• Journal of the Korean Geotechnical Society
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• v.34 no.5
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• pp.37-51
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• 2018

The slope failure due to the rainfall infiltration occurs frequently in Korea, since the depth of the weathered residual soil layer is shallow in mountainous region. Depth of the failure surface is shallow and tends to pass near the interface between impermeable bedrock and soil layer. Soil parameters that have a significant impact on the instability of unsaturated slopes due to rainfall infiltration inevitably include large uncertainties. Therefore, this study proposes a probabilistic analysis procedure by Monte Carlo Simulation which considers the hydraulic characteristics and strength characteristics of soil as random variables in order to predict slope failure due to rainfall infiltration. The Green-Ampt infiltration model was modified to reflect the boundary conditions on the slope surface according to the rainfall intensity and the boundary condition of the shallow impermeable bedrock was introduced to predict the stability of unsaturated soil slope with shallow bedrock under constant rainfall intensity. The results of infiltration analysis were used as inputs of infinite slope analysis to calculate the safety factor. The proposed analysis method can be used to calculate the time-dependent failure probability of soil slope due to rainfall infiltration.

• Journal of the Korean GEO-environmental Society
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• v.11 no.9
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• pp.15-25
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• 2010

The main objective of this study was to offer informations about long-term seepage behavioral characteristics and to find a leakage safety management method for Juam Dam and Imha Dam, a central cored rockfill dams in Korea by the evaluating the automatically monitored leakage data. In the water leakage monitoring of fill dam, the generation of abnormal water leakage is difficult to directly detect due to the effect of outside factors such as the component of rainfall inherent in the observation value. Therefore, conventionally estimation methods of water leakage quantity were applied by multiple regression analysis considering reservoir water level, rainfall, etc.. However, the estimated error of rainfall component is relatively big in these method. This paper identifies the seepage characteristic of each dams which is not directly affected by rainfall through the hydrograph separation analysis and 3 dimensional analytical method, and thinks a leakage management method. It was noticed that two dams had site specific seepage behaviour features and were in stable state with the decreasing leakage quantity. It was also found that hydrograph separation method might be applicable to leakage safety management method.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.263-267
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• 2007

낙동강유역의 강수량과 지하수위의 관계를 분석한 결과 갈수기에 지하수위가 현저히 저하됨을 확인하였다. 낙동강유역의 여러 관측소에서 지하수위와 강우이동평균의 상관관계를 분석한 결과 20일에서 110일 범위의 이동평균값에서 가장 높은 상관관계를 보여주었다. 유역평균 일최대침투량을 알아내기 위하여 강수량자료를 일정값 이상은 고정하여 수정된 강수량자료로 이동평균값을 구하고 이 값들과 지하수위와의 상관관계를 분석해 본 결과 10mm에서 130mm 범위의 일최대침투량으로 가정하였을 때 가장 높은 상관관계를 보여주었다. 이렇게 수정된 강수자료를 이용하여 이동평균을 구하여 지하수위와의 상관관계를 구해본 결과 낙동강유역의 자료에 대해서 한계침투량을 고려했을 때 상관관계가 더 높아짐을 알 수 있었다.

• The Journal of Engineering Geology
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• v.28 no.4
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• pp.687-699
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• 2018

Understanding rain infiltration into the ground is an important feature of landslide risk evaluation. In this study, a landslide risk index for the study area is suggested, wherein the result of the landslide risk evaluation, based on the factor of safety (FS), is used. The landslide risk index is a landslide risk prediction index that utilizes the saturated depth ratio of the ground. Based on the landslide risk result for the study area, it was found that the FS was first to decrease. However, it gradually became convergent over the 50-year rainfall intensity study period, a result that is similar to the relationship between the saturated depth ratio and soil thickness. Moreover, saturated depth was also found to be deeper on gentle slopes than steep slopes. As such, the landslide risk index, based on the Inhu-ri study result, is thus suggested. Additionally, the suggested landslide risk index was compared and analyzed against the rainfall intensity of previous landslide experience. Results thus revealed that almost all landslides that occurred were over 0.7, which is the second grade, based on the landslide risk index.

• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.4 s.15
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• pp.27-34
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• 2004

In this paper, in order to analyse the variation of runoff characteristics depending upon installation of the groundwater recharge facilities, the experiment basin was prepared and the ratio of infiltration and runoff volume were observed in the rainfall events. For the rainfall analysis, 4 types of rainfall events were examined during July 11${\sim}$July 17, 2004. The results show that the mean ratio of infiltration was 89.39% and the mean ratio of runoff was 10.61%. For the artificial rainfall events, which are in the range of rainfall intensities between 60mm/hr and 100mm/hr, all the rainfall volume was infiltrated through the groundwater recharging basin. However, it is necessary to be careful for the long term rainfall, the runoff can be occurred based on the groundwater table.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3C
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• pp.167-178
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• 2008

Rainfall-induced slope failures were simulated by seepage and stability analyses for actual slopes of weathered soils. After undisturbed sampling and testing on a specimen of unsaturated conditions, a seepage analysis was performed under actual rainfall and it was found that the pore water pressure increased at the boundary of soil and rock layers. The safety factor of slope stability decreased below 1.0 and the failure of actual slope could be simulated. Under design rainfall intensity, the seepage analysis could not include the effects of the antecedent rainfall and the rainfall duration. Due to these limitations, the safety factor of slope stability resulted in above 1.0, since the hydraulic head of soil layers had not be affected significantly. In the analysis of another slope failure, the parameters of unsaturated conditions were evaluated using artificial neural network (ANN). In the analysis of seepage, the boundary of soil and rock was saturated sufficiently and then the safety factor could be calculated below 1.0. It was found that the failure of actual slope can be simulated by ANN-based estimation.

• Journal of the Korean GEO-environmental Society
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• v.5 no.3
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• pp.41-50
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• 2004

The study of seepage behavior is very important to slope stability of road landfill for heavy rainfall season. This study is done to propose more stable of road landfill based on analysis of seepage behavior and slope stability for some cases of road landfill. The selected sections of collapsed road landfill are most general case of road landfill, a case is landfill on the ground area and another case is on the slope area. The results of this study is summarized as follows. It is founded that the road landfill on the ground area is increased saturation region due to rainfall infiltration, and the seepage behavior of road landfill is solved by theory of unsaturated flow. The road landfill is more unstable due to rainfall infiltration at the slope surface, especially during heavy rainfall. The case of road landfill on the slope area is analyzed in consideration of slope surface infiltration, and it is founded that the slope instability is increased because of rainfall infiltration. The drain layer located on the original ground which made by more permeable materials could be good action of slope stability in the case of road landfill on the slope area.

• Journal of the Korean GEO-environmental Society
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• v.14 no.12
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• pp.5-12
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• 2013

In this study, weathered granite model tests were performed to investigate the variation of volumetric water content and matric suction by the adsorption and desorption processes of artificial rainfall. It has been compared with numerical analysis in unsaturated condition. As the results, the behaviors of volumetric water content and matric suction were distinguished by the seepage distance separated into higher, middle and lower area, and the drainage layer located at the bottom of the experimental device. In the adsorption process, the instantaneously large change of matric suction and water content were related to the increase of permeability in soil. However, in the desorption process, the change of matric suction and water content were gradually small because of the decrease of permeability. The volumetric water content and matric suction showed the difference according to the seepage distance, however the typical characteristic curves were made by the adsorption and desorption processes.

• Journal of the Korean GEO-environmental Society
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• v.9 no.1
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• pp.33-40
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• 2008

In this research, model tests have been performed for researching the seepage characteristics in the finite soil slope during the rainfall using a manufactured rainfall simulator. On the basis of the results, it has been analyzed how to change the seepage characteristics due to the duration time of rainfall. We are found that the pore-water pressure was gradually increased as increasing the duration time of rainfall. Specially, at the beginning of rainfall, the pore-water pressure in the middle surface of slope was measured larger than any point. As increasing the duration time of rainfall, the pore-water pressure at the inner part of slope was increased greatly at the collapse due to infiltrating the pore-water within the slope. In the research, it was not easy to get various test results because measuring instruments are high sensitivity and difficult to handle. For the future, the model test results are needed for the various slope angle.

• Korean Journal of Soil Science and Fertilizer
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• v.13 no.1
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• pp.1-6
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• 1980

The infiltration rates of the upland soils on hill side slope were investigated in situ using rainulator of which rainfall intensity was 100mm/hr. The soil moisture profile after the water infiltration was compared with that calculated from Youngs' equation. The results obtained are as follows: 1. Time required for infiltration rate to reach constant during rainfall was 15 to 25 min. The infiltration rate measured after 30 min was considered to be final infiltration rate. 2. The final infiltration rates of clay soils were lower than 10mm/hr., loamy soils 10 to 20., coarse loamy soils 20 to 30, and sandy soils higher than 30mm/hr., respectively. 3. The saturated hydraulic conductivity of the surface soil of Samgag sandy loam was 0.47mm/min., Songjeong clay loam0.16 mm/min., and Jeonnam silty clay loam 0.14mn/min., respectively. 4. The soil moisture profile calculated from Young's equation was in close agreement with measured in situ.