• Journal of Soil and Groundwater Environment
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• v.8 no.4
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• pp.1-11
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• 2003

In order to measure aperture variation dependent on normal stress and to characterize on relationship between aperture variation and hydraulic conductivity this study measured apertures of rock fractures under a high resolution confocal laser scanning microscope (CLSM) with application of five stages of uniaxial normal stresses. From this method the response of aperture can be continuously characterized on one specimen by different loads of normal stress. The results of measurements showed a rough geometry of fracture bearing non-uniform aperture. They also revealed different values of aperture variations according to the load stages on each position along a fracture due to the fracture roughness. Laboratory permeability tests were also conducted to evaluate the changes of permeability coefficients related to the aperture variations by different loads. The results of permeability tests revealed that the hydraulic conductivity was not reduced at a fixed rate with increase of normal load. Moreover, the rates of aperture variations did not match to those of hydraulic conductivity. The hydraulic conductivity calculated in this study did not follow the cubic law, representing that the parallel plate model is not suitable to express the fracture geometry corresponding to the results of aperture measurements under the CLSM.

• Geotechnical Engineering
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• v.8 no.2
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• pp.59-70
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• 1992

This work is to study experimentally the measurment of pore air pressure according to rainfall in colluvium model and the characteristics of pore water pressure according to increasement of artesian ground water head. After modeling a geological feature of the Tertiary formation, the experiment was performed about sixty times on three kinds of soil. This experimental results showed the variation of pore water and pore air pressures with time, the change of void ratio and appling pressure head in the nonsaturated soil. It can be also expressed by the final pore water and the air reaction ratios and then formularizing the relationship between the permeability coefficient and the void ratio. In the results of this experiment, the patterns of the pore water pressure reaction are classified by the step-type and the wave-type, and the time-lag to reach final point of pore water pressure is in order sand, sandy silt and clayey sand.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.675-680
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• 1997

반구형 간극에서 히터 출력이 임계열유속(CHF)에 이르렀을 때 히터표면의 온도 변화와 CHF 값을 측정하였다. 반구형 히터의 직경은 498mm 이고 간극은 1, 2mm 에서 실험을 수행하였다. 히터표면의 온도는 항상 간극상단의 특정 부분에서부터 증가하기 시작하였다. 즉, 이곳에서 국부적인 dryout이 발생한 것으로 판단된다. 히터의 열속이 증가함에 따라 dryout 부분은 원주방향과 아래방향으로 확장되었다. 한편 임계열유속보다 작은 열속에서는 dryout 영역이 변하지 않는 정상상태가 존재하였으나 임계열유속에서는 열속이 고정되어 있어도 dryout 영역이 스스로 확장되어 나갔다. 이 실험은 계속 진행중이며 현재까지 측정된 CHF 값을 제시하였다. CHF 값은 간극을 대상으로 개발된 기존의 실험식보다 낮게 측정되었다.

• The Journal of Engineering Geology
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• v.14 no.1
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• pp.47-60
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• 2004

The permeability coefficients were calculated by the homogenization analysis method with sufficient consideration of fracture geometry dependent on aperture change. According to the results of aperture measurements using a confocal laser scanning microscope, apertures on each measuring point display different magnitudes, indicating that fracture walls can not be assumed as parallel feature. After construction of fracture model based on the aperture values measured on each pressure level, the homogenization analysis was conducted to compute permeability coefficients. The calculated permeability coefficients distribute in the ranges of $10^{-1}~10^{-3}cm/sec$. Most of the specimens show decreasing permeability coefficients with the increase of the applied pressure. However, the decreasing rates of permeability coefficients do not show a constant trend on each pressure level. This phenomenon is well matched to the observation results of Chae et al. (2003). It proves that aperture change strongly influences on permeability characteristics. Three sections of each specimen have all different values of permeability coefficient. It suggests that the variation of permeability coefficient depends sensitively on aperture magnitudes and characteristics of fracture geometry. It is very important to consider accurate fracture geometries for analysis of permeability characteristics in rock fractures bearing different aperture distribution. Therefore, it needs to consider sufficiently the fracture geometries for calculating the permeability coefficients of fractures.

• Journal of the Korean Geotechnical Society
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• v.17 no.4
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• pp.57-70
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• 2001

한계상태이론은 정규압밀 및 과압밀시료에 대한 비배수 전단강도와 간극수압계수에 관한 식을 제안하고 있는데, 이 식은 3가지 상수를 포함하고 있다. 한계상태상수(M), 한계상태 간격비(${\gamma}$), 한계상태 간극수압계수(Λ)가 바로 그것이며, 이러한 상수는 각 모델 및 구하는 방법에 따라 그 차이가 발생함으로서, 전단강도 및 간극수압계수의 예측시 적지 않은 영향을 미치게 된다. 본 논문에서는 재 성형된 이암풍화토를 이용하여 등방삼축압축시험을 정규압밀과 과압밀로 나누어 실시하고 그 결과를 분석하였으며 이를 토대로 각 모델 및 방법에 따른 상수를 도출하였다. 그리고 이러한 상수의 차이가 비배수 전단강도 및 간극수압계수의 예측에 미치는 영향을 살펴보았다. 시험결과 정규압밀시료의 경우 각 상수의 변화에 따른 비배수 전단강도 및 간극수압계수는 상당한 차이를 보였으며, 한계상태간격비와 Λ값을 강도비로부터 얻어진 값을 사용한 경우가 결과치에 가장 잘 근접함을 알 수 있었다. 과압밀시료의 경우 역시 이들 상수에 따라 전단강도의 변화폭이 크게 나타났으며 정규압밀과 마찬가지로 강도비에서부터 도출된 상수를 적요한 경우 실측치에 가장 근접하였다. 반면 간극수압계수의 예측시에는 상수에 따른 변화폭이 크지 않았으며, 특히 과압밀비가 증가할수록 각 상수에 대한 영향이 작게 나타났다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.4
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• pp.286-294
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• 2002

This study investigated the effects of stress and time history of overconsolidated clayey soils on pore pressure parameter, A. Laboratory tests were carried out under the conditions of both varying stress and time history. The stress history is classified into (i) rotation angle of stress path, (ii) overconsolidation ratio, and (iii) magnitude of length of recent stress path. The time history is divided into (i) loading rate of recent stress path and (ii) rest time. Pore pressure parameters are different both in the magnitude and trend with the rotation angle, depending on the magnitude of overconsolidation ratio but not in a trend. In addition, the pore pressure parameters have no effects on the magnitude of length of recent stress path except the level of initially small strain, while loading rates of recent stress path have effects on it. Finally, the pore pressure parameters of overconsolidated clays increase with the existence of the rest time, until either the deviator stress exceeds 70 kPa or the strain up to 0.1%.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.277-285
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• 2009

A series of undrained cyclic triaxial tests were carried out to investigate the cyclic shear stress strength characteristics of sands with respect to the silt content. Silty sand was collected around the basin of Nak-Dong River and remolded in laboratory with the range of silt content 0~50% in sand located. As results, with the change of silt content cyclic shear stress ratio (CSR) at N=10 showed the maximum value at 5% and the minimum at 20% in all relative density. The development tendency of the pore water pressure analyzed by the relationship cyclic ratio and pore water pressure ratio is unrelated the change of CSR varying silt content. Comparing the results of the void ratio and skeleton void ratio after consolidation, CSR varying silt content was much affected by skeleton void ratio which is known to affect shear behavior of silty sand.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.10
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• pp.24-35
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• 2017

This paper reports the results of afield appliance study of the hydraulic well method to prevent embankment seepage, the large-scale embankment experiment and seepage analysis to examine the traits of the seepage pressure. The experimental procedure was focused on the pore pressure after examining the detected value of the pore pressure gage. The inner water levels of hydraulic well were compared with the pore pressure data, which were used to inspect the seepage variations. Two different large-scale experiments were conducted according to the installation points of the hydraulic wells. The decrease in seepage pressure reached a maximum of 37% from the experimental results. The experimental pore pressure results were similar to those of the analyses. In addition, the pore pressure oriented from the water level variations of the hydraulic well showed similar patterns between the experiment and analysis, but if the hydraulic well was deeper, the analyzed water levels were larger than the experimental values.

• The Journal of Engineering Geology
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• v.31 no.1
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• pp.55-66
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• 2021

Hydraulic-mechanical (H-M) coupled numerical modeling was used to evaluate the evolution of hydrogeological properties in response to the installation and expansion of a borehole. A domain with a discrete fracture network was adopted for discontinuum modeling to simulate changes in fracture apertures. Comparison with real hydraulic test data shows that the effects of principal stress direction and expansion of borehole diameter were reasonably simulated by H-M coupled numerical modeling. The modeling confirmed that aperture changes depended on the principal stress direction, with an increase in aperture size due to vertical displacement being the dominant effect. A concentration of shear dilation around the borehole had an additional, subsidiary, effect on the hydrogeological evolution. These results show that the permeability of fractured rock can be increased by changing the hydraulic properties of a fracture through stress redistribution caused by the installation and expansion of a borehole.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.6
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• pp.357-363
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• 2016

In this study, we perform a series of aero-thermo-mechanical analyses to predict the running-tip clearance and the effects of impeller deformation on the performance using a centrifugal compressor. During operation, the impeller deformation due to a combination of the centrifugal force, aerodynamic pressure and the thermal load results in a non-uniform tip clearance profile. For the prediction, we employ the one-way fluid-structure interaction (FSI) method using CFX 14.5 and ANSYS. The predicted running tip clearance shows a non-uniform profile over the entire flow passage. In particular, a significant reduction of the tip clearance height occurred at the leading and trailing edges of the impeller. Because of the reduction of the tip clearance, the tip leakage flow decreased by 19.4%. In addition, the polytrophic efficiency under operating conditions increased by 0.72%. These findings confirm that the prediction of the running tip clearance and its impact on compressor performance is an important area that requires further investigation.