Directional sound wave-laser vibration measurement remote detection system and method for tunnel lining cavity

Abstract

The invention provides a directional sound wave-laser vibration measurement remote detection system and method for a tunnel lining cavity. The detection system comprises a directional sound wave excitation device, a laser vibration meter, a data processing unit and a supporting and positioning assembly, the method comprises the following steps: system layout and calibration, detection grid definition, collaborative excitation and scanning, and defect determination and imaging. According to the invention, remote and non-contact accurate detection of cavity defects in the tunnel lining can be realized, manual misjudgment is reduced, the detection efficiency is improved, and the coverage range is widened.

Description

Technical Field

[0001] This invention belongs to the field of non-destructive testing technology for tunnel engineering, specifically relating to a long-distance directional acoustic-laser vibration measurement system and method for tunnel lining cavities. Background Technology

[0002] Voids in tunnel lining are a common quality defect in tunnel construction, with various causes including concrete shrinkage, improper pumping pressure, inadequate waterproofing layer installation, insufficient concrete vibration, insufficient arch rigidity, karst formation, and the influence of groundwater. These voids disrupt the tight bond between the lining and the surrounding rock or waterproofing layer, leading to localized stress concentration and subsequently causing lining deformation, cracking, or even detachment, seriously threatening the structural and operational safety of the tunnel. Therefore, it is necessary to inspect the tunnel lining.

[0003] Currently, the commonly used tunnel lining inspection technologies in engineering have the following bottlenecks:

[0004] Contact detection is inefficient: Traditional methods such as impact echo and hammering require the sensor or striking device to directly contact the lining surface, which is cumbersome to operate. Especially in hard-to-access areas such as high arches, the efficiency is extremely low and there are safety hazards.

[0005] Reliance on human experience: Existing methods for identifying void defects mainly rely on the operator's experience and subjective judgment, such as judging whether there are voids inside the lining by tapping the sound or feeling the vibration, which can easily lead to misjudgment or omission.

[0006] Significant environmental interference: The internal components of the structure, such as steel bars and aggregates, severely interfere with the signal propagation of traditional detection methods such as ultrasonic waves and electromagnetic waves, resulting in inaccurate test results.

[0007] Limited detection depth: Some detection methods, such as infrared thermal imaging and ground-penetrating radar, are limited by the characteristics of concrete structures, resulting in limited detection depth and making it difficult to effectively identify internal voids in the lining.

[0008] Insufficient automation: Existing testing methods are mostly manual operations, lacking automated data collection and analysis mechanisms, making it difficult to guarantee the objectivity and consistency of test results. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a remote detection system and method for directional acoustic-laser vibration measurement of tunnel lining cavities, enabling remote, non-contact, and accurate detection of internal void defects in tunnel linings, reducing human error, and improving detection efficiency and coverage.

[0010] The technical solution of this invention is: a long-distance directional acoustic-laser vibration measurement system for tunnel lining cavities, comprising:

[0011] Directional acoustic vibration excitation device, laser vibration meter, data processing unit, and support and positioning components;

[0012] The directional acoustic vibration excitation device is installed inside the tunnel and is used to emit directional acoustic waves to the lining surface to excite its vibration.

[0013] The laser vibrometer is positioned adjacent to the directional acoustic excitation device and is used for non-contact measurement of the vibration response signal of the lining surface under acoustic excitation.

[0014] The support and positioning components are used to fix and adjust the spatial position and orientation of the directional acoustic excitation device and the laser vibrometer, ensuring that the effective areas of the two are consistent on the lining surface.

[0015] The data processing unit is communicatively connected to the laser vibration meter and is used to receive and process vibration response signals, and to determine whether there are voids or defects inside the lining by analyzing vibration characteristics.

[0016] Furthermore, the working distance of the directional acoustic wave excitation device is 5-20 meters, and the measuring distance of the laser vibration meter is 5-20 meters.

[0017] Furthermore, the support and positioning assembly includes a support frame and a positioning device. The directional acoustic excitation device and the laser vibrometer are mounted on the support frame, and their emission axes are kept coaxial or arranged at a small angle.

[0018] Furthermore, the data processing unit includes:

[0019] Signal acquisition module, spectrum analysis module, and defect determination module;

[0020] The signal acquisition module is used to record the vibration time-domain signal of each measuring point on the lining surface;

[0021] The spectrum analysis module is used to perform spectrum analysis on the vibration signal, extract the resonance frequency, and calculate the vibration energy ratio;

[0022] The defect determination module is used to determine and locate void defects based on the comparison between the vibration energy ratio and a preset threshold.

[0023] Furthermore, the method for calculating the vibration energy ratio is as follows:

[0024] Within a selected frequency range, the ratio of the integral value of the vibration velocity power spectrum at the measured point to the integral value of the vibration velocity power spectrum at a healthy reference point.

[0025] Furthermore, the tunnel lining void directional acoustic-laser vibration long-distance detection system also includes a mobile platform, and the support and positioning components are mounted on the mobile platform.

[0026] Long-distance directional acoustic-laser vibratory testing of tunnel lining cavities, employing any of the above-described testing methods, includes the following steps:

[0027] System deployment and calibration: Install and calibrate the directional acoustic excitation device and laser vibration meter inside the tunnel to ensure that they are aligned with the lining area to be inspected.

[0028] Define the detection grid: Delineate the detection area on the lining surface to be inspected, and define the scanning point grid for laser vibration measurement;

[0029] Coordinated excitation and scanning: The directional acoustic excitation device is controlled to emit acoustic excitation signals with preset parameters, while the laser vibrometer is controlled to scan the gridded measurement points point by point and collect the vibration response signals of each point;

[0030] Signal processing and feature extraction: Perform spectral analysis on the collected vibration signals, extract the resonant frequencies of each measuring point, and calculate the vibration energy ratio relative to the healthy reference area;

[0031] Defect identification and imaging: The system determines whether there is a cavity below the measuring point based on whether the vibration energy ratio exceeds a preset threshold, and performs spatial imaging on the identification results of all measuring points to generate a defect distribution map and inspection report.

[0032] Furthermore, in the collaborative excitation and scanning step, the parameters of the acoustic excitation signal include frequency range, signal form, and sound pressure level, which are set according to the characteristics of the lining material and the detection depth requirements.

[0033] Furthermore, in the signal processing and feature extraction steps, by comparing the vibration spectrum of the measured point with that of a nearby healthy reference point, excess response appearing in a specific frequency range is identified as an indicator of potential defects.

[0034] Furthermore, in the defect determination and imaging step, the preset threshold is determined by statistically analyzing the vibration energy ratio distribution of the healthy lining area and combining it with engineering experience.

[0035] The beneficial effects of this invention are:

[0036] (1) It eliminates the need for sensors or striking devices to directly contact the lining surface, thus avoiding damage or contamination to the lining surface caused by traditional methods.

[0037] (2) The directional acoustic wave excitation device can maintain effective sound pressure at a distance of 20m, and the laser vibration meter has a working distance of 5-20m, which is suitable for high altitude or dangerous areas, greatly improving the safety and convenience of detection;

[0038] (3) The laser vibrometer can quickly complete grid scanning, and the detection speed is far greater than that of manual tapping, which greatly improves the detection efficiency and coverage.

[0039] (4) By analyzing the vibration characteristics of the lining surface under directional acoustic excitation, including resonance frequency, vibration energy ratio and mode distribution, quantitative analysis and accurate location of void defects can be achieved, reducing human error and omission.

[0040] (5) The system has automated data acquisition and analysis capabilities, which improves the objectivity and consistency of the test results and reduces the reliance on human experience;

[0041] (6) The system is not sensitive to structural components such as steel bars and aggregates in tunnel lining, and can work stably in complex environments, which improves the reliability and accuracy of detection. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the structure of the tunnel lining void directional acoustic wave-laser vibration measurement long-distance detection system of the present invention.

[0043] Figure 2 This is a schematic diagram of the principle of the tunnel lining void directional acoustic wave-laser vibration measurement long-distance detection system in this invention.

[0044] Figure 3 This is a flowchart of the long-distance detection method for directional acoustic wave-laser vibration measurement of tunnel lining cavities in this invention. Detailed Implementation

[0045] Various exemplary embodiments of the invention will now be described in detail with reference to the accompanying drawings. The descriptions of the exemplary embodiments are merely illustrative and are in no way intended to limit the invention or its application or use. The invention can be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to make the invention thorough and complete, and to fully express the scope of the invention to those skilled in the art. It should be noted that, unless otherwise specifically stated, the relative arrangement of components and steps, the composition of materials, numerical expressions, and values ​​set forth in these embodiments should be interpreted as merely exemplary and not as limiting.

[0046] The terms "first," "second," and similar words used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different parts. Words such as "including" or "comprising" mean that the element preceding the word encompasses the element listed after it, without excluding the possibility of encompassing other elements. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0047] like Figure 1 and 2As shown, a long-distance detection system for directional acoustic wave-laser vibration measurement of tunnel lining cavities is disclosed, comprising: a directional acoustic wave excitation device 1, a laser vibrometer 2, a data processing unit 3, and a support and positioning assembly; the directional acoustic wave excitation device 1 is installed inside the tunnel and is used to emit directional acoustic waves to the lining surface to excite its vibration; the laser vibrometer 2 is arranged adjacent to the directional acoustic wave excitation device 1 and is used for non-contact measurement of the vibration response signal of the lining surface under acoustic wave excitation; the support and positioning assembly 4 is used to fix and adjust the spatial position and orientation of the directional acoustic wave excitation device 1 and the laser vibrometer 2 to ensure that their effective areas are consistent on the lining surface; the data processing unit 3 is communicatively connected to the laser vibrometer 2 and is used to receive and process the vibration response signal, and to determine whether there are cavities or defects inside the lining by analyzing the vibration characteristics.

[0048] In the above embodiment, during inspection, the system is first deployed inside the tunnel. The directional acoustic vibration device 1 and the laser vibrometer 2 are fixed and adjusted by the support and positioning assembly 4 so that they are aligned with the lining surface area to be inspected. Then, the directional acoustic vibration device 1 is activated to emit directional acoustic waves of specific frequency and energy to the lining surface, exciting it to vibrate. Almost simultaneously, the laser vibrometer 2 performs a non-contact scan of the area affected by the acoustic waves, accurately measuring the vibration response signal of the lining surface. Finally, the vibration signal is transmitted to the data processing unit 3, which analyzes the vibration spectrum, energy ratio, and other characteristics, and compares them with the baseline data of healthy lining to determine whether there are voids or defects inside the lining and locate the defect area. The entire process achieves remote, non-contact, automated, and highly efficient inspection.

[0049] In some embodiments, the working distance of the directional acoustic excitation device 1 is 5-20 meters, and the measuring distance of the laser vibration meter 2 is 5-20 meters.

[0050] Specifically, the distance between the directional acoustic vibration excitation device 1 and the lining surface is controlled within the range of 5-20 meters to ensure that the acoustic waves can effectively excite the vibration of the lining surface; the distance between the laser vibration meter 2 and the lining surface is controlled within the range of 5-20 meters to ensure that the vibration response of the lining surface can be captured non-contactly.

[0051] In some embodiments, the support positioning assembly includes a support frame 4 and a positioning device. The directional acoustic excitation device 1 and the laser vibrometer 2 are mounted on the support frame, and their emission axes are kept coaxial or arranged at a small angle to ensure that the detection area is consistent.

[0052] Specifically, the support frame 4 adopts a combination structure of a high-stability tripod and a multi-dimensional adjustable gimbal; the tripod provides wide span support to ensure the system is stably placed on the tunnel floor; the top of the support frame 4 is provided with mounting positions for installing and fixing the acoustic excitation device 1 and the laser vibration meter 2; each mounting position is equipped with a manual or electric precision adjustment mechanism for the pitch angle and horizontal deflection angle, allowing for independent and fine adjustment of the emission angle of each instrument.

[0053] A positioning device is integrated into the support frame 4 to ensure coordinated alignment of the two instruments. As an example of the positioning device, it includes dual laser pointers and a video aiming module; a visible light laser pointer is integrated near the acoustic wave outlet of the directional acoustic vibration device 1 and near the emitting lens of the laser vibrometer 2; the two laser pointers are pre-calibrated so that the pointing light spots they emit are parallel to and at a fixed distance from the effective working center axis of their respective instruments. A high-definition camera is mounted on the support frame 4, its field of view covering the area of ​​the lining to be measured in front. This camera is connected to the data processing unit 3, and its image can be displayed in real time on the control terminal. A virtual grid generated by the data processing unit 3 can be overlaid on the image to assist in defining the scanning area.

[0054] During alignment, the operator first adjusts the pan-tilt head to make the light spots of the two laser pointers overlap as much as possible on the lining surface. Then, using the video aiming module, the operator fine-tunes the pan-tilt head or the entire support frame to ensure that the overlapping light spots are within the target detection area of ​​the virtual grid. This method ensures intuitive and precise excitation and measurement of the same detection area by both instruments.

[0055] In some embodiments, the data processing unit includes:

[0056] Signal acquisition module, spectrum analysis module, and defect determination module;

[0057] The signal acquisition module is used to record the vibration time-domain signal at each measuring point on the lining surface;

[0058] The spectrum analysis module is used to perform spectrum analysis on vibration signals, extract resonant frequencies, and calculate vibration energy ratios.

[0059] The defect determination module is used to determine and locate void defects based on the comparison between the vibration energy ratio and a preset threshold.

[0060] Specifically, the signal acquisition module receives and stores the original vibration velocity time-domain signals of each measuring point obtained by the laser vibrometer 2 in real time; the spectrum analysis module performs a fast Fourier transform on the time-domain signal of each measuring point, converting it into a frequency-domain signal; subsequently, it extracts the significant resonance peak frequencies in the spectrum and calculates the vibration energy ratio of the measuring point in the key frequency band; this ratio is the ratio of the vibration energy of the measured point to the vibration energy of the preset healthy reference point. The defect judgment module automatically compares the vibration energy ratio of each measuring point with a preset threshold; if the energy ratio of a certain point exceeds the threshold, it is determined that there may be a void defect below it; finally, the system spatially integrates the judgment results of all measuring points to generate an intuitive probability distribution map of lining surface defects or a binary defect location map, completing automated diagnosis and report output. The entire process is software-controlled, realizing full automation of data acquisition, analysis, and judgment.

[0061] In some embodiments, the vibration energy ratio is calculated as follows:

[0062] Within a selected frequency range, the ratio of the integral value of the vibration velocity power spectrum at the measured point to the integral value of the vibration velocity power spectrum at a healthy reference point.

[0063] The vibration energy ratio between the measured point and a healthy reference point is calculated as an important indicator for cavity detection. Cavities (or peelings) exhibit specific bending resonance frequencies. Therefore, in the frequency domain, a defect is characterized by a peak in the vibration velocity spectrum that is absent in the intact area. A comparative method can be used during detection: comparing the vibration spectrum of the measured point with that of a nearby healthy reference point, a significant excess response in a certain frequency band can be considered an indication of a potential defect. This principle can be used for single-point scan detection and also for post-processing of scanned vibration data. The vibration velocity amplitude at the target frequency is calculated for each measurement point and then compared with the mean of the corresponding frequency in the intact area. When the ratio exceeds a predetermined threshold, the point is considered to have a potential defect. By repeating the above process at multiple frequencies, the frequency with the largest difference can be found, i.e., the inferred defect resonance frequency. Given that the spectral response of some defects may not have more than one narrow peak, but rather energy distributed over a frequency band, the Vibration Energy Ratio (VER) is introduced as a characteristic quantity for robustness. Specifically defined as: the ratio of the integral value of the vibration velocity power spectrum at the measured point to the integral value of the vibration power spectrum at a healthy reference point within a selected frequency range. The vibration energy ratio is calculated using the following formula:

[0064]

[0065] Where VER is the vibration energy ratio; f is the frequency; f1 and f2 are the upper and lower limits of the selected frequency range; PSD each The power spectral density of the vibration velocity at the measured point; PSD minVibrational velocity power spectral density at a healthy reference point.

[0066] In some embodiments, the tunnel lining void directional acoustic-laser vibration long-distance detection system further includes a mobile platform, on which the support and positioning components are mounted; to facilitate continuous detection along the tunnel longitudinal direction, the system can be further integrated into a mobile platform; wherein the mobile platform can be a rail trolley or a vehicle-mounted platform, etc.

[0067] In some embodiments, such as Figure 3 As shown, a method for long-distance directional acoustic-laser vibratory testing of tunnel lining cavities is disclosed, employing the detection method as described in any of the above embodiments, including the following steps:

[0068] System deployment and calibration: Install and calibrate the directional acoustic vibration device 1 and the laser vibration meter 2 inside the tunnel to ensure that they are aligned with the lining area to be inspected.

[0069] Define the detection grid: Delineate the detection area on the lining surface to be inspected, and define the scanning point grid for laser vibration measurement;

[0070] Coordinated excitation and scanning: The directional acoustic excitation device 1 is controlled to emit an acoustic excitation signal with preset parameters, while the laser vibration meter 2 is controlled to scan the gridded measuring points point by point and collect the vibration response signal of each point;

[0071] Signal processing and feature extraction: Perform spectral analysis on the collected vibration signals, extract the resonant frequencies of each measuring point, and calculate the vibration energy ratio relative to the healthy reference area;

[0072] Defect identification and imaging: The system determines whether there is a cavity below the measuring point based on whether the vibration energy ratio exceeds a preset threshold, and performs spatial imaging on the identification results of all measuring points to generate a defect distribution map and inspection report.

[0073] In some embodiments, during the system setup and calibration steps, the directional acoustic excitation device 1 and the laser vibrometer 2 are installed as required, and their positions and angles are adjusted so that the acoustic beam axis of the directional acoustic excitation device 1 and the optical axis of the laser vibrometer 2 are kept as coaxial as possible or arranged at a small angle. During the installation process, it is necessary to ensure that the directional acoustic excitation device 1 and the laser vibrometer 2 are in normal working condition and can stably emit acoustic waves and capture vibration signals.

[0074] In some embodiments, during the step of defining the detection grid, the detection area is divided according to the structural characteristics of the tunnel lining and the possible void defect areas. Within the divided detection area, a measuring point grid is defined using the aiming system of the laser vibrometer to determine the scanning range and the spacing between measuring points; the spacing between measuring points is generally 20-50cm, and is adjusted according to the size of the detection area and the size of the possible void defects.

[0075] In some embodiments, during the coordinated excitation and scanning step, the directional acoustic excitation device 1 is activated to emit acoustic waves, and the laser vibrometer 2 is activated simultaneously to scan the defined measurement point grid point by point. During operation, it is necessary to ensure that the operating parameters of the directional acoustic excitation device and the laser vibrometer are consistent, including frequency range, signal form, and sound pressure level, to ensure the accuracy and consistency of the detection results. The parameters of the acoustic excitation signal, including frequency range, signal form, and sound pressure level, are set according to the characteristics of the lining material and the required detection depth.

[0076] In some embodiments, during the signal processing and feature extraction steps, the laser vibrometer records the time-domain signal of vibration velocity at each measuring point on the lining surface; the collected vibration signal is subjected to spectral analysis to extract features such as resonant frequency and vibration energy ratio; the vibration energy ratio is calculated as the ratio of the integral value of the vibration velocity power spectrum of the measured point to the integral value of the vibration power spectrum of the healthy reference point within a selected frequency range; by comparing the vibration spectrum of the measured point with that of the adjacent healthy reference point, excess response occurring in a specific frequency range is identified as an indicator of potential defects.

[0077] In some embodiments, during the defect determination and imaging step, the presence of void defects is determined based on indicators such as vibration characteristics and vibration energy ratio; when the vibration energy ratio of a certain measuring point exceeds a predetermined threshold, it is determined that a void defect may exist below that measuring point; spatial distribution imaging is performed on the determined void defects to visually display the abnormal vibration areas on the lining surface; finally, a detection report is generated, including information such as the location, size, and severity of the void defects; the preset threshold is determined by statistically analyzing the vibration energy ratio distribution of healthy lining areas and combining it with engineering experience.

[0078] In some embodiments, the spectrum analysis module is further configured to calculate the spectral entropy of the vibration signal at each measuring point to quantify the complexity of its spectrum. The defect determination module combines the two characteristic parameters of vibration energy ratio and spectral entropy, and makes a comprehensive decision based on a preset dual threshold or machine learning model to determine the location and extent of void defects with higher accuracy and robustness.

[0079] The various embodiments of the present invention have now been described in detail. To avoid obscuring the concept of the invention, some details known in the art have not been described. Those skilled in the art will fully understand how to implement the technical solutions disclosed herein based on the above description.

[0080] The embodiments described above only illustrate some implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A long-distance directional acoustic-laser vibration measurement system for tunnel lining cavities, characterized in that, include: Directional acoustic vibration excitation device, laser vibration meter, data processing unit, and support and positioning components; The directional acoustic vibration excitation device is installed inside the tunnel and is used to emit directional acoustic waves to the lining surface to excite its vibration. The laser vibrometer is positioned adjacent to the directional acoustic excitation device and is used for non-contact measurement of the vibration response signal of the lining surface under acoustic excitation. The support and positioning components are used to fix and adjust the spatial position and orientation of the directional acoustic excitation device and the laser vibrometer, ensuring that the effective areas of the two are consistent on the lining surface. The data processing unit is communicatively connected to the laser vibration meter and is used to receive and process vibration response signals, and to determine whether there are voids or defects inside the lining by analyzing vibration characteristics.

2. The long-distance directional acoustic-laser vibration measurement system for tunnel lining cavities according to claim 1, characterized in that: The working distance of the directional acoustic wave excitation device is 5-20 meters, and the measuring distance of the laser vibration meter is 5-20 meters.

3. The long-distance directional acoustic-laser vibration measurement system for tunnel lining cavities according to claim 1, characterized in that: The support and positioning assembly includes a support frame and a positioning device. The directional acoustic excitation device and the laser vibrometer are mounted on the support frame, and their emission axes are kept coaxial or arranged at a small angle.

4. The long-distance directional acoustic-laser vibration measurement system for tunnel lining cavities according to claim 1, characterized in that, The data processing unit includes: Signal acquisition module, spectrum analysis module, and defect determination module; The signal acquisition module is used to record the vibration time-domain signal of each measuring point on the lining surface; The spectrum analysis module is used to perform spectrum analysis on the vibration signal, extract the resonance frequency, and calculate the vibration energy ratio; The defect determination module is used to determine and locate void defects based on the comparison between the vibration energy ratio and a preset threshold.

5. The long-distance directional acoustic-laser vibration measurement system for tunnel lining cavities according to claim 4, characterized in that, The method for calculating the vibration energy ratio is as follows: Within a selected frequency range, the ratio of the integral value of the vibration velocity power spectrum at the measured point to the integral value of the vibration velocity power spectrum at a healthy reference point.

6. The long-distance directional acoustic-laser vibration measurement system for tunnel lining cavities according to claim 1, characterized in that, It also includes a mobile platform, on which the supporting positioning component is disposed.

7. A method for long-distance directional acoustic-laser vibratory testing of tunnel lining cavities, employing the testing method described in any one of claims 1 to 6, characterized in that, Includes the following steps: System deployment and calibration: Install and calibrate the directional acoustic excitation device and laser vibration meter inside the tunnel to ensure that they are aligned with the lining area to be inspected. Define the detection grid: Delineate the detection area on the lining surface to be inspected, and define the scanning point grid for laser vibration measurement; Coordinated excitation and scanning: The directional acoustic excitation device is controlled to emit acoustic excitation signals with preset parameters, while the laser vibrometer is controlled to scan the gridded measurement points point by point and collect the vibration response signals of each point; Signal processing and feature extraction: Perform spectral analysis on the collected vibration signals, extract the resonant frequencies of each measuring point, and calculate the vibration energy ratio relative to the healthy reference area; Defect identification and imaging: The system determines whether there is a cavity below the measuring point based on whether the vibration energy ratio exceeds a preset threshold, and performs spatial imaging on the identification results of all measuring points to generate a defect distribution map and inspection report.

8. The method for long-distance directional acoustic-laser vibration measurement of tunnel lining cavities according to claim 7, characterized in that: In the coordinated excitation and scanning step, the parameters of the acoustic excitation signal include frequency range, signal form, and sound pressure level, which are set according to the characteristics of the lining material and the detection depth requirements.

9. The method for long-distance directional acoustic-laser vibration measurement of tunnel lining cavities according to claim 7, characterized in that: In the signal processing and feature extraction steps, by comparing the vibration spectrum of the measured point with that of a nearby healthy reference point, excess response appearing in a specific frequency range is identified as an indicator of potential defects.

10. The method for long-distance directional acoustic-laser vibration measurement of tunnel lining cavities according to claim 7, characterized in that: In the defect determination and imaging step, the preset threshold is determined by statistically analyzing the vibration energy ratio distribution of the healthy lining area and combining it with engineering experience.

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