• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2C
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• pp.109-117
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• 2010

Gas hydrate dissociation can generate large amounts of gas and water in gas hydrate bearing sediments, which may eventually escape from a soil skeleton and form voids within the sediments. The loss of fine particles between coarse particles or collapse of cementation due to water flow during heavy or continuous rainfall may form large voids within soil structure. In this study, the effect of void formation resulting from gas hydrate dissociation or loss of some particles within soil structure on the strength of soil is examined. Glass beads with uniform gradation were used to simulate a gas hydrate bearing or washable soil structure. Glass beads were mixed with 2% cement ratio and 7% water content and then compacted into a cylindrical sample with five equal layers. Empty capsules for medicine are used to mimic large voids, which are bigger than soil particle, and embedded into the middle of five equal layers. The number, direction, and length of capsules embedded into each layer vary. After two days curing, a series of unconfined compression tests is performed on the capsule-embedded cemented glass beads. Unconfined compressive strength of cemented glass beads with capsules depends on the volume, direction and length of capsules. The volume and cross section formed by voids are most important factors in strength. An unconfined compressive strength of a specimen with large voids decreases up to 35% of a specimen without void. The results of this study can be used to predict the strength degradation of gas hydrate bearing sediments in the long term after dissociation and loss of fine particles within soil structure.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.677-680
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• 2005

In numerical analysis on the thermal performance of the heat exchanger with phase change fluids, the numerical values of thermodynamic properties are needed. But the steam table should be modeled properly as the direct use of thermodynamic properties of the steam table is impossible. In this study the function approximation characteristics of neural networks was used in modeling the saturated vapor region of refrigerant R12. The neural network consists of one input layer with one node, two hidden layers with 10 and 20 nodes each and one output layer with 7 nodes. Input can be both saturation temperature and saturation pressure and two cases were examined. The proposed model gives percentage error of ${\pm}$0.005% for enthalpy and entropy, ${\pm}$0.02% for specific volume and ${\pm}$0.02% for saturation pressure and saturation temperature except several points. From this results neural network could be a powerful method in function approximation of saturated vapor region of R12.

• Journal of Korean Society of Steel Construction
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• v.10 no.3 s.36
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• pp.487-495
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• 1998

Recently, the space truss has been attracted by many designers because of their ability to support significant loads with a minimum material. And it is relatively flexible to design the configuration of structures. This paper presents a volume optimization for the space truss on the basis of result evaluated from nonlinear analysis. The optimization of the truss is done by nonlinear optimum GINO(General Interactive Nonlinear Optimizer) program. The objective function considered is the volume of the steel bars. The constraints for optimum design are the design limits, such as the axial force strength, maximum slenderness, minimum thickness, allowable deflection and ratio of the external diameter to thickness of the circular tube bars.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1897-1905
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• 2013

Rheological properties such as yield stress and viscosity is the main parameters to determine the fluidity of the debris flow. In this study, several series of rheometer tests were performed to investigate rheological properties of fine-grained soil samples with various sand contents and various liquidity indices. Test results indicated that the general shape of the flow curves for fine-grained soils had characteristics of a shear thinning fluid, with a decrease in viscosity as shear rate increases. The yield stress and viscosity of fine-grained soil samples with same sand content gradually decreased as the liquidity index increased. At the same liquidity index, yield stress and viscosity of fine-grained soil increased with an increase in sand content. The yield stress and viscosity of fine-grained soil greatly decreased with a slight increase in water content. Also, the yield stress and viscosity tend to increase with increasing concentration by volume($C_v$) of the fluid matrix. The values of the four coefficients ${\alpha}_1$, ${\alpha}_2$, ${\beta}_1$, and ${\beta}_2$ were obtained by regression analysis for each fine-grained soil.

• Journal of computational fluids engineering
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• v.6 no.3
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• pp.19-26
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• 2001

An Eulerian-Lagrangian method, so called immersed boundary method, is used for analysing viscous flow around arbitrary bodies, where governing equations are discretized on a regular grid by using a finite volume method. To improve the accuracy of flow near body boundaries, a second-order accurate interpolation scheme is used and a level-set based grid deformation method is presented to construct the adaptive grids around body boundaries. The present scheme is used to simulate steady flow around a semicircular cylinder mounted on the bottom of flow domain and calculated results are validated by results of a body fitted grid method. Finally, present method is applied to a complex flow around multi body and the usefulness is checked by investigating calculated results.

• Journal of the Society of Disaster Information
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• v.16 no.3
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• pp.577-585
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• 2020

Purpose: The presence of the matric suction in unsaturated soil increases the stability of the slope, but the reduction of the matric suction due to precipitation can cause sudden slope failure, resulting in a major disaster. In this paper, engineering characteristics in unsaturated state were analyzed for granite weathering soil, which is the representative mountain soil of Korea. Method: Experiments and analysis were conducted on granulated weathering soil as unsaturated shear strength relationships for moisture characteristic curves, unsaturated injection curves, and matric suction under unsaturated conditions. Result: It was analyzed that a rapid change in the matric suction for volumetric water content occurs compared to the case where the particle size distribution is poor and the particle size distribution is good. A good case for the particle size distribution indicates a relatively small permeability coefficient at the same matric suction capacity compared to a poor case. The greater thematric suction, the greater the shear strength. Conclusion: For Korea's representative soil, granulated weathering soil, the functional characteristic curves, unsaturated permeability coefficients, unsaturated shear strength, etc., which are engineering characteristics in unsaturated state, were tested to secure each correlation.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.65-74
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• 2003

Most of land reclamation projects are being implemented along the south and west coastal lines of the Korean Peninsula. The earth structures and in-ground LNG tank, and buildings can be constructed using artificial freezing method on the reclaimed land to control the uplift pressure caused by capillary forces. In this study, upon freezing a saturated soil in a closed-system from the top, a considerable frost heaving pressure was developed. Decomposed granite soils, silty soil, and sandy soil were used in the laboratory freeze test which is sometimes subjected to thermal gradients under closed-systems. A major concern has been the ability to predict the frost heaving pressure over the results of relatively short-term laboratory tests. The frost heaving pressure arising within the soil samples and the temperature of the samples inside were monitored with time elapse. The degree of saturation versus heaving pressure curve is presented for each soil sample and the maximum pressure is closely related to this curve. TDR apparatus was used to measure the volumetric water content by the measurement of unfrozen water contents of frozen soils. Unfrozen water increased in soils containing a high percentage of fine-grained particles. In fine-grained soils with strong attractive farces between soil grains and water molecules, additional water is attracted into the pores leading to further volume changes and ice segregation.

• The Journal of Engineering Geology
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• v.13 no.4
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• pp.405-418
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• 2003

Measurements of volumetric water content and saturation of porous media are very important factors in understanding the physical characteristics of soil, groundwater recharge by rainfall, pollutant movement, and slope failure. To measure such physical parameters, a permittivity method using electromagnetic wave is applied and use is made of the special permittivity response of understand to water and ethanol. In particular, the estimation is required because permittivity is influenced by the nature of the underground environment. In this study, we carried out experiments on the relative dependency of soil density, temperature and salinity of standard sand and granitic weathered soil using FDR-V system (Frequency domain reflectometry with vector network analyzer) within a frequency range of 1 - 18 GHz. The results of the study showed that the dielectric constants of standard sand and granitic weathered soil increased with increased volumetric water content of soil. However, the dependency of soil density was found to be a little low. Changes of dielectric constant with temperature appeared definitely in the real part of 1 GHz. That is, the dielectric constant of real part at 1 GHz of water and standard sand increased with the rise of temperature. However, ethanol showed decreased tendency. The study also showed that dielectric constant increased with increase in salinity at imaginary part of 1 GHz. It could be concluded from this study FDR-V system can adequately measure the physical properties of soil and the degree of salinity concentration of porous media within 1 GHz frequency range using dielectric constant.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.4C
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• pp.169-175
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• 2012

Soil water retention characteristics are influenced by factors of the confining stress and hysteresis in the variably saturated soil. In the description of effective stress based on hydraulic characteristics, the contribution of a matric suction to effective stress then varies with depth or is different between the processes of infiltration and evaporation. Unsaturated effective stress can be described based on suction stress characteristic curve, in which a representative soil water retention curve is required to evaluate. Pressure palate extractor tests under various confining stresses were performed and the hysteresis of drying and wetting process was also acquired. In the process of drying or wetting, a unique relationship has been estimated on the effective volumetric water content and the matric suction, which defines suction stress characteristic curve. In the unsaturated shear strength from triaxial tests, the suction stress and the effective stress were evaluated by matric suctions. The failure envelop by effective stress based on soil water retention characteristics was unique and the same as the saturated one. The measured suction stress from triaxial tests was similar to that from the soil water retention curve. Therefore it is verified that a representative soil water retention curve can be defined which is independent of the confining effect under wetting or drying process of the hysteresis.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.65-70
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• 2005

A low resistivity zone is found in many places such as a fractured fault zone, weathered zone and aquifer. The electrical resistivity is influenced mainly by pore fluid as well as the clay mineral types and contents, Hence, it is very important to understand the relationship between the electrical resistivity and clay contents associated with the low resistivity zone for geotechnical applications such as civil engineering. This study examines the characteristics of clay mineral types and contents to electrical resistivity through sample measurements, and proposes an expression relating the resistivity and clay content. The electrical resistivity is measured for an artificial agar specimen with clay minerals instead of a natural rock. The clay minerals used are Kaolinite and Montmorillonite. Montmorillonite shows remarkably lower resistivity than Kaolinite, although its clay content is fewer than that of Kaolinite. Also, the proposed expression shows a good correlation coefficient as high as 0.89 or more in all clay minerals.