• Journal of the Korean GEO-environmental Society
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• v.5 no.3
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• pp.31-39
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• 2004

The bored pile is widely used as a low noise and vibration piling method in Korea. However, there is design tendency to minimize the friction capacity of the bored pile because of uncertainty and the quality control specification is not set up. This research analysed the strength characteristics of cement paste after the uniaxial compression test with various condition. Test results show that the compressive strength of cement paste with w/c=0.83 was up to $156.0kgf/cm^2$, and the lower w/c ratio and the longer age, the strength of cement paste increased. Also the higher soil mixing ratio, the strength of soil cement decreased, and too high soil mixing ratio caused the malfuction of soil cement. Also this research analysed the 188 dynamic pile test results which were performed before and after hardening of cement paste. Analysis result showed that the average ultimate unit friction capacity was $9.1tf/m^2$ and this result surpassed the common design criteria of the bored pile.

• Journal of Korean Society of Transportation
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• v.23 no.4 s.82
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• pp.57-69
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• 2005

The goal of this paper is to develop freeway Origin-Destination (OD) demand estimation model using real-time traffic data collected from Freeway Traffic Management System (FTMS). In existing research, the micro-simulation models had been used to get a link distribution proportion by time process. Because of hi-level problem between the traffic flow model and the optimal OD solution algorithm, it is difficult for the existing models to be loaded at FTMS. The formulation of methodology proposed in this paper includes traffic flow technique to be able to remove the bi-level problem and optimal solution algorithm using a genetic algorithm. The proposed methodology is evaluated by using the real-time data of SOHAEAN freeway, South Korea.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.3
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• pp.247-254
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• 2008

The double-peak normal distribution function (DPDF) suggested by Cho et al.(2004) has the problems that the extremely high and low tidal elevations are frequently generated in the Monte-Carlo simulation processes because the upper and lower limits of the DPDF are unbounded in spite of the excellent goodness-offit results. In this study, the modified DPDF is suggested by introducing the upper and lower value parameters and re-scale parameters in order to remove these problems. These new parameters of the DPDF are optimally estimated by the non-linear optimization problem solver using the Levenberg-Marquardt scheme. This modified DPDF can remove completely the unrealistically generated tidal levations and give a slightly better fit than the existing DRDF. Based on the DPDF's characteristic power, the over- and under estimation problems of the design factors are also automatically intercepted, too.

• Tunnel and Underground Space
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• v.9 no.4
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• pp.328-336
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• 1999

To characterize the hydro-mechanical behavior of a rock joint, a rotary shear testing apparatus was devised in this study. Shear stress was driven by twisting the end of a sample in the rotary shear testing apparatus. The test results show that the rotary shear test underestimates the peak shear strength of a rock joint. The torque is known as a function of the radial distance from the axis of rotation, resulting in the radial variation of the shear stress. Fluid flow through rock joints is mainly dependent on the Joint roughness, contact area, initial aperture. To examine the dependency, the relationship between the hydraulic and the mechanical apertures for shear-flow was established by measuring the initial aperture. It shows that the mechanical aperture and the hydraulic aperture increase linearly with the dilatancy. The difference between the hydraulic and mechanical apertures describes the deviation from the behavior predicted by the parallel plate model.

• Journal of Korean Society of Steel Construction
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• v.16 no.1 s.68
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• pp.135-144
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• 2004

Since Modern bridges have a tendency to make the spans continuous and longer, the effect of concrete shrinkage and creep is very important and must be evaluated appropriately for the durability and safety of steel-concrete composite bridges. However, highway design specification in current use prescribes $180^{1\;2}$ as the final shrinkage strain. which is for less value than one resulted from many experimental researches and cause some problems in the construction of composite bridges due to the understimation of shrinkage strain. Thus, in this paper nonlinear analysis with time-steps applying the CEB-FIP(90) provision have been conducted for plate girder bridge, box girder bridge and Preflex beam bridge and the linear equivalent shrinkage strain for the design of composite bridges. which produces the stress equal to the values from the nonlinear analysis, has been calculated by comparing the results with the values following highway design specification. The results yield appropriately double values than $180^{1\;2}$ which highway design specification prescribes.

• Environmental and Resource Economics Review
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• v.22 no.3
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• pp.437-457
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• 2013

The purpose of this study is to explain the causes of the phenomenon that the Environmental Kuznets Curve hypothesis suggests that the increasing the emissions level of environmental pollutants starting to decrease as a certain income level is reached, associating microeconomic variables such as awareness level. Effects of the level of awareness differs depending on the characteristics of the impacts of pollutants- either regional or global. Furthermore, the study identifies that the impacts on the change in emissions inventory differ. The study empirically examines and concludes that the turning point where the emission level of environmental pollutants starts to decrease is over- or under-estimated if the differing responses between the level of awareness and its effect on pollutants are ignored. In addition, the level of emissions starts to decrease at a lower level of income in case of regional effect from pollutant than the global effect from it. Finally, the study implies that investing more efforts and resources to improve the level of people's awareness on environmental quality is effective if the government is to alter the increasing path of emission level.

• Environmental and Resource Economics Review
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• v.13 no.2
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• pp.175-194
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• 2004

Volumes of research have been implemented to estimate and predict the oil price. These models, however, fail in accurately predicting oil price as a model composed of only a few observable variables is limiting. Unobservable variables and news that have been overlooked in past research, yet have a high likelihood of affecting the oil price. Hence, this paper analyses the news impact on the price. The standard GARCH model fails in capturing some important features of the data. The estimated news impact curve for the GARCH model, which imposes symmetry on the conditional variances, suggests that the conditional variance is underestimated for negative shocks and overestimated for positive shocks. Hence, this paper introduces the asymmetric or leverage volatility models, in which good news and bad news have different impact on volatility. They include the EGARCH, AGARCH, and GJR models. The empirical results showed that negative shocks introduced more volatility than positive shocks. Overall, the AGARCH and GJR were the best at capturing this asymmetric effect. Furthermore, the GJR model successfully revealed the shape of the news impact curve and was a useful approach to modeling conditional heteroscedasticity.

• Journal of Korea Water Resources Association
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• v.51 no.8
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• pp.643-654
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• 2018

In order to generate the stable tsunami in a numerical wave tank, a two-dimensional numerical model, LES-WASS-2D has been introduced the non-reflected wave generation system for various tsunami waveforms. And then, comparing to existing experimental results it is revealed that computed results of the LES-WASS-2D are in good agreement with the experimental results on spatial and temporal tsunami waveforms in the vicinity of a seawall. It is shown that the applied model in this study is applicable to the numerical simulations on tsunami overtopping and inundation. Using the numerical results, the characteristics of overtopping and inundation on a seawall are also discussed with volume ratio of tsunami and relative tsunami height. The wider the tsunami waveform, tsunami overtopping quantity and inundation distances are linearly increased. Therefore, the hydraulic characteristics is highly likely to be underestimated against the real tsunami if the solitary wave of approximation theory is applied for the overtopping/inundation simulations due to a tsunami.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.89-97
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• 1999

In this study, fifteen reinforced high-strength lightweight concrete(HLC)beams were tested to investigate shear behavior of specimens according to shear reinforcement ratio. Test variables are shear span to effective depth ratio(a/d=2.5, 3.5, 4.5) and shear reinforcement ratio(0~1.0${\rho}_{v,ACI}$). Concrete compressive strength and tensile steel reinforcement ratio are constantly 439kg/$cm^2$ and 0.0203, respectively. Test results for the HLC beams showed that ACI code equation underestimates the shear strength of concrete($V_c$), and overestimates the shear strength of shear reinforcements($V_s$). It is revealed that the effectivenesses of shear reinforcements of reinforced HLC beams are lower than those of normal weight concrete beams. Then, the shear strengths of shear reinforcements are increased in proportion not to first degree of shear reinforcement ration but to square root of them.

• Water for future
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• v.28 no.4
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• pp.215-222
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• 1995

The water retention function which has the hysteresis phenomena is required to analyze the Richards equation which is a governing equation of the unsaturated flow, and its hysteresis phenomena has influence upon the characteristics of the unsaturated flow. The accuracy of the published hysteresis models is compared by using experimental data of the water retention function. The apparatus to experiment the hysteresis phenomena on the soil is developed, and experimental data for the main wetting process and the main drying process of the water retention function are obtained. The parameters of the van Genuchten equation are calibrated by using experimentally obtained data. As a result of the comparison of the selected hysteresis models which simulate the main drying curve from the main wetting curve, the Model I-1(Mualem) overestimates and the Model II-1(Mualem) underestimates but the Model III-2(Park and Sonu) similarly estimates the experimental data of the main drying curve.