Earth and rockfill dam seepage detector and detection method based on distributed optical fiber acoustic wave sensing

Abstract

The invention relates to the technical field of optical fiber sensing, in particular to an earth and rockfill dam seepage detector based on distributed optical fiber sound wave sensing and a detection method.The earth and rockfill dam seepage detector achieves continuous real-time detection under program control, facilitates rapid data collection of a detected section face, and can detect the seepage of an earth and rockfill dam through a demodulation algorithm. A waterfall plot, an apparent velocity profile map and the like are generated through a surface wave inversion algorithm, and the abnormal distribution condition in the earth and rockfill dam can be detected. Data are transmitted in real time, analyzed in real time, sampled at a high speed and digitally processed, a corresponding frequency dispersion curve and a geologic structure chart can be displayed while measurement is carried out, and great convenience is provided for field analysis and judgment. Meanwhile, by means of the permanently-buried optical fibers, irregular inspection can be conducted on the earth and rockfill dam, and the process is simple. Therefore, the equipment solves the problems that the seepage monitoring precision of the earth and rockfill dam is low and the timeliness is not high in a traditional mode.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to an earth-rock dam seepage detector and a detection method based on distributed optical fiber acoustic wave sensing. Background Art

[0002] As an emerging technology, distributed fiber optic sensing technology has shown great potential in many fields. Among the existing technologies that are most similar to the present invention, the distributed temperature and deformation sensor (DTSS) based on Brillouin scattering is mainly used for deformation monitoring of dams, tunnels, etc., and cannot monitor seepage; the technology based on distributed temperature sensors monitors soil moisture content through temperature changes. However, the precision and accuracy are low, and the detection range is limited. In addition, although technologies such as magnetotelluric field dam pipe burst detector, seepage detection device based on leakage temperature difference, and seepage detection device based on electric field can be applied to seepage monitoring, they cannot achieve fully automatic remote real-time monitoring, and are single-point sensors, which cannot achieve continuous and high-density imaging. At the same time, it is also necessary to excavate and bury the sensor in the dam body, which is a non-destructive monitoring technology.

[0003] At present, seepage monitoring of earth-rock dams mainly relies on traditional methods, but these methods have problems such as low monitoring accuracy, high cost, great construction difficulty, and long monitoring cycle, which limit their widespread application. Summary of the invention

[0004] The purpose of the present invention is to provide an earth-rock dam seepage detector and a detection method based on distributed optical fiber acoustic wave sensing, aiming to solve the problem of low accuracy and poor timeliness of earth-rock dam seepage monitoring in traditional methods.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a method for detecting seepage in an earth-rock dam based on distributed optical fiber acoustic wave sensing, comprising the following steps: The optical fiber is laid flat over the dam to be monitored and covered with cement; When the laser is working, it emits laser light into the optical fiber, and the laser light propagates toward the beam splitter at the same frequency; The acquisition card works to collect raw data and transmits the collected data to the demodulation module; The demodulation module performs phase adjustment on the collected data to obtain the strain rate, and transmits the strain rate to the algorithm module; The algorithm module analyzes the strain rate and obtains the S-wave propagation velocity profile at different depths of the dam.

[0006] Among them, in "the demodulation module performs phase adjustment on the collected data to obtain the strain rate, and transmits the strain rate to the algorithm module", the phase adjustment adopts the interference superposition principle in the time domain.

[0007] Among them, in "the algorithm module analyzes the strain rate to obtain the S-wave propagation velocity profile at different depths in the dam", the algorithm module uses the dispersion caused by refraction of surface waves generated by an external seismic source propagating between strata to invert the speed of the S-wave at different depths.

[0008] In the second aspect, a seepage detector for earth-rock dam based on distributed optical fiber acoustic wave sensing is used in the earth-rock dam seepage detection method based on distributed optical fiber acoustic wave sensing described in the first aspect, comprising a host computer and an optical fiber, wherein the host computer comprises a laser, a spectrometer, an acquisition card and a microprocessor; The laser and the optical splitter are connected to the optical fiber respectively, and the optical splitter, the acquisition card and the microprocessor are connected in sequence.

[0009] Wherein, the microprocessor comprises a demodulation module and an algorithm module, the demodulation module is connected to the acquisition card, and the algorithm module is connected to the demodulation module.

[0010] The earth-rock dam seepage detection method based on distributed optical fiber acoustic wave sensing of the present invention comprises the following steps: laying the optical fiber flat on the dam to be monitored and covering it with cement; the laser emits laser light into the optical fiber when the laser is working, and the laser propagates to the spectrometer at the same frequency; the acquisition card works to collect raw data and transmits the collected data to the demodulation module; the demodulation module performs phase adjustment on the collected data to obtain the strain rate, and transmits the strain rate to the algorithm module; the algorithm module analyzes the strain rate to obtain the propagation velocity profile of the S wave at different depths of the dam. The earth-rock dam seepage detector of the present invention realizes continuous real-time detection under program control, which is convenient for rapid data collection of the measured section surface, and generates waterfall diagrams, apparent velocity profiles, etc. through the above-mentioned demodulation algorithm and surface wave inversion algorithm, so as to find out the abnormal distribution inside the earth-rock dam. The data is transmitted and analyzed in real time, sampled at high speed, and processed digitally. The corresponding dispersion curve and geological structure map can be displayed while measuring, which provides great convenience for on-site analysis and judgment. At the same time, the permanently buried optical fiber can be used to conduct irregular inspections on the earth-rock dam, and the process is simple. Therefore, this equipment solves the problem of low accuracy and poor timeliness of seepage monitoring of earth-rock dams in traditional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0012] Figure 1It is a flow chart of the earth-rock dam seepage detection method based on distributed optical fiber acoustic wave sensing provided by the present invention.

[0013] Figure 2 This is a schematic diagram of earthquake source propagation.

[0014] Figure 3 It is a waterfall chart.

[0015] Figure 4 It is a dispersion curve diagram.

[0016] Figure 5 It is a one-dimensional stratigraphic inversion map.

[0017] Figure 6 This is a schematic diagram of the installation of stone dam monitoring equipment.

[0018] Figure 7 is the apparent velocity profile.

[0019] Figure 8 It is a structural schematic diagram of an earth-rock dam seepage detector based on distributed optical fiber acoustic wave sensing provided by the present invention.

[0020] In the figure: 1-host computer, 2-optical fiber, 3-laser, 4-splitter, 5-acquisition card, 6-microprocessor, 7-demodulation module, 8-algorithm module. DETAILED DESCRIPTION

[0021] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0022] See also Figures 1 to 7 In a first aspect, the present invention provides a method for detecting seepage in an earth-rock dam based on distributed optical fiber acoustic wave sensing, comprising the following steps: S1 lays the optical fiber 2 flat above the dam to be monitored and covers it with cement; Specifically, the optical fiber 2 is laid flat above the dam to be monitored and covered with cement to better couple to the measured dam structure. Any point on the optical fiber 2 can be a vibration sensor, and 0.8m is set as the interval between two sensors, and 4m is the sensor gauge length.

[0023] The S2 laser 3 works and emits laser light into the optical fiber 2, and the laser light propagates toward the beam splitter 4 at the same frequency; Specifically, the laser 3 in the host computer 1 emits laser light, which is injected into the optical fiber 2. There are impurities in the light, and these impurities interact with the light, changing the direction of light propagation but not changing the frequency of the light itself, which makes the emitted laser light propagate toward the host computer 1 at the same frequency.

[0024] S3 acquisition card 5 works to collect raw data and transmits the collected data to demodulation module 7; Specifically, when the laser is transmitted from the optical fiber 2 back to the optical splitter 4 in the host computer 1, the optical splitter 4 splits a portion of the light to the optical detector in the acquisition card 5 to collect the original data.

[0025] S4 demodulation module 7 performs phase adjustment on the collected data to obtain the strain rate, and transmits the strain rate to the algorithm module 8; The phase adjustment adopts the interference superposition principle in the time domain.

[0026] Specifically, the collected data is transmitted to the demodulation module 7 by the internal line for phase demodulation. Phase demodulation mainly uses the interference superposition principle in the time domain. If the optical fiber 2 generates strain, that is, the length of the change per unit length is , then a phase term is added to the light wave ,in is the speed of light propagation. At this time, the amplified reflected light can be demodulated by IQ phase demodulation principle or Hilbert demodulation to obtain phase difference information. The specific steps are described as follows: IQ phase demodulation: The reflected light and the original laser light after phase change are multiplied by the time-dependent sin and cos functions respectively to perform coherent interference. After low-pass filtering, the two components of I and Q are obtained. The phase information is the inverse tangent function of Q divided by I. Hilbert Demodulation: Received Signal After Hilbert transformation The generated signal is equivalent to the original signal Rotate 90 degrees. We get the analytical signal through coherent interference; This analytical signal contains the initial signal The phase information itself , That is, do a reverse analysis on the analytical signal.

[0027] After obtaining the phase change, according to the formula, the strain rate SR of optical fiber 2 is S5 algorithm module 8 analyzes the strain rate and obtains the S wave propagation velocity profile at different depths of the dam.

[0028] The algorithm module 8 uses the dispersion caused by the refraction of the surface waves generated by the external seismic source propagating between strata to invert the speed of the S wave at different depths.

[0029] Specifically, the host computer 1 transmits the obtained strain rate to the algorithm module 8 through the internal line, and uses the surface wave analysis method in the algorithm module 8 to obtain the S wave propagation velocity profile at different depths of the dam. This method uses the dispersion caused by the refraction of the surface wave generated by the external seismic source propagating between the strata to invert the speed of the S wave at different depths.

[0030] First, the external earthquake source propagates in different geological conditions. When the mechanical wave passes through the medium layers with different densities, refraction and scattering will occur. At this time, the relationship between the frequency and velocity of the mechanical wave will change, such as Figure 2 This signal is captured by our seepage monitor, such as Figure 3 ( Figure 3 The red in the middle is the peak of the surface wave, and the blue is the trough of the surface wave) is shown in the lower left corner. The xt data u(t) is transformed by ω-k (two-dimensional Fourier transform) to obtain a two-dimensional graph in the frequency-wave number plane. At the same time, the phase velocity is . So the ω-k graph is transformed into Figure, we get the dispersion curve diagram, such as Figure 4 Finally, according to the propagation formula of elastic waves in geology, The dispersion of the initial model is being performed. Figure 4 The dispersion shown in the figure is continuously optimized by the least squares method, which can invert the actual geological model, that is, Figure 5 A one-dimensional graph showing the relationship between S-wave propagation velocity and geological depth.

[0031] According to common sense, the deeper the geology, the stronger the rock, and the faster the S wave propagation speed. Therefore, the normal geological model is the result of the S wave speed increasing with depth. However, if the S wave speed suddenly decreases at a certain depth, it is speculated that the seepage here has changed the wave speed propagation speed of the rock. Therefore, we use the S wave depth map to infer the depth and location of the dam seepage. Figure 7 As shown in Figure 1, we show the S-wave profile of a certain earth-rock dam. It can be seen that there are abnormally low-velocity areas at the bottom and lower right, which are presumed to be two seepage points.

[0032] See also Figure 8 In the second aspect, a seepage detector for earth-rock dam based on distributed optical fiber acoustic wave sensing is used for the earth-rock dam seepage detection method based on distributed optical fiber acoustic wave sensing described in the first aspect, comprising a host computer 1 and an optical fiber 2, wherein the host computer 1 comprises a laser 3, a spectrometer 4, an acquisition card 5 and a microprocessor 6; The laser 3 and the beam splitter 4 are connected to the optical fiber 2 respectively, and the beam splitter 4, the acquisition card 5 and the microprocessor 6 are connected in sequence.

[0033] The microprocessor 6 includes a demodulation module 7 and an algorithm module 8 . The demodulation module 7 is connected to the acquisition card 5 , and the algorithm module 8 is connected to the demodulation module 7 .

[0034] In this embodiment, the laser 3 can emit laser light and inject the laser light into the optical fiber 2. A part of the light can be split to the acquisition card 5 through the beam splitter 4. The light detector in the acquisition card 5 can perform data acquisition. The demodulation module 7 can perform phase demodulation on the acquired data to obtain strain rate data. The algorithm module 8 can analyze the propagation velocity profile of the S wave at different depths of the dam based on the strain rate data.

[0035] Beneficial effects: 1. The earth-rock dam seepage monitor with the advantages of long distance, high density, simple deployment, no power supply, and non-destructive testing using DAS technology can obtain geological profiles and estimate the seepage position of the earth-rock dam.

[0036] 2. Different from single-point discrete imaging, the earth-rock dam seepage monitor based on DAS can provide profiles at multiple different locations of the earth-rock dam, forming three-dimensional geological imaging.

[0037] Third, the portability of the monitor allows it to be connected to the optical fiber permanently buried in the earth-rock dam at any time, facilitating high-frequency monitoring of the health of the earth-rock dam and possible seepage problems.

[0038] The above disclosure is only a preferred embodiment of the earth-rock dam seepage detector and detection method based on distributed optical fiber acoustic wave sensing of the present invention. Of course, this cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A method for detecting seepage in earth-rock dams based on distributed optical fiber acoustic wave sensing, characterized in that: The following steps are involved: The optical fiber is laid flat over the dam to be monitored and covered with cement; When the laser is working, it emits laser light into the optical fiber, and the laser light propagates toward the beam splitter at the same frequency; The acquisition card works to collect raw data and transmits the collected data to the demodulation module; The demodulation module performs phase adjustment on the collected data to obtain the strain rate, and transmits the strain rate to the algorithm module; The algorithm module analyzes the strain rate and obtains the S-wave propagation velocity profile at different depths of the dam.

2. The earth-rock dam seepage detection method based on distributed optical fiber acoustic wave sensing according to claim 1, characterized in that: In "the demodulation module performs phase adjustment on the collected data to obtain the strain rate, and transmits the strain rate to the algorithm module", the phase adjustment adopts the interference superposition principle in the time domain.

3. The earth-rock dam seepage detection method based on distributed optical fiber acoustic wave sensing as claimed in claim 2, characterized in that: In "the algorithm module analyzes the strain rate to obtain the S-wave propagation velocity profile at different depths in the dam", the algorithm module uses the dispersion caused by the refraction of the surface wave generated by the external seismic source propagating between the strata to invert the S-wave velocity at different depths.

4. A seepage detector for earth-rock dam based on distributed optical fiber acoustic wave sensing, used in a seepage detection method for earth-rock dam based on distributed optical fiber acoustic wave sensing as claimed in any one of claims 1 to 3, characterized in that: It includes a host computer and an optical fiber, wherein the host computer includes a laser, a spectrometer, a collection card and a microprocessor; The laser and the optical splitter are connected to the optical fiber respectively, and the optical splitter, the acquisition card and the microprocessor are connected in sequence.

5. The earth-rock dam seepage detector based on distributed optical fiber acoustic wave sensing as claimed in claim 4, characterized in that: The microprocessor comprises a demodulation module and an algorithm module. The demodulation module is connected to the acquisition card, and the algorithm module is connected to the demodulation module.

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