JPH0213249B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vibration wave propagation velocity measurement method for investigating the layer quality of an object to be measured, particularly the ground.

Generally, as a conventional method for measuring the propagation speed of vibration waves in the ground, a vibration detector is installed at one point on the ground, the ground is vibrated at a constant frequency, and the vibration point is There is a method of finding the position of the detector that is one wavelength away by observing the outputs of both detectors with an oscilloscope while moving another vibration detector in an extension of the set point of the vibration detector described above. be. The distance between both detectors obtained by this is Y (m), and the excitation frequency at that time is f (Hz).
Then, the average propagation velocity U (m/
s) can be determined by U=Y·f(m/s).

However, according to the above method, each time the excitation frequency is changed and measured, one side of the vibration detector is moved and one wavelength is checked using the same method as above.
We need to find the two wavelengths and their propagation speeds,
The drawback was that it required time and labor, resulting in poor measurement accuracy. Therefore, it would be desirable to be able to perform measurements while keeping the distance between both detectors constant.One way to do this is to find the cross-correlation of the output signals of both detectors, so that one wavelength can be measured without moving the detectors. You can measure the length of. However, in this method, the distance between both detectors must be set to be equal to or less than the length of one wavelength to be measured. The range of wavelength lengths is wide, for example 1:100, so if you know in advance the shortest distance of one wavelength to be measured and install both detectors at that distance, the measurement The drawback is that the accuracy naturally decreases as the wavelength becomes longer.

Therefore, it is an object of the present invention to eliminate the above-mentioned drawbacks, and to detect propagating waves over a wide range and with high precision, without requiring much time or manpower, while keeping the distance between the two vibration detectors fixed. An object of the present invention is to provide a vibration wave propagation velocity measurement method that can measure velocity and wavelength.

According to the present invention, there is provided a vibrator that vibrates the object to be measured to emit a propagating wave in a straight line on the surface of the object to be measured, such as the ground; Two vibration detectors are installed separated by a certain distance S selected without being constrained by any of the above, and separately, a drive wave which is a sine wave with a variable frequency f is set at the constant distance S. distance S
drive signal generating means for generating a wave modulated by a contour wave having a longer variable repetition period as a drive signal for driving the vibrator; and within the corresponding repetition period of each output of the two vibration detectors. cross-correlation means for determining the time τ during which a propagating wave propagates between these two vibration detectors from a point of abrupt change in amplitude existing at , and from the time τ the propagation velocity of the propagating wave v=
S/τ is calculated, and the calculated propagation velocity v
and means for calculating the wavelength λ=v/f of the propagating wave from the sine wave frequency f of the drive signal generating means, and calculating the wavelength λ=v/f of the propagating wave from the sine wave frequency f of the drive signal generating means, A vibration wave propagation velocity measurement method is obtained, which is characterized in that measurement is performed by selectively setting a repetition period.

Next, the method for measuring the propagation velocity of vibration waves according to the present invention will be described in detail by giving examples and referring to the drawings.

First, the installation state of equipment for applying the method of the embodiment according to the present invention will be explained with reference to FIG. The ground G to be measured
are placed at intervals above. Vibrator 1
As shown in Fig. 2, it has a function of generating a sine wave with a frequency f which is modulated in a combination mode of a soft start mode and attenuation. The vibration plate in contact with the ground G is driven, and the inside of the ground G,
Transmits vibrations to the surrounding area. On the other hand, vibration detector 2
is installed at an appropriate distance from the vibration exciter 1, and the vibration detector 3 is installed at a distance S from the vibration detector 2 because it is an extension of the vibration detector 2.

In the above equipment installation state, when the vibration exciter 1 is driven, for example, in the mode shown in Fig. 2, and the ground G is thereby excited, the vibration wave becomes a propagating wave within the ground G. and are detected by vibration detectors 2 and 3, respectively, with a time delay.
Figure 1b shows the operating waveforms in that case.
Of these, waveform A is the drive wave of exciter 1, waveform D ₁
is the detected wave of the vibration detector 2, and waveform _D2 is the detected wave of the vibration detector 3. Thus, the obtained waveform D ₁
By finding the cross-correlation between and waveform D ₂ ,
The detection time delay τ between the two can be known. Then, by dividing the distance S between the vibration detectors 2 and 3 by this τ, the propagation velocity of the propagating wave v=S/τ is obtained, and further by dividing this velocity v by the excitation frequency f. Therefore, the wavelength of the propagating wave λ=v/f is obtained. As is clear from this, the wavelength λ of the propagating wave can be obtained by using the excitation frequency after the propagation velocity is calculated from the measured delay time τ. As described above, the propagation velocity v calculated above corresponds to the stratum at a depth of λ/2 from the surface of the ground G.

Note that by changing the excitation frequency f, the propagating waves can be detected using the same method as described above, and if the time delay τ of the propagating waves at that point is determined, ultimately the propagation of the propagating waves in different strata can be determined. It will be seen that speed is gained. This makes it possible to accurately measure the propagation velocity in each layer over a wide range.

By the way, the fact that the excitation frequency f that drives the vibrator 1 is modulated in the mode shown in Fig. 2 means that the above-mentioned time delay τ can be calculated from the detected propagation wave by cross-correlation. When calculating, it is indispensable to make use of the points of rapid change in amplitude that exist therein, and to ensure temporal comparison. Note that in FIG. 2, Modei and Lo both utilize points of rapid change in amplitude in the same way. Therefore, for example, the ratio of the wave number of the sine wave included in the steep part of the contour wave forming the modulation mode, such as a modulation mode, may be at most at least at least. Furthermore, by making the waveform of the excitation frequency f into a sine wave, it is possible to calculate the wavelength λ of the propagating wave.

As can be seen from Figure 2, the period of the drive wave can be detected from 1/10 to 1/100 of the repetition period of the contour wave within a range where the repetition period of the contour wave is not shorter than the distance between the two vibration detectors. can. On the other hand, for those with long periods, both detectors are fixed near the vibration source at a certain interval, so the signal is large and there is little noise.
It is possible to measure up to about 100 meters.

FIGS. 3a and 3b are block diagrams showing specific configuration examples of the vibration excitation side device and the vibration detection side device, respectively, which are applied to the embodiment of the present invention. In Figure a, the mode oscillator 1-1 generates a contour wave for modulating a sine wave of frequency f in the mode shown in A or B of Figure 2, and the sine wave oscillator 1-2 generates a wave for contouring. a sine wave of frequency f,
For example, it oscillates in the range of 1 to 1000Hz. The respective outputs are given to amplitude modulators 1-3, and each time the frequency f of the sine wave is changed, the repetition period of the contour wave is appropriately changed to produce outputs in a sequentially modulated form. In addition, when the distance between two vibration detectors that are set constant is long, or because the propagation speed of each layer differs depending on the value of the excitation sine wave frequency f, for example, the repetition period If the distance between the two detectors becomes smaller than the distance between the two detectors and the sensor is operated as it is, many mode waves will be detected between the two detectors. Therefore, in such a case, in order to avoid errors in the measured value of the delay time τ obtained between vibration detectors 2 and 3 due to cross-correlation, the repetition period of the contour wave should be adjusted to the interval between the two vibration detectors. The length is selected so that the driving wave can be modulated within a range that does not become smaller than S. When taking cross-correlation, it is preferable that the repetition period of the contour wave be long, but since this requires a large amount of excitation energy, a short value is selected within a range that does not cause errors in the measured values. In this way, each time the frequency f is changed, the repetition period of the contour wave is selectively set and a series of measurements are performed.
This modulated output is amplified by a power amplifier 1-4 and given to the vibrator 1 for driving. The vibrator 1 is equipped with a heavy magnet, and is configured to drive a vibration plate directly connected to the movable wire by passing a current through the movable wire inserted into its magnetic circuit.

In FIG. 3b, two vibration detectors 2 and 3 pick up the mode-modulated propagation waves, and their outputs are guided to detectors 2-1 and 3-1, respectively. After its magnitude is detected, it is fed to the cross-correlation meter 4. As is known in the prior art, the cross-correlation meter 4 includes a multiplier for multiplying one detection signal by the other detection signal. The cross-correlation of the two detection inputs is determined, the time delay τ of the propagating wave at the point where the propagating wave is detected is calculated, and the value is output. The propagation velocity meter 5 has a time delay τ from the cross-correlation meter 4.
When we receive the calculated value of , vibration detectors 2 and 3 are
The propagation velocity v of the propagating wave is calculated by dividing the distance S between them, and the depth of the ground where the propagating wave was detected is calculated by obtaining the wavelength λ. Note that a storage device may be added to this propagation velocity meter 5 if necessary.
It is also possible to automatically store the measurement results in sequence and then obtain a table of propagation speeds of vibration waves in each stratum using recording paper or the like.

As is clear from the above description, according to the present invention, a sine wave is excited in the form of a modulated wave with a combination mode of soft start and attenuation, and a measured object is vibrated at a known distance. By detecting the propagating waves with two fixed vibration detectors and finding their cross-correlation each time the frequency of the sine wave is changed, the propagation velocity can be measured over a wide range without requiring time or manpower. Since it is possible to measure with high precision, it has a great effect on improving efficiency and accuracy when conducting qualitative investigations of objects to be measured, including the ground.

[Brief explanation of drawings]

FIGS. 1a and 1b are diagrams showing the installation state of equipment and operating waveforms according to this method, respectively, for applying the method of the embodiment according to the present invention, and FIG.
A diagram showing the types of mode modulated waves that drive the vibrator in Figure 1 a, and Figures 3 a and b are similar to Figure 1 a.
FIG. 3 is a block diagram showing specific configuration examples of the vibration excitation side and vibration detection side devices applied to the embodiment. In the figure, 1 is an exciter, 1-1 is a mode oscillator, 1-2 is a sine wave oscillator, 1-3 is an amplitude modulator, 1-4 is a power amplifier, 2 and 3 are vibration detectors, 2-1 , 3-1 is a detector, 4 is a cross-correlation meter,
5 is a propagation velocity meter.

Claims (1)

[Claims] 1. A vibrator that vibrates the object to be measured to emit a propagating wave in a straight line on the surface of the object to be measured, such as the ground; and two vibration detectors separated by a certain distance S selected without being restricted by any of the above. A drive signal generating means for generating a wave modulated by a contour wave having a variable repetition period longer than a certain distance S as a drive signal for driving the vibrator, and correspondence between each output of the two vibration detectors. cross-correlation means for determining the time τ during which a propagating wave propagates between these two vibration detectors from a point of sudden change in amplitude existing within a repetition period; and from the time τ the propagation velocity of the propagating wave v=S/ τ is calculated, and further, from the calculated propagation velocity v and the sine wave frequency f of the drive signal generating means, the wavelength λ of the propagation wave is determined as λ=v/
and means for calculating f, and the vibration wave propagation is characterized in that the measurement is performed by selectively setting the repetition period of the contour wave according to the frequency f of the sine wave emitted by the drive signal generating means. Speed measurement method.