JPH0752228B2 - Ground movement measuring method and device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and apparatus for measuring ground movement, and more specifically, a method for measuring movement in the vertical direction of the ground in detail for each depth or stratum inside the ground, And a device used for the measurement.

[Prior Art] In recent years, in Japan, land reclamation included in seaside airports and waterfront projects has been implemented or planned on a national scale. In addition, a deep underground utilization plan in large cities is being planned for the next century.

Since these works are seriously affected by the subsidence of the ground, that is, fluctuations, it is necessary to accurately know the fluctuations of the ground, and research is being conducted in relevant organizations and industries. In particular, it has become clear in recent years that when underground excavation work is performed, the balance of groundwater pressure is disrupted, and subtle changes occur in each stratum.For the purpose of predicting ground subsidence and accidents and taking preparatory measures, It is necessary to measure the variation of the depth of the river and the strata in detail.

As a method for quantitatively measuring the variation of the ground depending on the depth or the formation, there is a method disclosed in JP-A-59-195122 or JP-A-63-193304.

FIG. 5 (a) schematically shows the above-mentioned prior art method. First, after boring a measurement hole 2 perpendicular to the ground 1 from the surface of the earth, at a proper depth of the measurement hole 2, The rod-shaped permanent magnet 3 is embedded in the side wall surface. As a means for burying the permanent magnet 3, a method of driving with a hydraulic jack, a method of driving with a tucker, a method of driving with an explosive, or the like is adopted. If left in this state for a certain period of time, the depth position of the permanent magnet 3 changes due to the subsidence of the ground 1, or the like. By measuring the fluctuation amount of the permanent magnet 3,
The amount of ground fluctuation at that position can be measured. In addition,
A cylindrical protection tube 4 is installed in the measurement hole 2 to protect the hole wall.

In order to measure the depth position of the permanent magnet 3, the magnetic detection probe 6 suspended from the ground surface by the cable 5 is lowered into the measurement hole 2. In the magnetic detection probe 6, a magnetic detector 6a equipped with magnetic detection means such as a magnetoresistive element is mounted. When this magnetic detector 6a comes to the position of the permanent magnet 3, a detection signal flows through the magnetic detector 6a, and this detection signal is transmitted to the ground surface via the cable 5. By measuring the payout length of the cable 5 when the detection signal is obtained, the depth from the ground surface to the magnetic detector 6a, that is, the permanent magnet 3 can be measured. If the depth of the permanent magnet 3 is measured at regular intervals, it is possible to measure the ground variation amount at the buried position of the permanent magnet 3.
By embedding the permanent magnets 3 at a plurality of positions having different depths of the measurement hole 2, it is possible to measure the ground variation amount of the ground 1 for each depth or each stratum.

In the above method, the measurement hole 2 is dug in the ground 1, and the permanent magnet 3
Since it is only necessary to bury it, the measuring device such as the magnetic detection probe 6 is small and simple, and the measurement work can be easily performed by simply lowering the magnetic detection probe 6 into the measurement hole 2. It is a method that can measure the ground movement amount for each depth very easily and accurately without the need for complicated construction or installation of complicated machinery for the measurement.

[Problems to be Solved by the Invention]

However, in the above-described related art, there is a problem in that the detection sensitivity of the magnetic detector 6a greatly varies and the measurement accuracy is low.

This is because the magnetoresistive element that constitutes the magnetic detector 6a has directivity, and has, for example, a very high sensitivity in front of the magnetoresistive element, but almost no sensitivity in a plane orthogonal thereto. Therefore, when the magnetic detector 6a faces the front surface of the permanent magnet 3 as shown in FIG. 5 (b), the permanent magnet 3 can be reliably detected.
If the side surface of the magnetic detector 6a faces the permanent magnet 3 (state shown by a dotted line in the figure), the permanent magnet 3 cannot be detected. FIG. 5 (c) is a graph showing the measurement of the directivity of the magnetoresistive element. In the case where a permanent magnet is present on the front or back of the magnetoresistive element (θ = 0 °, 180 °).
Shows a very high sensitivity, while a permanent magnet is present on the side of the magnetoresistive element (θ = 90 °, −90
Shows little sensitivity in °).

In order to prevent the variation in sensitivity due to the posture of the magnetic detector 6a as described above, the magnetic detector 6a should always face the front of the permanent magnet 3 and the magnetic detection probe 6 should be lowered. Since the magnetic detection probe 6 and the magnetic detector 6a suspended by the flexible cord-shaped cable 5 can freely rotate in the horizontal plane and are extremely unstable,
It is impossible to keep the attitude of the magnetic detector 6a constant.
Further, it is difficult to confirm the attitude of the magnetic detection probe 6 from the ground surface, and if the magnetic detection probe 6 is lowered deeply, it is impossible to change the attitude of the magnetic detector 6a even if the cable 5 is operated. Is. As a result, the magnetic detector
Since the posture of 6a has changed, the target permanent magnet 3 cannot be detected, measurement data cannot be obtained, or the detection sensitivity is low, which causes a problem that the measurement accuracy decreases.

Conventionally, the sensitivity of the magnetic detector 6a is low or there are variations, relying on the skill and can of the measurer who reads the indicator indicating the detection signal of the magnetic detector 6a, or a plurality of magnetic detectors 6a, respectively. By arranging the magnets in the magnetic probe 6 with their orientations changed, even if the orientation of the magnetic probe 6 is changed, the detection sensitivity of the plurality of magnetic detectors 6a as a whole is not changed, and a device such as a device can be used. It had been. But,
It is not possible to expect improvement in measurement accuracy with the above-mentioned method that relies on the skill and skill of the measurer. Further, when the number of magnetic detectors 6a is increased, the structure of the magnetic probe 6 and the measurement circuit become complicated, and moreover,
The magnetoresistive element or the like constituting the magnetic detector 6a has a drawback that the detection accuracy as a whole cannot be sufficiently increased because the sensitivity characteristics and the temperature characteristics are not uniform depending on the elements, and any method can be practically satisfied. It wasn't something.

Therefore, an object of the present invention is to eliminate the unevenness of sensitivity due to the attitude of the magnetic detector in the ground movement measuring method in which the above-mentioned permanent magnet, that is, a magnetic generator, and a magnetic detector that detects the magnetism are combined. An object of the present invention is to provide a method capable of always performing accurate measurement and an apparatus used for the method.

[Means for Solving the Problems]

In the present invention for solving the above-mentioned problems, in the ground movement measuring method according to claim 1, a magnetic generator is embedded in a side wall surface of a measurement hole excavated in the ground, and the magnetic body is suspended from another table by a cable. By detecting the position of the magnetic generator with a magnetic detector, by measuring the depth position of the magnetic detector at that time, in the method of measuring the ground movement in the buried position of the magnetic generator, as a magnetic detector , The coil is arranged so that its axial direction coincides with the axial direction of the measuring hole, and the magnetic generator is arranged so that its magnetic flux direction is orthogonal to the axial direction of the measuring hole. The position of the magnetic generator is detected by using the electromotive force generated in the coil passing through the magnetic field of the magnetic generator as a detection signal.

That is, the electromotive force generated at both terminals of the coil by the interaction between the magnetic field generated by the magnetic generator embedded at the predetermined depth position inside the measurement hole and the coil serving as the magnetic detector,
It is measured as a detection signal of the magnetic generator. In particular, by arranging the axial direction of the coil so that it coincides with the axial direction of the measurement hole, it is possible to detect with certain sensitivity no matter which direction the coil, that is, the magnetic detector, has a magnetic generator. You can do it.

The ground fluctuation amount measuring device according to claim 2 includes a magnetic generator embedded in a side wall surface of a measurement hole excavated in the ground, a magnetic detector that is suspended from a surface of the earth by a cable and moves up and down, and a magnetic detector. In the ground movement measuring device having depth measuring means for measuring the depth position, a coil is used as the detecting means of the magnetic detector, and the coil has an axial direction that coincides with the axial direction of the measuring hole. And the magnetic generator is
The electromotive force detection means is arranged so that the direction of the magnetic flux is orthogonal to the axial direction of the measurement hole and detects electromotive force generated in the coil passing through the magnetic field of the magnetic generator.

If the above-mentioned permanent magnet is used as the magnetic generator, the cost is low, and even if the permanent magnet is buried in the ground for a long time, the magnetic force does not change and stable performance can be exhibited. The magnetic generator can be easily embedded in the hole wall of the measurement hole.
It is preferably formed in a rod shape such as a column. The method of burying the magnetic generator in the side wall of the measurement hole is the same as the conventional ground movement measuring method, such as a method of mechanically pushing with a hydraulic jack, a method of driving with a tucker, or a method of driving with explosives. Etc. can be adopted.

The coil, which serves as the magnetic detection means of the magnetic detector, is hung on the cable while being appropriately housed in the probe as in the conventional case. The detection signal detected by the coil is sent to a measuring device on the surface of the earth via a cable, processed by a predetermined amplification circuit or conversion circuit, and displayed on an indicator or recorded on a recorder as appropriate.

The depth position of the magnetic detector when the magnetic detector detects the magnetic generator is measured from the length of extension of the cable.
The cable extension length can be measured, for example, by calibrating the cable and visually measuring the graduation, or by electrically measuring and displaying the cable extension amount, and using a magnetic detector. Any method such as a method of reading the display length when the detection signal is obtained in step 1 can be adopted.

An example of a method for automatically measuring the depth position of the magnetic detector when the magnetic generator is detected will be described.

First, the amount of rotation of the length-measuring pulley that rotates with the extension of the cable is converted into an electrical pulse signal, and this pulse signal is counted by a counter circuit and digitized. This numerical signal indicates the amount of extension of the cable, that is, the depth position of the magnetic detector. When a detection signal is generated by the magnetic detector, the detection signal is electrically converted and the numerical value counted by the counter circuit is clipped. The clipped numerical value is displayed or recorded on an appropriate display. By using such a method, simply by pulling out the cable and lowering the magnetic detector to the measurement hole, when the magnetic generator is detected, the depth position of the magnetic detector is automatically displayed. Can be recorded and recorded.

[Action]

By aligning the axial direction of the coil, which is the magnetic detector, with the axial direction of the measurement hole, there is no directivity of the magnetic detection sensitivity in the circumferential direction of the coil, and in which direction of the coil the magnetic generator is located. Even if there is, a constant detection sensitivity is always obtained. Therefore, it is possible to reliably detect the magnetic force generator regardless of the direction of the magnetic detector suspended on the cable.

The magnetic detection sensitivity of the coil is highest in the axial direction of the coil. Therefore, in the conventional magnetic detector using the coil, the axial direction of the coil is usually oriented toward the object to be detected. However, in the present invention, the omnidirectionality described above is realized by orienting the circumferential direction of the coil toward the magnetization generator, which is the object to be detected. Then, by amplifying the detected signal with an appropriate signal amplifying means, a sufficiently practical detection sensitivity can be obtained.

〔Example〕

Next, the present invention will be described in detail below with reference to the drawings illustrating an embodiment.

FIG. 1 shows the overall structure of the ground variation measuring device according to the present invention. A measurement hole (20) perpendicular to the surface of the ground is bored in the ground (10), and magnetic generators (30) made of permanent magnets are embedded at a plurality of positions in the depth direction of the measurement hole (20). A protective tube 40 is inserted into the inner surface of the measurement hole 20 for protection.

A magnetic detector 61 including a coil is housed in the magnetic detection probe 60. A cable 50 is connected to the magnetic detection probe 60, and the cable 50 is wound around a winding drum 70 via a length measurement pulley 71 installed on the ground surface. Winding drum
By actuating 70 by a driving means (not shown) such as a motor, the cable 50 is extended and the magnetic detection probe
60 is lowered inside the measurement hole 20.

A pulse generator 72 is connected to the length-measuring pulley 71 so that the rotation of the length-measuring pulley 71 can be taken out and a pulse signal can be generated at a constant rotation amount. That is,
The length-measuring pulley 71 rotates as the cable 50 is fed, and the cable is calculated from the rotation amount and circumference of the length-measuring pulley 71.
Since the delivery amount of 50 can be calculated, the pulse signal from the pulse generator 71 described above is transmitted to the counter circuit unit 73,
The counter circuit unit 73 counts the numerical value corresponding to the feeding length of the cable 50, and the depth position of the magnetic detection probe 60 connected to the cable 50 can be output as a numerical signal.

When the magnetic detection probe 60 is lowered to the position of the magnetic generator 30, a detection signal is generated from the coil of the magnetic detector 61 and transmitted to the cable 50. The detection signal transmitted through the cable 50 is sent to the signal processing unit 80 through the slip ring (not shown) of the winding drum 70. In the signal processing unit 80, the detection signal is first amplified by the signal amplifier 81. The output from the signal amplifier 81 is sequentially sent to the rectangular wave shaping circuit 82, the pulse generating circuit 83, and the clipping circuit 84 for processing.

Since the strength of the detection signal generated from the coil of the magnetic detector 61, that is, the detection sensitivity is not always constant, it is important to amplify or shape the detection signal in the signal processing unit 80 as described above. That is, in order to smoothly lower the magnetic detection probe 60 into the protective tube 40, a gap of about several mm is provided between the magnetic detection probe 60 and the inner wall of the protective tube 40.
Therefore, the magnetic detection probe 60 moves in the diametrical direction within the protective tube 40. Then, the distance between the magnetic generator 30 buried and fixed in the ground 10 outside the protection tube 40 and the magnetic detection probe 60 changes, which affects the detection sensitivity of the magnetic detector 61. Therefore, the signal processing unit such as the signal amplifier 81 described above.
By amplifying or shaping the detection signal at 80, variations in detection sensitivity are eliminated and accurate detection results are always obtained.

In the clip circuit 84, in the counter circuit unit 73,
Clips the numerical signal unitized in length corresponding to the payout length of the cable 50. This clipped number is
It is displayed on the display 85 as a numerical value indicating the position of the magnetic generator 30, that is, the depth.

When the depth measurement for one magnetic generator 30 is completed, the cable 50 is further extended, the magnetic detection probe 60 is lowered, and the same measurement is performed at the position of the next magnetic generator 30 '. By calculating the difference between the depth measurement value of the upper magnetic force generator 30 and the depth measurement value of the lower magnetic force generator 30 ', the distance between both strata can be measured. By burying the required number of magnetic force generators 30 at predetermined depth positions, the depth in any formation can be measured.

Next, from the magnetic detector 61 by the coil to the signal processing unit 80, regarding the flow of the magnetic detection action and the signal processing,
explain in detail.

Generally, when a coil moves in a magnetic field, an electromotive force that is proportional to the magnetic flux intersecting the inner diameter of the coil and the number of turns of the coil and is inversely proportional to the time when the magnetic flux changes is induced between both terminals of the coil. . The magnitude of this electromotive force is expressed by the following equation according to Faraday's law.

E = −N · dφ / dt (1) E: electromotive force Vφ: cross magnetic flux G t: time sec N: total number of turns In the case of the present invention, as shown in FIG. Is oriented horizontally. On the other hand, the central axis of the coil 61, which is the magnetic detector, is oriented in the vertical direction. In this state, consider the electromotive force at two points A and B in the diameter direction of the coil 61. If the magnetic fluxes emitted from the magnetic generator 30 are all in the same direction and are the same at points A and B of the coil 61, the electromotive forces generated in the A section and the B section cancel each other out.
No electromotive force is generated at both ends 62, 63 of the coil 61. However, in reality, the magnetic generator 30 has a length and width of several tens of millimeters.
Since it is placed in a non-magnetic material having a magnetic permeability close to 1, that is, in the ground 10, the magnetic generator 30 produces a symmetrical and undistorted magnetic field. The strength has a distribution that is almost inversely proportional to the square of the distance.
For example, in the case of the magnetic generator 30 composed of a columnar rare earth magnet as shown in FIG. 3, the magnetic flux density on the magnetic pole axis shows a distribution as shown by the following equation.

Bx (X): Magnetic flux density at point X G Br: Residual magnetic flux density of magnet G R: Diameter of magnet cm L: Length of magnet cm X: Distance from magnet surface to point X cm Diameter and length and magnetic generator
By setting the distance to 30 appropriately
It can be seen that it is possible to make a difference in the magnetic flux density from the part.

When the magnetic flux densities at points A and B are different, both ends 62, 63 of coil 61
The electromotive force generated at is as follows.

Ee = −N (dφA / dt−dφB / dt) (3) Ee: Effective electromotive force V φA: Magnetic flux G at point A φB: Magnetic flux G at point B This electromotive force was measured for an actual coil. The results were as follows.

-Measurement conditions-Average coil diameter 45mmφ Number of coil turns 1800 Coil speed 100cm / sec Magnetic moment of magnet 7.8 × 10 ⁸ Wb A, B magnetic flux density ratio at point 5: 1 Under these conditions, electromotive force is approx. At 25 mV, a detection signal with a substantially sinusoidal waveform was obtained, and it was proved that it was sufficiently effective as a detector.

The detection signal generated in the coil 61 enters the signal processing unit 80 via the cable 50. FIG. 4 shows the circuit configuration of the signal processing unit 80 and the processing state of the detection signal.

The detection signal W ₁ entering the input unit 86 of the signal processing unit 80 has a sine wave shape. When this is subjected to appropriate voltage amplification by the feedback resistor Rf in the signal amplifier 81, the amplified output signal W ₂ is obtained. Next, in the rectangular wave shaping circuit 82, the constant voltage diode
A rectangular wave signal W ₂ with the ZD Zener voltage as the top side is obtained. In addition, the input voltage level of the rectangular wave shaping circuit 82 becomes a Zener voltage when the voltage is about 1/2 of its peak value,
It is desirable to set the amplification degree in the signal amplifier 81 at the previous stage. By doing so, the rectangular wave shaping circuit 82
In, the rectangular wave can be processed where the rate of change of the detected voltage is high, and the rising and falling edges of the rectangular wave are sharp, so the pulse generated by the pulse wave generating circuit 83 in the next stage becomes steep and the detection accuracy is improved. Can be made.

The rectangular wave voltage signal W ₃ is sent to the pulse generation circuit 83, and an inverted pulse is generated by the action of the pulse transformer T and the rectifier D.
A double-ended pulse wave signal W ₅ is obtained via W ₄ .

On the other hand, the amount of extension of the cable 50, that is, a numerical signal corresponding to the depth of the magnetic detection probe 60 is fetched from the counter circuit 73 to the clipping circuit 84, and the depth value is clipped by the double-headed pulse wave signal W ₅ described above, and displayed. Display a total of 85. The magnetic force generator 30 is obtained by calculating the average value of the two depth values clipped by the double-headed pulse wave signal W _5.
The center position of can be accurately known.

The method of the embodiment described above is a method that can be accurately detected even with a very slight ground movement, and it is preferable to apply it when high accuracy of detection accuracy ± 1 mm class is required, but such high detection accuracy If the above is not required, the method described below can be adopted. That is, for example, when land subsidence exceeds 1 m in a landfill, the detection accuracy is ±
About 5 to 6 mm is sufficient, and in such a case, the output signal of the rectangular wave shaping circuit 82 in the method of the above embodiment is used.
The W _3, without passing through the pulse generation circuit 82, directly clip circuit 84
If one depth value clipped by the single signal is obtained, the processing circuit can be simplified.

The information on the depth value displayed on the display 85 can be introduced into an arithmetic processing unit such as a personal computer to perform an average calculation or print a measurement result. In addition, it is possible to automatically collect and repeatedly statistically process arbitrary repeated measurement values for a large number of measurement points during a day or a month.

〔The invention's effect〕

According to the ground fluctuation amount measuring method and apparatus according to the present invention described above, the following effects can be exhibited.

A coil is used as the magnetic detector, and it is arranged so that the axial direction of this coil coincides with the axial direction of the measurement hole. Therefore, the directivity of the detector is lost, and it is completely independent of any horizontal direction. The position of the magnetic force generator can be detected with the same sensitivity. As a result, the omission of detection of the magnetic force generator and the error of the detection position are eliminated, and the measurement accuracy can be significantly improved.

In the conventional method, since the detection sensitivity varies depending on the directivity of the magnetic detector, the magnetic generator could not be detected unless the magnetic detector was moved while carefully observing the indicator on the ground. According to the invention, the magnetic generator can be detected reliably and quickly, so that the moving speed of the magnetic detector can be increased. Specifically, since it is possible to perform measurement at a speed of about 5 to 10 times that of the conventional method, for example, 100 to 200 m, where demand is expected to increase in the future.
When measuring a large depth of a class, the measurement time can be greatly shortened, which can contribute to the improvement of work efficiency.

Since only a simple coil needs to be used as the magnetic detector, the structure of the magnetic detector is simplified, the failure rate is low, and the handleability is good.

When transmitting the signal detected by the magnetic detector to the signal processing unit on the surface of the earth, a 4-wire type transmission line was required when the conventional magnetoresistive element was used. If it is used, a two-wire system will suffice, and the internal structure of the cable will be simple. As a result, if the cable diameter is the same as the conventional one, the extra space can be utilized for the physical reinforcement of the cable, and the strength of the cable can be improved.
In particular, in the case of the measurement at the large depth described above, the total length of the cable also becomes long, so the improvement of the cable strength is a very important problem.

In the conventional method using the magnetoresistive element, the DC amplification circuit is used for processing the detection signal, but this method causes a large voltage drift or temperature drift, which causes the detection accuracy to deteriorate. On the other hand, in the present invention, since the AC amplification method can be adopted by using the coil, stable amplification is possible in principle, and the detection accuracy can be improved.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment according to the present invention, FIG. 2 is an explanatory diagram showing a magnetic detection action, FIG. 3 is a schematic diagram showing a detection principle, and FIG. 4 is a circuit configuration diagram of a signal processing unit. , FIG. 5 shows a conventional example, FIG. 5 (a) is a schematic structural diagram of a measurement state, FIG. 5 (b) is a horizontal sectional view, and FIG. 5 (c) is a graph diagram showing detection sensitivity characteristics. is there. 20 ... Measuring hole, 30 ... Magnetic generator, 50 ... Cable, 60 ... Magnetic detection probe, 61 ... Magnetic detector (coil), 73 ... Counter section, 80 ... Signal processing section

Claims (2)

[Claims] 1. A magnetic generator is embedded in a side wall surface of a measurement hole excavated in the ground, and the position of the magnetic generator is detected by a magnetic detector suspended from the ground surface by a cable. In the method of measuring the ground movement at the buried position of the magnetic generator by measuring the depth position of the magnetic detector, as a magnetic detector, the coil is arranged so that its axial direction matches the axial direction of the measurement hole. The magnetic generator is placed so that the direction of its magnetic flux is orthogonal to the axial direction of the measurement hole, and the electromotive force generated in the coil passing through the magnetic field of the magnetic generator is detected. A method for measuring ground movement, characterized in that the position of a magnetic generator is detected. 2. A magnetic generator embedded in the side wall surface of a measurement hole excavated in the ground, a magnetic detector suspended from the ground surface by a cable and moved up and down, and a depth for measuring the depth position of the magnetic detector. In the ground movement measuring device equipped with
A coil is used as the detection means of the magnetic detector, the coil is arranged so that its axial direction coincides with the axial direction of the measurement hole, and the magnetic generator has a magnetic flux direction which is the same as the axial direction of the measurement hole. A ground movement measuring device comprising an electromotive force detection means for detecting an electromotive force generated in a coil which passes through a magnetic field of a magnetic generator and is arranged so as to be orthogonal to each other.