• Journal of the Korean Geotechnical Society
• /
• v.27 no.10
• /
• pp.93-104
• /
• 2011

In this paper, a numerical procedure of probabilistic steady seepage analysis that considers the spatial variability of soil permeability is presented. The procedure extends the deterministic analysis based on the finite element method to a probabilistic approach that accounts for the uncertainties and spatial variation of the soil permeability. Two-dimensional random fields are generated based on a Karhunen-Lo$\grave{e}$ve expansion in a fashion consistent with a specified marginal distribution function and an autocorrelation function. A Monte Carlo simulation is then used to determine the statistical response based on the random fields. A series of analyses were performed to verify the application potential of the proposed method and to study the effects of uncertainty due to the spatial heterogeneity on the seepage behavior of soil foundation beneath water retaining structure with a single sheet pile wall. The results showed that the probabilistic framework can be used to efficiently consider the various flow patterns caused by the spatial variability of the soil permeability in seepage assessment for a soil foundation beneath water retaining structures.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.58 no.6
• /
• pp.55-69
• /
• 2016

RUSLE (Revised Universal Soil Loss Equation) is the empirical formular widely used to estimate rates of soil erosion caused by rainfall and associated overland flow. Among the factors considered in RUSLE, rainfall erosivity factor (R factor) is the major one derived by rainfall intensity and characteristics of rainfall event. There has been developed various methods to estimate R factor, such as energy based methods considering physical schemes of soil erosion and simple methods using the empirical relationship between soil erosion and annual total rainfall. This study is aimed to quantitatively evaluate the variation among the R factors estimated using different methods for South Korea. Station based observation (minutely rainfall data) were collected for 72 stations to investigate the characteristics of rainfall events over the country and similarity and differentness of R factors calculated by each method were compared in various ways. As results use of simple methods generally provided greater R factors comparing to those for energy based methods by 76 % on average and also overestimated the range of factors using different equations. The variation coefficient of annual R factors was calculated as 0.27 on average and the results significantly varied by the stations. Additionally the study demonstrated the rank of methods that would provide exclusive results comparing to others for each station. As it is difficult to find universal way to estimate R factors for specific regions, the efforts to validate and integrate various methods are required to improve the applicability and accuracy of soil erosion estimation.

• Journal of Korean Society of Rural Planning
• /
• v.16 no.4
• /
• pp.109-116
• /
• 2010

Climate change is known to affect both natural and managed ecosystems, and will likely impact on the terrestrail carbon balance. This paper reports the effects of climate change on spatial-temporal changes in carbon reductions in South Korea's during 2000-2100. Future carbon (C) stock distributions are simulated for the same period using various spatial data sets including land cover, net primary production(NPP) and leaf area index (LAI) obtained from MODIS(Moderate Resolution Imaging Spectroradiometer), and climate data from Data Assimilation Office(DAO) and Korea Meteorological Administration(KMA). This study attempts to predict future NPP using multiple linear regression and to model dependence of soil respiration on soil temperature. Plants store large amounts of carbon during the growing periods. During 2030-2100, Carbon accumulation in vegetation was increased to $566{\sim}610gC/m^2$/year owing to climate change. On the other hand, soil respiration is a key ecosystem process that releases carbon from the soil in the form of carbon dioxide. The estimated soil respiration spatially ranged from $49gC/m^2$/year to $231gC/m^2$/year in the year of 2010, and correlating well with the reference value. This results include Spatial-Temporal C reduction variation caused by climate change. Therefore this results is more comprehensive than previous results. The uncertainty in this study is still large, but it can be reduced if a detailed map becomes available.

• Geotechnical Engineering
• /
• v.6 no.2
• /
• pp.5-20
• /
• 1990

In the seismic analysis of structures, where the dynamic soil-structure interaction (DSSI) is considred, earthquake input motions as well as dynamic soil properties are random in nature. To take into account the random nature of both the input motions and the dynamic soil properties systematically, a probabilistic analysis of the DSSI subjected to seismic loading is proposed in this paper, The complex response method formulized by the elastic half space theory, the random vibration theory, and the Rosenblueth's two-point estimate method are combined for the proposed probabilistic analysis. The conclusions drawn from this study are as follows ' 1) The uncertainty bands of the earthquake input motions proposed by Kanai-Tajimi as well as those of the dynamic properties are large the coefecients of variation of those parameters tinge from 0.4 to 0.6. 2) The uncertainties of the dynamic soil properties are more sensitive to the structural responses than those of the input motion parameters. 3) The effect of correlations between the input motion parameters and the dynamic soil properties is negligible.

• Journal of the Korean Geotechnical Society
• /
• v.37 no.10
• /
• pp.41-54
• /
• 2021

In this study, probabilistic steady seepage behavior of soil foundation beneath water retaining structures according to the location of cutoffs was studied. A Monte Carlo Simulation based on the random finite element method that considers the uncertainty and spatial variability of soil permeability was performed to evaluate the probabilistic seepage behavior. Fragility curves were developed by calculating the failure probability conditional on the occurrence of a given water level from the probability distribution obtained from Monte Carlo simulations. The fragility curve was prepared for the flow quantities such as flow rate through foundation soil, uplift force on the base of structure, and exit gradient in downstream to examine the reliability of the water retaining structure and the foundation soil. From the fragility curves, the effect of the location of cutoff wall on the reliability of water retaining structure and foundation soil according to the rise in water level was studied.

• Journal of the Korean Geotechnical Society
• /
• v.22 no.6
• /
• pp.51-61
• /
• 2006

An efficient and accurate hybrid reliability analysis method is proposed in this paper to quantify the risk of an axially loaded single pile considering pile-soil interaction behavior and uncertainties in various design variables. The proposed method intelligently integrates the concepts of the response surface method, the finite difference method, the first-order reliability method, and the iterative linear interpolation scheme. The load transfer method is incorporated into the finite difference method for the deterministic analysis of a single pile-soil system. The uncertainties associated with load conditions, material and section properties of a pile and soil properties are explicitly considered. The risk corresponding to both serviceability limit state and strength limit state of the pile and soil is estimated. Applicability, accuracy and efficiency of the proposed method in the safety assessment of a realistic pile-soil system subjected to axial loads are verified by comparing it with the results of the Monte Carlo simulation technique.

• Geomechanics and Engineering
• /
• v.5 no.3
• /
• pp.241-261
• /
• 2013

The bearing mechanism of pile during installation and loading process which controls the deformation and distribution of strain and stress in the soil surrounding pile tip is complex and full of much uncertainty. It is pointed out that particle crushing occurs in significant stress concentrated region such as the area surrounding pile tip. The solution to this problem requires the understanding and modeling of the mechanical behavior of granular soil under high pressures. This study aims to investigate the sand behavior around pile tip considering the characteristics of sand crushing. The numerical analysis of model pile loading test under different surcharge pressure with constitutive model for sand crushing is presented. This constitutive model is capable of predicting the dilatancy of soil from negative to positive under low confining pressure and only negative dilatancy under high confining pressure. The predicted relationships between the normalized bearing stress and normalized displacement are agreeable with the experimental results during the entire loading process. It is estimated from numerical results that the vertical stress beneath pile tip is up to 20 MPa which is large enough to cause sand to be crushed. The predicted distribution area of volumetric strain represents that the distributed area shaped wedge for volumetric contraction is beneath pile tip and distributed area for volumetric expansion is near the pile shaft. It is demonstrated that the finite element formulation incorporating a constitutive model for sand with crushing is capable of producing reasonable results for the pile loading problem.

• Journal of Radiation Protection and Research
• /
• v.35 no.3
• /
• pp.105-110
• /
• 2010

Using N-type HPGe gamma spectrometer, uranium analysis technique of soil sample is developed where the chemical preprocessing is not a necessity. The results of uranium activities using the method presented in this paper were compared with those results with conventional alpha spectrometer and two results were similar from within uncertainty range. Therefore, this new method will be applied in uranium activity analysis of soil sample.

• Proceedings of the Korean Geotechical Society Conference
• /
• 1997.03a
• /
• pp.161-168
• /
• 1997

The purpose of this study is to evaluate the possibility of normalization of the distibutions of soil parameters taken from soft ground and the reliability of the safety factors of specific objects on it, including sanitary landfill. Through this study it is found that distributions of soil parameters could be adjusted to appropriate normal distributions as possibility density functions(PDF), and that especially the group of initial cohesions and the coresponding safety factors has a perfect linear correlation. According to those results the PDF to initial cohesion as possibility parameter can not only be tmsformed to the PDF to safety factor but also, conseqently, the reliability of the safety factor(SF) simply based on the mean value of soil parameter(Co) can be calculated or easily picked up from the standrad normal distribution table. It is therefore concluded that even though calculated values of safety factors are over any standard requirements some possibility of risk both to the objects and natural soft ground could be still existing, and also a new standard value for this slope stability control system should be derived just by adjusting old one according to the magnitude of risk possibility.

• Geomechanics and Engineering
• /
• v.6 no.2
• /
• pp.99-115
• /
• 2014

Uncertainties in design variables and design equations have a significant impact on the safety of geotechnical structures like retaining walls and slopes. This paper presents a possible framework for obtaining the partial safety factors based on reliability approach for different random variables affecting the stability of a reinforced concrete cantilever retaining wall and a slope under static loading conditions. Reliability analysis is carried out by Mean First Order Second Moment Method, Point Estimate Method, Monte Carlo Simulation and Response Surface Methodology. A target reliability index ${\beta}$ = 3 is set and partial safety factors for each random variable are calculated based on different coefficient of variations of the random variables. The study shows that although deterministic analysis reveals a safety factor greater than 1.5 which is considered to be safe in conventional approach, reliability analysis indicates quite high failure probability due to variation of soil properties. The results also reveal that a higher factor of safety is required for internal friction angle ${\varphi}$, while almost negligible values of safety factors are required for soil unit weight ${\gamma}$ in case of cantilever retaining wall and soil unit weight ${\gamma}$ and cohesion c in case of slope. Importance of partial safety factors is shown by analyzing two simple geotechnical structures. However, it can be applied for any complex system to achieve economization.