Fiber Bragg grating measuring instrument for internal displacement of structure

Abstract

The invention discloses a fiber Bragg grating measuring instrument for internal displacement of a structure, and belongs to the technical field of geotechnical engineering, the fiber Bragg grating measuring instrument comprises an elastic rubber hose and an elastic plastic sleeve which are sleeved and attached inside and outside, the outer wall of the elastic rubber hose is circumferentially provided with a measuring optical fiber, and the measuring optical fiber extends along the axis direction of the elastic rubber hose; fiber Bragg grating strain sensors which are arranged at intervals are connected in series in the measuring optical fibers along the extension direction of the measuring optical fibers, the inner wall of the elastic plastic sleeve is circumferentially provided with accommodating grooves for embedding the measuring optical fibers, the accommodating grooves extend to the end part along the axis direction of the elastic plastic sleeve, and the number and the position of the accommodating grooves correspond to the number and the position of the measuring optical fibers. The device is simple in structure and high in automation degree, can monitor the internal displacement condition of the main body structure in real time, avoids the problem of untimely detection, and can avoid the error problem caused by the damage of the measuring optical fiber and the fiber bragg grating strain sensor in the measuring optical fiber under the protection of the elastic plastic sleeve.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering, and in particular to a fiber Bragg grating measuring instrument for internal displacement of a structure. Background Art

[0002] Landslides pose a serious threat to human life and infrastructure. The main cause of landslides is slope instability caused by slope displacement. Real-time monitoring and early warning of slope displacement are crucial for disaster prevention and mitigation. At present, the most common means of monitoring slopes is to conduct regular inspections of slopes through manually operated probe inclinometers. However, this method has some disadvantages: First, the degree of automation is low, and regular manual inspections are required. Real-time monitoring cannot be achieved, so the test results are not timely; second, the inclinometer is prone to wear or offset, which inevitably produces errors, especially the wear or offset of the data acquisition part and the guide wheel. Summary of the invention

[0003] The purpose of the present invention is to solve the above technical problems and provide a fiber Bragg grating measuring instrument for the internal displacement of a structure, which has a high degree of automation and can monitor the internal displacement of the main structure in real time to avoid the problem of untimely detection. Under the protection of an elastic plastic sleeve, the error problem caused by damage to the measuring optical fiber and the fiber Bragg grating strain sensor therein can be avoided.

[0004] To achieve the above-mentioned purpose, the present invention provides the following scheme: The present invention discloses a fiber Bragg grating measuring instrument for internal displacement of a structure, comprising an elastic rubber hose and an elastic plastic sleeve which are arranged and fitted inside and outside, a measuring optical fiber is circumferentially installed on the outer wall of the elastic rubber hose, the measuring optical fiber extends along the axial direction of the elastic rubber hose, and fiber Bragg grating strain sensors arranged at intervals are connected in series in the measuring optical fiber along its extending direction, and a receiving groove for embedding the measuring optical fiber is circumferentially provided on the inner wall of the elastic plastic sleeve, the receiving groove extends to the end along the axial direction of the elastic plastic sleeve, and the number and position of the receiving groove correspond to the measuring optical fiber.

[0005] Preferably, four measuring optical fibers are included, and the four measuring optical fibers are evenly arranged on the outer wall of the elastic rubber hose.

[0006] Preferably, the elastic plastic sleeve is made of ABS material.

[0007] Preferably, the accommodating groove is a U-shaped groove, the notch end of the U-shaped groove is flush with the inner wall of the elastic plastic sleeve, and the bottom end of the U-shaped groove protrudes from the outer wall of the elastic plastic sleeve.

[0008] Preferably, the elastic rubber hose is a silicone hose.

[0009] Preferably, the measuring optical fiber is arranged on the outer wall of the elastic rubber hose by bonding.

[0010] Preferably, the fiber Bragg grating strain sensor is a strain-free fiber Bragg grating strain sensor.

[0011] Preferably, the elastic plastic sleeve has a length of 600 mm, an inner diameter of 55 mm and an outer diameter of 65 mm; the elastic rubber hose has a length of 600 mm, an inner diameter of 54 mm and an outer diameter of 55 mm.

[0012] Preferably, the fiber Bragg grating strain sensor spacing is 100 mm.

[0013] Preferably, the fiber Bragg grating strain sensor is electrically connected to a fiber Bragg grating demodulator.

[0014] Compared with the prior art, the present invention has achieved the following technical effects:

[0015] The fiber Bragg grating measuring instrument designed in the present invention can realize real-time monitoring of the internal displacement of the main structure. Compared with the traditional inclinometer, it has higher accuracy and sensitivity, and solves the problem of low automation and untimely detection caused by the need for manual detection of the inclinometer. Under the protection of the elastic plastic sleeve, the measuring optical fiber and the fiber Bragg grating strain sensor inside it can be prevented from being damaged, unlike the traditional inclinometer which is prone to wear and tear of the data acquisition part. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 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 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.

[0017] Figure 1 It is a front view structural schematic diagram of a fiber Bragg grating measuring instrument;

[0018] Figure 2 It is a schematic diagram of the top view structure of the fiber Bragg grating measuring instrument;

[0019] Figure 3 It is a schematic diagram of the structure of the elastic rubber hose, optical fiber, and fiber Bragg grating strain sensor;

[0020] Figure 4 for Figure 3 A local enlarged view of point A;

[0021] Figure 5It is a schematic diagram of the structure of the elastic plastic sleeve;

[0022] Figure 6 It is a front view structural schematic diagram of the elastic plastic sleeve;

[0023] Figure 7 It is a schematic diagram of the top view of the elastic plastic sleeve;

[0024] Figure 8 This is a structural diagram of the slope displacement simulation system.

[0025] Explanation of the reference numerals in the accompanying drawings: 1. elastic plastic sleeve; 2. elastic rubber hose; 3. measuring optical fiber; 4. fiber Bragg grating strain sensor; 5. receiving groove; 6. fiber Bragg grating demodulator; 7. computer; 8. slide bed; 9. reaction frame; 10. slide rail; 11. slide body one; 12. slide body two; 13. hydraulic jack; 14. cylindrical specimen. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] This embodiment provides a fiber Bragg grating measuring instrument for internal displacement of a structure, such as Figures 1 to 8 As shown, it includes an elastic plastic sleeve 1, an elastic rubber hose 2 and a measuring optical fiber 3. A plurality of measuring optical fibers 3 are evenly arranged circumferentially on the outer wall of the elastic rubber hose 2, and the measuring optical fibers 3 extend along the axial direction of the elastic rubber hose 2. A plurality of fiber Bragg grating strain sensors 4 arranged at intervals are connected in series along the extending direction (i.e., the axial direction of the elastic rubber hose 2) of the measuring optical fiber 3. The elastic plastic sleeve 1 is sleeved outside the elastic rubber hose 2, and the inner wall of the elastic plastic sleeve 1 fits the outer wall of the elastic rubber hose 2. A receiving groove 5 is circumferentially provided on the inner wall of the elastic plastic sleeve 1, and the receiving groove 5 extends to two ends along the axial direction of the elastic plastic sleeve 1. The number and position of the receiving groove 5 correspond to the measuring optical fibers 3, and the measuring optical fibers 3 are used to be embedded therein.

[0028] Fiber Bragg grating strain sensor (FBG) has obvious advantages such as light weight, small size, high precision, high temperature resistance, corrosion resistance, and intelligence. However, fiber Bragg grating strain sensor can only measure the strain of the main material, and cannot directly obtain the deformation of the internal structure of the main body. Therefore, if the strain measured by the fiber Bragg grating strain sensor can be converted into a displacement response, it can be effectively applied to the internal displacement of the slope, the displacement caused by the internal deformation of large structures such as bridges, etc., so as to realize the monitoring of the health status of large structures such as slopes and bridges.

[0029] Working principle:

[0030] ① Fiber Bragg Grating strain sensor stress and strain sensing principle:

[0031] The fiber Bragg grating strain sensor 4 is a distributed Bragg reflector embedded in a short section of optical fiber, which can reflect light of a specific wavelength (Bragg wavelength) and transmit light of all other wavelengths. The refractive index distribution in the fiber Bragg grating strain sensor 4 is a periodic structure, which will cause the reflection of a specific wavelength of light, thereby forming a reflection spectrum of the fiber Bragg grating. The wavelength of the reflected light is very sensitive to temperature, stress and strain. As long as the fiber Bragg grating strain sensor 4 is attached to an elastic body, when the elastic body is subjected to pressure, the fiber Bragg grating strain sensor 4 and the elastic body will be strained together, resulting in the peak wavelength drift of the reflected light of the fiber Bragg grating strain sensor 4. By measuring the wavelength drift, the sensing of temperature, stress and strain can be achieved.

[0032] ② Principle of displacement measurement by fiber Bragg grating measuring instrument:

[0033] First, a monitoring position is selected on the main structure (such as a slope, a bridge, etc.), and an insertion hole is drilled in the vertical direction. If it is a slope, the hole needs to penetrate the potential sliding surface and reach the stable bedrock layer; then, the fiber Bragg grating measuring instrument is inserted into the preset insertion hole, and the insertion hole is grouted by injecting cement mortar; then, the fiber Bragg grating strain sensor 4 is electrically connected to the fiber Bragg grating demodulator 6. When the internal structure of the main body is deformed and displaced, such as internal slippage of the slope, the stress will cause the elastic plastic sleeve 1 to deform and bend, and the internal elastic rubber hose 2 and the measuring optical fiber 3 will also bend. The bending will cause the longitudinal strain of the measuring optical fiber 3. At this time, the wavelength of the fiber Bragg grating strain sensor 4 will change. This process can be demodulated by the connected fiber Bragg grating demodulator 6 to obtain the shear force or stress. The corresponding bending deformation is calculated according to the strain-displacement conversion method, and the internal deformation movement of the monitored main structure can be determined. In actual monitoring work, considering the deformation coordination between the fiber Bragg grating measuring instrument and the soil materials around the slope, it must be assumed that the bending deformation of the fiber Bragg grating measuring instrument is consistent with the bending deformation of the surrounding geotechnical materials.

[0034] The calculation formula of strain-displacement conversion method is as follows:

[0035]

[0036] Where W means shear stress; X means X direction; L means the initial length of the object; n means dividing the main deformation into n regions; P means average stress; Δλ B It means the change of Bragg wavelength; i means the average equivalent load distribution of the i-th unit; ζ means the distance from the fiber Bragg grating strain sensor to the neutral axis; Ke means the average strain sensitivity coefficient.

[0037] The fiber Bragg grating measuring instrument can monitor the internal displacement of the main structure in real time, solve the problems of low automation and untimely detection caused by manual labor, and under the protection of the elastic plastic sleeve 1, the measuring optical fiber 3 and the fiber Bragg grating strain sensor 4 inside it can be prevented from being damaged, thereby improving the service life and use accuracy. In addition, the internal elastic rubber hose 2 can be freely extended and retracted in the elastic plastic sleeve 1, and coupled with its good elasticity, the measuring optical fiber 3 can be quickly restored after bending, which plays a role in recycling. The fiber Bragg grating strain sensor 4 is placed inside the measuring optical fiber 3 at each distance to improve the accuracy of the detection data, and considering the significant influence of temperature on strain cross sensitivity, multiple measuring optical fibers 3 are arranged to monitor the same strain caused by temperature, and then the difference between the values ​​measured by two adjacent measuring optical fibers 3 is used as the sensing signal without being affected by temperature cross sensitivity.

[0038] In this embodiment, Figures 1 to 8 As shown, four measuring optical fibers 3 are included. The four measuring optical fibers 3 are evenly arranged on the outer wall of the elastic rubber hose 2. From a top view, the four measuring optical fibers 3 are located exactly on the cross center line of the elastic rubber hose 2.

[0039] Further, in this embodiment, if Figures 1 to 8 As shown, the elastic plastic sleeve 1 is made of ABS material. ABS material has excellent impact resistance and toughness, which ensures the monitoring quality and implements the stability of monitoring dams, slopes, foundation pits, etc. ABS material pipe is a new type of material with a nominal pressure of 0.6-1.6Mpa, a linear expansion coefficient of 0.9mm / (m·℃), and poor gas permeability resistance. ABS plastic pipe has low flow friction, which greatly reduces fluid resistance and pump horsepower, has good impact resistance, good mechanical strength and high impact toughness, and only undergoes toughness deformation when suddenly attacked, that is, it is lightweight, high-strength, high-flexible, high-gloss surface, high comprehensive precision and higher cost performance. Of course, in addition to the above-mentioned ABS material pipe, if there are other alternative materials, they can also be used.

[0040] In this embodiment, Figures 1 to 8 As shown, the receiving groove 5 is a U-shaped groove, the notch end of the U-shaped groove is flush with the inner wall of the elastic plastic sleeve 1, and the bottom end of the U-shaped groove protrudes from the outer wall of the elastic plastic sleeve 1. The U-shaped groove structure is more accurate and reliable in positioning.

[0041] In this embodiment, Figures 1 to 8 As shown, the elastic rubber hose 2 is a silicone hose. The silicone hose is a new type of polymer elastic material, which has excellent high temperature resistance (250-300°C) and low temperature resistance (-40-60°C), good physiological stability, and can withstand repeated harsh and sterilization conditions. It has excellent resilience and small permanent deformation. The silicone hose can freely move the homemade inclinometer in and out of the elastic plastic sleeve 1, playing a role of recycling.

[0042] In this embodiment, Figures 1 to 8 As shown, the measuring optical fiber 3 is arranged on the outer wall of the elastic rubber hose 2 by bonding. Epoxy resin can be used for bonding.

[0043] Because the measuring optical fiber 3 is placed under an ultraviolet light source with periodic spatial variation, the refractive index of the optical fiber core of the measuring optical fiber 3 will change. In the thermo-optical effect and thermal expansion effect of the fiber Bragg grating strain sensor 4, the temperature will directly affect the wavelength change of the grating. In order to measure the wavelength displacement caused by the strain change, temperature compensation is required to eliminate the wavelength change caused by temperature. Therefore, in addition to the above-mentioned setting of multiple measuring optical fibers 3 to monitor the same strain caused by temperature, and then using the difference between the values ​​measured by two adjacent measuring optical fibers 3 as the sensing signal to avoid the influence of temperature cross sensitivity, in this embodiment, as Figures 1 to 8 As shown, the fiber Bragg grating strain sensor 4 adopts a strain-free fiber Bragg grating strain gauge, and detects the absolute change of temperature through the wavelength shift of the strain-free fiber Bragg grating strain gauge to achieve temperature compensation.

[0044] In this embodiment, Figures 1 to 8 As shown, the elastic plastic sleeve 1 is a circular tube except for the U-shaped groove, and the elastic plastic sleeve 1 is 600 mm long, 55 mm in inner diameter and 65 mm in outer diameter. The elastic rubber hose 2 is also a circular tube, and the elastic rubber hose 2 is 600 mm long, 54 mm in inner diameter and 55 mm in outer diameter.

[0045] Further, in this embodiment, Figures 1 to 8 As shown, the spacing between the fiber Bragg grating strain sensors 4 is 100 mm.

[0046] Further, in this embodiment, Figures 1 to 8 As shown, the fiber Bragg grating strain sensor 4 is electrically connected to the fiber Bragg grating demodulator 6 .

[0047] In this embodiment, Figures 1 to 8As shown, a slope displacement simulation system is also provided, which is used to perform a large-scale direct shear test on the fiber Bragg grating measuring instrument to simulate the shear sliding failure and sliding state of the rock mass during the landslide process. The slope displacement simulation system is mainly composed of a fiber Bragg grating demodulator 6, a computer 7, a slide bed 8, a reaction frame 9, a slide rail 10, a sliding body 11, a sliding body 2 12, and a hydraulic jack 13. The sliding body 11 and the sliding body 2 12 are respectively composed of a concrete block. The height of the sliding body 11 is 1 / 3 of the length of the elastic plastic sleeve 1, and the height of the sliding body 2 12 is 2 / 3 of the length of the elastic plastic sleeve 1. If the length of the elastic plastic sleeve 1 is 600 mm, the heights of the sliding body 11 and the sliding body 2 12 are 200 mm and 400 mm respectively, and the widths are 800 mm and 400 mm. The sliding body 11 and the sliding body 2 12 will be used as sliding blocks to simulate the movement of the sliding body in the rock slope. The slide bed 8 is fixed and is considered to be a fixed stable bedrock. The height is set as needed, such as 200 mm. The reaction frame 9 is installed at one of the ends of the slide bed 8 in the length direction, and can withstand the application of load. The reaction frame 9 and the slide bed 8 can be cast by reinforced concrete. The steel cage hoop in the reaction frame 9 can avoid being damaged by loading and withstand a large reaction force. The slide rail 10 is laid on the slide bed 8 along the length direction of the slide bed 8. The slide body 2 12 is slidably connected to the slide rail 10, and the slide body 1 11 is slidably connected to the slide body 2 12. The hydraulic jack 13 is installed on the reaction frame 9. The telescopic end of the hydraulic jack 13 is used to push the slide body 11, and its telescopic direction is the same as the extension direction of the slide rail 10. The interface between the slide body 11 and the slide bed 8 is the first shear sliding surface, and the interface between the slide body 11 and the slide body 2 12 is the second shear sliding surface. A cylindrical hole is reserved in the middle of the slide body 11 and the slide body 2 12. The cylindrical hole is as vertical as possible, and the concave deviation is less than 3°. The slope simulation system can simulate the original landform as a tectonic denudation hill landform composed of monocline strata without faults. The fiber Bragg grating demodulator 6 is used to connect with the fiber Bragg grating strain sensor 4 of the fiber Bragg grating measuring instrument, and the computer 7 is connected with the fiber Bragg grating demodulator 6.

[0048] Experimental process:

[0049] First, the fiber Bragg grating measuring instrument is used to make a cylindrical specimen 14 made of cement mortar, and the cement mortar simulates the fine sandstone in the bedrock; then, the cylindrical specimen 14 is inserted into the cylindrical holes of the sliding body 11 and the sliding body 2 12, and the fiber Bragg grating strain sensor 4 is connected to the fiber Bragg grating demodulator 6; then, the test is loaded by two hydraulic jacks 13 with a maximum range of 100KN, and the wavelength of each fiber Bragg grating strain sensor 4 is recorded during the test. In this process, the shear force or stress can be obtained by demodulating the connected fiber Bragg grating demodulator 6; finally, the corresponding bending deformation is calculated by the computer 7 according to the strain-displacement conversion method, so as to determine the internal deformation movement of the monitored main structure.

[0050] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A fiber Bragg grating measuring instrument for internal displacement of a structure, characterized in that: It comprises an elastic rubber hose and an elastic plastic sleeve which are arranged and fitted inside and outside. A measuring optical fiber is circumferentially installed on the outer wall of the elastic rubber hose. The measuring optical fiber extends along the axial direction of the elastic rubber hose. Fiber Bragg grating strain sensors arranged at intervals are connected in series in the measuring optical fiber along its extending direction. A receiving groove for embedding the measuring optical fiber is circumferentially provided on the inner wall of the elastic plastic sleeve. The receiving groove extends to the end along the axial direction of the elastic plastic sleeve. The number and position of the receiving grooves correspond to the measuring optical fiber.

2. A fiber Bragg grating measuring instrument for internal displacement of a structure according to claim 1, characterized in that: It comprises four measuring optical fibers, which are evenly arranged on the outer wall of the elastic rubber hose.

3. The fiber Bragg grating measuring instrument for internal displacement of a structure according to claim 1, characterized in that: The elastic plastic sleeve is made of ABS material.

4. A fiber Bragg grating measuring instrument for internal displacement of a structure according to claim 3, characterized in that: The receiving groove is a U-shaped groove, the groove end of the U-shaped groove is flush with the inner wall of the elastic plastic sleeve, and the groove bottom end of the U-shaped groove protrudes from the outer wall of the elastic plastic sleeve.

5. The fiber Bragg grating measuring instrument for internal displacement of a structure according to claim 1, characterized in that: The elastic rubber hose is a silicone hose.

6. The fiber Bragg grating measuring instrument for internal displacement of a structure according to claim 1, characterized in that: The measuring optical fiber is arranged on the outer wall of the elastic rubber hose by bonding.

7. The fiber Bragg grating measuring instrument for internal displacement of a structure according to claim 1, characterized in that: The fiber Bragg grating strain sensor adopts a strain-free fiber Bragg grating strain sensor.

8. The fiber Bragg grating measuring instrument for internal displacement of a structure according to claim 1, characterized in that: The elastic plastic sleeve has a length of 600 mm, an inner diameter of 55 mm and an outer diameter of 65 mm; the elastic rubber hose has a length of 600 mm, an inner diameter of 54 mm and an outer diameter of 55 mm.

9. The fiber Bragg grating measuring instrument for internal displacement of a structure according to claim 8, characterized in that: The fiber Bragg grating strain sensor spacing is 100 mm.

10. A fiber Bragg grating measuring instrument for internal displacement of a structure according to any one of claims 1 to 9, characterized in that: The fiber Bragg grating strain sensor is electrically connected to the fiber Bragg grating demodulator.

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