• Geomechanics and Engineering
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• v.6 no.1
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• pp.17-31
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• 2014

This paper investigates the development of failure surfaces induced by an embankment on soft marine clay deposits and the characteristics of such surfaces through numerical simulations and its comparative study with monitoring results. It is well known that the factor of safety of embankment slopes is closely related to the vertical loading, including the height of the embankment. That is, an increase in the embankment height reduces the factor of safety. However, few studies have examined the relationship between the lateral movement of soft soil beneath the embankment and the factor of safety. In addition, no study has investigated the distribution of the pore pressure coefficient B value along the failure surface. This paper conducts a continuum analysis using finite difference methods to characterize the development of failure surfaces during embankment construction on soft marine clay deposits. The results of the continuum analysis for failure surfaces, stress, displacement, and the factor of safety can be used for the management of embankment construction. In failure mechanism, it has been validated that a large shear displacement causes change of stress and pore pressure along the failure surface. In addition, the pore pressure coefficient B value decreases along the failure surface as the embankment height increases. This means that the rate of change in stress is higher than that in pore pressure.

• Journal of Ecology and Environment
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• v.33 no.4
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• pp.317-323
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• 2010

Nutrient availability is a critical component of agroecosystems, and is relevant to both above- and below- ground interactions. The principal objective of this study was to determine how the cessation of fertilization affects the communities of weeds and soil organisms in a corn/wheat field. Changes in dominant weed species, substrate-induced respiration, and the population density of nematodes and microarthropods were evaluated. Microbial substrate-induced respiration (SIR) and the population density of microarthropods decreased following the cessation of fertilization and were partly correlated with the aboveground weed biomass. The cessation of organic fertilizer application but continuing application of inorganic fertilizer reduced the population density of nematodes. In response to the cessation of fertilization, weed communities were dominated by species with little dependency on fertilization. Amaranthus retroflexus was identified as the most dominant species in the corn field; however, it was replaced by Digitaria ciliaris after the cessation of fertilization. In the wheat field, the cessation of fertilization led to a rapid reduction in the biomass of most weeds, except for Vicia angustifolia, supposedly as the result of symbiotic nitrogen fixation. Additionally, the fact that weed biomass was partially correlated with SIR or the population density of microarthropods may reflect a mutual feedback between soil organisms and weeds. The results indicate that the cessation of fertilization alters communities of weeds and soil organisms through changes in weed biomass and interactions with symbiotic microorganisms.

• Korean Journal of Applied Biomechanics
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• v.26 no.3
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• pp.257-264
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• 2016

Objective: The purpose of this study was to determine the periodicity of shank-foot segment coupling and free torque before and after fatigue induced by prolonged running. Method: Fifteen young healthy male participants with a rear-foot strike ran on instrumented dual-belt treadmills at 70% of their maximum oxygen uptake for 65 min. Kinematic and ground reaction force data were collected for 20 continuous strides at 5 and 65 min (considered the fatigued condition). The approximate entropy tool was applied to assess the periodicity of the shank internal-external rotation, foot inversion-eversion, shank-foot segment coupling, and free torque for the two running conditions. Results: The periodicity of all studied parameters, except foot inversion-eversion, decreased after 65 min of running (fatigued condition) for 80% of the participants in this study. Furthermore, 60% of the participants showed similarities in the change of periodicity pattern in shank internal-external rotation, coupling, and free torque. Conclusion: The findings indicated that the foot inversion-eversion motion may pose a higher risk of injury than the shank internal-external rotation, coupling, and free torque in the fatigued condition during prolonged running.

• Journal of Korean Association for Spatial Structures
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• v.13 no.2
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• pp.37-45
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• 2013

Reduction of microvibration is regarded as important in high-technology facilities with high precision equipments. In this paper, smart control technology is used to improve the microvibration control performance. Mr damper is used to make a smart base isolation system amd fuzzy logic control algorithm is employed to appropriately control the MR damper. In order to develop optimal fuzzy control algorithm, a multi-objective genetic algorithm is used in this study. As an excitation, a train-induced ground acceleration is used for time history analysis and three-story example building structure is employed. Microvibration control performance of passive and smart base isolation systems have been investigated in this study. Numerical simulation results show that the multi-objective genetic algorithm can provide optimal fuzzy logic controllers for smart base isolation system and the smart control system can effectively reduce microvibration of a high-technology facility subjected to train-induced excitation.

• Korean Journal of Plant Resources
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• v.25 no.5
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• pp.652-655
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• 2012

'Blue Edge' (Hosta minor) was induced by ethyle methane sulfonate (EMS) to obtain mutants. Among induced leaf variegated hosta plants, some with deep-green color pattern on the edge of the leaves was selected. They were cultivated via vegetative propagation. Assessment of botanical characteristics was conducted for three years since 2003. The major characteristic of these cultivars is that they maintain their deep-green color on the edge of the leaves all year round. These cultivars are useful as materials for pot plant or as ground cover plant.

• Korean Journal of Plant Resources
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• v.25 no.4
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• pp.504-506
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• 2012

Hosta 'Yellow Tiara' was induced using methyle methane sulfonate (MMS) to obtain mutagens. Among the induced leaf-variegated hosta plants, some with yellow-green leaves were selected. They were cultivated via vegetative propagation. Assessment of the botanical characteristics was conducted for three years since 2004. The major characteristic of these cultivars is that they maintain their yellow-green leaves uniformly all year round. These cultivars are useful as materials for pot plants or as ground cover.

• Journal of the Earthquake Engineering Society of Korea
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• v.19 no.4
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• pp.145-159
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• 2015

A seismic response analysis method for three-dimensional floating offshore structures due to seaquakes is developed. The hydrodynamic pressure exerted on the structure is calculated taking into account the compressibility of the sea water, the fluid-structure interaction, the energy absorption by the seabed, and the energy radiation into infinity. To validate developed method, the hydrodynamic pressure induced by the vibration of a floating massless rigid circular disk is calculated and compared with an exact analytical solution. The developed method is applied to seismic analysis of a support structure for a floating offshore wind turbine subjected to the hydrodynamic pressures induced from a seaquake. Analysis results show that earthquake response of a floating offshore structure can be greatly influenced by the compressibility of fluid, the depth (natural frequencies) of the fluid domain, and the energy absorption capacity of the seabed.

• Geomechanics and Engineering
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• v.18 no.5
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• pp.545-554
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• 2019

The customary approach used in the blast vibration analysis is to derive empirical relations between the peak particle velocities of blast-induced waves and the scaled distance, and to develop patterns limiting the amounts of explosives. During the periods when excavations involving blasting were performed at sites far from residential areas and infrastructure works, this method based on empirical correlations could be effective in reducing vibrations. However, blasting procedures applied by the fast-moving mining and construction industries today can be very close to, in particular cities, residential areas, pipelines, geothermal sites, etc., and this reveals the need to minimize blast vibrations not only by limiting the use of explosives, but also employing new scientific and technological methods. The conventional methodology in minimizing blast vibrations involves the steps of i) measuring by seismograph peak particle velocity induced by blasting, ii) defining ground transmission constants between the blasting area and the target station, iii) finding out the empirical relation involving the propagation of seismic waves, and iv) employing this relation to identify highest amount of explosive that may safely be fired at a time for blasting. This paper addresses practical difficulties during the implementation of this conventional method, particularly the defects and errors in data evaluation and analysis; illustrates the disadvantages of the method; emphasizes essential considerations in case the method is implemented; and finally discusses methods that would fit better to the conditions and demands of the present time compared to the conventional method that intrinsically hosts the abovementioned disadvantages.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.277-292
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• 2018

This paper presents the development and implementation of an artificial intelligence (AI)-based deep excavation induced wall and ground displacements and wall support member forces prediction program (ANN-EXCAV). The program has been developed in a C# environment by using the well-known AI technique artificial neural network (ANN). Program used ANN to predict the induced displacement, groundwater drawdown and wall and support member forces parameters for deep excavation project and run the stability check by comparing predict values to the calculated allowable values. Generalised ANNs were trained to predict the said parameters through databases generated by numerical analysis for cases that represented real field conditions. A practical example to run the ANN-EXCAV is illustrated in this paper. Results indicate that the program efficiently performed the calculations with a considerable accuracy, so it can be handy and robust tool for preliminary design of wall and support members for deep excavation project.

• Geomechanics and Engineering
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• v.17 no.5
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• pp.413-420
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• 2019

The changes in earth pressure and ground settlement due to underground excavation near an existing retaining wall were studied experimentally according to the separation distance between the underground excavation and the retaining wall. In addition, this study attempted to experimentally prove that the arching phenomenon occurred during the construction of the underground space. A model tank having 120 cm in length, 160 cm in height, and 40 cm in width was manufactured to simulate underground excavation through the use of five separated base wall bodies. The variation of earth pressure on the retaining wall was measured according to the underground excavation phase through the use of 10 separated right wall bodies. The results showed that the earth pressure on the retaining wall was changed by the lowering of the first base bottom wall; however, the earth pressure was not changed significantly by the lowering of the third base bottom wall, since the third base wall had sufficient separation distance from the retaining wall. Lowering of the first base wall induced a decrease in the earth pressure in the lower part of the retaining wall; in contrast, lowering of the first base wall induced an increase in the earth pressure in the middle part of the retaining wall, proving the arching effect experimentally. It is necessary to consider the changes in earth pressure on the retaining wall in designing earth retaining structures for sections where the arching effect occurs.