JP5476528B2 - Soil moisture level detector and slope failure prediction system using the same - Google Patents

Description

  The present invention provides a soil moisture level detector capable of detecting both soil moisture level and groundwater level with a single device, and slope collapse based on soil moisture level and groundwater level detected using the soil moisture level detector. The present invention relates to a predicting slope failure prediction system.

  In recent years, in Japan, slope failure has occurred frequently due to rain during the rainy season or typhoon, and the slope failure prediction system that predicts the occurrence of slope failure by evaluating the risk of slope failure to minimize the damage. Has been proposed. Here, there are two main causes of slope failure due to rainfall: the soil's own weight increases with increasing soil moisture, and the slope's shear strength decreases with increasing groundwater level. Is mentioned. Therefore, when evaluating the risk of slope collapse, two factors are effective: soil moisture and groundwater level.

  As a device for measuring the moisture content in the soil, a tensiometer (see Patent Document 1) that measures the pore water pressure in the soil has been conventionally used. Here, the pore water pressure means the pressure of water as the pore fluid when the soil is divided into soil particles and pore fluid. And as FIG. 1 of patent document 1 shows, the inside of a tensiometer is filled with deaerated water, that is, water obtained by artificially removing dissolved air.

  Further, as another device for measuring the moisture content in the soil, a dielectric constant moisture meter (see Patent Document 2) for measuring a change in the dielectric constant in the soil has been conventionally used. For example, as shown in FIG. 1 of Patent Document 2, the dielectric constant soil moisture meter is a high-frequency transmitter 1 that generates a high-frequency signal, a cable 30 that transmits the generated high-frequency signal, and an input high-frequency signal. The capacity resonator 2 that resonates and outputs, the cable 38 that transmits the output high-frequency signal, and the detector 3 that receives the output high-frequency signal and detects a resonance point are configured.

JP 2006-58202 A JP 09-243578 A

  However, because the tensiometer has a structure in which deaerated water is filled inside as described above, the deaerated water is easily absorbed in dry soil in the summer, and the deaerated water freezes in the winter. It has the characteristic of being easy. Therefore, in order to perform accurate measurement of pore water pressure with a tensiometer throughout the year, maintenance such as replenishing escaped deaerated water or thawing frozen deaerated water is necessary, and dangerous maintenance work on the slope There is a problem that is regularly requested.

  On the other hand, a dielectric constant moisture meter does not require frequent maintenance work unlike a tensiometer. However, as shown in FIG. 1 of Patent Document 2, when installing the dielectric constant moisture meter, after excavating the slope to the depth to be installed and embedding the capacity resonator 2, the cable 30 and the cable 38 are connected. It is necessary to pull out to the ground and connect to the high-frequency transmitter 1 and the detector 3, and there is a problem that installation work is troublesome. The dielectric constant moisture meter also has a problem that when the moisture in the soil contains salt, the dielectric constant cannot be measured accurately due to the influence thereof.

  A tensiometer or a dielectric moisture meter can measure the amount of moisture in the soil, but cannot measure the groundwater level, which is another important index for evaluating the risk of slopes. Therefore, in order to construct a slope failure prediction system, it is necessary to install a device for measuring the groundwater level on the slope in addition to the tensiometer and the dielectric constant moisture meter. Is troublesome and leads to increased costs.

  The present invention has been made in view of such problems, and in a slope failure prediction system that predicts the occurrence of slope failure by detecting the amount of moisture in the soil and the groundwater level, the installation work and maintenance work are performed. Provided is a means for making it possible to detect both the moisture content in the soil and the groundwater level with a single device without increasing the burden.

In order to achieve the above object, a slope failure prediction system using a soil moisture level detection device according to the present invention is a tubular member having one end sealed and the other end opened, with the opening side down. An ultrasonic waveguide embedded in the soil so as not to enter the soil, an ultrasonic transmission element that is provided on the sealed side inside the ultrasonic waveguide and transmits ultrasonic waves toward the opening side, and Provided on the sealed side inside the ultrasonic waveguide, of the ultrasonic waves transmitted from the ultrasonic transmission element, reflected on the soil surface at the opening side end or penetrated into the ultrasonic waveguide An ultrasonic receiving element that receives the reflected wave that has been reflected and returned by the groundwater level surface, and the amount of moisture in the soil near the opening-side end of the ultrasonic waveguide. While detecting based on the maximum amplitude of the reflected wave received by the receiving element, A control unit that detects a position of a groundwater level based on a propagation time required from when the ultrasonic transmission element transmits an ultrasonic wave until the ultrasonic reception element receives the reflected wave. A moisture level detector is installed on the slope, and the control unit issues a warning that the slope is likely to collapse based on the detection result of the maximum amplitude of the reflected wave and the propagation time. A slope failure prediction system using a detection device, wherein the ultrasonic waveguide of the detector is embedded in the soil so that the whole is positioned below the ground surface, and the moisture level detection device in the soil When the state where the maximum amplitude of the reflected wave reaches a predetermined value or more continues continuously for a predetermined time or more, the risk of collapse of the slope reaches a risk level 1 And the propagation time When it starts to decrease, it is determined that the risk of slope collapse has risen to the risk level 2, and based on the relationship between the time during which the risk level 1 has continued and the elapsed time since the risk level 2 has been reached. The alarm is issued .
Further, the slope failure prediction system using the soil moisture level detection apparatus according to the present invention is a tubular member having one end sealed and the other end opened, and no soil enters the inside with the opening side down. An ultrasonic wave waveguide embedded in the soil, an ultrasonic wave transmitting element that is provided on the sealed side inside the ultrasonic wave waveguide and transmits ultrasonic waves toward the opening side, and the ultrasonic wave waveguide Of the ultrasonic wave transmitted from the ultrasonic transmission element, reflected on the soil surface at the opening side end or in the groundwater level surface that has entered the ultrasonic waveguide. The ultrasonic receiving element receives the detector having an ultrasonic receiving element that receives the reflected wave that has been reflected and returned, and the amount of moisture in the soil near the opening end of the ultrasonic waveguide. While detecting based on the maximum amplitude of the reflected wave, the position of the groundwater level in the soil A soil moisture level detecting device comprising: a control unit that detects based on a propagation time required from when the ultrasonic transmission element transmits an ultrasonic wave until the ultrasonic reception element receives the reflected wave. A slope using a moisture level detector in the soil, wherein the control unit issues a warning that the slope is likely to collapse based on the detection result of the maximum amplitude of the reflected wave and the propagation time. In the collapse prediction system, the ultrasonic waveguide of the detector is embedded in the soil so that the whole is positioned below the ground surface, and a plurality of the moisture water level detection devices in the soil are installed. When the control unit reaches N1 when the number of the soil water level detectors in which the maximum amplitude of the reflected wave has reached a predetermined value or more continues continuously for a predetermined time or more, there is a risk of collapse of the slope. Sex is overall system risk level 1 Then, when the number of the soil moisture level detectors in which the propagation time has started to decrease among the N1 reaches N2, the slope collapse risk is the overall system risk level 1 It is determined that the overall system risk level has been raised to 2, and the warning is issued.

Further, the slope failure prediction system using the soil moisture level detection device according to the present invention is characterized in that the soil moisture level detection device is a tubular member sealed at both ends, and is an ultrasonic wave guide of the detector. An ultrasonic waveguide embedded in the soil to the same depth position substantially parallel to the tube, an ultrasonic transmission element provided on the upper end side in the ultrasonic waveguide, and transmitting ultrasonic waves toward the lower end side Among the ultrasonic waves that are provided on the upper end side inside the ultrasonic waveguide and transmitted from the ultrasonic transmission element, the properties preliminarily spread on the inner bottom surface of the ultrasonic waveguide are known. An ultrasonic wave receiving element that receives a reflected wave that has been reflected and returned from the surface of the soil, and the control unit detects the maximum amplitude of the reflected wave and the propagation time detected by the detector. The reflected wave detected by the temperature corrector The maximum amplitude and the propagation time is to temperature compensation.

In the slope failure prediction system using the soil moisture level detection device according to the present invention, the temperature corrector is integrated with the detector.

  In addition, the slope failure prediction system using the soil moisture level detection device according to the present invention is such that an air discharge hole for discharging the internal air to the outside is formed in the ultrasonic waveguide of the detector. It is.

  Further, the slope failure prediction system using the soil moisture level detection device according to the present invention is formed such that the air discharge hole is inclined upward from the outside to the inside of the ultrasonic waveguide of the detector. It has been done.

  Further, in the slope failure prediction system using the soil moisture level detection device according to the present invention, the standard soil having a known particle size distribution is spread on the opening side end of the ultrasonic waveguide of the detector. Is.

  According to the soil moisture level detection apparatus according to the present invention, the control unit determines the amount of soil moisture near the opening side end of the ultrasonic waveguide, and the maximum amplitude of the reflected wave received by the ultrasonic receiving element. On the other hand, the position of the groundwater level in the soil is detected based on the propagation time required from when the ultrasonic transmission element transmits the ultrasonic wave until the ultrasonic reception element receives the reflected wave. Therefore, it is possible to detect both the soil water content and the groundwater level with a single soil water level detector. Therefore, compared with the case where the apparatus which detects the amount of moisture in the soil and the apparatus which detects the groundwater level are separately installed, the apparatus installation work can be simplified and the cost can be reduced.

  Further, according to the soil moisture level detection apparatus according to the present invention, the ultrasonic transmission element and the ultrasonic reception element of the detector have a large temperature dependency on the transmission characteristics and reception characteristics, but are detected by the detector. Since the maximum amplitude of reflected waves and the propagation time of ultrasonic waves are corrected by the temperature corrector, the moisture content in the soil and the groundwater level can be accurately measured even when the soil moisture level detector is installed in an environment where the temperature changes rapidly. Can be detected.

  In addition, according to the soil moisture level detection apparatus according to the present invention, the temperature corrector is configured integrally with the detector, so that the detector and the temperature corrector are compared with the case where they are installed apart from each other by a predetermined distance. Thus, a temperature difference due to the difference in installation location between the detector and the temperature corrector is unlikely to occur, so that the temperature correction of the detector can be performed more accurately. In addition, when the detector and the temperature corrector are integrated, the installation work can be simplified as compared with the case where the detector and the temperature corrector are separately embedded in the soil.

  Further, according to the soil moisture level detection device according to the present invention, when the groundwater level surface enters the ultrasonic waveguide by forming the air discharge hole in the ultrasonic waveguide of the detector, The air inside the extruded ultrasonic waveguide is discharged to the outside through the air discharge hole. Thereby, since the groundwater level surface rises inside the ultrasonic waveguide as well as outside, the groundwater level can be accurately detected inside the ultrasonic waveguide.

  Further, according to the soil moisture level detection device according to the present invention, the air discharge hole is formed so as to incline upward from the outside to the inside of the ultrasonic waveguide, so that the air discharge hole is formed in the rain. It is difficult for water to enter from the outside to the inside of the ultrasonic waveguide, and the groundwater level can be accurately detected.

  Further, according to the slope failure prediction system using the soil moisture level detection device according to the present invention, the soil moisture level detection device is installed on the slope, and the control unit warns that there is a high risk of the slope collapse. The system user can predict the occurrence of slope failure and take measures such as evacuation in advance. Also, since both the soil moisture level and the groundwater level can be detected by a single soil moisture level detector, the soil moisture level detector and the groundwater level detector are separately installed on the slope. Compared with the case of installation, the apparatus installation work can be simplified and the cost can be reduced. In addition, when there is a low risk of slope failure, that is, when the soil is dry or wet, the system operates normally by constantly monitoring the maximum amplitude of reflected waves and the propagation time of ultrasonic waves. Can be confirmed.

  In addition, according to the slope failure prediction system using the soil moisture level detection device according to the present invention, one soil moisture level detection device is installed, and the control unit has a risk level 1 for slope failure risk. Since the alarm is issued based on the relationship between the continued time and the elapsed time since the risk level 2 was raised, the control can be simplified and the cost can be reduced.

  Further, according to the slope failure prediction system using the soil moisture level detection device according to the present invention, a plurality of soil moisture level detection devices are installed, and the control unit determines that the slope failure risk is the overall system risk level. Since it is determined that the total system risk level has been raised to 2 after it has been determined to be 1, an alarm is not generated due to a malfunction or the like occurring in a certain detector, and the detection accuracy is improved. be able to.

  Further, according to the slope failure prediction system using the soil moisture level detection device according to the present invention, the ultrasonic wave guide of the detector is exposed in the soil so that its sealed end is exposed above the ground surface. Since the wiring of the ultrasonic transmission element and ultrasonic reception element of the detector is pulled out from the sealed side end of the ultrasonic waveguide to the outside, the wiring is also exposed above the ground surface. It is easy to perform an operation of connecting this wiring to a control unit or the like.

  Further, according to the slope failure prediction system using the soil moisture level detection device according to the present invention, the ultrasonic waveguide of the detector is embedded in the soil so that the whole is positioned below the ground surface. Therefore, the detector can be installed at a deep position from the ground surface regardless of the length of the ultrasonic waveguide.

  Further, according to the slope failure prediction system using the soil moisture level detector according to the present invention, the standard soil is spread on the opening side end of the ultrasonic waveguide of the detector, so The reflected state of the sound wave is stable, and the ultrasonic wave receiving element can receive a reflected wave with sufficient intensity.

The schematic diagram which shows the structure of the slope failure prediction system 1 in 1st Example of this invention. The schematic longitudinal cross-sectional view which shows the detector 5 which comprises the moisture-water level detection apparatus 3 in a soil. FIG. 6 is a schematic longitudinal sectional view showing a modification of the detector 5. Explanatory drawing for demonstrating the effect of the modification of the detector 5. FIG. The schematic longitudinal cross-sectional view which shows the other example of installation of the detector 5. FIG. The schematic longitudinal cross-sectional view which shows the other example of installation of the detector 5. FIG. The block diagram which shows the structure of the measuring device 6 which comprises the moisture water level detection apparatus 3 in a soil. The schematic longitudinal cross-sectional view for demonstrating the raise of the groundwater level surface 33. FIG. The figure which shows the relationship between the state of soil, and the waveform of the reflected wave 32. FIG. The figure which showed an example of the relationship between the elapsed time after raining began, and the maximum amplitude of the reflected wave 32, and an example of the relationship between the said elapsed time and the propagation time of the ultrasonic wave 30. The schematic diagram which shows the structure of the slope failure prediction system 40 which concerns on 2nd Example. FIG. 12 is a partially enlarged vertical sectional view in which the detector 5 and the temperature corrector 43 in FIG. 11 are enlarged. The schematic longitudinal cross-sectional view which shows the modification of the detector 5 and the temperature corrector 43. FIG. The schematic diagram which shows the structure of the slope failure prediction system 50 which concerns on 3rd Example. The block diagram which shows the structure of the measuring device 53. FIG.

  First, the slope failure prediction system according to the first embodiment of the present invention will be described. FIG. 1 is a schematic diagram showing a configuration of a slope failure prediction system 1 according to the first embodiment. The slope failure prediction system 1 is installed on a target slope 2 to detect a soil moisture level and a groundwater level, a soil moisture level detector 3, and a slope based on the detection result of the soil moisture level detector 3. And an alarm device 4 that issues an alarm indicating that the risk of collapse is high. The slope 2 on which the soil moisture level detector 3 is installed may be a natural slope such as a mountainous area or an artificially constructed slope.

  As shown in FIG. 1, the soil moisture level detector 3 has one detector 5 embedded in the slope 2 and a measuring device 6 electrically connected to the detector 5. doing. On the other hand, the alarm device 4 is a means that can recognize a dangerous state by appealing to the sight, hearing, smell, etc. of the system user. For example, a warning lamp, a liquid crystal display screen, a speaker appealing to hearing, etc. It is possible to use.

  FIG. 2 is a schematic longitudinal cross-sectional view showing the detector 5 constituting the soil moisture level detector 3. The detector 5 is provided with an ultrasonic transducer 8 (ultrasonic transmitting element and ultrasonic receiving element) via a damper material 7 on one end side inside the hollow ultrasonic waveguide 6. Here, the ultrasonic waveguide 6 is obtained by attaching a lid member 10 to a tubular waveguide body 9 having both ends opened, with its one end side opening being closed. Here, the waveguide body 9 is a brass pipe having a length of about 30 cm to 2 m, and has an inner diameter of about 18 mm and an outer diameter of about 22 mm. And the inner peripheral surface of this waveguide main body 9 is formed smoothly, and when the ultrasonic wave which propagates inside collides, it is easy to reflect in a fixed direction, without being scattered. In addition, an air discharge hole 34 for discharging the air inside the ultrasonic waveguide 6 to the outside so as to incline upward from the outside to the inside on the one end side of the waveguide body 9. It is formed through. Although not shown in detail in FIG. 2, a plurality of air discharge holes 34 are formed along the circumferential direction of the waveguide body 9, and even if any air discharge hole 34 is clogged with soil, Air is discharged from the other air discharge holes 34. On the other hand, the lid member 10 is a brass member having a cylindrical shape, and has a diameter that is approximately the same as the outer diameter of the waveguide body 9. The lid member 10 has a wiring lead hole 11 formed through the central portion thereof, and an aluminum plate 12 is attached to cover the inner surface of the lid member 10. As a result, one end of the ultrasonic waveguide 6 is sealed by the aluminum plate 12 regardless of the presence of the wiring lead-out hole 11. The material, cross-sectional shape, length, and the like of the waveguide body 9 are not limited to the present embodiment, and can be changed in design as appropriate. The lid member 10 and the aluminum plate 12 can also be changed in design accordingly. is there.

  On the other hand, the ultrasonic transducer 8 that constitutes the detector 5 is a device that converts an electric signal and mechanical vibration into energy by the piezoelectric effect, and as shown in FIG. 2, a transmission / reception element that transmits or receives ultrasonic waves. Part 13 and wiring 14 drawn from the element part. Although the transmitter / receiver element unit 13 is not shown in detail in the drawing, an element that combines ultrasonic transmission and ultrasonic reception is arranged on a semiconductor substrate, and when an electric signal of a certain frequency is given, While the ultrasonic transmission element outputs the ultrasonic wave of that frequency, when the ultrasonic reception element receives the ultrasonic wave of a certain frequency, the electric signal of that frequency is output. As shown in FIG. 2, the ultrasonic transducer 8 configured as described above has its transmitting / receiving element portion 13 fixed to the aluminum plate 12 covering the inner surface of the lid member 10 via the damper material 7. Yes. The damper material 7 is made of, for example, silicone rubber, and prevents the vibration of the ultrasonic transducer 8 from being transmitted to the ultrasonic waveguide 6 or the vibration of the ultrasonic waveguide 6 is ultrasonic transducer. 8 is prevented. A wiring 14 extending from the transmitting / receiving element portion 13 is inserted through the damper material 7 and the aluminum plate 12, and is drawn out of the ultrasonic waveguide 6 through the wiring drawing hole 11 of the lid member 10.

  In the present embodiment, a single ultrasonic transducer 8 having both a transmission function and a reception function is used in consideration of a mounting space for the ultrasonic waveguide 6 and the like. However, the present invention is not limited to this, for example, as shown in FIG. 3, a transmission-dedicated ultrasonic transducer 16 in which only an ultrasonic transmission element (not shown) is arranged on one end side inside the ultrasonic waveguide 15, A reception-only ultrasonic transducer 17 in which only a sound wave receiving element (not shown) is arranged may be provided side by side. In this case, ultrasonic waves are transmitted from the transmission-dedicated ultrasonic transducer 16, and the reflected waves are received by the reception-dedicated ultrasonic transducer 17. Thus, when the transmission-dedicated ultrasonic transducer 16 and the reception-dedicated ultrasonic transducer 17 are provided separately, there is an advantage that the moisture content in the soil and the groundwater level can be detected accurately. That is, when the ultrasonic transducers 16 and 17 dedicated for transmission and reception are separately provided, as shown in FIGS. 4A and 4B, the waveform of the transmitted ultrasonic wave (transmission waveform 18) and the waveform of the received reflected wave ( Since the received waveform 19) is detected separately without overlapping, the maximum amplitude of the reflected wave and the propagation time of the ultrasonic wave can be accurately measured. On the other hand, when the transmission / reception ultrasonic transducer 8 is used, if the time from transmission to reception is short, the reception waveform 19 is detected closer to the origin, so that the transmission waveform 18 is large as shown in FIG. 4C. It will overlap. This makes it difficult to distinguish between the transmission waveform 18 and the reception waveform 19, and it is difficult to measure the maximum amplitude of the reflected wave and the propagation time of the ultrasonic wave, as will be described later.

  As shown in FIG. 2, the detector 5 configured as described above is installed on the slope 2 in a state of being embedded in the soil 21 with the opening-side end 20 of the ultrasonic waveguide 6 facing down. The Here, since the ultrasonic wave guide 6 propagates ultrasonic waves through the air inside the ultrasonic wave guide 6, when the detector 5 is embedded in the soil 21, the ultrasonic wave guide 6 is placed inside the ultrasonic wave guide 6. It is necessary to prevent dirt from entering. In this embodiment, the procedure for embedding the detector 5 in the soil 21 is not shown in detail in the figure, but in consideration of the installation depth of the detector 5, an installation hole is previously excavated on the slope 2, The ultrasonic wave guide 6 is embedded in the soil 21 by placing the detector 5 in the installation hole and refilling the excavated soil. Then, the lid member 10 is removed from the ultrasonic waveguide 6, and a long rod-like member is inserted from the upper end opening of the waveguide main body 9, so that the soil that has entered the inside of the waveguide main body 9 is removed from the lower end opening. Push out. And after pulling out the rod-shaped member from the waveguide main body 9, the cover member 10 is attached again. By such a procedure, the ultrasonic waveguide 6 can be embedded in the soil 21 so that the soil does not enter inside.

  When the detector 5 is embedded in the soil 21, as shown in FIG. 2, the upper end portion of the ultrasonic waveguide 6, that is, the sealed end portion 23 is slightly exposed above the ground surface 22. deep. In this way, the wiring 14 drawn out from the wiring lead-out hole 11 is also exposed above the ground surface 22, so that when the wiring 14 is connected to the measuring instrument 6 shown in FIG. Compared with the case where the buried wiring 14 is pulled out to the ground and then connected to the measuring instrument 6, there is an advantage that the connection work is easy to perform. Furthermore, if the air discharge hole 34 formed in the waveguide main body 9 is also exposed above the ground surface 22, it is preferable that the air inside the ultrasonic waveguide 6 is easily discharged to the outside.

  When embedding the detector 5 in the soil 21, as shown in FIG. 5, the ultrasonic wave guide 6 is also positioned below the ground surface 22 so that the hermetically sealed end 23 of the ultrasonic wave guide 6 is positioned below the ultrasonic wave guide. The entire pipe 6 may be embedded in the soil 21. In this way, there is an advantage that the detector 5 can be installed at a deep position from the ground surface 22 regardless of the length of the ultrasonic waveguide 6.

  Further, when the detector 5 is embedded in the soil 21, as shown in FIG. 6, the standard soil 24 is spread on the bottom of the installation hole, and the lower end opening of the ultrasonic waveguide 6 is in close contact with the standard soil 24. It is preferable to arrange the detector 5 as described above. The standard soil 24 means soil having a known particle size distribution of soil particles, for example, soil having a substantially constant particle size. The reason for spreading the standard soil 24 in this way is to stabilize the reflection state of the ultrasonic waves. That is, as will be described later, the ultrasonic transducer 8 receives the reflected wave that has been reflected and returned from the lower end portion of the ultrasonic waveguide 6 among the ultrasonic waves transmitted by itself. Here, if a clot having an irregular particle size is located at the lower end opening of the ultrasonic waveguide 6, the reflected state of the ultrasonic wave is not stable, and the ultrasonic transducer 8 has sufficient strength. The reflected wave cannot be received. On the other hand, when the standard soil 24 is laid down, the reflected state of the ultrasonic wave becomes stable, so that the ultrasonic transducer 8 can receive a reflected wave having a sufficient intensity.

  On the other hand, FIG. 7 is a block diagram showing the configuration of the measuring device 6 constituting the soil moisture level detection device 3. The measuring device 6 is configured such that an ultrasonic transmission circuit 26, an ultrasonic reception circuit 27, and a signal processing circuit 28 are connected via a system bus 29 to a control unit 25 that controls the operation of each unit. . Here, the ultrasonic transmission circuit 26 applies an electrical signal having a predetermined frequency to the ultrasonic transducer 8 shown in FIG. On the other hand, the ultrasonic receiving circuit 27 receives an electric signal having a predetermined frequency from the ultrasonic transducer 8 and outputs the electric signal to the signal processing circuit 28. The signal processing circuit 28 detects the amount of moisture in the soil and the groundwater level based on the electrical signal input from the ultrasonic receiving circuit 27.

  Next, detection of the amount of soil moisture and detection of the groundwater level by the soil moisture level detector 3 will be described. When an electrical signal having a predetermined frequency is applied to the ultrasonic transducer 8 of the detector 5 from the ultrasonic transmission circuit 26 of the measuring device 6 under the control of the control unit 25, as shown in FIG. An ultrasonic wave 30 having a predetermined frequency is transmitted from the transducer 8. The ultrasonic wave 30 propagates downward in the ultrasonic waveguide 6, hits the soil surface 31 located at the lower end of the ultrasonic waveguide 6, and is reflected. The reflected wave 32 propagates upward in the ultrasonic waveguide 6 and is received by the ultrasonic transducer 8. Then, the ultrasonic transducer 8 outputs an electric signal having a predetermined frequency, and the ultrasonic receiving circuit 27 of the measuring instrument 6 receives this electric signal and outputs it to the signal processing circuit 28. Then, the signal processing circuit 28 detects the amount of moisture in the soil and the groundwater level based on the input electric signal under the control of the control unit 25.

  Here, the signal processing circuit 28 detects the amount of moisture in the soil on the slope 2 based on the maximum amplitude of the reflected wave 32. More specifically, soil is composed of a soil particle portion and a gap portion. When the soil is in a dry state, most of the gap portion is occupied by air. Therefore, when the ultrasonic wave 30 hits such soil, the ultrasonic wave 30 hitting the soil particle part returns as a reflected wave 32, but the ultrasonic wave 30 hitting the gap part is reflected by passing through the part. It does not come back as wave 32. Thereby, the maximum amplitude of the reflected wave 32 becomes small. On the other hand, when the soil contains a lot of water, most of the gaps are occupied by water. Therefore, when the ultrasonic wave 30 hits such soil, not only the ultrasonic wave 30 hitting the soil particle part but also the ultrasonic wave 30 hitting the gap part returns as the reflected wave 32. Thereby, the maximum amplitude of the reflected wave 32 becomes large. As described above, the moisture content in the soil can be detected by detecting the maximum amplitude of the reflected wave 32.

  On the other hand, the signal processing circuit 28 detects the groundwater level of the slope 2 based on the propagation time of the ultrasonic wave 30, that is, the time from when the ultrasonic transducer 8 transmits the ultrasonic wave 30 until receiving the reflected wave 32. . More specifically, as shown in FIG. 2, while the groundwater level surface 33 is at a position lower than the soil surface 31, the ultrasonic wave 30 transmitted from the ultrasonic transducer 8 is transmitted by the soil surface 31 as described above. Reflected. However, when the groundwater level surface 33 rises due to rain or the like and rises above the soil surface 31 as shown in FIG. 8, the ultrasonic wave 30 transmitted from the ultrasonic transducer 8 is not the soil surface 31 but the groundwater level surface 33. Is reflected by. Accordingly, since the distance from the ultrasonic transducer 8 to the groundwater level surface 33 is shortened as the groundwater level surface 33 rises inside the ultrasonic waveguide 6, the propagation time of the ultrasonic wave 30 is gradually shortened. . As described above, the groundwater level can be detected by detecting the propagation time of the ultrasonic wave 30. When the groundwater level surface 33 enters the inside of the ultrasonic waveguide 6, the pushed air inside the ultrasonic waveguide 6 is discharged to the outside through the air discharge hole 34. Thereby, since the groundwater level surface 33 rises inside the ultrasonic waveguide 6 similarly to the outside, the groundwater level can be accurately detected inside the ultrasonic waveguide 6. Further, since the air discharge hole 34 is inclined upward from the outside to the inside of the ultrasonic waveguide 6 as described above, it passes through the air discharge hole 34 from the outside of the ultrasonic waveguide 6 when it rains. It is difficult for water to enter inside, and the groundwater level surface 33 can be accurately detected.

  Here, FIG. 9 is a diagram showing the relationship between the state of the soil and the waveform of the reflected wave 32. FIG. 9A is an example of the waveform of the reflected wave 32 when the soil is dry, and FIG. FIG. 9C shows an example of the waveform of the reflected wave 32 when the soil is flooded. In this specification, “dry state” means a state where there is no rainfall and the soil contains only a small amount of water, and “water-containing state” means that the soil contains a certain amount or more of water due to rain or the like. The level surface 33 is in a lower position than the soil surface 31, and the “flooded state” means a state in which the groundwater level surface 33 is higher than the soil surface 31.

  First, the propagation time of the ultrasonic wave 30 will be described with reference to FIG. 9. In the dry state of FIG. 9A and the water-containing state of FIG. 9B, the ultrasonic wave 30 that started transmission at time T0 returns as a reflected wave 32 at time T2. The propagation time of the ultrasonic wave 30 is the same as (T2-T0). On the other hand, in the flooded state of FIG. 9C, the ultrasonic wave 30 that started transmission at time T0 returns as the reflected wave 32 at time T1 earlier than time T2, and the propagation time of the ultrasonic wave 30 is (T1-T0). Therefore, it is shorter than the propagation time in a dry state or a water-containing state. This is because the distance from the ultrasonic transducer 8 to the groundwater level surface 33 becomes shorter as the groundwater level surface 33 rises as described above.

  Next, the maximum amplitude of the reflected wave 32 will be described with reference to FIG. 9. The maximum amplitude IB of the reflected wave 32 in the water-containing state shown in FIG. 9B is greater than the maximum amplitude IA of the reflected wave 32 in the dry state shown in FIG. 9A. large. This is because, as described above, the ultrasonic wave 30 is transmitted through the gap portion of the soil in the dry state, whereas the ultrasonic wave 30 is reflected also in the gap portion of the soil in the wet state. On the other hand, the maximum amplitude of the reflected wave 32 in the flooded state shown in FIG. 9C is larger than the maximum amplitude I2 of the reflected wave 32 in the wet state shown in FIG. 9B. This is because the propagation distance of the ultrasonic wave 30 is shortened as the groundwater level surface 33 rises. For example, the ultrasonic wave 30 is attenuated on the propagation path by being absorbed by the air in the ultrasonic wave guide 6. This is because the amount is reduced.

  Next, the procedure in which the slope failure prediction system 1 according to the present embodiment issues a warning based on the detection result of the soil water level detector 3 will be described. FIG. 10 is a diagram showing an example of the relationship between the elapsed time from the start of rain and the maximum amplitude of the reflected wave 32, and an example of the relationship between the elapsed time and the propagation time of the ultrasonic wave 30. In FIG. 10, the maximum amplitude of the reflected wave 32 is indicated by a one-dot chain line, and the propagation time of the ultrasonic wave 30 is indicated by a solid line. In FIG. 10, the maximum amplitude of the reflected wave 32 is a plot of the ratio when the measured value at the first measurement time, that is, the elapsed time of 0 minutes, is 1.0.

  First, in FIG. 10, the maximum amplitude of the reflected wave 32 is approximately 1.0 and changes substantially constant in the interval from 0 minute to approximately 180 minutes. This is because while the rainwater poured on the ground surface 22 is gradually infiltrated into the soil 21, the amount of moisture in the soil does not change at the position of the lower end of the detector 5, and the ultrasonic wave reflected at the gap portion of the soil This is because the amount of 30 is constant. Here, the control unit 25 of the measuring device 6 determines that the soil is in a dry state while the maximum amplitude of the reflected wave 32 does not reach the predetermined threshold value S. On the other hand, in this section in the dry state, the propagation time of the ultrasonic wave 30 is also approximately constant at about 2.7. This is because the groundwater level surface 33 is still at a position lower than the soil surface 31, and the ultrasonic wave 30 transmitted from the ultrasonic transducer 8 is always reflected by the soil surface 31, so that the propagation distance of the ultrasonic wave 30 is constant. is there.

  Thereafter, when the elapsed time exceeds about 180 minutes in FIG. 10, the maximum amplitude of the reflected wave 32 starts to increase. This is because the amount of the ultrasonic wave 30 reflected by the gap portion gradually increases as the gap portion of the soil is gradually occupied by moisture as described above. Then, when the maximum amplitude of the reflected wave 32 reaches a predetermined threshold value S, the control unit 25 of the measuring device 6 determines that the soil has shifted from the dry state to the water-containing state. On the other hand, the propagation time of the ultrasonic wave 30 continues to be constant at about 2.7, as in the dry state section, even when the soil shifts from the dry state to the water-containing state. This is because the groundwater level surface 33 is still lower than the soil surface 31 shown in FIG.

  Thereafter, the maximum amplitude of the reflected wave 32 continues to increase until reaching about 1.4 at an elapsed time of about 220 minutes in FIG. 10, and then increases gradually. Here, the control unit 25 always shows that the maximum amplitude of the reflected wave 32 increases and the propagation time of the ultrasonic wave 30 changes constantly in a dry state or a water-containing state where there is a low risk of slope failure. By monitoring, it can be confirmed that the slope failure prediction system 1 is operating normally.

  Thereafter, when the elapsed time in FIG. 10 exceeds about 500 minutes, the propagation time of the ultrasonic wave 30 starts to decrease. This is because the groundwater level surface 33 becomes higher than the soil surface 31 shown in FIG. 8, and the ultrasonic wave 30 transmitted from the ultrasonic transducer 8 is reflected by the groundwater level surface 33 instead of the soil surface 31. This is because the propagation distance of the ultrasonic wave 30 gradually decreases as the groundwater level surface 33 rises. Here, the control unit 25 of the measuring instrument 6 determines that the soil has shifted from the water-containing state to the flooded state when the propagation time of the ultrasonic waves 30 starts to decrease. And the control part 25 judges that there exists a possibility that the slope 2 which installed the detector 5 may collapse with the transfer to this inundation state, and controls the said alarm device 4, and it is a slope with respect to a system user. An alarm is issued to notify that there is a risk of collapse. Thereby, the system user can predict the occurrence of slope failure and take measures such as evacuation in advance.

  On the other hand, with the transition to the flooded state, the maximum amplitude of the reflected wave 32 starts to increase from before the transition. This is because the amount of attenuation on the path decreases as the groundwater level surface 33 rises and the propagation distance becomes shorter.

  Thereafter, until the elapsed time reaches about 560 minutes in FIG. 10, the propagation time of the ultrasonic wave 30 continues to decrease, while the maximum amplitude of the reflected wave 32 continues to increase. Thereafter, both the propagation time of the ultrasonic wave 30 and the maximum amplitude of the reflected wave 32 are not detected. This is because the ultrasonic transducer 8 does not receive the reflected wave 32 when the groundwater level surface 33 rises and reaches near the position of the ultrasonic transducer 8. It is assumed that the soil immersion state continues even after the propagation time of the ultrasonic wave 30 and the maximum amplitude of the reflected wave 32 are not detected.

  In this embodiment, the alarm is issued simultaneously with the transition to the flooded state, but the timing of issuing the alarm is not limited to this, and may be determined by introducing the concept of “risk level”, for example. More specifically, the control unit 25 measures the elapsed time from the start point of the water-containing state, and when the water-containing state continues continuously for a predetermined time t0, the collapse risk of the slope 2 is “risk level 1”. Is determined. And the control part 25 performs the elapsed time measurement after the slope 2 becomes the danger level 1. FIG. Thereafter, the control unit 25 determines that the collapse risk of the slope 2 has increased to “risk level 2” at the time of transition to the flooded state. And the control part 25 measures the elapsed time t2 after the slope 2 becomes the danger level 2. FIG. Based on the above measurement, the time t1 when the risk level 1 continues, that is, the time t1 from when the slope 2 becomes the risk level 1 to the risk level 2, and the current level after the risk level 2 is reached. When it is determined that the relationship with the elapsed time t2 has reached a certain relationship, the control unit 25 controls the alarm device 4 to issue an alarm. An arbitrary relationship can be set as the relationship between the duration t1 of the risk level 1 and the elapsed time t2 of the risk level 2.

  Next, the slope failure prediction system 40 according to the second embodiment of the present invention will be described. FIG. 11 is a schematic diagram illustrating a configuration of a slope failure prediction system 40 according to the second embodiment. The slope failure prediction system 40 is installed on the target slope 2 and detects a soil moisture level and a groundwater level. The slope moisture level detection device 41 detects a slope based on the detection result of the soil moisture level detection device 41. And an alarm device 42 that issues an alarm indicating that the risk of collapse is high. When this embodiment is compared with the first embodiment, the structure of the soil moisture level detection device 41 is different, but the configuration of the alarm device 42 is the same as that of the alarm device 4 of the first embodiment, so it will be described here. Is omitted.

  As shown in FIG. 11, the soil moisture / water level detection device 41 is installed by being embedded in the slope 2 at a position adjacent to the detector 5 embedded in the slope 2 and adjacent to the detector 5. The temperature corrector 43 and the measuring device 6 electrically connected to the detector 5 and the temperature corrector 43 are provided. Since the detector 5 and the measuring device 6 have the same configuration as in the first embodiment, the same reference numerals as those in FIG. 1 are given in FIG. 11 and the description thereof is omitted here.

  FIG. 12 is a partially enlarged longitudinal sectional view in which the detector 5 and the temperature corrector 43 in FIG. 11 are enlarged. The temperature corrector 43 is for correcting the temperature of the detector 5. More specifically, the ultrasonic transducer 8 constituting the detector 5 has an element for both ultrasonic transmission and reception as described above, but its transmission characteristics and reception characteristics have a large temperature dependence. . Therefore, it is preferable to perform temperature correction on the transmission characteristics and the reception characteristics as long as these are used outdoors where the temperature changes drastically and the maximum amplitude of the reflected wave 32 and the propagation time of the ultrasonic wave 30 are detected. Here, as shown in FIG. 12, the temperature corrector 43 is a detector 5 in that an ultrasonic transducer 8 is provided on one end side inside a hollow ultrasonic waveguide 44 via a damper material 7. The configuration of the ultrasonic waveguide 44 is different from that of the detector 5. That is, the ultrasonic wave guide 44 of the temperature compensator 43 has a lid body 46 attached to a wave guide body 45 having the same length as the wave guide body 9 of the detector 5 with its both end openings closed. Is. In addition, the air discharge hole 34 is not formed in the waveguide main body 45 unlike the waveguide main body 9 of the detector 5, but in order to eliminate the influence of the internal pressure fluctuation due to the temperature change, An air discharge hole 34 may be formed in the tube body 45.

  The temperature compensator 43 configured in this manner has an end on the side where the ultrasonic transducer 8 is provided, and is parallel to the detector 5 with a predetermined distance therebetween, to the same depth as the detector 5. It is installed on the slope 2 in a state embedded in the middle 21. At this time, a small amount of soil 47 having a known property is spread on the inner side surface of the lid member 46 located at the lower end of the ultrasonic waveguide 44. Thereby, the ultrasonic wave 30 transmitted from the ultrasonic transducer 8 is reflected not by the lid member 46 but by the surface of the soil 47 spread. As the soil 47, for example, a soil having the same composition as the soil existing on the soil surface 31 of the detector 5 may be used. In this way, by installing the temperature corrector 43 in the soil 21 in substantially the same state as the detector 5, the maximum amplitude of the reflected wave 32 and the propagation time of the ultrasonic wave 30 are detected under the same temperature conditions as the detector 5. can do. Furthermore, the temperature corrector 43 is not affected by the change in the amount of moisture in the surrounding soil and the change in the groundwater level due to the presence of the lid member 46 attached to the lower end of the ultrasonic waveguide 44. Therefore, according to the temperature corrector 43, the maximum amplitude of the reflected wave 32 and the propagation time of the ultrasonic wave 30 can be detected in a state where only the influence of the temperature change is received.

  Next, temperature correction of the detector 5 by the temperature corrector 43 will be described. When an electrical signal having a predetermined frequency is applied from the ultrasonic transmission circuit 26 of the measuring device 6 to the ultrasonic transducer 8 of the temperature corrector 43 under the control of the control unit 25 of the measuring device 6, as shown in FIG. In addition, an ultrasonic wave 30 having a predetermined frequency is transmitted from the ultrasonic transducer 8. The ultrasonic waves 30 propagate downward in the ultrasonic waveguide 44 and are reflected by the soil 47 spread on the inner surface of the lid member 46. The reflected wave 32 propagates upward in the ultrasonic waveguide 44 and is received by the ultrasonic transducer 8. Then, the ultrasonic transducer 8 outputs an electric signal having a predetermined frequency, and the ultrasonic receiving circuit 27 of the measuring instrument 6 receives this electric signal and outputs it to the signal processing circuit 28. The signal processing circuit 28 corrects the temperature of the output value of the detector 5 by, for example, dividing the output value of the detector 5 by the output value of the temperature corrector 43 under the control of the control unit 25. In this manner, the maximum amplitude of the reflected wave 32 and the propagation time of the ultrasonic wave 30 can be temperature-corrected.

  Although the temperature corrector 43 is provided separately from the detector 5 in this embodiment, the temperature corrector 43 may be provided integrally with the detector 5 as shown in FIG. When the detector 5 and the temperature corrector 43 are integrally configured as described above, the detector 5 and the temperature corrector 43 are compared with the case where the detector 5 and the temperature corrector 43 are installed apart from each other by a predetermined distance. Therefore, there is an advantage that the temperature of the detector 5 can be corrected more accurately. In addition, the configuration in which the detector 5 and the temperature corrector 43 are integrally formed has an advantage that the installation work is simplified as compared with the case where the detector 5 and the temperature corrector 43 are separately embedded in the soil 21. is there.

  Next, a slope failure prediction system 50 according to a third embodiment of the present invention will be described. FIG. 14 is a schematic diagram showing a configuration of a slope failure prediction system 50 according to the third embodiment. The slope failure prediction system 50 is installed on the target slope 2 and detects the soil moisture level and the groundwater level. The soil moisture level detector 51 detects the slope based on the detection result of the soil moisture level detector 51. And an alarm device 52 that issues an alarm indicating that the risk of collapse is high. When this embodiment is compared with the first embodiment, the configuration of the soil moisture level detector 51 and the procedure for issuing an alarm are different, but the configuration of the alarm device 52 is the same as that of the alarm device 4 of the first embodiment. Therefore, the description is omitted here.

  The soil moisture level detector 51 includes a plurality of detectors 5 embedded in different positions on the slope 2 and measuring devices 53 electrically connected to the detectors 5 respectively. Yes. Here, since the configuration and the installation method of each detector 5 are the same as those in the first embodiment, the same reference numerals as those in the first embodiment are used, and the description thereof is omitted here. Similar to the second embodiment, a temperature corrector 43 for correcting the temperature of each detector 5 may be provided separately. Further, in this embodiment, the length of each detector 5 is changed variously so that the tip reaches a different depth position from the ground surface 22, and the moisture in the soil at a different depth position in each detector 5. Volume and groundwater level are detected. Of course, the present invention is not limited to this, and each detector 5 may detect the moisture content in the soil and the groundwater level at the same depth.

  On the other hand, FIG. 15 is a block diagram showing the configuration of the measuring instrument 53. In the measuring device 53, an ultrasonic transmission circuit 55, an ultrasonic reception circuit 56, a multiplexer 57, and a signal processing circuit 58 are connected to a control unit 54 that controls the operation of each unit via a system bus 59. It is a thing. Here, the ultrasonic transmission circuit 55 applies an electrical signal having a predetermined frequency to the ultrasonic transducer 8 shown in FIG. On the other hand, the ultrasonic receiving circuit 56 receives an electrical signal having a predetermined frequency from the ultrasonic transducer 8 and outputs it to the signal processing circuit 58. Further, the multiplexer 57 outputs the electrical signals input from the plurality of detectors 5 to the ultrasonic receiving circuit 56 while switching appropriately, or detects the plurality of electrical signals input from the ultrasonic transmitting circuit 55 while switching appropriately. 5 is output. The signal processing circuit 58 detects the moisture content in the soil and the groundwater level based on the electrical signal input from the ultrasonic receiving circuit 56.

  Next, a procedure in which the slope failure prediction system 50 according to the present embodiment issues an alarm based on the detection result of the soil water level detector 51 will be described. For each detector 5, the relationship between the elapsed time from the start of rain and the maximum amplitude of the reflected wave 32 and the relationship between the elapsed time and the propagation time of the ultrasonic wave 30 are the same as in the first embodiment. Therefore, it demonstrates using FIG.

  The control unit 54 of the measuring device 53 observes the trends of, for example, N detectors 5 installed on one slope 2 and detects that the water-containing state shown in FIG. 10 continues for a time t0 or more. If it is determined that the number of vessels 5 has gradually increased and the number has reached a predetermined number N1, it is determined that the collapse risk of the slope 2 has reached the “total system risk level 1”. Thereafter, the control unit 54 continuously observes the trend of each detector 5, and among the N1 detectors 5, the number of detectors 5 that have shifted to the flooded state shown in FIG. 10 has reached a predetermined N2. If it is determined that the risk of collapse of the slope 2 has risen to "the overall system risk level 2".

  Then, the control unit 54 determines that the slope 2 may collapse at the time when the risk of collapse of the slope 2 passes the overall system risk level 1 and then rises to the overall system risk level 2. Then, an alarm is issued to the system user by controlling the alarm device 52. As described above, by determining the state of the slope 2 based on the detection results of the plurality of detectors 5, an alarm is not generated due to a malfunction or the like occurring in one detector 5, and the detection accuracy is improved. Can be made.

  In the present embodiment, an alarm is issued when the risk of collapse of the slope 2 reaches the overall system risk level 2 after reaching the overall system risk level 1. However, the present invention is not limited to this. An alarm may be issued only when the risk of collapse of the system reaches the overall system risk level 2. In this case, the controller 54 does not depend on whether or not the risk of collapse of the slope 2 has reached the entire system risk level 1, that is, the detector 5 in which the water-containing state continues continuously over the time t0. Regardless of whether or not the number of detectors reaches N1, only the fact that the risk of collapse of the slope 2 has reached the entire system risk level 2, that is, the number of detectors 5 that have entered the flooded state is N2. An alarm is issued only when it is reached. In this way, it is preferable that only the fact that the overall system risk level 2 has been reached is a trigger because the processing by the control unit 54 can be simplified, but a detector that suddenly enters a flooded state without passing through a water-containing state. It is preferable to add the fact that the overall system risk level 1 has been reached as described above to the trigger in that the influence of the malfunction 5 can be eliminated.

  As described above, according to the slope failure prediction system according to the present invention, it is possible to detect both the soil moisture content and the groundwater level by a single soil moisture level detector. Therefore, compared with the case where the device for detecting the amount of moisture in the soil and the device for detecting the groundwater level are separately installed on the slope, the device installation work can be simplified and the cost can be reduced. In addition, when there is a low risk of slope failure, that is, when the soil is dry or wet, the system operates normally by constantly monitoring the maximum amplitude of reflected waves and the propagation time of ultrasonic waves. Can be confirmed.

  In addition, this slope failure prediction system is not only used for prediction of slope failure due to rainfall, but also, for example, slope failure caused by snowmelt water, that is, a slope caused by water that has melted snow on a sunny day in spring. It can also be used to predict collapse.

DESCRIPTION OF SYMBOLS 1 Slope failure prediction system 3 Underwater moisture level detector 5 Detector 6 Ultrasonic wave guide 8 Ultrasonic transducer (ultrasonic transmitting element and ultrasonic receiving element)
20 Opening End 21 Underground 25 Control Unit 30 Ultrasonic 31 Soil Surface 32 Reflected Wave 33 Groundwater Level Surface 34 Air Exhaust Hole

Claims (7)

An ultrasonic waveguide having one end sealed and the other end opened, the waveguide being embedded in the soil so that the soil does not enter the interior with the opening side down, and the inside of the ultrasonic waveguide An ultrasonic transmission element that transmits ultrasonic waves toward the opening side, and an ultrasonic transmission element that is provided on the sealing side inside the ultrasonic waveguide and transmits from the ultrasonic transmission element. Among them, a detector having an ultrasonic receiving element that receives a reflected wave that is reflected by the ground surface at the opening side end or reflected by the groundwater level surface that has entered the ultrasonic waveguide and returned. ,
While detecting the moisture content in the soil near the opening side end of the ultrasonic waveguide based on the maximum amplitude of the reflected wave received by the ultrasonic receiving element, the position of the groundwater level in the soil, A soil moisture level detection device is installed on the slope, comprising: a control unit that detects based on a propagation time required from when the ultrasonic transmission element transmits ultrasonic waves to when the ultrasonic reception element receives the reflected waves. And
In the slope failure prediction system using the moisture level detector in the soil, the control unit issues a warning that the slope is likely to collapse based on the detection result of the maximum amplitude of the reflected wave and the propagation time. There,
The ultrasonic waveguide of the detector is embedded in the soil so that its entirety is located below the ground surface ;
When one soil moisture level detector is installed and the control unit continues the state in which the maximum amplitude of the reflected wave reaches a predetermined value or more continuously for a predetermined time or more, there is a risk of the slope collapse. After determining that the risk level 1 has been reached, when the propagation time starts to decrease, it is determined that the slope collapse risk has increased to the risk level 2, and the time that the risk level 1 has continued and A slope failure prediction system using a soil moisture level detection device, characterized in that the alarm is issued based on a relationship with an elapsed time since the risk level 2 is reached. An ultrasonic waveguide having one end sealed and the other end opened, the waveguide being embedded in the soil so that the soil does not enter the interior with the opening side down, and the inside of the ultrasonic waveguide An ultrasonic transmission element that transmits ultrasonic waves toward the opening side, and an ultrasonic transmission element that is provided on the sealing side inside the ultrasonic waveguide and transmits from the ultrasonic transmission element. Among them, a detector having an ultrasonic receiving element that receives a reflected wave that is reflected by the ground surface at the opening side end or reflected by the groundwater level surface that has entered the ultrasonic waveguide and returned. ,
While detecting the moisture content in the soil near the opening side end of the ultrasonic waveguide based on the maximum amplitude of the reflected wave received by the ultrasonic receiving element, the position of the groundwater level in the soil, A soil moisture level detection device is installed on the slope, comprising: a control unit that detects based on a propagation time required from when the ultrasonic transmission element transmits ultrasonic waves to when the ultrasonic reception element receives the reflected waves. And
In the slope failure prediction system using the moisture level detector in the soil, the control unit issues a warning that the slope is likely to collapse based on the detection result of the maximum amplitude of the reflected wave and the propagation time. There,
The ultrasonic waveguide of the detector is embedded in the soil so that its entirety is located below the ground surface;
The number of the soil moisture level detectors in which a plurality of the soil moisture level detectors are installed, and the controller continues the state where the maximum amplitude of the reflected wave has reached a predetermined value or more continuously for a predetermined time or more. When the N1 reaches N1, it is determined that the slope collapse risk has reached the entire system risk level 1, and then the soil moisture level detection device of the N1 that has started to decrease the propagation time of the N1 When the number reaches N2, it is determined that the risk of collapse of the slope has increased from the overall system risk level 1 to the overall system risk level 2, and the alarm is issued. Slope failure prediction system using The soil moisture level detector is a tubular member sealed at both ends, and is embedded in the soil to the same depth position substantially parallel to the ultrasonic waveguide of the detector, An ultrasonic transmission element that is provided on the upper end side inside the ultrasonic waveguide and that transmits ultrasonic waves toward the lower end side, and that is provided on the upper end side in the ultrasonic waveguide and that transmits the ultrasonic wave Among the ultrasonic waves transmitted from the element, an ultrasonic wave receiving element that receives a reflected wave that has been reflected and returned from the surface of the soil, which is preliminarily spread on the inner bottom surface of the ultrasonic waveguide, A temperature corrector having
The control unit corrects the temperature of the maximum amplitude and the propagation time of the reflected wave detected by the detector based on the maximum amplitude and the propagation time of the reflected wave detected by the temperature corrector. Item 3. A slope failure prediction system using the soil moisture level detection device according to item 1 or 2. 4. The slope failure prediction system using a soil moisture level detection apparatus according to claim 3 , wherein the temperature corrector is integrated with the detector. The ultrasonic waveguide of the detector, soil moisture level detection device according to any one of claims 1 to 4, characterized in that the air discharge hole for discharging the internal air to the outside is formed Slope failure prediction system using The soil water level detection device according to claim 5 , wherein the air discharge hole is formed so as to be inclined upward from the outside to the inside of the ultrasonic waveguide of the detector. There was a slope failure prediction system. The soil water level detection in the soil according to any one of claims 1 to 6 , wherein a standard soil having a known particle size distribution is laid on the opening side end of the ultrasonic waveguide of the detector. Slope failure prediction system using equipment.

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