• Journal of the Korean Geotechnical Society
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• v.24 no.10
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• pp.17-24
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• 2008

In this study, two-dimensional finite element method has been developed to simply consider the nonlinear load-settlement behavior of piled raft foundation subjected to vertical loads. The raft is modeled as the plate finite element based on Mindline's theory and the pile is modeled as the proposed simple pile model that is easy to consider the complex nonlinear load-settlement behavior between pile and soil. The developed numerical method has been compared with the settlement data of lab-scaled experiment and numerical solutions to verify that the developed numerical method shows satisfactory prediction for the nonlinear load-settlement of piled raft foundation.

• Journal of the Korean GEO-environmental Society
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• v.13 no.12
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• pp.91-98
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• 2012

In this paper, the behavior of offshore wind turbine(OWT) foundation which is modeled by using existing design method and FEM is compared. When the same type of foundation is designed under the same sea and ground condition, the behavior characteristics with each model are compared. As a result, the member forces between apparent fixity and distributed spring type foundation which consider the ground stiffness are not different markedly, while fixed-base type foundation shows relatively lower member forces, which results in smaller safety margin. In other words, considering ground stiffness is reasonable because soil-pile interaction affects significantly on the analysis result. A case study with a monopile shows significant errors between p-y and FEM model at the head and tip of the pile. Also, it shows that the errors at the tip with diameter increase of the pile is larger. Thus, considering ground characteristics and engineering judgment are necessary in practice. A comparison of reliability analysis between tripod and monopile type foundation on the same condition shows larger probability of failure in monopile type and it indicates that the safety margin of monopile type can be lower.

• Journal of the Korean Geotechnical Society
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• v.36 no.11
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• pp.157-165
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• 2020

At present, there are no clearly stated criteria or theories in calculating additional vertical dynamic loads that occur at the machine foundation due to vibration and reflecting them in the design at home and abroad. According to the domestic standard, although it is not a serious vibration condition, the additional dynamic load due to vibration is considered up to 100% of the static load. This is an extremely conservative design. The purpose of this study is to propose a model test method for evaluating the quantitative magnitude of additional dynamic loads that are generated at certain static loads due to vertical mechanical vibrations. As preliminary basic tests for the model tests, the test for evaluating the effects of reflective wave that may occur within a limited size soil box and the test for estimating the natural frequency of the devised model soil-foundation system were carried out. From the analysis of results for basic tests, a method to minimize the influence of the reflected wave was prepared, and the effect of the resonance of the model system was minimized during the model tests. After the basic tests, the main model tests were conducted. Through the proposed main test, the quantitative magnitude of additional dynamic loads caused by machine vibration on a shallow foundation for machine on medium dense sand foundations were evaluated. From the results of the model test, the feasibility of design applied at home and abroad was reviewed.

• Korean Journal of Soil Science and Fertilizer
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• v.42 no.spc
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• pp.33-39
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• 2009

The practice of supplying nutrients for paddy soil with sustaining human health and ecological soundness is to utilize indicators considering soil chemical reactions. The long-term basis experiment of fertilizer and amendment of paddy soil and an experiment of yield response of soil types on nitrogen level from 2000 till 2002were used to search indicators of nutrient supplying capacity related to soil chemical reactions. Chemical reactions of paddy soil was composed of dissociating and/or adsorbing nutrients and of decomposing soil organic matter (SOM) into $H^+$, $e^-$, $CO_2$ in paddy soil. The indicators of nutrient supplying capacity, which were established by considering soil chemical reactions, were SOM or soil protein for nitrogen and available phosphate for phosphorus and cation exchangeable capacity (CEC) and exchangeable potassium for potassium. Korea has used fertilizer recommendation equations established with the indicators of nutrient supplying capacity for paddy soil.

• Structural Engineering and Mechanics
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• v.66 no.5
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• pp.637-648
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• 2018

When the centers of mass and stiffness of a building do not coincide, the structure experiences torsional responses. Such systems can consist of the underlying soil and the super-structure. The underlying soil may modify the earthquake input motion and change structural responses. Specific effects of the input motion shall also not be ignored. In this study, seismic demands of asymmetric buildings considering soil-structure interaction (SSI) under near-fault ground motions are evaluated. The building is modeled as an idealized single-story structure. The soil beneath the building is modeled by non-linear finite elements in the two states of loose and dense sands both compared with the fixed-base state. The infinite boundary conditions are modelled using viscous boundary elements. The effects of traditional and yield displacement-based (YDB) approaches of strength and stiffness distributions are considered on seismic demands. In the YDB approach, the stiffness considered in seismic design depends on the strength. The results show that the decrease in the base shear considering soft soil induced SSI when the YDB approach is assumed results only in the center of rigidity to control torsional responses. However, for fixed-base structures and those on dense soils both centers of strength and rigidity are controlling.

• Earthquakes and Structures
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• v.2 no.3
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• pp.257-277
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• 2011

An evaluation is presented of the response of a 3-storey R/C structure during the destructive Lefkada earthquake of 14/08/2003. Key aspects of the event include: (1) the unusually strong levels of ground motion (PGA = 0.48 g, $SA_{max}$ = 2.2 g) recorded approximately 10 km from fault, in downtown Lefkada; (2) the surprisingly low structural damage in the area; (3) the very soft soil conditions ($V_{s,max}$ = 150 m/s). Structural, geotechnical and seismological aspects of the earthquake are discussed. The study focuses on a 3-storey building, an elongated structure of rectangular plan supported on strip footings, that suffered severe column damage in the longitudinal direction, yet minor damage in the transverse one. Detailed spectral and time-history analyses highlight the interplay of soil, foundation and superstructure in modifying seismic demand in the two orthogonal directions of the building. It is shown that soil-structure interaction may affect inelastic seismic response and alter the dynamic behavior even for relatively flexible systems such as the structure at hand.

• Wind and Structures
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• v.14 no.2
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• pp.85-112
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• 2011

Wind turbine structures are long slender columns with a rotor and blade assembly placed on the top. These slender structures vibrate due to dynamic environmental forces and its own dynamics. Analysis of the dynamic behavior of wind turbines is fundamental to the stability, performance, operation and safety of these systems. In this paper a simplied approach is outlined for free vibration analysis of these long, slender structures taking the soil-structure interaction into account. The analytical method is based on an Euler-Bernoulli beam-column with elastic end supports. The elastic end-supports are considered to model the flexible nature of the interaction of these systems with soil. A closed-form approximate expression has been derived for the first natural frequency of the system. This new expression is a function of geometric and elastic properties of wind turbine tower and properties of the foundation including soil. The proposed simple expression has been independently validated using an exact numerical method, laboratory based experimental measurement and field measurement of a real wind turbine structure. The results obtained in the paper shows that the proposed expression can be used for a quick assessment of the fundamental frequency of a wind turbine taking the soil-structure interaction into account.

• Korean Journal of Soil Science and Fertilizer
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• v.49 no.6
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• pp.662-668
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• 2016

No-tillage dry-seeding of rice can offer potential benefits by reducing time and labor cost compared with conventional tillage practices. This study was conducted to investigate the effects of no-tillage dry-seeding on rice growth and soil hardness in comparison with other rice cultivation methods, machine transplanting and wet-hill-seeding on puddled paddy. The seedling stand fell within optimum range for both no-till dry-seeding and wet-hill-seeding on puddled paddy. Plant height, number of tillers and SPAD values in no-tillage dry-seeding cultivation were higher than those observed in other methods. There were no significant differences in grain yield of rice among three cultivation methods. The quality characteristics of milled rice grown in no-tillage dry-seeding were similar to those grown in other cultivation methods. Soil hardness in top 10 cm depth was significantly higher in no-tillage dry-seeding than other cultivation methods, while soil hardness below 10 cm depth was highest in machine transplanting cultivation. Results indicate that no-tillage dry-seeding practice is comparable to conventional tillage system in terms of seedling establishment, growth, yield and grain quality.

• Computational Structural Engineering : An International Journal
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• v.2 no.1
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• pp.33-42
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• 2002

A computationally efficient stiffness design method for building structures is proposed in which dynamic soil-structure interaction based on the wave-propagation theory is taken into account. A sway-rocking shear building model with appropriate ground impedances derived from the cone models due to Meek and Wolf (1994) is used as a simplified design model. Two representative models, i.e. a structure on a homogeneous half-space ground and a structure on a soil layer on rigid rock, are considered. Super-structure stiffness satisfying a desired stiffness performance condition are determined via an inverse problem formulation for a prescribed ground-surface response spectrum. It is shown through a simple yet reasonably accurate model that the ground conditions, e.g. homogeneous half-space or soil layer on rigid rock (frequency-dependence of impedance functions), ground properties (shear wave velocity), depth of surface ground, have extensive influence on the super-structure design.

• Journal of Soil and Groundwater Environment
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• v.27 no.2
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• pp.36-40
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• 2022

To respond to rapidly changing water circumstances such as climate change, drought, etc., the korean government (MOE) established four advanced strategies for integrated groundwater management. The first strategy is watershed-based management of groundwater. The second strategy is total quantity management of groundwater including improvement of groundwater preservation area policy and procedure of investigation for groundwater influence area, additional construction of groundwater dam, installation of large-scale public wells, extention of spilled groundwater use. The third strategy is prevention of groundwater contamination including expansion of monitoring wells, introducing declaration of groundwater contamination. The last strategy is advancement of groundwater information management including integrated management of data, setting up a big-data based open platform. The above-mentioned four strategies will be reflected in the 4th National Groundwater Management Plan to secure implementation power, and it is expected to laid the foundation for advanced and rational groundwater management system.