• The Journal of Engineering Geology
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• v.22 no.1
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• pp.15-25
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• 2012

Probabilistic design methods have been used as a design standard in Korea and abroad for achieving reasonable design by considering the statistical uncertainties of soil properties. In this study, the following techniques for reflecting geotechnical uncertainty are analyzed: quantification of the uncertainties of geotechnical random variables, and consideration of economic feasibility in design by minimizing the uncertainties related to the number of samples. To quantify the uncertainties, the techniques were applied to soil properties obtained from samples collected and tested in the field. The results showed an underestimation of the standard deviation by the 3-sigma approach in comparison with calculations using data from the samples. This finding indicates that economical design is possible in terms of probability. However, when compared with the Bayesian approach, which does not consider the number of samples, variability in the 3-sigma approach is underestimated for some variables. This finding also indicates a safety issue, whereas the number of samples based on the Bayesian approach showed the lowest variance. The variance of the probability density function showed a marked decrease with increasing number of samples, to converge at a certain level when the number exceeds 25. Of note, the estimation of values is more reliable for random variables having low variability, such as soil unit weight, and can be obtained with a small number of samples.

• Bulletin of the Society of Naval Architects of Korea
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• v.54 no.4
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• pp.39-46
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• 2017

Jack-up drilling rigs are widely used in offshore oil and gas exploration industry. It is originally designed for use in the shallow waters less than 60m of water depth; there is growing demand for their use in deeper water depth over 150m and harsher environmental conditions. In this study, global in-place analysis of jack-up rig leg for North-sea oil well is performed through numerical analysis. Firstly, environmental conditions and seabed characteristics at the North-sea are collected and investigated measurements from survey report. Based on these data, design specifications are established and the overall basic design is performed. Dynamic characteristics of the jack-up rig for North-sea are considered in the global in-place analysis both leg and hull and the basic stability against overturning moment is also analyzed. The structural integrity of the jack-up rig leg/hull is verified through the code checks and the adequate safety margin is observed. The uncertainty in jack-up behaviour is greatly influenced by the uncertainties in the soil characteristics that determine the resistance of the foundation to the forces imposed by the jack-up structure. Among the risks above mentioned, the punch-through during pre-loading is the most frequently encountered foundation problem for jack-up rigs. The objective of this paper is to clarify the detailed structure and installation engineering matters for prove the structural safety of jack-up rigs during operation. With this intention the following items are addressed; - Characteristics of structural behavior considering soil effect against environmental loads - Modes of failure and related pre-loading procedure and parameters - Typical results of structural engineering and verification by actual measurement.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.3
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• pp.599-606
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• 2015

Damage of landslide due to earthquake covers a considerable part of total damage due to earthquake. Landslide due to earthquake affects direct damage of human lives and structures, and social system can be paralyzed by losing functions of roads, basic industries, and so on. Therefore, systematic and specialized research examining the factors affecting the slope stability by earthquakes should be needed. However, method of evaluation of slope stability problems due to earthquake contains somewhat uncertainty since many soil properties are predicted or assumed. In this study, influences of change of soil properties such as degree of saturation and cohesion value are analyzed in factor of safety and displacement using seismic landslide hazard maps based on GIS. As the degree of saturation increases or cohesion decreases, it is found that seismic landslide hazard area marked with factors of safety or displacements tends to increase. Therefore, to draw more exact landslide hazard map during earthquake, it is necessary to obtain accurate soil property information preferentially from site investigation data in the field.

• Journal of the Korean Society of Radiology
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• v.12 no.2
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• pp.123-131
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• 2018

This study compared PENELOPE with measured values from low energy peak to high energy peak to reduce peak to compton ratio and continuum background spectrum using $^{60}Co$, $^{137}Cs$ and mixed volume source. In addition, the change in backscattering and compton edge efficiency was compared with that of PENELOPE through changes in the vicinity of low energy. The results from the mixed volume source are applied to the soil samples to determine how much the minimum detection limits of the soil samples are reduced in the suppression and unsuppressed mode. The compton suppression of the low energy region of $^{60}CO$ (1,173 keV) was considerable, and the Compton edge RF for the $^{137}Cs$ (661 keV) peak was 2.8. In particular, the $^{60}Co$ source emits coincidence gamma rays of 1,173.2 keV and 1,332.5 keV, so compton inhibition was reduced by approximately 21%. RF of compton edges of 1,173 keV and 1,332 keV emitted from a $^{60}Co$ source was 3.2 and 3.4, and the peak to compton edge ratio was improved to 8: 1. And Compared with Penelope, the uncertainty was well within 2%. In compton unsuppressed mode, MDA values of 661 keV, 1,173 keV and 1,332 keV were 0.535, 0.173 and 0.136 Bq/kg, respectively, but decreased in compton suppressed mode to 0.121, 0.00826 and 0.00728 Bq/kg. Thus, Compton suppressed could reduce the background radioactivity and the radioactivity contained in the detector itself.

• Journal of the Korean Geotechnical Society
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• v.20 no.2
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• pp.131-141
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• 2004

For geotechnical applications, engineers use data obtained from a site investigation to interpret the structure and potential behavior of the subsurface. In most cases, these data consist of samples that represent 1/100,000 or less of the total volume of soil. These samples and associated field and lab testing provide the information used to estimate soil parameter values. The resulting values are estimated ones and there exists some likelihood that actual soil conditions are significantly different from the estimates. This may be the case even if the sampling and interpretation procedures are performed in accordance with standard practice. Although these efforts have been made to characterize the uncertainty associated with geotechnical parameters, there is no commonly accepted method to evaluate quantitatively the quality of an investigation plan as a whole or the relative significance of individual sampling points or potential sampling points.

• Journal of the Korean GEO-environmental Society
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• v.16 no.1
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• pp.17-27
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• 2015

Recently, Korean government has tried out to set up earthquake hazards prevention system. In the system, several geotechnical hazard maps including liquefaction hazard map and landslide hazard map for the whole country have drawn to consider the domestic seismic characteristics. To draw the macro liquefaction hazard map, big data of site investigations in metropolitan areas and provincial areas has to be verified for its application. In this research, we carried out site response analyses using 522 borehole site investigation data in S city during a desirable earthquake. The soil classification was separately compared to shear wave velocity considering the uncertainty of site investigation data. Probability distribution and statistical analysis for the results of site response analyses was applied to the feasibility study. Finally, we suggest a new site amplification coefficient, hereby presented with the similar results of liquefaction hazard mapping using the calculated liquefaction potential index by the site response analyses. Above-mentioned study will be expected to help to follow research and draw liquefaction hazard map in moderate seismic region.

• Ecology and Resilient Infrastructure
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• v.3 no.1
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• pp.35-45
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• 2016

The correlation relationships and their corresponding equations between the geomorphological parameters and the Soil Water Assessment Tool (SWAT) model parameters by Sequential Uncertainty Fitting - version 2 (SUFI-2) algorithm of SWAT Calibration and Uncertainty Programs (SWAT-CUP) were developed at the Seom-river experimental watershed. The parameters of the SWAT model at the Soksa-river experimental watershed were estimated by the developed equations. The SWAT model parameters were estimated by SUFI-2 algorithm of SWAT-CUP with rainfall-runoff data from the Soksa-river experimental watershed from 2000 to 2007. Rainfall-runoff simulation of the SWAT model was carried out at the Soksa-river experimental watershed from 2000 to 2007 for the applicability of the estimated parameters by the developed equations. The root mean square errors (RMSE) between the observed and the simulated rainfall-runoffs using the estimated parameters by developed equations of correlation analysis and the optimum parameters by SUFI-2 of SWAT-CUP were $1.09m^3/s$ and $0.93m^3/s$ respectively at the Soksa-river experimental watershed from 2000 to 2007. Therefore, it is considered that the parameter estimation of the SWAT model by the geomorphological characteristics parameters has applicability.

• Journal of Korea Water Resources Association
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• v.45 no.5
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• pp.505-516
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• 2012

The study applies a hydrologic simulation model, HEC-1 developed by Hydrologic Engineering Center to Daecheong dam watershed for modeling hourly inflows of Daecheong dam. Although the HEC-1 model provides an automatic optimization technique for some of the parameters, the built-in optimization model is not sufficient in estimating reliable parameters. In particular, the optimization model often fails to estimate the parameters when a large number of parameters exist. In this regard, a main objective of this study is to develop Bayesian Markov Chain Monte Carlo simulation based HEC-1 model (BHEC-1). The Clark IUH method for transformation of precipitation excess to runoff and the soil conservation service runoff curve method for abstractions were used in Bayesian Monte Carlo simulation. Simulations of runoff at the Daecheong station in the HEC-1 model under Bayesian optimization scheme allow the posterior probability distributions of the hydrograph thus providing uncertainties in rainfall-runoff process. The proposed model showed a powerful performance in terms of estimating model parameters and deriving full uncertainties so that the model can be applied to various hydrologic problems such as frequency curve derivation, dam risk analysis and climate change study.

• Journal of the Korean Geotechnical Society
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• v.18 no.2
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• pp.51-64
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• 2002

Observational results of ground movement during the construction were very different from those predicted during the analysis of design step because of the uncertainty of the numerical analysis modelling, the soil parameter, and the condition of a construction field, etc., however accurately numerical analysis method was applied for prediction of ground movement per the excavation step. Therefore, the management system through the construction field measurement should be achieved for grasping the situation during the excavation. Until now, the measurement system restricted by 'Absolute Value Management system'analyzing only the stability of present step has been executed. So, it was difficult to expect the prediction of ground movement fur the next excavation step. In this situation, this study developed 'The Management system TOMAS-EXCAV'consisted of 'Absolute value management system'analyzing the stability of present step and 'Prediction management system'expecting the ground movement of next excavation step and analyzing the stability of next excavation step by 'Back Analysis'. TOMAS-EXCAV could be applied to all the uncertainty of earth retaining structures analysis by connecting 'Forward analysis program'and 'Back analysis program'and optimizing the main design variables using SQP-MMFD optimization method through measurement results. The applicability of TOMAS-EXCAV was confirmed by back analysis selecting two earth retains construction fields.

• Journal of the Korean GEO-environmental Society
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• v.10 no.7
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• pp.7-14
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• 2009

The correlation equation empirically proposed to obtain compression indexes has been proposed to conveniently obtain the value using the soil parameter that can be obtained through simple tests when the number of time of consolidation testing is low or the distribution is large but most of the analyzed regions are limited to certain regions abroad or in the country and multiple data were integrated for use in many cases, thus it is not very reasonable to apply it. Therefore, to establish a new design method considering the uncertainty of the ground, it was selected the Kwangyang port area of which the data have been collected recently thus are relatively more reliable as the subject region of the study in order to maximally reduce the uncertainty of test data. After performing the verification of the normality of the consolidation test data obtained from the selected region and the transformation of variables, a prediction formula was proposed through the regression model with the transformed variables and the proposed regression model with transformed variables was compared with existing empirical equations to verify the suitability of the proposed model formula. After analyzing, it was confirmed that the coefficient of determination was increased after the Box-Cox variable transformation, thus the explanatory power was being enhanced and through the root-mean-square-error method, it was confirmed that the proposed model formula showed the most closed value to the test value.