JP5283144B1 - Depth measurement system and depth measurement method - Google Patents

Abstract

A depth measurement system and a depth measurement method capable of improving the accuracy of position detection are provided.
A depth measurement system (1) includes a plurality of casing pipes (6, 7), a magnet (10), and a magnetic sensor (5). The plurality of casing pipes 6 and 7 are connected in the axial direction. The magnet 10 is provided in a reference casing pipe 7 serving as a reference among the plurality of casing pipes 6. The magnetic sensor 5 is inserted into the cylindrical holes of the plurality of casing pipes 6 and 7 and detects the magnetic force of the magnet 10.
[Selection] Figure 5

Description

  The present invention relates to a depth measurement system and a depth measurement method used when installing an observation device in a borehole.

  Conventionally, for earthquake research, a hole with a depth of 500 to 1000 m (hereinafter referred to as “boring hole”) is dug from the ground surface to the rock, and a strain gauge, stress meter, seismometer, thermometer is bored in the borehole. Installation of observation devices equipped with various sensors such as Usually, the observation apparatus is inserted into the borehole in a state where a cable made of a power supply line or a signal line strengthened against a load is attached and suspended from the cable.

  In addition, it is necessary to install an observation device at an accurate position in order to increase observation accuracy. In order to confirm the position of the observation apparatus, conventionally, the depth of the position where the observation apparatus is installed is obtained from the length of the cable that suspends the observation apparatus. However, since the cable extends depending on its own weight and the weight of the observation device, it is difficult to specify the exact position of the observation device.

  For this reason, as a technique for accurately confirming the depth of the observation apparatus, for example, a technique described in Patent Document 1 is disclosed. In the technique described in Patent Literature 1, an iron casing pipe that is a magnetic material and a stainless steel casing pipe that is a nonmagnetic material are provided as casing pipes that protect the hole wall of the boring hole. Further, an iron casing pipe and a stainless steel casing pipe are connected in the axial direction. And the installation depth of an observation apparatus is measured by detecting the change of the magnetic force which arises in the joint of an iron casing pipe and a stainless steel casing pipe with the magnetic sensor provided in the observation apparatus.

Next, a conventional method for measuring the installation depth of an observation apparatus will be described with reference to FIG.
FIG. 8 is an explanatory view schematically showing a conventional method for measuring the installation depth of an observation apparatus.

  As shown in FIG. 8, the conventional observation apparatus installation depth measuring method includes a first casing pipe 101 made of iron that protects a hole wall of a boring hole, and a second casing pipe 102 made of stainless steel. Yes. The magnetic properties of the first casing pipe 101 and the second casing pipe 102 are different. The first casing pipe 101 is made of a ferromagnetic material, and the second casing pipe 102 is made of a nonmagnetic material.

  The plurality of first casing pipes 101 are connected in the axial direction thereof. A second casing pipe is interposed at a predetermined location of the plurality of first casing pipes 101. Then, the observation device 103 suspended by the cable 104 is inserted into the cylindrical holes of the plurality of first casing pipes 101 and second casing pipes 102. Note that a magnetic sensor 105 is mounted on the observation device 103.

  When the observation device 103 passes through the first casing pipe 101 made of a ferromagnetic material, since the geomagnetism is shielded by the first casing pipe 101, the magnetic sensor 105 does not detect the geomagnetism, Magnetization of the casing pipe 101 is detected. However, since the geomagnetism easily leaks from the joint 106 of the casing pipes 101 and 102 into the cylindrical hole, the output of the magnetic sensor 105 changes slightly.

  Furthermore, since the second casing pipe 102 is made of a non-magnetic material, the geomagnetism leaks from the second casing pipe 102 into the cylindrical hole. Therefore, when the observation device 103 passes through the joint 106 between the first casing pipe 101 and the second casing pipe 102, the output of the magnetic sensor 105 changes greatly.

  Further, the position of the second casing pipe 102 is determined in advance. Thereby, in the conventional observation apparatus installation depth measurement method, the depth of the observation apparatus 103 is measured from the position where the magnetism has changed.

Japanese Patent Application Laid-Open No. 2005-114584

  However, in the technique described in Patent Document 1, the magnetic susceptibility of an iron casing pipe, which is a magnetic material, is not uniform, and it is often difficult to understand the magnetic change at the joint between the iron casing pipe and the stainless steel casing pipe. Furthermore, the amount of magnetic change detected by the magnetic sensor differs between the axial center of the cylindrical hole of the casing pipe and the wall surface side of the cylindrical hole. Therefore, in the technique described in Patent Document 1, it is difficult to accurately determine the joint between the iron casing pipe and the stainless steel casing pipe, and it is difficult to accurately detect the installation depth of the observation device. Had a problem.

  An object of the present invention is to provide a depth measurement system and a depth measurement method capable of improving the measurement accuracy of the installation depth of an observation apparatus in consideration of the actual situation in the above-described conventional technology.

  In order to solve the above problems and achieve the object of the present invention, the depth measurement system of the present invention includes a plurality of casing pipes, a magnet, and a magnetic sensor. The plurality of casing pipes are connected in the axial direction. The magnet is provided in a reference casing pipe serving as a reference among the plurality of casing pipes. The magnetic sensor is inserted into the cylindrical holes of the plurality of casing pipes, and detects the magnetic force of the magnet in the reference casing pipe.

The depth measurement method of the present invention includes the following steps (1) to (5).
(1) A step of drilling a borehole in the ground.
(2) A step of connecting a plurality of casing pipes in the axial direction and installing them in the boring holes.
(3) A step of inserting a magnetic sensor into a plurality of casing pipes.
(4) A step of detecting the magnetic force of a magnet provided in a reference casing pipe as a reference among a plurality of casing pipes by a magnetic sensor.
(5) A step of detecting the position of the magnetic sensor from the detection result of the magnetic sensor.

  According to the depth measuring system and the depth measuring method configured as described above, the position detection accuracy can be improved by detecting the magnetic force of the magnet provided in the reference casing pipe serving as a reference by the magnetic sensor.

It is explanatory drawing which shows typically the state which installs an observation apparatus in a boring hole. It is sectional drawing which expands and shows the principal part in the embodiment of the depth measurement system of this invention. It is sectional drawing which cut | disconnected the reference | standard casing pipe in the embodiment of the depth measurement system of this invention in the direction orthogonal to an axial direction. It is a side view which shows the reference | standard casing pipe in the example of embodiment of the depth measurement system of this invention. FIG. 5A is an explanatory diagram showing the direction of magnetic lines of force of a magnet, and FIG. 5B is an explanatory diagram showing a signal output by a magnetic sensor. FIG. 6A shows a modified example of the reference casing pipe in the depth measurement system of the present invention, FIG. 6A is a cross-sectional view showing the reference casing pipe according to the first modified example, and FIG. 6B shows the reference casing pipe according to the second modified example. FIG. 6C is a sectional view of a reference casing pipe according to a fourth modification. FIG. 7A is a side view of a reference casing pipe according to a third modified example, and FIG. 7B is a side view of a reference casing pipe according to a fourth modified example. FIG. It is explanatory drawing which shows the structure of the conventional depth measuring method typically.

  Hereinafter, the form for implementing a depth measurement system and the depth measurement method is demonstrated with reference to FIGS. In addition, the same code | symbol is attached | subjected to the common member in each figure. The present invention is not limited to the following form.

1. Embodiment 1-1. Configuration Example of Depth Measurement System First, an embodiment of the depth measurement system of the present invention (hereinafter referred to as “this example”) will be described with reference to FIGS.
FIG. 1 is an explanatory diagram schematically showing a state where an observation device is installed in a borehole, and FIG. 2 is an enlarged cross-sectional view showing a main part of the depth measurement system of this example.

  As shown in FIG. 1, the depth measurement system 1 of this example is used to measure the installation depth of the observation device 3 when the observation device 3 is installed in the borehole 2 for, for example, earthquake research. The observation device 3 includes various sensors such as a strain gauge, a stress gauge, a seismometer, a thermometer, and a magnetic sensor 5. The magnetic sensor 5 provided in the observation device 3 is a sensor having directivity in the vertical direction (hereinafter referred to as the Z-axis direction). And the cable 4 which consists of a power wire and a signal wire strengthened with respect to the load is attached to the observation apparatus 3.

  Further, on the ground, a pulley 11 on which the cable 4 is mounted, a winch 12 disposed in the vicinity of the pulley 11, and a monitoring device 13 that receives a signal from the observation device 3 are installed. A cable 4 is wound around the winch 12. Then, the observer moves the observation device 3 up and down by operating the winch 12.

  The observation device 3 is inserted into the bored hole 2 dug to a depth of, for example, 500 to 1000 m while being suspended by the cable 4 and is predetermined from the center position P1 of the magnet 10 provided in the reference casing pipe 7 described later. It is installed in the position of distance T2. The observation device 3 is embedded in a mortar filled in the borehole 2 and the rock mass M1, and strain, stress, ground motion, ground temperature, etc. of the rock mass M1 are transmitted to the observation device 3 through the mortar.

  Further, the depth measurement system 1 includes a plurality of casing pipes 6 and a reference casing pipe 7 in order to protect the hole wall of the boring hole 2. As shown in FIG. 2, the plurality of casing pipes 6 and the reference casing pipe 7 are each formed in a substantially cylindrical shape.

  In addition, although the example which formed the some casing pipe 6 and the reference | standard casing pipe 7 in the substantially cylindrical shape was demonstrated in this example, it is not limited to this, A plurality of the casing pipe 6 and the reference | standard casing pipe 7 are made into a square. You may form in square tube shapes, such as a cylinder and a hexagonal cylinder.

  Moreover, the connection part 8 is provided in the both ends of the axial direction in the some casing pipe 6 and the reference | standard casing pipe 7, respectively. The plurality of casing pipes 6 and the reference casing pipe 7 are connected in the axial direction via the connecting portion 8.

  The observation device 3 is inserted into the cylindrical hole 6 b of the connected casing pipe 6 and the cylindrical hole 7 b of the reference casing pipe 7 while being suspended from the cable 4.

  The plurality of casing pipes 6 are formed of a magnetic material, and are, for example, iron casing pipes. On the other hand, the reference casing pipe 7 is formed of a non-magnetic material and is, for example, a stainless steel casing pipe.

  3 is a cross-sectional view of the reference casing pipe 7 taken along a direction orthogonal to the axial direction, and FIG. 4 is a side view showing the reference casing pipe 7.

  As shown in FIGS. 2 and 3, the reference casing pipe 7 is provided with a magnet 10. As shown in FIGS. 3 and 4, a substantially circular spot facing hole 7 a is provided at a predetermined position on the outer peripheral surface of the reference casing pipe 7. A substantially columnar magnet 10 is attached to the spot facing hole 7a by a fixing method such as adhesion or fitting.

  In addition, as shown in FIG. 1, the reference | standard casing pipe 7 is interposed between the some casing pipe 6 so that it may become the position of predetermined distance T1 from the ground surface G1 to the center position P1 of the magnet 10. FIG. And the observation apparatus 3 is arrange | positioned in the position of predetermined distance T2 from the center position P1 of the magnet 10 by making the center position P1 of the magnet 10 of the reference | standard casing pipe 7 into a reference | standard. Further, the distance T1 from the center position P1 of the magnet 10 attached to the reference casing pipe 7 to the ground surface G1 and the distance T2 to the installation position of the observation device 3 are known.

  The magnet 10 is magnetized so that the magnetization direction is orthogonal to the axial direction of the reference casing pipe 7. In this example, the radially outer side of the reference casing pipe 7 is set to the N pole, and the radially inner side of the reference casing pipe 7 is set to the S pole. Note that the radially inner side may be set as the N pole and the radially outer side may be set as the S pole.

1-2. Depth Measurement Method Next, a depth measurement method of the observation apparatus 3 using the depth measurement system 1 having the above-described configuration will be described with reference to FIGS.
FIG. 5 is an explanatory diagram showing a measurement method of the depth measurement system.

  First, as shown in FIG. 1, a boring hole 2 reaching the ground to the hole bottom M2 is excavated. Then, in order to prevent the hole wall of the boring hole 2 from collapsing, the plurality of casing pipes 6 and the reference casing pipe 7 are connected and installed in the boring hole 2. In addition, the reference | standard casing pipe 7 is installed in the position of the distance T1 from the center position P1 of the fixed magnet 10 to the ground surface. A section T3 from the lower end of the casing pipe 6 to the hole bottom M2 is a bare hole in which the rock mass M1 is exposed.

  Next, as shown in FIG. 1 and FIG. 5A, the observation device 3 is inserted while being suspended by the cable 4 in the cylindrical holes 6 b of the plurality of connected casing pipes 6 and the cylindrical holes 7 b of the reference casing pipe 7. . In addition, a signal is transmitted from the observation device 3 being installed to the monitoring device 13 installed on the ground. Then, the observer monitors the output signal of the magnetic sensor 5 provided in the observation device 3 using the monitoring device 13.

  Since the casing pipe 6 is a magnetic body, when the observation device 3 passes through the plurality of casing pipes 6, the magnetic sensor 5 detects the magnetization of the casing pipe 6 and outputs an unstable signal.

  On the other hand, since the reference casing pipe 7 is a nonmagnetic material, it is not magnetized. Therefore, when the observation device 3 passes through the reference casing pipe 7, the signal of the magnetic sensor 5 is stable and becomes approximately 0V. In addition, since the geomagnetism is detected in the section of the reference casing pipe 7, the magnetic sensor 5 may offset the geomagnetism.

  When the observation device 3 passes the magnet 10 of the reference casing pipe 7, the magnetic sensor 5 detects the magnetic force of the magnet 10 provided on the reference casing pipe 7.

  Here, the magnetic sensor 5 provided in the observation device 3 is a sensor having directivity in the Z-axis direction orthogonal to the magnetization direction of the magnet 10. Further, the magnetizing direction of the magnet 10 is directed to the axial direction of the reference casing pipe 7, that is, the direction orthogonal to the vertical direction. Therefore, a magnetic field S1 as shown in FIG. When attention is paid to the component in the Z-axis direction of the magnetic field S1 in the magnet 10, the center position P1 of the magnet 10 in the Z-axis direction becomes the smallest, and the direction in which the magnetic lines of force change with the center position P1 as a boundary.

  Therefore, the magnetic sensor 5 outputs a signal as shown in FIG. 5B. Specifically, the signal in the Z-axis direction has a minimum value (approximately 0 V) at the center position P1 of the magnet 10. Moreover, since the direction of the magnetic lines of force of the magnet 10 faces in the opposite direction with respect to the center position P1, the sign of the signal output from the magnetic sensor 5 is reversed. Hereinafter, the point where the sign of the signal is reversed is referred to as a zero cross point Q1.

  Accordingly, the observer finds the zero cross point Q1 from the signal output from the magnetic sensor 5. And since this zero crossing point Q1 is the center position P1 of the magnet 10, the depth position of the observation apparatus 3 can be detected correctly.

  Moreover, the elongation rate of the cable 4 can be measured by using the installation depth of the center position P1 of the magnet 10 as a reference. Since the distance T1 from the ground surface G1 to the center position P1 of the magnet 10 is set in advance, the observation device 3 is moved to a predetermined position by further lowering the predetermined distance T2 after detecting the zero-cross point Q1. Can be installed.

  As shown in FIG. 5B, signals in the X-axis direction and the Y-axis direction, which are horizontal directions, are maximum at the center of the magnet 10. Therefore, you may detect the point where the value of the magnetic sensor 5 became the maximum as the center position P1 of the magnet 10. FIG.

  Since the magnetic force from the magnet 10 is stronger and more stable than the geomagnetism, a reproducible signal can be obtained by the magnetic sensor 5. For the same reason as described above, the magnetic sensor 5 does not need to have a particularly high accuracy, and a low-sensitivity and inexpensive product can be used. The magnitude of the magnetic force from the magnet 10 differs between the axial center of the cylindrical hole 7b of the reference casing pipe 7 and the wall surface side of the cylindrical hole 7b. However, the position of the zero cross point Q1 does not change even on the axial center of the cylindrical hole 7b or the wall surface of the cylindrical hole 7b. Therefore, even if the position of the magnetic sensor 5 changes in the horizontal direction of the cylindrical hole 7b, the depth position can be specified accurately.

  Moreover, although the example which offsets geomagnetism was demonstrated in this example, it is not limited to this, It is not necessary to offset geomagnetism. That is, when the geomagnetism is not offset, the signal output by the magnetic sensor 5 is obtained by adding the value of geomagnetism. Therefore, the observer can accurately identify the depth position of the observation device 3 by detecting the waveform as shown in FIG. 5B.

  In this example, the magnetization direction of the magnet 10 is set so as to be orthogonal to the Z-axis direction. However, the present invention is not limited to this, and the magnetization direction of the magnet 10 is set toward the Z-axis direction. May be. When the magnetization direction of the magnet 10 is directed in the Z-axis direction, the magnetic sensor 5 detects the magnetic force in the horizontal direction orthogonal to the Z-axis direction, that is, the XY-axis direction. That is, a sensor having directivity in the XY axis direction is used as the magnetic sensor 5.

  In this case, the magnetic sensor 5 outputs a signal in which the Z-axis signal and the X and Y-axis signals shown in FIG. 5B are interchanged. Therefore, even when the direction of magnetization is directed in the Z-axis direction, the position of the magnetic sensor 5, that is, the observation device 3 can be accurately detected by detecting the zero cross point Q1 from the X and Y axis signals.

  In addition, in the depth measurement system 1 of this example, although the example which provided only one reference | standard casing pipe 7 which provided the magnet 10 was demonstrated, it is not limited to this. For example, two or more reference casing pipes 7 provided with the magnets 10 may be provided. Thereby, reliability can be improved more by detecting the magnet 10 of the some reference | standard casing pipe 7, and measuring the space | interval of the magnet 10 of each reference | standard casing pipe 7. FIG.

2. Modification Example Next, a modification example of the reference casing pipe will be described with reference to FIGS.
FIG. 6 is a cross-sectional view of the reference casing pipe cut in a direction orthogonal to the axial direction, and FIG. 7 is a side view of the reference casing pipe 7.

  The reference casing pipe 27 shown in FIG. 6A has two magnets 10A and 10B provided on the outer peripheral surface thereof. The first magnet 10 </ b> A and the second magnet 10 </ b> B are arranged to face each other in a direction orthogonal to the axial direction of the reference casing pipe 27.

  The reference casing pipe 37 shown in FIG. 6B is provided with four magnets 10A to 10D on the outer peripheral surface thereof. The four magnets 10 </ b> A to 10 </ b> D are arranged at equiangular intervals on the outer peripheral surface of the reference casing pipe 37. The axial heights of the reference casing pipe 37 in the four magnets 10A to 10D are all set equal.

  The number of magnets 10 provided in the reference casing pipes 7, 27, 37 is not limited to that described above, and five or more magnets 10 may be installed in the reference casing pipes 7, 27, 37.

  The reference casing pipe 47 shown in FIG. 7A has a magnet 40 formed in a rectangular shape on the outer peripheral surface thereof. The shape of the magnets 10 and 40 is not limited to a substantially cylindrical shape or a rectangular shape, but may be various other shapes such as a prismatic shape or an elliptical column shape.

  A reference casing pipe 57 shown in FIGS. 6C and 7B is provided with a magnet 50 formed in a ring shape. The inner diameter of the magnet 50 is set substantially equal to the outer diameter of the reference casing pipe 57. The magnet 50 is fixed to the outer peripheral surface of the reference casing pipe 57 by a fixing method such as adhesion or fitting.

  According to the reference casing pipe 57 shown in FIGS. 6C and 7B, the magnetic force from the magnet 50 is the smallest at the axial center of the cylindrical hole 57b. However, the depth measurement system 1 of the present example detects a change in the direction of the lines of magnetic force, not the magnitude of the magnetic force of the magnet 50. Therefore, even if the reference casing pipe 57 and the magnet 50 as shown in FIGS. 6C and 7B are used, the detection accuracy does not decrease.

  The embodiments of the depth measurement system and the depth measurement method of the present invention have been described above including the effects thereof. However, the depth measurement system and the depth measurement method of the present invention are not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention described in the claims. is there.

  In the embodiment described above, the iron casing pipe 6 and the stainless steel reference casing pipe are used as the casing pipe that reinforces the boring hole 2, but the casing pipe may be entirely made of stainless steel.

  Moreover, although the example which provided the magnet in the outer peripheral surface of the reference | standard casing pipe was demonstrated, you may install a magnet inside a reference | standard casing pipe. Furthermore, the depth measuring system and the depth measuring method of the present invention may be used not only for vertical boring holes drilled perpendicularly to the ground surface but also for horizontal boring holes and oblique boring holes.

  DESCRIPTION OF SYMBOLS 1 ... Depth measurement system, 2 ... Boring hole, 3 ... Observation apparatus, 4 ... Cable, 5 ... Magnetic sensor, 6 ... Casing pipe, 6b ... Cylindrical hole, 7, 27, 37, 47, 57 ... Standard casing pipe, 7a ... Counterbore hole, 7b ... Tube hole, 10, 40, 50 ... Magnet, G1 ... Ground surface, M1 ... Rock bed, M2 ... Bottom of hole, P1 ... Center position, Q1 ... Zero cross point

Claims (4)

A plurality of axially connected casing pipes;
A magnet provided in a reference casing pipe serving as a reference among the plurality of casing pipes, and a magnetizing direction orthogonal to an axial direction of the reference casing pipe;
A magnetic sensor that is inserted into the plurality of casing pipes, moves in the axial direction of the plurality of casing pipes to detect the magnetic force of the magnet, and has an offset value of geomagnetism ,
The magnetic sensor is a depth measurement system that detects a magnetic force in a direction orthogonal to a magnetization direction of the magnet . The depth measurement system according to claim 1, wherein the reference casing pipe is formed of a nonmagnetic material. The depth measurement system according to claim 1, wherein the magnet is attached to an outer peripheral surface of the reference casing pipe. Drilling a borehole in the ground;
Connecting a plurality of casing pipes in the axial direction and installing them in a borehole;
Inserting a magnetic sensor in which the value of geomagnetism is offset so as to move in the axial direction of the plurality of casing pipes;
A step of detecting, by the magnetic sensor, a magnetic force of a magnet provided in a reference casing pipe serving as a reference among the plurality of casing pipes and having a magnetization direction orthogonal to an axial direction of the reference casing pipe;
Detecting the position of the magnetic sensor from the detection result of the magnetic sensor;
Only including,
The magnetic sensor is a depth measurement method for detecting a magnetic force in a direction orthogonal to a magnetization direction of the magnet .

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