Accurate detection method for thickness of tunnel secondary lining concrete protection layer

Abstract

The invention provides a method for accurately detecting the thickness of a tunnel secondary lining concrete protection layer. The method comprises the following steps: step 1, acquiring an actual detection image of a reinforcing steel bar in concrete; 2, processing the actual detection image of the reinforcing steel bar to obtain a corresponding geometrical relationship curve; 3, deducing a corresponding geometric equation according to the geometric characteristics of the geometric relation curve; 4, processing the geometric equation to obtain an electromagnetic wave propagation velocity v; 5, substituting the data to obtain an accurate electromagnetic wave speed; and step 6, performing time-depth conversion to obtain the accurate thickness of the concrete protection layer. According to the invention, the concrete thickness measurement precision is improved, the detection time is obviously shortened, and the field operation is simpler and more convenient.

Description

Technical Field

[0001] The invention belongs to the field of concrete detection, and in particular relates to a method for accurately detecting the thickness of a secondary lining concrete protective layer of a tunnel. Background Art

[0002] At present, the thickness of the concrete protective layer of the second phase of the tunnel lining is one of the important indicators of tunnel engineering quality, which is directly related to the safety and durability of the tunnel. If the thickness of the tunnel lining is insufficient, it may lead to unstable tunnel structure, potential safety hazards, and cause production safety accidents. The more commonly used detection methods for concrete thickness detection are ground penetrating radar, ultrasonic shear wave reflection three-dimensional imaging, and laser cross-section shifting. However, the most widely used method is the ground penetrating radar method. This is because compared with other methods, the ground penetrating radar method has the following advantages: while detecting the thickness, it can also detect the quality of backfill grouting and internal defects; it has high work efficiency and can be used for large-area inspections. The direct parameter of the ground penetrating radar method is the electromagnetic wave reflection time t, and the final thickness or defect depth needs to be calculated according to the formula Perform time-depth conversion calculation, where is the propagation speed of electromagnetic waves in the medium, is the reflection time of the reflected wave at the detection target interface, To detect the thickness of the target layer or the depth of the target interface. From the principle of time-depth conversion, it can be seen that the key to the accuracy of the thickness detection of the concrete secondary lining protective layer is the propagation speed of electromagnetic waves in the medium. ,Therefore, obtaining accurate electromagnetic wave propagation velocity is of great significance to improving the ,detection accuracy of the concrete secondary lining protective layer. Summary of the invention

[0003] In view of the above problems, the present invention proposes a method for accurately detecting the thickness of the secondary lining concrete protective layer of a tunnel, comprising the following steps: Step 1: Obtain the actual detection image of the steel bars inside the concrete; Step 2: Processing the actual inspection image of the steel bar to obtain the corresponding geometric relationship curve; Step 3, deriving the corresponding geometric equation through the geometric characteristics of the geometric relationship curve; Step 4: Process the geometric equation to obtain the electromagnetic wave propagation speed v; Step 5: Substitute the data to obtain the precise electromagnetic wave speed; Step 6: Time-depth conversion to obtain accurate concrete cover thickness.

[0004] Preferably, the actual detection image of the steel bars in step one sends high-frequency electromagnetic waves into the concrete through a ground penetrating radar transmitter, and the signal received by the receiver is processed by digital signals to generate a time domain reflectogram (TDR) or amplitude diagram that can show the position, depth and intensity of the reflection point.

[0005] Preferably, the specific processing step of the actual steel bar detection image in step 2 is to process the image according to the electromagnetic wave reflection principle and the single-point imaging principle to obtain a geometric relationship curve.

[0006] Preferably, in step 3, according to the relationship of the geometric features extracted from the geometric relationship curve, the following geometric relationship equation can be obtained by the Pythagorean theorem: ; where h x The vertical distance of the curve obtained by curve fitting from the emission point to the positions of multiple reflection points; h0 is the thickness of concrete above the steel bar to be tested; l is the shortest distance from the launch point to the surface of the steel bar; x It is the horizontal distance from the launch point to the vertical line passing through the geometric center of the steel bar and perpendicular to the concrete interface; r is the radius of the steel bar; From the principle of single-point imaging, we know h x =l ,Depend on h x =vt x It can be deduced that: ; in V The propagation speed of electromagnetic waves ； t0 is the vertical one-way travel time of the electromagnetic wave; t x is the one-way travel time of the electromagnetic wave horizontal offset; ; ; is the two-way travel time of the horizontal offset distance of the electromagnetic wave; It is the vertical two-way travel time of electromagnetic waves.

[0007] Preferably, the propagation speed of the electromagnetic wave in step 4 is: ; Where R is the diameter of the steel bar.

[0008] Preferably, in step 6, the electromagnetic wave velocity v obtained in step 5 is substituted into the time-depth conversion formula to obtain the accurate thickness of the concrete protective layer. ; Where h0 is the thickness of the concrete cover above the steel bar to be tested.

[0009] The present invention has the following beneficial effects: 1. The present invention innovatively proposes a method for accurately detecting the thickness of the secondary lining concrete protective layer. The existing specifications still do not have an accurate detection method for the thickness of the concrete protective layer that can be adopted. The speed is solved by using the arc of the reflection hyperbola on the target to be measured, ignoring the internal diameter of the target to be measured. The input speed is a conversion value of the empirical value of the dielectric constant, which belongs to the estimated speed. This method constructs a relationship based on the target to be measured, the thickness of the concrete protective layer and the distance to the measured point, and can solve the accurate speed. The present invention innovatively proposes a method for accurately detecting the thickness of the concrete protective layer; 2. The present invention can significantly shorten the test time. For the measurement of electromagnetic wave velocity, the "Specifications for Geophysical Exploration of Hydropower Engineering" (NB∕T 10227-2019) clearly states: On-site inspection work should comply with the following regulations: When using ground penetrating radar, ultrasonic shear wave reflection three-dimensional imaging, and acoustic wave reflection methods for inspection, an appropriate number of parameter calibration holes should be arranged; data compilation should meet the following requirements: The inspection results should be compared and analyzed with the parameter calibration holes, and the electromagnetic wave velocity and acoustic wave velocity of the concrete should be corrected. The parameter calibration holes need to be drilled by a coring machine and then the actual depth of the target layer is measured before electromagnetic wave velocity calibration. Drilling takes at least 0.5 hours, and 10 parameter calibration holes take at least 5 hours. The new method proposed in this patent completes all electromagnetic wave velocity calibrations within 0.5 hours; 3. The present invention can greatly eliminate the statistical error caused by too few calibration hole samples. By using the steel bar reflection arc to calibrate the electromagnetic wave velocity, all the steel bar data in the detection area can be collected, and the number is mostly 102~104. Compared with the traditional limited calibration holes, the statistical error is smaller; 4. The present invention has simple steps and is easy to use. Since it adopts a non-destructive testing method and the same equipment (ground penetrating radar) is used for thickness detection and velocity calibration, the difference is that the radar antenna frequency is different and the target object used is also the designed standard steel bars in the lining, so the entire on-site operation is very simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 A flow chart of a method for accurately detecting the thickness of a tunnel secondary lining concrete protective layer provided by the present invention; Figure 2 This is a schematic diagram of the principle of electromagnetic wave reflection in concrete provided by the present invention; Figure 3 Schematic diagram of the principle of electromagnetic wave single-point mapping in concrete provided by the present invention Figure 4 This is the actual inspection diagram of the steel bars in concrete provided by the present invention; Figure 5This is a schematic diagram of the calculation principle of electromagnetic wave velocity calibration in concrete provided by the present invention; Figure 6 This is a schematic diagram of reading the calibration parameters of electromagnetic wave velocity in concrete provided by the present invention; Figure 7 This is a schematic diagram of the radar image above the steel bars inside the concrete provided by the present invention. DETAILED DESCRIPTION

[0011] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: See also Figures 1 to 7 A method for accurately detecting the thickness of the secondary lining concrete protective layer of a tunnel comprises the following steps: Step 1: Obtain the actual detection image of the steel bars inside the concrete; Step 2: Processing the actual inspection image of the steel bar to obtain the corresponding geometric relationship curve; Step 3, deriving the corresponding geometric equation through the geometric characteristics of the geometric relationship curve; Step 4: Process the geometric equation to obtain the electromagnetic wave propagation speed v; Step 5: Substitute the data to obtain the precise electromagnetic wave speed; Step 6: Time-depth conversion to obtain accurate concrete cover thickness.

[0012] Preferably, the actual detection image of the steel bars in step 1 is generated by sending high-frequency electromagnetic waves into the concrete through a ground-penetrating radar transmitter, and the signal received by the receiver is processed by digital signal to generate a time domain reflectogram (TDR) or amplitude diagram that can show the location, depth and intensity of the reflection point. The transmitter of the ground-penetrating radar sends high-frequency electromagnetic waves underground. These electromagnetic waves can penetrate concrete and will be reflected when encountering the interface of different materials. When the electromagnetic waves encounter steel bars or other heterogeneous materials, they will be partially reflected back. The electromagnetic properties of different materials (such as dielectric constant) cause the reflected signal intensity and return time to be different. The receiver can capture the reflected signals, which will contain detailed information about the material interface and structure, and generate a time domain reflectogram (TDR) or amplitude diagram. These images can show the location, depth and intensity of the reflection point.

[0013] Preferably, the specific processing step of the actual steel bar detection image in step 2 is to process the image according to the electromagnetic wave reflection principle and the single-point imaging principle to obtain a geometric relationship curve.

[0014] Preferably, in step 3, according to the relationship of the geometric features extracted from the geometric relationship curve, the following geometric relationship equation can be obtained by the Pythagorean theorem: ; where h xThe vertical distance of the curve obtained by curve fitting from the emission point to the positions of multiple reflection points; h0 is the thickness of concrete above the steel bar to be tested; l is the shortest distance from the launch point to the surface of the steel bar; x It is the horizontal distance from the launch point to the vertical line passing through the geometric center of the steel bar and perpendicular to the concrete interface; r is the radius of the steel bar; From the principle of single-point imaging, we know h x =l ,Depend on h x =vt x It can be deduced that: ; in V The propagation speed of electromagnetic waves ； t0 is the vertical one-way travel time of the electromagnetic wave; t x is the one-way travel time of the electromagnetic wave horizontal offset; ; ; is the two-way travel time of the horizontal offset distance of the electromagnetic wave; It is the vertical two-way travel time of electromagnetic waves.

[0015] Preferably, the propagation speed of the electromagnetic wave in step 4 is: ; Where R is the diameter of the steel bar.

[0016] Preferably, in step 6, the electromagnetic wave velocity v obtained in step 5 is substituted into the time-depth conversion formula to obtain the accurate thickness of the concrete protective layer. ; Where h0 is the thickness of the concrete cover above the steel bar to be tested.

[0017] Embodiment 1: The diameter of the steel bar under the concrete at a certain location is 32mm. The vertical two-way travel time of electromagnetic waves is measured using ground penetrating radar. is 1.63s, and the horizontal offset of the electromagnetic wave is the two-way travel time It is 3.77s, and the horizontal offset distance x is 1.9m.

[0018] Substitute the measured data into the formula: ; The electromagnetic wave propagation speed v=1.06m / s; Substitute v into the time-depth conversion formula: ; The thickness of the concrete protective layer is obtained as h0=8.64cm.

[0019] The thickness of the concrete cover obtained by calculating the electromagnetic wave propagation velocity using the traditional method is 7.6 cm; The thickness of the concrete protective layer measured by a tape measure during on-site concrete demolition was 9.1 cm.

[0020] Embodiment 2: The diameter of the steel bar under the concrete at a certain location is 18 mm. The vertical two-way travel time of electromagnetic waves is measured using ground penetrating radar. is 1.73s, and the horizontal offset of the electromagnetic wave is the two-way travel time It is 3.64s, and the horizontal offset distance x is 1.8m.

[0021] Substitute the measured data into the formula: ; The electromagnetic wave propagation speed v=1.09m / s; Substitute v into the time-depth conversion formula: ; The thickness of the concrete cover is obtained as h0 = 9.43 cm; The thickness of the concrete cover obtained by calculating the electromagnetic wave propagation velocity using the traditional method is 8.4 cm; The thickness of the concrete protective layer measured by a tape measure during on-site concrete demolition was 9.4 cm.

[0022] The above embodiments are only preferred technical solutions of the present invention and should not be regarded as limiting the present invention. The protection scope of the present invention shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A method for accurately detecting the thickness of the secondary lining concrete protective layer of a tunnel, characterized in that: The following steps are involved: Step 1: Obtain the actual detection image of the steel bars inside the concrete; Step 2: Processing the actual inspection image of the steel bar to obtain the corresponding geometric relationship curve; Step 3, deriving the corresponding geometric equation through the geometric characteristics of the geometric relationship curve; Step 4: Process the geometric equation to obtain the electromagnetic wave propagation speed v; Step 5: Substitute the data to obtain the precise electromagnetic wave speed; Step 6: Time-depth conversion to obtain accurate concrete cover thickness.

2. According to claim 1, a method for accurately detecting the thickness of the secondary lining concrete protective layer of a tunnel, characterized in that: In the step 1, the actual detection image of the steel bars is transmitted through a ground penetrating radar transmitter to send high-frequency electromagnetic waves into the concrete. The signal received by the receiver is processed by digital signals to generate a time domain reflectogram (TDR) or amplitude diagram that can show the position, depth and intensity of the reflection point.

3. According to claim 1, a method for accurately detecting the thickness of the secondary lining concrete protective layer of a tunnel, characterized in that: The specific processing steps for the actual steel bar detection image in step 2 are: processing the image according to the electromagnetic wave reflection principle and the single-point imaging principle to obtain a geometric relationship curve.

4. According to claim 1, a method for accurately detecting the thickness of the secondary lining concrete protective layer of a tunnel, characterized in that: In step 3, the relationship between the geometric features extracted from the geometric relationship curve can be used to obtain the following geometric relationship formula based on the Pythagorean theorem: ； where h x The vertical distance of the curve obtained by curve fitting from the emission point to the positions of multiple reflection points; h0 is the thickness of concrete above the steel bar to be tested; l is the shortest distance from the launch point to the surface of the steel bar; x It is the horizontal distance from the launch point to the vertical line passing through the geometric center of the steel bar and perpendicular to the concrete interface; r is the radius of the steel bar; From the principle of single-point imaging, we know h x =l ,Depend on h x =vt x It can be deduced that: ； in V The propagation speed of electromagnetic waves ； t0 is the vertical one-way travel time of the electromagnetic wave; t x is the one-way travel time of the electromagnetic wave horizontal offset; ； ； is the two-way travel time of the horizontal offset distance of the electromagnetic wave; It is the vertical two-way travel time of electromagnetic waves.

5. A method for accurately detecting the thickness of the secondary lining concrete protective layer of a tunnel according to claim 4, characterized in that: The propagation speed of the electromagnetic wave in step 4 is: ； Where R is the diameter of the steel bar.

6. According to claim 1, a method for accurately detecting the thickness of the secondary lining concrete protective layer of a tunnel, characterized in that: In step 6, the electromagnetic wave velocity v obtained in step 5 is brought into the time-depth conversion formula to obtain the accurate thickness of the concrete protective layer. ； Where h0 is the thickness of the concrete cover above the steel bar to be tested.

Images