• 한국환경복원기술학회지
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• 제3권1호
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• pp.52-61
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• 2000

Permeability is important factor in the geotechnical problems, such as seepage discharge and dissipation of excess pore water pressure. The Kozeny-Carman equation works well for graded soils but serious discrepancies are found in clays. Major factor for these discrepancies is the tortuous flow path and unequal pore size. To estimate the permeability of fine grained soils, a permeability equation in which swelling potential is coupled with Kozeny-Carman equation is proposed in this study. To verify proposed equation, a series of variable head permeability test was carried out for steel making slag and sludge mixed with bentonite. The coefficients of permeability which is measured in the laboratory is compared with the values by the proposed equation. From the comparison, it is shown that the proposed equation can predict the coefficient of permeability of clays with satisfaction. As steel making slag and sludge is industry waste, it is reused as material of road foundation and cement but the rate of use is low. It mixed sodium-bentonite with high swelling property and permeability decrease effect. Then, Admixture investigates reuse possibility as liner of waste fill.

• Geomechanics and Engineering
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• 제5권3호
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• pp.263-281
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• 2013

Geotextiles and geogrids have been in use for several decades in variety of geo-structure applications including foundation of embankments, retaining walls, pavements. Geocells is one such variant in geosynthetic reinforcement of recent years, which provides a three dimensional confinement to the infill material. Although extensive research has been carried on geocell reinforced sand, clay and layered soil subgrades, limited research has been reported on the aggregates/ballast reinforced with geocells. This paper presents the behavior of a railway sleeper subjected to monotonic loading on geocell reinforced aggregates, of size ranging from 20 to 75 mm, overlying soft clay subgrades. Series of tests were conducted in a steel test tank of dimensions $700mm{\times}300mm{\times}700mm$. In addition to the laboratory model tests, numerical simulations were performed using a finite difference code to predict the behavior of geocell reinforced ballast. The results from numerical simulations were compared with the experimental data. The numerical and experimental results manifested the importance that the geocell reinforcement has a significant effect on the ballast behaviour. The results depicted that the stiffness of underlying soft clay subgrade has a significant influence on the behavior of the geocell-aggregate composite material in redistributing the loading system.

• Computers and Concrete
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• 제20권5호
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• pp.555-562
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• 2017

The accuracy and integrity of stress data acquired by bridge heath monitoring system is of significant importance for bridge safety assessment. However, the missing and abnormal data are inevitably existed in a realistic monitoring system. This paper presents a data reconstruction approach for bridge heath monitoring based on the wavelet multi-resolution analysis and support vector machine (SVM). The proposed method has been applied for data imputation based on the recorded data by the structural health monitoring (SHM) system instrumented on a prestressed concrete cable-stayed bridge. The effectiveness and accuracy of the proposed wavelet-based SVM prediction method is examined by comparing with the traditional autoregression moving average (ARMA) method and SVM prediction method without wavelet multi-resolution analysis in accordance with the prediction errors. The data reconstruction analysis based on 5-day and 1-day continuous stress history data with obvious preternatural signals is performed to examine the effect of sample size on the accuracy of data reconstruction. The results indicate that the proposed data reconstruction approach based on wavelet multi-resolution analysis and SVM is an effective tool for missing data imputation or preternatural signal replacement, which can serve as a solid foundation for the purpose of accurately evaluating the safety of bridge structures.

• Geomechanics and Engineering
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• 제17권5호
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• pp.439-444
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• 2019

It is generally known that high strength soil is indicative of well-graded particle size distribution. However, there are some special cases of firm ground despite poor grade distribution, especially a specific gap-graded soil. Based on these discoveries, this study investigated the development of an additive of gap-graded soils designed to increase soil strength. This theoretical concept was used to calculate the mixed ratio required for optimal soil strength of the ground sample. The gap-graded aggregate was added according to Plato's polyhedral theory and subsequently calculated ratio and soil strength characteristics were then compared to characteristics of the original soil sample through various test results. In addition, the underground stress transfer rate was measured according to the test conditions. The test results showed that the ground settlement and stress limit thickness were reduced with the incorporation of gap-graded soil. Further field tests would confirm the reproducibility and reliability of the technology by using gap-graded soil to reinforce soft ground of a new construction site. Gap-graded soil has the potential to reduce the construction cost and time of construction compared to other reinforcing methods.

• Computers and Concrete
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• 제32권5호
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• pp.439-454
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• 2023

In this article, the surface stress effects on the buckling analysis of the annular sandwich plate is developed. The proposed plate is composed of two face layers made of carbon nanotubes (CNT) reinforced composite with assuming of fully bonded to functionally graded porous core. The generalized rule of the mixture is employed to predict the mechanical properties of the microcomposite sandwich plate. The derived potentials energy based on higher order shear deformation theory (HSDT) and modified couple stress theory (MCST) is solved by employing the Ritz method. An exact analytical solution is presented to calculate the critical buckling loads of the annular sandwich plate. The predicted results are validated by carrying out the comparison studies for the buckling analysis of annular plates with those obtained by other analytical and finite element methods. The effects of various parameters such as material length scale parameter, core thickness to total thickness ratio (hc/h), surface elastic constants based on surface stress effect, various boundary condition and porosity distributions, size of the internal pores (e0), Skempton coefficient and elastic foundation on the critical buckling load have been studied. The results can be served as benchmark data for future works and also in the design of materials science, injunction high-pressure micropipe connections, nanotechnology, and smart systems.

• Advances in nano research
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• 제16권3호
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• pp.313-324
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• 2024

The main aims of this study are to develop a new nonlocal quasi-3D theory for the free vibration behaviors of the functionally graded sandwich nanobeams. The sandwich beams consist of a ceramic core and two functionally graded material layers resting on elastic foundations. The two layers, linear spring stiffness and shear layer, are used to model the effects of the elastic foundations. The size-effect is considered using nonlocal elasticity theory. The governing equations of the motion of the functionally graded sandwich nanobeams are obtained via Hamilton's principle in combination with nonlocal elasticity theory. Then the Navier's solution technique is used to solve the governing equations of the motion to achieve the nonlocal free vibration behaviors of the nanobeams. A deep parametric study is also provided to demonstrate the effects of some parameters, such as length-to-height ratio, power-law index, nonlocal parameter, and two parameters of the elastic foundation, on the free vibration behaviors of the functionally graded sandwich nanobeams.

• 콘크리트학회논문집
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• 제16권6호
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• pp.841-850
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• 2004

전 세계적으로 많은 수의 크고 작은 댐이 사용되고 있으나, 콘크리트 댐의 안전성 평가에 있어서 댐 내에 필연적으로 존재하는 균열을 함께 고려한 실질적 해석은 아직 미진한 실정이다. 따라서 향후 건설될 댐에 대해서는 설계 단계에서부터 이러한 파괴역학적 해석이 뒷받침되어야 댐의 안전성 확보에 매우 유리하다고 볼 수 있다. 특히 댐 제체와 지반이 접하는 경계면은 많은 균열 발생이 예상되는 영역으로써 이 균열 사이에 작용하는 양압력의 모델링은 중력식 콘크리트 댐 해석시 매우 중요한 요소이다. 즉, 콘크리트 댐의 균열 안정성 평가는 정확한 양압력의 모델링이 선행되어야 올바른 예측이 가능하다. 댐에 있어서 양압력의 취급은 단지 댐 체제 안정성 평가를 위한 전형적인 수계산 방법으로 널리 사용되고 있으나, 양압력에 대한 유한요소 모델링 방법은 연구가 부족한 실정이다. 본 연구에서는 중력식 콘크리트 댐과 지반이 접하는 부분에 발생된 균열에 양압력이 작용할 경우, 선형탄성파괴역학의 관점에서 접근하여 양압력이 응력확대계수에 미치는 영향을 비교 분석하였다. 양압력의 분포형상은 현재 등분포로 가정한 간략해석법으로 수행되고 있으나 최근의 연구 결과에 의하면 양압력 분포형상이 균열면에 따라 변화함을 보이고 있어, 본 연구에서는 수압의 형태를 등분포 형상 외에 삼각형 분포, 제형분포 및 포물선 분포 형상에 대해서도 각각 고려하여 각 분포형상별 응력확대계수를 평가하였다. 응력확대계수의 계산은 일반 8절점 등매개변수요소를 사용한 표면적분법을 사용하였으며, 자중의 영향 및 월류 수압의 영향도 함께 고려하여 해석 결과를 나타내었다.

• 한국재난정보학회 논문집
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• 제14권4호
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• pp.466-473
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• 2018

연구목적: 최근에는 지진에 대한 안정성을 위해 면진 또는 면진과 내진을 병용하는 추세로 가고 있는데, 신축할 중 저층 RC 구조물에 콘크리트 구 기초(CSF)를 설치하는 형태의 시스템을 사용할 때 기초로 사용할 콘크리트 구의 할열특성을 파악하고자 한다. 연구방법: 압축강도 60Mpa인 고강도 콘크리트 구의 할열강도를 알기 위하여 다양한 실험을 수행하고, 표준 실린더 공시체의 할열강도에 대한 구 공시체의 할열강도 비 및 구의 직경변화에 따른 치수효과 등을 실험적으로 구하고자 한다. 연구결과: 150mm 구 공시체의 할열강도는 $150mm{\times}150mm$, $150mm{\times}300mm$의 원주형 공시체 보다 작을 것으로 예상했으나, 실험결과는 각각 3.8%, 13.7% 큰 4.39Mpa로 나타났는데 이는 구 공시체의 점하중과 원주형 공시체의 선하중에 대한 내력작용이 다르기 때문이라 판단된다. 결론: 원주형 공시체에 대한 할열 인장강도는 많은 연구가 진행되어 표준화된 방법이 있으나, 구 공시체의 할열강도에 대한 연구는 보고된 바가 거의 전무하여 본 연구에서는 직경 50mm~150mm의 할열강도 특성을 파악하고, 그 방법을 확립하여 콘크리트 구의 할열강도 및 관련 연구에 대한 기본 자료를 제공하고자 한다.

• 사회복지연구
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• 제44권2호
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• pp.359-385
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• 2013

본 연구의 목적은 노인의 인터넷활용(인터넷활용빈도 및 인터넷활용능력)이 생활만족도에 미치는 영향력을 검증하고, 이 관계에서 사회활동의 매개효과를 분석하는 것이다. 연구에서 활용한 자료는 서울시복지재단에서 실시한 서울시 복지패널조사자료 중 2010년도 가구원용 데이터이며, 1862명이 분석대상이다. 연구방법은 빈도분석, 기술분석, 상관관계분석을 통해 대상자의 일반적 특성 및 주요 변수의 특성을 살펴보았으며, 구조방정식으로 연구모형을 검증하고, Sobel test를 통해 사회활동의 매개효과를 분석하였다. 분석 결과 첫째, 노인의 인터넷활용빈도는 생활만족도에 영향요인이 아닌 것으로 나타났고 반대로 인터넷활용능력은 생활만족도에 영향을 주는 것으로 나타났다. 둘째, 노인의 인터넷활용능력과 생활만족도의 관계에서 사회활동은 부분매개효과를 가지는 것으로 나타났다. 이러한 연구결과를 바탕으로, 노인 인터넷활용 활성화에 대한 이론적·실천적 함의를 제시하였다.

• Food Science and Biotechnology
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• 제16권5호
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• pp.715-721
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• 2007

In this study, the sphericity of calcium alginate gel beads was optimized using response surface methodology. The optimum conditions for bead sphericity were a concentration of 2.24% sodium alginate, a flow rate of 0.059 mL/sec for the sodium alginate solution, and a 459 rpm rotation for the calcium chloride solution. The predicted and experimental bead sphericities under the optimum conditions were 94.5 and 96.7%, respectively, showing close agreement. We also investigated the processing condition effects for the physical properties of the optimized calcium alginate gel beads. Immersion in hot water slightly decreased bead size and rupture strength. NaCl treatment increased bead size and decreased rupture strength. While the pH of the calcium chloride solution had little effect on bead sphericity, the bead sizes and gel strengths decreased with longer times in each pH solution. The beads coated with pectin and glucomannan showed no significant changes in sphericity, but their sizes decreased with time. The coated beads showed higher rupture strengths than the uncoated beads.