• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1693-1706
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• 2008

It is of importance to determine the zero effective stress void ratio($e_{00}$), which is the void ratio at effective stress equal to zero, and the relationships of void ratio-effective stress and of void ratio-hydraulic conductivity for characterizing non-liner finite strain consolidation behavior for ultra-soft dredged materials. The zero effective stress void ratio means a transitional status from sedimentation to self-weight consolidation of very soft soil deposits, and acts as a starting point for self-weight consolidation in the non-linear finite strain numerical analysis such as PSDDF. In this paper, a new method for determining the zero effective stress void ratio has been introduced with the aid of measuring electrical resistivity of the specimen. A correlation between the zero effective stress void ratio and the initial slurry void ratio has been proposed, which can be used in PSDDF analysis as an input parameter. Combining all of the accessible experimental data, the consolidation characteristics of a dredged soil from the Incheon area has been studied in detail.

• Journal of Powder Materials
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• v.13 no.2 s.55
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• pp.124-128
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• 2006

In recent years, equal channel angular pressing (ECAP) has been the subject of intensive study due to its capability of producing fully dense samples having a ultrafine grain size. In this paper, the ECAP process was applied to metallic powders in order to achieve both powder consolidation and grain refinement. In the ECAP process for solid and powder metals, knowledge of the internal stress, strain and strain rate distribution is fundamental to the determination of the optimum process conditions for a given material. The properties of the ECAP processed solid and powder materials are strongly dependent on the shear plastic deformation behavior during ECAP, which is controlled mainly by die geometry, material properties, and process conditions. In this study, we investigated the consolidation, plastic deformation and microstructure evolution behaviour of the powder compact during ECAP.

• Journal of the Korean Geotechnical Society
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• v.27 no.9
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• pp.13-24
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• 2011

The renowned Terzaghi's one-dimensional consolidation theory is not applicable to quantification of time-rate settlement for highly deformable soft clays such as dredged soil deposits. To deal with this special condition, a non-linear finite strain consolidation theory should be adopted to predict the settlement of dredged soil deposits including self-weight and surcharge-induced consolidation. It is of importance to determine the zero effective stress void ratio ($e_{00}$), which is the void ratio at effective stress equal to zero, and the relationships of void ratio-effective stress and of void ratio-hydraulic conductivity for characterizing non-linear finite strain consolidation behavior for deformable dredged soil deposits. The zero effective stress void ratio means a transitional status from sedimentation to self-weight consolidation of dredged soils. In this paper, laboratory procedures and equipments are introduced to measure such key parameters in the non-linear finite strain consolidation analysis. In addition, the non-linear finite strain consolidation parameters of the Incheon clay and kaolinite are evaluated with the aid of the proposed methods in this paper, which will be used as input parameters for the non-linear finite strain consolidation analyses being performed in the companion paper.

• Journal of Powder Materials
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• v.14 no.1 s.60
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• pp.26-31
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• 2007

Manufacturing bulk nanostructured materials with least grain growth from initial powders is challenging because of the bottle neck of bottom-up methods using the conventional powder metallurgy of compaction and sintering. In this study, bottom-up type powder metallurgy processing and top-down type SPD (Severe Plastic Deformation) approaches were combined in order to achieve both real density and grain refinement of metallic powders. ECAP (Equal Channel Angular Pressing), one of the most promising processes in SPD, was used for the powder consolidation method. For understanding the ECAP process, investigating the powder density as well as internal stress, strain distribution is crucial. We investigated the consolidation and plastic deformation of the metallic powders during ECAP using the finite element simulations. Almost independent behavior of powder densification in the entry channel and shear deformation in the main deformation zone was found by the finite element method. Effects of processing parameters on densification and density distributions were investigated.

• Geomechanics and Engineering
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• v.13 no.6
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• pp.963-975
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• 2017

Improvement of soft clay deposit by preloading with vertical drains is one of the most popular techniques followed worldwide. These drains accelerate the rate of consolidation by shortening the drainage path. Although the analytical and numerical solutions available are mostly based on equal strain hypothesis, the adoption of free strain analysis is more realistic because of the flexible nature of the imposed surcharge loading, especially for the embankment loading used for transport infrastructure. In this paper, a numerical model has been developed based on free strain hypothesis for understanding the behaviour of soft ground improvement by vertical drain with preloading. The unit cell analogy is used and the effect of smear has been incorporated. The model has been validated by comparing with available field test results and thereafter, a hypothetical case study is done using the available field data for soft clay deposit existing in the eastern part of Australia and important conclusions are drawn therefrom.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.10a
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• pp.65-94
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• 2001

The use of PBD(prefabricated band drain)far ground improvement is rapidly increased due to the merit of construction period and cost, environmental preservation compared with other vertical drain method, and the development of material. This paper presents the historical review, theoretical background, design procedure and method, and typical construction example for the PBD. Also, the direction of further technical development and study is recommended.

• Journal of Powder Materials
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• v.11 no.2
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• pp.97-104
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• 2004

In this paper processing and mechanical properties of Al-20 wt％ Si alloy was studied. A bulk form of Al-20Si alloy was prepared by gas atomizing powders having the powder size of 106-145 ${\mu}m$ and powder extrusion. The powder extrudate was subsequently equal channel angular pressed up to 8 passes in order to refine grain and Si particle. The microstructure of the gas atomized powders, powder extrudates and equal channel angular pressed samples were investigated using a scanning electron microscope and X-ray diffraction. The mechanical properties of the bulk sample were measured by compressive tests and a micro Victors hardness test. Equal channel angular pressing was found to be effective in matrix grain and Si particle refinement, which enhanced the strength and hardness of the Al-2OSi alloy without deteriorating ductility in the range of experimental strain of 30％.

• Journal of the Korean Geotechnical Society
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• v.15 no.1
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• pp.151-160
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• 1999

A series of laboratory tests for the marine clay sampled under the sea of Kwangyang bay have been conducted. The main types of tests are the general index property tests, the oedometer tests and the triaxial compression tests in both undrained(CIU) and drained(CID) conditions. The clayey samples, classified as CL, CH with natural water content of 38.3~84.6% and liquidity index of 0.71~0.98, are in the normally consolidated state with O.C.R. of 1.0l~l.60. The undrained stress path from CIU tests can be normalized with isotropic consolidation pressure$(p_0)$ and equal shear strain contour is linear passing through the origin in the (q, p) plot. The undrained shear strain is found to be the only function of the stress ratio($\eta$) and linear with intercept in the ($\varepsilon/\eta,\eta$) plot. The built-up pore pressure normalized with pc is also linear with respect to $\eta$. and its slope is defined by ´C´ as a pore pressure parameter. Equations to predict the undrained stress path and the shear strain are proposed. It is proved that the proposed equations give better agreements to the measured values than the Cam-clay theories. The failure points of the stress path are located on the same C.S.L. in (q, p) plot during both CIU and CID tests, which justifies the concept of critical state theory.