• Title/Summary/Keyword: pore pressure

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Autogenous Shrinkage of Cement Paste Considering Disjoining Pressure in Thin Adsorbed Region (흡착 영역 분리 압력을 고려한 시멘트페이스트의 자기 수축)

  • Lee, Chang-Soo;Park, Jong-Hyok
    • Journal of the Korea Concrete Institute
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    • v.18 no.2 s.92
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    • pp.213-218
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    • 2006
  • Meniscus, adsorbed layer thickness, capillary pressure and disjoining pressure was deduced in extended meniscus region in cement paste pore by hydrostatic equilibrium. From the results, the relationship between pore size and adsorbed layer thickness could be derived and adsorbed layer thickness represents $0.299{\sim}2.700nm$ according to pore size $1nm{\sim}1{\mu}m$. Especially, disjoining pressure rapidly Increased in less than 10 nm pore size according to adsorbed layer thickness. Therefore, it is interpreted that autogenous shrinkage of cement paste is highly increases in formation of less than 10 nm pore size. Predictions of autogenous shrinkage in cement paste considering driving force for autogenous shrinkage with capillary pressure and disjoining pressure was low in comparison with experiment values between $1{\sim}4$ days and high in later period. These tendency could be thought that pore damage by mercury injection in early age makes shrinkage driving force underestimate and assumption for unsaturated independent pore makes overestimate. These interactions might be needed corrections considering on hydration or pore replacement model.

A new geomechanical approach to investigate the role of in-situ stresses and pore pressure on hydraulic fracture pressure profile in vertical and horizontal oil wells

  • Saberhosseini, Seyed Erfan;Keshavarzi, Reza;Ahangari, Kaveh
    • Geomechanics and Engineering
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    • v.7 no.3
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    • pp.233-246
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    • 2014
  • Estimation of fracture initiation pressure is one of the most difficult technical challenges in hydraulic fracturing treatment of vertical or horizontal oil wells. In this study, the influence of in-situ stresses and pore pressure values on fracture initiation pressure and its profile in vertical and horizontal oil wells in a normal stress regime have been investigated. Cohesive elements with traction-separation law (XFEM-based cohesive law) are used for simulating the fracturing process in a fluid-solid coupling finite element model. The maximum nominal stress criterion is selected for initiation of damage in the cohesive elements. The stress intensity factors are verified for both XFEM-based cohesive law and analytical solution to show the validation of the cohesive law in fracture modeling where the compared results are in a very good agreement with less than 1% error. The results showed that, generally by increasing the difference between the maximum and minimum horizontal stress, the fracture pressure and its profile has been strongly changed in the vertical wells. Also, it's been clearly observed that in a horizontal well drilled in the direction of minimum horizontal stress, the values of fracture pressure have been significantly affected by the difference between overburden pressure and maximum horizontal stress. Additionally, increasing pore pressure from under-pressure regime to over-pressure state has made a considerable fall on fracture pressure in both vertical and horizontal oil wells.

Comparison of 1-g and Centrifuge Model Tests on Liquefied Sand Grounds (액상화 지반에 대한 1-g 모형실험과 원심모형실험의 비교 연구)

  • Kim, Sung-Ryul;Hwang, Jae-Ik;Ko, Hon-Yim;Kim, Myoung-Mo
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • 2006.03a
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    • pp.97-104
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    • 2006
  • The centrifuge and 1-g shaking table tests were performed simultaneously to compare the dynamic behaviors of loose sands of same geotechnical properties. The prototype soils were 10 m thick liquefiable loose sands. The geometric scaling factors were 20 for 1-g and 40 for centrifuge tests. The excess pore pressure, surface settlement, and acceleration in the soil were measured at the same locations in the 1-g and centrifuge tests. The total excess pore pressure from development to dissipation was measured. In the centrifuge test, viscous fluid was used as the pore water to eliminate the time scaling difference between dynamic time and dissipation time. In the 1-g tests, the steady state concept was applied to determine the unit weight of the model soil, and two different time scaling factors were applied for the dynamic time and the dissipationtime. It is concluded that the 1-g tests can simulate the excess pore pressure of the prototype soil if the permeability of the model soil is small enough to prevent dissipation of excess pore pressure during shaking and the dissipation time scaling factor is properly determined.

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Comparison of Characterization Techniques of the Pore in Paper Sheet (종이의 기공 특성 측정 기법의 비교)

  • Won, Jong-Myoung;Nam, Ki-Young;Chung, Soon-Ki
    • Journal of Korea Technical Association of The Pulp and Paper Industry
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    • v.39 no.4
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    • pp.1-6
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    • 2007
  • Paper is a composite consisted of various solid materials including pulp, filler and other additives. The pore is also one of components consisting the paper structure. Thus the characterization of pore structure of paper is very helpful in the understanding the structural properties of paper. Mercury intrusion technique is frequently used for the characterization of the porous paper, giving access to parameters such as pore size and pore distribution. But some researchers pointed out the problem that the distortion of the pore structure can be occurred by the application of high pressure during mercury intrusion. Thus in this study, we tried to evaluate the potential of SEM and image analysis method as means for analyzing pore structure of the paper. The new pore analysis technique with SEM and image analysis does not require the application of high pressure, and gave better relation between the measured pore characteristics and the bulk of sheet than mercury intrusion method.

Fundamental Study for Vertical Fracturing Pressure of Impervious Soil (불투수성(不透水性) 지반(地盤)에서의 종할열주입압(縱割裂注入壓)에 관한 기초적(基礎的) 연구(硏究))

  • Chun, Byung Sik
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.6 no.3
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    • pp.43-51
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    • 1986
  • Triaxial compression tests were performed with control of vertical stress, confined pressure(${\sigma}_H$), and injection velocity by means of impervious soil samples with a different grain size, density and grout density. By measuring pore water pressure at the time of vertical fracturing around the bore-hole, relationships between main factors are described, and the factors are pore water pressure, confined pressure, vertical fracturing injection pressure(${\sigma}$) and the tension strength(${\sigma}_t$). The hydraulic fracturing of soft clay was occurred at the pressure which was less than the pressure obtained by the theory of elasticity. It was found that the above result was the influence of pore water pressure due to injection pressure($U_a$) and pore water pressure due to confined pressure($U_i$). Therefore, the vertical injection pressure at the time of fracturing needs to be changed as follows. $${\sigma}=2{\cdot}{{\sigma}_H}-(U_a+U_i)+{\sigma}_t$$.

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Verification of the Effectiveness of Hydraulic well through Large-scale Embankment Test (대형제방실험을 통한 Hydraulic well의 효용성 검증)

  • Park, Min-Cheol;Kim, Jin-Man;Moon, In-Jong;Jin, Yoon-hwa
    • 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.

Overtopping Model Experiments and 3-D Seepage Characteristics of the Embankment of Deteriorated Homogeneous Reservoirs (노후화된 균일형 저수지 제체의 월류모형실험과 3차원 침투특성)

  • Lee, Young Hak;Lee, Tae Ho;Lee, Dal Won
    • Journal of The Korean Society of Agricultural Engineers
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    • v.61 no.2
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    • pp.13-23
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    • 2019
  • In this study, an overtopping model experiments and three dimensional seepage characteristics at the deteriorated homogeneous reservoirs were performed to investigate the behavior of failure for embankment and spillway transitional zone due to overtopping. The failure pattern, pore water pressure, earth pressure and settlement by overtopping were compared and analyzed. The pattern of the failure by overtopping was gradually enlarged towards reservoirs crest from the spillway transition zone at initial stage. In the rapid stage and peak stage, the width and depth of failure gradually increased, and the pattern of the failure appeared irregular and several direction of the erosion. In the early stage, the pore water pressure at spillway transitional zone was more affected as its variation and failure width increased. In the peak stage, the pore water pressure was significantly increased in all locations due to the influence of seepage. The earth pressure increased gradually according to overtopping stage. The pore pressure by the numerical analysis was larger than the experimental value, and the analysis was more likely to increase steadily without any apparent variation. The horizontal and vertical displacements were the largest at the toe of slope and at the top of the dam crest, respectively. The results of this displacement distribution can be applied as a basis for determining the position of reinforcement at the downstream slope and the crest. The collapse in the overtopping stage began with erosion of the most vulnerable parts of the dam crest, and the embankment was completely collapsed as the overtopping stage increased.

A Experimental Study on the Variation of the Pore-water Pressure in the Soil Slope during the Rainfall (강우시 토사사면내의 간극수압변화에 관한 실험적 고찰)

  • Jeung, Eujung;Kim, Hongtaek;Jang, Hyunik;Kim, Kyungsuk;Kang, Inkyu
    • Journal of the Korean GEO-environmental Society
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    • v.9 no.1
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    • pp.33-40
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    • 2008
  • In this research, model tests have been performed for researching the seepage characteristics in the finite soil slope during the rainfall using a manufactured rainfall simulator. On the basis of the results, it has been analyzed how to change the seepage characteristics due to the duration time of rainfall. We are found that the pore-water pressure was gradually increased as increasing the duration time of rainfall. Specially, at the beginning of rainfall, the pore-water pressure in the middle surface of slope was measured larger than any point. As increasing the duration time of rainfall, the pore-water pressure at the inner part of slope was increased greatly at the collapse due to infiltrating the pore-water within the slope. In the research, it was not easy to get various test results because measuring instruments are high sensitivity and difficult to handle. For the future, the model test results are needed for the various slope angle.

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Syunthesis of Silica Aerogel at Ambient Pressure and Characterization (I) (실리카에어로겔의 상압합성 및 특성연구(I))

  • 강신규;최세영
    • Journal of the Korean Ceramic Society
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    • v.33 no.12
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    • pp.1394-1402
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    • 1996
  • The Silica gel with the density of 0.2g/cm3 and porosity of 90% was synthesized. The silica wet gel was dried and heat-treated under the ambient pressure after modification of the wet gel surface by TMCS. Specific surface area total pore volume and mean pore radius of dried gel were all increased with increasing heat treatment temperature and confirmed about 1400m2/g, 4.5cc/g and 8 nm respectively after heat treatment above 25$0^{\circ}C$. But the pore size distribution of dried gel was in the range of 1-100nm and was almost indepen-dent of temperature. As the result of external shape pore characteristics and microstructure of gel using SEM similar properties were observed between the silica gel synthesized in this study and the silica aerogel through the super critical drying.

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An Experimental study on the Criterion of Leading Rate in the CRLC Test (CRLC 실험에서 재하속도 기준에 대한 실험적 고찰)

  • Chae Jum-Sik;Lee Song;Cho Woo-Chul;So choong-seop;Lee Du-Hwa
    • Proceedings of the KSR Conference
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    • 2003.05a
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    • pp.393-399
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    • 2003
  • This paper describes a proper criterion for the constant rate of loading consolidation (CRLC) test which is a kind of the continuous loading consolidation(CRLS) and widely used as alternative methods to the incremental loading consolidation(ILC)test. With those results, the preconsolidation pressure estimated by the CRLC test turned out to be comparatively larger than that of the ILC test and it is increased in proportion to the applied loading rates. However, the compression index in the CRLC test is less ifluenced on by the loading rates. The coeffcient of consolidation and permeability in the CRLC test are dependent on excess pore pressure ratio mainly. In other words, if the pore pressure ratios are too low, the coefficient of consolidation and permeability become smaller than those of the ILC test. On the other hand, if the excess pore pressure ratios are too high, the coefficient of consolidation and permeability become so larger than those of the ILC test. Therefore loading rates should be carefully determined to generate proper excess pore pressure ratio.

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