JP3653549B2 - Optical fiber sensor for investigation of landslide behavior - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber sensor for investigating landslide behavior, in which an optical fiber and a coil spring are disposed on a landslide slope, and the behavior of the landslide slope is regarded as a change in the amount of strain generated in the optical fiber, and the behavior of the landslide slope is observed. is there.
[0002]
[Prior art]
In the investigation of landslide slope behavior using conventional fiber optic sensors, optical fiber sensors can be embedded under the slope ground surface, or moving piles can be continuously placed on the ground surface to place the optical fiber sensors between the moving piles. A tensioning method is used.
[0003]
However, the conventional method observes the tensile strain generated in the optical fiber sensor, and the optical fiber may be disconnected when the tensile amount with respect to the optical fiber sensor increases with the landslide movement.
[0004]
On the other hand, although it is not an investigation of the behavior of a landslide slope, a technique for measuring the amount of deformation of a structure using an optical fiber sensor has been proposed (for example, Patent Document 1).
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 6-341814 (page 3, FIG. 1)
[0006]
This technique includes a coil spring, at least one optical fiber disposed along the longitudinal direction on the outer surface of the coil spring, and a coating for covering the periphery of the coil spring in which the optical fiber is disposed. When the structure is deformed and the coil spring expands and contracts, local bending occurs in the optical fiber, and the amount of light in the optical fiber changes. By detecting this amount of light, the amount of deformation of the structure is measured. Is.
[0007]
However, even in the case of the above-described technique, there is a problem that the optical fiber cannot be easily deformed because there is no portion with a sufficient length in the optical fiber, and the optical fiber is easily broken as in the conventional method. .
[0008]
[Problems to be solved by the invention]
Therefore, the present invention solves the conventional problems as described above, and even when the allowable expansion / contraction amount is large and the landslide slope has a large pull amount, the optical fiber is not broken and the amount of compression can be observed. An object is to provide a fiber sensor.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 is arranged such that an optical fiber and a coil spring are disposed on a landslide slope, and the behavior of the landslide slope is regarded as a change in the amount of strain generated in the optical fiber. A sensor for observing, wherein the optical fiber and the coil spring are formed by alternately and continuously connecting a coil spring and a portion of the optical fiber having a length in parallel and a portion of the optical fiber alone. It is configured. This configuration captures the expansion and contraction of the landslide slope as the expansion and contraction of the coil spring, converts the expansion and contraction of the coil spring into the strain of the optical fiber, and the expansion and contraction of the landslide slope that is much larger than that using the optical fiber alone as a sensor. Make the quantity observable.
[0010]
According to a second aspect of the present invention, in the first aspect, the portion of the optical fiber alone is attached to the optical fiber fixing bracket in a stretched state without a margin in length. According to a third aspect of the present invention, in the first or second aspect, the coiled spring and the portion where the optical fiber having a length is provided in parallel and the portion including only the optical fiber are a stretchable protective pipe. It is covered with. According to a fourth aspect of the present invention, in the third aspect, the protective pipe is embedded.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to the accompanying drawings.
[0012]
FIG. 1 is a diagram showing an outline of landslide observation by an optical fiber sensor for investigating landslide behavior. The landslide behavior investigation optical fiber sensor (this sensor) is composed of an optical fiber 1, a coil spring 2, a protective pipe 3, and the like as shown in FIG.
[0013]
Fixing piles 5 having fixing brackets 4 are driven at predetermined intervals along a landslide slope of a natural ground, which is a predicted landslide occurrence point, and an optical fiber 1 is partly connected in parallel with the coil spring 2 between these piles 5. Attached. That is, the optical fiber 1 between the fixed piles 5 includes a coil spring 2 and a portion A in which the optical fiber 1 having a length is provided in parallel, and a portion of the optical fiber 1 in a stretched state without a length. B and B are alternately and continuously connected, and a portion B only for the optical fiber 1 is fixed to the fixture 4. Due to the presence of the portion A, the expansion and contraction of the coil spring 2 and the optical fiber 1 can be freely deformed, and these portions A and B including the portion are covered with a stretchable protective pipe 3. ing. A measuring instrument 6 is connected to the end of the optical fiber 1 protruding from the ground surface during measurement.
[0014]
More specifically, the installation of the sensor on a landslide slope will be explained. First, the slope is excavated to a depth of several tens of centimeters to make a groove for installing the sensor. Thereafter, the optical fiber fixing bracket 4 is fixed by the pile 5. Next, the protective pipe 3 covering both portions A and B of the optical fiber 1 is disposed in the groove between the optical fiber fixing brackets 4, and the portion B is fixed to the fixing bracket 4. And after repeating this operation | work over predetermined length, the said groove | channel is finally backfilled with earth and sand. When the measuring instrument 6 is connected to the end protruding from the ground surface of the optical fiber 1 after backfilling, the installation work is completed.
[0015]
When a landslide occurs on the slope of the natural ground after installing this sensor as described above, the expansion / contraction of the landslide slope is regarded as the expansion / contraction of the coil spring 2, and the expansion / contraction of the coil spring 2 becomes the strain of the optical fiber 1. This is converted and measured by the measuring device 6.
[0016]
As a result, the amount of expansion / contraction of the landslide slope can be observed, but this sensor can observe a much larger amount of expansion / contraction of the landslide slope than the conventional sensor using the optical fiber 1 alone. It becomes.
[0017]
In this embodiment, the present sensor is embedded in the landslide slope. However, it is not always necessary to embed the sensor, and it may be disposed between the piles 5 placed on the landslide slope.
[0018]
【The invention's effect】
The inventions of claims 1 to 4 are as described above, and an optical fiber and a coil spring are arranged on the landslide slope, and the behavior of the landslide slope is observed as a change in the amount of strain generated in the optical fiber, and the behavior of the landslide slope is observed. An optical fiber and a coil spring are configured by alternately and continuously connecting a coil spring and a portion in which an optical fiber having a length is provided in parallel and a portion having only an optical fiber. Therefore, it is possible to observe a large amount of expansion and contraction of the slope as compared with the conventional optical fiber sensor. Moreover, since optical fiber is used for landslide behavior detection and signal transmission path, it is not affected by electrical noise and induced lightning. In addition, since an optical fiber is used for the signal transmission path, it is possible to observe movement over a wide range (maximum fiber extension distance 2 km). Furthermore, since a plurality of landslide behavior detection units are connected in series with an optical fiber, there is an excellent effect that the cost for the cable can be saved as compared with the conventional case.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of landslide observation by an optical fiber sensor for investigating landslide behavior according to an embodiment of the present invention.
[Explanation of symbols]
1 Optical fiber 2 Coil spring 3 Protective pipe 4 Optical fiber fixing bracket 5 Optical fiber fixing bracket fixing pile 6 Measuring instrument

Claims (4)

An optical fiber and a coil spring are arranged on the landslide slope, and the behavior of the landslide slope is observed as a change in the amount of strain generated in the optical fiber, and the behavior of the landslide slope is observed.
The optical fiber and the coil spring are constructed by alternately and continuously connecting a coil spring and a portion in which an optical fiber having a margin in length is arranged in parallel and a portion only of the optical fiber. Optical fiber sensor for landslide behavior investigation. The optical fiber sensor for investigating landslide behavior according to claim 1, wherein the portion of the optical fiber alone is in a stretched state with no margin in length and is attached to the optical fiber fixing bracket. 3. The landslide behavior investigation according to claim 1 or 2, wherein the coil spring and the optical fiber with a margin in length are arranged in parallel and the optical fiber only part is covered with a stretchable protective pipe. Optical fiber sensor. The optical fiber sensor for investigating landslide behavior according to claim 3, wherein the protective pipe is buried.

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