JP2001324358A - Optical fiber sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology transforming displacement or deformation of an unstable geologic bed existing in a natural ground slant face, for example, into deformation of an optical fiber for safely and quickly performing optical observation of a deforming condition (the displacement direction and the like of soil) with high precision. SOLUTION: In an optical fiber sensor 1, a sensor body 1A provided with a flexible long slot rod 5 and a plurality of optical fibers 6 dispersedly arranged in a plurality of circumferential positions of the outer circumference part of the slot rod 5 along the longitudinal direction of the slot rod 5 respectively is inserted into a boring hole 3 formed in the ground 2 so that it can be integrally deformed with the ground 2 around the boring hole 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber sensor for monitoring the deformation of the ground with light, and more particularly to an optical fiber sensor suitable for disaster management such as landslide or landslide.

[0002]

2. Description of the Related Art For example, disaster prevention management such as landslides and landslides is carried out by frequently patroling an area in which landslides and landslides are highly likely to occur (hereinafter referred to as "monitored area") and grasping the situation. Although measures have been taken in the past, there are many inconveniences such as the fact that the patrol itself is dangerous, that the movement takes time, the transmission of information is slow, and that it takes time to issue an alarm. For this reason, in recent years, as a technique for performing safe and quick monitoring, a technique using various electric sensors has been generally used. Examples of the electric sensor include a strain gauge, an inclinometer, a seismometer, an earth pressure gauge, an extensometer (a strain gauge or a differential transformer type sensor is applied), and an electric sensor installed in a monitoring target area. By electrically connecting a monitoring station installed in a safe place away from the monitoring target area, a monitoring system capable of safely monitoring the monitoring target area at the monitoring station can be constructed.

[0003]

However, the electric sensor has the following problems. That is, (1) a power source is required, so that the installation place is limited to a place where the power source can be secured, and maintenance work is troublesome. (2) An induced current due to a lightning strike or the like, or a civil engineering work nearby. It is susceptible to external disturbance factors such as vibration, and is likely to cause erroneous detection or failure. (3) It is necessary to lay signal lines or install radio equipment separately for management and collection of measurement data. 4) In view of the above (3), collecting data from each electric sensor requires a signal line for each sensor individually, so that it takes a great deal of time to lay signal lines and the like. (5) Since the data transmission speed is slower than that of light, it takes time and effort to process data from a large number of sensors. Furthermore, in disaster management such as landslides and landslides, it is more effective to monitor not only the surface layer of the ground but also the movement of the earth and sand inside the ground. Due to such factors, it is very difficult to install the device deep underground, so that it has been almost impossible to detect the deformation of the ground at the deep portion.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has excellent workability at a target position, is less susceptible to the environment after installation, and has a low cost for detecting ground deformation with high accuracy. It is an object of the present invention to provide an optical fiber sensor.

[0005]

According to the present invention, there is provided an optical fiber sensor for monitoring the deformation of the ground by means of light, comprising: a long slot rod having flexibility; A sensor body comprising an optical fiber dispersedly disposed at a location and each disposed along the longitudinal direction of the slot rod, is inserted into a boring hole formed in the ground, and the sensor body around the boring hole is inserted. An optical fiber sensor characterized in that it can be integrally deformed with the ground is a means for solving the above problem. In the optical fiber sensor of the present invention, it is more preferable to adopt the following configuration. According to a second aspect of the present invention, in the optical fiber sensor according to the first aspect, the slot rod has a slot groove in which the optical fiber is fitted from the outside on an outer peripheral portion. The invention according to claim 3 is
3. The optical fiber sensor according to claim 1, wherein a longitudinal elongation strain is given to the optical fiber as an initial strain.

In the optical fiber sensor of the present invention, when the ground is deformed, the slot rod inserted into the boring hole and the optical fiber disposed along the longitudinal direction of the slot rod are integrated with the ground. Be transformed. Here, light is incident on the optical fiber, and the return light thereof is observed (optical test). As a result, loss of the optical fiber is increased and Brillouin scattered light is detected, whereby deformation of the ground can be detected.

The optical fiber sensor of the present invention utilizes the fact that the amount of frequency shift of Brillouin scattered light, which is one of the non-linear phenomena, depends on the distortion of the optical fiber. By observing a precise distribution with high accuracy, it is possible to detect and monitor deformation of the ground. That is, the wavelength of the Brillouin scattered light, which is one of the backscattered light generated when the test light is incident on the optical fiber having the longitudinal strain, is shifted from the wavelength of the test light incident on the optical fiber. The amount of distortion of the optical fiber can be grasped from the amount of frequency shift. In addition, an outline of a strain occurrence position of the optical fiber can be grasped by a time (return time) from the entrance of the test light to the reception and observation of the Brillouin scattered light.

For example, an optical pulse tester (so-called BOTDR) for observing Brillouin scattered light is connected to an optical fiber that undergoes deformation integrally with the ground, and an optical test is performed on the optical fiber using this optical pulse tester. By observing the Brillouin scattered light by performing test light incidence and return light observation, deformation of the ground can be detected. By the way, in the sensor body constituting the optical fiber sensor of the present invention, since the optical fibers are dispersedly arranged at a plurality of positions in the circumferential direction of the outer peripheral portion of the slot rod, when the ground deforms such that the sensor body is bent, The optical fiber located outside the bend of the sensor body is given a longitudinal elongation strain as compared with the installation of the optical fiber sensor, and the optical fiber located inside the bend of the sensor body is not given the elongation strain. That is, the magnitude of the elongation strain given to the optical fiber differs depending on the installation position with respect to the slot rod. Therefore, for each of the plurality of optical fibers constituting the optical fiber sensor, by observing the change in the amount of strain in the longitudinal direction by an optical test, the distribution of the optical fibers subjected to the elongation strain due to the deformation of the ground can be determined. Thus, it is possible to grasp that the ground has been deformed and the direction of deformation of the ground. The direction of deformation of the ground is assuming that the earth and sand have been displaced from the installation position of the optical fiber where extension strain due to the deformation of the ground was not observed to the installation position of the optical fiber where extension strain was given by the deformation of the ground. I can understand. Further, since the distortion amount of the optical fiber can be grasped from the observed frequency shift amount of the Brillouin scattered light, the deformation amount of the ground can be grasped for each optical fiber. Further, the deformation position of the ground can be measured from the observed return time of the Brillouin scattered light.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing a connection state between a plurality of optical fibers 6 constituting a depth displacement sensor 1 according to an embodiment of the optical fiber sensor of the present invention, and FIG. (A) is a transverse sectional view (sectional view perpendicular to the longitudinal direction), and (b) is a side view.
3 to 5 are cross-sectional views illustrating a cross-sectional structure of an optical fiber cable applicable as the optical fiber 6, and FIG. 6 is a view illustrating a construction operation of the depth displacement sensor 1 and is illustrated in FIG. The insertion state of the sensor body 1A is shown.

As shown in FIGS. 1, 2 (a), (b), and FIG. 6, a depth displacement sensor 1 includes a pipe 4 inserted into a boring hole 3 formed in the ground 2, and a pipe 4 inserted into the pipe 4. And a long sensor body 1A.

The sensor body 1A includes a slot rod 5
And distributed at a plurality of locations on the outer peripheral portion of the slot rod 5 in the circumferential direction (in FIGS. 2A and 2B, distributed at four locations).
And an optical fiber 6 arranged along the longitudinal direction of the slot rod 5.
The slot rod 5 is formed of, for example, a synthetic resin such as polyethylene and has flexibility. Further, the slot rod 5 has a configuration in which slot grooves 7 into which the optical fiber 6 is fitted from the outside are dispersedly arranged at a plurality of locations in the circumferential direction of the outer peripheral portion.

In FIGS. 2A and 2B, specifically,
The slot rod 5 has four plate-like portions 5a having a central shaft portion 5b.
Are formed in a cross-shaped cross section which is evenly protruded in four directions from each other.
Are formed. The plate-shaped portion 5a is formed over the entire length of the slot rod 5 in the longitudinal direction, and the slot groove 7 is formed to extend through the entire length of the plate-shaped portion 5a along the length of the slot rod 5 in the extended direction. Have been. In this sensor body 1A, two pairs of optical fibers 6 arranged at positions facing each other in the cross-sectional direction of the slot rod 5 are formed by the optical fibers 6 fitted into the four slot grooves 7, respectively. I have.

As the optical fiber 6, various configurations such as an optical fiber cord and an optical fiber core can be adopted.
Here, in consideration of the maintenance of the optical characteristics at the time of the insertion work into the boring hole 3, the waterproofness that can stably maintain the optical characteristics of the internal optical fiber even after being buried, the measurement reliability of the elongation strain in the longitudinal direction, etc. Uses fiber cable. 3 to 5
FIG. 3 is a cross-sectional view showing a structural example of an optical fiber cable that can be used as the optical fiber 6. 3 to 5, corresponding to the difference in the cross-sectional structure of each optical fiber 6, the description is given with reference numerals 6a to 6c for convenience of explanation. In addition, when describing a configuration common to the optical fiber cables 6a to 6c, these optical fiber cables 6a to 6c
c may be collectively referred to as “optical fiber 6” or “optical fiber cable 6”. The internal optical fibers of the optical fiber 6 which is an optical fiber cable will also be described with reference numerals 9a to 9c for each optical fiber 6, but these internal optical fibers 9a to 9c will be referred to as "internal optical fibers 9".
In some cases.

The optical fiber cable 6a shown in FIGS.
Reference numerals 6c to 6c denote a resin sheath 8 having a circular cross section, in which an internal optical fiber 9 is embedded in the center of the cross section, and tension members 10 are embedded in the sheath 8 on both sides of the internal optical fiber 9 facing each other. , All have a solid cross-sectional structure. In addition, each of the optical fiber cables 6a to 6
The difference of c is that the internal optical fiber embedded in the center of the cross section of the sheath 8 is different.

The optical fiber cable 6a shown in FIG. 3 has a sheath 8 in which a single optical fiber is buried as an internal optical fiber 9a in the center of the cross section. The optical fiber cable 6b shown in FIG. 4 has a multi-core optical fiber ribbon (FIG.
In this example, a four-core tape is embedded. The internal optical fiber 9b, which is the optical fiber ribbon, is formed by fixing a plurality of optical fiber wires 11 in parallel in a resin coating and forming the tape into a tape shape, and has a width perpendicular to the cross-section thickness direction. It is embedded so that the direction (the arrangement direction of the internal optical fiber wires 11) coincides with the straight line connecting the tension members 10 on both sides of the internal optical fiber 9b. In the optical fiber cable 6b, a plurality of optical fiber wires 11 arranged in parallel in the internal optical fiber 9b and the tension members 10 on both sides of the internal optical fiber 9b are arranged in parallel on the same plane. The optical fiber cable 6c shown in FIG. 5 is one in which a single-core optical fiber as an internal optical fiber 9c and a temperature-correcting optical fiber 12 are buried in parallel at the center of the cross section of the sheath 8. It is. In this optical fiber cable 6c, two optical fibers 9c at the center of the cross section,
12 and tension members 1 opposed to each other on both sides thereof
0 are arranged in parallel on substantially the same plane.

The optical fiber cable 6 shown in FIGS.
Are all provided by tension members 10 (here, steel wires) arranged on both sides facing each other in the cross-sectional direction.
It has a bending characteristic in which it is difficult to bend in a direction along a plane (arrangement plane) on which the tension members 10 are arranged, and easily bends in a direction perpendicular to the arrangement plane. And
These optical fiber cables 6 are fitted into the slot grooves 7 of the slot rod 5 in such a direction that the plane in which the tension members 10 are provided is perpendicular to the radius of the slot rod 5 centered on the central shaft portion 5b. . Thereby, when bending deformation is given to the depth displacement sensor 1 due to partial deformation of the ground 2, the optical fiber cable 6 is smoothly deformed integrally with the ground 2. Further, the optical fiber cable 6b shown in FIG. 4 is hardly bent in the plane direction to the internal optical fiber 9b which is the optical fiber ribbon,
Although there is a bending characteristic that is easy to bend in the thickness direction, since the plane direction of the internal optical fiber 9b substantially coincides with the plane in which the tension member 10 is provided, the optical fiber cable provided by the two tension members 10 6b has little effect on the bending characteristics. Also in the optical fiber cable 6c shown in FIG. 5, the positions of the internal optical fiber 9c and the temperature correcting optical fiber 12 buried in parallel in the sheath 8 are substantially coincident with the plane on which the tension member 10 is provided. Therefore, the bending characteristics of the optical fiber cable 6c provided by the two tension members 10 are hardly affected.

FIG. 6 is a view showing an operation of inserting the slot rod 5 and the optical fiber 6 into the pipe 4 inserted and buried in the boring hole 3, and shows the insertion rear end side of the slot rod 5 inserted into the pipe 4. It is a perspective view which shows the vicinity. FIG. 7 is a cross-sectional view showing the vicinity of an insertion head 13 provided at an insertion end portion of the slot rod 5 into the boring hole 3. 8A and 8B are views showing a cross-sectional structure of the insertion head 13 in FIG. 7, wherein FIG. 8A is a cross-sectional view taken along the line AA of FIG. 7, and FIG. 8B is a cross-sectional view taken along the line BB of FIG. FIG. 7C shows FIG.
FIG. 5 is a sectional view taken along line CC of FIG.

In FIGS. 7 and 8 (a) to 8 (c),
The insertion head 13 includes a fixing portion 15 fixed to the insertion end portion of the slot rod 5 by a fixing component 14, and a casing 16 connected to the fixing portion 15 further in the insertion end direction (right side in FIG. 7). It is configured.

The fixing portion 15 is in the form of a pipe having therein a receiving groove 15a having a shape substantially coinciding with the insertion end portion 5c of the slot rod 5. Specifically, a bolt as the fixing component 14 is connected to the slot rod 5. The slot rod 5 is fixed to the insertion end 5c of the slot rod 5 by tightening the bolt from both sides of the fixing portion 15.

The casing 16 is formed in a cylindrical shape with a bottom, and accommodates therein an optical connection portion 17 between the optical fibers 6 arranged along the slot rod 5. The optical connection part 17 is specifically,
Inside 6, there is a connecting portion between the internal optical fibers 9 led out from the optical fiber 6, which is an optical fiber cable, such as a fusion splicing portion or a connector connecting portion. The internal optical fiber 9 is a single-core or multi-core optical fiber core wire, an optical fiber strand, or the like. For example, the internal optical fibers 9a to 6c of the optical fiber cables 6a to 6c shown in FIGS.
9c and the like.

The watertightness of the inside of the casing 16 is ensured in order to maintain the characteristics of the optical fiber 6 and the optical connection portion 17. FIG. 7 and FIG.
The casing 16 shown in FIG.
a and a tip lid 16b for sealing the insertion tip of the sleeve 16a into the boring hole 3. The insertion rear end of the sleeve 16a (tip lid 16b
The rear end opening 16 c (opposite side to the front side) is sealed by a rubber bush 18. The rubber bush 18
Is provided at the distal end of a fitting protrusion 15b protruding from the fixing portion 15 constituting the insertion head 13, and the rear end opening 16c is securely inserted by the fitting protrusion 15b. Sealed. Thereby, the watertightness inside the casing 16 is ensured. Also, components of the casing 16,
Specifically, in view of the fact that the material of the sleeve 16a, the tip lid 16b, and the like can stably secure water tightness over a long period of time and has sufficient strength against earth pressure and the like,
For example, a corrosion-resistant metal material such as stainless steel is used.

The optical fiber 6 is drawn into the casing 16 through the rubber bush 18, and an optical connection 17 between the optical fibers 6 (specifically, an optical connection between the internal optical fibers 9) is provided. It is stored together with the extra length 19. The optical fiber 6 drawn into the casing 16 is fixed by an optical fiber fixing section 20 provided in the casing 16. The optical fiber fixing section 20
Here, the optical fiber 6 is an optical fiber cable.
This is a gripping component for gripping and fixing the. The optical connection section 17 connects the optical fibers 6 constituting a pair disposed at positions facing each other to the slot rod 5. Specifically, the optical connection portion 17 is a fusion splicing portion between the internal optical fibers 9 of the optical fiber 6, a connector connecting portion, or the like.
The optical connection between the pair of optical fibers 6 disposed at the opposing positions of the slot rod 5 is performed by the optical connection unit 1.
7 is not limited. For example, a configuration in which one optical fiber cable is inverted in the casing 16 can be adopted. In this case, the space between the two optical fibers 6 forming a pair facing the slot rod 5 is the casing 1.
6 is optically connected via the inversion section.

In the casing 16, the optical connection portion 17 is provided.
Is provided, and a surplus length processing unit 22 for curving and holding the surplus length 19 is provided. Specifically, the holder 21 and the excess length processing unit 22 are provided on a fixing plate 23 fixed inside the casing 16. The holder 21 is provided at a plurality of locations on the fixing plate 23. The extra-length processing unit 22 is configured to press the internal optical fibers 9 that are curved and routed along the fixing plate 23 into the fixing plate 23 by using a support (not shown). Further, the optical fiber fixing portion 20 is also assembled to the fixing plate 23, and the tensile force applied to the optical fiber 6 is transmitted to the casing 16 via the optical fiber fixing portion 20 and the fixing plate 23.

To install the depth displacement sensor 1 in the ground 2, first, as shown in FIG. 6, a pipe 4 is inserted into a boring hole 3 formed in the ground 2, and then the pipe 4
Then, the slot rod 5 is inserted into the pipe 4 together with the optical fiber 6. That is, the sensor body 1A is inserted into the pipe 4 while being assembled at the site. The slot rod 5 is inserted into the pipe 4 from an insertion head 13 (see FIG. 7) attached to the insertion tip.

The optical fiber 6 is inserted into the slot groove 7 around the slot rod 5 and
Together with the pipe 4. As shown in FIGS. 2A and 2B, there is no projecting portion of the optical fiber 6 fitted into the slot groove 7 from the slot rod 5, so that the pipe 4
When the optical fiber 6 integrated with the slot rod 5 is inserted into the pipe 4, the optical fiber 6 does not come into contact with the inner surface of the pipe 4, thereby displacing the optical fiber 6 with respect to the slot rod 5 or separating from the slot groove 7. And the like can be prevented.

It is preferable that the slot rod 5 is inserted so that no gap is formed between the slot rod 5 and the inner surface of the pipe 4.
As a result, the pipe 4 and the slot rod 5 can be integrally deformed by the deformation of the ground 2, and further, the extension strain accompanying the deformation of the optical fiber 6 integrated with the slot rod 5 can be reliably applied to the optical fiber 6. Because you can give
The detection accuracy of the deformation of the ground 2 can be improved.

Optical fiber 6 constituting depth displacement sensor 1
In order to secure longitudinal elongation strain as initial strain,
Attach the optical fiber 6 to the slot rod 5 while securing a predetermined tension (specifically, fit into the slot groove 7).
Then, the operation of inserting the slot rod 5 into the pipe 4 proceeds while maintaining the tension. The tension is applied to each of the optical fibers 6 of the completed depth displacement sensor 1 so that a longitudinal elongation strain is secured as an initial strain.

As shown in FIG. 6, the slot rod 5 can be extended, and when the insertion length into the pipe 4 becomes short, a new slot rod 5 is extended and the insertion into the pipe 4 is continued. good. The addition of the slot rods 5 provided with a plurality of plate-shaped portions 5a is, for example, as shown in FIG.
As shown in (1), the plate-like portions 5a of the respective slot rods 5 can be easily realized by a method of connecting the plate-like portions 5a to each other via the connection plate 31. Also, between the slot rods 5, it is necessary to fix the position around the central axis,
In the extension of the slot rods 5 each having a plurality of projecting portions a, by using a fixing structure using each plate-like portion 5a as in, for example, connection using the connection plate 31, positioning around the central axis is performed. Fixing can be performed efficiently and easily, and moreover, it is easy to secure sufficient strength at the refill portion. For example, there is an advantage that a displacement such as a displacement around the central axis of the replenishing portion or a disconnection of the replenishing portion is less likely to occur due to a torsion force or the like acting on the insertion operation into the pipe 4. .

An optical fiber 6 is attached to the newly added slot rod 5 at the site of insertion into the pipe 4. The optical fiber 6 can be easily attached to the slot rod 5 by fitting the optical fiber 6 into the slot groove 7 of the slot rod 5.

When the insertion of the slot rod 5 and the optical fiber 6 into the pipe 4 is completed, the pipe 4 is filled with a filler 24 to integrate the slot rod 5 and the optical fiber 6 with the pipe 4. As the filler,
A pipe that can be filled in the pipe 4 without gaps and that does not restrict the behavior of the pipe 4, the slot rod 5, and the optical fiber 6 accompanying the deformation of the ground 2 after the filling is adopted. Moreover,
More preferably, it has waterproofness. As a filler that can be used, for example, there are many suitable fillers such as bentonite. Since bentonite becomes a gel state or a colloid state by adding water, it can be easily filled without gaps by injecting it into the pipe 4. After filling and drying, the particles become fine particles. Therefore, the behavior of the pipe 4, the slot rod 5, and the optical fiber 6 with respect to the deformation of the ground 2 is not restricted, and the whole depth displacement sensor 1 and the ground 2 of the sensor body 1A are integrated. Deformation can be realized. Further, even in the gel state (for example, gelation due to penetration of rainwater or groundwater), the deformation behavior of the depth displacement sensor 1 with respect to the deformation of the ground 2 is not restricted, so even in this case, the depth displacement sensor 1 is integrated with the ground 2. Deformation can be realized. Furthermore, bentonite (bentonite muddy water) is often excellent in waterproofness, and by using bentonite that provides excellent waterproofness, water in the pipe 4 can be prevented, and thereby the depth displacement sensor 1 and the sensor body can be prevented. It is possible to realize the stability of the deformation characteristics of 1A and the stable maintenance of the optical characteristics of the optical fiber 6 and the optical connection portion 17 in the insertion head 7. In addition, it is preferable that the gap between the pipe 4 and the inner surface of the boring hole 3 is also buried by filling the filler. However, it is necessary that the filler does not restrict the deformation of the pipe 4 with respect to the deformation of the ground 2, and for example, the bentonite is used. As a result, the pipe 4 behaves more integrally with the ground 2, so that the ground 2 and the depth displacement sensor 1 can be more integrally deformed.

As shown in FIG. 1, all the optical fibers 6 constituting the sensor body 1A are continuously connected to the boring hole 3 at the insertion end side and at the insertion rear end side, that is, at the ground side. To form a single optical line,
One end of this optical line is connected to an optical pulse tester 26 (BOTDR) via an optical fiber cable 25. FIG.
Specifically, the optical fiber 6 connected to the optical pulse tester 26 via the optical fiber cable 25 (hereinafter, may be referred to as “optical fiber 61” for convenience of description).
Is connected to one end of another optical fiber 6 (hereinafter, may be referred to as “optical fiber 62” for convenience of explanation) at the deepest part of the depth displacement sensor 1 in the depth direction (extending direction from the ground surface). I have. As shown in FIG. 2A, the optical fiber 62 is
The optical fiber is arranged to face the optical fiber. In FIG. 1, the other end of the optical fiber 62 is connected to one end of another optical fiber 6 (hereinafter, may be referred to as “optical fiber 63” for convenience of explanation) at a connection box 27 on the ground. The other end of the optical fiber 63 is the deepest part of the depth displacement sensor 1 in the depth direction, and
The optical fiber 6 is connected to one end of the optical fiber 6 (hereinafter, may be referred to as “optical fiber 64” for convenience of description) arranged opposite to the optical fiber 3. Therefore, in the depth displacement sensor 1, since the optical fibers 6 arranged at a plurality of locations around the slot rod 5 form one optical path, the optical test using the test light from the optical pulse It is possible to observe the Brillouin scattered light for all the optical fibers 6 only by performing this operation once.

The optical connecting part 17 for connecting the optical fibers 61 and 62 and the optical connecting part 17 for connecting the optical fibers 63 and 64 are specifically arranged at the deepest part of the depth displacement sensor 1 in the depth direction. Insertion head 13 (not shown in FIG. 1)
In the casing 16. An optical fiber cable 25 and an optical fiber 6 are connected to a connection box 27 provided on the ground.
1 and an optical connection portion 29 for connecting the optical fibers 62 and 63 to each other. In FIG. 1, the connection box 27 is installed on the boring hole 3,
It also has a function of protecting the depth displacement sensor 1, such as preventing the boring hole 3 from being flooded.

Further, the optical fibers 6 of the sensor body 1A are connected to each other between the depth displacement sensors 1 installed at a plurality of locations on the ground 2 (in FIG. 1, the optical fiber 64 of one depth displacement sensor 1 and the other By connecting the displacement sensor 1 to the optical fiber 61), a plurality of optical fibers 6 constituting each sensor body 1A of the plurality of depth displacement sensors 1 can form one continuous optical path. is there. In this case, when the test light from the optical pulse tester 26 is incident on the formed optical path, the optical test of the optical fibers 6 of the plurality of connected depth displacement sensors 1 can be performed at one time. Test efficiency can be greatly improved. In FIG. 1, specifically,
Optical fiber 64 of one connected depth displacement sensor 1
And the optical fiber 61 of the other depth displacement sensor 1 via the optical fiber cable 30 to connect one continuous optical line in each depth displacement sensor 1 to perform an optical pulse test. One continuous optical line is formed for the container 26. According to this configuration, by connecting the optical fibers 6 between the depth displacement sensors 1, the number of the depth displacement sensors 1 to be optically tested by one optical path can be freely set, and a large number of depth displacements can be set. The optical test of the optical fiber 6 of the displacement sensor 1 can be performed once. Thereby, the optical test of the plurality of optical fibers 6 can be performed substantially simultaneously. The optical connection part 32 between the optical fiber 6 of the depth displacement sensor 1 and the optical fiber cable 30 for connection between the depth displacement sensors 1 is housed in the connection box 27.

In the depth displacement sensor 1, the installation dimension in the depth direction can be easily adjusted by the depth dimension of the boring hole 3, the length of the pipe 4, and the length of the slot rod 5 inserted into the pipe 4. FIG. 1 illustrates a state in which a plurality of depth displacement sensors 1 having the same installation dimension in the depth direction are formed on the ground 2, but the present invention is not limited to this.
A plurality of depth displacement sensors 1 can be formed on the same ground 2 with different dimensions in the depth direction. Thereby, for example, the drilling hole 3 is prevented from reaching the groundwater vein, so that the workability of the depth displacement sensor 1 is improved,
The advantage that the deepest part of the depth displacement sensor 1 in the depth direction reaches a stable ground such as a bedrock to secure a stable observation reference position with respect to the ground to be subjected to the deformation, thereby improving the detection accuracy of the deformation of the ground 2. There is.

In the sensor body 1A, the optical fiber 6 provided on the outer peripheral portion of the slot rod 5 is basically provided with a longitudinal elongation strain as an initial strain. As the initial strain, for example, a longitudinal elongation strain of about 0.1% with respect to the length of the optical fiber 6 is given. In addition,
Since the optical fiber 6 constituting the sensor body 1A is fixed to the optical fiber fixing section 20 of the insertion head 13 and the optical fiber fixing section 32 (see FIG. 1) provided near the ground, a depth displacement sensor is provided. Both ends will not be drawn into the pipe 4 due to the bending deformation or the like.

The depth displacement sensor 1 and the sensor body 1A
Are integrally deformed following the deformation of the ground 2. Depth displacement sensor 1 due to deformation of ground 2
When the bending deformation occurs, the optical fiber 6 integrated with the slot rod 5 is deformed integrally with the entire depth displacement sensor 1 together with the slot rod 5, and as a result, the sensor body 1 is deformed.
An optical fiber 6 whose elongation strain increases due to the deformation of A and an optical fiber 6 whose elongation strain decreases conversely occur. That is, in addition to the initial strain, the optical fiber 6 located outside the bend is subjected to an elongation strain due to an increase in the length of the outside of the curve of the sensor body 1A. The elongation strain of the optical fiber 6 located on the inner side is reduced due to the decrease in the strip length due to the bending deformation of the sensor body 1A.

The amount of frequency shift of the Brillouin scattered light observed by the optical test of the optical fiber depends on the magnitude of the elongation strain given to the optical fiber. The deformation of the ground 2 is detected by detecting that the frequency shift amount of the observed Brillouin scattered light deviates from the value obtained by the initial strain given to the optical fiber 6 based on the observation result of the Brillouin scattered light in the optical test. Occurrence can be detected. Further, since the approximate position (distance from the optical pulse tester 26) of the extension strain occurrence location can be measured from the return time of the Brillouin scattered light, the position of the depth displacement sensor 1 where the optical fiber 6 in which the extension strain has occurred exists. By determining, the deformation position of the ground 2 can be grasped. Further, by grasping the distribution of the optical fiber 6 whose elongation strain has increased and the optical fiber 6 whose elongation strain has decreased, the deformation direction of the sensor body 1A or the depth displacement sensor 1, that is, the sensor body 1A or the depth displacement sensor 1 Since the direction of the external force (deformation force) that deforms the ground can be grasped, the direction of displacement of the ground 2 can be grasped. In addition, the displacement of the ground 2 is calculated from the change amount (increase or decrease) of the elongation strain of each optical fiber 6 that is grasped from the change amount (increase or decrease) of the frequency shift amount of the observed Brillouin scattered light. Convert and understand the quantity. Note that the optical test of the optical fiber 6 by the optical pulse tester 26 is performed intermittently or continuously as needed, whereby substantially constant monitoring of deformation of the ground 2 is substantially realized.

In the vicinity of the boundary between the outside and inside of the bent sensor body 1A, an optical fiber 6 that does not undergo any expansion or contraction may occur. Since the initial distortion is maintained in the optical fiber 6 without increasing or decreasing, Brillouin scattered light having a frequency shift amount obtained by the initial distortion is observed from the optical test result of the optical fiber 6. Conversely, by detecting this optical fiber 6, it can be used to grasp the boundary position between the outside and the inside of the bending of the deformed depth displacement sensor 1.

In the case of the bending deformation of the depth displacement sensor 1 and the sensor body 1A due to the displacement of the soil on the ground 2, the deformation direction and the amount of displacement of the ground 2 can be grasped by assuming a bending model of the beam. For example, in the bending deformation of the depth displacement sensor 1 caused only by the movement of the soil on the surface of the ground 2, the depth displacement sensor 1
The portion located closer to the ground surface is curved and deformed with respect to the portion fixed in the stable ground 2 at a deeper portion in the depth direction. By assuming a bending model of the cantilever for the depth displacement sensor 1 and the sensor body 1A,
The displacement direction and displacement amount of the ground 2 are grasped. Further, in the deformation of the depth displacement sensor 1 due to the movement of the earth and sand in the depth direction center, the ground 2
The direction of deformation and the amount of displacement. In either case,
The change of the elongation strain given by the bending deformation of the depth displacement sensor 1 and the amount of change of the elongation strain are converted and calculated for each optical fiber 6 from the frequency shift amount of the Brillouin scattered light observed by the optical test of the optical fiber 6. And the ground 2 deformed integrally with the depth displacement sensor 1 and the sensor body 1A.
The state of deformation and the amount of displacement can be grasped.

For example, as illustrated by the phantom line in FIG. 2B, when the sensor body 1A is bent and deformed by the deformation of the ground 2, the extension strain of the optical fiber 61 located outside the curve is increased. Conversely, in the optical fiber 62 located inside the curve, the elongation strain decreases. As a result of the optical test of each optical fiber 6, the optical fibers 61 to 64 constituting the sensor body 1A
If the change in the frequency shift amount of the Brillouin scattered light is observed in at least one of the two, the deformation of the ground 2 has been detected. In this sensor body 1A, the optical fibers 61 facing the inside and outside of the curve are used. , 62, the change in the frequency shift amount of the Brillouin scattered light is reversed, so that the direction of deformation of the sensor body 1A can also be grasped.

The optical fibers 63 and 64 located between the optical fiber 61 outside the curve and the optical fiber 62 inside the curve have an increased length due to the integral bending with the sensor body 1A. Elongation strain increases. However, the amount of increase in the extension strain of the optical fibers 63 and 64 is much smaller than that of the optical fiber 61 outside the curve.
If the deformation of the sensor body 1A is extremely small or complicated, the optical fibers 63 and 64 may not be given an elongation strain. And the sensor body 1A
The optical test of each of the optical fibers 6
The change of the frequency shift amount of the 64 individual Brillouin scattered light is grasped, and the distribution of the optical fiber having the increased elongation strain and the distribution of the optical fiber having the reduced elongation strain, that is, the position and elongation of the optical fiber 6 where the elongation strain is the largest increase By grasping the position of the optical fiber 6 where the decrease of the strain is the largest, increase / decrease of the extension strain of the other optical fibers 6, and the like, and further grasping the change amount of the extension strain of each of the optical fibers 61 to 64, the sensor body 1A is obtained. The displacement direction and the displacement amount of the ground 2 having deformed the ground can be grasped in detail.

Each optical fiber 61 constituting the sensor body 1A
1 to 64, a strip length capable of observing Brillouin scattered light corresponding to the spatial resolution of the optical pulse tester 26 is secured, and furthermore, as shown in FIG.
In the vicinity of the optical connection portions 17 and 29 between the optical fibers 62 and 63 and between the optical fibers 63 and 64, the remaining length 6 in an undistorted state is provided.
6, 65 and 66 are secured. Optical fibers 61-6
In the optical test of No. 4, since Brillouin scattered light is not observed at the positions of these extra lengths 66, 65, 66, the observation result of Brillouin scattered light can be individually grasped for each of the optical fibers 61 to 64. The optical fibers 61 and 62
The extra length 65 secured between the optical fibers 63 and 64 is, in detail, the extra length of the internal optical fiber 9 pulled out from the terminal of each of the optical fibers 61 to 64, and as shown in FIG. The head 13 is stored in the extra length processing unit 22 without distortion. On the other hand, the extra length 66 associated with the connection between the optical fibers 62 and 63 is also the extra length of the internal optical fiber 9 drawn out from the terminals of the optical fibers 62 and 63, and as shown in FIG. It is stored without distortion.

When a local elongational strain is given to a part of the optical fibers 61 to 64 in the longitudinal direction, the position of the elongational strain occurrence position in the depth direction is grasped with the accuracy of the spatial resolution of the optical pulse tester 26. It is also possible. Thereby, it is possible to grasp the deformation position of the ground 2 in the depth direction in detail.

With a configuration in which a plurality of optical fibers 6 provided in the sensor body 1A are subjected to an optical test as one continuous optical line, data on changes in elongation strain regarding these optical fibers 6 can be obtained simultaneously. Observation with high reliability can be realized with respect to the ever-changing deformation of the ground 2.
With the configuration in which one continuous optical path is formed by connecting the optical fibers 6 of the plurality of depth displacement sensors 1,
With one optical test of this optical path, the presence or absence of deformation of the ground 2 can be monitored for the plurality of depth displacement sensors 1. The displacement direction and displacement amount of the ground 2 due to deformation can also be measured and calculated individually for the plurality of depth displacement sensors 1. In addition, since the optical test data of each optical fiber 6 of each of the plurality of depth displacement sensors 1 can be obtained substantially simultaneously, the deformation state of the ground 2 in the area where the depth displacement sensor 1 is installed can be comprehensively analyzed by analyzing these data. And specifically.

FIG. 10 shows an optical monitoring system 40 for detecting and monitoring the occurrence of distortion of the ground 2 which is a predictive phenomenon of a disaster such as a landslide or a landslide in an unstable ground on a ground slope. In FIG. 10, reference numeral 41 is a monitoring station, 42 is a branch connection box, 43 is a surface displacement sensing unit, 44 is a depth displacement sensing unit, 45 is a pressure receiving box, 46 is a connection box, 47 is an optical fiber cable, and 48 is a monitoring target. Area.

As shown in FIG. 10 and FIG. 11, the surface displacement sensing section 43
Of the optical fiber 49 linearly buried and laid in the surface layer 55 of the monitoring target area 48 in the longitudinal direction at a plurality of positions in the surface layer 55. The optical fiber 49 is fixed between the buried pressure receiving box 45 and between the pressure receiving box 45 and the connection box 46.
Are stretched between the pressure receiving boxes 45 and between the pressure receiving box 45 and the connection box 46. The depth displacement sensing unit 44 includes the depth displacement sensors 1 (FIGS. 1 and 2) installed at a plurality of locations in the monitoring target area 48 of the ground 2.
The optical fibers 6 constituting (a) and (b) are connected to form a single continuous optical line 50. This optical line 50 is, specifically, a depth displacement sensor 1
, An optical fiber cable laid between the depth displacement sensors 1 to connect the optical fibers 6 of the respective depth displacement sensors 1, an optical fiber cable forming both ends in the longitudinal direction of the optical line 50, and the like. You. The depth displacement sensor 1 is formed to extend from the surface layer of the ground 2 in the monitoring target area 48 in the depth direction.

As shown in FIGS. 10 and 11, the optical fiber 49 stretched between the pressure receiving box 45 and the optical fiber 49 stretched between the pressure receiving box 45 and the connection box 46 are both A single surface layer displacement sensor 5 for detecting displacement of the surface layer 55 in the sliding direction (direction along the surface)
6, 57 are constituted. Since the surface displacement sensing unit 43 is configured by arranging the pressure receiving box 45 and the connection box 46 such that the connection box 46 is at one end or both ends, the surface displacement sensor 56 is an extension of the surface sensing unit 43. Surface displacement sensor 5
7 are arranged between the surface displacement sensors 56 at both ends.

Each of the surface displacement sensors 56 and 57 has a surface 55
, A slide pipe 58 embedded in the slide pipe 58, an optical fiber 49 inserted into the slide pipe 58, and an exterior pipe 59 provided outside the slide pipe 58. Slide pipe 58 and exterior pipe 5
9 functions as a protection tube for protecting the optical fiber 49. As the slide pipe 58 and the exterior pipe 59, those that hardly bend due to rigidity and have corrosion resistance enough to withstand long-term burial and do not affect the change in the elongation strain of the internal optical fiber 49 are employed. You. As a resin pipe that can be adopted as the pipes 58 and 59, for example, there is a pipe made of FEP (tetrafluoroethylene-hexafluoropropylene copolymer). FEP is excellent in strength, heat resistance, and chemical resistance, hardly bends with respect to lateral pressure, and does not decrease in strength even when the temperature of the ground 2 rises due to sunshine or the like, and has excellent corrosion resistance that can withstand long-term burial. Demonstrate. As the optical fiber 49, an optical fiber cable or the like is employed. As an optical fiber cable that can be adopted as the optical fiber 49, for example, FIGS.
The sectional structure shown in FIG. In the optical fiber cable having the cross-sectional structure shown in FIGS. 3 to 5, the stretching members can be stably provided with the expansion and contraction characteristics by the tension members 10 arranged on both sides of the center of the cross section.

As shown in FIGS. 11, 12 (a) and 12 (b), the pressure receiving box 45 comprises a pedestal 45a made of concrete or the like, and pipe holders provided on both sides of the pedestal 45a facing each other. 45b and an optical fiber fixing portion 45c provided between the pipe holder portions 45b on both sides.
And a cover 45 which covers the pedestal 45a and accommodates the pipe holder 45b and the optical fiber fixing portion 45c.
d. 11 and 13
As shown in (a) and (b), the connection box 46 includes a pedestal 46a made of concrete or the like and a pedestal 4a.
Pipe holder portions 46 provided on opposite sides on the upper surface 6a
b, a connection part storage part 46c provided at the center between the pipe holder parts 46b on both sides, and optical fiber fixing parts provided respectively between the connection part storage part 46c and the pipe holder parts 46b on both sides. 46d, covering the pedestal 46a, the pipe holder portion 46b, the connection portion storage portion 46c,
And a cover 45e for accommodating the optical fiber fixing portion 46d.

As shown in FIGS. 10 to 13 (a) and 13 (b), both ends in the longitudinal direction of the slide pipe 58 of the surface layer displacement sensor 56 constituted by the optical fiber 49 stretched between the pressure receiving boxes 45. , A pair of adjacent pressure receiving sensors 4
5 are respectively slidably supported by the pipe holder portions 45b. Pressure receiving sensor 45 and connection box 46
The slide pipe 58 of the surface displacement sensor 56 disposed between the two ends slides in the pipe holder 46b of the connection box 46 and the pipe holder 45b of the pressure sensor 45 adjacent thereto. It is freely supported.

The optical fiber 49 is drawn through the pressure receiving box 45, and the optical fiber fixing portion 45 c of the pressure receiving box 45 fixes the optical fiber 49 in the middle. The optical fiber 49 constituting each of the surface layer displacement sensors 56 and 57 includes:
By being fixed to these optical fiber fixing portions 45c and 46d, the longitudinal elongation strain given as the initial strain is maintained.

The optical fiber fixing portions 45c and 46d are fixed to a fixing block 60 for fixing the optical fiber 49, and a frame-like frame fixed to the pedestals 45a and 46a of the pressure receiving box 45 and the connection box 46, and for accommodating the fixing block 60. 61, and a pair of fixed position adjusting members 62 that sandwich the fixed block 60 from opposite sides of the frame 61. The fixed position adjusting member 62
By changing the projecting dimension from the frame 61, the fixing position of the fixing block 60 in the frame 61 can be adjusted along the longitudinal direction of the optical fiber 49. Optical fiber fixing part 45 of pressure receiving box 45 or connection box 46
By adjusting the fixed position of the fixed block 60 by the fixed position adjusting member 62 at c and 46d, adjustment of the initial strain of the optical fiber 49 in each of the surface layer displacement sensors 56 and 57, maintenance and other operations can be easily performed. Can be.

The connection box storage section 46c of the connection box 46
Are the optical fibers 4 constituting the surface displacement sensing unit 43
9 and an optical connection portion to another external optical fiber with an extra length. As shown in FIGS. 10 and 11,
The surface displacement sensing units 43 are connected to each other by the connection box 4.
The optical fibers 49 can be connected by optically connecting them via the optical fiber 6. The surface displacement sensing unit 43 and the depth displacement sensing unit 44 are
, An optical fiber 49 and a depth displacement sensing unit 4
Optical fibers (optical fiber cables) constituting both ends of the fourth optical line 50 can be optically connected via the connection box 46 to be connected. The optical connection part between the optical fibers 49 and the optical connection part between the optical fiber 49 and the optical fiber constituting the optical line 50 are stored in the connection part storage part 46c together with the extra length. FIG. 13A exemplifies a connection between optical fibers 49 which are optical fiber cables, and an optical fiber (optical fiber core wire, optical fiber element wire, etc.) connected to the end of each optical fiber 49. The connection portion is stored in the connection portion storage portion 46c together with the extra length, and the connection portion storage portion 4 is stored.
The cable extra length processing section 46f disposed between the optical fiber 6c and the optical fiber fixing sections 46d on both sides of the optical fiber 49b is configured to bend the extra length secured in the optical fiber cable portion of the optical fiber 49. As described above, since the optical fiber 49 of the surface displacement sensing unit 43 can be easily optically connected to an optical line such as another optical fiber cable by the connection unit 46, for example, a plurality of surface displacement sensing The connection between the units 43, the connection with another optical fiber sensor (such as the depth displacement sensing unit 44, etc.) can be realized. The “optical connection part” is a fusion splicing part between optical fibers or a connector connecting part.

For example, the monitoring line 53 shown in FIG.
Surface displacement sensing unit 43 and depth displacement sensing unit 4
4 and the surface displacement sensing unit 43 are connected in series in this order, and the optical fiber 49 and the optical line 50 of each of the sensing units 43 and 44 are connected to each other to form one continuous optical line for sensing. Make up. Further, another monitoring line 54 is formed by connecting three surface layer displacement sensing units 43 in series, and the optical fibers 49 constituting each surface layer displacement sensing unit 43 are connected to each other so as to be continuous.
This constitutes a sensing optical line. The terminal farthest from the optical pulse tester 26 of the optical path for sensing constituting each of the monitoring lines 54, 54 is subjected to non-reflection processing.

The optical fiber 49 of the surface displacement sensing unit 43 installed on the ground 2 in the monitored area 48 and the optical line 50 of the depth displacement sensing unit 44 are connected to the branch connection box 42 installed near the monitored area 48. Via the optical fiber cable 47 on the monitoring station 41 side, the optical fiber cable 47 is connected via the optical fiber cable 47 to the optical pulse tester 26 installed at the monitoring station 41 so that test light can enter. By the optical pulse tester 26, the optical fiber 49 of the surface displacement sensing unit 43 and the depth displacement sensing unit 4
By performing the optical test of the optical path 50 of No. 4, it is possible to monitor the deformation and displacement of the ground 2 in the monitoring target area 48 at the monitoring station 41 installed at a location away from the monitoring target area 48. This makes it possible to monitor the deformation and displacement of the ground 2 from a safe place where there is no danger of landslide or landslide.

In FIG. 10, specifically, the monitoring lines 53 and 54 installed on the ground 2 in the monitoring target area 48 are both provided with a surface displacement sensing unit 43 at the end.
The connection between the sensing optical line of each of the monitoring lines 53 and 54 and the optical fiber cable 47 on the monitoring station 41 side is performed by connecting the optical fiber cable 51 laid from the branch connection box 42 to the monitoring target area 48, This is realized by connecting 52 to an optical fiber 49 at a connection box 46 provided at the end of the surface displacement sensing unit 43 at the end of each of the monitoring lines 53 and 54. Thereby, the sensing optical lines of the respective monitoring lines 53 and 54 are connected to the optical pulse tester 26 so that an optical test is possible.

The optical test is repeatedly performed on the sensing optical lines of the monitoring lines 53 and 54 by switching the connection to the optical pulse tester 26 and inputting the test light. By performing an optical test intermittently with respect to the sensing optical line of each of the monitoring lines 53 and 54, substantially constant monitoring can be realized. In the optical test of the sensing optical line of the monitoring line 53, the optical fiber 49 of the two surface displacement sensing units 43 and the optical line 50 of the depth displacement sensing unit 44 constituting the monitoring line 53 are tested once. A light test can be performed by light incidence. Monitoring line 54
In the optical test of the sensing optical line, the optical test of the optical fibers 49 of the three surface displacement sensing units 43 can be performed once. Therefore, in the optical monitoring system 40, the number of optical tests on the optical lines of the surface displacement sensing unit 43 and the depth displacement sensing unit 44 constituting the optical monitoring system 40 can be reduced, and the efficiency of the optical test can be increased. Can be. In addition, since the optical test data of a plurality of optical fiber sensors (depth displacement sensor 1, surface displacement sensors 56 and 57) provided on one monitoring line can be acquired substantially simultaneously, the deformation of the ground 2 over a wide range can be obtained. Can be monitored simultaneously.

The optical fiber 4 of the surface displacement sensing unit 43
When it is found from the data of the optical test No. 9 that the frequency shift amount of the Brillouin scattered light has changed from the value given by the initial strain, the occurrence of deformation or displacement of the surface layer 55 has been detected. If it is found from the data of the optical test of the optical fiber 6 of each depth displacement sensor 1 of the depth displacement sensing 44 that the frequency shift amount of the Brillouin scattered light has changed from the value given by the initial strain, the deformation and displacement of the ground 2 Has been detected. The optical test data between the sensing units 43, 44, 43 forming the monitoring line 53, and the sensing units 43, 4 forming the monitoring line 54,
The optical test data of Nos. 3 and 43 can be determined for each sensing unit because a portion where Brillouin scattered light is not observed occurs due to the undistorted extra length secured in the connection box 46.

The surface displacement sensors 56 and 57 are provided so as to be in the displacement direction of the landslide expected when a landslide or a landslide occurs. Due to the displacement of the soil on the surface layer 55 of the ground 2, the pressure receiving box 45 and the connection box 46 are displaced integrally with the soil on the surface layer 55, and the distance between the pressure receiving boxes 45 and the distance between the pressure receiving box 45 and the connection box 46 are increased. As the distance increases, the elongation strain of the optical fiber 49 increases. The optical fiber 49 is obtained by an optical test of the optical fiber 49.
Observation of Brillouin scattered light from
By detecting an increase in elongation strain (an increase in the frequency shift amount of Brillouin scattered light) of No. 9, the occurrence of deformation or displacement of the surface layer 55 can be detected by the surface layer displacement sensors 56 and 57. In addition, an optical pulse tester 2 for Brillouin scattered light
6, the surface displacement sensors 56 and 57 that have detected the deformation and displacement of the surface layer 55 can be specified, whereby the positions of the locations where the deformation and displacement occur can be grasped. Further, the displacement amount of the ground 2 can be calculated from the increase amount of the frequency shift amount of the Brillouin scattered light. Thereby, the deformation of the surface layer 55 can be grasped in detail.

On the other hand, in the surface displacement sensors 56 and 57 which receive a deformation force such that the distance between the pressure receiving boxes 45 and the distance between the pressure receiving boxes 45 and the connection boxes 46 are reduced, the elongation strain of the optical fiber 49 is reduced. . However, when the stoppers 58a provided at both ends in the longitudinal direction of the slide pipe 58 abut against the pipe holders 45b and 46b, the slide pipe 58 bears an axial force, so that the pressure receiving boxes 45 are connected to each other and connected to the pressure receiving box 45. Since further reduction of the separation distance between the pressure receiving box 45 and the connection box 46 is restricted, further reduction of the separation distance between the pressure receiving box 45 and the connection box 46 increases. When the deformation and displacement 2 occur, the initial strain of the optical fiber 49 is maintained without reduction.

In the light monitoring system 40, the deformation position of the ground 2 and the vertical position data are obtained based on the surface data obtained by the optical test of the optical fibers 49 and 6 of the surface displacement sensing unit 43 and the depth displacement sensing unit 44 and the vertical direction data. Deformation scale etc. can be grasped in detail. Moreover, since the surface displacement sensing unit 43 and the depth displacement sensing unit 44 have a simple configuration and are easy to install, even if the monitoring target area 48 is large, it can be efficiently installed in a short period of time, and the cost can be reduced.

The depth displacement sensor 1 and the surface displacement sensors 56 and 57 constituting the surface displacement sensing unit 43 and the depth displacement sensing unit 44 are optical fibers 6 and 4 constituting these components.
Since 9 itself functions as a communication line for data transmission, it is not necessary to separately provide a communication line for data transmission. Moreover, since sensing can be performed without a power supply, there is no need to secure a power supply. In addition, since it is not affected by electromagnetic noise such as induced current, it can be installed without any problem even in places where electrical equipment is installed, such as near a building where a lightning strike is likely to occur, such as in a mountainous area. The degree of freedom of the installation location is improved. In addition, the depth displacement sensor 1 and the surface displacement sensors 56 and 57
Since the configuration is such that the change in the elongation strain of the optical fibers 6 and 49 to which the initial strain has been applied is detected, it is possible to accurately detect minute deformation and displacement of the ground 2. For this reason, it can be effectively used for detecting minute deformation or displacement of the ground 2, which is a predictive phenomenon such as a landslide or a landslide. In particular,
The depth displacement sensor 1 has an advantage that it is possible to realize high-precision detection of deformation and displacement in the depth direction, which has conventionally been difficult to detect.

If the Fresnel reflected light is detected when the test light enters the optical fibers 6 and 49 from the optical pulse tester 26, a break such as breakage of the optical fibers 6 and 49 is detected. In this case, the optical fibers 6 and 49 depend on the elapsed time from the entrance of the test light to the reception of the Fresnel reflected light.
Of the optical fiber 6, 49 that has been erroneously cut due to, for example, construction, can be easily found, and the repair work time and the like can be shortened. As described above, according to the optical monitoring system 40, the optical pulse tester 26 performs an optical test on the optical fibers 6 and 49 as needed, so that a failure in the optical transmission system can be monitored.

The frequency shift amount of the Brillouin scattered light with respect to the incident light is about 1M even when the optical fiber has no distortion.
Since it has a temperature dependency of about Hz / ° C., it is necessary to correct measurement data when a large temperature change over several tens of degrees C. occurs. The optical fiber is used for
For example, it may be heated to several tens of degrees Celsius or higher than normal temperature due to sunshine or geothermal heat in volcanic areas.For more precise monitoring, temperature correction of Brillouin scattered light measurement data is required. Is essential.

In consideration of this, the optical fiber 6c shown in FIG.
Separately, optical fibers 12 for temperature correction are juxtaposed. The temperature compensating optical fiber core 12 is one in which an optical fiber 12b (temperature compensating optical fiber) is loosely housed in a protective tube 12a made of stainless steel or the like. No elongational strain acts on the temperature compensating optical fiber 12b, and the strain-free state can be maintained, so that the optical characteristics of the temperature compensating optical fiber 12b are not affected at all. It goes without saying that even if the internal optical fiber 9c to which the initial distortion is applied is given an expansion / contraction distortion, the optical characteristics of the temperature correcting optical fiber 12b are not affected at all.

That is, since the optical test data of the temperature compensating optical fiber 12b to which no longitudinal distortion is given reflects only the influence of the temperature change, it is necessary to use the optical test data of the temperature compensating optical fiber 12b. Thus, the optical test data of the internal optical fiber 9c for distortion detection can be corrected. From the optical test data of the temperature compensating optical fiber 12b, the shift amount of the frequency of the Brillouin scattered light with respect to the incident light due to the temperature change can be grasped, and the grasped frequency shift amount is observed by the optical test of the internal optical fiber 9c. By subtracting from the frequency shift amount of the Brillouin scattered light thus performed (the frequency shift amount of the initial distortion is also taken into consideration), the frequency shift amount of the Brillouin scattered light caused by the expansion and contraction distortion of the internal optical fiber 9c can be grasped.

At the end of the optical fiber 6c farther from the optical pulse tester 26 side, an optical fiber 9c for distortion detection and an optical fiber 12b for temperature correction are connected to form a loop. Optical test is performed on both optical fibers 9c and 12b by inputting test light from one of the fibers 9c and 12b,
Observing Brillouin scattered light also enables temperature correction of the measured data. In this case, the optical fiber 9c
Although the data of the Brillouin scattered light due to the initial strain can be obtained from the optical test results of the above, the detection data of the Brillouin scattered light can hardly be obtained from the optical test results of the optical fiber 12b for temperature correction. From the measurement data obtained by one optical test, each optical fiber 9c, 1
The measurement data of 2b can be discriminated and grasped individually. Then, as described above, the shift amount due to the temperature change of the frequency with respect to the incident light of the Brillouin scattered light, which is grasped from the optical test data of the temperature correcting optical fiber 12b,
By subtracting from the shift amount of the frequency of the Brillouin scattered light observed by the optical test of the internal optical fiber 9c, the shift amount of the frequency of the Brillouin scattered light due to the stretching strain of the internal optical fiber 9c can be grasped. According to this temperature correction method, both optical fibers 9c and 12b of the optical fiber 9c for distortion detection and the optical fiber 12b for temperature correction can be optically tested by one optical test. In the case of monitoring the occurrence of distortion while switching the optical fibers of the sensor to the optical pulse tester, the number of switching of the optical fibers to the optical pulse tester can be reduced, which simplifies the monitoring work, It is possible to shorten the optical test interval (time) of the optical fiber of the fiber sensor.

The method for correcting the temperature of the measured data is not limited to the above-described method.
It is also possible to adopt a method of correcting measurement data of Brillouin scattered light from data obtained by receiving and observing the backscattered light of the Raman scattered light of the incident light to the 2b with an optical pulse tester. In addition,
Since it is necessary to maintain the distortion-free optical fiber 12b, for example, the temperature-correcting optical fiber 1b is placed in a termination box installed at an appropriate position in the middle of the optical fiber 6c.
When an extra length of 2b is secured and an extension strain is given to the optical fiber 6c, an extension strain is given to the internal optical fiber 9c for detecting Brillouin scattered light, while the temperature compensating optical fiber 12b is attached to the extra fiber. A configuration in which the distortion-free state is maintained by drawing the length into the optical fiber 6c (specifically, the protection tube 12a) can be adopted.

In the above embodiment, the sensor body 1A having the configuration in which the optical fibers 6 with the initial strain are provided at a plurality of positions around the slot rod 5 is used as the sensor body constituting the depth displacement sensor 1. Although illustrated, the present invention is not limited to this, and a configuration in which an optical fiber in a substantially strain-free state is stretched around the slot rod can be adopted. In this case, since the optical fiber located inside the curved deformation of the sensor body constituting the depth displacement sensor, which is the optical fiber sensor according to the present invention, is not given an elongation strain, even if an optical test is performed, Brillouin scattered light is Although not detected, Brillouin scattered light is observed by an optical test from an optical fiber located outside the curve and subjected to elongation strain. The direction of the external force (deformation force) that deforms the optical fiber sensor or the sensor body can be grasped from the distribution of the optical fiber where the Brillouin scattered light is observed and the distribution of the optical fiber where the Brillouin scattered light is not observed. In addition, when there are a plurality of optical fibers in which Brillouin scattered light is observed, the direction of the external force that deforms the optical fiber sensor or the sensor body is obtained from the distribution of the frequency shift amount of the Brillouin scattered light observed in these optical fibers. Can be grasped in more detail, and the magnitude of the external force can be calculated. However, the change in the elongation strain of the optical fibers on both the inside and outside of the curved deformation of the sensor body can be reliably detected, and the change in the frequency shift amount of the Brillouin scattered light by the optical test of the optical fibers on both the inside and outside of the curved deformation (sensor body) In the point that the amount of displacement of the ground that deformed the sensor body can be calculated from the amount of change in comparison with before deformation), an optical fiber provided with an elongation strain in the longitudinal direction as the initial strain is provided. It is advantageous to employ a sensor body that:
There is an advantage that the deformation of the ground can be monitored in more detail and with high accuracy.

Object to be monitored by optical monitoring system to which optical fiber sensor of the present invention is applied (position where optical fiber sensor is installed)
It is not limited to soil masses and unstable strata on a mountain slope where there is a risk of occurrence of landslides and landslides.For example, rock strata on a mountain slope, flat terrain, unstable strata such as wetlands, river embankments, etc. Various types of embankments can be adopted. In the optical monitoring system to which the optical fiber sensor (depth displacement sensor) according to the present invention is applied, the surface displacement sensor applied in addition to the depth displacement sensor includes the above-described FIGS.
The configuration is not limited to those illustrated in (a) and (b), and various configurations can be employed.

[0071]

According to the optical fiber sensor of the present invention, the sensor body inserted into the boring hole formed in the ground,
When the bend is given by being integrally deformed by the deformation of the ground, of the optical fibers dispersed and disposed around the slot rods constituting the sensor body, the optical fibers outside the curve of the sensor body due to the bending deformation. While the optical fiber is subjected to elongation strain due to deformation, the fact that the elongation strain due to deformation is not applied to the optical fiber inside the curve can be used to detect deformation of the ground, By grasping the distribution of the optical fibers having different elongation strains, it is possible to grasp the direction of the external force (deformation force) that gives the sensor body a curved deformation, that is, the deformation direction of the ground. Since the elongation strain of each optical fiber can be determined by observing Brillouin scattered light as backscattered light due to the incidence of test light (optical test), a signal line for data collection is separately laid or a power supply for detection is used. There is no need to secure Further, the detection accuracy can be stably secured without being affected by an induced current such as a lightning strike. In addition, the optical fiber sensor,
By simply inserting the drilling hole into the borehole, it can be installed so as to extend in the depth direction of the ground over the entire length of the borehole, so that an excellent effect of easily detecting the deformation of the ground in each part in the depth direction is achieved.

According to the optical fiber sensor of the present invention, since the slot rod is provided with a slot groove in which the optical fiber is fitted from the outside, the operability of assembling the sensor body can be improved. As a result, for example, assembling of the sensor body at the site is also facilitated, and a sensor body having a length corresponding to the length of insertion into the boring hole can be easily obtained at the site. It has an excellent effect of improving efficiency.

According to the optical fiber sensor of the third aspect, since the optical fiber disposed around the slot rod is subjected to the elongational strain in the longitudinal direction as the initial strain, the optical fiber is located outside the curve of the sensor body. By grasping the distribution of the optical fiber having the increased elongation strain and the distribution of the optical fiber inside the bend and having reduced elongation strain, the direction of the external force that has deformed the sensor body can be grasped in more detail. Also, if the increase or decrease of the elongation strain of each optical fiber is grasped from the change of the frequency shift amount of the Brillouin scattered light observed by the optical test of the optical fiber, the magnitude (intensity) of the external force that deforms the sensor body is obtained. ) Can be calculated.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a depth displacement sensor which is an embodiment of an optical fiber sensor according to the present invention, and schematically shows a connection state between optical fibers constituting a sensor body.

FIGS. 2A and 2B are diagrams showing a sensor body applied to the optical fiber sensor of FIG. 1, wherein FIG. 2A is a cross-sectional view (a cross-sectional view perpendicular to the longitudinal direction), and FIG.

FIG. 3 is a view showing an example of a cross-sectional structure of an optical fiber applied to the sensor body of FIG. 2, and as an internal optical fiber, an optical fiber cable in which one optical fiber is buried in a central portion of a sheath; FIG.

FIG. 4 is a view showing an example of a cross-sectional structure of an optical fiber applied to the sensor body of FIG. 2, in which a multi-core optical fiber ribbon is buried in the center of the cross-section of the sheath as an internal optical fiber. It is sectional drawing which shows an optical fiber cable.

5 is a view showing an example of a cross-sectional structure of an optical fiber applied to the sensor body of FIG. 2, wherein an internal optical fiber for sensing and an optical fiber core for temperature correction are used as internal optical fibers; It is sectional drawing which shows the optical fiber cable buried in the center part of the cross section of a sheath.

FIG. 6 is a perspective view showing a state in which a sensor body is inserted into a pipe inserted into a boring hole, showing a work of installing the optical fiber sensor of FIG. 1;

7 is a cross-sectional view showing an insertion head attached to a tip of the sensor body of FIG. 2 inserted into a boring hole.

8A and 8B are diagrams showing a cross-sectional structure of the insertion head of FIG. 7, wherein FIG. 8A is a cross-sectional view taken along line AA of FIG. 7, and FIG.
FIG. 8C is a cross-sectional view taken along line BB of FIG. 7, and FIG.

FIG. 9 is a side view showing an example of a connection structure for adding a slot rod of a sensor body inserted into a boring hole in the construction work of FIG. 6;

FIG. 10 is an optical wiring diagram showing an optical monitoring system configured using the optical fiber sensor of the present invention.

FIG. 11 is a front sectional view showing an example of a surface displacement sensing unit applied to the light monitoring system of FIG. 10;

12A and 12B are diagrams showing a pressure receiving box constituting the surface displacement sensing unit in FIG. 11, wherein FIG. 12A is a plan view (with a cover removed) and FIG. 12B is a side sectional view.

13A and 13B are diagrams showing a connection box constituting the surface displacement sensing unit of FIG. 11, wherein FIG. 13A is a plan view (with a cover removed), and FIG. 13B is a side sectional view.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical fiber sensor (depth displacement sensor), 1A ... Sensor body, 2 ... Ground, 3 ... Boring hole, 5 ... Slot rod, 6, 61, 62, 63, 64 ... Optical fiber (optical fiber cable), 7 ... Slot groove.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoshikazu Nomura 1440 Mutsuzaki, Sakura-shi, Chiba F-term in Fujikura Sakura Office (reference) 2D044 EA07 2F065 AA65 DD11 DD15 EE01 FF33 FF41 GG08 LL02 PP01 QQ44 2F076 BA11 BB09 BD01 BD02 BD06 2H038 AA05 AA12

Claims (3)

[Claims] An optical fiber sensor for monitoring deformation of a ground (2) by light, comprising: an elongated slot rod (5) having flexibility; A sensor body (1A) including optical fibers (6, 61, 62, 63, 64) distributed and arranged along the longitudinal direction of the slot rod, respectively, comprises a boring hole formed in the ground. An optical fiber sensor (1) inserted into (3) and capable of being integrally deformed with the ground around the boring hole. 2. The optical fiber sensor according to claim 1, wherein the slot rod has a slot groove (7) in which the optical fiber is fitted from the outside. 3. The optical fiber sensor according to claim 1, wherein a longitudinal elongation strain is given to the optical fiber as an initial strain.