JP3773005B2 - Plane strain compression test equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plane strain compression test for examining the deformation characteristics and strength constant of a soil material in a plane strain state.
[0002]
[Prior art]
Conventionally, in order to examine the deformation characteristics and strength constants of soil materials, a triaxial compression test apparatus using a solid cylindrical specimen is generally used.
In this triaxial compression test apparatus, a known hydraulic pressure is applied as a lateral pressure to the peripheral surface of a cylindrical specimen, and the sample is sheared and fractured by applying axial pressure as a main stress difference thereto. When measuring stress, strain, pore water pressure, volume change, etc.
[0003]
[Problems to be solved by the invention]
By the way, in the above-mentioned triaxial compression test apparatus, since a uniform pressure is applied to the peripheral surface of a cylindrical specimen and sheared in the axial direction, the deformation characteristics and strength constants required by this apparatus are tested. Is limited to a so-called axisymmetric stress state in which the specimen is in a uniform stress state over the entire circumferential surface.
In other words, the deformation characteristics and strength characteristics of the soil material are strongly dependent on the stress state in which the soil element is placed, so it is essential to conduct tests under conditions that are as close to the original stress state as possible. The triaxial compression test apparatus described above often has a deviation from the stress state where the soil element is actually placed.
[0004]
On the other hand, as shown in FIG. 12, for example, in a stress state received by an element of soil in an actual earth structure such as a fill dam or a dike elongated in the longitudinal direction, a plane strain state (ε ₂ without displacement in the longitudinal direction). = 0) is often idealized.
However, although a plane strain compression test that reproduces such plane strain conditions has also been performed, there are very few examples of practical use other than special research applications. This is because the structure of the test apparatus and the test operation are complicated, and thus the test cost is high and not general.
[0005]
Therefore, in view of the actual situation as described above, the present invention can determine the deformation characteristics and strength constant of the soil in a plane strain state close to the stress state received by the soil element in the actual soil structure, An object of the present invention is to provide a plane strain compression test apparatus with a simple structure and test operation so that it can be easily applied to general use.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides three pairs of stresses in the first principal stress direction, the second principal stress direction, and the third principal stress direction orthogonal to each other, perpendicular to each of the three principal stress directions. In a plane strain compression test apparatus for performing a test in addition to each side surface of a substantially rectangular parallelepiped specimen having a side surface, a pressure chamber in which the specimen is disposed and a loading means outside the pressure chamber are generated. A compressive stress applying means including a pair of sandwiching bodies for applying a compressive stress in a first principal stress direction to the specimen by transmitting a force to the specimen, and a second principal stress of the specimen. Deformation restraining means for restraining deformation in the direction, and pressure generating means for generating a pressure inside the pressure chamber and using the pressure as a compressive stress in the third principal stress direction applied to the specimen. The compressive stress applying means One of the pair of sandwiching bodies is a cap that is movable in the first principal stress direction relative to the pressure chamber, and the other of the pair of sandwiching bodies of the compressive stress applying means is relative to the pressure chamber. The test piece is a soil material enclosed in a flexible sleeve having one end fastened to the cap and the other end fastened to the pedestal. In the pedestal, an end facing the specimen is formed in a rectangular shape corresponding to the shape of the specimen to form a specimen pressing part, and a midway part is formed in a circular shape in cross section. It comprises a sleeve fixing part for fixing the sleeve .
[0007]
Further, the present invention is characterized in that the deformation restraining means is equipped with a load measuring means for measuring a load in the second principal stress direction applied from the deformation restraining means to the specimen.
Or the present invention, the deformation restriction means, said flexible sleeve of said specimen includes a pair of restraint plates facing each other in contact, their pair of restraint plates floating on the first principal stress direction Supported by the pressure chamber, and the deformation restraining means further includes an adjustable coupling mechanism that couples the pair of restraining plates to each other in a state where the distance between the pair of restraining plates is adjustable. And
[0008]
According to the present invention, the deformation restraining means includes a pair of restraining plates opposed to each other that abut against the flexible sleeve of the specimen, and the pair of restraining plates float in the first main pressure direction. The deformation restraining means supported by the pressure chamber further allows a position adjusting mechanism fixed to the pressure chamber and operable from the outside of the pressure chamber, and movement of the restraining plate in the first main stress direction. The position adjusting mechanism and the restraint plate are connected to each other, and the position adjusting mechanism can determine the position of the restraint plate in the second main stress direction.
Or the present invention is characterized in that interposed a rectangular plate to reduce friction between each said specimen of said cap and said Bedesutaru.
The present invention is characterized in that a sliding agent is applied to a contact surface between each of the pair of restraining plates of the deformation restraining means and the flexible sleeve.
[0009]
The present invention also provides a pore water discharge means for discharging the pore water of the soil material enclosed in the flexible sleeve to the outside of the pressure chamber, and an amount of the pore water entering and exiting through the gap water discharge means. And measuring means for measuring the volume change amount of the specimen.
Further, the present invention is characterized by comprising a measuring means for measuring a load in the first principal stress direction of the specimen.
Further the invention features in that it comprises a measuring means for measuring a deformation amount of the first main stress direction of the specimen.
[0010]
According to the plane strain compression test apparatus or the plane strain compression 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 orthogonal to each other. And, in a state where the deformation in the second principal stress direction of the third principal stress direction is constrained, the compressive stress or the deformation amount in the first principal stress direction and the compressive stress in the third principal stress direction can be arbitrarily set. it can.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the plane strain compression test apparatus according to the present invention will be described.
FIG. 1 is a cross-sectional view showing an overall configuration example of a plane strain compression test apparatus according to the present invention.
In this compression test apparatus, a triaxial cell (pressure chamber) TC for storing cell water is arranged inside a loading frame LF, and a vertical load is applied to a specimen 10 installed in the triaxial cell TC. A device VL is provided.
The vertical load loading device VL includes a screw jack, a cylinder, or the like, and the main body VLa of the device is provided on the upper portion of the loading frame LF. Further, the rod portion VLb suspended from the main body portion VLa is inserted from the insertion hole LFa of the loading frame LF, and the loading shaft 12 is connected to the tip portion thereof.
A displacement meter 16 is provided between the flange portion 12a provided at the upper end of the loading shaft 12 and the loading frame LF so as to measure the deformation of the specimen 10 in the vertical direction.
The loading shaft 12 is suspended in the triaxial cell TC through a bearing portion 18 provided on the upper surface of the triaxial cell TC.
[0012]
In the triaxial cell TC, the cap 20 is connected to the loading shaft 12 and arranged on the upper surface of the specimen 10 via the rectangular plate 22A, and is arranged on the lower surface of the specimen 10 via the rectangular plate 22B. Pedestal 24, a deformation restraint system 30 that restrains deformation of the specimen 10 in the horizontal direction, a support device 26 that supports the deformation restraint system 30, and a connecting portion between the loading shaft 12 and the cap 20. A load cell 14 for measuring the vertical load is provided.
Further, around the triaxial cell TC, a cell pressure load device 40 for applying a cell pressure (σ _c ) to the specimen 10 in the triaxial cell TC, a Bourdon gauge 50 for measuring the cell pressure, A control circuit 60 that controls the drainage conditions in the specimen 10, a volume change measurement system 70 for the specimen 10, and a pressure converter 80 that measures the excess pore water pressure in the specimen 10 are provided.
Hereinafter, the configuration of each unit will be sequentially described in detail.
[0013]
FIG. 2 is a perspective view showing an example of the specimen 10 used in this plane strain compression test apparatus.
As shown in the figure, a rectangular shape is used for this specimen 10, and the ratio of the length (L), width (W), and height (H) of the specimen 10 is the ratio of height to width. As a guide, H / W = 2.0, and the length should be greater than the height (L ≧ H).
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 direction (first principal stress direction) of the specimen 10 is the maximum principal stress with respect to the load by the vertical load loading device VL, and the length direction (second principal stress). The stress σ _{2 in the} direction) is an intermediate principal stress with respect to the restraining force of the deformation restraint system 30, and the stress σ _{3 in} the width 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.
[0014]
3 is a three-side view showing the structure of the cap 20. FIG. 3 (1) is a front view, FIG. 3 (2) is a bottom view, FIG. 3 (3) is a side view, and FIG. 4 (1) is a top view, FIG. 4 (2) is a side view, FIG. 4 (3) is a front view, and FIG. 5 is an assembled state of the specimen 10, cap 20 and pedestal 24. FIG.
The cap 20 and the pedestal 24 are arranged on the upper and lower surfaces of the specimen 10 via the rectangular plates 22A and 22B as described above.
The rectangular plates 22A and 22B are a porous plate as a filter layer, or a device for reducing friction, for example, an acrylic plate with grease applied and a thin rubber sheet attached thereto.
Further, the end surfaces of the cap 20 and the pedestal 24 on the side in contact with the specimen 10 are formed as rectangular cross sections 20A and 24A corresponding to the rectangular shape of the specimen 10 in length × width (L × W). However, the width is a value (W ′) larger than W so that when the specimen 10 is compressed in the height direction, it does not protrude when expanded in the width direction. Specifically, W ′ = W + ΔW and ΔW / W ≧ 0.05.
[0015]
The rectangular plates 22A and 22B have the same shape as the end surface shape (L × W ′) of the cap 20 and the pedestal 24 on the specimen 10 side.
Further, when the rubber sleeve 2 is used, the part of the cap 20 and the pedestal 24 opposite to the specimen 10 is fixed in a sealed state with O-rings 4A, 4B, etc., as shown in FIG. The circular cross sections 20B and 24B are provided so as to be easy.
In this example, the case of using a generally thin-walled cylindrical rubber sleeve 2 is shown, but it is also possible to use a rectangular cylindrical rubber sleeve.
Further, the cap 20 and the pedestal 24 are formed with drain holes 20a, 24a for draining the pore water in the specimen (soil material) 10, and these drain holes 20a, 24a are, as shown in FIG. It is connected to the drainage condition control circuit 60 via the connecting pipes 6A and 6B, and further connected to the volume change measuring system 70 and the pressure transducer 80 of the specimen 10.
[0016]
The control circuit 60 controls the drainage flow rate from the specimen 10 by controlling a valve or the like, and the volume change measuring system 70 controls the water level of the burette 72 indicating the amount of water flowing in and out from the specimen under test. It is measured by a differential pressure gauge 74.
The pressure converter 80 measures the excess pore water pressure (non-drainage condition) in the specimen 10. In addition, cocks 82 and 84 for opening and closing such drainage paths are provided.
Further, the cell pressure load device 40 shown in FIG. 1 controls the air pressure (σ _c ) from the pressure source HP such as a compressor to a predetermined value by the pressure adjustment regulator 42 and applies it to the triaxial cell TC. The pressure is converted into water pressure by the cell water stored in the cell TC and added to the specimen 10.
In addition, the cell pressure (σ _c ) by such a cell pressure load device 40 is measured by a Bourdon gauge 50.
[0017]
6 is a sectional view showing the deformation restraining system 30, FIG. 7 is a sectional view taken along line (1)-(1) in FIG. 6 showing the deformation restraining system 30, and FIG. 8 is (2)-(2) in FIG. It is sectional drawing.
This deformation restraint system 30 restrains the deformation of the specimen 10 in the length L direction, that is, the longitudinal direction in the horizontal direction. The restraint plates 32 and 34 are arranged on both side surfaces of the specimen 10 in the length L direction. These are connected by a connecting rod 36 arranged along the length L direction of the specimen 10.
One restraint plate 32 has a structure in which a front plate 32A that abuts the specimen 10 and a reference plate 32B disposed behind the front plate 32A, and a load cell 48 is provided therein. The load cell 48 measures a longitudinal load that should restrain deformation of the specimen 10 by detecting a force applied to the front plate 32A.
The other restraining plate 34 is formed in a single flat plate shape.
[0018]
Further, four connecting rods 36 are provided corresponding to the upper, lower, left, and right corner portions of the respective restraining plates 32 and 34. As shown in FIG. 7, the end of the connecting rod 36 on the restraint plate 32 side is fixed to the reference plate 32B.
Further, a threaded portion is formed at the end of the connecting rod 36 on the restraint plate 34 side. Then, the end 10 is passed through an insertion hole formed in the restraint plate 34, and a nut 38 is screwed into the threaded portion of this end to be tightened, whereby the specimen 10 is sandwiched between the restraint plates 32 and 34. Hold in the state.
[0019]
Each of the restraining plates 32 and 34 is supported in a vertically movable state by a floating system 90 provided on the bottom plate portion 44 of the triaxial cell TC.
As shown in FIG. 8, the floating system 90 includes four spring rods 92 disposed on the upper surface of the bottom plate portion 44 of the triaxial cell TC and compression coil springs 94 attached to the outer peripheral portions of the spring rods 92. And have.
On the other hand, a pair of vertical mounting holes 30a is formed on the lower surface of each of the restraining plates 32, 34, and a spring rod 92 is fitted to a linear motion bearing 96 provided in these mounting holes 30a. The compression coil spring 94 is interposed between the lower surface of each of the restraining plates 32 and 34 and the flange portion 92 a provided at the base end of the spring rod 92.
[0020]
Further, as shown in FIG. 6, the rubber sleeve 2 is mounted so as to surround the specimen 10, the rectangular plates 22 </ b> A and 22 </ b> B, the rectangular cross sections 20 </ b> A and 24 </ b> A of the cap 20 and the pedestal 24. The circular cross sections 20B and 24B are fixed by O-rings 4A and 4B, and surround the specimen 10 in a sealed state.
A sliding agent 54 made of grease or the like is interposed in the contact portion between the rubber sleeve 2 and the specimen 10 so as to reduce the frictional resistance when the specimen 10 is displaced.
[0021]
Next, a test procedure using the plane strain compression test apparatus having the above configuration will be described.
First, a rectangular specimen 10 of a soil sample to be tested is prepared. In this case, the preparation of the specimen differs depending on the sandy soil, the viscous soil, or the case where the specimen is collected in an undisturbed state from the original position. And are surrounded by the rubber sleeve 2 and fixed by the O-rings 4A and 4B at the circular cross sections 20B and 24B of the cap 20 and the pedestal 24.
Then, a predetermined negative pressure (σ _NE <0) is applied to the specimen 10 to advance to a self-supporting state (FIG. 5).
Next, the dimensions of the specimen 10 are measured, and a lubricant such as grease for friction removal is thinly applied on both surfaces (H × W surface) on which the intermediate principal stress σ ₂ acts, and the deformation restraint system 30 is installed. (FIG. 6).
[0022]
Next, after pouring the cell water into the triaxial cell TC to a predetermined water level, the triaxial cell TC is assembled, and the negative pressure (σ _NE ) and the cell pressure (σ _c ) applied in the specimen 10 are exchanged. (Σ _c = | σ _NE |).
Next, the triaxial cell TC is installed on the loading frame LF (FIG. 1). Then, after the specimen 10 is compacted to a predetermined compacting pressure level, that is, a compacting pressure level corresponding to the original stress state, a vertical load is applied to the specimen 10 by the loading frame LF and sheared. At this time, vertical load during shearing, vertical displacement, horizontal load in a direction constraining deformation, volume change (drainage condition) or excessive pore water pressure (non-drainage condition) are measured and recorded.
[0023]
The specimen 10 being sheared is compressed and displaced in the vertical direction, and the restraint plates 32 and 34 and the specimen 10 are displaced relatively to generate friction, but as described above, Since the lubricant is applied and the restraint plates 32 and 34 are displaced by the floating system 90 of the displacement restraint system 30, the influence of the friction can be reduced.
According to the above procedure, at least two specimens with different consolidation pressure levels are tested, the deformation characteristics (stress-strain relationship) at each consolidation pressure level, and the strength of the soil under the consolidation pressure range where the test was conducted. Find a constant.
[0024]
As described above, in the plane strain compression test apparatus of the present example, the deformation restraint system 30 can perform the compression test in a state where the deformation in the intermediate principal stress direction in the rectangular specimen 10 is restrained.
And compared with the conventional plane strain compression test, the structure and operation procedure are simple, and an inexpensive plane strain compression test can be realized. Therefore, it is possible to easily perform more rational behavior prediction calculation and design calculation of the earth structure.
[0025]
In the above example, the example in which the mechanism for fixing the restraint plates 32 and 34 of the deformation restraint system 30 is provided inside the triaxial cell TC has been described. It is also possible to provide it outside the TC.
FIG. 9 is a cross-sectional view showing a configuration example in the case where such an out-cell type deformation restraint system 30 ′ is provided.
In this deformation restraint system 30 ′, the restraint plates 32, 34 are adjusted from the outside of the triaxial cell TC in place of the connecting rod 36 described above and brought into contact with the specimen 10.
That is, horizontal shafts 54A and 54B are connected to the back surfaces of the restraining plates 32 and 34 via linear motion guide bearings 52A and 52B, and the horizontal shafts 54A and 54B are connected to the side plates of the triaxial cell TC. It protrudes to the outside of the triaxial cell TC through the provided linear motion bearings 56A and 56B, and is fixed by stoppers 58A and 58B attached to the protruding end portions.
With such a structure, the operation portions 54a and 54b of the horizontal shafts 54A and 54B are operated from the outside of the triaxial cell TC to bring the restraint plates 32 and 34 into contact with the side surfaces of the specimen 10 and stoppers 58A and 58B. The specimen 10 can be displaced in the vertical direction by the linear motion guide bearings 52A and 52B, and is arranged in a state in which the deformation in the longitudinal direction is restrained by the restraining plates 32 and 34.
[0026]
Further, in the example shown in FIG. 1, the cell pressure (σ _c ) measured by the cell pressure load device 40 is measured by the Bourdon gauge 50, but instead, it is measured by the pressure transducer PT as shown in FIG. You may make it do.
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. You may provide load cell 14 'in the connection part of the rod part VL2 of the load loading apparatus VL, and the loading shaft 12. FIG.
[0027]
【The invention's effect】
As described above, according to the plane strain compression test apparatus or the plane strain compression test method according to the present invention, the first principal stress directions of the specimens that are substantially orthogonal to each other are used. In the state where the deformation in the second principal stress direction of the second principal stress direction and the third principal stress direction is constrained, the compressive stress or the deformation amount in the first principal stress direction and the compressive stress in the third principal stress direction are It can be set arbitrarily.
For this reason, for example, an embankment or the like that is sufficiently elongated in one direction and the cross-sectional shape is uniform in the longitudinal direction, the earth structure having a two-dimensional structure is effectively in the original stress state of the earth structure. It is possible to conduct a compression test of soil materials under close conditions.
In addition, a plane strain test can be performed with a structure and procedure similar to those of a conventional triaxial compression test apparatus, the structure and test operation are simple, and it is easy to apply to general use.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration example of a plane strain compression test apparatus according to the present invention.
FIG. 2 is a perspective view showing an example of a specimen used in the plane strain compression test apparatus shown in FIG.
3 is a three-sided view showing the structure of a cap in the plane strain compression test apparatus shown in FIG.
4 is a trihedral view showing the structure of a pedestal in the plane strain compression test apparatus shown in FIG. 1. FIG.
5 is a cross-sectional view showing an assembled state of a specimen, a cap, and a pedestal in the plane strain compression test apparatus shown in FIG. 1. FIG.
6 is a cross-sectional view showing a deformation restraint system in the plane strain compression test apparatus shown in FIG. 1. FIG.
7 is a cross-sectional view taken along line (1)-(1) in FIG.
8 is a cross-sectional view taken along the line (2)-(2) in FIG.
9 is a cross-sectional view showing another example of a deformation restraint system in the plane strain compression test apparatus shown in FIG. 1. FIG.
10 is a front view showing another example of the cell pressure measuring apparatus in the plane strain compression test apparatus shown in FIG. 1. FIG.
11 is a front view showing another example of a vertical load measuring apparatus in the plane strain compression test apparatus shown in FIG. 1; FIG.
FIG. 12 is an explanatory diagram for explaining a stress state that a soil element in a soil structure receives.
[Explanation of symbols]
LF Loading frame TC Triaxial cell (pressure chamber)
VL Vertical load loading device 2 Rubber sleeve 10 Specimen 12 Loading shaft 14, 14 ', 48 Load cell,
24 Bedestal 30, 30 ′ Deformation restraint system 32, 34 Restraint plate 36 Connecting rod 40 Cell pressure load device 50 Bourdon gauge 60 Drainage condition control circuit 70 Volume change measurement system 90 Floating system

Claims (9)

A specimen having a substantially rectangular parallelepiped shape having three pairs of side surfaces perpendicular to each of the three principal stress directions, the stresses in the first principal stress direction, the second principal stress direction, and the third principal stress direction orthogonal to each other. In plane strain compression test equipment that performs the test in addition to each side of
A pressure chamber in which the specimen is disposed;
Compressive stress applying means comprising a pair of clamping bodies for applying compressive stress in the first principal stress direction to the specimen by transmitting the force generated by the loading means outside the pressure chamber to the specimen. When,
Deformation restraining means for restraining deformation of the specimen in the second principal stress direction;
To generate pressure inside the pressure chamber, provided with the pressure, for the third principal stress direction of compressive stress applied to the specimen, and a pressure generating means,
One of the pair of sandwiching bodies of the compressive stress applying means is a cap movable in the first principal stress direction relative to the pressure chamber, and the other of the pair of sandwiching bodies of the compressive stress applying means Is a pedestal fixed relative to the pressure chamber;
The specimen is a soil material enclosed in a flexible sleeve having one end fastened to the cap and the other end fastened to the pedestal.
The cap and the pedestal are formed in a rectangular shape corresponding to the shape of the specimen with an end facing the specimen to form a specimen pressing portion, and a midway portion is formed in a circular cross section. Forming a sleeve fixing portion for fixing the flexible sleeve;
Plane strain compression test apparatus according to claim and this.   2. The plane strain compression test according to claim 1, wherein the deformation restraining means is equipped with a load measuring means for measuring a load in the second principal stress direction applied from the deformation restraining means to the specimen. apparatus. The deformation restraining means includes a pair of opposing restraining plates that abut against the flexible sleeve of the specimen, and the pair of restraining plates are supported in the pressure chamber in a floating state in a first principal stress direction. are, the deformation restriction means further claim 1, characterized in that it contains an adjustable connection mechanism for connecting them together pair of restraining plate spacing of the pair of restraining plate is adjustable state or 2. The plane strain compression test apparatus according to 2. The deformation restraining means includes a pair of opposing restraining plates that contact the flexible sleeve of the specimen, and the pair of restraining plates are supported in the pressure chamber in a floating state in a first main pressure direction. The deformation restraining means is further fixed to the pressure chamber and can be operated from the outside of the pressure chamber, and the position adjustment to allow the restraint plate to move in the first principal stress direction. The coupling mechanism which connects a mechanism and the said restraint board, and makes it possible to determine the position of the 2nd main stress direction of the said restraint board with the said position adjustment mechanism, The Claim 1 or 2 characterized by the above-mentioned. Plane strain compression test equipment. The plane strain compression test apparatus according to any one of claims 1 to 4, wherein a rectangular plate for reducing friction is interposed between each of the cap and the pedestal and the specimen. The plane strain compression according to any one of claims 1 to 5 , wherein a sliding agent is applied to a contact surface between each of the pair of restraining plates of the deformation restraining means and the flexible sleeve. Test equipment. Based on the pore water discharge means for discharging the pore water of the soil material enclosed in the flexible sleeve to the outside of the pressure chamber, and the amount of pore water entering and exiting through the gap water discharge means. plane strain compression test apparatus according to any one of claims 1 to 6, characterized in that a measuring means for measuring a volume change of specimen. The plane strain compression test apparatus according to any one of claims 1 to 7 , further comprising measuring means for measuring a load in the first principal stress direction of the specimen. The plane strain compression test apparatus according to any one of claims 1 to 8 , further comprising measuring means for measuring a deformation amount of the specimen in the first principal stress direction.

Images