• Journal of the Korean Society of Safety
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• v.29 no.6
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• pp.46-48
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• 2014

This paper compared and demonstrated the performance of the earth plate for conventional type and early streamer discharging type developed a new plate in order to improve the performance of the ground plate for use in grounding. The results obtained are shown below; early streamer discharge earth plate was high 5 kV on DC flashover voltage and corona discharge current was higher than about 2 times under the same test conditions compared to the conventional earth plate. From the experiential result, streamer discharge earth plate had a function of rapid inflow/out flow than the general ground plane because of by corona discharge current to be generated in the sharp serrated in formed the ground plane when strike current occurred. In the future, the newly developed early streamer discharge ground plate would be beneficial for grounding work to be widely used to promote the convenience and economy of construction.

• Journal of the Korean GEO-environmental Society
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• v.7 no.6
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• pp.23-34
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• 2006

In this study, the centrifugal tests were performed to evaluate the behavior of reinforced retaining wall that allows the settlement of reinforcement strip. To analyze the stability of reinforced retaining wall, which drives the settlement of reinforcement strip, the results were compared with the conventional reinforced retaining wall. In the centrifugal tests, the aluminum plate for the face was used and the aluminum foil was used as a reinforcement. The decomposed granite soil was adopted as a backfill. As a result, the settlement free reinforced retaining wall reached to the failure at 80g-level. In contrast, the conventional reinforced retaining wall was collapsed at 69g-level. It means that the settlement free reinforced retaining wall has the stronger stability than the conventional reinforced retaining wall. Also, vertical earth pressure of the settlement free reinforced retaining wall near the base of wall was higher 16% than that of the conventional reinforced retaining wall.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.8
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• pp.94-100
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• 2010

Grounding system insures a reference potential point for electric devices and also provides a low impedance path for fault currents or transient currents in the earth. The ground impedance as function of frequency is necessary for determining its performance since fault currents could contain a wide range of frequencies. In this paper, the grounding resistance, grounding impedance and transient grounding impedance are measured by using 3-point fall-of-potential method in order to analyse grounding characteristics of the stainless-steel plate grounding electrode. An equivalent transfer function model of the grounding impedance and transient grounding impedance are identified from the measured values by using ARMA method and evaluated by comparing conventional grounding impedances.

• Journal of the Korean Society of Safety
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• v.21 no.4 s.76
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• pp.85-94
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• 2006

In this study, in order to evaluate the effect of two types of connector systems in reinforced retaining wall, the centrifugal tests for the conventional connector and new settlement connector system were performed. In the centrifugal tests, the aluminum plate for the face was used and the aluminum foil was used as a reinforcement. The granite soil was adopted as a fill. As a result, The settlement reinforced retaining wall reached to the failure at 80g-level. In contrast, the conventional reinforced retaining wall was collapsed at 69g-level. It means that the settlement reinforced retaining wall has the stronger stability than the conventional reinforced retaining wall. In addition, it was shown that the settlement connector system is more effective to release the stress concentration occurred at the face of reinforced retaining wall than the conventional connector system.

• Wind and Structures
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• v.8 no.2
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• pp.107-120
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• 2005

The quasi-steady approaches to simulate the wind induced vibrations of inclined cables, especially on the rain-wind induced vibration, have been tried by many researchers. However, the steady wind force coefficients used in those methods include only the effects of water rivulet, but not the axial flow effects. The problem is the direct application of the conventional techniques to the inclined cable aerodynamics. Therefore, in this study, the method to implement the axial flow effects in the quasi-steady theory is considered and its applicability to the inclined cable aerodynamics is investigated. Then, it becomes clear that the perforated splitter plate in the wake of non-yawed circular cylinder can include the effects of axial flow in the steady wind force coefficients for inclined cables to a certain extent. Using the lateral force coefficients measured in this study, the quasi-steady theory may explain the wind induced instabilities of the inclined cables only in the relatively high reduced wind velocity region. When the Scruton number is less than around 40, the high speed vortex-induced vibration occurs around the onset wind velocity region of the galloping, and then, the quasi-steady approach cannot be applied for estimating the response of wind-induced vibration of inclined cable.

• Wind and Structures
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• v.12 no.5
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• pp.441-455
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• 2009

Studying the spatial distribution in coherent fields such as turbulence and turbulence-induced force is important to model and evaluate turbulence-induced forces and response of structures in the turbulent flows. Turbulence field-based coherence function is commonly used for the spatial distribution characteristic of the turbulence-induced forces in the frequency domain so far. This paper will focus to study spectral coherent structure of the turbulence and induced forces in not only the frequency domain using conventional Fourier transform-based coherence, but also temporo-spectral coherence one in the time-frequency plane thanks to wavelet transform-based coherence for better understanding of the turbulence and force coherences and their spatial distributions. Effects of spanwise separations, bluff body flow, flow conditions and Karman vortex on coherent structures of the turbulence and induced pressure, comparison between turbulence and pressure coherences as well as intermittency of the coherent structure in the time-frequency plane will be investigated here. Some new findings are that not only the force coherence is higher than the turbulence coherence, the coherences of turbulence and forces depend on the spanwise separation as previous studies, but also the coherent structures of turbulence and forces relate to the ongoing turbulence flow and bluff body flow, moreover, intermittency in the time domain and low spectral band is considered as the nature of the coherent structure. Simultaneous measurements of the surface pressure and turbulence have been carried out on some typical rectangular cylinders with slenderness ratios B/D=1 (without and with splitter plate) and B/D=5 under the artificial turbulent flows in the wind tunnel.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.2
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• pp.213-224
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• 2014

Recently, tunnelling with TBM is getting popular for the construction of cable tunnel in urban area. Mechanized tunnelling method using shield TBM has various advantages such as minimization of ground settlement and prevention of vibration induced by blasting that should be accompanied by conventional tunnelling. In Korea, earth pressure balance (EPB) type shield TBM has been mainly used. Despite the popularity of EPB shield TBM for cable tunnel construction, study on the mechanical behavior of cable tunnel driven by shield TBM is insufficient. Especially, the effect of backfill grout injection on the behavior of cable tunnel driven by shield TBM is investigated in this study. Tunnelling with shield TBM is simulated using 3D FEM. The distance of backfill grout injection from the end of shield skin varies. Sectional forces such as axial force, shear force and bending moment are monitored. Vertical displacement at the ground surface is measured. Futhermore, the relation between volume loss and the distance of backfill grout injection from the end of skin plate is derived. Based on the stability analysis with the results obtained from the numerical analysis, the most appropriate injection distance can be obtained.

• Geomechanics and Engineering
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• v.5 no.4
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• pp.363-377
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• 2013

Any structure constructed on the earth is supported by the underlying soil. Foundation is an interfacing element between superstructure and the underlying soil that transmits the loads supported by the foundation including its self weight. Foundation design requires evaluation of safe bearing capacity along with both immediate and long term settlements. Weak and compressible soils are subjected to problems related to bearing capacity and settlement. The conventional method of design of footing requires sufficient safety against failure and the settlement must be kept within the allowable limit. These requirements are dependent on the bearing capacity of soil. Thus, the estimation of load carrying capacity of footing is the most important step in the design of foundation. A number of theoretical approaches, in-situ tests and laboratory model tests are available to find out the bearing capacity of footings. The reliability of any theory can be demonstrated by comparing it with the experimental results. Results from laboratory model tests on square footings resting on sand are presented in this paper. The variation of bearing capacity of sand below a model plate footing of square shape with variation in size, depth and the effect of permissible settlement are evaluated. A steel tank of size $900mm{\times}1200mm{\times}1000mm$ is used for conducting model tests. Bearing capacity factor $N_{\gamma}$ is evaluated and is compared with Terzaghi, Meyerhof, Hansen and Vesic's $N_{\gamma}$ values. From the experimental investigations it is found that, as the depth of sand cushion below the footing ($D_{sc}$) increases, ultimate bearing capacity and settlement values show an increasing trend up to a certain depth of sand cushion.