• Tunnel and Underground Space
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• v.5 no.3
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• pp.214-222
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• 1995

Geological events which are undetected by the surface geophysical or geological survey phase can cause many problems, especially when the tunnel is excavated by TBM. To detect the geological events ahead of tunnel face, a seismic method applied from VSP method is used. Generally uniaxial geophone has been used in surface seismic survey. But this time, triaxial geophone is used to reduce the noise of tunnel wave. DME(Dip moveout Enhancement) filter and diffraction stack method are used. Applying these techniques to the road tunnel in construction, it is proved that the geological events ahead of tunnel face is fairly well predicted. From the seismic trace, Vp and Vs which are related to the rock property can be also obtained. Rock property and proper support design can be dedced from these parameters.

• Geophysics and Geophysical Exploration
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• v.26 no.4
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• pp.211-228
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• 2023

Ground-penetrating radar (GPR) surveys are commonly used to monitor embankments, which is a nondestructive geophysical method. The results of GPR surveys can be complex, depending on the situation, and data processing and interpretation are subject to expert experiences, potentially resulting in false detection. Additionally, this process is time-intensive. Consequently, various studies have been undertaken to detect cavities in GPR survey data using deep learning methods. Deep-learning-based approaches require abundant data for training, but GPR field survey data are often scarce due to cost and other factors constaining field studies. Therefore, in this study, a deep- learning-based model was developed for embankment GPR survey cavity detection using data augmentation strategies. A dataset was constructed by collecting survey data over several years from the same embankment. A you look only once (YOLO) model, commonly used in computer vision for object detection, was employed for this purpose. By comparing and analyzing various strategies, the optimal data augmentation approach was determined. After initial model development, a stepwise process was employed, including box clustering, transfer learning, self-ensemble, and model ensemble techniques, to enhance the final model performance. The model performance was evaluated, with the results demonstrating its effectiveness in detecting cavities in embankment GPR survey data.

• 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.

• Ocean and Polar Research
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• v.44 no.4
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• pp.355-364
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• 2022

When the 60-ton-class patrol boat '72' of the Korea Coast Guard (KCG) was on duty and she accidentally collided with another patrol boat ('207', 200-ton-class) and sank. A month-long search found a small amount of lost items, but neither the crew nor the ship was found. For the first time in 39 years since the accident, the Korea Institute of Ocean Science and Technology (KIOST) searched the boat 72 using the latest integrated geophysical techniques. A number of sonar images presumed to be of a sunken ship was acquired using a combined system of side scan sonar and marine magnetometer, operated at an altitude of approximately 30 m from the seabed. At the same time, a strong magnetic anomaly (100 nT) was detected in one place, indicating the presence of an iron ship. A video survey using a remotely operated underwater vehicle (ROV) confirmed the presence of a shielding part of a personal firearm at the stern of the sunken vessel. Based on these comprehensive data, the sunken vessel discovered in this exploration was assumed to be '72'. This result is meaningful in terms of future ocean exploration and underwater archaeology, as the integrated system of various geophysical methods is an efficient means of identifying objects present in the water.

• 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.

• 한국지구물리탐사학회:학술대회논문집
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• 1999.08a
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• pp.240-257
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• 1999

More than 16 percent of the total 18,032 reservoirs over the country were reported to have leakage problems and need to be improved. Recently, a great deal of progress was made in geophysical survey techniques, particularly in electrical resistivity, and the techniques are used for variety of Purposes in groundwater and dam management due to its economical advantages. This document describes the re-evaluation of existing resistivity data including newly surveyed data, mapping of modeled value in 2-D analysis to locate seepage pathways, This contains also discussion results of more than eighteen years of professional experiences in the field of dam efficiency improvement. In comparison of surface resistivity data with several soil analysis data in laboratory, it is evident that the surface resistivity value shows a qualitative proportionality with the sand contents of the filling materials in earth dam. The result from the study also indicates that the SP method in subsurface investigation is effective to detect seepage in earth filled dam as well as piping through rock/earthfill dike.

• Journal of Soil and Groundwater Environment
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• v.25 no.2_spc
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• pp.86-100
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• 2020

Analyzing and monitoring environmental contaminants based on geophysical exploration techniques have become important and it is now widely applied to delineate spatial distribution geophysical characteristics in wide area. Among the techniques, induced polarization (IP) method, which measures polarization effects on electrical potential distribution, has drawn much attention as an effective tool for environmental monitoring since IP is sensitive to changes in biochemical reactions. However, various reactions stemming from the presence of multiple contaminants have greatly enhanced heterogeneity of polluted sites to result in highly variable electrical characteristics of the site. Those contaminants influence chemical and physical state of soil and groundwater to alter electrical double layer, which in turn influences polarization of the media. Since biochemical reactions between microbes and contaminants result in various IP effects, IP laboratory experiments were conducted to investigate IP responses of the contaminated soil samples under various conditions. Field IP surveys can delineate the spatial distribution of contamination, while providing additional information about electrical properties of a target medium, together with DC resistivity. Reviewing IP effects of contaminants as well as IP surveys can serve as a good starting point for the application of IP survey in site assessment for environmental remediation.

• The Journal of Engineering Geology
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• v.29 no.4
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• pp.553-563
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• 2019

In order to survey archaeological sites, drilling and excavation are carried out at the final stage. However, at the preliminary stage, non-excavation geophysical prospection is used for assessing underground archaeological ruins. Among the geophysical prospecting techniques, Ground Penetration Radar (GPR) prospection has effectively been applied to historical sites due to its high resolution at shallow depths. In this study, the GPR prospection was conducted to find underground ruins near Suseong-Dang, the place of ancient rituals in Buan area, Korea. First, the GPR prospection was conducted at three sites (Site-1, 2, and 3), and subsequently, the GPR prospection was carried out at Site-3 in more detail. As a result of the prospection, the underground layered structure of the survey area consists of three layers, which are soil layer, weathered rock, and sound rock from the surface. And the GPR anomaly to the archaeological structure was clearly identified at around 100-cm depth showing est-west direction that is parallel to the long-axis array. This GPR anomaly of irregular geomorphological features and intermittent distribution may be related to the ritual remains found in Suseong Dang. The GPR prospection could be effectively used to detect archaeological sites or remains buried in the ground.

• 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.

• Economic and Environmental Geology
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• v.39 no.4 s.179
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• pp.403-416
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• 2006

Magnetic method is rapid, cheap and simple geophysical exploration technique, and has wide range of applications such as resources prospecting, geological structure investigation and even geotechnical and environmental problems. Especially, aeromagnetics gives fundamental and useful geoscientific data fnr not only assessment of potential resources, but also national land planning. Magnetic method, perhaps the oldest geophysical technique, was relatively early introduced into Korea. Documents during Japanese occupation says that magnetic method was used for exploring metallic ore deposits and hot spring, and that a geomagnetic observatory was operated. From mid 1950's, after Korean War, magnetic explorations for natural resources such as metallic ore, uranium, coal, and groundwater were intensively executed for industrialization. Apache aeromagnetic survey project during $1958{\sim}1959$ and its ground follow-up surveys are typical and important cases in those days. Magnetic survey techniques were rapidly advanced during 1970's and 1980's with improvements of instruments, growth of geophysical manpower, and availability of computers. The national aeromagnetic mapping project by KIGAM in 1981 showed the improved technical capability of those days. Decline of mining industry since mid 1980's moved the exploration objects from traditional resources to new ones such as groundwater and geothermal resources, and applications to investigation of geological structure were revived. Recently appeared applications such as natural hazard assessment, and engineering and environmental studies increased the magnetic method's utility in the realm of exploration.