A method for evaluating disturbance degree of influence of underground goaf on limit stability of power transmission tower

Abstract

The present application belongs to the field of secondary engineering hazard monitoring and evaluation of geological disasters, and proposes a disturbance degree evaluation method for the influence of underground goaf on the ultimate stability of power transmission towers, which comprises: monitoring of power transmission tower vibration modal evolution under environmental excitation; power transmission tower vibration modal parameter identification based on environmental excitation; power transmission tower pile-soil dynamic stiffness inversion based on operational modal analysis; calculation of critical pile-soil dynamic stiffness of power transmission tower based on stiffness reduction dynamic buckling stability analysis; calculation of disturbance degree of underground goaf influence on ultimate stability; the present application monitors the vibration modal response of the power transmission tower under environmental excitation during the underground goaf process, uses operational modal analysis to invert the pile-soil dynamic stiffness evolution of the power transmission tower during the underground goaf process from the vibration modal response, uses dynamic buckling stability analysis with pile-soil dynamic stiffness reduction to obtain the critical pile-soil dynamic stiffness, and finally calculates the disturbance degree to evaluate the influence of underground goaf disturbance on the long-term service performance of the power transmission tower.

Description

Technical Field

[0001] This invention belongs to the field of monitoring and assessment technology of secondary engineering hazards of geological disasters, specifically involving a method for assessing the disturbance degree of the impact of underground mining on the ultimate stability of power transmission towers. Background Technology

[0002] Power transmission lines are vital infrastructure on the nation's energy transmission arteries, and their safe operation is crucial for ensuring the normal functioning of national industrial production and daily life. Power transmission lines inevitably traverse mountainous areas affected by mining subsidence. This subsidence disturbance impacts the stress state of the bearing zones of existing transmission tower foundations, severely weakening the load-bearing capacity of adjacent existing tower foundations. Consequently, the constraint effect of the subsidence disturbance pile foundations on the stability control of the transmission towers is weakened, leading to a decline in the long-term service performance stability of the transmission tower structure.

[0003] Traditional monitoring, early warning, and safety assessment methods mainly focus on indicators such as stress, deformation, and tilt at key points of exposed structures above the ground. However, this approach can only determine whether underground mining disturbances have caused damage to the above-ground structures. For the lower pile foundations, it is impossible to deploy sensors or conduct dynamic tests on bearing capacity and small strain, so the disturbance damage cannot be directly monitored.

[0004] Because the damage to pile foundations caused by underground mining disturbances is often hidden, the absence of damage to the superstructure does not necessarily indicate that the pile foundations are in good working order. Transmission towers are tall, flexible structures whose long-term safety control condition is the ultimate limit state under the superposition of variable loads (wind loads) or accidental loads (earthquakes). Damage to the pile foundations alone can potentially compromise their ultimate limit state stability, posing a significant threat to long-term service safety. Therefore, it is necessary to implement early warning systems based on pile foundation safety control, using the assessment of whether pile foundation disturbance weakens the ultimate limit state dynamic stability of the superstructure as a safety criterion for tunnel construction near transmission towers.

[0005] Chinese invention patent CN115288704A discloses a safety risk assessment and construction method for pile foundation settlement caused by tunnel boring machine (TBM) excavation. The method includes: during TBM construction, predicting the settlement values ​​of pile foundations at several different locations based on a pre-established finite element numerical model, and verifying this prediction with actual settlement measurements; adjusting the horizontal distance between the pile and the tunnel and the pile length; predicting the settlement values ​​of pile foundations at different locations based on the finite element numerical model; and generating a two-dimensional isopleth map of settlement, classifying the safety risk levels of pile foundations at different locations, based on the pile foundation settlement safety risk levels; and conducting TBM construction after implementing corresponding protection measures according to the predicted safety risk level of the pile foundations. This method verifies the numerical model by summarizing TBM construction parameters and then generates the two-dimensional isopleth map of pile foundation settlement safety risk levels, ensuring the timeliness and reliability of the safety risk level assessment of nearby pile foundations during subsequent construction.

[0006] Chinese invention patent CN117988869A discloses a method and system for predictive control of shield tunneling proximity structure safety based on intelligent algorithms. The method includes collecting shield construction parameters to obtain sample data, preprocessing the sample data, introducing the B0 method to optimize the hyperparameters of the NGB00ST prediction model, constructing and training a B0-NGBoost prediction model with the output variable as the control target based on the normalized sample dataset, predicting the output variable using the B0-NGBoost prediction model, and outputting the prediction results; classifying the safety risk level of the shield tunneling proximity structure based on the prediction results; and outputting corresponding safety control strategies based on the safety risk level of the shield tunneling proximity structure, thereby realizing intelligent prediction and control of proximity structure safety risks during shield tunneling construction.

[0007] The two invention patents mentioned above respectively monitor settlement caused by tunnel construction, predict the safety risk of pile foundation based on settlement value, and output prediction results by establishing a high-precision prediction model and classify the safety risk level of shield tunneling proximity structure according to the prediction results. However, neither of them considers the impact of underground foundation on superstructure, nor establishes the relationship between underground foundation damage and superstructure dynamic response, making it difficult to assess the impact of underground mining on the ultimate stability of power transmission towers.

[0008] The long-term safety control condition of power transmission towers is the ultimate state of superimposed variable loads (wind loads) or accidental loads (earthquakes). Damage to the pile foundation alone may cause insufficient stability of the ultimate state. Therefore, this invention proposes to use the assessment of whether the disturbance degree of the pile foundation will weaken the dynamic stability of the ultimate state of the superstructure as a safety criterion for tunnel construction near power transmission towers. Summary of the Invention

[0009] The present invention aims to provide a disturbance degree assessment method for the impact of underground mining on the ultimate stability of transmission towers, in order to solve the problems of existing technologies that do not consider the impact of underground foundations on the superstructure, do not establish the relationship between underground foundation damage and the dynamic response of the superstructure, and are difficult to assess the impact of underground mining on the ultimate stability of transmission towers.

[0010] This invention is achieved using the following technical solution: This invention provides a method for assessing the disturbance degree of the impact of underground mining on the ultimate stability of transmission towers, comprising the following steps: Step 1: Monitoring the modal evolution of transmission tower vibration under environmental excitation; Step 2: Identification of vibration mode parameters of transmission towers based on environmental excitation; Step 3: Inversion of dynamic stiffness of transmission tower pile and soil based on operational modal analysis; Step 4: Calculate the critical pile-soil dynamic stiffness of the transmission tower based on stiffness reduction dynamic buckling stability analysis; Step 5: Calculation of the degree of disturbance affecting the ultimate stability of underground mining.

[0011] As a preferred technical solution: Step one specifically includes: Before underground mining disturbance, a vibration mode monitoring system is deployed to continuously track the vibration mode evolution of power transmission towers during underground mining.

[0012] As a preferred technical solution: The monitoring system includes a vibration pickup, a dynamic signal acquisition instrument, and modal analysis software.

[0013] As a preferred technical solution: Step two specifically includes: Step 2.1: Use empirical mode decomposition response data to obtain the eigenmode function components representing different orders of modal responses; Step 2.2: Apply the random decrement method or natural excitation technique to obtain the free decay response signals of each mode of the system; Step 2.3: Use the Hilbert-Huang transform to convert the free decay response data to obtain the analytical signal; Step 2.4: Calculate and output the modal parameters, including frequency, damping ratio and mode shape.

[0014] As a preferred technical solution: Step 2.1 specifically includes the following steps: Step 2.1.1: Find the original signal The upper envelope of the signal is obtained from all extreme points using cubic spline interpolation. With lower envelope ; Step 2.1.2: Let ; Step 2.1.3: Determine Does it satisfy the two conditions of the Intrinsic Mode Function (IMF)? (Equation 1) (Equation 2) like If both conditions are met, then This is the first IMF component; like If one of the conditions is not met, repeat steps 2.1.1 and 2.1.2 until the [condition is not met]. After the second screening If the two conditions for the Intrinsic Mode Function (IMF) are satisfied, then... As the first IMF component ; Step 2.1.4: Transfer the remaining signal As new data, repeat steps 2.1.1 to 2.1.3 for filtering until new IMF components are obtained. ; Step 2.1.5: When the residual signal component The filtering process stops when the preset conditions are met or the function is monotonic. In step 2.3: For the original signal Perform Hilbert-Huang transform on the original signal. Transform into Then its analytic signal z(t) is expressed as: (Equation 3) In the formula: i is the index of the IMF component, and the magnitude A(t) and phase are... It can be represented in the following form: (Equation 4) In the formula: The instantaneous amplitude of the modal free decay vibration at t=0; The damping ratio; Let be the natural angular frequency of the mode in the undamped state; The damped natural angular frequency; This is the initial phase; In step 2.4: The frequencies and damping ratios of each order are obtained by least-squares fitting of the amplitude and phase of the analytical signal. Specifically: Find the logarithm of the magnitude A(t) in Equation 4, and differentiate the logarithm of the magnitude A(t) with respect to time to obtain the following form: (Equation 5) (Equation 6) For the phase in Equation 4 Taking the time derivative yields the following form: (Equation 7) The relationships between the undamped natural frequency, the damped natural frequency, and the damping ratio are as follows: (Equation 8) In the formula: , , Let be the i-th undamped natural frequency, the i-th damped natural frequency, and the i-th damping ratio, respectively. From the relationship between these three, the undamped frequency and the damping ratio can be obtained: (Equation 9) (Equation 10) In the formula: The natural vibration frequency under undamped conditions, expressed in Hz; The final output frequencies of each order Modal parameters such as damping ratio and mode shape.

[0015] As a preferred technical solution: Step three specifically includes: Step 3.1: Finite element modeling; Step 3.2: Solving the characteristic problem; Step 3.3: Calibration of calculated and measured modes in operational modal analysis; Step 3.4: Optimize the search process for calibration of calculated and measured modes.

[0016] As a preferred technical solution: In step 3.1: The finite element substructure method is used to analyze the structure of the transmission tower. With the surrounding limited foundation Finite element modeling is performed, and the truncated unbounded soil at the boundary of the finite element model is simulated by a perfectly matched layer, taking into account dynamic soil-structure interaction. In step 3.2: Solve the characteristic equations for the modal properties of the coupled soil-structure system:

[0017] in: Here is the stiffness matrix; Here is the damping matrix; This is the quality matrix; and The first Each eigenvalue and eigenvector; For pile-soil dynamic stiffness; In step 3.3: The mean root square error is used to evaluate the difference between the calculated natural frequency and the measured natural frequency. Quantitative evaluation of modal shape calibration using modal confidence level; In step 3.4: The Fibonacci search method was used to optimize the search process. The modal parameter indices before and after the correction were compared. The frequency difference rate between the corrected modal frequency and the target modal frequency was controlled within a set range. The modal confidence criterion between the corrected modal strain energy and the target modal strain energy was also controlled within a set range. At this point, after calibrating the calculated and measured modes, the forward-modeled pile-soil dynamic stiffness is taken as the pile-soil dynamic stiffness under the corresponding measured modal parameters. .

[0018] As a preferred technical solution: Step four specifically includes: Step 4.1: Determination of dynamic buckling instability based on pile-soil dynamic stiffness reduction; Step 4.2: Calculate the critical pile-soil dynamic stiffness of the transmission tower.

[0019] As a preferred technical solution: Step 4.1 specifically includes: Step 4.1.1: Determine the form of the micro-perturbation; The micro-disturbance process was changed to a successive reduction process of pile-soil dynamic stiffness, with the initial value of the pile-soil dynamic stiffness reduction being the initial pile-soil dynamic stiffness before the underground mining disturbance. ; Step 4.1.2: Apply dynamic buckling load; The applied load in the dynamic buckling analysis is changed to a fixed load, and the ultimate state wind load or seismic load used in the design of the corresponding transmission tower is adopted to gradually reduce the dynamic stiffness of the pile and soil as a micro-disturbance path. Step 4.1.3: Critical state determination of ultimate stability: Using the Hsu criterion and the most unfavorable tower top displacement phase diagram method, when the trajectory of the phase diagram of the displacement and velocity of the transmission tower top is not closed, exhibiting chaotic characteristics, the structure is determined to have reached the ultimate stability state. In step 4.2: When the structure reaches its ultimate stability state, the corresponding reduction value of the pile-soil dynamic stiffness is the critical pile-soil dynamic stiffness. .

[0020] As a preferred technical solution: Step five specifically includes: Calculate the perturbation degree according to the definition formula. :

[0021] In the formula: The initial dynamic stiffness of the pile and soil before underground mining disturbance; The dynamic stiffness of the pile and soil during a certain stage of underground mining disturbance; The critical dynamic stiffness of the pile and soil.

[0022] The beneficial effects of the technical solution provided by this invention are: 1. This invention reflects the weakening process of the constraint effect of the underground mining pile foundation on the stability control of the transmission tower by tracking and monitoring the vibration mode evolution of the transmission tower during underground mining disturbance; it uses the pile-soil dynamic stiffness to characterize the constraint effect of the pile foundation on the stability control of the transmission tower. On the one hand, the pile-soil dynamic stiffness can be obtained by inversion from operational mode analysis based on vibration mode tracking and monitoring and modal parameter identification, and on the other hand, its corresponding ultimate stability critical value can be obtained by dynamic buckling stability analysis with reduced pile-soil dynamic stiffness, thereby realizing a disturbance degree assessment value based on pile-soil dynamic stiffness to characterize the disturbance range and disturbance state; based on Modal analysis was used to invert and characterize the pile-soil dynamic stiffness, which represents the constraint effect of the pile foundation on the stability control of the transmission tower. The Hsu criterion and the most unfavorable tower top displacement phase diagram method were employed. The tower was determined to be in a limit stability state by the appearance of a chaotic state where the trajectory of the tower top displacement and velocity phase diagram is not closed during the dynamic buckling analysis. Using the Lyapunov stability definition and the BR criterion for dynamic buckling instability, the pile-soil dynamic stiffness was successively reduced in the dynamic buckling analysis of the transmission tower until the tower reached the limit stability state. The reduced pile-soil dynamic stiffness at this point is the critical pile-soil dynamic stiffness. ; through initial pile-soil dynamic stiffness Dynamic stiffness of pile and soil during a certain stage of underground mining disturbance and critical pile-soil dynamic stiffness Calculate the perturbation degree This invention enables vibration response monitoring under environmental excitation, and proposes an assessment method to evaluate the impact of underground mining disturbance on the long-term service performance of transmission towers. It avoids the mismatch between monitoring and evaluating the overall safety and stability of the structure and the time lag of early warning assessment using traditional local reference quantities such as stress, strain, deformation and displacement, and achieves quantitative characterization of the impact of underground mining disturbance on the long-term service performance of existing transmission towers.

[0023] 2. Since damage to the superstructure and underground foundation can alter the stiffness, mass, or energy dissipation characteristics of the overall structural system, thereby changing the system's dynamic response performance, this invention proposes monitoring the vibration modal response of transmission towers under environmental excitation conditions during underground mining. Dynamic response monitoring is a technology that assesses the structural health status by real-time acquisition and analysis of the response data of the structure and foundation under dynamic excitation. Damage identification based on vibration modes is an effective method for superstructure health monitoring. Foundation disturbance damage also changes the dynamic response of the superstructure. Traditional structural health monitoring neglects the influence of the foundation, while this invention considers the influence of pile foundations and assesses the impact of underground mining disturbance on the long-term service performance of existing transmission towers through disturbance degree. Attached Figure Description

[0024] Figure 1This is a flowchart illustrating the disturbance degree assessment method for the impact of underground mining on the ultimate stability of power transmission towers as described in this invention. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0026] Example 1 like Figure 1 As shown in the figure, this embodiment proposes a disturbance degree assessment method for the impact of underground mining on the ultimate stability of transmission towers, including the following steps: Step 1: Monitoring the modal evolution of transmission tower vibration under environmental excitation; Step one specifically includes: Step 1.1: Before underground mining disturbance, deploy a vibration modal monitoring system for transmission towers under environmental excitation; the vibration modal monitoring system includes a DHDAS dynamic signal acquisition instrument (sampling frequency of 200Hz), DASP V11 analysis software, and a 941B type magnetoelectric low-carbon vibration pickup; the pickup is installed on the transmission tower and is used to collect the response signals of the transmission tower, including acceleration, velocity, and displacement. The pickup is connected to the acquisition instrument and transmits the signals to the acquisition instrument. The acquisition instrument is connected to the analysis software, which converts the analog signals into digital signals to obtain response data, and then transmits the response data to the analysis software for finite element modal analysis.

[0027] The placement principle of the vibration pickups is as follows: based on finite element modal analysis, they are placed at the locations of maximum modal displacement, with increased density around them. The orientation of the pickups is correctly set according to the modal shape and acceleration acquisition direction. The pickups are fixed with 502 glue and rigidly connected to the transmission tower structure. Their sensitivity is calibrated after fixing.

[0028] Other auxiliary equipment for the vibration modal monitoring system includes communication cables, adapters, timers, metronomes, computers, power supplies, and cables.

[0029] Step 1.2: After the vibration mode monitoring system is deployed, the vibration mode evolution of the transmission towers during underground mining disturbance is continuously tracked and monitored.

[0030] Step 2: Identification of vibration mode parameters of transmission towers based on environmental excitation; The Hilbert-Huang transform (HHT) method is used to identify the modal parameters of transmission towers under environmental excitation. This method is mainly suitable for processing nonlinear and non-stationary signals. The method is as follows: first, empirical mode decomposition (EMD) is performed, then a stochastic decrement method is used, and finally the Hilbert-Huang transform is applied.

[0031] Step two specifically includes: Step 2.1: Use empirical mode decomposition response data to obtain the eigenmode function components representing different orders of modal responses; Step 2.2: Apply the random decrement method or natural excitation technique to obtain the free decay response signals of each mode of the system (i.e., the intrinsic mode function components obtained in Step 2.1); Step 2.3: Use the Hilbert-Huang transform to convert the free decay response data to obtain the analytical signal; Step 2.4: Calculate and output the modal parameters, including frequency, damping ratio and mode shape.

[0032] In step 2.1: For the original signal (This signal is response data, which is data converted by the data acquisition instrument.) The purpose of Empirical Mode Decomposition (EMD) is to obtain the intrinsic mode functions of the structure. When the signal... When the following two conditions are met (signal) From the original signal The extracted signal components to be screened), signal It can be viewed as an Intrinsic Mode Function (IMF): (Equation 1) (Equation 2) Where: EP is the signal The number of extreme points (including maxima and minima) in the time domain, ZP is the signal. The number of zeros in the time domain; for The upper envelope defined by the maxima in the time domain. for The lower envelope determined by the minimum value in the time domain.

[0033] In order to obtain from the original signal To extract the response IMF from the original signal, you need to analyze the original signal. EMD decomposition, step 2.1 specifically includes the following steps: Step 2.1.1: Find the original signal The upper envelope of the signal is obtained from all extreme points using cubic spline interpolation. With lower envelope ; Step 2.1.2: Let ; Step 2.1.3: Determine Whether the two conditions of the Intrinsic Mode Function (IMF) are satisfied (Equation 1 and Equation 2); like If both conditions are met, then This is the first IMF component; like If one of the conditions is not met, repeat steps 2.1.1 and 2.1.2 until the [condition is not met]. After the second screening If the two conditions for the Intrinsic Mode Function (IMF) are satisfied, then... As the first IMF component ; Step 2.1.4: Transfer the remaining signal As new data, repeat steps 2.1.1 to 2.1.3 for filtering until new IMF components are obtained. ; Step 2.1.5: When the residual signal component Stop filtering when the preset conditions are met or the function is monotonic.

[0034] in, ~ These are the eigenmode function components of different orders of modal response.

[0035] In step 2.1.1, during the initial execution, the interpolation object is the original signal. Interpolation yields the original signal. Upper envelope With lower envelope In subsequent iterations, the envelope fitting is performed on the components to be selected obtained in the previous step. Continue until the component meets the IMF conditions, thus completing the extraction of the current IMF.

[0036] In step 2.3: For the original signal Perform Hilbert-Huang transform on the original signal. Transform into Then its analytic signal z(t) is expressed as: (Equation 3) In the formula: i is the index of the IMF component, and the magnitude A(t) and phase are... It can be represented in the following form: (Equation 4) In the formula: The instantaneous amplitude of the modal free decay vibration at t=0 represents the energy level at the start of the modal response. The damping ratio is dimensionless and reflects the rate at which structural vibration energy is dissipated. The natural angular frequency of the mode in the undamped state, in rad / s, depends only on the mass m and stiffness k of the structure; The damped natural angular frequency; The initial phase is the initial phase angle of the modal free decay vibration at t=0, which is determined by the initial conditions and is measured in rad. It reflects the phase state of the signal at the start of the vibration.

[0037] In step 2.4: The frequencies and damping ratios of each order are obtained by least-squares fitting of the amplitude and phase of the analytical signal. Specifically: Find the logarithm of the magnitude A(t) in Equation 4, and differentiate the logarithm of the magnitude A(t) with respect to time to obtain the following form: (Equation 5) (Equation 6) For the phase in Equation 4 Taking the time derivative yields the following form: (Equation 7) The relationships between the undamped natural frequency, the damped natural frequency, and the damping ratio are as follows: (Equation 8) In the formula: , , Let be the i-th undamped natural frequency, the i-th damped natural frequency, and the i-th damping ratio, respectively. From the relationship between these three, the undamped frequency and the damping ratio can be obtained: (Equation 9) (Equation 10) In the formula: The natural vibration frequency under undamped conditions, expressed in Hz; The final output frequencies of each order ( Modal parameters such as damping ratio and mode shape.

[0038] Step 3: Inversion of dynamic stiffness of transmission tower pile and soil based on operational modal analysis; Operational Modal Analysis (OMA) is based on the assumption of steady-state white noise. It can calculate the modal parameters of a structure using only the measured output response data of the structure, and then compare the modal parameters obtained by simulation with the values ​​of the actual data.

[0039] The present invention relates to the dynamic stiffness inversion of the pile-soil dynamic stiffness of transmission towers, specifically by using forward modeling to adjust the pile-soil dynamic stiffness to ensure that the calculated modal parameters are consistent with the measured modal parameters, thereby achieving the inversion of the pile-soil dynamic stiffness of the transmission tower under the measured modal parameters. .

[0040] Step three specifically includes: Step 3.1: Finite element modeling; The dynamic soil-structure interaction problem is described using the finite element substructure method and perfectly matched layer (PML).

[0041] The finite element substructure method is used to analyze the structure of the transmission tower. With the surrounding limited foundation Composition of generalized structure Finite element modeling is performed, and the truncated unbounded soil at the boundary of the finite element model is simulated by a perfectly matched layer (PML), taking into account dynamic soil-structure interaction.

[0042] Step 3.2: Solving the characteristic problem; Solve the characteristic equations for the modal properties of the coupled soil-structure system:

[0043] in: Here is the stiffness matrix; Here is the damping matrix; This is the quality matrix; and The first Each eigenvalue and eigenvector; This refers to the dynamic stiffness of the pile and soil.

[0044] Step 3.3: Calibration of calculated and measured modes in operational modal analysis; Taking natural frequencies and mode shapes as examples: The mean root mean square error is used to evaluate the difference between the calculated natural frequencies and the measured natural frequencies:

[0045] in, To calculate the first First frequency, For the actual measurement First frequency, For the sample size, It is the order.

[0046] Quantitative evaluation of modal calibration using modal confidence scores (MAC):

[0047] in, Indicates the calculation of the first First-order mode shape vector, Indicates the measured number First-order mode shape vector.

[0048] , The closer the value is to 1, the smaller the difference between the calculated value and the measured value, and the better the accuracy of the operational modal analysis.

[0049] Step 3.4: Optimize the search process for calibration between calculated and measured modes; The Fibonacci search method was used to optimize the search process. The modal parameter indices before and after the correction were compared. The frequency difference rate between the corrected modal frequency and the target modal frequency was controlled within 5%, and the modal confidence criterion between the corrected modal strain energy and the target modal strain energy was controlled within 10% as the optimization objectives.

[0050] At this point, after calibrating the calculated and measured modes, the forward-modeled pile-soil dynamic stiffness is taken as the pile-soil dynamic stiffness under the corresponding measured modal parameters. .

[0051] Step 4: Calculate the critical pile-soil dynamic stiffness of the transmission tower based on stiffness reduction dynamic buckling stability analysis; Traditional dynamic buckling instability assessment and critical load determination: Based on Lyapunov's definition of stability and the BR criterion, the dynamic buckling instability criterion is defined as follows: For a small disturbance input to the system... Then, if the response disturbance amount If the increase is significant, the system is considered to have experienced "dynamic instability".

[0052] Assume that the same increment is applied with each load, i.e.:

[0053] in, The initial load, For the first The load applied in this cycle This is the proportionality coefficient.

[0054] make For the system in the first The response during the next load is taken as the maximum value of the response:

[0055] When with Increase to a certain value hour, A rapid increase indicates that the system is experiencing dynamic buckling. Also known as the critical load factor, the corresponding load is the critical load.

[0056] Step four specifically includes: Step 4.1: Determination of dynamic buckling instability based on pile-soil dynamic stiffness reduction; Step 4.1.1: Determine the form of the micro-perturbation; Adopting the concepts of Lyapunov's stability definition and BR criterion for dynamic buckling instability, the form of each loading micro-disturbance is changed to a process of successive reduction of pile-soil dynamic stiffness. The initial value of the pile-soil dynamic stiffness reduction is the initial pile-soil dynamic stiffness before the underground mining disturbance. .

[0057] Step 4.1.2: Apply dynamic buckling load; The traditional method of using a continuous loading mode does not conform to the concept of limit state reliability in civil engineering design, but rather to the concept of maximum bearing capacity of mechanical mechanisms. Therefore, the applied load in dynamic buckling analysis is changed to a fixed load, and the limit state wind load or seismic load used in the design of transmission towers is adopted to gradually reduce the dynamic stiffness of the pile and soil as a "micro-disturbance" path.

[0058] Step 4.1.3: Critical state determination of ultimate stability: Using the Hsu criterion and the most unfavorable tower top displacement phase diagram method, when the trajectory of the phase diagram of the displacement and velocity of the transmission tower top is not closed, exhibiting chaotic characteristics, the structure is determined to have reached the ultimate stability state.

[0059] Step 4.2: Calculate the critical pile-soil dynamic stiffness of the transmission tower; When the structure reaches its ultimate stability state, the corresponding reduction value of the pile-soil dynamic stiffness is the critical pile-soil dynamic stiffness. .

[0060] Step 4.1.2 Determining the wind load: When wind loads act perpendicularly on the surface of a structure, the average standard value of the load is obtained using the following formula:

[0061] In the formula: This represents the standard value of wind load. For height The wind vibration coefficient at the location; This is the wind load shape coefficient; This is the wind pressure height variation coefficient; This is the basic wind pressure.

[0062] The limit state stability of the transmission tower structure was solved using nonlinear dynamic buckling analysis of wind load in ANSYS. The transmission tower structure was subjected to wind load in three sections. The specific parameters were specified in the "Design Code for 110kV~750kV Overhead Transmission Lines" (GB50545). The overall model constraints and wind load application methods were also specified.

[0063] Step 5: Calculation of the degree of disturbance affecting the ultimate stability of underground mining; Calculate the perturbation degree according to the definition formula. :

[0064] In the formula: The initial dynamic stiffness of the pile and soil before underground mining disturbance; The dynamic stiffness of the pile and soil during a certain stage of underground mining disturbance; The critical dynamic stiffness of the pile and soil.

[0065] According to the control standard that the limit stability safety factor is greater than 2, it should be controlled .

[0066] This invention monitors the vibration modal response of transmission towers under environmental excitation during underground mining. It employs operational modal analysis to invert the evolution of the dynamic stiffness of the transmission tower's pile-soil dynamics during underground mining by analyzing the vibration modal response. Through dynamic buckling stability analysis with reduced pile-soil dynamic stiffness, it obtains the critical pile-soil dynamic stiffness characterizing the ultimate stability state of the transmission tower. Finally, based on the initial pile-soil dynamic stiffness, disturbed pile-soil dynamic stiffness, and critical pile-soil dynamic stiffness, it calculates the disturbance degree to assess the impact of underground mining on the ultimate stability of the transmission tower and the long-term service performance of the transmission tower due to underground mining disturbance. The disturbance degree serves as a quantitative characterization of the impact of underground mining disturbance on the long-term service performance of existing transmission towers.

[0067] The following example is provided for verification: Tower: 220kV single-circuit self-supporting angle steel tower, the superstructure has been completed, and the tower and foundation are rigidly connected.

[0068] On-site conditions: There is an underground goaf 180m north of the tower site. The goaf is being gradually advanced. Environmental stimulation monitoring was carried out before the goaf (baseline) and when the goaf was advanced to the S2 stage.

[0069] Sensor and sampling: 914B magnetoelectric vibration pickup, sampling frequency 200Hz, first / second mode displacement peak value and its neighborhood arranged on the transmission tower (fixed with 502 glue and sensitivity calibrated).

[0070] Vibration modal evolution monitoring + modal parameter identification (HHT / EMD+OMA): EMD → random decrement → HHT were performed on the two periods of data (S0 baseline and S2 disturbance period) to obtain the frequencies and damping ratios of each order. Then, the numerical model modes were calibrated (frequency RMSE, mode shape MAC index). The optimization search adopted the Fibonacci search method.

[0071] Target: Frequency difference controlled at approximately 5%, mode shape MAC deviation controlled at approximately 10%.

[0072] The measured results obtained are as follows: S0 (before mining): First-order natural frequency =2.10Hz, second order =5.40Hz; S2 (disturbance period): First-order natural frequency =1.80Hz, second order =5.00Hz.

[0073] Note: The first-order frequency is most sensitive to the basic flexibility and serves as the main control index for subsequent inversion. The second-order frequency is used for cross-verification (in conjunction with MAC).

[0074] Inversion of dynamic stiffness of pile and soil: Approach: In the soil-structure coupling model, the dynamic stiffness K of pile and soil is taken as the quantity to be determined. K is adjusted to make the calculated mode consistent with the measured mode (f, φ), thereby obtaining K at each stage, that is, the dynamic stiffness of pile and soil.

[0075] Using the "first-order equivalent method," a manually calculated approximation is given. If the first-order method is the dominant basic flexibility, the system's equivalent stiffness is... (The effective modal mass remains approximately constant). Therefore, the equivalent stiffness ratio between the two periods is approximately:

[0076] The equivalent stiffness ratio indirectly quantifies the degree of degradation of the constraint stiffness of a structural system by using measurable frequency changes, under the assumption of constant modal mass. Under the dominance of this mode, the pile-soil dynamic stiffness ratio can be approximated. .

[0077] Initial pile-soil dynamic stiffness Set to 1.00 (normalized baseline); Dynamic stiffness of pile and soil during disturbance period =0.735.

[0078] Critical stiffness analysis: Load values: The standard ultimate limit state wind load is adopted (applied in three stages, with parameters in accordance with the "Design Code for 110kV~750kV Overhead Transmission Lines" (GB50545)). In the dynamic analysis, instead of "continuously adding load", the fixed design wind load is maintained, and the dynamic stiffness of the pile and soil is gradually reduced as a "micro-disturbance" path.

[0079] Instability criterion: When the displacement-velocity phase diagram at the top of the tower shows a non-closed trajectory / chaos (Hsu criterion), it is determined that the ultimate stability state has been reached. The reduced stiffness at this point is the critical pile-soil dynamic stiffness. .

[0080] (Assuming one calculation has been completed) we get

[0081] — Typically between 0.5 and 0.7 (related to tower type, soil layer and wind load rating).

[0082] Disturbance calculation: The case study uses linear normalization:

[0083] =0 indicates that it is equivalent to the baseline. =1 indicates that the limit stability boundary has been approached.

[0084] when = This indicates that 59% of the safety margin has been "consumed" compared to the limit boundary, and a state of close monitoring and control should be entered, combined with the control concept that "the limit stability safety factor must be ≥2".

Claims

1. A method for assessing the disturbance degree of the impact of underground mining on the ultimate stability of transmission towers, characterized in that: Includes the following steps: Step 1: Monitoring the modal evolution of transmission tower vibration under environmental excitation; Step 2: Identification of vibration mode parameters of transmission towers based on environmental excitation; Step 3: Inversion of dynamic stiffness of transmission tower pile and soil based on operational modal analysis; Step 4: Calculate the critical pile-soil dynamic stiffness of the transmission tower based on stiffness reduction dynamic buckling stability analysis; Step 5: Calculation of the degree of disturbance affecting the ultimate stability of underground mining.

2. The disturbance degree assessment method for the impact of underground mining on the ultimate stability of transmission towers according to claim 1, characterized in that: Step one specifically includes: Before underground mining disturbance, a vibration mode monitoring system is deployed to continuously track the vibration mode evolution of power transmission towers during underground mining.

3. The disturbance degree assessment method for the impact of underground mining on the ultimate stability of transmission towers according to claim 2, characterized in that: The monitoring system includes a vibration pickup, a dynamic signal acquisition instrument, and modal analysis software.

4. The disturbance degree assessment method for the impact of underground mining on the ultimate stability of transmission towers according to claim 1, characterized in that: Step two specifically includes: Step 2.1: Use empirical mode decomposition response data to obtain the eigenmode function components representing different orders of modal responses; Step 2.2: Apply the random decrement method or natural excitation technique to obtain the free decay response signals of each mode of the system; Step 2.3: Use the Hilbert-Huang transform to convert the free decay response data to obtain the analytical signal; Step 2.4: Calculate and output the modal parameters, including frequency, damping ratio and mode shape.

5. The disturbance degree assessment method for the impact of underground mining on the ultimate stability of transmission towers according to claim 4, characterized in that: Step 2.1 specifically includes the following steps: Step 2.1.1: Find the original signal All extreme points, by cubic spline interpolation to get the envelope line on the signal With the lower envelope line ; Step 2.1.2: Let ; Step 2.1.3: Judging whether two conditions of intrinsic mode function, IMF, are satisfied: (Formula 1) (Equation 2) like If both conditions are met, then This is the first IMF component; like If one of the conditions is not met, repeat steps 2.1.1 and 2.1.2 until the [condition is not met]. After the second screening If the two conditions for the Intrinsic Mode Function (IMF) are satisfied, then... As the first IMF component ; Step 2.1.4: Transfer the remaining signal As new data, repeat steps 2.1.1 to 2.1.3 for filtering until new IMF components are obtained. ; Step 2.1.5: When the residual signal component The filtering process stops when the preset conditions are met or the function is monotonic. In step 2.3: For the original signal Perform Hilbert-Huang transform on the original signal. Transform into Then its analytic signal z(t) is expressed as: (Equation 3) In the formula: i is the index of the IMF component, and the magnitude A(t) and phase are... It can be represented in the following form: (Equation 4) In the formula: The instantaneous amplitude of the modal free decay vibration at t=0; The damping ratio; Let be the natural angular frequency of the mode in the undamped state; The damped natural angular frequency; This is the initial phase; In step 2.4: The frequencies and damping ratios of each order are obtained by least-squares fitting of the amplitude and phase of the analytical signal. Specifically: Find the logarithm of the magnitude A(t) in Equation 4, and differentiate the logarithm of the magnitude A(t) with respect to time to obtain the following form: (Equation 5) (Equation 6) For the phase in Equation 4 Taking the time derivative yields the following form: (Equation 7) The relationships between the undamped natural frequency, the damped natural frequency, and the damping ratio are as follows: (Equation 8) In the formula: , , Let be the i-th undamped natural frequency, the i-th damped natural frequency, and the i-th damping ratio, respectively. From the relationship between these three, the undamped frequency and the damping ratio can be obtained: (Equation 9) (Equation 10) In the formula: The natural vibration frequency under undamped conditions, expressed in Hz; The final output frequencies of each order Modal parameters such as damping ratio and mode shape.

6. The disturbance degree assessment method for the impact of underground mining on the ultimate stability of transmission towers according to claim 1, characterized in that: Step three specifically includes: Step 3.1: Finite element modeling; Step 3.2: Solving the characteristic problem; Step 3.3: Calibration of calculated and measured modes in operational modal analysis; Step 3.4: Optimize the search process for calibration of calculated and measured modes.

7. The disturbance degree assessment method for the impact of underground mining on the ultimate stability of transmission towers according to claim 6, characterized in that: In step 3.1: The finite element substructure method is used to analyze the structure of the transmission tower. With the surrounding limited foundation Finite element modeling is performed, and the truncated unbounded soil at the boundary of the finite element model is simulated by a perfectly matched layer, taking into account dynamic soil-structure interaction. In step 3.2: Solve the characteristic equations for the modal properties of the coupled soil-structure system: in: Here is the stiffness matrix; Here is the damping matrix; This is the quality matrix; and The first One eigenvalue and one eigenvector; For pile-soil dynamic stiffness; In step 3.3: The mean root square error is used to evaluate the difference between the calculated natural frequency and the measured natural frequency. Quantitative evaluation of modal shape calibration using modal confidence level; In step 3.4: The Fibonacci search method was used to optimize the search process. The modal parameter indices before and after the correction were compared. The frequency difference rate between the corrected modal frequency and the target modal frequency was controlled within a set range. The modal confidence criterion between the corrected modal strain energy and the target modal strain energy was also controlled within a set range. At this point, after calibrating the calculated and measured modes, the forward-modeled pile-soil dynamic stiffness is taken as the pile-soil dynamic stiffness under the corresponding measured modal parameters. .

8. The disturbance degree assessment method for the impact of underground mining on the ultimate stability of transmission towers according to claim 1, characterized in that: Step four specifically includes: Step 4.1: Determination of dynamic buckling instability based on pile-soil dynamic stiffness reduction; Step 4.2: Calculate the critical pile-soil dynamic stiffness of the transmission tower.

9. The disturbance degree assessment method for the impact of underground mining on the ultimate stability of transmission towers according to claim 8, characterized in that: Step 4.1 specifically includes: Step 4.1.1: Determine the form of the micro-perturbation; The micro-disturbance process was changed to a successive reduction process of pile-soil dynamic stiffness, with the initial value of the pile-soil dynamic stiffness reduction being the initial pile-soil dynamic stiffness before the underground mining disturbance. ; Step 4.1.2: Apply dynamic buckling load; The applied load in the dynamic buckling analysis is changed to a fixed load, and the ultimate state wind load or seismic load used in the design of the corresponding transmission tower is adopted to gradually reduce the dynamic stiffness of the pile and soil as a micro-disturbance path. Step 4.1.3: Critical state determination of ultimate stability: Using the Hsu criterion and the most unfavorable tower top displacement phase diagram method, when the trajectory of the phase diagram of the displacement and velocity of the transmission tower top is not closed, exhibiting chaotic characteristics, the structure is determined to have reached the ultimate stability state. In step 4.2: When the structure reaches its ultimate stability state, the corresponding reduction value of the pile-soil dynamic stiffness is the critical pile-soil dynamic stiffness. .

10. The disturbance degree assessment method for the impact of underground mining on the ultimate stability of transmission towers according to claim 9, characterized in that: Step five specifically includes: Calculate the perturbation degree according to the definition formula. : In the formula: The initial dynamic stiffness of the pile and soil before underground mining disturbance; The dynamic stiffness of the pile and soil during a certain stage of underground mining disturbance; The critical pile-soil dynamic stiffness.

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