• Journal of the Korean GEO-environmental Society
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• v.7 no.1
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• pp.55-66
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• 2006

Laboratory tests have revealed that the liquefaction resistance of sands depends strongly upon the degree of saturation, which is expressed in terms of the pore pressure coefficient, B. The velocity of compression waves(i.e. P-waves), which have been known to be influenced largely by the degree of saturation and can be measured conveniently in the field, appears as an indicator of saturation. In this paper, the Stokoe type torsional shear(TS) testing equipment is modified to saturate the specimen and measure the velocities of P-wave and S-wave and pore pressure buildup. The velocities of P-wave and S-wave for Toyoura sand from Japan is measured and compared at the various B-value (degree of saturation) which are partially saturated to fully saturated conditions. Additionally, the variation of the pore water pressure induced during undrained TS tests at the various B-value is measured and analyzed.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.255-264
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• 2009

Soils containing vanishing materials lead changes in the microstructure of particulate media due to water inflow. Thus, dissolution renders some local unstability. As the moisture contents decease, the component of the vanished materials may affects on the cementation of paniculate materials. This cementation phenomenon has a huge influence on the stiffness, strength and stability under lower stress level. The goal of this study is to introduce the cementation effects on a compressional wave velocity, a shear wave velocity, and the resonant frequency of shear waves. The glass bead and salt water with different mole contents are used. Test results show that the changes of shear and compressional wave velocities consist of three stages. In the first region, compressional wave velocities increase and shear wave velocities decrease with a decreases in reducing water contents from 100% to 90~95%. In the second region, shear and compressional wave velocities become stable at 90~95% to 10% of the water contents. In the third region, shear and compressional wave velocities increases dramatically with a decrease in the water content due to the capillary force and cementation of salt. Furthermore, the resonant frequency of the shear waves shows similar phenomenon. Specimens prepared by glass beads and salt water are proved to be able to provide a meaningful insight in under structural behaviors of the cementation.

• Geomechanics and Engineering
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• v.3 no.3
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• pp.189-206
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• 2011

Amplification based on empirical relations is widely used for seismic microzonation of urban centers. Amplifications are used to represent the site effects of a particular soil column. Many empirical correlations are available to estimate the amplification of seismic waves. These correlations are based on the ratio of shear wave velocity of foundation/rock to soil velocity or 30 m equivalent shear wave velocity ($Vs^{30}$) and are developed considering deep soil data. The aim of this work is to examine the applicability of available amplification relations in the literature for shallow engineering bedrock sites by carrying out site response studies. Shear wave velocity of thirteen sites having shallow engineering bedrock have been selected for the study. In these locations, the depth of engineering bedrock (> 760 ${\pm}$ 60 m/s) is matched with the drilled bore hole. Shear wave velocity (SWV) has been measured using Multichannel Analysis of Surface Wave survey. These sites are classified according to the National Earthquake Hazards Reduction Program (NEHRP) classification system. Amplifications for an earthquake are arrived for these sites using empirical relations and measured SWV data. Site response analysis has been carried out in SHAKE using SWV and using synthetic and real earthquake data. Amplification from site response analysis and empirical relations are compared. Study shows that the amplification arrived using empirical relations does not match with the site response amplification. Site response amplification is much more than empirical values for same shear wave velocity.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.5
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• pp.336-342
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• 2006

Uniaxial stress in ail axisymmetric body is the simplest example of ultrasonic stress measurement. However, the birefringence theory cannot be applied for axisymmetric solids because the axisymmetric stress field in the body does not make shy velocity difference in SH waves propagating in the axisymmetric direction. Conventional ultrasonic technique using the time-of-flight method also needs ultrasonic lengths of the unstressed and stressed body, which is very impractical. In this paper, the birefringence effect in axisymmetric solids under uniaxial stress is formulated to evaluate the axial stress inside the solid without measuring tile ultrasonic length. Theoretical derivation for the birefringence characteristics in the axisymmetric solids is made using the longitudinal and shear waves instead of two horizontally polarized shear waves. Tension test is conducted for carbon-steel specimen to measure the birefringence coefficient and investigate the validity of the theory. It is observed from experimental results that the velocity difference in two differently polarized acoustic waves is proportional to the uniaxial stress in the axisymmetric solid with a good agreement with the theoretical value.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.5
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• pp.628-636
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• 1997

Flow visualization technique incorporating photochromic dye is used to study the flow characteristics of the gravity driven laminar wavy film. The film thickness and wave speed are successfully measured by flow visualization. As the inclination angle increases, the waves have higher peaks and lower substrate thickness. The measured cross stream velocity at the free surface is up to 10% of stream wise velocity, which shows enhanced mixing in the lump of the film. The measured stream wise velocity profiles are close to parabolic profile near the substrate and the peak but show significant velocity defect near the rear side of the wave. The measured wall shear rate distributions show good agreement with the previous workers' numerical results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.207-218
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• 2013

One of the input parameters in the evaluation of seismic performance of rockfill dams is shear-wave velocity of rock debris and clay core. Reliable evaluation of shear-wave velocity by surface-wave methods requires overcoming the problems of rock-debris discontinuity, material inhomogeneity and sloping boundary. In this paper, for the shear-wave velocity investigation of rockfill dams, SBF (Short-Array Beamforming) technique was proposed using the principles of conventional beamforming technique and adopted to solve limitations of the conventional surface-wave techniques. SBF technique utilizes a 3- to 9-m long measurement array and a far-field source, which allowed the technique to eliminate problems of near-field effects and investigate local anomalies. This paper describes the procedure to investigate shear-wave velocity profile of rockfill dams by SBF technique and IRF (Impulse-response filtration) technique with accuracy and reliability. Validity of the proposed SBF technique was verified by comparisons with downhole tests and CapSASW (Common-Array-Profiling Spectral-Analysis-of-Surface-Waves) tests at a railroad embankment compacted with rock debris.

• Journal of the Korean Geotechnical Society
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• v.33 no.5
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• pp.15-23
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• 2017

The evaluation of earthquake load on the surface is very important factor for the seismic reinforcement of existing building, and the magnitude of earthquake load depends on a shear wave velocity profile of soil under a building. To determine a shear wave velocity profile under a existing building, test method should be able to determine a reliable shear wave velocity profile under conditions such as heavy background noise and the small test area, and be sensitive to the variation of material property. In this research, HWAW (Harmonic Wavelet Analysis of Waves) method is applied to determine a shear wave velocity profile under a existing building. In this paper, through numerical simulations and field tests, the feasibility of the proposed method was shown.

• Journal of the Korean Geotechnical Society
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• v.21 no.4
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• pp.71-81
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• 2005

Surface wave techniques were initially based on 2-D plane waves and were later improved to the techniques based the 3-D based cylindrical waves. However, body-wave interference, near-field effect and limited technology in surface wave measurements restricted the use of 3-D cylindrical waves to the 1-D evaluation of subgrade stiffness. In this study, by the numerical simulation of SASW measurements, the dispersion properties of surface waves including vertical, horizontal Rayleigh waves and Love waves were thoroughly investigated in the 3-D domain, and a new filter criteria to minimize the near-field effect was established, which led to CAP (common-array-profiling)-SASW technique. The CAP-SASW technique enabled the evaluation of subgrade stiffness fur a specific subgrade segment, not for a whole section of measurement array. Therefore, a contour plot of subgrade stiffness with a ground-truth quality can be obtained by the CAP-SASW technique. The procedure proposed in this study was verified by comparing the shear-wave velocity profiles with the shear-wave velocity profiles of downhole testing at two geotechnical sites.

• The Journal of Engineering Geology
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• v.23 no.4
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• pp.503-510
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• 2013

Shear wave velocity is widely used as an parameter for investigating subsurface characteristics and for obtaining the design parameters based on theoretical equations. This study seeks to estimate the coefficient of shear wave velocity in Busan clay via laboratory tests. Eight specimens were extracted at depths of 10, 12, 15, 20, 22, 25, 30, and 31 m. The specimens were subjected to the consolidation test to determine the relationship between effective stress and shear wave velocity. The relationship shows a non-linear trend and is similar to the results of a previous study. The coefficient shows constant coverage and a relationship between ${\alpha}$ and ${\beta}$ is suggested. The results demonstrate that this coefficient could be used as a reference value to determine engineering parameters based on the shear wave velocity.