• The Journal of Engineering Geology
• /
• v.29 no.1
• /
• pp.23-35
• /
• 2019

Landslides occur due to heavy rainfall in the summer season. Some of water may infiltrate into the ground; it causes a high saturation condition capable of causing a landslide. Soil properties are crucial in estimating slope stability and debris flow occurrence. The main study areas are Gwanaksan, Suraksan and Bukhansan (Mountain) in Seoul. A total of 44 soil samples were taken from the study area; and a series of geotechnical tests were performed. Physical and mechanical properties were obtained and compared based on region. As a result, among well-graded soils, they are classified as a clayey sand. Coarse-grained and fine-grained contents are approximately 95% and 5%, respectively, with very low amount of clay content. Density, liquid limit and dry unit weight are ranged in $2.62{\sim}2.67g/cm^3$, 27.93~38.15% and $1.092{\sim}1.814g/cm^3$. Cohesion and internal friction angle are 4 kPa and $35^{\circ}$ regardless of mountain area. Coefficient of permeability is varied between $3.07{\times}10^{-3}{\sim}4.61{\times}10^{-2}cm/sec$; it means that it results in great seepage. Permeability is inversely proportional to the uniformity coefficient and is proportional to the effective particle size. In the formal case, there was a difference by mountain area, while in the latter, the tendency was almost similar.

• Journal of the Korean GEO-environmental Society
• /
• v.12 no.7
• /
• pp.57-65
• /
• 2011

Numerical simulations by three-dimensional Particle Flow Code($PFC^{3D}$, Itasca) considering distinct element method (DEM) were carried out for prediction of triaxial compression test with sand material. The effect of scale conditions for numerical model and distinct material on final prediction results was analyzed by numerical models under various scale conditions, and following observations were made from the numerical experiments. It is very useful to model the initial material condition without any porosity conversion from 2-D to 3-D DEM. Numerical experiments have shown that in all cases considered, 3D distinct element modeling could provide good agreement on stress-strain behavior, volume change and strength properties with laboratory testing results. It was important thing to assess reasonable scale ratio of numerical model and distinct elements for saving calculation time and securing calculation efficiency under condition with accuracy and appropriateness as numerical laboratory. As results of DEM simulations under various scale conditions, most of results show that shear strength properties as cohesion and internal friction angle are similar in condition of $D_{mod}/D_{gmax}$ < 10. It shows that 3-D distinct element method could be used as efficient tool to assess strength properties by numerical laboratory technique.

• Journal of the Korean Geosynthetics Society
• /
• v.11 no.4
• /
• pp.17-25
• /
• 2012

In this study, it was carried out reliability analysis and slope stability analysis in a standard cross-sectional embankment on high speed railway. It was confirmed that changing tendency of safety factor with various parameter of each soil materials properties and trends of the probability of failure according to the reliability index. The results have shown that a safety factor were relatively large affected an cohesions and internal friction angle of soil compared to the unit weight of soil. Also, most of the standard cross-sectional embankment in high speed railway was generally evaluated the level of below average (below average) by the reliability analysis according to criterion in US. Army but the 12m height of dry embankment case was shown bad condition as Poor.

• Journal of the Korean GEO-environmental Society
• /
• v.15 no.12
• /
• pp.43-51
• /
• 2014

Organic matter in dredged soil has a lot of engineering problem in ground including a large settlement, crack propagation, low bearing capacity and low friction angle. From an agricultural point of view, however, organic matter contributes greatly soil quality and plant health. This paper investigated the relationship between engineering and germination characteristics of stabilized mixture consisting of different ratios of organic content (0 %, 10 %, 20 %, 30 %) for recycling dredged soil including organic matter. Several series of laboratory tests such as flow test, unconfined compressive test and consolidation test were performed to find out engineering characteristics. pH, percent of germination and growth of plants were also measured to investigate the germination characteristics. The experimental results indicated that, as organic content increased, unconfined compressive stress decreased and compression and swelling indices increased. However, percent of germination and plant growth increases as organic content increases.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.5 no.4
• /
• pp.89-98
• /
• 2010

Recently, many researches on bottom ash which is produced in the burning process of power plant are actively performed for its utilization for soil-subbase materials. In this paper, bottom ashes from 5 different power plants are prepared and several tests including compaction, CBR, and tri-axial compression are carried out for mixed bottom ash and weathered soil considering 3 replacement ratio of 30%, 50%, and 70%. Through the tests, CBR result over 20 are evaluated without plastic property, which shows availability of subbase material. With higher increase in replacement ratio of bottom ash, CBR of mixed soil increases due to the higher mechanical performance of bottom ash. However, replacement effects of bottom ash on friction angle and cohesion are evaluated to be little since bottom ash plays a little role in rearrangement of mixed soil. Bottom ash with a good mechanical property is evaluated to have reasonable bearing capacity which shows a good property for subbase materials.

• The Journal of Engineering Geology
• /
• v.21 no.3
• /
• pp.247-257
• /
• 2011

In this study the infinite slope model, one of the physical landslide models has been suggested to evaluate the susceptibility of the landslide. However, applying the infinite slope model in regional study area can be difficult or impossible because of the difficulties in obtaining and processing of large spatial data sets. With limited site investigation data, uncertainties were inevitably involved with. Therefore, the probabilistic analysis method such as Monte Carlo simulation and the GIS based infinite slope stability model have been used to evaluate the probability of failure. The proposed approach has been applied to practical example. The study area in Boeun area been selected since the area has been experienced tremendous amount of landslide occurrence. The geometric characteristics of the slope and the mechanical properties of soils like to friction angle and cohesion were obtained. In addition, coefficient of variation (COV) values in the uncertain parameters were varied from 10% to 30% in order to evaluate the effect of the uncertainty. The analysis results showed that the probabilistic analysis method can reduce the effect of uncertainty involved in input parameters.

• Journal of the Korea Convergence Society
• /
• v.6 no.4
• /
• pp.153-159
• /
• 2015

Dental assistant in South Korea, The work is overlapped considerably between dental hygienist and dental practical nurse. Moreover, dental technician, hospital coordinator work in dentistry consultation deeply. It cause friction among work scope of occupation's type. Accordingly It is purpose to get basic data which is necessary to deduce division of work training and utilization of human resources in oral health distinguish clearly between business occupations. Also compared and analyzed via analysis of frequency and ANOVA above 10 works around something legal work of dental hygienist regarding work reality of dental assistant in dental clinic and hospital. Compare with scaling, representative item about 10 works center on legal work of dental hygienist, is implementing dental technician 9(75%), practical nurse 64(87.67%), etc. 11(64.71%). Dental assistant except dental hygienist is implementing indigenous legal work of dental hygienist. Dental institution secure enough man power, It is suggested necessity for policy means regarding role and work scope of dental assistant.

• Journal of Korean Society of Forest Science
• /
• v.103 no.2
• /
• pp.218-225
• /
• 2014

Landslides, one of earth's natural disasters, increase every year due to heavy rainfall, and cause damage to human life and assets. This study used the SHALSTAB to predict places at risk of landslides, in accordance with the intensity of rainfall. The parameter value of transmissivity was $19.58m^2/day$, the internal friction angle $36.3^{\circ}$, and the saturated unit weight $2.03t/m^3$. The slope stability status was classified into four categories, namely: unconditionally stable, stable, unstable and unconditionally unstable. In order to evaluate the applicability of the SHALSTAB, actual landslide areas were checked, with the unstable area under 263 mm rainfall. 85.1% of them were consistent. And so we can identify the distribution of places at risk of landslides, on the basis of the intensity of rainfall by means of SHALSTAB.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.26 no.1
• /
• pp.33-40
• /
• 2014

Reliability analysis of jacket type offshore wind turbine (OWT) support structure under extreme ocean environmental loads was performed. Limit state function (LSF) of OWF support structure is defined by using structural dynamic response at mud-line. Then, the dynamic response is expressed as the static response multiplied by dynamic response factor (DRF). Probabilistic distribution of DRF is found from response time history under design significant wave load. Band limited beta distribution is used for internal friction angle of ground soil. Wind load is obtained in the form of thrust force from commercial code called GH_Bladed and then, applied to tower hub as random load. In a numerical example, the response surface method (RSM) is used to express LSF of jacket type support structure for 5MW OWF. Reliability index is found using first order reliability method (FORM).

• Tunnel and Underground Space
• /
• v.24 no.3
• /
• pp.187-200
• /
• 2014

After excavation or blasting, rock properties within an excavation damaged zone can be perpetually weakened on account of stress redistribution or blasting impact. In the present study, the excavation damaged zone is applied to a rock slope. The objective of this research is to compare the mechanical stability of the rock slope depending on the presence of the damaged zone using 2-dimensional modeling and analyze factors affecting factor-of-safety. From the modeling, it was founded that the mechanical stability of the rock slope is significantly dependent on the presence of the damaged zone. In particular, factor-of-safety with a consideration of the damaged zone decreased by approximately 49.4% in comparison with no damaged zone. Factor analysis by fractional factorial design was carried out on factor-of-safety. It showed that the key parameters affecting factor-of-safety are angle of the slope, cohesion, internal friction angle and height.