JP3210923B2 - Visualized triaxial piping test apparatus and test method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piping and boiling (hereinafter abbreviated as "piping") test apparatus and a test method for grasping and confirming the water permeability (piping characteristics and boiling characteristics) of soil on actual ground. In particular, the present invention relates to a three-axis piping test apparatus and a test method that visualize the state of a piping test performed under a triaxial stress state equal to actual ground so that the state can be directly visually observed.

[0002]

2. Description of the Related Art It is important to grasp and confirm the piping characteristics or boiling characteristics of soil on actual ground, for example, when constructing a dam, as a ground survey item of a dam site.
The test method can be roughly classified into a case where a specimen is artificially made and a case where an undisturbed sample is collected from actual ground to make a specimen. As for the stress state, there are a non-triaxial type and a case where a test is performed in a triaxial stress state as close as possible to actual ground.

[0003] When the above-mentioned specimen is artificially made, and the result of a non-triaxial type test in which the stress state has no correlation with the same actual ground, it cannot be said that the results conform to the properties of the actual ground.
The in-situ soil permeability cannot be accurately determined. Next, the conventional triaxial piping test method and apparatus corresponding to the above, as illustrated in FIG.
The upper and lower ends of the specimen 4 are sandwiched between the pedestal 2 and the top cap 3, and the piston 5 applies a mounting pressure on the actual ground to the specimen 4 via the top cap 3. The cell liquid filled in the pressure vessel 1 is pressurized, and an arbitrary constraint pressure is applied to the peripheral side surface of the specimen 4. Lower end of specimen 4 and pedestal 2
The water supply pipe 6 is connected to the specimen 4 through a porous stone 25 interposed between the water supply pipe 6 and the water supply pipe 6. Further, a drain pipe 7 is connected to the specimen 4 through a porous stone 25 interposed between the upper end of the specimen 4 and the top cap 3. The pressure of the cell liquid in the pressure vessel 1 is adjusted by the lateral pressure control device 8.

According to the above-described conventional test apparatus, a predetermined amount of overload pressure is applied to the specimen 4 through the piston 5, and a predetermined amount of confining pressure is applied to the peripheral side surface of the specimen 4 by the lateral pressure control device 8. Above, the water supplied through the water supply pipe 6,
The water to be removed through the drain pipe 7 is set to a back pressure H ₀ that eliminates bubbles in the water to increase the saturation of the specimen 4 to nearly 100%, and a head difference H ₁ of a size necessary for the piping test. Then, a test is conducted to confirm the pressure of piping and boiling that generate water channels.

[0005]

The conventional three-axis type piping test method and apparatus shown in FIG. 4 employs a three-axis type piping test in which an upper mounting pressure by a piston 5 and a constraining pressure on a peripheral side surface of a specimen by a cell liquid are applied. A stress state is realized, but this stress state only strictly realizes an isotropic stress state. In particular, the confining pressure on the peripheral side surface of the test specimen is not in the so-called K ₀ state, in which a pressure large enough to restrict lateral strain is applied, so it cannot be said that this is a piping test under the stress condition of the actual ground. There are problems with the accuracy and reliability of the test results.

Further, since the upper end of the specimen 4 comes into direct contact with the top cap 3 entirely through the porous stone 25 and receives an overload, the occurrence of piping and boiling is restricted by mechanical force. There is a high possibility that the piping characteristics and the boiling characteristics are underestimated. in short,
If the occurrence of piping can be observed directly with the naked eye, there is no danger of the underestimation. However, conventionally, there is no visualized test apparatus and test method, and this point is a problem to be solved.

[0007]

As a means for solving the above-mentioned problems in the prior art, a visualized three-axis piping test apparatus according to the present invention is provided as shown in FIGS. In a test apparatus for performing a piping test on a specimen in a triaxial pressure vessel, (a) a pedestal 2 and a top cap 3 sandwiching upper and lower ends of a specimen 4 are vertically moved above and below a substantially central portion in the pressure vessel 1. The top cap 3 is attached to a piston 5 for applying an overload to the specimen 4, a water supply pipe 6 for supplying deaerated water to the lower end of the specimen 4 is connected to the pedestal 2, and the top cap 3 To 3, a drain pipe 7 for removing water that has passed through the specimen 4 is connected. (B) At the outer peripheral position of the specimen 4 sandwiched between the pedestal 2 and the top cap 3 in the pressure vessel 1, the upper end is opened to the pressurized space 10 in the upper part of the pressure vessel 1 and the inner diameter is relatively small. A cell 11 is installed, and a cell liquid 1 filled to the extent that the specimen 4 is submerged in the inner cell 11.
A water level sensor 13 for measuring the liquid level change of the second is provided. (C) Between the upper end of the specimen 4 and the top cap 3
A spacer 14 having a structure for transmitting the upper mounting pressure of the top cap 3 to the specimen 4 but not restraining the boiling is interposed, and a television camera for photographing the behavior of the upper end of the specimen 4 through the space 14 a of the spacer 14 in the pedestal 2. A monitor device 26 and a photographing device 28 are connected to the television camera 27. (D) The head difference H ₁ and the back pressure H ₀ required for the piping test are provided between the deaerated water supplied through the water supply pipe 6 and the drainage discharged through the drain pipe 7.
Is provided.

[0008] The visualized triaxial piping test method according to the second invention is a method for performing a piping test on a specimen under a condition where triaxial stress is applied.
The test piece 4 is sealed by covering the outer peripheral surface thereof with a rubber film 15. (B) Applying an overload pressure of the same size as the original ground to both ends of the test piece 4 in the axial direction, and (C) a spacer having a structure that transmits the overload pressure but does not restrain the boiling between the member 3 for applying the overload pressure to the specimen 4 and the end of the specimen 4 A television camera 2 for photographing the behavior of the upper end of the specimen 4 on the member 3 for applying the above-mentioned loading pressure with the interposition of
(D) Water passing in the axial direction of the specimen 4 should be degassed water or air bubbles to eliminate the saturation of the specimen 4.
Using water multiplied by the back pressure to increase from 00 per cent performs piping tests on the supply pressure and drainage pressure of water by applying a water head difference H ₁ of size required for the piping test, the test conditions It is characterized in that the behavior of the upper end of the specimen 4 is directly observed through the screen of the monitor device 26 and a photograph is taken as necessary.

[0009]

[Action] on No圧equal the real ground in the axial direction of the specimen 4 was added, the peripheral side surface so that the K ₀ state by applying a pressure of a magnitude to restrain the distortion laterally, reproduce the stress state of the real ground A good piping test can be performed. In addition, since the piping or boiling at the upper end of the specimen through which water passes is not restricted by the presence of the spacer 14, the piping characteristic or the boiling characteristic of the specimen 4 is not hindered. Further, the state of occurrence of piping and boiling, the critical behavior, and the like can be visually observed directly on the television screen of the monitor device 26, and a photograph can be taken as needed.

[0010]

Next, an embodiment of the present invention shown in FIGS. 1 to 3 will be described. The three-axis piping test apparatus shown in FIG.
A pedestal 2 and a top cap 3 sandwiching the upper and lower ends of a test piece 4 are arranged above and below a substantially central portion in a pressure vessel 1 composed of an upper panel 16, a lower panel 17 and an outer cell. The pedestal 2 is fixed to a lower plate 17, and the top cap 3 is attached to a piston 5 that applies an overload to the specimen 4. Each of the pedestal 2 and the top cap 3 is configured to hold the specimen 4 via a porous stone 25. The pedestal 2 contains the porous stone 25
A water supply pipe 6 for supplying degassed water is connected to the lower end of the specimen 4 via the. A drain pipe 7 is connected to the top cap 3 for removing water that has passed through the specimen 4 in the axial direction through the porous stone 25.

In the pressure vessel 1, the pedestal 2
And a top cap 3 or a pressurized space 1 in a pressure vessel 1 at an outer peripheral position of a specimen 4 sandwiched between them.
A transparent inner cell 11 which is open to zero and has an inner diameter that is as small as necessary and minimum is provided. Thus, the inside of the pressure vessel 1 is formed in a double pipe structure, and each chamber contains a cell liquid 12 such as water or antifreeze. In particular, the inner cell 11 is filled with the cell liquid 12 to such a level that the specimen 4 is completely submerged. An instrument housing 18 is provided above the inner cell 11 as shown in detail in FIG. 2, and a water level sensor 13 is provided. That is, the gap sensor 19 is installed at the lower bottom of the instrument housing 18, the float 20 is floated on the cell liquid level right above the instrument housing 18, and the vertical displacement (gap size) of the float 20 is generated by the gap sensor 19. The change (magnitude) of the voltage is measured as an electric value in real time.

[0012] In short, this three-shaft piping device is
An overload pressure equal to the actual ground is applied to the specimen 4 by the piston 5. Further, the air pressure 22 adjusted by the central controller 21 is applied to the pressurized space 10 in the pressure vessel 1, and the lateral strain is constrained on the peripheral side surface of the specimen 4 through the cell liquid 12 in the inner cell 11. Pressure to act to bring it to the K ₀ state. That is, the occurrence of the lateral strain of the specimen 4 is grasped by the water level sensor 13 as a change in the liquid level of the cell liquid 12 in the inner cell 11, and the measured value is input to the central control device 21 to perform the pressure processing. By adjusting the magnitude of the air pressure 22 in the space 10, K ₀ equal to the stress state of the actual ground is obtained.
The state is realized.

The specimen 4 used in this test is made from an undisturbed sample. Conventionally, block sampling, tube sampling, freeze sampling, and the like are known and implemented as methods for collecting undisturbed samples that are not disturbed from actual ground. Specimen 4 is obtained by cutting an undisturbed sample collected by any of the above methods into a cylindrical piece of an appropriate size (diameter 7 cm, axial length about 10 m), and covering the outer peripheral surface with a rubber film 15. Sealed and formed. As a method of cutting a cylindrical piece from an undisturbed sample, a cylindrical piece having an axis in a direction parallel to the boundary layer of the soil layer structure on the actual ground is cut out to produce a specimen 4, and piping along the boundary layer is performed. It is very meaningful to be able to test the characteristics.

In the case of the present invention, the specimen 4 prepared as described above is placed between the upper end of the specimen 4 and the top cap 3 as shown in FIG. It is characterized in that a ring-shaped spacer 14 is interposed, which transmits pressure to the specimen 4 but does not hinder piping or boiling at the upper end of the specimen. The ring-shaped spacer 14 is formed of a transparent acrylic resin, has a thickness of 5 mm,
The outer diameter is about 70 mm and the inner diameter is about 50 mm.
However, the spacer 14 transmits the above-mentioned mounting pressure,
Any structure that does not hinder boiling may be used, and a cross-girder structure, a lattice structure, or a plurality of concentric ring structures or lattice structures can be used in the same manner.

The next feature of the present invention is that, as shown in FIG. 3, the test piece 4 is formed on the side of the top cap 3 and the porous stone 25 through the space 14a of the spacer 14.
Camera 25 in such a manner that the behavior of the upper end of the
Is installed, and the television camera 25 is connected to the external monitor device 2.
6 and the photographing device 28.
Therefore, in the three-axis piping test apparatus having the above-described configuration, the upper end of the test piece 4
And the piping between the water supply pipe 6 and the drain pipe 7 after realizing the triaxial stress state by the K ₀ state that restrains the overload pressure and the lateral strain equal to the actual ground stress state as described above. is piping tests carried out the size of the water head difference H ₁ required for the test by giving. Checking the water head difference H ₁ to piping or boiling occurs is monitored 26
Is observed directly through the screen. Photographs are recorded as needed. When the inner cell 11 and the rubber film 15 are formed of a transparent material, it becomes possible to visually check the piping characteristics or the boiling characteristics from outside. If the water used for the piping test not perfectly degassed water, the water head difference H ₁ of said inclusion the necessary back pressure to raise the degree of saturation of the specimen 4 close to 100% erase bubbles in water (See FIG. 4).

[0016]

According to the visualized three-axis piping test apparatus and test method according to the present invention, a test is performed under conditions suitable for actual ground, and the test results can be obtained easily and accurately. In addition to being able to confirm and evaluate the piping characteristics or boiling characteristics with high reliability, it is also possible to directly observe the state of occurrence of piping and boiling on the screen of the monitor device 26, and to take and record a photograph with the photographing device 28, There is no risk of misunderstanding the confirmation and evaluation, greatly improving the effectiveness of the ground survey.

[Brief description of the drawings]

FIG. 1 is an overall view of a three-axis piping test apparatus according to the present invention.

FIG. 2 is an enlarged sectional view showing a water level sensor portion of an inner cell.

FIG. 3 is a cross-sectional view showing in detail the relationship among a specimen, a spacer, a top cap, and a television camera.

FIG. 4 is an overall view of a conventional piping test apparatus.

[Explanation of symbols]

 4 Specimen 2 Pedestal 3 Top cap 1 Pressure vessel 5 Piston 6 Water supply pipe 7 Drain pipe 10 Pressurized space 11 Inner cell 12 Cell liquid 13 Water level sensor 14 Spacer H Head difference 25 TV camera 26 Monitor television 15 Rubber film

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shuji Sakaguchi 8-21-1, Ginza, Chuo-ku, Tokyo Co., Ltd. (72) Inventor Akira Morishima 8-21-1, Ginza, Chuo-ku, Tokyo Co., Ltd. Takenaka Civil Engineering (72) Inventor Mitsuhiko Takahashi 8-21-1, Ginza, Chuo-ku, Tokyo, Japan Takenaka Civil Engineering Co., Ltd. Inside the Technical Research Institute (72) Yoshio Suzuki 2-5-1-14 Minamisuna, Koto-ku, Tokyo Inside the Technical Research Center Takenaka Corporation (72) Inventor Akihiko Uchida 2--14 Minamisuna, Koto-ku, Tokyo Takenaka Corporation (58) Investigated field (Int. Cl. ⁷ , DB name) G01N 33/24

Claims (2)

(57) [Claims] 1. A test apparatus for performing a piping test of a specimen in a triaxial pressure vessel, wherein (a) a pedestal and a top cap sandwiching upper and lower ends of the specimen are located above and below a substantially central portion in the pressure vessel. The top cap is attached to a piston that applies an overload to the specimen, the pedestal is connected to a water supply pipe that supplies deaerated water to the lower end of the specimen, and the top cap passes through the specimen. That a drain pipe is connected to eliminate the water that has been drained, (b)
At the outer peripheral position of the specimen sandwiched between the pedestal and the top cap in the pressure vessel, an inner cell whose upper end is open to the pressurized space in the upper part of the pressure vessel and whose inner diameter is relatively small is installed. A water level sensor for measuring a change in the liquid level of the cell liquid filled to such an extent that the specimen is submerged therein; (c) mounting the top cap between the upper end of the specimen and the top cap; A spacer having a structure for transmitting pressure to the specimen but not constraining the boiling is interposed, and a television camera for photographing the behavior of the upper end of the specimen through the space of the spacer is provided on the pedestal. The photographing device is connected, and (d) the deaerated water supplied through the water supply pipe and the drainage discharged through the drain pipe are subjected to a piping test. The water head difference of the essential magnitude is applied, characterized by each visualized triaxial type piping test equipment. 2. A method for performing a piping test on a specimen under a condition in which triaxial pressure acts, wherein (a) the specimen comprises:
(C) covering the outer peripheral surface with a rubber film and sealing;
Applying an overload pressure equal in magnitude to the in-situ ground to both ends in the axial direction of the specimen, and applying a pressure large enough to restrain lateral strain to the peripheral side surface; (c) Applying an overload pressure to the specimen Between the member and the end of the test piece, a TV camera that captures the behavior of the upper end of the test piece is installed on the member that applies the mounting pressure while interposing a spacer that transmits the mounting pressure but does not restrict the boiling. (D) As the water to be passed in the axial direction of the specimen, use degassed water or water in which air bubbles have been eliminated by applying back pressure. The supply pressure and drainage pressure of the water are necessary for the piping test. A visualized triaxial piping test method, characterized in that a piping test is performed with a large difference in head and a behavior of the upper end of the specimen is observed directly through a television screen during the piping test.