• Journal of the Korea institute for structural maintenance and inspection
• /
• v.21 no.1
• /
• pp.1-8
• /
• 2017

Three small scale hollow circular reinforced concrete columns with aspect ratio 4.5 were tested under cyclic lateral load with constant axial load. Diameter of section is 400 mm, hollow diameter is 200 mm. The selected test variable is transverse steel ratio. Volumetric ratios of spirals of all the columns are 0.302~0.604% in the plastic hinge region. It corresponds to 45.9~91.8% of the minimum requirement of confining steel by Korean Bridge Design Specifications, which represent existing columns not designed by the current seismic design specifications or designed by seismic concept. The longitudinal steel ratio is 2.017%. The axial load ratio is 7%. This paper describes mainly crack behavior, load-displacement hysteresis loop, seismic performance such as equivalent damping ratio, residual displacement and effective stiffness and flexural over-strength of circular reinforced concrete bridge columns with respect to test variable. The regulation of flexural over-strength is adopted by Korea Bridge Design Specifications (Limited state design, 2012). The test results are compared with nominal strength, result of nonlinear moment-curvature analysis and the design specifications such as AASHTO LRFD and Korea Bridge Design Specifications(Limited state design).

• Journal of the Korean Geotechnical Society
• /
• v.33 no.10
• /
• pp.5-14
• /
• 2017

The hazard maps for predicting collapse on natural slopes consist of a combination of topographic, hydrological, and geological factors. Topographic factors are extracted from DEM, including aspect, slope, curvature, and topographic index. Hydrological factors, such as soil drainage, stream-power index, and wetness index are most important factors for slope instability. However, most of the urban areas are located on the plains and it is difficult to apply the hazard map using the topography and hydrological factors. In order to evaluate the risk of subsidence of flat and low slope areas, soil depth and groundwater level data were collected and used as a factor for interpretation. In addition, the reliability of the hazard map was compared with the disaster history of the study area (Gangnam-gu and Yeouido district). In the disaster map of the disaster prevention agency, the urban area was mostly classified as the stable area and did not reflect the collapse history. Soil depth, drainage conditions and groundwater level obtained from boreholes were added as input data of hazard map, and disaster vulnerability increased at the location where the actual subsidence points. In the study area where damage occurred, the moderate and low grades of the vulnerability of previous hazard map were 12% and 88%, respectively. While, the improved map showed 2% high grade, moderate grade 29%, low grade 66% and very low grade 2%. These results were similar to actual damage.

• Journal of the Korean Geosynthetics Society
• /
• v.8 no.1
• /
• pp.33-40
• /
• 2009

The laboratory tests and field plate load test were carried out to evaluate the reinforcement effect of geocell for road construction. The geocell-reinforced subgrade shows the increment of cohesion and friction angle with comparison of non-reinforced subgrade. In addition, the field plate load test was performed on the geocell-reinforced subgrade to estimate the bearing capacity of soil. The direct shear test was conducted with utilizing a large-scale shear box to evaluate the internal soil friction angle with geocell reinforcement. The number of cells in the geocell system is varied to investigate the effect of soil reinforcement. The theoretical bearing capacity of subgrade soil with and without geocell reinforcement was estimated by using the soil internal friction angle. The field plate load tests were also conducted to estimate the bearing capacity with geocell reinforcement. It is found out that the bearing capacity of geocell-reinforced subgrade gives 2 times higher value than that of unreinforced subgrade soil. The settlement and the distribution of deformation were also estimated by using the finite element method. The magnitude of settlements on the geocell-reinforced subgrade and unreinforced subgrade are 6.8cm and 1.2cm, respectively.

• Journal of the Korean Geotechnical Society
• /
• v.18 no.3
• /
• pp.51-59
• /
• 2002

This paper deals with development of a damage risk assessment system for adjacent buildings to under-passing tunnel face considering 3D-ground movement. The system consists of building and ground information module, monitoring data module, settlement evaluation module, and building damage risk assessment module. The major modules, settlement evaluation module and building damage assessment module, are based on settlement estimation model suggested by Attewell et al (1982) and the building damage assessment method by Mair et al. (1996). After estimating 3D-ground movements due to tunneling with settlement evaluation module, damage assessment far buildings is performed using building damage risk assessment module. The developed system has two major functions; 1) calculation of 3D-settlement with ground loss ($V_{s}$)or maximum settlement ($w_{max}$) and inflection point (i) using various empirical formulae, monitoring data, numerical results, and so on; 2) assessment of damage risk for adjacent buildings of arbitrary section with position change of tunnel face. The field data given by Boscadin and Cording (1989) leer the case of two-storied masonry building near the Metro tunnel in Washington D.C. was simulated to verify the applicability of the developed system.

• Geophysics and Geophysical Exploration
• /
• v.12 no.1
• /
• pp.105-113
• /
• 2009

The interpretation of observed waveform characteristics identified in refraction and wide-angle reflection data increases confidence in the crustal structure model obtained. When calculating traveltimes and raypaths, wavefront methods on a regular grid based on graph theory are robust even with complicated structures, but basically compute only first arrivals. In this paper, we develop new algorithms to compute traveltimes and raypaths not only for first arrivals, but also for fast and later reflection arrivals, later refraction arrivals, and converted waves between P and S, using the modified wavefront method based on slowness network nodes mapped on a multi-layer model. Using the new algorithm, we can interpret reflected arrivals, Pg-later arrivals, strong arrivals appearing behind Pn, triplicated Moho reflected arrivals (PmP) to obtain the shape of the Moho, and phases involving conversion between P and S. Using two models of an ocean-continent transition zone and an oceanic ridge or seamount, we show the usefulness of this algorithm, which is confirmed by synthetic seismograms using the 2D Finite Difference Method (2D-FDM). Characteristics of arrivals and raypaths of the two models differ from each other in that using only first-arrival traveltime data for crustal structure analysis involves risk of erroneous interpretation in the ocean-continent transition zone, or the region around a ridge or seamount.

• Geophysics and Geophysical Exploration
• /
• v.22 no.4
• /
• pp.177-185
• /
• 2019

Ground roll is a surface wave which is usually observed in the land seismic data. It is one of the typical coherent noise. During the reflection data processing, ground roll is removed because it is considered as noise. This removal process often causes the loss of reflection signals if the ground roll overlaps reflection signals. In this study, we look over Karhunen-Loeve Transform (KLT) and analyze its effects to suppress the ground roll appropriately while reducing the reflection loss. Numerical tests in homogeneous elastic media show that the ground roll has been properly rejected. However, the field data application reveals that there is no significant suppression of ground roll when compared to band-pass filtering. This can be considered that it is hard to calculate horizontally aligned gathers in the field data because the ground roll contains a wide range of frequency bands. On the contrary, the result of singular value decomposition (SVD) filtering shows that the ground roll has been significantly reduced. It is thought that the SVD filtering performs better in the ground roll suppression than KLT because it is easy to calculate the horizontally aligned gathers in the SVD filtering.

• Journal of Korea Water Resources Association
• /
• v.50 no.9
• /
• pp.587-595
• /
• 2017

Hydraulic characteristics affecting sediment transport capacity due to the weir operations were investigated and developed sediment rating curves for four gaging stations (Nakdong, Gumi, Waegwan, and Jindong) in Nakdong River. Analysis found that the sediment transportaion capability had been decreased and it could be proved from the field measurement records in 2013. Applicabilities of nine sediment transport prediction techniques, which are imbeded in GUIDE program, were examined and adopted for the four gaging stations. Analysis of sediment balance for Nakdong River, including 9 major tributaries, had been carried out with pseudo 2-D numerical model and found that: 1) sedimentation phenomena will be prevailed along the Nakdong River. 2) Engelund-Hansen technique shows the least error in estimation of sediment balance. 3) Engelund-Hansen technique most appropriately describes the sediment characteristics for four gaging stations. 4) Estimated error from the sediment balance for Nakdong River was smaller than the error caused by the estimation of sediment incomming from 9 tributries. Therefore, it is necessary to improve the accuracy of predicting the sediment incomming from the tributaties for better sediment balance analysis.

• Geophysics and Geophysical Exploration
• /
• v.16 no.2
• /
• pp.71-78
• /
• 2013

The one-way wave equation migration is much more computationally efficient comparing with reverse time migration and it can provide better image than the migration algorithm based on the ray theory. We have developed the prestack depth migration module adopting (GS) propagator designed for vertical transverse isotropic media. Since GS propagator considers the higher-order term by expanding the Taylor series of the vertical slowness in the thin slab of the phase-screen propagator, the GS migration can offer more correct image for the complex subsurface with large lateral velocity variation or steep dip. To verify the validity of the developed GS migration module, we analyzed the accuracy with the order of the GS propagator for VTI media (GSVTI propagator) and confirmed that the accuracy of the wavefield propagation with the wide angles increases as the order of the GS propagator increases. Using the synthetic seismic data, we compared the migration results obtained from the isotropic GS migration module with the anisotropic GS migration module. The results show that the anisotropic GS migration provides better images and the improvement is more evident on steeply dipping structures and in a strongly anisotropic medium.

• Journal of Digital Convergence
• /
• v.18 no.9
• /
• pp.103-112
• /
• 2020

The purpose of this study is to examine the current status and components of Korean National Debt and to analyze the effects of each component on National Debt. In the Korean Statistical Information Service (KOSIS), we searched for data such as General Accounting Deficit Conservation, For Foreign Exchange Market Stabilization, For Common Housing Stability, Local Government Net Debt Public Funds, etc that constitute National Debt. The analysis period used a total of 23 annual data from 1997 to 2019. The data collected in this study use the rate of change compared to the previous year for each component. Using this, this study attempted index analysis, numerical analysis, and model analysis. Correlation analysis result, the National Debt has a high relationship with the For Common Housing Stability. For Foreign Exchange Market Stabilization, Public Funds, etc., but has a low relationship with the Local Government Net Debt. Since 1997, National Debt has been increasing similarly to the For Foreign Exchange Market Stabilization, For Common Housing Stability and Public Funds etc. Since 2020, Korea is expected to increase significantly in terms of For Common Housing Stability and Public Funds, etc due to Corona19. At a time when the global economic situation is difficult, Korea's National Debt is expected to increase significantly due to the use of national disaster subsidies. However, if possible, the government expects to operate efficiently for economic growth and financial market stability.

• Journal of the Korean Association of Geographic Information Studies
• /
• v.15 no.1
• /
• pp.119-132
• /
• 2012

Recently, forest soil sediment disasters resulting from locally concentrated heavy rainfall have been occurring frequently in steep slope areas. The importance of landslide hazard map is emerging to analyze landslide vulnerable areas. This study was carried out to develop HyGIS-Landslide based on Hydro Geographic Information System in order to analyze forest soil sediment disaster in the mountainous river basin. HyGIS-Landslide is one of HyGIS components designed by considering the landslide hazard criteria of Korea Forest Service. It could show the distribution of landslide hazard areas after calculating the spatial data. In this system, the user could reset the weight of hazard criteria to reflect the regional characteristics of the landslide area. This component provided user interface that could make the latest spatial data available in the area of interest. HyGIS-Landslide could be applied to the surveyor's compensation score and it was possible to reflect the landslide risk exactly through it. Also, it could be used in topographic analysis techniques providing spatial analysis and making topographical parameters in HyGIS. Finally the accuracy could be acquired by calculating the landslide hazard grade map and landslide mapping data. This study applied HyGIS-Landslide at the Gangwon-do province sample site. As a result, HyGIS-Landslide could be applied to a decision support system searching for mountainous disaster risk region; it could be classified more effectively by re-weighting the landslide hazard criteria.