JPH028754A - Soil inspection using radio wave - Google Patents

Abstract

PURPOSE:To enable the obtaining of a resistivity of soil at a high accuracy by a method wherein a radio wave is emitted to a pipe body in the soil from the ground surface to measure reflected wave from the pipe body and attenuance is determined from the size and ratio of the radio wave emitted from the ground surface. CONSTITUTION:A monopulse is generated with a signal generator 11 to be applied to a transmitter 15 and a radio wave of the monopulse is emitted to soil 19 to receive reflected wave thereof with a receiver 16. The reflected wave undergoes a signal processing with a signal processor 12 and the results are shown on a signal display section 13. In this case, the reflected wave includes a ground surface reflected wave component P1 as indicated by the arrow E3 reflected from the ground surface 18 and a pipe surface reflected wave component P2 as indicated by the arrow E2 reflected from a pipe body 20 in the soil 19. Then, for example, the processor 12 performs a signal processing to determine a peak value of each pipe surface reflected wave component from a reflection waveform at a plurality of measuring points arranged in the direction of the axis of the pipe body 20 right thereabove 20. Thus, a distribution of resistivity is obtained to allow prediction that corrosion of the pipe body 20 is the most severe in the soil at a point where the resistivity is the smallest.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a ±M survey method using radio waves to measure the resistivity of soil. Used for anti-corrosion measures for pipe bodies such as water pipes.

(Prior art) When conductive pipes such as gas pipes, water pipes, and sewage pipes are buried in the soil, soil with low resistivity has low contact resistance with the pipes. In areas where concrete/soil macrocells occur, current flows intensively from the pipe into the soil at locations with low resistivity, causing corrosion in the pipe.

In addition, when a pipe is buried between different types of soil with different resistivities, current flows intensively from the pipe to the soil at locations with low resistivity due to macrocells between the different types of soil.
The pipe body corrodes intensively in that area.

To prevent such corrosion of the pipe body, insulating joints should be inserted on both sides of the pipe body where current cannot flow out. All you have to do is change the pipe body to an insulating coated pipe in the original small part buried in the soil, or replace the soil itself.

In order to take such anti-corrosion measures, it is first necessary to investigate the soil ratio.

Conventionally, the resistivity of soil has been investigated as follows. The resistivity of soil near the ground surface, especially the soil under roads paved with asphalt or concrete, can be measured by drilling holes in the paved surface and sampling the soil by polling, or by using a resistivity measurement method. Measurements were taken by inserting a probe.

[Problem to be solved by the invention]

In this measurement method, it is necessary to drill holes in the road in order to measure the resistivity, which is extremely troublesome. Furthermore, due to the drilling process, the distance between the measurement points was quite large, and the accuracy of the measurement results of the resistivity distribution was low.

This invention was made in view of the above-mentioned problems, and it is possible to determine the resistivity of soil without making a hole in the ground surface, and it is also possible to measure the resistivity distribution with high precision using radio waves. The purpose is to provide high-quality research methods.

[Means for Solving the Problems] This invention provides that when a radio wave passes through soil, the degree of attenuation varies depending on the specific resistance of the soil, and the smaller the specific resistance, the thicker the attenuation. This was done with a focus on

The soil survey method using radio waves of the present invention is based on the following method: 1. ! 11! Radio waves are emitted from the earth's surface to the installed pipe body, the reflected wave is received from the pipe body, the size of this reflected wave is measured, and the size of the reflected wave and the size of the radio wave emitted from the ground surface are calculated. This method calculates the degree of attenuation from the ratio of the height and the specific resistance of the soil between the ground surface and the pipe body from this degree of attenuation.

[Effect]

The soil investigation method using radio waves of this invention emits radio waves from the ground surface to a pipe in the soil, receives reflected waves from the pipe, measures the size of the reflected waves, and measures the size of the reflected waves. The degree of attenuation is determined from the ratio of the size of the radio waves emitted from the ground surface and the magnitude of the radio waves emitted from the ground surface, and the specific resistance is determined from this degree of attenuation. Therefore, the specific resistance of the soil can be directly determined in a 1:11 ratio without drilling a hole in the ground surface. I can do it. As a result, the spacing of measurement points on the ground surface for determining the soil resistivity distribution along the pipe body is not limited as in conventional methods, and the soil resistivity can be measured at extremely short intervals. , the resistivity distribution can be determined with high accuracy. Furthermore, since there is no need to drill holes in the ground surface, costs such as polling costs and restoration costs are completely eliminated, and survey costs can be reduced.

〔Example〕

Embodiments of the present invention will be described based on FIGS. 1 to 8. This soil investigation method using radio waves was developed based on the fact that when radio waves penetrate soil, the degree of attenuation varies depending on the specific resistance of the soil, and the smaller the specific resistance, the greater the attenuation. It is.

In particular, when radio waves are emitted from the ground surface to a pipe buried at a certain depth from the ground surface, the amplitude of the reflected waves from the pipe decreases as the specific resistance of the soil between the ground surface and the pipe becomes smaller. By understanding the correlation between this and the fact that the lower the specific resistance of the soil, the more severe the corrosion of pipes buried in the soil, the corrosion of pipes buried in the soil can be detected without contact. This is what we are trying to explore.

This soil survey method using radio waves is as shown in Figure 1.
Pulsed radio waves are emitted from the ground surface 3 in the direction of arrow A to a pipe body 2 buried at a certain depth in soil l, and the reflected wave from the pipe body 2 in the direction of arrow B is received. The magnitude of this reflected wave is measured, the attenuation rate is determined from the ratio of the magnitude of the reflected wave and the magnitude of the radio wave emitted from the ground surface 3, and from this attenuation rate, the soil l between the ground surface 3 and the pipe body 2 is This is a method to find the specific resistance of

The specific resistance measurement by the above method is performed sequentially at a number of measurement points set directly above the tube axis along the tube axis of the tube body 2,
The distribution of the specific resistance of the upper jl l can be known from the measurement results at each measurement point. Based on the measurement result of this ratio 11° C. resistance, it is possible to know the location of the tube body 2 where 1g corrosion is expected to be severe, and it is possible to take anti-corrosion measures to this location.

Here, the relationship between the degree of attenuation of radio waves in soil and specific resistance will be explained. Attenuation degree of radio waves in soil α (d[1/m)
is given by ......fl.

However, σ is the soil conductivity, which is generally 10-' to 10-
's/m. μ is the magnetic permeability of the soil, approximately 4πXl0
-'H/m. ε is the dielectric constant of soil, ε=ε0・ε
It is 3. ε. is the dielectric constant in vacuum, 8.854XlO
- eyes F/m. ε is the dielectric constant of soil, which is -4 to 4o. r is the frequency.

As is clear from the formula fi1, the attenuation rate α of radio waves in the soil is proportional to the conductivity σ of the soil, and the specific resistance ρ of the soil is ρ = Ω ・ C−...
・Old... (2) Since σ, the attenuation rate α of radio waves in the soil is the specific resistance ρ of the soil.
will be inversely proportional to.

As is clear from Equation (11), the attenuation rate α of radio waves in the soil depends on the frequency f, that is, for the same resistivity ρ, the higher the frequency f becomes, the larger it becomes.

This characteristic is shown in FIG.

As described above, since the attenuation factor α depends on the frequency f, it is necessary not to change it during one measurement, and the frequency used is preferably around 0.5 G Ilz, which is easy to measure.

On the other hand, the relationship between the specific resistance ρ of soil and the corrosivity is as shown in Table 1, and the smaller the specific resistance ρ, the more severe the corrosion.

Table 1 Next, Figure 3 shows the measurement results of the correlation between soil resistivity, soil corrosion factors (control ground potential distribution, ground-to-ground potential distribution, pipe current), and the corrosion amount distribution on the pipe surface. Same figure (A)
shows a cross section of the soil 1, and shows a state in which the pipe body 2 is buried at a fixed depth. Figure (B) shows the distribution of resistivity in Figure (A), and shows that the resistivity of region C2 is smaller than the resistivity of regions C, C3 on both sides thereof. Figure (C) shows the distribution of the ground potential (P/S) and the distribution of the ground-to-ground potential (S/S) in Figure (A), where the ground potential (P/S) is low in area C2; It is high in areas C,, C3 on both sides, and it is ll! ! The potential (S/S) is high in region C2, and the regions C,...
It is low at C2. In the same figure (D), the current in the tube flows in the direction of the arrow D2 in the region C, , C3, and this current flows from the tube body 2 in the region C2 to the direction of the arrow D3. D shows that the water is flowing into the soil. FIG. 3(E) shows the corrosion amount distribution of the tube body 2, and shows that corrosion occurs in region C2.

Next, a soil investigation device for implementing the soil investigation method using radio waves will be explained based on FIGS. 4 to 8. This soil survey device has a signal generator 1 as shown in FIG.
1. Signal processor 12. It is composed of a signal display section 13 and an antenna section 14. The antenna section 14 is located on the ground surface 18
A transmitter 15 and a receiver 16 are built into a freely movable vehicle body 17. Radio waves (monopulse) are emitted from the transmitter 15 toward the soil 19 as shown by arrow E1, and the reflected wave (arrow E2 and E3) are grooved to receive the signals.

This soil investigation device creates a monopulse using a signal generator 11 and transmits this monopulse i? By adding it to i15, a monopulse radio wave is emitted toward Sat tn19, the reflected wave is received by the receiver 16, and the signal is processed by the signal processor 12, and the signal display section! It will be displayed in 3.

In this case, the reflected wave includes an arrow E reflected from the ground surface 18.
The ground surface reflected wave component P shown in 3 and the pipe body 2 in the soil 19
There is a tube surface reflected wave component P2 indicated by an arrow E2 that is reflected at 0, and its waveform is as shown in FIG.

The No. 48 processor 12 is, for example, a pipe 20 directly above the pipe 20.
Figure 6 (A) at multiple measurement points lined up in the tube axis direction.
, (B), and (C) are subjected to signal processing to obtain the peak value of each tube surface reflected wave component. The signal display unit 13 displays each a with the peak value of each reflected waveform on the horizontal axis.
The measurement results are displayed as shown in FIG. 7, with the distance from the fixed point to the reference point taken as the vertical axis. As a result, the distribution of peak values can be found, and this distribution of peak values corresponds to the distribution of the attenuation rate of instant radio waves, and further corresponds to the distribution of resistivity, where the peak value is small, the attenuation rate of radio waves is large, This is a place where the specific resistance of the soil is low.

It is expected that the pipe body 20 will be severely corroded in the soil in this part.

FIG. 8 shows the actual measurement results when the frequency was set to 0.5 G Ilz. As shown in the same figure (A), soil 2
In the case where a cast iron pipe 22 with a diameter of 300 mm is buried in soil 21, the specific resistance of area F1 of soil 21 is 15000.
When the specific resistance of the area F2 of the soil 21 is 2000Ω·Bi, the reflected waveform when the antenna part 17 is placed on F1 is as shown in the same figure (B), and the tube surface reflected wave component The peak value of P2 is large. On the other hand, the reflected waveform when the antenna section 17 is placed on the area F2 is shown in the same figure (C
), and the peak value of the tube surface reflected wave component P2 is small. FIG. 5(D) shows the distribution of the peak value of the tube surface reflected wave component when the antenna section 17 in FIG. 4(A) is moved in the X direction on the ground surface 23. In this figure, the attenuation rate in the region F1 is 5 dB, and the region F1 has a damping rate of 5 dB.
The attenuation factor of part 2 is 40 dB.

As mentioned above, radio waves are emitted from the ground surface to a pipe buried at a certain depth in the soil, the waves reflected from the pipe are received, and the magnitude of this reflected wave is measured. The attenuation rate is calculated from the ratio of the size of the reflected wave and the size of the radio wave emitted from the ground surface, and the specific resistance of the soil is calculated from this attenuation rate, so the specific resistance of the soil can be calculated without drilling a hole in the ground surface. I can do it.

As a result, when determining the soil resistivity distribution along the pipe body, the spacing of measurement points on the ground surface is no longer limited as in the conventional case (the soil resistivity is measured at very short intervals). It is possible to determine the resistivity distribution of the soil with high accuracy.In addition, since there is no need to drill holes in the ground surface, costs such as polling costs and restoration costs are completely eliminated, and survey costs can be reduced.

By determining the specific resistance of the soil between the ground surface and the tube in this way, it is possible to find the low resistance grounding portion of the tube where concrete/soil macrocells are occurring. In addition, the resistivity distribution of the soil mentioned above and the 1ff of the pipe body
By examining the i-electricity (using another method), it is possible to determine whether macrocells between different types of soil have occurred in the buried pipe. As a result, locations where the pipe body is expected to be severely corroded can be found without excavating, and the pipe body can be easily protected against corrosion.

〔Effect of the invention〕

According to the soil investigation method using radio waves of this invention, radio waves are emitted from the ground surface to a tube in the soil, the reflected wave from the tube is received, the magnitude of this reflected wave is measured, and this The degree of attenuation is calculated from the ratio of the size of the reflected wave and the size of the radio wave emitted from the ground surface, and the specific resistance is calculated from this degree of attenuation, so the specific resistance of the soil can be calculated indirectly without drilling a hole in the ground surface. be able to. As a result, when determining the soil resistivity distribution along the pipe body, the spacing of measurement points on the ground surface is not limited as in the conventional example, and the soil resistivity can be measured at extremely short intervals. , and the resistivity distribution can be determined with high accuracy. Furthermore, since there is no need to drill holes in the ground surface, costs such as polling costs and restoration costs are completely eliminated, and survey costs can be reduced.

[Brief explanation of the drawing]

Figure 1 is a detailed explanatory diagram of the present invention, Figure 2 is a diagram showing the relationship between radio wave attenuation rate and frequency, Figure 3 is a diagram showing the relationship between soil resistivity and soil corrosion factors, and Figure 4 is a diagram showing the relationship between soil resistivity and soil corrosion factors. A block diagram showing the configuration of an embodiment of the soil investigation device, FIG. 5 is a waveform diagram of reflected waves, FIGS. 6 and 7 are diagrams for explaining the operation of the soil investigation device, and FIG. 8 shows the actual measurement results. FIG. l...Soil, 2...Pipe body, 3...Ground surface diagram diagram diagram diagram diagram diagram diagram diagram

Claims (1)

[Claims] Radio waves are emitted from the ground surface to a tube buried at a certain depth in the soil, the reflected wave from the tube is received, the magnitude of this reflected wave is measured, and the magnitude of the reflected wave and the ground are calculated. A soil survey method using radio waves that determines the degree of attenuation from the ratio of the magnitudes of radio waves emitted from the surface, and from this degree of attenuation determines the resistivity of the soil between the ground surface and the pipe body.