• Title/Summary/Keyword: suction stress

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Hydro-mechanical Behavior of Partially Saturated Soil Slopes under Rainfall (강우시 불포화토 사면에서의 수리역학적 거동 해석에 관한 연구)

  • Kim, Jae-Hong;Im, Jae-Seong;Park, Seong-Wan
    • Journal of the Korean Geotechnical Society
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    • v.28 no.11
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    • pp.69-78
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    • 2012
  • Conventional numerical analysis for rainfall-induced slope stability has been estimated by separating seepage and stress-strain behavior, respectively. Many researchers' models from commercial softwares and literatures define that partially saturated permeability is the only function of degree of saturation (or matrix suction) and then they do not consider hydraulic-mechanical characteristics for the analysis. However, in practice, the water flow processes in a deformable soil are influenced by soil skeleton movement and the pore water pressure changed due to seepage will lead to changes in stress and to deformation of a soil. The relationship between seepage and soil behavior causes a change of partially saturated permeability as well as saturated permeability with the lapse of time. Instability of partially saturated soil slopes due to infiltration would be analyzed from reduction of negative pore water pressure calculating the process of water flow based on predicted partially saturated permeability. Therefore, partially saturated permeability should be defined by the function of degree of saturation (or matric suction) and porosity. The paper presents the comparison between staggered and monolithic coupled analysis regarding seepage and stress deformation problems. As a result, the decrease in matric suction on soil slope from monolithic analysis is slower than that from staggered analysis.

A Study on Dynamic Characteristics of Reed Valve in Hermetic Compressor (압축기 밸브의 동적 특성에 대한 연구)

  • 조성욱;박성근;김형석;임종윤
    • Journal of KSNVE
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    • v.3 no.2
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    • pp.163-167
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    • 1993
  • Suction and discharge valves of special type refrigerant compressor are designed by finite element method for effective valve design development procedure. It is well known that valve dynamic characteristics, for example, the natural frequencies and vibration modes, are necessary for the computer simulation of compressor valve dynamics, the analysis of flow patterns, noise, impact stresses and their propagation phenomena. This paper has analysed the natural frequencies and vibration modes for the first three orders under the given special boundary conditions and the experiments are conducted by laser holography. And also stress distribution is analysed and experiment by strain gage is followed.

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Evaluation of Overburden Pressure on Soil-Water Retention Characteristics of Unsaturated Weathered Soils (상재하중의 영향을 고려한 불포화 풍화토의 함수특성 평가)

  • Park, Jai-Young;Park, Seong-Wan
    • Proceedings of the Korean Geotechical Society Conference
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    • 2008.03a
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    • pp.111-118
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    • 2008
  • The purpose of this paper was to investigate the overburden effect on soil-water characteristic curve and unsaturated permeability of unsaturated weathered soils. For this, unsaturated suction and permeability tests under various overburden stress were conducted respectively. Then, the coefficient of unsaturated permeability and moisture capacity of weathered soils were estimated and compared. All these results are presented in the paper.

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Coupling Effects in Rainfall-induced Slope Stability Considering Hydro-mechanical Model (강우침투에 의한 비탈면 안정해의 수리-역학적 모델을 이용한 커플링 효과)

  • Kim, Yong-Min;Jeong, Sang-Seom
    • Journal of the Korean Geotechnical Society
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    • v.31 no.9
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    • pp.5-15
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    • 2015
  • In this study, rainfall-induced slope stability and coupling effect are investigated using hydro-mechanical finite element model. This model is developed by formulating constitutive and coupled balance equations and is verified by comparing the numerical results with field matric suction. The homogeneous soil layer (soil column) and soil slope are modeled by this model, and the results of variation in matric suction, mean effective stress, porosity, displacement, factor of safety are compared with those of staggered analysis. It is found that the vertical and horizontal displacement from coupling analysis considering change in porosity is larger than that of staggered analysis. The displacement and matric suction from coupling analysis by rainfall infiltration can affect slope instability, which shows a progressive failure behavior. The lowest factor of safety is observed under short-term rainfall. This results confirm the fact that coupling analysis is needed to design soil slope under severe rain condition.

Characteristics of Pore Pressure and Volume Change During Undrained lending of Unsaturated Compacted Granite Soil (비배수전단시 불포화 다짐화강토의 간극압과 체적변형특성)

  • 김찬기;김태형;이종천
    • Journal of the Korean Geotechnical Society
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    • v.19 no.4
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    • pp.15-21
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    • 2003
  • A series of triaxial compression tests were performed on samples of compacted granite soil in a modified triaxial cell that allowed separate control of pore air pressure ($U_a$) and pore water pressure ($U_w$) in order to examine the characteristics of pore pressure, volume change and stress-strain behavior during undrained loading conditions. Triaxial samples of unsaturated and saturated compacted granite soil, 50mm in diameter and 100mm in height, were prepared by compaction in a mould. These samples were tested at 3 different suction values (0.5, 1.0, 2.0 kgf/cm$^2$) for unsaturated compacted granite soil and at 3 different confining stresses (1.0, 2.0, 4.0 kgf/cm$^2$). Results showed that only effective cohesion increased with little variation of friction angle, according to matric suction.

Heat Transfer and Flow Measurements on the Turbine Blade Surface (터빈 블레이드 표면과 선형익렬에서의 열전달 및 유동측정 연구)

  • Lee, Dae Hee;Sim, Jae Kyung;Park, Sung Bong;Lee, Jae Ho;Yoon, Soon Hyun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.5
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    • pp.567-576
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    • 1999
  • An experimental study has been conducted to investigate the effects of the free stream turbulence intensity and Reynolds number on the heat transfer and flow characteristics In the linear turbine cascade. Profiles of the time-averaged velocity, turbulence intensity, and Reynolds stress were measured in the turbine cascade passage. The static pressure and heat transfer distributions on the blade suction and pressure surfaces were also measured. The experiments were made for the Reynolds number based on the chord length, Rec = $2.2{\times}10^4$ to $1.1{\times}10^5$ and the free stream turbulence intensity, $FSTI_1$ = 0.6% to 9.1 %. The uniform heat flux boundary condition on the blade surface was created using the gold film Intrex and the surface temperature was measured by liquid crystal, while hot wire probes were used for the flow measurements. The results show that the free stream turbulence promotes the boundary layer development and delays the flow separation point on the suction surface. It was found that the boundary layer flows on the suction surface for all Reynolds numbers tested with $FSTI_1$ = 0.6% are laminar. It was also found that the heat transfer coefficient on the blade surface increases as the free stream turbulence intensity increases and the flow separation point moves downstream with an increasing Reynolds number. The results of skin friction coefficients are in good agreement with the heat transfer results in that for $FSTI_1{\geq}2.6%$, the turbulent boundary layer separation occurs.

Stability analysis of an unsaturated expansive soil slope subjected to rainfall infiltration

  • Qi, Shunchao;Vanapalli, Sai K.;Yang, Xing-guo;Zhou, Jia-wen;Lu, Gong-da
    • Geomechanics and Engineering
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    • v.19 no.1
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    • pp.1-9
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    • 2019
  • Shallow failures occur frequently in both engineered and natural slopes in expansive soils. Rainfall infiltration is the most predominant triggering factor that contributes to slope failures in both expansive soils and clayey soils. However, slope failures in expansive soils have some distinct characteristics in comparison to slopes in conventional clayey soils. They typically undergo shallow failures with gentle sliding retrogression characteristics. The shallow sliding mass near the slope surface is typically in a state of unsaturated condition and will exhibit significant volume changes with increasing water content during rainfall periods. Many other properties or characteristics change such as the shear strength, matric suction including stress distribution change with respect to depth and time. All these parameters have a significant contribution to the expansive soil slopes instability and are difficult to take into consideration in slope stability analysis using traditional slope stability analysis methods based on principles of saturated soil mechanics. In this paper, commercial software VADOSE/W that can account for climatic factors is used to predict variation of matric suction with respect to time for an expansive soil cut slope in China, which is reported in the literature. The variation of factor of safety with respect to time for this slope is computed using SLOPE/W by taking account of shear strength reduction associated with loss of matric suction extending state-of-the art understanding of the mechanics of unsaturated soils.

Structural Behavior Analysis of Cap Shaped as an Arch for Suction-Installed Cofferdam (아치형 석션 가물막이 상판의 구조거동 분석)

  • Kim, Jeongsoo;Jeong, Youn-Ju;Park, Min-Su;Song, Sunghoon
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.33 no.6
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    • pp.391-399
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    • 2020
  • In this study, the behaviors of a suction cap shaped as an arch were analyzed using finite element models. The fundamental structural behaviors of both flat- and arch-type caps were compared, and the advantages of the arch-shaped cap were explained. Moreover, the effects of geometric parameters and stiffener arrangements on the stress and deformation of the arch-shaped caps were investigated by comparisons of the changes in the behaviors of the caps. Additionally, the effects of boundary condition at the edge of the cap were analyzed to study the interactions between the cap and cofferdam walls; these results were used to derive the fundamental structural design of stiffened arch caps. Unlike flat caps, the results showed that ring stiffeners could improve the structural behaviors of arch caps remarkably, while the contributions of the radial stiffeners to the structural behaviors of the caps are dependent on constraints at the edges of the caps.

Prediction of Tensile Strength of Wet Sand (II) : Validation (습윤 모래에서 인장강도의 예측 (II) : 검증)

  • Kim, Tae-Hyung
    • Journal of the Korean Geotechnical Society
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    • v.24 no.6
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    • pp.37-44
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    • 2008
  • At low normal stress levels, tensile strength of sand characteristically varies with either saturation or suction of soil in an up-and-down manner with a peak tensile strength that can occur at any degree of saturation. A theory that accurately predicts tensile strength of wet sand was presented in the previous study. In this study, the results of uniaxial tensile, suction-saturation and direct shear tests obtained from three sands (Esperance sand from Seattle, Washington, clean sand from Perth, Australia, and Ottawa sand) are used to validate the proposed theory. The closed form expression of the proposed theory can predict well the experimental data obtained from these sands in terms of the variation patterns of tensile strength over the entire saturation regimes, the magnitude of the tensile strength, its peak value, and the corresponding degree of saturation when the peak strength occurs.

Shear Strength-strain Behavior of Unsaturated Weathered Soil (SM) (화강풍화토(SM soil)의 불포화 전단거동 분석)

  • Jeong, Sang-Seom;Lee, Seong-Cheol;Jeong, Seung-Hwa
    • Journal of the Korean Geotechnical Society
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    • v.38 no.2
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    • pp.5-13
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    • 2022
  • The unsaturated behavior of sandy silt (SM soil) was investigated experimentally. Special attention was given to the stress-strain behavior of unsaturated weathered soil (SM) prior to failure and behavior at failure under monotonic loading. A sandy silt (SM) weathered soil containing a certain amount of fine contents distributed in Korea, was chosen to form samples with different densities of Dr=25%, 60%, and 75%. and matric suctions. The isotopically Consolidated Drain test (CD-test) was performed to maintain a constant matric suction during the shearing process. Based on the experimental results, it was qualitatively identified that the higher the relative density, the greater the virtual friction angle (ϕb) value and AEV (Air Entry Value) were induced. Also it is found that the internal friction angle (ϕ') is more or less constant. even if the matric suction is increased.