JP2002071828A - Underground electromagnetic surveillance method, device and information storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an underground electromagnetic surveillance method capable of accurately grasping a monoclinic structure of a bedrock which is hard to accurately grasp by TDEM surveillance. SOLUTION: In this underground electromagnetic surveillance method, electromagnetic surveillance of cutting off energization to a transmission loop, producing a smoke ring phenomenon in which an eddy current propagates to the bedrock, and measuring attenuation of the eddy current as a change of a time function of an electromagnetic field using a receiving loop is repeatedly performed along a plurality of measurement points in a ground surface side (S1-S4). A geological structure of the bedrock is calculated on the basis of measurement data obtained at each measurement point (S5 and S6). Particularly, in the step S6, a process is performed determining positions of the monocline structure in relation to measurement points where measured values change.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underground electromagnetic survey method, apparatus and information storage medium for obtaining the geological structure of a ground using a time domain electromagnetic survey technique.

[0002]

BACKGROUND ART Underground electromagnetic surveys using a technique such as TDEM have been conventionally performed. In particular, when excavating a mountain tunnel or the like, the geological structure of the ground is surveyed in advance to grasp the geological structure of the planned tunnel excavation route.

[0003] In such a preliminary survey, first of all, a rough survey of the terrain is performed by performing a surface survey, and then, for example, T
Conduct geophysical surveys such as DEM to understand the stratification structure from the ground surface. Next, if necessary, a boring survey or the like is performed from the surface of the ground to grasp how the geology actually changes at each measurement point at predetermined intervals.

[0004] By comprehensively judging such measurement results, for example, as shown in FIG. 4, the geological structure of the ground is grasped in advance as a resistivity distribution, and a tunnel excavation schedule is determined based on the measurement results. The route 200 is set and the tunnel structure is designed.

[0005] In the conventional TDEM survey used for the above-described resistivity distribution measurement, for example, as shown in FIG.
Are set, and a plurality of measurement points P1, P2,... Are virtually set at predetermined intervals on the survey line 2000.
Then, a transmission loop 10 as a current source for smoke ring generation is installed at a predetermined position on the survey line 2000, and a reception loop 20 as an electromagnetic wave reception unit is installed at any of the measurement points P. Then, the power supply to the transmission loop 10 is interrupted, a smoke ring phenomenon in which the eddy current propagates to the ground is generated, and the attenuation of the eddy current is measured as a change in the time function of the electromagnetic wave using the reception loop 20. Such a measurement is performed by setting the reception loop 20 to measurement points P1, P2,.
Repeat while moving along.

[0006] Investigation line 2000A in transmission loop 10
The measurement along the line is called an in-loop measurement, and the measurement along the survey line 2000B outside the loop 10 is called an out-loop measurement. By analyzing these measurement results, the resistivity distribution of the ground as shown in FIG. Structure can be obtained.

[0007]

The resistivity distribution structure obtained in this way is extremely effective for grasping the stratum structure of the ground, but a fault running diagonally along the stratum, for example, Monoclinic structure 1100 such as crushed bodies and rhyolite
There is a problem that B cannot be grasped.

In particular, crushed materials, rhyolite, etc. are areas that require great care in tunnel excavation due to extremely poor geological conditions, and it is necessary to accurately detect them.

For example, when the monoclinic structure 1100B is rhyolite, the surrounding geology is deteriorated due to the heat of the magma at the time of forming the rhyolite. Further, when the monoclinic structure 1100B is a crushed body, a large amount of water is contained therein, so that sufficient care must be taken when tunnel excavating this location.

The present invention has been made in view of such a problem, and an object of the present invention is to accurately grasp a monoclinic structure of a ground, which was difficult to accurately grasp by conventional TDEM exploration. It is an object of the present invention to provide an underground electromagnetic exploration method, apparatus, and information storage medium that can be used.

[0011]

Means for Solving the Problems (1) In order to achieve the above-mentioned object, the present invention provides a method of generating a smoke ring phenomenon in which an electric current to a current source for generating smoke ring is cut off and an eddy current propagates to the ground. Electromagnetic exploration, which measures the attenuation of the eddy current as a time function change of an electromagnetic field using an electromagnetic wave receiving unit, is repeatedly performed along a plurality of measurement points on the ground surface side, and the ground is measured based on the measurement values obtained at each measurement point. An underground electromagnetic survey method for calculating a geological structure of a mountain is characterized in that a position of a monoclinic structure of the ground is obtained in association with a measurement point at which the measured value changes.

Further, the apparatus of the present invention interrupts the supply of current to the current source for generating smoke ring, generates a smoke ring phenomenon in which the eddy current propagates to the ground, and attenuates the eddy current by using an electromagnetic wave receiving unit to generate an electromagnetic field. Electromagnetic surveys that measure as changes in the time function of the ground are repeated along a plurality of measurement points on the ground surface side, and an underground electromagnetic survey device that determines the resistivity distribution of the ground based on the measurement values obtained at each measurement point And an underground structure calculating means for estimating and calculating the position of the monoclinic structure of the ground based on the measured value at each measuring point in association with the measuring point at which the measured value changes.

The program according to the present invention, which is stored in a computer readable information storage medium, shuts off a current to a current source for generating a smoke ring and generates a smoke ring phenomenon in which an eddy current propagates to the ground. An electromagnetic survey that measures the attenuation of the eddy current as a time function change of an electromagnetic field using an electromagnetic wave receiving unit, and a measurement value at each measurement point obtained by repeatedly performing along a plurality of measurement points on the ground surface side Is a computer-usable program for determining the resistivity distribution of the ground, based on the measured values at each measurement point, the monoclinic structure of the ground associated with the measurement point at which the measured value changes The program is a program for realizing an underground structure calculating means for estimating and calculating the position of the vehicle.

Here, the program according to the present invention is a program usable by a computer (a program embodied in an information storage medium or a carrier wave), and includes a processing routine for realizing the above means in the computer. It is characterized.

The inventor has found that when a monoclinic structure is located near a measurement point in the ground, the measurement value at the measurement point fluctuates as compared with the measurement values at surrounding measurement points. .

Therefore, according to the present invention, the position of the monoclinic structure at the ground can be accurately obtained based on the measured value obtained at each measuring point, for example, the measured voltage value.

(2) The present invention is characterized in that a transmission loop is used as the smoke ringing current source, and a reception loop is used as the electromagnetic wave receiving unit.

(3) Further, according to the present invention, the measurement at each measurement point may be performed by moving at least the electromagnetic wave reception unit along the measurement point, or by using the current source for generating smoke ring and the electromagnetic wave reception unit. And moving the portion along the measurement point in a state where the relative positions of the two are fixed.

By employing the above configuration, the relative positional relationship between the current source for smoke ring generation and the electromagnetic wave receiving unit does not change significantly at adjacent measurement points.

Therefore, when the monoclinic structure does not exist in the ground, the change of the measurement data at the adjacent measurement point becomes small, and when the monoclinic structure exists, the change becomes large. The position of the monoclinic structure of the ground can be detected more accurately.

In particular, according to the present invention, the measurement at the measurement point is performed by moving the current source for generating the smoke ring and the electromagnetic wave receiving section along each measurement point with their relative positions fixed. It is preferred to do so.

By doing so, the spatial positional relationship between the current source for smoke ring generation and the electromagnetic wave receiving unit at each measurement point is fixed, so that the existence of the monoclinic structure is regarded as a change in the measured value. More accurate detection is possible.

(4) Further, according to the present invention, each of the measurement points is set along a side line assumed on the ground surface side, and among the measurement points set along the side line, adjacent measurement points are set. The position of the monoclinic structure is determined relative to a measurement point at which the measured value shows a given change.

In this case, it is preferable that the side line is set, for example, along a planned tunnel excavation route.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described in detail with reference to the drawings.

FIGS. 1 and 9 show a preferred embodiment of the time domain underground electromagnetic survey according to the present invention.

The device of the embodiment includes a transmission loop 10 and a reception loop 20.

The transmission loop 10 functions as a current source for generating smoke ring, and is configured to be installed at an arbitrary position on the ground surface side. In the example,
It is formed in a loop shape of 60 m in length and 60 m in width. Then, the transmission loop 10 is transmitted from the transmission energizing device 30.
, The transmission current is supplied.

The receiving loop 20 functions as an electromagnetic wave receiving unit. The receiving loop 20 has a small diameter of, for example, a radius of about 40 to 50 cm. It has become.

When an underground electromagnetic survey around a tunnel is performed using this device, a survey line (measurement line) 2000 on the ground surface side is set in advance in accordance with the survey area. Further, as shown in FIG.
A plurality of measurement points P1, P2,... Are set on 0 in advance. Then, the transmission loop 10 and the reception loop 2
The measurement using 0 is repeated for each measurement point,
The measurement data is stored in the memory 58 in the receiving device 50.

Then, based on the measurement data obtained for each measurement point, the underground specific resistance distribution around the tunnel is calculated, and the underground structure around the tunnel is obtained based on the obtained specific resistance distribution.

FIGS. 1 to 3 schematically show the principle of the time domain search method.

At the time of measurement, the transmission loop 10 is first set on the survey line 2000 on the ground surface side, and the reception loop 2 is set at a predetermined measurement point P on the survey line 2000.
Set 0. Then, a transmission current is supplied to the transmission loop 10, and the transmission current is rapidly cut off as shown in FIG. As a result, as shown in FIG. 3B, an electromotive force for maintaining the same magnetic field as before the interruption is generated by the law of electromagnetic induction, and an eddy current is generated on the ground surface. This eddy current is
A new eddy current is generated in the ground that attenuates according to the resistivity of the ground, but prevents this change in current. This process is repeated, and a phenomenon occurs as if the eddy current 100 propagates from the ground surface to the deep part of the stratum, and this phenomenon is called a smoke ring phenomenon.

FIGS. 2A to 2D show the current density distribution underground at this time in a time-series manner. It can be seen that the portion showing the maximum value of the current density permeates deep underground with time.

These eddy currents are attenuated according to the specific resistance of the stratum in the propagation path. For this reason, the attenuation of the eddy current is detected as a change in the time function of the magnetic field using the reception loop 20 installed in the tunnel premises corresponding to the search position, and the underground resistivity distribution can be known. For example, when the underground has a high resistivity, the eddy current attenuates rapidly, but when the resistivity is low, it attenuates slowly.

Accordingly, the receiving loop 20 is moved one after another in accordance with the measurement point P, and thus obtained.
By analyzing the received data, as shown in FIG.
The resistivity distribution of the ground can be obtained along the survey line 2000, and the ground structure can be known based on the resistivity distribution.

The feature of this embodiment is that, in addition to the measurement of the resistivity distribution of the ground, as shown in FIG. 4, the existence of the monoclinic structure 1100B in the ground and the detection of its position can be accurately detected. It is possible to do it.

For this reason, in this embodiment, FIG.
As shown in (1), a configuration is adopted in which the measurement at each measurement point P is performed with the relative positional relationship between the transmission loop 10 and the reception loop 20 fixed. Specifically, when performing measurement at the measurement point Pn, the transmission loop and the reception loop are set as 10-1 and 10-2, and when the measurement at the next measurement point P (n + 1) is performed. Moves the transmission loop and the reception loop to positions 10-2 and 20-2. That is, while the relative positions of the transmission loop 10 and the reception loop 20 are fixed, the transmission loop 10 and the reception loop 20 are moved along the measurement points P, and the measurement at each measurement point P is performed.

By adopting the above configuration, the spatial relative positional relationship between the transmission loop 10 and the reception loop 20 becomes constant. Therefore, when the monoclinic structure 1100B exists in the ground, this monoclinic structure 1100B The effect of 1100B will be noticeable as a change in the measured value (voltage in the embodiment) of the receiving loop 20 itself.

Therefore, according to the present embodiment, among the measurement points P set along the survey line 2000, the vicinity of the measurement point at which the measured value shows a given change as compared with the adjacent measurement points It is recognized that the monoclinic structure 1100B exists. In this way, according to the present embodiment, the existence and position of the monoclinic structure 1100B of the ground can be measured in association with the measurement point P at which the measurement value changes.

FIG. 8A shows a temporal change of the measured voltage of the receiving loop measured at each measurement point P in this manner. In the figure, the horizontal axis represents the position of the measurement point, and the vertical axis represents the measured voltage of the receiving loop 20. Here, the series 1, 2, 3,... Represent the temporal change of the voltage measured in the reception loop 10, and the series 1 is the measured voltage in the reception loop 20 immediately after the transmission current of the transmission loop 10 is cut off, and the series 2 Is the measured voltage when 6.8 μS elapses, series 3 is the measurement voltage when further 6.8 μS elapses (measured voltage when 13.6 μS elapses from the measurement start), and similarly, series 4, 5,. 8μS
The measured voltages at the lapse of time are respectively shown.

FIG. 8B shows the actual rock mass type of the ground, which is actually measured near each measurement point. As shown in FIG.
~ 39, 42-43, 46-47, 50-51,
The bedrock which comprises the monoclinic structure 1100B exists.

The actual excavation results shown in FIG.
The reception loop 20 at each measurement point shown in FIG.
Comparing with the measurement voltage, the change that the measured value is sharply reduced in the vicinity of the measurement points 35, 39, 43, 47, and 50 where the monoclinic structure 1100B is present as compared with the adjacent measurement points. Is appearing. These change points 〜 coincide with the position of the actually measured monoclinic structure 1100B.

Therefore, according to the present embodiment, based on the measured voltage of the receiving loop 20, the monoclinic structure 1100B
It can be understood that the presence and location of the can be accurately measured.

FIG. 9 shows a specific configuration of the transmitting energizing device 30 and the receiving device 50.

The transmission energizing device 30 includes a clock 32
And a transmission current supply unit 34 and a transmission control unit 36.

The transmission current supply section 34 is formed so as to supply the transmission current shown in FIG. 3A in accordance with a command from the transmission control section 36.

The receiving device 50 has a clock 52
, An amplifier 62, an A / D converter 54, and a CPU 56
, A memory 58, and an input / output unit 60. Then, the output of the receiving loop 20 is amplified by the amplifier 62, and is then converted from analog to digital by the A / D converter 54 and input to the CPU 56. The CPU 56
Based on a command from the input / output unit 60, data from the A / D converter 54 is stored in the memory 58.

The transmitting energizing device 30 and the receiving device 50 are configured to operate while being synchronized with each other by clocks 32 and 52. Specifically, since the energizing device 30 and the receiving device 50 are formed separately, the clocks 32 and 52 are adjusted so as to be completely synchronized before the start of measurement. As a result, even if the two devices 32 and 52 are completely separated from each other, the two devices will operate in perfect synchronization with each other.

FIG. 10 shows a flowchart of a procedure for performing measurement while moving and installing the receiving loop 20 at each measurement point P1, P2... In the tunnel premises.

First, the transmission loop 10 and the reception loop 20
Is set corresponding to the first measurement point P1 (step S1).

Next, the transmission current shown in FIG. 3A is supplied to the transmission loop 10, and the transmission current is rapidly cut off (step S2).

When the transmission current is cut off, as shown in FIGS. 1 and 2, a smoke ringing phenomenon in which an eddy current propagates underground occurs. At this time, the attenuation of the eddy current is detected as shown in FIG. 3C as a change in the time function of the electromagnetic wave using the reception loop 20 installed at the measurement point P1.
This detection data is output from the amplifier 54 and converted into a digital signal by the A / D converter 54,
Is written and stored in the memory 58.

A series of search steps consisting of steps S1, S2 and S3 are performed at all measurement points P1 and P2.
Perform on ...

When the measurement at all the measurement points is completed (step S4), the CPU 56 functions as underground structure calculation means, and based on the measurement data at each measurement point stored in the memory 58, the ground level is calculated. Is calculated to create, for example, an underground structure model shown in FIG. 7 (step S5).

In particular, in the time domain underground electromagnetic exploration method as in the embodiment, the underground structure model is estimated and calculated from the measurement data at each measurement point using the least squares inversion and other methods.

In this way, an underground structural model can be accurately obtained.

Further, the CPU 56 functions as an underground structure calculating means, and determines whether or not the monoclinic structure 1100B exists in the ground and its position based on the measurement data (measurement voltage) at each measurement point stored in the memory 58. Calculate,
As shown in FIG. 7, an underground structure model representing the position of the monoclinic structure 1100B is estimated and calculated.

With the above configuration, the underground structure of the ground can be accurately measured along the survey line 2000. In particular, the presence or absence of the monoclinic structure 1100B included in the ground, which could not be measured conventionally, can be measured. And its position can also be accurately measured.

After the position of the monoclinic structure 1100B existing in the ground is specified in this way, a more detailed geology is checked by, for example, a boring survey of the corresponding location. For example, as shown in FIG. It is also possible to obtain an underground structure model that accurately represents the specific resistance distribution of the ground, the division of the rock forming the ground, and the specific composition of the monoclinic structure 1100B, and prepare for the excavation of the tunnel.

In this embodiment, the monoclinic structure 1100
In the vicinity of the measurement point existing at B, the above-mentioned change point-appears in a region where the monoclinic structure 1100B has a high moisture content, and the measurement voltage of the reception loop 20 greatly changes under the influence thereof. It is estimated to be.

It is to be noted that a program for causing the CPU 56 to function as the underground structure calculating means in steps S5 and S6 described above may be formed in a storage means such as a ROM (not shown).

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention.

For example, in the above-described embodiment, the case where the transmission loop is used as the current source for generating the smoke ring and the reception loop is used as the electromagnetic wave receiving unit has been described.
The present invention is not limited to this. For example, a transmission source on a line may be used as a current source for generating smoke ring. In this case,
Both ends of the transmission source on the line may be installed on the ground, and a transmission current supply source may be provided in the middle of the both ends.

Similarly, as the electromagnetic wave receiving unit, for example, a receiving unit on a line having both ends installed on the ground may be used to detect eddy current attenuation as a current or voltage change.

Further, in the above-described embodiment, the case where the relative positions of the transmission loop and the reception loop are fixed and both of them are moved along the measurement points and the measurement at each measurement point is performed has been described. For example, the transmission loop may be fixedly set in a predetermined state, and only the reception loop may be moved along the measurement points to perform measurement at each measurement point.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of the principle of smoke ring generation.

2 (A) to 2 (D) show the progress of time,
It is explanatory drawing of a mode that the eddy current spreads to the ground.

FIG. 3 is a timing chart in the case of performing electromagnetic exploration in the time domain.

FIG. 4 is an explanatory diagram of a resistivity distribution of a ground measured using a TDEM technique and a monoclinic structure existing in the ground.

FIG. 5A is an explanatory diagram showing a relationship between a transmission loop and a reception loop provided along a survey line;
FIG. 7B is an explanatory diagram of a case where both the transmission loop and the reception loop are moved along the measurement point while maintaining the relative positional relationship.

FIG. 6 is an explanatory diagram of a geological structure of a ground obtained by an electromagnetic survey result and an actual boring survey.

FIG. 7 is an explanatory diagram of a ground resistivity distribution and a monoclinic structure measured using the method of the present embodiment.

FIG. 8A shows a measurement result of the transmission loop obtained at each measurement point, the horizontal axis represents the measurement point, the vertical axis represents the reception voltage, and FIG. It is explanatory drawing of the actual rock mass classification in.

FIG. 9 is a block diagram showing a preferred example of the underground electromagnetic survey device of the present embodiment.

FIG. 10 is a flowchart of the underground electron exploration method of the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Transmission loop 20 Receiving loop 30 Transmission energizing device 56 CPU 58 Memory 1100B Monoclinic structure 2000 Measurement line

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsumasa Okamura 1-7-1 Kyobashi, Chuo-ku, Tokyo Toda Construction Co., Ltd. (72) Inventor Masafumi Naito 1-7-1 Kyobashi, Chuo-ku, Tokyo Inside Toda Construction Co., Ltd. (72) Inventor Akira Saito 1-23-1 Oi, Shinagawa-ku, Tokyo Inside Mitsui Kinzoku Resources Development Co., Ltd. (72) Inventor Kazunari Wada 1-23-1 Oi, Shinagawa-ku, Tokyo No. Mitsui Kinzoku Resource Development Co., Ltd. F-term (reference) 2G005 CA05 2G053 AB21 BB05 BC14 CA03 CA19

Claims (12)

[Claims] An electric current to a current source for generating smoke ring is cut off to generate a smoke ring phenomenon in which an eddy current propagates to the ground, and the attenuation of the eddy current is converted into a time function change of an electromagnetic field using an electromagnetic wave receiving unit. In the underground electromagnetic survey method of repeating the electromagnetic survey to be measured along a plurality of measurement points on the ground surface side and calculating the geological structure of the ground based on the measurement values obtained at each measurement point, An underground electromagnetic exploration method, wherein a position of a monoclinic structure of a ground is determined in relation to a changing measurement point. 2. The underground electromagnetic exploration method according to claim 1, wherein a transmission loop is used as the current source for generating smoke ring, and a reception loop is used as the electromagnetic wave receiving unit. 3. The method according to claim 1, wherein the measurement at each of the measurement points is performed by moving at least the electromagnetic wave reception unit along the measurement point, or the current source for generating the smoke ring and the electromagnetic wave reception. And moving the part along the measurement point in a state where the relative positions of the two parts are fixed. 4. The measuring point according to claim 1, wherein each of the measurement points is set along a side line assumed on the ground surface side, and the measurement points adjacent to each other are set among the measurement points set along the side line. An underground electromagnetic exploration method, wherein a position of the monoclinic structure is obtained in association with a measurement point at which a measured value shows a given change as compared with the measurement point. 5. An electric current to a current source for generating smoke ring is cut off to generate a smoke ring phenomenon in which an eddy current propagates to the ground, and the attenuation of the eddy current is converted into a time function change of an electromagnetic field using an electromagnetic wave receiver. The underground electromagnetic survey device that repeats the electromagnetic survey to be measured along a plurality of measurement points on the ground surface side and obtains the resistivity distribution of the ground based on the measurement values obtained at each measurement point, An underground electromagnetic exploration apparatus comprising: underground structure calculation means for estimating and calculating a position of a monoclinic structure of a ground based on the measurement value in association with a measurement point at which the measurement value changes. 6. The underground electromagnetic exploration apparatus according to claim 5, wherein a transmission loop is used as the current source for generating smoke ring, and a reception loop is used as each of the electromagnetic wave receiving units. 7. The method according to claim 5, wherein the measurement at each of the measurement points is performed by moving at least the electromagnetic wave receiving unit along the measurement point, or by using the current source for generating the smoke ring. An underground electromagnetic exploration apparatus, wherein the electromagnetic wave receiving unit is moved by moving the electromagnetic wave receiving unit along the measurement point with their relative positions fixed. 8. The measurement method according to claim 5, wherein each of the measurement points is set along a side line assumed on the ground surface side, and the underground structure calculation unit sets the measurement set along the side line. An underground electromagnetic exploration apparatus, wherein a position of the monoclinic structure is estimated and calculated in association with a measurement point at which a measured value shows a given change as compared with an adjacent measurement point. 9. An electric current to a current source for generating smoke ring is cut off to generate a smoke ring phenomenon in which an eddy current propagates to the ground, and the attenuation of the eddy current is converted into a time function of an electromagnetic field using an electromagnetic wave receiving unit. A computer-usable program to determine the resistivity distribution of the ground based on the measured values at each measurement point obtained by repeatedly performing the electromagnetic survey to be measured along multiple measurement points on the ground surface side There is stored a program for realizing underground structure calculating means for estimating and calculating the position of the monoclinic structure of the ground based on the measured value at each measuring point and associating with the measuring point at which the measured value changes. A computer-readable information storage medium characterized by the above-mentioned. 10. The information storage medium according to claim 9, wherein a transmission loop is used as the smoke ring generation current source, and a reception loop is used as the electromagnetic wave reception unit. 11. The current source for generating the smoke ring according to claim 9, wherein the measurement at each of the measurement points is performed by moving at least the electromagnetic wave reception unit along the measurement point. An information storage medium, which is performed by moving the electromagnetic wave receiving unit along the measurement point with the relative position between the two fixed. 12. The measurement point according to claim 9, wherein the measurement points are set along a side line assumed on the ground surface side, and the underground structure calculation means is configured to perform the measurement set along the side line. An information storage medium for estimating and calculating the position of the monoclinic structure in relation to a measurement point at which a measured value shows a given change as compared with an adjacent measurement point.