance spectrum curve;

[0026] Preferably, in step 3, the quality of the filling layer under each measuring point on the measured track slab is preliminarily determined by the following method:

[0027] When the in - slab admittance rate R I ≤ R IT or the corner - slab admittance rate R C ≤ R CT , the perfusion quality of the filling layer under this measuring point is good;

[0028] When the in - slab admittance rate R I >R IT or the corner - slab admittance rate R C >R CT , there are quality defects in the filling layer under this measuring point;

[0029] Preferably, in step 3, the admittance rate threshold is determined by the following method:

[0030] Preferably, in step 3, the in - slab admittance rate threshold R IT and the corner - slab admittance rate threshold R CT are taken as follows:

[0031] For geotextile - type subway slab - ballastless tracks, the in - slab admittance rate threshold R IT is 1.0, and the corner - slab admittance rate threshold R CT is 2.5;

[0032] For vibration - damping pad - type subway slab - ballastless tracks, the in - slab admittance rate threshold R IT is 4.5, and the corner - slab admittance rate threshold R CT is 8.0;

[0033] Step 4: Obtain the admittance rate reference value through multiple detections:

[0034] Continuously detect multiple ballastless track slabs according to the method described in steps 1 - 3, and measure the in - slab admittance rate R I and the corner - slab admittance rate R C, select N pieces (N≥5) of slab track plates with good grouting quality at all measurement points from all measured slab track plates as reference slab track plates, and select one measurement point within the slab and at the slab corner that meet the I R ≤ 1 / 2R IT 、R C ≤ 1 / 2R CT condition from each reference slab track plate, and calculate the mean of the admittance ratios of the N measurement points within the slab and at the slab corner as the admittance ratio reference values for the within-slab and slab-corner;

[0035] Preferably, in step 4, the admittance ratio reference values are calculated according to formulas (5) and (6):

[0036] R I0 =(R I1 +R I2 +R I3 +···+R IN ) / N (5)

[0037] R C0 =(R C1 +R C2 +R C3 +···+R CN ) / N (6)

[0038] In the formula: R I0 represents the admittance ratio reference value within the slab, R C0 represents the admittance ratio reference value at the slab corner, N is the number of reference slab track plates, R I1 、R I2 、R I3 、···、R IN are the admittance ratios of any measurement points on the N reference slab track plates that meet the I R ≤ 1 / 2R IT condition, and R C1 、R C2 、R C3 、···、R CN are the admittance ratios of any measurement points on the N slab track plates that meet the C R ≤ 1 / 2R CT condition;

[0039] Step 5, refined assessment of the degree of filling layer defects:

[0040] According to the admittance ratio reference values obtained in step 4, calculate the quality defect evaluation index of the filling layer under each measurement point of the measured slab track plates with quality defects in the filling layer, and evaluate the degree of defects of the self-compacting concrete filling layer in the test section according to the filling layer quality defect grading standard;

[0041] Preferably, in step 5, the quality defect evaluation index ROC is calculated according to formulas (7) and (8):

[0042] For the inner points of the slab:

[0043] ROC = (R IS - R I0 ) / R I0 (7)

[0044] For the corner points of the slab:

[0045] ROC = (R CS - R C0 ) / R C0 (8)

[0046] In the formula, ROC is the quality defect evaluation index, representing the mapping relationship between the filling layer defect and the admittance spectrum characteristic signal parameters, defined as the similarity degree between the admittance rate of the measuring point at the position with quality defect in the filling layer and the admittance rate reference value. ROC ≥ 1, R IS and R CS represent the admittance rate of the measuring point at the position with quality defect in the filling layer;

[0047] Preferably, in step 5, the grading standard for the quality defect of the filling layer under any measuring point is as follows:

[0048] When ROC ≤ 2, it is a grade I defect, indicating that there are small air bubbles with an area of 6 cm 2 to 30 cm 2 distributed on the surface of the self-compacting concrete filling layer within a range of 30 cm 2 below the measuring point, and the number is 10 - 20;

[0049] When 2 ≤ ROC ≤ 3, it is a grade II defect, indicating that there are air bubbles with an area of 30 cm 2 to 50 cm 2 distributed on the surface of the self-compacting concrete filling layer within a range of 30 cm 2 below the measuring point, and the number is 5 - 10;

[0050] When ROC ≥ 3, it is a grade III defect, indicating that there are defects with an area of more than 50 cm 2 distributed on the surface of the self-compacting concrete filling layer within a range of 30 cm 2 below the measuring point, and the number is 1 - 3;

[0051] Preferably, the grading standard for the quality defect of the filling layer is determined according to the following method:

[0052] When ROC ≤ 2, count the area of the self-compacting concrete filling layer surface within a range of 30 cm 2 below the measuring point, which is 6 cm 2 to 30 cm 2The number of small air bubbles, the number of measured points to be counted is not less than 20, and the quantity distribution range is recorded, which is defined as Class I defect;

[0053] When 2 ≤ ROC ≤ 3, count the surface area of the self-compacting concrete filling layer within 30 cm below the measured point 2 ranging from 30 cm 2 to 50 cm 2 for the number of air bubbles, the number of measured points to be counted is not less than 20, and the quantity distribution range is recorded, which is defined as Class II defect;

[0054] When ROC ≥ 3, count the surface area of the self-compacting concrete filling layer within 30 cm below the measured point 2 ranging from 50 cm 2 and above for the defects, the number of measured points to be counted is not less than 20, and the quantity distribution range is recorded, which is defined as Class III defect;

[0055] Step 6, Overall quality assessment of the filling layer of the measured slab track:

[0056] If N Ⅰ + 3 * N Ⅱ ≤ 3 and N Ⅲ ≤ 1, the overall quality of the filling layer is Grade A, indicating excellent pouring quality;

[0057] If 3 < N Ⅰ + 3 * N Ⅱ ≤ 6 and N Ⅲ ≤ 1, the overall quality of the filling layer is Grade B, indicating average pouring quality;

[0058] If N Ⅰ + 3 * N Ⅱ > 6 or N Ⅲ > 1, the overall quality of the filling layer is Grade C, indicating unqualified pouring quality;

[0059] Among them, N Ⅰ is the total number of measured points reaching Class I defect, N Ⅱ is the total number of measured points reaching Class II defect, N Ⅲ is the total number of measured points reaching Class III defect.

[0060] Preferably, the surface of the measured ballastless track slab is kept dry or wet and there is no ponding.

[0061] Preferably, the geotextile or vibration damping pad in the structure of the measured ballastless track slab is located between the track slab and the self-compacting concrete filling layer.

[0062] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0063] (1) The present invention uses a polycapability hammer as the excitation device. The shock wave can effectively penetrate the geotextile and the vibration damping pad, and obtain the vibration response signal of the self-compacting concrete filling layer. By analyzing the admittance spectrum, the defects of the filling layer can be effectively detected and identified.

[0064] (2) The detection equipment of the present invention is lightweight and easy to carry, can be used for detection in complex environments, has strong anti-environmental interference, and at the same time has simple operation and high repeatability.

[0065] (3) The present invention is a non-destructive testing method. By detecting the change of the admittance rate at the corner detection points of the plate and multiple in-plate detection points, it avoids the disadvantages of traditional testing methods such as low efficiency, strong subjectivity, taking a point as the whole, time-consuming and laborious, and can achieve rapid, efficient and accurate detection of the self-compacting concrete filling layer.

[0066] (4) The present invention constructs the mapping relationship between the admittance spectrum characteristic signal parameters and the quality defects of the filling layer, proposes the defect identification threshold of the filling layer, and provides refined evaluation indexes and methods for defects, providing an efficient and reliable detection method for project acceptance. Description of the Drawings

[0067] Figure 1 is a schematic diagram of the geotextile-type subway slab ballastless track structure;

[0068] In the figure: from top to bottom are the ballastless track slab, the geotextile, the self-compacting concrete filling layer, and the concrete base.

[0069] Figure 2 is the flow chart of the admittance method for detecting the geotextile-type subway slab ballastless track.

[0070] Figure 3 is the schematic diagram of the measuring point distribution of the geotextile-type subway slab ballastless track.

[0071] Figure 4 is the time history curve of the velocity of the measuring point No. 1;

[0072] Figure 5 is the time history curve of the impact force of the measuring point No. 1;

[0073] Figure 6 is the admittance spectrum curve of the measuring point No. 1;

[0074] Figure 7 is the schematic diagram of different defects on the surface of the self-compacting concrete filling layer;

[0075] Among them, a is a grade I defect, b is a grade II defect, and c is a grade III defect. Detailed Embodiment

[0076] The technical solution of the present invention will be clearly and completely described below in conjunction with embodiments and the accompanying drawings. The following embodiments are only for explaining the technical concept and features of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. However, the protection scope of the present invention cannot be limited thereby. Any equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

[0077] Embodiment 1:

[0078] See Figures 1 - 7 , in this embodiment, a geotextile-type subway slab ballastless track structure is taken as an example ( Figure 1 ), and the structure from top to bottom is successively a ballastless track slab, a geotextile, a self-compacting concrete filling layer, and a concrete base; in this embodiment, the non-destructive detection method for defects in the self-compacting concrete filling layer of a subway slab track described in the present invention is used for inspection, and the non-destructive detection process of the admittance method is as Figure 2 , and the method specifically includes the following steps:

[0079] Step 1. Detection preparation:

[0080] Divide grids on the upper surface of the measured ballastless track slab, and arrange a velocity sensor as a measuring point at the intersection position of each grid. Connect the velocity sensor, a concentrated energy hammer with a built-in stress sensor, and a detection host arranged outside the track slab to be measured;

[0081] Main technical parameters of the detection instrument: (1) Detection host: Pulse response tester, the main body is a portable computer, in which the hardware and software systems are used to collect, record, and process the input of the stress sensor in the hammer and the output of the velocity sensor, and are respectively equipped with dual-channel data acquisition cards, with a range of ±5V voltage and 8-bit resolution. After impacting and storing the test results, the instrument can immediately display the admittance spectrum; (2) Concentrated energy hammer: A hammer weighing 1 kg, equipped with a cylindrical rubber head with a diameter of 50 mm, having sufficient hardness, generating an impact force amplitude spectrum in a frequency range of at least 2 kHz. Its built-in stress sensor can measure a dynamic force of up to 50 kN, and its resonance frequency does not exceed 10 kHz. During the knocking test of the track slab, a typical force-time waveform and force amplitude spectrum are generated by knocking with a hammer with a hard rubber hammer head; (3) Velocity sensor: Piezoelectric ceramic type velocity sensor (seismic geophone), which can respond to normal surface movement. The natural frequency of this sensor should be less than 15 Hz, have a constant sensitivity in the frequency range of 15 - 1000 Hz, and no coupling agent is required during the test process.

[0082] Figure 3The size of the measured track slab is 4.7 m × 2.3 m (length × width). The grid size arranged on the measured track slab is less than or equal to 600 mm. The velocity sensors at the grid intersections need to avoid the sleeper positions on the measured track slab, and the distance from the long side of the track slab is 300 mm, and the distance from the short side of the track slab is 550 mm. There are 35 measuring points in total. The 35 measuring points are numbered in sequence. Among them, the measuring points numbered 1#, 7#, 29#, and 35# are the slab corner measuring points, and the remaining measuring points are the in-slab measuring points;

[0083] Step 2, Non-destructive testing and data processing:

[0084] Use a polycapability hammer to conduct a standard percussion test within any of the grids described in Step 1. The distance between the percussion point and the velocity sensor is 10 ± 2.5 cm. The detection host obtains the force time history curve and the corresponding velocity time history curve of this measuring point based on the time history data measured by the stress sensor and the velocity sensor. Compare the velocity spectrum and the force spectrum obtained after performing a fast Fourier transform on these two time history curves, and then the admittance spectrum curve of this measuring point can be obtained; Conduct standard percussion tests in other grids in the same way to obtain the admittance spectrum curves of all measuring points on the measured track slab;

[0085] Taking the measuring point 1# on the measured ballastless track slab as an example, use a polycapability hammer to conduct a standard percussion test at the percussion point within the corresponding grid. The detection host obtains the velocity time history curve ( Figure 4 ) and the impact force time history curve ( Figure 5 ) of the measuring point 1#. According to Equation (1), compare (divide) the velocity spectrum obtained through a fast Fourier transform with the force spectrum to obtain the admittance spectrum curve ( Figure 6 ) of the vibration signal of the measuring point 1#;

[0086] The admittance of the measured ballastless track slab is calculated according to Equation (1):

[0087]

[0088] In the formula, V(f) is the velocity spectrum after a fast Fourier transform, F(f) is the force spectrum obtained after a fast Fourier transform, and H(ω) is the admittance spectrum;

[0089] Step 3, Preliminary determination of the quality of the filling layer:

[0090] According to the admittance spectrum curves obtained in Step 2, calculate the admittance ratio R of each measuring point to obtain the in-slab admittance ratio R I and the slab corner admittance ratio R C . According to the in-slab admittance ratio threshold R IT and the slab corner admittance ratio threshold R CT , preliminarily determine whether the quality of the self-compacting concrete filling layer is qualified;

[0091] The admittance rate R is calculated according to Equations (2) to (4):

[0092] H S = f(x) max , 0 ≤ x ≤ 100 (2)

[0093]

[0094]

[0095] where x is the frequency, and H S is the admittance peak value within the frequency range of 0 to 100 Hz in the admittance spectrum; is the average admittance value within the frequency range of x1 to x2 Hz in the admittance spectrum, with x1 = 100 and x2 = 1200; R is the admittance rate, that is, the ratio of the admittance peak value to the average admittance value within a specific frequency range in the admittance spectrum curve;

[0096] According to Figure 6 it can be obtained that the admittance peak value within the frequency range of 0 to 100 Hz in the admittance spectrum curve of Measuring Point 1 is H S = 4.60, and the average admittance value within the frequency range of 100 to 1200 Hz Then the admittance rate R = 3.48; the admittance rates R of all measuring points on the measured track slab are shown in Table 1;

[0097] Table 1 Admittance Rates of All Measuring Points on the Measured Track Slab

[0098]

[0099]

[0100] The quality of the filling layer under each measuring point on the measured track slab is preliminarily judged according to the following method:

[0101] When the admittance rate R of the measuring point inside the slab I ≤ R IT and the admittance rate R of the measuring point at the slab corner C ≤ R CT , then the perfusion quality of the filling layer under this measuring point is good;

[0102] When the admittance rate R of the measuring point inside the slab I > R IT or the admittance rate R of the measuring point at the slab corner C > R CT , then there are quality defects in the filling layer under this measuring point;

[0103] It should be noted that the admittance rate thresholds R IT and R CT are determined according to the following method:

[0104] Threshold R of the admittance rate inside the slab IT and threshold R of the admittance rate at the slab corner CT are determined as follows:

[0105] For the geotextile slab ballastless track, the threshold R of the admittance rate inside the slab IT is 1.0, and the threshold R of the admittance rate at the slab corner CT is 2.5;

[0106] For the vibration isolation pad slab ballastless track, the threshold R of the admittance rate inside the slab IT is 4.5, and the threshold R of the admittance rate at the slab corner CT is 8.0;

[0107] Since this embodiment is a geotextile slab ballastless track, R IT is taken as 1.0, and R CT is taken as 2.5. According to Table 1, it can be preliminarily determined that there are quality defects in the self-compacting concrete filling layer in the local range under the detection points No. 1, 19, 20, and 21 on the measured track slab;

[0108] Step 4: Obtain the admittance rate reference value through multiple detections:

[0109] Continuously detect multiple ballastless track slabs according to the method described in Steps 1 to 3, and measure the admittance rate R inside the slab I and the admittance rate R at the slab corner C . Select N (N≥5) track slabs with good filling layer perfusion quality at all measurement points from all the measured track slabs as reference track slabs, and select one measurement point inside and at the corner of each reference track slab that satisfies R I ≤1 / 2R IT , R C ≤1 / 2R CT . Calculate the mean values of the admittance rates of the N measurement points inside and at the corner of the slab as the admittance rate reference values inside and at the corner of the slab respectively;

[0110] The admittance rate reference values are calculated according to Formulas (5) and (6):

[0111] R I0 =(R I1 +R I2 +R I3 +···+R IN ) / N (5)

[0112] R C0 =(R C1 +R C2 +R C3 +···+R CN ) / N (6)

[0113] In the formula, R I0Represents the admittance rate reference value within the slab, R C0 Represents the admittance rate reference value at the slab corner, N is the number of reference track slabs, R I1 、R I2 、R I3 、···、R IN Are the admittance rates of any measurement points on N reference track slabs that satisfy R I ≤1 / 2R IT Condition, R C1 、R C2 、R C3 、···、R CN Are the admittance rates of any measurement points on N ballastless track slabs that satisfy R C ≤1 / 2R CT Condition;

[0114] Due to certain differences in reference track slabs under different work areas and construction conditions, several ballastless tracks need to be tested on-site within the test section. In this embodiment, a total of 20 ballastless track slabs are tested, and 5 reference track slabs are selected. The admittance rates of the measurement points within the slab and at the slab corner are shown in Table 2. According to Equations (5) and (6), the admittance rate reference value R I0 Is 0.45, and the admittance rate reference value R C0 Is 1.2;

[0115] Table 2 Admittance Rates of Reference Points within the Reference Track Slab

[0116] Reference slab number JZ1# JZ2# JZ3# JZ4# JZ5# Reference value Admittance rate inside the slab 0.48 0.45 0.50 0.42 0.45 0.45 Admittance rate at the slab corner 1.25 1.20 1.17 1.15 1.23 1.2

[0117] Step 5, Refined Evaluation of the Degree of Defects in the Filling Layer:

[0118] According to the admittance rate reference value obtained in Step 4, calculate the quality defect evaluation index of the filling layer under each measurement point of the measured ballastless track slab with quality defects in the filling layer, and evaluate the degree of defects in the self-compacting concrete filling layer within the test section according to the grading standard of filling layer quality defects;

[0119] The quality defect evaluation index ROC is calculated according to Equations (7) and (8):

[0120] For the measurement points within the slab:

[0121] ROC = (R IS -R I0 ) / R I0 (7)

[0122] For the measurement points at the slab corner:

[0123] ROC = (R CS -R C0 ) / R C0 (8)

[0124] In the formula, ROC is the quality defect evaluation index, representing the mapping relationship between the filling layer defect and the admittance spectrum characteristic signal parameters, defined as the proximity degree between the admittance rate of the measuring point at the position with quality defect in the filling layer and the reference value of the admittance rate. ROC ≥ 1, R IS and R CS represents the admittance rate of the measuring point at the position with quality defect in the filling layer;

[0125] The grading standard for the quality defect of the filling layer under any measuring point is as follows:

[0126] When ROC ≤ 2, it is a grade I defect, indicating that there are small air bubbles with an area of 6 cm 2 to 30 cm 2 distributed on the surface of the self-compacting concrete filling layer within a range of 30 cm below the measuring point, and the number is 10 - 20; 2

[0127] When 2 ≤ ROC ≤ 3, it is a grade II defect, indicating that there are air bubbles with an area of 30 cm 2 to 50 cm 2 distributed on the surface of the self-compacting concrete filling layer within a range of 30 cm below the measuring point, and the number is 5 - 10; 2

[0128] When ROC ≥ 3, it is a grade III defect, indicating that there are defects with an area of more than 50 cm 2 distributed on the surface of the self-compacting concrete filling layer within a range of 30 cm below the measuring point, and the number is 1 - 3; 2

[0129] It should be noted that the grading standard for the quality defect of the filling layer is determined according to the following method:

[0130] When ROC ≤ 2, count the number of small air bubbles with an area of 6 cm 2 to 30 cm 2 on the surface of the self-compacting concrete filling layer within a range of 30 cm below the measuring point. The number of measuring points to be counted is not less than 20, and record the number distribution range, which is defined as a grade I defect, 2 Figure 7 a is the photo of the self-compacting concrete interface corresponding to the measuring point with an ROC value of 1.51 below. There are 15 small air bubbles with an area of 6 cm 2 to 30 cm 2 on the surface of the self-compacting concrete filling layer within a range of 30 cm below the measuring point; 2

[0131] When 2 ≤ ROC ≤ 3, count the number of air bubbles with an area of 30 cm 2 to 50 cm 2 on the surface of the self-compacting concrete filling layer within a range of 30 cm below the measuring point. 2The number of bubbles, the number of measuring points to be counted is not less than 20, and the quantity distribution range is recorded, which is defined as a Class II defect. Figure 7 b) That is, the photo of the self-compacting concrete interface corresponding to the measuring point with an ROC value of 2.35. The area within 30 cm 2 below this measuring point is 6 cm 2 ~30 cm 2 has 7 small bubbles;

[0132] When ROC≥3, count the surface area of the self-compacting concrete filling layer within 30 cm 2 below this measuring point, which is 50 cm 2 or more of the defects. The number of measuring points to be counted is not less than 20, and the quantity distribution range is recorded, which is defined as a Class III defect. Figure 7 -(c) That is, the photo of the self-compacting concrete interface corresponding to the measuring point with an ROC value of 3.74. The area within 30 cm 2 below this measuring point is 6 cm 2 ~30 cm 2 has 3 small bubbles.

[0133] In this embodiment, according to Table 1, the ROC values of the detection points at the quality defect locations of the geotextile-type subway slab track filling layer are calculated, as shown in Table 3. Therefore, the measuring points No. 1, 19, 20, and 21 are all rated as Class I defects, indicating that the self-compacting concrete interfaces within 30 cm 2 below these four measuring points are all 6 cm 2 ~30 cm 2 with small bubbles, and the quantity is in the range of 10 - 20. Other measuring points are rated as good, indicating that the quality of the self-compacting concrete filling layer below other measuring points is good;

[0134] Table 3 Evaluation Results of the Grouting Quality of Each Measuring Point

[0135]

[0136]

[0137] Step 6. Overall Quality Evaluation of the Filling Layer under the Tested Track Slab:

[0138] If N Ⅰ +3*N Ⅱ ≤3 and N Ⅲ ≤1, the overall quality of the filling layer is Class A, indicating excellent grouting quality;

[0139] If 3<N Ⅰ +3*N Ⅱ ≤6 and N Ⅲ ≤1, the overall quality of the filling layer is Class B, indicating average grouting quality;

[0140] If N Ⅰ + 3*N Ⅱ > 6 or N Ⅲ > 1, the overall quality of the filling layer is Class C, indicating that the perfusion quality is unqualified;

[0141] In this embodiment, N Ⅰ is 4, N Ⅱ and N Ⅲ are both 0. According to the above method, the quality grade of the geotextile-type subway slab track filling layer is Class B.

[0142] The above is only the preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, should not be regarded as excluding other embodiments, but 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 techniques 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 nondestructive detection of defects in self-compacting concrete filling layer of subway slab track, characterized in that: The method comprises the following steps: Step 1: Test preparation: Divide the upper surface of the ballastless track slab into grids, obtain 4 slab corner measuring points and multiple slab internal measuring points, and arrange a speed sensor as a measuring point at the intersection of each grid. Step 2: Nondestructive testing and data processing: A knock test is performed in any of the grids described in step 1 using a vibration excitation device with a built-in stress sensor. The detection host obtains the force time history curve and the corresponding velocity time history curve of the measuring point according to the time history data obtained by the stress sensor and the velocity sensor test. The velocity spectrum and force spectrum obtained by fast Fourier transforming the two time history curves are compared to obtain the admittance spectrum curve of the measuring point. A standard knock test is performed in the same way in other grids to obtain the admittance spectrum curves of all measuring points on the track plate under test. Step 3: Preliminary determination of filling layer quality: According to the admittance spectrum curve obtained in step 2, calculate the admittance of each measuring point R , and obtain the plate internal admittance R I and plate angular conductance R C , according to the plate admittance threshold R IT and plate angle conductance threshold R CT , preliminarily determine whether the quality of the self-compacting concrete filling layer is qualified; Step 4: Perform multiple tests to obtain the baseline value of the admittance: Continuously test multiple ballastless track slabs according to steps 1 to 3 to measure the slab internal admittance R I and plate angular conductance R C , select from all the ballastless track slabs tested N Block, where N ≥5, the track slab with good filling quality at all measuring points is used as the reference track slab, and one track slab that meets the requirements is selected from each reference track slab. R I ≤1 / 2 R IT , R C ≤1 / 2 R CT The plate inner and plate corner measuring points of the conditions are calculated separately N The average of the admittances of the measuring points in the plate and at the plate corners is taken as the reference value of the admittances in the plate and at the plate corners; Step 5: Refined assessment of filling layer defect level: According to the admittance reference value obtained in step 4, the quality defect evaluation index of the filling layer under each measuring point of the ballastless track slab under test with quality defects in the filling layer is calculated, and the degree of defects of the self-compacting concrete filling layer in the test section is evaluated according to the filling layer quality defect classification standard; Step 6: Overall quality assessment of the tested slab track filling layer: If N Ⅰ +3* N Ⅱ ≤3 and N Ⅲ ≤1, the overall quality of the filling layer is grade A, indicating excellent filling quality; If 3<N Ⅰ +3* N Ⅱ ≤6 and N Ⅲ ≤1, the overall quality of the filling layer is Class B, indicating that the filling quality is average; If N Ⅰ +3* N Ⅱ >6 or N Ⅲ >1, the overall quality of the filling layer is C, indicating that the filling quality is unqualified; in N Ⅰ To achieve the total number of measurement points for level I defects, N Ⅱ To achieve the total number of measurement points for level II defects, N Ⅲ The total number of measurement points that reach level III defects.

2. The method for nondestructive detection of defects in self-compacting concrete filling layer of subway slab track according to claim 1 is characterized in that: In step 1, the detection grid and speed sensor are arranged according to the following scheme: The grid length and width are both less than or equal to 600mm; the speed sensor should avoid the sleeper position on the track plate to be tested, and the distance from the edge of the track plate to be tested should be greater than or equal to 30cm.

3. The method for nondestructive detection of defects in self-compacting concrete filling layer of subway slab track according to claim 1 is characterized in that: In step 2, the admittance of the ballastless track slab under test is calculated according to formula (1): (1) In the formula, is the velocity spectrum after fast Fourier transform, is the force spectrum obtained after fast Fourier transform, This is the admittance spectrum.

4. The method for nondestructive detection of defects in self-compacting concrete filling layer of subway slab track according to claim 1, characterized in that: In step 3, the admittance R Calculate according to formula (2) to (4): (2) (3) (4) In the formula, is the frequency, It is the admittance peak value in the frequency range of 0~100Hz in the admittance spectrum; is the frequency in the admittance spectrum x 1~ x The mean value of admittance within the 2Hz range is taken as x 1=100, x 2=1200; R It is the admittance ratio, that is, the ratio of the admittance peak value to the admittance mean value within a specific frequency range in the admittance spectrum curve.

5. The method for nondestructive detection of defects in self-compacting concrete filling layer of subway slab track according to claim 1, characterized in that: In step 4, the admittance reference value is calculated according to formula (5) and (6): (5) (6) Where: R I0 Indicates the reference value of the plate admittance. R C0 Indicates the reference value of plate angular conductance, N is the number of reference track plates, R I1 、 R I2 、R I3 、···、R IN for N Block reference track plate meets R I ≤1 / 2 R IT The admittance of any measuring point under the conditions, R C1 、R C2 、 R C3 、···、R CN for N Ballastless track slabs meet R C ≤1 / 2 R CT The admittance of any measuring point under certain conditions.

6. The method for nondestructive detection of defects in self-compacting concrete filling layer of subway slab track according to claim 1, characterized in that: In step 5, the quality defect evaluation index ROC Calculate according to formula (7) and (8): For on-board measurement points: (7) For the board corner measurement points: (8) Where, ROC It is a quality defect evaluation index, which indicates the mapping relationship between the filling layer defect and the characteristic signal parameters of the admittance spectrum. It is defined as the degree of similarity between the admittance of the measuring point at the location where the quality defect of the filling layer exists and the admittance reference value. ROC ≥1, R IS and R CS Indicates the admittance of the measuring point where there are quality defects in the filling layer.

7. The method for nondestructive detection of defects in self-compacting concrete filling layer of subway slab track according to claim 6, characterized in that: In step 5, the grading standard of the filling layer quality defects at each measuring point is: when ROC When ≤2, it is a level I defect, indicating that 30cm below the measuring point 2 The surface of the self-compacting concrete filling layer within the range is distributed with an area of ​​6cm 2 ~30cm 2 Small bubbles, the number is 10~20; When 2≤ ROC When ≤3, it is a level II defect, indicating that 30cm below the measuring point 2 The surface of the self-compacting concrete filling layer within the range is distributed with an area of ​​30cm 2 ~50cm 2 The number of bubbles is 5~10; when ROC ≥3, it is a level III defect, indicating that 30cm below the measuring point 2 The surface of the self-compacting concrete filling layer within the range is distributed with an area of ​​50cm 2 The number of the above defects is 1~3.

8. The method for nondestructive detection of defects in self-compacting concrete filling layer of subway slab track according to claim 7, characterized in that: In step 5, the grading standard of filling layer quality defects is determined by the following method: when ROC When ≤2, count the 30cm below the measuring point 2 The surface area of ​​the self-compacting concrete filling layer within the range is 6cm 2 ~30cm 2 The number of small bubbles counted shall be no less than 20 measuring points, and the distribution range of the number shall be recorded, which is defined as Grade I defect; When 2≤ ROC When ≤3, count the 30cm below the measuring point 2 The surface area of ​​the self-compacting concrete filling layer within the range is 30cm 2 ~50cm 2 The number of bubbles counted shall be no less than 20 measuring points, and the distribution range of the number shall be recorded, which is defined as Level II defect; when ROC ≥3, count the 30cm below the measuring point 2 The surface area of ​​the self-compacting concrete filling layer within the range is 50cm 2 For the above defects, the number of measurement points counted shall be no less than 20, and the quantity distribution range shall be recorded, which is defined as Level III defects.

9. The method for nondestructive detection of defects in self-compacting concrete filling layer of subway slab track according to claim 1, characterized in that: The surface of the ballastless track slab under test remains dry or moist, and there is no water accumulation.

10. The method for nondestructive detection of defects in self-compacting concrete filling layer of subway slab track according to claim 1, characterized in that: The geotextile or vibration damping pad in the tested ballastless track slab structure is located between the track slab and the self-compacting concrete filling layer.

Images