Underground engineering leakage monitoring method based on distributed piezoelectric film

Abstract

The invention discloses an underground engineering leakage monitoring method based on a distributed piezoelectric film, and the method comprises the steps: obtaining tunnel structure information, and arranging the distributed piezoelectric film on the inner wall of a tunnel based on the tunnel structure information and monitoring requirements; connecting the distributed piezoelectric film with a multi-channel voltage acquisition instrument, and acquiring a charge signal of the distributed piezoelectric film through the multi-channel voltage acquisition instrument; adopting fast Fourier transform to extract time domain features and frequency domain features of the charge signals, and obtaining tunnel leakage conditions and stress change information based on the time domain features and the frequency domain features; and a grading early warning mechanism is constructed, and alarm information is sent based on the grading early warning mechanism, the tunnel leakage condition and the stress change information. According to the monitoring method based on the distributed piezoelectric film, the monitoring distance and range are increased, the piezoelectric effect of the piezoelectric film is utilized, the modern sensing technology is combined, and the tunnel leakage condition is monitored in real time, so that the safety of a tunnel structure is guaranteed, and the service life of the tunnel structure is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel engineering monitoring, and in particular relates to an underground engineering leakage monitoring method based on a distributed piezoelectric film. Background Art

[0002] As an important part of modern transportation and infrastructure, the safety and durability of tunnels directly affect public safety and economic development. The development of tunnel transportation is to improve urban traffic efficiency, alleviate ground traffic congestion, reduce environmental pollution, enhance regional connectivity, enhance traffic safety, and adapt to complex and changing terrain and environmental conditions, thereby promoting the sustainable development of the economy and society. Tunnel leakage is one of the key factors affecting the safety and service life of tunnel structures. If it is not discovered and handled in time, it may cause structural damage, operational interruption and even major accidents. Leaking water may corrode the steel bars in reinforced concrete, resulting in a decrease in structural strength and durability, and may even cause damage to the lining structure. Long-term humid environment will aggravate the corrosion of equipment in the tunnel, reducing the working efficiency and service life of the equipment. Therefore, it is particularly important to develop efficient and reliable leakage monitoring technology.

[0003] Traditional tunnel leakage monitoring methods mainly rely on manual inspections and simple sensors, which have obvious limitations. Manual inspections are not only time-consuming and labor-intensive, but the monitoring results are easily affected by environmental factors, such as the lighting conditions, humidity, and temperature inside the tunnel, which may interfere with the judgment of the monitoring personnel, resulting in the inability to ensure the comprehensiveness and accuracy of the monitoring. In addition, manual inspections cannot achieve continuous real-time monitoring and can only be carried out periodically, which means that leakage problems that may occur between two inspections cannot be discovered and handled in a timely manner.

[0004] At the same time, traditional sensors are mostly point-based monitoring, which can only monitor the situation at a specific location and it is difficult to achieve comprehensive coverage of the entire tunnel. This limitation may lead to missed detection of leakage points, especially in the case of long tunnels or complex structures, where single-point monitoring is difficult to capture all potential leakage risks. Moreover, these traditional sensors are relatively simple in data collection and processing. Once a leakage occurs, they often fail to issue an alarm in time, thus delaying the timing of treatment, which may lead to the deterioration of the leakage problem and increase subsequent maintenance costs and safety risks.

[0005] Distributed fiber optic monitoring is a technology that uses optical fiber as a sensing medium. It can continuously monitor multiple physical parameters such as temperature, strain, vibration, etc. along the length of the fiber. Although distributed fiber optic monitoring technology provides an efficient and sensitive monitoring method, it also has some disadvantages, including high initial investment costs, professional maintenance requirements due to technical complexity, fiber optic vulnerability in harsh environments, signal-to-noise ratio limitations in signal processing, and possible false alarms or missed alarms in some cases. Summary of the invention

[0006] In order to solve the above technical problems, the present invention proposes an underground engineering leakage monitoring method based on distributed piezoelectric film to solve the problems existing in the above prior art.

[0007] To achieve the above object, the present invention provides an underground engineering leakage monitoring method based on distributed piezoelectric film, comprising:

[0008] Obtain tunnel structure information, and arrange distributed piezoelectric films on the inner wall of the tunnel based on the tunnel structure information and monitoring requirements;

[0009] Connecting the distributed piezoelectric film to a multi-channel voltage collector to collect charge signals of the distributed piezoelectric film through the multi-channel voltage collector;

[0010] Extracting the time domain characteristics and frequency domain characteristics of the charge signal by fast Fourier transform, and obtaining tunnel leakage and stress change information based on the time domain characteristics and the frequency domain characteristics;

[0011] A hierarchical early warning mechanism is constructed, and alarm information is issued based on the hierarchical early warning mechanism, the tunnel leakage situation and the stress change information.

[0012] Optionally, the process of arranging a distributed piezoelectric film on the inner wall of the tunnel includes:

[0013] The inner wall of the tunnel is cleaned until it reaches a preset cleanliness level, and the inner wall of the tunnel is processed by grinding or filling until it meets the flatness requirements; based on the tunnel structure information and monitoring requirements, a distributed piezoelectric film is installed at the joint of the tunnel segments, and the distributed piezoelectric film sensor is attached to the inner wall surface of the tunnel and connected to the multi-channel voltage collector; the distributed piezoelectric film sensor is polarized and packaged.

[0014] Optionally, the process of installing a distributed piezoelectric film at the joint of the tunnel segments includes:

[0015] At the circumferential connection seam of the segment, the length and width of the distributed piezoelectric film are cut to half of the length and width of the segment respectively; at the longitudinal connection seam, the distributed piezoelectric film is cut into a square with a side length of half the width of the segment.

[0016] Optionally, the polarization process includes:

[0017] After the distributed piezoelectric film is heated to above the corresponding Curie temperature, a DC electric field is applied and maintained for a fixed time so that the dipole moment inside the material can be rearranged under the action of the electric field. While maintaining the DC electric field, the temperature is gradually lowered to room temperature to complete the polarization, wherein the voltage of the DC electric field is higher than the breakdown voltage of the material.

[0018] Optionally, the distributed piezoelectric film includes a PVDF piezoelectric film, a platinum electrode, a polyimide protective layer, a conductive silver paste, an epoxy resin and a connecting wire; the platinum electrodes are provided on both sides of the PVDF piezoelectric film, a positive electrode is provided on one platinum electrode, and a negative electrode is provided on the other platinum electrode; the polyimide protective layer is bonded to both sides of the PVDF piezoelectric film by epoxy resin.

[0019] Optionally, the thickness of the polyimide protective layer is not less than 1 / 5 of the PVDF piezoelectric film.

[0020] Optionally, the method further comprises leading out a PVDF piezoelectric thin film electrode, and the PVDF piezoelectric thin film electrode leading out process comprises:

[0021] Use acetone to clean the surface of the PVDF piezoelectric film and the connecting wires; smooth the cut edges of the PVDF piezoelectric film, and use acetone as a corrosive agent to treat the cut PVDF piezoelectric film; apply conductive silver glue to the surface of the piezoelectric film and the platinum electrode for bonding; place the bonded piezoelectric film and platinum electrode at room temperature to cure, and complete the lead-out of the electrode.

[0022] Optionally, the graded early warning mechanism includes four states and corresponding early warning levels. If no leakage occurs, it is a normal state and the early warning level is green; if there is a slight leakage, it is an alert state and the early warning level is yellow; if there is a moderate leakage, it is a warning state and the early warning level is orange; if there is a serious leakage, it is an emergency state and the early warning level is red; among them, slight leakage, moderate leakage and serious leakage are divided according to preset thresholds.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] The present invention discloses a method for monitoring underground engineering leakage based on distributed piezoelectric film. Firstly, tunnel structure information is obtained, and distributed piezoelectric film is arranged on the inner wall of the tunnel based on the tunnel structure information and monitoring requirements; then, the distributed piezoelectric film is connected to a multi-channel voltage collector, and the charge signal of the distributed piezoelectric film is collected by the multi-channel voltage collector; then, the time domain characteristics and frequency domain characteristics of the charge signal are extracted by fast Fourier transform, and the tunnel leakage situation and stress change information are obtained based on the time domain characteristics and frequency domain characteristics; finally, a hierarchical early warning mechanism is constructed, and alarm information is issued based on the hierarchical early warning mechanism, the tunnel leakage situation and stress change information.

[0025] The piezoelectric film sensor used in the present invention can capture very weak vibration signals, even displacement changes at the micron level; for weight-sensitive structures such as tunnels, the piezoelectric film sensor will not cause additional burden on the tunnel structure. The present invention flexibly arranges the distributed piezoelectric film along a predetermined path on the inner wall of the tunnel, covering potential leakage areas and structural stress concentration areas on the inner wall of the tunnel. Compared with traditional monitoring methods, the distributed piezoelectric film monitoring method of the present invention increases the monitoring distance and range. The present invention utilizes the piezoelectric effect of the piezoelectric film, combined with modern sensing technology, to achieve real-time monitoring of tunnel leakage, thereby ensuring the safety of the tunnel structure and extending its service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0027] Figure 1 A diagram showing the structure of a sensor according to an embodiment of the present invention;

[0028] Figure 2 A schematic diagram of a sensor according to an embodiment of the present invention;

[0029] Figure 3 A sensor layout diagram of an embodiment of the present invention;

[0030] Figure 4 A flow chart of a water leakage monitoring method according to an embodiment of the present invention;

[0031] Figure 5 A schematic diagram of a hierarchical warning mechanism according to an embodiment of the present invention;

[0032] Among them, 1. PVDF piezoelectric film, 2. Platinum electrode, 3. Conductive silver glue, 4. Connecting wires, 5. Polyimide protective layer, 6. Tunnel segment, 7. Distributed piezoelectric film. DETAILED DESCRIPTION

[0033] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0034] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0035] Embodiment 1

[0036] Piezoelectric film, especially polyvinylidene fluoride (PVDF) film, has attracted widespread attention due to its excellent performance. The advantages of piezoelectric film monitoring over distributed optical fiber monitoring are its high sensitivity and broadband response, small size and light weight, long-term stability and durability. Piezoelectric film can generate significant electrical signals in response to small pressure changes, making it suitable for dynamic strain monitoring. The flexibility of piezoelectric film enables it to adapt to complex tunnel structures and is easy to install and arrange. Piezoelectric film can generate electrical energy when subjected to force, without the need for an external power source, reducing maintenance costs and complexity. Piezoelectric film monitoring is used in structural health monitoring, vibration analysis, damage diagnosis and intelligent structure design in civil engineering to assess the integrity and stability of the structure by capturing and analyzing small vibration changes in the structure.

[0037] like Figure 1-4 As shown, this embodiment provides an underground engineering leakage monitoring method based on a distributed piezoelectric film, including:

[0038] Acquire tunnel structure information, and arrange distributed piezoelectric film 7 on the inner wall of the tunnel based on the tunnel structure information and monitoring requirements;

[0039] The structure of piezoelectric film is usually composed of a piezoelectric material layer and a polyester insulating outer surface layer. In the piezoelectric material layer, two groups of vertically intersecting strips of piezoelectric material form a grid, and each node is a pressure measuring unit.

[0040] To achieve distributed monitoring, multiple piezoelectric film sensors can be arranged at different locations in the monitoring area, and the sensors can be connected to the data acquisition system by wired or wireless means. Each sensor acts as a measurement point and can independently detect and transmit the dynamic stress changes at its location. By setting up a coordination server and a field server, the data measured by the sensor can be transmitted to the corresponding data server to achieve centralized data processing and analysis.

[0041] Furthermore, the process of arranging the distributed piezoelectric film 7 on the inner wall of the tunnel includes:

[0042] The inner wall of the tunnel is cleaned until it reaches the preset cleanliness, and the inner wall of the tunnel is processed by grinding or filling until it meets the flatness requirements; based on the tunnel structure information and monitoring requirements, a distributed piezoelectric film 7 is installed at the connection seam of the tunnel segment 6, and the distributed piezoelectric film 7 sensor is attached to the surface of the inner wall of the tunnel and connected to the multi-channel voltage collector; the distributed piezoelectric film 7 sensor is polarized and packaged.

[0043] Furthermore, the process of installing the distributed piezoelectric film 7 at the joint of the tunnel segment 6 includes:

[0044] At the circumferential connection seam of the tube segment, the length and width of the distributed piezoelectric film 7 are cut to half of the length and width of the tube segment respectively; at the longitudinal connection seam, the distributed piezoelectric film 7 is cut into a square with a side length of half the width of the tube segment.

[0045] Exemplarily, the arrangement of the piezoelectric film in the tunnel is divided into the following steps:

[0046] 1) Thoroughly clean the surface of the tunnel to remove all dust, oil and loose particles to ensure that the surface is flat and unobstructed. This is to improve the adhesion between the sensor and the tunnel surface and ensure the stability of the sensor.

[0047] 2) According to the structural characteristics and monitoring requirements of the tunnel, a piezoelectric film is installed at the joint of the tunnel segment 6.

[0048] 3) The piezoelectric film installed at the circumferential joint of the segment is cut into a length and width that are half of the length and width of the segment, and the piezoelectric film installed at the longitudinal joint is cut into a square with a side length that is half of the width of the segment. After cutting, the piezoelectric film sensor is glued to the tunnel surface using epoxy resin glue.

[0049] 4) The electrodes of the sensor are brought out and connected to the data acquisition system. Next, the connected piezoelectric film sensor is polarized. This is a key step in activating its piezoelectric properties. Through polarization, the sensor can respond more sensitively to tiny stress changes.

[0050] 5) In order to protect the sensor from physical damage and environmental factors such as humidity and temperature changes, the sensor is packaged and protected.

[0051] Specifically, first, you need to use a high-pressure water gun, brush or other cleaning tools to thoroughly remove dust, oil and loose particles from the tunnel surface. This step is critical because any surface uncleanliness may lead to insufficient adhesion between the sensor and the tunnel surface, affecting the stability of the sensor and the accuracy of the monitoring data. During the cleaning process, pay special attention to the joints, cracks and other areas of the tunnel that may harbor dirt and ensure that these areas are also thoroughly cleaned. After cleaning, in order to improve the adhesion between the sensor and the tunnel surface, it is necessary to ensure that the tunnel surface is flat and unobstructed. This can be achieved by grinding or filling uneven areas to ensure that the sensor can fit closely to the tunnel surface, thereby improving the sensitivity and reliability of monitoring.

[0052] Next, according to the structural characteristics of the tunnel and the monitoring requirements, piezoelectric film sensors are installed at the joints of the tunnel segments 6. This is because the joints are often areas with high incidence of leakage, so special attention is needed. At the circumferential joints of the segments, the piezoelectric film needs to be cut into a length and width that are half the length and width of the segment to ensure that the sensor can cover the entire joint area. At the longitudinal joints, the piezoelectric film is cut into a square with a side length of half the width of the segment, which ensures that the sensor can cover the entire width of the longitudinal joint.

[0053] After cutting, the piezoelectric film sensor is glued to the tunnel surface using epoxy glue. Epoxy glue is ideal for fixing the sensor due to its high adhesion and resistance to environmental corrosion. During the gluing process, make sure there are no bubbles between the sensor and the tunnel surface to avoid affecting the performance of the sensor. After gluing, wait for the epoxy glue to fully cure to ensure the stability and long-term reliability of the sensor.

[0054] Finally, after installation, the sensor needs to be calibrated and tested to ensure that it can accurately monitor the leakage in the tunnel. This includes checking the sensor's response speed, sensitivity, and signal stability to ensure that it can provide accurate data in actual monitoring. Through these meticulous steps, it can be ensured that the piezoelectric film sensor can play the greatest role in tunnel leakage monitoring.

[0055] Electrode connection: The piezoelectric film uses a platinum electrode 2, which serves as the input and output interface of the signal. The electrode needs to be connected to an external multi-channel voltage acquisition instrument.

[0056] Furthermore, the process of polarization treatment includes:

[0057] After the distributed piezoelectric film 7 is heated to above the corresponding Curie temperature, a DC electric field is applied and maintained for a fixed time so that the dipole moment inside the material can be rearranged under the action of the electric field. While maintaining the DC electric field, the temperature is gradually lowered to room temperature to complete polarization, wherein the voltage of the DC electric field is higher than the breakdown voltage of the material.

[0058] Specifically, the piezoelectric film is first heated to above its Curie temperature, then a DC electric field higher than the breakdown voltage of the material is applied, and maintained for a certain period of time so that the dipole moment inside the material can be rearranged under the action of the electric field, and finally the temperature is gradually lowered to room temperature while maintaining the electric field to "freeze" the orderly arrangement of the dipole moment and complete the polarization process. This process can significantly improve the piezoelectric performance of the piezoelectric film.

[0059] Furthermore, the distributed piezoelectric film 7 includes a PVDF piezoelectric film 1, a platinum electrode 2, a polyimide protective layer 5, a conductive silver paste 3, an epoxy resin and a connecting wire 4; there are platinum electrodes 2 on both sides of the PVDF piezoelectric film 1, a positive electrode is provided on one platinum electrode 2, and a negative electrode is provided on the other platinum electrode 2; the polyimide protective layer 5 is bonded to both sides of the PVDF piezoelectric film 1 by epoxy resin.

[0060] In this embodiment, a polyimide protective layer 5 is added to both sides of the piezoelectric film. Before adding the protective layer, the surface of the PVDF piezoelectric film 1 is cleaned to remove dust, grease and other contaminants to ensure that the bonding surface is clean. A scraper is used to evenly coat the epoxy resin on the surface of the PVDF piezoelectric film 1. The polyimide protective layer 5 is precisely aligned and bonded to the PVDF piezoelectric film 1 coated with an adhesive. A roller or a pressure roller is required to remove air to ensure that there are no bubbles between the protective layer and the PVDF film. The PVDF piezoelectric film 1 bonded with the protective layer is placed in an oven for curing. After curing, the bonding quality of the protective layer is checked to ensure that there are no defects such as bubbles, cracks or unbonded areas.

[0061] Furthermore, the thickness of the polyimide protective layer 5 is not less than 1 / 5 of the thickness of the PVDF piezoelectric film 1 .

[0062] Furthermore, the method further includes leading out the PVDF piezoelectric film 1 electrode, and the PVDF piezoelectric film 1 electrode leading out process includes:

[0063] Use acetone to clean the surface of the PVDF piezoelectric film 1 and the connecting wire 4; smooth the cut edge of the PVDF piezoelectric film 1, and use acetone as an etchant to treat the cut PVDF piezoelectric film 1; apply conductive silver glue 3 on the surface of the piezoelectric film and the platinum electrode 2 for bonding; place the bonded piezoelectric film and platinum electrode 2 at room temperature to cure, and complete the lead-out of the electrode.

[0064] Exemplarily, the electrode lead-out method of the PVDF piezoelectric film 1 is:

[0065] 1) Use acetone to clean the surface of the piezoelectric film and the wire to ensure that the surface is clean and free of oil and dirt, thereby improving the bonding effect of the conductive silver glue 3.

[0066] 2) Process the cut edges of the piezoelectric film to prevent the edge burrs of the electrodes from interconnecting and causing short circuits. Use acetone as an etchant to process the cut film to achieve non-metallized edge processing

[0067] 3) Apply an appropriate amount of conductive silver glue 3 on the surface of the piezoelectric film and the copper foil for bonding. The application should be as thin as possible to improve adhesion and avoid short circuit.

[0068] 4) The bonded piezoelectric film and copper foil are cured at room temperature to complete the electrode lead-out.

[0069] Connect the distributed piezoelectric film 7 to a multi-channel voltage collector, and collect the charge signal of the distributed piezoelectric film 7 through the multi-channel voltage collector;

[0070] Specifically, a multi-channel voltage acquisition instrument is used to monitor the voltage changes of the piezoelectric film. These devices are able to provide high-resolution measurements and can process signals from multiple sensors. The electrodes of the piezoelectric film are connected to the data acquisition device through wires. The connection needs to ensure good contact between the electrodes to avoid signal loss. Start the data acquisition device and begin to monitor the impedance and voltage changes of the piezoelectric film in real time. These data will reflect the stress state of the inner wall of the tunnel and possible leakage.

[0071] Fast Fourier transform is used to extract the time domain and frequency domain features of the charge signal, and tunnel leakage and stress change information are obtained based on the time domain and frequency domain features;

[0072] Specifically, when the piezoelectric film generates charge signals due to deformation, these signals will be processed by the charge amplifier and then connected to the data acquisition instrument for display and recording. The collected data needs to be analyzed by the fast Fourier transform (FFT) signal processing algorithm to extract the time domain and frequency domain waveform characteristics. After the collected data passes through these processing algorithms, the characteristics of the leaking water can be determined by comparing the signal differences when there is no leakage and when there is leakage. For example, the leakage point may produce specific vibration patterns or pressure changes, which will be reflected in the output signal of the piezoelectric film sensor. By analyzing the changes in these signals, the location and severity of the leak can be determined.

[0073] Build a graded early warning mechanism and issue alarm information based on the graded early warning mechanism, tunnel leakage conditions and stress change information.

[0074] Furthermore, the graded early warning mechanism includes four states and corresponding early warning levels. If no leakage occurs, it is a normal state and the early warning level is green; if there is a slight leakage, it is an alert state and the early warning level is yellow; if there is a moderate leakage, it is a warning state and the early warning level is orange; if there is a serious leakage, it is an emergency state and the early warning level is red; among them, slight leakage, moderate leakage and serious leakage are divided according to preset thresholds.

[0075] Specifically, the collected data is analyzed and processed to determine the stress changes and leakage conditions of the tunnel inner wall. Based on the data analysis results, an early warning system is established. When the monitored data exceeds the preset safety threshold, the system will automatically issue an alarm to prompt the management personnel to take appropriate measures. The data collected by the piezoelectric film leakage monitoring is graded for early warning processing, which is usually divided into the following levels:

[0076] Normal status (green level): Data indicates that no leakage has occurred, the system is stable, and no action is required.

[0077] Alert Status (Yellow Level): Data indicates signs of minor leakage, requiring attention and preparation for preventive measures.

[0078] Warning status (orange level): Data confirms a moderate leak and immediate action is required to prevent the situation from deteriorating.

[0079] Emergency (Red Level): Data indicates a serious leak and emergency measures need to be taken immediately to avoid potential structural damage or safety accidents.

[0080] Embodiment 2

[0081] like Figure 1-4 As shown, this embodiment discloses a method for monitoring underground engineering leakage based on a distributed piezoelectric film, comprising the following steps:

[0082] (1) Before installing the piezoelectric film, clean the inner wall of the tunnel to ensure that the surface of the inner wall is clean, flat, and free of oil and dust to ensure good contact between the piezoelectric film and the inner wall of the tunnel. After cleaning, the inner wall of the tunnel needs to be dried to ensure that there is no residual moisture. Use epoxy resin glue to stick the piezoelectric film to the inner wall of the tunnel.

[0083] (2) Use a multi-channel voltage acquisition instrument to collect data; the PVDF piezoelectric film 1 will generate charges when subjected to pressure changes, and these charges need to be converted into voltage signals through a charge amplifier. After the charges generated by the PVDF piezoelectric film 1 are converted into voltage signals through a charge amplifier, they can be directly measured using a multi-channel voltage acquisition instrument. If the voltage signal generated by the PVDF piezoelectric film 1 is weak, it may be necessary to amplify it through a preamplifier to improve the signal-to-noise ratio of the signal, filter the amplified signal, remove high-frequency noise and power frequency interference to improve signal quality, convert the analog voltage signal into a digital format through an analog-to-digital converter, and use professional software to store and analyze the collected digital data to understand the voltage changes of the PVDF piezoelectric film 1.

[0084] (3) Analyze the collected data to determine the location and extent of the leakage. Set the warning threshold. When the signal changes beyond the threshold, the system automatically issues an alarm.

[0085] When a piezoelectric film is subjected to an external force, the ions inside it are displaced, resulting in the separation of positive and negative charges, thereby generating a voltage or charge between the two surfaces of the material. The generated electrical signal (charge or voltage) is proportional to the deformation. This linear relationship allows piezoelectric films to be used for precise measurements, and this effect is reversible, that is, deformation can also occur under the action of an electric field.

[0086] When a leak occurs in a tunnel, the flow of water or changes in pressure will cause the piezoelectric film to deform, generating an amount of charge proportional to the stress. These charges are collected by sensors and converted into electrical signals. The collected electrical signals are further analyzed. This may include extracting features such as the frequency, amplitude, and duration of the signal. These features can be used to determine the presence and severity of the leak. Since the piezoelectric film sensors are distributed and each sensor covers a specific area, when a sensor detects an abnormal signal, the approximate location of the leak can be determined. Combining data from multiple sensors can further pinpoint the leak point.

[0087] (4) Maintenance and optimization

[0088] Regular inspection: Regularly check the installation status of the piezoelectric film and the stability of the electrode connection to ensure the reliability of the monitoring system.

[0089] System optimization: According to the monitoring results and the actual conditions of the tunnel, the arrangement of the piezoelectric film and the monitoring strategy are adjusted to improve the accuracy and efficiency of monitoring.

[0090] The piezoelectric film sensor used in the present invention can capture very weak vibration signals, even displacement changes at the micron level, due to its extremely thin structure and precise manufacturing process; for weight-sensitive structures such as tunnels, the lightweight advantage of piezoelectric film sensors is particularly important and will not impose additional burdens on tunnel structures. Piezoelectric film materials have high durability and can maintain stable output performance during long-term use; distributed piezoelectric films can be flexibly arranged along a predetermined path on the inner wall of the tunnel, covering potential leakage areas and structural stress concentration areas on the inner wall of the tunnel. Compared with traditional monitoring methods, the distributed piezoelectric film monitoring method of the present invention increases the monitoring distance and range. The present invention utilizes the piezoelectric effect of piezoelectric film, combined with modern sensing technology, to achieve real-time monitoring of tunnel leakage, thereby ensuring the safety of the tunnel structure and extending its service life.

[0091] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for monitoring underground engineering leakage based on distributed piezoelectric film, characterized in that: The following steps are involved: Obtain tunnel structure information, and arrange distributed piezoelectric films on the inner wall of the tunnel based on the tunnel structure information and monitoring requirements; Connecting the distributed piezoelectric film to a multi-channel voltage collector to collect charge signals of the distributed piezoelectric film through the multi-channel voltage collector; Extracting the time domain characteristics and frequency domain characteristics of the charge signal by fast Fourier transform, and obtaining tunnel leakage and stress change information based on the time domain characteristics and the frequency domain characteristics; A hierarchical early warning mechanism is constructed, and alarm information is issued based on the hierarchical early warning mechanism, the tunnel leakage situation and the stress change information.

2. The underground engineering leakage monitoring method based on distributed piezoelectric film according to claim 1 is characterized in that: The process of arranging distributed piezoelectric film on the inner wall of the tunnel includes: The inner wall of the tunnel is cleaned until it reaches a preset cleanliness level, and the inner wall of the tunnel is processed by grinding or filling until it meets the flatness requirements; based on the tunnel structure information and monitoring requirements, a distributed piezoelectric film is installed at the joint of the tunnel segments, and the distributed piezoelectric film sensor is attached to the inner wall surface of the tunnel and connected to the multi-channel voltage collector; the distributed piezoelectric film sensor is polarized and packaged.

3. The underground engineering leakage monitoring method based on distributed piezoelectric film according to claim 2 is characterized in that: The process of installing distributed piezoelectric film at the joint of tunnel segments includes: At the circumferential connection seam of the segment, the length and width of the distributed piezoelectric film are cut to half of the length and width of the segment respectively; at the longitudinal connection seam, the distributed piezoelectric film is cut into a square with a side length of half the width of the segment.

4. The underground engineering leakage monitoring method based on distributed piezoelectric film according to claim 2 is characterized in that: The polarization process includes: After the distributed piezoelectric film is heated to above the corresponding Curie temperature, a DC electric field is applied and maintained for a fixed time so that the dipole moment inside the material can be rearranged under the action of the electric field. While maintaining the DC electric field, the temperature is gradually lowered to room temperature to complete the polarization, wherein the voltage of the DC electric field is higher than the breakdown voltage of the material.

5. The underground engineering leakage monitoring method based on distributed piezoelectric film according to claim 1 is characterized in that: The distributed piezoelectric film includes a PVDF piezoelectric film, a platinum electrode, a polyimide protective layer, a conductive silver paste, an epoxy resin and a connecting wire; the platinum electrodes are provided on both sides of the PVDF piezoelectric film, a positive electrode is provided on one platinum electrode, and a negative electrode is provided on the other platinum electrode; the polyimide protective layer is bonded to both sides of the PVDF piezoelectric film by epoxy resin.

6. The underground engineering leakage monitoring method based on distributed piezoelectric film according to claim 5 is characterized in that: The thickness of the polyimide protective layer is not less than 1 / 5 of the PVDF piezoelectric film.

7. The underground engineering leakage monitoring method based on distributed piezoelectric film according to claim 1 is characterized in that: The method further includes leading out the PVDF piezoelectric thin film electrode, and the PVDF piezoelectric thin film electrode leading out process includes: Use acetone to clean the surface of the PVDF piezoelectric film and the connecting wires; smooth the cut edges of the PVDF piezoelectric film, and use acetone as a corrosive agent to treat the cut PVDF piezoelectric film; apply conductive silver glue to the surface of the piezoelectric film and the platinum electrode for bonding; place the bonded piezoelectric film and platinum electrode at room temperature to cure, and complete the lead-out of the electrode.

8. The underground engineering leakage monitoring method based on distributed piezoelectric film according to claim 1 is characterized in that: The hierarchical early warning mechanism includes four states and corresponding early warning levels. If there is no leakage, it is a normal state and the early warning level is green; if there is a slight leakage, it is an alert state and the early warning level is yellow; if there is a moderate leakage, it is a warning state and the early warning level is orange; If there is a serious leakage, it is an emergency state and the warning level is red; among them, minor leakage, moderate leakage and serious leakage are divided according to preset thresholds.

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