JP2004163329A - Optical fiber sensor for investigation of landslide behavior - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber sensor large in an allowable elongation, without a breakage of the optical fiber even in a case of large amount of dragging at a large landsliding slope, and also capable of observing an amount of compression. <P>SOLUTION: An optical fiber 1 and a coil spring 2 are laid on the landsliding slope, and a behavior of the landsliding slope is acquired as a difference in the strain occurring in the optical fiber. The sensor for observing the behavior of the landsliding slope is characterized in that parallel circuits A composed of the coil springs and the optical fibers having a redundancy in length and a part B only of the optical fibers are constituted by connecting the A and B alternately and serially. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical fiber sensor for investigating a landslide behavior in which an optical fiber and a coil spring are disposed on a landslide slope, 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]
Investigations on the behavior of landslide slopes using conventional optical fiber sensors include methods of burying optical fiber sensors below the ground surface of the slope or continuously placing moving piles on the ground surface and placing the optical fiber sensors between the moving piles. The method of stretching is used.
[0003]
However, in the conventional method, the tensile strain generated in the optical fiber sensor is observed, and the optical fiber may be disconnected when the amount of tension applied to the optical fiber sensor increases due to landslide movement.
[0004]
On the other hand, a technique for measuring the amount of deformation of a structure using an optical fiber sensor has been proposed, although it is not an investigation of the behavior of a landslide slope (for example, Patent Document 1).
[0005]
[Patent Document 1]
JP-A-6-341814 (page 3, FIG. 1)
[0006]
This technique comprises a coil spring, at least one optical fiber disposed on the outer surface of the coil spring along its longitudinal direction, and a coating for covering the periphery of the coil spring on 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 light amount of the optical fiber changes. By detecting this light amount, the deformation amount of the structure is measured. Things.
[0007]
However, in the case of the above-described technique, there is a problem that the optical fiber does not have a sufficient length, so that it cannot cope with a large deformation, 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 and contraction amount is large and the amount of pulling of the landslide slope is large, the optical fiber does not break and the optical compression amount can be observed. It is an object to provide a fiber sensor.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes disposing an optical fiber and a coil spring on a landslide slope, grasping the behavior of the landslide slope as a change in the amount of strain generated in the optical fiber, and measuring the behavior of the landslide slope. A sensor for observing, wherein the optical fiber and the coil spring are alternately and continuously connected to a portion in which the coil spring and an optical fiber having a margin in length are arranged in parallel, and a portion of only the optical fiber. It is characterized by comprising. With this configuration, the expansion and contraction of the landslide slope is regarded as the expansion and contraction of the coil spring, and the expansion and contraction of the coil spring is converted into the strain of the optical fiber. Make the quantity observable.
[0010]
According to a second aspect of the present invention, in the first aspect, the portion of only the optical fiber is attached to the optical fiber fixing bracket in a stretched state with no extra length. According to a third aspect of the present invention, in the first or second aspect, a portion in which an optical fiber having a margin in length is arranged in parallel with the coil spring and a 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 protection pipe is buried.
[0011]
BEST MODE FOR CARRYING OUT 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 using an optical fiber sensor for landslide behavior investigation. The optical fiber sensor for landslide behavior investigation (this sensor) is composed of an optical fiber 1, a coil spring 2, a protection pipe 3, and the like as shown in FIG.
[0013]
Fixed piles 5 having fixing brackets 4 are installed at predetermined intervals along a landslide slope of a ground which is a predicted landslide occurrence point, and an optical fiber 1 is partially interposed between the piles 5, and partly in parallel with the coil spring 2. It is attached. That is, the optical fiber 1 between the fixed piles 5 has a portion A in which the coil spring 2 and the optical fiber 1 with a margin are arranged in parallel, and a portion of only the stretched optical fiber 1 without the margin. B are connected alternately and continuously, and a portion B of only the optical fiber 1 is fixed to the fixing bracket 4. The presence of the portion A allows the expansion and contraction of the coil spring 2 and the optical fiber 1 to be freely deformed, and these portions A and B including the portion are covered with the elastic protective pipe 3. ing. A measuring device 6 is connected to an end of the optical fiber 1 protruding from the ground surface in measurement.
[0014]
The installation of the present sensor on a landslide slope will be described more specifically. First, a slope is excavated at a depth of about several tens of cm to form a groove for installing the sensor. After that, the optical fiber fixing fitting 4 is fixed by the pile 5. Next, a protection pipe 3 covering both parts A and B of the optical fiber 1 is arranged in the groove between the optical fiber fixing fittings 4, and the part B is fixed to the fixing fitting 4. Then, after repeating this work for a predetermined length, the groove is finally backfilled with earth and sand. When the measuring device 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 the landslide occurs on the slope of the ground after installing the sensor as described above, the expansion and contraction of the landslide slope is regarded as expansion and contraction of the coil spring 2, and the expansion and contraction of the coil spring 2 causes the distortion of the optical fiber 1. It is converted and measured by the measuring device 6.
[0016]
As a result, the amount of expansion and contraction of the landslide slope is observed, but the present sensor can observe a much larger amount of expansion and contraction of the landslide slope than the conventional sensor using the optical fiber 1 alone. It becomes.
[0017]
Although the present sensor is embedded in the landslide slope in the above embodiment, it is not always necessary to embed the sensor, and it is needless to say that the sensor may be arranged between the driving piles 5 on the landslide slope.
[0018]
【The invention's effect】
The invention according to claims 1 to 4 is as described above, wherein an optical fiber and a coil spring are disposed on the 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. An optical fiber and a coil spring are configured by connecting a coil spring and a portion in which an optical fiber having a margin in length is arranged in parallel, and a portion including only the optical fiber in an alternately continuous manner. Therefore, it is possible to observe a large amount of expansion and contraction of the slope as compared with the conventional optical fiber sensor. In addition, since an optical fiber is used for the landslide behavior detection and the signal transmission path, it is not affected by electric noise and induced lightning. In addition, since an optical fiber is used for the signal transmission path, it is possible to observe the movement in a wide range (the maximum fiber extension distance is 2 km). Furthermore, since a plurality of landslide behavior detecting units are connected in series by optical fibers, there is an excellent effect that the cost for cables can be reduced as compared with the related art.
[Brief description of the drawings]
FIG. 1 is a schematic view of landslide observation using an optical fiber sensor for investigating landslide behavior according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION 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 grasped as a change in the amount of strain generated in the optical fiber, and a sensor for observing the behavior of the landslide slope,
The optical fiber and the coil spring are configured by alternately and continuously connecting a portion in which the coil spring and an optical fiber having a margin in length are arranged in parallel and a portion including only the optical fiber. Optical fiber sensor for landslide behavior investigation. The optical fiber sensor for investigating landslide behavior according to claim 1, wherein a portion of only the optical fiber is in a stretched state with no extra length and attached to an optical fiber fixing bracket. The landslide behavior investigation device according to claim 1 or 2, wherein the portion in which the coil spring and the optical fiber having a sufficient length are arranged in parallel and the portion of the optical fiber alone are covered with an elastic 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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