• Title/Summary/Keyword: pore pressure

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3-D Dynamic Response Characteristics of Seabed around Composite Breakwater in Relation to Wave-Structure-Soil Interaction (파랑-구조물-지반 상호작용에 의한 혼성제 주변 해저지반의 3차원 동적응답 특성)

  • Hur, Dong-Soo;Park, Jong-Ryul;Lee, Woo-Dong
    • Journal of Ocean Engineering and Technology
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    • v.30 no.6
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    • pp.505-519
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    • 2016
  • If the seabed is exposed to high waves for a long period, the pore water pressure may be excessive, making the seabed subject to liquefaction. As the water pressure change due to wave action is transmitted to the pore water pressure of the seabed, a phase difference will occur because of the fluid resistance from water permeability. Thus, the effective stress of the seabed will be decreased. If a composite breakwater or other structure with large wave reflection is installed over the seabed, a partial standing wave field is formed, and thus larger wave loading is directly transmitted to the seabed, which considerably influences its stability. To analyze the 3-D dynamic response characteristics of the seabed around a composite breakwater, this study performed a numerical simulation by applying LES-WASS-3D to directly analyze the wave-structure-soil interaction. First, the waveform around the composite breakwater and the pore water pressure in the seabed and rubble mound were compared and verified using the results of existing experiments. In addition, the characteristics of the wave field were analyzed around the composite breakwater, where there was an opening under different incident wave conditions. To analyze the effect of the changed wave field on the 3-D dynamic response of the seabed, the correlation between the wave height distribution and pore water pressure distribution of the seabed was investigated. Finally, the numerical results for the perpendicular phase difference of the pore water pressure were aggregated to understand the characteristics of the 3-D dynamic response of the seabed around the composite breakwater in relation to the water-structure-soil interaction.

Investigation on the responses of offshore monopile in marine soft clay under cyclic lateral load

  • Fen Li;Xinyue Zhu;Zhiyuan Zhu;Jichao Lei;Dan Hu
    • Geomechanics and Engineering
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    • v.37 no.4
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    • pp.383-393
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    • 2024
  • Monopile foundations of offshore wind turbines embedded in soft clay are subjected to the long-term cyclic lateral loads induced by winds, currents, and waves, the vibration of monopile leads to the accumulation of pore pressure and cyclic strains in the soil in its vicinity, which poses a threat to the safety operation of monopile. The researchers mainly focused on the hysteretic stress-strain relationship of soft clay and kinds of stiffness degradation models have been adopted, which may consume considerable computing resources and is not applicable for the long-term bearing performance analysis of monopile. In this study, a modified cyclic stiffness degradation model considering the effect of plastic strain and pore pressure change has been proposed and validated by comparing with the triaxial test results. Subsequently, the effects of cyclic load ratio, pile aspect ratio, number of load cycles, and length to embedded depth ratio on the accumulated rotation angle and pore pressure are presented. The results indicate the number of load cycles can significantly affect the accumulated rotation angle of monopile, whereas the accumulated pore pressure distribution along the pile merely changes with pile diameter, embedded length, and the number of load cycles, the stiffness of monopile can be significantly weakened by decreasing the embedded depth ratio L/H of monopile. The stiffness degradation of soil is more significant in the passive earth pressure zone, in which soil liquefaction is likely to occur. Furthermore, the suitability of the "accumulated rotation angle" and "accumulated pore pressure" design criteria for determining the required cyclic load ratio are discussed.

The Effect of Pressure on the Properties of Carbon/Carbon Composites during the Carbonization Process

  • Joo, Hyeok-Jong;Oh, In-Hwan
    • Carbon letters
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    • v.3 no.2
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    • pp.85-92
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    • 2002
  • 4D carbon fiber preforms were manufactured by weaving method and their carbon fiber volume fractions were 50% and 60%. In order to form carbon matrix on the preform, coal tar pitch was used for matrix precursor and high density carbon/carbon composites were obtained by high densification process. In this process, manufacture of high density composites was more effective according to pressure increasement. When densificating the preform of 60% fiber volume fraction with 900 bar, density of the composites reached at 1.90 $g/cm^3$ after three times processing. Degree of pressure in the densification process controls macro pore but it can not affect micro pore. During the carbonization process, micro pore of the preform were filled fully by once or twice densification processing. But micro pore were not filled easily in the repeating process. Therefore, over three times densification processing is the filling micro pore.

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Effect of Heating Rate and Pressure on Pore Growth of Porous Carbon Materials

  • Cho, Kwang-Youn;Kim, Kyong-Ja;Riu, Doh-Hyung
    • Carbon letters
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    • v.7 no.4
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    • pp.271-276
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    • 2006
  • Porous carbon materials were prepared with a thermal treatment of coal tar pitch at 550 in the Ar gas. Growth, merger, and distribution of pore were characterized with scanning electron microscopy as variation ascending temperature gradient and chamber pressure. After graphitizing at the 2600 (1 hr.), walls and connecting parts between pores were investigated with X-ray diffraction patterns. Wall thickness and pore size decreases as increasing ascending temperature gradient, and pore size becomes homogeneous. Graphite quality and thermal conductivity become higher due to the enhanced orientation of walls and connecting parts between pores.

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Characterization on the Relationships among Rainfall Intensity, Slope Angle and Pore Water Pressure by a Flume Test : in Case of Gneissic Weathered Soil (산사태 모형실험을 통한 강우강도 및 사면경사 변화와 간극수압과의 관계 연구 : 편마암 풍화토를 대상으로)

  • Chae, Byung-Gon;Lee, Seong-Ho;Song, Young-Suk;Cho, Yong-Chan;Seo, Yong-Seok
    • The Journal of Engineering Geology
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    • v.17 no.1 s.50
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    • pp.57-64
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    • 2007
  • This study was conducted to characterize on the relationships among rainfall intensity, slope angle and pore water pressure in the gneissic weathered soil by landslide laboratory flume tests. Under the several test conditions dependent on rainfall intensity and slope angle, the authors measured pore water pressure, failure and displacement of slope on a regular time interval. According to the test results, the increasing times of pore water pressures have direct proportional trends to the rainfall intensity. The pore water pressure was increased earlier at the head part of slope than the toe part. Compared with the test results of Chae et al(2006), the results of this study explain that the seepage velocity in the gneissic weathered soil is slower than that in the standard sands. It results in faster and ear-lier increase of pore water pressure at the head part of slope due to slow flow of water in the gneissic weathered soil. In case of the relationship between slope angle and pore water pressure, gentle slope angle has faster increase of pore water pressure than steeper slope angle. It is also thought to be due to slow seepage velocity and flow velocity in the gneissic weathered soil.

Pore Water Pressure Behavior due to Undrained Creep of Saturated Clay (포화점성토의 비배수 CREEP 성질에 의한 공극수압의 거동)

  • 강우묵;조성섭;지인택
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.30 no.3
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    • pp.38-50
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    • 1988
  • carried out to present a rheology model which is able to treat time-dependent properties of clay. The results were summarized as follow ; 1. The slope (a(e1)) of deviator stress in strain rate test was independent on axial strain, and pore water pressure was decreased with increment of strain rate. 2. The pore water pressure in a stress relaxation condition was not changed when the strain rate before stress relaxation was 0.05%/min., but it was increased with increment of time when the strain rate before stress relaxation was 0.2%/min 3. The greater the stress condition (q/qmax) and the strain rate before creep test became, the greater the increment rate of axial strain in creep test became. 4. SEKIGUCHI's constitutive equation was slightly overpredicted while empirical equation proposed in the study was well coincided with measured values. 5. The constitutive equation induced by a strain function could be dealed with a behavior of the pore water pressure increased with increment of elapsed time after primary consolidation.

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Pore Pressure Behavior of Normally Consolidated Deep Sea Clay (정규압밀된 심해점토의 간극수압 거동)

  • 박용원
    • Geotechnical Engineering
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    • v.6 no.4
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    • pp.65-74
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    • 1990
  • This paper presents triaxial test (CIVC and CKOUC) results on normally consolidated deep sea clay samples. Based on the test results the pore pressure-strain relations for both isotropicaly and anisotropicaly consgidated samples are expressed with hyperbolic functions of the major princpal strain. The analysis of the difference in pore pressure behavior due to the anisotropy in consolidation stress is carried out with the effective stress pathos of CIVC and CKOUC and finds a factor which correlates the pore pressure of two types of test.

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Study on the Undrained Strength Characteristics of Fiber Mixed Clay (섬유혼합 점토의 비배수 강도 특성에 대한 연구)

  • 박영곤;장병욱
    • Proceedings of the Korean Society of Agricultural Engineers Conference
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    • 1998.10a
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    • pp.382-387
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    • 1998
  • Triaxial compression tests were run to study on the undrained strength characteristics of fiber mixed kaolin clay(Hadong). The influence of various test parameters such as amount and aspect ratio(ratio of length to diameter) of fiber, confining stress was also investigated. Test results showed that the increase in aspect ratio was increased in deviator stress at failure, but no effect on pore water pressure at failure. Deviator stress at failure was also increased at 0.5% mixing ratio(weight fraction of fiber to that of soil solid) of fiber but it was, thereafter, decreased and wits reached to constant after 2% mixing ratio. On the contrary, Pore water pressure at failure was increased as mixing ratio of fiber was greater than 1%. Deviator stress and pore water pressure of both clay and fiber mixed clay(FMC) at failure were increased as confining stress was increased. Deviator stress of FMC at failure was about 10% larger than that of clay, but pore water pressure of FMC at failure was almost similar to that of clay.

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Prediction of Excess Pore Water Pressure of Reservoir Embankment on Soft Ground (연약지반상에 축조된 저수지 제방의 과잉공극수압 예측)

  • Min, Hag-Gyou;Lee, Dal-Won
    • Journal of The Korean Society of Agricultural Engineers
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    • v.50 no.2
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    • pp.37-44
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    • 2008
  • A theoretical equation was proposed to consider the effect of ponding for the excess pore water pressure in agricultural reservoir on soft clay ground. The value of excess pore water pressure predicted using the proposed equation was compared to those predicted with the Terzaghi's method and the finite difference method(FDM), respectively, for the purpose of verification. The degree of consolidation according to ponding predicted by applying the proposed equation was close to the observed degree of consolidation on the double drainage condition(at DP-3) but it was less than the observed degree of consolidation on the single drainage condition(at DP-5). The equation was very applicable to practice because the analysis result by the equation was close to the observed data.

Cyclic Threshold Shearing Strains of Sands Based on Pore Water Pressure Buildup and Variations of Deformation Characteristics (간극수압증가와 동적변형특성 변화에 근거한 사질토 지반의 반복한계전단변형률)

  • Kim, Dong-Soo;Choo, Yun-Wook
    • Proceedings of the Korean Geotechical Society Conference
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    • 2004.03b
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    • pp.274-281
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    • 2004
  • In this paper, the existing Stokoe type torsional shear equipment is modified to saturate the specimen and measure excess pore water pressure during undrained testing. Two types of sands, Geumgang and Toyoura sands, were collected and TS tests were performed at various densities drainage conditions, and confining pressures. The cyclic threshold shearing strains were estimated based on the variations of shear modulus, material damping ratio and pore pressures with loading cycles. The effects of relative density, confining pressure, and drainage condition on the cyclic threshold shearing strains were investigated.

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