• Journal of the Korean Geotechnical Society
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• v.20 no.2
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• pp.115-124
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• 2004

Granular compaction pile has the load bearing capacity of the soft ground increase and has the settlement of foundation built on the reinforced soil reduce. The granular compaction group piles also have the consolidation of the soft ground accelerate and prevent the liquefaction caused by earthquake using the granular materials such as sand, gravel, stone etc. However, this method is not widely used in Korea. The granular compaction piles are constructed by grouping them with a raft system. The confining pressure at the center of bulging failure depth is a major variable in estimating the ultimate bearing capacity of the granular compaction piles. Therefore, a share of loading is determined considering the effect of load concentration ratio between the granular compaction piles and surrounding soils, and the variation of the magnitude of the confining pressure. In this study, a method for the determination of the ultimate bearing capacity is proposed to apply a change of the horizontal pressure considering bulging failure depth, surcharge, and loaded area. Also, the ultimate bearing capacity of the granular compaction pile is evaluated on the basis of previous study(Kim et al., 1998) on the estimation of the ultimate bearing capacity and compared with the results obtained from laboratory scale model tests and DEM numerical analysis using the PFC-2D program.

• Magazine of the Korea Concrete Institute
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• v.9 no.4
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• pp.167-176
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• 1997

The current study is a part of series of research about the evaluation method of the unbonded tendon stress in prestressed concrete member at flexural failure. As the first part. previous design equations were examined in oder to find whether any modifications may be needed. A total of 167 experimental results tested for more than 40 years were gathered to build D/B and then previous proposed and codified equations were evaluated with the experimental relsults. The ACI Code equation and Naaman, Harajli, and Chakrabarti's equations were chosen for the purpose of examination. Then, the followings were obtained from the analytical examination. It is desirable to compute the tendon stress with the member analysis method instead of the sectional analysis method which has been used in the current ACI Code. The tendon stress may also be influenced significantly by the amount of ordinary bonded reinforcements and the loading types. And the current ACI Code overestimated the effect of span/depth ratio. As results, it was concluded that the revision of the ACi Code equation should be considered positively. Then, a new design has to be proposed with the reasonable and comprehensive investigation about influential factors on the tendon stress variation.

• Journal of Korea Water Resources Association
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• v.41 no.12
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• pp.1219-1230
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• 2008

Stream inflows induced by flood runoffs have a higher density than the ambient reservoir water because of a lower water temperature and elevated suspended sediment(SS) concentration. As the propagation of density currents that formed by density difference between inflow and ambient water affects reservoir water quality and ecosystem, an understanding of reservoir density current is essential for an optimization of filed monitoring, analysis and forecast of SS and nutrient transport, and their proper management and control. This study was aimed to quantify the characteristics of inflow density current including plunge depth($d_p$) and distance($X_p$), separation depth($d_s$), interflow thickness($h_i$), arrival time to dam($t_a$), reduction ratio(${\beta}$) of SS contained stream inflow for different flood magnitude in Daecheong Reservoir with a validated two-dimensional(2D) numerical model. 10 different flood scenarios corresponding to inflow densimetric Froude number($Fr_i$) range from 0.920 to 9.205 were set up based on the hydrograph obtained from June 13 to July 3, 2004. A fully developed stratification condition was assumed as an initial water temperature profile. Higher $Fr_i$(inertia-to-buoyancy ratio) resulted in a greater $d_p,\;X_p,\;d_s,\;h_i$, and faster propagation of interflow, while the effect of reservoir geometry on these characteristics was significant. The Hebbert equation that estimates $d_p$ assuming steady-state flow condition with triangular cross section substantially over-estimated the $d_p$ because it does not consider the spatial variation of reservoir geometry and water surface changes during flood events. The ${\beta}$ values between inflow and dam sites were decreased as $Fr_i$ increased, but reversed after $Fr_i$>9.0 because of turbulent mixing effect. The results provides a practical and effective prediction measures for reservoir operators to first capture the behavior of turbidity inflow.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2003.09a
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• pp.44-44
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• 2003

As a basic measurement tool in the areas of animal models of human disease, gene expression and therapy, and drug discovery and development, small animal PET imaging is being used increasingly. An ideal small animal PET should have high sensitivity and high and uniform resolution across the field of view to achieve high image quality. However, the combination of long narrow pixellated crystal array and small ring diameter of small animal PET leads to the degradation of spatial resolution for the source located at off center. This degradation of resolution can be improved by determining the depth of interaction (DOI) in the crystal and by taking into account the information in sorting the coincident events. Among a number of 001 identification schemes, dual layer phsowich detector has been widely investigated by many research groups due to its practicability and effectiveness on extracting DOI information. However, the effects of each crystal length composing dual layer phoswich detector on DOI measurements and image qualities were not fully characterized. In order to minimize the DOI effect, the length of each layer of phoswich detector should be optimized. The aim of this study was to perform simulations using a simulation tool, GATE to design the optimum lengths of crystals composing a dual layer phoswich detector. The simulated small PET system employed LSO front layer LuYAP back layer phoswich detector modules and the module consisted of 8${\times}$8 arrays of dual layer crystals with 2 mm ${\times}$ 2 mm sensitive area coupled to a Hamamatsu R7600 00 M64 PSPMT. Sensitivities and variation of radial resolutions were simulated by varying the length of LSO front layer from 0 to 10 mm while the total length (LSO + LuYAP) was fixed to 20 mm for 10 cm diameter ring scanner. The radial resolution uniformity was markedly improved by using DOI information. There existed the optimal lengths of crystal layers to minimize the variation of radial resolutions. In 10 cm ring scanner configuration, the radial resolution was kept below 3.4 mm over 8 cm FOV while the sensitivity was higher than 7.4% for LSO 5 mm : LuYAP 15 mm phoswich detector. In this study, the optimal length of dual layer phoswich detector was derived to achieve high and uniform radial resolution.

• Advances in concrete construction
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• v.10 no.2
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• pp.171-183
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• 2020

The main objective of this study is the assessment of the ability of limestone mortars to resist to different chemical attacks. The ability of polypropylene (PP) fibres waste used as reinforcement of these concrete materials to enhance their durability is also studied. Crushed sand 0/2 mm which is a fine limestone residue obtained by the crushing of natural rocks in aggregates industry is used for the fabrication of the mortar. The fibres used, which are obtained from the waste of domestic plastic sweeps' fabrication, have a length of 20 mm and a diameter ranging between 0.38 and 0.51 mm. Two weight fibres contents are used, 0.5 and 1%. The durability tests carried out in this investigation included the water absorption by capillarity, the mass variation, the flexural and the compressive strengths of the mortar specimens immersed for 366 days in 5% sodium chloride, 5% magnesium sulphate and 5% sulphuric acid solutions. A mineralogical analysis by X-ray diffraction (XRD) and a visual inspection are used for a better examination of the quality of tested mortars and for better interpretation of their behaviour in different solutions. The results indicate that the reinforcement of limestone mortar by PP fibres waste is an excellent solution to improve its chemical resistance and durability. Moreover, the presence of PP fibres waste does not affect significantly the water absorption by capillarity of mortar nether its mass variation, when exposed to chloride and sulphate solutions. While in sulphuric acid, the mass loss is higher with the presence of PP fibres waste, especially after an exposure of 180 days. The results reveal that these fibres have a considerable effect of the flexural and the compressive behaviour of mortar especially in acid solution, where a reduction of strength loss is observed. The mineralogical analysis confirms the good behaviour of mortar immersed in sulphate and chloride solutions; and shows that more gypsum is formed in mortar exposed to acid environment causing its rapid degradation. The visual observation reveals that only samples exposed to acid attack during 366 days have showed a surface damage extending over a depth of approximately 300 ㎛.

• The korean journal of orthodontics
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• v.15 no.1
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• pp.123-140
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• 1985

Variation in the facial pattern and effect of the rotational jaw growth on the facial proportion were studied in serial cephalometric radiographs of 40 Korean children (25 boys, 15 girls) ranging in age from 6 to 13 years. According to Y-axis (N-S-Gn) growth change during the 7 years of period, the subject who had exhibited 'wave-like' manner of Y-axis growth change within ${\pm}\;2^{\circ}$ was classified to the Parallelwise group and the subject who had exhibited Y-axis increase more than $+2^{\circ}$ was classified to the Clockwise rotation group and the subject who had exhibited Y-axis decrease more than $-2^{\circ}$ was classified to the Counterclockwise rotation group. For the comparison of each group, a total of 22 morphologic variables were employed and the data were analyzed by means of computer morphometrics and statistical methods. On the basis of the finding of this study, the following trends were established. 1. The Parallelwise group was $75\%$, the Clockwise rotation group was $12.5\%$ and the Counter-clockwise rotation group was $12.5\%$. 2. The growth pattern of cranial base was related to the rotation of mandible. 9. Maxillary prognathism was occured in the Counterclockwise rotation group and the rotation of palatal plane was occured in the Clockwise rotation group. 4. Mandibular prognathism was occured in the Parallelwise and the Counterclockwise rotation groups, especially in the Counterclockwise rotation group. 5. The degree of maxillo-mandibular divergency was constant in the Clockwise rotation group but decreased in the Counterclockwise rotation and the Parallelwise groups, especially in the Counterclockwise group. 6. There were no differences in the size of the anterior upper facial height (N-ANS) and the posterior lower facial height ((Go-Me)-PNS) but there were differences in the size of the anterior lower facial height (ANS-Me) and the posterior upper facial height ((S-N)-PNS) between each group. 7. The growth increment and the size of the facial depth was not related to the growth pattern of the face but the growth increment and the size of the facial height was related to the growth pattern of the face. 8. Proportional change due to the facial growth rotation was concentrated in the anterior lower face. 9. The most apparent difference between each group was happened in the size of the posterior cranial base (S-Ba) and the facial length (S-Gn).

• Korean Journal of Fisheries and Aquatic Sciences
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• v.24 no.1
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• pp.9-20
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• 1991

The characteristics of the unconsolidated sediment in Gwangyang bay was analyzed from the core samples. The porosity of the sediment showed irregular variation with respect to the sedimentation depth, which indicated that sediment weight-induced consolidation was not significant. Numerical analysis for the mechanical and hydraulic behavior of the unconsolidated sediment due to the tidal sea level change was processed. Because of the delayed excessive pore pressure change in the very low permeable mud medium, the magnitude of the excessive pore pressure for the duration of the minimum sea level exceeded the total stress from the sea water weight, which resulted in the negative (tensional) effective stress below the top surface. The in-situ effective stress, obtained by superposing the tensional effective stress on the solid weight-induced compressive stress, was remained to be tensile (quick-sand condition) near the top surface of the mud deposit. The occurrence of the quirk-sand condition provided a theoretical evidence for the insignificant consolidation and the irregular porosity variation of the sediment. When the sand is distributed on the top surface of the mud layer, the quick-sand condition occurred below the sandy mud layer and the downward movement of sand particles was facilitated.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.236-245
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• 2021

It is very important for structure designer to understand the service life variation since a wide range of service life is evaluated with changing exposure conditions and design parameters. Recently, for zero-carbon, waste plastic has been used for fuel for clinker production and this yields increase in chloride content in cement. This study is for evaluation of changing service life in the concrete with increasing initial chloride content due to usage of plastic-SRF(Solid Refuse Fuel) considering various exposure conditions and design parameters. For this, 4 levels of initial chloride content were assumed, and the service life was assessed using LIFE 365 program considering various environmental conditions including 3 levels of surface chloride content. As for analysis parameters, critical/initial chloride content, blast furnace slag powder replacement ratio, W/B(Water to Binder) ratio, cover depth, and unit mass for binder are adopted. Service life decreases with increasing initial chloride content and a significant reduction of service life is not evaluated permitting up to 1,000ppm of initial chloride content. With increasing slag replacement ratio, a longer service life can be secured since blast furnace slag powder has the effect of reducing the diffusion of external chloride ions and fixing the free chloride. It is thought that increasing initial chloride content up to European standard is helpful for enhancing sustainability and reducing carbon emission. Though the reduction in service life due to an increase in the initial chloride content is not significant in slag-concrete with low surface chloride content, careful consideration for mixing design should be paid for the exposure environment with high surface chloride content.

• Journal of Korean Society of Forest Science
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• v.86 no.2
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• pp.177-185
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• 1997

The influences of fertilizer treatment and clones of five willows and one hybrid poplar on above ground and soil carbon (C) accumulations in a willow bioenergy plantation were studied. The aboveground and soil samples were collected in the winter of 1992 and 1993 from the previously established willow plantation at Tully, New York, U.S.A. in 1987. Half of the plots were fertilized annually with 336kg/ha N, 112kg/ha P, and 224kg/ha K. All trees were harvested annually. The most productive clone, willow clone SV1 with fertilization, accumulated 5.4 and 6.8 t/ha/yr aboveground C contents during the sixth(1992) and seventh(1993) growing seasons, respectively. The average percentage of C in bolewood, bolebark, and branches for the five willow clones and one hybrid poplar clone ranged from 51.1 to 57.5, from 54.0 to 55.4, and from 55.6 to 56.5, respectively, among all treatment combinations. Only tyro of the six clones(SA22 and SA2) responded significantly to the addition of fertilizer by increasing the amount of aboveground C accumulated for the 1992 sampling period(clone-by-fertilizer interaction). No fertilization effect, on aboveground C content, was noted for the 1993 sampling period. No significant fertilization effect on soil C accumulation for all soil sampling depths(0-10, 10-20, and 20-40cm) was found in 1992 and 1993 sampling years. Little clone effect on soil C content was found in 1992 and 1993 sampling years, except at 0-10cm soil depth in 1992. The significant clonal effect on soil C content at 0-10cm soil depth could be because of stone content variation rather than clonal effect. The significant clone-by-fertilizer treatment interaction observed requires that evaluation of response to fertilization by willows be made for each clone individually.

• 한국해양학회지
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• v.30 no.4
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• pp.279-287
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• 1995

The vertical profiles of natural ²¹⁰Pb, ²¹⁰Po and ²³⁴Th activities were measured for the upper 100 m of water column at three stations in the middle region of the Korean East Sea during May 1992. And the distribution of these radionuclides was discussed associated with the formation of warm eddy or water mass. The main thermocline was maintained between the depth of 50 and 100 m at the southern station (Sta. A1), and between the depth of 10 to 50 m at the coastal station of Sockcho (Sta. B10). Contrastingly, a main thermocline at Sta. A10, which locates near the center of warm eddy, was observed below 230 m depth. Between 50 and 220 m depth of Sta. A10 is there a relatively homogeneous water mass of 10.1${\pm}$0.5$^{\circ}C$, which is significantly higher in temperature and lower in nutrient than the other two stations. It seems to be due to sinking of the warm surface water in which nutrients were completely consumed. Both ²¹⁰Pb and ²¹⁰Po show the highest concentration at Sta. A1 and the lowest at Sta. B10 among the three stations. Also, the ²¹⁰Pb activity is generally higher in the upper layer than in the lower layer, while ²¹⁰Po activity represents the reversed pattern at all three stations. At Sta. A1 and Sta. B10, the activities of ²¹⁰Po relative to its parent ²¹⁰Pb were deficient in the water column above the main thermocline, but were excess below the thermocline. However, the station near the center of warm eddy(Sta. A10), shows no excess of ²¹⁰Po in the depths below 50 m, although its defficiency is found in the upper layer like the other stations. At Sta. A1 and b10. ²³⁴Th activities are slightly lower in the surface mixed layer than in the deeper region However, at Sta. A10, ²³⁴Th activity in the upper 30 m is higher than below 50 m or in the same depth of the other stations, probably because of the high concentration of particulate matter. The residence time of ²¹⁰Po in the surface mixed layer at Sta. A10 is 0.4 year, much shorter than at the other two stations(about one year). Above 100 m depth, the residence times of ²³⁴Th range from 18 to 30 other two stations(about on year). Above 100 m depth, the residence times of ²³⁴Th range from 18 to 30 days at all stations, without significant regional variation. The percentages of recycled ²¹⁰Po within the thermocline are 39% and 92% at Sta. A1 and Sta. B10, respectively. Much higher value at Sta. B10 may be due to a thin thickness of the mixed layer as well as the slower recycling rate of ²¹⁰Po in the main thermocline.