• Geomechanics and Engineering
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• v.30 no.2
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• pp.211-218
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• 2022

This study characterizes Proctor and geophysical properties in a broad range of grading and fines contents. The results show that soil index properties such as uniformity and fines plasticity control the optimum water content and peak dry unit trends, as well as elastic wave velocity. The capillary pressure at a degree of saturation less than S = 20% plays a critical role in determining the shear wave velocity for poorly graded sandy soils. The reduction in electrical resistivity with a higher water content becomes pronounced as the water phase is connected A parallel set of compaction and geophysical properties of sand-kaolinite mixtures reveal that the threshold boundaries computed from soil index properties adequately capture the transitions from sand-controlled to kaolinite-controlled behavior. In the transitional fines fraction zone between F_F ≈ 20 and 40%, either sand or kaolinite or both sand and kaolinite could dominate the geophysical properties and all other properties associated with soil compaction behavior. Overall, the compaction and geophysical data gathered in this study can be used to gain a first-order approximation of the degree of compaction in the field and produce degree of compaction maps as a function of water content and fines fraction.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.12a
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• pp.1-14
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• 2007

This paper briefly reviews the history of the Korean geophysics and analyze the current status of geophysical researches. And the future prospects of geophysics are discussed based on social demands for the science and technology in Korea. About thirty universities offer geophysics courses in their academic curricula. Although the number of Ph.D. graduates in geophysics had been small until the year of 1990, but is rapidly increasing. In recent years about $7{\sim}8$ Ph.D's are produced every year. The major geophysical methods used in Ph.D. theses are seismic, electrical and electromagnetic methods, and earthquake waves and research themes are computational geophysics, which involve data processing, modelling, inversion and tomography, geological structures, and paleomagnetic studies in the order of numbers. The Solid Earth Geophysics is generally distinguished in two categories such as "Global Geophysics" and "Exploration Geophysics". However, they are intimately connected, and overlap in many sectors, especially in large scale research projects. The global geophysics has a more academic and general scientific meaning, and several research groups in Korean universities are carrying out the earthquake seismology and paleomagnetic studies. On the other hand the exploration geophysics focuses on practical application of geophysical concepts, and the public research institutes conduct large projects for exploration of energy and mineral resources and to cope with environmental and natural disaster problems. The geophysical studies for local geology and regional crustal structure utilize various survey methods and usually cover both academic and exploration purposes. The computational geophysics constitutes the indispensable theoretical backgrounds for all geophysical sectors. Many young Korean geophysicists, who have strong background in mathematics and physics, devote to the computational geophysics and several groups have made the internationally highest level achievements. But, Korean geophysicists have to expand their research interests to include more global-scale, high-tech researches and collaborative works with various other science groups.

• Geophysics and Geophysical Exploration
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• v.9 no.4
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• pp.271-278
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• 2006

Investigations of underground cavities are required to provide useful information for the reinforcement design and monitoring of the ground subsidence areas. It is, therefore, necessary to develop integrated geophysical techniques incorporating different geophysical methods in order to accurately image and to map underground cavities in the ground subsidence areas. In this study, we conducted geophysical investigations for development of integrated geophysical techniques to detect underground cavities at the field test site in the ground subsidence area, located at Yongweol-ri, Muan-eup, Muan-gun, Jeollanam-do. We examined the applicability of geophysical methods such as electrical resistivity, electromagnetic, and microgravity to cavity detection with the aid of borehole survey results. The underground cavities are widely present within the limestone bedrock overlain by the alluvial deposits in the test site where the ground subsidences have occurred in the past. The limestone cavities are mostly filled with groundwater or clays saturated with water in the site. The cavities, thus, have low electrical resistivity and density compared to the surrounding host bedrock. The results of the study have shown that the zones of low resistivity and density correspond to the zones of the cavities identified in the boreholes at the site, and that the geophysical methods used are very effective to detect the underground cavities. Furthermore, we could map the distribution of cavities more precisely with the study results incorporated from the various geophysical methods. It is also important to notice that the microgravity method, which has rarely used in Korea, is a very promising tool to detect underground cavities.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.215-218
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• 2007

Tunnel detection is known to be one of the challenging problems in geophysical society. Among various geophysical methods, we tried to examine the applicability of electrical resistivity tomography (ERT) method to detect empty tunnel. In this study, we analyzed the ERT data acquired at the test site for tunnel detection. The inversion results have shown reasonable image of the tunnel although the resolution is quite poor. Moreover, we could obtain the three-dimensional attitude of tunnel through 3-D ERT imaging. Therefore, we expect that ERT can make contribution to the tunnel detection problem and further research effort such as fusion of geophysical methods will provide more reliable tunnel detection capability.

• Economic and Environmental Geology
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• v.55 no.1
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• pp.111-125
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• 2022

Since landslide can cause huge damages to many facilities, close characterization of slopes is needed for appropriate reinforcements for the unstable ones in order to prevent the damages. Geophysical surveys, which can characterize a large area at a relatively low cost without disturbing slopes, have been widely employed for the assessment of slope stability in other countries. However, only conventional direct investigation methods are mainly used in Korea. In this paper, we analyzed various cases, which evaluated slope stabilities by characterizing slopes using geophysical exploration. First, we introduced changes in geophysical properties due to unstable media of slope like fracture location, fracture connectivity and distribution of groundwater level, and subsequently discussed the applicability of geophysical methods to the detection of the changes; the methods include electrical resistivity survey, seismic survey, self-potential survey, induced polarization survey and ground penetrating radar. Based on this description, we analyzed how geophysical surveys were performed on various slopes.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.245-248
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• 2001

During the core drilling for the design of a railway bridge crossing over the inferred fault system along the river, fracture zone, extends vertically more than the bottom of borehole, filled with fault gouge was found. The safety of bridge could be threatened by the excessive subsidence or the reduced bearing capacity of bedrock, if a fault would be developed under or around the pier foundation. Thus, a close examination of the fault was required to rearrange pier locations away from the fault or to select a reinforcement method if necessary. Geophysical methods, seismic reflection method and electrical resistivity survey over the water covered area, were applied to delineate the weak zone associated with the fault system. The results of geophysical survey clearly showed a number of faults extending vertically more than 50m. Reinforcement was not desirable because of the high cost and the water contamination, etc. The pier locations were thus rearranged based on the results of geophysical surveys to avoid the undesirable situations, and additional core drillings on the rearranged pier locations were carried out. The bedrock conditions at the additional drilling sites turned out to be acceptable for the construction of piers.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.113-118
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• 2008

Among the geophysical methods, Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) comprise the most promising techniques in resolving buried archaeological structures in urban territories. In this work, two case studies which involve an integrated geophysical survey employing the surface three dimensional (3D) ERT and GPR techniques, in order to archaeologically characterize the investigated areas, are presented. Totally more than 4000 square meters were investigated from the test field sites, which are located at the centre of two of the most populated cities of the island of Crete, in Greece. The ERT and the GPR data were collected along dense and parallel profiles. The subsurface resistivity structure was reconstructed by processing the apparent resistivity data with a 3D inversion algorithm. The GPR sections were processed with a systematic way applying specific filters to the data in order to enhance their information context. Finally, horizontal depth slices representing the 3D variation of the physical properties were created and the geophysical anomalies were interpreted in terms of possible archaeological structures. The subsequent excavations in one of the sites verified the geophysical results, enhancing the applicability of ERT and GPR techniques in the archaeological exploration of urban territories.

• Journal of the Korean Geophysical Society
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• v.6 no.3
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• pp.165-177
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• 2003

The purpose of this paper is to analyze the behavior and to study the safety evaluation of the Unmun Dam located in Cheongdo-Gun of GyeongBuk Province, Korea. For this purpose, soil analyses including boring data, geophysical surveys were conducted. In this paper, especially many geophysical methods were adopted to configure out the subsurface situation of dam. Applied geophysical methods were: 1) electric resistivity survey, 2) high frequency magnetotelluric (HFMT) survey, 3) ground penetrating radar (GPR) survey, 4) seismic refraction survey, 5) seismic cross-hole tomography survey, and 6) high frequency impedance (ZHF) survey. Each of geophysical surveys were analyzed and joint analyses between geophysical surveys were also performed to deduce the more reliable subsurface information of Dam by using the features and characteristics of each geophysical survey. Since many defects, such as gravel and weathered rock blocks in the dam core, and lots of amounts of leakage, by boring analyses were found, reinforcement by compaction grouting system (CGS) has been conducted in some range of dam. Some geophysical data and data of geotechnical gauges were also used to confirm the effects of reinforcement. Electric resistivity, EM, GPR, ZHF, seismic refraction and seismic tomography surveys show that left side of dam is weak, which means the possibility of existence of gravel, rock block, water and cavities in the core of dam. This result coincides with the boring data. Especially, electric survey after reinforcement shows that even the right side of the dam has been deformed by the strong pressure during the reinforcement itself. As a conclusion, some problems in the dam found. Especially, the dam near spillway shows the high possibility of leakage. It should be pointed out that only the left side of he dam has not a leakage problem. As a whole, the dam has problems of weakness, because of unsatisfactory construction. It is strongly recommended that highly intensive monitoring is required.

• Geophysics and Geophysical Exploration
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• v.21 no.4
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• pp.244-254
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• 2018

The first geophysical technique applied to the agricultural sector in Korea was electrical resistivity sounding and conducted in purpose of groundwater exploitation in the 1970s. According to the diversity of agricultural activities since the 1990s, various geophysical methods including electrical resistivity, electromagnetic induction, and self-potential method were applied to several agricultural fields such as soil characterization with saline concentration in vast reclaimed area, delineation of seawater intrusion regions in costal aquifer, safety inspection of embankment dikes with leakage problem, detection of ground subsidence from overpumping and tracing of groundwater aquifer contamination by leachate from livestock mortality burial or waste burial site. This paper introduces representative geophysical techniques that have been utilized in various agricultural fields and suggests several ways to develop the geophysical methods required for the precision agriculture field in the near future based on the past achievements.

• Journal of the Korean GEO-environmental Society
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• v.7 no.6
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• pp.35-44
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• 2006

Various geophysical methods and geological survey were applied for prospecting of geothermal resources and the attitude of volcanic body at northern part of Kumseongsan, Euiseong. They include magnetic, self-potential, radioactive and resistivity methods, temperature logging near the earth's surface and geological survey. The results of this study are summarized as follows. Various geophysical anomalies is related to the geologically Cretaceous conduit. Anomalies of resistivity and temperature logging seem to be related to the geological structure and terrestrial heat. Small radioactive and self-potential anomalies seem to be associated with chemical character of rocks. The sedimentary rocks dip steeply toward the volcanic rocks, aquifuge. Ideal geological structure for bearing ground water and geothermal resources was founded in the study area. The study area and the adjacent two hot springs area consist of Cretaceous sedimentary and volcanic rocks, and have similar geology.