• Journal of the Korean Geotechnical Society
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• v.36 no.11
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• pp.21-33
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• 2020

Ground response analysis has been conducted for each borehole data in Pohang area, using 1D equivalent linear method program, to investigate the applicability of amplification factor to estimate peak ground acceleration. Earthquake motions for ground response analysis were prepared by matching response spectrums for return period of 500, 1000, and 2400 years suggested by seismic design code (MOIS, 2017). Ground survey data were acquired from Geotechnical Information DB System. It has been confirmed that response spectrum obtained from ground response analysis showed good agreement with those from seismic design code irrespective of ground classification. However, PGA (Peak Ground Accelerations) of ground response analysis did not coincide with PGA calculated using amplification factor suggested by seismic design code.

• The Journal of Engineering Geology
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• v.17 no.1 s.50
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• pp.49-55
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• 2007

Various away methods are required in the electrical resistivity survey in order to find anomalous zone reliably. Array methods are classified as several groups. Among these group, a curved survey along the fixed elevation is designed to increase the mobility of men and survey equipments at the rough terrain. Another method is performed at the survey using inclined, curved, and horizontal boreholes. A survey can also be conducted in an arbitrary location by measurements of potentials for a multi sources. The complex data acquired using various away methods are represented by a correct images reconstructed from the 3D inversion. The element division is applied to the region in which the boreholes are curved and inclined because of a spatial discrepancies between the coordinate of each electrode and the nodal point in a model. The resistivity images are obtained from a good agreement for the anomalous zones in open slope and in survey using an inclined borehole.

• Geophysics and Geophysical Exploration
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• v.9 no.1
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• pp.93-101
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• 2006

In this study, we propose a joint inversion method, using genetic algorithms, to determine the shear-wave velocity structure of deep sedimentary layers from receiver functions and surface-wave phase velocity. Numerical experiments with synthetic data indicate that the proposed method can avoid the trade-off between shear-wave velocity and thickness that arises when inverting the receiver function only, and the uncertainty in deep structure from surface-wave phase velocity inversion alone. We apply the method to receiver functions obtained from earthquake records with epicentral distances of about 100 km, and Rayleigh-wave phase velocities obtained from a microtremor array survey in the Kanto Plain, Japan. The estimated subsurface structure is in good agreement with the previous results of seismic refraction surveys and deep borehole data.

• Proceedings of the Korean Geotechical Society Conference
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• 2007.09a
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• pp.266-292
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• 2007

Round Robin Test (RRT) on ground response analyses was conducted for three sites in Korea based on several site investigation data, which include borehole logs with the N values from standard penetration test (SPT) for all three sites and additionally cone tip resistance profiles for two sites. Three input earthquake motions together with the site investigation data were provided for the RRT. A total of 12 teams participating in this RRT presented the results of ground response analyses using equivalent-linear and/or nonlinear method. Each team determined input geotechnical properties by using empirical relationships and literatures based on own judgment, with the exception of the input motions. Herein, the characteristics of input motions were compared in terms of the frequency and period, and the selection of the depth to bedrock, on which the motions is impinged, was discussed considering geologic conditions in Korea. Furthermore, a variety of geotechnical properties such as shear wave velocity profiles and soil nonlinear curves were investigated with the input properties used in this RRT.

• Explosives and Blasting
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• v.22 no.3
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• pp.103-111
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• 2004

The existing methods that can be adopted for measuring joints involve either to use borehole or photogrammetry. Due to restricted space, acquisition of data in limited area, and measurement errors, above methods have limitations acquiring the objective and correct results. To get over defects of existing joint measurement methods, joints have been measured using 3D-Laser scanner with accuracy and efficiency. This research aims to investigate an accuracy and applicabiliy of 3D-Laser scanner for measuring rock slope joints. Measurement of rock slope joints has been executed using 3D-Laser scanner & clinometer and then, results from both methods are compared. Results from both methods indicate that they show nearly equal features for joint distributions and numbers of joint information obtained by 3D-Laser scanner are much more than ones measured using clinomer. Therefore, 3D-Laser scanner turns out to be very effective by the fact that it contributes to reduce investigation costs & periods, objectify data from rock slope joints.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.63-67
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• 2008

Geostatistical inverse approach using geophysical data was applied to indirectly make the RMR classification at points apart from boreholes. The geostatistical appoach was usually used to find optimized estimation which supports two or more different physical properties at unsampled points. However, in this study, an approach to solve inverse problem was proposed. The primary variable, RMR values obtained at known boreholes, is geostatistically simulated with many realization at pre-defined grid point according to the variogram model. The simulated values are sequentially compared with the physical property resulted from geophysical survey at an arbitrary grid point, and the most similar one is chosen. This process means that the spatial distribution of primary variable, RMR, is conformed well to the original pattern of the borehole observation, and ensure to fit the geophysical survey result to reflect the correlation between different physical properties.

• Geophysics and Geophysical Exploration
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• v.15 no.4
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• pp.190-198
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• 2012

A series of density log data were obtained from the standoff experiments made in the four physical model boreholes of different densities, and the properties of spine and rib curves have been derived by the analysis of the gamma-gamma data. Particularly, the shape of gamma ray propagation path between source and detector, the geometrical property of spine and rib curves, the influence of borehole density and the detector combination on the properties of the curves, and the adequate detector combination for standoff compensation could be discussed. It was also confirmed that spine and rib slopes can be expressed as proportional to source-to-detector distance ratio between far and near detectors. The result of this experiment was also effectively applied for understanding the basic concept of spine and rib slopes.

• Journal of Soil and Groundwater Environment
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• v.17 no.5
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• pp.56-67
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• 2012

In the present study, an enhanced subsurface prediction algorithm based on a non-parametric geostatistical model and a history matching technique through Gibbs sampler is developed and the iterative prediction improvement procedure is proposed. The developed model is applied to a simple two-dimensional synthetic case where domain is composed of three different hydrogeologic media with $500m{\times}40m$ scale. In the application, it is assumed that there are 4 independent pumping tests performed at different vertical interval and the history curves are acquired through numerical modeling. With two hypothetical borehole information and pumping test data, the proposed prediction model is applied iteratively and continuous improvements of the predictions with reduced uncertainties of the media distribution are observed. From the results and the qualitative/quantitative analysis, it is concluded that the proposed model is good for the subsurface prediction improvements where the history data is available as a supportive information. Once the proposed model be a matured technique, it is believed that the model can be applied to many groundwater, geothermal, gas and oil problems with conventional fluid flow simulators. However, the overall development is still in its preliminary step and further considerations needs to be incorporated to be a viable and practical prediction technique including multi-dimensional verifications, global optimization, etc. which have not been resolved in the present study.

• Journal of the Korean earth science society
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• v.43 no.1
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• pp.188-198
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• 2022

Some deep faults do not reach the ground surface and are seldom recognized. Gokgang Fault area in the east of the Heunghae area of the Pohang basin has been selected to confirm the feasibility of the Horizontal-to-Vertical Spectral Ratio (HVSR) approach to identify blind faults. Densely spaced microtremor data have been acquired along two lines in the study area and processed to obtain resonance frequencies. An empirical relationship between the resonance frequency and the bedrock depth was proposed using borehole data available in the study area. Resonance frequencies along two lines were then converted to bedrock depths. The resulting depth profiles show significant lateral variations in the bedrock depth. As expected, considerable variation in the resonance frequency is observed near the Gokgang fault. The depth profiles also present additional significant variations in the resonance frequencies and the bedrock depths. The feature is presumably related to a blind fault that is previously unknown. Therefore, this case study confirms the feasibility of the HVSR technique to identify faults otherwise not recognized on the surface.

• Journal of the Korean Geotechnical Society
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• v.23 no.11
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• pp.27-37
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• 2007

Downhole seismic method is very economic and easy to operate because it uses only one borehole and simple surface source to obtain the shear wave velocity profile of a site. In this study, automatic shear wave source was developed for efficient downhole seismic testing. This source is motor-spring type and easy to control. It can lessen the labor of operator and the working time. Moreover, it can provide better and repetitive signals for data interpretation. By combining developed automatic source with automatic receiver system, PC based data acquisition system, advanced managing program, and semi-automatic downhole performing system were constructed. Through comparison test with manual source, advantages of automatic source were verified. Constructed semi-automatic downhole testing system including automatic shear wave source was applied to the soft soil site. The applicability and reliability were verified and the importance of automating testing system for obtaining reliable result was emphasized.