JP3717163B2 - Nondestructive measurement method and apparatus using multiple earthquakes using pseudo-random waves - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nondestructive measurement method and apparatus using multiple earthquakes using pseudo-random waves, and in particular, ground investigations related to construction work, resource mining, etc., damage inside existing structures such as dams, dikes, bridges, and tunnels. The present invention relates to a nondestructive measurement method and apparatus using multiple earthquakes using pseudo-random waves suitable for use in surveys.
[0002]
[Prior art]
In order to elucidate the liquefaction of the ground in earthquake disaster prevention, it is necessary to carry out a liquefaction experiment using a model soil layer. It was not possible to measure dynamic changes only by measuring only. That is, the spatial and temporal changes could not be grasped simultaneously. Since liquefaction is a dynamic change in the ground, it is not enough to elucidate the liquefaction model simply by performing static measurement with existing methods, and a method capable of dynamic measurement is required. It was.
[0003]
In addition, it is not only the problem of ground liquefaction that requires continuous measurement in space and time, but the same applies to inspections and structures inside the human body. That is, in order to measure the human body, there are existing methods such as CT scan, MRI, and ultrasound, but all of them have a large influence on the human body due to the measurement method itself (for example, X-ray irradiation etc.) Measurement could not be performed. Moreover, it is physically impossible to apply these methods to the ground due to the problem of the dimensions of the measurement object.
[0004]
On the other hand, when investigating structures such as dams, embankments, bridges, and tunnels, it is difficult to stop the original functions of the structure due to the measurement work. It was large and it was difficult to perform sufficient measurement. For example, when measuring dams and dikes, it is necessary to lower the internal water level or stop the discharge, and it is necessary to block traffic in surveys of roads, bridges, and tunnels. Considering the impact, high-precision surveys could not be conducted in a short time, and as a result, halfway surveys were often completed.
[0005]
A method for accurately measuring the inside of the ground includes a boring survey and the like, but in order to grasp the continuous change of the ground, two or more measuring holes proposed in Patent Document 1 and Patent Document 2 are used. It is necessary to perform tomography measurement using.
[0006]
[Patent Document 1]
JP-A-6-294793 [Patent Document 2]
JP-A-10-319132 [0007]
At this time, unlike the CT scan for measuring the human body, the tomographic measurement on the ground is usually performed by moving one seismograph 20 up and down as shown by the arrow A in the seismic hole 10 as shown in FIG. It is necessary to perform measurement so that the sound wave line B propagates uniformly in the cross section of the ground 6 by receiving vibrations with a plurality of geophones 30 installed in the holes 12.
[0008]
[Problems to be solved by the invention]
However, in the method of FIG. 1, since it takes time and effort to move the oscillator 20, static state changes can be measured, but the state of the ground changing in time in a short time continuously It was impossible to capture. In addition to dynamic measurement, in normal measurement, for example, a measurement time of about 8 hours is required to measure at a depth of 50 m. In some cases, sufficient accuracy could not be measured.
[0009]
An example of a conventional configuration is shown in FIG. In the figure, 40 is a control device, 42 is a code generator, 44 is an oscillation waveform generator, 46 is an acoustic amplifier, 50 is a signal amplifier including a filter, and 52 is a filter for eliminating the influence of noise, for example, seismic wave and vibration A correlation calculator 54 for calculating the cross-correlation by the time shift synergistic sum of the waves is an output device.
[0010]
Also, as shown in FIG. 3, when measuring the inside of the structure 8 or when exploring the resources of the ground 6 by the reflection method as shown in FIG. On the other hand, if there are multiple focal points, it is not possible to identify the wave that originated from multiple focal points at the same time. Measurement takes time.
[0011]
Further, according to Biot's theory concerning fluid behavior in a porous medium as described in Patent Document 3, the hydraulic conductivity of the ground is directly calculated using the relationship of elastic wave vibration = speed of water passing through = water permeability. In acoustic permeation tomography that can be measured, the permeability coefficient distribution as shown in FIG. 5 can be grasped by changing the measurement frequency and measuring and calculating the frequency characteristics of the ground.
[0012]
[Patent Document 3]
JP 2000-35483 A
However, in order to measure at different frequencies, it is necessary to oscillate the number of frequencies and repeat the measurement for each frequency, as shown in FIG. Therefore, the measurement time is several times as long as the measurement at a single frequency, which is a great restriction for practical use in the field. For example, in order to obtain data of 5 frequencies with respect to the number of 20 points, 20 points × 5 frequencies = 100 earthquakes are required, and it takes 100 minutes even if 1 minute per earthquake.
[0014]
In order to save time and effort to move the sound generator 20, it is necessary to prepare a plurality of sound generators and simultaneously generate a shock as shown in FIG. 7, but in the conventional method, the output signals from the individual sound generators are distinguished. It was impossible to separate the mixed sound because it could not be done, and therefore no attempt was made to squeeze at the same time.
[0015]
On the other hand, in the pseudo random code signal used in the communication field, changing the code arrangement in order to identify the oscillation signal has already been put into practical use, for example, for identifying an individual mobile phone. In addition, the use of pseudo-random codes inside the ground has already been proposed in Patent Documents 1 and 2, but (1) Since the signal attenuation is significant inside the ground, it is difficult to restore the pseudo-random codes. , Separation is difficult even if the code sequence is changed, and it is difficult to separate. (2) The amount of calculation for separating multiple pseudo-random codes by multiple correlation calculation is enormous, and considering the calculation time, the separation work itself is not practical. (3) Since each of the transducers is very expensive compared to other measuring instruments such as geophones, there is no idea of using a plurality of transducers at the same time. Using it alone could not exceed the limits of existing technology. Therefore, it has not been considered to apply the multiple pseudo-random code signal to ground investigation or the like.
[0016]
The present invention has been made to solve the above-described conventional problems, and it is an object of the present invention to make it possible to separate signals that have been generated simultaneously from a plurality of oscillators, thereby enabling quick measurement by multiple oscillations.
[0017]
[Means for Solving the Problems]
The present invention uses a plurality of pseudo-random code signals that are different from each other in code arrangement and are resistant to noise, and simultaneously generates and receives a plurality of pseudo-random waves from a plurality of oscillators, and performs analysis. The above-mentioned problem is solved by separating only the above signals.
[0018]
The present invention also provides a non-destructive measuring apparatus using multiple earthquakes using pseudo-random waves, a means for generating a plurality of pseudo-random code signals that are different from each other in code arrangement and are resistant to noise, and the pseudo-random code signal is provided. A plurality of transducers that oscillate a plurality of pseudo-random waves substantially simultaneously; a geophone that receives a plurality of pseudo-random waves that are oscillated from the seismograph; and a multi-correlation of signals received by the geophones The above-mentioned problem is solved by calculating and configuring with analysis means that separates the signals from the respective oscillators.
[0019]
In order to solve the problems described in the prior art, the applicant has made a new attempt on the following points.
[0020]
(1) Selective extraction of pseudo-random codes that are less susceptible to attenuation by ground and structures and are more resistant to noise.
[0021]
Pseudorandom codes used in the communication field do not have to worry about the effects of noise, so there was no particular problem with using any code, but the effects of noise were limited in places with large attenuation such as the ground and structures. Therefore, it is necessary to selectively create a pseudo-random code that is resistant to noise. For this reason, a special pseudo-random code that is rarely used normally is created because the number of code arrangements is limited. However, there are a sufficient number of code arrangements compared to the number of sound generators used for ground surveys.
[0022]
(2) A device for converting a plurality of created pseudo-random codes into sound that can be used inside the ground.
[0023]
Incorporating a pseudo-random code into a sine wave or the like has already been put into practical use, but in order to accurately represent the synthesis of multiple signals, it is necessary to create and output an oscillation waveform at high speed. is necessary. In the present invention, although the number of bits is inferior, the seismic waveform is created using a measuring device capable of performing AD / DA conversion at high speed.
[0024]
(3) Adopting a high-speed correlation calculation method using FFT-inverse FFT transform in order to perform huge correlation calculation at high speed.
[0025]
Although it is a general technique to perform correlation calculation at high speed using FFT-inverse FFT transform, it has not been used for correlation calculation of multiple pseudo-random codes. In view of this, a method using the discrete fast Fourier transform (DFFT) was studied and realized by utilizing the relationship (Weiner Khinchin) that the cross-correlation is equal to the inverse Fourier transform of the cross spectrum.
[0026]
(4) Simplification of existing piezo-type transducers and production of low-cost versions in order to assemble multiple transducers as a system.
[0027]
In the present invention, by utilizing the fact that pseudo-random code signals having different code arrangements have mutually exclusive properties (become noises), as shown in FIG. Different pseudo-random code signals are oscillated, received by the geophone 30, and analyzed, thereby separating only the signals from the individual geophones. As a result, it is possible to obtain the same effect as separately generated from a plurality of occurrence positions, so that it is possible to measure the inside of the ground and the structure in a non-destructive manner in an instant.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0029]
The configuration of the present embodiment is shown in FIG. In the conventional configuration shown in FIG. 2, since the generator 20 is a single unit, both the generating side and the receiving side have a simple configuration. However, according to the present invention, a signal with a different code arrangement is created. A multiple code generator 60 and a multiple oscillation waveform generator 62 and a multiple correlation calculator 64 for separating different codes are required.
[0030]
FIG. 10 shows a simulation result by calculation. The composite wave of the five waves is mixed while being affected by the arrival and loses its original form (almost sinusoidal wave), and at first glance looks like noise, but by performing the multiple correlation calculation, the five signals (numbers) 1-5) could be extracted.
[0031]
This was the same even when three frequencies were mixed as shown in FIG.
[0032]
The application target of the present invention is not limited to the ground and structures, and can be applied to the human body. When applied to the human body, the movement of muscles and internal organs (for example, the stomach) can be inspected using sound waves that are harmless to the human body without using X-rays or barium.
[0033]
【The invention's effect】
According to the present invention, it is possible to separate signals that have occurred simultaneously from a plurality of occurrence points.
[0034]
Therefore, as shown in FIG. 12, it is possible to measure instantaneously without moving the vibrator up and down, and to measure the internal state of the ground and structures in real time continuously in space and time. . Therefore, for example, when the ground moves sideways in a relatively short time due to liquefaction of the ground or the state where the ground erupts to the ground surface, as shown in FIG. Can be measured accurately.
[0035]
Further, as shown in FIG. 14, the measurement of a plurality of frequencies can be completed with only one measurement without increasing the number of earthquakes.
[0036]
Furthermore, as shown in Fig. 15 and Fig. 16, by deploying multiple generators and geophones in the structure or strata, the destruction status of structures such as piers and tunnels (cracks, etc.) and the cross section of the stratum by the reflection method can be obtained. Measurement can be performed instantaneously or in a short time.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a ground for explaining conventional problems. FIG. 2 is a block diagram showing a conventional configuration example. FIG. 3 is a perspective view of a structure for explaining conventional problems. Plan view [Fig. 4] Cross-sectional view of the same formation [Fig. 5] Diagram showing an example of hydraulic conductivity distribution obtained by the prior art [Fig. 6] Diagram for explaining problems in measurement at multiple frequencies [ FIG. 7 is an explanatory diagram for explaining the conventional problems. FIG. 8 is an explanatory diagram showing an outline of the present invention. FIG. 9 is a block diagram showing a configuration of an embodiment of the present invention. FIG. 11 is a diagram showing the results of cross-correlation calculation at the same frequency. FIG. 12 is a cross-sectional view of the ground for showing the effect of the present invention. [Fig. 13] Diagram showing time-dependent continuous change of the ground [Fig. 14] Frequency characteristics Cross-sectional view of the ground showing the state of instantaneous measurement [Fig. 15] Perspective view of the state of measuring the internal state of the structure [Fig. 16] Similarly, the state of exploring resources in the formation Sectional view [Explanation of symbols]
6 ... Ground 8 ... Structure 10 ... Shooting hole 12 ... Sensing hole 20 ... Shooting device 30 ... Shooting device 50 ... Signal amplifier 60 ... Multicode generator 62 ... Multiple oscillation waveform generator 64 ... Multiple correlation calculator

Claims (2)

By using multiple pseudo-random code signals that are different from each other in code arrangement and resistant to noise, multiple pseudo-random waves are simultaneously generated and received from multiple oscillators, and analysis is performed, so that only the signals of individual oscillators are obtained. Non-destructive measurement method by multiple earthquakes using pseudo-random waves characterized by separating. Means for generating a plurality of pseudo-random code signals resistant to noise, the code arrangements of which are different from each other;
A plurality of exciters that are provided with the pseudo-random code signal and generate a plurality of pseudo-random waves substantially simultaneously;
A geophone that receives a plurality of pseudo-random waves generated from the hypocenter substantially simultaneously,
Analysis means for performing multiple correlation calculation on the signal received by the geophone and separating the signal from each of the geophones;
A non-destructive measuring device using multiple earthquakes using pseudo-random waves.

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