JPH0746073B2 - Method and apparatus for measuring S wave velocity using large triaxial cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an S wave velocity using a large triaxial cell for grasping the degree of disturbance of a sample due to sampling, particularly in sand ground, gravel ground, etc. The present invention relates to a measuring method and a measuring device.

[Conventional technology]

Conventionally, important structures such as nuclear power plants use rock as support ground, but it is expected that the area where rock will be used as support ground will decrease in the future, so recently, support ground for nuclear power plants As a result, gravel ground is drawing attention. In important structures such as nuclear power plants, stability especially in earthquake is important, and dynamic characteristics are
It is necessary to investigate not only the properties under a small strain such as an in-situ elastic wave test, but also the properties under a large strain by a laboratory test of sampling.

Generally, when sampling is performed by sampling, it is necessary to sample so that the test can be performed in the original position without disturbing the sample. Therefore, in order to collect a sample without disturbance in the sand ground or gravel ground, a method of freezing the ground and then sampling is proposed. It was confirmed that the sample thus sampled was not disturbed by comparing the N value of the standard penetration test at the in-situ position with the result of the liquefaction test of the collected sample.

In addition, PS logging method has been conventionally known as a method for measuring the dynamic characteristics of the ground in situ. This is to measure the S wave velocity V _S and P wave velocity V _P of the ground.
Since V _S is related to the shear stiffness G of the ground by the following equation, if the stiffness decreases due to turbulence, the S wave velocity V _S
Changes.

G = ρV _S ² (ρ is the density) In the PS logging method, as shown in Fig. 3, the borehole pick can be attached and detached at any depth, and vibration is given by the plate hitting method, weight drop or explosive explosion. The waveform of each depth is captured by a monitor pick, and the velocity distribution is obtained from the travel time curve in the depth direction after detecting the S wave phase.

On the other hand, as a method of measuring the S wave velocity in the laboratory test, the ultrasonic pulse method is typical. This is originally popular as a method for measuring the elastic wave velocity of rock samples, and is effective for small samples such as sand ground.
Then, it was confirmed that the sample was not disturbed by comparing the S wave velocity by the PS logging method at the in-situ and the result of the S wave velocity by the laboratory test.

[Problems to be solved by the invention]

Among the above-mentioned future methods, the method of comparing the N value of the standard penetration test at the in-situ position with the result of the liquefaction test of the collected sample cannot be compared with high accuracy, and the degree of turbulence of the sample can be accurately measured. It had a problem that it could not be grasped.

In addition, the method of measuring the S wave velocity by the ultrasonic method in the laboratory test is a special cap that transmits and receives pulses,
A pedestal is required, and in order to perform the measurement using a normal triaxial test device, a significant improvement in the device is required, and the adhesion state between the end face of the specimen, the cap and the pedestal has a great influence on the measurement. In general, it is difficult to measure ordinary soil samples, and ultrasonic waves have a large distance attenuation.Therefore, they have a problem that they cannot be applied to the test of large specimens obtained from gravel ground. It was

The present invention solves the above-mentioned problems and enables measurement of S wave velocity by simply adding a simple device to an existing large-scale triaxial test device, and by comparing the result with the PS logging method in situ. , The purpose is to accurately grasp the degree of disturbance of the sample.

[Means for solving problems]

For that purpose, the measuring method and the measuring apparatus of the S wave velocity using the large triaxial cell of the present invention, in the large triaxial cell, set the specimen coated with the film-like body between the cap and the pedestal,
The S-wave velocity is measured by striking the cap from the outside of the large triaxial cell while applying stress from the triaxial directions, and measuring the S wave velocity by accelerometers installed above and below the film-like body. Is a large triaxial cell that sets a specimen coated with a film between the cap and the pedestal, and applies stress from the triaxial direction, with a horizontal striking piston striking the cap on the side wall of the large triaxial cell, It is characterized in that accelerometers are provided above and below the film-like body.

[Action]

In the method and apparatus for measuring the S-wave velocity using the large triaxial cell according to the present invention, the specimen is covered with a film-like body and set in the large triaxial cell 1, and then water is supplied into the cell to form the triaxial cell. Apply pressure from the direction to bring the same stress state as the ground at the original position.
Next, by horizontally striking the cap on the upper part of the specimen from the outside of the triaxial cell with a horizontal striking piston, S
It is what causes waves. An elastic wave generated by such a method is received by an accelerometer mounted on the film-like body on the side surface of the specimen, and the difference in the initial motion time of the elastic wave is read from the two obtained acceleration waveforms to determine the S wave velocity. To measure.

〔Example〕

 Embodiments will be described below with reference to the drawings.

FIG. 1 (a) shows the S using the large triaxial cell according to the present invention.
Schematic view of the measurement position of wave velocity, (B) is a cross-sectional view of the specimen, FIG. 2 is a cross-sectional view of the main part of FIG. 1 (A), FIG. 4 is a diagram showing the measurement results, FIG. FIG. 4 is a diagram for comparatively explaining the results of the measuring method of the present invention, the results of the dynamic deformation test and the results of the PS logging method.

In the figure, 1 is a large triaxial cell, 2 is a cell, 3 is a specimen, 4 is a loading shaft, 5 is a membrane, 6 is a cap, 7 is a pedestal,
8 is a horizontal striking piston, 9 is a cylinder, 10 is a bearing, 11 is a piston, 12 is a bellowram, 13 is a pressure chamber, C is a compressor, 14 is an accelerometer, 15 is a DC amplifier, 16 is a digital storage scope, and 17 is a microcomputer. , 18 are acceleration measuring circuits.

As shown in FIG. 1 and FIG. 2, the large triaxial cell 1 is
This is a triaxial test apparatus in which the specimen 3 is placed in the cell 2 and can be repeatedly pressurized by the loading shaft 4. The sample 3 has, for example, a diameter =
It is a cylindrical test piece having a height of 300 mm and a height of 600 mm, and is covered with a film body 5 such as a rubber membrane, and a cap 6 and a pedestal 7 are set on the upper and lower sides, respectively. The cell 2 is filled with water, the cell pressure is applied by the compressor C, and the restraining pressure is applied to the side surface of the sample 3.

On the other hand, a horizontal striking piston 8 is installed penetrating the side wall of the cell 2, and as shown in detail in FIG. Air having the same cell pressure as that of the cell pressure is supplied from the compressor C to the pressure chamber 13 partitioned by the bellows 12, 12, so that the piston 11 can freely move under any cell pressure. One end of piston 9 is specimen 3
It comes in contact with the cap 6 on the upper part of.

Further, the piston 11 forms an angle of 90 degrees from the point at which the cap 6 is hit, and accelerometers 4 and 14 are attached to the upper and lower portions of the membranous body 5 on the vertical line, respectively.
Is connected to an acceleration measuring circuit 18 composed of a DC amplifier 15, a digital storage scope 16 and a microcomputer 17. As the accelerometer 14, for example, a piezoelectric accelerometer with a built-in preamplifier is used, and a small and lightweight accelerometer is adopted so that the deformation characteristics of the sample do not change when the accelerometer is attached.

Next, the measurement method will be described. After covering the sample 3 with the film body 5 and setting the cap 6 and the pedestal 7 in the large triaxial cell 1, water is supplied into the cell 2 from the triaxial direction. Apply pressure to bring the same stress state as the ground at the original position. Then, the horizontal striking piston 8 is striking the cap 6 on the upper part of the specimen 3 to strike (shear striking) horizontally from the outside of the triaxial cell 1 to generate an S wave. The elastic wave generated by such a method is used for the specimen 3
The signals are received by accelerometers 14 and 14 mounted on the film body 5 on the side surface. The elastic wave velocity is calculated by the following equation by reading the difference in initial motion time of the elastic wave from the two acceleration waveforms obtained by the acceleration measuring circuit 18.

V _S = d / t where V _S is the S wave velocity (m / sec), d is the distance between the accelerometers (m), and t is the difference in initial motion time (sec).

This method is a very simple one that does not require any electric pulse or complicated equipment, and does not hinder the execution of the usual dynamic deformation test and liquefaction test.

FIG. 4 shows a travel time curve obtained by measuring the S wave velocity of an iron specimen (diameter 300 mm, height 600 mm) by the measuring device according to the present invention. The straight line in the figure shows the elastic wave velocity of iron quoted from the science chronology, but the measured value shows a very strong correlation with this, demonstrating that the S wave velocity can be accurately measured by this measuring method. ing.

FIG. 5 shows the relationship between the S wave velocity measured by the measuring method of the present invention and the S wave velocity obtained from the result of the dynamic deformation test, and the confining pressure for the sample collected by the connection sampling. According to this, both are almost parallel straight lines, and a good correlation is recognized between them. Also,
It is in good agreement with the result of PS logging in the sampling layer (assuming that the static earth pressure coefficient K ₀ = 1), indicating that there is almost no disturbance in the sampling sample.

It should be noted that the present invention is not limited to the above-mentioned embodiment and can be variously modified. For example, in the above examples, samples of sand ground, gravel ground, etc. are described, but it is also possible to measure other samples such as rocks.

〔The invention's effect〕

As described above, according to the present invention, it is possible to measure the S-wave velocity under the same stress condition as the in-situ ground by simply adding a simple device called a horizontal striking piston to the existing large triaxial test device. , By comparing the results of this laboratory test with the results of in-situ PS logging method, it is possible to accurately grasp the degree of disturbance of the sample at the time of sampling.

Moreover, since the acceleration measuring circuit is composed of the digital storage scope and the microcomputer, the time required for one measurement and data storage can be shortened to less than 30 seconds.

[Brief description of drawings]

FIG. 1 (a) shows the S using the large triaxial cell according to the present invention.
Schematic diagram of wave velocity measuring device, the same figure (b) is a sectional view of the specimen, FIG. 2 is a sectional view of the main part of FIG. 1 (a), and FIG. 3 is a diagram showing the principle of the PS logging method. , FIG. 4 shows the measurement results, and FIG.
The figure is a figure for comparing and explaining the result of the measuring method of this invention, the result of a dynamic deformation test, and the result of PS logging method. 1 ... Large triaxial cell, 2 ... cell, 3 ... specimen, 4 ...
… Loading shaft, 5 …… Membrane, 6 …… Cap, 7 …… Pedestal, 8 …… Horizontal impact piston, 9 …… Cylinder, 10
...... Bearing, 11 ...... Piston, 12 ...... Bellofrum,
13 ... Pressure chamber, C ... Compressor, 14 is accelerometer, 15
...... DC amplifier, 16 …… Digital storage scope,
17 …… Microcomputer, 18 …… acceleration measuring circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiro Shinomoto 2-16-1, Kyobashi, Chuo-ku, Tokyo Within Shimizu Corporation (72) Inventor Satoshi Akagawa 2-16-1, Kyobashi, Chuo-ku, Tokyo Shimizu Construction Co., Ltd. (72) Inventor Kokichi Baba 2-16-1, Kyobashi, Chuo-ku, Tokyo Shimizu Construction Co., Ltd. (56) Reference JP 62-88940 (JP, A) JP 62 -88939 (JP, A)

Claims (4)

[Claims] 1. A test piece coated with a film-like material is set between a cap and a pedestal in a large triaxial cell, and the cap is hit from the outside of the large triaxial cell with stress applied in the triaxial directions. Then, the S wave velocity is measured by using an accelerometer installed above and below the film-like body, and the S wave velocity is measured using a large triaxial cell. 2. In a large triaxial cell in which a sample covered with a film is set between a cap and a pedestal, and a stress is applied in the triaxial direction, a horizontal striking piston for striking the cap is attached to the side wall of the large triaxial cell. An apparatus for measuring S-wave velocity using a large triaxial cell, which is provided with accelerometers above and below the film body. 3. The accelerometer is installed on the vertical line of the film body at an angle of 90 degrees from the point where the horizontal striking piston strikes the cap.
An apparatus for measuring an S-wave velocity using the large triaxial cell described in the paragraph. 4. The large triaxial cell according to claim 2 or 3, wherein the pressure acting on the horizontal striking piston is made equal to the pressure in the large triaxial cell. S-wave velocity measuring device.