Tunnel anchor rod based on piezoelectricity and monitoring method

Abstract

The invention relates to the technical field of anchor rod monitoring, in particular to a piezoelectric-based tunnel anchor rod and a monitoring method.The piezoelectric-based tunnel anchor rod comprises an anchor rod body, and the anchor rod body comprises an anchor head, an anchor tail and a hollow anchor rod body; the piezoelectric sensing unit comprises a first piezoelectric module, a second piezoelectric module and a third piezoelectric module, the first piezoelectric module is arranged at the anchor tail, the third piezoelectric module is arranged at the anchor head, the second piezoelectric module is arranged in the middle of the hollow anchor rod, and the third piezoelectric module is arranged in the middle of the hollow anchor rod. According to the invention, integrated synchronous monitoring and effective distinguishing of two main failure modes of anchor rod body damage and interface bonding failure are realized, and the limitations in the prior art that long-term on-line monitoring of hidden engineering is difficult and a specific damage mode cannot be identified are overcome.

Description

Technical Field

[0001] This invention relates to the field of anchor bolt monitoring technology, and more specifically, to a piezoelectric-based tunnel anchor bolt and its monitoring method. Background Technology

[0002] In underground structure support fields such as tunnel engineering, anchor bolts, as core load-bearing components, directly affect the overall safety and stability of the project through their long-term performance. However, anchor bolt systems are deeply embedded in rock and soil, making their health a typical hidden engineering issue, and traditional methods struggle to achieve effective, real-time monitoring of their service status. Currently, engineering practice primarily relies on destructive testing methods such as pull-out tests for anchor bolt quality assessment. These methods are not only destructive and unable to provide long-term online monitoring of installed anchor bolts, but they also only offer single-point, static load-bearing capacity information, failing to effectively monitor the anchor bolts themselves. Summary of the Invention

[0003] The purpose of this invention is to provide a piezoelectric-based tunnel anchor bolt and its monitoring method to improve the aforementioned problems. To achieve this purpose, the technical solution adopted by this invention is as follows:

[0004] On one hand, this application provides a piezoelectric-based tunnel anchor bolt, comprising: an anchor bolt and a piezoelectric sensing unit, wherein the anchor bolt is disposed in the tunnel concrete, and the anchor bolt includes an anchor head, an anchor tail, and a hollow anchor bolt; the piezoelectric sensing unit includes a first piezoelectric module, a second piezoelectric module, and a third piezoelectric module, wherein the first piezoelectric module is disposed at the anchor tail, the third piezoelectric module is disposed at the anchor head, and the second piezoelectric module is disposed in the middle of the hollow anchor bolt.

[0005] On the other hand, this application provides a piezoelectric-based method for monitoring tunnel anchor bolts, the method comprising:

[0006] The first signal and the second signal are acquired. The first signal is obtained by the first piezoelectric module emitting a swept sine wave and the third piezoelectric module receiving and collecting it. The second signal is obtained by the second piezoelectric module transmitting and receiving signals to both ends of the anchor bolt.

[0007] Based on the first signal, a first feature information is obtained, which includes the energy growth rate and the bonding coefficient of the signal.

[0008] The second signal is processed based on impedance indices to obtain the second characteristic information.

[0009] The first feature information and the second feature information are fused from multiple sources to obtain the fused comprehensive state confidence of the anchor bolt.

[0010] Based on the confidence level of the integrated anchor bolt status, the status level is determined to obtain the current health assessment result of the anchor bolt.

[0011] The beneficial effects of this invention are as follows:

[0012] This invention acquires a first signal and a second signal through three piezoelectric modules deployed at the head, tail, and middle of the anchor bolt. The first signal is used to determine first characteristic information reflecting the bond state between the anchor bolt and the surrounding rock, while the second signal is used to determine second characteristic information reflecting the health status of the anchor bolt itself. Furthermore, through multi-source data fusion processing based on DS evidence theory, a precise assessment of the overall condition of the anchor bolt is obtained. This method achieves integrated synchronous monitoring and effective differentiation of the two main failure modes: anchor bolt body damage and interface bonding failure. It overcomes the limitations of existing technologies in long-term online monitoring of concealed works and inability to identify specific damage modes.

[0013] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing embodiments of the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of a piezoelectric-based tunnel anchor structure as described in an embodiment of the present invention.

[0016] Figure 2 This is a schematic diagram of the second piezoelectric module.

[0017] The markings in the diagram are: 1. First piezoelectric module; 2. Second piezoelectric module; 3. Third piezoelectric module; 4. Piezoelectric sensor; 5. Protective layer; 6. Wire. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0019] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0020] Example 1:

[0021] like Figure 1 As shown, this embodiment provides a piezoelectric-based tunnel anchor bolt, including: an anchor bolt and a piezoelectric sensing unit. The anchor bolt is installed in the tunnel concrete and includes an anchor head, an anchor tail, and a hollow anchor bolt. The piezoelectric sensing unit includes a first piezoelectric module 1, a second piezoelectric module 2, and a third piezoelectric module 3. The first piezoelectric module 1 is located at the anchor tail, the third piezoelectric module 3 is located at the anchor head, and the second piezoelectric module 2 is located in the middle of the hollow anchor bolt. In this invention, the first piezoelectric module 1 and the third piezoelectric module 3 constitute a stress wave transmission path. The first piezoelectric module 1 acts as a driver to emit a swept-frequency sine wave, and the third piezoelectric module 3 acts as a sensor to receive the stress wave voltage signal propagating along the anchor bolt axis. The second piezoelectric module 2, based on the principle of mechanical impedance, transmits and receives high-frequency electrical signals to both ends of the anchor bolt to collect the electrical admittance response. By analyzing these two signals, integrated synchronous monitoring and effective differentiation of the two main failure modes—anchor bolt body damage and interface bonding failure—is achieved, overcoming the limitations of existing technologies that are difficult to monitor concealed works online for a long time and cannot identify specific damage modes.

[0022] In one specific embodiment of this disclosure, the outer diameter of the first piezoelectric module 1 is the same as the outer diameter of the hollow anchor rod. In the high confining pressure environment of tunnel engineering, this size matching ensures that after the anchor rod is inserted into the borehole, the first piezoelectric module 1 can form a smooth and continuous cylindrical surface with the anchor rod, avoiding stress concentration points at the edge of the module or hindering the uniform flow of grouting material due to the difference in outer diameter. When the first piezoelectric module is in seamless contact with the concrete medium, it can maximize the energy radiation dissipation of stress waves from the anchor rod to the surrounding rock.

[0023] like Figure 2 As shown, in one specific embodiment of this disclosure, the second piezoelectric module 2 includes a piezoelectric sensor 4, a protective layer 5, and a wire 6. The piezoelectric sensor 4 is disposed inside the protective layer 5, and the wire 6 is disposed on the protective layer 5.

[0024] In one specific embodiment of this disclosure, the piezoelectric sensor 4 is a sheet-like piezoelectric sensor 4. When energized, the sheet-like piezoelectric sensor mainly generates expansion and contraction vibrations along the thickness direction, thereby exciting stress waves with vibration directions perpendicular to the plane of the sheet. When this sheet-like sensor is excited, the vibration energy it generates can be most effectively coupled to the anchor wall along the radial direction of the anchor rod and converted into guided waves propagating along the axial direction of the anchor rod. This vibration mode is highly matched with the geometric characteristics of the anchor rod as a slender wave conductor. Compared with other forms of piezoelectric elements, it can significantly improve the excitation efficiency and propagation distance of stress waves in the anchor rod, ensuring that the stress wave signal can effectively cover the entire length of the anchor rod from the tail to the head, thereby providing a stable and high signal-to-noise ratio original signal for the bond state assessment based on wave energy attenuation.

[0025] In one specific embodiment of this disclosure, two sheet piezoelectric sensors 4 are provided, and the two sheet piezoelectric sensors 4 are stacked. After aligning the polarization directions of the two sheet piezoelectric sensors 4 in opposite directions along the thickness direction, they are physically stacked and electrically connected by conductive adhesive, so that the two sheet piezoelectric sensors 4 constitute a composite oscillator that is mechanically connected in series and electrically connected in parallel. When an alternating electric field is applied to the composite oscillator, due to the inverse piezoelectric effect, the two piezoelectric ceramic sheets will produce opposite phase expansion and contraction deformations due to their opposite polarization directions. When one sheet elongates along the thickness direction, the other sheet shortens synchronously. This working mode enables the composite oscillator to generate a stronger effective strain than a single piezoelectric ceramic sheet, thereby significantly enhancing the amplitude of the stress wave signal excited when it is used as an actuator. At the same time, when used as a sensor, this structure can also convert weaker mechanical vibrations into more easily detectable electrical signals through the direct piezoelectric effect. In the limited space and strong background noise monitoring environment inside the tunnel anchor bolt, this signal enhancement effect is particularly critical. It effectively improves the signal-to-noise ratio and sensitivity of the electromechanical impedance method for detecting small stiffness changes in the anchor bolt body, providing a reliable signal basis for accurately identifying early damage to the anchor bolt.

[0026] Example 2:

[0027] It is understood that in this embodiment, a scenario can be set up, such as a scenario for long-term online monitoring of tunnel anchor bolts.

[0028] This embodiment provides a piezoelectric-based method for monitoring tunnel anchor bolts, the method comprising steps S1-S5, specifically including:

[0029] Step S1: Acquire the first signal and the second signal. The first signal is obtained by the first piezoelectric module 1 emitting a swept sine wave and the third piezoelectric module 3 receiving and collecting it. The second signal is obtained by the second piezoelectric module 2 transmitting and receiving signals to both ends of the anchor bolt.

[0030] In this step, two types of raw data with different physical meanings are simultaneously captured by piezoelectric modules preset at different key locations on the anchor bolt: the active stress wave transmission signal composed of the first and last modules, i.e., the first signal, and the transceiver impedance signal executed by the middle module, i.e., the second signal.

[0031] Step S2: Calculate based on the first signal to obtain first feature information, which includes the energy growth rate and the bonding coefficient of the signal;

[0032] Step S2 further includes steps S21-S23, which specifically include:

[0033] Step S21: Calculate the energy value based on the first signal;

[0034] Step S22: Obtain the reference energy value under the condition that the anchor bolt is in good bonding condition;

[0035] Step S23: Calculate the energy growth rate based on the energy value and the reference energy value.

[0036] In this embodiment, the specific formula for calculating the energy growth rate is as follows:

[0037]

[0038] In the above formula, Indicates the energy growth rate; Indicates energy value. The energy growth rate represents the baseline energy value. It is extremely sensitive to the dissipation of wave energy at the anchor-surrounding rock interface. When the interface is well bonded, the stress wave energy will be effectively dissipated to the surrounding rock, resulting in low received energy. However, when the interface debonds or has voids, the wave energy is confined to the anchor, leading to a significant increase in received energy. Using the energy growth rate as a characteristic indicator can highly sensitively capture the early and minor degradation of the interface bonding state.

[0039] Step S2 further includes steps S24-S27, which specifically include:

[0040] Step S24: Determine the attenuation coefficient of the stress wave in the anchor bolt based on the anchor bolt material;

[0041] Step S25: Determine the stress wave peak during monitoring based on the first signal;

[0042] Step S26: Calculate the distance between the first piezoelectric module 1 and the third piezoelectric module 3 to obtain distance information;

[0043] Step S27: Calculate the bonding coefficient based on the attenuation coefficient, the stress wave peak, and the distance information.

[0044] In this embodiment, the specific formula for calculating the adhesion coefficient is as follows:

[0045]

[0046] In the above formula, Indicates the coefficient of adhesion; Indicates the peak value of the stress wave during monitoring; This indicates the stress wave peak when the anchor bolt is in a well-bonded state. The attenuation coefficient is an inherent property determined by the anchor material, typically taken as 0.62; L represents distance information.

[0047] Understandably, given the complex and variable stress in tunnel surrounding rock and the uneven density of grout, relying solely on absolute changes in signal energy or amplitude is susceptible to environmental interference. This proposed solution, by introducing material intrinsic attenuation and propagation distance for normalization, effectively eliminates the influence of non-interface factors on wave peak values, allowing the adhesion coefficient to more purely reflect the true effect of interfacial bonding on wave energy dissipation. This coefficient is highly sensitive to abnormal wave energy enrichment caused by interfacial defects. When bonding is intact, wave energy is effectively dissipated through the interface, resulting in lower measured stress wave peaks and higher adhesion coefficients. When debonding occurs at the interface, forming a waveguide effect, wave energy is confined within the anchor bolt, leading to a significant increase in stress wave peaks and a corresponding decrease in adhesion coefficients. This allows the solution to accurately capture early degradation of interfacial bonding.

[0048] Step S3: Perform impedance index processing on the second signal to obtain the second feature information;

[0049] Step S3 further includes steps S31-S34, which specifically include:

[0050] Step S31: Determine the electrical admittance information based on the second signal;

[0051] Step S32: Perform mechanical impedance inversion processing based on the electrical admittance information to obtain the mechanical impedance value of the anchor bolt;

[0052] In this step, the mechanical impedance value of the anchor bolt is obtained by inversion using the force-electric coupling model formula. The force-electric coupling model formula is as follows:

[0053]

[0054] In the above formula, Admittance, representing the electrical conductivity of a piezoelectric element at a given frequency. The response under these conditions is directly measured by the second piezoelectric module 2; Represents the imaginary unit; Indicates angular frequency; , , Width, length, and thickness of each individual piezoelectric element; It represents the free permittivity, an inherent property of piezoelectric materials; Indicates the mechanical resistance of the anchor bolt; This represents the mechanical impedance of the second piezoelectric module 2; Represents the piezoelectric strain constant; This represents the Young's modulus of a piezoelectric material under short-circuit conditions. The mechanical impedance of the anchor bolt can be calculated using the above formula.

[0055] Step S33: Determine the peak sequence of the signal based on the second signal;

[0056] In this step, the second signal is processed by a peak detection algorithm to identify all local maxima (peaks) and their corresponding frequencies, resulting in a sequence composed of peak values ​​and their corresponding frequencies.

[0057] Step S34: Perform deviation calculation processing based on the peak sequence of the signal and the reference peak sequence to obtain the conductivity deviation index.

[0058] In this step, the specific formula for calculating the conductivity deviation index is as follows:

[0059]

[0060] In the above formula, Indicates the conductivity deviation index; The peaks of the signal are represented by a peak sequence. This represents the peaks of the electrical conductivity signal under undamaged anchor bolt conditions.

[0061] In the context of long-term tunnel operation facing stress corrosion and fatigue loads, anchor bolt damage often accumulates from microscopic defects, which are difficult to detect using traditional methods. This invention utilizes the properties of piezoelectric materials to transform abstract structural stiffness changes into precisely measurable changes in electrical parameters. A decrease in overall stiffness leads to a systematic reduction in mechanical impedance, while defects such as local cracks cause drastic fluctuations in the peak value of a specific resonant frequency point. This anomaly is significantly amplified by the conductivity deviation index. By combining global inversion with local feature amplification, the simultaneous and accurate perception of two different scale damage modes—overall performance degradation of the anchor bolt body and the initiation of local damage—is achieved.

[0062] Step S4: Perform multi-source data fusion processing on the first feature information and the second feature information to obtain the fused anchor bolt comprehensive state confidence level;

[0063] Step S4 further includes steps S41-S44, which specifically include:

[0064] Step S41: Perform fuzzy basic probability allocation for the interface adhesion failure proposition based on the first feature information to obtain the first basic probability allocation function;

[0065] In this step, the energy growth rate and adhesion coefficient, which are part of the first feature information, are converted into fuzzy sets using a preset membership function. Then, a fuzzy rule base based on expert knowledge is applied to map the fuzzy inputs to fuzzy support for the output propositions, namely interface adhesion failure, non-interface adhesion failure, and uncertainty. Finally, these fuzzy outputs are converted into precise probability values ​​using a defuzzification method, resulting in the first basic probability assignment function. It should be noted that the membership function is a triangular membership function.

[0066] Step S42: Based on the second feature information, perform basic probability allocation of the neural network for the anchor bolt body damage proposition to obtain the second basic probability allocation function;

[0067] The input feature vector is constructed and normalized based on the mechanical impedance value and conductivity deviation index included in the second feature information. These two dimensionless indices, reflecting the overall stiffness degradation and local damage sensitivity of the anchor bolt respectively, are combined into a two-dimensional feature vector and processed using the max-min normalization method to obtain the normalized feature vector. The normalized feature vector is then processed through forward propagation calculations and input into a pre-trained multilayer perceptron neural network with a single hidden layer. The input layer of this network has two nodes corresponding to the feature vector, and the hidden layer uses the Sigmoid activation function to introduce nonlinear mapping capabilities. The output... The layer has 3 nodes, and its output is normalized to a probability distribution using the Softmax function to obtain the initial output probabilities of the network for three propositions: anchor bolt damage, non-anchor bolt damage, and uncertainty. Based on the initial output probabilities, a basic probability allocation correction process is performed. By introducing an uncertainty adjustment factor and applying the basic axioms of DS evidence theory, the probability of the uncertain proposition is multiplied by the uncertainty adjustment factor, and the remaining probabilities are redistributed to the anchor bolt damage and non-anchor bolt damage propositions, resulting in a corrected probability set. Based on the corrected probability set, a second basic probability allocation function is generated to obtain the second basic probability allocation function.

[0068] Step S43: Use DS evidence theory to fuse the first basic probability allocation function and the second basic probability allocation function to obtain the joint basic probability allocation function;

[0069] In this step, the joint basic probability assignment function is specifically as follows:

[0070]

[0071] In the above formula, Represents the joint fundamental probability assignment function; K represents the conflict coefficient, with a value between 0 and 1. K=0 indicates that the two pieces of evidence are completely consistent and there is no conflict; K=1 indicates that the evidence is highly conflicting. and Let K and K represent the first and second fundamental probability allocation functions, respectively. It should be noted that a high K value occurs in the contradictory situation where the stress wave indicator interface fails while the impedance indicator body remains intact.

[0072] Step S44: Calculate the overall confidence level and uncertainty based on the joint basic probability allocation function to obtain the overall confidence level of the anchor bolt state.

[0073] In this step, for proposition A such as interface bonding failure, its confidence function Bel(A) equals the sum of the basic probabilities assigned to all subsets of proposition A by the joint basic probability assignment function, representing the minimum support for proposition A; its likelihood function Pl(A) equals the sum of the basic probabilities of all propositions intersecting with A, representing the highest possible support for proposition A. [Bel(A),Pl(A)] constitutes the confidence interval for proposition A, yielding the quantified overall confidence level of the anchor bolt's condition. This step not only includes the degree of support for the core damage proposition but also explicitly includes a measure of uncertainty caused by conflicting evidence or insufficient information, providing a decision-making basis for the condition assessment of tunnel anchor bolts.

[0074] It should be noted that in the long-term operation of tunnels, under the dynamic adjustment of surrounding rock stress and complex electromagnetic interference environment, stress wave and impedance signals may contradict each other due to local damage or noise. For example, the wave energy may be abnormal while the impedance is stable. Traditional single-indicator judgment is prone to false alarms. This embodiment can not only accurately distinguish between the two coupled faults of body damage and interface failure by integrating these two types of indicators, but also intuitively reflect the reliability of the diagnostic conclusion through confidence level. This provides key technical support for the robust and interpretable intelligent assessment of anchor bolt status in noisy environments.

[0075] Step S5: Perform state level determination processing based on the integrated anchor bolt state confidence level to obtain the current health assessment result of the anchor bolt.

[0076] In this step, a pre-established mapping table is used to map the confidence level values ​​to specific mechanical performance and pull-out strength grades. Specifically, the anchor condition is divided into 10 levels per 10%, with level 10 representing intact and level 1 representing severely deteriorated. This mapping relationship is obtained based on training with a large number of damage samples. Further, a weighted comprehensive processing is performed based on the mapped mechanical performance and pull-out strength grades, specifically:

[0077]

[0078] In the above formula, This indicates the overall degree of damage to the anchor bolt; and These represent the degree of damage assessed based on the interface bonding state and the degree of damage assessed based on the health status of the anchor bolt body, respectively. and These represent the weighting coefficients corresponding to the damage degree assessed by the interfacial bonding state and the damage degree assessed by the anchor bolt body health status, respectively. The weighting strategy is adaptively adjusted based on the severity of damage: in cases of minor damage, interfacial bonding failure has a more significant impact on the anchor bolt's working condition; in cases of severe damage, damage to the anchor bolt body poses a greater threat.

[0079] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0080] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0082] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A piezoelectric-based tunnel anchor, characterized in that, include: An anchor bolt, wherein the anchor bolt is installed in the tunnel concrete, and the anchor bolt includes an anchor head, an anchor tail, and a hollow anchor bolt; The piezoelectric sensing unit includes a first piezoelectric module (1), a second piezoelectric module (2), and a third piezoelectric module (3). The first piezoelectric module (1) is located at the anchor tail, the third piezoelectric module (3) is located at the anchor head, and the second piezoelectric module (2) is located in the middle of the hollow anchor rod.

2. The piezoelectric-based tunnel anchor bolt according to claim 1, characterized in that: The outer diameter of the first piezoelectric module (1) is the same as the outer diameter of the hollow anchor rod.

3. The piezoelectric-based tunnel anchor bolt according to claim 1, characterized in that: The second piezoelectric module (2) includes a piezoelectric sensor (4), a protective layer (5), and a wire (6). The piezoelectric sensor (4) is disposed inside the protective layer (5), and the wire (6) is disposed on the protective layer (5).

4. The piezoelectric-based tunnel anchor bolt according to claim 3, characterized in that: The piezoelectric sensor (4) is a sheet-shaped piezoelectric sensor (4).

5. The piezoelectric-based tunnel anchor bolt according to claim 4, characterized in that: Two sheet piezoelectric sensors (4) are provided, and the two sheet piezoelectric sensors (4) are arranged overlappingly.

6. A piezoelectric-based method for monitoring tunnel anchor bolts, characterized in that, include: The first signal and the second signal are acquired. The first signal is obtained by the first piezoelectric module (1) sending a swept sine wave and the third piezoelectric module (3) receiving and collecting it. The second signal is obtained by the second piezoelectric module (2) transmitting and receiving signals to both ends of the anchor rod. Calculations are performed based on the first signal to obtain first feature information, which includes the energy growth rate and the bonding coefficient of the signal. The second signal is processed based on impedance indices to obtain the second characteristic information. The first feature information and the second feature information are fused from multiple sources to obtain the fused comprehensive state confidence of the anchor bolt. Based on the confidence level of the integrated anchor bolt status, the status level is determined to obtain the current health assessment result of the anchor bolt.

7. The piezoelectric-based tunnel anchor monitoring method according to claim 6, characterized in that, The first feature information is obtained by calculating based on the first signal, including: The energy value is obtained by calculating the energy based on the first signal; Obtain the baseline energy value under the condition that the anchor bolt is in good bonding condition; The energy growth rate is calculated based on the energy value and the baseline energy value.

8. The piezoelectric-based tunnel anchor monitoring method according to claim 6, characterized in that, The first feature information is obtained by calculating based on the first signal, including: Determine the attenuation coefficient of the stress wave in the anchor bolt based on the anchor bolt material; The stress wave peak during monitoring is determined based on the first signal; The distance between the first piezoelectric module (1) and the third piezoelectric module (3) is calculated to obtain the distance information; The adhesion coefficient is calculated based on the attenuation coefficient, the stress wave peak, and the distance information.

9. The piezoelectric-based tunnel anchor monitoring method according to claim 6, characterized in that, Impedance index processing is performed based on the second signal, including: The admittance information is determined based on the second signal; The mechanical impedance value of the anchor bolt is obtained by performing mechanical impedance inversion processing based on the electrical admittance information. The peak sequence of the signal is determined based on the second signal; The conductivity deviation index is obtained by calculating the deviation between the peak sequence of the signal and the reference peak sequence.

10. The piezoelectric-based tunnel anchor monitoring method according to claim 6, characterized in that, The first feature information and the second feature information are subjected to multi-source data fusion processing, including: Based on the first feature information, a fuzzy basic probability assignment is performed for the proposition of interface adhesion failure to obtain the first basic probability assignment function; Based on the second feature information, a basic probability allocation of the neural network is performed for the proposition of anchor bolt body damage, resulting in a second basic probability allocation function; By fusing the first and second basic probability assignment functions using DS evidence theory, a joint basic probability assignment function is obtained. The overall confidence level and uncertainty are calculated based on the joint basic probability allocation function to obtain the overall confidence level of the anchor bolt.

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