• Geomechanics and Engineering
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• v.30 no.5
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• pp.423-435
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• 2022

Ground vibration generated repeatedly in blasting tunnel excavation sites is known to be one of the major hazards induced by blasting operations. Various studies have been conducted to minimize these hazards, both theoretical and empirical methods using electronic detonator, the deck charge method, the center-cut method among others Among these various existing methods for controlling the ground vibration, in this study, we investigated the cut method. In particular, we analyzed and compared the V-cut method, which is commonly used in tunnel blasting, to the double-drilled parallel method, which has recently been introduced in tunnel excavation site. To understand the rock fragmentation efficiency as well as the ground vibration controllability of the two methods, we performed in-situ field blasting tests with both cut methods at a tunnel excavation site. Additionally, numerical analysis by FLAC3D has been executed for a better understanding of fracture propagation pattern and ground vibration generation by each cut method. Ground vibration levels, by PPVs measured in field blasting tests and PPVs estimated in numerical simulations, showed a lower value in the double-drilled parallel compared with the V-cut method, although the exact values are quite different in field measurement and numerical estimation.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1167-1174
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• 2008

Vertical drain method, which is one of the soft ground improvement methods, shorten s drain path to accelerate consolidation process and is applied in many sites. At a recent, composite discharge capacity experiment that analyze discharge amount by consolidation behavior with overburden pressure of soft ground in laboratory, simulates similarly with actuality. Geotechnical engineering problems such a s soft ground improvement are solved by numerical analysis by development of computer and numerical analysis techniques. Numerical analysis does that result is contrary by user's inexperience for choice of constitution model and application of analysis method. Therefore, this thesis experiments on composite discharge capacity test and study discharge capacity of drain and consolidation behavior of soft ground installed prefabricated vertical drain boards. Also, This thesis studied reasonable input parameters and constitution model by compare results of composite discharge capacity test and numerical analysis using PLAXIS that is 2D finial element numerical analysis program.

• Journal of the Korean GEO-environmental Society
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• v.25 no.4
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• pp.29-35
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• 2024

This is an analytical study to confirm the passive resistance effect before post-tensioning of steel bar anchors. When using a steel bar as a permanent anchor, if displacement occurs within the slope even before the head load is applied, the displacement is suppressed by the passive resistance caused by the interaction between the steel bar, grout, and surrounding soil. Accordingly, the shape of the failure surface and changes in the safety factor were examined using limit equilibrium analysis and finite element analysis targeting sites where steel bar anchors were actually applied. It was found that the safety factor of the slope reinforced with steel bar anchors is 2.02 using finite element analysis, which is about 5.9% smaller than 2.14 using limit equilibrium analysis. Also, the location of the failure surface was found to be deeper compared to the unreinforced slope. Likewise, the factor of safety has a 153% and 163% increase using finite element method and limit equilibrium analysis, respectively. In addition, the maximum displacement occurs in the lower unreinforced section within the slope, and the displacement is found to be reduced by 42 to 83% at the location where the steel bar anchors are installed.

• Water for future
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• v.24 no.4
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• pp.49-58
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• 1991

Flood routing in the Youngsan River was performed for the flood event of July, 1989 by two finite difference methods. The Saint Venant eq., a kind of hyperbolic partial differential equation is employed as governing equation and the explicit scheme (Leap Frog) and implicit scheme (Preissmann) are used to discretize the GE. As for the external boundary conditions, discharge and tidal elevation are upstream and downstream BC, respectively and estuary dam is included in internal BC. Lateral inflows and upstream discharges are the hourly results from storage function method, At Naju station, a Relatively upstream points in this river, the outputs are interpreted as good ones by comparing two numerical results of FDMs with the observed data and the calibrated results by storage function method. and two computational results are compared at the other sites, from middle stream and downstream points, and thus are considered reliable. Therefore, we can conclude from this research that these numerical models are adaptable in simulating and forecasting the flood in natural channels in Korea as well as existing hydrologic models. And the study about optimal gate control at the flood time is expected as further study using these models.

• Journal of Korean Society of Disaster and Security
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• v.6 no.1
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• pp.79-86
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• 2013

As car-oriented road policies have been made forward so far, relatively pedestrians' walking conditions are so in poor environments that more than two thousand pedestrians die from car accidents every year. Pedestrians' walking right has been severely invaded like that. Pedestrians' walking right is a right that people are able to walk safely and comfortably in pleasant surroundings as long as they don't threaten the public safety, order maintenance, and welfare. The government has an obligation to provide safe, comfortable, and pleasant environments to pedestrians. Recently interests in pedestrians' safety are increasing, government-driven supports have been made to make safe, pleasant, and healthy walking surroundings. As poor walking condition improvement projects cost high, they should be progressed to accomplish maximal effects using finite finances efficiently, and post feasibility evaluations of the projects should be severely estimated. However site selecting indicators which satisfy with the goal for composing safe working surroundings have not been decided yet, though currently it has a legal basis to specify walking condition improvement sites by the Law for Pedestrians' safety and Comfort Increasement. Therefore this study focuses on suggesting improved ways for selecting sites where pedestrians' safe environment project by reviewing previous research. When project sites are selected, evaluation indicators related to awareness survey of residents and history should be excluded, and disaster safety assessments for walking safety facilities, latent human hazards and natural disasters like a strong wind are proposed besides evaluations on pedestrians' safety and walking environment for matching with the purpose of the project to make safe working surroundings.

• Journal of the Korea Concrete Institute
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• v.29 no.3
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• pp.249-257
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• 2017

The purpose of this study was to contribute to the field application cost effectively and reasonably by developing the functional piles that make up for the defects of PHC piles. CFP (Concrete Filled Pretensioned Spun High Strength Concrete Pile with Ring type Composite shear connectors) piles developed in this study increases the compressive stress through enlarged cross section by rearranging composite shear connectors and filling the hollow part of PHC pile with concrete. And it improved shear and bending performance placing the rebar (H13-8ea) within the PHC pile and the hollow part of PHC pile of rebar (H19-8ea). In addition, the composite shear connectors were placed for the composite behavior between PHC pile and filled concrete. Placing Rebars (H13-8ea) of PHC pile into composite shear connector holes are sleeve-type mechanical coupling method that filling the concrete to the gap of the two members. Nonlinear finite element analyzes were performed to verify the performance of shear and bending moments and it deduced the spacing of the composite shear connectors. Through a various interpretation of CFP piles, it's proved that the CFP pile can increase the shear and bending stiffness of the PHC pile effectively. Therefore, this can be utilized usefully on the construction sites.

• Journal of the Korea Society for Simulation
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• v.27 no.1
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• pp.101-109
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• 2018

Field experiments as well as numerical analyses with finite element analysis codes are two valuable and complemental ways to understand the structural response under explosive blast load. However, there seems to be only limited information available about finite element analysis and experimental validation on the response of structural components under internal explosions. For complementary use of the two ways, the numerical analyses should be validated with field experiments by comparing their results. In this paper, a small-scaled reinforced concrete building with a room is employed for experimental investigations. An amount of TNT is detonated at the center of the room. Pressure at three different sites in the room, displacement of centers of two walls, and damage patterns of four walls are measured and compared to results from numerical analyses. The experimental results are much similar to the numerical analyses results. The finite element analysis code ANSYS AUTODYN is employed to numerically analyze both pressure distribution inside the room and response of walls subjected to blast pressure. The feasibility and validity of the numerical analysis on the reponses of structural components under internal explosions are discussed in terms of structural damage assessment, and evaluated as the same damage in the analysis and the experiments.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.6 s.177
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• pp.1456-1469
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• 2000

Mechanical behaviors of uniaxially fiber-reinforced metal matrix composites under transverse loading conditions were studied at room and elevated temperatures. A mono-filament composite was selecte d as a representative analysis model with perfectly bonded fiber/matrix interface assumption. The elastic-plastic and visco-plastic models were investigated by both theoretical and numerical methods. The product of triaxiality factor and effective strain as well as stress components and strain energy was obtained as a function of location to estimate the failure sites in fiber-reinforced metal matrix composite. Results showed that fiber/ matrix interfacial debond plays a key role for local failure at the room temperature, while void creation and growth in addition to the interfacial debond are major concerns at the elevated temperature. It was also shown that there would be an optimal diameter of fiber for the strong fiber-reinforced metal matrix composite.

• Journal of the Korean GEO-environmental Society
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• v.5 no.1
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• pp.5-12
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• 2004

Soft foundation is extensively distributed in coastal areas including our local regions. Embankment load on such soft foundation causes displacement due to lack of base ground supports. Long-term consolidation can result in settlement and destruction of shear failure and structure. Therefore, a variety of vertical drain methods are applied to construction sites to prevent base from breaking and changing for secure construction. This study analyzed the patterns of changes displacement to determine efficient range of improvement since range of vertical drain material determines vertical and horizontal changes based on the width range of under ground improvement. Changes of intensity with distance from embankment edge were also analyzed in the field study of embankment slope.

• The Journal of Korea Robotics Society
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• v.14 no.2
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• pp.81-86
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• 2019

Robots are used in various industrial sites, but traditional methods of operating a robot are limited at some kind of tasks. In order for a robot to accomplish a task, it is needed to find and solve accurate formula between a robot and environment and that is complicated work. Accordingly, reinforcement learning of robots is actively studied to overcome this difficulties. This study describes the process and results of learning and solving which applied reinforcement learning. The mission that the robot is going to learn is bottle flipping. Bottle flipping is an activity that involves throwing a plastic bottle in an attempt to land it upright on its bottom. Complexity of movement of liquid in the bottle when it thrown in the air, makes this task difficult to solve in traditional ways. Reinforcement learning process makes it easier. After 3-DOF robotic arm being instructed how to throwing the bottle, the robot find the better motion that make successful with the task. Two reward functions are designed and compared the result of learning. Finite difference method is used to obtain policy gradient. This paper focuses on the process of designing an efficient reward function to improve bottle flipping motion.