• Journal of the Korean Geotechnical Society
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• v.27 no.12
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• pp.27-37
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• 2011

Uplift phenomenon occurs when the apparent unit weight of buried geo-structures becomes smaller than that of the liquefied backfill due to the increase of an excess pore water pressure during strong earthquakes. In order to explain the relationship between the uplift displacement of the buried geo-structures and the increase of the excess pore water pressure ratio in backfill, dynamic centrifuge model tests are conducted. In the present study, primary and secondary factors against uplift behavior of the buried geo-structures are considered in the dynamic centrifuge model tests. Among these factors, the most important factors affecting the increase in the excess pore water pressure ratio were the ground water depth, the relative density of backfill, and the amplitude of the input acceleration, which were also largely affect the uplift amount of the buried geo-structures.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.68-68
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• 2016

하천의 사행 및 합류 형상은 복잡한 나선 흐름을 발생시킨다. 그 중 이차류는 사행에 의한 편수위 형성과 횡단 압력의 불균형, 그리고 수심에 따라서 변화하는 원심력에 의하여 형성된다. 이러한 흐름은 주로 3차원 모형으로 재현할 수 있으며 이에 관련된 연구는 계속 이루어졌으나 3차원 모형의 구성과 사용에는 상당한 시간 및 노력이 요구된다. 본 연구에서는 이러한 이차류의 영향을 수심적분된 2차원 모형으로 구현하고자 하였으며 이를 위해 이차류 연직 분포에 대한 기존 연구를 확인하고, 이러한 연직 분포를 표현할 수 있는 경험식을 3차원 모형인 FLOW3D를 통해 모의하고 개발하였다. 3차원 모형을 다양한 사행반경을 갖는 실험 사행수로에 적용하여 사행도에 따른 민감도를 분석하고 경험식을 개발하였다. 개발된 식은 2차원 수리해석 모형인 RAMS(River Analysis and Modeling System)에 적용되었다. RAMS는 수심 적분된 2차원 천수 방정식을 지배방정식으로 사용하는 수리해석모형인 HDM-2D를 해석엔진으로 사용하며, 이차류의 영향을 반영하기 위하여 개발한 수직분포 경험식을 분산 응력항 형태로 적용하였다. 모형의 적용성 확인을 위하여 사행 실험수로 및 합류수로에 모의를 수행하였다. 사행수로 및 합류수로는 실험 경계조건과 동일한 상류 입력 유량과 하류 경계조건을 사용하여 결과를 비교하였다. 사행수로 모의 결과 유속분포의 거동이 실험수로의 사행으로 인하여 2차류 효과로 주 흐름이 바깥쪽으로 기울어짐을 일부 재현하였다. 합류수로의 경우 기존 모형에 비하여 분산 응력항이 포함된 본 모형이 실측값에 근접하였는데 이는 이차류가 발생하는 영향으로 하류에 유속편차가 줄어드는 영향을 더 정확히 묘사한 것으로 판단된다.

• Journal of the Korean Geotechnical Society
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• v.26 no.8
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• pp.67-75
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• 2010

In this study, a series of 1 g shaking table tests were carried out for a single pile in soft clay with various input acceleration amplitudes and frequencies. Based on the results, dynamic p-y curves were drawn and, in turn, the dynamic p-y backbone curve was formed by connecting the peak points, corresponding to the maximum soil resistance, of the dynamic p-y curves. In order to represent the p-y backbone curve numerically, Matlock's p-y formulations for clay was used to find the initial stiffness ($k_{ini}$) and the ultimate capacity ($p_u$) of the clay, both of which are required to formulate the p-y backbone curve as a hyperbolic function. The suggested p-y backbone curve was verified through comparisons with currently available p-y curves as well as other researchers' centrifuge test results and numerical analysis results.

• Journal of the Korean GEO-environmental Society
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• v.16 no.12
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• pp.23-35
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• 2015

Nonlinear soil behavior before failure under dynamic loading is often implemented in a numerical analysis code by a mathematical fitting function model with Masing's rule. However, the model may show different behavior with an experimental results obtained from laboratory test in damping ratio corresponding secant shear modulus for a certain shear strain rage. The difference may come from an unique soil characteristics which is unable to implement by using the existing mathematical fitting model. As of now, several fitting models have been suggested to overcome the difference between model and real soil behavior but consequence of the difference in dynamic analysis is not reviewed yet. In this paper, the effect of the difference on site response was examined through nonlinear response history analysis. The analysis was verified and calibrated with well defined dynamic geotechnical centrifuge test. Site response analyses were performed with three mathematical fitting function models and compared with the centrifuge test results in prototype scale. The errors on peak ground acceleration between analysis and experiment getting increased as increasing the intensity of the input motion. In practical point of view, the analysis results of accuracy with the fitting model is not significant in low to mid input motion intensity.

• Journal of the Korean Geotechnical Society
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• v.25 no.11
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• pp.27-38
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• 2009

In this study, a series of 1 g shaking table model pile tests were carried out in saturated dense and loose sand to evaluate dynamic p-y curves for various conditions of flexural stiffness of a pile shaft, acceleration frequency and acceleration amplitude for input loads. Dynamic p-y backbone curve which can be applied to pseudo static analysis for saturated dense sand was proposed as a hyperbolic function by connecting the peak points of the experimental p-y curves, which corresponded to maximum soil resistances. In order to represent the backbone curve numerically, empirical equations were developed for the initial stiffness ($k_{ini}$) and the ultimate capacity ($p_u$) of soils as a function of a friction angle and a confining stress. The applicability of a p-y backbone curve was evaluated based on the centrifuge test results of other researchers cited in literature, and this suggested backbone curve was also compared with the currently available p-y curves. And also, the scaling factor ($S_F$) to account for the degradation of soil resistance according to the excess pore pressure was developed from the results of saturated loose sand.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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• pp.622-628
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• 2016

As the suction pad-supporting bike carrier attached to a car may be subject to an excessive dynamic load due to random vibrations and centrifugal forces during driving, its structural safety is of great concern. To examine this, the finite-element method with a fluid-structure interaction should be used because the pressure on the pad bottom is changed in real time according to the fluctuations of the force or the moment applied on the pad. This method, however, has high computing costs in terms of modeling efforts and software expense. Moreover, the accuracy of computation is not easily guaranteed. Therefore, a new method combining the experiment and computation is proposed in this paper: the bottom pressure and contact area of the pad under varying loads was measured in real time and the acquired data are then used in the nonlinear elastic finite-element calculations. The computational and experimental results obtained with the product under development showed that the safety margin of the pad under the axial loading is relatively sufficient, whereas with an excessive rotational loading, the pad is vulnerable to separation or a local surface damage; hence, the safety margin may not be secured. The predicted contact behavior under the variation of the magnitude and type of the loading were in good agreement with the one from the experiment. The proposed analysis method in this study could be used in the design of similar vacuum pad systems.

• Journal of the Korean Geotechnical Society
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• v.38 no.11
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• pp.149-161
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• 2022

This study selected the indexes for evaluating the damage of the railway embankments due to liquefaction from the earthquake damage cases of railway embankments. The study correlated the selected indexes and the settlement of the embankment crest from the dynamic numerical analysis. Further, the correlation was used to develop a method for evaluating the liquefaction damage to the railway embankment. The damage cases and damage types were analyzed, and referring to the liquefaction damage assessment method for other structures, the embankment height (H), the non-liquefiable layer thickness (H₁), and the liquefaction potential index were selected as indexes for evaluating the damage. The study performed dynamic effective stress analyses on the railway embankment, and the PM4-Sand model was applied as the constitutive liquefaction model for the embankment foundation ground. The model's validity was first verified by comparing it with the existing dynamic centrifugal model test results performed on the railway embankment. Nine sites where the foundation ground can be liquefied were selected from the data of 549 embankments of the Honam High-speed Railway in Korea. Further, dynamic numerical analyses using four seismic waves as input earthquake load were performed for the selected site sections. The numerical analysis results confirmed the correlation between the evaluation indexes and the embankment crest settlement. A method for efficiently evaluating the damage to the embankment due to liquefaction was proposed using the chart obtained from this correlation.

• Journal of the Korean Geotechnical Society
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• v.38 no.12
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• pp.45-65
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• 2022

In this paper, a diaphragm wall that supports soils and rock was modeled using FLAC, a finite difference analysis program, to evaluate the seismic behavior of temporary retaining structures in a deep excavation. The appropriateness of the numerical model was verified by comparing its results with those of the centrifuge test performed in a similar condition. The bending moment distribution along the diaphragm wall shows a very similar tendency, and the maximum acceleration obtained at the backfill and top of the wall shows a difference within 5%. Based on the developed model, a parametric study was conducted in various input earthquake, ground, and excavation conditions. The maximum structural forces and bending moment under earthquake loading were compared with the maximum values during excavation, from which the critical condition that requires a seismic design was roughly sorted out. The maximum bending moment of a wall that retains soil layers increased 17%. Particularly, the axial force of struts located in loose soils increased 32% under 100 years return period of an earthquake event, which strongly is estimated to require seismic design for structural safety.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.5
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• pp.470-478
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• 2008

Statement of problem: Use of all-ceramic prostheses fabricated with CAD/CAM systems is increasing in the dentistry. Marginal fidelity in production of all-ceramic restoration has important clinical implications and is a key consideration issue in CAD/CAM production as well. Purpose: The objective of this study was to analyse marginal fidelities of $Procera^{(R)}$ Allceram Crown. Material and methods: On 56 patients treated with $Procera^{(R)}$ system Allceram Crown at Dankook Dental Hospital, marginal discrepancies of 101 abutments were measured by stereomicroscope at coping and final restoration stages. Paired t-test and one-way analysis of variance on marginal discrepancy data were conducted to determine the presence of significant differences between measurement and measuring point stages. Results: Marginal discrepancies of final restoration ($45.82{\pm}30.84\;{\mu}m$) were lower than alumina coping ($53.84{\pm}38.83\;{\mu}m$). Furthermore, the differences were found to be statistically significant at 95% confidence level. Anterior marginal discrepancies were lower than posterior marginal discrepancies, but they were not statistically significant. Lingual marginal discrepancies were higher than other measurement sites, and the differences were found to be statistically significant at 95% confidence level. Conclusion: Within the conditions of this study, marginal fidelities of $Procera^{(R)}$ Allceram Crown were acceptable, and after porcelain build-up, marginal fitness improved over alumina coping. More careful scanning is needed for better results.

• The Korean Journal of Nuclear Medicine Technology
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• v.22 no.2
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• pp.97-100
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• 2018

Purpose The glomerular filtration rate (GFR) test is an important indicator of glomerular filtration and has been used to test renal function and the extent of its function. The GFR test is performed by intravenous injection of radioactive medicines made of $^{51}Cr$-EDTA, and blood concentration is measured by taking blood according to the elapsed time. also, PET-CT, bone scan, transfusion and so on will affect the outcome. Therefore, we will improve the quality of the test by providing guidelines for the GFR test for more accurate testing. Materials and Methods 5 mL of physiological saline solution and 2 mL of $^{51}Cr$-EDTA solution are used to make 5 mL of the radiopharmaceutical solution to be injected into the patient. First, the syringe weight is measured before the injection, and then the radioactive medicine is injected into the patient's vein and the syringe weight is measured after the injection. Blood sampling is performed twice in total. In adults, blood is collected 3 hours / 5 hours after injection and in children 2 hours / 5 hours after injection. The blood sample is centrifuged at 3300 rpm for 5 minutes. Standard solution is prepared by filling diluent water up to the scale indicated in the 200-mL volumetric flask, discarding $500{\mu}L$, injecting $500{\mu}L$ of GFR reagent and mixing well. $500{\mu}L$ each of the standard solution is dispensed into two test tubes, and $500{\mu}L$ of each of the plasma samples collected in time is dispensed into two test tubes and measured with a Cobra Counter. Results At present, the reference range applied in this study is $119.5{\pm}30.3ml/min/1.73m2$ for males and $125.2{\pm}28.2ml/min/1.73m^2$ for females. Conclusion The GFR test is conducted using radioactive medical products. GFR testing is performed as a scheduled test, but PET-CT, dialysis and transfusion, which may affect GFR testing, may be scheduled during GFR testing. Therefore, we could get accurate GFR test results by notifying the ward and department beforehand when booking.