JP4043568B2 - In-situ hole bottom triaxial compression test method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an in-situ hole bottom triaxial compression test method used for measuring deformation characteristics and strength characteristics of ground in ground surveys for design and construction of structures. More specifically, the present invention relates to an in-situ hole bottom triaxial compression test method using a hollow cylindrical test body provided at the hole bottom.
[0002]
[Prior art]
In-situ tests are conducted to understand the deformation characteristics and strength characteristics of the ground such as rock. The in-situ test is performed at the in-situ location using the ground excavated at the in-situ location as a test body in order to obtain data that matches the actual site.
[0003]
The triaxial compression test, which is one of the in-situ tests, differs from other in-situ test methods such as the plate loading test method and the rock shear test method. Therefore, there is an advantage that a strain distribution and a stress distribution become a relatively uniform element test inside the specimen. With respect to this in-situ triaxial compression test method, a test method has been proposed in which the strength characteristics are more easily obtained as disclosed in JP-A-7-35663.
[0004]
In addition, a method of carrying out a sample such as a boring core collected at the original position as a specimen and performing a triaxial compression test in a test room or the like is also employed. In this case, there is an advantage that it is possible to perform a rigorous test using a device provided in the room and there is no trouble of installing or adjusting the test device set in its original position.
[0005]
[Problems to be solved by the invention]
However, when performing a triaxial compression test in a place other than the original position such as a test room, it takes time to mine and carry out the sample. In addition, it may be difficult to maintain the sample in the same state as before being mined, and there is a problem that the measurement accuracy may be inferior due to the influence of disturbance during the handling of the sample on the test results. Yes.
[0006]
Moreover, when performing a test at the original position, there is a problem that costs are incurred when deeply digging the ground or digging a test mine.
[0007]
Further, in the invention disclosed in Japanese Patent Laid-Open No. 7-35663, the measured displacement includes a measurement error such as a bedding error and a deformation of the ground directly under the specimen, so that a deformation characteristic is obtained even if the strength constant can be obtained. It has disadvantages such as being unable to do so.
[0008]
Accordingly, an object of the present invention is to provide an in-situ triaxial compression test method capable of accurately evaluating the deformation characteristics and strength characteristics of the ground with the same rigor as in a triaxial compression test in a room.
[0009]
[Means for Solving the Problems]
In order to achieve such an object, according to the first aspect of the present invention, the ground at the bottom of the borehole provided in the ground is cut out to form a hollow cylindrical specimen made of the ground, and the outer periphery of the hollow cylindrical specimen is restrained by the restraining means. While applying constant restraining pressure in the radial direction to the inner peripheral surface of the surface and the central small hole, the load in the axial direction by the axial load loading means is changed to constrain the inner peripheral surface of the central small hole of the hollow cylindrical specimen. The displacement measuring means provided in the restraining member that forms the restraining means for loading pressure is used to measure the change in the distance between the two axial points excluding the hole bottom and hole of the central small hole of the hollow cylindrical specimen. The relative displacement between the two points is obtained, and the relationship between the stress and the axial strain is obtained from the obtained displacement.
[0010]
Therefore, in this compression test method, the hollow cylindrical specimen is compressed by applying a load in the axial direction while applying a constant isotropic restraining pressure in the radial direction, and the strain against the stress of the hollow cylindrical specimen is obtained. ing. In this case, the hollow cylindrical specimen is provided by cutting out the ground at the bottom of the boring hole, and the characteristics obtained for this specimen can be used as the properties of the ground as they are. The axial displacement of the hollow cylindrical specimen is measured by a displacement measuring means provided in a restraining member forming a restraining means for loading restraining pressure on the inner peripheral surface of the central small hole of the hollow cylindrical specimen. Since it is calculated | required based on the distance between the two axial points of the intermediate part except a hole bottom and a hole opening of a small hole, the distortion | strain of a hollow cylindrical test body is calculated | required more strictly and correctly. Furthermore, the stress circle of the molding at the time of failure defined by the principal stress can be directly obtained from the axial load and the restraining pressure.
[0011]
The in-situ hole bottom triaxial compression test method according to claim 2, wherein a slit is provided between the inner peripheral surface of the boring hole and the hollow cylindrical specimen, and a restraining member is formed between the slit and the central small hole. Is provided. Therefore, an isotropic and constant restraining pressure can be applied to the hollow cylindrical specimen from the outside and the inside. In addition, since the restraining member provided in the slit is supported by the inner peripheral surface of the boring hole in the slit, it can receive a reaction from the inner peripheral surface and apply a more effective restraining pressure to the hollow cylindrical specimen. it can.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the configuration of the present invention will be described in detail based on an example of an embodiment shown in the drawings.
[0013]
1 to 5 show an embodiment of an in-situ hole bottom triaxial compression test method using the hollow cylindrical specimen of the present invention. In this in-situ hole bottom triaxial compression test method, a hollow cylindrical specimen 3 made of the ground 1 is formed on the bottom of the bore hole 2 provided in the ground 1 at the original position, and the hollow cylindrical specimen 3 is triaxially formed. By performing compression, the relationship between axial stress and axial strain under triaxial stress compression is obtained. Therefore, first, the configuration necessary for performing the test method of the present invention will be sequentially described.
[0014]
First, as shown in FIG. 2, the ground 1 is drilled vertically by boring at the original position to provide a cylindrical boring hole 2. The bottom of the boring hole 2 is polished as necessary. Then, a cylindrical test body is formed by digging into a slit shape so that the inner peripheral surface of the boring hole 2 extends in the vertical direction toward the bottom of the hole, and further in the vertical direction at the center of the test body. A small hole 5 is excavated to form a hollow cylindrical specimen 3 as shown in FIG. In this case, the radial width of the slit 4 between the boring hole 2 and the hollow cylindrical specimen 3 and the diameter of the central small hole 5 are not particularly limited. However, in this embodiment, the width of the slit 4 is necessary and sufficient to accommodate the restraining means 6, and the diameter of the central small hole 5 is also necessary to accommodate the restraining means 6 and the displacement measuring means 8. It is considered sufficient.
[0015]
Next, the restraining means 6 is provided in the slit 4 and the central small hole 5. Here, the restraining means 6 applies a restraining force to the hollow cylindrical test body 3 by applying a lateral pressure in the radial direction from the outer peripheral surface and the inner peripheral surface of the hollow cylindrical test body 3. In this embodiment, the restraining means 6 is composed of a restraining member made of a bag-like rubber film (rubber sleeve), a membrane 7 and the like, and a pressure source for supplying pressure fluid into the membrane 7 as the restraining member. ing. The membrane 7 is provided in each of the slit 4 and the central small hole 5. The membrane 7 has an inlet through which a gas such as air can be injected, and applies a restraining pressure σ _c in the radial direction to the hollow cylindrical specimen 3 by a gas pressure. The gas is compressed by a restraining pressure load device (not shown) and sent to the membrane 7. Note that the side pressure can be applied by using a liquid such as water instead of applying the side pressure by the compressed gas.
[0016]
Displacement measuring means 8 for measuring the axial strain of the hollow cylindrical specimen 3 is provided in the central small hole 5. In this case, the displacement measuring means 8 is provided in the central small hole 5 so as to measure a change in length between any two points A and B set in the axial direction. The strain is obtained by obtaining the displacement. As the displacement measuring means 8, a specific one can be used as long as it can measure the distance between two locations (two points of different heights) of the membrane 7 that loads the restraining pressure σ _c on the inner peripheral surface of the central small hole 5. It is not limited to the measurement system. For example, it may measure between the universal joints held at two points A and B by using a displacement meter such as an operating transformer type, strain gauge type or potentiometer type, or a laser. You may make it measure the movement amount of the target set to 2 points | pieces using non-contact type displacement meters, such as a type | mold and an eddy current type.
[0017]
In the present embodiment, a cap 11 is placed on the upper part of the hollow cylindrical specimen 3, and a center hole type load cell 12 is further placed thereon, and a load is applied by the axial load loading means 9 through these. The axial load loading means 9 in this case is not limited to a specific one. For example, a center hole jack that applies an axial load to the hollow cylindrical specimen 3 is used in this embodiment. Further, the axial load loading means 9 is fixed to the ground 1 so as to receive a reaction force when an axial load is applied to the hollow cylindrical specimen 3. In the present embodiment attached to the casing 10 in a portion of the inner peripheral surface of the borehole 2, as shown in FIG. 4, so as to fix the axial load loading means 9 such as a cell down coater hole jack with the casing 10 Yes.
[0018]
In order to perform the in-situ hole bottom triaxial compression test using each of the devices provided as described above, first, isotropic and constant using the restraining means 6 and the axial load loading means 9 on the hollow cylindrical specimen 3. Then, the axial load on the hollow cylindrical specimen 3 is increased by the axial load loading means 9. In this case, until the hollow cylindrical specimen 3 is broken, compression is performed by increasing the load by the axial load loading means 9 little by little. And the displacement of the hollow cylindrical test body 3 in the meantime is measured using the displacement measuring means 8, and the relationship between axial stress and axial strain is calculated | required.
[0019]
According to the in-situ hole bottom triaxial compression test method in which the test is performed as described above, the displacement of the hollow cylindrical specimen 3 during axial compression is obtained by the displacement measuring means 8 provided in the central small hole 5. Therefore, a strict axial displacement can be obtained. Therefore, the relationship between the axial stress and the axial strain under an arbitrary triaxial stress condition can be obtained, and the deformation characteristics / strength characteristics of the ground 1 can be accurately evaluated directly at the original position. Therefore, it is not necessary to carry out the sample used as a specimen, and it is not necessary to consider the influence of disturbance during the handling of the sample. In addition, even in the deep ground where it is difficult to excavate the horizontal test pit 20, it is possible to perform an in-situ test using a vertical hole by boring, so the deformation characteristics and strength characteristics of the ground 1 are evaluated. can do.
[0020]
The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited to this, and various modifications can be made without departing from the scope of the present invention. For example, in this embodiment, the boring hole 2 is directly excavated from the ground surface of the ground 1, but the boring hole 2 may be provided by excavating from the test pit 20 in the vertical direction. In this case, the axial load loading means 9 provided in the boring hole 2 is attached at one end to the ceiling 21 of the test pit 20 as shown in FIG. You can also.
[0021]
Further, in the present embodiment, the slit 4 having an appropriate width is provided between the inner peripheral surface of the boring hole 2 and the outer peripheral surface of the hollow cylindrical specimen 3, but the present invention is not particularly limited thereto. In the case where the width of the slit 4 is excessively larger than the width of the restraining member 7, the restraining member 7 provided around the hollow cylindrical specimen 3 is further replaced with an inner surface such as a cylindrical body provided around the same. What is necessary is just to make it contact and hold.
[0022]
【The invention's effect】
As is clear from the above description, in the in-situ hole bottom triaxial compression test method of the invention according to claim 1, the displacement of the hollow cylindrical specimen during triaxial compression is restrained on the inner peripheral surface of the central small hole. Is obtained based on the distance between two axial points in the middle portion excluding the hole bottom and the hole opening of the central small hole measured by the displacement measuring means provided in the restraining member forming the restraining means for loading Therefore, more strict strain can be obtained. As a result, even in a triaxial compression test on the ground having properties that make it difficult to obtain a sample free of disturbances, the deformation characteristics and strength characteristics of the ground can be accurately evaluated directly at the original position. Furthermore, the stress circle of the molding at the time of fracture can be directly obtained.
[0023]
Moreover, according to this test method, an in-situ test can be performed in a vertical hole by boring. Therefore, even in the deep ground where it is difficult to excavate the horizontal test mine, the deformation characteristics and strength characteristics of the ground can be evaluated at the original position.
[0024]
In the in-situ hole bottom triaxial compression test method according to the second aspect of the present invention, a slit is provided between the inner peripheral surface of the boring hole and the hollow cylindrical specimen, and a restraining member for forming restraining means is provided in the slit. Thus, the restraining member can be received and supported by the inner peripheral surface of the boring hole. Therefore, even if a member for supporting the restraining member is not provided, a restraining load can be applied to the hollow cylindrical specimen using the restraining means.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of an in-situ ground showing a bore hole used in an in-situ hole bottom triaxial compression test method of the present invention and a hollow cylindrical test body provided in the hole bottom.
FIG. 2 is a longitudinal section showing a boring hole excavated in the in-situ ground.
FIG. 3 is a longitudinal sectional view showing a boring hole and a hollow cylindrical specimen formed at the bottom of the hole.
FIG. 4 is a longitudinal sectional view showing a state in which a reaction force of a load applied to a hollow cylindrical specimen is received by a wall surface of a boring hole.
FIG. 5 is a longitudinal sectional view showing a state in which a reaction force of a load on a hollow cylindrical specimen is received by a ceiling of a test pit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ground 2 Boring hole 3 Hollow cylindrical test body 4 Slit 5 Center small hole 6 Restriction means 7 Membrane (restraint member)
8 Displacement measuring means 9 Axial load loading means

Claims (2)

The ground at the bottom of the borehole provided in the ground is cut out to form a hollow cylindrical test body made of the ground, and the restraining means radially extends the outer peripheral surface of the hollow cylindrical test body and the inner peripheral surface of the central small hole. A restraining member for forming the restraining means for loading the restraining pressure on the inner peripheral surface of the central small hole of the hollow cylindrical specimen while changing the axial load by the axial load loading means while applying a constant restraining pressure. By measuring the change in the distance between two points in the axial direction excluding the hole bottom and hole of the central small hole of the hollow cylindrical specimen by the displacement measuring means provided inside, the relative displacement between the two points is obtained. An in-situ hole bottom triaxial compression test method characterized in that a relationship between stress and axial strain is obtained from the obtained displacement.   The raw material according to claim 1, wherein a slit is provided between an inner peripheral surface of the boring hole and a hollow cylindrical specimen, and a constraining member for forming the constraining means is provided in the slit and the central small hole. Position hole bottom triaxial compression test method.

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