• The Journal of Engineering Geology
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• v.23 no.3
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• pp.283-292
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• 2013

A calcareous rock slope failed during excavation of the slope for construction of a tunnel entrance. The slope is located at the construction site for widening highway in Yeongwol, Korea. Field surveys, laboratory tests, and numerical analyses were performed to determine the reason for the slope failure. The numerical analysis revealed that the safety factor of the slope before construction of the entrance was less than 1, and that this decreased after construction. After construction of the entrance, the sliding zone of the slope increased and slope stability decreased because the shear strain and plastic zone in the slope over the tunnel entrance showed an increase relative to the lower part of the slope. To enhance the stability of the slope for construction of the tunnel entrance, countermeasures such as rock bolts, rock anchors, and FRP (Fiber glass Reinforced Plastic) grouting were adopted in light of the field conditions. Serial field monitoring performed to confirm the reinforcing effects of the adopted countermeasures revealed a small amount of horizontal deformation of the slope soils, most of the elastic deformation that can regain its former value. In addition, the axial forces of the rock bolt and anchor were more strongly affected by slope excavation during construction of the tunnel entrance than by tunnel excavation or the rainy season, and the axial forces tended to converge after excavation of the tunnel. Therefore, we can confirm that the slope is currently safe.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.34-34
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• 2012

Heavy storms rainfall has caused many landslides and slope failures especially in the mountainous area of the world. Landslides and slope failures are common geologic hazards and posed serious threats and globally cause billions in monetary losses and thousands of casualies each year so that studies on slope stability and its failure mechanism under rainfall are being increasing attention of these days. Rainfall-induced slope failures are generally caused by the rise in ground water level, and increase in pore water pressures and seepage forces during periods of intense rainfall. The effective stress in the soil will be decreased due to the increased pore pressure, which thus reduces the soil shear strength, eventually resulting in slope failure. During the rainfall, a wetting front goes downward into the slope, resulting in a gradual increase of the water content and a decrease of the negative pore-water pressure. This negative pore-water pressure is referred to as matric suction when referenced to the pore air pressure that contributes to the stability of unsaturated soil slopes. Therefore, the importance is the study of saturated unsaturated soil behaviors in evaluation of slope stability under heavy rainfall condition. In an actual field, a series of failures may occur in a slope due to a rainfall event. So, this study attempts to develop a numerical model to investigate this failure mechanism. A two-dimensional seepage flow model coupled with a one-dimensional surface flow and erosion/deposition model is used for seepage analysis. It is necessary to identify either there is surface runoff produced or not in a soil slope during a rainfall event, while analyzing the seepage and stability of such slopes. Runoff produced by rainfall may result erosion/deposition process on the surface of the slope. The depth of runoff has vital role in the seepage process within the soil domain so that surface flow and erosion/deposition model computes the surface water head of the runoff produced by the rainfall, and erosion/deposition on the surface of the model slope. Pore water pressure and moisture content data obtained by the seepage flow model are then used to analyze the stability of the slope. Spencer method of slope stability analysis is incorporated into dynamic programming to locate the critical slip surface of a general slope.

• The Journal of Engineering Geology
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• v.32 no.2
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• pp.209-219
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• 2022

To experimentally investigate the variation of soil characteristics in slope during rainfall and the shape of slope failure, the model test was performed using soil box and artificial rainfall simulator. The model test of slope formed by the homogenous sand was performed, and the saturation pattern in the model slope due to rainfall infiltration was observed. The slope model with the inclination of 35° was set up on the slope of 30°, and the rainfall intensity of 50 mm/hr was applied in the test. The soil depth of 35 cm was selected by considering the size of soil box, and the TDR (time domain reflectometry) sensors were installed at various depths to investigate the change of soil characteristics with time. As the result of model test, the slope model during rainfall was saturated from the soil surface to the subsurface, and from the toe part to the crest part due to rainfall infiltration. That is, the toe part of slope was firstly saturated by rainfall infiltration, and then due to continuous rainfall the saturation range was enlarged from the toe part to the crest part in the slope model. The failure of slope model was started at the toe part of slope and then enlarged to the crest part, which is called as the retrogressive failure. At the end of slope failure, the collapsed area increased rapidly. Also, the mode of slope failure was rotational. Meanwhile, the slope failure was occurred when the matric suction in the slope was reached to the air entry value (AEV) estimated in soil-water characteristic curve (SWCC).

• Journal of the Korean Geotechnical Society
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• v.31 no.2
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• pp.5-11
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• 2015

Slope stability is affected by duration of precipitation, probable rainfall intensity, unsaturated soil property, and soil strength. The recent analyses of slope stability tend to include unsaturated analysis based on infiltration properties of soil, while researches of unsaturated soil slope tend to include the analysis of deformation and stress distribution of soil over time. However, infiltration property of unsaturated soil slope depends not only on intensity or duration of precipitation, but also on relief and surface condition, which is not considered in status quo. This research uses hydrologic model parameters of soil in order to consider effects of inclination on filtration, and carries out analysis of unsaturated soil slope to confirm the effects according to slope inclination and surface condition. In conclusion, using slope stability analysis, the need to consider infiltration rate according to inclination and surface condition was confirmed even under the same precipitation conditions.

• The Journal of Engineering Geology
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• v.27 no.3
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• pp.267-274
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• 2017

Behavior of rock mass depend on the mechanical properties of intact rock and geometrical property of discontinuity distributed in rock mass. In case of rock slope, particularly, location of slope failure surface and behavior after failure are changed due to discontinuities. In this study, two 3D slope stability analysis methods were developed for two different failure types which are circular failure and planar failure, considering that failure type of rock slope is dependent on scale of discontinuity which was then applied to real rock slope to review the applicability. In case of circular failure, stable condition was maintained in natural dry condition, which however became unstable when the moisture content of the surface was increased by rainfall. In case of planar failure, rock slope become more unstable comparing to dry condition which is attributable to decrease in friction angle of discontinuity surface due to rainfall. Viewing analysis result above, analysis method proved to have well incorporated the phenomenon occurred on real slope from the analysis result, demonstrating its applicability to reviewing the slope stability as well as to maintaining the slope.

• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.3 s.14
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• pp.9-17
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• 2004

In recent years slope failure due to heavy rainfalls or local downpours usually accompanied by typhoons has increasingly occurred in Korea. Also, the damages caused by slope failure have a tendency to be more disastrous than before. This study has been conducted to prepare an early warning system for slope failure by : (1) analyzing types and causes of slope failure, (2) examining the published evaluation criteria for slope stability, (3) estimating slope stability by considering the properties of slope-forming materials as well as the topographical and geological properties of slopes, and (4) determining the most important variables of affecting the stability of the slope under consideration. The data on the variations of slope conditions measured by an automatic in-situ measurement system and then transmitted to the central analysis system by using an internet. The most important variables can be back-calculated in the central system and compared with the values for the first and second management criteria. These management criteria should be modified and corrected continuously in the future by accumulated data and knowledge related to the early warning system for slope failure.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.11 no.5
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• pp.92-103
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• 2008

Development of new approaches to achieve naturally good ecological potential of forest road cut-slope by making the best use of advantages of gabion systems with vegetation base materials to prevent slope failure and erosion, in the area with highly erodible soil. As a result on the type analysis of gabion systems already installed in road cut-slopes, gabion systems were generally established to prevent slope failure. Existing gabion systems can be divided into monolithic and modular system and can be divided into ten subtypes according to the purpose of establishment and combination of other measures. As a result on the monitoring of erosion amount from forest road cut-slopes in the test applications, the order of erosion amount from largest to smallest is as follows : the curved road cut-slope site where normal gabion system was established ($7,911cm^3$); the control site ($7,632cm^3$); the straight road cut-slope site where normal gabion system was established ($7,301cm^3$); the curved road cut-slope site where the new gabion system was established ($5,684cm^3$); and the straight road cut-slope site where the new gabion system ($5,325cm^3$). Therefore, the result shows that the new gabion system is more effective than the normal gabion system to reduce erosion amount from forest ! road cut-slopes. During the study period, vegetation coverages of the straight and curved road cut-slope site where the new gabion system was established were about 45% and about 36%, so average vegetation coverage of the sites where the new gabion systems was established was higher than the sites where the normal gabion systems was established. Therefore, it was concluded that the new gabion system can be more effective for cut-slope revegetation.

• Journal of the Korean Geotechnical Society
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• v.29 no.5
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• pp.65-74
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• 2013

The natural disaster occurrences and the loss of lives caused by the steep-slope failures in Korea were investigated in this study. The investigation includes the frequency rate of the steep-slope failures with respect to the characteristics of precipitation, underlying bedrock, and weathered soils. Analysis on the problems in the existing estimation methods of steep-slope failure was also undertaken, and a new model using unsaturated infinite slope stability was developed for the better slope failure estimation. The slope analyses by the newly developed model were performed considering unsaturated infinite slope, the gradient of slope, and hydro/mechanical properties of soils. Steep-slope failure estimation criterion is proposed based on the analysis results. In addition, the precipitation amount corresponding to warning stages against steep-slope failure is provided as an equation of Intensity-Duration criterion.

• Journal of the Korean School Mathematics Society
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• v.22 no.4
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• pp.351-367
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• 2019

Slope is an important mathematical concept that is connected to advanced mathematics as well as a basic concept as an indicator of the steepness of a straight line. The purpose of this study is to see how the concept of slope is presented in mathematics textbooks of middle school. For this study, we analyzed the types of slope concepts in the textbooks. In particular, we analyzed motivation activity, definition, examples of slope in them and used a concept framework of slope by Stump(1999, 2001), Moore-Russo, Connor & Rugg (2011). As a result, it was shown that middle school mathematics textbooks use the types of slope concepts to be biased when explaining the slope or presenting the slope problems. In addition, the real contexts of slope is poorly presented, and the concept types change from visual aspect to analytical aspect in the processes. This study provides suggestions on how to present the slope concepts in mathematics curriculum and middle school textbooks.

• Geotechnical Engineering
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• v.11 no.4
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• pp.111-124
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• 1995

On development of mountaneous or hilly area, stability of cut slope should be provided to prevent undesirable landslides. When piles are used as a countermeasure to stabilize existing landslide, stabilities for both piles and slope should be simultaneously satisfied to obtain the whole stability of the slope reinforced by piles. In order to confirm the effect of stabilizing piles on slope stabilization, it is necessary to investigate the behavior of the slope, in which the piles are installed. In this paper, first, the countermeasures used commonly to control unstable slope in Korea were summerized systematically. Nezt, the behavior of piles and slope soil was investigated by instrumentation installed into a cut slope for an apartment stabilized by a row of piles. Instrumentation could present sufficient effect of piles on slope stabilization Construction works in front of the row of piles affected the displacement of piles and slope. The construction works were divided into four stages, i.e. initial cutting stage of slope, excavation stages for retaining wall and parking space, and construction of retaining wall. As the result of research, the applicability of the proposed design method could be confirmed sufficiently.