JPH08122279A - Underground relative permittivity measuring method, geological measuring method, and position measuring method - Google Patents

Abstract

(57) [Abstract] [Purpose] To be able to measure the relative permittivity in the ground with high accuracy, and also to measure the distance to the reflector and the geology with high accuracy. [Structure] An electromagnetic wave having a constant frequency f0 is transmitted to the ground from a transmitting antenna 3, a surface reflected wave obtained by combining the transmitting waves is received by a receiving antenna 4, and the frequency f is discriminated from the attenuation period of the first period. The corresponding relative permittivity is obtained by collating the frequency f with the frequency / relative permittivity characteristic data showing the correlation with the relative permittivity. The voltage peak point of the cross-correlation function between the received target signal waveform and the natural attenuation waveform when there is no obstacle reflection, etc. is found, and the time T at that peak point and the electromagnetic wave propagation speed found from the previously measured relative permittivity The position of the reflector or the like is calculated from ν. Furthermore, the attenuation factor is obtained from the natural attenuation waveform when there is no obstacle reflection, etc., and the specific resistance or conductivity is calculated from this attenuation factor, and this value and the previously measured relative permittivity are used as parameters from the database. Extract geological classification.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of transmitting an electromagnetic wave to the ground and receiving the reflected wave to measure the relative permittivity in the ground, and measuring the geology using the measured relative permittivity. And a method of measuring the position of an obstacle in the ground using the measured relative permittivity.

[0002]

2. Description of the Related Art Conventionally, as a method for measuring the relative permittivity in the ground and the distance to a reflecting object in order to perform an underground survey in front of a face in a shield construction method, for example, Japanese Patent Laid-Open No. 5-529.
There was a method described in Japanese Patent Publication No. 49. In this method, the transmitting antenna and the receiving antenna are arranged apart from each other by a distance X1, and the relative permittivity εr is obtained from the following expression (2) from this distance X1 and the propagation time t _{1 of the} received surface propagation wave. εr = {(t ₁ × c) / X1} ² (2) where c is the speed of light. In addition, the electromagnetic wave velocity ν is ν
= C / √εr, the distance X2 to the reflector is calculated from the velocity and the propagation time t ₂ at the peak point of the received reflected wave by the following equation (3). _{X2 = ν · t 2/2} ····· (3)

However, this has the following problems. Since the method is based on the assumption that the transmitting antenna and the receiving antenna are separated from each other, the transmitting antenna and the receiving antenna inevitably have a positional relationship with a predetermined angle, and their geometrical error It greatly affects the measurement accuracy. Since electromagnetic waves pass through places where they can easily propagate,
The presence of the angle between the transmitting antenna and the receiving antenna causes a non-linear element in the propagation / reflection path of the electromagnetic wave, resulting in a decrease in measurement accuracy. When applied to the shield construction method, a separate electromagnetic radar antenna in which the transmitting antenna and the receiving antenna are separated is used, and the transmitting antenna and the receiving antenna are separately mounted on the cutter face plate of the shield machine, but the cutter face plate is Due to its structure, there is a limit to the mounting space,
The size of the radar antenna also differs depending on the selected frequency. For this reason, in order to attach a radar antenna with a predetermined frequency capable of sufficient exploration, it is necessary to modify the cutter face plate, which increases cost and construction period. On the other hand, if the cutter face plate cannot be modified, the frequency of the radar antenna that can be used is limited, and a satisfactory search cannot be performed.

As a method of measuring the geology (soil quality) during the shield excavation, there is a method disclosed in Japanese Examined Patent Publication No. 5-25994. In this method, earth and sand are sampled from the chamber of a shield machine, the particle size is measured by a particle size measuring device, and the soil quality is judged from the measured particle size.

However, since this is a soil quality judgment using only the average grain size of the earth and sand taken into the chamber as a parameter, when mud or mud is mixed in the excavated soil, it is affected, and the shield excavation proceeds. When the ground around the front of the machine is composed of different geology, it is difficult to say that the result shows the geology around the front of the shield machine because the geology cannot be distinguished.

[0006]

The object of the present invention is to solve the above-mentioned problems and to measure the relative permittivity in the ground with high accuracy, and the forward direction of the shield machine. An object of the present invention is to provide a geological measurement method that can clearly measure the surrounding geology and a position measurement method that can accurately measure the distance to a reflector or the like.

[0007]

In the relative permittivity measuring method according to the present invention, an electromagnetic wave having a constant frequency f0 is transmitted from the transmitting antenna to the ground, and the reflected wave is received by the receiving antenna, and the attenuation period of the first period. Then, the frequency f is discriminated and the frequency f is compared with the frequency / dielectric constant characteristic data showing the correlation between the frequency and the dielectric constant obtained in advance to obtain the corresponding dielectric constant.

FIG. 5 is a graph of this frequency / dielectric constant characteristic data. If the frequency f is plotted on the horizontal axis and the relative dielectric constant εγ is plotted on the vertical axis, the value of the relative dielectric constant εγ with respect to changes in the frequency f is shown. Draw an exponential curve. This can be expressed by the following relational expression (4), and the discriminated frequency f can be applied to this relational expression (4) to obtain the relative permittivity εγ. εγ = a × b ^{1 / f} (4) where a is the first relative permittivity regression coefficient and b is the second relative permittivity regression coefficient.

Electromagnetic waves are transmitted and received by an electromagnetic wave radar in which the transmitting antenna and the receiving antenna are integrated without being separated from each other as in the conventional case.

Further, in the geological measuring method according to the present invention, the attenuation rate is obtained from the natural attenuation waveform when there is no obstacle reflection, etc., and the specific resistance or the reciprocal of the electrical conductivity is calculated from this attenuation rate, and the calculated ratio is calculated. The resistivity or conductivity and the relative permittivity measured as described above are compared with each parameter value of a database that is pre-built by geologically classifying the conductivity or resistivity and the relative permittivity as parameters, and this database The relevant geology is extracted from the inside.

Further, in the position measuring method according to the present invention, the voltage peak point of the cross-correlation function between the received target signal waveform and the natural attenuation waveform when there is no obstacle reflection or the like is obtained, and the time T of the peak point, The position of the reflection object or the like is calculated from the propagation velocity ν of the electromagnetic wave obtained from the relative permittivity measured as described above.

[0012]

When an electromagnetic wave of a certain modulation frequency f0 propagates through a substance, the frequency shifts, and the shift amount Δf is determined by the relative permittivity of the substance. When an electromagnetic wave penetrates into a substance having a different relative dielectric constant, the electromagnetic wave is reflected at the interface between the two substances. When electromagnetic waves are generated periodically like electromagnetic wave exploration, they are repeatedly reflected from the boundary surface,
The reflected signal has a frequency characteristic determined by the relative permittivity of the permeated substance, and is Δf with respect to the transmission frequency f0.
It will be frequency-shifted. This means that the electromagnetic wave transmitted from the transmitting antenna has a frequency f0 and a signal strength V1, and the signal strength V2 frequency-shifted by Δf.
Signal is combined and detected by the receiving antenna.

Therefore, in the present invention, the relative permittivity is obtained by using the frequency of the first period of the surface reflected wave which is the interference of the transmitted wave and the reflected wave propagating in the ground. If the transmission frequency f0 is constant, the frequency shift amount Δf corresponding to this is
Since the relationship between the change in R and the value of the relative permittivity is determined as described above, the relationship between the change in the frequency f of the frequency-shifted received signal and the value of the relative permittivity is also determined. As shown in FIG. The value of the relative permittivity εγ with respect to the change of f draws an exponential curve.

Therefore, if the frequency f of the attenuation period of the first period of the surface reflected wave is applied to this exponential curve,
The relative permittivity εγ in the ground obtained by shifting the transmission frequency f0 to the frequency f can be known.

The characteristic graph of FIG. 5 can be expressed by the above relational expression (4).
The relative permittivity regression coefficient a and the second relative permittivity regression coefficient b can be obtained as follows. The relational expression (4) is replaced with Ln · εγ = Ln (a × b ^{1 / f} ) = Ln · a + (1 / f) Ln · b, and y = α + βx (where y = Ln · εγ, x
= 1 / f, α = Ln · a, β = Ln · b), the relative permittivity regression coefficients a and b are obtained by f and εγ by linear regression.

On the other hand, when the received signal of the receiving antenna has a natural attenuation waveform, it means that there is no obstacle such as an obstacle in the ground. That is, the natural attenuation waveform can be regarded as a reflection signal from the ground surface affected by only its relative permittivity in the ground without a specific reflector. On the other hand, when there is an obstacle in the ground, the reflected signal is influenced by the relative permittivity of the underground and the relative permittivity of the obstacle. Therefore, if the natural attenuation waveform is used as a temporary reference waveform and cross-correlation processing is performed with the reflection signal including the reflection from the obstacle,
Only the propagation time difference between the ground surface and the obstacle can be extracted. Then, the propagation velocity ν (ν = c / of the electromagnetic wave obtained from this propagation time difference T and the previously measured relative permittivity εγ
For example, the distance L from √εγ) to the obstacle can be calculated from the following equation (5). L = ν × T (5)

Further, the attenuation rate α can be obtained by performing a waveform analysis of the natural attenuation waveform in a known manner.
The attenuation characteristics of the natural attenuation waveform differ depending on the geology that is the propagation medium, and the attenuation rate α and the specific resistance ρ (conductivity σ
The relation of the following equation (6) is established with the reciprocal of, that is, ρ = 1 / σ. α = (60π / ρ) × √εr (6) where π is the circular constant.

11 (A), (B), and (C) show changes in the natural attenuation waveform due to the difference in the specific resistivity ρ of the geology. In this figure, 5 is an electromagnetic wave radar. Further, FIG. 12 is a graph showing the change in the attenuation characteristic due to the change in the specific resistance ρ. As can be seen from this figure, when the specific resistance ρ is large (the electrical conductivity σ is small), the attenuation rate α is small, and when the specific resistance ρ is small (the electrical conductivity σ is large), the attenuation rate α is large. Therefore, the specific resistance ρ can be obtained from the attenuation rate α, and the specific resistance ρ
The type of geology can be estimated from this. However, in such a geological judgment using only the specific resistance ρ as a parameter,
Since it is based on the attenuation characteristics of the natural attenuation waveform,
It is easy to make an error. Therefore, in the present invention, since the relative permittivity also varies depending on the geology, in addition to the specific resistance ρ (or its inverse conductivity σ), the relative permittivity obtained as described above is also used as a parameter and the The accuracy is improved by determining the type.

[0019]

Embodiments of the present invention applied to a shield construction method will be described in detail below with reference to the drawings.

As shown in FIG. 1, an electromagnetic wave radar 5 in which a transmitting antenna 3 and a receiving antenna 4 are integrated in one place on the front face of a cutter face plate 2 of a shield machine 1 remains housed in a radar protection box 6. Embedded and transmitting antenna 3
When the electromagnetic wave 8 is reflected from the ground to the ground 7, the reflected wave from the ground is received by the reception antenna 4 at the same point as the transmission antenna 3. The front surface of the radar protection box 6 is closed by a front protection plate 6a.

FIG. 2 shows a system configuration for implementing the method according to the present invention. This system includes a transmission / reception processing circuit 9 for controlling transmission / reception of the electromagnetic wave radar 5, an A / D converter 10 for converting a reception analog signal received by the reception antenna 3 and input through the transmission / reception processing circuit 9 into a digital signal, CPU and DSP (Digital Signal Processor)
And a computer 11 including a memory (ROM, RAM, disk storage medium, etc.), a transmission signal output unit 12 for transmitting a transmission signal to a transmission / reception processing circuit 9 according to an instruction of the computer 11, and a display output device 13 such as a CRT or a printer. Has been done.

In this embodiment, after measuring the relative permittivity in the ground by this system, the distance to the obstacle is measured and the type of geology is also measured. First, the method for measuring the relative permittivity will be described. To do.

As shown in FIG. 1, when an electromagnetic wave 8 is transmitted as a search signal from the transmitting antenna 3, a reflected wave from the natural ground is received by the receiving antenna 4. The reflected wave is roughly divided into the surface of the natural rock. A reflected wave 15A from 14 and a reflected wave 15B from the inside that penetrates into the ground 7. The reflected wave 15A from the ground surface 14 is equivalent to the fundamental frequency component of the transmitted electromagnetic wave 8, while the reflected wave 15B from the inside of the ground is affected by the relative permittivity εγ of the ground. The received signal waveform at the transmission / reception processing circuit 9 is changed (shifted) in response to the reflected waves 15A.
15B becomes the synthesized attenuation waveform, which is generally called a surface reflected wave. However, in the figure, the surface wave region 16 is the attenuation signal of the first period.

This received surface wave is the electromagnetic wave 8 that has penetrated into the ground 7 changed according to the relative permittivity εγ of the ground 7 as described above. As shown in FIG. If the relative permittivity of εγ1 is εγ1, for example, the frequency is f1 (peak point is t1 hour) in the exploration signal time domain, and if the relative permittivity of the underground 7 is εγ2, the frequency f2 is in the exploration signal time domain.
(The peak point is t2 hours). When the relationship between the relative permittivity and the frequency is represented by a characteristic graph, an exponential curve as shown in FIG. 5 is obtained, which can be expressed by the relational expression (4) as described above.

Therefore, in this embodiment, this relational expression (4)
Is stored in the computer 11 in advance, the received analog signal is converted into a digital signal by the A / D converter 10, and the frequency f is discriminated from the attenuation period of the first period. The relative dielectric constant εγ corresponding to the frequency f is obtained by evaluation according to the relational expression (4) by calculation or collation processing by 11. The obtained relative permittivity εγ is stored in the memory as a parameter for distance measurement. Further, if necessary, the display output device 1
3 can be displayed on the display screen or can be printed out.

Next, an example of measuring the distance to an obstacle existing in the ground 7 by the position measuring method according to the present invention will be described.

The present invention utilizes the cross-correlation method as a signal analysis method. First, an outline of this method will be described. A reference signal x (t) and a target signal y (t) for comparing a time difference k with the reference signal x (t). The cross-correlation function of is the following equation (7) or (8)
It can be represented by a formula.

[0028]

[Equation 1]

[0029]

[Equation 2]

Therefore, in the present embodiment, as the waveform of the reference signal, a waveform close to a natural attenuation waveform is set as shown in FIG. 6, and the reference signal and the target signal actually received by the receiving antenna 4 are set. The correlation function is calculated by the computer 11. 7 is a received waveform when there is no obstacle, FIG. 8 is a received waveform when there is an obstacle, and when cross-correlation processing is performed with the reference waveform of FIG. 6, the cross-correlation waveform when there is no obstacle Is as shown in FIG. 9, and the cross-correlation waveform when there is an obstacle is as shown in FIG. In the example of the figure, the cross-correlation waveforms when there is no obstacle are correlation peaks P1 and P2 with large absolute values.
Then, the correlation peak does not occur after the correlation peak P3 having a small absolute value occurs, whereas the cross-correlation waveform when there is an obstacle shows the correlation peaks P4 and P5 after P3.
・ P7 and P8 have appeared.

Therefore, in this embodiment, the correlation peaks P1, P2, and P3 that occur even when there is no obstacle are excluded, and P3 is excluded.
Correlation peaks P4, P5, P7, P8 that are later in time than
Correlation peak of which absolute value is maximum (P7 in the figure)
Is extracted, and the distance L to the obstacle is obtained from the time T at that time and the previously obtained relative permittivity εγ from the following equation (9). Then, the shield machine 1 is excavated by repeating such processing in real time.

L = (c / √εγ) × T (9) where c is the speed of light.

Finally, an example of measuring the type of geology by the geological measurement method according to the present invention will be described.

A natural attenuation waveform is extracted from the received signal received as described above, and this is analyzed by a well-known transient phenomenon analysis method to obtain an attenuation rate α. From this attenuation rate α, the above (6)
Then, the specific resistance ρ (or conductivity σ) is calculated in accordance with. On the other hand, since the relative permittivity εγ has already been obtained as described above, the type of geology can be specified from both the relative permittivity εγ and the specific resistance ρ (or the conductivity σ).

In identifying this, in this embodiment,
A database in which the geology is distinguished is previously constructed by using the specific permittivity and the specific resistance (or conductivity) as parameters. FIG.
3 shows this as a table model (in the form of table data in the computer 11), and when both the relative permittivity εγ and the specific resistance ρ (or the conductivity σ) are given as a logical matrix, one corresponding Geological type is extracted.
FIG. 14 is a conceptual diagram of the extraction method based on the logical matrix. Assuming an XY coordinate system in which the specific resistance ρ (or conductivity σ) is taken in the X axis direction and the relative dielectric constant εγ is taken in the Y axis direction, the X value is assumed. The specific resistance ρ (or the conductivity σ) is given as, and the relative permittivity εγ is given as the Y value, and the geological types in which the both match or approximate are extracted.

FIG. 15 shows the overall flow of the above processing. First, in step S1, various kinds of initial data are input from the database as initial settings, and an exploration signal (natural decay waveform) at the time of exploration start is input as reference data, and initial relative permittivity (propagation velocity) and geology are primarily measured. To do. In the next step S2, the received signal is A / D converted and subjected to processing of reference data, logical judgment and cross-correlation judgment,
When it is determined that the waveform is a natural decay waveform, the relative permittivity is measured by the surface wave component and the propagation velocity is calculated in step S3. Then, in the next step S4, the attenuation rate is calculated for the natural attenuation waveform, and the specific resistance (or conductivity) obtained therefrom and the relative permittivity obtained in step S3 are used as parameters to correspond from the database as described above. Extract geological classification.

On the other hand, when the reflected waveform from the obstacle is recognized, the position (distance) of the obstacle is calculated and measured in step S5 as described above. Then, after step S5 or step S4, the measurement result is displayed and output in step S6, the data is updated, and if it is in the repeated search mode, the process returns to step S2 and the same process is repeated for the next search signal.

It is needless to say that the present invention can be applied not only to the measurement from inside the tunnel as in the shield construction method but also to the measurement from the ground surface.

[0039]

According to the method for measuring the relative permittivity of the present invention, the following effects are obtained. Since the relative permittivity is obtained by capturing the frequency change of the surface reflected wave that is caused by the interference of the transmitted wave and the reflected wave propagating in the ground, the relative permittivity can be accurately measured. Since transmission and reception are performed by an electromagnetic wave radar that integrates a transmitting antenna and a receiving antenna, the arrangement does not cause a decrease in measurement accuracy as in the conventional example in which the transmitting antenna and the receiving antenna are separated, and is applied to the shield construction method. In such a case, unlike the conventional example, the cutter face plate does not need to be largely modified, the cost is low and the size can be reduced.

Further, according to the geological measurement method of the present invention, the attenuation rate is obtained from the natural attenuation waveform when there is no obstacle reflection, etc., and the specific resistance or the reciprocal of the electrical conductivity is calculated from this attenuation rate. Since the relevant geological type is extracted from the database using the specific resistance or conductivity and the relative permittivity as parameters, accurate geological determination can be performed.

Further, according to the position measuring method of the present invention, the voltage peak point of the cross-correlation function between the received target signal waveform and the natural attenuation waveform when there is no obstacle reflection or the like is obtained, and the time of the peak point is calculated. Since the position of the reflection target or the like is calculated from the propagation velocity of the electromagnetic wave obtained from the relative permittivity measured as described above, highly accurate measurement can be performed.

[Brief description of drawings]

FIG. 1 is an explanatory view of an embodiment in which the present invention is applied to a shield construction method.

FIG. 2 is a block diagram of a system for implementing the method of the present invention.

FIG. 3 is a waveform diagram showing attenuation of a reflected wave with respect to a transmitted wave.

FIG. 4 is a waveform diagram showing that the frequency of a reflected wave shifts due to a difference in relative permittivity in the ground.

FIG. 5 is a characteristic graph showing the relationship between relative permittivity and frequency.

FIG. 6 is a waveform diagram of a reference signal for cross-correlation.

FIG. 7 is a received waveform diagram when there is no obstacle.

FIG. 8 is a received waveform diagram when an obstacle is present.

FIG. 9 is a cross-correlation waveform diagram when there is no obstacle.

FIG. 10 is a cross-correlation waveform diagram when an obstacle is present.

FIG. 11 is a diagram showing that the attenuation characteristic of the natural attenuation waveform changes due to the difference in specific resistance due to the difference in geology.

FIG. 12 is a characteristic graph showing a relationship between an attenuation rate and a specific resistance.

FIG. 13 is a diagram showing, as a table model, a database in which geology is distinguished by using relative permittivity and conductivity as parameters.

14 is a conceptual diagram illustrating a method of extracting a corresponding geological type from the database of FIG.

FIG. 15 is a flowchart showing an extraction process of the above.

[Explanation of symbols]

 1 shield machine 2 cutter face plate 3 transmitting antenna 4 receiving antenna 5 electromagnetic wave radar 6 radar protection box 7 ground 8 electromagnetic wave 9 transmission / reception processing circuit 10 A / D converter 11 computer 12 transmission signal output unit 13 display output device 14 ground surface 15A Reflected wave from the ground surface 15B Reflected wave from the inside that penetrated into the ground 16 Surface wave region

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location G01V 3/12 B 9406-2G (72) Inventor Masahiro Fujiwara 1-4, 6 Sumiyoshi, Uozumi-cho, Akashi-shi, Hyogo Stock Company Kos

Claims (5)

[Claims] 1. An electromagnetic wave having a constant frequency f0 is transmitted to the ground from a transmitting antenna, the reflected wave is received by a receiving antenna, and the frequency f is discriminated from the attenuation period of the first period. Measurement of the relative permittivity in the ground characterized by obtaining the corresponding relative permittivity by comparing with the frequency / relative permittivity characteristic data showing the correlation with the relative permittivity previously obtained from the change of the shift amount Δf with respect to Method. 2. An electromagnetic wave having a constant frequency f0 is transmitted to the ground from a transmitting antenna, the reflected wave is received by a receiving antenna, and the frequency f is discriminated from the attenuation period of the first period. A method for measuring the relative permittivity in the ground, characterized by applying the formula (1) to obtain the relative permittivity εγ. εγ = a × b ^{1 / f} (1) where a is the first relative permittivity regression coefficient and b is the second relative permittivity regression coefficient. 3. An electromagnetic wave radar in which a transmitting antenna and a receiving antenna are integrated for transmission and reception.
Or the method for measuring the relative dielectric constant in the ground according to 2. 4. The attenuation factor is obtained from a natural attenuation waveform when there is no obstacle reflection, etc., the resistivity or the conductivity of its reciprocal is calculated from this attenuation factor, and the calculated resistivity or conductivity is used. Or, the relative permittivity measured by the method of 2 or 3 is compared with each parameter value of a database that is pre-constructed by geologically classifying the electrical conductivity or the specific resistance and the relative permittivity as parameters, and from this database, A geological measurement method characterized by extracting relevant geology. 5. The voltage peak point of the cross-correlation function between the received target signal waveform and the natural attenuation waveform when there is no obstacle reflection or the like is determined, and the time T at that peak point and the time T of the peak point are defined. A method for measuring the position in the ground, which comprises calculating the position of a reflection target or the like from the propagation velocity ν of an electromagnetic wave obtained from the relative dielectric constant measured by the method.