JPH01142486A - Subsoil through-vision method - Google Patents

Abstract

PURPOSE:To enable quick and accurate inspection of structure of a subsoil, by concentrating a plurality of elastic waves or electromagnetic waves varied in the phase at a desired point of the subsoil to perform a image display of the reflected waves thereof. CONSTITUTION:A plurality of elastic wave oscillators or electromagnetic wave transmitters 1 are set on the surface of a subsoil 2 or a bore hole and elastic waves or electromagnetic waves 8 shifted in the phase from one another are transmitted to a desired point P in the subsoil from the oscillators or transmitters 1. Then, the reflected waves thereof are received with a receiving transducer 7 to be transmitted to a computer 4, which 4 analyzes an input data to be shown on a CRT display 5. With such an arrangement, the phase of the electromagnetic waves or elastic waves outputted from the oscillators or the transmitters 1 is controlled thereby enabling inspection of the structure at the desired point in the subsoil by direct view through an image.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of investigating the structure of the ground using elastic waves or electromagnetic waves.

(Conventional technology) Conventionally, methods for understanding the structure of the ground using elastic waves include:
Reflection methods, refraction methods, elastic wave CT methods, etc. are known (Practical Rock Mechanics in Civil Engineering: May 25, 1985, published by Ohmsha Co., Ltd.: p. 30).

The reflection method and refraction method are relatively old geophysical exploration methods that mainly use reflected waves or refracted waves to investigate relatively large geological structures.

This exploration method is easy to measure and is suitable for rock surveys in the civil engineering field, where the depth of exploration is generally shallow and it is necessary to precisely survey a narrow range. However, if the lower layer has a lower velocity than the upper layer, and the sum of the angle between the lower layer and the surface and the critical angle of the elastic wave is greater than 90°, the refracted waves will not return to the surface and cannot be measured. In such cases, investigation must be conducted using other methods.

Furthermore, the elastic wave CT method is a relatively new technology in which elastic waves are propagated along a number of paths using a shaft or a poling hole, and a cross-sectional image is obtained by analyzing the waves using a computer. However, with elastic wave CT, it is possible to know the velocity structure in the material, but if there is something in the material that blocks the propagation of elastic waves, such as an opening joint or a fracture zone with large attenuation, the structure in the vicinity Not only will this become unclear, but the waves of surrounding garbage will also lead to incorrect information being obtained.

Each of these methods has its own characteristics, but none of them are perfect, so they are used differently depending on the survey area and the geology of the survey location, but they are not satisfactory.

Furthermore, in recent years, techniques using electromagnetic waves have been developed to investigate the structure of the ground and the location of buried objects. The analysis principle for investigation methods using electromagnetic waves is the same as that for elastic waves, and reflection methods, electromagnetic CT methods, etc. are used. However, it is similar to the case where elastic waves are used in that there are restrictions on the survey range and survey points.

On the other hand, in the field of metal materials, etc., ultrasonic waves are used to visualize defects under the surface of materials using ultrasonic waves of elastic waves.
Something called a mirror was put into practical use (December 1986)
Monthly issue Materials Volume 35 No. 399; P1341-135
1. Ultrasonic microscope and its application to material evaluation), as shown in Figure 3, uses a sonic lens 102 to capture elastic waves in the form of plane waves oscillated from a piezoelectric transducer 101 that also serves as an oscillating and receiving device. It is transmitted to the test material 104 through a medium 103 such as water while being refracted and concentrated, and is focused below the surface of the test material 104. On the other hand, reflected waves, scattered waves, and refracted waves from defects in the test material 104 are transmitted to the test material 104 by a piezoelectric transducer. This is detected by the user 101. In addition, in the figure, the reference numeral 105
106 is a high frequency pulse generator, and 106 is a signal processing system.

This device scans the focal position and converts the reflected, scattered, and refracted ultrasound waves into electrical signals according to the acoustic characteristics within the material 104, and displays the electrical signals in shading on a CRT display (cathode tube) or the like. Get the footage.

If it is possible to image the structure of the ground using the principles of such an ultrasonic microscope, it is expected to become a powerful exploration method along with the reflection method, refraction method, elastic wave CT method, etc. mentioned above.

(Problems to be solved by the invention) However, the range that can be inspected by an ultrasound microscope is narrow;
Since it is shallow (usually a few ions to several 100 μj), it cannot be used as it is for ground exploration in the civil engineering field.

In addition, if the ultrasonic microscope is made larger, it is thought that it will be possible to inspect a wider and deeper area. As long as the principle of transmitting information into a material and focusing it within the material is used, it is practically impossible to create a device large enough to handle the investigation of the structure of the ground. Note that there is no conventional investigation method that uses the same principle as this ultrasonic microscope for electromagnetic waves, focuses the electromagnetic waves into a material, and observes the reflected waves.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a new ground exploration method, particularly a method that enables non-destructive ground inspection.

(Means for Solving the Problems) In order to achieve the above object, the ground perspective method of the present invention controls the phase of each of a plurality of elastic wave oscillators or electromagnetic wave oscillators installed on the ground surface or in the polling hole. By outputting elastic waves or electromagnetic waves that are out of phase with each other, the reflected waves are focused on an arbitrary point in the ground and the reflected waves are measured with an elastic wave geophone or electromagnetic wave receiver on the ground surface or in a polling hole. The structure of the ground is visualized from the waveform information of the reflected waves.

(Function) Therefore, by controlling the phase of the elastic wave or electromagnetic wave output from each elastic wave oscillator or electromagnetic wave oscillator, it is possible to focus on any point in the ground and output the elastic wave or electromagnetic wave. While scanning vertically and horizontally, an elastic wave geophone or electromagnetic wave receiver installed on the ground surface or inside a polling hole reflects, refracts, and scatters depending on the structure within the ground (fault plane, strata surface, etc.). By converting the intensity and waveform of elastic waves or electromagnetic waves into electrical signals and displaying them on a CRT display or the like in shades or colors corresponding to the intensity of the electrical signals, it is possible to visualize the ground structure.

(Example) Hereinafter, the configuration of the present invention will be described in detail based on an example shown in the drawings. In this embodiment, a case will be described in which elastic waves are used. Incidentally, the same principle applies when using electromagnetic waves.

Explain burying. Figure 1 (*) shows the wavefront when a plurality of wavefronts oscillated from one transducer (piezoelectric sensor) 1 are lined up and oscillated with the same phase.In this case, each transducer (piezoelectric sensor) The elastic waves 8 oscillated from the deducer 1 are combined, become a substantially plane wave, and propagate downward. Figure 1 (I) shows the wavefront when a plurality of transducers 1 are arranged and the phases of each transducer 1 are shifted from each other. The elastic wave 8 becomes an arcuate wave opposite to that shown in FIG. 1 (#) and propagates downward.

Then, they reach point P at the same time.

In order to concentrate the elastic waves 8 at point P as shown in FIG. 1, the following phase control is performed.

Now, if X transducers 1 are arranged from number 1 to X'#, any i-th transducer 11
Considering, if the distance between the transducer and point 1 is 11, the frequency of the elastic wave 8 is h (Hz), and the propagation speed of the elastic wave 8 is V, then the elastic wave 8 generated from the transducer is The time it takes to reach point P is tl = j! l/v.

Similarly, for the i+1th I transducer, the time to reach point P is t, =1. ．． It becomes 1/V.

1+1 Therefore, in the i-th transducer, at the time to-tl earlier than the reference time to, i+1
By controlling the oscillation time of each transducer, the elastic waves 8 oscillated from all the transducers 1 are transmitted at the time t'o -t, , for the th transducer 1. If we represent each transducer as a 0 phase that reaches point P at the same time as
It is sufficient to oscillate faster by φl=2π·Ll·h.

FIG. 2 shows an example of a specific device for carrying out the method of the present invention. This device includes a large number of elastic wave oscillators, such as transducers 1, installed at a constant pitch or irregularly on the surface of the ground 2 to be explored. At the same time, this transducer 1 is connected to each terminal of a multi-channel high frequency pulse phase difference oscillator 3 so that each transducer 1 oscillates an elastic wave with a controlled phase. An elastic wave geophone, such as a vibration receiving transducer 7, is installed at , receives the reflected wave from the measurement point P, and converts the waveform information of the reflected wave into an electrical signal in the signal processing device 6, and then inputs it to the computer 4. Then, predetermined image processing is performed to display the ground structure on the CRT display 5 as a grayscale image.

An example of signal processing in this device is shown in FIG. 3. In the figure, 3a is a timing controller, 3b is an oscillator, 3C is a power amplifier, 1 is a piezoelectric sensor, 7 is a piezoelectric sensor for receiving vibrations, 6a is a signal amplifier, 6b is a time amplifier, and 6C is an in-window amplitude extractor. In the case of this embodiment, a multi-channel high frequency pulse phase difference oscillator 3 is configured by a timing controller 3a, an oscillator 3b, and a power amplifier 3c, and a signal processing is performed by a signal amplifier 6a, a time-based amplifier 6b, and an in-window amplitude extractor 6C. A container 6 is configured.

This signal processing uses an elastic wave oscillated from one of the oscillators 3a as a main trigger, and causes the other elastic waves to oscillate by shifting their phases from each other. The elastic wave at this time may be a monopulse,
When the waveforms of this elastic wave are shown in (1), (2), and (3) in Figure 4, the elastic waves (2), 9, and (3) of the pond are respectively different from the elastic wave (1) that is the main trigger. Out of phase. These elastic waves concentrate at an arbitrary point P in the ground as explained in FIG. 1(c). The elastic wave oscillated toward an arbitrary point P is reflected, refracted, and scattered within the ground 2, and is received by the piezoelectric sensor 7 for receiving vibration.

Since the zero elastic wave shown in FIG. 4 (4) is attenuated in the ground, this received wave is amplified in relation to time. That is, only the elastic waves received during a certain period of time are amplified. The amplification factor at that time is, for example, α·eβ5, which changes depending on the time from the main trigger. The state is shown in FIG. 4 (5). A part of the received wave is extracted by the in-window amplitude extractor 6c and used as an image signal. The in-window amplitude extractor 6C opens (Wl) just before the reflected wave from the focal point P reaches the reception sensor 7, and closes after reaching it (W2).
, only the received waves between them are extracted and sent to the computer 4. The signal extracted at this time is the fourth
As shown in the waveform diagram in Figure (6), this is the maximum amplitude value or energy amount of the elastic wave while the window is open.

This electric signal is subjected to predetermined image processing in a computer/image processing means 4, and displayed on an image display means such as a CRT display 5 with a density level corresponding to its intensity or a color specified by threshold processing. be done. By scanning the position of the focal point P and the gray scale display position of the CRT 5, a cross section of the plane scanned by the focal point P is obtained on the CRTS.

Although the embodiment described above is one of the preferred embodiments, it is not limited thereto, and various modifications can be made without departing from the gist of the present invention. It is also possible to install it inside the polling hole instead of installing it in the polling hole, oscillating an elastic wave from the polling hole, and receiving the reflected wave inside the polling hole.・By using a receiver, electromagnetic waves may be used instead of elastic waves.

(Effects of the Invention) As is clear from the above explanation, the Jiwa perspective method of the present invention uses a plurality of elastic wave oscillators or electromagnetic wave oscillators installed on the ground surface or in a polling hole to generate elastic waves by controlling the phase of each one. By shifting and outputting waves or electromagnetic waves,
Since the focus is focused on an arbitrary point in the ground and the reflected wave is measured by an elastic wave geophone or electromagnetic wave receiver on the ground surface or in a poling hole, it is possible to control the phase of each elastic wave oscillator or electromagnetic wave oscillator. It is possible to output elastic waves or electromagnetic waves by focusing on any point in the ground.

Therefore, while the focal point is scanned vertically and horizontally, an elastic wave geophone or electromagnetic wave receiver installed on the ground surface or in a polling hole is used to reflect and reflect according to the structure in the ground (I!lr layer surface, geological layer surface, etc.). An image of the ground structure can be obtained by converting the intensity and waveform of refracted and scattered elastic waves or electromagnetic waves into electrical signals and displaying them in shading on a CRT display or the like.

In this way, the basic principle of imaging the subsurface structure of an object using an ultrasound microscope can now be applied to ground investigation, and it is expected that information on the ground structure that cannot be obtained using conventional methods will be obtained. In particular, there is a high possibility of obtaining underground information non-destructively and accurately in the range of several meters to several meters.Also, with conventional methods, relatively complex calculation processing is required after collecting measurement data, so large-scale A computer is required,
Moreover, the analysis took a long time and the cost of the analysis increased, but since this method does not require complicated calculations, it is expected that the structure of the ground can be elucidated immediately while taking measurements as an easy-to-understand image. The place of the scene! In many cases, accurate =Fn information of the ground structure is required as soon as possible in a single survey, and this method is applicable to such cases as well.

An explanatory diagram showing the principle, Fig. 2 is a block diagram showing an example of the method of the present invention, Fig. 3 is a block diagram showing an example of signal processing, Fig. 4 is a waveform diagram of signal processing, and Fig. 5 is a block diagram showing an example of the method of the present invention. It is a principle diagram of an ultrasonic microscope used in the field of materials testing.

■...Oscillation transducer (acoustic wave oscillator),
2... Ground, 3... Multi-channel high frequency pulse phase difference oscillator, 4...
... Computer, 5... CRT display, 6.
...Signal processing device, 7...Resonance transducer (acoustic wave geophone).

Figure 1 (A) Figure 1 (B) Figure 1 (C) Figure 5

Claims (1)

[Claims] Outputs phase-shifted elastic waves or electromagnetic waves from multiple elastic wave oscillators or electromagnetic wave oscillators installed on the ground surface or inside a polling hole, concentrates the elastic waves or electromagnetic waves at any point in the ground, and reflects the waves. Ground perspective method is characterized by inputting waves using an elastic wave geophone or electromagnetic wave transmitter on the ground surface, and imaging the structure in the ground from the waveform information.