JP2001249035A - Optical fiber sensor and method for detecting structural state change using the same - Google Patents

Abstract

(57) [Abstract] [Problem] Daily management of levees, grasp of dike conditions in emergencies such as floods, and collection of basic data necessary for judgment on river management are possible without manual inspection and patrol. Do
Provided is an optical fiber sensor and a method for detecting a state change of a structure using the optical fiber sensor. A covering member (3) for covering an optical fiber (2).
And an optical fiber cable 4 having cloth pieces 1 bonded and fixed at a plurality of locations arranged in the longitudinal direction, and a part or all of the optical fiber cable 4 is buried inside the structure, and light is incident on the optical fiber cable 4. When the state of the structure changes due to an external factor, a change in light scattering due to the strain of the optical fiber core wire 2 generated in accordance with the change is measured by an optical fiber strain measuring device, and thereby, the structure of the structure is measured. A method for detecting a state change of a structure, characterized by detecting a state change.

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 detecting a state change of a structure such as a river embankment, and a method for detecting a state change of the structure using the sensor.

[0002]

2. Description of the Related Art Here, as a description of a conventional technique, a description will be given of a technique of managing a river embankment, which is a typical example of a structure made of earth and sand.

[0003] Conventionally, management of structures made of earth and sand, such as river embankments, is performed by regular inspection and patrol by humans. The river levees are extremely long, and the soil structure inside the levees is complicated. Therefore, the movement of water inside the levees, which is an effective item for management, and the movement of the levees themselves accompanying them are daily and unusual. At present, it relies on visual inspections based on daily patrol experience.

[0004]

It is economically difficult to constantly monitor the entire length of a river by manual inspection or patrol.
In addition, there is a problem that confirmation work at the time of the flood involves danger. It is easy to empirically or remotely install a sensor at a location where a river is expected to break due to the river structure, but it is easy to consider, but it is a means to implement a monitoring system economically over the entire length of the river. Did not previously exist.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been carried out by a manual inspection of daily management of a dike, grasping of a dike condition in an emergency such as a flood, and collection of basic data necessary for judgment of river management. It is an object of the present invention to provide an optical fiber sensor and a method for detecting a change in the state of a structure using the optical fiber sensor, which can be performed without patrol.

[0006]

In order to achieve the above object, according to the present invention, there is provided an optical fiber core having a property that a light scattering characteristic is changed by a strain, An optical fiber sensor comprising: a covering member for covering a fiber core, wherein the optical fiber sensor has cloth pieces adhered and fixed at a plurality of locations located at intervals in the longitudinal direction. Construct a fiber sensor.

Further, in the present invention, as described in claim 2, the optical fiber sensor according to claim 1, wherein the cloth piece is directly adhered and fixed to the optical fiber core. Constitute.

According to a third aspect of the present invention, there is provided a method for detecting a change in the state of a structure using the optical fiber sensor according to the first or second aspect. A part or all of the fiber portion of the optical fiber is embedded in the structure, light is incident on the optical fiber sensor, and when the state of the structure changes due to an external factor, the optical fiber is changed according to the change. Detecting a change in the state of the structure by measuring scattered light in the optical fiber which changes due to strain generated in the core; detecting a change in the state of the structure using an optical fiber sensor; Configure a method for detecting

In the present invention, the position and magnitude of the strain in the optical fiber core are specified by inputting the scattered light to an optical fiber strain measuring device. A method for detecting a state change of a structure using an optical fiber sensor according to claim 3 is configured.

Further, in the present invention, as described in claim 5, the structure is a river embankment, and the structure is formed by using an optical fiber sensor according to claim 3 or 4. A method for detecting a state change is configured.

If the present invention is applied to the above-mentioned daily management of the embankment, grasp of the state of the embankment in the event of an emergency such as a flood, or collection of basic data necessary for the judgment of river management, the items effective in management are as follows. The movement of a certain embankment itself can be grasped as a physical change amount by the optical fiber sensor instead of the visual inspection based on the experience of the patrol member, but by the optical fiber sensor.

The optical fiber itself is a continuous sensor and at the same time a means for transmitting measurement signals. By using this optical fiber, it is possible to economically construct a measurement system over a long distance, and it is possible to constantly monitor an extremely long structure such as a river embankment. This makes the invention particularly suitable for monitoring very long structures, such as river embankments.

Further, the present invention is characterized in that the deformation of the embankment can be automatically measured almost continuously over a long distance, not at discrete points, and that the measuring system can be constructed economically.

An optical fiber sensor according to claim 1 or 2 of the present invention is, for example, such that a part or all of a fiber portion of an optical fiber sensor is buried in a bank of a river embankment, which is a kind of structure. Used. When a part of the earth and sand moves inside the embankment due to an external factor, it is utilized that the cloth piece adhered and fixed to the optical fiber sensor moves together with the moving earth and sand. In other words, the piece of cloth in the position where the earth and sand does not move is fixed in the structure, while the piece of cloth in the position where the earth and sand moves moves together with the movement of the earth and sand in the structure. The relative positional relationship between the two pieces of cloth changes, thereby causing a strain in the optical fiber core of the optical fiber sensor between the two pieces of cloth. By measuring the strain with an optical fiber strain measuring device, a change in the state inside the target structure can be detected.

In the optical fiber sensor according to the first aspect of the present invention, the cloth piece and the fiber optic cable are used, and the cloth piece is adhered and fixed to an arbitrary portion of the fiber optic cable to easily perform the fiber optic sensor. Can be produced. When the optical fiber cable is buried inside the structure as a fiber portion of the optical fiber sensor, the cloth piece bonded and fixed to the optical fiber cable is displaced together with the inside of the structure with respect to the displacement inside the structure. Accordingly, it has an effect of causing distortion in the optical fiber. In addition, in the construction of the fabricated optical fiber sensor, the fiber part of the optical fiber sensor can be buried in the dike in any shape during the renovation work of the embankment or the work of excavating the embankment partially. it can.

In the measurement of the optical fiber sensor, light is incident on the embedded optical fiber sensor from the optical strain measuring device,
By measuring the return light from the embedded optical fiber sensor, the amount of strain change at each position of the optical fiber can be specified. By using this strain amount as a parameter of the movement of the earth and sand, a change in the state of the embankment can be continuously and easily monitored over a long distance of the entire embankment.

In the optical fiber sensor according to the present invention, the movement of the earth and sand is directly transmitted to the optical fiber core by directly bonding and fixing only the optical fiber core in the optical fiber cable to the cloth piece. From this fact, even if there is a difference in the movement of earth and sand due to the difference in soil composition depending on the embankment body, by changing the optical fiber core wire, it is possible to provide an optimal optical fiber sensor for each dike with different soil composition Can be.

[0018]

(Embodiment 1) Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

The optical fiber sensor is composed of an optical fiber cable having a covering member and a cloth piece for the purpose of protecting the optical fiber core from corrosion by water and the like due to earth pressure and water inside the optical fiber core and the structure. I have. Such an optical fiber sensor (corresponding to the optical fiber sensor according to claim 1) is shown in FIG.

Here, the core 2 of this optical fiber cable
Must have a property that the light scattering property changes due to strain, but a commonly used core material, for example, fused silica satisfies this condition.

In this case, as the cloth piece, a nonwoven cloth piece 1 produced by cutting out a part of a nonwoven fabric which is a material for civil engineering structures is used. Such a nonwoven fabric can be easily and inexpensively obtained, and when it is buried in a river embankment, the nonwoven fabric has good compatibility with earth and sand, and the earth and the optical fiber are displaced integrally. This is an extremely effective member.

The optical fiber cable 4 is an optical fiber core 2
And the covering member 3 are integrated without loosening,
When the optical fiber cable is pulled, the optical fiber core wire and the protection member extend by the same amount.

The optical fiber sensor is, as shown in FIG.
A plurality of rectangular non-woven fabric pieces 1 are formed by being adhesively fixed in a sandwich shape with an adhesive 5 at a plurality of locations which are bent at certain intervals along the longitudinal direction of the optical fiber cable 4.

Hereinafter, an example in which the above-mentioned optical fiber sensor is applied to a river embankment (corresponding to the method for detecting a state change of a structure using an optical fiber sensor according to the third, fourth or fifth aspect) will be described. This will be described with reference to FIG.

FIG. 2A shows the optical fiber sensor of FIG.
As shown in (b), portions a, b, c of optical fibers made of earth and sand, which are parallel to the slope 7 of the river embankment 6 having the slope 7 and the top end 9 and which are perpendicular to the longitudinal direction without loosening. , D
In parallel with this, it is buried, for example, at a depth 8 from the embankment slope (slope 7) in a state where sharp bending does not occur. The optical fiber sensor buried in the river embankment is connected to the same type of wiring optical fiber 10 (illustrated by dotted lines), and furthermore, to an optical fiber strain measuring device 11 (B
-OTDR: Brillouin Optical Time Domain Reflecto
meter) (for example, see Japanese Patent Application Laid-Open No. 05-240699).

Here, as shown in FIG. 3, the optical fiber strain measuring device 11 is a device that receives an optical pulse 15 from one end of the optical fiber and measures the return light (scattered light) from the optical fiber. Brilloui in the scattered light
n) Scattered light has the property of changing the frequency in proportion to the amount of distortion when a part of the optical fiber (16 in FIG. 3) is distorted (the amount of change is indicated by 17 in FIG. 3). ).
Utilizing this characteristic, the frequency change in the optical fiber 17
Is measured to determine the amount of strain in the optical fiber, the return time of the scattered light is measured, and the measured value is converted into a distance in the length direction of the optical fiber to determine the position 18 of the strain generation region. be able to.

In monitoring the embankment, observation is performed using the optical fiber strain measuring device 11 and the optical fiber sensor of FIG. 1 embedded in the river embankment 6.

First, when there is no change in the embankment, there is no change in the earth and sand inside the embankment, and therefore, it can be observed that the state of the optical fiber sensor does not change from the initial installation state. On the other hand, when the top of the embankment moves like the portion 12 in FIG. 2, the nonwoven fabric piece 1 (a) moves together with the earth and sand, and thus the nonwoven fabric piece 1 ( The distance between b) and the nonwoven fabric piece 1 (a) extends from 13 to 14 in FIG.
By measuring the magnitude of the elongation (14 in FIG. 2) and the position of the strain generation region with the optical fiber strain measuring device 11, a point where the state change inside the embankment occurs (the position of c in FIG. 2). And its size.

The result of an experiment conducted with the optical fiber sensor according to the present embodiment will be described with reference to FIG. An embankment simulating a river embankment was made, and an optical fiber sensor was installed in the embankment in a state as shown in FIGS. 2 (a) and 2 (b). In the embankment, a flood tank was provided on the side of the embankment to flood the river, and high-level water was flooded there for a long time. When the embankment collapses, water permeates into the sediment, and if the condition continues for a long time, the sediment inside the embankment starts to swell, and then the sediment starts to move from near the foot of the embankment, leading to collapse. In the experiment, this phenomenon of the embankment collapse was simulated.

FIG. 4 shows data of the optical fiber sensor measured using the optical fiber strain measuring device from the start of the experiment. In the graph, the horizontal axis indicates the elapsed time from the start of the experiment, and the vertical axis indicates the amount of change in strain of the optical fiber sensor (for example, c in FIG. 2A). The strain of the optical fiber sensor hardly changed for about one hour from the start of the experiment, but after one hour, the strain value began to increase, and after three hours, the strain increased more rapidly. Such changes continued until the end of the experiment. Here, the collapse of the embankment could be visually observed from about 4 hours after the start of the experiment, whereas the strain in the optical fiber sensor changed from 2.5 hours before that, so the inside of the embankment could be observed. The state change was detected with high sensitivity, and a sign of collapse could be detected early. From the above experiment,
It has been verified that monitoring of a structure such as a river embankment using the optical fiber sensor according to the first embodiment of the present invention is more effective than human patrol inspection instead of human patrol inspection. (Embodiment 2) Hereinafter, an embodiment different from Embodiment 1 will be described with reference to FIG.
This will be described with reference to FIG.

The optical fiber sensor according to claim 1 is parallel to the slope 7 of the river embankment 6 and parallel to the longitudinal direction as shown in FIGS. It is buried at a certain depth 8 from the embankment slope (slope 7). In this case, when the upper part of the embankment (12 in the figure) moves in the direction of the white arrow in the figure, the nonwoven fabric piece 1 (a) in the figure
Move together, and the non-woven fabric pieces 1 on both sides of the non-woven fabric piece
(B) 1 (c) becomes a fixed point, and the portions b and c of the optical fiber cable extend (13 extends in the figure by 14). By measuring the elongation 14 with the optical fiber strain measuring device 11 as in the first embodiment, it is possible to specify a change in the state of the embankment and its position. (Embodiment 3) Next, an embodiment of the invention according to claim 2 will be described with reference to FIG.

The optical fiber cable 4 comprises an optical fiber core 2 and a covering member 3 as in the first embodiment.
Make them in a loose state. When the non-woven fabric piece 1 is fixed to the optical fiber cable 4 with the adhesive 5, FIG.
As shown in (1), the covering member 3 in a part of the covering part of the optical fiber cable 4 is cut off with a cutter knife or the like, and only the optical fiber core wire 2 exposed in the part is fixed to the nonwoven fabric piece 1 with an adhesive 5. Thus, an optical fiber sensor is manufactured. When the optical fiber sensor manufactured here is applied to a bank, it is the same as in the first or second embodiment. The effect is that only the optical fiber core in the optical fiber cable is bonded and fixed to the non-woven fabric piece, and the movement of earth and sand is directly transmitted to the optical fiber core. Even if there is a difference between them, it is possible to provide an optimal optical fiber sensor for each embankment having a different soil composition by changing the optical fiber core wire.

[0033]

As described above, by implementing the present invention, the daily management of the levees, grasping the state of the levees in the event of an emergency such as a flood, and collecting the basic data necessary for the judgment of river management are performed by manual inspection. It is possible to provide an optical fiber sensor and a method of detecting a change in the state of a structure using the optical fiber sensor, which can be performed without patrol.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of the optical fiber sensor according to the first embodiment.

FIG. 2 is a diagram illustrating an example of a method for detecting a change in the state of a river embankment using an optical fiber sensor according to a third embodiment.

FIG. 3 is an explanatory view showing the principle of a method for measuring the intensity and position of strain generated in an optical fiber by an optical fiber strain measuring device.

FIG. 4 is a graph showing the results of an experiment performed using the method shown in FIG.

FIG. 5 is a diagram illustrating another example of a method for detecting a change in the state of a river embankment using an optical fiber sensor according to the third embodiment.

FIG. 6 is an explanatory view showing an example of the optical fiber sensor according to the second embodiment.

[Description of Signs] 1 ... Nonwoven fabric piece, 2 ... Optical fiber core wire, 3 ... Coating member, 4
... optical fiber cable, 5 ... adhesive, 6 ... river embankment, 7
... embankment slope, 8 ... depth from embankment slope, 9 ... embankment top end,
DESCRIPTION OF SYMBOLS 10 ... Wiring optical fiber cable, 11 ... Optical fiber strain measuring device, 12 ... The part which moved on the embankment, 13 ...
Distance between non-woven fabric pieces, 14: Elongation of distance between non-woven fabric pieces, 1
5: light pulse, 16: strain generation area, 17: change in frequency, 18: position of strain generation area.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masaki Shima 2-3-1 Otemachi, Chiyoda-ku, Tokyo F-term in Nippon Telegraph and Telephone Corporation (reference) 2D018 AA00 2F051 AA06 AB03 2F065 AA04 AA06 AA09 AA20 AA65 CC14 FF12 FF41 GG04 KK01 LL02 PP01 PP22 UU03 2F076 BA11 BB09 BD01 BD02 BD06 2G024 AD36 BA27 CA04

Claims (5)

[Claims] 1. An optical fiber sensor comprising: an optical fiber core having a property that a light scattering characteristic is changed by a strain; and a covering member that covers the optical fiber core, wherein the optical fiber sensor has a longitudinal direction. An optical fiber sensor comprising cloth pieces adhered and fixed at a plurality of positions spaced apart from each other. 2. The optical fiber sensor according to claim 1, wherein the cloth piece is directly adhered and fixed to the optical fiber core. 3. A method for detecting a state change of a structure using the optical fiber sensor according to claim 1 or 2, wherein a part or all of a fiber portion of the optical fiber sensor is provided inside the structure. When the state of the structure changes due to an external factor, the optical fiber core is changed by a strain generated in the optical fiber core according to the change. A method for detecting a state change of a structure using an optical fiber sensor, wherein the state change of the structure is detected by measuring scattered light in the inside. 4. The optical system according to claim 3, wherein the position and magnitude of the strain in the optical fiber core are specified by inputting the scattered light to an optical fiber strain measuring device. A method of detecting a state change of a structure using a fiber sensor. 5. The method according to claim 3, wherein the structure is a river embankment, and the state change of the structure is detected using an optical fiber sensor.