• Geophysics and Geophysical Exploration
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• v.12 no.2
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• pp.215-220
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• 2009

Cement based mortars are widely used to improve the soft ground of a dam site, highway construction, and karst voids. The mechanical properties of the mortar are well documented in literature, however very limited work is done on their physical properties such as electrical resistivity which is considered as one of the most important physical property known while improving the soft grounds. In this paper, electrical resistivity of the Portland cement mortars is examined by employing the Wenner technique. Cylindrical specimens with various water/cement ratios (w/c) ranges from 0.35, 0.45, 0.50 and 0.65 were cast and tested. The test results showed that the electrical resistivity of the mortar increases with increasing curing time and decreases with increasing water content and w/c. A reasonable, good relation was found between electrical resistivity and compressive strength of mortar.

• Geophysics and Geophysical Exploration
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• v.21 no.2
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• pp.82-93
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• 2018

Resistivity monitoring data at embankment dams are affected by the seasonal temperature variation. Especially when the seasonal temperature variation is large like Korea, the temperature effects may not be ignored in the longterm resistivity monitoring. Therefore, temperature effects can make it difficult to accurately interpret the resistivity monitoring data. In this study, through analyzing the time series of ground temperature collected at an embankment dam, ground temperature variations are calculated approximately. Then, based on the calculated temperature profile with depth, the inverted resistivity model of the embankment dam is corrected to remove the temperature effects. From these corrections, it was confirmed that the temperature effects are significant in the upper, superficial part of the dam, but can be ignored at depth. However, temperature correction based only on the temperature distribution in the dam body cannot remove the temperature effect thoroughly. To overcome this problem, the effect of temperature variation in the reservoir water seems to be incorporated together with the air temperature variation.

• Geophysics and Geophysical Exploration
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• v.13 no.4
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• pp.388-396
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• 2010

As a part of basic studies on monitoring and saturation estimation of carbon dioxide ($CO_2$) storage using resistivity survey, laboratory experiment has been conducted to measure the change of the electrical resistivity through repeated experiments of supercritical $CO_2$ and brine water injection into homogeneous and heterogeneous sandstones. The $CO_2$ saturation is estimated by using resistivity index based on the resistivity measurements. The experimental results of two types of sandstones show that the effect of pore structure in the rock and the effect of contained clay minerals in the rock can be affected to calculate the $CO_2$ saturation. The result can be useful to evaluate the $CO_2$ saturation based on resistivity survey at the site where $CO_2 sequestrates.

• Journal of the Korean Geotechnical Society
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• v.26 no.4
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• pp.59-68
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• 2010

Piping, a common form of internal embankment erosion, is caused by progressive movement of soil particles through an embankment. The phenomenon commonly occurs with precursory signs of development of fractures in dam structures, but also occurs without any noticeable signs in dams that showed satisfactory dam performance for several years, due to dissolution of soluble material in an embankment. While piping accounts for nearly 50% of the causes for dam failure, few studies have been made for systematic evaluation of the phenomenon. In this study, we attempted to monitor the changes in electrical resistivities of fill-dam material while a saddle dam is dismantled for the construction of emergency spillways of Daechung dam. Two artificial subhorizontal boreholes were drilled into the embankment structure to simulate piping along the two artificial flow channels. Monitoring of changes in electrical resistivity showed an increase in resistivity values during piping. Thus, the investigation of resistivity over time could be an effective method for piping prediction.

• Geotechnical Engineering
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• v.14 no.4
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• pp.91-102
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• 1998

Electrical resistivity method, one of the most widely used geophysical prospecting methods. has been usually applied to explorations for groundwater and underground resources. However, it has been extending its scope to civil & environmental engineering areas since it twas been developed so as to image underground structures effectively. A FEM algorithm for the dipole-dipole array was developed to correct topographic effects which have a serious influence on electrical methods. Applicability of the electrical resistivity imaging technique to civil & environmental engineering areas was verified through three case histories in this study First, thickness of soil layers was profiled to judge the possibility of developing borrow-pits tn an industrial complect site. Second, weak zones such as fractures and coal seams were detected to provide geological information for design and construction in a high mountain tunnel site. Third, horizontal/vertical distribution of the contaminated zone and depth of waste disposal were delineated in a completed industrial waste disposal site.

• Geophysics and Geophysical Exploration
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• v.11 no.3
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• pp.214-220
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• 2008

The distortion effect of electrical response for two-dimensional (2-D) DC resistivity method was verified in terms of 2-D inversion result of synthetic data obtained by three-dimensional (3-D) modeling, which is frequently applied to assess the safety of center core-type fill dam structure. The distortion effect is due to 2-D interpretation for 3-D structure. By the modeling analysis, we found that the water level is correctly described in the resistivity section around the middle part rather than each end side of the embankment due to the 3-D terrain effect, when the material of the embankment is assumed as horizontally uniform. And when we set the slope of outer rock fill part as uniform. the sharper the slope of the center core is, the more similar the resistivity section reflects. On the other hand, when the slope of the rock fill is steep, the resistivity section shows the water level at lower position than the real one, and the 3-D distortion effect at the end side of the embankment was enhanced.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2001.09a
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• pp.212-215
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• 2001

남악지역에 분포하는 조간대 퇴적층의 층서구조와 퇴적심도 및 기반암의 단열구조를 파악하기 위한 전기비저항탐사를 실시하였다. 조간대 퇴적물에서 비저항은 하부로 갈수록 증가하며 대부분 3.0 Ohm-m이하의 비저항으로 고비저항의 기반암의 기반암과 뚜렷한 경계를 보여준다. 퇴적층의 층후는 퇴적지 중앙부에서 30m를 최대로 북쪽 (고해안선)과 남쪽 (영산강)으로 갈수록 감소하는 경향을 보여주는데 선행 조사된 시추결과와 일치한다. 일부 지역의 전기비저항 해석단면과 시추단면에서 견고한 점토질 (stiff)의 지층이 분포하는데 이 지층은 북서-남동 방향의 고해안선과 나란하게 분포한다. 이것은 퇴적물을 공급한 흐름의 방향과 조간대의 확장방향이 북서-남동 방향임을 지시한다. 기반암의 단열구조로 판단되는 저비저항대는 조사지역의 동부에 집중되어 있으며 단열대의 연장방향은 북서-남동 방향이 우세하다.

• The Journal of Engineering Geology
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• v.30 no.1
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• pp.31-42
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• 2020

Electrical resistivity and downhole seismic surveys were conducted together with bore investigations and well-logging to examine subsurface structures in small-scale landslides at Sinjindo-ri, Geunheung-myeon, Taean-gun, Chungcheongnam-do, Republic of Korea in 2014. On the basis of the low N-values at depths of 5~7 m in borehole BH-2, downhole seismic and electrical dipole-dipole resistivity surveys were performed to delineate geological weak zones. The low-resistivity zones (<150 Ω·m) measure ~8 m in thickness and show a close depth correspondence to weathered soils consisting mainly of silty clays as identified from the bore investigations and well-logging data. Compared with weak zones in borehole BH-1, weak zones in BH-2 are characterized by lower densities (1.6~1.8 g/㎤) and resistivities (<150 Ω·m) and greater variation in Poisson's ratio. These observations can be explained by the presence of wet silty clays rich in weathered soil material that have resulted from heavy rainfall and rises in groundwater level. Downslope movements are probably caused by the sliding of wet clay that acts to reduce the strength of the weathered soil.

• The Journal of Engineering Geology
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• v.24 no.4
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• pp.525-534
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• 2014

Environmental problems typically occurring in abandoned mine lands (AML) include: contaminated and acidic surface water and groundwater; stockpiled waste rock and mill tailings; and ground subsidences due to mining operations. This study examines the effectiveness of various geophysical techniques for mapping potential hazard and contaminated zones. Four AML sites with sedimentation contamination problems, acid mine drainage (AMD) channels, ground subsidence, manmade liner leakage, and buried mine tailings, were selected to examine the applicability of various geophysical methods to the identification of the different types of mine hazards. Geophysical results were correlated to borehole data (core samples, well logs, tomographic profiles, etc.) and water sample data (pH, electrical conductivity (EC), and heavy metal contents). Zones of low electrical resistivity (ER) corresponded to areas contaminated by heavy metals, especially contamination by Cu, Pb, and Zn. The main pathways of AMD leachate were successfully mapped using ER methods (low anomaly peaks), self-potential (SP) curves (negative peaks), and ground penetrating radar (GPR) at shallow penetration depths. Mine cavities were well located based on composite interpretations of ER, seismic tomography, and well-log records; mine cavity locations were also observed in drill core data and using borehole image processing systems (BIPS). Damaged zones in buried manmade liners (used to block descending leachate) were precisely detected by ER mapping, and buried rock waste and tailings piles were characterized by low-velocity zones in seismic refraction data and high-resistivity zones in the ER data.

• Journal of the Korean Geophysical Society
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• v.6 no.3
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• pp.179-188
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• 2003

The object of grounding of electrical facility is to protect human and machine damage from the power supply interruption high voltage by use of the accident current dissipating into the ground. Generally, it is not easy to make suitable ground design for inhomogeneous subsurface geology and the variability of accident current in magnitude and duration time. To make efficient ground, ground potential rise must be controlled in the way of overall lowering and evenness. This study shows the case of optimized ground design by use of subsurface resistivity structure from electrical soundings.