JPH10206303A - Triaxial testing device and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a triaxial testing device which can find a deformation characteristic and a strength parameter of earth in a three-dimensional stress condition close to a stress condition applied to an earth element in an actual earth structure by controlling a triaxial directional stress condition and whose structure and test operation are simple. SOLUTION: A cubic specimen 10 is arranged in a triaxial cell TC, and one among two main stress directions orthogonal to its horizontal direction is set to the intermediate main stress direction, and a load by an intermediate main stress control system 30 is imparted. The other is also to the minimum main stress direction, and pressure by a cell liquid is imparted. The vertical direction is set to the maximum main stress direction, and a vertical load is imparted by a vertical compressive load device VL. A deformation characteristic and a strength parameter in a three-dimensional stress condition between a triaxial compressive stress condition, a plane strain compressive stress condition and a triaxial elongation stress condition close to a stress condition applied to an earth element in an actual earth structure, are found by controlling intermediate main stress by the intermediate main stress control system 30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intermediate principal stress control type for examining deformation characteristics and strength constant of soil in an arbitrary intermediate principal stress state between a triaxial compressive stress state and a triaxial elongation stress state. It relates to an axis test device.

[0002]

2. Description of the Related Art Conventionally, a triaxial compression test or a triaxial extension test using a solid cylindrical specimen has been generally used to examine the deformation characteristics and strength constant of a soil material.
In this triaxial compression test apparatus, a known liquid pressure was applied as a lateral pressure to the peripheral surface of a cylindrical specimen, and a pressure was applied in the axial direction as a main stress difference to compress the specimen, thereby causing the sample to shear and break. It measures the stress, strain, pore water pressure, volume change, etc. at that time.

[0003]

In the above-described triaxial compression test apparatus, the test is performed by applying uniform pressure to the peripheral surface of a cylindrical test specimen to cause shearing fracture in the axial direction. Deformation characteristics and strength constants required by the device are:
It is limited to a so-called axisymmetric stress state in which the specimen is in a uniform stress state over the entire peripheral surface.
In other words, since the deformation characteristics and strength characteristics of the soil material strongly depend on the stress state in which the soil element is placed, it is essential to perform the test under conditions as close as possible to the in-situ stress state, The above-described triaxial compression test apparatus often has a deviation from the stress state in which the soil element is actually placed.

On the other hand, for example, as shown in FIG.
Soil elements 10 in actual soil structures such as fill dams
In a stress state where 0 is applied, it is often possible to achieve idealization in a plane strain state where there is no displacement in the longitudinal direction. However, strictly speaking, it does not mean that there is no displacement in the longitudinal direction at all, and in the example of FIG. 13, an elongation displacement occurs, and this state corresponds to a stress state between the triaxial compression state and the plane strain compression state. And is in a three-dimensional stress state. However, at present,
Tests in stress conditions between triaxial compression and plane strain compression in which soil elements in actual soil structures as described above are undergoing have rarely been performed except for special research applications. This is because there is no test equipment other than special research applications that can control the intermediate principal stress, and the equipment used for special research applications has complicated structure and test operation, and the test cost is high, This is because it could not be used in general business.

In view of the above circumstances, the present invention provides a three-dimensional stress state between a triaxial compressive stress state and a plane strain compressive state close to a stress state received by an earth element in an actual earth structure. It is necessary to provide an intermediate principal stress control type triaxial testing device whose structure and test operation are simple so that the deformation characteristics and strength constant of the soil below can be obtained, and it can be easily applied to general use. Aim.

[0006]

In order to achieve the above-mentioned object, the present invention provides a method in which stresses in a first principal stress direction, a second principal stress direction, and a third principal stress direction, which are orthogonal to each other, are reduced. In a triaxial test apparatus for performing a test in addition to each side of a substantially rectangular parallelepiped specimen having three pairs of sides perpendicular to each other, a pressure chamber in which the specimen is disposed, A first compressive stress applying means including a pair of holding bodies for applying a compressive stress in a first principal stress direction to the specimen by transmitting a force generated by a loading means outside the chamber to the specimen; And a second compressive stress applying means including a pair of sandwiching members for applying a compressive stress in a second principal stress direction to the test specimen, and a pressure generated inside the pressure chamber, Third to be added to the specimen
Pressure generating means for obtaining a compressive stress in the main stress direction, wherein the second compressive stress applying means is provided with a stress control means for controlling the compressive stress in the second main stress direction. Features.

Further, according to the present invention, the stress control means may include a second
The magnitude of the compressive stress in the main stress direction can be controlled at least in a range between the magnitude of the compressive stress in the first principal stress direction and the magnitude of the compressive stress in the third principal stress direction. Further, the present invention is characterized in that the specimen has a substantially cubic shape. Further, in the present invention, one of the pair of holding members of the first compressive stress applying means is a cap movable in a first principal stress direction relative to the pressure chamber, and The other of the pair of holding bodies of the means is a pedestal fixed relative to the pressure chamber, and the specimen has one end fixed to the cap and the other end fixed to the pedestal. It is a soil material enclosed in a flexible sleeve.

Further, in the present invention, the second compressive stress applying means further includes a caliper bracket supported by the pressure chamber in a floating state, and one of the pair of holding members of the second compressive stress applying means is provided. A pressure plate attached to the caliper bracket via a piston-cylinder mechanism so as to be movable in a second principal stress direction, and a pressing plate abutting on the flexible sleeve of the specimen. The other of the pair of holding members is formed of a reaction plate substantially fixed to the caliper bracket opposite to the pressing plate and abutting on the flexible sleeve of the test sample, and the second compressive stress applying means is provided. Further, it is characterized by having pressure control means for controlling the pressure supplied to the piston / cylinder mechanism. Also, in the present invention, one of the pair of holding members of the second compressive stress applying means is formed of a pressing plate supported by the pressure chamber in a floating state and abutting on the flexible sleeve of the specimen, (2) The other of the pair of holding members of the compressive stress applying means comprises a reaction plate which is supported by the pressure chamber in a floating state opposite to the pressing plate and abuts on the flexible sleeve, An applying means further comprising: a piston / cylinder mechanism fixed to the pressure chamber;
A connection mechanism for connecting the piston / cylinder mechanism and the pressing plate so as to allow movement in the main stress direction, and pressure control means for controlling a pressure supplied to the piston / cylinder mechanism; The compressive stress applying means further connects the position adjusting mechanism fixed to the pressure chamber with the position adjusting mechanism and the reaction force plate so as to allow the reaction force plate to move in the first principal stress direction. A connection mechanism that enables the position adjusting mechanism to determine the position of the reaction force plate in the second principal stress direction.

Further, according to the present invention, the cap and the pedestal may have an end facing the specimen formed in a rectangular shape corresponding to the shape of the specimen to form a specimen pressing portion, and Are formed in a circular cross section to form a sleeve fixing portion for fixing the flexible sleeve. Further, the present invention is characterized in that a rectangular plate for reducing friction is interposed between each of the cap and the pedestal and the specimen. The present invention also relates to the second aspect,
A lubricant is applied to a contact surface between each of the pair of holding members of the compressive stress applying means and the flexible sleeve. The present invention also provides a pore water discharging means for discharging pore water of the soil material sealed in the flexible sleeve to the outside of the pressure chamber, and an amount of pore water flowing in and out through the pore water discharging means. Measuring means for measuring the volume change of the specimen based on

Further, the present invention is characterized in that it comprises a measuring means for measuring a load of the specimen in a first principal stress direction and a measuring means for measuring a load of the specimen in a second principal stress direction. . Further, the invention is characterized in that it comprises a measuring means for measuring a deformation amount of the specimen in a first principal stress direction and a measuring means for measuring a deformation amount of the specimen in a second principal stress direction. Further, in the present invention, the stresses in the first principal stress direction, the second principal stress direction, and the third principal stress direction, which are orthogonal to each other, are substantially formed by three pairs of side surfaces perpendicular to each of the three principal stress directions. In a triaxial test method for performing a test in addition to each side surface of a rectangular parallelepiped specimen, the specimen is disposed inside a pressure chamber, and a force generated by a loading unit outside the pressure chamber is
By transmitting to the specimen through the first compressive stress applying means including a pair of clamping bodies, a compressive stress in a second principal stress direction is applied to the specimen, and the first specimen includes a pair of clamping bodies. 2 A second compressive stress is applied to the specimen by
A compressive stress in a main stress direction is applied to generate a pressure inside the pressure chamber, and a first main pressure of the specimen is determined by a compressive stress applied to the specimen from the first compressive stress applying means and the pressure in the pressure chamber. The compressive stress in the second main pressure direction of the specimen is determined by the compressive stress applied to the specimen from the second compressive stress applying means and the pressure in the pressure chamber. By determining the compressive stress in the third principal stress direction of the specimen by the above, and controlling the compressive stress applied to the specimen from the second compressive stress applying means, the compression state of the specimen is reduced to three. The test is performed as an arbitrary compression state between the axial compression state and the triaxial extension state, including the plane strain compression state.

According to the triaxial test apparatus or the triaxial test method according to the present invention, a substantially rectangular parallelepiped specimen is used, and the first principal stress direction and the second principal stress direction of the specimen are orthogonal to each other. And the relationship between the respective compressive stresses in the third principal stress direction can be arbitrarily set, so that the triaxial compressive stress state and the plane strain close to the stress state received by the soil element in the actual soil structure The deformation characteristics and strength constant of the soil under the three-dimensional stress state between the compression stress state and the triaxial extension stress state can be easily obtained. In addition, the test can be performed by a structure and a procedure similar to those of the conventional triaxial compression test apparatus, so that the structure and the test operation are simple and easily applicable to general use.

[0012]

Next, an embodiment of a triaxial test apparatus according to the present invention will be described. FIG. 1 is a front sectional view showing an overall configuration example of a three-axis test apparatus according to the present invention. This triaxial test apparatus arranges a triaxial cell (pressure chamber) TC for storing cell water inside a loading frame LF and applies a vertical load to a specimen 10 installed in the triaxial cell TC. It is provided with a loading device VL. The vertical load loading device VL is composed of a screw jack or a cylinder, etc., and the main body VLa of the device is loaded with a loading frame LF.
It is provided on the upper part. Further, the rod portion VLb suspended from the main body portion VLa is inserted into the insertion hole L of the loading frame LF.
The loading shaft 12 is connected to the distal end of the loading shaft 12. A displacement gauge 16 is provided between the flange portion 12a provided at the upper end of the loading shaft 12 and the loading frame LF, and measures the deformation of the specimen 10 in the vertical direction. Also, the loading shaft 12
It is suspended in the triaxial cell TC through a bearing 18 provided on the upper surface of the triaxial cell TC.

In the triaxial cell TC, a rectangular plate 22A is connected to the loading shaft 12 and
And a pedestal 24 arranged on the lower surface of the specimen 10 via a rectangular plate 22B,
An intermediate principal stress control system 30 for controlling an intermediate principal stress in the horizontal direction of the specimen 10;
0, and a load cell 14 which is mounted on a connection between the loading shaft 12 and the cap 20 and measures a vertical load. In addition, triaxial cell TC
Around the cell pressure (σ) on the specimen 10 in the triaxial cell TC.
₀ ), a Bourdon gauge 50 for measuring cell pressure, a control circuit 60 for controlling drainage conditions in the specimen 10, and a volume change measuring system 70 for the specimen 10. And a pressure transducer 80 for measuring the excess pore water pressure in the specimen 10. Hereinafter, the configuration of each unit will be sequentially described in detail.

FIG. 2 is a perspective view showing an example of the test specimen 10 used in this triaxial test apparatus. As shown in the figure, the specimen 10 has a rectangular shape and a substantially cubic shape having three sides of length (L), width (W), and height (H) substantially equal. I do. This is to make the shape convenient for controlling the intermediate principal stress as described above. The specimen 10 is a soil material surrounded by a flexible sleeve such as a rubber sleeve 2 described later, and is disposed in the triaxial cell TC. In this example, the stress σ _{1 in} the height H direction (first principal stress direction) of the specimen 10 shown in FIG.
The maximum principal stress with respect to the load by the vertical load loading device VL, the stress σ _{2 in} the length L direction (second principal stress direction) is the intermediate principal stress with respect to the load applied by the intermediate principal stress control system 30, and the width is The stress σ _{3 in the} W direction (third principal stress direction) is the minimum principal stress with respect to the cell pressure. These three principal stress directions are orthogonal to each other.

Next, FIGS. 3A and 3B are a front view and a bottom view showing the structure of the cap 20. FIG. FIGS. 4A and 4B are a top view and a front view showing the structure of the pedestal 24, respectively. Further, FIG.
FIG. 6 is a cross-sectional view showing an assembled state of the test piece 10, the cap 20, and the pedestal 24. FIG.
It is sectional drawing which shows the assembly state of the intermediate | middle principal stress control system 30 to 0. This cap 20 and pedestal 24
Are arranged on the upper and lower surfaces of the specimen 10 via the rectangular plates 22A and 22B as described above. Rectangular plate 22A,
22B is a porous plate as a filter layer or a device for reducing friction, for example, a device in which grease is applied to an acrylic plate and a thin rubber sheet is attached.

The cap 20 and the pedestal 24
The end surface of the side in contact with the specimen 10 is formed as square cross sections 20A and 24A corresponding to the surface shape of the specimen 10. However, the length of one side (L ′ × W ′) is slightly smaller than the length of one side (L × W) of the specimen 10 (L> L ′, W> W ′). This is to prevent the specimen 10 from becoming smaller than the cross section of the cap 20 and the pedestal 24 due to a volume change during the consolidation process. When the rubber sleeve 2 is used, the portion of the cap 20 and the pedestal 24 on the opposite side of the specimen 10 is connected to the O-ring 4 as shown in FIG.
A, 4B and the like have circular cross sections 20B and 24B so as to be easily fixed in a sealed state. In this example,
Although the case where a thin cylindrical rubber sleeve 2 that is widely used is used is shown, a rectangular cylindrical rubber sleeve may be used. The cap 20 and the pedestal 24 are formed with drain holes 20a and 24a for draining pore water in the specimen (soil material) 10, and the drain holes 20a and 24a are formed as shown in FIG. Connection pipe 6
A, 6B is connected to the drainage condition control circuit 60,
Further, it is connected to a volume change measuring system 70 and a pressure transducer 80 of the specimen 10.

The control circuit 60 controls the valve, etc.
The volume change measuring system 70 controls the water flow rate of the burette 72 indicating the amount of water flowing in and out of the test specimen under test by the differential pressure gauge 74. The pressure transducer 80 measures the excess pore water pressure in the specimen 10 (non-draining condition). Also, cocks 82 and 84 for opening and closing such a drainage path are provided. The cell pressure load device 40 shown in FIG. 1 controls the air pressure (σ ₀ ) from a pressure source HP such as a compressor to a predetermined value by a pressure adjustment regulator 42 and applies the air pressure (σ ₀ ) to a triaxial cell TC. Cell T
Specimen 1 converted to water pressure by cell water stored in C
It is added to 0. The cell pressure (σ ₀ ) of the cell pressure load device 40 is measured by a Bourdon gauge 50.

7 and 8 are views showing an intermediate principal stress control system 30. FIG. 7 (1) is a front sectional view,
7 (2) is a left side view, FIG. 7 (3) is a right side view, and FIG. 7 (4) is a cross-sectional view taken along line-in FIG. 7 (4). FIG. 8 is a cross-sectional plan view of FIG. The intermediate principal stress control system 30 controls the stress in the length L direction of the specimen 10, that is, the stress in the intermediate principal stress direction. In FIG. 7, the pressing body unit 300 is disposed on the left side of the specimen 10. , A reaction force unit 330 disposed on the right side. Then, the intermediate main stress is controlled by controlling the load applied to the pressing body unit 300 by a piston mechanism described later by the pressure control device 360 shown in FIG.

The pressing body unit 300 includes a base member 302 disposed opposite to the side surface of the specimen 10, a piston mechanism 304 incorporated in the base member 302, and supported by the piston mechanism 304. Press plate 30 abutting on the side surface of specimen 10 through
6. The base member 302 has a cylinder portion 308 that is open on the side facing the specimen 10.
The piston head 310 of the cylinder mechanism 304 is slidably fitted. On the opposite side of the base member 302 from the specimen 10, there is provided a bearing 314 into which a piston rod 312 connected to the piston head 310 is slidably fitted. The inner wall of the base member 302 and the piston head 310 and the piston rod 31
2 is sealed with an O-ring or the like. Then, inside the cylinder portion 308 of such a base member 302, through the supply passage 316, the pressure P _A by the pressure controller 360 are supplied. Further, the pressing plate 306 is fixed to the tip of the piston head 310. Specimen 10 of this pressing plate 306
Is formed flat and has a size to completely cover one side surface of the test sample 10.

Further, the pressure control device 360, as shown in FIG. 1, is converted to water pressure P _A of the air pressure controlled by a precision regulator 362 in the pressure tank WT, were supplied to a cylinder unit 308 described above, the piston head It controls the pressure on 310. In addition, instead of converting the air pressure to the water pressure and supplying the same to the cylinder unit 308 as in the present example, the configuration may be such that the air pressure is supplied as it is,
Instead of the hydraulic tank WT, a hydraulic tank may be provided to supply hydraulic pressure. Also, the reaction force unit 33
Reference numeral 0 denotes a base member 3 which is arranged to face the side surface of the test piece 10.
32, and a reaction plate 334 supported by the base member 332 and abutting on the side surface of the specimen 10 via the rubber sleeve 2 described above. Further, between the base member 332 and the reaction plate 334, a load cell 336 for measuring a load in an intermediate principal stress direction is provided.

The base members 302 and 332 of the pressing body unit 300 and the reaction force body unit 330 are
The caliper bracket is connected by four horizontal connecting rods 320, and is thereby supported in a floating state by the pressure chamber. That is, the connecting rod 32
Numeral 0 is installed between the corners of the base members 302 and 332, and as shown in FIG.
An insertion hole 332a whose end on the 0 side is provided in the base member 332
, The end on the pressing body unit 300 side penetrates an insertion hole provided in the base member 302, and a nut 322 is screwed into a screw portion formed at the penetrating end. Therefore, by tightening and adjusting the nut 322,
The distance between the base members 302 and 332 can be adjusted. In addition, the pressing plate 306 and the reaction force plate 334 include:
Extension portions 306a, 334a respectively extended upward
A displacement gauge 340 is installed in the horizontal direction so that a change in the interval between the pressing plate 306 and the reaction force plate 334 can be measured.

The base members 302 and 332 of the pressing body unit 300 and the reaction body unit 330 are supported by the floating system 90 provided on the bottom plate 44 of the triaxial cell TC so as to be movable in the vertical direction. Have been. This floating system 90 has four spring rods 92 arranged on the upper surface of the bottom plate portion 44 of the triaxial cell TC, and a compression coil spring 94 mounted on the outer periphery of these spring rods 92. On the other hand, each base member 302, 3
As shown in FIG. 7 (4), a pair of vertical mounting holes 370 are formed on the lower surface of each of the holes 32, and a spring rod 92 is fitted into a linear motion bearing 96 provided in each of the mounting holes 370. ing. Further, the compression coil spring 94 includes a flange portion 92 provided on the lower surface of each of the base members 302 and 332 and the base end of the spring rod 92.
a.

Further, as shown in FIG.
Are the specimen 10, the rectangular plates 22A and 22B, the cap 20
And the O-ring 4A, which is attached so as to surround the square cross-sections 20A and 24A of the pedestal 24, and the cap 20 and the circular cross-sections 20B and 24B of the pedestal 24.
4B, and surrounds the specimen 10 in a sealed state. A lubricant such as grease is applied to a contact surface between the pressing plate 306 and the reaction plate 334 and the rubber sleeve 2 and a contact portion between the rubber sleeve 2 and the specimen 10 so that the specimen 10 is displaced. When trying to reduce the frictional resistance.

Next, a description will be given of a test procedure performed by the three-axis test apparatus having the above configuration. First, a cubic specimen 10 of an earth sample to be tested is prepared. in this case,
The preparation of the test specimen differs depending on the sandy soil, the cohesive soil, or the case where the specimen is collected in an undisturbed state from the original position.
C, and is surrounded by the rubber sleeve 2, and the cap 20 and the circular cross sections 20B and 24B of the pedestal 24 are O
It is fixed by rings 4A and 4B. And the specimen 10
Then, a predetermined negative pressure (σ _NE <0) is applied to the inside to advance to a self-standing state (FIG. 5).

Next, the dimensions of the specimen 10 are measured, and a lubricant such as grease for removing friction from the rubber sleeve 2 is applied to both surfaces (H × W surfaces) on which the intermediate principal stress σ ₂ acts. , And the pressing unit 300 and the reaction unit 330 of the intermediate principal stress control system 30 are installed (FIG. 6). In this case, the test piece 10 is installed with some clearance between the pressing plate 306 and the reaction force plate 334 and the test piece 10. Next, a cell cylinder is installed, and after pouring cell water into the triaxial cell TC to a predetermined water level, the triaxial cell TC is assembled, and the negative pressure (σ _NE ) applied to the specimen 10 and the cell pressure are set. (Σ ₀ ) and (σ ₀ = | σ _NE |). Next, the triaxial cell TC is installed on the loading frame LF (FIG. 1). And specimen 1
After consolidating 0 to a predetermined consolidation pressure level, that is, a consolidation pressure level corresponding to the stress state at the original position, a vertical load (maximum main stress) is applied to the specimen 10 by the loading frame LF and sheared.

At this time, the cell pressure, which is the minimum principal stress (σ ₃ ), is kept constant and a load in the direction of the intermediate principal stress (σ ₂ ) is applied, so that the intermediate principal stress (σ ₂ ) and the maximum principal stress (σ ₁₎ )
Is controlled so that the intermediate stress coefficient b = (σ ₂ −σ ₃ ) / (σ ₁ −σ ₃ ), which indicates the relative magnitude with respect to the above, becomes a predetermined value. Specifically, the measured value of the vertical load applied to the specimen 10 by the load cell 14 is P _H = (σ ₁ −σ ₃ ) × L × W. Then, since the load in the direction of the intermediate principal stress is P _L = (σ ₂ −σ ₃ ) × H × W, considering that the specimen 10 is a cube (L = W = H), b = (Σ ₂ −σ ₃ ) / (σ ₁ −σ ₃ ) = P _L / P _H Therefore, the load in the direction of the intermediate principal stress is controlled by the intermediate principal stress control system 30 so that P _L = b × P _H with respect to the vertical load.

The magnitude of the intermediate principal stress ranges from a triaxial compression state (b = 0, σ ₂ −σ ₃ ) to a plane strain compression state (σ ₁ > σ ₂ > σ ₃ ) to a triaxial expansion state ( b = 1.0, σ
_Although control is performed within the range of ₁ = σ ₂ ), the deformation of the specimen in the direction of the intermediate principal stress changes in the direction from elongation deformation to compression deformation depending on the magnitude of the intermediate principal stress. That is, as shown in FIGS. 9 (1) and (2), when the intermediate principal stress is between the triaxial compression state and the plane strain compression state, the specimen undergoes elongation deformation (ε ₂ ≦ 0). The height H ′ of the surface of the pressing plate 306 and the reaction force plate 334 in contact with the test piece 10 may be larger than the height H of the test piece 10 (H <H ′, FIG. 9A). Conversely, when the intermediate principal stress is between the plane strain compression state and the triaxial extension state, the specimen 10 undergoes compressive deformation (ε ₂ ≧ 0), and thus the specimen 10 of the pressing plate 306 and the reaction force plate 334. Is smaller than the height H of the specimen 10 (H>
H ′, FIG. 9 (2)), when the specimen 10 is compressed in the height direction and deformed as shown by δH shown in FIG.
6, reaction plate 334, cap 20, and pedestal 24
Need to avoid collisions.

Further, the vertical load during the shearing, the vertical displacement, the load and the displacement in the direction of the intermediate principal stress, the volume change (drainage condition) or the excess pore water pressure (non-drainage condition) are measured and recorded. The specimen 10 being sheared is compressed and displaced in the vertical direction, and between the pressing plate 306 and the reaction force plate 334 and the specimen 10,
Although friction occurs due to the relative displacement, the pressure plate and the reaction plate are also displaced by the floating system 90 of the intermediate principal stress control system 30, so that the influence of the friction can be reduced. In accordance with the same procedure as above, at least two specimens with different consolidation pressure levels were tested, and the deformation characteristics (stress-strain relationship) at each consolidation pressure level and the test soil in the range of the consolidation pressure at which the test was performed were performed. Find the strength constant.

The following effects can be obtained in the three-axis test apparatus of the present embodiment as described above. (1) By providing the above-described intermediate principal stress control system 30, the intermediate principal stress (σ ₂ ) of the three principal stresses (σ ₁ , σ ₂ , σ ₃ ) acting on the cubic test piece 10 is obtained. From the triaxial compression state (b = 0, σ ₂ = σ ₃ ) to the plane strain compression state (σ ₁ > σ ₂ > σ ₃ ) to the triaxial expansion state (b = 1.0, σ ₁ = Control within the range of σ ₂ ) enables a test in a three-dimensional stress state taking into account the influence of the intermediate principal stress. (2) The structure and operation of the test apparatus are simple, and a test in a three-dimensional stress state in consideration of the influence of inexpensive intermediate principal stress is possible. (3) If the intermediate principal stress is controlled in accordance with the stress state applied to the soil element in the actual soil structure, the deformation characteristics and strength of the soil material in a three-dimensional stress state closer to the in-situ stress state Constants can be obtained. (4) Therefore, it is possible to perform more rational behavior prediction calculation and design calculation of the earth structure.

In the above example, the piston / cylinder mechanism 304 of the intermediate principal stress control system 30 is disposed inside the triaxial cell TC.
The structure in which these units 300 and 330 are completely accommodated in the triaxial cell TC by positioning the reaction force unit 330 with the connecting rod 320 has been described. However, the piston mechanism and the positioning mechanism of each unit 300 and 330 are described. It may be provided outside the triaxial cell TC. FIG. 10 is a cross-sectional view showing an example of a configuration in a case where such an intermediate main stress control system 30 ′ of the extra-cell type is provided. In this intermediate main stress control system 30 ', instead of the piston / cylinder mechanism 304 incorporated inside the pressing body unit 300 described above, a piston / cylinder mechanism 404 provided outside the triaxial cell TC provides an intermediate main stress direction. Is applied. Further, instead of the connecting rod 320 described above, the pressing body unit 300
And the reaction force unit 330 are adjusted and positioned from outside the triaxial cell TC.

First, the pressing body unit 400 of this embodiment has a pressing plate 402 formed to be slightly thick.
02 on the back of linear motion guide bearing 406
The horizontal shaft 408 is connected via the. Also,
A bearing portion 410 that supports the horizontal shaft 408 is provided on the outer peripheral wall of the triaxial cell TC.
10, a horizontal shaft 408 projects outside the triaxial cell TC. Note that a sealing such as an O-ring is interposed between the bearing 410 and the horizontal shaft 408. A mounting member 412 is provided outside the bearing 410, and a pneumatic cylinder 416 is provided via a plurality of support rods 414 horizontally supported by the mounting member 412. Specifically, the tip of the support rod 414 is inserted into a mounting hole formed in a flange 416A provided on the front end surface of the pneumatic cylinder 416,
By screwing a fixing nut 418 into a thread provided at the tip of the support rod 414, the pneumatic cylinder 416 is
Are mounted so as to be adjustable in the direction of the intermediate principal stress.

In the middle of the horizontal shaft 408,
Stopper 4 for regulating the position of horizontal shaft 408
20 are provided. The piston rod 422 of the pneumatic cylinder 416 of the piston-cylinder mechanism 404 is connected to the end of the horizontal shaft 408 on the protruding side. Then, by supplying compressed air from a pressure control device (not shown) into the pneumatic cylinder 416, the load in the intermediate principal stress direction is controlled. That is, in the example of FIG. 1 described above, the air pressure controlled by the regulator is converted into the water pressure and supplied, but in this example, the air pressure is supplied as it is to control the load in the direction of the intermediate principal stress. is there. A vertical detecting piece 428 is provided at the protruding end of the horizontal shaft 408. The detecting piece 428 is provided with a displacement meter 426 for measuring the displacement in the direction of the intermediate principal stress. The displacement of the specimen 10 in the direction of the intermediate principal stress is measured by the displacement meter 426.

On the other hand, the reaction force unit 430 of this embodiment has a base member 432, a reaction force plate 444, and a load cell 446 having the same structure as the reaction force unit 330 described above. Instead, the positioning is performed by a mechanism that can be adjusted from the outside of the triaxial cell TC. That is, the reaction force unit 43
A horizontal shaft 438 is connected to the rear surface of the base member 432 via a linear motion guide bearing 436. A bearing 440 that supports the horizontal shaft 438 is provided on the outer peripheral wall of the triaxial cell TC, and the horizontal shaft 4 extends through the bearing 440.
38 project outside the triaxial cell TC. A sealing such as an O-ring is interposed between the bearing 440 and the horizontal shaft 438. Further, a stopper 442 for regulating the position of the horizontal shaft 438 is provided at an end of the horizontal shaft 438 on the protruding side.

In the example shown in FIG. 1, each of the base members 30 of the pressing unit 300 and the reaction unit 330
2 and 332 are supported by the floating system 90. In this example, the reaction member unit 430 includes the base member 4
32 are supported by a similarly configured floating system 90. Further, since the pressing body unit 400 does not have the base member, the pressing plate 402 is supported by the floating system 90 having the same configuration. However, since the function of the floating system 90 is the same as that of the above-described example, the description will be omitted. In addition, other configurations are the same as those in the example of FIG. 1 described above, and thus, the same reference numerals are given and the description is omitted.

In the above configuration, when the intermediate principal stress is not controlled, the pressing plate 402 of the pressing body unit 400 is not controlled.
And the reaction force plate 444 of the reaction force unit 430 and the specimen 1
However, when the intermediate principal stress is applied to the specimen 10, the gap between the pressing plate 402 and the reaction force plate 444 is generated by the displacement of the horizontal shafts 408 and 438 from the outside of the triaxial cell TC. Is adjusted so that there is no gap with the specimen 10. Then, only the horizontal shaft 438 on the reaction force unit 430 side is fixed to the triaxial cell TC by the stopper 442. In this state, a test in a three-dimensional stress state in which the intermediate principal stress is controlled is performed by the same procedure as in the above-described example.

In the example shown in FIG. 1, the cell pressure (σ ₀ ) by the cell pressure load device 40 is measured by the Bourdon gauge 50. Instead, as shown in FIG. You may make it measure by PT. Further, in the example shown in FIG. 1, the load cell 14 for measuring the vertical load by the vertical load loading device VL is provided at the connecting portion between the loading shaft 12 and the cap 20, but instead, as shown in FIG. A load cell 14 ′ may be provided at a connecting portion between the rod portion VL 2 of the load loading device VL and the loading shaft 12.

[0037]

As described above, according to the triaxial test apparatus or the triaxial test method according to the present invention, a substantially rectangular parallelepiped specimen is used, and the first specimens which are orthogonal to each other are used.
Since the relationship between the respective compressive stresses in the principal stress direction, the second principal stress direction, and the third principal stress direction can be set arbitrarily, the stress state received by the soil element in the actual soil structure is reduced. The deformation characteristics and strength constant of the soil under the three-dimensional stress state between the near triaxial compressive stress state, the plane strain compressive stress state, and the triaxial elongation stress state can be easily obtained. Further, with a simple configuration and procedure, a triaxial test in consideration of an intermediate principal stress can be performed, and an inexpensive and simple triaxial test can be realized. Accordingly, it is possible to easily perform more rational behavior prediction calculation and design calculation of the earth structure.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration example of a triaxial test apparatus according to the present invention.

FIG. 2 is a perspective view showing an example of a test piece used in the triaxial test apparatus shown in FIG.

3 is a front view and a bottom view showing a structure of a cap in the triaxial test apparatus shown in FIG.

4 is a top view and a front view showing a structure of a pedestal in the triaxial test apparatus shown in FIG.

5 is a cross-sectional view showing an assembled state of a test piece, a cap, and a pedestal in the triaxial test apparatus shown in FIG.

FIG. 6 is a cross-sectional view showing a state where the pressing body unit and the reaction force body unit of the intermediate principal stress control system are assembled to the test specimen in the triaxial test apparatus shown in FIG.

FIG. 7 is a front view, a side view, and a cross-sectional view of a main part showing an intermediate principal stress control system in the triaxial test apparatus shown in FIG.

FIG. 8 is a sectional view taken along line − in FIG. 7;

9 is a front view of an essential part for explaining an arrangement of a pressing body unit of the intermediate principal stress control system in the triaxial test apparatus shown in FIG.

10 is a cross-sectional view showing another example of the intermediate principal stress control system in the triaxial test device shown in FIG.

11 is a front view showing another example of the cell pressure measuring device in the triaxial test device shown in FIG.

FIG. 12 is a front view showing another example of the vertical load measuring device in the triaxial test device shown in FIG.

FIG. 13 is an explanatory diagram illustrating a stress state applied to a soil element in an earth structure.

[Description of Signs] LF Loading Frame TC Triaxial Cell (Pressure Chamber) VL Vertical Load Loading Device 2 Rubber Sleeve 10 Specimen 12 Loading Shaft 14, 14 ', 336, 446 Load Cell, 20 Cap 24 Vedestal 30, 30' Stress control system 40 Cell pressure load device 50 Bourdon gauge 60 Drainage condition control circuit 70 Volume change measurement system 90 Floating system 300, 400 Press body unit 302, 332, 432 Base member 304, 404 Piston mechanism 306, 402 Press plate 320 Connecting rod 330, 430 reaction force unit 334, 444 reaction force plate 360 pressure control device

Claims (13)

[Claims] 1. A method according to claim 1, wherein the stresses in the first principal stress direction, the second principal stress direction, and the third principal stress direction, which are perpendicular to each other, are substantially equal to three pairs of side surfaces perpendicular to each of the three principal stress directions. In a three-axis test apparatus for performing a test in addition to each side surface of a rectangular parallelepiped specimen, a pressure chamber in which the specimen is disposed, and a force generated by a loading unit outside the pressure chamber are applied to the specimen. First compressive stress applying means including a pair of holding members for applying a compressive stress in a first principal stress direction to the specimen by transmitting the compressive stress to the specimen; A second compressive stress applying means including a pair of holding bodies for applying pressure, and generating a pressure inside the pressure chamber, and applying the pressure to the third main stress direction applied to the test piece. Pressure generating means for performing Compressive stress applying means, are equipped with stress control means for controlling the compressive stress of the second principal stress direction, triaxial test apparatus characterized by. 2. The stress control means according to claim 1, wherein the magnitude of the compressive stress in the second principal stress direction is in a range between at least the magnitude of the compressive stress in the first principal stress direction and the magnitude of the compressive stress in the third principal stress direction. The three-axis test apparatus according to claim 1, wherein the apparatus can be controlled by: 3. The three-axis test apparatus according to claim 1, wherein the specimen has a substantially cubic shape. 4. One of said pair of holding members of said first compressive stress applying means is a cap which is movable in a first principal stress direction relative to said pressure chamber, and said first compressive stress applying means is a cap. The other of the pair of holding bodies of the means is a pedestal fixed relative to the pressure chamber, and the specimen has one end fixed to the cap and the other end fixed to the pedestal. The triaxial test apparatus according to any one of claims 1 to 3, wherein the apparatus is a soil material sealed in a flexible sleeve. 5. The second compressive stress applying means further includes a caliper bracket which is supported by the pressure chamber in a floating state, and one of the pair of holding members of the second compressive stress applying means is a piston. A pressure plate attached to the caliper bracket via a cylinder mechanism so as to be movable in a second principal stress direction, and configured to abut on the flexible sleeve of the specimen; The other of the bodies comprises a reaction force plate substantially fixed to the caliper bracket opposite to the pressing plate and abutting against the flexible sleeve of the test sample, and the second compressive stress applying means further comprises: 5. The three-axis test apparatus according to claim 4, further comprising pressure control means for controlling a pressure supplied to the piston / cylinder mechanism. 6. One of said pair of holding members of said second compressive stress applying means comprises a pressing plate which is supported by said pressure chamber in a floating state and abuts on said flexible sleeve of said specimen. (2) The other of the pair of holding members of the compressive stress applying means comprises a reaction plate which is supported by the pressure chamber in a floating state facing the pressing plate and abuts on the flexible sleeve,
The second compressive stress applying means further includes a piston / cylinder mechanism fixed to the pressure chamber, and the piston / cylinder mechanism and the pressing plate so as to allow the pressing plate to move in a first principal stress direction. A coupling mechanism for coupling, and pressure control means for controlling a pressure supplied to the piston / cylinder mechanism, wherein the second compressive stress applying means further comprises a position adjusting mechanism fixed to the pressure chamber; The position adjusting mechanism and the reaction force plate are connected so as to allow movement of the force plate in the first principal stress direction, and the position of the reaction force plate in the second principal stress direction can be determined by the position adjustment mechanism. The three-axis test apparatus according to claim 4, further comprising a connection mechanism configured to perform the operation. 7. An end of the cap and the pedestal facing the specimen is formed in a rectangular shape corresponding to the shape of the specimen to form a specimen pressing portion, and an intermediate portion has a circular cross section. The triaxial test apparatus according to any one of claims 4 to 6, wherein the three-axis test apparatus is formed as a sleeve fixing portion for fixing the flexible sleeve. 8. A three-axis test apparatus according to claim 7, wherein a rectangular plate for reducing friction is interposed between each of said cap and said pedestal and said specimen. 9. A sliding agent is applied to a contact surface between each of the pair of holding members of the second compressive stress applying means and the flexible sleeve. 3. The three-axis test apparatus according to claim 1. 10. A pore water discharge means for discharging pore water of a soil material enclosed in the flexible sleeve to the outside of the pressure chamber, and an amount of pore water flowing in and out via the pore water discharge means. 10. The three-axis test apparatus according to claim 4, further comprising: a measuring unit configured to measure a volume change amount of the specimen based on the measurement. 11. The apparatus according to claim 1, further comprising: measuring means for measuring a load of the specimen in a first principal stress direction; and measuring means for measuring a load of the specimen in a second principal stress direction. The three-axis test apparatus according to any one of claims 10 to 10. 12. The apparatus according to claim 1, further comprising measuring means for measuring an amount of deformation of said specimen in a first principal stress direction and measuring means for measuring an amount of deformation of said specimen in a second principal stress direction. Item 12. The three-axis test apparatus according to any one of Items 1 to 11. 13. A first principal stress direction orthogonal to a second direction,
The stress in the principal stress direction and the third principal stress direction is applied to each side of a substantially rectangular parallelepiped specimen having three pairs of sides perpendicular to each of the three principal stress directions. In the axial test method, the test piece is disposed inside a pressure chamber, and a force generated by a loading means outside the pressure chamber is applied to the test piece via a first compressive stress applying means including a pair of holding bodies. By transmitting the test piece to the test piece, a compressive stress in the first main stress direction is applied to the test piece, and the test piece is compressed in the second main stress direction by a second compressive stress applying means including a pair of holding members. A stress is generated, a pressure is generated inside the pressure chamber, and the compressive stress applied to the specimen from the first compressive stress applying means and the pressure in the pressure chamber reduce the compressive stress in the first main pressure direction of the specimen. Determined, and the second compressive stress applying means The compression stress in the second main pressure direction of the specimen is determined by the compression stress applied to the specimen and the pressure in the pressure chamber, and the compression stress in the third principal stress direction of the specimen is determined by the pressure in the pressure chamber. By controlling the compressive stress applied to the specimen from the second compressive stress applying means, the compression state of the specimen,
A triaxial test method, wherein the test is performed as an arbitrary compression state including a plane strain compression state between a triaxial compression state and a triaxial extension state.