Resistivity measuring device, ground improvement body management method, and resistivity measuring method

Abstract

To improve accuracy of specific resistance measurement in the ground.SOLUTION: In a specific resistance measuring device 1A, a capacitor electrode device 10A has a pair of capacitor electrodes 10 composed of dielectric bodies 13 opposite to a porous wall W of a hole H in a ground E and conductors 14 connected to the dielectric bodies 13 as a pair of current electrodes 11 arranged in an extension direction of the hole H, has the pair of capacitor electrodes 10 as a pair of potential electrodes 12 arranged in the extension direction of the hole H while causing AC current to flow into the ground E by applying an AC voltage between the pair of current electrodes 11, and measures a potential between the pair of potential electrodes 12. A measuring part 20 measures specific resistance in the ground E by a potential between the AC current flowing into the ground E by the current electrodes 11, and the potential electrodes 12 measured by the potential electrodes 12. The current electrodes 11 and the potential electrodes 12 can be measured by only approaching the pore wall W, which measures the specific resistance in the ground E while reducing the influence of irregularity of the porous wall W and can improve accuracy of specific resistance measurement of the ground E.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a resistivity measuring device, a method for managing a ground improvement body, and a method for measuring resistivity. [Background technology]

[0002] Techniques for measuring resistivity underground have been proposed. For example, Patent Document 1 discloses a technique for measuring resistivity underground using a current electrode and a potential electrode attached to a cone at the tip of a rod that is inserted into the ground. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-119277 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above-mentioned technology has the disadvantage that the measured resistivity is easily affected by the unevenness of the hole wall formed in the ground by the rod, the gravel outcropping on the hole wall, and the local contact state between the electrode and the ground, making it difficult to make high-precision measurements.

[0005] Therefore, an object of the present invention is to provide a resistivity measuring device, a method for managing ground improvement bodies, and a resistivity measuring method that can improve the accuracy of underground resistivity measurements. [Means for solving the problem]

[0006] The present invention provides a resistivity measuring device that includes a capacitor electrode device in which a pair of capacitor electrodes consisting of a dielectric facing the hole wall of a hole in the ground and a conductor connected to the dielectric are arranged as a pair of current electrodes along the extension direction of the hole, and an AC voltage is applied between the pair of current electrodes to pass an AC current through the ground, while the pair of capacitor electrodes consisting of a dielectric facing the hole wall and a conductor connected to the dielectric are arranged as a pair of potential electrodes along the extension direction of the hole and measure the potential between the pair of potential electrodes, and a measuring unit that measures the resistivity of the ground using the AC current passed through the ground by the current electrodes of the capacitor electrode device and the potential between the potential electrodes measured by the potential electrodes of the capacitor electrode device.

[0007] According to this configuration, the capacitor electrode device of the resistivity measuring device arranges a pair of capacitor electrodes, each consisting of a dielectric facing the hole wall of a hole in the ground and a conductor connected to the dielectric, as a pair of current electrodes along the extension direction of the hole, and applies an AC voltage between the pair of current electrodes to pass an AC current through the ground. The pair of capacitor electrodes, each consisting of a dielectric facing the hole wall and a conductor connected to the dielectric, is arranged as a pair of potential electrodes along the extension direction of the hole, and measures the potential between the pair of potential electrodes. The measuring unit of the resistivity measuring device measures the resistivity of the ground based on the AC current passed through the ground by the current electrodes of the capacitor electrode device and the potential between the potential electrodes measured by the potential electrodes of the capacitor electrode device. Because the current and potential electrodes, which are capacitor electrodes, can be measured simply by being close to the hole wall, the resistivity of the ground can be measured while reducing the effects of unevenness on the hole wall, gravel outcropping on the hole wall, and the local contact state between the electrodes and the natural ground, thereby improving the accuracy of the resistivity measurement of the ground.

[0008] In this case, the capacitor electrode device preferably has an electrode spacing change mechanism that changes the spacing between the current electrode and the potential electrode within the hole in the extending direction of the hole.

[0009] According to this configuration, in the capacitor electrode device, the electrode spacing change mechanism changes the spacing between the current electrode and the potential electrode in the direction of extension of the hole, so that the position underground where the resistivity is measured in a direction perpendicular to the direction of extension of the hole can be changed as desired.

[0010] The capacitor electrode device preferably has a distance adjusting mechanism for changing the distance between the dielectric of the current electrode and the potential electrode and the hole wall.

[0011] According to this configuration, in the capacitor electrode device, the distance between the dielectric of the current electrode and the potential electrode and the hole wall is changed by the distance adjustment mechanism, so when the current electrode and the potential electrode move within the hole, the distance between the dielectric of the current electrode and the potential electrode and the hole wall can be increased, making it easier for the current electrode and the potential electrode to move within the hole.On the other hand, when measuring the potential between the potential electrodes while passing an AC current through the ground using the current electrode, the distance between the dielectric of the current electrode and the potential electrode and the hole wall can be decreased, making it possible to accurately measure the resistivity of the ground.

[0012] When the capacitor electrode device has a separation adjustment mechanism, the separation adjustment mechanism may change the separation between the dielectric and the hole wall by expanding and contracting the tubular, flexible dielectric.

[0013] According to this configuration, the distance adjustment mechanism changes the distance between the dielectric and the hole wall by expanding and contracting the tubular, flexible dielectric, so that the distance between the dielectric and the hole wall can be changed with a simple mechanism.

[0014] In addition, if the capacitor electrode device has a distance adjustment mechanism, the distance adjustment mechanism may change the distance between the dielectric and the hole wall by expanding and contracting the tubular dielectric, which is formed by winding a plate-shaped dielectric around the extension direction of the hole while including an overlapping portion.

[0015] According to this configuration, the distance adjustment mechanism changes the distance between the dielectric and the hole wall by expanding and contracting the tubular dielectric, which is formed by winding the plate-shaped dielectric around the extension direction of the hole while including the overlapping portion, and therefore the distance between the dielectric and the hole wall can be changed with a simple mechanism.

[0016] Furthermore, when the capacitor electrode device has a distance adjustment mechanism, the distance adjustment mechanism may change the distance between the dielectric and the hole wall by expanding and contracting a tubular dielectric that includes a folded portion.

[0017] According to this configuration, the distance adjustment mechanism changes the distance between the dielectric and the hole wall by expanding and contracting the tubular dielectric including the folded portion, so that the distance between the dielectric and the hole wall can be changed with a simple mechanism.

[0018] In addition, in the capacitor electrode device, the dielectric of the current electrode and potential electrode may be a tubular casing that supports the hole wall, and the conductor of the current electrode and potential electrode may be arranged inside the casing along the extension direction of the hole and connected to the casing.

[0019] According to this configuration, in the capacitor electrode device, the dielectric of the current electrode and potential electrode is a tubular casing that supports the hole wall, and the conductors of the current electrode and potential electrode are arranged inside the casing along the extension direction of the hole and connected to the casing, thereby preventing the hole wall from collapsing. Furthermore, the casing itself acts as a dielectric and forms a capacitor electrode together with the conductors arranged inside the casing. Therefore, a separate member that acts as a dielectric is not required for the conductor that moves up and down inside the casing, allowing the capacitor electrode device to have a simple configuration.

[0020] In this case, the capacitor electrode device preferably has a conductor spacing change mechanism that changes the spacing between the conductors of the current electrode and the potential electrode in the extending direction of the hole inside the casing.

[0021] According to this configuration, in the capacitor electrode device, the conductor spacing change mechanism changes the spacing between the conductors of the current electrode and the potential electrode in the direction of extension of the hole inside the casing, so that the position underground where the resistivity is measured in a direction perpendicular to the direction of extension of the hole can be changed as desired.

[0022] The capacitor electrode device preferably has a drainage mechanism for draining water between the dielectric of the current electrode and the potential electrode and the pore wall.

[0023] According to this configuration, in the capacitor electrode device, the drainage mechanism drains water between the dielectric of the current electrode and potential electrode and the hole wall, thereby reducing the effect of water in the hole.

[0024] On the other hand, the present invention is a method for managing a ground improvement body, which comprises placing a capacitor electrode device of the resistivity measuring device of the present invention in a hole formed in the ground improvement body, applying an AC voltage between a pair of current electrodes of the capacitor electrode device to pass an AC current through the ground improvement body, measuring the potential between a pair of potential electrodes of the capacitor electrode device, and measuring the resistivity of the ground improvement body using the measuring unit of the capacitor electrode device.

[0025] According to this configuration, in the method for managing a ground improvement body, a capacitor electrode device of the resistivity measurement device of the present invention is placed in a hole formed in the ground improvement body, an AC voltage is applied between a pair of current electrodes of the capacitor electrode device to pass an AC current through the ground improvement body, the potential between a pair of potential electrodes of the capacitor electrode device is measured, and the resistivity of the ground improvement body is measured by the measurement unit of the capacitor electrode device. Since the current electrode and potential electrode, which are capacitor electrodes, can be measured simply by being brought close to the hole wall, the influence of unevenness of the hole wall formed in the ground improvement body, gravel outcropping on the hole wall, and the local contact state between the electrode and the ground can be reduced, and the accuracy of management of the ground improvement body can be improved by measuring the resistivity of the ground improvement body.

[0026] The present invention also provides a resistivity measurement method comprising an electrode arrangement step of arranging a pair of capacitor electrodes, each consisting of a dielectric facing the hole wall of a hole in the ground and a conductor connected to the dielectric, as a pair of current electrodes along the extension direction of the hole, and arranging a pair of capacitor electrodes, each consisting of a dielectric facing the hole wall and a conductor connected to the dielectric, as a pair of potential electrodes along the extension direction of the hole; and a measurement step of measuring the potential between the pair of potential electrodes arranged in the electrode arrangement step while applying an AC voltage between the pair of current electrodes arranged in the electrode arrangement step to flow an AC current into the ground, and measuring the resistivity of the ground from the AC current flowed into the ground by the current electrodes and the potential between the potential electrodes measured by the potential electrodes. [Effects of the Invention]

[0027] According to the resistivity measuring device, the method for managing a ground improvement body, and the method for measuring resistivity of the present invention, the accuracy of measuring resistivity in the ground can be improved. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a diagram showing an overview of a resistivity measuring device and a resistivity measuring method according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing details of the resistivity measuring device of FIG. [Figure 3] (A) is a diagram showing a state in which the distance between the dielectric of the distance adjustment mechanism of the resistivity measuring device of the first embodiment and the hole wall is large, (B) is a diagram showing a state in which the distance between the dielectric of the distance adjustment mechanism of (A) and the hole wall is small, (C) is a diagram showing a state in which the distance between the dielectric of the distance adjustment mechanism of the resistivity measuring device of the second embodiment and the hole wall is large, (D) is a diagram showing a state in which the distance between the dielectric of the distance adjustment mechanism of (C) and the hole wall is small, (E) is a diagram showing a state in which the distance between the dielectric of the distance adjustment mechanism of the resistivity measuring device of the third embodiment and the hole wall is large, and (F) is a diagram showing a state in which the distance between the dielectric of the distance adjustment mechanism of (E) and the hole wall is small. [Figure 4] 10 is a diagram showing the relationship between the distance between the current electrode and the potential electrode in the capacitor electrode device and the position in the ground where the resistivity is measured in a direction perpendicular to the extension direction of the hole. FIG. [Figure 5] FIG. 10 is a diagram showing a resistivity measuring device according to a fourth embodiment. [Figure 6] FIG. 10 is a diagram showing an outline of a resistivity measuring device and a resistivity measuring method according to a fifth embodiment. [Figure 7] FIG. 7 is a diagram showing details of the resistivity measuring device of FIG. 6. [Figure 8] A diagram showing a management method for a ground improvement body of the sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0029] An embodiment of the present invention will be described below with reference to the drawings. As shown in FIGS. 1 and 2, a resistivity measurement device 1A of this embodiment includes a capacitor electrode device 10A and a measurement unit 20. The resistivity measurement device 1A of this embodiment measures, for example, the distribution of resistivity in the lateral and depth directions of the ground E. It is known that there is a correlation between the resistivity of the ground E and the dry density of the ground E. It is also known that there is a correlation between the resistivity of the ground E and the wet density of the ground E. Therefore, the distribution of the dry density and wet density in the lateral and depth directions of the ground E can be derived based on the distribution of the resistivity of the ground E. The resistivity measurement device 1A of this embodiment can measure the resistivity of the ground E based on the distribution of the dry density or wet density in the lateral and depth directions of the ground E.

[0030] In this embodiment, a hole H extending in the vertical direction is formed in the ground E by boring or the like. In this embodiment, as shown in Figures 3(A) and 3(B), the cross-sectional shape of the hole H is circular. The inner diameter of the hole H can be, for example, several hundred mm. Note that the hole H does not necessarily have to be artificially formed by boring or the like, but may have existed naturally before the resistivity measurement by the resistivity measurement device 1A. The cross-sectional shape of the hole H may also be elliptical or polygonal. The hole H does not necessarily have to extend vertically, but may extend in a direction inclined less than 90° from the vertical. The hole H does not necessarily have to extend linearly, but may extend while bending. The inner diameter of the hole H does not necessarily have to be constant at each position in the extension direction of the hole H.

[0031] As shown in Figures 2, 3(A), and 3(B), in the capacitor electrode device 10A, a pair of capacitor electrodes 10, each consisting of a dielectric 13 facing the hole wall W of a hole H in the ground E and a conductor 14 connected to the dielectric 13, are arranged as a pair of current electrodes 11 along the extension direction of the hole H. In the capacitor electrode device 10A, an AC voltage is applied between the pair of current electrodes 11 to cause an AC current to flow through the ground E. The dielectric 13 is, for example, a cylindrical member made of a general synthetic resin. The conductor 14 is a cylindrical electrode made of a conductive metal. The capacitor electrode 10 is waterproofed.

[0032] In the capacitor electrode device 10A, an AC current is passed through the ground E by a pair of current electrodes 11, and a pair of capacitor electrodes 10, each consisting of a dielectric 13 facing the hole wall W and a conductor 14 connected to the dielectric 13, is arranged as a pair of potential electrodes 12 along the extension direction of the hole H. In the capacitor electrode device 10A, an AC current is passed through the ground E by the pair of current electrodes 11, and the potential between the pair of potential electrodes 12 is measured.

[0033] Each of the capacitor electrodes 10 of the capacitor electrode device 10A has a cylindrical shape that follows the shape of the hole wall W of the hole H. Adjacent capacitor electrodes 10 are connected to each other via cables 15c along the extension direction of the hole H. The capacitor electrode 10 closest to the ground surface S is connected via cable 15c to a measurement unit 20 installed near the hole H on the ground surface S. Each of the capacitor electrodes 10 of the capacitor electrode device 10A is suspended into the hole H from the measurement unit 20 installed on the ground surface S via the cable 15c. The cable 15c connecting the capacitor electrode 10 closest to the ground surface S and the measurement unit 20 is wound around a winch 20w of the measurement unit 20. The winch 20w allows the resistivity measurement device 1A to freely change the depth of the capacitor electrode device 10A from the ground surface S.

[0034] The measurement unit 20 is electrically connected to each of the capacitor electrodes 10 of the capacitor electrode device 10A via a cable 15c. The measurement unit 20 measures the resistivity of the ground E based on the alternating current passed through the ground E by the current electrodes 11 of the capacitor electrode device 10A and the potential between the potential electrodes 12 measured by the potential electrodes 12 of the capacitor electrode device 10A. Note that the connection between the measurement unit 20 and the capacitor electrode device 10A and the physical connection between each of the adjacent capacitor electrodes 10 may be made by a rope, chain, rod, or the like other than the cable 15c, and the electrical connection between the measurement unit 20 and the capacitor electrode device 10A and the electrical connection between each of the adjacent capacitor electrodes 10 may be made by the cable 15c.

[0035] When a voltage is applied to the conductors 14 of a pair of current electrodes 11 that are not in contact with the hole wall W of the hole H, an electric charge accumulates between the conductors 14 and the ground E at the hole wall W, and the current electrodes 11 become capacitors. If the polarity of the voltage is switched before the current electrodes 11 that have become capacitors are completely charged or discharged, an AC current can be continuously passed through the ground E. As a result, an electric field is formed in the ground E. When an electric field is formed in the ground E, and the potential is measured by a pair of potential electrodes 12 at a position slightly away from the current electrodes 11, the apparent resistivity of the ground E can be measured only between the current electrodes 11 and the potential electrodes 12.

[0036] In the capacitor electrode device 10A of this embodiment, a pair of current electrodes 11 are arranged on the side closer to the ground surface S along the extension direction of the hole H, and a pair of potential electrodes 12 are arranged on the side farther from the ground surface S along the extension direction of the hole H. However, in the capacitor electrode device 10A, the current electrodes 11 and the potential electrodes 12 may be arranged in a Wenner arrangement. In the Wenner arrangement, a pair of current electrodes 11 are arranged along the extension direction of the hole H, and a pair of potential electrodes 12 are arranged between the pair of current electrodes 11 along the extension direction of the hole H.

[0037] The capacitor electrode device 10A has an electrode spacing change mechanism 15A that changes the spacing between the current electrode 11 and the potential electrode 12 within the hole H in the direction in which the hole H extends. The electrode spacing change mechanism 15A includes a cable 15c that connects adjacent capacitor electrodes 10, and a winch 15w that is fixed to each of the capacitor electrodes 10 and winds up the cable 15c. The winch 15w enables the capacitor electrode device 10A to freely change the spacing between the current electrode 11 and the potential electrode 12 within the hole H in the direction in which the hole H extends.

[0038] As shown in Figures 3(A) and 3(B), the capacitor electrode device 10A has a distance adjustment mechanism 16A that changes the distance between the dielectric 13 of the current electrode 11 and the potential electrode 12 and the hole wall W. In this embodiment, the distance adjustment mechanism 16A changes the distance between the dielectric 13 and the hole wall W by expanding and contracting the tubular, flexible dielectric 13. The distance adjustment mechanism 16A is made of, for example, a dielectric 13 having an outer tube 16o and an inner tube 16i inside the outer tube 16o, which are hermetically sealed together. A conductor 14 is attached to the outer tube 16o of the dielectric 13 so as to fit along the inner surface thereof.

[0039] As shown in Figure 3(A), separation adjustment mechanism 16A contracts dielectric 13 by, for example, discharging gas from between outer tube 16o and inner tube 16i, thereby increasing the distance between dielectric 13 of current electrode 11 and potential electrode 12 and hole wall W. As shown in Figure 3(B), separation adjustment mechanism 16A expands dielectric 13 by, for example, introducing gas between outer tube 16o and inner tube 16i, thereby decreasing the distance between dielectric 13 of current electrode 11 and potential electrode 12 and hole wall W. Note that, in addition to discharging and introducing gas, an electric motor or the like can also be used as the power source for separation adjustment mechanism 16A.

[0040] As shown in Figure 2, the capacitor electrode device 10A has a drainage mechanism 19 that drains water between the dielectric 13 of the current electrode 11 and the potential electrode 12 and the hole wall W. The drainage mechanism 19 includes, for example, a tubular member whose tip is located further below the capacitor electrode 10 that is located farthest from the ground surface S. The drainage mechanism 19 sucks water from the tip of the tubular member and drains it to the outside, such as the ground surface S. The drainage mechanism 19 includes a pump (not shown) that serves as a power source for drainage, located either underground E or on the ground surface S.

[0041] The drainage mechanism 19 need only drain water present in only the portion of the hole H where the capacitor electrode 10 is located, rather than the entire hole H. In other words, the drainage mechanism 19 does not necessarily have to drain water from the underground E down to the ground surface S. Furthermore, in order to prevent the capacitor electrode device 10A from floating up, a weight may be installed on the capacitor electrode 10 located farthest from the ground surface S, or on each of the capacitor electrodes 10.

[0042] In the resistivity measurement method using the resistivity measurement device 1A of this embodiment described above, an electrode arrangement process is carried out in which a pair of capacitor electrodes 10 consisting of a dielectric 13 facing the hole wall W of a hole H in the ground E and a conductor 14 connected to the dielectric 13 are arranged along the extension direction of the hole H as a pair of current electrodes 11, and a pair of capacitor electrodes 10 consisting of a dielectric 13 facing the hole wall W and a conductor 14 connected to the dielectric 13 are arranged along the extension direction of the hole H as a pair of potential electrodes 12.

[0043] In the electrode placement process, after all of the capacitor electrodes 10 of the capacitor electrode device 10A have been lowered into the hole H, the capacitor electrode device 10A is suspended from the winch 20w of the measurement unit 20 and lowered below the hole H. In the electrode placement process, the capacitor electrodes 10 are placed while the positions (depths) of the respective capacitor electrodes 10 in the hole H are measured.

[0044] In the resistivity measurement method using the resistivity measurement device 1A of this embodiment, a measurement step is performed in which an AC voltage is applied between a pair of current electrodes 11 arranged in an electrode arrangement step to flow an AC current into the ground E, while measuring the potential between the pair of potential electrodes 12 arranged in the electrode arrangement step, and the resistivity of the ground E is measured from the AC current flowed into the ground E by the current electrodes 11 and the potential measured between the potential electrodes 12 by the potential electrodes 12. In the measurement step, for example, measurement is performed from the lower end of the measurement range in the hole H, and measurement is performed while the capacitor electrodes 10 are pulled up. In the measurement step, measurement is performed while the resistivity of the ground E and the respective positions (depths) of the capacitor electrodes 10 in the ground E are associated and recorded.

[0045] If the underground E is not natural ground but is made of a known material such as fill, it is possible to measure absolute dry density distribution and wet density distribution by determining the relationship between resistivity and dry density or the relationship between resistivity and wet density through prior calibration. After the measurement is completed, the capacitor electrode device 10A and the measurement unit 20 are removed.

[0046] Conventional methods for measuring underground density include soil density tests using the sand-thrust method (JGS1611) and the sand-displacement method (JIS A 1214). With the sand-thrust and sand-displacement methods, a test hole is excavated at the ground surface and known reference sand is replaced. The soil density is obtained from the ratio between the mass of the excavated soil and the amount of replaced reference sand. With the sand-thrust and sand-displacement methods, the density of the target ground can be directly evaluated, but the evaluation depth is limited to the surface layer up to several tens of centimeters from the ground surface, and there is a drawback in that the density distribution in the depth direction cannot be measured.

[0047] Another conventional method for measuring underground density is soil density testing using an RI meter (JGS1614). In soil density testing using an RI meter, a radiation source rod that emits gamma rays is inserted into the ground from the ground surface. The amount of gamma rays emitted from the radiation source rod that reaches the ground is detected by a detection tube installed on the ground surface. Soil density testing using an RI meter is a method that utilizes the fact that the proportion of gamma rays absorbed in the ground has a constant relationship with the wet density of the soil. Soil density testing using an RI meter can be performed in a short time, making multi-point measurements possible. In addition, soil density testing using an RI meter has little error due to the operator. However, a drawback is that the evaluation depth of soil density testing using an RI meter is about the same as that of the sand displacement method.

[0048] Another conventional method for measuring underground density is density logging. In density logging, a gamma-ray emitting source is placed inside a borehole, and the amount of gamma rays emitted from the source is detected by a detector tube installed on the ground surface. Density logging is based on the same principle as the RI method, but it can measure wet density continuously along the depth direction. RI cones, which do not require boreholes, have also been put into practical use for density logging. Density logging can accurately measure density distribution along the depth direction. However, density logging using RI cones is applicable to soils with low penetration resistance (N-values of around 20 or less), but has the disadvantage that it cannot be used for harder soils. Furthermore, since the measurement range of density logging is limited to the vicinity of the borehole, the presence or absence of a casing and looseness of the borehole wall can affect the measured values.

[0049] Another conventional method for measuring underground density is electrical exploration. In electrical exploration, multiple electrodes placed on the ground surface measure the resistivity of the soil, and the physical properties of the soil are estimated from the resistivity. Electrical exploration allows for two-dimensional measurements, but because resistivity is measured from the ground surface, it has the disadvantage of having lower resolution in the depth direction the deeper it is.

[0050] As described above, with conventional methods for measuring underground density, the sand-thrust method allows evaluation to a depth of approximately 0.3 m from the ground surface. With the RI method, the evaluation depth is limited to a depth of approximately 0.2 to 0.5 m from the ground surface. With density logging, the evaluation depth is limited to the depth of the borehole drilled, but the radial depth is approximately 0.3 m from the borehole wall. With electrical prospecting, the evaluation depth is approximately 2 to 5 m for shallow exploration, and approximately 5 to 100 m for general exploration, but the resolution in the depth direction is low. As described above, with conventional methods for measuring underground density, the evaluation depth is limited to a shallow range, or even at deep depths, the lateral range and measurement accuracy are limited.

[0051] On the other hand, according to this embodiment, capacitor electrode device 10A of resistivity measuring device 1A arranges a pair of capacitor electrodes 10, each consisting of a dielectric 13 facing hole wall W of hole H in the ground E and a conductor 14 connected to dielectric 13, as a pair of current electrodes 11 along the extension direction of hole H, and applies an AC voltage between the pair of current electrodes 11 to pass an AC current through the ground E, while also arranging the pair of capacitor electrodes 10, each consisting of a dielectric 13 facing hole wall W and a conductor 14 connected to dielectric 13, as a pair of potential electrodes 12 along the extension direction of hole H, and measures the potential between the pair of potential electrodes 12. Measurement unit 20 of resistivity measuring device 1A measures the resistivity of the ground E from the AC current passed through current electrode 11 of capacitor electrode device 10A into the ground E and the potential between potential electrodes 12 measured by potential electrode 12 of capacitor electrode device 10A. The current electrode 11 and potential electrode 12, which are capacitor electrodes 10, can be measured simply by being close to the hole wall W, so the accuracy of measuring the resistivity of underground E can be improved by measuring the resistivity of underground E while reducing the effects of unevenness on the hole wall W, gravel outcropping on the hole wall W, and the local contact state between the electrodes and the ground.

[0052] That is, in this embodiment, the capacitor electrode 10 that is not in contact with the hole wall W serves as an electrode that passes current through the ground E, and therefore the capacitor electrode 10, which is relatively insensitive to local contact conditions, makes it possible to measure the resistivity of the ground E while reducing the effects of unevenness of the hole wall W, gravel outcropped on the hole wall W, and the local contact condition between the electrode and the ground. Also, changes in the physical properties of the ground E in the depth direction can be grasped continuously and accurately.

[0053] Furthermore, according to this embodiment, in capacitor electrode device 10A, electrode spacing change mechanism 15A changes the spacing between current electrode 11 and potential electrode 12 in the extension direction of hole H within hole H, so that the position in the ground E where resistivity is measured in a direction perpendicular to the extension direction of hole H can be changed arbitrarily. In other words, in this embodiment, by arbitrarily changing the spacing between current electrode 11 and potential electrode 12, it is possible to measure the resistivity, dry density, and wet density of the ground E at any measurement radius.

[0054] 4, for example, in a capacitor electrode device 10A, it is assumed that the length of each of the capacitor electrodes 10 is l and the width of each of the capacitor electrodes 10 is w. It is also assumed that the length of the cable 15c connecting each of a pair of current electrodes 11 and a pair of potential electrodes 12 is c1, and the length of the cable 15c connecting adjacent current electrodes 11 and potential electrodes 12 is c2.

[0055] The distance between a pair of current electrodes 11 and a pair of potential electrodes 12 is assumed to be a. The distance between adjacent current electrodes 11 and potential electrodes 12 is assumed to be an integer multiple na of the distance a. Note that the distance between each of the capacitor electrodes 10 is based on the midpoint of the length l of the capacitor electrode 10. In this case, the approximate range in which the resistivity can be measured in the extension direction of the capacitor electrode device 10A, i.e., in the direction perpendicular to the extension direction of the hole, can be determined by any of a(n+1) / 2, a(n+1) / 3, and a(n+1) / 4. Note that there are various theories about the denominators 2 to 4.

[0056] For example, in Figure 4, if the length l is 0.3 m, the width w is 0.1 m, the length c1 is 0.4 m, and c2 is 1.1 m, then the interval a is 0.7 m, and the integer multiple na of the interval a is 1.4 m. The approximate range in which the resistivity in the direction perpendicular to the extension direction of the hole can be measured can be any of a(n+1) / 2 = 1.05 m, a(n+1) / 3 = 0.7 m, and a(n+1) / 4 = 0.525 m.

[0057] Furthermore, according to this embodiment, in capacitor electrode device 10A, distance adjustment mechanism 16A changes the distance between dielectric 13 of current electrode 11 and potential electrode 12 and hole wall W, so that when current electrode 11 and potential electrode 12 move through hole H, the distance between dielectric 13 of current electrode 11 and potential electrode 12 and hole wall W can be increased, facilitating movement of current electrode 11 and potential electrode 12 within hole H. On the other hand, when measuring the potential between potential electrode 12 while passing an AC current through the ground E using current electrode 11, the distance between dielectric 13 of current electrode 11 and potential electrode 12 and hole wall W can be decreased, allowing the resistivity of the ground E to be measured with high accuracy.

[0058] Furthermore, according to this embodiment, the distance adjustment mechanism 16A changes the distance between the dielectric 13 and the hole wall W by expanding and contracting the tubular and flexible dielectric 13, so that the distance between the dielectric 13 and the hole wall W can be changed using a simple mechanism.

[0059] Furthermore, according to this embodiment, in the capacitor electrode device 10A, the drainage mechanism 19 drains water between the dielectric 13 of the current electrode 11 and the potential electrode 12 and the hole wall W, thereby reducing the effect of water in the hole H.

[0060] A second embodiment of the present invention will be described below. As shown in Figures 3(C) and 3(D), in a resistivity measuring device 1B of this embodiment, a distance adjusting mechanism 16B of a capacitor electrode device 10B changes the distance between the dielectric 13 and the hole wall W by expanding and contracting the plate-like dielectric 13, which is formed by winding the plate-like dielectric 13 around the hole H in the extending direction while including an overlapping portion 16l. The conductor 14 is attached so as to fit along the inner surface of the dielectric 13.

[0061] As shown in FIG. 3(C), separation adjustment mechanism 16B contracts dielectric 13 by increasing the area of overlapping portion 16l, thereby increasing the distance between dielectric 13 of current electrode 11 and potential electrode 12 and hole wall W. As shown in FIG. 3(D), separation adjustment mechanism 16B expands dielectric 13 by decreasing the area of overlapping portion 16l, thereby decreasing the distance between dielectric 13 of current electrode 11 and potential electrode 12 and hole wall W. The power source for separation adjustment mechanism 16B can be the exhaust and introduction of gas from inside conductor 14. The power source for separation adjustment mechanism 16B can also be an electric motor or the like.

[0062] In this embodiment, the distance adjustment mechanism 16C changes the distance between the dielectric 13 and the hole wall W by expanding and contracting the plate-shaped dielectric 13, which is formed by winding the plate-shaped dielectric 13 around the extension direction of the hole H while including the overlapping portion 16l, thereby making it possible to change the distance between the dielectric 13 and the hole wall W using a simple mechanism.

[0063] A third embodiment of the present invention will now be described. As shown in Figures 3(E) and 3(F), in a resistivity measuring device 1C of this embodiment, a capacitor electrode device 10C has a distance adjustment mechanism 16C that expands and contracts a tubular dielectric 13 including a folded portion 16h, thereby changing the distance between the dielectric 13 and the hole wall W. A conductor 14 is attached to the dielectric 13 so as to fit along its inner surface.

[0064] As shown in FIG. 3(E), the separation adjustment mechanism 16C folds the folding portion 16h to contract the dielectric 13 and increase the distance between the dielectric 13 of the current electrode 11 and the potential electrode 12 and the hole wall W. As shown in FIG. 3(F), the separation adjustment mechanism 16C expands the folding portion 16h to expand the dielectric 13 and decrease the distance between the dielectric 13 of the current electrode 11 and the potential electrode 12 and the hole wall W. The power source of the separation adjustment mechanism 16C can be the exhaust and introduction of gas from inside the conductor 14. The power source of the separation adjustment mechanism 16C can also be an electric motor or the like.

[0065] In this embodiment, the distance adjustment mechanism 16C changes the distance between the dielectric 13 and the hole wall W by expanding and contracting the tubular dielectric 13 including the folded portion 16h, so that the distance between the dielectric 13 and the hole wall W can be changed using a simple mechanism.

[0066] A fourth embodiment of the present invention will now be described. As shown in Fig. 5, in a capacitor electrode device 10D of a resistivity measuring device 1D of this embodiment, the dielectric 13 of the current electrode 11 and the potential electrode 12 is a tubular casing 17 that supports the hole wall W, and the conductor 14 of the current electrode 11 and the potential electrode 12 is arranged inside the casing 17 along the extension direction of the hole H and connected to the casing 17. That is, in this embodiment, the casing 17 itself plays the role of the dielectric 13, and forms a capacitor electrode 10 together with the conductor 14 arranged inside the casing 17. Since the casing 17 is the dielectric 13, it is, for example, a cylindrical member made of an insulating synthetic resin such as general polyvinyl chloride (PVC).

[0067] The capacitor electrode device 10D has a conductor spacing change mechanism 18 that changes the spacing between the conductors 14 of the current electrode 11 and the potential electrode 12 in the extension direction of the hole H inside the casing 17. Each of the conductors 14 of the capacitor electrodes 10 of the capacitor electrode device 10D has a cylindrical shape that conforms to the shape of the inner surface of the casing 17 and is slidable along the inner surface of the casing 17. The conductors 14 of adjacent capacitor electrodes 10 are connected to each other along the extension direction of the hole H via a cable 18c. The cable 18c that connects the conductor 14 of the capacitor electrode 10 closest to the ground surface S to the measurement unit 20 is wound around a winch 20w of the measurement unit 20. The winch 20w allows the resistivity measurement device 1D to freely change the depth of the capacitor electrode device 10D from the ground surface S.

[0068] The measuring unit 20 is electrically connected to each of the capacitor electrodes 10 of the capacitor electrode device 10D via a cable 18c. Note that the connection between the measuring unit 20 and the capacitor electrode device 10D and the physical connection between each of the conductors 14 of the adjacent capacitor electrodes 10 may be made by a rope, chain, rod, or the like other than the cable 18c, and the electrical connection between the measuring unit 20 and the capacitor electrode device 10D and the electrical connection between each of the conductors 14 of the adjacent capacitor electrodes 10 may be made by the cable 18c.

[0069] The conductor spacing change mechanism 18 includes a cable 18c that connects the conductors 14 of adjacent capacitor electrodes 10, and a winch 18w that is fixed to each of the conductors 14 and winds up the cable 18c. The winch 18w enables the capacitor electrode device 10D to freely change the spacing between the conductors 14 of the current electrode 11 and the potential electrode 12 in the extension direction of the hole H inside the casing 17.

[0070] In this embodiment, in capacitor electrode device 10D, dielectric 13 of current electrode 11 and potential electrode 12 is a tubular casing 17 that supports hole wall W, and conductor 14 of current electrode 11 and potential electrode 12 is arranged inside casing 17 along the extension direction of hole H and connected to casing 17, thereby preventing collapse of hole wall W. Furthermore, casing 17 itself plays the role of dielectric 13, and forms capacitor electrode 10 together with conductor 14 arranged inside casing 17. Therefore, conductor 14, which moves up and down inside casing 17, does not require a separate member that serves as dielectric 13, and capacitor electrode device 10D can be configured simply.

[0071] In addition, in this embodiment, in the capacitor electrode device 10D, the conductor spacing change mechanism 18 changes the spacing between the conductors 14 of the current electrode 11 and the potential electrode 12 in the extension direction of the hole H inside the casing 17, so that the position underground E where the resistivity is measured in a direction perpendicular to the extension direction of the hole H can be changed arbitrarily.

[0072] A fifth embodiment of the present invention will now be described. As shown in Figures 6 and 7, in the resistivity measurement device 1E of this embodiment, measurement is performed using a hole H extending in a horizontal direction, including the horizontal direction, in the same manner as in the above-described embodiment, in which a hole H extending in a vertical direction is bored. The hole H is a pipeline or the like buried underground. In this embodiment, the capacitor electrode 10 of the capacitor electrode device 10E is placed in the hole H extending in a horizontal direction, including a pipeline or the like buried underground E. Before placing the capacitor electrode 10 in the hole H, water is drained from inside the hole H of the pipeline or the like. The resistivity measurement device 1E includes a drainage mechanism 19 similar to that of the above-described embodiment.

[0073] In this embodiment, a traction force and a propulsion force are separately required to move the capacitor electrode 10 laterally. Therefore, as shown in FIG. 7 , in this embodiment, adjacent capacitor electrodes 10 are connected to each other via rods 15r along the extension direction of the hole H, and can apply a traction force in a direction to pull the capacitor electrode 10 toward the front side of the hole H and a propulsion force in a direction to push the capacitor electrode 10 toward the back side of the hole H to each other. The capacitor electrode 10 closest to the measurement unit 20 and the base 21 of the measurement unit 20 are connected to each other via the rods 15r. A rack 15k provided on the rod 15r and a pinion 20n on the base 21 mesh with each other. By rotating the pinion 20n, the capacitor electrode device 10E can freely change the position of the hole H in the horizontal direction.

[0074] Furthermore, the rod 15r connecting adjacent capacitor electrodes 10 and the rod 15r connecting the capacitor electrodes 10 and the measuring unit 20 include joints 15j that are bendable while transmitting traction and propulsion forces. The joints 15j allow the rods 15r to bend, allowing the capacitor electrode device 10E to accommodate bending of the hole H. The measuring unit 20 is electrically connected to each of the capacitor electrodes 10 of the capacitor electrode device 10E via the rods 15r. Note that the connection between the measuring unit 20 and the capacitor electrode device 10E and the physical connection between each of the adjacent capacitor electrodes 10 are made by the rods 15r, and the electrical connection between the measuring unit 20 and the capacitor electrode device 10E and the electrical connection between each of the adjacent capacitor electrodes 10 may be made by cables or the like, as in the above embodiment.

[0075] The capacitor electrode device 10E has an electrode spacing change mechanism 15B that changes the spacing between the current electrode 11 and the potential electrode 12 within the hole H in the direction in which the hole H extends. The electrode spacing change mechanism 15B includes a rod 15r that connects adjacent capacitor electrodes 10, a rack 15k provided on the rod 15r, and a pinion 15n that meshes with the rack 15k. By rotating the pinion 15n, the capacitor electrode device 10E can freely change the spacing between the current electrode 11 and the potential electrode 12 within the hole H in the direction in which the hole H extends.

[0076] The resistivity measurement device 1E of this embodiment is considered effective for preliminary investigations of linear structures such as tunnels, shields, and pipelines. Furthermore, many lifelines, such as water supply and sewerage, gas, and electricity, are buried underground E as pipelines, but they may be damaged due to aging or may be subject to scouring of the surrounding ground due to leaks. Some scouring may affect the ground surface S, potentially resulting in road flooding or sinkholes. To prevent these events, it is essential to predict and investigate them in advance. Therefore, in this embodiment, the capacitor electrode 10 is passed through a hole H extending laterally, including a pipeline buried underground E, and the resistivity, dry density, and wet density of the underground E are measured. This allows the condition of the underground E around the hole H to be understood, enabling early detection of cavities and abnormalities.

[0077] A sixth embodiment of the present invention will now be described. As shown in Fig. 8, in this embodiment, a method for managing the finished shape of a ground improvement body B is carried out. The ground improvement body B is columnar, and is cast into the ground E to improve, for example, each of the layers of clayey soil s1, soft sand s2, and hard sand s3 in the ground E. A hole H extending in the vertical direction is formed in the ground improvement body B in advance by boring or the like.

[0078] Capacitor electrode devices 10A, 10B, 10C, 10D, 10E of the resistivity measuring devices 1A, 1B, 1C, 1D, 1E in the above embodiments are placed in holes H formed in the ground improvement body B. By applying an AC voltage between a pair of current electrodes 11 of the capacitor electrode device 10A or the like, an AC current is passed through the ground improvement body B, the potential between a pair of potential electrodes 12 of the capacitor electrode device 10A or the like is measured, and the resistivity of the ground improvement body B is measured by the measuring unit 20 of the capacitor electrode device 10A or the like.

[0079] Conventionally, the completed form management of ground improvement body B underground E involves determining the dimensions of ground improvement body B at the ground surface S, conducting sampling borings near the center of ground improvement body B, and checking the strength of the improvement body. However, this method does not allow for confirmation that columnar improvement has been carried out adequately underground E.

[0080] On the other hand, in this embodiment, the current electrode 11 and potential electrode 12, which are capacitor electrodes 10, can be measured simply by being brought close to the hole wall W, so the resistivity of the ground improvement body B can be measured while reducing the influence of unevenness on the hole wall W of the hole H formed in the ground improvement body B and gravel outcropping on the hole wall W, thereby improving the accuracy of management of the ground improvement body B. By arbitrarily changing the spacing between the capacitor electrodes 10, differences in the dry density of the ground improvement body B in the lateral direction can be confirmed, and the effective improvement diameter d of the ground improvement body B can be confirmed. In this embodiment, it is possible to measure parts where the dry density is discontinuous, such as to confirm the effective improvement diameter d of the ground improvement body B.

[0081] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be embodied in various forms. [Explanation of symbols]

[0082] 1A, 1B, 1C, 1D, 1E... resistivity measuring device, 10... capacitor electrode, 10A, 10B, 10C, 10D, 10E... capacitor electrode device, 11... current electrode, 12... potential electrode, 13... dielectric, 14... conductor, 15A, 15B... electrode spacing changing mechanism, 15c... cable, 15w... winch, 15r... rod, 15k... rack, 15n... pinion, 15j... joint, 16A, 16B, 16C... separation adjustment mechanism, 16o... outer Pipe, 16i...inner pipe, 16l...overlapping section, 16h...folded section, 17...casing, 18...conductor spacing change mechanism, 18c...cable, 18w...winch, 19...drainage mechanism, 20...measuring section, 20w...winch, 20n...pinion, 21...base, S...ground surface, E...underground, H...hole, W...hole wall, a...spacing, na...integer multiple, l...length, w...width, c1, c2...length, B...ground improvement body, d...effective improvement diameter, s1...clay soil, s2...soft sand, s3...hard sand.

Claims

1. a capacitor electrode device which arranges a pair of capacitor electrodes, each consisting of a dielectric facing a hole wall of a hole in the ground and a conductor connected to the dielectric, as a pair of current electrodes along the extension direction of the hole, and measures the potential between the pair of potential electrodes while applying an AC voltage between the pair of current electrodes to cause an AC current to flow in the ground; a measuring unit that measures the resistivity of the ground based on an AC current passed through the ground by the current electrode of the capacitor electrode device and a potential between the potential electrodes measured by the potential electrode of the capacitor electrode device; Equipped with the capacitor electrode device has an electrode spacing change mechanism that changes a spacing between the current electrode and the potential electrode in the extension direction of the hole, The electrode spacing change mechanism includes: A resistivity measuring device comprising: a cable connecting adjacent capacitor electrodes; and a winch fixed to the capacitor electrodes and winding up the cable.

2. a capacitor electrode device which arranges a pair of capacitor electrodes, each consisting of a dielectric facing a hole wall of a hole in the ground and a conductor connected to the dielectric, as a pair of current electrodes along the extension direction of the hole, and measures the potential between the pair of potential electrodes while applying an AC voltage between the pair of current electrodes to cause an AC current to flow in the ground; a measuring unit that measures the resistivity of the ground based on an AC current passed through the ground by the current electrode of the capacitor electrode device and a potential between the potential electrodes measured by the potential electrode of the capacitor electrode device; Equipped with the capacitor electrode device has an electrode spacing change mechanism that changes a spacing between the current electrode and the potential electrode in the extension direction of the hole, The electrode spacing change mechanism includes: A resistivity measuring device comprising: a rod connecting adjacent capacitor electrodes; a rack provided on the rod; and a pinion provided on the capacitor electrode and meshing with the rack.

3. A capacitor electrode device which arranges a pair of capacitor electrodes, each consisting of a dielectric facing the hole wall of a hole in the ground and a conductor connected to the dielectric, as a pair of current electrodes along the extension direction of the hole, and applies an AC voltage between the pair of current electrodes to cause an AC current to flow in the ground, while also arranging a pair of capacitor electrodes, each consisting of a dielectric facing the hole wall and a conductor connected to the dielectric, as a pair of potential electrodes along the extension direction of the hole, and measures the potential between the pair of potential electrodes; a measuring unit that measures the resistivity of the ground based on an AC current passed through the ground by the current electrode of the capacitor electrode device and a potential between the potential electrodes measured by the potential electrode of the capacitor electrode device; Equipped with The capacitor electrode device has a distance adjustment mechanism for changing the distance between the dielectric of the current electrode and the potential electrode and the hole wall.

4. 4. The resistivity measuring device according to claim 3, wherein the distance adjusting mechanism changes the distance between the dielectric and the hole wall by expanding and contracting the flexible tubular dielectric.

5. 4. The resistivity measuring device according to claim 3, wherein the distance adjustment mechanism changes the distance between the dielectric and the hole wall by expanding and contracting the plate-shaped dielectric, which is formed into a tubular shape by being wound around the extension direction of the hole while including an overlapping portion.

6. The resistivity measuring device according to claim 3 , wherein the distance adjusting mechanism changes the distance between the dielectric and the hole wall by expanding and contracting the tubular dielectric including a folded portion.

7. A capacitor electrode device which arranges a pair of capacitor electrodes, each consisting of a dielectric facing the hole wall of a hole in the ground and a conductor connected to the dielectric, as a pair of current electrodes along the extension direction of the hole, and applies an AC voltage between the pair of current electrodes to cause an AC current to flow in the ground, while also arranging a pair of capacitor electrodes, each consisting of a dielectric facing the hole wall and a conductor connected to the dielectric, as a pair of potential electrodes along the extension direction of the hole, and measures the potential between the pair of potential electrodes; a measuring unit that measures the resistivity of the ground based on an AC current passed through the ground by the current electrode of the capacitor electrode device and a potential between the potential electrodes measured by the potential electrode of the capacitor electrode device; Equipped with In the capacitor electrode device, the dielectric of the current electrode and the potential electrode is a tubular casing that supports the hole wall, and the conductors of the current electrode and the potential electrode are arranged inside the casing along the extension direction of the hole and connected to the casing, the capacitor electrode device includes a conductor spacing change mechanism that changes the spacing between the conductors of the current electrode and the potential electrode in the extension direction of the hole inside the casing, The conductor spacing changing mechanism includes: A resistivity measuring device comprising: a cable connecting adjacent conductors; and a winch fixed to the conductors and winding up the cable.

8. The resistivity measuring device according to any one of claims 1 to 7, wherein the capacitor electrode device has a drainage mechanism that drains water between the dielectric of the current electrode and the potential electrode and the hole wall.

9. A method for managing a ground improvement body, comprising: A method for managing a ground improvement body, comprising: placing the capacitor electrode device of the resistivity measuring device described in any one of claims 1 to 8 in the hole formed in the ground improvement body; applying an AC voltage between the pair of current electrodes of the capacitor electrode device to pass an AC current through the ground improvement body; measuring the potential between the pair of potential electrodes of the capacitor electrode device; and measuring the resistivity of the ground improvement body using the measuring unit of the capacitor electrode device.

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