• Journal of the Korean Geotechnical Society
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• v.17 no.6
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• pp.149-162
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• 2001

Longitudinal cracks have occurred on the crest of dams soon after their construction of two earth-rocfill dams located in Samlangjin. They are a pair of pumped storage dams constructed for generation of electrical power. The upper dam and lower dam are subjected to the variation of water level more than 10m once in a day alteratively. This paper deals with the finding of possible causes for longitudinal cracks about upper dam. The dominant cause was considered to be due to fluctuation of water load, for which numerical analysis was carried out using the hyperbolic model. In order to obtain parameters necessary to the analysis, a series of triaxial tests was performed for both core and rock material. Also dynamic triaxial test was performed to obtain dynamic properties of soils, which could be used as input data to simulate frequent variation of stress change due to the water fluctuation. It was known from the numerical analysis that the confining pressure of upper 4m from the top of the crest become negative after repeating of water load, meaning that tension cracks occurred in the top portion of the crest. The depth of longitudinal cracks has been investigated by digging test pit on the crest. This results agree with the field observation.

• Journal of Astronomy and Space Sciences
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• v.28 no.1
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• pp.27-36
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• 2011

The present study examines the morning-afternoon asymmetry of the geosynchronous magnetic field strength on the dayside (magnetic local time [MLT] = 06:00~18:00) using observations by the Geostationary Operational Environmental Satellites (GOES) over a period of 9 years from February 1998 to January 2007. During geomagnetically quiet time (Kp < 3), we observed that a peak of the magnetic field strength is skewed toward the earlier local times (11:07~11:37 MLT) with respect to local noon and that the geosynchronous field strength is larger in the morning sector than in the afternoon sector. That is, there is the morning-afternoon asymmetry of the geosynchronous magnetic field strength. Using solar wind data, it is confirmed that the morning-afternoon asymmetry is not associated with the aberration effect due to the orbital motion of the Earth about the Sun. We found that the peak location of the magnetic field strength is shifted toward the earlier local times as the ratio of the magnetic field strength at MLT = 18 (B-dusk) to the magnetic field strength at MLT = 06 (B-dawn) is decreasing. It is also found that the dawn-dusk magnetic field median ratio, B-dusk/B-dawn, is decreasing as the solar wind dynamic pressure is increasing. The morning-afternoon asymmetry of the magnetic field strength appears in Tsyganenko geomagnetic field model (TS-04 model) when the partial ring current is included in TS-04 model. Unlike our observations, however, TS-04 model shows that the peak location of the magnetic field strength is shifted toward local noon as the solar wind dynamic pressure grows in magnitude. This may be due to that the symmetric magnetic field associated with the magnetopause current, strongly affected by the solar wind dynamic pressure, increases. However, the partial ring current is not affected as much as the magnetopause current by the solar wind dynamic pressure in TS-04 model. Thus, our observations suggest that the contribution of the partial ring current at geosynchronous orbit is much larger than that expected from TS-04 model as the solar wind dynamic pressure increases.

• Journal of the Korean GEO-environmental Society
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• v.18 no.11
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• pp.27-33
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• 2017

Nonlinear dynamic analysis is performed to calculate the response of U-shaped cantilever retaining structure under seismic loading using the finite element (FE) analysis program OpenSees. A particular interest of the study is to evaluate whether the moment demand in the cantilever can be accurately predicted, because it is an important component in the seismic design. The numerical model is validated against a centrifuge test that was performed on cantilever walls with dry medium dense sand in backfill. Seismic analysis is performed using the pressure-dependent, multi-yield-surface, plasticity based soil constitutive model implemented in OpenSees. Normal springs are used to simulate the soil-structure interface. Comparison with centrifuge show that FE analysis provides good estimates of both the acceleration response and bending moment. The lateral earth pressure near the bottom of the wall is overestimated in the numerical model, but this does not contribute to a higher prediction of the moment.

• Journal of the Korean Geotechnical Society
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• v.22 no.1
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• pp.15-23
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• 2006

During earthquake, force components acting on quay walls consist of inertia force, earth pressure and water pressure. The earth pressure is largely influenced by the backfill condition such as soil density and the installation of gravel backfill. Therefore, shaking table tests were performed by using four different model sections, which were designed by varying the soil density and the backfill materials. The magnitude and the phase of force components acting on quay wall were analyzed. Test results showed that the gravel backfill and the soil compaction were effective to reduce the excess pore pressure in backfill and the magnitude and phase of backfill thrust were much influenced by the excess pore pressure in backfill. When the input acceleration was 0.10g, the average ratios of the inertia force, the front dynamic water force and the thrust to the total force were $64\%,\;21\%\;and\;16\%$, respectively. As the excess pore pressure increased, the ratio of the thrust to the total force increased.

• Journal of the Korean Geophysical Society
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• v.6 no.4
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• pp.221-230
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• 2003

Many hydraulic structures are damaged by under flood flow and storm waves year after year. Many cases of dike and breakwater failure are caused by the suck out of sand from behind the revetment. This type of failure will be in close relation to the dynamic behavior of sand bed around the revetment. In this paper, from this point of view we investigated the basic characteristics of such sand movement by small model tests and tried to explanation the hydro- and soil mechanical mechanism of this phenomenon theoretically.

• Journal of Advanced Navigation Technology
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• v.16 no.6
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• pp.900-909
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• 2012

Low Earth orbit satellites with satellite navigation receiver use onboard navigation filters for filtering measurement signals and for orbit prediction under signal loss. Precision satellite dynamic models, core of the navigation filter, are studied and a computation program is developed. Gravity acceleration, precision coordinate transform, third-body gravity, atmospheric drag, and solar radiation pressure models are combined into an orbit prediction algorithm, and a proven precision orbit determination software is used to validate the program. Orbit prediction accuracy is analyzed with simulated and flight orbit data. The program meets an accuracy level for onboard real-time navigation filter.

• Geotechnical Engineering
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• v.1 no.1
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• pp.21-30
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• 1985

The reasonable static and dynamic earth pressure equations were developed by applying the Dubrova's theory and Chang's method to the following cases of wall movements; (1) Active case rotating about the top (2) Active case rotating about the bottom (3) Passive case rotating about the top (4) Passive case rotating about the bottom The equations are presented in accordance with particular wall displacements for the sand and cohesive back-fill, respectively. The results computed by the proposed equations are compared with the conventional theoretical values.

• Structural Engineering and Mechanics
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• v.73 no.5
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• pp.599-612
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• 2020

A combination of a gravity wall and an anchor beam is widely used to support the high soil deposit on rock mass. In this study, two groups of shaking table test were performed to investigate the responses of such combined retaining structure, where the rock masses were shaped with a flat surface and a curved surface, respectively. Meanwhile, the dynamic numerical analysis was carried out for a comparison or an extensive study. The results were studied and compared between the combined retaining structures with different shaped rock masses with regard to the acceleration response, the earth pressure response, and the axial anchor force. The acceleration response is not significantly influenced by the surface shape of rock mass. The earth pressure response on the combined retaining structure with a flat rock surface is more intensive than the one with a curved rock surface. The anchor force is significantly enlarged by seismic excitation with a main earthquake-induced increment at the first intensive pulse of Wenchuan motion. The value of anchor force in the combined retaining structure with a flat rock surface is generally larger than the one with a curved rock surface. Generally, the combined retaining structure with a curved rock surface presents a better seismic performance.

• Journal of the Korean earth science society
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• v.30 no.5
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• pp.630-645
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• 2009

The tropopause fold event that took place on January 1, 1997 over mid-region on the Korean Peninsula is examined by means of a numerical simulation based on a Mesoscale Model (MM5). The purpose of this paper is to investigate the effects of moisture in reinforcing a tropopause fold linked to an explosive cyclone. Two types of simulations were carried out; 1) simulations for moist conditions in which full physical and dynamic processes are considered and 2) simulations for dry conditions in which cumulus parameterization and cloud microphysics process are excluded. The results of the moist condition simulations demonstrate that the intensity of the central pressure of the cyclone was overestimated compared with the observed values and that the location of the center and the pressure deepening rates (-17 hPa/12 hr) complied with the observed values. The potential vorticity (PV) anomaly on the isentropic surface at 305 K continued to move in a southeast direction on January 1, 1997 and thus created a single tube of tropopause fold covering the northern and the middle area of the Korean Peninsula and reaching the ground surface at 0300 UTC and 0600 UTC. The results of the dry condition simulations show that the tropopause descended to 500 and 670 hPa in 0300 and 0600 UTC, respectively at the same location for the moist condition simulation; however, there was no deep tropopause fold observed. A comparison of the simulated data between the moist and the dry conditions suggests that a deep tropopause fold should happen when there is sufficient moist in the atmosphere and significantly large PV in the lower atmosphere pulls down the upper atmosphere rather than when the tropopause descends itself due to dynamic causes. Thus, it is estimated that moisture in the atmosphere should have played a crucial role in a deep tropopause fold process.

• Journal of the Korean Geotechnical Society
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• v.39 no.9
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• pp.35-50
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• 2023

A preliminary study is conducted to develop seismic design guidelines for temporary retaining structures in a deep excavation. The study involved a comprehensive literature review of the seismic design standards applied domestically and internationally, as well as various methods to calculate seismic earth pressure for pseudostatic analysis. The FLAC 2D, a two-dimensional finite difference analysis program, was utilized to perform pseudostatic analysis using the Semirigid pressure method, Wood method, and Mononobe-Okabe method. The resulting analysis data for the wall moment and axial force of the strut were compared with the dynamic analysis outcomes to evaluate the applicability of pseudostatic analysis. The Semirigid pressure method predicted the most reasonable moment for Stiff walls experiencing horizontal displacements up to 0.4%H. Predicting the axial force of the strut exactly was challenging because the pseudostatic analysis cannot consider dynamic soil-structure interaction; however, it is deemed available for conservative preliminary review to ensure safety.