Landslide monitoring method based on multi-core grating sensor

Abstract

The invention relates to the technical field of geological monitoring, in particular to a multi-core grating sensor and a landslide monitoring method based on the sensor, a multi-core optical fiber serves as a sensing medium, and the interior of the multi-core optical fiber comprises four independent optical fiber cores which are respectively a first fiber core, a second fiber core, a third fiber core and a fourth fiber core; wherein the fiber cores are uniformly distributed on the concentric circumference, the grating structure parameters are kept consistent, and all the fiber cores can be used as an independent sensing channel to realize distributed measurement; the distance between the fiber cores is within the range of [50 [mu] m and 80 [mu] m], and the fiber cores are fixedly placed in the strain gauge by applying corresponding prestress. The landslide monitoring method based on the sensor comprises the steps that the multi-core grating sensor is placed on the inner wall of a side inclined pipe in a mountain; when the slope body generates vibration displacement, wavelength change signals of all fiber cores in the multi-core grating sensor are monitored and demodulated based on a demodulator, and corresponding strain values are obtained; and when it is determined that the strain value is greater than a preset early warning value, early warning prompt information is fed back.

Description

Technical Field

[0001] The invention relates to the technical field of geological monitoring, and in particular to a landslide monitoring method based on a multi-core grating sensor. Background Art

[0002] Landslide is the most common disaster in infrastructure projects in mountainous areas. The deformation and damage of slopes and the adverse geological environment they cause can cause serious harm to human engineering activities, cause imbalance and damage to the ecological environment, and may bring about a wider range and more far-reaching negative impacts. The instability and damage of landslides have a development process from gradual to sudden changes. Generally, it is difficult to detect it based on people's intuition alone. It must rely on precise monitoring instruments and appropriate technical methods for careful monitoring.

[0003] At present, domestic and foreign scholars and experts have studied a variety of landslide detection technologies, such as: three-dimensional laser scanning technology, satellite remote sensing automatic detection system, GPS one machine multiple antenna system, multi-sensor integrated system, etc. These technologies have improved the accuracy and timeliness of landslide detection to a certain extent. However, traditional landslide detection technology still has some shortcomings: 1. Insufficient timeliness: Although 3D laser scanning technology, satellite remote sensing automatic detection system, GPS one machine multiple antenna system and other technologies have been applied to landslide monitoring, their timeliness in landslide early warning still needs to be improved. These technologies can only play an early warning role when the landslide undergoes obvious deformation or mutation, leaving relatively little time for human intervention; 2. Lack of directional monitoring: Traditional landslide detection technology often has difficulty in accurately monitoring the directionality of landslides, which increases the uncertainty of landslide monitoring. The directionality of landslides is crucial for assessing the degree of landslide damage and formulating effective prevention and control measures. If the directionality of landslides cannot be accurately monitored, the implementation of prevention and control measures may not be accurate enough, and even wrong response measures may be taken due to misjudgment of the landslide direction, thereby exacerbating the damage of landslides; 3. High cost and high technical threshold: Some previous landslide monitoring systems have high costs and high technical thresholds, which limit their popularization and application in most mountainous areas. This has led to a lack of effective monitoring methods in many potential landslide risk areas.

[0004] In summary, although landslide monitoring technology has made certain progress, an effective intelligent means is still needed to further improve the accuracy and timeliness of landslide monitoring. Summary of the invention

[0005] In order to improve the accuracy and timeliness of landslide monitoring, the purpose of the present invention is to provide a landslide monitoring method based on a multi-core grating sensor. The technical solution adopted is as follows: In the first aspect, the present application discloses a multi-core grating sensor, in which a multi-core optical fiber is used as a sensing medium. The interior of the multi-core optical fiber includes four independent optical fiber cores, namely a first core, a second core, a third core, and a fourth core, wherein: the cores are evenly distributed on concentric circles, and the grating structure parameters are kept consistent, and can all be used as an independent sensing channel to achieve distributed measurement; the core spacing between the cores is within the range of [50μm, 80μm], and is fixedly placed in a strain gauge by applying corresponding prestress.

[0006] Furthermore, the material of the multi-core grating is silica quartz material, and the core spacing between each of the cores is set to 60 μm.

[0007] Furthermore, the grating structure parameters include central wavelength, reflectivity, 3dB bandwidth, and side mode suppression ratio, wherein: the central wavelength is within the range of [1520nm-1620nm], the reflectivity is greater than 90%, the 3dB bandwidth is less than and equal to 0.3nm, and the side mode suppression ratio is greater than 10dB.

[0008] Furthermore, the central wavelength is set to be within the range of [1530nm-1570nm], and the wavelength interval is set to be 4nm; The reflectivity is set to 91%, the 3dB bandwidth is set to 0.27nm, and the side mode suppression ratio is set to 15dB.

[0009] Furthermore, each of the fiber cores is fixedly placed in the strain gauge after being applied with a prestress in the range of [0.5N-5N] and cured for a certain period of time by a fixing device.

[0010] Furthermore, the cladding diameter of each of the fiber cores is within the range of [150 μm, 240 μm], and the coating diameter is within the range of [200 μm, 300 μm].

[0011] In a second aspect, the present application discloses a landslide monitoring method based on the multi-core grating sensor described in any one of the above items, the method comprising: S1, placing the multi-core grating sensor on the inner wall of the side inclined tube inside the mountain; S2. When the slope body vibrates and displaces, the wavelength change signal of each fiber core in the multi-core grating sensor is monitored by a demodulator, and each wavelength change signal obtained is demodulated to obtain a corresponding strain value; S3. When it is determined that the strain value is greater than a preset warning value, corresponding warning prompt information is fed back.

[0012] Furthermore, the number of channels of the demodulator is in the range of [4,32], the detection wavelength range is C+L band, the wavelength demodulation resolution is less than or equal to 10pm, and the sampling frequency is less than or equal to 4khz.

[0013] Furthermore, in step S2, the demodulation of each wavelength change signal obtained to obtain a corresponding strain value includes: S21. Demodulate the various wavelength change signals obtained by the following formula: ; ; ;

[0014] in, is the distance from each outer fiber core to the center of the optical fiber, is the bending angle of the optical fiber, is the bending radius vector of the optical fiber is the decomposition vector of the optical fiber at the 0° azimuth, is the decomposition vector of the optical fiber at 270°, The first fiber core Reflection wavelength bending sensitivity when bending toward 0° azimuth, The second fiber core Reflection wavelength bending sensitivity when bending to 90°, The first fiber core With the third core The wavelength difference between The second fiber core With the fourth core The wavelength difference between them.

[0015] The present invention has the following beneficial effects: 1) Since the multi-core optical fiber contains four independent and evenly distributed cores on concentric circles, each core can be used as an independent sensing channel, so the sensor can achieve distributed measurement. This means that it can obtain measurement data at multiple locations on the same optical fiber at the same time, greatly improving the efficiency and accuracy of the measurement; 2) By keeping the grating structure parameters of each fiber core consistent, the stability and consistency of the sensor during the measurement process can be ensured. At the same time, due to the special structure of multi-core optical fiber, when the external environment (such as temperature, pressure, strain, etc.) changes, the length, diameter and refractive index of the fiber core will change, causing the phase of the light wave to change. This change can be accurately captured by the grating sensor and converted into an electrical signal for output, so the sensor has a high sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic structural diagram of a multi-core grating sensor provided by an embodiment of the present invention; Figure 2 A flow chart of a landslide monitoring method based on the multi-core grating sensor provided by an embodiment of the present invention.

[0017] In the accompanying drawings, the components represented by the reference numerals are listed as follows: 1. The first fiber core, 2. The second fiber core, 3. The third fiber core, 4. The fourth fiber core. DETAILED DESCRIPTION

[0018] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of the multi-core grating sensor proposed by the present invention and the landslide monitoring method based on the sensor, its specific implementation method, structure, characteristics and effects, in combination with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0019] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0020] A multi-core grating sensor provided by the present invention and a specific solution of a landslide monitoring method based on the sensor are described in detail below in conjunction with the accompanying drawings.

[0021] See also Figure 1 , which shows a schematic structural diagram of a multi-core grating sensor provided by an embodiment of the present invention, wherein the multi-core optical fiber is used as a sensing medium, and the interior of the multi-core optical fiber includes four independent optical fiber cores, namely a first fiber core 1, a second fiber core 2, a third fiber core 3, and a fourth fiber core 4, wherein: the fiber cores are evenly distributed on concentric circles, and the grating structure parameters are kept consistent, and can all be used as an independent sensing channel to realize distributed measurement; the core spacing between the fiber cores is within the range of [50μm, 80μm], and is fixedly placed in the strain gauge by applying corresponding prestress.

[0022] Among them, multi-core optical fiber, as a sensing medium, can utilize the transmission and reflection characteristics of optical signals in the fiber core to sense changes in external physical quantities (such as temperature, stress, displacement, etc.).

[0023] For details, please refer to Figure 1, the four cores are evenly distributed on concentric circles. This distribution helps ensure the consistency and accuracy of each core during the measurement process. The optical structure parameters of each core are consistent, which enables each core to respond to changes in external physical quantities in the same way. Each core can serve as an independent sensing channel, which also enables the multi-core grating sensor to achieve distributed measurement, that is, to monitor changes in multiple different positions or physical quantities at the same time.

[0024] It should be noted that setting the core spacing between the fiber cores within the range of [50μm, 80μm] can effectively reduce the risk of optical signal crosstalk and ensure that each fiber core can independently and accurately transmit and reflect optical signals. In addition, by using high-strength and high-flexibility optical fiber materials and combining them with precise manufacturing processes, it can also ensure that the optical fiber is not easily broken or deformed under external forces such as bending and stretching, thereby improving the stability and reliability of the sensor. This design enables the multi-core grating sensor to better adapt to various complex application environments and ensure the accuracy and long-term stability of the measurement results.

[0025] It should be further explained that by applying corresponding prestress, the multi-core optical fiber is fixedly placed in the strain gauge, and the grating structure of the optical fiber is stabilized to reduce the influence of factors such as temperature changes on the measurement progress. At the same time, applying prestress can also compensate for the change in optical fiber length caused by external forces (such as bending force, stretching, etc.), thereby ensuring the accuracy of the measurement results.

[0026] As can be seen from the above, the multi-core grating sensor disclosed in the present application can realize distributed measurement because the multi-core optical fiber contains four independent and evenly distributed cores on concentric circles, and each core can be used as an independent sensing channel. This means that it can obtain measurement data at multiple positions on the same optical fiber at the same time, greatly improving the efficiency and accuracy of the measurement; by keeping the grating structure parameters of each core consistent, the stability and consistency of the sensor during the measurement process can be ensured. At the same time, due to the special structure of the multi-core optical fiber, when the external environment (such as temperature, pressure, strain, etc.) changes, the length, diameter and refractive index of the core will change, resulting in a change in the phase of the light wave. This change can be accurately captured by the grating sensor and converted into an electrical signal for output, so the sensor has a high sensitivity.

[0027] In one embodiment, the multi-core grating is made of silica quartz material, and the core spacing between each of the cores is set to 60 μm.

[0028] In one embodiment, the grating structure parameters include center wavelength, reflectivity, 3dB bandwidth, and side mode suppression ratio, wherein: the center wavelength is in the range of [1520nm-1620nm], the reflectivity is greater than 90%, the 3dB bandwidth is less than and equal to 0.3nm, and the side mode suppression ratio is greater than 10dB.

[0029] It should be noted that the central wavelength is an important parameter of the grating structure, which determines the operating wavelength range of the sensor. Selecting the central wavelength within the range of [1520nm-1620nm] can ensure that the sensor is compatible with commonly used light sources and detection systems, and it is also beneficial to reduce the attenuation and interference of optical signals during transmission. Reflectivity indicates the reflectivity of the grating structure to optical signals, and high reflectivity means that more optical signals can be reflected back, thereby improving the sensitivity and measurement accuracy of the sensor. At the same time, high reflectivity also helps to reduce the loss of optical signals and improve the overall performance of the system. Therefore, this application sets the reflectivity to be greater than 90%. 3dB bandwidth is an important performance indicator of the grating structure, which determines the resolution of the sensor to the optical signal. Setting a bandwidth less than and equal to 0.3nm also means that the sensor can more accurately identify optical signals of different wavelengths, thereby improving the accuracy and reliability of the measurement. The side mode suppression ratio indicates the ability of the grating structure to suppress the power ratio between the main mode and the side mode. Setting the side mode suppression ratio to be greater than 10 dB can ensure that the sensor mainly responds to the main mode optical signal during the measurement process, reduce the interference of the side mode on the measurement result, and thus improve the stability and accuracy of the measurement.

[0030] In one of the embodiments, the central wavelength is set to be within the range of [1530nm-1570nm], and the wavelength interval is set to 4nm; the reflectivity is set to 91%, the 3dB bandwidth is set to 0.27nm, and the side mode suppression ratio is set to 15dB.

[0031] It should be noted that when the central wavelength is set within the range of [1530nm-1570nm] and the wavelength interval is set to 4nm, the possible central wavelengths include 1530nm, 1534nm, 1538nm, 1542nm, ..., 1566nm, etc. This distribution method helps to realize wavelength division multiplexing in optical fiber communication, that is, to simultaneously transmit multiple optical signals of different wavelengths in the same optical fiber, thereby improving the capacity and efficiency of data transmission.

[0032] It should be noted that the reflectivity is set to 91%, which means that when the optical signal encounters the optical interface, 91% of the optical power will be reflected back to the original direction. The 3dB bandwidth is set to 0.27nm, which means that the optical signal has a higher power density and a narrower spectrum width within this wavelength range. The side mode suppression ratio is set to 15dB, which means that the main mode power of the optical signal is 15dB higher than the secondary mode power. This high suppression ratio helps to reduce noise and interference in the optical signal and improve the system's signal-to-noise ratio and transmission quality.

[0033] In one embodiment, each of the fiber cores is fixed in the strain gauge after being applied with a prestress in the range of [0.5N-5N] and cured for a certain period of time by a fixing device.

[0034] Specifically, appropriate prestress can improve the sensitivity and stability of the sensor, but excessive prestress may cause damage to the optical fiber or degradation of its performance. Therefore, the force needs to be precisely controlled when applying prestress. Glue curing is a key step to firmly fix the fiber core in the strain gauge.

[0035] In one of the embodiments, the fixing device used in the present application includes glue, and specifically, the bonding effect of the glue is used to ensure that the fiber core in the strain gauge will not loosen or fall off due to external force.

[0036] In another embodiment, a mechanical fixing method may be used to fix the fiber core by a bracket or a buckle; a welding fixing method may also be used to fix the fiber core and the strain gauge together by a laser beam.

[0037] It should be noted that the prestress in the range of [0.5N-5N] can ensure the stability of the fiber core without causing excessive pressure on the fiber core, thereby avoiding damage or performance degradation.

[0038] In a specific embodiment, both ends of each fiber core are placed in a strain gauge by applying 4.53N prestress, and are fixed in the strain gauge after being heated with 353ND glue for 60 minutes, thereby completing the packaging of a multi-core grating sensor.

[0039] In one embodiment, the cladding diameter of each of the fiber cores is in the range of [150 μm, 240 μm], and the coating diameter is in the range of [200 μm, 300 μm].

[0040] Specifically, the cladding is the part of the multi-core grating that surrounds the core, usually made of a material with a lower refractive index than the core. Its main function is to limit the transmission of the optical signal in the core and prevent the optical signal from leaking into the external environment. The coating is a layer of protective material outside the cladding, usually made of polymer. Its main function is to provide additional mechanical protection and enhance the flexibility of the optical fiber, while preventing the optical fiber from being eroded by environmental factors such as moisture and dust.

[0041] It should be noted that the cladding diameter in the range of [150μm, 240μm] can ensure the effective transmission of the optical signal in the fiber core, while reducing the excitation of high-order modes and ensuring the single-mode transmission of the optical signal. The coating diameter in the range of [200μm, 300μm] can provide better mechanical strength and wear resistance to prevent the optical fiber from being damaged during use.

[0042] In a specific embodiment, the cladding diameter of each of the fiber cores is set to 180 μm, and the coating diameter is set to 250 μm.

[0043] Please refer to Figure 2 The present application discloses a landslide monitoring method based on the multi-core grating sensor described in any one of the above items, comprising: Step S1, placing the multi-core grating sensor on the inner wall of the side inclined tube inside the mountain.

[0044] Specifically, the multi-core grating sensor is placed on the inner wall of the side inclined pipe inside the mountain in order to directly monitor the inside of the mountain. The side-slant pipe is a pipe pre-installed in the mountain to monitor the stability of the mountain. During the installation process, it is necessary to ensure that the multi-core grating sensor fits tightly against the inner wall of the side-slant pipe to reduce the impact of the external environment on the sensor and ensure that the sensor can accurately capture the strain changes inside the mountain.

[0045] Step S2, when the slope body vibrates and displaces, the wavelength of each fiber core in the multi-core grating sensor is monitored by a demodulator. The wavelength change signals are demodulated to obtain the corresponding strain values.

[0046] Specifically, when the slope vibrates and displaces, the fiber cores in the multi-core grating sensor will be affected by strain, causing the wavelength of its reflection to change. At this time, the demodulator receives these wavelength change signals and calculates the corresponding strain value through demodulation. In actual operation, it is necessary to ensure a reliable connection between the demodulator and the sensor to reduce loss and interference during signal transmission.

[0047] Step S3: when it is determined that the strain value is greater than the preset warning value, corresponding warning prompt information is fed back.

[0048] Specifically, the preset warning value is determined based on factors such as the stability requirements of the mountain, historical monitoring data, and engineering experience. When the monitored strain value exceeds this preset value, it means that the mountain may have undergone significant displacement or vibration, which requires attention. In one embodiment, when the strain value exceeds the preset warning value, it is necessary to immediately feedback the warning prompt information. This information can be transmitted to relevant personnel through sound and light alarms, SMS notifications, remote monitoring interfaces, etc., to prompt them to evacuate as soon as possible.

[0049] As can be seen from the above, the present application discloses a landslide monitoring method based on a multi-core grating sensor as described in any of the above items. On the one hand, by placing the multi-core grating sensor on the inner wall of the lateral inclined tube inside the mountain, the vibration displacement of the slope can be monitored in real time. Once the slope vibrates or displaces abnormally, the sensor can immediately capture this change and convert the wavelength change signal into a strain value through a demodulator. On the other hand, through the multiple independent optical fiber cores contained in the multi-core grating sensor, each of the optical fiber cores can be used as an independent sensing channel for distributed measurement. This can ensure that accurate measurement data can be obtained at different locations on the slope, improving the accuracy and reliability of monitoring. Finally, when the strain value exceeds the preset warning value, the warning prompt information will be immediately fed back. This also helps relevant personnel to take timely measures to avoid the occurrence of geological disasters such as landslides or reduce their impact.

[0050] In one of the embodiments, the number of channels of the demodulator is in the range of [4,32], the detection wavelength range is C+L band, the wavelength demodulation resolution is less than or equal to 10pm, and the sampling frequency is less than or equal to 4khz.

[0051] In one embodiment, in step S2, demodulating each wavelength change signal to obtain a corresponding strain value includes: Step S21, demodulating each wavelength change signal obtained by the following formula: ; ; ; in, is the distance from each outer fiber core to the center of the optical fiber, is the bending angle of the optical fiber, is the bending radius vector of the optical fiber is the decomposition vector of the optical fiber at the 0° azimuth, is the decomposition vector of the optical fiber at 270°, The first fiber core Reflection wavelength bending sensitivity when bending toward 0° azimuth, The second fiber core Reflection wavelength bending sensitivity when bending to 90°, The first fiber core With the third core The wavelength difference between The second fiber core With the fourth core The wavelength difference between them.

[0052] It should be noted that the sequence of the above embodiments of the present invention is for description only and does not represent the advantages and disadvantages of the embodiments. The processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A landslide monitoring method based on a multi-core grating sensor, characterized in that: The method comprises: S1. Place the multi-core grating sensor on the inner wall of the side inclined pipe inside the mountain; S2. When the slope body vibrates and displaces, the wavelength change signal of each fiber core in the multi-core grating sensor is monitored by a demodulator, and each wavelength change signal obtained is demodulated to obtain a corresponding strain value; S3, when it is determined that the strain value is greater than the preset warning value, feedback corresponding warning prompt information; In step S2, the obtained wavelength change signals are demodulated to obtain corresponding strain values, including: S21. Demodulate the various wavelength change signals obtained by the following formula: ； ； ； in, is the distance from each outer fiber core to the center of the optical fiber, is the bending angle of the optical fiber, is the bending radius vector of the optical fiber, is the decomposition vector of the optical fiber at the 0° azimuth, is the decomposition vector of the optical fiber at 270°, The first fiber core Reflection wavelength bending sensitivity when bending toward 0° azimuth, The second fiber core Reflection wavelength bending sensitivity when bending to 90°, The first fiber core With the third core The wavelength difference between The second fiber core With the fourth core The wavelength difference between them.

2. The method according to claim 1, characterized in that The number of channels of the demodulator is in the range of [4,32], the detection wavelength range is C+L band, the wavelength demodulation resolution is less than or equal to 10pm, and the sampling frequency is less than or equal to 4khz.

3. The landslide monitoring method based on a multi-core grating sensor according to claim 1 is characterized in that: The multi-core optical fiber is used as the sensing medium. The multi-core optical fiber includes four independent optical fiber cores, namely the first fiber core, the second fiber core, the third fiber core, and the fourth fiber core, wherein: The fiber cores are evenly distributed on concentric circles, and the grating structure parameters are consistent, and can all be used as an independent sensing channel to achieve distributed measurement; The core spacing between the fiber cores is within the range of [50 μm, 80 μm], and is fixedly placed in the strain gauge by applying corresponding prestress.

4. The landslide monitoring method based on a multi-core grating sensor according to claim 1 is characterized in that: The material of the multi-core grating is silicon dioxide quartz material, and the core spacing between the cores is set to 60 μm.

5. The landslide monitoring method based on a multi-core grating sensor according to claim 1 is characterized in that: The grating structure parameters include central wavelength, reflectivity, 3dB bandwidth, and side mode suppression ratio, wherein: The central wavelength is within the range of [1520nm-1620nm], the reflectivity is greater than 90%, the 3dB bandwidth is less than and equal to 0.3nm, and the side mode suppression ratio is greater than 10dB.

6. The landslide monitoring method based on a multi-core grating sensor according to claim 5 is characterized in that: The central wavelength is set to be within the range of [1530nm-1570nm], and the wavelength interval is set to be 4nm; The reflectivity is set to 91%, the 3dB bandwidth is set to 0.27nm, and the side mode suppression ratio is set to 15dB.

7. The landslide monitoring method based on a multi-core grating sensor according to any one of claims 1 to 6, characterized in that: Each of the fiber cores is fixedly placed in the strain gauge after being applied with a prestress in the range of [0.5N-5N] and cured for a preset time by a fixing device.

8. The landslide monitoring method based on a multi-core grating sensor according to any one of claims 1 to 6, characterized in that: The cladding diameter of each of the fiber cores is within the range of [150 μm, 240 μm], and the coating diameter is within the range of [200 μm, 300 μm].

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