• Geomechanics and Engineering
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• v.13 no.2
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• pp.353-370
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• 2017

This paper presents a case study and numerical investigation to study the hydro-mechanical response of a shallow landslide in unsaturated slopes subjected to rainfall infiltration using a coupled model. The coupled model was interpreted in details by expressing the balance equations for soil mixture and the coupled constitutive equations. The coupled model was verified against experimental data from the shearing-infiltration triaxial tests. A real case of shallow landslide occurred on Mt. Umyeonsan, Seoul, Korea was employed to explore the influence of rainfall infiltration on the slope stability during heavy rainfall. Numerical results showed that the coupled model accurately predicted the poromechanical behavior of a rainfall-induced landslide by simultaneously linking seepage and stress-strain problems. It was also found that the coupled model properly described progress failure of a slope in a highly transient condition. Through the comparisons between the coupled and uncoupled models, the coupled model provided more realistic analysis results under rainfall. Consequently, the coupled model was found to be feasible for the stability and seepage analysis of practical engineering problems.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1029-1037
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• 2008

The finite element analysis of transient water flow through unsaturated soils was used to investigate effects of hydraulic characteristics, initial relative degree of saturation, methods to consider boundary condition, and rainfall intensity and duration on water pressure in slopes. The finite element method with shear strength reduction technique was used to evaluate the stability of slopes under rainfall. The slope-related disasters in Korea usually occur between July and September during the typhoon and localized heavy rain. This means that the rainfall is the most important factor that leads to the slope-related disasters. The slope-related disasters can happen at very short time and lead to big damage. To forecast the change of the heave of the groundwater in slope the Seep/w program was used.

• 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.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.663-668
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• 2005

The present study proposed to examine the appropriateness of the ground water level condition that had a significant effect on the stability of the slopes and, for this purpose, analyzed the rise of ground water level during the rainy season by applying the average daily rainfall of Seoul for the last 30 years. The result showed that the rise of ground water level was 6.0$\sim$41.0% of the slope height, which suggests that the currently applied condition of ground water level is somewhat overestimated. In addition, the result of interpreting the stability of slopes during the rainy season, slopes were unstable in all conditions when the ground water level was at the ground surface and base failure occurred. This suggests the importance of ground water level condition in stability analysis.

• Journal of the Korean Geotechnical Society
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• v.20 no.7
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• pp.159-169
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• 2004

Surface failures of slopes in weathered soil are caused by infiltration due to prolonged rainfall. These failures are mainly triggered by the deepening of the wetting band accompanied by a decrease in suction induced by the infiltrating water. This paper reports trends of rainfall-induced wetting band depth in two types of weathered soils that are commonly found in Korea. Both theoretical and numerical analyses are presented based on the soil-water characteristic curve (SWCC) obtained using filter paper as well as tensiometer tests. It is found that the magnitude of wetting front suction plays a key role in the stability of slopes in weathered soils. Theoretical analysis based on modified Green and Ampt model tends to underestimate the wetting band depth for typical Korean weathered soils. It was also deduced that for Korean weathered soils, the factor of safety drops rapidly once the wetting band depth of 1.2 m is reached.

• Journal of the Korean Geotechnical Society
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• v.22 no.7
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• pp.55-64
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• 2006

Shallow failures of slopes in weathered soils are caused by infiltration caused by prolonged rainfall. These failures are mainly triggered by the deepening of the wetting band accompanied by a decrease in suction induced by the water infiltration. In this paper, hysteresis on soil-water characteristic curve (SWCC) of granite and gneiss weathered soils is investigated using transient flow analysis respectively. Each case was subjected to artificial rainfall intensities and time duration depending on the laboratory-based drying and wetting processes. The results show that the unsaturated seepage on weathered slopes are very much affected by the initial suction of soils and unsaturated permeability of the soils. In addition, a granite weathered soil has a lower air-entry value, residual matric suction, and wetting front suction and less hysteresis loop than a gneiss weathered soil.

• Geotechnical Engineering
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• v.8 no.1
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• pp.81-102
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• 1992

Landslides on hillside slopes with shallow soil cover over a sloping bedrock are frequently caused by increases in porewater pressures following of heavy rainfall and it is one of the most important factors of assessing the risk of landslide to predict the groundwater level fluctuations in hillslopes. This paper presents the comparative study of three unsaturated flow models developed by Sloan et al., Reddi, L.N., and Thomas, H.A., Jr., respectively, which are used to predict the increase of groundwater levels in hillside slopes. The parametric study for each of models is also presented. The Kinematic Storage Model(KSM) developed by Sloan et at. is utilized to predict the saturated groundwater flow. They are applied to the two sites in Korea so as to examine the possibility of use in the groundwater flow model. The results show that two unsaturated models developed by Sloan et al. and Reddi, L. N. are largely affected by the uncertain parameters like saturated permeability and saturated water content : the abed model has the potential of use in unsaturated flow model with the optimal estimates of model parameters utilizing available optimization techniques. And it is also found that the KSM must be modified to account for the time delay effect in the saturated zone. The results of this paper are able to be utilized in developing the predictive model of groan dwater level fluctuations in a hillslope.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.921-926
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• 2010

To examine saturation characteristics of an unsaturated soil in the steep slope area with collapse, it separated dry season from rainy season and measured water content and permeability, and measured permeability by using a tension infiltrometer in the site. In addition, it conducted electrical resistivity survey to look into thickness of ground and geological structure of underground. The collapsed slope increased depth of weathered zone compared to upper slope, and there electrical resistivity anomalous zone caused by the filtrated underground water was observed. The permeability of the collapsed area was observed high compared to upper and lower slopes of retarding basin without collapse, and the permeability measured by dividing the dry season and rainy season was measured high in case of dry season.

• Journal of the Korean Geotechnical Society
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• v.17 no.4
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• pp.135-143
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• 2001

강우에 의한 잔류토에서의 얕은 사면파괴는 세계적으로 흔히 볼 수 있는 사면파괴의 형태이다. 본 연구에서는 침투가 사면 표면의 안정에 미치는 영향을 평가하기 위해 한계평형법을 이용하는 무한사면 해석법을 연구하였다. 재현기간에 따른 강우강도가 지속기간이 고려되는 임의의 강우에 의해 유발되는 얕은 사면파괴의 가능성을 평가하기 위해서 Green-Ampt 모델에 바탕을 둔 간략법들이 적용되었다. 간략법들에 의한 결과들과 비교하기 위하여 일련의 수치해석이 수행되었다. 그 결과에 의하면 적절하게 선택된 입력값을 사용하면 수정간략법이 더욱 엄밀한 해석법인 유한요소해석과 근사한 합리적인 결과를 줌을 알 수 있다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.3
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• pp.359-369
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• 2022

In slope stability analysis for landslides, mountains have various slopes and geographical features, and hence it is necessary to estimate stability using rigorous analysis methods. In this study, after the analysis of infiltration behavior through unsaturated layers due to rainfall, the stability of landslide was estimated to account for the variation of pore water pressures. In the analysis of slope stability, a three-dimensional slope analysis was compared with an infinite slope analysis in a case study of terrain in which an actual landslide occurred. In the three-dimensional slope stability analysis, it was found that the location of the failure and the failure area were predicted accurately based on the detailed geological information despite the variation of geographical features.