• Korean Journal of Fisheries and Aquatic Sciences
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• v.27 no.4
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• pp.434-444
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• 1994

Physical and acoustic properties of sediment core samples recovered from the Kwangyang Bay, the Yeosu Sound, and the inner shelf of central South Sea, Korea were investigated. Compressional wave velocity, density, porosity, and shear strength were measured at 10cm interval's along the core depth. Sediment texture(grain size, sand, silt, and clay contents) were also measured and correlated with the physical properties(density, porosity, and shear strength). The physical and acoustic properties of the sediment changed gradually from the Kwangyang Bay to the shelf area in accordance with the distance from the input source of the terrigenous sediment. The Yeosu Sound acted as a route of sediment transport from the estuary(the Seomjin River) to the shelf and vice versa. The physical and acoustic properties of the Yeosu Sound sediment conformed to an intermediate stage between river mouth and shelf areas. These results can be utilized to trace the influence of the Seomjin River on the so-called mud belt of Korea.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.4 s.44
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• pp.29-42
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• 2005

Total 350 borehole profiles were selected from the database of borehole logs in Seoul, for the site-specific seismic evaluation at two 4km${\times}$4km plain areas. Equivalent-linear site response analyses for the selected 350 sites were conducted based on shear wave velocity (Vs) Profiles, which were determined from the N-Vs correlation established using borehole seismic testing results in the inland areas of Korea. Most sites were categorized as site classes C and D based on the mean Vs to 30 m in depth (Vs30) ranging from 250 to 550 m/s. The she periods of the plains in Seoul ranging between 0.1 and 0.4 sec were significantly lower than those of the western US, from which the site coefficients in Korea were derived. For plains in Seoul, the site coefficients, Fa's and Fv's specified in the Korean seismic design guide, underestimate the ground motion in short-period (0.1-0.5 sec) band and overestimate the ground motion in mid-period (0.4-2.0 sec) band, respectively, because ol the differences in the geotechnical conditions between Seoul and the western US, although the Fa's in several sites overestimate the motion due to the base Isolation effect resulted from the soft layer in soil deposit.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.1 s.53
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• pp.67-77
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• 2007

Site coefficients in IBC and KBC codes have some limits to predict the rational seismic responses of a structure, because they take into account only the effect of the soil amplification without the effects of the structure-soil interaction. In this study, upper and lower limits of the site coefficients are estimated through the pseudo 3-D elastic seismic response analyses of structures built on the linear or nonlinear soil layers taking Into account the effects of the structure-soil interaction. Soil characteristics of site classes of A, B and C were assumed to be linear, and those of site classes of D and E were done to be nonlinear and the Ramberg-Osgood model was used to evaluate shear modulus and damping ratio of a soil layer depending on the shear wave velocity of the soil layer, Seismic analyses were performed with 12 weak or moderate earthquake records scaled the peak acceleration to 0.1g or 0.2g and deconvoluted as earthquake records at the bedrock located at 30m deep under the outcrop. With the study results of the elastic seismic response analyses of structures, new standard response spectrum and upper and lower limits of the site coefficients of $F_{a}\;and\;F_{v}$ at the short period range and the period of 1 second are suggested including the effects of the structure-soil interaction, and new site coefficients for the KBC code are also suggested.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.4
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• pp.55-61
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• 2010

This paper is concerned with an experimental research to random vibration control caused by external loads specially in bridges which tend to be structurally flexible. Experimenting on a reduced structure modelled on Seohae Grand Bridge, we inflicted a reduced form of El-centro wave on the model structure to a proper proportion. On the center of its middle span, we placed a shear type MR damper which was to control its vibration and also acquire its structural responses such as displacement and acceleration at the same site. The experiments concerning controlling vibration were performed according to a variety of theories including un-control, passive on/off control, and Lyapunov stability theory. Its control performance was evaluated in terms of the peak absolute displacements, the peak absolute accelerations and the total power required to control the bridge which differ from each different experiment method. Among all the methods applied in this paper, case of Lyapunov control method turned out to be the most effective to reduces of displacement and acceleration. Also, this method could to decrease consuming of external power for vibration control. Finally, it was noteworthy that Lyapunov control method was specially effective in the vibration control employing a semi-active damper such MR damper.

• Journal of the Korean GEO-environmental Society
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• v.14 no.5
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• pp.33-39
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• 2013

A drilling exploration in deep sea is being processed to develop new energy resource in the world. In 2007, the presence of the gas hydrate had been confirmed during the UBGH1 (Ulleung Basin Gas Hydrate Expedition 1) in the Ulleung Basin. Geotechnical properties of the deep marine sediment are important factors for assessing the safety of gas production facility and productivity from the hydrate bearing sediment. In this study, comprehensive laboratory tests are conducted to investigate the geotechnical engineering characteristics of the deep marine sediments recovered from the hydrate occurrence regions during the UBGH2 (Ulleung Basin Gas Hydrate Expedition 2) in the Ulleung Basin, East Sea, Korea. The index properties of the specimens including the specific gravity, atterberg limits, specific surface, and particle size distribution are measured, and these are compared to the results reported by previous studies. A zero-lateral strain cell, which houses bender elements, is used to determine stress-dependant characteristics and shear wave velocities with the vertical effective stresses. Furthermore, the hydraulic conductivity is calculated based on the consolidation test results.

• Geophysics and Geophysical Exploration
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• v.17 no.2
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• pp.66-73
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• 2014

To estimate the shear-velocity ($v_s$) structure beneath the WIZ station on White Island in New Zealand, we applied receiver function (RF) inversion and H-${\kappa}$ stacking methods to 362 teleseismic events (Mw > 5.5) recorded during April 20, 2007 to September 6, 2013. Using 71 RFs with errors less than 20% after 200 iterative computations, we determined that the depth to Moho of $v_s$ = 4.35 km/s is $24{\pm}1km$ within a 15 km radius of the station. In an 1-d $v_s$ model derived by RF inversions, a 4-km thick low-velocity layer (LVL) at depths of 18 ~ 22 km was identified in the lower crust. This LVL, which is 0.15 km/s slower than the rocks above and below it, may indicate the presence of a deep magma reservoir. The H-${\kappa}$ stacking method yielded an estimate of the depth to the Moho of 24.5 km, which agrees well with the depth determined by RF inversions. The low $v_p/v_s$ ratio of 1.64 may be due to the presence of gas-filled rock or hot crystallizing magma.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.129-137
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• 2020

In performing the structural analysis, the foundation is considered to be a fixed end as a plastic hinge model. In this study, the displacements of the foundation, pier, and shoe were compared when the foundation modeled as a fixed end, a shallow foundation constructed on bedrock of 2m depth, and a pile foundation constructed in the 10m to 20m depth of bedrock. The shear force was also compared, and the probability of damage was calculated and compared for the critical condition. When calculated as a fixed end, the displacement of the foundation converged to 0mm, but the shallow foundation built on the bedrock with a depth of 2m caused relatively displacement, and the pile foundation constructed to contact the bedrock with a depth of 18m caused a larger displacement. In addition, it was analyzed that the displacement of the foundation, which is the lower structure, affects the displacement of the super structure, but the difference in shear force applied to the foundation was insignificant in the three cases. There was no difference between the shallow foundation and the pile foundation in the influence on the displacement of the top of the pier, but there was a big difference from the analysis assuming as a fixed end.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2C
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• pp.83-94
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• 2008

In this study an effective stress analysis was performed to evaluate liquefaction potential and ground settlement for reclaimed sites. The effective stress model can simulate the stiffness degradation due to excess pore pressure and resulting ground deformation. It is applicable to a wide range of strain. An equivalent linear analysis suitable for low strain levels was also carried out to compare the effective stress analysis. Shear stress ratio calculated from an equivalent linear analysis was used to determine SPT blow count to prevent liquefaction. Depending on the magnitude of potential earthquake and fine contents, the SPT blow count was converted into an equivalent cone tip resistance. It was compared with the measured cone tip resistance. The measured elastic shear wave velocity and cone tip resistance from two reclaimed sites in Incheon were used to perform liquefaction analyses. Two liquefaction evaluation methods showed similar liquefaction potential which was evaluated continuously. The predicted excess pore pressure ratio of upper 20 m was between 40% and 70%. The calculated post-shaking settlement caused by excess pore pressure dissipation was less than 10 cm.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.427-435
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• 2009

Cylindrical structures such as pipes and shafts are widely used in various industrial facilities. Recently, researches on magnetostrictive transduction of torsional waves have been actively reported for the nondestructive evaluation of those cylindrical structures. However, the existing magnetostrictive patch transducer has somewhat inconvenient and time.consuming process like patch bonding to a structure since it should employ a magnetostrictive patch having strong magnetostriction. To overcome these limitations of the existing transducer, in this work, we develop a novel modular magnetostrictive transducer to generate and measure torsional waves to inspect a cylindrical structure. The proposed transducer can be applied as viscous liquid coupling with shear couplant or dry coupling without coupling media instead of patch bonding to a structure. We describe a detailed structure of the modular transducer and conduct some experiments to verify its performance.

• The Journal of the Acoustical Society of Korea
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• v.15 no.6
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• pp.81-89
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• 1996

It is very important for ultrasonic test method to evaluate the integrity of the class I components in nuclear power plants. However, as the rltrasonic test is affected by internal structures and configurations of test materials, backscattering, that is, time invariant noise is generated in large grain size materials. Due to the above reason, the received signal results in low signal to noise(S/N) ratio. Split spectrum processing(SSP) technique is effective to suppress the grain noise. The conventional SSP technique. however, has been applied to unique algorithm. This paper shows that MPO(minimization and polarity threshold) algorithm which two algorithms are applied simulatancously, was utilized, the signal processing time was shorten by using the new constant-Q SSP with the FIR filter which frequency to bandwidth ratio is constant and the optimum parameters were analysed for the signal processing to longitudinal wave and shear wave with the same requirements of inspection on nuclear power plant site. Moreover, the new ultrasonic test instrument, the reference block of the same product form and material specification, stainless stell test specimens and copper test specimens block of the same fabricated for the application of new SSP technique. As the result of experimental test with new ultrasonic test instrument and test specimens, the signal to noise ratio was improved by appying the new SSP technique.