Monitoring Method for Dynamic Parameters of Debris Flow Based on Vibration Sensors

Abstract

The present invention discloses a monitoring method for the dynamic parameters of debris flow based on vibration sensors. Based on vibration sensors, taking the amplitude, frequency, duration, vibration waveform shape of debris flow vibration and the vibration characteristics of other phenomena as a benchmark, a monitoring method for dynamic parameters such as the occurrence time, duration, scale, flow rate and moving speed of debris flow is proposed. The rising part of the waveform is approximated by an exponential function, and the relationship between the correlation coefficient and the set threshold for the occurrence of debris flow is established to judge the occurrence of debris flow, supplemented by two detection benchmarks of vibration intensity and duration to improve the accuracy. The duration and moving speed of debris flow are estimated through the vibration waveform, and the flow rate and scale of debris flow are deduced from the positive correlation between the vibration acceleration of debris flow and the flow rate, so as to realize the real-time judgment of the danger of debris flow occurring on site, and make the monitoring and early warning system and emergency avoidance system of debris flow more perfect.

Description

Technical Field

[0001] The present invention relates to a method for monitoring debris flow dynamic parameters based on vibration sensors, belonging to the field of mountain disasters. Background Art

[0002] Debris flow disasters pose a huge threat to the safety of human life and property and the stability of the living environment. The mechanism of debris flow generation, development and change is one of the current research hotspots and technical problems. Therefore, the research on the monitoring of debris flow dynamic parameters is undoubtedly an important basis for debris flow early warning, thereby reducing losses.

[0003] There are currently a large number of practices in debris flow monitoring and early warning, but there are few successful early warning examples in monitoring. One of the reasons is that there are obvious defects in the idea of debris flow monitoring and early warning. Debris flow monitoring and early warning often monitor through environmental quantity indicators (such as rainfall, water level, etc.). Through environmental indicators such as rainfall, although its occurrence can be identified, since rainfall and other environmental conditions are not the necessary and sufficient conditions for debris flow occurrence, the accuracy of its early warning remains to be further discussed; therefore, these indicators can play a certain role in the early warning of debris flow disasters, but there is a certain gap in the realization of early warning in the early stage of disasters.

[0004] Second, the current fluid and dynamic monitoring and early warning indicators for debris flow cannot meet the requirements of key early warning indicators such as the fluid properties and multiple dynamic parameters of debris flow; currently, the general method for monitoring debris flow fluid dynamics is to use a debris flow wire break alarm, which is a device that ties a wire to a stream and issues an alarm when the debris flow cuts the wire. Once the wire is cut, if it is not re-tightened on site again, it is impossible to monitor the next occurrence of debris flow. This is the same for situations where the wire is cut by wind, rain, snow, falling rocks, animals, etc. Moreover, most traditional sensors are based on fluid impact for monitoring and cannot accurately judge the properties of the fluid, such as being unable to distinguish between mountain floods and debris flows.

[0005] Debris flow contains a large amount of gravel, which flows down at a speed of several meters or even more than ten meters per second. Therefore, debris flow will bring great vibrations to the surrounding foundation. Therefore, based on the foundation vibrations generated when the rocks, gravel, etc. contained in the debris flow collide with the foundation, various dynamic parameters such as the gravel content, gravel scale, occurrence time, duration, scale, flow rate and moving speed of the debris flow can be reflected, and the properties of the debris flow can be accurately identified, as well as the danger and risk of the debris flow can be accurately predicted.

[0006] Vibration sensors are non-contact sensors, which have the characteristic of not affecting secondary use after one monitoring. A method for monitoring debris flow dynamic parameters based on vibration sensors is proposed. An early monitoring and early warning indicator system based on dynamic indicators such as debris flow occurrence time, duration, scale, flow rate and moving speed is obtained, which will surely provide an effective solution for improving the quantification and accuracy of forecasts in disaster monitoring and early warning. Summary of the invention

[0007] The purpose of the present invention is to address the deficiencies of existing debris flow monitoring methods and to propose a debris flow dynamic parameter monitoring method based on a vibration sensor.

[0008] To achieve the above object, the present invention is implemented by the following technical solution: a method for monitoring dynamic parameters of debris flow based on vibration sensor, mainly comprising the following steps:

[0009] Step 1: Determine the area where debris flow may occur based on on-site geological survey, select the location of monitoring points, and formulate a monitoring plan.

[0010] Step 2: Carry out real-time monitoring site construction and sensor installation, realize real-time monitoring, and transmit and store data to the control center.

[0011] Step 3: Fit an exponential function to the rising shape of the observed vibration waveform induced by the debris flow, supplemented by two detection benchmark monitoring methods: vibration intensity and duration; calculate the debris flow flow and scale based on the positive correlation between the debris flow vibration acceleration and flow rate, and estimate the duration and moving speed of the debris flow through the vibration waveform, and perform calculations, display and storage.

[0012] Step 4: The control center determines the hazard level of the debris flow based on the calculation results and comparison of evaluation indicators, conducts real-time monitoring and early warning of debris flow disasters, and announces them to the public.

[0013] In step 1, the monitoring point is set in the debris flow near field such as the weir cofferdam revetment in the debris flow flow area or accumulation area, and the receiver is set in a position that is not impacted or buried by the debris flow. After the debris flow occurs, the signal of the debris flow will be wirelessly sent through the sensor. In addition, the sensor is identified by the ID of each sensor.

[0014] In step 2, since the amplitudes and shapes of the vibration waveforms in the horizontal and vertical directions are roughly the same, from the perspective of cost reduction of sensor prices, a piezoelectric vibration sensor was selected. This detection element detects the acceleration in the vertical direction as the bending caused by the inertia of the weight at the front end of the cantilever. The bending of the cantilever, as a reaction of the piezoelectric element, is output as a voltage through the electrodes. The principle of the wireless vibration sensor embedded with the above detection element is to preset a predetermined detection voltage and output a contact signal when the detection voltage is exceeded, thereby monitoring debris flows. Installing the vibration sensor in the soil can avoid false alarms caused by weather conditions such as the sensor shaking due to strong winds and the vibration caused by hailstones hitting the sensor housing.

[0015] Furthermore, the wireless communication method uses a specific low-power wireless communication method with a relatively long transmission distance. The communication distance can be extended through repeaters, and the data is transmitted and stored in the control center. By using wireless, engineering such as cable laying like that of wired systems can be omitted, which is beneficial for the installation of emergency sensors. Also, in the case of relocation operations when there is a risk of sediment deposition at the sensor installation site due to riverbed changes, etc., it is simpler and more mobile than wired systems.

[0016] In step 3, an exponential function fitting is performed on the rising shape of the vibration waveform, and two detection criteria, vibration intensity and duration, are used for monitoring; the positive correlation between the debris flow vibration acceleration and the flow rate is used to estimate the debris flow rate and scale, and the debris flow duration and moving speed are estimated through the vibration waveform. This is the core work of the present invention and is specifically implemented according to the following method.

[0017] (1) Perform an exponential function fitting on the rising shape of the vibration waveform

[0018] The rising shape of the vibration waveform is fitted to a curve described by an exponential function, and the occurrence of debris flow is judged by evaluating its applicability (correlation coefficient). Specifically, the vibration waveform of the foundation caused by the debris flow is recorded by the sensor, and the maximum value within 1 second is obtained. Then, the waveform of the maximum value is approximated by an exponential function, and the correlation coefficient is obtained. When the correlation coefficient exceeds a preset threshold, it is determined that a debris flow has occurred. The determination is performed sequentially using the data from the measurement time point to the previous 80 seconds. The approximate formula is as follows.

[0019] Y = b * exp(at) (1)

[0020] Where Y: the rising shape of the vibration, a, b: the coefficients obtained by fitting, t: time (seconds)

[0021] Furthermore, to improve the accuracy of monitoring, a monitoring algorithm based on vibration amplitude and its duration is also set inside the sensor. By observing the waveform in the vertical direction of the waveform, the maximum value of the absolute value of the amplitude within 1 second unit time is obtained. When it exceeds the preset vibration threshold and duration, it is determined that a debris flow has occurred.

[0022] (2) Calculate the duration and moving speed of the debris flow through the vibration waveform

[0023] The greater the moving speed of the debris flow, the greater the increase in vibration, and the smaller the moving speed, the smaller the increase in vibration. That is, the moving speed of the debris flow can be inferred from the amplification trend of the vibration waveform. Assuming that the tip of the debris flow is a point source of vibration, the distance attenuation of the vibration is evaluated by the following equation (2), and equation (3) is a transformation of equation (2).

[0024]

[0025]

[0026] p: Vibration amplitude at distance d (gal), p′: Amplitude of the reference vibration at a position at distance d′ (gal), α: Attenuation constant inside the foundation, d, d′: Distances from the vibration source (m), n: Geometric attenuation constant.

[0027] Equations (2) and (3) observe the vibration of the same vibration source in d and d′, and estimate p when obtaining the reference vibration p′.

[0028] Considering the vibration of the debris flow, the maximum amplitude vibration generated by the debris flow is observed when the debris flow is closest to the debris flow vibration sensor, that is, at the moment when the line connecting the vibration sensor and the river channel is perpendicular (referred to as point A) and the debris flow passes through. Therefore, the vibration at point A is used as the reference vibration source. In this case, according to equation (3), the distance d from the vibration source is equal to the distance d′ from the reference point vibration source.

[0029] On the other hand, the amplification trend of the vibration is affected by the moving speed of the debris flow. That is, if the debris flow as the vibration source approaches the vibration sensor, the vibration will increase. To express this phenomenon with a formula, we use "d: distance from the vibration source" in formula (2) to reflect the moving speed of the debris flow. As a result, equations (4) and (5) are obtained.

[0030]

[0031]

[0032] P b : Distance D bMagnitude of vibration at a distant position (gal), P: Magnitude of vibration at a position at distance D, D b : Distance between debris flow and vibration sensor (m), D: Distance between debris flow and point A (m), D: Distance between vibration sensor and point A (m), t: Time (s), V: Moving speed of debris flow (m / s).

[0033] Here, D′ - V in equation (5) t is replaced with equation (7).

[0034]

[0035]

[0036] t′: Time required for the debris flow to be closest to the vibration sensor (assuming the time when the debris flow is closest to the vibration sensor is 0)

[0037] The focus of this formula is that as t′ increases, P b gradually decreases. That is, by setting the time when the debris flow is closest to 0 and tracing back from that time point, the vibration attenuation process of the debris flow can be traced. Conversely, the amplification trend of the debris flow vibration can be evaluated.

[0038] Furthermore, when the vibration amplitude above the set threshold lasts for more than the set time, the relationship between the flow velocity of the debris flow and the ground vibration is coordinated. The duration of the vibration is approximately the same as the duration of the debris flow. Therefore, it is considered that the vibration will continue while the debris flow continues to flow. Thus, the schematic fluid diagram of the debris flow can be estimated from the shape (amplitude, duration) of the vibration waveform.

[0039] (3) Deducing the debris flow discharge and scale based on the positive correlation between debris flow vibration acceleration and discharge

[0040] There is a strong positive correlation between the peak discharge of the fluid and the vibration acceleration. The reason for the correlation is that the larger the peak discharge, the greater the movement of the largest - sized gravel in the fluid. Let the peak acceleration be x and the peak discharge be y, then

[0041] y = 2.93 * (x - 10) 2 / 3 (8)

[0042] Regarding the scale of the debris flow, it can be determined through the amplitude A of the vibration acceleration a(t) Estimation of the integral value in the same time band. Here, the starting time t1 of the fluid flow is determined by the characteristic of a sharp rise in the flow rate, while the ending time t2 is not objectively determined. Therefore, the flow rate at point t2 is generally taken as the flow rate at the moment when the peak flow rate decreases by 20%. However, in the case of a small-scale fluid, when the flow rate does not drop to 20% of its peak flow rate and the next fluctuation occurs, the end point is taken as 30 s after the peak of the flow rate appears. When the next fluctuation occurs immediately after 30 s, the end point of the previous fluctuation is taken as the starting point of the next fluctuation. The amplitude A of the vibration acceleration is obtained by the following formula a (t) The integral value in the same time band.

[0043]

[0044] Let the fluid volume be y, and I A be x, and their relationship is

[0045] y = 1.39x - 174 (10). Description of the drawings

[0046] Figure 1 is the overall flowchart of the method of the present invention;

[0047] Figure 2 is the schematic diagram of the monitoring method of the present invention. Detailed implementation manners

[0048] To make the objectives, technical solutions and advantages of the present invention clearer, the following will further describe the implementation manners of the present invention in conjunction with the drawings, and detailed implementation manners and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0049] As Figure 1 shown in the flow chart, it includes the following steps:

[0050] According to the on-site geological exploration situation, as Figure 2 shown, monitoring points are selected, vibration sensors are buried at the monitoring points, and thresholds are preset through past observation records or other means. From the waveforms obtained by the sensors, when observing the correlation coefficient calculated simultaneously with the waveform acquisition, as the waveform rises, the correlation coefficient gradually increases and exceeds the threshold. The information with the coefficient exceeding the threshold is transmitted and received wirelessly to the receiver. At the same time, the algorithm based on the amplitude and duration set inside the sensor also transmits and receives the information exceeding the threshold wirelessly to the receiver. To further improve the accuracy, sensors can also be set at the upstream and downstream of the stream respectively, and the identification of the sensors is through the ID identification possessed by each sensor.

[0051] The sampling frequency of the vibration sensor is set to 100 Hz. The accuracy is improved by increasing the number of samples. For the received data, it is first judged whether it contains the influence of wind, rain and other noise, and then the waveform to be analyzed is extracted. According to the effective vibration waveform obtained by measurement, the dynamic parameters such as moving speed and flow rate are calculated. The internal attenuation constant α of the foundation and the geometric attenuation constant n are set during the calculation. α is expressed by the following formula.

[0052]

[0053] α: Internal attenuation constant of the foundation, f: Vibration frequency (Hz), V s : Propagation speed (m / s), η: Loss coefficient.

[0054] The value of the geometric attenuation constant n varies according to the type of wave (0.5 for surface waves and 1.0 for body waves). However, it is difficult to separate surface waves and body waves from the actual vibration waveform of debris flow. Therefore, assuming that the two are mixed waves, using 0.75 is a practically feasible method.

[0055] Regarding the use of acceleration, as a representative value, the maximum acceleration is often used. However, there are many deviations in the maximum acceleration, and the situation where the acceleration protrudes in a pulsed manner is considered. Using the acceleration value with a relative degree of 99% (the relative degree of 100% is the maximum acceleration) has better accuracy than using the maximum acceleration for evaluation.

[0056] The control center classifies the risk level according to the early warning level formulated in combination with the local actual geological conditions for the calculated relevant motion parameters and issues early warning information.

[0057] An example application of Tianmogou located in the Yigong Zangbo - Palong Zangbo deep fault zone using the method of the present invention is provided. The steep terrain and developed modern glaciers in Tianmogou provide good conditions for the formation of debris flow. At the same time, due to the continuous increase in temperature, the melting of glaciers accelerates, and a large amount of moraine, rockfall ice and snow, and residual deposits are formed in the basin, providing a rich source of loose solid materials for debris flow activities. Now, aiming at the geological condition characteristics of the Tianmogou area, real-time monitoring of debris flow dynamic parameters is carried out.

[0058] Step 1: Through on-site investigation, according to the engineering geological conditions of the debris flow ditch, a monitoring point is selected at the upstream and downstream positions of the flow area of the debris flow ditch respectively.

[0059] Step 2: One monitoring device based on a vibration sensor is arranged at each monitoring point. The device is buried in the soil to avoid false measurement events caused by the shaking of the frame due to strong wind and the collision of hail and other objects with the device frame. After turning on the switch, the monitoring data can be transmitted to the receiver in real time through the wireless data transmission system.

[0060] Step 3: Conduct data analysis and research on the vibration data of historical debris flow events in Tianmogou, determine the warning threshold suitable for this area and input it into the program algorithm, perform real-time processing and analysis on the data transmitted by the monitoring equipment, and issue an alarm and report it to the control center when the parameters reach two detection benchmarks; after the program realizes the early warning, it enters the calculation of the debris flow discharge, scale, duration, and moving speed modules, and transmits the calculation results to the control center in real time.

[0061] Step 4: According to the calculation results, the control center compares and evaluates the indicators, determines the debris flow hazard level and announces it to the public.

Claims

1. A monitoring method for debris flow dynamic parameters based on vibration sensors, characterized in that, It mainly includes the following steps: Step 1: Determine the areas where debris flows may occur based on on-site geological surveys, select the locations of monitoring points, and formulate monitoring plans; Step 2: Carry out the construction of real-time monitoring stations and the installation of sensors, achieve real-time monitoring, and transmit and store the data to the control center; Step 3: Fit the rising shape of the vibration waveform induced by debris flow with an exponential function, supplemented by two detection benchmarks of vibration intensity and duration for monitoring; Deduce the debris flow discharge and scale from the positive correlation between the debris flow vibration acceleration and the flow rate, estimate the debris flow duration and moving speed through the vibration waveform, and perform calculations, displays, and storage; Specifically, according to the following method: (1) Fit the rising shape of the vibration waveform with an exponential function The rising shape of the vibration waveform is fitted to a curve described by an exponential function, and the occurrence of debris flow is judged by evaluating its applicability, that is, the correlation coefficient; The approximate formula is as follows: Y = b * exp(at) (1) Where Y: the rising shape of the vibration, a, b: the coefficients obtained by fitting, t: time, in seconds; A monitoring algorithm based on the vibration amplitude and its duration is also set inside the sensor; When the vibration threshold and duration preset are exceeded, it is determined that a debris flow has occurred; (2) Calculate the debris flow duration and moving speed through the vibration waveform Assume that the tip of the debris flow is a point seismic source, and the distance attenuation of the vibration is expressed by Equation (2), and Equation (3) is the deformation of Equation (2); p: the vibration amplitude (gal) at distance d, p': the reference vibration amplitude (gal) at a position at distance d', α: the internal attenuation constant of the foundation, d, d': the distance (m) from the vibration source, n: the geometric attenuation constant; Use "d: the distance from the vibration source" in Equation (2) to reflect the moving speed of the debris flow; When the leading edge of the debris flow approaches the position closest to the vibration sensor in the flow area, Equations (4) and (5) are obtained; P b : Magnitude of vibration at a distant position D (gal), P: Magnitude of vibration at the position of distance D (gal), D b : Magnitude of vibration at a distant position D (gal), P: Magnitude of vibration at the position of distance D (gal), D b : Distance between the debris flow and the vibration sensor (m), D′: Distance between the debris flow and point A (m), D: Distance between the vibration sensor and point A (m), t: Time (s), V: Moving speed of the debris flow (m / s); After the moving position of the leading edge of the debris flow moves away from the position closest to the vibration sensor in the flow area, D'-Vt in Equation (5) is replaced by Equation (7); t': the time required for the debris flow to be closest to the vibration sensor, and the time when the debris flow is closest to the vibration sensor is set to 0; The duration of the vibration is approximately the same as the duration of the debris flow, so the duration of the debris flow is estimated from the shape of the vibration waveform; (3) Deduce the debris flow discharge and scale from the positive correlation between the debris flow vibration acceleration and the flow rate According to the empirical formula, let the peak acceleration be x and the peak flow rate be y, then y = 2.93 * (x - 10) 2 / 3 (8) The scale of debris flow can be estimated by the integral value of the amplitude A of the vibration acceleration a (t) over the same time band; the amplitude A of the vibration acceleration is obtained by the following formula a (t) over the same time band; t1 is the start time and t2 is the end time; According to the empirical formula, assuming the fluid volume is y and I A is x, the fluid volume can be estimated, and the relationship is: y = 1.39x - 174 (10) Step 4: The control center determines the debris flow hazard level based on the calculation results and compares the evaluation indicators.

2. The monitoring method of debris flow dynamic parameters based on a vibration sensor according to claim 1, characterized in that In Step 1, the monitoring points are set at the debris flow near-field of the weir cofferdam revetment in the debris flow flow area or deposition area, and the receiver is set at a position not affected by debris flow impact and burial; After a debris flow occurs, the signal of the debris flow occurrence will be wirelessly sent through the sensor; In addition, the identification of the sensor is carried out through the ID possessed by each sensor.

3. The monitoring method of debris flow dynamic parameters based on a vibration sensor according to claim 1, characterized in that, In step 2, a piezoelectric vibration sensor is adopted; the detection element detects the acceleration in the vertical direction, which is caused by the inertia of the weight at the front end of the cantilever; a predetermined detection voltage is set in advance, and a contact signal is output when the detection voltage is exceeded, thereby monitoring debris flow.

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