• Geomechanics and Engineering
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• v.24 no.1
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• pp.67-79
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• 2021

The influence of ground motions on the seismic response of utility tunnels was investigated. A series of small-scale shaking table model tests were carried out under uniform excitation in the transverse direction. Different peak accelerations of EL-Centro and Taft earthquake waves were applied. The acceleration responses, earth pressure, seismic strain, bending moment and structure deformations were measured and discussed. The results showed that the types of earthquake waves had significant influences on the soil-structure acceleration responses. However, the amplitude of the soil acceleration along the depth showed consistent variation regardless of the types of earthquake waves and tunnels. The horizontal soil pressure near the top and bottom slabs showed obviously larger values than those at other depths. In general, the strain response in the outer surface was more significant than that on the inner surface, and the peak strain in the end section of the model was larger than that in the middle section. Moreover, the bending moment at the corner points was much larger than that at middle point, and the bending moment was greatly affected by both input accelerations and seismic wave types. The opposite direction of shear deformation on the top and bottom slabs presented a rotation trend of the model structure.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.53-53
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• 2015

Basin-scale motions in a stratified lake rely on interactions of spatially and temporally varying wind force, bathymetry, density variation, and earth's rotation. These motions provide a major driving force for vertical and horizontal mixing of inorganic and organic materials, dissolved oxygen, storm water and floating debris in stratified lakes. In Lake Tahoe, located between California and Nevada, USA, basin-scale circulations are obviously important because they are directly associated with the fate of the suspended particulate materials that degrade the clarity of the lake. A three-dimensional hydrodynamic model, ELCOM, was applied to Lake Tahoe to investigate the underlying mechanisms that determine the characteristics of basin-scale circulations. Numerical experiments were designed to examine the relative effects of various mechanisms responsible for the horizontal circulations for two different seasons, summer and winter. The unique double gyre, a cyclonic northern gyre and an anti-cyclonic southern gyre, occurred during the winter cooling season when wind stress curl, stratification, and Coriolis effect were all incorporated. The horizontal structure of the upwelling and downwelling formed due to basin-scale internal waves found to be closely related to the rotating direction of each gyre. In the summer, the spatially varying wind field and the Coriolis effect caused a dominant anti-cyclonic gyre to develop in the center of the lake. In the winter, a significant wind event excited internal waves, and a persistent (2 week long) cyclonic gyre formed near the upwelling zone. Mechanism of the persistent cyclonic gyre is explained as a geostrophic circulation ensued by balancing of the baroclinc pressure gradient (or baroclinic instability) and Coriolis effect. Topographic effect, examined by simulating a flat bathymetry with constant depth of 300m, was found to be significant during the winter cooling season but not as significant as the wind curl and baroclinic effects.

• Nuclear Engineering and Technology
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• v.53 no.11
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• pp.3635-3642
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• 2021

Natural circulation systems (NCSs) are extensively applied in nuclear power plants because of their simplicity and inherent safety features. For some passive natural circulation systems in floating nuclear power plants (FNPPs), the ocean is commonly used as the heat sink. Condensation induced water hammer (CIWH) events may appear as the steam directly contacts the subcooled seawater, which seriously threatens the safe operation and integrity of the NCSs. Nevertheless, the research on the formation mechanisms of CIWH is insufficient, especially in NCSs. In this paper, the characteristics of flow rate and fluid temperature are emphatically analyzed. Then the formation types of CIWH are identified by visualization method. The experimental results reveal that due to the different size and formation periods of steam slugs, the flow rate presents continuous and irregular oscillation. The fluid in the horizontal hot pipe section near the water tank is always subcooled due to the reverse flow phenomenon. Moreover, the transition from stratified flow to slug flow can cause CIWH and enhance flow instability. Three types of formation mechanisms of CIWH, including the Kelvin-Helmholtz instability, the interaction of solitary wave and interface wave, and the pressure wave induced by CIWH, are obtained by identifying 67 CIWH events.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2016.05a
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• pp.135-136
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• 2016

SUPER concrete poontoon is developed to overcome shortcomings about corrosion problem of steel pontoon and the insufficient freeboard line of concrete pontoon. Top slab of Pontoon resists truck load or sidewalk live load. The soffit slab and outer wall of Pontoon resist the horizontal and vertical components of wave pressure, and those were loaded along X and Y-axis of Pontoon. Global analysis for the Pontoon is carried out to design its cross-sections economically using a geometric non-linear time history analysis method by Strand7 and buoyance-stability calculated automatically on non-vertical boundary conditions. And the load-capacity of Pontoon is confirmed through mock-up tests.

• Journal of the Korean Geosynthetics Society
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• v.20 no.4
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• pp.85-93
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• 2021

The seventy percentage of Korean Peninsular is covered by the mountainous area, and the depth of west sea and south sea is relatively shallow. Therefore, a large scale land reclamation from the sea has been implemented for the construction of industrial complex, residental area, and port and airport facilities. The common problem of reclaimed land is consisted of soft ground, and hence it has low load bearing capacity as well as excessive settlement upon loading on the ground surface. The hollow concrete block has been used to reinforce the loose and soft foundation soil where the medium-high apartment or one-story industrial building is being planned to be built. Recently the earthquakes with the magnitude of 4.0~5.0 have been occurred in the west coastal and southeast coastal areas. Lee (2019) reported the advantages of hollow concrete block reinforced shallow foundation through the static laboratory bearing capacity tests. In this study, the dynamic behavior of hollow concrete block reinforced sandy ground with filling the crushed stone in the hollow space has been investigated by the means of shaking table test with the size of shaking table 1000 mm × 1000 mm. Three types of seismic wave, that is, Ofunato, Hachinohe, Artificial, and two different accelerations (0.154 g, 0.22 g) were applied in the shaking table tests. The horizontal displacement of structure which is situated right above the hollow concrete block reinforced ground was measured by using the LVDT. The relative density of soil ground are varied with 45%, 65%, and 85%, respectively, to investigate the effectiveness of reinforcement by hollow block and measured the magnitude of lateral movement, and compared with the limit value of 0.015h (Building Earthquake Code, 2019). Based on the results of shaking table test for hollow concrete block reinforced sandy ground, honeycell type hollow block gives a large interlocking force due to the filling of crushed stone in the hollow space as well as a great interface friction force by the confining pressure and punching resistance along the inside and outside of hollow concrete block. All these factors are contributed to reduce the great amount of horizontal displacement during the shaking table test. Finally, hollow concrete block reinforced sandy ground for shallow foundation is provided an outstanding reinforced method for medium-high building irrespective of seismic wave and moderate accelerations.

• The Journal of Engineering Geology
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• v.26 no.1
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• pp.101-115
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• 2016

We carried out laboratory material tests on two cements (KS-1 ordinary Portland and Class G) with changing W/S (Water/Solid) and the content of fly ash in order to evaluate their physical and mechanical properties. The specimens of KS-1 ordinary Portland cement were prepared with varying W/S (Solid=cement) in weight, while those of Class G cement were prepared with changing the content of fly ash in volume but maintaining W/S (Solid=cement+fly ash). The results of the material tests show that as the W/S in KS-1 ordinary Portland cement and the content of fly ash in Class G cement increase, the properties (density, sonic wave velocity, elastic constants, compressive and tensile strengths, thermal conductivity) decrease, but porosity and specific heat increase. In addition, an increase in confining pressure and in the content of fly ash leads to plastic failure behavior of the cements. The laboratory data were then used in a stability analysis of cement sheath for which an analytical solution for computing the stress distribution induced around a cased, cemented well was employed. The analysis was carried out with varying the injection well parameters such as thickness of casing and cement, injection pressure, dip and dip direction of injection well, and depth of injection well. The analysis results show that cement sheath is stable in the cases of relatively lower injection pressures and inclined and horizontal wells. However, in the other cases, it is damaged by mainly tensile failure.

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.109-122
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• 2003

In order to release the pressure fluctuations and micro-pressure wave induced by the entering of train into the small cross sectional tunnel, it has been reported that the construction of air shaft has more advantages with respect to economy and constructability than the enlargement of cross section of existing tunnel. The field monitorings and analytical studies were conducted simultaneously in this study to analyze the mechanical behavior of existing railway tunnel, new cross tunnel and new shaft by the construction of new shaft nearby. The results showed that the minimum distance from existing tunnel to new shaft which secures the stability of existing tunnel was found to be half diameter of existing tunnel. On the three dimensional mechanical behavior of existing tunnel by the construction of new shaft, the results from the analytical study and field monitoring had a similar trend. The analytical study and field monitoring results, however, produced somewhat different results on the mechanical behavior of new shaft itself. These conclusions induce that the analytical method which has been applied on the analyses of horizontal tunnel could not be applied in the same way on the analysis of vertical shaft.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.1
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• pp.21-30
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• 1985

The tension leg platform (TLP) is a kind of compliant structures, and is also a type of moored stable platform with a buoyancy exceeding the weight because of having tensioned vertical anchor cables. In this paper, among the various kinds of tension leg structures, Deep Oil Technology (DOT) TLP was analyzed because it has large-displacement portions of the immersed surface such as vertical corner pontoons and small-diameter elongated members such as cross-bracing. It also has results of hydraulic model tests, comparable with theorectical analysis. Because of the vertical axes of symmetry in the three vertical buoyant legs and because there are no larger horizontal buoyant members between these three vertical members, it was decided to develop a numerical algorithm which would predict the dynamic response of the DOT TLP using the previously developed numerical algorithm Floating Vessel Response Simulation (FVRS) for vertically axisymmetric bodies of revolution. In addition, a linearized hydroelastic Morison equation subroutine would be developed to account for the hydrodynamic pressure forces on the small member cross bracing. Interaction between the large buoyant members or small member cross bracings is considered to be negligible and is not included in the analysis. The dynamic response of the DOT TLP in the surge mode is compared with the results of the TLP algorithm for various combinations of diffraction and Morison forces and moments. The results which include the Morison equation are better than the results for diffraction only. This is because the vertically axisymmetric buoyant members are only marginally large enough to consider diffractions effects. The prototype TLP results are expected to be more inertially dominated.