• Journal of the Korean Geotechnical Society
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• v.22 no.8
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• pp.129-136
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• 2006

Engineered mixtures, which consist of rigid sand particles and soft fine-grained rubber particles, are tested to characterize their small and large-strain responses. Engineered soils are prepared with different volumetric sand fraction, sf, to identify the transition from a rigid to a soft granular skeleton using wave propagation, $K_{o}-loading$, and triaxial testing. Deformation moduli at small, middle and large-strain do not change linearly with the volume fraction of rigid particles; instead, deformation moduli increase dramatically when the sand fraction exceeds a threshold value between sf=0.6 to 0.8 that marks the formation of a percolating network of stiff particles. The friction angle increases with the volume fraction of rigid particles. Conversely, the axial strain at peak strength increases with the content of soft particles, and no apparent peak strength is observed in specimens when sand fraction is less than 60%. The presence of soft particles alters the formation of force chains. While soft particles are not part of high-load carrying chains, they play the important role of preventing the buckling of stiff particle chains.

• Journal of the Korean Geotechnical Society
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• v.24 no.2
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• pp.87-97
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• 2008

Behaviors of cemented engineered soils, composed of rigid sand particle and soft rubber particle, are investigated under $K_o$ condition. The uncemented and cemented specimens are prepared with various sand volume fractions to estimate the effect of the cementation in mixtures. The vertical deformation and elastic wave velocities with vertical stress are measured. The bender elements and PZT sensors are used to measure elastic wave velocities. After cementation, the slope of vertical strain shows bilinear and is similar to that of uncemented specimen after decementation. Normalized vertical strains can be divided into capillary force, cementation, and decementation region. The first deflection of the shear wave in near field matches the first arrival of the primary wave. The elastic wave velocities dramatically increase due to cementation hardening under the fixed vertical stress, and are almost identical with additional stress. After decementation, the elastic wave velocities increase with increase in the vertical stress. The effect of cementation hinders the typical rubber-like, sand-like, and transition behaviors observed in uncemented specimens. Different mechanism can be expected in decementation of the rigid-soft particle mixtures due to the sand fraction. a shape change of individual particles in low sand fraction specimens; a fabric change between particles in high sand fraction specimens. This study suggests that behaviors of cemented engineered soils, composed of rigid-soft particles, are distinguished due to the cementation and decementation from those of uncemented specimens.

• Korean Journal of Soil Science and Fertilizer
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• v.44 no.2
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• pp.316-319
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• 2011

Biopiles which offer the potential for cost-effective treatment of contaminated soils are above-ground, engineered systems that use oxygen to stimulate the growth and reproduction of aerobic bacteria for degradation of the petroleum constituents adsorbed to soil in excavated soils. This technology involves heaping contaminated soils into piles and stimulating aerobic microbial activity within the soils through the aeration and/or addition of minerals, nutrients, and moisture. Inside the biopile, microbially mediated reactions by blowing or extracting air through the pipes can enhance degradation of the organic contaminants. The influence of a aeration system on the biopile performance was investigated. Air pressure made to compare the efficiency of suction in the pipes showed that there were slightly significant difference between the two piles in the total amount of TPH biodegradation. The normalised degradation rate was, however, considerably higher in the aeration system than in the normal system without aeration, suggesting that the vertical venting method may have improved the efficiency of the biological reactions in the pile.

• Journal of Soil and Groundwater Environment
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• v.18 no.4
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• pp.32-39
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• 2013

This research focused on the effects of heavy metals on the biomonitoring activity of genetically engineered bioluminescent bacteria, Pseudomonas putida mt-2 KG1206. KG1206 was exposed to single or binary mixtures of different heavy metals as well as soils contaminated with heavy metals. In case of single exposure with different inducer pollutant, the toxicity order was as followings : As(III) > Cd, As(V) >> Cu, Cr(VI). The toxic effects of the binary mixtures was compared to the expected effect based on a simple theory of probabilities. The interactive effects were mostly additive, while in few cases antgonistic and synergistic mode of action was observed for some concentration combinations. No considerable correlation was found between the total metal contents in soils and the bioluminescence activity of each sample. However, statistically significant differences (p = 0.0102) were observed between two groups, classified based on arsenite contamination. These results demonstrate the usage of recombinant bioluminescent microorganism in biomonitoring and the complex interactive effects of metals.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2000.11a
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• pp.153-162
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• 2000

A field study was performed to test effectiveness of a bloluminescent genetically engineered microorganism (GEM) for bioremediation process monitoring and control. The study employed Pseudomonas fluorescens HK44 that was the first strain approved for field application in the U.S. for bioremediation purposes. HK44 contains lux gene fused within a naphthalene degradative pathway, allowing this GEM to bioluminesce as it degrades naphthalene as well as substituted naphthalenes and other polycyclic aromatic hydrocarbons (PAHs) , Results showed that HK44 was maintained in both PAH-contarninated and uncontaminated soils even 660 days after inoculation. HK44 was able to produce bioluminescence in response to PAHs in soil. Although effectiveness of chemical remediation was not assessed due to heterogeneous distribution of contaminants, decreased concentration of naphthalene was shown in the soils, Taken together, HK44 was useful for in situ bioremediation process monitoring and control. This work is so far the only field release of a GEM for bioremediation purposes.

• Geomechanics and Engineering
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• v.33 no.1
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• pp.113-120
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• 2023

Coastal and offshore structures such as ports and offshore wind farms will often need to be built on fine-grained sediments. Geotechnical properties associated with sediment compressibility are key parameters for marine construction designs especially on soft grounds, which involve clay-mineral dominated fines that can consolidate and settle significantly in response to engineered and environmental loads. We conduct liquid limit tests and 1D consolidation tests with fine-grained soils (silica silt, mica, kaolin and bentonite) and biogenic soils (diatom). The pore fluids for the liquid limit tests include deionized water and a series of brines with NaCl salt concentrations of 0.001 m, 0.01 m, 0.1 m, 0.6 m and 2.0 m, and the pore fluids for the consolidation tests deionized water, 0.01 m, 0.6 m, 2 m. The salt concentrations help the liquid limits of kaolin and bentonite decrease, but those of diatom slightly increase. The silica silt and mica show minimal changes in liquid limit due to salt concentrations. Accordingly, compression indices of soils follow the trend of the liquid limit as the liquid limit determined the initial void ratio of the consolidation test. Diatoms are more likely to be broken than clastic sediments during to loading, and diatom-rich sediment is therefore generally more compressible than clastic-rich sediment.

• Geomechanics and Engineering
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• v.19 no.1
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• pp.1-9
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• 2019

Shallow failures occur frequently in both engineered and natural slopes in expansive soils. Rainfall infiltration is the most predominant triggering factor that contributes to slope failures in both expansive soils and clayey soils. However, slope failures in expansive soils have some distinct characteristics in comparison to slopes in conventional clayey soils. They typically undergo shallow failures with gentle sliding retrogression characteristics. The shallow sliding mass near the slope surface is typically in a state of unsaturated condition and will exhibit significant volume changes with increasing water content during rainfall periods. Many other properties or characteristics change such as the shear strength, matric suction including stress distribution change with respect to depth and time. All these parameters have a significant contribution to the expansive soil slopes instability and are difficult to take into consideration in slope stability analysis using traditional slope stability analysis methods based on principles of saturated soil mechanics. In this paper, commercial software VADOSE/W that can account for climatic factors is used to predict variation of matric suction with respect to time for an expansive soil cut slope in China, which is reported in the literature. The variation of factor of safety with respect to time for this slope is computed using SLOPE/W by taking account of shear strength reduction associated with loss of matric suction extending state-of-the art understanding of the mechanics of unsaturated soils.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.5
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• pp.507-512
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• 2005

This research focuses on the development and application of a method for the detection of m-toluate in soils using a genetically engineered bioluminescent bacteria, Pseudomonas putida mt-2 KG1206. KG1206 produces light by direct (m-toluate and benzoate) and indirect (toluene analogs) inducers. For detection of m-toluate in soil system, 9.9 mL strain was amended with 0.1 mL soil ethanol extractant. A high correlation ($r^2>0.97$) was observed between bioluminescence and m-toluate concentration. The unknown concentrations of m-toluate in soil samples were pre-determined using a method developed based on bioluminescence activity of strain with extracted inducers. Values between by LC analysis and bioluminescence activity show moderate statistical results. These results demonstrate the feasibility of recombinant bioluminescent microorganism, engineered to generate a quantifiable bioluminescence signal in response to specific pollutants, may serve as combined sensing and reporting tools in environmental monitoring.

• Geomechanics and Engineering
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• v.22 no.3
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• pp.207-217
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• 2020

Slope reliability analysis and risk assessment for spatially variable soils under rainfall infiltration are important subjects but they have not been well addressed. This lack of study may in part be due to the multiple and diverse evaluation indexes and the low computational efficiency of Monte-Carlo simulations. To remedy this, this paper proposes a highly efficient computational method for investigating random field problems for slopes. First, the probability density evolution method (PDEM) is introduced. This method has high computational efficiency and does not need the tens of thousands of numerical simulation samples required by other methods. Second, the influence of rainfall on slope reliability is investigated, where the reliability is calculated from based on the safety factor curves during the rainfall. Finally, the uncertainty of the sliding mass for the slope random field problem is analyzed. Slope failure consequences are considered to be directly correlated with the sliding mass. Calculations showed that the mass that slides is smaller than the potential sliding mass (shallow surface sliding in rainfall). Sliding mass-based risk assessment is both needed and feasible for engineered slope design. The efficient PDEM is recommended for problems requiring lengthy calculations such as random field problems coupled with rainfall infiltration.

• Proceedings of the Korean Environmental Health Society Conference
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• 2002.04a
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• pp.9-12
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• 2002

Diffusive transport of volatile organic compounds(VOCs) and their degradation by bacteria in unsaturated soils are couple by poorly understood mass transfer kinetics at the gas/water interface. Determination of the fate of VOCs in unsaturated soil is necessary to evaluate the feasibility of natural attenuation as a VOC remediation strategy. The objective of this study was to develop a mechanistically based mathematical model that would consider the interdependence of VOC transport, microbial activity, and sorptive interaction in a moist, unsaturated soil. Because the focus of the model was on description of natural attenuation, the advective VOC transport that is induced in engineered remediation processes such as vapor extraction was not considered. The utility of the model was assessed through its ability to describe experimental observations form diffusion experiments using toluene as a representative VOC in well-defined soil columns that contained a toluene degrading bacterium, Pseudomonas Putida, as the sole active microbial species. The coefficient for gas-liquid mass-transfer, K$\sub$LA/, was found to be a key parameter controlling the ability of bacteria to degrade VOCs. This finding indicates that soil size and geometry are likely to be important parameters in assessing the possible success of natural attenuation of VOCs in contaminated unsaturated soils.