KR100795474B1 - Soil Testing Apparatus for various stress path tests under plane strain condition - Google Patents

Abstract

The present invention relates to a soil tester including a housing providing a sealed space, a sample installed in the housing and a sample placed thereon, and a pressurizing device for providing a pressure in the housing. Press the sample 150 while blocking the two side walls 142 and 144 supported by the lower side, the lower cap 122 blocking the lower portion between the side walls 142 and 144, and the upper portion between the side walls 142 and 144. The upper cap 124 is installed so as to be able to move up and down, the inner membrane 152 surrounding the side of the sample 150, the outer side surrounding the outer surface between the lower cap 122 and the upper cap 124 It characterized in that it comprises a membrane 154, and the pore pressure pipe (L1, L2) connected to the sample 150 from the outside of the housing. According to the present invention, it is possible not only to test the various stress paths while accurately measuring the volume deformation or the pore water pressure of the sample, but also to reproduce the only fracture surface of the actual site, and to visually accurately observe the deformation process of the sample. Can facilitate the shaping of the sample.

Plane deformation, various stress paths, double membrane, pore water pressure, volume deformation, mold

Description

Soil Testing Apparatus for various stress path tests under plane strain condition

1 is a view for explaining a conventional planar strain tester;

2 is a stress path graph for explaining a stress path when a plane strain condition is broken;

3 is a view for explaining a soil tester according to the present invention;

4 is a view for explaining a process of molding the sample 150 of FIG.

<Description of reference numbers for the main parts of the drawings>

12, 112: base plate 14, 114: cover

22, 122: lower cap 24, 124: upper cap

30, 42, 44, 130, 142, 144: side walls

46, 246: connecting plate 50, 150: sample

62, 162: vertical clamp 70, 170: load ram

80: vertical deformation measuring device 90: pressurizing device

122a, 124a, 122b, 124b: O-ring

146: molding plate 146a: suction port

152: inner membrane 154: outer membrane

202: linear bearing 204: control unit

300: earth pressure gauge L1, L2: pore water pressure pipe

L3: restraint pressure tube

The present invention relates to a soil tester for evaluating soil behavior, and more particularly, to a soil tester capable of testing various stress paths under planar strain conditions.

Plane strain conditions occur frequently in the geotechnical arts. Therefore, it is very important to accurately assess the stress strain behavior of soil under planar strain conditions.

1 is a view for explaining a conventional planar strain tester. Plane strain tester uses the frame of a general triaxial tester including a loading device, a pressure regulator, a pore water pressure measuring device, and the like. The housing includes a pedestal 12, a cylinder-shaped side wall 30, and a lid 14, and provides a closed space. Since the bottom plate 12 and the cover 14 are fastened to each other by the vertical fastening table 62, such sealing is securely performed.

A sampler is installed in the housing, and the sampler includes two sidewalls 42 and 44, a lower cap 22, and an upper cap 24 supporting the sample on both sides. The lower cap 22 and the upper cap 24 close the lower and upper portions between the side walls 42 and 44, respectively.

A sample 50 such as soil is placed on the lower cap 22, and the sample 50 is covered with a rubber membrane (not shown). The side walls 42 and 44 suppress the deformation of the sample 50 in the left and right directions to form a planar strain condition. Side walls 42 and 44 are connected to each other by connecting plates 46 to completely confine the side walls 42 and 44. The upper cap 24 is placed on the sample 50.

When the sample 50 is placed in the sample machine, water is supplied to the PT end of the restraint pressure tube L3 to fill the housing with water. The pressurization device 90 then applies pneumatic pressure to the filled water to increase the restraint pressure applied to the sample 50. In some cases, the sample is supplied by supplying water to the sample 50 through the pore pressure pipes L1 and L2 connected to the sample 50 through the lower cap 22 and the upper cap 24 from the outside of the housing. Saturation can also lead to the formation of pore water pressure. The pore-pressure pipes L1 and L2 are also used to drain water contained in the sample to the outside or to remove air from the sample. L4 is a line for releasing air in the housing.

As a result of applying a restraining pressure to the sample 50, the shape of the sample 50 is maintained, and then pressing down the upper cap 24 with a loading ram 70 to compress and destroy the sample 50. Obtain necessary data such as strain relationship and shear strength. The height change of the sample is measured by a vertical strain measuring device (LVDT) 80 connected to the load ram 70. The cylinder-type side wall 30 is made of a transparent material so that the test process can be observed.

The conventional plane strain tester described above has the following problems.

First, when the upper cap 24 is pressed by the load ram 70, the sample 50 spreads sideways and the side walls 42 and 44 are pressed outward. When the restraining pressure exerted by the pressurizer 90 in the inward direction of the sidewalls 42 and 44 is greater than the pressure exerted in the outward direction of the sidewalls 42 and 44, the sidewalls 42 and 44 and the sample 50 are separated. Water will penetrate. This changes to the normal triaxial test conditions (strictly axisymmetric conditions), breaking the planar strain conditions.

When the plane strain condition is broken, it occurs when the stress path goes below the KO line in the stress path graph of FIG. That is, in the case of performing the test along the paths ①, ⑤, and ⑥ in FIG. 2, the restraining pressure by the pressurizer 90 becomes larger than the outward pressure applied to the side walls 42 and 44. ) Is penetrated between the sample and the sample 50. If this occurs, testing of various stress paths is not possible.

In order to solve this problem, the membrane may be covered on the outside of the tester. In this case, however, water cannot penetrate between the sidewalls 42 and 44 and the sample 50, but there is a gap between the membrane and the sample device. There is a problem that cannot be measured accurately.

Secondly, because the plane strain tester has the direction of the fracture surface, it is possible to more accurately observe the strain localization (part where the fracture occurs is part of the sample) unlike the triaxial test. However, in the conventional tester, the lower cap 22 is fixed, resulting in overlapping fracture surfaces. However, in general geotechnical sites, fracture occurs with one fracture surface. Therefore, in the conventional case, there is a problem in that the site cannot be accurately simulated due to the occurrence of overlapping fractured surfaces.

Third, in order to measure strain localization more accurately, it is necessary to visually observe the deformation of the sample accurately. However, the sidewalls 42 and 44 of the sampler are opaque, so that the lateral change of the sample 50 cannot be observed accurately. In addition, the housing side wall 30 is made of a transparent material, but because of the cylindrical shape, it is deflected when observing the inside, so that a simple visual observation is possible, but it is difficult to accurately grasp the size and ratio of deformation, and thus, digital imaging is difficult.

Fourth, when the sample is sand, a mold for forming the sample is required and the rubber membrane must be closely adhered to the mold, and in the conventional case, the rubber membrane is closely adhered to the rectangular mold. There is a problem that is difficult to make.

Fifth, conventional planar strain testers are mainly focused on large strains, and thus sufficient conditions for measuring small strains are not provided.

Therefore, the technical problem to be achieved by the present invention is not only to test the various stress paths while accurately measuring the volume deformation and the pore water pressure of the sample, but also to reproduce the only fracture surface of the actual site, and to visualize the deformation process of the sample. The present invention provides a soil tester that can be observed precisely and that can easily mold a sample.

Soil tester according to the present invention for achieving the above technical problem, the housing consisting of a bottom plate, side walls, and a cover to provide a closed space; A sampler installed in the housing and on which a sample is placed; And a pressurizing device for providing a pressure in the housing, wherein the sampler comprises: two side walls for supporting the sample on both sides; A lower cap installed to block a lower portion between the side walls; A load ram installed to penetrate the cover of the housing to move up and down; An upper cap connected to the load ram and interlocked with the movement of the load ram to block the upper portion between the side walls; An inner membrane surrounding the side of the sample; An outer membrane surrounding an outer surface between the lower cap and the upper cap; And a pore water pressure pipe connected to the sample from the outside of the housing. Characterized in that comprises a.

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At least one of the sidewalls is preferably made of a transparent material.

The side of the housing is preferably in the shape of a flat square.

The lower cap is preferably installed to be movable in the direction of the surface without the side wall.

The upper end of the inner membrane is preferably fixed by the O-ring to the upper cap and the lower end is fixed by the O-ring to the lower cap.

The upper end of the outer membrane is preferably fixed by the O-ring to the upper cap and the lower end is fixed to the lower cap by the O-ring.

The pore water pressure pipe is preferably connected to the sample through the upper cap and the lower cap.

The soil tester according to the present invention preferably further includes two molding plates which can be erected on the side without the side wall so that the four sides of the sample are blocked, and in this case, the suction plate is preferably provided.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in detail. The following examples are only presented to understand the content of the present invention, and those skilled in the art will be capable of many modifications within the technical spirit of the present invention. Therefore, the scope of the present invention should not be construed as limited to these embodiments.

3 is a view for explaining the soil tester according to the present invention, Figure 4 is a view for explaining the process of forming the sample 150.

Referring to FIG. 3, the housing is composed of a bottom plate 112, a side wall 130, and a cover 114, and a sampler is installed in the housing. The sampler includes two sidewalls 142 and 144 supporting the sample on both sides, a lower cap 122, and an upper cap 124. The lower cap 122 and the upper cap 124 block the lower and upper portions between the side walls 142 and 144, respectively.

The lower cap 122 is first covered with the inner membrane 152 and the O-ring 122a is fitted to the outer circumferential surface of the lower cap 122 to fix the lower end of the inner membrane 152 to the lower cap 122. Then, as shown in FIG. 4, two molding plates 146 (one hidden and invisible) are installed on the front and rear surfaces (front and back of the ground) without sidewalls 142 and 144 and two molding plates 146 and The two side walls 142 and 144 are blocked in all directions.

The inner membrane 152 is raised above the molding plate 146 and the sidewalls 142 and 144 to be folded outward, and the air is sucked out through the inlet 146a formed in the molding plate 146. Then, the inner membrane 152 is in close contact with the inner wall of the mold formed of the molding plate 146 and the side walls 142 and 144 so that a gap does not occur.

In such a state that the inner membrane 152 is adsorbed on the mold inner wall, the sample 150 is put into the mold and molded at a desired relative density (density) and a water content ratio. Then, the upper cap 144 is placed on the sample 150, and then the inner membrane 152 is rolled up to fix the upper end of the inner membrane 152 to the outer circumferential surface of the upper cap 144 with the O-ring 124a. The two molding plates 146 shown in FIG. 4 are then removed.

After removing the molding plate 146, the suction of the vacuum through the pore pressure pipe (L1, L2) so that the shape of the sample 150 can be maintained. The gap hydraulic pipes L1 and L2 are connected to the sample 150 through the upper cap 124 and the lower cap 122. Next, the connecting plate 246 is installed so that this form is not torn down. The outer membrane 154 surrounds all of the outer surfaces from the upper cap 124 to the lower cap 122, and O-rings 122b and 124b are installed on the lower cap 122 and the upper cap 124, respectively. Secure the bottom and top of (154).

If only the outer membrane 154 is present, it is difficult to accurately measure the flow rate of the pore water and the pore water pressure generated during the drainage or non-drainage pressurization process (making the site ground state), so that the inner membrane 152 is installed as described above. To have a double membrane structure.

Next, assembling the load ram 170 to the upper cap 124 to move the upper cap 124 up and down. Then, the side wall 130 is placed on the bottom plate 112 and the cover 114 is fitted thereon. At this time, the load ram 170 penetrates the cover 114, and when the load ram 170 moves up and down, the upper cap 124 also moves up and down. By tightening the bottom plate 112 and the cover 114 with each other using a vertical clamp 162, the interior of the housing is watertight. An O-ring is installed between the bottom plate 112, the side wall 120, and the cover 114 to help achieve such watertightness.

Subsequently, water is filled into the housing through the confining pressure tube L3. When the water is filled inside the housing, the configuration of FIG. 3 is connected to a frame of a general triaxial tester (including a load device, a pressure regulator, and a pore water pressure measuring device). Then, a little pneumatic pressure is applied through the restraint pressure tube L3 and the sample 150 can be properly stood to release the vacuum suction through the pore pressure tubes L1 and L2. Then, the air of the sample 150 is removed through the pore-pressure pipes L1 and L2, and water is supplied to saturate.

In order to accurately describe the site, the lower cap 122 is movably installed without friction in the direction of the surface (front and back of the ground) without the side walls 142 and 144 by the linear bearing 202. The lower cap 122 is fixed when the control device 204 is moved up, and the lower cap 122 is movable when the controller 204 is raised. In the shear test, the control device 204 is lowered to allow the lower cap 122 to move freely back and forth on the ground.

At least one of the sidewalls 142 and 144 of the sampler is made of a transparent material such as acrylic in order to visually observe the fracture process of the sample 150, and the sidewall 130 of the housing to eliminate the effect of refraction. Uses a rectangular box that is not cylindrical. This is advantageous for digital imaging using a digital camera outside of the housing. The earth pressure gauge 300 is installed on the side wall 144 that is not made of acryl to more accurately grasp the stress state under the planar deformation condition.

 If necessary, a transducer can be installed inside to measure small strain. In the case of measuring such small strains, it is preferable to use only the inner membrane 152 in consideration of precision problems, and in this case, various stress path tests other than the compression test are difficult. If the outer membrane 154 is not covered, replace the lower cap 122 so that water does not leak. At this time, the pore water pressure pipe L2 installed in the lower cap 122 may come out in the horizontal direction where the displacement is not restricted.

As described above, according to the present invention, it is possible not only to test various stress paths while accurately measuring the volume deformation and the pore water pressure of the sample, but also to reproduce the only fracture surface of the actual site, and to visualize the deformation process of the sample. It can also be observed exactly, and it can make the shaping | molding of a sample easy.

Claims (8)

A housing comprising a bottom plate, a side wall, and a cover to provide a sealed space; A sampler installed in the housing and on which a sample is placed; And a pressurizing device for providing pressure in the housing. The sample device, Two side walls for supporting the sample on both sides; A lower cap installed to block a lower portion between the side walls; A load ram installed to penetrate the cover of the housing to move up and down; An upper cap connected to the load ram and interlocked with the movement of the load ram to block the upper portion between the side walls; An inner membrane surrounding a side of the sample; An outer membrane surrounding an outer surface between the lower cap and the upper cap; And A pore water pressure pipe connected to the sample from the outside of the housing; Soil tester, characterized in that comprises a. The soil testing machine according to claim 1, wherein at least one of the side walls is made of a transparent material. The soil tester according to claim 1, wherein the side of the housing has a flat rectangular shape. The soil tester according to claim 1, wherein the lower cap is movably installed in a direction of a surface without the side wall. The soil tester of claim 1, wherein an upper end of the inner membrane is fixed to the upper cap by an O-ring and a lower end is fixed to the lower cap by an O-ring. The soil tester according to claim 1, wherein an upper end of the outer membrane is fixed to the upper cap by an O-ring and a lower end is fixed to the lower cap by an O-ring. The soil tester according to claim 1, wherein the pore-pressure pipe is connected to the sample through the upper cap and the lower cap. The soil tester according to claim 1, further comprising two molding plates that can be erected on the side without the sidewalls to block all sides of the sample, wherein the molding plates are provided with suction ports.

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