• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1C
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• pp.1-9
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• 2009

In this study, the influence of wetting band depth by continuous rainfall and the magnitude of wetting front suction on the stability of slopes in weathered soils were investigated by using finite element programs SEEP/W and SLOPE/W. Three different intensities of rainfall (10mm/hr, 30mm/hr, 50mm/hr) were chosen, and the total duration of rainfall was 96 hours. Three infinite slopes with the inclination of 1:1.5 and 1:1.8, 1:2.0 were considered and the typical properties and the shear strength parameters of the weathered soil were applied. It is shown that rainfall duration plays an important role in slope stability. Based on the analytical results, it is found that as the rainfall duration increases, the wetting band depth also increases. Also, the increasing rate of the wetting band depth was decreased as the soil density was increased. These results come from the decrease of the coefficient of permeability and the increase of the soil suction. Finally, it is also shown that the safety factors of slopes by unsaturated analysis are mostly larger than those by saturated analysis. Therefore, commonly used saturated analysis may substantially underestimate the degree of safety factor in realistic situations.

• The Journal of Engineering Geology
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• v.29 no.4
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• pp.541-552
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• 2019

In this study, landslide flume tests were performed to analyze characteristics of ground characteristics and landslide occurrence due to rainfall infiltration. As test materials, weathered granite soil and gneiss soil, the most frequent landslides in Korea, were used, and landslides were triggered by heavy rain (Intensity = 200 mm/hr). The measurement sensors were installed with 3 sets at toe, slope, top part and shallow (GL-0.2 m), middle (GL-0.4 m), and deep (GL-0.6 m) depth in the slope and measured at 10 second intervals. After landslide flume tests, the slope stability analysis was performed by applying the unsaturated soil theory based on the change of ground characteristics and compared with actual landslide occurrence from flume test. As a result of the analysis, factor of safety reflected the landslide occurrence from flume test and factor of safety decreased as rainfall infiltration, leading to slope failure. Finally we compared to the factor of safety below 1 and actual landslide occurrence time, the average difference was 1,600 seconds for weathered granite soil and 5,400 seconds for weathered gneiss soil.

• Journal of the Korean Geotechnical Society
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• v.21 no.6
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• pp.137-146
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• 2005

299 railroad slopes were investigated and the failure characteristics and reinforcement patterns were analyzed. Stability analyses on the 14 cut-off soil slopes were carried out. Surficial failures were predicted by infinite slope analyses assuming the temporarily perched ground water table at soil surface during rainfall period. Limit equilibrium analyses were also carried out and 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 adequacy of those analyses was evaluated by comparing the slope failure characteristics between analysis results and the past failure records. From the comparison results, it was deduced that the limit equilibrium analyses were not appropriate to estimate the shallow failure that occurred at most of the railroad cut-off soil slopes. For the better estimation of the surficial failure, not only the increase of pore-water pressure (reduction of matric suction), but also the influence of water flows over slope surface which erode soil mass, should be evaluated and considered.

• Journal of Korean Society of Forest Science
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• v.112 no.4
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• pp.426-441
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• 2023

This study investigated the predictive accuracy of a model of landslide displacement in Jecheon-si, where a great number of landslides were triggered by heavy rain on both natural (non-clear-cut) and clear-cut slopes during August 2020. This was accomplished by applying three flow direction methods (single flow direction, SFD; multiple flow direction, MFD; infinite flow direction, IFD) and the degree of root cohesion to an infinite slope stability equation. The application assumed that the soil saturation and any changes in root cohesion occurred following the timber harvest (clear-cutting). In the study area, 830 landslide locations were identified via landslide inventory mapping from satellite images and 25 cm resolution aerial photographs. The results of the landslide modeling comparison showed the accuracy of the models that considered changes in the root cohesion following clear-cutting to be improved by 1.3% to 2.6% when compared with those not considered in the area under the receiver operating characteristics (AUROC) analysis. Furthermore, the accuracy of the models that used the MFD algorithm improved by up to 1.3% when compared with the models that used the other algorithms in the AUROC analysis. These results suggest that the discriminatory application of the root cohesion, which considers changes in the vegetation condition, and the selection of the flow direction method may influence the accuracy of landslide predictive modeling. In the future, the results of this study should be verified by examining the root cohesion and its dynamic changes according to the tree species using the field hydrological monitoring technique.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.737-741
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• 2012

본 연구에서는 2011년 7월 27일 집중호우로 인한 서울시 우면산 산사태 지역을 대상으로 뿌리의 보강효과와 분포형 습윤지수를 고려한 GIS기반의 무한사면안 해석기법을 이용하여 사면안정해석을 실시하였다. 사면안정해석을 위한 지형 지질학적 매개변수는 수치지도, 정밀토양도 및 임상도(임상도와 영급도)로부터 추출하여 $10m{\times}10m$ 해상도의 공간분 포형 데이터베이스로 변환하였다. 또한, 분포형 습윤지수의 산정을 위한 비집수면적(specific catchment area)은 무한방향흐름 기법(IFD, infinity flow direction)을 이용하여 결정하였으며, 모형의 입력 강우자료는 서울시 서초와 남현 AWS의 산사태 발생초기와 종기시의 평균 일강우량을 적용하였다. 대상유역의 사면안정해석을 위해 격자별 안전률은 4개의 등급(unstable, quasi stable, moderately stable, stable)으로 구분하여 도시하였다. 산사태 발생인자별 분석결과, 무한사면안정해석기법을 이용하여 산정된 사면안전률은 사면경사에 매우 민감하게 반응하는 것으로 분석되었으며, 거주지 주변의 절개지 부근과 산지정상부근의 급경사지에서 불안정 지역이 집중적으로 분포하고 있음을 확인하였다.

• The Journal of Engineering Geology
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• v.33 no.4
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• pp.555-571
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• 2023

Due to South Korea's concentrated summer rainfall, constituting 70% of the annual total, landslides frequently occur during the rainy season, necessitating accurate prediction methods to mitigate associated damage. In this study, a reduced-scale and full-scale slope was configured using weathered granite soil to find the possibility of establishing measurement management criterias through landslide reproduction. The experiment focused on matric suction, analyzing changes in ground properties and failure patterns caused by rainfall infiltration. Subsequently, an unsaturated infinite slope stability analysis was conducted. By calculating the failure time when the safety factor falls below 1 for each experiment, landslide prediction was demonstrated to be possible, approximately 17 minutes prior for the reduction-scale experiment and 6.5 hours for the full-scale experiment. These findings provide useful data for establishing Korean soil slope measurement management criteria that consider the characteristics of weathered granite soil.

• Journal of Korean Society of Rural Planning
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• v.21 no.3
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• pp.171-179
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• 2015

The objectives of this research have been focussed on 1) developing prediction techniques for the flash flood and landslide based on rainfall prediction data in agricultural area and 2) developing an integrated forecasting system for the abrupt disasters using USN based real-time disaster sensing techniques. This study contains following steps to achieve the objective; 1) selecting rainfall prediction data, 2) constructing prediction techniques for flash flood and landslide, 3) developing USN and communication network protocol for detecting the abrupt disaster suitable for rural area, & 4) developing mobile application and SMS based early warning service system for local resident and tourist. Local prediction model (LDAPS, UM1.5km) supported by Korean meteorological administration was used for the rainfall prediction by considering spatial and temporal resolution. NRCS TR-20 and infinite slope stability analysis model were used to predict flash flood and landslide. There are limitations in terms of communication distance and cost using Zigbee and CDMA which have been used for existing disaster sensors. Rural suitable sensor-network module for water level and tilting gauge and gateway based on proprietary RF network were developed by consideration of low-cost, low-power, and long-distance for communication suitable for rural condition. SMS & mobile application forecasting & alarming system for local resident and tourist was set up for minimizing damage on the critical regions for abrupt disaster. The developed H/W & S/W for integrated abrupt disaster forecasting & alarming system was verified by field application.