KR101028783B1 - Consolidation testing apparatus for observing the inside of specimen under radial drainage condition - Google Patents

Abstract

Disclosed is a consolidation tester. The apparatus of the present invention comprises: a fan-shaped upper and lower plates positioned to face each other; A guide penetrating up and down a predetermined area of the upper plate; A pressure plate installed at one end of the guide and positioned between the upper plate and the lower plate; In addition to the upper plate and the lower plate is characterized in that the side plates are provided to form a space having a cross-section fan-shaped inside. According to the present invention, when the conventional cylindrical consolidation tester is used, the inside of the sample cannot be observed, but the inside of the sample can be observed while simulating the radial drainage under the axisymmetric condition.

Consolidation Tester, Radial Drain, Fan, Vertical Drain

Description

Consolidation testing apparatus for observing the inside of specimen under radial drainage condition

The present invention relates to a consolidation tester, and more particularly to a possible consolidation tester capable of observing the deformation of a sample under radial drainage consolidation conditions.

In general, for civil engineering materials such as steel and concrete, deformation occurs immediately when a load is applied, whereas for soil, depending on the type of soil, the deformation time is short, such as sand, and the deformation time is relatively long, such as clay. The deformation time is different. In particular, the soil is composed of water and air filled between the particles, and the volumetric deformation means that the water or air filling the gap is released. In the case of sand, the gap is relatively large, so water or air can easily escape, and compression occurs quickly.However, in the case of clay having a very small gap due to the small particle size, the compression is not only slow but over a long time. Engineering is a big problem. Consolidation is a phenomenon in which saturated clay is loaded and subsided over a long period of time while pore water escapes.

In order to design a soft ground improvement site that stabilizes saturated clay layers, it is necessary to understand the consolidation characteristics. This can be calculated through the consolidation test and the values indicating consolidation characteristics are as follows.

Consolidation coefficient (Cv): Expresses the density over time

Second Compression Index (Cα): Creep over time after consolidation

Compression Index and Recompression Index (Cc, Cr): Express settlement amount according to load

(If the current load is less than the previous consolidation load, the <overconsolidation> recompression index is applied.)

(If the current load is the maximum load experienced by the soil, apply the <Normal Consolidation> compression index.)

Preceding Consolidation Load (Pc '): Maximum Consolidation Load Experienced by Soil

In addition to these consolidation characteristics, there are also consolidation characteristics that reflect spatial properties including boundary conditions. Basically, it is common to calculate the consolidation coefficient of the vertical drainage condition, but when transverse drainage occurs during consolidation, the transverse permeability coefficient and consolidation coefficient, etc. considering the difference in the structural characteristics of the vertical and transverse directions of soil should be considered. Needs to be.

The above mentioned consolidation characteristics can be obtained by consolidation test. The types of consolidation tests for obtaining consolidation characteristics are as follows.

1. Standard consolidation test

Figure 1a is a view showing a standard consolidation tester according to the prior art, Figure 1b is a graph measuring the volume deformation over time using the consolidation tester according to Figure 1a, Figure 1c using the consolidation tester according to Figure 1a This is a graph measuring volumetric deformation with load.

In Figure 1a (1) is a schematic diagram of a standard consolidation tester, (2) is a photograph during the standard consolidation test, (3) is a standard consolidation test box and consolidation ring photograph.

Figure 1a shows the basic shape of a standard consolidation tester. The load is transmitted to the clay sample inside the consolidation ring through the pressure plate, and the pore water in the clay sample is freely drained through the porous plate. And the dial gauge or LVDT measures the vertical displacement of the platen, which makes it easy to estimate the volume change of the soil.

The consolidation test is divided into several loading stages to calculate the consolidation coefficients from the time-volume graph of FIG. 1B at each stage. In addition, a stress-volume relationship as shown in FIG. 1C may be obtained by using a volume value corresponding to consolidation completion of each load step.

2. CRS Consolidation Equipment

Figure 2a is a schematic diagram showing a CRS compaction equipment according to the prior art.

The Constant Rate of Strain (CRS) consolidation tester utilizes a speed-controlled loading frame that is typically used for strength testing in the way of loading. In other words, the load is applied by pressing the pressure plate at a constant speed. Unlike standard consolidation tests, the additional pore water pressure should be measured continuously during the test because it does not generate additional load after completion of consolidation. The stress-volume relationship as shown in Fig. 2 is obtained by calculating the effective stress of the soil with the total load considering the excess pore water pressure, and the consolidation coefficient is calculated by theoretically analyzing the change of stress and the pore water pressure at arbitrary time intervals.

3. Rowe Cell Test Equipment

Figure 2b is a schematic diagram showing a Rowe Cell test equipment according to the prior art.

The Rowe Cell Consolidation Tester applies the load by pneumatic or hydraulic pressure using a diaphragm. This allows flexible loads (Equal Stress) as well as loads due to rigid plates (Equal Strain). The pore water pressure can also be measured internally. Test steps and interpretations are done in the same way as standard consolidation test methods.

4. Large consolidation test equipment

Figure 2c is a view showing a large compaction test equipment according to the prior art.

Most of the testers described above have only been performed on small samples of about 6 cm in diameter, but large consolidation testers exist from 30 cm in diameter to more than 1 m. Both the Rigid Plate method and the Diaphragm method are used to apply the load. If necessary, the pore water pressure inside the sample was measured using a needle.

Figure 2d is a schematic diagram showing the vertical drainage method used in the soft ground improvement site.

The sample utilized in the conventional tester as described above is easy to sample, cylindrical to facilitate the test, and most of the drainage is designed to be made only in the vertical direction (up, down direction). Radial drainage consolidation tests can also be carried out by blocking vertical drainage (removing the upper and lower perforated plates and preventing drainage), and inducing drainage in the radial or inward direction. have. That is, the radial drainage condition required for the vertical drainage method design as shown in FIG. As shown in FIG. 2C, a vertical drainage material, such as sand, may be inserted into the middle of the sample to induce radial inward drainage, or drainage may be made of a material such as porous plastic in the consolidation ring to induce drainage in the radial outward direction. This can be applied to both small and large samples.

2E is a schematic diagram showing test equipment for estimating movement inside a sample using magnets.

Regardless of the drainage conditions, the existing theoretical methods for consolidation analysis assume that only vertical compression occurs during the consolidation process. However, recent experimental studies have shown that even in the ground where the load in the vertical direction is loaded, transverse deformation occurs in the sample during radial consolidation. Therefore, as shown in FIG. 2e, the magnet was read from the magnetometer to determine the movement of the magnet at several positions within the sample using the magnet.

As described above, the existing theoretical methods for consolidation analysis regardless of the drainage conditions are mostly performed assuming that only vertical compression occurs during the consolidation process. Under these assumptions, it is not necessary to observe the deformation inside the sample, so the test may be performed on the cylindrical sample. Recently, however, it has been found that transverse deformation occurs inside the sample during radial drainage consolidation, even if the ground is loaded vertically.

Uneven deformation behavior along the radial direction inside the sample may result in uneven and locational strength differences, increase of total settlement and time required for consolidation. In addition, even after the improvement of the soft ground, it is not possible to secure a homogeneous ground state, which may cause problems in the stability of the structure in the future. Therefore, it is very important to observe and evaluate the deformation in the ground under the condition of drainage.

Despite this importance, however, there have been no developments in which lateral deformations that cause soil inhomogeneities during radiation drainage consolidation are easily observed. That is, in the conventional consolidation test, the test is performed on almost all cylindrical samples, and the overall deformation inside the sample cannot be observed. Research using magnets and magnetometers can only find deformations in some locations, and there are disadvantages in terms of difficulty in analysis and expensive equipment. In addition, even if the inside of the cylindrical sample is visually observed, it is impossible to measure the deformation by continuously observing because it must be cut and examined at the end of the test.

Accordingly, the problem to be solved by the present invention is to provide a consolidation tester that can observe the overall deformation inside the sample.

Consolidation tester according to the present invention for achieving the above object: a fan-shaped upper and lower plates positioned to face each other; A guide penetrating up and down a predetermined area of the upper plate; A pressure plate installed at one end of the guide and positioned between the upper plate and the lower plate; In addition to the upper plate and the lower plate is characterized in that the side plates are provided to form a space having a cross-section fan-shaped inside.

At this time, the vertical drainage material is installed in the space.

According to the present invention, when the conventional cylindrical consolidation tester is used, the inside of the sample cannot be observed, but the inside of the sample can be observed while simulating the radial drainage under the axisymmetric condition.

At this time, it is possible to study the deformation of the entire sample through analysis from the images obtained continuously, thereby it is possible to grasp the transverse deformation according to the position in the radial drainage consolidation conditions that are very important geotechnical.

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

3a to 3c are schematic diagrams for explaining each component of the consolidation tester according to an embodiment of the present invention, Figure 3d is a schematic diagram showing the assembly form of the consolidation tester according to an embodiment of the present invention, Figure 3e It is a schematic diagram for demonstrating the drainage direction of the consolidation tester which concerns on the Example of this invention.

3A to 3C, the consolidation tester according to the embodiment of the present invention includes a top plate, a bottom plate, side plates, a pressure plate, a guide, and an O-ring.

The upper plate 100 and the lower plate 200 are positioned to face each other in a fan shape.

Pressure plate 300 is also made of a floating shape, is located between the upper plate 100 and the lower plate 200.

The guide 400 penetrates up and down a predetermined area of the upper plate so that the upper end thereof is exposed above the upper plate 100, and the pressing plate 300 is installed at the lower end thereof. Therefore, the sample is pressurized by the pressing plate 300 by moving the guide 400 up and down after the sample is located inside the consolidation tester.

The side plates 510, 520, and 530 are installed together with the upper plate 100 and the lower plate 200 to form a space having a fan-shaped cross section therein. At this time, the side plates are formed of a transparent material such as transparent acrylic to observe the cross section of the sample.

Vertical drainage (Porous Plastic, 600) is installed inside the tester to induce the direction of the drainage. Accordingly, the vertical drain 600 is installed in a fan-shaped space, preferably in a region where the side plates are opposed to each other.

Referring to FIG. 3D, the upper plate, the lower plate and the side plates are fixed using a screw rod, and an O-ring is used to prevent drainage in an area other than the area where the vertical drainage material is installed.

The present invention relates to a tester that can continuously visually observe the deformation of the sample during the consolidation test of the radial drainage conditions, taking an image of the observed deformation of the sample in the image, and interprets the image at a desired time interval This is to allow the deformation to be estimated.

Conventional consolidation tests have conducted tests on almost all cylindrical samples, so that the overall deformation inside the sample could not be visually observed. Overcoming these limitations and simulating radial drainage conditions, it is possible to visually and continuously observe the deformation inside the sample.

4 is a schematic view of a part of a sample used in the consolidation tester according to an embodiment of the present invention.

One side of the fan-shaped sample removed from the cylindrical sample according to Figure 4 becomes the inner cross section in the actual cylindrical consolidation sample, observing this side has the same effect as observing the inside of the sample. In addition, the cylindrical consolidation tester in the radial drainage condition satisfies the Axis-Symmetry Condition around the center of the cylinder, so the observed cross-sections represent all cross-sections.

Therefore, it is possible to continuously observe the deformation inside the sample while selecting a fan-shaped column instead of a cylinder to simulate the radially consolidation state in the axisymmetric condition.

Hereinafter will be described the operation of the consolidation tester according to the practice of the present invention.

Grease is applied evenly to remove friction on the tester walls prior to testing using the assembled tester according to an embodiment of the present invention. This is an important task for the face observed from the transparent side to represent the cross section inside the sample. Insert the sample with the tester lower plate and the transparent side plate assembled, and assemble the top plate connected to the pressure plate. The load can be either standard consolidation test methods (using weights and levers) or commonly used frames (for testing the strength of soil backings) to control deformation or load.

Referring to FIG. 4, when a test is performed on a fan-shaped sample cut and formed into a cake shape, a portion of the cylindrical sample is simulated, and the observed surface is a deformation in the cylindrical sample. At this time, the radial drainage is induced using a vertical drainage material (Porous Plastic) for the radial drainage. Drainage occurs as shown in FIG. 3E, and the deformation shape of the sample was continuously observed through the transparent side while the consolidation test of the clay sample was performed.

1A shows a standard consolidation tester according to the prior art;

Figure 1b is a graph measuring the volumetric deformation over time using the consolidation tester according to Figure 1a;

Figure 1c is a graph measuring the volume deformation according to the load using the consolidation tester according to Figure 1a;

2A is a schematic diagram showing CRS compaction equipment according to the prior art;

2B is a schematic diagram showing Rowe Cell test equipment according to the prior art;

2C shows a large compaction test equipment according to the prior art;

Figure 2d is a schematic diagram showing the vertical drainage method used in the soft ground improvement site;

FIG. 2E is a schematic diagram illustrating test equipment utilizing a magnet to calculate movement inside a sample; FIG.

3A-3C are schematic diagrams for explaining respective components of the consolidation tester according to the embodiment of the present invention;

3D is a schematic view showing the assembly form of the consolidation tester according to the embodiment of the present invention;

3E is a schematic view for explaining the drainage direction of the consolidation tester according to an embodiment of the present invention; And

4 is a schematic view of a part of a sample used in the consolidation tester according to an embodiment of the present invention.

Claims (4)

A fan-shaped upper and lower plates positioned to face each other; A guide penetrating up and down a predetermined area of the upper plate; A pressure plate installed at one end of the guide and positioned between the upper plate and the lower plate; Side plates together with the upper plate and the lower plate to form a space having a fan-shaped cross section inside, and made of a transparent material; And Consolidation tester, characterized in that it comprises a vertical drain installed in the space. delete The consolidation tester of claim 1, wherein the vertical drainage material is installed in an area in which the side plates face each other. delete

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