JPH049885B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring acoustic emission (hereinafter referred to as AE) in a clay ground.

<A> What is AE? When an external force is applied to a material and microscopic cracks occur inside the material, a large amount of energy is released as the strain is released.

This energy generally emits ultrasonic waves, and AE attempts to detect changes within the material and predict fractures by detecting these ultrasonic waves.

<B> Current status of AE use Recently, AE has been used to evaluate the deformation behavior and stability of rock and sandy ground.

This is a powerful method, especially when the ground material itself actively generates AE, such as sandy bedrock.

<C> Limitations of AE use As described above, it can be used on rocks and sand, but it was difficult to use on clay ground.

The reason for this is that in cohesive soil, the AE generated by microfractures is extremely weak, and the AE that occurs is greatly attenuated by distance, making it difficult to observe.

The present invention has been made to improve the above points, and is an excellent means of observing dynamics.
The purpose of the present invention is to provide a measurement method that can be used especially in clayey soil.

First Example <A> AE Detector The AE detector of this example is constructed by filling a flexible cylindrical body 1 with a good AE generating material 2.

As the flexible cylinder 1, for example, a vinyl chloride pipe is used.

In this case, the flexible cylindrical body 1 has the following characteristics: it can protect the measuring device such as the AE receiver, it can be filled with the good AE generating material 2 smoothly, and it can easily follow the deformation of the ground G. Must be.

Examples of good AE generating materials 2 include sand, glass powder,
Use granular materials such as fine-grained rock and cassia, or materials that are sensitive to AE, such as cemented materials.

Inside the flexible cylinder 1, a plurality of AE receivers 3 and preamplifiers 4 are further arranged in the longitudinal direction of the cylinder 1.

The AE receiver 3 is basically a transducer (piezoelectric element) that detects AE waves and converts them into AE signals.
It is. The preamplifier 4 is an amplifier that amplifies the transducer output from the AE receiver.

<B> Burying the AE detector During measurement, first open a borehole 5 in the sticky ground G to be measured.

This boring hole 5 is formed to have an inner diameter somewhat larger than the outer diameter of the flexible cylinder 1, and the above-mentioned detection body is inserted into the bore hole 5.

The voids existing outside the cylindrical body 1 are filled with backfilling sand 6.

In some cases, a boring hole 5 with an inner diameter approximately equal to the outer diameter of the cylindrical body 1 is drilled, and a
It is also possible to adopt a method of press-fitting the AE detection body.

<C> Operation confirmation Next, in order to confirm the arrangement and operation status of the AE receiver 3, a pulse voltage is applied to one AE receiver 3 to generate pseudo AE, which is then transmitted to the other AE receiver 3. Receive.

As a result, it is possible to check whether the AE detector is functioning properly after it has been installed underground, and to measure the propagation velocity of AE.

<D> Detection of ground deformation (Fig. 2) When installed as described above, the ground G
If a change occurs in the ground G, the cylinder itself is deformed in accordance with the change in the ground G because the cylinder is flexible.

As the flexible cylindrical body 1 deforms, the good AE generating material 2 moves relative to its position, and at this time AE is generated, and this AE can be observed by each AE receiver 3.

The AE generated in the good AE generating material 2 releases more energy than the AE generated in the actual viscous ground G.

Therefore, each AE receiver 3 can reliably detect and observe AE.

The deformation of the ground G can be evaluated based on changes in the frequency of occurrence of AE as a result of observation and aggregation, and the stability of the ground G can be evaluated by measuring the position of the slip surface.

Second Example (Fig. 3) The first method is a method of observing AE generated in the good AE generating material 2 inside the flexible cylinder 1, but the second method is not to fill the inside of the cylinder. , is a method of observing AE generated in the cylinder itself.

<A> Detector The cylinder 1' is made of a material that has high rigidity and produces good AE, such as aluminum, aluminum,
Made of iron, other alloys, etc.

The inside of this good AE generating cylinder 1' is left hollow without being filled, and the AE transmitter 3 and preamplifier 4 are directly attached inside it.

<B> Measuring method (1) A boring hole 5 with a diameter slightly larger than the outer diameter of the cylinder 1' is drilled in the sticky ground G to be measured, and the cylinder 1' is inserted. In order to reliably grasp changes in the ground G, the gap created between the bore hole 5 and the hole 5 is sufficiently filled with backfilling sand 6.

In this way, the circumferential surface of the cylindrical body 1' is in indirect contact with the ground G through the backfilling sand, and the ground G
When there is a change in the AE, the AE generated in the cylinder 1', which deforms with the ground G, is observed.

The changes and stability of the ground G are evaluated from the AE generated in the cylinder 1'.

<C> Measurement method (2) Drill a bore hole 5 with an inner diameter approximately equal to the outer diameter of the cylinder 1'.

Then, the cylindrical body 1' is forcefully press-fitted into the hole.

In this way, no gap will be created between the outer surface of the cylinder 1' and the inner surface of the borehole 5, resulting in surface contact with the cohesive soil.

The generation and measurement of AE are the same as in the previous example.

In the second embodiment using the cylindrical body 1', expensive measuring devices such as the AE receiver 3 can be recovered by pulling out the cylindrical body 1' after the observation is completed.

<D> Selection of measurement method The first method and the second method described above are used appropriately depending on the rigidity of the ground G.

That is, when the ground G has relatively low rigidity, it is effective to use the method of the first embodiment, and when the ground G is the opposite, it is effective to use the method of the second embodiment.

As explained above, the present invention uses a flexible cylinder filled with a material that generates AE well, or a cylinder made of a material that generates AE well.
The AE generated from this good AE-generating material is installed in a sticky ground, and the cylinder deforms due to changes in the ground.
This is a method of measuring

Therefore, it is now possible to measure AE even in cohesive ground, where it has been difficult to use AE generation in the past, and by observing and aggregating the measurement results, it is possible to evaluate the stability of the cohesive ground and determine the location of the landslide surface. It is now available for use.

[Brief explanation of drawings]

FIG. 1: An explanatory diagram of an embodiment of the measurement method of the present invention,
Figure 2: An explanatory diagram when the ground changes. Figure 3: An explanatory diagram of the measurement method when using another cylinder. 1: Flexible cylinder, 1': Good AE generating cylinder, 2: Good
AE generating material, 3: AE receiver, 4: preamplifier,
5: Borehole, 6: Backfilling sand (filling material).

Claims (1)

[Claims] 1. A flexible cylinder filled with a material that produces good acoustic emission (AE), or a cylinder made of a material that produces good AE, is buried in a clay ground. A method for detecting ground changes in cohesive soil by measuring the AE generated from this good AE generating material by the deformation of the cylinder using a receiver inside the cylinder.