• Geophysics and Geophysical Exploration
• /
• v.12 no.3
• /
• pp.268-277
• /
• 2009

Recently as the interest in the development of domestic ore deposits has increased, we can easily find some studies on exploration geophysics-based ore deposit survey in literature. Geophysical surveys have been applied to the investigation of both metallic and non-metallic ore deposit. For metallic ore-deposit survey, the 2D electrical resistivity method has been popularly used, because metallic mineral deposits are generally more conductive than surrounding media. However, geological structures are 3D rather than 2D structures, which may lead to misinterpretation in 2D inversion section. In this study, 3D effects are examined for several 3D structures such as a width-varying dyke model and a wedge-shaped model. We also investigate the effects of the direction of survey line. Numerical results show that the width-varying dyke model yields some low resistivity zone in the deep part, which is independent of real ore-body location. For the wedge-shaped model, even though the survey line is located apart from the ore body, the 2D inversion section still shows low resistivity zone in the deep part. When the survey line is not perpendicular to the strike of the ore body, the low resistivity zone is slightly broader but shallower than that obtained along the survey line perpendicular to the strike. For the survey lines that have an angle smaller than $45^{\circ}$ with the strike of the ore body, the inversion results are totally distorted. From these results, we conclude that 2-D survey and interpretation can lead to misinterpretation of subsurface structures, which may be linked to economical loss. Eventually, we recommend to apply 3-D rather than 2-D electrical resistivity survey for ore-deposit survey.

• Geophysics and Geophysical Exploration
• /
• v.12 no.3
• /
• pp.239-245
• /
• 2009

To verify the reinforcing effect of grouting materials composed of colloid cement and ordinary portland cement on the water leakage region in a small scale dike, we performed a tubecasing method and applied surface electrical resistivity survey including electrical resistivity tomography (ERT) to find resistivity variation before and after grouting. Hydraulic conductivities after grouting show 10 times lower than those of before grouting. These variation indicates that the cement grout blocks the leakage pathway effectively. As the results of dipole-dipole resistivity survey along the dike, resistivity distribution after grouting did not represent noticeable spatial variation in time. Resistivity monitoring results at the dike with vertical electrical sounding (VES) showed that the region of decreasing apparent resistivity was occupied by the grout after grouting. Predicted resistivities from the inversion of ERT data well matched with results of VES at the same regions. From the ERT using check holes to inspect the effect of grouting, we could find that the ERT is quite effective to identify spatially the grout region in a dike.

• The Journal of Engineering Geology
• /
• v.27 no.1
• /
• pp.9-20
• /
• 2017

To date, several studies have been carried out to partially compare and analyze the resistivity values within the Yangsan fault zone through the electrical resistivity survey of the exposed fault zone. However, it is not easy to directly observe a large scaled fault like Yangsan fault that has been weathered, especially due to the weathering of the fault core. This study aimed to reveal the characteristics of location, geometry, the fault core zone as well as underground distribution of the associated fault damage zone, based on the results of electrical resistivity and micro-topographic surveys as well as field geology survey in the southern Yangsan fault zone (Eonyang area). The resistivity anomaly zones developed in the NNE to NE direction were confirmed by the electrical resistivity survey. According to the electrical resistivity, micro-topographic, and field geologic surveys, the Yangsan fault has been formed by three to five fault cores, fault damage zones and/or fractured zones.

• The Journal of Engineering Geology
• /
• v.31 no.4
• /
• pp.533-540
• /
• 2021

Gravity field analysis and density modeling were performed to evaluate the internal state of the rock mass, which is the cause of cut slope collapse. The shape of the weathered zone and the depth of basement could be confirmed from the complete Bouguer anomaly and density model. The basement depth at the center of the cut slope calculated using the Euler deconvolution inverse method is 30 m, which is about 10 m deeper than the surrounding area. In addition, the depth of basement and the thickness of the weathered zone are similar to the boundary between low resistivity and high resistivity in dipole-dipole survey. From the study results, gravity field analysis and density modeling recognizes the internal state of the rock slope and can be used for slope safety analysis, and is particularly suitable as a method to determine the shape of weathered zones in interpreting the safety of cut slopes

• The Journal of Engineering Geology
• /
• v.26 no.4
• /
• pp.497-503
• /
• 2016

The cement grouting by vibration method (CGVM), a new construction technology developed in Korea, aims to efficiently reinforce a target ground area by injecting vibrated grout into it. The present study applies the CGVM to test sites and verifies its effect. Standard penetration tests (SPTs), field permeability tests, and geophysical surveys were conducted in two study areas, and the results were compared between before and after CGVM application. The SPT conducted before and after the CGVM application showed that the N value was increased by 33.57% point to 60.90% point. The field permeability test showed that the permeability coefficient decreased. These results indicate that CGVM may increase imperviousness and improve reservoir system stability. In addition, a resistivity survey found no low-resistivity zone, unlike before the CGVM application, thereby indicating the excellent grouting effect of the CGVM.

• Geophysics and Geophysical Exploration
• /
• v.11 no.4
• /
• pp.350-360
• /
• 2008

Electrical resistivity is one of physical property of the earth and measured by electrical resistivity survey, electrical resistivity logging and laboratory test. Recently, electrical resistivity is widely used in determination of rock quality in support pattern design of road and railway tunnel construction sites. To get more reliable rock quality data from electrical resistivity, it needs a lot of test and study on correlation of resistivity and rock quality. Firstly, we did rock property test in laboratory, such as P wave velocity, Young's modulus, uniaxial compressive strength (UCS) and electrical resistivity. We correlate each test results and we found out that electrical resistivity has highly related to P wave velocity, Young's modulus and UCS. Next, we accomplished electrical resistivity survey in field site and carried out electrical resistivity logging at in-situ area. We also performed rock classification, such as RQD, RMR and Q-system and we correlate electrical resistivity to RMR data. We found out that electrical resistivity logging data are highly correlate to RMR. Also we found out that electrical resistivity survey data are lower than electrical resistivity logging data when there are faults or fractures. And it cause electrical resistivity survey data to lowly correlate to RMR.

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

• Economic and Environmental Geology
• /
• v.48 no.4
• /
• pp.351-360
• /
• 2015

Hamangun Dohangri $6^{th}$ tumulus was characterized by using geological, geophysical, and geotechnical surveys in terms of the shape of the tombs, origin and geotechnical properties of tomb materials, safety of grave mound and burial chamber. The bedrock (Haman Formation sedimentary rock) forming the ground of the tomb, is weathered such that men can excavate the ground. The mound tomb is classified into soil part and rock part by low resistivity and high resistivity, respectively, through electrical resistivity survey. The burial chamber is mostly made by Haman Formation while some part is composed of granitic rock that is distributed in the most southern district of the study area. According to soil tests, the soil part of mound tomb shows low water content, low pore ratio, and proper unit weight that indicate highly compacted material. Additionally, the mound tomb is safe because the strength of the rock part of the mound tomb exceeds that of general rock.

• Geophysics and Geophysical Exploration
• /
• v.9 no.4
• /
• pp.261-270
• /
• 2006

Two-dimensional (2-D) inversion of magnetotelluric (MT) data for two survey lines having south-north direction from Jeju Island has been carried out. Broad band MT sounding curves with good quality could be gathered by performing audio-frequency magnetotelluric (AMT) survey during the MT survey and by operating the remote reference in Kyushu Island, Japan. Comparison of the 2-D inversion model using MT band only and that using both AMT and MT bands for the field data as well as for the data from numerical 2-D modeling said that high frequency information from AMT survey can be useful for interpreting not only the shallow part but also the deep structures, especially when the formation is resistive. The 2-D inversion models of field data show a thick layer having around 10 ohm-m in the depth of a few hundred meters throughout the survey area, which can be considered as the unconsolidated sedimentary layer. And they also show a conductive anomaly at the central part of each survey lines. It can be either the effect of the surrounding sea water, or the structures due to ancient volcanic events. But unfortunately by now, we do not have any further information about the anomaly.

• The Korean Journal of Petroleum Geology
• /
• v.2 no.2 s.3
• /
• pp.43-50
• /
• 1994

The geologic structure of Gongju Basin, which is a Cretaceous sedimentary basin located on the boundary of Gyeonggi Massif and Ogcheon Belt, is modeled by using gravity data and interpreted in relation with basin forming tectonism. The electrical survey with dipole-dipole array was also conducted to uncover the development of fractures in the two fault zones which form the boundaries of the basin. In the process of gravity data reduction, the terrain correction was performed by using the conic prism model, which showed better results specially for topography having a steep slope. The gravity model of the geologic structure of Gongju basin is obtained by forward modeling based on the surface geology and density inversion. It reveals that the width of the basin at its central part is about $4{\cal}km$ and about $2.5{\cal}km$ at the southern part. The depth of crystalline basement beneath sedimentary rocks of the basin is about $700{\~}400{\cal}m$ below the sea level and it is thinner in the center than in margin. The fault of the southeastern boundary appears more clearly than that of the northwestern boundary, and its fracture zone may extended to the depth of more than $1{\cal}km$. Therefore, it is thought that the tectonic movement along the fault in the southeastern boundary was much stronger. These results coincide with the appearance of broad low resistivity anomaly at the southeastern boundary of the basin in the resistivity section. The fracture zones having low density are also recognized inside the basin from the gravity model. The swelling feature of basement and the fractures in sedimentary rocks of the basin suggest that the compressional tectonic stress had also involved after the deposition of the Cretaceous sediments.