• Journal of the Korean Society of Environmental Restoration Technology
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• v.6 no.3
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• pp.69-78
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• 2003

The main purpose of this study was to verify the shore margin protection effect of the root system of Salix gracilistyla Miq. developed from direct sticking cuttings on wetland, focusing on the effect of the root system reducing soil particle dissociation rate in water. The soil dissociation rate was examined through slaking tests with cylindric pure soil column at maximum particle density and the same size column of root reinforced soil. The dry weight of remained soil was measured after 5, 10, 15, 30minutes and 1, 6, 12, 24, 48hours inundation. As results, the soil particles began to dissociate severely at 10 minutes and only 10% of soil particles were left after 25minutes inundation. The stable slope angle of pure soil was $36^{\circ}$after 24 hours. On the other hand, the columns of root reinforced soil were stable even after 24hours, being dissociated only 7.2% of soil particles. So, it was revealed that the root system was very effective materials protecting more than 80% of soil particle from dissociation in inundation.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.399-404
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• 2008

The influence of gas hydrate dissociation on submarine slope stability was studied in this paper. Gas hydrates are stable under high pressure and low temperature conditions. Once gas hydrate dissociates due to natural or human activities, it generates large amount of gas and water. During gas hydrate dissociation, a pore pressure between soil particles increases and results in the loss of an effective stress and degradation of soil stiffness. A pore pressures model was proposed to calculated excess pore pressures generated by gas hydrate dissociation at the Storegga Slide. A slope stability analysis for the Storegga Slide using a two dimensional finite difference method was carried out by considering excess pore pressures due to gas hydrate dissociation. Since the excess pore pressure calculated by the proposed method resulted in the considerable loss of stiffness and strength in slope, a submarine slope failure occurred at the Storegga slide was well simulated.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.888-892
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• 2008

If gas hydrate dissociates due to natural and/or human activities, it generates large amount of gas and water. Upon gas hydrate dissociation, a generated pore water pressure between soil particles increases and results in the loss of an effective stress and degradation of soil stiffness and strength. In order to predict the generated excess pore water pressure due to gas hydrate dissociation, two methods based on small hydrate concept (SHC) and large hydrate concept (LHC) are proposed. An excess pore water pressure generated by the gas hydrate dissociation in the Storegga Slide was calculated using two proposed methods.

• Korean Journal of Soil Science and Fertilizer
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• v.29 no.4
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• pp.328-335
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• 1996

Using literature data on back titration curves of some typical Korean soils and minerals we calculated the distribution functions of aparent surface dissociation constants for these materials using site heterogeneity approach. The studied materials exhibited broad range of apparent surface dissociation constants. The dominant surface sites for all samples appeared to be very weakly acidic. However, the relative amounts of surface sites differed among particular materials.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.577-583
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• 2010

In this study, the effect of void formation resulting from gas hydrate dissociation or loss of some particles within soil structure on the strength of soil is examined. Beag-ma river sands with uniform gradation were used to simulate a gas hydrate bearing or washable soil structure. Empty capsules for medicine are used to mimic large voids, which are bigger than soil particle. Beag-ma river sand was miced with 8% cement ratio and 14% water content and compacted into a shear box. The number and direction embedded into a specimen. After 4 hours curing, a series of direct shear test is performed on the capsule embedded cemented sands. Shear strength of cemented sands with capsules depends on the volume and direction. The volume and direction formed by voids are most important factors in strength. A shear strength of a specimen with large voids decreases up to 39% of a specimen without void. The results of this study can be used to predict the strength degradation of gas hydrate bearing sediments after dissociation and loss of fine particles within soil structure.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2C
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• pp.109-117
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• 2010

Gas hydrate dissociation can generate large amounts of gas and water in gas hydrate bearing sediments, which may eventually escape from a soil skeleton and form voids within the sediments. The loss of fine particles between coarse particles or collapse of cementation due to water flow during heavy or continuous rainfall may form large voids within soil structure. In this study, the effect of void formation resulting from gas hydrate dissociation or loss of some particles within soil structure on the strength of soil is examined. Glass beads with uniform gradation were used to simulate a gas hydrate bearing or washable soil structure. Glass beads were mixed with 2% cement ratio and 7% water content and then compacted into a cylindrical sample with five equal layers. Empty capsules for medicine are used to mimic large voids, which are bigger than soil particle, and embedded into the middle of five equal layers. The number, direction, and length of capsules embedded into each layer vary. After two days curing, a series of unconfined compression tests is performed on the capsule-embedded cemented glass beads. Unconfined compressive strength of cemented glass beads with capsules depends on the volume, direction and length of capsules. The volume and cross section formed by voids are most important factors in strength. An unconfined compressive strength of a specimen with large voids decreases up to 35% of a specimen without void. The results of this study can be used to predict the strength degradation of gas hydrate bearing sediments in the long term after dissociation and loss of fine particles within soil structure.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2003.11a
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• pp.113-118
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• 2003

An investigation has been carried out on collision-induced dissociation (CID) in the development of an analytical protocol for the determination of polycyclic aromatic hydrocarbons (PARs) by ion trap tandem mass spectrometry. Two different considerations were used to choose the optimal CID conditions for complex matrix environmental samples, namely, to determine the highest signal-to-noise (SIN) ratio and the other to eliminate the background interferences originated from complex matrix samples. The PAR content of agricultural soil was measured to estimate overall distribution of PAR in throughout the country, we collected and analyzed 226 soil samples from paddy and upland soil. The average content of total PAR in all samples was 236 ${\mu}g$ $kg^{-1}$, and the range was from 23.3 to 2, 834 ${\mu}g$ $kg^{-1}$. The overall distribution of PAR was found to be closely related to the pollution sources, the size of city and the type of industry.

• Bulletin of the Korean Chemical Society
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• v.23 no.8
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• pp.1097-1102
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• 2002

The mass spectrometry using an ion trap tandem mass spectrometer has been investigated to find optimum conditions for the analysis of benzo(a)pyrene (3,4-benzpyrene). The applicability to a real soil sample was also investigated to verify the usef ulness of the MS/MS (or collision induced dissociation, CID) analysis. The optimum CID condition was 1.5 and 0.45 for the RF excitation voltage and the q value, respectively. For comparison, CID and EI were applied to the analysis of a soil sample. CID analysis was more sensitive than EI analysis of the soil sample. The limit of detection (LOD) of benzo(a)pyrene was 3.18 ng mL-1 and 0.85 ng mL,-1 for EI and MS/MS analysis, respectively. The precision at the soil sample for EI and CID showed relative standard deviations of 6.1% and 4.1%, respectively, and the concentrations were 168 ㎍ kg-1 and 162 ㎍ kg-1 , respectively.

• Korean Journal of Soil Science and Fertilizer
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• v.37 no.6
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• pp.378-382
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• 2004

Soil pH is an important indicator for soil reactions and crop growth. pH buffer capacity and lime requirements are necessary to comprehend and manage soils well. The characteristics related with soil pH were analyzed and 5 field trials were conducted to elucidate pH buffer capacity of soil and lime requirements and liming factor for Korean acid soils. Soil minerals were analyzed for the soil of 2 years after treating $CaCO_3$ using X-ray diffraction. The amount of neutralized $H^+$ was regarded as the exchangeable aluminium overcoming ${\Delta}pH$, because pH buffer capacity of soil depended on exchangeable aluminium. Lime requirement was somewhat similar to the KCl exchangeable aluminium and it was also affected by the exchangeable cation by added lime. X-ray diffraction analyses revealed that an aluminium dissociation from Korean acid soils was equilibrated with kaolin minerals and changed into anorthite ($CaAl_2Si_2O_8$) by neutralizing with $CaCO_3$. Neutralizing process was composed of changing process of $Al^{3+}$ into $H^+$ and $Al(OH)_4{^-}$ ionic species and of neutralizing $H^+$ by, the amount of which was lime requirement. The fact that anorthite dissociates an aluminium ion higher than kaolinite does enabled to consider a liming factor (LF) the content of exchangeable cation and ${\Delta}pH$, $LF=1.5+0.2{\times}{\sum} Cations{\times}{\Delta}pH$.

• Journal of the Korean Geotechnical Society
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• v.30 no.9
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• pp.67-75
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• 2014

Methane gas hydrate which is considered energy source for the next generation has an urgent need to develop reliable numerical simulator for coupled THM phenomena in the porous media, to minimize problems arising during the production and optimize production procedures. International collaborations to improve previous numerical codes are in progress, but they still have mismatch in the predicted value and unstable convergence. In this paper, FEM code for fully coupled THM phenomena is developed to analyze methane hydrate dissociation in the porous media. Coupled partial differential equations are derived from four mass balance equations (methane hydrate, soil, water, and hydrate gas), energy balance equation, and force equilibrium equation. Five main variables (displacement, gas saturation, fluid pressure, temperature, and hydrate saturation) are chosen to give higher numerical convergence through trial combinations of variables, and they can analyze the whole region of a phase change in hydrate bearing porous media. The kinetic model is used to predict dissociation of methane hydrate. Developed THM FEM code is applied to the comparative study on a Masuda's laboratory experiment for the hydrate production, and verified for the stability and convergence.