• Journal of the Korean Geotechnical Society
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• v.38 no.10
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• pp.41-48
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• 2022

The mass density of the medium (ρ) used to calculate the maximum shear modulus (G_max) of the saturated ground based on the shear wave velocity is unclear. Therefore, to determine the mass density, a verification formula and five scenarios were established. Laboratory tests were conducted, and the obtained results were compared. The mass density of the medium was assumed to be saturated (ρ_sat), wet (ρ_t), dry (ρ_dry), and submerged conditions (ρ_sub), and the V_s ratios of saturated to dry condition were obtained from each case. Assuming the saturated density (ρ_sat), the V_s ratio was consistent with the value from the resonant column test (RCT) results, and the value from the bender element test results was consistent with the wet density assumption (ρ_t). Considering the frequency range of earthquakes, it is concluded that applying the saturated density (ρ_sat) is reasonable as in the RCT results.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.5
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• pp.91-96
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• 2018

The oleophobic property of surfaces modified with micro-post structures are investigated for a range of micro-post diameter ($11-23{\mu}m$) and pitch ($20-40{\mu}m$). The contact angle of an oil droplet on surfaces with various micro-post dimensions was calculated using the Cassie-Baxter model and did not show a good agreement with the measured contact angle. From measurement, the micro-post with diameter of $23{\mu}m$ and pitch of $32{\mu}m$ was found to have the highest contact angle ($134.3^{\circ}$).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.3 no.3
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• pp.53-61
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• 1983

The Green-Ampt equation for infiltration has been intensively investigated by many researchers because of its simplicity and adequacy for fitting experimental data to theoretical one. The infiltration equation derived from the theory of two phase flow coincides with the Green-Ampt equation except the viscouse resistance correction factor. This approach clearly defines variables in the Green-Ampt equation and also encounters the effect of viscosity of two fluids. A new equation for infiltration into multilayered soil is derived from the theory of two phase flow and compared with conventional equation. The new equation shows lower infiltration rate than that of conventional one and it is believed that this caused from the inclusion of viscosity in the derivation.

• Journal of the Korean Geotechnical Society
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• v.17 no.5
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• pp.71-82
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• 2001

불포화토에 있어서 함수상태는 지반이 건조할수록 수축하고 습윤상태로 진행할수록 파괴에 이르게 하는 추가적인 입자간 응력을 발생시키며, 이러한 간극수와 흙입자 사이에 발생하는 현상을 규명하기 위해서는 정확한 모형화가 필요하다. 흙입자와 간극수 사이의 상호작용에서 흡입유발 유효응력(suction-induced effective stress)을 규명하기 위해 정규모형(regular packing)과 임의모형(random packing)이 적용될 수 있다. 최근의 연구결과에 따르면 흙은 흡입유발 유효응력과 밀접한 관계가 있으며, 흙의 비등방텐서(anisotropic tensor)를 구하기 위해 적용된 ALTERNAT 모델을 이용하여 구조텐서(fabric tensor)를 개략적으로 정의할 수 있다. Thornton의 임의모형 시뮬레이션은 구조텐서에 상응하는 파괴응력 상태를 포함하고 있으며, 미소역학 시뮬레이션을 통하여 구조텐서를 구하였다. 본 연구에서는 상기에 언급된 구형의 흙입자 모형에 대한 이론적 고찰이 수행되었고, ALTERNAT 모델을 적용한 간단한 비등방텐서의 결과를 구조텐서와 비교하였다. 본 연구결과 비등방텐서는 미소역학 시뮬레이션에 의한 구조텐서에 비해 약 20~40%정도 큰 값을 나타내었다.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.25-30
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• 2006

When wet soil overlies dry soil, which can be found in the infiltration test, the radar wave is not attenuated and guided within wet soil layer. This phenomenon is known to be the dispersive guided wave and happens when the thickness of upper wet layer is less than or comparable to the wavelength of radar wave. In this study, we have conducted the FDTD modeling and obtained the velocity dispersion curve to identify the dispersive guided wave through F-K analysis. This guided wave can be explained by modal propagation theory and a simple inversion code was developed to obtain the two layer's dielectric constants as well as layer thickness. By inverting the dispersion curve from synthetic modeling data, we could obtain the accurate dielectric constants and layer thickness. Moreover, we could enhance the accuracy by including the higher mode data. We expect this method will be very useful to get the quantitative property of subsurface when the condition is similar.

• Geophysics and Geophysical Exploration
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• v.15 no.4
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• pp.235-244
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• 2012

Nuclear magnetic resonance (NMR) logging has been considered one of the most complicated nevertheless, one of the most powerful logging methods for the characterization on of both rocks and natural fluids in formation. NMR measures magnetized signals (polarization and relaxation) between the properties of hydrogen nucleus called magnetic moment and applied magnetic fields. The measured data set contains two important petrophysical properties such as density of hydrogen in the fluids inside the pore space and the distinct decay rate for fluid type. Therefore, after the proper data processing, key petrophysical information, not only the quantities and properties of fluids but also supplies of rock characterization in a porous medium, could be archived. Thus, based on this information, several ongoing researches are being developed in estimating aspects of reservoir productivity information, permeability and wettability since it is the key to having correct interpretation. This study goes through the basic theory of NMR at first, and then reviews NMR logging tools as well as their technical characteristics. This paper also briefly discusses the basic knowledge of NMR simulation algorithm by using Random walk.

• Geophysics and Geophysical Exploration
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• v.9 no.4
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• pp.304-315
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• 2006

We have examined the applicability of f-k analysis to the GPR direct wave measurement for water content to characterize vadose zone condition. When the vadose zone consists of a dry surface layer over wet substratum, we obtained f-k spectra where most of the energy is bounded by the air and dry soil velocities. In this case, dry soil velocity was successfully estimated by using high frequency data. On the other hands, when wet soil overlies dry substratum, the f-k spectra show a contrasting response where most of the energy travels with the velocity bounded by dry and wet soil velocities. In this case, the radar waves are trapped and guided within wet soil layer, exhibiting velocity dispersion. By adopting modal propagation theory, we could formulae a simple inversion code to find two layer's dielectric constants as well as layer thickness. By inverting the velocity dispersion curve obtained from f-k spectra of synthetic modeling data, we could obtain good estimates of dielectric constants of each layer as well as first layer thickness. Moreover, we could obtain more accurate results by including the higher mode data. We expect this method will be useful to get the quantitative property of real subsurface when the field condition is similar.

• Journal of Korea Water Resources Association
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• v.30 no.6
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• pp.699-708
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• 1997

The effective unsaturated hydraulic conductivity in stratified soils is evaluated using a three-dimensional stochastic approach. Because of the disparity of the correlation scales in a stratified soil, the general stochastic equations are simplified. This allows analytical evaluation of generic expressions for the effective hydraulic conductivities. Simple asymptotic expressions, valid at particular ranges(wetting front, drying condition, wetting condition) of the mean flow characteristics, are also derived. An example of applying the derived theoretical result to a imaginaryl clay soil is presented. It reveals found that the effective unsaturated hydraulic conductivity showed large-scale hysteresis. Such large-scale hysteresis was produced by the spatial variability of hydraulic soil properties rather than hysteresis of the local parameters. In addition the results show that the effective hydraulic conductivities were larger in the case of accommodating heterogeneity of soil preperties rather than neglecting heterogeneity of soil properties.

• Composites Research
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• v.25 no.2
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• pp.46-53
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• 2012

Using pultrusion process, FRP composite structural members having various cross-section shapes can be produced with unlimited lengths. Because of such reasons, these members are suitable for the application in the construction field. Especially, this material is highly appreciated if the material is to be used in the corrosive environments such as aquatic or oceanic environments due to its high corrosion resistance. However, design criteria for the FRP structural member are not developed yet. So, the research on the development of design guideline is needed ungently. In order to use the pultruded structural FRP member efficiently, the members are composed of thin plate components, and thus, the member is prone to buckle easily and the buckling is one of the governing strength limit states for the design. In this paper, we present the analytical study results pertaining to the buckling behavior of I-shape FRP compression member. In addition, design procedure and flow-chart are also proposed based on the study results including previous experimental results. Proposed design procedure is similar to that in ANSI/AISC 360-10 with minor modification. Therefore, it is convinced that the structural design of pultruded FRP compression member could be done easily by following design procedure proposed in this paper.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.207-207
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• 2011

본 연구에서는 유역 특성의 판단에 적절한 호우사상을 선별하여 사용하는 것이 어느 정도 효과적인지를 평가하였다. 토양의 습윤 정도에 따른 유역의 특성을 반영하기 위해 AMC 조건을 고려하였으며, 유역의 집중시간 및 저류상수의 추정방법으로는 Nash 모형의 구조를 이용하는 방법을 적용하였다. 아울러 강우의 공간변동 정도를 파악하기 위해 변동계수를 이용하여 평가하였으며, 추정된 매개변수들의 대푯값 및 가능범위를 도시적으로 결정하였다. 이를 유역면적이 큰 충주댐 유역의 영춘 지점과 상대적으로 작은 평창강 방림 지점을 대상유역으로 선정하여, 다양한 호우사상에 대한 분석이 유역의 규모에 대비되어 수행될 수 있도록 하였다. 그 결과를 정리하면 다음과 같다. 강우의 공간변동 정도를 변동계수로 평가한 결과 AMC-III 조건에서 강우강도의 공간적 변동폭이 작음을 확인하였다. 따라서 AMC-III 조건에서 유도한 유출특성이 단위도의 이론에 부합하는 것으로 판단된다. 아울러 AMC 조건에 따라 추정된 집중시간과 저류상수는 AMC-I보다 AMC-III 경우에서 상대적으로 변동폭도 작았으며, 선형저수지의 특성 역시 일관됨을 확인하였다. 특히, AMC-I 조건의 경우는 선행강우가 없는 상태에서의 호우사상들로서 일단 그 크기가 작을 가능성이 크다는 문제점을 가지고 있다. 따라서 AMC-I 조건의 호우사상 보다는 AMC-III 조건의 호우사상을 이용하는 게 보다 홍수 유출 해석에 유리하다고 판단된다. 추정된 매개변수의 대푯값과 그의 가능범위 결정에 앞서, AMC-III 조건에서 추정된 매개변수들이 군집해 있는 구간을 설정한 후, 이를 벗어나는 매개변수를 제외하였다. 다음으로 매개변수의 무게중심 즉, 평균을 중점으로 하여 사분위수(25%, 50%, 75%)에 해당되는 매개변수 개수가 선택되도록 사변형을 작성하였다. 이 때 집중시간과 저류상수 사이의 상관성을 고려하기 위해 사변형은 선형저수지 개수의 선과 선형저수지의 저류상수의 선이 만나는 점을 연결하여 작성하였다. 영춘 지점의 경우, 집중시간의 대푯값은 20.6 hr, 저류상수의 대푯값은 18.4 hr, 방림 지점은 각각 7.5 hr, 8.2 hr이다. 매개변수의 대푯값 가능범위는 충주댐 영춘 지점의 경우 1사분에서 집중시간 18-25 hr, 저류 상수는 17-20 hr 정도, 방림 지점의 경우 집중시간은 5-10 hr, 저류상수는 7-11 hr 정도이다. 아울러 추정된 대푯값의 가능 범위를 이용하여 기존의 경험공식을 평가하였다. 그 결과 집중시간의 경우 Kraven 공식, 정성원 공식이, 저류상수의 경우 Sabol 공식, 정성원 공식, 윤태훈 공식이 대푯값의 범위에 속하는 것으로 분석되었다. 그러나 분석 지점의 부족으로 기존의 경험공식의 정량적 평가는 어렵다. 추후에 보다 많은 지점을 대상으로 분석한다면 보다 설득력이 있는 경험공식의 평가와 다양한 유역에 적합한 경험공식의 산정도 가능할 것이다.