• The Journal of Engineering Geology
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• v.24 no.1
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• pp.1-8
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• 2014

Numerical stability analysis of an unsaturated infinite slope under rainfall-induced infiltration conditions was performed using generalized effective stress to unify both saturated and unsaturated conditions The soil-water characteristic curve (SWCC) of sand with a relative density of 75% was initially measured for both drying and wetting processes. The hydraulic conductivity function (HCF) and suction stress characteristic curve (SSCC) were subsequently estimated. Under the rainfall-induced infiltration conditions, transient seepage analysis of an unsaturated infinite slope was performed using the finite element analysis program, SEEP/W. Based on these results, the stability of an unsaturated infinite slope under rainfall-induced infiltration conditions was examined in relation to suction stress. According to the results, the negative pore-water pressure and water content within the slope soil changed over time due to the infiltration. In addition, the variation of the negative pore-water pressure and water content led to a variation in suction stress and a subsequent change in the slope's factor of safety during the rainfall period.

• Earthquakes and Structures
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• v.25 no.2
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• pp.135-148
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• 2023

The structure-soil-structure interaction (SSSI) effect in adjacent structures may affect the liquefaction-induced damage of shallow foundation structures. The existing studies only analysed the independent effects on the structural dynamic response but ignored the coupling effect of height difference and distance of adjacent structures (F) on liquefied foundations on the dynamic response. Therefore, this paper adopts finite element and finite difference coupled dynamic analysis method to discuss the effect of the F on the seismic response of shallow foundation structures. The results show that the effect of the short structure on the acceleration response of the tall structure can be neglected as F increases when the height difference reaches 2 times the height of the short structure. The beneficial effect of SSSI on short structures is weakened under strong seismic excitations, and the effect of the increase of F on the settlement ratio gradually decreases, which causes a larger rotation hazard. When the distance is smaller than the foundation width, the short structure will exceed the rotation critical value and cause structural damage. When the distance is larger than the foundation width, the rotation angle is within the safe range (0.02 rad).

• Economic and Environmental Geology
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• v.38 no.5 s.174
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• pp.547-561
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• 2005

General characteristics of groundwater contamination by As were reviewed with several recent researches, and its occurrence in groundwater of Korea was investigated based on a ffw previous studies and a groundwater quality survey in Nonsan and Geumsan areas. In Bangladesh, which has been known as the most serious arsenic calamity country, about $28\%$ of the shallow groundwaters exceeded the Bangladesh drinking water standard, $50{\mu}g/L$, and it was estimated that about 28 million people were exposed to concentrations greater than the standard. Groundwater was characterized by circum-neutral pH with a moderate to strong reducing conditions. Low concentrations of $SO_4^{2-}$ and $NO_3^-$, and high contents of dissolved organic carbon (DOC) and $NH_4^+$ were typical chemical characteristics. Total As concentrations were enriched in the Holocene alluvial aquifers with a dominance of As(III) species. It was generally agreed that reductive dissolution of Fe oxyhydroxides was the main mechanism for the release of As into groundwater coupling with the presence of organic matters and microbial activities as principal factors. A new model has also been suggested to explain how arsenic can naturally contaminate groundwaters far from the ultimate source with transport of As by active tectonic uplift and glaciatiion during Pleistocene, chemical weathering and deposition, and microbial reaction processes. In Korea, it has not been reported to be so serious As contamination, and from the national groundwater quality monitoring survey, only about $1\%$ of grounwaters have concentrations higher than $10{\mu}g/:L.$ However, it was revealed that $19.3\%$ of mineral waters, and $7\%$ of tube-well waters from Nonsan and Geumsan areas contained As concentrations above $10{\mu}g/:L.$. Also, percentages exceeding this value during detailed groundwater quality surveys were $36\%\;and\;22\%$ from Jeonnam and Ulsan areas, respectively, indicating As enrichment possibly by geological factors and local mineralization. Further systematic researches need to proceed in areas potential to As contamination such as mineralized, metasedimentary rock-based, alluvial, and acid sulfate soil areas. Prior to that, it is required to understand various geochemical and microbial processes, and groundwater flow characteristics affecting the behavior of As.

• Journal of Soil and Groundwater Environment
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• v.10 no.4
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• pp.33-44
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• 2005

On the basis of a stepwise and careful integration of various field and laboratory methods the analysis of groundwater flow characterization was performed with five boreholes (BH-1, -2, -3, -4, -5) on a pilot site of Natural Forest Park in Guemsan-gun, Chungcheongbook-do, Korea. The regional lineaments of NW-SE are primarily developed on the area, which results in the development of many fractures of NW-SE direction around boreholes made in the test site for the study. A series of surface geological survey, core logging, geophysical logging, tomography, tracer tests, and heat-pulse flowmeter logging were carried out to determine fracture characteristics and fracture connectivity between the boreholes. In the result of fracture connectivity analysis BH-1 the injection well has a poor connectivity with BH-2 and BH-3, whereas a good with BH-4 and BH-5. In order to analyse the hydraulic connectivity between BH-1 and BH-5, in particular, a conspicuous groundwater outflux in the depth of 12 m and influx in the depth of 65 m and 70 m, but partly in/outflux occurred in other depths in BH-5 were observed as pumping from BH-1. On the other hand, when pumping from BH-5 the strong outflux in the depths of 17 m and 70 m was occurred. The spatial connectivity between the boreholes was examined in the depth of 15 m, 67 m, and 71 m in BH-1 as well as in the depth of 15 m, 17 m, 22 m, 72 m, and 83 m in BH-5.

• The Journal of Engineering Geology
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• v.33 no.3
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• pp.475-487
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• 2023

We surveyed the distribution of soil layers on Dongdo and Seodo of Dokdo and measured the physical properties of the soils. To investigate the distribution of soil layers, the soil depth was measured directly in accessible locations, and visual observations of inaccessible locations were carried out using drones and boats. Soil depths ranged from 3 to 50 cm, and most soil layers had depths of 10~20 cm. Based on these results, a map of the soil layer was drawn using 5 cm intervals for soil depth. To analyze the soil characteristics of Dokdo, soil samples were collected from 13 locations on Dongdo and 13 locations on Seodo, in consideration of various geological settings. According to the results of grain size distribution tests, sand contents were >75%, and soil from Seodo contained more gravel-sized particles than that from Dongdo. Using the unified soil classification system (USCS) and textural classification chart of the United States Department of Agriculture (USDA), most of the soil samples from Dokdo are classified as sand, and some are classified as loamy or clayey sand. In addition, well-graded loamy or clayey sands are more common in Dongdo, and poorly graded sands with gravel are more common in Seodo. These results are expected to be important for studying soil characteristics on Dokdo.

• 한국지구물리탐사학회:학술대회논문집
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• 2004.06a
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• pp.3-17
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• 2004

Space-borne Earth observation technique is one of the most cost effective and rapidly advancing Earth science research tools today and the potential field and micro-wave radar applications have been leading the discipline. The traditional optical imaging systems including the well known Landsat, NOAA - AVHRR, SPOT, and IKONOS have steadily improved spatial imaging resolution but increasing cloud covers have the major deterrent. The new Earth observation satellites ENVISAT (launched on March 1 2002, specifically for Earth environment observation), ALOS (planned for launching in 2004 - 2005 period and ALOS stands for Advanced Land Observation Satellite), and RADARSAT-II (planned for launching in 2005) all have synthetic aperture radar (SAR) onboard, which all have partial or fully polarimetric imaging capabilities. These new types of polarimetric imaging radars with repeat orbit interferometric capabilities are opening up completely new possibilities in Earth system science research, in addition to the radar altimeter and scatterometer. The main advantage of a SAR system is the all weather imaging capability without Sun light and the newly developed interferometric capabilities, utilizing the phase information in SAR data further extends the observation capabilities of directional surface covers and neotectonic surface displacements. In addition, if one can utilize the newly available multiple frequency polarimetric information, the new generation of space-borne SAR systems is the future research tool for Earth observation and global environmental change monitoring. The potential field strength decreases as a function of the inverse square of the distance between the source and the observation point and geophysicists have traditionally been reluctant to make the potential field observation from any space-borne platforms. However, there have recently been a number of potential field missions such as ASTRID-2, Orsted, CHAMP, GRACE, GOCE. Of course these satellite sensors are most effective for low spatial resolution applications. For similar objects, AMPERE and NPOESS are being planned by the United States and France. The Earth science disciplines which utilize space-borne platforms most are the astronomy and atmospheric science. However in this talk we will focus our discussion on the solid Earth and physical oceanographic applications. The geodynamic applications actively being investigated from various space-borne platforms geological mapping, earthquake and volcano .elated tectonic deformation, generation of p.ecise digital elevation model (DEM), development of multi-temporal differential cross-track SAR interferometry, sea surface wind measurement, tidal flat geomorphology, sea surface wave dynamics, internal waves and high latitude cryogenics including sea ice problems.

• Economic and Environmental Geology
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• v.51 no.2
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• pp.149-166
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• 2018

Many large earthquakes have continuously been reported and resulted in significant human casualties and extensive damages to properties globally. The accident of Fukushima nuclear power plant in Japan was caused by a mega-tsunami, which is a secondary effect associated with the Tohoku large earthquake (M=9.0, 2011. 3. 11.). Most earthquakes occur by reactivation of pre-existing active faults. Therefore, the importance of paleoseismological study have greatly been increased. The Korean peninsula has generally been considered to be a tectonically stable region compared with neighboring countries such as Japan and Taiwan, because it is located on the margin of the Eurasian intra-continental region. However, the recent earthquakes in Gyeongju and Pohang have brought considerable insecurity on earthquake hazard. In particular, this region should be secure against earthquake, because many nuclear facilties and large industrial facilities are located in this area. However, some large earthquakes have been reported in historic documents and also several active faults have been reported in southeast Korea. This study explains the evaluation methods of geological structures on active fault, fault damage zone, the relationship between earthquake and active fault, and respect distance. This study can contribute to selection of safe locations for nuclear facilities and to earthquake hazards and disaster prevention.

• The Journal of Engineering Geology
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• v.17 no.1 s.50
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• pp.101-113
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• 2007

A landslide was occurred due to soil cutting for construction to expand the Donghae express highway in Dong-hae-City, Korea. The total area of the landslide was about $9,550m^2$ with 100 m of width and 87m of height. The landslide was occurred due to the internal factor of the unstable geological structure including the clay layer and the external factor of continuous heavy rainfalls. As the result of field instrumentation during the landslide, the horizontal displacement of the slope ground increases with increasing the accumulated rainfall by continuous rainfall during the rainy season. Also, the depth of sliding failure was decided by the horizontal displacement distribution during landslide occurrence. It makes sure that the horizontal displacement starts from the depth of sliding failure and the depth of sliding failure matches well with the location of the clay layer. As the slope stability analysis using Bishop's Simplified Method at the landslide area, the safety factor of slope during the rainy season was 0.53. This safety factor of slope was enough to trigger the landslide at this area. The depth of sliding failure obtained by analytical method matches well with the depth of the clay layer.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.23-27
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• 2013

The risks of debris flows caused by climate change have increased significantly around the world. Recently, landslide disaster prevention technology is more focused on the failure and post-failure dynamics to mitigate the hazards in flow-prone area. In particular, we should define the soil strength and flow characteristics to estimate the debris flow mobility in the mountainous regions in Korea. To do so, we selected known ancient landslides area: Inje, Pohang and Sangju debris flows. Firstly we measured physical and mechanical properties: liquidity index and undrained shear strength by fall cone penetrometer. From the test results, we found that there is a possible relationship between liquidity index and undrained shear strength, $C_{ur}=(1.2/I_L)^{3.3}$, in the selected areas, even though they were different in geological compositions. Assuming that the yield stress is equal to the undrained shear strength at the initiation of sliding, we examined the flow characteristics of weathered soils in Korea. When liquidity index is given as 1, 1.5 and 3.0, the debris flow motion of weathered soils is compared with that of mud-rich sediments, which are known as low-activity clays. At $I_L=1$, it seems that debris flow could reach approximately 250m after 5 minutes. As liquidity index increased from 1 to 3, the debris flow propagation of weathered soils is twice than that of low-activity clays. It may be due to the fact that soil masses mixed with the ambient water and then highly fragmented during flow, thereby leading to the high mobility. The results may help to predict the debris flow propagation and to develop disaster prevention technology at similar geological settings, especially for the weathered soils, in Korea.

• Journal of Korean Tunnelling and Underground Space Association
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• v.25 no.6
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• pp.403-421
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• 2023

As the number of underground structures has increased in recent decades, it has become crucial to predict geological hazards ahead of a tunnel face during tunnel construction. Consequently, this study developed a finite element (FE) numerical model to simulate electrical resistivity surveys in tunnel boring machine (TBM) operations for predicting mixed ground conditions in front of tunnel faces. The accuracy of the developed model was verified by comparing the numerical results not only with an analytical solution but also with experimental results. Using the developed model, a series of parametric studies were carried out to estimate the effect of geological conditions and sensor geometric configurations on electrical resistivity measurements. The results of these studies showed that both the interface slope and the difference in electrical resistivity between two different ground formations affect the patterns and variations in electrical resistivity observed during TBM excavation. Furthermore, it was revealed that selecting appropriate sensor spacing and optimizing the location of the electrode array were essential for enhancing the efficiency and accuracy of predictions related to mixed ground conditions. In conclusion, the developed model can serve as a powerful and reliable tool for predicting mixed ground conditions during TBM tunneling.