• KCID journal
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• v.13 no.2
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• pp.254-261
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• 2006

We applied electrical resistivity survey using modified pole-pole array and small-loop electromagnetic survey to delineate the zone of seawater inflow through a tide embankment. The tide embankment is generally affected by tidal variation and has low resistivity characteristic due to the high saturation of seawater. For this reason, the electrical resistivity survey using modified pole-pole array, which is relatively more effective to the conductive media, was carried out to detect the inflow zone of seawater and small-loop electromagnetic survey using multi-frequency with 300 to 20,010 Hz was conducted. As a result of both electrical resistivity survey using modified pole-pole array and small -loop electromagnetic survey, these survey methods are found to be quite effective for investigation of seawater inflow zone in the sea dike.

• Geophysics and Geophysical Exploration
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• v.18 no.3
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• pp.115-124
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• 2015

A modified electrical resistivity survey has been suggested and applied to a leakage detection problem of concrete barrage. We suggest the modified electrical resistivity methods using electrodes floating on the water and apply line current sources instead of conventional point current sources in order to facilitate simple analysis. In addition, the study introduced the following three variations of modified electrode array: Direct potential array, Parallel potential array and Cross potential array. These arrays were tested and investigated through numerical experiment, physical model experiment and geophysical field exploration in order to verify their applicability to the water leakage detection of a concrete barrage. When water leakage occurred, all kind of array operations demonstrated distinct changes of aspects of potential difference in graphs obtained by not only the numerical and physical model experiments but also geophysical field exploration. Therefore, this modified electrode arrays of electrical resistivity survey, which has been adapted to the concrete barrage, has been found to be a useful method to detect water leakage.

• Geomechanics and Engineering
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• v.19 no.1
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• pp.93-104
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• 2019

Anomalies and/or fractured grounds not detected by the surface geophysical and geological survey performed during design stage may cause significant problems during tunnel excavation. Many studies on prediction methods of the ground condition ahead of the tunnel face have been conducted and applied in tunneling construction sites, such as tunnel seismic profiling and probe drilling. However, most such applications have focused on the drill and blast tunneling method. Few studies have been conducted for mechanized tunneling because of the limitation in the available space to perform prediction tests. This study aims to predict the ground condition ahead of the tunnel face in TBM tunneling by using an electrical resistivity tomography survey. It compared the characteristics of each electrode array and performed an investigation on in-situ tunnel boring machine TBM construction site environments. Numerical simulations for each electrode array were performed, to determine the proper electrode array to predict anomalies ahead of the tunnel face. The results showed that the modified dipole-dipole array is, compared to other arrays, the best for predicting the location and condition of an anomaly. As the borehole becomes longer, the measured data increase accordingly. Therefore, longer boreholes allow a more accurate prediction of the location and status of anomalies and complex grounds.

• Geophysics and Geophysical Exploration
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• v.4 no.3
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• pp.59-69
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• 2001

Five kinds of modified electrode arrays were proposed to overcome the weak points of the commonly used arrays using dipole and/or pole in two-dimensional resistivity surveys. The modified pole-pole array was suggested to overcome the inefficiency caused by distant earthing in pole-pole array. Four kinds of modified arrays using dipole were designed to enhance the signal-to-noise ratio of the conventional dipole-dipole and pole-dipole arrays through boosting up the measured potential difference. In the numerical experiments using the two-dimensional modeling and inversion, the effects of the ambient electrical noise and the resolving power were examined and the results showed the validity of the modified arrays proposed in this study.

• Geomechanics and Engineering
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• v.20 no.6
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• pp.475-484
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• 2020

The prediction of the ground conditions ahead of a tunnel face is very important, especially for tunnel boring machine (TBM) tunneling, because encountering unexpected anomalies during tunnel excavation can cause a considerable loss of time and money. Several prediction techniques, such as BEAM, TSP, and GPR, have been suggested. However, these methods have various shortcomings, such as low accuracy and low resolution. Most studies on electrical resistivity tomography surveys have been conducted using numerical simulation programs, but laboratory experiments were just a few. Furthermore, most studies of scaled model tests on electrical resistivity tomography were conducted only on the ground surface, which is a different environment as compared to that of mechanized tunneling. This study performed a laboratory experimental test to extend and verify a prediction method proposed by Lee et al., which used electrical resistivity tomography to predict the ground conditions ahead of a tunnel face in TBM tunneling environments. The results showed that the modified dipole-dipole array is better than the other arrays in terms of predicting the location and shape of the anomalies ahead of the tunnel face. Having longer upper and lower borehole lengths led to better accuracy of the survey. However, the number and length of boreholes should be properly controlled according to the field environments in practice. Finally, a modified and verified technique to predict the ground conditions ahead of a tunnel face during TBM tunneling is proposed.

• Geophysics and Geophysical Exploration
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• v.19 no.4
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• pp.200-211
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• 2016

To support cross potential array and direct potential array, the array for leakage detection of all kinds of water facilities is proposed and it is named as the D-Lux array. The D-Lux array data are arranged to a coloured matrix and it is called the D-Lux view. Low potential difference of anomalous zone shown in D-Lux view implies the indication of leakage zone. Furthermore, for an intuitive interpretation of D-Lux array, equipotential distribution map is made by using D-Lux and direct potential array data. Equipotential distribution map makes us possible to predict import point, export point and the path of water leakage that we could have not anticipated in D-Lux view and the graphs. The water tank experiment and numerical analysis were carried out as preparatory experiment and the field explorations were conducted at a concrete weir and a fill dam. As a result, effective and specific detection of leakage path was possible for the concrete weir and the fill dam.