• Geomechanics and Engineering
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• v.23 no.2
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• pp.151-163
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• 2020

Grouting method is an effective way of reinforcing cracked rock masses and plugging water gushing. Current grouting diffusion models are generally developed for horizontal cracks, which is contradictory to the fact that the crack generally occurs in rock masses with irregular spatial distribution characteristics in real underground environments. To solve this problem, this study selected a cement-sodium silicate slurry (C-S slurry) generally used in engineering as a fast-curing grouting material and regarded the C-S slurry as a Bingham fluid with time-varying viscosity for analysis. Based on the theory of fluid mechanics, and by simultaneously considering the deadweight of slurry and characteristics of non-uniform spatial distribution of viscosity of fast-curing grouts, a theoretical model of slurry diffusion in an oblique crack in rock masses at constant grouting rate was established. Moreover, the viscosity and pressure distribution equations in the slurry diffusion zone were deduced, thus quantifying the relationship between grouting pressure, grouting time, and slurry diffusion distance. On this basis, by using a 3-d finite element program in multi-field coupled software Comsol, the numerical simulation results were compared with theoretical calculation values, further verifying the effectiveness of the theoretical model. In addition, through the analysis of two engineering case studies, the theoretical calculations and measured slurry diffusion radius were compared, to evaluate the application effects of the model in engineering practice. Finally, by using the established theoretical model, the influence of cracking in rock masses on the diffusion characteristics of slurry was analysed. The results demonstrate that the inclination angle of the crack in rock masses and azimuth angle of slurry diffusion affect slurry diffusion characteristics. More attention should be paid to the actual grouting process. The results can provide references for determining grouting parameters of fast-curing grouts in engineering practice.

• Korean Journal of Social Welfare
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• v.59 no.3
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• pp.5-32
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• 2007

Using a national survey data conducted by the Beautiful Foundation, this study attempts to examine the bilateral relationships between philanthropic effort and social trust and between volunteering effort and social trust by using simultaneous equation model. This study also attempts to examine the socialization effect and intergenerational effect of philanthropy and volunteering in family, school, and community. This study found that both philanthropic effort and volunteering effort have a bilateral relationship with social trust. The bilateral relationship between giving and volunteering and social trust suggests that not only can social trust affect the increase of giving and volunteering but giving and volunteering can also influence social trust. Thus, by strengthening trust and facilitating giving and volunteering, we can construct and promote culture of sharing in our society. On the other hand, in the analysis on individual's educational experience in giving and volunteering during school years and individual's family experience (parental practice) in giving and volunteering during school years, it was found that family experience was statistically significant on philanthropic effort and volunteering effort. The result suggests that considering the validity of intergenerational effect in giving and volunteering, it is strategically vital for our society to facilitate and promote family practice in giving and volunteering throughout diverse programs and social marketing. Although this study has a limitation due to the limitedness of the original data, it made a significant contribution to advancing knowledge on the relationship between giving and volunteering and social trust by using elaborate analysis methods. This study emphasizes the necessity of continuous research; more advanced and systematic study based on a more elaborate model and solid data such panel data should be continued for a better understanding of philanthropic and volunteering behavior that can be an important soil for the development of nonprofit human service organizations. Finally, based on the results of the study, this study discusses research directions and practical implications to deepen and broaden the culture of sharing in Korea.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.387-395
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• 2003

Model tests were conducted to study the behavior of the piled raft foundation system on sands. Especially in this study, the method using the triaxial compression apparatus was devised and used to apply the confining pressure which is considered difficult in the existing model test on the soil. Steel rods (6mm dia.) and aluminum plates (8mm thickness, 50mm dia.) were used to simulate piles and rafts respectively. Jumunjin standard sands were used to ensure the homogeneity of the sample. After the sample with the piled raft model was laid inside the triaxial cell, the confining pressure was applied and then the compressive force was applied. The increase and/or decrease ratio of the bearing capacity, the load distribution ratio between raft and piles and the effect of settlements decrease depending on the confining pressure, the number of piles and the length of piles were analyzed and the bearing capacity and skin friction of the pile was calculated. By the results of these experiments, the bearing capacity increased and the settlement decreased with this piled raft foundation system. Especially the effect was larger with the increase of the number of piles than with the increase of length of piles. Hereafter, the study of the load transfer mechanism of piles under confining pressure would be made possible using these small model tester like triaxial compression apparatus.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.1
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• pp.37-47
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• 2007

The shield tunneling method has been increasingly employed to minimize environmental damages and civil complaints in the populated and developed area. A lining segment, which is a main structure of the shield tunnel, consists of joints. Conventional foreign and domestic design data have been commonly used for design practices without a specific verification of structural analysis models, design load, and the effect of soil characteristics on the performance of lining segment. In this study, the suitability of existing analytic models used for the design of shield tunnel lining segment has been evaluated through a comparison between analytical and numerical solutions. Based on the evaluation of their suitability performed in the study, a full-circumferential beam jointed spring model (1R-S0) is proposed for design practices by considering user's convenience, the applicability of field conditions and the accuracy of analysis result. By using the proposed model, the parameter analysis was performed to investigate the effects of joint stiffness, ground rigidity, joint distribution and the number of joints on the behavior of lining segment. Parameters considered in the investigation have been appeared to affect the behavior of lining segment. Among those parameters, joint stiffness has been appeared to have the most significant effect on the bending moment and displacement of lining segment.

• Korean Journal of Agricultural and Forest Meteorology
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• v.9 no.4
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• pp.247-259
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• 2007

In this study, we examined the flux of carbon and water using an eco-hydrological model, Regional Hydro-Ecologic Simulation System (RHESSys). Our purposes were to develop a set of parameters optimized for a well-designed experimental watershed (Gwangneung Research Watershed, GN) and then, to test suitability of the parameters for predicting carbon and water fluxes of other watershed with different regimes of climate, topography, and vegetation structure (i.e Gangseonry Watershed in Mt. Jumbong, GS). Field datasets of stream flow, soil water content (SWC), and wood biomass product (WBP) were utilized for model parameterization and validation. After laborious parameterization processes, RHESSys was validated with the field observations from the GN watershed. The parameter set identified at the GN watershed was then applied to the GS watershed in Mt. Jumbong, which resulted in good agreement for SWC but poor predictability for WBP. Our study showed that RHESSys simulated reliable SWC at the GS by adjusting site-specific porosity only. In contrast, vegetation productivity would require more rigorous site-specific parameterization and hence, further study is necessary to identify primary field ecophysiological variables for enhancing model parameterization and application to multiple watersheds.

• Journal of Radiation Protection and Research
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• v.30 no.3
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• pp.99-105
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• 2005

A model for evaluating radioactive contamination in the urban environment, named METRO-K, was developed as a basic step for accident consequence analysis in case of an accidental release. The three kind of radionuclides $(^{137}Cs,\;^{106}Ru,\;^{131}I)$ and the different chemical forms of iodine (particulate, organic and elemental forms) are considered in the model. The radioactive concentrations are evaluated for the five types of surface (roof, paved road, wall, lawn/soil, tree) as a function of time. Using the model, the contaminative impacts of the surfaces were intensively investigated with respect to with and without precipitation during the measurement periods of radionuclides in air. In addition, a practical application study was conducted using $^{137}Cs$ concentration in air and precipitation measured in an European country at the Chernobyl accident. As a result precipitation was an influential factor in surface contamination. The degree of contamination was strongly dependent on the types of radionuclide and surface. Precipitation was more influential in contamination of $^{137}Cs$ than that of $^{131}I$ (elemental form).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.2
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• pp.529-536
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• 2013

The semi-distributed rainfall runoff model of SWAT is applied to the Seom-river experimental watershed. The simulations of various antecedent periods before the targeted simulation periods of 2002 to 2009 are not necessary despite of the slight appearance of corresponding changes in simulated total runoff. The simulated results of total runoff by using various numbers of soil layer maps have little differentiated nevertheless the slight changes in simulated results have been appeared. The 7 parameters of CANMX, $CN_2$, ESCO, GW_REVAP, SOL_ALB, SOL_AWC, and SOL_K greatly govern the rainfall runoff are confirmed and their sensitivity analyses have been carried out. The optimal parameters used in SWAT are derived by SUFI-2 of SWAT-CUP. The NS and $R^2$ are 0.99 and 0.98, respectively which is shown the good agreement between the observed and the simulated results. The uncertainty factors of P-factor and R-factor are 0.85 and 0.06, respectively which is also shown the high efficiency of the model. The high applicability is also shown with improving the RMSE in SWAT model simulation using the parameters estimated by SUFI-2 of SWAT-CUP.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.2
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• pp.507-519
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• 2013

This study is to evaluate agricultural water supply capacity in Geum river basin (9,865 $km^2$), one of the 5 big river basin of South Korea using MODSIM-DSS (MODified SIMyld-Decision Support System) model. The model is a generalized river basin decision support system and network flow model developed at Colorado State University designed specifically to meet the growing demands and pressures on river basin management. The model was established by dividing the basin into 14 subbasins and the irrigation facilities viz. agricultural reservoirs, pumping stations, diversions, culverts and groundwater wells were grouped and networked within each subbasin and networked between subbasins including municipal and industrial water supplies. To prepare the inflows to agricultural reservoirs and multipurpose dams, the Soil and Water Assessment Tool (SWAT) was calibrated using 6 years (2005-2010) observed dam inflow and storage data. By MODSIM run for 8 years from 2004 to 2011, the agricultural water shortage had occurred during the drought years of 2006, 2008, and 2009. The agricultural water shortage could be calculated as 282 $10^6m^3$, 286 $10^6m^3$, and 329 $10^6m^3$ respectively.

• Journal of Korea Water Resources Association
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• v.53 no.9
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• pp.637-646
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• 2020

The shallow landslide-trigerred debris flow in hillslope catchments is the primary geological phenomenon that drives landscape changes and therefore imposes risks as a natural hazard. In particular, debris flows occurring in urban areas can result to substantial damages to properties and human injuries during the flow and sediment transport process. To alleviate the damages as a result of these debris flow, analytical models for flow and damage prediction are of significant importance. However, the analysis of debris flow model parameters is not yet sufficient, and the analysis of the entrainment, which has a significant influence on the flow process and the damage extent, is still incomplete. In this study, the effects of erosion and erosion process on the flow and the impact area due to the change in the soil parameters are analyzed using Deb2D model, a flow analysis model of debris developed in Korea. The research is conducted for the case of the Mt. Umyeon landslide in 2011. The resulting impacted area, total debris-flow volume, maximum velocity and inundated depth from the Erosion model are compared to the field survey data. Also, the effect of the entrainment changing parameters is analyzed through the erosion shape and depth. The debris flow simulation for the Raemian and Shindong apartment catchment with the consideration of entrainment effect and erosion has been successful. Each parameter sensitivity could be analyzed through sensitivity analysis for the two basins based on the change in parameters, which indicates the necessity of parameter estimation.

• Journal of the Korean Geotechnical Society
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• v.18 no.5
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• pp.37-42
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• 2002

Artificial neural networks are efficient computing techniques that are widely used to solve complex problems in many fields. In this paper a liquefaction potential was estimated by using a back propagation neural network model applicated to cyclic triaxial test data, soil parameters and site investigation data. Training and testing of the network were based on a database of 43 cyclic triaxial test data from 00 sites. The neural networks are trained by modifying the weights of the neurons in response to the errors between the actual output values and the target output value. Training was done iteratively until the average sum squared errors over all the training patterns were minimized. This generally occurred after about 15,000 cycles of training. The accuracy from 72% to 98% was shown for the model equipped with two hidden layers and ten input variables. Important effective input variables have been identified as the NOC,$D_10$ and (N$_1$)$_60$. The study showed that the neural network model predicted a CSR(Cyclic shear stress Ratio) of silty-sand reasonably well. Analyzed results indicate that the neural-network model is more reliable than simplified method using N value of SPT.