• The Journal of Engineering Geology
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• v.25 no.1
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• pp.93-102
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• 2015

The characteristics of frozen soils are one of most important factors for foundation design in cold region. The objective of this study is to evaluate the shear strength and stiffness of frozen soils according to the confining conditions during the freezing and shearing phase. A direct shear box is constructed for the frozen specimens and bender elements are mounted on the wall of the shear box to measure shear wave velocities. Specimens are prepared by mixing sand and silt with a silt fraction of 30% in weight and the degree of saturation of 10%, giving a relative density of 60% for all tests. The temperature of the specimens in the freezer is allowed to fall below -5℃, and then direct shear tests are performed. A series of vertical stresses are applied during the freezing and shearing phase. Shear stress, vertical displacement, and shear wave along the horizontal displacement are measured. Experimental results show that in all the tests, shear strength increases with increasing vertical stress applied during the freezing and shearing phases. The magnitude of the increase in shear strength with increasing vertical stress during shearing under fixed vertical stress in the frozen state is smaller than the magnitude of the increase in vertical stress during freezing and shearing. In addition, the change in shear wave velocities varies with the position of the bender elements. In the case of shear waves passing through the shear plane, the shear wave velocities decrease with increasing horizontal displacement. This study provides an evaluation of the properties of shear strength and stiffness of frozen soils under varied confining condition.

• Economic and Environmental Geology
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• v.52 no.2
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• pp.169-188
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• 2019

This study was carried out unmanned aerial photography and terrestrial laser scanning to establish digital database on original wall of Gyejoksanseong fortress, and measured ground control points for continuity of the monitoring. It also performed precise examination with the naked eye, unmanned aerial photogrammetry, endoscopy, total station and handy measurement to examine the structural stability of the original walls. The ground control points were considered as a point where visual field can be secured, 3 points were selected around each of the south and north walls. For the right side of the south original wall, aerial photogrammetry was conducted using drones and a deviation analysis of 3-dimensional digital models was performed for short-term monitoring. As a result, the two original walls were almost matched in range within 5mm, and no difference indicating displacement of stones was found, except for partial deviation. Regular monitoring of the areas with structural deformation such as bulging, weak and fracture zone by precisely examining with the naked eye and using high-resolution photo data revealed no distinct change. The inner foundation observed through endoscopy found out that filling stones of the original walls were still remained, while most filling soil was lost. As a result of measuring the total station focusing around the points with structural deformation on the original walls, the maximum displacements of the north and south walls were somewhat high with 6.6mm and 3.8mm, respectively, while the final displacements were relatively stable at below 2.9mm and 1.4mm, respectively. Handy measurement also did not reveal clear structural deformation with displacements below 0.82mm at all points. Even though the results of displacement monitoring on the original walls are stable, it is hard to secure structural stability due to the characteristics of ramparts where sudden brittle fracture occurs. Therefore, it is necessary to conduct conservational scientific diagnosis, precise monitoring, and structural analysis based on the 3-dimensional figuration information obtained in this research.

• Journal of the Korean GEO-environmental Society
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• v.18 no.4
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• pp.31-40
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• 2017

In this study, a simple method to evaluate the seismic vulnerability of river levees was examined considering the structural characteristic of river levee, that is long, and the functional characteristic of river levee that performs temporary function against flood but is a permanent structure in the ordinary way. Considering the fact that one of the main failure modes of the levee during the earthquake are the settlement due to the strength reduction of the ground caused by the increase of the excess pore pressure in the levee body and foundation and the settlement due to liquefaction, the 2-dimensional section of the levee was regarded as the 1-dimensional section and the liquefaction potential index (LPI) for the regarded section was estimated. The estimated LPI was correlated with the seismic vulnerability of river levees. The relationship between the displacement of the levee crest caused by the earthquake and the seismic vulnerability of the levees was obtained from the results of previous researches and the correlation between the displacements of the levee crest computed by 2-dimensional dynamic coupled analyses and LPIs based on the results of 1-dimensional seismic response analyses was investigated. In connection with this correlation, as a result of examination of the correlation between LPI and the seismic vulnerability of the levee, it was concluded that the method for evaluation of the seismic vulnerability of the Korean river levee using LPI is applicable.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.3
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• pp.211-221
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• 2009

With recent trends of super-tallness, atypical plan shapes and zoning constructions in high-rise buildings, a structural stability of the building under construction is arising as a key issue for design and construction plan. To ensure the structural stability under construction, the differential column shortening of vertical members, the lateral displacement of tower frames, and differential settlement of raft foundation by unbalanced distributions of a tower self-weight before the completion of a lateral load resisting system should be checked by construction sequence analysis, which should be performed by systematic combinations with structural health monitoring, construction compensation program, and construction panning. This paper presents the scheme of zone-based construction sequence analysis by using the existing commercial analysis program, to check the stability of high-rise building under construction. This scheme is applied to 3-dimensional structural analysis for a real high-rise building under construction. The analysis includes real construction zoning plans and schedules as well as creep and shrinkage effects and time-dependent properties of concrete. The simplified construction sequence and assumed material properties were continuously updated with the change on construction schedule and correlations with in-situ measurement data.

• Journal of the Korean Geotechnical Society
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• v.30 no.4
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• pp.5-19
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• 2014

In this study, the structural analysis is performed on the method of shallow block and deep cement mixing pile, and then their characteristics and associated behaviors were analyzed. In the case of continuous beam analysis, the predicted settlement was very small, and shear force and bending stress are somewhat overestimated. The frame method is similar to numerical analysis in the internal force shallow block and long pile, but because the settlement of pile is underestimated, the additional calculation using the reaction of the long pile is necessary. For soil arching method and piled raft foundation method, the excessive axial force of long pile was predicted because the load sharing of pile is very large compared to the other methods. In the behavior of the shallow block and deep pile method, the settlement of shallow block and contact pressure are much in the center than the edge. In the estimating method considering the interaction between improved material and ground, the load sharing of the soil-cement pile ranges from 20% to 45%, and the stress ratio is 2.0~5.0 less than piled DCM. The maximum member forces at the boundary conditions of pile head are similar, but in fixed head the axial force and vertical displacement are different in accordance with pile arrangement.

• Journal of the Korean Society of Clothing and Textiles
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• v.39 no.3
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• pp.369-378
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• 2015

Various forms of wearable bio-signal monitoring systems have been developed recently. Acquisition of stable bio-signal data for health care purposes needs to be unconscious and continuous without hindrance to the users' daily activities. The garment type is a suitable form of a wearable bio-signal monitoring system; however, motion artifacts caused by body movement degrade the signal quality during the measurement of bio-signals. It is crucial to stabilize the electrode position to reduce motion artifacts generated when in motion. The problems with motion artifacts remain unresolved despite their significant effect on bio-signal monitoring. This research creates a foundation for the design of garment-type wearable systems for everyday use by finding a method to reduce motion artifacts through modular design. Two distinct garment-type wearable systems (tee-shirt with a motion artifact-reducing module (MARM) and tee-shirt without a MARM) were designed to compare the effects of modular design on the measurement of heart activity in terms of electrode position displacement, signal quality index value, and morphological quality. The tee-shirt with MARM showed superior properties and yielded higher quality signals than the tee-shirt without MARM. In addition, the tee-shirt with MARM showed a better repeatability of the heart activity signals. Therefore, a garment design with MARM is an efficient way to acquire stable bio-signals while in motion.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.190-198
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• 2018

In recent years, non-welded building hardware has been installed by bolt assembly is used. The non-welded building hardware method can reduce accidents caused by welding, and can be constructed by bolt assembly, which can reduce labor costs and shorten the construction period. However, there is a need for a method to compensate for the occurrence of buckling at the time of construction. The purpose of this study is to evaluate the behavior of joints between steel pipe and fastener and to evaluate the behavior of joints of non-welded and welded hardware frame. As a result, it was found that the foundation steel structure without welded joints was deformed to a rotation angle of member much larger than the allowable interlayer displacement angle 0.01 to 0.02 required according to the seismic load rating in the seismic load resistance system.

• Korean Journal of Optics and Photonics
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• v.22 no.1
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• pp.46-52
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• 2011

A confocal microscope was developed utilizing a scanning sample stage based on a home-built double-compound flexure guide. A scanning sample stage with nano-scale resolution consisted of a double leaf spring based flexure, a displacement amplifying lever, a Piezo-electric Transducer(PZT) actuator and capacitance sensors. The performance of the two-axis stage was analyzed using a commercial finite element method program prior to the implementation. A single line laser was employed as the light source along with the Photo Multiplier Tube(PMT) that served as the detector. The performance of the developed confocal microscope was evaluated with a mouse ear skin imaging test. The designed scanning stage enabled us to build the confocal microscope without the two optical scanning mirror modules that are essential in the conventional laser scanning confocal microscope. The elimination of the scanning mirror modules makes the optical design of the confocal microscope simpler and more compact than the conventional system.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.5
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• pp.685-703
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• 2017

Recently, as the number of high-rise building and earthquake occurrence are increasing, it is more important to consider horizontal load such as wind and seismic loads, earth pressure, for the pile foundation. Also, development of underground space in urban areas is more demanded to meet various problem induced by growing population. Many studies on pile subjected to horizontal load have been conducted by many researchers. However, research regarding interactive behavior on pile subjected to horizontal load with tunnel are rare, so far. In this study, therefore, study on the behaviors of ground and horizontal and vertical loads applied to single pile was carried out using laboratory model test and numerical analysis. The pile axial force and ground deformation were investigated according to offset between pile and tunnel (0.0D, 1.0D, 2.0D: D = tunnel diameter). At the same time, close range photogrammetry was used to measure displacement of underground due to tunnelling during laboratory model test. The results from numerical analysis were compared to that from laboratory model test.

• Journal of the Korean Geosynthetics Society
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• v.13 no.4
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• pp.97-107
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• 2014

Finite element modelling and analysis were conducted for the roll-type steel mats which were placed on loose sand and subjected to a standard truck wheel load in this study. The roll-type steel mats mean that the steel mats can be folded as a circle shape for the carrying to fields in cold regions where workability is limited and are developed for a rapid rehabilitation method for roadway across soft ground which is caused by thawing during the summer season in cold regions. The model is composed of link elements to simulate nonlinear behavior of connections between steel mats, thick shell elements to have flexural stiffness of the steel mats, and springs to simulate characteristics of foundation soils. The structural behaviors of the shell, link elements, and springs were verified at each modelling step through experiment and analysis. Beam and shell analysis without the link elements were conducted and compared to results obtained from the model presented in this study. Significant vertical displacement is shown in the shell model with hinge connections. Therefore, the results demonstrate that the analysis model for the roll-type steel mats on loose sand needs further detail parametric studies.