JP2003121276A - Bender element for shearing wave velocity measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely measure shearing wave velocity in a hard material such as improved ground or concrete. SOLUTION: A resonator protection layer 20 is formed on an end face of a base block 11 of this bender element 10 by covering the circumference of a piezoelectric resonator 12 having its root part fixed with a soft material having a Young's coefficient of 100 MPa or less and a predetermined thickness, or the resonator protection layer is formed by housing the base block supporting the piezoelectric resonator in a recess of an armoring block and by filling the soft material in at least the circumference of the piezoelectric resonator in the recess, so that the shearing wave velocity in the hard material such as improved ground or concrete can surely be measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shear wave velocity measuring bender element, and more particularly to a shear wave velocity measuring bender element capable of reliably measuring shear wave velocity in a hard material such as improved ground or concrete. .

[0002]

2. Description of the Related Art A bender element, which is a kind of piezoelectric ceramic oscillator, is known as a sensor for measuring shear wave velocity of the ground. For example, various types of bender elements 50 as shown in FIGS. 10A and 10B have been proposed depending on the installation position. Figure 10
(A) is a basic type rectangular parallelepiped acrylic base block 51 and the piezoelectric ceramic vibrator 5 on the upper surface thereof.
2 shows that it is fixed. This oscillator 52 has a beam length (l) of a bimorph type cantilever beam shape whose one end 52a is fixedly supported by the base block 51, as shown by the reference numerals in FIG. Oscillator 52
Is integrally laminated to have a plate thickness (t). FIG.10 (b) has shown the bender element 50 measured and installed in the middle point. As shown in the figure, a vibrator 52S as an oscillating unit is provided on the upper surface 51a of the base block 51, and a vibrator 52R as a receiving unit is provided on the lower surface 51b.
Is stuck.

FIG. 12 shows a method for measuring the shear wave velocity of the ground using this type of bender element.
As shown in FIG. 12, the vendor elements 50S, 5
0R is buried in the ground separated by a predetermined distance L, a shear wave is transmitted from one bender element 50S, and a shear wave is received by the other bender element 50R,
The shear wave velocity of the target ground is calculated by dividing the distance L between the bender elements by the shear wave propagation time (delay time).

That is, when the buried bender element 50 receives a predetermined vibration from the ground and the cantilever is displaced (flexed), its displacement direction is generated by the piezoelectric effect (see FIG. 1).
1: Electric polarization occurs in the direction of the arrow in the element), and a voltage (V) proportional to the bending amount (u) of the tip is generated with a polarity according to the bending direction. Therefore, the bender elements 50 having the same shape are arranged in the ground so that the oscillators 52 face each other, and the oscillator 52S of one of the bender elements 50 serves as an oscillating portion, and the oscillator 52R of the other bender element 50 is received. Of the two oscillators 52S, 5S
By determining the arrival time of the wave for the distance between the 2Rs,
The shear wave velocity (V _s ) at this ground position can be calculated. In addition, in each drawing of FIG.
Although the circuit is shown to be connected in the vicinity of b, the lead wire from the power supply is actually connected to the terminal (not shown) of the vibrator 52 in the base block 51.

[0005]

By the way, when the shear wave velocity of a hard material such as improved ground or concrete is measured using the bender element described above,
A set of receiving and transmitting bender elements must be installed on the surface of the hard material such as the improved ground to be measured. The shear wave velocity measured at this time is likely to vary depending on the installation state of the bender element, and it is difficult to obtain stable measurement accuracy. In addition, the reproducibility of the installation of the bender element is not ensured by the method of installing the bender element every time the measurement is performed, and when the shear wave velocity of the same improved ground is repeatedly measured over time, the shear wave velocity is inevitable. Reproducibility of measurement results cannot be ensured.

In this case, in order to improve the reproducibility of the measurement by the bender element in the improved ground, it is also considered that the bender element is embedded in the improved ground in advance and the shear wave velocity is measured before the improved ground is hardened. To be However, if the conventional bender element is buried in the improved ground as it is, as the hardening of the improved ground progresses, the vibration around the bender element is restrained by the surrounding improved ground, and the oscillator cannot vibrate sufficiently, resulting in shear waves. It may not be possible to measure speed. Further, as described above, if the conventional bender element is directly embedded in the improved ground, vibration cannot be transmitted as the improved ground hardens, so the shear wave velocity propagating vertically in the in-situ improved ground is measured. I couldn't do that. Furthermore, it is required to facilitate the recovery, including the consideration of the environment and the repeated use of the vendor element after the measurement is completed. Due to the above technical background, when the bender element is embedded in the improved ground in advance, there has been a demand for the development of a bender element that allows the vibrator to transmit vibration even after the improved ground is hardened.

[0007] Therefore, an object of the present invention is to solve the problems of the above-mentioned conventional techniques, and to reliably vibrate and transmit a vibrator in a state where hard material such as improved ground or hardened concrete has hardened. Another object of the present invention is to provide a shear wave velocity measuring bender element which can be easily collected after measurement.

[0008]

In order to achieve the above object, according to the present invention, a vibrator protective layer is formed by coating the periphery of a piezoelectric vibrator fixed to a base block with a soft material having a predetermined thickness. Is characterized by.

At this time, it is preferable that the soft material has a Young's modulus of 100 MPa or less.

The vibrator protection layer may be formed by fixing an off-the-shelf member to the piezoelectric vibrator, or by integrally forming the piezoelectric vibrator by coating. preferable.

Another feature is that the base block supporting the piezoelectric vibrator is housed in the recess of the outer cover block, and at least the periphery of the piezoelectric vibrator in the recess is filled with a soft material so as to protect the vibrator. There is a point that formed.

The outer block is preferably formed of a lightweight foamed resin molding member.

Further, the soft material filled to cover the piezoelectric vibrator is preferably a material having a Young's modulus of 100 MPa or less.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a shear wave velocity measuring bender element of the present invention will be described below with reference to the accompanying drawings. FIG. 1A is a plan view schematically showing a structural example of a bender element 10 according to the present invention, and FIGS. 1B and 1C. As shown in the figure,
A piezoelectric ceramics vibrator (hereinafter, referred to as a vibrator 12) is attached to a rectangular parallelepiped acrylic base block 11 at a substantially central portion of an upper surface thereof with a root portion embedded therein. Furthermore, the vibrator 1 protruding from the base block
A vibrator protection layer is formed around the element 2. In the present embodiment, the vibrator protection layer 20 is composed of a synthetic rubber block as a soft material, and is bonded to the surface of the base block 11. The vibrator protection layer 20 is used for the vibrator 12
Only the tip of the is exposed. When the bender element 10 having such a structure is embedded in a hard material such as improved ground or hardened concrete,
Since the vibrator 12 is covered with the vibrator protection layer 20, the vibration of the vibrator 12 is not hindered by the hard material. This makes it possible to measure shear wave velocity in various hard materials such as improved ground and concrete.

The material of the vibrator protection layer 20 is a soft material and has a relatively lower rigidity than the hard material in which the bender element 10 is embedded, and has a rigidity that does not hinder the vibration generation of the vibrator 12. However, specifically, a material having a Young's modulus of 100 MPa or less is assumed. For example, in addition to silicone rubber, thermoplastic elastomer, expanded polystyrene and expanded polyurethane foam, natural materials such as natural rubber, sponge, agar and gelatin can be processed. In the following description, the oscillator protective layer 2
When the portion forming 0 is a ready-made molded product such as a resin molded product, it is called a protective layer member 21, and when the vibrator 12 is covered with a solidified material in an unsolidified state to form a protective layer,
The material in an unsolidified state is referred to as a protective layer material 22.

2 to 5 show another modification of the vibrator protection layer 20 provided on the bender element 10. Each of FIGS. 2A and 2B shows a structure in which the vibrator protection layer 20 can be reliably formed on the base block 11. As shown in FIG. 2B, the vibrator protection layer 20 is formed around the vibrator 12 and is housed in the recess 11 b formed in the base block 11. For example, when the protective layer member 21 is a resin molded product, it is securely fixed to the base block 11 by surrounding the vibrator 12 and fixing its root portion to the recess 11b as shown in FIG. 2B. can do. Further, in the case of a molded product having sufficient flexibility, as shown in FIG. 2 (c), it may be fixed by fitting it into a dovetail-shaped recess 11c formed on the upper surface of the base block 11. .

The size of the vibrator protective layer 20 is appropriately determined according to the required rigidity of the material used as the protective layer (protective layer material 22) and the rigidity of the hard material in which the bender element 10 is embedded. It is preferable to set.

FIG. 3 shows the bender element 1 in which the vibrator 12 is attached to the base block 11 in advance.
0 shows a modification in which an unsolidified and amorphous soft material is adhered to the periphery of the vibrator 12 by various means and then solidified to form the vibrator protective layer 20 of a predetermined shape. . For example, the vibrator protective layer 20 shown in FIG. 3B shows an application example in which the unsolidified protective layer material 22 is applied to the side surface of the vibrator 12 so that the cross section has a substantially triangular shape. There is. When the protective layer material 22 is a liquid or the like and has a large surface tension, the hemispherical protective layer 20 can be formed as shown in FIG. 3C.

Each of FIGS. 4 and 5 shows a modification in which the vibrator protection layer 20 is formed of a plate-shaped protection layer material having a size enough to completely cover the upper surface of the base block 11 and the bender element 10 as a whole. It is the top view and sectional view which showed the modification made to cover with a protective layer material. For example, by covering the entire upper surface of the base block 11 with the plate-shaped protective layer member 21, the influence of the hard material in which the bender element 10 is embedded can be reliably blocked. Further, by covering the entire bender element 10 with the protective layer material 22 and integrally molding, the bender element 10 embedded in the hard material can be easily recovered from the hard material after the shear wave velocity measurement is completed. .

FIG. 4B shows a type in which the plate-shaped protective layer member 21 is fixed to the upper surface of the base block 11. Further, FIG. 4C shows a side surface of the base block 11,
In order to cover the upper surface, FIG.
In this example, an unsolidified protective layer material 22 is integrally molded so as to cover the entire surface of. In the bender element 10 of FIG. 4B, the base block 11 to which the vibrator 12 is attached may be additionally provided with the protective layer member 21 formed in a plate shape in advance. In the case of FIGS. 4C and 4D, the bender element 1 to which the vibrator 12 is attached
It is preferable that 0 is installed in a predetermined mold (not shown), and the unsolidified protective layer material 22 is filled into the periphery of the mold to mold the member to integrate the members. 5A to 5C show a case where a ready-made disc member is attached as the plate-shaped protective layer member 21 or a vibrator layer 20 of the bender element 10 is formed by a protective layer material 22 using a hemispherical mold. An example of integrally molding around the periphery is shown. Also in this case, the same manufacturing method as that shown in each of FIGS. 4A and 4B can be applied. In the case of FIGS. 4C and 4D as well, the periphery of the base block 11 may be covered by assembling a ready-made protective layer member.

6 to 8 show another embodiment in which the bender element can be easily embedded in the hard material and the bender element can be easily recovered from the hard material after the shear wave velocity measurement. Is shown.

In FIGS. 6 (a) and 6 (b), the entire base block 11 incorporating the vibrator 12 is referred to as the tip 1 of the vibrator 12.
The bender element 10 is shown covered with a protective layer 20 such that 2a is exposed, and the entire protective layer 20 is housed in the recess of the jacket block 30. As shown in FIG. 6B, the bender element 10 is configured by only the base block 11 according to another embodiment, by housing the base block 11 supporting the vibrator 12 in the outer cover block 30. It is configured as a relatively large member with respect to the bender element 10. Therefore, there is an advantage that the workability in embedding the bender element 10 is improved and the bender element 10 can be easily recovered after the measurement is completed.

7 (a) to 7 (c) are sectional views showing the manufacturing process of the bender element 10 shown in FIG. 6 (a). The vendor element 10 will be described below with reference to the drawings.
The manufacturing procedure of will be described. FIG. 7A is a cross-sectional view of the jacket block 30 that has been preliminarily bored into a predetermined size. In the present embodiment, the jacket block 30 is manufactured by processing a polystyrene foam block. Since the jacket block 30 is rich in heat insulation and cushioning property, even when it is embedded in a hard material, the inner bender element 10 can be properly treated. Can be protected. Further, in this embodiment, the resin bottom plate 32 is attached to the bottom of the square hole formed by hollowing out the block, and the recess 31 is formed. The inside of the recess 31 is filled to a predetermined depth with a soft resin material 23 that exhibits the same properties as the protective layer material 22 at the time of solidification and solidifies relatively quickly. Then, when the soft resin material 23 starts to solidify in the recess 31 and becomes sufficiently viscous, as shown in FIG. 7C, the base block 11 is pushed in and attached to a predetermined depth. At this time, it is also preferable to attach a small piece, not shown, on the bottom plate 32 filled with the soft resin material 23 so that the base block 11 is held at a predetermined depth. In this state, the soft resin material 23 is solidified, and the periphery of the base block 11 and the vibrator 12 above the recess 31 is filled with the protective layer material 22 to the extent that the upper end of the vibrator 12 slightly projects. At this time, since the protective layer material 22, the soft resin material 23, and the outer cover block 30 have good adhesiveness, the base block 11 can be housed in the recess 31 of the outer cover block 30 while being surrounded by the flexible material. It is possible (FIG. 6 (a)).

Each of FIGS. 8A and 8B shows a modified example of the bender element 10 using the jacket block 30. As shown in FIG. 8 (a), in order to eliminate the need for a bottom plate, a block in which the recess 31 is formed only by the outer cover block 30 is manufactured, and the recess 31 is filled with the soft resin material 23. Then, the base block 11 is fixed, and the protective layer material 2
A modified example filled with 2 is shown. This makes it possible to provide the inexpensive vendor element 10. Figure 8
In (b), a support protrusion 34 is formed from the bottom surface 33 of the recess 31, and the base block 11 is bonded onto the protrusion 34,
The bottom of the base block 11 with a slight gap,
The side surface and the upper surface can be completely filled with the protective layer material 22 so as to cover the entire base block 11. In this modification, the vendor element 1 shown in FIG.
Performance close to the characteristic of 0 is obtained. FIG. 8C shows a modified example in which the base block 11 is directly bonded to the bottom surface 33 of the recess 31 of the jacket block 30 to fix the base block 11 in the recess 31, and the periphery thereof is filled with the protective layer material 22. Is shown. With this structure, performance similar to the characteristics of the bender element 10 shown in FIG. 4B is obtained. Figure 8
(D) shows the outer cover block 30 in which the recess 31 is formed so that the bottom area of the recess 31 and the bottom area of the base block 11 are substantially equal. In this modified example, the base block 11 is attached so as to be fitted into the recess 31, and the upper surface thereof is filled with the protective layer material 22.
It is possible to use the cheapest bender element 10 among the modified examples using the jacket block 30. Also in this case, since the vibrator 12 is surely covered with the protective layer 20, the same sensitivity and performance can be obtained.

As the outer cover block 30, in addition to the above-described expanded polystyrene, a light-weight expanded resin material such as hard expanded polyurethane that can be easily processed can be used.

As shown in each of the above-mentioned modified examples, it is preferable that the vibrator protection layer 20 is formed so that at least the tip 12a of the vibrator 12 is slightly exposed or projected from the surface. It is preferable that the exposed amount or the protruding amount of the tip 12a is appropriately determined according to the rigidity of the hard material in which the bender element 10 is embedded and the characteristics of the assumed vibration medium. In this way, the tip portion 12a of the vibrator 12 is
By exposing and slightly embedding in the hard material, the vibration generated from the vibrator 12 is directly propagated to the hard material, so that the accuracy of shear wave velocity measurement can be improved.

As described above, by using the bender element 10 of the present invention, it is possible to accurately measure the shear wave velocity propagating vertically in the improved ground at the original position, which could not be measured conventionally. Becomes Further, the structure having the vibrator protection layer 20 made of this soft material can be applied to the bender element 10 on the receiving side.

In order to examine the effectiveness of the bender element according to the present invention, FIG. 9 shows a vibration wave emitted from a bender element embedded in concrete and an ordinary bender in an exposed state in which it is not embedded in concrete as a comparative example. This is a comparison of the vibration waves emitted from the elements. It can be seen that the waveforms of the received waves of both are almost the same within a predetermined elapsed time. From this, it was confirmed that by using the bender element according to the present invention, it is possible to reliably transmit the vibration even in the vibrator that is used by being embedded in the hard material.

[0029]

As described above, even when the bender element is embedded in a hard material such as improved ground or concrete and used, a predetermined vibration can be transmitted and received. In addition, by embedding it in a hard material, the position of the bender element can always be kept constant, and the reproducibility of the installation of the bender element is completely ensured, and highly accurate shear wave velocity measurement can be performed. it can. Furthermore, by projecting the tip portion of the oscillator into the hard material, the vibration generated from the oscillator is reliably transmitted to the hard material, and the accuracy of shear wave velocity measurement is improved. In addition, after the measurement of the shear wave velocity, the bender element can be easily taken out from the hard material, and thus can be recycled.

[Brief description of drawings]

FIG. 1 is a plan view and a cross-sectional view showing an embodiment of a shear wave velocity measuring bender element according to the present invention.

FIG. 2 is a plan view and a cross-sectional view showing another embodiment of the shear wave velocity measuring bender element.

FIG. 3 is a plan view and a cross-sectional view showing a modified example of the bender element for shear wave velocity measurement.

FIG. 4 is a plan view and a cross-sectional view showing a modified example of the shear wave velocity measuring bender element.

FIG. 5 is a plan view and a cross-sectional view showing a modified example of the shear wave velocity measuring bender element.

FIG. 6 is a plan view and a cross-sectional view showing another embodiment of the shear wave velocity measuring bender element.

FIG. 7 is a process explanatory view showing a manufacturing process of the shear wave velocity measuring bender element shown in FIG. 6;

8 is a cross-sectional view showing a modified example of the shear wave velocity measuring bender element of FIG.

FIG. 9 is a vibration characteristic diagram showing vibration characteristics when the shear wave velocity measuring bender element of the present invention is buried.

FIG. 10 is a perspective view showing an example of a conventional shear wave velocity measuring bender element.

11 is a schematic explanatory view showing an electromotive principle of the shear wave velocity measuring bender element shown in FIG.

12 is an explanatory diagram showing an example of a measurement situation by the shear wave velocity measuring bender element shown in FIG.

[Explanation of symbols]

10 Bender element 11 base block 12 oscillators 20 Transducer protection layer 22 Protective layer material 23 Soft resin material 30 jacket block 31 recess

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Claims (7)

[Claims] 1. A shear wave velocity measuring bender element, characterized in that a piezoelectric protective layer adhered to a base block is covered with a soft material having a predetermined thickness to form a transducer protective layer. 2. The soft material has a Young's modulus of 100 MP.
The shear wave velocity measuring bender element according to claim 1, wherein: 3. The shear wave velocity measuring bender element according to claim 1, wherein the vibrator protection layer is formed by fixing a ready-made member to the piezoelectric vibrator. 4. The shear wave velocity measuring bender element according to claim 1, wherein the vibrator protection layer is formed by integrally molding the piezoelectric vibrator. 5. A base block supporting a piezoelectric vibrator,
A shear wave velocity measuring bender element, characterized in that it is housed in a recess of a jacket block, and at least the periphery of the piezoelectric vibrator in the recess is filled with a soft material to form a vibrator protective layer. 6. The shear wave velocity measuring bender element according to claim 5, wherein the jacket block is a lightweight foamed resin molded member. 7. The shear wave velocity measuring bender element according to claim 5, wherein the filled soft material has a Young's modulus of 100 MPa or less.