• Journal of the Korean Geotechnical Society
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• v.38 no.8
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• pp.17-27
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• 2022

To characterize the dynamic properties of Gimhae Plains sediments, we calculated natural frequencies using microtremor horizontal-to-vertical spectral ratios and derived shear wave velocity profiles by inversion of Rayleigh-wave dispersion curves obtained by the high frequency-wavenumber and modified spatial autocorrelation methods. Our results suggest that in this region, strong amplification of ground motion is expected in the vibration frequency (f ≥ 1 Hz). Additionally, obtained velocity profiles show that shear wave velocities are ~200 and 400 m/s for the shallow marine and old fluvial sediments, respectively. Bedrock is possibly encountered at depths of 60-100 m at most sites. We developed a simplified shear wave velocity model of shallow sediments based on the obtained profiles. Our results suggest that a large area in the Gimhae Plains could be categorized as an S6 site based on the Korean seismic design code (KDS 17 10 00).

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1124-1131
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• 2008

Thanks to a new in-situ seismic probe, using bender elements and penetration scheme, a simple linear relationship between undrained shear strength(Cu) and shear wave velocity(Vs) was obtained. This priceless relationship is worthy to be illuminated further in ideal laboratory environment. To avoid sampling disturbance effect, special consolidation cylinders were used to make normally consolidated specimens from kaolinite suspension. The undrained shear strengths of the specimens were measured using unconsolidated undrained triaxial compression tests. Also shear wave velocity measurements were performedprior to shearing the same specimens, using the bender elements installed in the base pedestal and the top cap of the triaxial compression cell. The Cu-Vs relationship is fairly linear and supports the linear trend of clayey silt obtained using field testing. Also the classic density-shear modulus relationship for soft clay proposed by Hardin and Black(1969) was once more verified hereby.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.1417-1421
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• 2008

Temperature variation affect the response of asphalt pavement and should be considered in the evaluation of performance of the pavement. In this paper, HWAW method is applied to evaluate shear wave velocity(or shear modulus) of the asphalt pavement with temperature. HWAW method which is based on time-frequency analysis using harmonic wavelet transform have been developed to determine phase and group velocities of waves. This method minimize effect of noise and is not affected by mode jump effect which cause erroneous result when surface wave method is applied to pavement evaluation. In order to estimate the applicability of HWAW method, field tests were performed in 1 site and preliminary correlation between shear wave velocity(shear modulus) and asphalt pavement average temperature.

• Structural Engineering and Mechanics
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• v.69 no.2
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• pp.121-129
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• 2019

The present study investigates the propagation of shear waves in a composite structure comprised of imperfectly bonded piezoelectric layer with a micropolar half space. Piezoelectric layer is considered to be initially stressed. Micropolar theory of elasticity has been employed which is most suitable to explain the size effects on small length scale. The general dispersion equations for the existence of waves in the coupled structure are obtained analytically in the closed form. Some particular cases have been discussed and in one particular case the dispersion relation is in well agreement to the classical-Love wave equation. The effects of various parameters viz. initial stress, interfacial imperfection and micropolarity on the phase velocity are obtained for electrically open and mechanically free system. Numerical computations are carried out and results are depicted graphically to illustrate the utility of the problem. The phase velocity of the shear waves is found to be influenced by initial stress, interface imperfection and the presence of micropolarity in the elastic half space. The theoretical results obtained are useful for the design of high performance surface acoustic devices.

• Journal of the Korean earth science society
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• v.24 no.6
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• pp.549-557
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• 2003

Surface wave exploration method has many advantages over other conventional exploration methods. Only limited accumulation of the study results has been made due to the recent development of the method. In this study the characteristics of the phase dispersion curves of four sites with different geo-technical properties have been identified. A generalized inversion method was used to obtain the shear wave velocity profiles of the study areas. The shear wave velocity profiles were compared with the columnar sections of the boreholes at the sites. This study shows that the rapid changes in the shear wave velocities are consistent with the changes in the sedimentary or lithologic faces found in the borehole measurements. This implicates that the surface wave exploration method could be used to identify changes in the physical properties of sediments or rocks.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1997.10a
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• pp.133-140
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• 1997

Based on the Green's function technique, an analytical approach is developed to examine the surface wave screening effectiveness of composite wave barriers. The composite barrier consists of a high velocity layer sandwiched between two thin layers of low shear velocity materials. The high velocity layer is represented by differential matrix operators which relate the wave fields on each side of the layer. The low velocity layers are modeled by non-rigid contact conditions which allow partial sliding at the interfaces. Screening ratio of barriers with various combination of material, geometric, and non-rigidness parameters are compared and discussed in some detail.

• Journal of the Korean Geotechnical Society
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• v.30 no.1
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• pp.65-74
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• 2014

Cemented soils have been widely used in road and dam construction, and recently ground improvement of soft soils. The strength of such cemented soils can be tested by using cored sample or laboratory-prepared specimen through unconfined compression or triaxial tests. It takes time to core a sample or prepare a testing specimen in the laboratory. In a certain situation, it is necessary to determine the in-situ strength of cemented soils very quickly and on time. In this study, the relation between unconfined compressive strength and shear wave velocity was investigated for predicting the in-situ strength of cemented soils. A small cemented specimen with 5 cm in diameter and 10 cm in height was prepared by Nakdong river sand and ordinary Portland cement. Its cement ratios were 4, 8, 12, and 16% and air cured for 7, 14, and 28 days. For recycling of resources, a blast furnace slag was also used with sodium hydroxide as an alkaline activator. The shear wave velocity for cemented soils was measured and then unconfined compressive strength test was carried out. As a cement ratio increased, the shear wave velocity and unconfined compressive strength increased due to increased density and denser structure. The relation between unconfined compressive strength and shear wave velocity increased nonlinearly for cemented soils with less than 16% of cement ratio.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.1 s.53
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• pp.45-57
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• 2007

The mean shear wave velocity to the depth of 30 m (Vs30) derived from the western Vs is the current site classification criterion for determining the design seismic ground motion taking into account the site amplification potential. In order to evaluate the Vs30 at a site, a shear wave velocity (Vs) Profile extending to at least 30 m in depth must be acquired from in-situ seismic test. In many cases, however, the resultant depth of the Vs profile may not extend to 30 m, owing to the unfavorable field condition and the limitation of adopted testing techniques. In this study, the Vs30 and the mean shear wave velocity to a depth shallower, than 30 m (VsDs) were computed from the Vs profiles more than 30 m in depth obtained by performing various seismic tests at total 72 sites in Korea, and a correlation between Vs30 and VsDs was drawn based on the computed mean Vs data. In addition, a method for extrapolating the Vs profile from shallow depth to 30 m was developed by building a shape curve based on the average data of all Vs profiles. For evaluating the Vs30 from the shallow Vs profiles, both the methods using VsDs and shape curve result in less bias than the simplest method of extending the lowermost Vs equally to 30 m in depth, and are usefully applicable particularly in the cases of the Vs profiles extending to at least 10 m in depth.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.2
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• pp.69-79
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• 1996

Dynamic stress intensity factors are derives when the crack is propagating with constant velocity under longitudinal shear stress in orthotropic disk plate. General stress fields of crack tip propagating with constant velocity and least square method are used to obtain the dynamic stress intensity factor. The dynamic stress intensity factors of GLV/GTV=1(=isotropic material or transversely isotropic material) which is obtained in out study nearly coincides with Chiang's results when mode Ⅲ stress is applied to boundary of isotropic disk. The D.S.I.F. of mode Ⅲ stress is greater when α(=angle of crack propagation direction with fiber direction) is 90° than that when α is 0°. In case of a/D(a:crack length, D:disk diameter)<0. 58, the faster crack propagation velocity, the less D.S.I.F. but when crack propagation velocity arrive on ghear stress wave velocity, the D.S.I.F. but when crack propagation velocity arrive on shear stress wave velocity, the D.S.I.F. unexpectedly increases and decreases to zero.

• Geophysics and Geophysical Exploration
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• v.7 no.1
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• pp.14-18
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• 2004

High levels of ambient noise and safety factors often limit the use of 'active-source' seismic methods for geotechnical investigations in urban environments. As an alternative, shear-wave velocity-depth profiles can be obtained by treating the background microtremor wave field as a stochastic process, rather than adopting the traditional approach of calculating velocity based on ray path geometry from a known source. A recent field test in Melbourne demonstrates the ability of the microtremor method, using only Rayleigh waves, to resolve a velocity inversion resulting from the presence of a hard, 12 m thick basalt flow overlying 25 m of softer alluvial sediments and weathered mudstone. Normally the presence of the weaker underlying sediments would lead to an ambiguous or incorrect interpretation with conventional seismic refraction methods. However, this layer of sediments is resolved by the microtremor method, and its inclusion is required in one-dimensional layered-earth modelling in order to reproduce the Rayleigh-wave coherency spectra computed from observed seismic noise records. Nearby borehole data provided both a guide for interpretation and a confirmation of the usefulness of the passive Rayleigh-wave microtremor method. Sensitivity analyses of resolvable modelling parameters demonstrate that estimates of shear velocities and layer thicknesses are accurate to within approximately $10\%\;to\;20\%$ using the spatial autocorrelation (SPAC) technique. Improved accuracy can be obtained by constraining shear velocities and/or layer thicknesses using independent site knowledge. Although there exists potential for ambiguity due to velocity-thickness equivalence, the microtremor method has significant potential as a site investigation tool in situations where the use of traditional seismic methods is limited.