JP2022159608A - Surface landslide detection method and surface tiltmeter used therefor - Google Patents

Abstract

To provide a technology that can be used for disaster prevention by early and accurate detection of surface landslide of the ground.SOLUTION: A tilt sensor capable of measuring changes in the tilt angle of an unconsolidated soil layer 21 is installed in the unconsolidated soil layer 21 at a depth of 80 cm or more from the ground surface. Next, it is determined whether the amount of change in the tilt angle detected by the tilt sensor exceeds a threshold. As a result, the risk of occurrence of surface landslide can be accurately and early determined.SELECTED DRAWING: Figure 1

Description

Patent Law Article 30, Paragraph 2 application filed October 12, 2020 Announced in "Hazard Mapping Sensor Surface Inclinometer Clinopol" pamphlet (publisher: OYO Corporation) October 14, 2020 OYO Website of the company (https://www.oyo.co.jp/exhibition-oyo-fair-2020/, https://www.oyo.co.jp/exhibition-oyo-fair-2020/online-exhibition /_Modal/02-2.html, https://www.oyo.co.jp/exhibition-oyo-fair-2020/online-exhibition/_Modal/02-4.html)

TECHNICAL FIELD The present invention relates to a technique for detecting surface failure, which is a type of ground slope failure.

Slope failures include landslides and surface failures. Landslides are caused by the sliding of a mass of soil (landslide part) on the surface of the soil. That is, in a landslide, the landslide portion moves parallel to the soil surface by sliding against the underlying soil. On the other hand, surface failure is caused by creep (flow) of unconsolidated soil. Surface failures account for about 80% of slope failures.

Patent Literature 1 below proposes a technique for estimating a slope failure by measuring the tilt and displacement of the ground by arranging a tilt sensor in a buried pipe buried in the ground.

JP 2011-169705 A

The technique of Patent Literature 1 mentioned above is mainly for detecting landslides, and it is considered difficult to detect surface collapses at an early stage.

Further, according to the studies of the present inventors, it is necessary to accurately detect a slight tilt angle of soil in order to detect surface collapse at an early stage. However, the signal from the tilt sensor contains noise due to temperature changes in the natural environment, etc., so there is also the problem that it is difficult to detect the tilt angle with high precision.

As a result of various studies, the inventors of the present invention have found that surface collapse can be detected early and accurately by devising the installation position and installation depth of the tilt sensor.

The present invention has been made in view of the circumstances described above. A main object of the present invention is to provide a technique capable of early and accurate detection of surface landslides, which is useful for disaster prevention.

The present invention can be expressed as inventions described in the following items.

(Item 1)
A step of installing an inclination sensor capable of measuring a change in inclination angle at a position in the unconsolidated soil layer and at a depth of 80 cm or more from the ground surface;
and determining the risk of occurrence of a surface landslide based on whether the amount of change in the tilt angle detected by the tilt sensor exceeds a threshold.

(Item 2)
A step of forming a prepared hole with a depth of 80 cm or more from the ground surface in the unconsolidated soil layer;
A method of installing a tilt sensor for detecting a surface collapse, comprising the step of arranging a tilt sensor inside the prepared hole and at a depth of 80 cm or more from the ground surface.

(Item 3)
A surface layer inclinometer comprising a sensor section, a body section, and a communication section,
The main body is formed in a long shape with a length of about 80 cm or more,
The sensor section is attached to one end side of the body section,
The communication unit is attached to the other end of the main body,
The sensor unit includes an inclination sensor capable of detecting an inclination of the soil layer,
The communication section is exposed to the ground surface with the body section and the sensor section buried in the soil layer, and is configured to be capable of transmitting detection data from the tilt sensor to the outside via a communication line. A surface inclinometer.

(Item 4)
A method of installing a tilt sensor using the surface layer inclinometer according to item 3,
measuring the depth of the unconsolidated soil layer from the ground surface;
A step of forming a prepared hole having a depth of 80 cm or more from the ground surface in the unconsolidated soil layer;
placing the tilt sensor at a depth of 80 cm or more in the unconsolidated soil layer by inserting the sensor portion of the surface layer inclinometer into the prepared hole;
The tilt sensor installation method, wherein the body portion and the sensor portion are brought into close contact with the inner surface of the pilot hole.

According to the technology of the present invention, it is possible to detect surface collapses early and with high accuracy, and use them for disaster prevention.

1 is a perspective view of a surface layer inclinometer according to one embodiment of the present invention; FIG. FIG. 2 is a schematic cross-sectional view in the vicinity of the upper end of the main body of the surface layer inclinometer of FIG. 1; FIG. 2 is an explanatory diagram for explaining a procedure for installing the surface layer inclinometer of FIG. 1; It is a schematic explanatory drawing for demonstrating the structure of the slope which installs a surface layer inclinometer. FIG. 2 is a schematic explanatory diagram for explaining the mechanism of surface collapse. It is an explanatory diagram for explaining the work of installing the surface inclinometer in the ground, FIG. (a) is at the time of preparing the pilot hole, FIG. indicates the state of It is explanatory drawing which shows typically the state which installed the surface-layer inclinometer in the prepared hole. It is a graph showing the time change of the tilt angle detected by the tilt sensor, wherein the horizontal axis is time (arbitrary unit) and the vertical axis is the tilt angle. 4 is a graph showing the relationship between the installation depth (cm) of the tilt sensor and the standard deviation σ of the output value of the tilt sensor.

A method for detecting surface collapse according to one embodiment of the present invention will be described with reference to the accompanying drawings. First, a surface layer inclinometer used in this method will be described with reference to FIGS. 1 and 2. FIG.

(Configuration of Surface Inclinometer)
The surface layer inclinometer 1 of this embodiment has a sensor section 11 , a body section 12 , a communication section 13 and a support section 14 .

The body portion 12 is formed in a long cylindrical shape having a length of approximately 80 cm or more. Specifically, the body portion 12 of the present embodiment is cylindrical (see FIG. 2). However, the cross-sectional shape of the main body 12 may be polygonal such as triangular or quadrangular, or elliptical. In addition, the length of the body portion 12 of the present embodiment is preferably about 1.0 m to 1.4 m, more preferably about 1.2 m. In addition, the outer diameter of the main body portion 12 is approximately 25 mm in this example.

The sensor section 11 is attached to one end side (lower end in FIG. 1) of the main body section 12 in the longitudinal direction. A tilt sensor (not shown) capable of detecting the tilt of the soil layer is provided inside the sensor section 11 . As this tilt sensor, for example, a commercially available tilt sensor capable of measuring two-axis tilt angles (a so-called two-axis inclinometer) can be used. A tilt sensor that can measure the tilt angle of one axis or three axes can also be used. The sensor unit 11 sends a signal (inclination angle signal) from the tilt sensor to the communication unit 13 via wiring (not shown) inside the main body 12 . The tilt sensor used in the sensor section 11 preferably has a high resolution of, for example, about 0.01°. The sensor portion 11 has a cylindrical shape coaxial with the main body portion 12 and has an outer diameter of about 25 mm, like the main body portion 12 . The output from the sensor unit 11 may be the amount of change in the angle or the angle itself. Both are referred to as tilt angles in this specification.

The communication unit 13 is attached to the other end of the main body 12 (upper end in FIG. 1). The communication unit 13 is exposed to the ground surface when the main unit 12 and the sensor unit 11 are buried in the soil layer (see FIG. 6C described later), and receives detection data from the sensor unit 11 (tilt sensor) (that is, tilt angle) can be transmitted to the outside via an appropriate communication line. The communication line is, for example, a cell phone line (3G, LTE, 4G, 5G, etc.), but may be a WiFi line. In short, the communication line in this embodiment may be a line capable of transmitting data to the outside, and is not restricted by its communication protocol or hardware configuration.

Further, the communication unit 13 of the present embodiment may receive signals from the outside in addition to the function of transmitting signals to the outside. For example, by receiving GPS, it is possible to obtain its own position and accurate time. In addition, updating of the communication unit 13, security countermeasures, change of measurement interval (or communication interval), confirmation of operation state, etc. can be performed remotely from the external server side.

Further, the communication unit 13 has a power supply (not shown) for operating itself. A rechargeable or non-rechargeable battery (eg, lithium battery) can be used as the power source. However, as a power supply, it is also possible to use wireless power supply or a commercial power supply. Also, different power supplies may be used for the sensor unit 11 and the communication unit 13 .

The support portion 14 is composed of three blades 141 to 143 in this embodiment (see FIGS. 1 and 2). These blades 141 to 143 are attached near the upper end of the body portion 12 . In the support portion 14, the two blades 141 and 142 (see FIG. 2) are longer than the remaining blade 143. As shown in FIG. Also, the angles between the blades are not uniform, and the angles between the blades 141 and 142 are wide (for example, about 130° to 170°). As will be described later, when the surface layer inclinometer 1 is installed, this wide-angle portion (wide-angle portion) is oriented downward in the slope inclination direction (see FIG. 2).

(Installation and usage of surface inclinometer)
Next, with further reference to FIG. 3, a method for installing and using the above-described surface layer inclinometer will be described.

(Slope ground structure)
First, as a premise of the description, the configuration of a typical sloped ground 2 will be described with reference to FIGS. 4 and 5. FIG. A portion of the ground 2 is unconsolidated soil (moving portion) 21 . Of course, at the time of installation of the surface layer inclinometer 1, it is not decided which part will actually be the moving part 21, but for convenience of explanation, the moving part 21 is specified and described in FIG.

At the time of installation of the surface layer inclinometer 1, it is preferable to select and install the ground in which a surface layer failure is likely to occur. For example, it is known that surface landslides are likely to occur when the topography is a zero-order valley. In addition, the susceptibility of surface landslides can be estimated with a certain degree of certainty from the properties of the ground and the history of past disasters.

The mechanism when the moving part 21 slides against the immovable part 22, which is the underlying ground, in a surface failure will be described with reference to FIG. In surface collapse, the moving part 21 is unconsolidated and has high fluidity. Therefore, as schematically shown in FIG. 5, the moving part 21 moves so as to rotate about the point of contact with the unconsolidated soil (that is, moves by creep). Therefore, if such rotation can be accurately detected within a minute angle, it is thought that surface collapse can be estimated with accuracy.

(Step SA-1 in FIG. 3)
In this embodiment, first, the depth of the unconsolidated soil layer from the ground surface is measured. For example, this can be measured by manually inserting a probe having a length of about 1 to 2 m from the ground surface toward the ground. If the probe is thin and has a somewhat sharp tip, it can be manually inserted into the unconsolidated soil layer. The depth of the unconsolidated soil layer can be estimated based on the insertion depth of the probe when it can no longer be inserted. This operation is performed at the required number of points. This operation allows the location of unconsolidated soil layers that are at least 80 cm deep.

In this embodiment, the depth of the unconsolidated soil layer can be estimated without using a boring device. This can be expected to reduce the installation cost.

(Step SA-2 in FIG. 3)
Next, a pilot hole 25 is formed at the position of the unconsolidated soil layer having a depth of at least 80 cm (Fig. 6(a)). Since the formation of the pilot hole 25 is performed in the unconsolidated soil layer, it can be manually performed by an operator using, for example, a drill 3 having a cutting edge at its tip. Instead of the drill 3, the pilot hole 25 can be formed by using a hollow pipe (not shown) whose tip is obliquely cut and sharpened.

It is preferable that the inner diameter of the pilot hole 25 is approximately the same as or slightly smaller than the outer diameters of the body portion 12 and the sensor portion 11 of the surface layer inclinometer 1 . In this example, the diameter of this inner diameter is set to 25 mm, but it is not limited to this.

_The depth L1 of the pilot hole 25 is preferably 80 cm or more, and is 1.1 m in this example (see FIG. 6(b)).

(Step SA-3 in FIG. 3)
Next, the sensor section 11 of the surface layer inclinometer 1 is inserted into the prepared hole 25 (FIG. 6(c)). As a result, the inclination sensor can be arranged at a position deeper than 80 cm in the unconsolidated soil layer (see FIG. 7). In this example, since the inner diameter of the pilot hole 25 is set to be substantially the same as or smaller than the outer diameters of the body portion 12 and the sensor portion 11, the surfaces of the body portion 12 and the sensor portion 11 are in close contact with the inner surface of the pilot hole 25. can be made

Also, when the surface layer inclinometer 1 is installed in the pilot hole 25, as already described, the wide-angle portion between the blades 141 and 142 should face the lower side in the inclination direction (see FIGS. 2 and 6(c)). Install so that it faces

After installation, the switch (not shown) of the surface layer inclinometer 1 is pressed to activate it. After activation, the tilt angle periodically output from the tilt sensor of the sensor unit 11 can be received by the system side (server side) via the communication unit 13 .

(Step SA-4 in FIG. 3)
The system can monitor whether the tilt angle variation of the surface inclinometer 1 is above a threshold value (eg, 0.1° or 0.2°). When there is an anomaly, the system can alert the user. Here, the threshold can be set variously by the user.

As a result, in this embodiment, it is possible to quickly determine the risk of surface collapse based on whether or not the amount of change in the detected tilt angle exceeds the threshold value, and based on this determination, quickly implement disaster prevention measures. measures can be taken.

Here, the solid line in FIG. 8 shows an example of the temporal change of the tilt angle output from the tilt sensor. However, according to the findings of the present inventors, when the position of the tilt sensor is close to the ground surface (for example, when placed on the ground surface), the output from the tilt sensor is affected by changes in the natural environment such as temperature. It will fluctuate. FIG. 9 shows the relationship between the sensor installation depth and the standard deviation of the tilt sensor output. The standard deviation σ is large when the sensor installation depth is shallow. The sensor output in this case is schematically shown by the dashed line in FIG. This makes it difficult to accurately determine the tilt angle.

Further, from the results shown in FIG. 9, it can be seen that by positioning the tilt sensor at a depth of 80 cm or more from the ground surface, the variation in the sensor output value can be suppressed to a low value (that is, to about σ≦0.001). Here, in this embodiment, as described above, since the installation position of the tilt sensor is set to a depth of 80 cm or more from the ground surface, the tilt angle with little variation (that is, with high accuracy) as shown by the solid line in FIG. 8 is detected. be able to. Therefore, according to this embodiment, it is possible to accurately determine the risk of surface collapse.

Further, in this embodiment, since the sensor section 11 (that is, the tilt sensor) is arranged in the unconsolidated soil layer, creep (rotation) in the moving section 21 as shown in FIG. 5 can be accurately detected. There is also the advantage of

Furthermore, in this embodiment, the surface layer inclinometer 1 is installed so that the wide-angle portion between the blades 141 and 142 faces downward in the tilt direction (see FIGS. 2 and 6C). The pressing force due to the movement of the soil toward the side can reliably act on these vanes 141 and 142 . Here, it is presumed that in surface failures, the soil often rotates toward the lower side of the slope. Therefore, in the present embodiment, these blades 141 and 142 make it possible to detect creep (rotation) in the moving part 21 with higher accuracy.

It should be noted that the description of the above embodiment is merely an example, and does not show the configuration essential to the present invention. The configuration of each part is not limited to the above as long as the gist of the present invention can be achieved.

1 surface inclinometer 11 sensor unit (tilt sensor)
12 main unit 13 communication unit 14 support unit 141 to 143 blade 2 inclined ground 21 soil moving unit (unconsolidated soil layer)
22 Immovable part of soil 25 Prepared hole 3 Drill

Claims (4)

A step of installing an inclination sensor capable of measuring a change in inclination angle at a position in the unconsolidated soil layer and at a depth of 80 cm or more from the ground surface;
and determining the risk of occurrence of a surface landslide based on whether the amount of change in the tilt angle detected by the tilt sensor exceeds a threshold. A step of forming a prepared hole with a depth of 80 cm or more from the ground surface in the unconsolidated soil layer;
A method of installing a tilt sensor for detecting a surface collapse, comprising the step of arranging a tilt sensor inside the prepared hole and at a depth of 80 cm or more from the ground surface. A surface layer inclinometer comprising a sensor section, a body section, and a communication section,
The main body is formed in a long shape with a length of about 80 cm or more,
The sensor section is attached to one end side of the body section,
The communication unit is attached to the other end of the main body,
The sensor unit includes an inclination sensor capable of detecting an inclination of the soil layer,
The communication section is exposed to the ground surface with the body section and the sensor section buried in the soil layer, and is configured to be capable of transmitting detection data from the tilt sensor to the outside via a communication line. A surface inclinometer. A method for installing an inclination sensor using the surface layer inclinometer according to claim 3,
measuring the depth of the unconsolidated soil layer from the ground surface;
A step of forming a prepared hole having a depth of 80 cm or more from the ground surface in the unconsolidated soil layer;
placing the tilt sensor at a depth of 80 cm or more in the unconsolidated soil layer by inserting the sensor portion of the surface layer inclinometer into the prepared hole;
The tilt sensor installation method, wherein the body portion and the sensor portion are brought into close contact with the inner surface of the pilot hole.

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