Soil permeability estimation device, soil permeability estimation system, and soil permeability estimation method

Abstract

Provided are a soil permeability estimation device, a soil permeability estimation system, and a soil permeability estimation method that can estimate the permeability of soil, i.e., how easily air flows out of an outlet into the soil. [Solution] The soil permeability estimation device 4 of the present invention is a soil permeability estimation device 4 that estimates the permeability of an inserted soil layer by being lowered from above the soil until its lower end 6c is inserted into the soil, and is equipped with a tube body 6 that forms a hollow cylinder, the tube body having an outlet 11 formed at its lower part that passes through from the inside to the outside, a piston 8 that is slidable up and down within the tube body and separates a lower compartment 6b and an upper compartment, the piston 8 applying pressure to the lower compartment 6b due to inertia when descending when the tube body comes to rest on the soil, and a pressure sensor 10 that is provided within the tube body and measures the pressure within the tube body.

Description

[Technical Field]

[0001] The present invention relates to a soil permeability estimation device, a soil permeability estimation system, and a soil permeability estimation method. [Background technology]

[0002] It has been known for some time that landslides and sediment runoff generally occur when the soil absorbs a lot of water due to continuous rainfall, etc. Furthermore, as shown in Patent Document 1, it is known that work machines are more likely to be affected by landslides in areas where the geology is relatively weak than in areas where the geology is relatively hard. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-129434 [Patent Document 2] Japanese Patent Application Publication No. 7-113733 Summary of the Invention [Problem to be solved by the invention]

[0004] As mentioned above, it is expected that if soil becomes more porous due to the incorporation of a large amount of water, and the soil becomes relatively fragile, the risk of landslides and other sediment disasters will increase. Therefore, technology for measuring soil hardness, such as that described in Patent Document 2, has been studied. However, there are risks involved in sending workers to sites in mountainous areas where landslides are likely to occur to conduct soil surveys, and there are also problems with the effort and difficulty involved for workers to physically reach measurement points in mountainous areas, etc. Also, checking the soil on river banks, etc. when the river water level is rising poses safety risks to workers.

[0005] In response to such problems, the inventors of the present invention provide a soil air permeability estimation device that can estimate the air permeability, i.e., how easily air flows out of the soil from the outlet, in a relatively simple manner.

[0006] The present invention has been made to solve such problems, and aims to provide a soil permeability estimation device, a soil permeability estimation system, and a soil permeability estimation method that can estimate the permeability of soil, i.e., how easily air flows out of an outlet, into the soil, in a relatively simple manner. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, according to one embodiment of the present invention, there is provided a soil permeability estimation device that estimates the permeability of an inserted soil layer by being lowered from above the soil so that its lower end is inserted into the soil, the device comprising: a tube body that forms a hollow cylinder, the tube body having an outlet formed at its lower part that penetrates from the inside to the outside; a piston that can slide up and down within the tube body and that separates a lower compartment and an upper compartment, the piston applying pressure to the lower compartment due to the inertia of the piston as it descends when the tube body stops on the soil; and a pressure sensor that is provided within the tube body and measures the pressure within the tube body. According to one embodiment of the present invention, the soil permeability estimation device estimates the permeability of a soil layer by lowering the tube body from above the soil until its lower end is inserted into the soil. The tube body of the soil permeability estimation device is lowered from above the soil until its lower end is inserted into the soil. During this process, the piston moves downward due to inertia during the downward movement, exerting pressure on the lower compartment within the tube body. Air in the lower compartment within the tube body is released into the soil through an outlet. The permeability of the soil layer into which the tube body is inserted can be estimated by measuring pressure changes within the tube body with a pressure sensor. For example, the permeability of the soil layer can be estimated without the need for workers to reach the site, even in cases where the site is difficult for workers to reach and there is a risk of landslides. Furthermore, since measurements can be performed without the need for workers to reach the site, even if a measurement cannot be completed for some reason, retrying the measurement is easy. Estimating the permeability of the soil layer to a certain extent can contribute to determining the risk of landslides. For example, a simple soil permeability estimation device can be provided that allows workers to perform measurements without reaching the site.

[0008] According to one embodiment of the present invention, the piston is preferably connected to the cylindrical body by an elastic means. According to one embodiment of the present invention configured in this manner, the piston is maintained within the cylindrical body at an initial position within the cylindrical body in the initial state before descending, and when the cylindrical body is inserted into the soil, the piston can apply pressure to the lower section due to the inertia of the piston as it descends against the stop of the cylindrical body.

[0009] According to one embodiment of the present invention, the piston is preferably formed to have a weight within a range of 500 g to 2000 g. According to one embodiment of the present invention configured as described above, the piston is formed to have a weight within a range of 500 g to 2000 g, and the piston can apply a predetermined pressure to the lower section by inertia when it descends relative to the stop of the cylindrical body. Also, for example, the pressure applied to the lower section can be set within a predetermined range, making it easier to estimate the permeability of the soil.

[0010] According to one embodiment of the present invention, the lower end of the cylindrical body is preferably formed in a downwardly pointing cone shape. According to one embodiment of the present invention configured as described above, the lower end of the tube body is formed in a downward cone shape. This makes it easier for the tube body to be lowered from above the soil and for the lower end to be inserted into the soil. This makes it easier to more reliably measure the permeability of the soil at a desired point.

[0011] According to one embodiment of the present invention, the barrel body preferably includes an anti-return latch between the initial position and the lower position of the piston. According to one embodiment of the present invention configured as described above, the cylindrical body includes a return latch between the initial position and the lower position of the piston. This prevents the piston from stopping against the return latch when the piston applies a predetermined pressure to the lower compartment due to inertia during its downward movement relative to the stopped position of the cylindrical body, and the piston stops against the return latch while applying pressure to the lower space beyond the return latch. This makes it easier to maintain the state in which pressure is applied to the lower space. This also prevents fluctuations in the pressure in the lower space due to fluctuations in the position of the piston.

[0012] According to one embodiment of the present invention, the cylindrical body preferably includes a one-way valve at a position above the initial position of the piston. According to one embodiment of the present invention configured as described above, the cylindrical body is provided with a one-way valve located above the initial position of the piston. When the piston moves downward due to inertia during descent and pressure is applied to the lower section of the cylindrical body, air flows into the upper space of the piston through the one-way valve. The piston attempts to move upward due to the increased pressure in the lower space, but the air in the upper space cannot flow back through the one-way valve and move out, restricting the piston's upward movement. The piston applies pressure to the lower space, and the air in the lower section of the cylindrical body flows out through the outlet into the soil. By measuring pressure changes within the cylindrical body with a pressure sensor, the air permeability, or the ease with which air can flow out of the soil through the outlet, can be estimated. Therefore, the air permeability of the soil layer into which the cylindrical body is inserted can be estimated.

[0013] According to one embodiment of the present invention, the outlet of the cylindrical body preferably forms a circular opening. According to one embodiment of the present invention configured as described above, when the piston applies pressure to the lower section due to inertia during its downward movement relative to the stop of the tube body on the soil, the outlet forms a circular opening, making it easier to estimate the choking state of the air flowing out of the outlet. Therefore, it is possible to estimate the change in the actual air permeability of the soil in response to the outflow of air due to the choking phenomenon, and to further improve the accuracy of estimating the permeability of the soil layer into which the tube body is inserted.

[0014] According to one embodiment of the present invention, preferably, a soil permeability estimation system for estimating the permeability of soil comprises a cylindrical body forming a hollow cylinder, the cylindrical body having an outlet formed at the bottom that penetrates from the inside to the outside, a piston that can slide up and down within the cylindrical body, a pressure sensor that is provided within the cylindrical body and measures the pressure within the cylindrical body, and a flying object that flies above the soil while supporting the cylindrical body and has the function of descending the cylindrical body from the air toward the soil. According to one embodiment of the present invention configured as described above, the flying object causes the cylindrical body to descend from the air toward the soil, and the cylindrical body is inserted into the soil by its own weight. At this time, the piston moves downward due to inertia, and pressure is applied inside the cylindrical body. The air inside the cylindrical body escapes into the soil through the outlet. Therefore, by measuring the pressure change inside the cylindrical body with a pressure sensor, it is possible to estimate the air permeability, i.e., how easily air can escape from the outlet into the soil. Therefore, it is possible to estimate the air permeability of the soil layer into which the cylindrical body is inserted.

[0015] According to one embodiment of the present invention, the flying object and the cylindrical body are preferably connected via a wire of a predetermined length, and the cylindrical body descends toward the soil. After the measurement is completed, the flying object can lift the cylindrical body out of the soil into the air via the wire. According to one embodiment of the present invention configured as described above, the cylindrical body is lowered from the flying object toward the soil, and after the measurement is completed, the flying object can pull the cylindrical body up into the air from the soil via the wire. This allows soil permeability to be estimated, for example, in mountainous areas or cliffs where it is difficult for people to reach the site, or in soil on river banks that are at risk of disasters, and the cylindrical body lowered from the flying object can be pulled up into the air and recovered from the soil. This allows soil permeability to be easily estimated without people being present at the site.

[0016] According to one embodiment of the present invention, there is provided a soil permeability estimation method for estimating the permeability of an inserted soil layer by lowering the tube body from above the soil until its lower end is inserted into the soil, the method comprising the steps of: a tube body forming a hollow cylinder, the tube body having an outlet formed at its lower part that penetrates from the inside to the outside; a preparation step of preparing a piston that can slide up and down within the tube body and separates a lower compartment from an upper compartment; a lowering step of lowering the tube body from above the soil; a pressure step in which the piston applies pressure to the lower compartment due to the inertia of the piston as it descends relative to the tube body stopping on the soil; and a measurement step in which the pressure sensor measures the pressure within the tube body. According to one embodiment of the present invention configured as described above, a method for estimating the permeability of a soil layer is provided, in which a tube body is lowered from above the soil until its lower end is inserted into the soil. The tube body is lowered from above the soil until its lower end is inserted into the soil. At this time, the piston moves downward due to inertia during the downward movement, exerting pressure on the lower compartment within the tube body. Air in the lower compartment within the tube body is released into the soil through an outlet. The permeability of the soil layer into which the tube body is inserted can be estimated by measuring the pressure change within the tube body with a pressure sensor. [Effects of the Invention]

[0017] According to the soil permeability estimation device, soil permeability estimation system, and soil permeability estimation method of the present invention, it is possible to estimate the permeability of soil, i.e., how easily air flows out of the outlet into the soil. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic configuration diagram of a soil permeability estimation system including a soil permeability estimation device according to a first embodiment of the present invention. [Figure 2] 1 is a schematic diagram showing a state in which a lower end portion of a soil permeability estimation device is inserted into soil in a soil permeability estimation system including a soil permeability estimation device according to a first embodiment of the present invention. [Figure 3] 1 is a schematic diagram showing the internal structure of a soil permeability estimation device according to a first embodiment of the present invention. [Figure 4] This is a schematic diagram showing the internal structure of a soil permeability estimation device in a soil permeability estimation system equipped with a soil permeability estimation device according to the first embodiment of the present invention, with the lower end of the soil permeability estimation device inserted into the soil. [Figure 5] 1 is a block diagram showing the configuration of a flying object in a soil permeability estimation system according to a first embodiment of the present invention. FIG. [Figure 6] 3 is a diagram illustrating the movement of a piston of a soil permeability estimation device in a soil permeability estimation system including the soil permeability estimation device according to the first embodiment of the present invention. FIG. [Figure 7]FIG. 1 is a diagram showing a flowchart of processing related to the soil air permeability estimation system according to the first embodiment of the present invention. [Figure 8] FIG. 2 is a diagram illustrating a target point for descent of the soil permeability estimation device according to the first embodiment of the present invention. [Figure 9] FIG. 3 is a diagram illustrating the relationship between pressure changes and the passage of time in the lower section of the soil permeability estimation device according to the first embodiment of the present invention. [Figure 10] FIG. 4 is a schematic diagram showing the internal structure of a soil permeability estimation device according to a second embodiment of the present invention. [Figure 11] This is a schematic diagram showing the internal structure of a soil permeability estimation device in a soil permeability estimation system equipped with a soil permeability estimation device according to a second embodiment of the present invention, with the lower end of the soil permeability estimation device inserted into the soil. [Figure 12] FIG. 10 is a diagram illustrating the relationship between pressure changes and the passage of time in the lower section of the soil permeability estimation device according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, a soil permeability estimation system 1 including a soil permeability estimation device according to a first embodiment of the present invention will be described with reference to the accompanying drawings. The embodiments of the present disclosure have been described as examples, and it will be apparent to those skilled in the art that many variations, modifications, and substitutions can be made within the spirit and scope of the present invention. Therefore, the present invention is not limited to the disclosed embodiments, and various variations, modifications, etc. can be made in form and details without departing from the scope of the claims. Furthermore, the components disclosed in the specification can be freely combined.

[0020] 1, a soil permeability estimation system 1 according to a first embodiment of the present invention estimates the permeability of soil. The soil permeability estimation system 1 includes a flying object 2 and a soil permeability estimation device 4.

[0021] The flying object 2 is, for example, a multicopter drone. The flying object 2 has six arms extending from the center of the main body to the periphery, each of which has a blade (rotor). In this embodiment, the flying object 2 has six arms and six blades, but the number of arms and blades may be changed to another number, such as four or eight. The flying object 2 flies in the air above the soil G (see FIG. 2) and has the function of lowering the tubular body 6 from the air toward the soil G. The flying object 2 flies above the soil G while supporting the soil permeability estimation device 4. Specifically, the flying object 2 can fly while supporting the tubular body 6 of the soil permeability estimation device 4 via a wire 21 connected to a winch 22, and can release the winch 22 to lower the soil permeability estimation device 4 at any time. Alternatively, the soil permeability estimation device 4 may be attached to a support arm, and the soil permeability estimation device 4 may be released and lowered at any time. The soil G is a soil layer J1 (see FIGS. 2 and 4) below the ground surface, for example, a soil layer approximately 30 cm to 1 m below the ground surface, and includes surface soil and sand that may be washed away by landslides due to rainfall, etc.

[0022] The flying object 2 and the cylindrical body 6 are connected via a wire 21 of a predetermined length, and the cylindrical body 6 falls toward the soil G. After the measurement is completed, the flying object 2 can lift the cylindrical body 6 into the air from the soil G via the wire 21. At this time, the flying object 2 further includes a winch 22, which can reel in the wire 21 to lift the cylindrical body 6 from the soil G to the flying object 2. The winch 22 includes a rotating drum, and the drum is equipped with a speed-controllable governor function, allowing the falling speed to be controlled. Because the drum is equipped with a governor, the governor can adjust the penetration speed of the cylindrical body 6 into the ground to a predetermined speed. In addition, the governor can adjust the penetration energy of the cylindrical body 6 into the ground to a predetermined penetration energy each time. Therefore, even if the drop start altitude of the flying object 2 changes slightly, the speed at which the cylindrical body 6 is inserted into the ground G is adjusted to a predetermined speed. Strictly speaking, the acceleration of the insertion into the ground changes depending on the hardness of the ground G, which changes the speed of the piston's movement, and so the initial pressure rise may change. However, as will be described later, the outflow of air from the outlet 11 causes a choking phenomenon, so the amount of air flowing out remains constant regardless of changes in the pressure rise. Therefore, the soil permeability estimation device 4 can estimate permeability without being affected by the hardness of the ground G. If it becomes difficult to pull the soil permeability estimation device 4 up towards the flying object 2, the wire 21 may be detached from the flying object 2 for flight safety.

[0023] 5, the flying object 2 further includes a camera 23, an altitude measuring device 24, a GPS device 27, an operation unit 25, a monitor unit 28, and a control unit 26. The flying object 2 may also include an alarm unit that issues a voice message to advise the flying object 2 to move away from the predicted descent point if a person or the like is spotted nearby. The flying object 2 also includes a communication unit (not shown) that performs wireless communication with the operation unit 25 and the like.

[0024] The camera 23 can photograph and visually confirm the surrounding conditions from the flying object 2. The camera 23 allows a user to remotely check the conditions around the flying object 2. The camera 23 is installed so that the conditions directly below the flying object 2 can also be visually confirmed in order to confirm the conditions at the destination where the soil permeability estimation device 4 descends.

[0025] As shown in FIG. 2 , the altitude measurement device 24 can measure the altitude H (distance) of the flying object 2 relative to the soil G. The altitude measurement device 24 uses, for example, an ultrasonic altimeter that can measure the height to the soil G. The altitude measurement device 24 may be configured with any one of or any combination of a barometric pressure measurement sensor that can measure flight altitude by measuring air pressure, an ultrasonic sonar that can measure the distance from the flying object 2 to the soil G, a laser measurement sensor that can measure the distance from the flying object 2 to the soil G, a LIDAR sensor that can measure the distance from the flying object 2 to the soil G, etc. In this way, the altitude measurement device 24 can measure the altitude H (distance) from the flying object 2 to the soil G. For example, the altitude measurement device 24 can measure the altitude H (distance) within a predetermined distance range from 2 m to 10 m from the flying object 2 to the soil G, more preferably within a range from 5 m to 10 m. After the altitude measurement device 24 recognizes the altitude H (distance) to the soil G, for example, the control unit 26 controls the descent of the cylindrical body 6 of the flying object 2.

[0026] The GPS device 27 is capable of identifying the current position of the flying object 2 using satellites.

[0027] The operation unit 25 can issue operation commands for operating the flying object 2 and for descending and recovering the soil permeability estimation device 4. As shown in FIG. 1, the operation unit 25 is provided at a location separate from the main body of the flying object 2 and is electrically connected via wireless communication to the control unit 26 (described later). The operation unit 25 can be remotely operated, for example, by a user. The flight of the flying object 2 can also be controlled by the user's operation of the operation unit 25. The descent start position and timing of the soil permeability estimation device 4 may be controlled by the control unit 26 (described later), or the descent start position and timing of the soil permeability estimation device 4 may be instructed and controlled by the user's operation of the operation unit 25. The operation unit 25 can also operate only any part of the flight and descent operation of the soil permeability estimation device 4. For example, only the descent start position may be operated by the operation unit 25, while other operations may be automatically controlled by the control unit 26. The operation unit 25 may be displayed on a monitor unit 28 that displays images. In this manner, the operation unit 25 may be an information terminal device such as a smartphone or tablet terminal. As another example, the operation device may be a dedicated controller such as a radio-controlled controller.

[0028] The monitor unit 28 displays images and videos captured by the camera 23, allowing the user to check the images, etc. This allows the user to fly while visually checking the surroundings and also check the status of the target point. The monitor unit 28 can also display the results of pressure measurement by the pressure sensor 10, etc. The monitor unit 28 is electrically connected to the control unit 26, which will be described later, via wireless communication.

[0029] As shown in FIGS. 2 and 5 , the control unit 26 is provided in the flying object 2. The control unit 26 may be provided in an information terminal device or the like on the operating unit 25 side. The control unit 26 controls the soil permeability estimation system 1 and the flight of the flying object 2. More specifically, the control unit 26 can control the descent start position (coordinates, altitude) and timing of the soil permeability estimation device 4. The control unit 26 can also control the flight altitude of the flying object 2, the flight route, the number of rotations of each blade, the attitude (including left and right roll and yawing in the rotation direction), the release operation of the wire by the winch, and the lifting operation of the wire by the winch. The control unit 26 can control the flying object 2 to reach a predetermined altitude above the target point and to cause the soil permeability estimation device 4 to free fall toward the soil G. The control unit 26 also performs functions such as acquiring measurements from pressure sensors and the like (described later) and controlling the lifting of the soil permeability estimation device 4 from the soil G toward the flying object 2. The control unit 26 has a built-in CPU, memory, etc., and controls the connected devices to execute predetermined control based on a predetermined control program recorded in the memory, etc. The control unit 26 is electrically connected to the winch 22, camera 23, altitude measurement device 24, GPS device 27, operation unit 25, monitor unit 28, etc. These electrical connections may be made via wireless communication, etc.

[0030] The control unit 26 may be equipped with a safety program or the like that realizes a safety function unit 29 that determines using AI or a program that there are no people or the like around the predicted descent point of the soil permeability estimation device 4 based on images acquired by the camera 23. The control unit 26 may be equipped with a descent point analysis program or the like that realizes a descent point analysis unit 31 that uses AI or a program to determine whether there are any rocks, stones, plantings, etc. at the predicted descent point of the soil permeability estimation device 4 based on images acquired by the camera.

[0031] As shown in Figures 2 to 4, the soil permeability estimation device 4 is configured to estimate the permeability A of the soil G (ease of passage of air flow A indicated by arrows in Figure 4) by lowering it from above the soil G so that the lower end 6c (see Figure 4) of the tubular body 6 is inserted into the soil G. The soil permeability estimation device 4 comprises a cylindrical body 6 that forms a hollow cylinder extending in the vertical direction, a piston 8 that can slide up and down within the cylindrical body 6 while maintaining a surface (e.g., a horizontal surface) that is approximately parallel to the soil G, and a pressure sensor 10 that is provided within the cylindrical body 6 and measures the pressure within the cylindrical body 6.

[0032] The lower end 6c of the cylindrical body 6 is formed in a downward cone shape. The lower end 6c of the cylindrical body 6 forms a downward cone. As shown in FIG. 4, for example, the value of the height h1 / radius r1 of the cone is set to a value in the range of 1 to 10, preferably a value in the range of 2 to 5. When the height h1 of the cone is the same as or longer than the radius r1, the lower end 6c of the cylindrical body 6 can easily penetrate into the soil G as it descends and can easily penetrate deeper into the soil. The lower end 6c of the cylindrical body 6 may be formed in a shape such as a square pyramid or a triangular pyramid.

[0033] The cylindrical body 6 has an outlet 11 formed on the side surface of its lower portion, penetrating from the inside to the outside. The outlet 11 forms a circular opening. Forming a circular opening makes it easier to estimate the choking phenomenon related to gas flow (fluid flow) compared to a rectangular opening, which tends to make the air flow through the opening more complex. In this embodiment, when the pressure in the internal space (e.g., the lower section 6b) within the cylindrical body 6 increases and the difference between the pressure in the internal space and the pressure in the external space 6d increases, a choking phenomenon occurs in the air passing through the outlet 11. Theoretically, the amount of air passing through the outlet 11 is constant per unit time. In this way, the amount of air passing through the outlet 11 under the choking phenomenon is determined based on the cross-sectional area of ​​the outlet 11. For example, the outlet 11 forms a circular opening with a radius ranging from 3 mm to 10 mm, more preferably from 3 mm to 5 mm.

[0034] The soil permeability estimation device 4 equipped with the cylindrical body 6 is configured to have a weight within a range of 5 kg to 10 kg, for example. By setting the weight of the soil permeability estimation device 4 to a predetermined weight, the cylindrical body 6 can be easily inserted into the soil G up to above the outlet 11 when it hits the soil G. The cylindrical body 6 is formed from, for example, metal.

[0035] The piston 8 separates the upper compartment 6a and the lower compartment 6b of the cylindrical body 6. The piston 8 is slidable up and down within the cylindrical body 6. The piston 8 is circular in top view. The piston 8 is guided to move along the inner wall 6e of the cylindrical body 6 while maintaining a 90-degree angle with respect to the inner wall 6e. Furthermore, when the cylindrical body 6 stops on the soil G, the piston 8 applies pressure to the air in the lower compartment 6b due to inertia during descent. The piston 8 is formed to have a weight within the range of 500 g to 2000 g so as to apply a predetermined pressure to the lower compartment 6b. The piston 8 and the inner wall 6e of the cylindrical body 6 may be coated with Teflon (registered trademark) or the like to reduce sliding resistance.

[0036] The piston 8 is connected to the cylindrical body 6 by elastic means 14. The elastic means 14 is, for example, a spring. The upper surface of the piston 8 is connected to the ceiling 6f of the cylindrical body 6 (see FIG. 4) by the elastic means 14. Therefore, before the piston 8 starts to descend, it is stationary at an initial position L1 (see FIG. 6) above the cylindrical body 6. At the initial position L1, the force pulling up the piston 8 by the elastic means 14 is balanced with the force of its own weight.

[0037] As shown in Fig. 4, the pressure sensor 10 measures the pressure in the lower section 6b of the internal space of the cylindrical main body 6. The pressure sensor 10 is, for example, a semiconductor piezo-resistance diffusion pressure sensor. The pressure sensor 10 may also be, for example, a capacitance-type pressure sensor. The pressure sensor 10 is electrically connected to the control unit 26 via wireless communication or the like, and transmits the acquired pressure value data to the control unit 26.

[0038] As shown in Figures 3, 4, and 6, the cylindrical body 6 is provided with a return prevention latch 12 between the initial position L1 and the lower position L2 of the piston 8. The return prevention latch 12 includes a pawl 12a extending inward from the inner wall 6e of the side surface and rotatable about the inner wall, and a spring portion 12b that biases the pawl 12a inward. The spring portion 12b is fixed to the inner wall 6e of the side surface. When the piston 8 moves downward from above the pawl 12a to below it, it can move downward over the pawl 12a, but it cannot move upward in the opposite direction by passing over the pawl 12a, and the piston 8 is locked by the pawl 12a. In this way, the pawl 12a is biased inward by the spring portion 12b. Therefore, when the piston 8 attempts to move upward in the opposite direction by passing over the pawl 12a, it is stopped by the pawl 12a. Therefore, the anti-return latch 12 has a structure in which, like the notch structure of a bicycle, when the piston 8 moves downward, the pawl 12a falls down so as to spread outward, and is then urged inward again by the spring portion 12b. The initial position L1 (see FIG. 6) is the position where the piston 8 is located when it is installed inside the cylindrical body 6 (before it is lowered). In FIG. 6, the positional relationship (initial position L1, lower position L2) and the movement (movement trajectory K of the piston) are illustrated by dashed lines. The lower position L2 is the position where the piston 8 has moved to the lowest position within the cylindrical body 6 due to inertia. As shown in FIG. 6, the piston 8 moves from the initial position L1 along the movement trajectory K to the lower position L2, and then returns slightly upward and is stopped by the return prevention latch 12.

[0039] Next, a technique for estimating soil air permeability will be described with reference to Figure 9. Figure 9 shows the change in pressure over time in the lower section 6b of the tube main body 6. The vertical axis shows air pressure (kPa), which indicates the increase in pressure from atmospheric pressure. The horizontal axis shows the time (seconds) elapsed since the start of pressure application. At time 0 seconds, the lower end 6c of the tube main body 6 is inserted into the soil G, and the piston 8 begins applying pressure to the lower section 6b due to inertia. As shown by arrow A (see FIG. 4), the soil permeability estimation device 4 estimates whether air easily flows out into the soil when air is sent into the soil from the outlet 11 at a predetermined pressure, as the permeability.

[0040] Theoretically, if air flows out of the outlet 11 into the atmosphere in a choked state, the pressure in the internal space (lower compartment 6b) theoretically decreases as a linear function. This theoretical change in pressure over time is indicated by dashed line B in Figure 9. The derivative B1 (slope) of the theoretical linear function is also illustrated on dashed line B. The derivative B1 is the derivative of the pressure decay portion of dashed line B after time T2. As shown in Figure 9, regarding an example of a derivative as an indicator of soil permeability, for example, when the outside is atmospheric, the outflow of air is not suppressed and air flows out in accordance with the theory of the choking phenomenon, so the slope of the pressure decrease (derivative B1) is relatively steep. In the theoretical change indicated by dashed line B, the lower end of the tube body 6 is inserted into the soil G at time 0 seconds, and the pressure in the lower compartment 6b is increased by the piston 8 until time T1. At elapsed time T2, the piston 8 is prevented from moving upward by the anti-return latch 12 and is stopped. After that, from time T2, as air flows out from the outlet 11 due to the choking phenomenon, the pressure decreases with a predetermined gradient of a linear function (differential coefficient B1).

[0041] The above discussion first describes the theoretical case in which air flows out of the outlet 11 into the atmosphere in a choked state. However, when the tube body 6 is inserted into the soil G and the outlet 11 is buried in the soil, soil G from the soil layer J1 exists outside the outlet 11. Therefore, the soil G acts as a resistance to the air flow, and the pressure change in the lower section 6b is affected by the soil resistance. The pressure change over time in this case is shown by the dashed line C in Figure 9. Note that the dashed line C indicates the pressure change after time T2, but the dashed line B is used instead for the period before time T2 because the pressure change is similar to that shown by the dashed line B. Even when the outlet 11 is actually located underground, the tube body 6 is inserted into the soil as shown by the dashed line B above, and the piston 8 increases the pressure on the lower section 6b. The piston 8 is then prevented from moving upward by the return latch 12, and is stopped. Thereafter, from time T2, as air flows out of the outlet 11 while experiencing resistance from the soil, the pressure decreases with a predetermined slope of a linear function (differential coefficient C1). As shown by the dashed-dotted line C, the pressure decreases from a state where the pressure is approximately at its peak with a predetermined slope (differential coefficient C1 which is a predetermined linear function) as the air flows out of the outlet 11 and is affected by the resistance of the soil. The dashed-dotted line C illustrates the slope of the differential coefficient affected by the resistance of the soil. The differential coefficient C1 of the pressure change in the lower section 6b is the differential coefficient of the attenuation portion from the pressure at time T2 at the dashed-dotted line C. In this way, the permeability of the soil can be estimated from the differential coefficient C1. Here, the differential coefficient C1 is a differential coefficient measured, for example, for soft soil (soil that is easily permeable to air). For example, if the value of the differential coefficient C1 approaches the differential coefficient B1, it can be determined that the soil's permeability (ease of air passing through) is increasing, and that the soil is becoming loose or is more likely to collapse. For example, the differential coefficient C1 may be measured by excluding the upper 10% and the lower 10% over a predetermined period from the pressure peak, for example, a period of one second, and measuring the differential coefficient of the remaining 80%. Furthermore, when additional air begins to flow in, a flow path is formed, reducing resistance and increasing the flow rate. Therefore, a method may be used in which the inflection point at which the flow path is formed is analyzed using machine learning such as AI. On the other hand, when measuring the air permeability of hard soil, for example, the outflow of air from the outlet 11 is suppressed, so the rate of pressure decrease is suppressed and the slope (differential coefficient D1) becomes gentler. The differential coefficient D1 of the pressure change when measuring the air permeability of hard soil is illustrated by the two-dot chain line D in Figure 9.

[0042] The permeability of soil does not necessarily need to be measured specifically as an actual amount of permeability, but is measured as an index of the ease of permeability. For example, the index may be the value of the differential coefficient of pressure change. In another variation, the index may be the magnitude of the difference between differential coefficient C1 (actual pressure change) and differential coefficient B1 (pressure change in a choked state). For example, if the soil permeability value exceeds a predetermined value (e.g., if the slope increases), it can be determined that there is an increased risk of a landslide, embankment collapse, or other such phenomenon. For example, it is expected that, during prolonged rainfall, the soil will absorb a lot of moisture, loosen, and become more air-permeable, resulting in a relatively increased permeability index value. For example, the control unit 26 may store in advance, as certain reference indicators, values ​​of the differential coefficient of pressure change when dry, hard soil is present, values ​​of the differential coefficient of pressure change when soil is in a state where the likelihood of a landslide or other such event is gradually increasing, and values ​​of the differential coefficient of pressure change when soil is in a state where the likelihood of a landslide or other such event is increased, in a data table or the like. Such soil permeability values ​​may be stored in advance in a data table or the like by the control unit 26, broken down by the properties of the soil constituting the soil. For example, it is preferable to obtain data on the soil to be measured in advance as a reference.

[0043] Next, a series of operations relating to the soil air permeability estimation system of this embodiment will be described with reference to FIG. As shown in FIG. 7, in the preparation step S1 of the soil permeability estimation system 1, the soil permeability estimation device 4 and the flying object 2 of the soil permeability estimation system 1 are prepared. The soil permeability estimation device 4 is detachably attached to the flying object 2. The soil permeability estimation device 4 can be released from the flying object 2 at any time based on the control function of the control unit 26 or an operation command from the operation unit 25, allowing it to descend. For example, the winch 22 is released to allow the soil permeability estimation device 4 to fall approximately free. The control unit 26 also prepares or acquires flight data for the flying object 2 (e.g., coordinates of a target point X (see FIG. 8), a flight route, altitude data from the soil at the target point coordinates (descent start altitude data), etc.). For reference, FIG. 8 shows an example of a map M using contour lines, illustrating the coordinates of the target point X (the target point where the soil permeability estimation device 4 will descend) on the map. In FIG. 8, contour lines corresponding to the terrain around the target point X are drawn in a top view. In Figure 8, the coordinates of a target point X in a mountainous region are specified. For example, the target point X may be a slope such as a cliff in a mountainous region, or a levee constructed of river sediment. The departure point R of the flying object 2 is also depicted. The control unit 26 also prepares or acquires data necessary for controlling the descent of the soil permeability estimation device 4 from the flying object 2 and the lifting of the soil permeability estimation device 4 from the soil G. When the preparation step S1 is completed, the process proceeds to S2.

[0044] In S2, the control unit 26 executes a flight step S2 in which the flying object 2 flies from the departure point R (see FIG. 8 ) to the target point X while supporting the soil permeability estimation device 4 in a suspended state. The control unit 26 moves the flying object 2 from the departure point R toward the target point X. In the flight step S2, the control unit 26 moves the flying object 2 to a descent start altitude above the target point X. At this time, the control unit 26 appropriately performs control necessary for the flight of the flying object 2, such as an autopilot. When the flying object 2 reaches the vicinity of the target point (for example, within a peripheral area within a radius of several meters to several tens of meters), the control unit 26 checks the state of the predicted descent point (ground arrival point) using the camera 23. For example, the control unit 26 determines, based on the image from the camera 23, whether there are any obstacles, such as rocks, stones, or plantings, at the predicted descent point that may interfere with the insertion of the soil permeability estimation device 4 into the soil G. Alternatively, the control unit 26 may transmit an image acquired by the camera 23 to the operation unit 25, allowing the user to remotely check the status of the target location. When the flying object 2 reaches the vicinity of the target location (e.g., within a peripheral area within a radius of several meters to several tens of meters), the control unit 26 uses the camera 23 to check whether there are people, animals, etc., around the predicted descent point. For example, the control unit 26 determines whether there are people, animals, etc., around the predicted descent point based on the image from the camera 23 using the safety function unit 29. Alternatively, the control unit 26 may transmit an image acquired by the camera 23 to the operation unit 25, allowing the operator to check whether there are people, animals, etc., around the predicted descent point. If necessary, a notification unit (not shown) may be used to notify people, animals, etc., to move away. The flying object 2 checks downward from a height of, for example, several meters to 10 meters above the soil G, allowing the user to adequately confirm the situation below and ensure safety using the camera 23. When flight step S2 ends, the control unit 26 proceeds to S3.

[0045] In S3, the control unit 26 executes a descent step S3 in which the soil permeability estimation device 4 is lowered from the descent start altitude of the target point X. The control unit 26, for example, causes the soil permeability estimation device 4 to freely fall toward the soil G at the target point X. When the soil permeability estimation device 4 descends, the lower end 6c of the tubular body 6 of the soil permeability estimation device 4 descends in a position facing vertically downward. When the soil permeability estimation device 4 reaches the soil G from above, the lower end 6c is formed in a pointed cone shape, making it easy to insert the lower part of the tube body 6 into the soil. Figure 2 shows the state in which the lower part of the tube body 6 has been inserted into the soil. At this time, the outlet 11 of the tube body 6 is located in the soil G below the ground surface.

[0046] As shown in FIG. 4, when the soil permeability estimation device 4 reaches the soil G, the tube body 6 is stopped by the resistance of the soil G. However, the internal piston 8 attempts to move downward due to inertia, applying pressure to the air in the lower compartment 6b. The piston 8 moves downward due to inertia and moves below the return prevention latch 12. Therefore, the piston 8 automatically applies pressure to the air in the lower compartment 6b by using inertia. The piston 8 moves upward slightly in response to the increase in air pressure in the lower compartment 6b, but is prevented from moving upward by the return prevention latch 12. Therefore, the piston 8 stops in a state where the air in the lower compartment 6b is maintained at a predetermined high pressure. This increases the air pressure in the lower compartment 6b, and the air flows out of the outlet 11 due to the difference between the pressure in the lower compartment 6b and the pressure in the space outside the tube body 6. The pressure difference between the lower compartment 6b (internal space) and the external space becomes relatively large temporarily. Therefore, when air flows out of the outlet 11, the amount of air passing through the outlet 11 becomes constant per unit time due to the choking phenomenon. This amount of air passing through is determined based on the cross-sectional area of ​​the outlet 11, and a theoretical differential coefficient of pressure change is obtained.

[0047] In reality, the outlet 11 of the tube body 6 is located below the soil G, and the soil wall is located immediately outside the outlet 11. As a result, the amount of air exiting the outlet 11 varies depending on the soil's air permeability (an index of how easily air passes through). The amount of air flowing out of the outlet 11 varies depending on the soil's permeability, relative to a theoretical value based on the outlet 11. As shown in FIG. 9, the pressure sensor 10 measures the pressure value of the lower section 6b over time. Therefore, based on the pressure change in the lower section 6b, the control unit 26 obtains a differential coefficient C1 of the pressure change (the slope of the pressure change). For example, the control unit 26 obtains the value of the differential coefficient C1 of the pressure change as an index of the soil's air permeability. For example, as the tube body 6 is inserted into the soil G, the control unit 26 measures the differential coefficient of the pressure change from 0.1 seconds to 1 second, more preferably from 0.1 seconds to 0.5 seconds, and even more preferably from 0.1 seconds to 0.3 seconds after the internal pressure of the tube body 6 reaches the peak value PM. In this manner, in the descending step S3, the control unit 26 may estimate the permeability state of the soil G from the differential coefficient value of the pressure change. When measuring the differential coefficient value of the pressure change, the control unit 26 may measure a portion of the differential coefficient whose slope is close to a linear function over a predetermined period after the internal pressure of the tube body 6 reaches the peak value PM as the differential coefficient value, and calculate the average of the measured values ​​at multiple times. Furthermore, the control unit 26 does not have to immediately measure and calculate the differential coefficient value, and may instead calculate the differential coefficient value by analyzing the pressure change using, for example, another computer. After the descending step S3 is completed, the control unit 26 proceeds to S4.

[0048] In S4, the control unit 26 executes a recovery step S4 in which the soil permeability estimation device 4 is pulled up from the soil G toward the flying object 2. The control unit 26 activates the winch 22 to pull up the soil permeability estimation device 4 from the soil G. After the control unit 26 has pulled up the soil permeability estimation device 4 from the soil G toward the flying object 2, the control unit 26 proceeds to S5.

[0049] In S5, the control unit 26 executes a return flight step S5 in which the flying object 2 flies to the starting point R while supporting the soil permeability estimation device 4 in a suspended state. If the soil permeability estimation device 4 can be used continuously to measure the permeability of the soil at multiple target points without the flying object 2 returning to the starting point R, the control unit 26 may return to S1 or S2 and repeatedly execute the steps up to S5. When the return flight step S5 is completed, the control unit 26 proceeds to END and terminates the series of processes.

[0050] According to the first embodiment of the present invention configured as described above, the soil permeability estimation device 4 is lowered from above the soil G until its lower end 6c is inserted into the soil, thereby estimating the permeability of the inserted soil layer. The tube body 6 of the soil permeability estimation device 4 is lowered from above the soil until its lower end 6c is inserted into the soil. At this time, the piston 8 is moved downward due to inertia during the descent, and pressure is applied to the lower section 6b within the tube body 6. The air in the lower section 6b within the tube body 6 is released into the soil G through the outlet. The permeability of the soil layer into which the tube body 6 is inserted can be estimated by measuring the pressure change within the tube body 6 with a pressure sensor.

[0051] According to the first embodiment of the present invention configured in this manner, the piston 8 is maintained in its initial position within the cylindrical body 6 in the initial state before descending, and when the cylindrical body 6 is inserted into the soil G, the piston 8 can apply pressure to the lower section 6b due to the inertia of the piston 8 descending against the stop of the cylindrical body 6.

[0052] According to the first embodiment of the present invention configured as described above, the piston 8 is formed to have a weight within a range of 500 g to 2000 g, and the piston 8 can apply a predetermined pressure to the lower section 6b by the inertia when it descends relative to the stop of the cylindrical main body 6. Furthermore, for example, the pressure applied to the lower section 6b can be set within a predetermined range, making it easier to estimate the air permeability of the soil G.

[0053] According to the first embodiment of the present invention configured as described above, the lower end 6c of the tube body 6 is formed in a downward cone shape. This makes it easier for the tube body 6 to be lowered from above the soil G so that the lower end 6c is inserted into the soil G. Since the lower end 6c can be easily inserted into the soil G, it becomes easier to measure the air permeability of the soil G at a desired point more reliably.

[0054] According to the first embodiment of the present invention configured as described above, the cylindrical body 6 is provided with a return prevention latch 12 between the initial position and the lower position of the piston 8. As a result, when the piston 8 applies a predetermined pressure to the lower section 6b due to inertia when descending relative to the stopped cylindrical body 6, the piston 8 passes over the return prevention latch 12 and applies pressure to the lower section 6b, and the piston 8 is stopped relative to the return prevention latch 12. This makes it easier to maintain the state in which pressure is applied to the lower section 6b. In addition, it is possible to suppress fluctuations in the pressure on the lower section 6b due to fluctuations in the position of the piston 8.

[0055] According to the first embodiment of the present invention configured as described above, when the piston 8 applies pressure to the lower section 6b due to the inertia of descending relative to the stop of the tube body 6 on the soil G, the outlet 11 forms a circular opening, which makes it easier to estimate the state of choking of the air flowing out from the outlet 11. Therefore, by comparing the outflow of air based on the choking phenomenon with an estimate of the actual air permeability of the soil G, it is possible to further improve the accuracy of estimating the permeability of the soil layer into which the tube body 6 is inserted.

[0056] According to the first embodiment of the present invention configured as described above, the flying object causes the cylindrical body 6 to descend from the air toward the soil G, and the cylindrical body 6 is inserted into the soil G due to its own weight. At this time, the piston 8 is moved downward due to inertia, and pressure is applied inside the cylindrical body 6. The air inside the cylindrical body 6 is released into the soil G from the outlet 11. Therefore, by measuring the pressure change inside the cylindrical body 6 with the pressure sensor 10, it is possible to estimate the air permeability, i.e., whether the air can easily flow out from the outlet 11 into the soil G. Therefore, it is possible to estimate the air permeability of the soil layer into which the cylindrical body 6 is inserted.

[0057] According to the first embodiment of the present invention configured as described above, after the cylindrical body 6 is lowered from the flying body 2 toward the soil G and measurement is completed, the flying body 2 can pull the cylindrical body 6 up into the air from the soil G via the wire 21. This makes it possible to estimate the permeability of soil, for example, in mountainous areas or cliffs where it is difficult for people to reach the site, or in soil on river banks that are at risk of disasters, and also makes it possible to collect the cylindrical body 6 that has been lowered from the flying body 2 by pulling it up into the air from the soil G. This makes it possible to easily estimate the permeability of the soil G without a person being present at the site of the target point X.

[0058] According to the first embodiment of the present invention configured as described above, the soil permeability estimation method estimates the permeability of an inserted soil layer by lowering the tube body 6 from above the soil G until the lower end 6c is inserted into the soil G. The tube body 6 is lowered from above the soil G until the lower end 6c is inserted into the soil G. At this time, the piston 8 is moved downward due to inertia during the descent, and pressure is applied to the lower section 6b inside the tube body 6. The air in the lower section 6b inside the tube body 6 is released into the soil G through the outlet 11. The permeability of the soil layer into which the tube body 6 is inserted can be estimated by measuring the pressure change inside the tube body 6 with the pressure sensor 10.

[0059] Next, a soil permeability estimation system 101 equipped with a soil permeability estimation device 104 according to a second embodiment of the present invention will be described with reference to Figures 10 and 11. The second embodiment is an example in which a one-way valve 130 is applied to the soil permeability estimation device 104. Fig. 10 is a schematic diagram showing the internal structure of a soil permeability estimation device according to a second embodiment of the present invention. Fig. 11 is a schematic diagram showing the internal structure of a soil permeability estimation device in a state where the lower end of the soil permeability estimation device is inserted into soil in a soil permeability estimation system including the soil permeability estimation device according to the second embodiment of the present invention. Since the soil permeability estimation system 101 according to the second embodiment has almost the same structure as the soil permeability estimation system 1 according to the first embodiment described above, only the differences between the second embodiment of the present invention and the first embodiment will be described, and similar parts will be given the same reference symbols in the drawings and will not be described again.

[0060] The soil permeability estimation system 101 includes a flying object 2 and a soil permeability estimation device 104. The flying object 2 is the same as in the first embodiment, and therefore a description thereof will be omitted. As shown in Figures 10 and 11, the soil permeability estimation device 104 is configured to estimate the permeability of the soil (ease of passage of air flow A indicated by arrows in Figure 4) by lowering it from above the soil G so that the lower end 6c (see Figure 11) of the tubular body 6 is inserted into the soil G below the ground surface. The soil air permeability estimation device 104 includes a cylindrical body 6 , a piston 8 , a pressure sensor 10 , a one-way valve 130 , and an air release valve 131 .

[0061] The one-way valve 130 allows fluids such as air to flow in one direction while preventing backflow. The one-way valve 130 is located on the ceiling 6f of the tube body 6 and is configured to allow air from outside the tube body 6 to flow into the upper compartment 6a. Therefore, when the piston 8 moves downward and negative pressure is created within the upper compartment 6a, air is automatically introduced from outside the tube body 6 into the upper compartment 6a. After atmospheric air is introduced into the upper compartment 6a, when the piston 8 attempts to move upward, the air in the upper compartment 6a cannot flow out through the one-way valve 130, causing the air pressure in the upper compartment 6a to increase. This restricts the upward movement of the piston 8, and once the air pressure in the upper compartment 6a and the air pressure in the lower compartment 6b become equal, the piston 8 is temporarily stopped. The piston then gradually moves downward as the air pressure in the lower compartment 6b decreases. The air pressure in the lower compartment 6b also gradually decreases.

[0062] The atmosphere release valve 131 is a solenoid valve that can open the upper compartment 6a to the atmosphere. The atmosphere release valve 131 can open and close the flow path connecting the upper compartment 6a to the space outside the tube body 6. The atmosphere release valve 131 is electrically connected to the control unit 26 and is configured to open and close the flow path in response to commands. More specifically, the atmosphere release valve 131 releases air from a high air pressure state in the upper compartment 6a to the atmosphere, lowering the air pressure in the upper compartment 6a to atmospheric pressure. This allows the piston 8 to return to its initial position. Therefore, after measuring the permeability at one point, the winch 22 can be operated to lift the tube body 6 and the atmosphere release valve 131 can be opened to move the piston 8 to its initial position, allowing the soil permeability estimation device 104 to be used again during flight without returning to the starting point R. Therefore, the permeability of multiple soil layers can be estimated in a single flight. The atmosphere release valve 131 may be omitted, and the piston 8 can be reset to its initial position when the flying object 2 returns to the starting point R.

[0063] Next, a technique for estimating soil air permeability in the second embodiment will be described with reference to Fig. 12. Fig. 12 shows the change in pressure over time in the lower section 6b of the tube main body 6. The vertical axis shows air pressure (kPa), which indicates the increase in pressure from atmospheric pressure. The horizontal axis shows the time (seconds) elapsed since the start of pressure application. At time 0 seconds, the lower end 6c of the tube main body 6 is inserted into the soil G, and the piston 8 begins applying pressure to the lower section 6b due to inertia. As shown by arrow A (see FIG. 4), when air is sent into the soil from outlet 11 at a predetermined pressure, soil permeability estimation device 104 estimates whether air easily flows out into the soil as permeability.

[0064] In this embodiment, as described above, the piston 8 first moves downward, creating a negative pressure in the upper compartment 6a, and air is automatically introduced into the upper compartment 6a through the one-way valve 130. Due to inertia, the piston 8 applies pressure to the lower compartment 6b, causing the internal pressure to reach a peak value PM. As the pressure in the lower compartment 6b increases, the piston 8 is pushed back upward, and when the air pressure in the upper compartment 6a and the air pressure in the lower compartment 6b reach a pressure P1 equal to that of the upper compartment 6a, the piston 8 is temporarily stopped. The soil permeability is estimated by measuring the pressure change from this pressure P1.

[0065] Theoretically, if air flows out of the outlet 11 into the atmosphere in a choked state, the pressure in the internal space (lower section 6b) theoretically decreases as a linear function. This theoretical change in pressure over time is shown by dashed line E in FIG. 12 . The derivative coefficient E1 (slope) of the theoretical linear function is also shown on dashed line E. The derivative coefficient E1 is the derivative of the decay portion of the pressure from the dashed line E at time T3. As shown in FIG. 12 , regarding an example of a derivative coefficient as an indicator of soil permeability, for example, when the outside is the atmosphere, the outflow of air is not suppressed and the air flows out in accordance with the theory of the choking phenomenon, so the slope of the pressure decrease (derivative coefficient E1) is relatively steep. In the theoretical change shown by dashed line E, from time T3, as air flows out of the outlet 11 in a choked state, the pressure decreases at a predetermined slope of the linear function (derivative coefficient E1). Thereafter, the piston gradually moves downward as the air pressure in the lower section 6b decreases. The air pressure in the lower section 6b is also gradually reduced.

[0066] The above discussion first describes the theoretical case in which air flows out of the outlet 11 into the atmosphere in a choked state. However, when the tube body 6 is inserted into the soil G and the outlet 11 is buried in the soil, soil G from the soil layer J1 exists outside the outlet 11. Therefore, the soil G acts as a resistance to the outflow of air under the pressure of the piston 8, and the pressure change in the lower section 6b is affected by the resistance of the soil. The time change in pressure in this case is shown by the dashed-dotted line F in Figure 12. Note that the dashed-dotted line F represents an example of soft soil (soil that is easily permeable to air), as described below. Starting at time T3, as air flows out of the outlet 11 while encountering the resistance of the soil, the pressure decreases with a slope of a predetermined linear function (differential coefficient F1). As shown by the dashed-dotted line F, the pressure decreases from a pressure P1 state with a slope (predetermined linear function F1) as the air flows out of the outlet 11, affected by the resistance of the soil. The slope of the differential coefficient affected by the resistance of the soil is illustrated by the dashed-dotted line F. The differential coefficient F1 of the pressure change in the lower section 6b is the differential coefficient of the attenuation portion from the pressure at time T3 on the dashed-dotted line F. In this way, the permeability of the soil can be estimated using the differential coefficient F1. For example, if the value of the differential coefficient F1 approaches the differential coefficient E1, it can be determined that the permeability (ease of air passing through) of the soil is increasing, and the soil is loose or is more likely to collapse. On the other hand, for example, when measuring the air permeability of hard soil, the outflow of air from outlet 11 is suppressed, so the rate of pressure drop is suppressed and the slope (differential coefficient H1) becomes gentler. The differential coefficient H1 of the pressure change when measuring the air permeability of hard soil is shown by the two-dot chain line H in Figure 12. Furthermore, for example, in the case of soft soil (soil that is easily permeable to air), the outflow of air is slightly suppressed, the rate of pressure drop is somewhat suppressed and the slope (differential coefficient F1) is steeper than the differential coefficient H1 for hard soil.

[0067] The permeability of soil does not need to be measured precisely and specifically, but is measured as an index of the ease of ventilation. For example, the index may be the value of the differential coefficient of pressure change. In another variation, the index may be the magnitude of the difference between the differential coefficient F1 (actual pressure change) and the differential coefficient E1 (pressure change in a choked state). For example, if the soil permeability value exceeds a predetermined value (e.g., if the slope increases), it can be determined that there is an increased risk of a landslide, embankment collapse, or other such phenomenon. For example, it is expected that, during prolonged rainfall, the soil will absorb a lot of moisture, loosen, and become more air-permeable, resulting in a relatively increased permeability index value. For example, the control unit 26 may store in advance, as certain reference indicators, values ​​of the differential coefficient of pressure change when dry, hard soil is present, values ​​of the differential coefficient of pressure change when soil is in a state where the likelihood of a landslide or other such event is gradually increasing, and values ​​of the differential coefficient of pressure change when soil is in a state where the likelihood of a landslide or other such event is increased, in a data table or the like. Such soil permeability values ​​may be stored in advance in a data table or the like by the control unit 26, broken down by the properties of the soil constituting the soil. For example, it is preferable to obtain data on the soil to be measured in advance as a reference.

[0068] Next, a series of operations related to the soil permeability estimation system of this embodiment will be described with reference to Fig. 7. Regarding the explanation of the operations in the second embodiment, explanations of parts that overlap with the explanation of the operations in the first embodiment will be omitted. Steps S1 to S5 of the soil permeability estimation system 101 in the second embodiment are basically the same as steps S1 to S5 of the soil permeability estimation system 1 in the first embodiment, so a series of operations will be described with reference to Fig. 7. 7, in preparation step S1, the soil permeability estimation device 104 of the soil permeability estimation system 101 and the flying object 2 of the soil permeability estimation system 101 are prepared. The soil permeability estimation device 104 is detachably attached to the flying object 2. The soil permeability estimation device 104 can be released from the flying object 2 at any timing based on the control function of the control unit 26 or an operation command from the operation unit 25, and can be lowered. For example, the winch 22 can be released to allow the soil permeability estimation device 104 to fall approximately freely. When the preparation step S1 is completed, the process proceeds to S2.

[0069] The flight step S2 of the soil permeability estimation system 101 in the second embodiment is similar to the flight step S2 of the soil permeability estimation system 1 in the first embodiment, so a description thereof will be omitted. When the flight step S2 ends, the control unit 26 proceeds to S3.

[0070] In step S3, the control unit 26 executes a descent step S3 in which the soil permeability estimation device 104 descends from the descent start altitude at the target point X. The control unit 26, for example, causes the soil permeability estimation device 104 to free fall toward the soil G at the target point X. As the soil permeability estimation device 104 descends, the lower end 6c of the tube body 6 of the soil permeability estimation device 104 descends with the lower end 6c facing vertically downward. When the soil permeability estimation device 104 reaches the soil G from above the soil G, the lower end 6c is formed in a conical shape, making it easy for the lower part of the tube body 6 to be inserted into the soil. Figure 11 shows the state in which the lower part of the tube body 6 has been inserted into the soil. At this time, the outlet 11 of the tube body 6 is located in the soil G below the ground surface.

[0071] As shown in FIG. 11, when the soil permeability estimation device 104 reaches the soil G, the tube body 6 is stopped by the resistance of the soil G. However, the internal piston 8 attempts to move downward due to inertia, exerting pressure on the air in the lower compartment 6b. As the piston 8 moves downward and negative pressure is created in the upper compartment 6a, air is automatically introduced from outside the tube body 6 into the upper compartment 6a through the one-way valve 130. As shown in FIG. 12, the piston 8 exerts pressure on the lower compartment 6b due to inertia, and the internal pressure reaches a peak value PM. As the pressure in the lower compartment 6b increases, the piston 8 is pushed back upward. When the piston 8 attempts to move upward, the air in the upper compartment 6a cannot flow out through the one-way valve 130, and the air pressure in the upper compartment 6a increases. Therefore, the upward return of the piston 8 is restricted, and the piston 8 is stopped once the air pressure in the upper compartment 6a and the air pressure in the lower compartment 6b reach an equal pressure P1. The air permeability of the soil G is estimated by measuring the pressure change from this pressure P1. Thereafter, the piston is gradually moved downward as the air pressure in the lower compartment 6b decreases. The air pressure in the lower compartment 6b is also gradually decreased.

[0072] The piston 8 brings the air in the lower section 6b to a predetermined high pressure P1. As a result, the difference between the air pressure in the lower section 6b and the air pressure in the external space of the tube body 6 causes the air to flow out of the outlet 11. The pressure difference between the lower section 6b (internal space) and the external space is temporarily relatively large. Therefore, when the air flows out of the outlet 11, the amount of air passing through the outlet 11 becomes constant per unit time due to the choking phenomenon. This amount of air passing through is determined based on the cross-sectional area of ​​the outlet 11, and a theoretical differential coefficient of pressure change is obtained.

[0073] In reality, the outlet 11 of the tube body 6 is located below the soil G, and the wall of the soil is located just outside the outlet 11. As a result, the amount of air about to leave the outlet 11 varies depending on the air permeability of the soil (an index of how easily air passes through). After the pressure P1 state, the amount of air flowing out from the outlet 11 varies depending on the soil's permeability, relative to a theoretical value based on the outlet. As shown in FIG. 12, the pressure sensor 10 measures the pressure value in the lower section 6b over time. Therefore, the control unit 26 acquires a differential coefficient F1 (the slope of the pressure change) of the pressure change based on the pressure change in the lower section 6b. For example, the control unit 26 acquires the value of the differential coefficient F1 of the pressure change as an index of the soil's permeability. For example, as the tube body 6 is inserted into the soil G, the control unit 26 measures the differential coefficient of the pressure change from 0.1 seconds to 1 second after the internal pressure of the tube body 6 reaches pressure P1, more preferably from 0.1 seconds to 0.5 seconds, and more preferably from 0.1 seconds to 0.3 seconds. In this way, the control unit 26 may estimate the permeability of the soil G from the differential coefficient of the pressure change in the descending step S3. When measuring the value of the differential coefficient of pressure change, the portion of the differential coefficient where the slope is close to a linear function for a predetermined period after the internal pressure of the tube body 6 reaches the pressure value P1 may be measured as the value of the differential coefficient, and the average of the measured values ​​at multiple times may be calculated. Furthermore, the control unit 26 does not need to immediately measure and calculate the value of the differential coefficient, and may instead analyze the pressure change using another computer, for example. The softer the soil G, the faster the flow path formation, and the shorter the period for measuring the differential coefficient of pressure change. Therefore, the control unit 26 may measure the differential coefficient of pressure change over several different periods and determine to use the preferred differential coefficient. After the lowering step S3 is completed, the control unit 26 proceeds to S4.

[0074] In S4, the control unit 26 executes a recovery step S4 in which the soil permeability estimation device 104 is pulled up from the soil G toward the flying object 2. The control unit 26 activates the winch 22 to pull up the soil permeability estimation device 104 from the soil G. At this time, the atmosphere release valve 131 reduces the air pressure in the upper compartment 6a from a high state to atmospheric pressure, and the piston 8 can return to its initial position. Therefore, the soil permeability estimation device 104 can be reused during flight without returning to the starting point R, and step S3 may be executed toward multiple soil layers in a single flight. When S4 ends, the control unit 26 proceeds to S5. The return flight step S5 of the soil permeability estimation system 101 in the second embodiment is similar to the return flight step S5 of the soil permeability estimation system 1 in the first embodiment, and therefore will not be described further. When the return flight step S5 is completed, the control unit 26 proceeds to END and terminates the series of processes.

[0075] According to the second embodiment of the present invention configured as described above, the soil permeability estimation device 104 estimates the permeability of the soil layer by being lowered from above the soil G until the lower end 6c is inserted into the soil G. The tube body 6 of the soil permeability estimation device 104 is lowered from above the soil G until the lower end 6c is inserted into the soil G. At this time, the piston 8 is moved downward due to inertia during the descent, and pressure is applied to the lower section 6b within the tube body 6. The air in the lower section 6b within the tube body 6 is released into the soil G through the outlet 11. The pressure sensor 10 measures the pressure change within the tube body 6, allowing the permeability of the soil layer into which the tube body 6 is inserted to be estimated.

[0076] According to the second embodiment of the present invention configured as described above, the cylindrical body 6 includes a one-way valve 130 located above the initial position of the piston 8. When the piston 8 moves downward due to inertia during descent and pressure is applied to the lower section 6b within the cylindrical body 6, air flows through the one-way valve 130 into the upper space above the piston 8. The piston 8 attempts to move upward due to the increased pressure in the lower space, but the air in the upper space cannot flow back through the one-way valve 130 and move out, restricting the upward movement of the piston 8. The piston 8 applies pressure to the lower space, causing the air in the lower section 6b within the cylindrical body 6 to flow out through the outlet 11 into the soil G. By measuring the pressure change within the cylindrical body 6 with the pressure sensor 10, the air permeability, or the ease with which air can flow out through the outlet 11 into the soil G, can be estimated. Therefore, the air permeability of the soil layer into which the cylindrical body 6 is inserted can be estimated.

[0077] According to the second embodiment of the present invention configured as described above, the flying object 2 causes the cylindrical body 6 to descend from the air toward the soil G, and the cylindrical body 6 is inserted into the soil G by its own weight. At this time, the piston 8 is moved downward by inertia, and pressure is applied inside the cylindrical body 6. The air inside the cylindrical body 6 is released into the soil G through the outlet 11. Therefore, by measuring the pressure change inside the cylindrical body 6 with the pressure sensor 10, it is possible to estimate the air permeability, i.e., whether the air can easily flow out from the outlet 11 into the soil G. Therefore, it is possible to estimate the air permeability of the soil layer into which the cylindrical body 6 is inserted.

[0078] The embodiments for carrying out the present invention are not limited to the above, and other modifications may be applied. Various alternative embodiments and examples will be apparent to those skilled in the art based on the disclosed technology. For example, the soil permeability estimation device 4 does not necessarily have to be lowered from the flying object 2, but may be dropped from a certain height from a holding device installed on the ground. For example, the soil permeability estimation device 4 may be inserted into the soil G by being freely dropped from a height of about 2 m into the soil G within a cylindrical guide extending to a height of 2 m from the soil. [Explanation of symbols]

[0079] 1: Soil permeability estimation system 2: Flying object 4: Soil permeability estimation device 6: Cylinder body 6a: Upper compartment 6b: Lower section 6c: Bottom end 8: Piston 10: Pressure sensor 11: Outlet 12: Anti-return latch 14: Elastic means 21: Wire 101: Soil Permeability Estimation System 104: Soil permeability estimation device 130: One-way valve G: Soil

Claims

1. A soil permeability estimation device that estimates the permeability of an inserted soil layer by lowering the device from above the soil so that the lower end is inserted into the soil, A cylindrical body forming a hollow cylinder, the cylindrical body having an outlet formed at a lower portion thereof, the outlet opening penetrating from the inside to the outside; a piston that is slidable up and down within the cylindrical body and that separates a lower section and an upper section, the piston applying pressure to the lower section due to inertia when the cylindrical body stops on the soil; a pressure sensor provided in the tube body and configured to measure a pressure in the lower section of the tube body; A soil permeability estimation device that estimates the permeability of the soil outside the outlet based on the decrease in pressure in the lower space due to air flowing out of the outlet into the soil when pressure is applied to the lower section by the descent of the piston.

2. 2. The soil permeability estimation device according to claim 1, wherein the piston is connected to the cylindrical body by an elastic means.

3. 2. The soil permeability estimation device according to claim 1, wherein the piston is formed to have a weight within a range of 500 g to 2000 g.

4. The soil permeability estimation device according to claim 1 , wherein a lower end of the cylindrical body is formed into a downward cone shape.

5. The soil permeability estimation device of claim 1 , wherein the tube body includes an anti-return latch between the initial position and the lower position of the piston.

6. The soil permeability estimation device according to claim 1 , wherein the cylindrical body is provided with a one-way valve at a position above an initial position of the piston.

7. The soil permeability estimation device according to claim 1 , wherein the outlet of the tube body forms a circular opening.

8. A soil permeability estimation system for estimating soil permeability, comprising: A cylindrical body forming a hollow cylinder, the cylindrical body having an outlet formed at a lower portion thereof, the outlet opening penetrating from the inside to the outside; a piston that is slidable up and down within the cylindrical body and that separates a lower compartment from an upper compartment; a pressure sensor disposed within the tube body for measuring the pressure within the lower section of the tube body; A soil permeability estimation system comprising: a flying body that flies above the soil while supporting the cylindrical body and has the function of lowering the cylindrical body from the air toward the soil; and a flying body that, when pressure is applied to the lower section by the descent of the piston, estimates the permeability of the soil outside the outlet based on the decrease in pressure in the lower space caused by air flowing out of the outlet into the soil.

9. The projectile and the tube body are connected via a wire of a predetermined length, The soil permeability estimation system according to claim 8 , wherein the cylindrical body descends toward the soil, and after measurement is completed, the flying object can lift the cylindrical body out of the soil into the air via the wire.

10. A soil air permeability estimation method for estimating the air permeability of an inserted soil layer by lowering a device from above the soil so that a lower end portion thereof is inserted into the soil, a preparation step of preparing a cylindrical body that forms a hollow cylinder and has an outlet formed at a lower part thereof that penetrates from the inside to the outside, and a piston that is slidable up and down within the cylindrical body and that separates a lower compartment from an upper compartment; a lowering step of lowering the tube body from above the soil; a pressure step in which the piston applies pressure to the lower section due to inertia when descending against the stop of the tube body on the soil; a measuring step in which a pressure sensor measures the pressure in the lower section of the cylindrical body, and estimates the permeability of the soil outside the outlet based on the decrease in pressure in the lower space caused by air flowing out of the outlet into the soil when pressure is applied to the lower section by the descending of the piston.

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