JP2015102472A - Triaxial test device and triaxial test method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine or measure the deformation and stress of a test piece resulting from anisotropy by one or a few triaxial tests, thereby identifying the anisotropy of deformation properties of a ground material and identifying an anisotropic direction without relying on visual observation.SOLUTION: A cap (7) of a triaxial test device (1) includes a displacement-measurement cap mechanism (17) and/or a load-measurement cap mechanism (18) interposed between a load shaft (9) and a cap main body (7a). The displacement-measurement cap mechanism (17) includes movable means (23, 33) allowing a lateral displacement or a horizontal displacement of the cap main body (7a) at a time of loading an axial load (Q). The load-measurement cap mechanism (18) includes stress detection means (50) prohibiting or constraining the lateral displacement or the horizontal displacement of the cap main body (7a) at the time of loading the axial load (Q), and detecting a stress acting on the cap (7) in a direction crossing or orthogonal to an axial force direction of the axial load (Q).

Description

  The present invention relates to a triaxial test apparatus and a triaxial test method, and more specifically, a columnar specimen collected from the ground made of soil or rock is inserted between a pedestal and a cap in a triaxial cell. The present invention relates to a triaxial test apparatus and a triaxial test method in which an axial load is applied to a specimen by a loading shaft of the loading apparatus to compact and axially compress the specimen.

  As a test apparatus for examining the deformation characteristics and strength characteristics of the ground, there is known a triaxial test apparatus that applies an axial load to the specimen in a state where a side pressure is applied to the cylindrical specimen taken from the original position (for example, Patent Documents 1 and 2). The configuration of a conventional triaxial test apparatus is schematically shown in FIG.

  As shown in FIG. 7, the triaxial testing apparatus 100 includes a triaxial cell (triaxial pressure chamber) 101 that can accommodate the specimen S. The triaxial cell 101 is formed by a bottom plate 102, a pressure cylinder 103 and an upper plate 104. The specimen S is disposed between the pedestal 105 and the cap 106. The outer peripheral surface of the specimen S is covered with a rubber sleeve 107. A loading shaft 108 of the loading device penetrates the upper plate 104 and applies an axial force to the specimen S. A load meter 109 for measuring the axial load Q is interposed in the loading shaft 108. The loading shaft 108 includes an axial displacement detection rod 121 associated with the detection unit of the axial displacement meter 120. A cell pressure supply path 111 passes through the bottom plate 110 and opens on the upper surface of the bottom plate 110. A cell pressure supply path 115 passes through the upper board 104 and opens on the lower surface of the upper board 104. Porous plates (porous stones) 114 and 115 are disposed on the upper and lower surfaces of the specimen S, and are connected to the double-pipe puree 122, the pore water pressure system 123 and the like via the pipes 112 and 113. The triaxial testing apparatus 100 further includes a cell pressure supply device, a loading frame, a loading device, etc. (not shown), and an external control device or an external control system such as a recording device, a storage device, a display device, etc. for processing measurement data. (Not shown).

  In the triaxial test for examining the anisotropy of the deformation characteristics of the ground material using such a triaxial testing apparatus, as shown in FIG. 8, the cores K in different sampling directions are sampled from the ground J, and each core K is obtained. A test method has been adopted in which the specimen S is arranged between the pedestal 105 and the cap 106 and a three-axis test is performed while measuring the strain generated in each specimen S in multiple directions (Non-Patent Document 1).

  In addition, in the investigation of anisotropy for linear elastic bodies assuming in-plane isotropic properties, three or more prismatic specimens collected in different sampling directions are set in a triaxial test apparatus, and strain is measured in multiple directions. However, a method of specifying five elastic parameters by performing a triaxial test on each specimen is proposed (Non-Patent Document 2). Furthermore, a strain measurement method using a cylindrical specimen by a similar method has been proposed (Non-Patent Document 3).

Japanese Patent Laid-Open No. 10-206303 Japanese Patent Laid-Open No. 6-138007

Oka, F., Kimoto, S., Kobayashi, H. & Adachi, T .: Anisotropic behavior of soft sedimentary rock, Soils & Foundations, Vol.42, No.5, pp.59-70, 2002. Amadei, B .: Importance of anisotropy when determining and measuring in-situ stresses in rock, Int.J. of Rock Mech. & Min. Sci., Vol.33, pp.293-325, 1996. Hakala, M., Kuula, H. & Hudson, J, A .: Estimating the transversely isotropic elastic intact rock properties, Int. J. of Rock Mech. & Min. Sci., Vol.44, pp.14-46, 2007.

  However, the following problems are inherent in the conventional investigation method for examining the anisotropy related to the mechanical properties of the ground material using a triaxial testing apparatus.

(1) The deformation and stress peculiar to anisotropic materials generated at the time of triaxial loading cannot be considered or specified.
FIG. 9 (A) is a perspective view schematically showing a consolidation deformation mode at the time of triaxial loading of the specimen S made of an isotropic material, and FIG. 9 (B) shows an anisotropic material (in-plane etc. It is a schematic perspective view which shows the compaction deformation mode at the time of triaxial loading of the test body S which consists of an anisotropic material).

  When the specimen S of the isotropic material shown in FIG. 9A is subjected to a loading test, the axial symmetry condition is satisfied, and therefore the principal stress direction and the principal strain direction coincide with each other. Compress evenly. On the other hand, when the specimen S of anisotropic material is loaded, the axial symmetry condition is not always satisfied, and therefore the main stress direction and the main strain direction do not match. For this reason, in the loading test of the specimen S of anisotropic material, when loading is performed under the condition that does not restrain the deformation of the specimen S, as shown in FIG. Will occur. For example, according to the simulation of the present inventors assuming soft rock as the in-plane isotropic elastic body, it is considered that the behavior of the specimen S due to the material anisotropy occurs.

  Such deformation or behavior of the specimen S is a behavior peculiar to anisotropic materials, and is an important factor in specifying the anisotropy of the sample. However, in the conventional loading test, it is not performed to specify the anisotropy of the material by measuring such deformation.

  Moreover, in the conventional triaxial test, the cap that restrains the specimen S can only be displaced in the axial direction, and is a loading test of the specimen S of in-plane isotropic material having anisotropy. However, the specimen S can only be deformed only in the axial direction. That is, in the conventional triaxial test apparatus, the displacement of the specimen S that can occur in the direction (side direction) intersecting or orthogonal to the axial force direction is prohibited or restrained. Shear stress acts. This kind of shear stress is a stress peculiar to anisotropic materials due to the material anisotropy, and is an important factor in specifying the material anisotropy. No attempt has been made to measure the shear stress.

(2) The direction of anisotropy cannot be specified.
In the conventional investigation method for examining the anisotropy of deformation characteristics, a loading test is performed after the direction of anisotropy is estimated by visually observing a rock core or the like. According to such a survey method, the direction of anisotropy is assumed based on the deposition surface, the direction of joints, the direction in which mineral particles are oriented, etc. About the rock etc. which have, the direction of anisotropy cannot be specified by visual observation.

(3) Many loading tests are required.
Even in the study assuming in-plane isotropic, which is the simplest anisotropy of deformation characteristics, a test using a core sampled in at least three directions is required. Considering variation in test results, it is necessary to further increase the number of tests. As a result, a relatively high test cost and a long test time are required.

  The present invention has been made in view of such circumstances, and its purpose is to perform a single or a small number of triaxial tests using a columnar specimen collected from the ground made of soil or rock. To measure or measure the deformation or stress of the specimen due to anisotropy, thereby identifying the anisotropy of the deformation characteristics of the ground material and determining the direction of anisotropy without depending on visual observation. An object of the present invention is to provide a triaxial test apparatus and a triaxial test method that can be specified.

In order to achieve the above object, the present invention includes a triaxial cell that accommodates a columnar specimen collected from the ground, and the loading shaft of the loading apparatus with respect to the specimen in the triaxial cell constrained by a pedestal and a cap. In a three-axis test apparatus for applying a shaft load to compress the specimen and compress the shaft,
The cap has a displacement measurement type cap mechanism and / or a load measurement type cap mechanism interposed between the load shaft described above and a cap main body disposed on the top of the specimen,
The displacement measuring type cap mechanism has movable means for allowing lateral displacement or horizontal displacement of the cap body when an axial load is loaded,
The load-measuring cap mechanism prohibits or restrains lateral displacement or horizontal displacement of the cap body when the axial load is loaded, and acts on the cap by the axial load and the axial force direction of the axial load. There is provided a triaxial test apparatus having stress detection means for detecting a shear stress acting in a crossing or orthogonal direction.

The present invention also includes a triaxial cell that accommodates a columnar specimen collected from the ground, and an axial load is applied to the specimen in the triaxial cell constrained by a pedestal and a cap by a loading shaft of a loading device. In a triaxial testing apparatus for compacting and axially compressing the specimen,
The pedestal has a displacement measurement type pedestal mechanism and / or a load measurement type pedestal mechanism,
The displacement measuring pedestal mechanism has movable means that allows lateral displacement or horizontal displacement of the pedestal body when an axial load is loaded,
The load measurement type pedestal mechanism prohibits or restrains a lateral displacement or a horizontal displacement of the pedestal body when the axial load is loaded, and acts on the pedestal by the axial load and an axial force direction of the axial load. There is provided a triaxial test apparatus having stress detection means for detecting a shear stress acting in a crossing or orthogonal direction.

From another point of view, the present invention includes a columnar specimen collected from the ground in a triaxial cell, restrained by a pedestal and a cap, and applies an axial load to the specimen by a loading shaft of a loading device. In the triaxial test method in which the specimen is compacted and axially compressed,
A displacement measurement type cap mechanism or a load measurement type cap mechanism is interposed between the cap body and the loading shaft arranged at the top of the specimen,
The lateral displacement or horizontal displacement of the cap body is allowed by the displacement measuring type cap mechanism when the axial load is loaded, and the lateral displacement or horizontal displacement of the cap body with respect to the load shaft described above is detected, or the axial load is detected. A shear stress acting on the cap by the axial load and acting in a direction intersecting or orthogonal to the axial force direction of the axial load in a state where lateral displacement or horizontal displacement of the cap body is prohibited or restrained at the time of loading is applied to the load. A triaxial test method characterized by detecting by a measuring cap mechanism.

The present invention further includes accommodating a columnar specimen taken from the ground in a triaxial cell, constraining it by a pedestal and a cap, and applying an axial load to the specimen by a loading shaft of a loading device to consolidate the specimen. And in the triaxial test method for axial compression,
Displacement measurement type pedestal mechanism or load measurement type pedestal mechanism is installed in or built into the pedestal arranged at the bottom of the specimen,
When the axial load is loaded, the lateral displacement or horizontal displacement of the pedestal body is allowed by the displacement measurement type pedestal mechanism, and the lateral displacement or horizontal displacement of the pedestal body with respect to the load shaft described above is detected, or the loading of the axial load is performed. Measurement of the shear stress acting on the pedestal by the axial load and in the direction intersecting or orthogonal to the axial force direction of the axial load with the lateral or horizontal displacement of the pedestal body prohibited or constrained. A triaxial test method characterized by detecting by a pedestal mechanism.

  According to the above configuration of the present invention, at least one of the displacement measurement type cap mechanism and the load measurement type cap mechanism is provided on the cap in the loading test apparatus, or at least one of the displacement measurement type pedestal mechanism and the load measurement type pedestal mechanism. Is provided on the pedestal in the loading test apparatus. In a triaxial test using a displacement measurement type cap mechanism or displacement measurement type pedestal mechanism, lateral displacement or horizontal displacement of the cap body or pedestal body is allowed when an axial load is loaded. Deformation specific to the specimen occurs. The deformation of the specimen appears as relative lateral displacement or horizontal displacement between the loading shaft and the cap body, or relative lateral displacement or horizontal displacement between the bottom plate and the pedestal body. Further, in the triaxial test using the load measuring type cap mechanism or the load measuring type pedestal mechanism, lateral displacement or horizontal displacement of the cap body or pedestal body is prohibited or restrained. Since the movement is also prohibited or constrained, the shear stress inherent in the anisotropic material acts on the specimen end face and the cap or pedestal in a direction crossing or perpendicular to the axial force direction of the axial load.

  Therefore, according to the three-axis test apparatus and the three-axis test method configured as described above, the relative lateral displacement or horizontal displacement of the cap body or pedestal body with respect to the loading shaft is measured or measured, or acts on the cap or pedestal. By measuring or measuring the shear stress, the deformation and stress of the specimen due to anisotropy can be known or grasped, and the anisotropy direction of the specimen can be specified without depending on visual observation. .

  Further, according to the triaxial test apparatus and the triaxial test method having the above-described configuration, a single or a small number of specimens can be used once or a small number of times without repeating the triaxial test using a large number of specimens. Through the three-axis test, the deformation and stress of the specimen caused by anisotropy can be known or grasped, and thereby the anisotropy of deformation characteristics can be examined.

  Preferably, the displacement measurement type cap mechanism or the displacement measurement type pedestal mechanism includes a first member integrated with the loading shaft, a second member integrated with the cap body or the pedestal body, and the first and second members. And the above-mentioned movable means for interposing and relatively displacing the first and second members. More preferably, the displacement measurement type cap mechanism or the displacement measurement type pedestal mechanism further includes a third member interposed between the first and second members, and the movable means is between the first member and the third member. And is interposed between the second member and the third member. The movable direction of the third member and the movable direction of the second member relative to the third member are separated from each other by a predetermined angular interval around the central axis of the loading shaft, and the cap body or the pedestal body is around the central axis of the loading shaft. Displace in any angular direction.

  In a preferred embodiment of the present invention, the movable means has a bearing device having a rolling element, a sliding element or a sliding element. Preferably, the movable means comprises a roller or ball bearing device having a number of rolling elements.

  Preferably, the displacement measuring type cap mechanism or the displacement measuring type pedestal mechanism is such that the displacement of the end face (upper end face or lower end face) of the specimen that occurs when the axial load is loaded is the same as the lateral displacement or horizontal displacement of the cap body or pedestal body. It is assumed that the displacement detection means for detecting a lateral displacement or a horizontal displacement of the cap body or the pedestal body is provided. Further, the load measurement type cap mechanism or the load measurement type pedestal mechanism has a two-way load cell that detects a shear stress acting on the end face of the specimen. A bi-directional load cell detects shear stress acting in at least two different directions. As the two-way load cell, a parallel plate type load cell can be preferably used. The anisotropy of the specimen is specified based on the amount of lateral displacement or horizontal displacement of the end face or cap or pedestal of the specimen, or the shear stress acting on the end face of the specimen.

  According to the triaxial test apparatus and the triaxial test method of the present invention, the single axis or a small number of triaxial tests using columnar specimens collected from the ground made of soil, rock, etc. caused the anisotropy. The deformation or stress of the specimen is measured or measured, whereby the anisotropy of the deformation characteristics of the ground material can be specified, and the anisotropy direction can be specified without depending on visual observation.

FIG. 1 is a longitudinal sectional view schematically showing a cell (pressure chamber) of a triaxial test apparatus according to a first embodiment of the present invention. The cap disposed in the cell is a displacement measuring type cap mechanism. Prepare. FIG. 2 is a longitudinal sectional view schematically showing the structure of another triaxial testing apparatus according to the second embodiment of the present invention, and the cap disposed in the cell includes a load measuring type cap mechanism. 3 is a plan view, a front view, and a side view showing the structure of the displacement measurement type cap mechanism shown in FIG. FIG. 4 is a plan view and a side view illustrating the behavior of the displacement measuring type cap mechanism in the triaxial test of the specimen having anisotropy. FIG. 5 is a plan view and a development view showing the arrangement of strain gauges attached to the side surface of the specimen. 6 is a plan view, a front view, and a side view showing the structure of the load measurement type cap mechanism shown in FIG. FIG. 7 is a longitudinal sectional view schematically showing a cell of a conventional triaxial test apparatus. FIG. 8 is a perspective view schematically showing a sampling method for collecting a plurality of specimens from the ground of an in-plane isotropic body for the purpose of examining anisotropy in a conventional triaxial test. FIG. 9A is a perspective view schematically showing a compaction deformation mode at the time of triaxial loading of a specimen made of an isotropic material, and FIG. 9B is a perspective view of the specimen made of an anisotropic material. It is a schematic perspective view which shows the deformation | transformation aspect at the time of triaxial loading. FIG. 10 is a conceptual diagram illustrating the inclination of an isotropic surface (discontinuous surface) and the direction of anisotropy. FIG. 11 is a flowchart showing a procedure for obtaining the anisotropy of the deformation characteristics of the rock using a displacement measurement type cap mechanism (or a load measurement type cap mechanism). In the procedure using the load measurement type cap mechanism, portions that are different from the case of the displacement measurement type cap mechanism are shown in parentheses in FIG. FIG. 12 is a diagram showing a method for setting an orthogonal coordinate system (X, Y, Z). FIG. 13 is a conceptual diagram showing the relationship between the specimen and the coordinate axes. FIG. 14 is a diagram illustrating a method for setting the direction of anisotropy.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  1 and 2 are longitudinal sectional views schematically showing the structure of a triaxial test apparatus according to the present invention.

  The triaxial test apparatus 1 has a triaxial cell (triaxial pressure chamber) 2 that can accommodate the specimen S. The triaxial cell 2 is formed by a bottom plate 3, a pressure cylinder 4 and an upper plate 5. The specimen S is disposed between the pedestal 6 and the cap 7. The outer peripheral surface of the specimen S is covered with a rubber sleeve 8. A loading shaft (or loading rod) 9 that applies an axial load Q to the specimen S passes through the bearing portion 5 a of the upper panel 5. The loading shaft 9 is coupled to a driving source of a loading device that is a hydraulic cylinder device or the like.

  A load cell (load cell) 10 for measuring the axial load Q is interposed in the loading shaft 9. A cell pressure supply path 11 constituting the cell pressure supply device passes through the bottom plate 3 and opens on the upper surface of the bottom plate 3. The cell pressure supply path 12 passes through the upper board 5 and opens on the lower surface of the upper board 5. The cell pressure supply path 12 is connected to a pressure source such as a compressor constituting the cell pressure supply device. Cell water W at a predetermined water level is stored in the triaxial cell 2. The cell pressure of the cell pressure supply device supplied via the air supply path 12 is converted into the water pressure of the cell water W.

  Porous plates (porous stones) 13 and 14 are disposed on the upper and lower surfaces of the specimen S, respectively. The porous plates 13 and 14 are connected to a drainage condition control circuit and a back pressure supply device (not shown) via pipes 15 and 16. The triaxial test apparatus 1 further includes a pore water pressure gauge 62 for measuring a volume change and a double pipe pureette 63 connected to the pipe line 16.

  In the triaxial test, the output of the loading device acts on the loading shaft 9 as the axial load Q, and the loading shaft 9 applies the axial load Q to the specimen S through the cap 7. The axial load Q is measured by the load meter 10. The loading shaft 9 includes an axial displacement detection rod 61 associated with the detection unit of the axial displacement meter 60. The axial displacement and volume change of the specimen S are measured or measured by the axial displacement meter 60, the pore water pressure meter 62, and the double tube puret 63. Measurement data of each measuring device is input to an external control device or an external control system (not shown) including a recording device, a storage device, a display device, etc. via a control signal line (not shown). A plurality of strain gauges G can be attached to the outer surface of the specimen S. Each strain gauge G is connected to an external control device or an external control system via a control signal line (not shown).

  In the triaxial testing apparatus 1 according to the present invention, one of the following two types of cap mechanisms for specifying the anisotropy of the deformation characteristics of the ground material is disposed in the triaxial cell 2. That is, the first-type cap mechanism is a displacement-measuring-type cap mechanism that allows the cap 7 to be displaced laterally and enables measurement of deformation due to anisotropy, and the second-type cap mechanism includes: It is a load measurement type cap mechanism that enables measurement or measurement of shear stress caused by anisotropy. The displacement condition of the cap 7 provided with the load measuring type cap mechanism is the same displacement condition as that of the normal three-axis test (that is, the lateral displacement is not allowed and only the axial displacement of the loading shaft 9 is allowed. The displacement condition).

  The displacement measurement type cap mechanism is for measuring the lateral displacement or horizontal displacement of the cap 7 caused by the anisotropy of the specimen S, and the load measurement type cap mechanism is used for the anisotropy of the specimen S. This is for measuring or measuring the shear stress acting on the cap 7 due to this. Any mechanism can investigate the anisotropy of the specimen S by a single (one time) triaxial test.

  In the triaxial test apparatus 1 shown in FIG. 1, a cap 7 having a displacement measurement type cap mechanism 17 is disposed in the triaxial cell 2. On the other hand, in the triaxial testing apparatus 1 shown in FIG. 2, a cap 7 having a load measuring type cap mechanism 18 is disposed in the triaxial cell 2. The triaxial test apparatus 1 shown in FIG. 1 will be described below as a first example (Example 1), and the triaxial test apparatus 1 shown in FIG. 2 will be described below as a second example (Example 2).

  In the triaxial test apparatus 1 shown in FIG. 1, the displacement measurement type cap mechanism 17 of the cap 7 is interposed between the cap body 7 a of the cap 7 and the lower end portion of the loading shaft 9.

  FIG. 3 is a plan view, a front view, and a side view showing the structure of the displacement measuring type cap mechanism 17.

  The displacement measurement type cap mechanism 17 includes a first carriage 20 that is displaceable in a side direction (X-axis direction) orthogonal to the central axis direction (Z-axis direction) of the loading shaft 9, and a side direction orthogonal to the Z-axis and X-axis. A second carriage 30 that is displaceable in the (Y-axis direction), a first rail 21 that is fixed to the upper surface of the cap body 7a and supports the first carriage 20 so as to be displaceable in the X-axis direction, and an upper surface of the first carriage 20 And a second rail 31 that supports the second carriage 30 so as to be displaceable in the Y-axis direction. A lower end portion of the loading shaft 9 is fixed to the center portion of the upper surface of the second carriage 30. Each of the carriages 20 and 30 and the rails 21 and 31 is made of a highly rigid metal member that is integrally formed, for example, a stainless steel member.

  The carriages 20 and 30 have open-side recesses 20a and 30a that can partially accommodate the rails 21 and 31, respectively. Between the carriages 20 and 30 and the rails 21 and 31, roller-type or ball-type bearing devices 23 and 33 in which a large number of metal rollers or metal balls are arranged are interposed. The bearing device 23 relatively displaces the first carriage 20 in the X-axis direction with respect to the cap body 7a, and the bearing device 33 displaces the carriage 30 in the Y-axis direction relative to the first carriage 20. Therefore, the lower end portion of the loading shaft 9 and the cap body 7a can be relatively displaced in an arbitrary direction on the XY plane shown in FIG. As the carriages 20 and 30, the rails 21 and 31, and the bearing devices 23 and 33, for example, a mechanism such as NSK linear guide (registered trademark) manufactured by NSK Ltd. can be suitably used.

  FIG. 4 is a plan view and a side view illustrating the behavior of the displacement measurement type cap mechanism 17 generated in the triaxial test of the specimen S having anisotropy.

  As shown in FIG. 4, when the axial load Q is loaded on the specimen S by the loading shaft 9, the cap body 7 a is lowered in accordance with the consolidation deformation of the specimen S and the specimen S due to anisotropy is caused. It is displaced in the X-axis direction and the Y-axis direction according to the deformation. The displacement of the cap body 7 a in the X-axis direction is caused by the relative displacement of the first rail 21 with respect to the first carriage 20. The displacement of the cap body 7 a in the Y-axis direction is caused by the relative displacement of the second rail 31 with respect to the second carriage 30. That is, the displacement measuring type cap mechanism 17 follows the shear deformation of the specimen S and displaces the cap body 7a in the in-plane direction of the XY plane. Therefore, the center axis C of the cap body 7a has the X axis direction and the Y axis Displace in the direction and move to position C ′.

  Since the friction generated between the carriages 20 and 30 and the rails 21 and 31 can be substantially ignored due to the presence of the bearing devices 23 and 33, the triaxial test apparatus 1 does not generate shear stress on the specimen S. It can be loaded on the end surface of the specimen S under conditions, and the specimen S can be sheared and deformed. In order for the cap body 7a to reliably follow the shear deformation of the specimen S, preferably, the end surface of the specimen S, the surface of the cap body 7a, and the surface of the pedestal 6 that are in contact with each other are set to rough friction conditions. Alternatively, these parts are fixed to each other by gypsum, adhesive or the like.

  As conceptually shown in FIG. 4, the displacement measurement type cap mechanism 17 includes a first displacement meter 22 and a second displacement meter 32 that detect horizontal displacement amounts ΔX and ΔY of the carriages 20 and 30. The first displacement meter 22 detects a displacement in the Y direction of the first carriage 20 with respect to the first rail 21, and the second displacement meter 32 detects a displacement in the X direction of the second carriage 30 with respect to the second rail 31. The detection results of the displacement meters 22 and 32 are input to the aforementioned external control device or external control system via a control signal line (not shown). Note that an eddy current type or contact type displacement meter or the like is used as the displacement meters 22 and 32, and the detectors of the displacement meters 22 and 32 are caused by the displacement of the rails 21 and 31 (that is, due to the anisotropy of the specimen S). The cell triaxial cell 2 is arranged at an appropriate position so as to measure the deformation.

  FIG. 5 is a plan view and a development view showing the arrangement of the strain gauges G.

The strain gauge G is disposed on the outer surface of the specimen S as shown in FIG. 5 with respect to the geographic coordinate system (E, W, S, N) at the site where the test is performed. Each strain gauge G is bonded to the outer surface of the specimen S with an adhesive or the like. It is desirable to stop the plate surface of each strain gauge G with paraffin or silicon rubber. Regarding the strain gauges G of numbers 1 to 6 shown in FIG. 5, if the strain measured by the i-th strain gauge 42 is x _i , the strain tensor component of the geographic coordinate system can be calculated by the following Equation 1.

Γ _ij is an engineering strain, and there is a relationship of γ _ij = ε _ij (i ≠ j) (i, j = S, E, V) between the engineering strain γ _ij and the tensor strain ε _ij .

  Next, an embodiment of the triaxial testing apparatus 1 provided with the load measuring type cap mechanism 18 in the cap 7 will be described with reference to FIGS. 2 and 6.

  The load measuring type cap mechanism 18 of the cap 7 is interposed between the cap body 7 a of the cap 7 and the lower end portion of the loading shaft 9. The load measuring type cap mechanism 18 has a parallel plate type two-way load cell 50 that measures shear stress in two directions (X-axis direction and Y-axis direction) orthogonal to the central axis direction (Z-axis direction) of the specimen S. . In this example, since it is necessary to prevent slipping between the specimen S and the cap body 7a in order to prohibit or restrain the shear deformation of the specimen S, the specimen which is in mutual contact with the upper end surface of the specimen S. The end face of S, the surface of the cap body 7a, and the surface of the pedestal 6 are set to rough friction conditions, or these portions are fixed to each other by gypsum, adhesive, or the like.

  FIG. 6 is a plan view, a front view, and a side view showing the structure of the load measuring type cap mechanism 18.

  The load measuring type cap mechanism 18 includes a substrate 40 fixed to the upper surface of the cap body 7a, a two-way load cell 50 fixed to the substrate 40, and a top plate 43 fixed to the upper surface of the two-way load cell 50. . A lower end portion of the loading shaft 9 is fixed to the upper surface of the top plate 43. The substrate 40, the two-way load cell 50, and the top plate 43 are arranged concentrically with respect to the central axis of the loading shaft 9.

  The two-way load cell 50 has openings 51 and 52 having a square cross section extending in the Y-axis direction and the X-axis direction. The flat plates 53 and 54 positioned below and above the opening 51 constitute parallel plates for measuring stress in the X-axis direction, and the flat plates 54 and 55 positioned below and above the opening 52 are A parallel plate for measuring stress in the Y-axis direction is formed. The substrate 40, the two-way load cell 50, and the top plate 43 are made of, for example, phosphor bronze having excellent elasticity, and are in rigid contact with each other.

  A plurality of strain gauges 57 extending in the X-axis direction and a plurality of strain gauges 58 extending in the Y direction are attached to the outer surface of the two-way load cell 50 at predetermined positions. Each strain gauge 57, 58 is connected to the aforementioned external control device or external control system (not shown) via a control signal line (not shown). When the axial load Q is loaded on the specimen S by the loading shaft 9, the external control device or the external control system measures the shear load in the X-axis direction and the Y-axis direction based on the change in the electrical resistance of the strain gauges 57 and 58. be able to. The average value of the shear stress acting on the end face of the specimen S is obtained as a value obtained by dividing the measured shear load by the area of the end face of the specimen.

  Since the loading test is performed under the condition that shear deformation of the specimen S does not occur, it is equivalent to the loading condition in a general triaxial test. However, since the triaxial test apparatus 1 can measure the shear stress caused by the anisotropy by the load measuring type cap mechanism 18, it becomes possible to specify the anisotropy of the deformation characteristics of the specimen S. . The axial load Q is measured by the load meter 10. If desired, it is possible to measure the axial load Q with an external load cell (load cell) arranged outside the cell. However, since the loading shaft 9 may receive a frictional force in the bearing portion 5a of the upper panel 5, It is desirable to correct the measured value of the external load cell by the calibration. Further, the strain of the specimen S is measured by a strain gauge G attached to the outer surface of the specimen S as shown in FIG.

  As described above, the triaxial test apparatus 1 including the displacement measurement type cap mechanism 17 has been described as the first embodiment, and the triaxial test apparatus 1 including the load measurement type cap mechanism 18 has been described as the second embodiment. The triaxial test apparatus 1 provided with a mechanism is effectively used for a triaxial test of a specimen S having a discontinuous surface and the like and assumed to not satisfy the axial symmetry condition. According to the triaxial test apparatus 1 provided with such mechanisms 17 and 18, the following effects can be obtained as compared with the triaxial test apparatus that does not include these mechanisms.

(1) Measurement of deformation or shear stress due to the anisotropy of the specimen S In the triaxial test using the displacement measuring type cap mechanism 17, the test specimen S is subjected to different conditions under the test conditions in which no shear stress is generated. It becomes possible to measure the shear deformation in the lateral direction due to the directionality. In the triaxial test using the load-measuring cap mechanism 18, the same conditions as in the normal triaxial test, that is, the test conditions that do not cause the specimen S to undergo lateral shear deformation or lateral displacement of the specimen end face. The shear stress acting on the specimen S due to anisotropy can be measured. Such measurement of shear deformation or shear stress is a technical matter that has not been considered in the conventional triaxial test that has been aimed at isotropic and homogeneous specimens.

(2) Mechanical basis for specifying the direction of anisotropy According to the triaxial test apparatus 1 provided with the displacement measurement type cap mechanism 17 or the load measurement type cap mechanism 18, shear deformation or shear stress caused by anisotropy Therefore, the direction of principal strain or principal stress can be specified, which makes it possible to specify the direction of anisotropy coaxial with the direction of principal strain and stress on a mechanical basis. Become.

(3) Identification of deformation anisotropy by single or small number of triaxial tests By measuring and analyzing strain or stress in a plurality of directions, the specimen S can be analyzed by one or a few triaxial tests. The deformation anisotropy can be obtained or grasped.

  Next, a method for specifying the anisotropy of the deformation characteristics assuming in-plane isotropic properties by a triaxial test using the displacement measuring cap mechanism 17 and the load measuring cap mechanism 18 will be described.

[Method of identifying anisotropy using displacement measurement type cap mechanism]
An in-plane isotropic elastic body is an elastic body in which the elastic constant of an isotropic surface is different from the elastic parameter in the direction of the elastic main axis (direction orthogonal to the isotropic surface), and is a discontinuous surface. Used as an equivalent continuum equivalent to the elastic behavior of the rock (Goodman RE: Introduction to Rock Mechanics. J. Wiley, New York, 1989), and as a constitutive relationship of sedimentary rocks (Oka F., Kimoto S., Kobayashi H., Adachi T .: Anisotropic behavior of soft sedimentary rock. Soils and Foundations, Vol.42, No.5, pp.59-70, 2002) (Akai K., Yamamoto K., Arioka M .: Experimental research on the structural anisotropy of crystalline schist. J. JSCE, Vol. 170, pp. 23-36, 1969) is known.

FIG. 10 is a conceptual diagram showing an inclination ξ of an isotropic surface (discontinuous surface) with respect to a geographic coordinate system, a traveling x ′, an inclination direction y ′, and a normal direction z ′ of the isotropic surface. . In this example, the elastic parameters (Young's modulus, Poisson's ratio, shear stiffness) in the x 'and y' directions are (E _{x '} , ν _x' , G _{x '} (= E _x' / 2 (1 + ν _{x ′} )), and the elastic parameters in the z ′ direction are represented by (E _{z ′} , ν _{z ′} , G _{z ′} ).

  FIG. 11 is a flow chart showing a procedure for obtaining the anisotropy of the deformation characteristics of the ground assuming in-plane isotropic using the displacement measurement type cap mechanism 17. In addition, the procedure shown in parentheses in FIG. 11 is a procedure that is adopted when determining the anisotropy of the deformation characteristics of the ground using the load measuring type cap mechanism 18, and this will be described later.

  By visual observation of the specimen S, the angle ζ and the inclination ξ formed by the inclination direction y ′ of the surface whose rigidity is estimated to be isotropic and the E axis are estimated (Step 1), and the geographic coordinate system and the specimen S are estimated. The measuring instrument such as the strain gauge G is disposed at a proper position of the specimen S (Step 2). As shown in FIG. 5, the strain gauge G is disposed at a predetermined position of the specimen S with respect to the geographic coordinate system.

Next, isotropic consolidation (Step 3) and axial compression (Step 4) are performed, and the stress and strain of the specimen S are measured. Preferably, loading is performed with the strain level set in the elastic range (10 ⁻⁵ or less). In the loading process, it is possible to determine the presence or absence of plastic deformation by raising or lowering the stress to be loaded in stages, or to measure the change in rigidity accompanying plastic deformation.

Next, the inclination angle (ξ, ζ) of the anisotropic direction (x ′, y ′, z ′) in the geographic coordinate system shown in FIG. The coordinate axes are set (Step 5). The strain increment tensor Δε ′ during isotropic consolidation in geographic coordinates is expressed by the following equation 2. Based on Δε ′ obtained by Expression 2, the main distortion is obtained by Expression 3 below.

In diagonalizing the distortion tensor of Equation 3, the Jacobi method or the like is used, and the unit direction vector e of the main strain expressed by Equation 4 below is obtained. During isotropic consolidation, the anisotropy direction (x ', y', z ') and the principal strain direction (1, 2, 3) are co-axial, so the vector e is composed of the above ξ and ζ. For example, although ξ and ζ are specified based on the following equation 5, the value of ζ may be obtained from the vector e ₁₂ , and the value of ξ may be obtained from the vector e _23. Alternatively, a plurality of obtained values of ξ and ζ may be averaged.

Here, by using the value of ζ, as shown in FIG. 12, the orthogonal coordinate system (X, Y, Z) is set. By this operation, the X axis and the x ′ axis become coaxial. Further, when a cylindrical coordinate system (R, Θ, Z) is set so as to match this coordinate system (X, Y, Z) coordinate system and the measurement result of the angle ξ is combined, a specimen as shown in FIG. The relationship between S and the coordinate axis is obtained. The alignment of the above-mentioned ξ and ζ obtained in the above-mentioned visual observation (Step 1 in FIG. 11) is confirmed at this time. Further, in order to organize the test results described later, the incremental tensor during the isotropic consolidation of the geographic coordinate system of Equation 2 is transformed into an orthogonal coordinate system (X, Y, Z) by the following Equation 6.

As described above, theoretically, when [the rigidity of the x′y ′ plane <the rigidity of the z ′ plane], the plane x′y formed in the maximum principal strain direction 1 and the intermediate principal strain direction 2. 'Plane, minimum principal strain 3 direction = z' direction, maximum principal strain ε ₁ = intermediate principal strain ε ₂ , and in the case of [z ′ plane stiffness <x′y ′ plane stiffness], 2 directions and 3 It is predicted that the plane formed by the direction = x'y 'plane, 1 direction = z' direction, ε ₂ = minimum principal strain ε ₃ , but if ε ₁ ≠ ε ₂ ≠ ε ₃ As shown in FIG. 14, an anisotropic direction is set.

Next, the elastic parameter is determined based on the measured stress and strain (Step 3 and Step 4 in FIG. 11) (Step 6 in FIG. 11). The theoretical solution of the direct stress and the shear stress at the time of isotropic consolidation based on the elasticity theory is expressed by the following formula 7. As the strain tensor component, the value obtained by Equation 6 is used, and as Δσ _c , the value measured by the load cell in the loading axis direction (load meter 10) or the cell pressure gauge is used. D _ijkl , (i, j, k, l = 1, 2, 3) is a compliance tensor, and the components of the compliance tensor of the in-plane isotropic elastic body are (D ₁₁₁₁ , D ₁₁₂₂ , D _1133). , D ₃₃₃₃ , D ₂₃₂₃ ). The relationship between the compliance tensor component and the elastic parameter will be described later.

Similarly, the theoretical solution of the strain tensor component at the time of axial compression is expressed by Equation 8 below. The distortion at the time of axial compression is measured, the coordinate is converted into the EWSN system by the above-described equation 1, and then the value obtained by converting this into the orthogonal coordinate system by the above-described equation 6 is used. As Δσ _a , a value measured by a load cell (load meter 10) in the loading axis direction is used.

Next, the elastic constant is specified from the measured stress data using the least square method expressed by the following equation 9 (for example, Haruhisa Kawasaki, “Basics of Numerical Analysis by C & FORTRAN” (Kyoritsu Shuppan, 1993)).

k and A are coefficient matrices calculated by the aforementioned mathematical expressions 7 and 8, and are expressed by a measurement value matrix and ξ. C is a compliance matrix composed of compliance tensor components. k, A, and C are represented by the following expressions 10 and 11.

Based on the value of C obtained by Equation 9, the following equation 12 is used to determine the elastic parameter of the ground assuming an in-plane isotropic elastic body using the compliance tensor component.

[Method of identifying anisotropy using load measurement type cap mechanism]
The procedure for obtaining the deformation anisotropy of the ground assuming in-plane isotropic using the load measuring type cap mechanism 18 will be described below.

  Even when the load measuring type cap mechanism 18 is used, estimation of the above ξ and ζ by visual observation of the specimen S (Step 1), confirmation of the positional relationship between the geographic coordinate system and the specimen S, measurement of the strain gauge G, etc. Installation of devices (Step 2) is performed in the same manner as the procedure using the displacement measurement type cap mechanism 17. However, the strain gauge G may be installed on the specimen S so as to measure only the strain in the loading axis direction.

Next, isotropic consolidation (Step 3) and axial compression (Step 4) are performed in the same manner as the procedure using the displacement measurement type cap mechanism 17. Using the measured value of the stress during isotropic consolidation, the inclination (ξ, ζ) in the anisotropic direction from the geographic coordinate system shown in FIG. 10 is specified, and the coordinate axis is set (Step 5). The stress increment tensor Δσ ′ at the time of isotropic consolidation in the geographic coordinate system is expressed by the following Expression 13. Based on Δσ ′, the principal stress is obtained by the following equation (14). The axial pressure Δσ _a or the cell pressure Δσ _c is input as the increment of the direct stress (Δσ _S , Δσ _E , Δσ _V ), and the detected value of the two-way load cell 50 of the cap 7 is used as (Δσ _SV , Δσ _EV ). Is required. Note that Δσ _SE = 0MPa.

The value of (ξ, ζ) is obtained by using Equation 5 from the unit direction vector e equation (Equation 4) of the main stress. Since the process of setting the coordinate axes is as described above, the description thereof is omitted. In order to organize the test results to be described later, the stress increment tensor of the geographic coordinate system in Equation 13 is transformed into an orthogonal coordinate system (X, Y, Z) by Equation 15 below.

  Since the evaluations of the mathematical expressions 11, 12, and 13 are substantially the same as those described for the process using the load measurement type cap mechanism 18, the description thereof will be omitted.

Next, an elastic parameter is determined using the stress and strain values measured in Step 3 and Step 4 (Step 6). The theoretical solution of the direct stress and the shear stress at the time of isotropic consolidation determined by the elasticity theory is expressed by the following equation (16). As the stress tensor component, the value obtained by Equation 6 described above is used, and as the value of Δε _c , the value measured by the strain gauge axis displacement meter in the loading axis direction is used. D _ijkl , (i, j, k, l = 1, 2, 3) is a stiffness tensor, and the components of the stiffness tensor of the in-plane isotropic elastic body are (D ₁₁₁₁ , D ₁₁₂₂ , D ₁₁₃₃ , D ₃₃₃₃ , D ₂₃₂₃ ). The relationship between the stiffness tensor component and the elastic parameter will be described later.

Similarly, the theoretical solution at the time of triaxial loading is expressed by the following Expression 17. The stress at the time of triaxial loading is measured, converted into the Cartesian coordinate system by Equation 15 above, and substituted into Equation 17 below. For Δε _a , a value measured with a strain gauge in the loading axis direction is used.

In addition, the stress tensor at the time of triaxial loading in the EWSN type | system | group which performs coordinate transformation by Numerical formula 15 is obtained by the following formula. As in the case of isotropic pressure loading, (Δσ _SV , Δσ _EV ) is obtained from the detected value of the two-way load cell 50 in the cap 7.

Next, based on the measured stress data, the elastic parameter is specified by the least square method represented by the following Expression 16.

Note that k ′ and A ′ are based on the measurement value matrix calculated by Equations 16 and 17 above, the coefficient matrix composed of ξ, and D is the stiffness matrix composed of the stiffness tensor components, It is represented as the following formula 20.

Based on the following equation (21), the elastic parameter of the rock mass assuming an in-plane isotropic elastic body is determined based on the following equation (21) using D obtained by the above equation (19).

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the above-described embodiments, and various modifications or changes can be made within the scope of the present invention described in the claims. Is possible.

  For example, in the above embodiment, the configuration in which the displacement measurement type or load measurement type cap mechanism is arranged on the cap arranged on the upper part of the specimen has been described. 1 and 2, it can be arranged or incorporated in the pedestal 6 as a displacement measuring pedestal mechanism 17 'or a load measuring pedestal mechanism 18'. When these mechanisms 17 ′ and 18 ′ are arranged on the pedestal 6, for example, as shown as a pipe line 16 ′ in FIGS. A design change such as interposing a flexible pipe or a flexible joint (not shown) in the pipe line 16 'is appropriately adopted.

  In addition, the triaxial test apparatus provided with the displacement measurement type cap mechanism has been described as the first embodiment, and the triaxial test apparatus provided with the load measurement type cap mechanism has been described as the second embodiment. It is also possible to dispose both the displacement measurement type cap mechanism and the load measurement type cap mechanism obtained in the same triaxial test apparatus.

  Further, the displacement measuring type cap mechanism according to the above embodiment includes a bearing device including a rolling element (roller or ball) as a movable unit. You may use the support apparatus which has as a movable means.

  Moreover, in the said Example, although the loading test of the columnar specimen was demonstrated, you may apply this invention in the loading test of the specimen which has other cross-sectional forms, such as a prismatic specimen.

  In addition, the triaxial test apparatus includes a measurement apparatus such as a displacement measurement apparatus and a volume change measurement apparatus, and an external control apparatus or an external control system for recording measurement data. The apparatus configuration can be appropriately adopted.

  The present invention is preferably applied to a triaxial test apparatus and a triaxial test method for examining or specifying the deformation characteristics and strength characteristics of ground having mechanical anisotropy. Specifically, the test method and the test method of the present invention can be preferably used for ground investigation for construction of a ground structure or the like. Examples of ground structures include dams located on rocks, long bridges, foundations of large structures such as nuclear power plants, underground slopes located in rock slopes or rocks, and surrounding rocks such as mountain tunnels.

  According to the triaxial test apparatus and the triaxial test method of the present invention, the single axis or a small number of triaxial tests using columnar specimens collected from the ground made of soil, rock, etc. caused the anisotropy. Measure or measure the deformation and stress of the specimen, thereby identifying the anisotropy of the deformation characteristics of the ground material and the direction of the anisotropy without depending on visual observation. The practical value is remarkable.

1 Triaxial test equipment 2 Triaxial cell chamber (Triaxial pressure chamber)
3 Bottom plate 4 Pressure cylinder 5 Upper plate 6 Pedestal 7 Cap 7a Cap body 9 Loading shaft (loading rod)
10 Load cell (load cell)
17 Displacement measurement type cap mechanism 17 'Displacement measurement type pedestal mechanism 18 Load measurement type cap mechanism 18' Load measurement type pedestal mechanism 20, 30 First and second carriages 21, 32 First and second rails 23, 33 Roller type or Ball bearing device 50 Two-way load cell S Specimen Q Axial load W Cell water G Strain gauge

Claims (15)

A triaxial cell containing a columnar specimen collected from the ground is provided. The specimen in the triaxial cell constrained by a pedestal and a cap is subjected to an axial load by a loading shaft of a loading device, and the specimen is mounted. In a triaxial testing device that performs compaction and axial compression,
The cap has a displacement measurement type cap mechanism and / or a load measurement type cap mechanism interposed between the load shaft described above and a cap main body disposed on the top of the specimen,
The displacement measuring type cap mechanism has movable means for allowing lateral displacement or horizontal displacement of the cap body when an axial load is loaded,
The load-measuring cap mechanism prohibits or restrains lateral displacement or horizontal displacement of the cap body when the axial load is loaded, and acts on the cap by the axial load and the axial force direction of the axial load. A triaxial test apparatus comprising stress detection means for detecting a shear stress acting in an intersecting or orthogonal direction. A triaxial cell containing a columnar specimen collected from the ground is provided. The specimen in the triaxial cell constrained by a pedestal and a cap is subjected to an axial load by a loading shaft of a loading device, and the specimen is mounted. In a triaxial testing device that performs compaction and axial compression,
The pedestal has a displacement measurement type pedestal mechanism and / or a load measurement type pedestal mechanism,
The displacement measuring pedestal mechanism has movable means that allows lateral displacement or horizontal displacement of the pedestal body when an axial load is loaded,
The load measurement type pedestal mechanism prohibits or restrains a lateral displacement or a horizontal displacement of the pedestal body when the axial load is loaded, and acts on the pedestal by the axial load and an axial force direction of the axial load. A triaxial test apparatus comprising stress detection means for detecting a shear stress acting in an intersecting or orthogonal direction.   The displacement measurement type cap mechanism or the displacement measurement type pedestal mechanism includes a first member integrated with the load shaft or the bottom plate of the triaxial cell, a second member integrated with the cap body or the pedestal body, The triaxial testing apparatus according to claim 1, further comprising: a movable unit that is interposed between the first and second members and relatively displaces the first and second members.   The displacement measurement type cap mechanism or the displacement measurement type pedestal mechanism further includes a third member interposed between the first and second members, and the movable means includes the first member and the third member. The triaxial test apparatus according to claim 3, wherein the three-axis test apparatus is interposed between the second member and the third member.   The movable direction of the third member relative to the first member and the movable direction of the second member relative to the third member are separated from each other by a predetermined angular interval around the center axis of the load shaft, The triaxial testing apparatus according to claim 4, wherein the pedestal body is displaced in an arbitrary angular direction around the central axis.   The triaxial testing apparatus according to any one of claims 1 to 5, wherein the movable means comprises a roller type or ball type bearing device.   The triaxial testing apparatus according to any one of claims 1 to 6, further comprising a displacement detection unit that detects a lateral displacement or a horizontal displacement of the cap body that occurs when the axial load is loaded.   The triaxial test apparatus according to claim 1 or 2, wherein the load measurement type cap mechanism or the load measurement type pedestal mechanism has a two-way load cell.   The triaxial test apparatus according to claim 8, wherein the two-way load cell is a parallel plate type load cell. A columnar specimen collected from the ground is accommodated in a triaxial cell, restrained by a pedestal and a cap, and an axial load is applied to the specimen by a loading shaft of a loading device to compress and axially compress the specimen. In the axial test method,
A displacement measurement type cap mechanism or a load measurement type cap mechanism is interposed between the cap body and the loading shaft arranged at the top of the specimen,
The lateral displacement or horizontal displacement of the cap body is allowed by the displacement measuring type cap mechanism when the axial load is loaded, and the lateral displacement or horizontal displacement of the cap body with respect to the load shaft described above is detected, or the axial load is detected. A shear stress acting on the cap by the axial load and acting in a direction intersecting or orthogonal to the axial force direction of the axial load in a state where lateral displacement or horizontal displacement of the cap body is prohibited or restrained at the time of loading is applied to the load. A triaxial test method characterized by detecting by a measuring cap mechanism. A columnar specimen collected from the ground is accommodated in a triaxial cell, restrained by a pedestal and a cap, and an axial load is applied to the specimen by a loading shaft of a loading device to compress and axially compress the specimen. In the axial test method,
Displacement measurement type pedestal mechanism or load measurement type pedestal mechanism is installed in or built into the pedestal arranged at the bottom of the specimen,
When the axial load is loaded, the lateral displacement or horizontal displacement of the pedestal body is allowed by the displacement measurement type pedestal mechanism, and the lateral displacement or horizontal displacement of the pedestal body with respect to the load shaft described above is detected, or the loading of the axial load is performed. Measurement of the shear stress acting on the pedestal by the axial load and in the direction intersecting or orthogonal to the axial force direction of the axial load with the lateral or horizontal displacement of the pedestal body prohibited or constrained. A triaxial test method characterized by detecting by a pedestal mechanism.   The triaxial test method according to claim 10 or 11, wherein the anisotropy of the specimen is specified based on a displacement amount of the lateral displacement or horizontal displacement, or a stress value of the stress.   The triaxial test method according to any one of claims 10 to 12, wherein the cap body or the pedestal body is moved in at least two directions at an angular interval around the central axis of the load shaft.   The triaxial test method according to any one of claims 10 to 12, wherein a stress acting in at least two directions with an angular interval around the central axis of the load shaft is detected.   The triaxial test method according to claim 14, wherein the stress value of the stress is detected by a load cell that constitutes the load measurement type cap mechanism or the load measurement type pedestal mechanism.

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