• Korean Journal of Fisheries and Aquatic Sciences
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• v.46 no.2
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• pp.201-215
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• 2013

The characteristics of the oceanographic environment in the Aleutian Basin of the Bering Sea during spring in 1996, 1997, and 1999 were clarified. An investigation of the water properties revealed five basic layers in the Bering Sea during spring: (1) a surface layer of warm and low-salinity water induced by solar heating, (2) a subsurface layer of cold and low-salinity water propagated slowly by heat from the surface layer, (3) a thermocline layer where salinity was constant but temperature sharply decreased, (4) a temperature inversion layer, and (5) a deep layer with a gradual decrease in temperature and increase in salinity toward the bottom. The ranges of water temperature and salinity were $1.8-5.5^{\circ}C$ and 31.81-34.08 in 1996, $1.5-7.2^{\circ}C$ and 31.9-34.06 in 1997, and $0.5-5.6^{\circ}C$ and 32.0-34.11 in 1999, respectively. The water temperature of the surface layer was approximately $1.6^{\circ}C$ higher in 1997 than in 1996 and 1999. The lowest temperature at a depth of 100-150 m was about $1^{\circ}C$ lower in 1999 than in 1996 and 1997. Nutrient levels (nitrate, phosphate, and silicate) contributing to the control of the growth of phytoplankton were higher in the Aleutian Basin than in the eastern continental shelf and Bogoslof Island area. This was closely associated with the phytoplankton distribution. Nutrient concentrations were lowest at a depth of 25 m. The high primary production at that depth was confirmed from the vertical distribution of chlorophyll a. Chlorophyll a levels were above $4.0{\mu}L^{-1}$ in some areas in 1996 and 1999, but below $2.0{\mu}L^{-1}$ in most areas in 1997. Zooplankton density was about three times higher in 1999 than in 1997.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.376-383
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• 2005

In this study, we conducted geophysical investigations for the organization of integrated geophysical methods to detect underground cavities of ground subsidence area at the field test site, located at Yongweol-ri, Muan-gun. We examined the applicability of geophysical methods such as electrical resistivity, electromagnetic, and microgravity to cavity detection with the aid of borehole survey results. Underground cavities are widely present within the limestone bedrock overlain by the alluvial deposits in the area of the test site where the ground subsidences have occurred in the past. The limestone cavities are mostly filled with groundwater and clays in the test site. Thus, cavities 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 underground cavities. Furthermore, we could map the distribution of cavities more precisely with the test results incorporated from the various geophysical methods. It is also important to notice that the microgravity method is a very promising tool since it has rarely used for the cavity detection in korea. Beyond the investigation of underground cavities, the geophysical methods are required to provide useful information for the reinforcement design for the ground subsidence areas. It is, therefore, necessary to develop integrated geophysical technique incorporating different geophysical methods to precisely map underground cavities and image the subsurface of the ground subsidence areas.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.142-149
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• 2003

Blind hydraulic backfilling is a commonly used technique for subsidence control of the strata over unapproachable waterlogged underground excavations. In this investigation model studies on all the three variants of this technique, namely, hydro-pneumatic or air-assisted gravity backfilling, pumped-slurry backfilling and simple gravity backfilling, have been carried out in fully transparent models of the underground excavations. On examination of the filling process, it was revealed that in all the three cases, the basic process of filling occurs by sand transport along one or more meandering channels. The relative influence of sand, water and air flow rates on the area of filling from a single inlet point and the hydraulic pressure loss per unit length were studied in details. In hydro-pneumatic backfilling process, the air bubbles while moving upward through the meandering channels provide an additional buoyant force over and above the available hydraulic head. In this way the area of filling from a single borehole may be quite large even at small flow rates of water. During actual field implementation the injected air, if not released completely from the rise side holes, may cause troubles by way of creating potholes on the surface. The pumped-slurry technique has shown its capability of filling a relatively larger area at faster rate, especially when high-volume, low-pressure method was selected. But simple gravity filling was also found to be equally effective method as slurry pumping, especially when flow rates were high. In the second and third method discussed above, examination of variations of injection pressure was also done and its relation with physical phenomenon was also attempted. Some empirical relationships were also developed using multivariate regression with a view to help the practicing engineers.

• Journal of the Korean Geotechnical Society
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• v.18 no.6
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• pp.129-139
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• 2002

Dielectric constant measurement has drawn much attention in the investigation of the properties and contaminations of subsurface. In this study, by varying the frequency from 75 kHz to 12 MHz, dielectric constant was measured for the weathered granite soil and Jumunjin sand having different water contents and dry density. The dielectric constant of sand showed the dispersive behavior indicating that dielectric constant decreased with frequency of an electric field. And the dielectric constant of soil increased as water content and/or dry density increased due to the decrease of air portion and/or the increase of amount of water molecules which could contribute to the development of orientation polarization. The dielectric constant of sand showed a linear relationship with the moisture density, considering both water content and dry density. At low frequency, the dielectric constants calculated by Maxwell's, Topp's and CRIM equation deviated from measured values. It could be explained by the fact that those equations did not consider dispersive behavior of dielectric constant with the frequency.

• Economic and Environmental Geology
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• v.36 no.4
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• pp.269-274
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• 2003

This study, one of the projects for investigation of the precious metal deposits of the Circum-Pacific Ocean coon-tries, was performed in a gem field of Pailling, Cambodia, in which there are numbers of undeveloped mineral resources. The gem fields in the Pailling area are typically distributed in the laterite, lying on of weathered basalts. The gem grade of corundum is low in the surface soil horizon(less than 1 m in depth), but is higher in the subsurface. Occurrence and genetic environment of the precious stone are not concerned in the soils. A Precious stone that is already made from at the least upper part of volcanic rocks is produced in large quantities to undergoing to weathering of the rocks. A precious stone is made from upper part of the formation under the high temperature when volcano is vomiting or after vomiting. and/or made from between the formation under the high temperature when other volcano is vomiting. Volcanic rocks including precious stone are a little different from other volcanic rocks when volcano is vomiting, but chemical composition of rocks is not far different from other volcanic rocks.

• Journal of Soil and Groundwater Environment
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• v.9 no.3
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• pp.1-11
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• 2004

To evaluate the applicability of dielectric constant measurement method on the geoenvironmental investigation of subsurface contaminated by landfill leachate, the analysis on dielectric characteristics of sand containing contaminated pore water by landfill leachate was performed. The separate real and imaginary parts of dielectric constant were investigated in the frequency range of 75kHz to 12MHz. The real part of dielectric constant increased at the lower frequency wherea the real part of dielectric constant decreased at the higher frequency as the concentration of leachate increased. These results can be explained by the frequency dependence of space charge polarization and orientation polarization. The imaginary part of dielectric constant on the contaminated sand with leachate increased with their concentration for whole frequency range. These results are caused by the increase of energy loss due to the enhancement of conduction in soil with leachate concentration. The results in this study indicate that the dielectric constant measurement method has potential in evaluating the contaminated soil and pore water by landfill leachate.

• Journal of the Korean GEO-environmental Society
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• v.6 no.1
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• pp.23-31
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• 2005

The "Silt Pond" is 180 hectares in size and contained ultra soft slurry-like soil varying between 3 to 20 meters in thickness. Reclamation works in the Silt Pond commenced in the mid of 1990s. A considerable amount of subsurface investigation inclusive of sampling, field vane and density logging tests were carried out prior to the reclamation of the Silt Pond. Since material in the Silt Pond is extremely soft, filling was done by spreading sand with high water content in thin and equal thickness lifts, allowing the stability of the slurry-like foundation. Despite the extreme care taken, failures occurred during the sand spreading phase. A large piece of high strength geotextile measuring $900m{\times}700m$ was placed to strengthen the slurry like soil foundation at locations where the ultra-soft soil was found to be exposed. Following the remedial works, the Silt Pond was again reclaimed by sand spreading up to +4.0m CD. The success of the reclamation was confirmed by marine CPT profiling.

• Economic and Environmental Geology
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• v.52 no.2
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• pp.141-158
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• 2019

The quantity of heavy metals in agricultural surface and subsurface soils around coal-fired power plants located in Samcheonpo and Hadong, Gyeongnam Province, were determined. The analytical results for 48 and 61 soils in Samcheonpo and Hadong, respectively, showed that the concentrations of Cu, Hg, Ni, Pb, and Zn were below the warning criteria regulated by Korean Soil Conservation Act; however, Cd in 38 and 13 soils in Samcheonpo and Hadong, respectively, exceeded the criterion. As a result of calculation of the geoaccumulation index and the enrichment factor, the soils were extremely contaminated with Cd and such high loading of Cd to the soils was due to anthropogenic source(s). Sequential extraction of the soils, however, showed that heavy metals including Cd existed as hardly extractable phases, which represented a low bioavailability of the heavy metals. Our results indicated that Cd contamination around the coal-fired power plants was due to artificial source(s) and may unlikely deteriorate nearby ecosystems.

• Geomechanics and Engineering
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• v.28 no.5
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• pp.531-546
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• 2022

Ground displacements caused by the construction of overlapping twin shield tunnels with small turning radius are complex, especially under special geological conditions of construction. To investigate the ground displacements caused due to shield machines in the unique calcareous sand layers in Israel for the first time and determine the main factors affecting the ground displacements, field monitoring, laboratory geological analysis, theoretical calculations, and parameter studies were adopted. By using rod extensometers, inclinometers, total stations, and automatic segment-displacement monitors, subsurface tunneling-induced displacement, surface settlement, and displacement of the down-track tunnel segments caused by the construction of an up-track tunnel were analyzed. The up-track tunnel and the down-track tunnel pass through different stratum, resulting in different construction parameters and ground displacements. The laws of variation of thrust and torque, soil pressure in the chamber, excavated soil quantity, synchronous grouting pressure, and grout volume of the two tunnels from parallel to fully overlapping orientations were compared. The thrust and torque of the shield in the fine sand are larger than those in the Kurkar layer, and the grouting amount in fine sand is unstable. According to fuzzy statistics and Gaussian curve fitting of the shield tunneling speed, the tunneling speed in the Kurkar stratum is twice that in the fine-sand stratum.

• Tunnel and Underground Space
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• v.33 no.4
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• pp.265-280
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• 2023

Water leakage in tunnels is a defect that can affect tunnel stability and the ground movement by changing the stress and pore water pressure of the surrounding ground. Long-term or large-scale water leaks may lead to damage of tunnel structure and the surrounding environment, such as tunnel lining instability and ground surface settlement. The present study numerically investigated the effects of water leakage on the structural stability of a tunnel and the ground behavior. The tunnel was assumed to be under undrained conditions for preventing the inflow of the surrounding water and leaks occurred in the concrete lining after completion of the tunnel construction. A coupled hydro-mechanical analysis using a TOUGH-FLAC simulator developed in Python was conducted for assessing the leakage induced-behavior of the tunnel structure and ground under different conditions of the amount and location of water leak. Additionally, the effect of hydro-mechanical coupling terms on the results of coupled response was investigated and discussed.