Wide-range high-precision tubular static leveling instrument based on optical fiber sensing technology

Abstract

The utility model provides a wide-range high-precision tubular static level gauge based on an optical fiber sensing technology, which relates to the technical field of settlement monitoring and comprises a sensing system, a high-strength water pipe and a liquid storage barrel, after liquid is injected into the water pipe, the liquid also enters an elastic corrugated pipe of the sensing system and generates water pressure on the pipe wall, and the water pipe is filled with the liquid. When the position where the sensing system is located is settled or lifted, water pressure in the elastic corrugated pipe changes, the corrugated pipe can be driven to stretch out and draw back, strain is transmitted to the sensing optical fiber through the strain beam, optical fiber grating points on the sensing optical fiber are pulled or pressed, and the wavelength of reflected light is changed. The static force level measuring device is simple in structure, easy to install, capable of achieving settlement monitoring of the earth and rockfill dam under complex conditions through application of the optical fibers, high in sensitivity, precision and reliability, free of current electromagnetism, capable of being used for measuring static force level and capable of being applied to the earth and rockfill dam under the complex conditions. And the safety performance is relatively good.

Description

Technical Field

[0001] The utility model relates to the technical field of settlement monitoring, in particular to a large-range and high-precision tubular static level based on optical fiber sensing technology. Background Art

[0002] Excessive deformation of earth-rock dams can cause huge casualties and economic losses. For example, the Johnston Reservoir flood dam breach in the United States in 1889 caused more than 2,000 deaths; in 1975, due to the heavy rains brought by typhoons, multiple reservoirs in Zhumadian, Henan, collapsed, causing more than 20,000 casualties; in 2019, a dam breach occurred in Brumadinho, Brazil, killing about 300 people. The collapse of earth-rock dams is affected by various factors, such as rainfall, reservoir water level, rock and soil properties, construction disturbance, etc., but the instability of earth-rock dams is usually accompanied by obvious displacement. Therefore, accurate monitoring of earth-rock dam displacement is crucial in the early warning of earth-rock dam safe operation.

[0003] Earth-rock dam displacement monitoring can be divided into horizontal displacement monitoring and vertical displacement monitoring according to its nature, and can be divided into deformation during construction and deformation after construction according to time. At present, the main means of deformation monitoring of earth-rock dams mainly include surface settlement monitoring, inclinometers, electromagnetic settlement tubes, soil displacement meters, etc. These monitoring methods have their own shortcomings. For example, surface settlement monitoring cannot obtain internal deformation information of landslides. Traditional inclinometers have some shortcomings in monitoring accuracy, monitoring efficiency, and anti-interference. Electromagnetic settlement tubes and soil displacement meters involve electromagnetics, and their failure rates and safety are insufficient. At the same time, the above traditional monitoring methods are difficult to monitor the settlement and displacement of earth-rock dams during the construction period. They are also low in real-time performance and automation. Therefore, accurate monitoring of the settlement and displacement of earth-rock dams is still very difficult.

[0004] Fiber optic sensing is a new type of sensing technology that has developed rapidly in recent years. It uses optical fiber as a medium and light as a carrier. Compared with traditional monitoring technology, it has a series of advantages such as high sensitivity, anti-electromagnetic interference, long monitoring distance, and low cost. It has been widely used in petrochemical, aerospace, water conservancy and hydropower, civil engineering, geology and other engineering fields.

[0005] Commonly used fiber optic sensing technologies include FBG, UWFBG, OFDR, OTDR, BOTDR, BOTDA, etc.

[0006] Fiber Bragg grating (FBG) utilizes the ultraviolet wavelength sensitivity of optical fiber. Within a certain length, a notch is etched on the fiber core that can cause the refractive index to change periodically, so that an intra-core grating is formed inside the fiber core. When broadband incident light enters the optical fiber, the incident wavelength band that meets the Bragg condition will be reflected at the grating. The peak wavelength of the reflected light can be detected from the incident end. This wavelength is called the Bragg wavelength. The central wavelength value of the reflected light has a linear relationship with the axial strain and temperature value of the Bragg grating, that is:

[0007]

[0008] In the formula, λ B is the initial center wavelength of the grating; Δλ B is the drift of the fiber Bragg grating center wavelength; ε, ΔT are the strain and temperature changes of the grating respectively; K ε , K T are the strain and temperature calibration coefficients of the fiber Bragg grating, respectively. For the fiber K used for FBG ε =0.78×10-6με-1, K T =6.67×10-6℃-1.

[0009] When the fiber Bragg grating generates axial strain, the working wavelength of the fiber Bragg grating sensor will change, so the reflected wavelength will change. Therefore, by measuring the change in the reflected light wavelength of the fiber Bragg grating buried in the structure or pasted on the surface of the structural material, the strain change of the structure at that point can be known, and it can be easily read and visualized through appropriate modulation and demodulation means (usually composed of a Fabry-Perot interferometer connecting a light source and a coupler).

[0010] Through the above analysis, the main problem to be solved by the utility model is: in view of the fact that current technology cannot accurately realize the settlement and displacement monitoring of earth-rock dams, a large-range and high-precision tubular static level based on optical fiber sensing technology is provided. The tubular static level can realize large-range and high-precision real-time settlement monitoring of the foundation surface of earth-rock dams, and can realize the monitoring of settlement during the construction period and after the construction of earth-rock dams.

[0011] The significance of solving the above technical problems lies in that fiber optic sensing is a new sensing technology that has developed rapidly in recent years and uses optical fiber as a medium and light as a carrier. Compared with traditional monitoring technology, it has a series of advantages such as high sensitivity, resistance to electromagnetic interference, long monitoring distance and low cost. Utility Model Content

[0012] The purpose of the utility model is to provide a large-range and high-precision tubular static level based on optical fiber sensing technology, which is mainly used for early warning monitoring of foundation pit deformation, early warning monitoring of settlement displacement of earth-rock dams and their cofferdams, etc. Compared with traditional monitoring technology, it has a series of advantages such as high sensitivity, resistance to electromagnetic interference, long monitoring distance and low cost.

[0013] The utility model provides the following technical solutions:

[0014] A large-range, high-precision tubular static level based on optical fiber sensing technology, comprising a water pipe with water pressure inside and distributed horizontally, wherein a sensing system is arranged in the water pipe, wherein the sensing system comprises a group of outer cylinders horizontally positioned in the water pipe, wherein the two ends of the outer cylinders are respectively sealed by an upper cover of the cylinder body, a beam fixing support, and a lower cover of the cylinder body to form an internal cavity, wherein a group of elastic bellows are also installed therein through the beam fixing support, wherein one end of the elastic bellows is sealed by an upper cover of the bellows, and the other end is fixed to the beam fixing support, wherein liquid enters the elastic bellows from a water permeable hole of the beam fixing support to form a pressure difference between the inside and outside of the elastic bellows, wherein a pre-stretched sensing optical fiber passes through the outer cylinder, the beam fixing support, and the elastic bellows to be fixed on a strain beam, wherein the strain beam is installed in the elastic bellows and fixed on the beam fixing support to transmit the strain of the elastic bellows to ensure that the sensing optical fiber can sense the strain transmitted by the strain beam;

[0015] After liquid is injected into the water pipe, the liquid also enters the elastic bellows of the sensing system and generates water pressure on the pipe wall. When the sensing system sinks or rises, the water pressure inside the elastic bellows changes, which drives the bellows to expand and contract. The strain is transmitted to the sensing optical fiber through the strain beam. The optical fiber grating points on the sensing optical fiber are therefore pulled or compressed, causing the wavelength of the reflected light to change. The change in water pressure is then indirectly calculated through the change in the strain and converted into the required physical quantity to achieve static level measurement.

[0016] Preferably, the sensing system in the same water pipe is provided with multiple groups, and they are arranged in series inside the water pipe through sensing optical fibers. One end of the water pipe is closed, and the other end is connected to a vertically extending liquid storage tank. If the height of the liquid storage tank remains unchanged, when the water pipe sinks by ΔH, it can be determined that the water pressure at the sensing system location increases accordingly, so as to monitor the changes before and after the settlement. By connecting multiple sensing systems in series in the same water pipe, quasi-distributed settlement monitoring inside the earth-rock dam can be better realized, so as to perform long-distance, multi-point static leveling measurements.

[0017] Preferably, the water pipe is blocked at both ends, and during the test, the water pressure is increased step by step by using a pressurizing device, so that the calibration test of the tubular static level can be carried out conveniently.

[0018] Preferably, an annular permeable stone is arranged on the beam fixing support and at the position corresponding to the permeable hole, and the annular permeable stone is used to introduce liquid into the interior of the sensor system to increase the water permeability rate.

[0019] Preferably, the sensing optical fiber is a quasi-distributed optical fiber or a distributed optical fiber, and the sensing optical fiber led out from the outer tube is connected to the optical fiber demodulation device through a jumper.

[0020] Preferably, the sensing optical fiber is fixed to the strain beam using epoxy adhesive to sense the strain amount transmitted by the strain beam.

[0021] The beneficial effects of the utility model are:

[0022] First, the utility model has a simple structure and is easy to install. It adopts optical fiber sensing technology and can monitor the settlement of earth-rock dams under complex conditions. It has high sensitivity and accuracy, strong reliability, and does not involve current and electromagnetics, so its safety performance is relatively good.

[0023] Second, since most of the settlement of earth-rock dams occurs during the construction period, compared with traditional monitoring methods that can only monitor the settlement of earth-rock dams after construction, the utility model can start monitoring immediately after the filling of any horizontal monitoring section is completed, and can realize automatic settlement monitoring of earth-rock dams throughout their life cycle, reducing the error of manual measurement and reducing the workload;

[0024] Thirdly, the utility model can connect multiple fiber grating level meters in series in the same water pipe, thereby being able to better realize quasi-distributed settlement monitoring inside the earth-rock dam. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0026] Figure 1 It is a structural cross-sectional view of a large-range tubular static level based on optical fiber sensing technology of the utility model;

[0027] Figure 2 It is a schematic diagram of the change of the settlement ΔH of the large-range tubular static level instrument based on the optical fiber sensing technology of the utility model;

[0028] Figure 3 It is a partial cross-sectional view of the change of the settlement ΔH of the large-range tubular static level instrument based on the optical fiber sensing technology of the utility model;

[0029] Figure 4 This is a schematic diagram of an indoor calibration test in an embodiment of the utility model;

[0030] Figure 5It is the wavelength-water pressure relationship obtained from the indoor calibration test in the embodiment of the utility model;

[0031] Figure 6 yes Figure 1 Schematic diagram of the structure after rendering color;

[0032] Markings in the figure:

[0033] 101. Water pipe; 102. Liquid storage barrel; 103. Sensing optical fiber; 104. Outer cylinder; 105. Upper cover of cylinder; 106. Lower cover of cylinder; 107. Elastic bellows; 108. Upper cover of bellows; 109. Annular permeable stone; 110. Strain beam; 111. Beam fixing support; 112. Cavity; 113. Optical fiber grid point; 114. Permeable hole; 115. Demodulation equipment; 116. Pressurizing pipe; 117. Pressurizing equipment. DETAILED DESCRIPTION

[0034] As Figure 1-6 As shown, a large-range high-precision tubular static level based on optical fiber sensing technology, in this embodiment, includes a sensing system, a high-strength water pipe 101 and a liquid storage tank 102; the water pipe 101 contains liquid and is horizontally distributed, one end of which is sealed, and the other end is connected to a vertically extending liquid storage tank, and the sensing system is arranged in the water pipe 101.

[0035] The sensing system includes a group of outer cylinders 104 horizontally positioned in the water pipe 101, and the two ends of the outer cylinder 104 are respectively blocked by the cylinder upper cover 105, the beam fixing support 111, and the cylinder lower cover 106 to form an internal cavity 112, and a group of elastic bellows 107 are also installed therein through the beam fixing support 111, and one end of the elastic bellows 107 is sealed with a bellows upper cover 108, and the other end is fixed to the beam fixing support 111, and the liquid enters the elastic bellows 107 from the water permeable hole 114 of the beam fixing support 111 to form a pressure difference between the inside and outside of the elastic bellows 107, and the pre-stretched sensing optical fiber 103 passes through the outer cylinder 104, the beam fixing support 111, and the elastic bellows 107 and is fixed on the strain beam 110, and the strain beam 110 is installed in the elastic bellows 107 and fixed to the beam fixing support 111;

[0036] When the sensing system is provided with multiple groups, the sensing optical fibers 103 can be arranged in series inside the water pipe 101. After the liquid is injected into the water pipe 101, the liquid also enters the elastic bellows 107 of the sensing system and generates water pressure on the pipe wall. When the sensing system is located at a position where it sinks or rises, the water pressure inside the elastic bellows 107 changes, which can drive the elastic bellows 107 to expand and contract. The strain is transmitted to the sensing optical fiber 103 through the strain beam 110. The optical fiber grid point 113 is therefore pulled or compressed, resulting in a change in the wavelength of the reflected light. The change in water pressure is then indirectly calculated through the change in the strain amount and converted into the required physical quantity to achieve the measurement of the static level.

[0037] The outer cylinder 104 is hollow and used to isolate and protect the internal structure of the sensor system. A cylinder upper cover 105 is arranged at one end, and the other end is connected to the beam fixing support 111. A cylinder lower cover 106 is arranged at the end of the beam fixing support 111, and the whole constitutes an external high-strength metal structure of "cylinder upper cover 105 - outer cylinder 104 - beam fixing support 111 - cylinder lower cover 106";

[0038] The beam fixing support 111 is provided with a circle of water-permeable holes 114, and a ring-shaped water-permeable stone 109 is arranged at the position of the water-permeable holes 114, which is mainly used to introduce liquid into the sensor, thereby improving the water permeability rate;

[0039] One end of the elastic bellows 107 is sealed with a bellows cover 108, and the other end is fixed to a beam fixing support 111. Liquid enters the bellows from a water-permeable hole 114 of the beam fixing support 111, isolating the remaining part of the outer tube 104 to form a cavity 112, so as to ensure a pressure difference between the inside and outside of the bellows.

[0040] The sensing optical fiber 103 adopts a non-stripping coating grating writing process to write strain gratings and temperature compensation gratings, thereby avoiding damage to the optical fiber structure caused by the grating writing process and greatly improving the tensile strength of the optical fiber. At the same time, the optical fiber needs to be pre-stretched and fixed to the strain beam 110 with a high-strength epoxy adhesive to sense the strain transmitted by the strain amount.

[0041] In this embodiment, the sensing optical cable is a quasi-distributed strain sensing optical cable, which is fixed on the strain beam 110 and then led out of the outer tube 104, and then connected to the optical fiber demodulation device 115 through a jumper; the sensing system is arranged in series inside the water pipe 101 through the sensing optical fiber 103, one end of the water pipe 101 is sealed, and the other end is connected to an external liquid storage tank; the liquid storage tank is fixed, and after the liquid is injected into the water pipe 101, the liquid also enters the bellows of the sensing system and generates water pressure on the wall of the bellows. When the position of the sensing system sinks or rises, the water pressure inside the elastic bellows 107 changes, which can drive the bellows to expand and contract, and transmit the strain to the optical fiber through the strain beam 110. The optical fiber grid point 113 is therefore pulled or compressed, resulting in a change in the wavelength of the reflected light, and then the change in water pressure is indirectly calculated through the change in the strain amount, and converted into the required physical quantity to achieve the measurement of static leveling. The invention has a simple structure and is easy to install. It can realize structural settlement monitoring under complex deformation conditions, has high sensitivity and accuracy, does not involve current and electromagnetics, and has relatively good safety performance.

[0042] The working principle of the utility model is:

[0043] When the location of the sensing system sinks or rises, the water pressure inside the elastic bellows 107 changes, which can drive the bellows to expand and contract. The strain is transmitted to the optical fiber through the strain beam 110. The optical fiber grid point 113 is thus pulled or compressed, causing the wavelength of the reflected light to change. The change in water pressure is then indirectly calculated through the change in strain and converted into the required physical quantity to achieve the measurement of static leveling.

[0044] The measuring principle of the utility model is as follows Figure 2-3 As shown, the height of the external liquid storage barrel 102 remains unchanged. When the position of the sensor system settles ΔH, the water pressure at the position increases accordingly.

[0045] ΔP=ρgΔH (2)

[0046] The increase in water pressure will cause the elastic bellows 107 to stretch, which in turn causes the optical fiber to strain. The bellows, as a linear elastic material, obeys Hooke's theorem. According to Hooke's theorem, the strain of the elastic bellows 107 is:

[0047] Δε=kΔP (3)

[0048] From formula (1), we can see that there is a linear relationship between the central wavelength of the reflected light and the axial strain and temperature of the Bragg grating. Substituting formula (3) into formula (1), we can get:

[0049]

[0050] remember Therefore, when the temperature is constant, the central wavelength value of the reflected light has a linear relationship with the water pressure at the location of the sensor. At this time, it is necessary to determine the proportional coefficient K of the liquid level and wavelength change through indoor calibration test. λ In addition, a temperature compensation grating that is not subject to force is arranged inside the sensor to eliminate the influence of temperature changes, thereby accurately measuring the change in water pressure ΔP, and then calculating the settlement value or uplift value through formula (2).

[0051] As mentioned above, the key to determining the relationship between the optical fiber strain value and the water pressure is to determine the proportional coefficient K between the liquid level and the wavelength change. λ , the tubular static level needs to be calibrated. Figure 4 As shown, the specific steps are as follows: put the tubular static level into the pressurized tube 116 and fix it, lead the sensing optical fiber 103 out and connect it to the demodulation device 115, then seal the pressurized tube 116 and fill it with water, wait for about half an hour until the sensor bellows is fully saturated with water before starting the test. The test uses the pressurized device 117 to increase the water pressure step by step, with 10% of the range as one level until the full range is 0.5MPa, and finally fits and analyzes the collected data. The relationship between water pressure and wavelength in some experiments is shown in the figure. Figure 5 As shown in the figure, the straight line is the water pressure-wavelength relationship curve obtained by least squares fitting, and the equation is the corresponding water pressure-wavelength linear equation. The linear correlation coefficient R2 of the test value is greater than 0.999, indicating that the test water pressure of the sensor has a relatively obvious linear relationship with the wavelength. Therefore, the measured wavelength can be substituted into the correlation function to obtain the change of water pressure, thereby indirectly obtaining the settlement value.

[0052] The present utility model provides a large-range and high-precision tubular static level based on optical fiber sensing technology. The optical fiber sensing technology used in the above embodiment is FBG technology. It should be pointed out that distributed or quasi-distributed optical fiber sensing technologies including but not limited to BOTDR, BOTDA, UWFBG, etc. are also equally applicable. Therefore, the application of other optical fiber sensing technologies in the present utility model should also be regarded as the protection scope of the present utility model.

[0053] The above description is only a preferred embodiment of the utility model and is not intended to limit the utility model. Although the utility model is described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions recorded in the above embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the utility model shall be included in the protection scope of the utility model.

Claims

1. A high-precision tubular static level with a large range based on optical fiber sensing technology, characterized in that: The invention comprises a water pipe (101) having water pressure therein and being distributed horizontally, wherein a sensor system is arranged in the water pipe (101), wherein the sensor system comprises a group of outer cylinders (104) horizontally positioned in the water pipe (101), wherein two ends of the outer cylinder (104) are respectively blocked by a cylinder upper cover (105) and a beam fixing support (111) and a cylinder lower cover (106) to form an internal cavity (112), wherein a group of elastic bellows (107) is installed in the outer cylinder through the beam fixing support (111), wherein one end of the elastic bellows (107) is sealed by a bellows upper cover (108), and the other end is fixed to the beam fixing support (111). 11), liquid enters the elastic bellows (107) from the water permeable hole (114) of the beam fixing support (111) to form a pressure difference between the inside and outside of the elastic bellows (107), and the pre-stretched sensing optical fiber (103) passes through the outer cylinder (104), the beam fixing support (111), and the elastic bellows (107) to be fixed on the strain beam (110). The strain beam (110) is installed in the elastic bellows (107) and fixed on the beam fixing support (111) to transmit the strain of the elastic bellows (107) to ensure that the sensing optical fiber (103) can sense the strain transmitted by the strain beam (110).

2. According to claim 1, a large-range and high-precision tubular static level based on optical fiber sensing technology, characterized in that: The sensing system is provided with a plurality of groups, and is arranged in series inside a water pipe (101) via sensing optical fibers (103); one end of the water pipe (101) is sealed, and the other end is externally connected to a vertically extending liquid storage tank.

3. According to claim 1, a large-range and high-precision tubular static level based on optical fiber sensing technology, characterized in that: The water pipe (101) is a pressurized pipe (116) with both ends blocked, and during the test, the water pressure is increased step by step by using a pressurizing device (117).

4. According to claim 1, a large-range and high-precision tubular static level based on optical fiber sensing technology is characterized in that: An annular permeable stone (109) is arranged on the beam fixing support (111) and at a position corresponding to the permeable hole (114). The annular permeable stone (109) is used to guide liquid into the interior of the sensor system to increase the water permeability rate.

5. According to claim 1, a large-range and high-precision tubular static level based on optical fiber sensing technology, characterized in that: The sensing optical fiber (103) is a quasi-distributed optical fiber or a distributed optical fiber. The sensing optical fiber (103) led out from the outer tube (104) is connected to the optical fiber demodulation device (115) through a jumper.

6. The large-range and high-precision tubular static level based on optical fiber sensing technology according to claim 1, characterized in that: The sensing optical fiber (103) is fixed to the strain beam (110) by using epoxy adhesive to sense the strain amount transmitted by the strain beam (110).

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