CN110285769B - Range expanding device for distributed optical fiber strain sensing - Google Patents
Range expanding device for distributed optical fiber strain sensing Download PDFInfo
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- CN110285769B CN110285769B CN201910628100.1A CN201910628100A CN110285769B CN 110285769 B CN110285769 B CN 110285769B CN 201910628100 A CN201910628100 A CN 201910628100A CN 110285769 B CN110285769 B CN 110285769B
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
- G01B11/18—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge using photoelastic elements
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Abstract
The invention discloses a range expansion device for distributed optical fiber strain sensing, which consists of a tube body, pulleys, a bolt, a protective cover, a clamp and a protective sleeve. Two pulleys are embedded in each section of the pipe body and fixed at the positions of two ends of the pipe body to form a pair of pulley blocks, the optical cable is guided by the pulleys to form a three-section type reciprocating structure in each section of the pipe body, and then the pipe body is packaged by a protecting cover and a protecting sleeve. The optical cable is clamped at the two ends of the tube body by tightly attaching the clamp to the outer side of the protecting cover, so that the optical cable in the tube body obtains a prestress. When large-scale sensing is carried out, a plurality of identical pipe bodies are connected in series at certain intervals by using one optical cable and are embedded into an object to be measured, strain measurement at each position can be realized by distributed optical fiber strain sensing equipment, the measuring range of the sensing optical cable is effectively increased, and the measuring precision is also improved.
Description
Technical Field
The invention belongs to the field of civil engineering monitoring and distributed optical fiber sensing, and particularly relates to a range expansion device for distributed optical fiber strain sensing.
Background
In large civil engineering such as highway maintenance, slope monitoring, and various projects such as tunnels, bridges, hydro hubs and the like, due to the action of external loads or environments, the structures can deform to different degrees, namely, large-range or integral uniform and non-uniform deformation, and the deformation is not easy to observe by naked eyes in the initial stage; secondly, local deformation mainly comprising various cracks, wherein the width of the cracks is as small as a few microns and as large as a few tens of centimeters, and the cracks are distributed unevenly. Corresponding methods and means are needed to be adopted for monitoring in engineering, however, due to large difference of engineering environment and complex engineering conditions, monitoring personnel cannot frequently go to the site for monitoring, and the traditional observation means is backward, the information collection amount is seriously insufficient and lagged, and even disasters cannot be predicted.
Due to the characteristics of small influence of environmental factors and good durability of the optical fiber, the distributed optical fiber strain sensing technology is gradually applied to monitoring of civil engineering at present. The distributed optical fiber strain monitoring system can reflect external strain changes by collecting Brillouin scattering signals along the optical fiber, and realize real-time monitoring of large-range and arbitrary position strain. At present, optical fibers are laid in two ways, one is a comprehensive adhesion way, the optical fibers are straightened and then completely adhered to a structure, and the other is a fixed-point adhesion way, the optical fibers are straightened and then fixed on the structure at intervals. In the overall adhesion mode, the optical cable is comprehensively adhered to the civil engineering structure, when the structure body is locally deformed, the optical cable can be directly broken, the maximum strain borne by the optical fiber is generally 1 to 2 percent, and the large strain range in the actual engineering environment cannot be matched; the fixed-point adhesion mode cannot provide good protection for the optical cable, the optical cable is easy to break in the construction and operation and maintenance period after construction, and the spatial fineness of monitoring the structure and the spatial resolution of a sensing system are difficult to be considered simultaneously.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems, the invention provides a range expansion device for distributed optical fiber strain sensing, which is characterized in that the structure of a sensing optical cable is designed by applying a pulley block, so that the strain on a short distance is averagely expanded to the whole optical cable in a tube body, the range of the sensing optical cable is effectively increased, and the measurement precision is also improved.
The technical scheme is as follows: in order to realize the purpose of the invention, the technical scheme adopted by the invention is as follows: a measuring range expanding device for distributed optical fiber strain sensing comprises a sensing optical cable, a tube body, a bolt, a pulley, a protective cover, a clamp and a protective sleeve.
Preferably, the protective sleeve is a rubber tube; the length of the protective sleeve is 5-10 cm.
Preferably, the pipe body is a pvc pipe.
The pulleys are embedded into the positions of the two ends of the pipe body through the bolts respectively to form a pair of pulley blocks, the two ends of the pipe body are respectively covered by the protecting covers, and the aim is to isolate the inner space of the pipe body. Protecting cover center below is equipped with the perforation, and the sensing optical cable outside that is located the body both ends adds and is equipped with protective case, and protective case wears out the body through the protecting cover perforation for the sensing optical cable of body is worn out in the protection. The sensing optical cable enters the tube body through the protecting cover perforation at one end of the tube body and is wound on the pulley block to form a three-section type reciprocating structure, and then penetrates out of the protecting cover perforation at the other end of the tube body.
In large-scale civil engineering such as highway maintenance, slope monitoring, and tunnel, bridge, hydro-junction engineering, the structure can deform to different degrees due to the action of external load or environment, so that the structure needs to be monitored in engineering, and the structure is the measured object. In practice, the device of the present invention is mounted in a structure.
According to the stress conduction mode of the sensing optical cable, the optical cable prestress setting scheme of the device can be two, which respectively correspond to two different pipe body end connection modes:
the protective cover and the protective sleeve at two ends of the tube body are not fixed at the protective cover hole, the protective sleeve and the sensing optical cable inside the protective sleeve are clamped by tightly attaching clamps to the outer side of the protective cover respectively, and the sensing optical cable, the protective sleeve and the clamps synchronously stretch outwards but cannot shrink inwards, so that prestress is applied to the sensing optical cable inside the tube body. When a plurality of the devices are connected in series on one sensing optical cable for use, the strain of the structural body is transmitted to the sensing optical cable in the pipe bodies of two adjacent devices.
Secondly, a protecting cover at one end of the tube body and the protecting sleeve are fixed together at a protecting cover hole, and then the protecting sleeve and the sensing optical cable inside the protecting sleeve are clamped by tightly clinging to the outer side of the protecting cover by using a clamp, so that the sensing optical cable and the tube body do not slide relatively; the protecting cover and the protecting sleeve at the other end of the tube body are not fixed at the protecting cover hole, the clamp is also used for tightly clinging to the outer side of the protecting cover to clamp the protecting sleeve and the sensing optical cable inside the protecting sleeve, and the sensing optical cable, the protecting sleeve and the clamp synchronously stretch outwards but cannot shrink inwards the tube body, so that a prestress is applied to the sensing optical cable inside the tube body. In the manufacturing process, the clamp for reserving the unfixed end of the protective sleeve can prevent the sensing optical cable from loosening in the tube body. In the construction process, because the pipe body and the structural body are fixed together, the clamp of the unfixed end of the protective sleeve can be removed or retained. After the clamp at the unfixed end of the protective sleeve is removed, the sensing optical cable can be stretched towards the outside of the tube body or contracted towards the inside of the tube body according to the deformation direction of the structure body, so that the strain in different directions can be measured; after the clamp at the unfixed end of the protective sleeve is reserved, only the strain stretching outwards the pipe body can be measured, but the integrity of the structure in the pipe body is ensured. When a plurality of the devices are connected in series on one sensing optical cable for use, the strain of the structural body is only transmitted to the sensing optical cable in the tube body of the corresponding section of the device.
A plurality of identical inventive devices may be connected in series on one sensing cable. The number of pulleys in the tube body and the number of winding turns of the sensing optical cable are set according to actual requirements. The length, the diameter and the pipe wall thickness of each section of pipe body are adjusted according to the required measuring range, the spatial resolution and the engineering requirements, and the lengths of all the series-connected pipe bodies can be the same or different.
Has the advantages that: compared with the prior art, the technical scheme of the invention has the following beneficial technical effects:
(1) according to the invention, each section of the tube body is adopted to protect the sensing optical cable, and the small section of the optical cable penetrating out between the tube body and the tube body is protected by the protective sleeve, so that the risk that the optical cable is directly exposed in the structure body and is easy to damage in actual engineering is avoided.
(2) The invention enlarges the original tension-strain bearing range of the optical cable by a plurality of times through the structure of the pulley block, thereby greatly improving the measuring range and the service life of the sensing optical cable in the actual engineering.
(3) According to the invention, through two stress conduction modes, when tension is generated, only one section of tube body or the optical cable in two adjacent sections of tube body generates strain, so that the strain of the measured object in a very short distance is conducted to a longer length of the sensing optical cable, and the measurement precision of a strain event is improved.
(4) The invention can conveniently and reliably maintain the prestress of the optical cable during construction.
(5) The invention has simple structure and low manufacturing cost.
Drawings
FIG. 1 is a schematic side view of the apparatus of the present invention;
FIG. 2 is a schematic cross-section of the apparatus of the present invention;
FIG. 3 is a schematic view of the end construction of the apparatus of the present invention;
FIG. 4 is a schematic view of an embodiment of the apparatus of the present invention;
FIG. 5 is a schematic view of a second embodiment of the apparatus of the present invention;
FIG. 6 is a pictorial representation of an apparatus of the present invention;
FIG. 7 is a schematic diagram of the series use of the apparatus of the present invention;
FIG. 8 is a graph showing the results of field experiments according to the present invention;
FIG. 9 is a partial enlarged view of the results of the field experiment of the present invention;
wherein: 1-protective sleeve I, 2-clamp I, 3-perforation I, 4-protective cover I, 5-bolt I, 6-pulley I, 7-tube body, 8-sensing optical cable, 9-pulley II, 10-bolt II, 11-protective cover II, 12-perforation II, 13-clamp II and 14-protective sleeve II.
Detailed Description
The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.
The description will be given by taking the slope monitoring in the actual civil engineering as an example. The frame beam on the side slope has the advantages of firm combination with the side slope and convenience for gridding arrangement, so that the frame beam can be an effective support for arranging the optical cable. However, the frame beam is an integral solid structure, and when the optical cable is directly poured into the frame beam, the maximum strain borne by the optical fiber is generally between 1% and 2%, and beyond this limit, the optical cable is very easy to break.
The invention discloses a measuring range expanding device for distributed optical fiber strain sensing, which comprises a tube body 7, a first protecting cover 4, a second protecting cover 11, a first bolt 5, a second bolt 10, a first pulley 6, a second pulley 9, a first protecting sleeve 1, a second protecting sleeve 14, a first clamp 2, a second clamp 13 and a sensing optical cable 8, wherein the first protecting cover, the second protecting cover, the first bolt and the second bolt are connected through a first connecting rod and a second connecting rod respectively. The diameter of the pipe body 7 is 50mm, and the length is 0.5 m. The first protective sleeve 1 and the second protective sleeve 14 are rubber tubes. The tube body 7 is a pvc tube.
The first pulley 6 and the second pulley 9 are embedded into the positions of the first bolt 5 and the second bolt 10 at the two ends of the pipe body 7 respectively to form a pair of pulley blocks, the two ends of the pipe body 7 are respectively covered by the first protective cover 4 and the second protective cover 11, and the purpose is to isolate the inner space of the pipe body 7. Protecting cover one 4, two 11 center undersets of protecting cover are equipped with and perforate one 3, perforate two 12, and the sensing optical cable 8 that is located body 7 both ends is outside to be equipped with protective case one 1, protective case two 14 additional, and protective case one 1, protective case two 14 wear out body 7 through perforating one 3, two 12 respectively for the sensing optical cable 8 of body 7 is worn out in the protection. The sensing optical cable 8 enters the tube body 7 through the first perforation 3 on the first protective cover 4 at one end of the tube body 7, winds on the first pulley 6 and the second pulley 9 to form a three-section type reciprocating structure, and then penetrates out of the second perforation 12 on the second protective cover 11 at the other end of the tube body 7. The cross section of the device of the invention is shown in figure 2.
According to the stress conduction mode of the sensing optical cable, the optical cable prestress setting scheme of the device can be two, which respectively correspond to two different pipe body end connection modes: the enlarged partial view at the end of the tube is shown in fig. 3, and is embodied as follows:
in the first embodiment, the first protective sleeve 1, the second protective sleeve 14, the first protective cover 4 and the second protective cover 11 are not fixed at the first perforation 3 and the second perforation 12, the first clamp 2 and the second clamp 13 are respectively tightly attached to the first protective cover 4 and the second protective cover 11 to clamp the first protective sleeve 1, the second protective sleeve 14 and the sensing optical cable 8 inside the first protective sleeve, the sensing optical cable 8, the first protective sleeve 1 and the first clamp 2 are synchronously stretched outside the tube body 7 but cannot be shrunk inside the tube body 7, and the sensing optical cable 8, the second protective sleeve 14 and the second clamp 13 are synchronously stretched outside the tube body 7 but cannot be shrunk inside the tube body 7, so that a prestress is applied to the optical cable sensing optical cable 8 inside the tube body 7.
When multiple devices of this embodiment are used in series on a single sensor cable, as shown in fig. 4, assuming a strain event point C exists between any two adjacent segments of device A, B, the strain event is a ramp tensile deformation event, and due to the simultaneous mobility of the clamps, protective sleeves, and cable at the two ends of device A, B, the ramp strain will be and will only be transmitted to the sensor cables in device a and device B.
In the second embodiment, the second protection sleeve 14 penetrates out of the second through hole 12 in the second protection cover 11 at one end of the tube body 7, the second protection cover 11 and the second protection sleeve 14 are fixed by epoxy resin glue at the second through hole 12, and then the second clamp 13 is tightly attached to the outside of the second protection cover 11 to clamp the second protection sleeve 14 and the sensing optical cable 8 inside the second protection sleeve, so that the sensing optical cable 8 and the tube body 7 do not slide relatively. Protecting cover one 4 and protective sleeve one 1 are not fixed in perforation one 3 department, use anchor clamps one 2 to hug closely the protecting cover one 4 outside and clip protective sleeve one 1 and inside sensing optical cable 8, protective sleeve one 1 and anchor clamps one 2 are synchronous to body 7 external stretching, nevertheless can't contract in to body 7, just so exert a prestressing force for the inside sensing optical cable 8 of body 7.
In the manufacturing process, the clamp for reserving the unfixed end of the protective sleeve can prevent the sensing optical cable from loosening in the tube body. In the construction process, because the pipe body and the structural body are fixed together, the clamp of the unfixed end of the protective sleeve can be removed or retained. After the clamp at the unfixed end of the protective sleeve is removed, the sensing optical cable can be stretched towards the outside of the tube body or contracted towards the inside of the tube body according to the deformation direction of the structure body, so that the strain in different directions can be measured; after the clamp at the unfixed end of the protective sleeve is reserved, only the strain stretching outwards the pipe body can be measured, but the integrity of the structure in the pipe body is ensured.
During the manufacturing process, the first retaining clamp 2 can prevent the sensing optical cable 8 from loosening in the tube body 7. In the construction process, because the pipe body 7 and the side slope frame beam are poured together, the first clamp 2 can be removed and can also be reserved. After the first clamp 2 is removed, the sensing optical cable 8 can be stretched towards the outside of the tube body 7 or contracted towards the inside of the tube body 7 according to the deformation direction of the frame beam, and the strain in different directions can be measured; after retaining the first clamp 2, only the strain stretching out of the tube body 7 can be measured, but the structural integrity inside the tube body 7 is ensured.
As shown in fig. 5, when a plurality of the same devices of this embodiment are connected in series on a sensing cable, two segments A, B connected adjacently are provided, and the sensing cable at the right end of the device A, B is fixed, i.e. the sensing cable and the tube body do not slide relatively; the sensing optical cable, the protective sleeve and the clamp at the left end of the device A, B move synchronously, namely, the sensing optical cable, the protective sleeve and the clamp stretch out of the tube body synchronously but cannot shrink into the tube body; assuming that there is a strain event point C between the devices A, B, the strain event is a slope tensile deformation event, and since the sensing optical cable at the right end of the device a and the tube body do not slide relatively, the clamp, the protective sleeve and the sensing optical cable at the left end of the device B move synchronously, the slope strain will be and only will be transmitted to the sensing optical cable in the device B.
FIG. 6 is a pictorial representation of the apparatus of the present invention. FIG. 7 shows a device E made according to example twoa、Eb、EcAnd (3) connecting the real object images in series, wherein the sensing optical cable at the right end of each section of device is fixed, and the sensing optical cable at the left end moves freely.
A highway slope monitoring method based on a distributed optical fiber strain sensing range expansion device comprises the following steps:
(1) according to the second embodiment, a three-section device E connected in series on a sensing optical cable is manufactureda、Eb、Ec；
(2) The three-section series device is connected into a BOTDR system through an optical cable junction box;
(3) selecting a section of slope body and selecting a position on the section of slope body, and arranging a groove with the length of l and the depth of h at the position; in the embodiment of the method, the length L of the slope body is 1000m, the selected position is 475m of the slope body, the length L of the gap is 2m, and the depth h of the gap is 30 cm;
(4) placing the three sections of series devices in the slot, filling soil, burying and compacting;
(5) in the burial of EcApplying external load to the soil body of the segment device to displace the surface of the soil body and to Eb、EcThe sensing optical cable between the section devices generates tension and the stress is transmitted to EcStrain is generated on the optical fiber inside the sensing optical cable in the section device; in the embodiment of the method, an external load event is set as a person standing event;
(6) the strain in the step (5) can change the refractive index of the optical fiber through an elasto-optical effect, and can also change the sound velocity in the optical fiber through the Young modulus, the Poisson ratio and the optical fiber density; sound velocity v in optical fiberaIs represented as follows:
wherein Y is Young's modulus, κ is Poisson's ratio, and ρ is the density of the optical fiber;
obtaining Brillouin spectrum frequency shift v in optical fiber according to sound velocity in optical fiberBNamely:
wherein n is the refractive index of the optical fiber, v is the frequency of the pump light, and c is the speed of light in vacuum;
by the step (5) of said EcOffset amount Deltav of Brillouin spectral frequency shift in optical fiber of segment deviceBAnd calculating the strain value generated by the optical fiber in the device section according to the following formula:
ΔvB＝(Δn+ΔY+Δκ+Δρ)vB(T0,0)
wherein v isB(T00) amount of Brillouin spectral frequency shift under the condition of no strain, T0Represents normal temperature, 0 represents no strain; delta Y、Δκ、Δρ、ΔnRespectively performing Taylor expansion first-order terms at a position where Young modulus Y, Poisson ratio kappa, density rho of the optical fiber and refractive index n of the optical fiber are equal to 0; and finally, obtaining the strain state of the slope body where the external load event occurs according to the strain value by inversion.
Fig. 8 and 9 show the result of the test using the above test method by the sensing optical cable device designed according to the second embodiment of the present invention, and it is apparent that an external load is generated at 475 m.
While the foregoing is directed to embodiments of the present invention and test results, other and further modifications may be devised by those skilled in the art without departing from the principles of the invention and the scope thereof is determined by the appended claims.
Claims (8)
1. A range extension device for distributed optical fiber strain sensing is characterized in that: the device comprises a pipe body (7), a first protecting cover (4), a second protecting cover (11), a first bolt (5), a second bolt (10), a first pulley (6), a second pulley (9), a first protecting sleeve (1), a second protecting sleeve (14), a first clamp (2), a second clamp (13) and a sensing optical cable (8); a pulley I (6) and a pulley II (9) are respectively embedded in the positions of two ends of a pipe body (7) through a bolt I (5) and a bolt II (10) to form a pair of pulley blocks, two ends of the pipe body (7) are respectively covered by a protecting cover I (4) and a protecting cover II (11), a perforation I (3) and a perforation II (12) are arranged below the centers of the protecting cover I (4) and the protecting cover II (11), a sensing optical cable (8) positioned at two ends of the pipe body (7) is additionally provided with a protecting sleeve I (1) and a protecting sleeve II (14), the protecting sleeve I (1) and the protecting sleeve II (14) respectively penetrate out of the pipe body (7) through the perforation I (3) and the perforation II (12), the sensing optical cable (8) enters the pipe body (7) through the perforation I (3) on the protecting cover I (4) at one end of the pipe body (7) and is wound, then the pipe body penetrates out of a second through hole (12) on a second protective cover (11) at the other end of the pipe body (7);
the second protective cover (11) and the second protective sleeve (14) are fixed at the second through hole (12), and the second protective sleeve (14) and the sensing optical cable (8) inside the second protective cover (11) are clamped by tightly attaching the second clamp (13) to the outer side of the second protective cover (11), so that the sensing optical cable (8) and the tube body (7) do not slide relatively; protecting cover one (4) and protective sleeve one (1) are not fixed in perforation one (3) position, clamp protective sleeve one (1) and inside sensing optical cable (8) thereof tightly attached to the outside of protecting cover one (4) by using clamp one (2), and sensing optical cable (8), protective sleeve one (1) and clamp one (2) synchronously stretch out of pipe body (7) but can not shrink into pipe body (7).
2. The span extension device for distributed optical fiber strain sensing of claim 1, wherein: a plurality of identical devices are connected in series on one sensing optical cable, and the number of pulleys in the tube body (7) and the number of winding turns of the sensing optical cable (8) are set according to actual requirements; the length, the diameter and the pipe wall thickness of each section of pipe body (7) are adjusted according to the required measuring range, the spatial resolution and the engineering requirement.
3. The span extension device for distributed optical fiber strain sensing according to claim 1 or 2, wherein: the protective sleeve I (1) and the protective sleeve II (14) are rubber tubes; the pipe body (7) is a pvc pipe; and the second protective cover (11) and the second protective sleeve (14) are fixed by epoxy resin glue at the second through hole (12).
4. The span extension device for distributed optical fiber strain sensing according to claim 1 or 2, wherein: when the first clamp (2) is removed, the sensing optical cable (8) stretches towards the outside of the tube body (7) or contracts towards the inside of the tube body (7) according to different deformation directions, and strain in different directions is measured.
5. A range extension device for distributed optical fiber strain sensing is characterized in that: the device comprises a pipe body (7), a first protecting cover (4), a second protecting cover (11), a first bolt (5), a second bolt (10), a first pulley (6), a second pulley (9), a first protecting sleeve (1), a second protecting sleeve (14), a first clamp (2), a second clamp (13) and a sensing optical cable (8); a pulley I (6) and a pulley II (9) are respectively embedded in the positions of two ends of a pipe body (7) through a bolt I (5) and a bolt II (10) to form a pair of pulley blocks, two ends of the pipe body (7) are respectively covered by a protecting cover I (4) and a protecting cover II (11), a perforation I (3) and a perforation II (12) are arranged below the centers of the protecting cover I (4) and the protecting cover II (11), a sensing optical cable (8) positioned at two ends of the pipe body (7) is additionally provided with a protecting sleeve I (1) and a protecting sleeve II (14), the protecting sleeve I (1) and the protecting sleeve II (14) respectively penetrate out of the pipe body (7) through the perforation I (3) and the perforation II (12), the sensing optical cable (8) enters the pipe body (7) through the perforation I (3) on the protecting cover I (4) at one end of the pipe body (7) and is wound, then the pipe body penetrates out of a second through hole (12) on a second protective cover (11) at the other end of the pipe body (7);
the protective sleeve I (1), the protective sleeve II (14), the protective cover I (4) and the protective cover II (11) are not fixed at the through hole I (3) and the through hole II (12), and the protective sleeve I (1), the protective sleeve II (14) and the sensing optical cable (8) inside the protective sleeve I (1), the protective sleeve II (14) and the protective cover II (11) are clamped at the outer sides of the protective cover I (4) and the protective cover II (13) respectively by using a clamp I (2) and a clamp II (13); the sensing optical cable (8), the protective sleeve I (1) and the clamp I (2) are synchronously stretched out of the tube body (7) but cannot be retracted into the tube body (7); the sensing optical cable (8), the second protective sleeve (14) and the second clamp (13) are synchronously stretched out of the tube body (7) but cannot be retracted into the tube body (7).
6. The span extension device for distributed fiber optic strain sensing of claim 5, wherein: a plurality of identical devices are connected in series on one sensing optical cable, and the number of pulleys in the tube body (7) and the number of winding turns of the sensing optical cable (8) are set according to actual requirements; the length, the diameter and the pipe wall thickness of each section of pipe body (7) are adjusted according to the required measuring range, the spatial resolution and the engineering requirement.
7. The span extension device for distributed optical fiber strain sensing of claim 5 or 6, wherein: the protective sleeve I (1) and the protective sleeve II (14) are rubber tubes; the pipe body (7) is a pvc pipe.
8. A method for monitoring a highway slope, which is implemented by the device according to claim 1 or 2, and is characterized in that: the method comprises the following steps:
(1) three-section device E connected in series on sensing optical cablea、Eb、Ec；
(2) The three-section series device is connected into a BOTDR system through an optical cable junction box;
(3) selecting a section of slope body and selecting a position on the section of slope body, and arranging a groove with the length of l and the depth of h at the position;
(4) placing the three sections of series devices in the slot, filling soil, burying and compacting;
(5) in the burial of EcApplying external load to the soil body of the segment device to displace the surface of the soil body and to Eb、EcThe sensing optical cable between the section devices generates tension and the stress is transmitted to EcStrain is generated on the optical fiber inside the sensing optical cable in the section device;
(6) changing the sound velocity in the optical fiber through the strain according to the Young modulus, the Poisson ratio and the optical fiber density; sound velocity v in optical fiberaIs represented as follows:
wherein Y is Young's modulus, κ is Poisson's ratio, and ρ is the density of the optical fiber;
obtaining Brillouin spectrum frequency shift v in optical fiber according to sound velocity in optical fiberBNamely:
wherein n is the refractive index of the optical fiber, v is the frequency of the pump light, and c is the speed of light in vacuum;
by the step (5) of said EcOffset amount Deltav of Brillouin spectral frequency shift in optical fiber of segment deviceBAnd calculating the strain value generated by the optical fiber in the device section according to the following formula:
ΔvB＝(Δn+ΔY+Δκ+Δρ)vB(T0,0)
wherein v isB(T00) amount of Brillouin spectral frequency shift under the condition of no strain, T0Represents normal temperature, 0 represents no strain; delta Y、Δκ、Δρ、ΔnRespectively performing Taylor expansion first-order terms at a position where Young modulus Y, Poisson ratio kappa, density rho of the optical fiber and refractive index n of the optical fiber are equal to 0; and finally, obtaining the strain state of the slope body where the external load event occurs according to the strain value by inversion.
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| CN112697997A (en) * | 2020-12-09 | 2021-04-23 | 南京大学 | Slope state inversion method based on distributed optical fiber strain sensing |
| CN115031652B (en) * | 2022-08-09 | 2022-11-08 | 中交第一公路勘察设计研究院有限公司 | Continuous optical fiber large deformation testing device and testing method |
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