• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 봄 학술발표회 논문집
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• pp.49-54
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• 2002

This paper describes a systematic way of simultaneously identifying the ambient pore pressure and the rigidity index (=G/s$\_$u/) of soil by applying an optimization technique to the piezocone dissipation test result. An ambient pore pressure and optimal rigidity index were determined by minimizing the differences between theoretical excess pore pressures developed by Randolph ＆ Wroth(1979) and measured excess pore pressures from piezocone using optimization technique. The effectiveness of the proposed back-analysis method was examined against the well-documented performance of piezocone dissipation tests (Tanaka ＆ Sakagami, 1989), from the viewpoints of proper determination of selected target parameters and saving of test duration. It is shown that the proposed back-analysis method can evaluate properly the ambient pore pressure and the rigidity index by using only the early phase of the dissipation test data. Also, it is shown that with the optimized rigidity index and ambient pore pressure the proposed back-analysis method permits the horizontal coefficient of consolidation to be identified rationally.

• 한국세라믹학회지
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• 제33권12호
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• pp.1394-1402
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• 1996

The Silica gel with the density of 0.2g/cm3 and porosity of 90% was synthesized. The silica wet gel was dried and heat-treated under the ambient pressure after modification of the wet gel surface by TMCS. Specific surface area total pore volume and mean pore radius of dried gel were all increased with increasing heat treatment temperature and confirmed about 1400m2/g, 4.5cc/g and 8 nm respectively after heat treatment above 25$0^{\circ}C$. But the pore size distribution of dried gel was in the range of 1-100nm and was almost indepen-dent of temperature. As the result of external shape pore characteristics and microstructure of gel using SEM similar properties were observed between the silica gel synthesized in this study and the silica aerogel through the super critical drying.

• 한국지반공학회논문집
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• 제18권2호
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• pp.161-170
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• 2002

본 논문은 최적화기법을 이용하여 현장에서 수행된 피에조콘 소산시험의 초기 경향으로부터 평형간극수압과 지반의 강성지수$(=G/s_u)$를 역해석하는 기법에 관하여 기술하였다. 피에조콘 관입으로 인해 콘 주변에 발생된 초기 과잉간극 수압의 크기 및 분포, 그리고 연속된 간극수압 소산과정은 Randolph & Wroth(1979)가 제안한 해석적 해를 이용하여 지반의 강성지수의 함수로 표현되었다. 제안된 기법에서는 주어진 강성지수에 대해 정규화 된 이론 소산곡선과 평형간극수압으로 정규화 된 피에조콘 관측 소산곡선이 가장 일치하도록 하는 평형간극수압과 지반의 강성지수가 최적화기법을 이용하여 결정되었다. 제안된 기법을 압밀이 진행중인 지반에서 관측된 피에조콘 소산시험 결과(Tanaka & Sakagami, 1989) 해석에 적용하였고 역해석된 평형간극수압과 현장에서 관측된 평형간극수압의 크기를 비교하였다. 또한 제안된 기법으로 얻어진 지반의 강성지수와 평형간극수압을 바탕으로 수평압밀계수를 추정하였으며 일차원 압밀실험 결과와 비교하였다. 그 결과 제안된 기법이 지반에 잔류하는 평형간극수압의 크기를 매우 정확하게 예측함을 알 수 있었고 역해석 된 강성지수를 이용한 압밀계수의 추정이 타당함을 알 수 있었다. 또한 얻어진 강성지수의 변형 률수준에 관한 검토결과 피에조콘 해석을 위한 강성지수는 중간 또는 대변형 상태의 변형상태에 해당하는 값을 사용하는 것이 타당할 것으로 판단되었다.

• Geomechanics and Engineering
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• 제12권4호
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• pp.707-721
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• 2017

The objective of this paper is to experimentally study the consolidation of saturated silty clay subjected to repeated heating-cooling cycles using a modified temperature-controlled triaxial apparatus. Focus is placed on the influence of the water content, confining pressure, and magnitudes and number of thermal loading cycles. The experimental results show that the thermally induced pore pressure increases with increasing water content and magnitude of thermal loading in undrained conditions. After isothermal consolidation at an elevated temperature, the pore pressure continues to decrease and gradually falls below zero during undrained cooling, and the maximum negative pore pressure increases as the water content decreases or the magnitude of thermal loading increases. During isothermal consolidation at ambient temperature after one heating-cooling cycle, the pore pressure begins to rise due to water absorption and finally stabilizes at approximately zero. As the number of thermal loading cycles increases, the thermally induced pore pressure shows a degrading trend, which seems to be more apparent under a higher confining pressure. Overall, the specimens tested show an obvious volume reduction at the completion of a series of heating-cooling cycles, indicating a notable irreversible thermal consolidation deformation.

• 센서학회지
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• 제16권6호
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• pp.395-400
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• 2007

Ambient drying sol-gel processing was used for monolithic silica ambigels in the temperature range of $130-250^{\circ}C$. A new method of mesopore ambigels, which mean the aerogels prepared by ambient pressure drying process synthesis, is suggested at first. This method includes two important approaches. The first point is that $SiO_{2}$ surface modification of wet gel was performed by trimethylchlorosilane in n-butanol solution. This procedure is provided the silica gel mesopore structure formation. The second point is a creation of the ternary azeotropic mixture water/n-butanol/octane as porous liquid, which is effectively provided removing of water such a low temperature by 2 step drying condition under ambient pressure. The silica aerogels, which were prepared by ambient pressure drying from azeotropic mixture of water/n-butanol/octane, are transparent, crack-free and mesoporous (pore size ${\sim}$ 5.6 nm) with surface area of ${\sim}$ $923{\;}m^2/g$, bulk density of $0.4{\;}g/cm^3$ and porosity of 85 %.

• 공업화학
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• 제22권2호
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• pp.209-213
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• 2011

낮은 열전도율, 높은 비표면적과 기공률을 갖는 소수성 실리카 에어로겔 과립을, 저가의 물유리를 실리카 전구체로 사용하고 상압건조하여 제조하였다. 별도의 과립화 첨가제 및 과립화 기구를 사용하지 않고, 산도(~5)를 변화시켜 모노리스 형태의 습윤겔을 먼저 제조하여, 용매치환/소수성화 동시공정과 상압건조공정 과정에서 습윤겔이 깨져 0.5~2 mm 크기의 과립형태 실리카 에어로겔을 제조하였다. 제조된 실리카 에어로겔 과립은 비표면적, 평균기공크기, 기공부피가 각각 $593m^2/g$, 34.9 nm, $4.4cm^3/g$으로 실리카 에어로겔 분말과 거의 유사한 다공도를 가지고 있으며, 열전도율도 $20^{\circ}C$에서 19.8 mW/mK으로 나타나 같은 조건에서 제조된 실리카 에어로겔 분말과 거의 같은 단열성을 나타내었다.

• 대한금속재료학회지
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• 제47권8호
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• pp.516-521
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• 2009

In this study we report a rapid synthesis of nanoporous organo-functional silica (OFS) with unimodal and bimodal pore structures encompassing pores ranging from meso-to macroscale. The problems of tediousness and high production cost in the conventional syntheses are overcome by co-condensation of an inexpensive inorganic precursor, sodium silicate with an organosilane containing trimethyl groups. The insitu covalent anchoring of the non-polar trimethyl groups to the inner pore walls prohibits irreversible shrinkage of the wet-gel during microwave drying at ambient pressure and thus larger size pores (from ca. 20 to ca. 100 nm) can be retained in the dried silica. The drying process of the silylated wet-gels at an ambient pressure can be greatly accelerated upon microwave exposure instead of drying in an oven or furnace. Using this approach, anoporous and superhydrophobic silicas showing a wide variation in texture and morphology can be readily synthesized in roughly two hours. The effects of various sol-gel parameters solely on the textural properties of the organo-functional silica (OFS) have been investigated and discussed.

• Journal of Ceramic Processing Research
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• 제13권spc1호
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• pp.145-148
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• 2012

Spherical silica aerogel powders were fabricated via an emulsion polymerization method from a water glass. A water-in-oil emulsion, in which droplets of a silicic acid solution are emulsified with span 80 (surfactant) in n-hexane, was produced by a high power homogenizer. After gelation, the surface of the spherical silica hydrogels was modified using a TMCS (trimethylchlorosilane)/n-hexane solution followed by solvent exchange from water to n-hexane. Hydrophobic silica wet gel droplets were dried at 80 ℃ under ambient pressure. A perfect spherical silica aerogel powder between1 to 12 ㎛ in diameter was obtained and its size can be controlled by mixing speed. The tapping density, pore volume, and BET surface area of the silica aerogel powder were approximately 0.08 g·cm-3, 3.5 ㎤·g-1 and 742 ㎡·g-1, respectively.

• 한국초전도ㆍ저온공학회논문지
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• 제8권3호
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• pp.5-8
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• 2006

The effect of annealing time in Metal Organic Deposition(MOD) method was investigated at reduced total pressure. As the total annealing pressure was reduced, the growth rate of YBCO films increased from 0.14nm/sec at atmospheric pressure to 4.2nm/sec at 1 Torr. For the total pres sure of 700, 500, 300, 100, and 1 Torr, the optimal annealing times of 60, 40, 20, 10, 2minutes were found in our experimental conditions. When the an nealing time was short, poor crystallinity or un-reacted phase was obtained. Also, the degradation of YBCO films occurred when exposed longer to the humid ambient at the high annealing temperature. The reduced pressure was found effective to in crease the growth rate and to control the pore size of the YBCO films in MOD method. A fast growth of MOD-YBCO films was realized with high critical current density over $1MA/cm^2$ using reduced pressure annealing. Large pores, usually observed at atmospheric pressure in MOD method, disappeared and also, the number of pores was reduced.

• 센서학회지
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• 제15권3호
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• pp.173-178
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• 2006

Silica aerogel with ultra low density and high porosity has been focused on versatile application due to its fascinating properties. Ambient drying process of waterglass, in this study was researched to fabricate a crack-free monolith body in the point view of cost effective way. Wet gel was obtained by removing of $Na^{+}$ ions in waterglass, which contains 8 wt% of $SiO_{2}$. Xylene, which has a low vapor pressure, was used as a solution substitutor to prevent the formation a cracks during drying. Various surface modifiers like as hexamethyldisilazane (HMDSZ), trimethylchlorosilane (TMCS), methyltriethoxylsilane (MTES), methyltrimethoxysilane (MTMS) and phenyltriethoxysilane (PTES) were used in order to improve hydrophobicity of the waterglass Silica aerogel. Some physical properties of the surface modified aerogels were investigated by FT-IR, TGA, BET and SEM. Hydrophobicity and hydrophilicity of Silica aerogel is attributed to the Si-OH bond and the non-polar C-H bond groups on the surface of aerogel. Crack-free waterglass aerogel with >90 % of porosity, 17 nm of pore size and <0.15 $g/cm^{3}$ of density was prepared. HMDSZ and TMCS are effective as a surface modifier