• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.135-146
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• 2003

Uphole test is a seismic field test using receivers on ground surface and a source in depth. In this paper, the uphole test using SPT(standard penetration test) which is economical and reliable for obtaining shear wave velocity profile was introduced. In the proposed uphole test, SPT sampler which is common in site investigation, was used as a source and several 1Hz geophones in line were used as receivers. Test procedures in field and interpretation methods for obtaining interval times and for determining shear wave velocity profile considering refracted ray path were introduced. Finally, uphole test was performed at three sites, and the applicability of the proposed uphole test was verified by comparing wave velocity profiles determined by the uphole test with the profiles determined by downhole test, SASW test and SPT-N values.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.48-51
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• 2004

This paper is to study the response of flat plate slab-column connections consisting of various types of shear reinforcement and steel plate subjected to gravity loadings, mainly punching shear forces using the non-destructive testing, spectral analysis of surface waves and structural experiments. The base specimen failed due to punching shear generated from the gravity. The three other types of slab shear reinforcement and steel plate showed effective in resisting punching shear for these types of connections under gravity loading. This study has focused in evaluating the velocity response of a Surface wave during the early age as the poured concrete specimens have been hardened, the possibility of damage detection in the slab-column connection and the relationship between the punching shear forces and the surface wave velocities under the condition that the punching shear forces had gradually increased until the flat plate slab in slab-column connection had been failed.

• Journal of Biosystems Engineering
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• v.23 no.6
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• pp.615-620
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• 1998

The nondestructive internal quality evaluation of agricultural products has been strongly required from the needs for individual inspection. In recent, ultrasonic wave has been considered as a solution for this problem. It transmit well through most materials and can handle safely and easily. However, specially in a watermelon, it is known that general frequency band (higher than 20kHz) ultrasonic waves do not transmitted well due to severe attenuation. The objectives of this study were to find out the proper waveform and frequency of the ultrasonic waves that transmit well inside the watermelon, and to analyze the transmitted waveform in order to make clear the structure of wave propagation in watermelon. The result of several experiments showed that 2kHz shear wave was the most suitable for the detection of internal cavity in the watermelon. Also, it was found that the surface wave did not influence the directly transmitted bulk wave. These results could be a basis of application of ultrasonic wave on the evaluation of internal quality of the watermelon.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.287-291
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• 2005

Two-dimensional velocity tomograms of P- and S-waves were obtained by inverting traveltimes of first arrivals. The two sections of shear-wave velocity show similar features as a whole, with smaller values on the section from surface wave dispersions. Difficulties in picking SH-wave phases due to noise and later arrivals than P waves and PS converted waves are experienced. In addition, a flat layer model based on the surface wave inversion prohibits applications of the method where sgear wave velocities vary strongly in the lateral direction.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.3
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• pp.594-599
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• 2011

A SAW strain sensor based on Shear Horizontal wave with an 92 MHz central frequency was developed. It consists of SAW sensor, PCB substrate and bonding material (Loctite 401). External force applied to PCB substrate bonded to a piezoelectric substrate induces strain at the substrate surface, which causes changes in the elastic constant and density of the substrate and hence the propagation velocity of the SAW. The change in the velocity of the SAW result in a frequency shift of the sensor and by measuring a frequency shift, we can extract the strain induced by the external force. The $41^{\circ}$ YX $LiNbO_3$ was used because it has a Leaky shear horizontal(SH) wave propagation mode and a high electromechanical coupling coefficient ($K^2$=17.2%). And to compare with Rayleigh wave mode, $128^{\circ}$ YX $LiNbO_3$ was used. And to make a stable and low insert loss, Split IDT structure was used. The obtained sensitivity and linearity of the SAW strain sensor in the case of Split IDT were measured to be 17.2 kHz / % and 0.99, respectively.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.1
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• pp.141-152
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• 2015

The objective of this study is to estimate shear wave velocity of rockfill materials by making practical use of the micro-earthquake records which are ordinarily obtained at a domestic rockfill dam and to verify its applicability. Micro-earthquake records were obtained at the site of Heongseong dam and Soyanggang dam, which are the existing multi-purpose dams in Korea. In the previous study, the fundamental periods of each dam were already evaluated by analyzing the response spectrum of the observed records. In this study, numerical analyses varying shear moduli of rockfill zone were carried out using the acceleration histories measured at the abutment as input ground motions. From comparison between the fundamental periods calculated by numerical analyses and measured records, the shear wave velocities with depth were estimated. It is found that the effect of different earthquake events on shear wave velocity estimation for the target dam materials is negligible and the shear wave velocity can be consistently evaluated. Furthermore, comparing the shear wave velocity with the previous researchers' empirical relationships and field test results, applicability of suggested method is verified. Therefore, in case that it is impossible to conduct field tests and estimation is preliminary, the suggested method can be practically used.

• Journal of the Korean GEO-environmental Society
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• v.15 no.9
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• pp.37-45
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• 2014

An embedded length of monopile caused by a scouring should be evaluated to monitor the stability of offshore foundations, because offshore foundations are affected by horizontal load. The objective of this study is to evaluate the scouring around offshore foundation by using electrical resistivity and to estimate ground stiffness by using shear wave tomography. The electrical resistivity profiles and shear wave tomography were measured according to the scour depth of model ground prepared with sand and cement. Several electrodes and bender elements were used to measure the electrical resistivity and shear waves, respectively. The electrode sets are attached on the monopile surface and bender elements are arranged in $7{\times}7$ arrays by using nylone frames. The electrical resistivity profiles and shear wave tomography are acquired by laboratory experiment. Maximum scour depth was estimated by electrical resistivity profiles and the ground stiffness of model ground was estimated by shear wave tomography. This study suggests that the electrical resistivity profiles and shear wave tomography may be useful for monitoring the stability of the offshore foundations.

• Journal of the Korean earth science society
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• v.21 no.6
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• pp.675-682
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• 2000

25 seismic shot gathers were obtained to study the two dimensional subsurface shear wave velocities in a landfilled area near the Keum river estuary. Borehole(BH#1 and BH#2) tests at two sites were made in the same area. Standard Penetration Tests were also performed at the same time. The 2-D shear wave velocity structure resulted from the inversion of the seismic data shows that the subsurface of the studied area consists of the upper 1${\sim}$3 meter thick layer(200 m/sec${\sim}$700 m/sec), the middle 5${\sim}$8 m thick low velocity layer(100 m/sec${\sim}$400 m/sec), and the lower layer of 1000m/sec or higher shear wave velocities. The thickness of the low velocity layer decreases from the BH #1 site to the BH #2 site. The depth to the basement also decreases toward the BH #2 site. The examination of the S wave velocity structure, the description of the geologic contents, and the Standard Penetration Test values indicate that the middle layer of low shear wave velocity may be related to the clay content of the layer. On the other hand, the Standard Penetration test values increase with depth, showing no significant relationship with the geologic contents of the subsurface. This study shows that the inversion of surface waves can be effective in the study of the shear wave velocity, especially in the area where low velocity layers can be found. The method of inversion of surface waves also can be used as a viable technique to overcome the limit of the seismic refraction method.

• Economic and Environmental Geology
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• v.52 no.6
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• pp.555-560
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• 2019

One-dimensional shear wave velocity structure of North Korea is constrained using short (2-sec) to long period (30-sec) Rayleigh waves generated from four seismic events in China. Rayleigh waves are well recorded at the five broadband seismic stations (BRD, SNU, CHNB, YKB, KSA) which are located near to the border between North and South Korea. Group velocities of fundamental-mode Rayleigh waves are estimated with the Multiple Filter Analysis and refined by using the Phase Matched Filter. Average group velocity dispersion curve ranging from 2.9 to 3.2 km/s, is inverted to constrain the shear wave velocity structures. Relatively low group velocity dispersion curves along the path between the events to BRD at period from 4 to 6 seconds may correspond to the sedimentary sequence of the West Korea Bay Basin (WKBB) in the Yellow Sea. The low velocity zone in deep layers (14-20 km) may be related to the deep sedimentary structure in Pyongnam basin. The fast shear wave velocity structure from the surface to the depth of 14 km is consistent with the existence of metamorphic rocks and igneous bodies in Nangrim massif and Pyongnam basin.

• 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.