• Journal of the Korean Geotechnical Society
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• v.38 no.11
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• pp.31-42
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• 2022

This study verified numerical analysis of the liquefaction phenomenon using LEAP-2017 international round-robin centrifuge test results. Dynamic centrifuge test is performed by applying a 1 Hz tapered sine wave to the model soil deposit, which was formed under a water table in a surface slope of 5° using Ottawa F-65 sand. A numerical model was made on a prototype scale and analyzed using the finite difference method in 2D and 3D conditions. The analyses were verified for acceleration and pore-water pressure histories with depth and residual displacement. Verification results revealed that all numerical liquefaction models agree reasonably with the test result for acceleration histories but not for pre-water pressure histories. Numerical analyses showed much smaller residual displacement than the centrifuge test. Thus, it is necessary to compare the results of numerical analysis with the centrifuge test performed by other institutes in the future.

• Journal of the Korean Society for Heat Treatment
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• v.36 no.3
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• pp.161-173
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• 2023

This study investigated the effects of K_N and process time on the formation of a compound layer at a nitriding temperature of 540℃ for SCR420H material. As a result of controlled nitriding from 3 h to 20 h at K_N 1.2 atm^-1/2, compound layers were formed up to about 10 ㎛, and an effective hardening depth of about 460 ㎛ was obtained. Initially, an ε+γ' complex phase was formed, and the phase fraction changed over time, and finally, the fraction of ε phase decreased to less than 1%. With higher K_N, the compound thickness increased, a pore layer was formed on the surface, and the surface hardness decreased. By applying the controlled nitriding process, it was possible to produce annulus gears with a compound thickness of 12.8 ㎛ and an ε phase of 5% or less. The annulus gears made through controlled nitriding were mounted on a 6-speed transmission and tested for durability. As a result, the durability test of 250,000 km was satisfied, and the transmission efficiency was also confirmed to be expected.

• The Korea Journal of Herbology
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• v.39 no.3
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• pp.1-9
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• 2024

Objectives : The purpose of this study was to find out the efficacy of placenta on the skin by comparing the difference effect between only MTS (microneedle therapy system) and the placenta extract application after MTS treatment. Methods : The present author performed once a week and total 4 times of MTS treatment. The treatment time took about 5~10 minutes and the depth of the needle was adjusted according to the participant's skin condition. One week after each treatment, the change of skin condition was measured. Two weeks after the end of the clinical trial, the skin condition was checked again. Results : In the case of moisture and elasticity, significant increases were observed in both the experimental and control groups. In the experimental group, skin temperature significantly decreased one week after the second treatment, and pore size significantly increased one week after the third treatment. In the case of skin tone, there was a significant temporary decrease after the first treatment in the control group, and in the experimental group, the skin tone showed a total decrease. Conclusion : When placenta extract was applied after MTS, skin temperature decreased and pores enlarged in the second and third treatments, and side effects such as rash and itchiness appeared. The final result showed a significant increase in skin moisture and elasticity. When animal-based ingredients containing high fat content are applied to the skin, the effect on the skin is good, but hypersensitivity reactions may occur, so use them with caution.

• The Journal of Engineering Geology
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• v.25 no.1
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• pp.57-66
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• 2015

A numerical analysis was performed of the seepage from and stability of a mine waste-dump slope in Imgi, Busan, considering rainfall intensity. The 40-45° slope angle of the waste dump is relatively steep, and the depth of the waste dump down to bedrock is 7-8 m. The groundwater level was 6.6 m below the surface. Various laboratory tests on samples obtained from the waste dump were performed to determine the input data for seepage and stability analyses of the waste-dump slope during rainfall. The results of seepage analysis for various rainfall intensities using the SEEP/W program show that the wetting front moved down with increasing rainfall duration. When the rainfall intensity was > 50 mm/ hour and the duration was > 24 hours, the waste dump became fully saturated because the wetting front reached the groundwater level. The results of slope stability analysis coupled with seepage analysis using the SLOPE/W program show that the safety factor of the slope decreased as the wetting front moved down due to rainfall infiltration. After continuous rainfall for 5-6 hours, the safety factor of the slope suddenly decreased but then recovered and converged. The sudden decrease was induced by an increase in pore-water pressure and a decrease in matric suction down to a certain depth as the wetting front approached the potential sliding surface.

• Journal of the korean academy of Pediatric Dentistry
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• v.24 no.3
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• pp.660-677
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• 1997

The purpose of this study was to examine the morphological characteristics and combined effects of fluoride application and laser irradiation on artificial caries-like lesion formation in bovine enamel. Enamel specimens were divided into five experiment group and placed in no-treatment(group C), APF application alone(group F), laser irradiation alone(group L), APF application before laser irradiation (group FL), and APF application after laser irradiation(group LF) on artificial caries-like lesion. Sound enamel was used as a control group. The ultrastructural changes and physical effects of the fluorided and lased enamel has been investigated by using SEM, enamel solubility and microhardness test as well as distributions of calcium, phosphorus and fluoride in internal enamel by using EPMA. The following results were obtained. 1. In the all experiment groups, the amounts of dissolved calcium of enamel surfaces significantly decreased according to increasing exposure time of acid solution than control group(P<0.001). Group L showed higher than that group FL and LF in 30 and 60min(P<0.05). 2. The microhardness values of enamel surface in the control group was highest than that in the other experiment groups. Group F, L, FL and LF were significantly increased than group C(P<0.001). The enamel surface treated with APF produced deposites of numerous small globules and lased enamel showed a cracker-like appearance with microcrack and small pore. Numerous deposits were infiltrated in the fissured portion of enamel treated with APF after laser irradiation. 4. In the case of APF application alone, the elevation of the fluoride profile can be seen within $5{\mu}m$ of the outermost layer and a similar profile observed in the specimen treated with APF before laser irradiation. However, the specimen treated with APF after laser Irradiation showed a large elevation within $10{\mu}m$ of the outermost layer of the enamel. 5. The higher Ca/P ratios were observed in $10{\mu}m$ depth of lased and fluorided enamel when compared to the sound and carious enamel. The fluoride content decreased rapidly with distance from enamel surface, in the group F, fluoride concentration was significantly higher than that in the group C, L, FL, LF and control group according to increasing enamel depth (P<0.05).

• Journal of the Korean Geophysical Society
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• v.7 no.3
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• pp.207-215
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• 2004

As the sea connecting with the East Sea, the Sea of Okhotsk is the most potential area of gas hydrates in the world. In other to examine geophysical structures of gas hydrate-bearing sediments in the Sea of Okhotsk, the CHAOS (hydro-Carbon Hydrate Accumulation in the Okhotsk) international research expedition was carried out in August 2003. In the expedition, high-resolution seismic and geochemical survey was also conducted. Sparker seismic profiles show only diffusive high-amplitude reflections without BSRs at BSR depth. It means that BSR appears to be completely different images on seismic profiles obtained using different frequencies. Many gas chimneys rise up from BSR depth to seafloor. The chimneys can be divided into two groups with different seismic characteristics; wipe-out (WO) and enhanced reflection (ER) chimneys. Different seismic responses in the chimneys would be caused by amount of gas and gas hydrates filling in the chimneys. In hydroacoustic data, a lot of gas flares rise up several hundreds meters from seafloor to the water column. All flares took placed at the depths within gas hydrate stability zone. It is interpreted that gas hydrate-bearing sediments with low porosity and permeability due to gas hydrate filling in the pore space make good pipe around gas chimneys in which gas is migrating up without loss of amount. Therefore, large-scale gas flare at the site on gas chimney releases into the water column.

• Journal of the Korean Geotechnical Society
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• v.18 no.6
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• pp.73-81
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• 2002

Various CPT-based prediction models far profiling stress history of marine clay at the southern part of the Korean peninsula were investigated by using both statistical analysis and case history study. Preconsolidation pressures($\sigma'$p) and overconsolidation ratio(OCR) estimated by empirical correlations and cone penetration tests were compared with those of laboratory odometer test results. Stress history of marine clay determined by odometer test results was in general overconsolidated at below 10m depth from the mudline, whereas marine clay at below l0m depth from the mudline which has an around 0.3 overconsolidation ratio showed variable stresses and unstable states. Preconsolidation pressures were computed by both empirical methods of the Chen and Mayne(1996) and theoretical method of Konrad and Law(1987). It is estimated that Chen and Mayne(1996)'s prediction method based on pore water pressure is more reliable than any other prediction methods, and their method proved to be the most reliable for overconsolidation ratio estimation. However, it is recommended that Mayne & Holtz(1988) and Mayne & Bachus(1988) methods are more suitable than any other methods for predicting the overconsolidation ratio at an underconsolidated (OCR<1) clay. For these reasons, rather than making use of existing prediction models, development of site specific empirical correlations which considers local characteristics and site conditions may be required due to different local stress history and variable soil properties.

• Korean Journal of Soil Science and Fertilizer
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• v.30 no.3
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• pp.226-233
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• 1997

To investigate the salt accumulation in the plastic film house soils, bulk density, electrical conductivity(EC), exchangeable canons and water soluble anions were determined at different depths(0~60cm) in the salt-accumulated plastic film house soils in Yesan, Chungnam, Korea. Bulk density were increased from $1.2Mg/m^3$ to $1.5Mg/m^3$ as the depth changed from 0cm(top soil) to 30cm(subsoil) below the soil surface, whereas the bulk densities between 30cm to 60cm slightly decreased to $1.42Mg/m^3$. These changes of soil bulk densities might influence the porosity and pore size distribution, resulting in affecting the water flow throughout, soil layers. Electrical conductivity and Exchangeable sodium percentage(ESP) for 0 to 10cm soil layer were 5.08 dS/m and 6.4, respectively, while the EC was decreased to less than 1.63 dS/m in 20~30cm depth and about 0.7 dS/m. Salt accumulation patterns in the plastic film house soils might be influenced by the changes of the bulk densities in soil.

• Resources Recycling
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• v.29 no.1
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• pp.53-61
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• 2020

This study aimed to develop a foam concrete material for a ground repair system that has low strength and low fluidity by using an eco-friendly binder, which substitutes industrial by-products for more than 90% of cement. Basic properties were evaluated after substituting a small amount of calcium sulfo aluminate (CSA) for the binder to improve the sinking depth rate and volume change, commonly found when it had a large amount of industrial by-products. The substitution rates of CSA for the eco-friendly binder used for the foam concrete were 2.5, 5, and 10%. Fresh properties, hardened properties, pore structure, and hydrates were analyzed. Experimental results showed that using only 2.5% of CSA could improve the deep sinking depth which occurred when using an eco-friendly binder. As a result, the weight difference between the upper, middle, and lower parts of cast specimens was improved even after being hardened. The addition of CSA also contributed to the formation of small, uniformly sized closed pores and improved initial strength. However, when the proportion of CSA increased, the long-term strength decreased. However, it satisfied the target strength when 5% or less of CSA was used. The results of this study revealed that it was possible to manufacture foam concrete with low strength and high fluidity for repairing ground satisfying target qualities by adding 2.5% of CSA to the eco-friendly binder containing a large amount of industrial by-products.

• Journal of the Korean Geotechnical Society
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• v.37 no.11
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• pp.71-81
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• 2021

The purpose of this study is liquefaction phenomenon was simulated using the 1g shaking table test. Analysis of liquefaction and Re-liquefaction behavior according to the ground conditions was analyzed when an embankment exists above the ground. The soil used in the experiment was silica sand and the ground composition was a liquefied layer of 50cm (Case 1), a non-liquefied layer of 17.5cm and a liquefied layer of 32.5cm (Case 2). The embankment was formed by fixing the height of 10cm and the slope of the slope at a ratio of 1:1.8. For seismic waves, excitation of a 5Hz sine wave was performed for 8 seconds, and a total of 5 case excitations were performed. In Case 1, it was confirmed that liquefaction occurred at all depths during the first vibration excitation at the free-field and that liquefaction did not occur at all depths except 5cm at the third vibration excitation. At the center of the embankment, liquefaction occurred up to a depth of 20cm during the first vibration excitation, and it was confirmed that liquefaction did not occur at all depths except for a depth of 5cm during the second vibration excitation.