• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.3
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• pp.257-267
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• 2008

Tunnels acting as drains involve groundwater-related problems such as deterioration of drainage systems or leakage through the linings. Generally initial and minor leakage problems can not be recognized by naked eyes. When the leakage over the linings is noticed, damages to structures and facilities have already occurred and could be considerable. Therefore it is vital to recognize initial leakage as early as possible and provide appropriate measures. Detection of leakage under operation requires installing piezometer. However, that may cause destruction of water proofing sheet which is generally not allowed. In this study electric resistivity method, one of the geophysical surveys, was adopted to detect possible leakage through tunnel linings. Physical lining models were made in the laboratory. The electric response was monitored for varying hydraulic conditions. It is shown that the method is very useful to detect initial leakage and monitor the malfunction of drainage system. Furthermore the method can also be used to check the quality of any repairing works of linings.

• Geophysics and Geophysical Exploration
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• v.7 no.3
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• pp.197-206
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• 2004

Because the minute displacement of ground accompanied by excessive pumping of groundwater at specified site is mainly generated from ill-balancing of water budget within groundwater basin, It is necessary to monitor the variation of micro-subsidence for a long time at representative points. We made up the conceptual model using two-dimensional electrical resistivity survey and three-dimensional soil profile consisted of loam and sand. In verifying the reliability of this conceptual model using numerical modeling for ground settlement and groundwater flowing, two-dimensional electrical resistivity survey with short distance of electrode following soil sampling with hand auger would be useful for interpreting hydrogeological structure related to the minute displacement of ground consisted of loam and sand.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.47-50
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• 2008

Streamer resistivity surveys in shallow marine environments were carried out to analyze sediment characteristics at the bottom of reservoir. Because the resistivity values of reservoir water are very low and those of sediment are relatively high, apparent resistivity values increase with depth. And it is necessary to eliminate the apparent resistivity data decreased highly when the number of separation increases. According to the repeated data processing, we proposed the resistivity ratio of upper-to-lower layer is $0.6{\sim}0.8$ because the RMS error of inversion leads to the minimum in these range. As a result of the inversion for two- and three-layer model, the inversion including water depth is proved to be more effective than conventional method.

• The Journal of Engineering Geology
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• v.7 no.2
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• pp.113-126
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• 1997

Electrical resistivity methods of dipole - dipole array profiling and Schiumberger array sounding were tested on a segment of the Woraksan granitic batholith for the research into the imaging of irregular attitudes of fracture zones in the crystaaline rock in terms of processing and interpretation schemes. By the dipole - dipole array method, inhomogeneities such as small scale of fracture zones were properly delineated down at some depth even within hard rock environment. Fracture zones were interpreted to be at the boundaries between the high amplitude zone and very low amplitude zone in the resistivity plot and they were also successfully outlined in two - dimensional layer and pseudo - three - dimensional volume constructed by the incorporation of vertical sounding data. The surface location of the fracture zones was correlated by the zero - crossing point in the VLF(very low frequency) electromagnetic data. Pseudo - three - dimensional attitudes of fracture zones were efficiently illuminated by optimum projection angle. The mean of bulk resistivity for the Woraksan granite and the near fracture zones is estimated to be approximately of 4,000 ohm - m which is much higher than the value of 700 ohm - m for the Rwachunri limesilicate environment. This difference is due to both the rock type, i.e., biotite granite vs limesilicate, and the occurrence of secondary openings of fold and fault associated with the intrusion of granite. In this study statistical analyses on the resistivity color plot were performed in terms of three representative statistical moments, i.e., standard deviation, skewness, and kurtosis. The fracture zones in the standard deviation plot were characterized by the higher value, compared to the value of homogeneous portion. The upper boundary of the high resistivity zone was also successfully delineated in the skewness and kurtosis plots.

• Journal of the Korean Geophysical Society
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• v.2 no.3
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• pp.217-224
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• 1999

Although faults can be found by geological surveys, the surface traces of faults are not easily discovered by traditional geological surveys due to alluvia. In and around faults and fracture zones, the electrical resistivity appears to be lower than that of the surroundings due to the content of groundwater and clay minerals. Therefore, electrical resistivity surveys are effective to search buried faults and fracture zones. The dipole-dipole array electrical resistivity surveys, which could show the two dimensional subsurface electrical resistivity structure, were carried out in two areas, Yongdang-ri, Woongsang-eup, Yangsan-si, Kyungsangnam-do and Malbang-ri, Woedong-eup, Kyungju-si, Kyungsangpook-do. The one was next to the Dongrae Fault and the other near the Ulsan Fault was close to the region in which debatable quaternary fault traces had been found recently. From each measured data set, the electrical resistivity cross-section was obtained using the inversion program the reliability of which was analyzed using analytic solutions. A low resistivity zone was found in the inverted cross-section from the Yongdang-ri area survey data, and two low resistivity zones were found in that from the Malbang-ri area survey data. They were almost vertical and were 15∼20 m wide. Accounting the shape and the very low resistivity values of those zones (<100 Ωm)in the inverted section, they were interpreted as fracture zones although they should be proven by trenching. The reliability of the interpretation might be improved by adding some more parallel resistivity survey lines and interpreting the results in 3 and/or adding other geophysical survey.

• 한국지구물리탐사학회:학술대회논문집
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• 2009.10a
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• pp.93-98
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• 2009

Comprehension of physical properties distribution of underground cavity must be made primarily to show the clear image of the state of the cavity. A physical scale model experiment is executed assuming that underground cavity in filled with air or water of different ratio. The state of cavity wall is considered wet. Cavity model is made of agar. As a experimental result, even if the cavity wall is wet, high air and water ratio cavity shows high anomaly.

• The Journal of Engineering Geology
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• v.29 no.2
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• pp.137-151
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• 2019

Geophysical exploration techniques are effective for monitoring changes in the ground condition around the excavation project to prevent subsidence risks during excavation work, therefore, improving analysis techniques is required for applying and supplementing various geophysical exploration technologies. In this study, a field-scale on-site test was conducted to detect possible ground subsidence hazards and areas of relaxation zone that may occur during excavation work and due to underground water level changes. In order to carry out the field test, a real-scale excavation test bed was constructed and the geophysical exploration methods, such as electrical resistivity survey and multi-channel analysis of surface wave (MASW) survey for urban sites condition, have researched for optimal geophysical exploration parameter, design and correlation analysis between the results by reviewing the validity of each individual geophysical exploration and modeling. The results of this study showed the impact of each geophysical exploration on the relaxation zone and, in particular, the location of the underground water surface and the effects of excavation were identified using electrical resistivity survey. Further research on modeling will be required, taking into account the effects of excavation and groundwater.

• Geophysics and Geophysical Exploration
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• v.11 no.4
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• pp.335-342
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• 2008

Electrical resistivity and seismic refraction surveys were conducted to investigate geologic structures and geotechnical characteristics of the subsurface, along with rock physical property measurements in Dokdo island. The survey results in Seodo island show that the fault adjacent to the fisherman's shelter is a normal fault and extended towards the NW direction, and that Bedded Lapilli Tuff in the downstream was more severely influenced by weathering and erosion than Trachy Andesite II in the upstream of the survey area. In Dongdo island, Trachy Andesite III and Scoria Bedded Lapilli Tuff were severely weathered and eroded, considered as weathered to soft rock formations, and their weathered zone becomes thicker towards the antiaircraft facility in the NE direction of the survey area. The study results also illustrate that Trachyte and Trachy Andesite are hardest, Massive Tuff Breccia is next, and Stratified Ash Tuff is the most soft rock in Dokdo island.

• Geophysics and Geophysical Exploration
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• v.2 no.2
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• pp.96-103
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• 1999

Most of saline water inousions have been diagnosed by geophysical or geochemical approach independently. The objective of this study is to provide the effective method to detect the saline water intrusion on the ground water in the vicinity of seashore using these two methods. Schulumberger sounding, frequency domain electromagnetic sounding and geochemical analysis of ground water were carried out to explore saline water intrusion. Schulumberger sounding was implemented in dry surface condition before irrigation water was introduced into the field, while electromagnetic sounding was carried out in wet ground condition after the irrigation. The purpose of duplicated measurements on the equivalent spot at different times was to investigate the variation of anomaly zone depending on the amount of ground water. It was possible to discriminate the anomalous zone due to high water saturation from the low electric resistivity zone by high salt concentrations through this way. For the verification of the geophysical result, the ground water samples in the study area were collected and analysed at the 23 points near the measuring spots. The groundwater at the spot nearest to the sea water intrusion identified by geophysical method indicates higher salinity than the standard limit concentration for agricultural irrigation water (250 mg/1). Isotope analysis of $D({^2}H)$ vs. is ${^18}O$ and PCA analysis were used to discriminate the anthropogenic pollution from those of high salinity from sea water intrusion.

• Journal of the Korean Geotechnical Society
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• v.38 no.10
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• pp.49-60
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• 2022

Underground urbanization appears to be a promising solution in response to the shortage of construction sites in the above-ground space. In this context, an accurate evaluation of a construction site ensures the long-term performance of geosystems. This study characterizes potential sites for complex plants built in underground space using geophysical methods (i.e., seismic refraction exploration and electrical resistivity survey) and in situ tests (i.e., standard penetration tests (SPTs) and downhole tests). SPTs are conducted in nine boreholes BH-1-BH-9 to estimate the groundwater level and vertical distribution of geological structures. The seismic refraction method enables us to obtain the elastic wave velocity and thickness of each soil layer for each cross-sectional area. An electrical resistivity survey conducted using the dipole array method provides the electrical resistivity profiles of the cross-sectional area. Data obtained using geophysical techniques are used to assess the classification of the soil layer and bedrock, particularly the fracture zone. This study suggests that geotechnical information using in situ tests and geophysical methods are useful references to design an underground complex plant construction.