JPH08338796A - Convenient method and system for triaxial compression test - Google Patents

Abstract

PURPOSE: To test a large number of samples easily and quickly using a monoaxial compression test machine by filling the gap between the sample and a steel pipe with a cement-based expansion material and applying a side pressure against the sample through the solidification expansion. CONSTITUTION: A strain gauge is applied to a sample 1 having upper and lower loading plates 2 and a polyfluoroethylene friction reducing sheet 4 is wound around the periphery of the strain gauge before the sample 1 is set in a steel pipe 5. The steel pipe 5 has an inside diameter being set slightly larger than the diameter of sample 1 in order to provide a gap being filled with an expansion material 3. Such thickness of the steel pipe is set so that the steel pipe 5 yields at a specified side pressure when the side pressure rise accompanying deformation of the sample 1 is allowed to a specified side pressure, otherwise the steel pipe 5 does not yield at the specified side pressure. Subsequently, a cement-based expansion material 3 principally comprising a silicate is poured into the gap between the steel pipe 5 and the sample 1. When the expansion material 3 is solidified to produce an expansive pressure and thereby a specified side pressure, or the steel pipe 5 yield due to the side pressure, load test can be performed by means of a uniaxial compression test machine.

Description

Detailed Description of the Invention

[0001]

[Industrial application] A simple triaxial compression test method and its equipment suitable for the examination of the load bearing properties of rock and concrete, which are particularly necessary in the construction of structures subject to large lateral pressure such as underground and seabed, are the main objects of the present invention. However, of course, other applications are possible.

[0002]

2. Description of the Related Art Conventionally, a dedicated triaxial compression tester for hydraulically controlling the lateral pressure applied to a specimen has been used for the triaxial compression test of rock or concrete.

[0003]

[Problems to be Solved by the Invention] Although land prices in Japan are still higher than those in other countries even though the bubble economy has collapsed, the overcrowding of population in urban areas remains a major obstacle to infrastructure development. Cage,
For these reasons, in recent years road and rail construction is planned for deep underground use, large-scale tunnels, etc., as well as for seabed use, and actual construction is also underway. In order to understand the load bearing properties of the ground and structures under the soil pressure and water pressure peculiar to these construction sites,
It is indispensable to carry out triaxial compression test of rocks and concrete that compose the ground or structure in order to safely design and construct the structure.

Conventionally, a tester called a high-pressure triaxial compression tester has been used to perform these tests, but these have the following problems. The dedicated triaxial compression tester that has been used in the past has a structure that controls the side pressure by hydraulic pressure, it is a precise and complicated device, so it is extremely expensive, prone to failure, and its maintenance cost is expensive. There was a flaw. For this reason, the number of companies and research institutes that own the device is limited, and the higher the side pressure, the smaller the number.Therefore, the number of triaxial compression tests that should be carried out with the construction work should be reduced. It was the current situation that the number was kept to the minimum necessary or not implemented.

Since a dedicated triaxial compression tester can apply only one side pressure to one tester per tester, when investigating changes in properties of rock, concrete, etc. due to long side pressure, The tester was restrained while the side pressure was applied, and there was a problem that the number of specimens was naturally constrained or the test was actually difficult. The size of the specimen that can be tested by the conventional method is greatly restricted by the testing machine, and it is practically impossible to test with a large specimen. In order to prevent the oil used as lateral pressure from penetrating into the columnar specimen and changing its properties, it was necessary to cover the columnar specimen with a rubber film in the conventional method, which required a considerably troublesome work. When investigating the strain properties of a cylindrical specimen under a triaxial compression test, the conventional method required a great deal of effort to remove the strain gauge lead wire attached to the specimen surface from the pressure vessel while sealing it. .

[0006]

SUMMARY OF THE INVENTION A simple triaxial compression test method of the present invention is a short cylindrical body, and after a friction reducing treatment is applied to a peripheral surface of a triaxial compression test specimen having both ends as main loading surfaces. , This is inserted coaxially in the center of a steel pipe having a room for the inner diameter and length, and a cement-based expansive material is poured into the gap between the specimen and the inner circumference of the steel pipe, and the specimen is solidified and expanded. In view of the increase in side pressure to the peripheral surface, the uniaxial compression tester is used to increase the direct pressure on the main loading surface of the test piece, and if necessary, to cause destruction. It is preferable to wind a friction-reducing polyfluoroethylene sheet on the peripheral surface of the test piece, the strain gauge attached to the peripheral surface, and the conductive wire.

The value of the direct pressure can be calculated from the display of the uniaxial compression tester, and the value of the side pressure can be calculated from the strain amount of vertical and horizontal strain gauges attached to the outer circumference of the steel pipe. Further, the material and thickness of the steel pipe can be selected to yield the steel pipe by the expansion pressure of the expansion material and prevent the side pressure from increasing due to the deformation of the sample due to the loading of the direct pressure. Similarly, in the case of allowing a finite or infinite increase in the lateral pressure due to the loading of the direct pressure, the steel pipe yields during the loading of the direct pressure, or the material of the steel pipe to sufficiently resist the increase of the side pressure, A triaxial compression test can be performed by selecting the wall thickness.

The simple triaxial compression test apparatus of the present invention is a test apparatus for a triaxial compression test specimen which has a short cylindrical body and has both ends as main loading surfaces. When the two loading plates with the same diameter as the test piece and the same thickness as the test piece and the above test piece are received in the center of the inside, an inner diameter that creates a gap suitable for filling cementitious expansive material on the outer circumference of the test piece Is a restraint steel pipe longer than the specimen by 10 mm or more, a uniaxial compression tester that clamps both end faces of the specimen through the above-mentioned packing plate, and two strain gauges that are attached to the outer circumference of the restraint steel pipe vertically and horizontally. The expansion material is filled in the gap between the inner wall of the restraining steel pipe and the outer periphery of the specimen, and lateral pressure is applied to the specimen by its solidification and expansion.

Further, as an axial restraint jig for the specimen, a pair of restraint plates for clamping and clamping both ends of the specimen via the above-mentioned load plates and a long bolt and nut for tightening the pair of restraint plates are provided. Before the test direct pressure is applied to the sample via the loading plate, a direct pressure commensurate with the side pressure by the expander may be applied to the sample by holding the long bolt and nut.

[0010]

According to the triaxial compression test method of the present invention, the test piece whose frictional surface is reduced is put in a steel pipe, the gap is filled with an expansive material, and the expansion pressure is waited for for uniaxial compression test. It only needs to be loaded by the testing machine, and there is no need to use a dedicated triaxial compression testing machine. Steel pipes and expansive materials can use commercially available materials, and the uniaxial compression tester used for loading can be a general uniaxial compression tester used in companies and research institutions. The cost is low and it can be tested by most companies and research institutes (which have a uniaxial compression tester).

Further, in the case of the triaxial compression test, the loading load during the compression test acts only on the test piece, and the steel pipe only resists the side pressure due to the deformation of the test piece, and resists the vertical force due to the loading load. Although it is necessary to devise a method to prevent this, this can be easily performed by only performing a friction reduction treatment such that a commercially available Teflon (trademark) sheet or the like is wound around the sample by hand. At the same time, the expansive material does not penetrate into the Teflon sheet or the specimen, so no rubber film is required and the strain gauge measurement is easy. Furthermore, when testing a large number of specimens, it is possible to apply a confining pressure at the same time by preparing the same number of steel pipes, so a large number of tests can be performed in a shorter period than when using a triaxial compression tester. Therefore, when investigating the long-term characteristics of the specimen, it is possible to give a continuous restraining pressure simply by leaving it in a state of being filled with the expansive material.

The triaxial compression test method is usually a method of allowing an increase in lateral pressure due to deformation of the specimen (generally called a non-drainage type test in the field of soil engineering), and a deformation of the specimen with respect to a predetermined lateral pressure. There are two types of methods (generally called drainage type tests in the field of soil engineering) that do not allow an increase in lateral pressure due to the above. In the present invention, in the former method, the steel pipe thickness is made sufficiently thick with respect to lateral pressure. The latter case can be implemented by adjusting the steel pipe thickness so that the steel pipe yields when a predetermined lateral pressure occurs. Furthermore, there is a method of giving the binding pressure only in advance from the side surface of the specimen, and a method of giving both to the loading surface and the side surface of the specimen, but in the present invention, in the case of the former method, the steel pipe and the specimen are Due to the expansion pressure of the expansive material filled in the void, in the case of the latter method,
Applying a loading load in advance using a uniaxial compression tester and tightening the bolts placed on the restraint jig in that state,
Both the direct pressure and the side pressure can be artificially applied by applying the expansion pressure of the expansive material as the lateral pressure in the same manner as the former, after performing the load equivalent to the restraining pressure at once or stepwise. .

In summary, the present invention utilizes the property that the liquid expansive material becomes solid when the expansion pressure appears at the time of filling, and the lateral pressure conventionally generated by the mechanical method is replaced by the chemical method, and the triaxial method is used. By simplifying the hydraulic control device, which is the side pressure generating mechanism of the compression tester, to an expansive material and a steel pipe, not only the device but also the measuring method thereof is simplified.

[0014]

1 shows a longitudinal section of an embodiment of the present invention, and FIG. 2 shows a transverse section thereof. In the figure, 1 is a rock or concrete columnar specimen, a thick plate 2 applied to the upper and lower ends thereof is a loading plate, and 3 is a loading plate.
Is a cement-based expansive material, 4 is an anti-friction sheet wrapped around the peripheral surface of the specimen as a friction reducing measure, and the material is polyethylene fluoride (trade name Teflon), and 5 is a restraining steel pipe. The anti-friction sheet 4 enters between the solidified expansive material 3 and the specimen 1, and smoothes the relative sliding between the two. R is the pedestal of the uniaxial compression tester, and P is its pressure head. FIG. 3 is a perspective view of the appearance.

FIG. 4 shows the elevation of a rock specimen or a concrete specimen. The sample to be collected is usually cylindrical,
Rock specimens are cut from the ground by a boring machine. Generally, the upper and lower surfaces of the core test piece are cut in parallel with a concrete cutter so that the height is about twice the core diameter, and the loading surface is finished smooth. Of course, this test piece can also be a cylindrical test piece used for the strength test of concrete. Disposable strain gauges (strain gauges) C and D are attached to the outer circumference of the sample 1 in the vertical and horizontal directions, as in the conventional case.

FIG. 5 shows the shape of the loading plate. The loading plate 2 has a shape of a short column made of steel and has the same diameter as that of the cylindrical specimen 1, and has a loading surface A
・ B finishes smooth and parallel. FIG. 6 shows the shape of the steel pipe 5. In order to fill the expansive material, the inner diameter of the steel pipe 5 is set to be slightly larger than the diameter of the cylindrical specimen 1. Usually, the extra of the inner diameter is secured at 10 mm or more with respect to the diameter of the cylindrical test piece 1, and is set within a range of about 1/10 to 1 / 2.5 of the diameter of the cylindrical test piece.

The outer diameter of the steel pipe 5 depends on the type of test and the material of the steel pipe. When the lateral pressure is not allowed to rise due to the deformation of the specimen with respect to the predetermined lateral pressure, the steel pipe thickness may be determined so that the steel pipe 5 yields due to the predetermined lateral pressure, and this may be added to the inner diameter.
The stress level of this steel pipe can be easily calculated. On the contrary, if the lateral pressure is allowed to rise due to the deformation of the specimen, the steel pipe thickness may be determined so that the steel pipe 5 does not yield due to the assumed lateral pressure, and this is added to the inner diameter.

Since the expansive material with which the voids are filled has the property that expansion pressure is unlikely to occur near the end of the steel pipe 5, the length of the steel pipe 5 is set to be longer than the height of the specimen 1. Usually, this length is added to the length of the specimen 1 by at least 10 mm, and the expansive material filling margin thickness [(inner diameter of the steel pipe 5 −
The diameter of the test piece 1) / 2] is about 1 to 3 times per side. After the materials are prepared, a specimen for a load test is prepared, and the procedure will be described with reference to FIGS.

First, as shown in FIG. 7, the disc of the anti-friction sheet 4 having the same diameter is placed on the specimen 1, and the loading plate 2 is placed on the disc to combine the specimen and the loading plate. Although the outline diagram is shown in FIG. 7 only for the upper surface of the specimen, the same applies to the lower surface. If the test does not require high accuracy, this sheet 4'is unnecessary. Next, the anti-friction sheet 4 is wound on the test piece (with a strain gauge attached) combined according to the procedure shown in FIG. By winding the sheet 4, the friction between the cylindrical specimen and the steel pipe can be reduced to a negligible level in terms of test accuracy. The number of turns is preferably double or more, but even with a single turn, the friction reduction effect is high, and it is meaningless to unnecessarily increase the number of turns.

When this is installed in the steel pipe 5, the expansive material can be filled, but since the expansive material when filling the steel pipe 5 is a liquid, a jig as shown in FIGS. 9 and 10 is used. And the packing is used to perform the leak prevention process in advance. 6 in the figure
Is a jig for holding the steel pipe, and 7 is a packing material. The jig for holding the steel pipe is placed in a state where it is floated from the lower loading plate 2 and the steel pipe 5
A steel material is usually used, but any material may be used. The packing material 7 is for preventing the expansion material from leaking, and sponge rubber or the like is usually used, but a sealing material or clay may be used. Needless to say, at this time, it is necessary to take care so that the sample 1 is vertically installed at the center of the steel pipe 5.
After that, a method of applying a restraining pressure only from the side surface of the specimen 1,
The process is slightly different depending on the method of applying the restraining pressure to both the loading surface and the side surface of the sample 1.

In the former case, the expansion material is simply poured into the gap between the steel pipe 5 and the specimen 1 in the state shown in FIG. 9, and after the jig 6 and the packing material 7 are removed after the expansion pressure is generated, the expansion material shown in FIG. There are a few states. In the latter case, FIG. 11 and FIG.
A jig for vertical restraint as shown in 2 is used. The jig for vertical restraint is composed of restraint plate and long bolt with nut. In the figure, 8 is a restraint plate, and 9 is a long bolt with a nut. In the vertical restraint jig set, the lower loading plate 2'of FIG. 11 is arranged, and then the lower restraint plate 8 is placed, and the specimen 1 is installed in the same manner as in FIG. 9, and the restraint plate 8 is placed thereon. And the loading plate 2'are arranged and four long bolts 9 are attached. The vertical restraining pressure is applied in this state by applying a vertical load corresponding to a predetermined restraining pressure by the uniaxial compression tester and then tightening the nut of the long bolt 9. After this work, the expansive material is poured and filled in the same manner as the former.

When a vertical load equivalent to the constraining pressure is applied at one time to cause a problem such as deterioration of the cylindrical specimen, the vertical load is applied to a level that does not cause any problems, and then the expansive material is filled to expand. The load loading and the tightening and fixing work of the long bolt 9 are repeated stepwise according to the development of the pressure, and the vertical load corresponding to the predetermined restraining pressure is loaded. As the expansive material, a cement-based expansive material mainly composed of silicate is usually used, but it is possible to develop a predetermined constraining pressure, and if the fluidity at the time of filling and the hardening property after the expansive pressure is satisfied, other expansion materials will be used. It is also possible to use wood.

Since the expansion pressure increases with time, it is necessary to control the expansion pressure. Both C and D in FIG. 13 represent strain gauges (strain gauges), but if strain gauges are attached to the surface of the steel pipe in the axial and circumferential directions, the lateral pressure can be calculated from this strain before the steel pipe yields. After the steel pipe yields, it can be known that the lateral pressure at the time of designing the steel pipe is generated by the rapid increase in the strain amount with respect to time. It goes without saying that after the steel pipe yields, the lateral pressure does not increase even if the strain increases. The lateral pressure calculation formula is illustrated in the attached document.

[Equation 1] The strain amount of the specimen can be measured with a strain gauge attached to the outer periphery as usual. Since the expansion amount of the expansive material depends on the size of the gap between the specimen 1 and the inner wall of the steel pipe 5, it is necessary to complete the expansion of the expansive material before the yielding of the restraining steel pipe and maintain its lateral pressure. You can also A load test can be performed when a predetermined side pressure is expressed or the steel pipe yields due to the side pressure due to the expansion pressure expression of the expansion material. When a vertical force is applied to a steel pipe without yielding it, it is preferable that the expansion reaction be carried out as quickly as possible because the chemical reaction of the expansive material continues to occur. However, the expansion pressure of the expansion material is about 10 to 20 kgf / cm ² or less per hour except for the initial stage within about 1 day after filling,
Actually, the side pressure increase due to the chemical reaction during the load test can be ignored.

The loading method during the triaxial compression test may be such that a constraining pressure is applied only from the side surface of the specimen as described above, or a constraining pressure is applied to both the loading surface and the side surface of the specimen. The jig 6 for holding the steel pipe is simply removed from the state at the time of filling the expansive material, and loading is performed. In the case of applying a restraining pressure to both the loading surface and the side surface of the specimen, the jig for vertical restraint of Fig. 11 is attached, but even if the jig is loaded as it is, There is no problem because the loaded load is not constrained and the tension of the long bolt 9 is only reduced. Further, regarding the processing of the test result, the steel pipe 5 only holds the lateral pressure as a restraint body, so that the rigidity of the steel pipe does not affect the test result itself. Although one embodiment has been described above, it goes without saying that the present invention can be variously changed and applied according to the implementation conditions without changing the gist thereof.

[0025]

EFFECTS OF THE INVENTION By utilizing the present invention, it is possible to easily and quickly perform a triaxial compression test on many specimens without using a special device. As the background of this invention, the load-bearing property of rock or concrete in the structure of the underground or the seabed is mentioned, but there are many problems in the academic field that require the triaxial compression test such as the understanding of the constitutive law of concrete itself. Therefore, if the present invention makes it possible to easily carry out a triaxial compression test, it will be possible to carry out a more detailed grasp of load resistance, which will greatly contribute to the improvement of the safety of structures and the development of academic research. .

[Brief description of drawings]

FIG. 1 is an elevation sectional view of an embodiment of the present invention.

2 is a cross-sectional view of FIG.

FIG. 3 is a perspective view of a main part of FIG.

FIG. 4 is a perspective view of the test piece of FIG. 1.

5 is a perspective view of the loading plate of FIG. 1. FIG.

6 is a perspective view of the restraining steel pipe of FIG. 1. FIG.

FIG. 7 is an explanatory view of a procedure for placing a loading plate on the test piece.

FIG. 8 is an explanatory view of a procedure of winding a sheet around a test piece as a friction reducing measure.

FIG. 9 is an elevational sectional view showing a state in which preparation for injecting an expansive material is completed.

FIG. 10 is an explanatory view of the assembling procedure of FIG. 9;

FIG. 11 is an elevational view showing a state in which a vertical restraining jig is attached in addition to the restraining steel pipe for applying a lateral pressure to the specimen.

FIG. 12 is a plan view of FIG.

FIG. 13 is a perspective view showing a state in which vertical and horizontal strain gauges are attached to the outer circumference of the restraint steel pipe.

[Explanation of symbols]

 1 Specimen 2 Loading plate 3 Expanding material 4 Friction reducing sheet 5 Steel pipe for restraint

Claims (5)

[Claims] 1. A triaxial compression test specimen, which is a short cylindrical body and whose both ends are main loading surfaces, is subjected to friction reduction treatment on the peripheral surface thereof, and then is coaxial with the center of a steel pipe having a room for inner diameter and length. Insert a cement-based expansive material into the gap between the test piece and the inner circumference of the steel pipe, and observe the increase in side pressure on the circumferential surface of the test piece due to solidification and expansion of the expansive material. A simple triaxial compression test method characterized by increasing the direct pressure to the above-mentioned main loading surface of the test piece by a compression tester and causing it to break if necessary. 2. The test method according to claim 1, wherein a friction-reducing polyethylene fluoride sheet is wound around the peripheral surface of the specimen, the strain gauge attached to the peripheral surface, and the conductor. A simple triaxial compression test method characterized by. 3. The test method according to claim 1, wherein a material and a wall thickness of the steel pipe are selected to yield the steel pipe during expansion of the expansive material, or wait for completion of expansion,
A simple triaxial compression test method comprising increasing the direct pressure on the test piece by the compression tester while keeping the side pressure on the test piece almost constant. 4. A test device for a triaxial compression test specimen, which is a short cylindrical body and has both ends as main loading surfaces, and has a diameter substantially the same as that of the specimen, which is applied to both loading surfaces of the above-mentioned specimen. When two thick loading plates and the above-mentioned specimen are received in the center of the interior, the inner diameter creates a gap suitable for filling the cement-based expansive material on the outer periphery of the specimen, and the length is about 10 mm or more longer than the specimen. Steel pipe, a uniaxial compression tester that presses both end faces of the specimen through the above-mentioned packing plate, and two strain gauges that are vertically and horizontally attached to the outer circumference of the restraint steel pipe, and are provided together with the restraint steel pipe inner wall. A simple triaxial compression testing device characterized in that the expansive material is filled in a gap between the outer circumference of the sample and a lateral pressure is applied to the sample by its solidification and expansion. 5. The apparatus according to claim 4, further comprising, as an axial restraint jig for the specimen, a pair of restraint plates for clamping and clamping both ends of the specimen via the above-mentioned load plate, and long bolts and nuts for tightening the restraint plates. By applying a preliminary direct pressure to the test piece through the constraining plate and the loading plate by the uniaxial compression tester and holding the direct pressure by tightening the bolts and nuts, the uniaxial compression tester A simple triaxial compression testing device characterized in that the elongation of the specimen due to the side pressure of the expansion material can be restrained even after the removal.