• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.5
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• pp.103-109
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• 2008

Precipitation on slope is separated into infiltration and outflow according to physical properties of soil and slope. However, the slope analysis is assumed that all precipitation are percolated. So, groundwater level is excessive tend to be calculated. In this paper, NRCS model and Horton models that have a suitability were used for agro-type analysis of Seoul station after precipitation was separated into infiltration and outflow. Also, gradient of slope was analyzed about seepage behavior and underground water level aspect through numerical analysis. After inclination correction, the estimated infiltration was compose of slopes much applied by domestic design standard. The change of groundwater level is appeared greatly as agro-type goes from D type to A type in the analysis results.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.71-78
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• 2010

The stability analysis of unsaturated infinite slope under rainfall-induced infiltration condition was performed using the generalized effective stress that unifies both saturated and unsaturated condition recently proposed by Lu and Likos(2004, 2006). The Soil-Water Characteristic Curve (SWCC) of the sand with the relative density of 75% was first measured for both drying and wetting processes. The Hydraulic Conductivity Function (HCF) and Suction Stress Characteristic Curve (SSCC) were subsequently estimated. Also, under the rainfall-induced infiltration condition transient seepage analysis of unsaturated infinite slope was performed using the finite element program, SEEP/W. Based on these results, the stability of unsaturated infinite slope under rainfall-induced infiltration condition was examined considering the suction stress. According to the results, the negative pore water pressure and water content within the soil changed with time due to the infiltration. Also, the variation of those caused the variation of suction stress and then the factor of safety of slope changed consequently during the rainfall period.

• Journal of the Korean Geotechnical Society
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• v.30 no.10
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• pp.45-54
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• 2014

Many studies have been made on investigation, design, explanation and treatments etc. to minimize slope failure. However, the problem is that failures of cutting slope and natural slope due to Typhoon and localized heavy rainfall are still not reduced. It is difficult to treat the problem by only strengthening the design standard. And it is very necessary to carry out design and safety analysis under the most suitable conditions considering foundation and rainfall characteristics. In this study, variations of safety factor were discussed from different aspects to investigate the influence of different parameters of rainfall and analysis conditions. Rainfall and foundation conditions are supposed to be the most sensitive parameters to slope stability, and numerical analysis were performed by changing parameters of the two conditions. Rainfall behavior is based on the domestic statistical rainfall and foundation condition is selected as unsaturated soils. Study results show that, application of rainfall characteristics in different area and parameters of unsaturated soils are responding sensitively to variations of slope safety. Therefore, the input parameters should be fully examined when performing the practical design.

• Journal of the Korean GEO-environmental Society
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• v.8 no.5
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• pp.57-65
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• 2007

Slope collapse occurs mostly at the rainy season or thawing season in Korea. From a engineer point of view, the design criterion in recent of soil slopes during the rainfall have a conservative tendency because a slope stability is evaluated in the condition that ground water level is located in the surface. However, for the rational design of soil slopes during rainfall, the raining conditions and the unsaturated soil characteristics of soil slopes have to be considered. For the unsaturated soil characteristics of soil slopes, the laboratory tests for unsaturated soils and the seepage analyses for the raining conditions have to be performed. Due to these difficulties, a conservative design of soil slopes in the current design criterion has been carried out. In this paper, therefore, a simple design method is proposed. The method is considered to the unsaturated soil characteristics and the results of seepage analysis without numerical analysis. To verify the suggested design method, it is compared with both analysis results by current design criterion and analysis results based on the seepage analysis. Through the comparative study, it was found that the current design criterion has been excessively conservative. Hence, simple design method in this study was evaluated as the rational design for the soil slopes during rainfall.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.811-818
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• 2005

Stability analyses on the 17 railroad cut-off soil slopes were carried out. The influences of rainfall infiltration on the slope stabilities were taken into account by seepage analyses using finite element method and by assuming ground water tables to be located adjacent to soil surface. The validity of those analyses were evaluated by comparing the slope failure characteristics between analysis results and the past failure records. The analyses were not appropriate to estimate the failure surface and the method considering only the increase of pore-water pressure (reduction of matric suction) as the influence of rainfall cannot appropriately estimate the surficial failures that occurred most of the cut-off soil slopes. For the better estimation of the surficial failure, the influence of water flows over slope surface which erode soil mass and/or increase driving force, should be evaluated and considered.

• The Journal of Engineering Geology
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• v.17 no.1 s.50
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• pp.57-64
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• 2007

This study was conducted to characterize on the relationships among rainfall intensity, slope angle and pore water pressure in the gneissic weathered soil by landslide laboratory flume tests. Under the several test conditions dependent on rainfall intensity and slope angle, the authors measured pore water pressure, failure and displacement of slope on a regular time interval. According to the test results, the increasing times of pore water pressures have direct proportional trends to the rainfall intensity. The pore water pressure was increased earlier at the head part of slope than the toe part. Compared with the test results of Chae et al(2006), the results of this study explain that the seepage velocity in the gneissic weathered soil is slower than that in the standard sands. It results in faster and ear-lier increase of pore water pressure at the head part of slope due to slow flow of water in the gneissic weathered soil. In case of the relationship between slope angle and pore water pressure, gentle slope angle has faster increase of pore water pressure than steeper slope angle. It is also thought to be due to slow seepage velocity and flow velocity in the gneissic weathered soil.

• Land and Housing Review
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• v.9 no.2
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• pp.51-57
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• 2018

The causes of landslides are dependant on rainfall events and the soil characteristics of a slope. For the conventional slope stability, the slope stability analysis has been carried out assuming the saturated soil theory. But, in order to clearly explain a proper soil slope condition by rainfall, the research should be performed using the unsaturated soil mechanism suitable for a soil slope in the field. In the study, by using two major categories of soils in Korea, such as granite and gneiss weathered soils, landslide model test and finite element method have been compared with the difference of seepage and soil stability analysis. The hydraulic conductivity of gneiss weathered soil is slower than that of granite weathered soil, and the gneiss weathered soil contains much finer soils than the granite weathered soil. It was confirmed that the instability of the slope was progressing slowly due to the slow rate of volumetric water content of the surface layer.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.33-41
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• 2017

In this study, the increment effect of safety factor according to increasing of horizontal permeability coefficient is analyzed when geocell is installed on the slope for protection. To evaluate the horizontal permeability and reinforcement effect, the laboratory tests such horizontal permeability test were conducted. According to the laboratory test results, as the porosity rate of geocell increases, the coefficient of horizontal permeability is also increased. And also, regardless of the different types of filled materials, the coefficient of horizontal permeability is improved in a geocell reinforced ground compare with the non-reinforced ground. Laboratory test results and the rainfall intensity were applied to the numerical modeling of slope for seepage analysis and stability analysis of slope by using Soilworks, numerical analysis program. As a result of the slope stability analysis, it is confirmed that the installed geocell on the slope facilitates the drainage of water on the surface of slope. Hence, the ground water elevation is suppressed. Therefore, the safety factor of the slope is increased by the increasing of the internal friction angle, apparent cohesion, and coefficient of horizontal permeability by reinforcing the slope with geocell.

• Journal of the Korean GEO-environmental Society
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• v.17 no.5
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• pp.5-16
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• 2016

A rainfall induced slope failure is a common natural hazard in mountainous areas worldwide. Sudden and rapid failures which have a high possibility of occurrence in a steep slope are always the most dangerous due to their suddenness and high velocities. Based on a series of experiments this study aimed to determine a critical angle which could be considered as an approximate threshold for a sudden failure. The experiments were performed using 0.42 mm mean grain size sand in a 200 cm long, 60 cm wide and 50 cm deep rectangular flume. A numerical model was created by integrating a 2D seepage flow model and a 2D slope stability analysis model to predict the failure surface and the time of occurrence. The results showed that, the failure mode for the entire material will be sudden for slopes greater than $67^{\circ}$; in contrast the failure mode becomes retrogressive. There is no clear link between the degree of saturation and the mode of failure. The simulation results in considering matric suction showed good matching with the results obtained from experiment. A subsequent discarding of the matric suction effect in calculating safety factors will result in a deeper predicted failure surface and an incorrect predicted time of occurrence.

• Geomechanics and Engineering
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• v.33 no.2
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• pp.167-174
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• 2023

This study evaluated slope stability through a case study to determine the disaster risks associated with increased deforestation in structures, including schools and apartments, located in urban areas adjacent to slopes. The slope behind the ○○ High School in Gwangju, Korea, collapsed owing to heavy rain in August 2018. Historically, rainwater drained well around the slope during the rainy season. However, during the collapse, a large amount of seepage water flowed out of the slope surface and a shallow failure occurred along the saturated soil layer. To analyze the cause of the collapse, the images of the upper area of the slope, which could not be directly identified, were captured using unmanned aerial vehicles (UAVs). A digital elevation model of the slope was constructed through image analysis, making it possible to calculate the rainfall flow direction and the area, width, and length of logging areas. The change in the instability of the slope over time owing to rainfall lasting ten days before the collapse was analyzed through numerical analysis. Imaging techniques based on the UAV images were found to be effective in analyzing ground disaster risk maps in urban areas. Furthermore, the analysis was found to predict the failure before its actual occurrence.