• Geophysics and Geophysical Exploration
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• v.11 no.3
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• pp.184-196
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• 2008

We perform MT soundings in Bendigo, the northern part of Victoria, Australia, to investigate the deep subsurface geologic structure. The primary purpose of this survey is to figure out whether the discontinuity such as faults extends northward. The time series of MT signal were measured over 11 days at 71 measurement stations together with at remote reference, which help enhance the quality of impedance estimation and its interpretation. The impedances are estimated by robust processing using remote reference technique and then inverted with 2D MT 2D inversion. We can see that known faults are clearly imaged in MT 2D inversion. Comparing resistivity images from MT 2D inversion with interpreted boundary from reflection seismic exploration, two interpretations match well each other.

• Journal of the Earthquake Engineering Society of Korea
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• v.16 no.3
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• pp.13-22
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• 2012

Even with its significant influence on the dynamic analysis and foundation design of structures, sometimes the soil-structure interaction has been ignored during the design process. One of the reasons is due to the fact that the modeling procedures are too complicated to meet the requirements in practice. In this study, using the Cali(IT)2 building in California with high and frequent seismic activities, the analysis differences for different boundary conditions are reviewed. The Beam on Nonlinear Winkler Foundation Model, one of the foundation modeling methods, is modified for easy use by the Linear Matrix Inequalities Model Reduction Technique. The product of the proposed process is applied to create the Finite Element Model. The results show fairly good agreement with the real data acquired from the Cal(IT)2 building.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.2
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• pp.207-216
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• 2005

External confinement by CFS (Carbon Fiber Sheet) is a very effective retrofit method for the reinforced concrete columns subject to either static or seismic loads. For the reliable and cost-effective design of CFS, an accurate stress-strain model is required for CFS-confined concrete. In this paper, uniaxial compression test on short RC column with square section was performed. To evaluate the effect of confinement on the stress-strain relationship of CFS-confined concrete, CFS area ratio and tie area ratio are considered. Based on the experimental results, a stress-strain model is proposed for concrete confined by CFS wraps. In the development of the model, the method to compute the actual hoop strains in CFS jackets at the rupture was examined and resolved. Overall, the results of the model agree well with test data.

• Journal of the Korean earth science society
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• v.37 no.4
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• pp.200-210
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• 2016

Geoacoustic modeling is used to predict sound transmission through submarine bottom layers of sedimentary strata and acoustic basement. This study reconstructed four geoacoustic models for sediments of 50 m thick at the Jeongdongjin area in the western continental margin of the East Sea. Bottom models were based on the data of the highresolution air-gun seismic and subbottom profiles (SBP) with sediment cores. P-wave speed was measured by the pulse transmission technique, and the resonance frequency of piezoelectric transducers was maintained at 1MHz. Measurements of 42 P-wave speeds and 41 attenuations were fulfilled in three core sediments. For actual modeling, the P-wave speeds of the models were compensated to in situ depth below the sea floor using the Hamilton method. These geoacoustic models of coastal bottom strata will be used for geoacoustic and underwater acoustic experiments reflecting vertical and lateral variability of geoacoustic properties in the Jeongdongjin area of the East Sea.

• Earthquakes and Structures
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• v.11 no.2
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• pp.327-346
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• 2016

The 2012 Emilia (Italy) earthquakes struck a highly industrialized area including several thousands of industrial prefabricated buildings. Due to the lack of specific design and detailing for earthquake resistance, precast reinforced concrete (RC) buildings suffered from severe damages and even partial or total collapses in many cases. The present study reports a data inventory of damages from field survey on prefabricated buildings. The damage database concerns more than 1400 buildings (about 30% of the total precast building stock in the struck region). Making use of the available shakemaps of the two mainshocks, damage distributions were related with distance from the nearest epicentre and corresponding Pseudo-Spectral Acceleration for a period of 1 second (PSA at 1 s) or Peak Ground Acceleration (PGA). It was found that about 90% of the severely damaged to collapsed buildings included into the database stay within 16 km from the epicentre and experienced a PSA larger than 0.12 g. Moreover, 90% of slightly to moderately damaged buildings are located at less than 25 km from the epicentre and were affected by a PSA larger than 0.06 g. Nevertheless, the undamaged buildings examined are almost uniformly distributed over the struck region and 10% of them suffered a PSA not lower than 0.19g. The damage distributions in terms of the maximum experienced PGA show a sudden increase for $PGA{\geq}0.28g$. In this PGA interval, 442 buildings were collected in the database; 55% of them suffered severe damages up to collapse, 32% reported slight to moderate damages, whereas the remaining 13% resulted undamaged.

• Journal of the Korean earth science society
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• v.39 no.2
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• pp.154-163
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• 2018

Geoacoustic model comprises physical and acoustic properties of submarine bottom layers influencing sound transmission through sea water and underwater. This study suggested for the first time that we made a geoacoustic model of long-coring bottom layers at the SSDP-105 drilling site of the Ulsan coastal area, which is located in the southwestern inner shelf of the East Sea. The geoacoustic model of 52 m depth below seafloor with three-layer geoacoustic units was reconstructed in the coastal sedimentary strata at 79 m in water depth. The geoacoustic model was based on the data of a deep-drilled sediment core of SSDP-105 and sparker seismic profiles in the study area. For actual modeling, the geoacoustic property values of the models were compensated to in situ depth values below the sea floor using the Hamilton modeling method. We suggest that the geoacoustic model be used for geoacoustic and underwater acoustic experiments of mid- and low-frequency reflecting on the deep bottom layers in the Ulsan coastal area of the East Sea.

• 한국해양학회지
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• v.26 no.4
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• pp.332-339
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• 1991

The sedimentation pattern in Namhaepo Bay, a macrotidal coastal embayment of western Korea, was investigated by means of analysing high-resolution seismic profiles, sediment samples, and tidal currents. Recent sediments up to 20 m which overlie the irregular surface of the acoustic basement. The sediments consist mainly of sandy silt and silt; the mean grain size of these sediments ranges from 4 to 5.5 phi, showing a shoreward-fining distribution pattern. This distribution pattern agrees are largely reversed during ebb, with a maximum velocity of 39 cm/sec. The calculated shear velocity of the tidal currents at sea bed ranges from 0.5 to 3.3 cm/sec during flood and from 0.7 to 2.5 cm/sec during ebb. The mean values of these velocities exceed the critical shear velocity for the silt particles. The data suggest that the tidal currents play an important role in the transportation and deposition of sediments in the bay and the surface topography of the sea floor is largely deter-mined by tidal sedimentation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.2
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• pp.177-186
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• 2005

World widely, the occurrences of earthquakes have been increased recently including to nations which earthquake often happen to like Japan. Taking into account that the earthquake acceleration at design was 0.154 g at the contigency level earthuake (CLE) with its geological condition, it resulted that this method must be the most efficient condition against the earthquake vibration to two lane cut-and cover tunnel. The correlations between the result of the shaking table test and its numerical analysis showed that the test data of the bending stress due to the earthquake vibration have been underestimated about 5 percents in case of the cut slope 1 : 0.6 and about 10 percent in case of the cut slope 1 : 1.2. However, on average, the results showed a similar tendency that the higher the height of the backfill of the EPS block was, the less the bending stress was.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.3
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• pp.229-240
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• 2007

The 3D absolute displacement monitoring system has been developed to analyze the tunnel convergence measured under construction of underground structures and to manage effectively the measured data. The system is comprised of the total station, the anchor-typed target pin and the 3D absolute displacement measurement and management program. In this paper, the types and specifications of the 3D total station were presented. The anchor-typed target pin, an improved model of traditional one, was developed and its sightable distance and measurement accuracy were checked by field tests. Also a 3D absolute displacement measurement and management program, TEMS 3D, was developed to provide some analysis tools including the trend and influence lines. L/C ratio, S/C ratio and the like. The developed system was applied the construction stage of a railway tunnel for testing purpose. It is verified that the developed system is capable of predicting weak zones ahead of tunnel face by comparing with results of TSP (Tunnel Seismic Prediction) survey.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.267-272
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• 2005

Geophysical surveys were performed in three abandoned mines: Jangpoong, Kwangyang, Imchon. The main objectives of the researches include delineating the pathways of leachate from acid mine drainage(AMD), mapping buried rock wastes and tailings, detecting drainage pipes, and investigating the gallery and membrane, if they exist, Geophysical responses were well correlated with the results from water sample data(i.e., pH, EC, heavy metal contents, $SO_4^{-2}$). Main pathways of the leachate were successfully detected in electrical resistivity sections and self-potential(SP) profiles, whereas waste rocks, drainage pipes, and membranes were effectively located by incorporating seismic refraction, electrical resistivity and GPR methods.