• Journal of the Korean GEO-environmental Society
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• v.11 no.2
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• pp.13-21
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• 2010

The unsaturated slope usually is stable for a long time, but fails during heavy rainfall. And the factors of the rainfall intensity exhibit significant roles because the water content and the shear stress developed along the potential failure surface will be changed by the rainfall intensity. The objective of the study presented in this paper is to analyze the relationship between rainfall intensity and shear stress of the soil slopes by applying the laboratory slope model apparatus and undrained direct shear test with rainfall intensity controlled. The soil sample was taken from the field slope of Youngdong, and particle size analysis was done. To look over the relationship between rainfall intensity and shear strength of slope, the three-dimensional relationships among shear strength, normal stress and water content of the slope soil samples are examined; those are based on the data from the TDR sensor and undrained direct shear test.

• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.1 s.12
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• pp.25-31
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• 2004

Infiltration of rainfall causes railway embankment to be unstable and may result in failure. Basic relationship between the rainfall and stability of railway embankment is defined to analyze the stability of embankment by rainfall. An experimental study for defining of infiltration rate of rainfall into slope is conducted in the lab. The results of Rainfall Infiltration show that rainfall Infiltration is not equal to infiltration as like reservoir because rate of rainfall infiltration is controlled by slope angle. Based on these results, boundary condition of rainfall is altered and various numerical analysis are performed. The variation of shear strength, the degree of saturation and pore-water pressure for railway slope during rainfall can be predicted and the safety factor of railway slope can be expressed as the function of rainfall amount, namely rainfall index. Therefore, it is judged that this rainfall index can be a good tool for the rail-transport operation control.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.201-201
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• 2011

산지유역의 지표 환경이 급격히 교란된 지역에서 집중 호우가 발생하면, 과대한 토사유출로 인해 하천유역 홍수 재해요인으로 작용할 수 있다. 본 연구에서는 산불발생지역, 벌목지역, 도로공사지역과 같이 산지환경이 급변한 지역을 토사유출 시험유역으로 운영하였다. 세 개의 시험유역 중에 지표교란이 심각한 도로공사시험유역에서 강우유출 및 토사유출이 가장 크게 발생하였다. 그림 1은 각 시험유역별 강우강도에 따른 첨두유량 관계를 나타낸 것이다. 또한 산불 후 10년이 경과된 급경사 산불시험유역이 벌목시험유역보다 유출 및 토사유출량이 많았다. 벌목시험유역은 벌목이후 잔류물과 빠른 식생회복으로 지표상태가 빠르게 안정화되어 유출 및 토사유출량이 적게 발생하였다. 도로공사 시험유역 나지사면에서 시행된 사면처리 공법 시공 전 후로 토사유출량의 변화가 현저히 크며(그림 2), 이는 공사를 진행하는 중에 적절한 사면관리 처리를 통한 토사유출량 저감이 필요하다는 것을 나타낸다.

• Journal of the Korean Geotechnical Society
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• v.37 no.6
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• pp.21-28
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• 2021

The factors of landslides depend on rainfall intensity, duration, and the characteristics of the soil slope. The conventional slope stability analysis has been carried out by assuming that the slope is saturated. But, a site slope consisting of unsaturated ground must be imitated and interpreted in order to explain a proper behavior of the slope due to rainfall. In this study, by using two major categories of soils in Korea, such as granite and gneiss weathered soils, landslide model test and numerical analysis have been compared with the difference of seepage and volumetric water content. In general, the permeability of gneiss weathered soil, which contains a lot of fines content, is slower than that of granite weathered soil. As a result, in extreme rainfall, numerical analysis can show results that can penetrate quickly, resulting in saturation or more dangerous collapse.

• The Journal of Engineering Geology
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• v.25 no.1
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• pp.57-66
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• 2015

A numerical analysis was performed of the seepage from and stability of a mine waste-dump slope in Imgi, Busan, considering rainfall intensity. The 40-45° slope angle of the waste dump is relatively steep, and the depth of the waste dump down to bedrock is 7-8 m. The groundwater level was 6.6 m below the surface. Various laboratory tests on samples obtained from the waste dump were performed to determine the input data for seepage and stability analyses of the waste-dump slope during rainfall. The results of seepage analysis for various rainfall intensities using the SEEP/W program show that the wetting front moved down with increasing rainfall duration. When the rainfall intensity was > 50 mm/ hour and the duration was > 24 hours, the waste dump became fully saturated because the wetting front reached the groundwater level. The results of slope stability analysis coupled with seepage analysis using the SLOPE/W program show that the safety factor of the slope decreased as the wetting front moved down due to rainfall infiltration. After continuous rainfall for 5-6 hours, the safety factor of the slope suddenly decreased but then recovered and converged. The sudden decrease was induced by an increase in pore-water pressure and a decrease in matric suction down to a certain depth as the wetting front approached the potential sliding surface.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.5
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• pp.1073-1082
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• 2015

The behavior of the unsaturated soil slope can be influenced by the various factors such as the hydraulic characteristics, the mechanical characteristics, the coefficient of conductivity, the stratifications, the rainfall conditions i.e. the rainfall intensity, the rainfall pattern, the duration time of the rainfall and the antecedent rainfall etc. It is known that the slope failure is influenced greatly by the antecedent rainfall rather than the rainfall condition at the failure time, so the antecedent rainfall is supposed to be a very important factor in slope stability analysis among these factors. To predict and to prevent the slope failure by the rainfall, the distribution of the matric suction by the antecedent rainfall must be considered first of all and the slope stability analysis should be carried out by considering the successive rainfall characteristics. In this research, 3 samples with different quantity (5%, 10%, 20%) of silts were prepared and the SWCC (Soil-water characteristic curve) tests were carried out and the associated parameters were analyzed. After analyzing the distribution of the matric suction and the change of the mechanical characteristics such as the stress and the strength when applying the antecedent rainfall for one month and the successive intensive rainfall for 12 hours, the slope stability analyses were carried out numerically. And the influence of the antecedent rainfall for one month and the SWCC on the stability of a slope were compared and analyzed.

• Journal of the Korean Geotechnical Society
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• v.25 no.2
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• pp.55-66
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• 2009

At the mudstone slope located on the roadside of the Seokri area in Donghae-myeon, Pohang, Gyeongsangbuk-do, this study was performed to analyze the effects of rainfall on the stability of slope through seepage analysis according to the precipitation type of the mudstone slope, referring to the actual case of slope failure. For this, precise geological survey, geophysical exploration and drilling survey for the slope where the failure occurred were performed and followed by analysis of detailed soil layer. For the section where failure surface located, the durability reduction of rocks was measured through slaking/swelling tests and the permeability was measured through in-situ permeability tests for each soil layer. In addition, the change of strength parameter and process of instability were analyzed by back analysis, using Talren 97 and Slope/W programs, in the slope. By applying different precipitation conditions to the geographical conditions of the slope that had actual failure records, the slope stability was analyzed by seepage analysis according to duration of rainfall and rise of groundwater level resulting from the flow of rainfall caused by development of geological structures and the slope surface condition.

• Journal of the Korean Geotechnical Society
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• v.17 no.3
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• pp.51-58
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• 2001

본 연구에서는 종자와 비료, 부직포 지오텍스타일, 마 네트로 구성된 토목섬유 식생매트 시스템을 개발하였다. 개발된 식생매트를 흙 사면에 설치한 결과 사면의 식생성장과 사면안정에 긍정적인 효과를 얻었으며 이것은 실물시험을 통하여 강우와 사면에서의 유출수량, 부유물질, 토사침식량 등을 8개의 시험구에 식생매트를 분석하였다. 유출수량은 모든 시험구에서 강우량이 클수록 증가하였으며 식생매트를 설치한 곳이 안한 곳보다 유출수량이 작았으며 총부유물질은 유출수량에 크게 영향을 받는다. 식생매트는 흙 침식과 부유물질의 이동을 감소시켜 흙사면의 안정에 매우 유익하다. 또한 식생성장환경을 개선하며 특히 가뭄시에 성장에 매우 효과적이다.

• The Journal of Engineering Geology
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• v.16 no.2 s.48
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• pp.135-143
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• 2006

This study presents the results of a series of laboratory scale slope failure experiments aimed at clarifying the process and the condition leading to the initiation of rainfall-induced slope failures. For the evaluation of hydrologic response of the model slopes in relation the process of failure initiation, measurements were focused on the changes in volumetric water content during the initiation process. The process leading to failure initiation commences by the development of a seepage face. It appears reasonable to conclude that slope failures are a consequence of the instability of seepage area formed at the slope surface during rainfall period. Therefore, this demonstrates the importance of monitoring the development seepage area for useful prediction about the timing of a particular failure event. The hydrologic response of soil slopes leading to failure initiation is characterized by three phases (phase I, II and III) of significant increase in volumetric water content in association with the ingress of wetting front and the rise of groundwater level within the slope. The period of phase III increase in volumetric water content can be used to initiate advance warning towards a failure initiation event. Therefore, for the concept outlined above, direct and continuous monitoring of the change in volumetric water content is likely to provide the possibility for the development of a reliable and effective means of predicting the occurrence of rainfall-induced slope failures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5C
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• pp.191-198
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• 2009

It has been reported in Korea that surface slope failures in weathered soil are mainly caused by downward infiltration due to rainfall. These failures are triggered by the deepening of the wetting band in soils accompanied by a decrease in matric suction induced by the water infiltration. So, a need exists that these trends of wetting path in gneiss weathered soils, which is commonly found in Korea, are assessed by phenomenological approach. In this paper, numerical analyses of unsaturated soil slope under rainfall conditions are presented based on the wetting path soil-water characteristic curve in the laboratory. As the field SWCC matches well with the wetting path of the laboratory SWCC from the literatures, it seems reasonable to adopt the laboratory wetting SWCC as an upper boundary condition in the assessment of unsaturated slope instability.