JP7429008B2 - Sound wave transducer for measuring objects with rough internal structure - Google Patents

Description

The present invention relates to a sonic transducer for measuring objects having a rough internal structure, such as a ground improvement body that cuts the ground by ultra-high pressure injection of a cement-based hardener to create a cylindrical improvement body.

In order to solidify the foundations of people's lives and the activities of society, ground improvement technology for improving soft ground to high strength is currently in great demand. The high-pressure injection stirring method has been put into practical use as a ground improvement method. The high-pressure injection stirring method is a construction method in which the ground is cut by ultra-high-pressure injection of cement-based hardener from a rod nozzle inserted into the ground, creating a cylindrical improved body.

In the high-pressure injection stirring method, the shear strength of the soil layer targeted for ground improvement and the so-called hardness such as the N value, which is a standard penetration test value, affect the diameter of the improved body formed. Therefore, when carrying out ground improvement work, it is necessary to appropriately set the injection pressure, injection flow rate, etc. of the cement-based hardener, taking into account the soil quality of the soil to be improved. It is necessary to secure the diameter that will be used.

Furthermore, the diameter of the ground improvement body created by the high-pressure injection stirring method varies depending on various factors, such as the shear strength of the target soil and the non-uniformity of the target soil layer. Therefore, in order to guarantee the diameter of the soil improvement body, it is necessary to know the diameter of the soil improvement body that is actually constructed.

However, since the soil improvement body is constructed underground, it is not possible to visually confirm the soil improvement body or directly measure the diameter of the soil improvement body unless the soil improvement body is exposed by excavation.

Therefore, a technique has been proposed for determining the diameter of the improved body during its construction. Patent Document 1 discloses that the shape of the soil improvement body is developed by utilizing the reflection of sound waves at the interface between the ground (also called the original ground, but in order to clarify the distinction, hereinafter referred to as soil) and the soil improvement body. Techniques for measuring are described. Moreover, Patent Document 2 discloses an underwater sonic wave transducer that can be used for such measurements.

Japanese Patent Application Publication No. 2012-172329 Japanese Patent Application Publication No. 2009-194889

However, the technology described in Patent Document 1 does not disclose any requirements for the sonic wave oscillator and the sonic receiver to propagate and receive sound waves to the ground improvement body under construction, and is merely an idea. It was something that should have been done.

Furthermore, by combining the technology described in Patent Document 1 and the technology described in Patent Document 2, it is possible to measure the shape of a ground improvement body. It has been found that when using a transducer with a built-in transducer, there are the following problems.

(1) Since sound waves are transmitted and received over a 360° azimuth, the sound wave energy per azimuth angle tends to be small. In particular, the viscous attenuation and scattering attenuation of sound waves inside the ground improvement body are large, so the sound wave energy rapidly decreases, making meaningful measurements impossible.

(2) Since sound waves are transmitted and received in 360° directions, reflected waves are generated from various parts and become noise echoes. Therefore, it is difficult to determine which echo, which causes a decrease in S/N, is a reflected wave from the boundary between the ground improvement body and the soil.

The present invention has been made to solve the above problems, and its purpose is to measure objects having rough internal structures with large scattering attenuation and viscous attenuation of sound waves, such as ground improvement bodies immediately after construction. An object of the present invention is to provide a sound wave transducer suitable for

The present invention provides that in order to detect the boundary between a ground improvement body and soil, it is effective to transmit sound waves from a directional sound wave transducer toward the boundary and receive reflected waves from the boundary. They discovered this and completed the present invention.

That is, the gist of the present invention is as follows.

(1) A sound wave transducer used to measure objects with a rough internal structure, in which multiple columnar piezoelectric elements are arranged in parallel and used as a vibrator to excite and detect sound waves. A sound wave transducer characterized by having a built-in composite vibrator having a structure hardened with resin.

(2) In the sound wave transducer, it is preferable that the area ratio of the columnar piezoelectric element surface to the vibration surface that transmits and/or receives sound waves is 60% or more and 80% or less.

(3) In the sound wave transducer, the diameter D satisfies D≧29×λ/240, where D is the diameter of the vibration surface that transmits and/or receives sound waves, and λ is the wavelength of the sound waves. In this manner, it is preferable to transmit and receive sound waves having directivity with a frequency of 2 kHz to 10 kHz .

(4) The target object having a rough internal structure shall be ground, soil, ground improvement material which is a mixture of soil and hardening agent, aggregate, concrete containing reinforcing steel, brick, carbon compact, or rock. Can be done.

(5) The sound wave transmitted by the sound wave transducer is preferably a pseudo-random wave that is a phase modulated wave based on a binary code string.

The present invention aims at transmitting sound waves and suppressing reflected waves from the boundary between the ground improvement body and the soil for a ground improvement body that cuts the ground and creates a cylindrical improvement body by ultra-high-pressure injection of a cement-based hardening agent. A composite vibrator has a structure in which a plurality of columnar piezoelectric elements (for example, PZT columns, PZT is an abbreviation for lead zirconate titanate) are arranged in parallel and hardened with epoxy resin. Since the sound wave transmitter/receiver has directivity, it is possible to obtain good reflected waves from the boundary between the soil improvement body and the soil. can be accurately determined immediately after construction.

In addition, the present invention is not limited to a ground improvement body immediately after construction, but also uses sound waves of objects with rough internal structures such as ground, soil, concrete (including aggregates and reinforcing bars), bricks, carbon molded bodies, rocks, etc. This is effective for obtaining good reflected waves in measurements where the

An explanatory diagram showing a vertical cross-sectional structure of an embodiment of a sound wave transducer according to the present invention A cross-sectional view showing the arrangement of columnar piezoelectric elements (PZT columns) on the vibration plane of the acoustic wave transducer according to the present invention Explanatory diagram showing the configuration of an experiment to detect echoes from the side edges of a simulated test object Waveform diagram showing an example of echo detection from the side edge of a simulated test object A diagram showing an example of the relationship between the ratio (area ratio) of the columnar piezoelectric element (PZT column) surface built in the sound wave transducer according to the present invention to the area of the vibration surface, and the echo amplitude and noise level. A diagram showing an example of the relationship between the ratio of the area of the vibration surface of the columnar piezoelectric element (PZT column) built in the sound wave transducer according to the present invention to the area of the vibration surface (area ratio) and the SN ratio of the echo. A diagram showing an example of the relationship between the diameter D of the vibration surface of the composite vibrator built in the sound wave transducer according to the present invention and the SN ratio of the echo. A waveform diagram showing an example (part) of a waveform of a pseudorandom wave transmitted from a sound wave transducer according to the present invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the contents described in the following embodiments and examples. Further, the constituent elements in the embodiments and examples described below include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Further, the constituent elements disclosed in the embodiments and examples described below may be combined as appropriate, or may be appropriately selected and used.

FIG. 1 shows a longitudinal cross-sectional structure that is the basic configuration of a sound wave transducer 10 according to the present invention. As a transducer for transmitting and receiving sound waves, a composite transducer 12 made of a plurality of prismatic PZT columns 14 arranged side by side and hardened with an epoxy resin 16 is incorporated, as shown in the cross section in FIG. The vibration mode of the columnar PZT (14) is longitudinal vibration rather than thickness vibration, and the electro-mechanical coupling coefficient can be increased.

To explain the structure of the sound wave transducer 10, electrodes 18A and 18B are connected to the upper and lower surfaces of the composite vibrator 12, respectively, and are connected to an electrical signal connector 22 via electric wires 20A and 20B. . Further, the composite vibrator 12 is housed in a case 24, and a front plate 26 is attached to the front surface of the vibrator 12 (the surface that transmits and receives sound waves) (lower surface in the drawing) to protect the vibrator 12.

Since the object to be measured using the transducer according to the present invention has a rough internal structure, the scattering attenuation and viscous attenuation of sound waves are large. Therefore, it is effective to use techniques for improving the SN ratio, such as pulse compression. In such SN improvement technology, it is necessary to faithfully convert an electric signal waveform applied to a transducer to a sound wave signal waveform for sound wave transmission. PZT has a relatively large mechanical Q value, and even when driven with a spike-like pulse, it generates a sound wave with a slightly long pulse width. However, due to the damping effect of the epoxy resin 16 that hardens the surrounding area, the pulse width becomes shorter and the frequency increases. It begins to exhibit characteristics with a wide band. This increases the similarity between the waveform of the input electrical signal and the waveform of the transmitted sound wave. However, if the amount of epoxy resin 16 is too large, the sound pressure (power) of the transmitted wave will decrease, which is not preferable. In addition, the area ratio of the PZT pillar surfaces (the ratio of the total area of the PZT pillars 14 to the vibration surface area of the composite vibrator 12; however, in the cross section parallel to the vibration surface, the area ratio of the PZT pillars 14 is the same everywhere) increases. If it is too high, the frequency band will be narrowed, and the similarity between the waveform of the electric signal and the waveform of the transmitted sound wave will become low, which is not preferable. That is, the area ratio of the PZT column surface to the surface that transmits and/or receives sound waves is important, and as a result of research in the present invention, it has been found that the area ratio is preferably 60% or more and 80% or less.

Further, the directivity of the sound wave transmitted and received by the sound wave transducer 10 is proportional to the wavelength λ of the sound wave and inversely proportional to the diameter D of the vibration surface of the vibrator 12 (see FIG. 1). In order to receive echoes with large amplitudes, it is required that the transmitted sound waves have high directivity (small directivity angle). In the present invention, as a result of research, it has been found that if the diameter D of the vibration surface satisfies D≧29×λ/240, echoes with sufficiently high directivity and large amplitude can be received in the frequency range of 2 kHz to 10 kHz, for example. .

Objects with rough internal structures envisioned by the present invention include ground and a mixture of soil and hardening agent (so-called ground improvement material), as well as ground, soil, concrete (including aggregate and reinforcing bars), bricks, These are carbon molded bodies and rocks.

The sound waves transmitted and received by the sound wave transducer 10 of the present invention are pseudo-random waves (phase modulated waves using binary code strings) as illustrated in FIG. Good.

An example will be described in which measurements were performed using the embodiment of the acoustic wave transducer 10 according to the present invention shown in FIG. 1, using a simulated test body (designed diameter 5 m) of the same geology as the ground improvement body as a test subject.

FIG. 2 is a cross-sectional view showing the arrangement of the PZT pillars 14 on the vibration plane, where the area ratio is 68.4%. The shaded portion is the PZT pillar 14, and the halftone dotted portion is the epoxy resin 16. Transmits and receives sound waves in the direction perpendicular to the plane of the paper.

As shown in FIG. 3, the transducer 10 was inserted into the measurement tube 52 installed at the center of the simulated test body 50 of the ground improvement body, and the sound waves 30 were transmitted toward the side ends of the simulated test body 50. At this time, the sound wave 30 transmitted from the transducer 12 and reaching the side end of the simulated test body 50 is reflected and returned to the transducer 10 as an echo 32 and received, and the detected signal is shown in FIG. Shown below. An echo signal with a good SN ratio is obtained. In this case, the diameter D of the vibration surface was 100 mm, and the area ratio of the 14 PZT columns was 61.6%.

FIG. 5 shows the side end of a simulated test specimen 50 by changing the ratio of the 14 PZT pillars built into the transducer 10 to the area of the vibration surface (by replacing and incorporating a plurality of vibrators with different area ratios). FIG. 6 shows the results of calculating the echo signal-to-noise ratio (S/N in the figure) using the data in FIG. 5. When the area ratio is 60 to 80%, the S/N ratio of the echo is within 3 dB from the peak (area ratio 68%), and it is found that there is no problem in practical use.

FIG. 7 shows the side end of a simulated test specimen 50 using a transducer 10 with a built-in vibrator 12 manufactured by setting the area ratio of the 14 surfaces of the PZT column to about 62% and changing the diameter D of the vibration surface in multiple ways. This is the result of measuring the magnitude of the echo 32 from the same position. It can be seen that if the diameter D of the vibration surface satisfies D≧29×λ/240, the magnitude of the echo will be within 3 dB from the peak, and there will be no problem in practice. The speed of sound during the experiment was 1500 m/s, and the frequency λ of the sound wave transmitted from the transducer 10 was equivalent to 2 kHz. Note that when the transducer material is PZT and the height of the column is 135 mm, it is possible to transmit sound waves with a frequency of 2 kHz to 12 kHz.

FIG. 8 is a waveform example of a sound wave (pseudo-random wave) transmitted from the transducer 10. FIG. 8 shows a part of the pseudorandom wave, which is actually a signal having a pulse width of 1000 cycles or more. The signal shown in Figure 8 is amplified to a high voltage and applied to the sound wave transducer 12 built into the directional transducer 10 to transmit a sound wave with the same waveform, and the received signal is pulse compressed. Process the signal using this method to obtain an echo signal. The results shown in FIGS. 4 to 7 are obtained as a result of signal processing of the received signal using a pulse compression technique.

Since the present invention is configured in this way, it is not limited to a ground improvement body immediately after construction, but can also be applied to objects having the rough internal structure such as ground, soil, concrete (including aggregate and reinforcing bars), bricks, carbon molded bodies, rocks, etc. It is effective in obtaining good reflected waves in measurements using sound waves from objects.

In the above explanation, the transducer 10 is used to transmit sound waves and receive echoes, but the transducer 10 is used only for transmitting sound waves and not for receiving echoes. It is possible to use conventionally known wave receiving means such as a hydrophone. Further, the cross-sectional shape of the PZT pillar 14 is not limited to a rectangular shape, and may have another shape. The type of piezoelectric element is not limited to PZT, but may also be lead titanate, piezoelectric single crystal PMN-PT, or the like.

10...Sonic wave transducer 12...Composite vibrator 14...PZT column (column piezoelectric element)
16...Epoxy resin 18A, 18B...Electrode 20A, 20B...Electric wire 22...Connector 24...Case 26...Front plate 30...Sound wave 32...Echo 50...Mock test object 52...Measurement tube D...Diameter of vibration surface

Claims (3)

A sound wave transducer used for measuring an object having a rough internal structure ,
As a vibrator for exciting and detecting sound waves, it has a built-in composite vibrator with a structure in which multiple columnar piezoelectric elements are arranged side by side and hardened with epoxy resin .
The area ratio of the columnar piezoelectric element surface to the vibration surface that transmits and/or receives sound waves is 60% or more and 80% or less,
When the diameter of the vibration surface that transmits and/or receives sound waves is D, and the wavelength of the sound wave is λ, the diameter D satisfies D≧29×λ/240, and the directivity at a frequency of 2 kHz to 10 kHz is achieved. 1. A sound wave transducer characterized by transmitting and receiving sound waves having a characteristic . The object having a rough internal structure is characterized in that it is ground, soil, a ground improvement body that is a mixture of soil and a hardening agent, aggregate, concrete containing reinforcing bars, bricks, carbon molded bodies, or rocks. The acoustic wave transducer according to claim 1. 3. The sound wave transducer according to claim 1 , wherein the sound wave transmitted by the sound wave transducer is a pseudo-random wave that is a phase modulated wave based on a binary code string.

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