• Journal of the Korean Geotechnical Society
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• v.30 no.6
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• pp.41-49
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• 2014

Intensive rainfall causes frequent slope failures at the shallow depths of slopes. Because soil layers at shallow depths of slopes usually become dense, and its permeability and soil strength vary according to depth, forensic studies and stability analyses of shallow slope failure need to consider the depth-variant soil properties. In this study, the effect of depth-variant soil properties on surface failure of slopes during rain infiltration is investigated using numerical analysis. Three different cases considering depth-variant soil properties were conducted and the results were compared. For the analysis, undisturbed soils at three different depths were sampled at actual slope failure sites and the properties including strength and permeability characteristics at each depth were obtained. Stability analysis and seepage analysis were conducted using actual rainfall records. The comparison of the results shows that analysis could lead to an erroneous conclusion according to the way of considering depth-variant soil properties. The case in which depth-variant soil properties were considered predicted similar failure times and failure shapes with the actual failure. Therefore it is recommended that the depth-variant soil properties should be considered for the analysis of shallow slope failure during rain infiltration.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.03a
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• pp.277-284
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• 1999

This study describes the influence factors related to slope failure pattern and dimension in the southern Kyounggi area. Intrusive and metamorphic rocks are distributed in the study area. Geological condition, rainfall property and slope geometry are influence on slope failure characteristics in the study we& Geological factors related to slope failure are rock type, geological structure and weathering condition. Because of deep soil (RS-CW) depth of granite region, circular failure type is major failure pattern in granite region. Almost granite slopes with circular or surface failure pattern are failed during heavy rainfall season. But typical wedge failure type related to geological structure factor is a main failure pattern of metamorphic rock slope. Additionally failure dimension is influenced by geological factors and several factors, i.e. natural slope condition, failure type, rainfall intensity and etc. failure height/width ratio and thickness/length ratio of granite slope are 0.88 and 0.23. But the ratios of metamorphic rock slope are 1.36 and 0.19.

• Geomechanics and Engineering
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• v.31 no.4
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• pp.375-384
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• 2022

The variation of the undrained shear strength (c_u) is an important consideration for assessing slope stability in engineering practice. Previous studies focused on the three-dimensional (3D) stability of slopes in normally consolidated clays generally assume the undrained shear strength increases linearly with depth but does not vary in the horizontal direction. To assess the 3D stability of slopes with spatially varying undrained shear strength, the kinematic approach of limit analysis was adopted to obtain the upper bound solution to the stability number based on a modified failure mechanism. Three types failure mechanism: the toe failure, face failure and below-toe failure were considered. A serious of charts was then presented to illustrate the effect of key parameters on the slope stability and failure geometry. It was found that the stability and failure geometry of slopes are significantly influenced by the gradient of c_u in the depth direction. The influence of c_u profile inclination on the slope stability was found to be pronounced when the increasing gradient of c_u in the depth direction is large. Slopes with larger width-to-height ratio B/H are more sensitive to the variation of c_u profile inclination.

• Journal of the Korean Geotechnical Society
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• v.18 no.2
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• pp.23-37
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• 2002

Failure of the cut slope is triggered by combination of internal and extemal failure factors. Internal failure factors are related to geological and geometrical conditions of slope itself, and natural and/or artificial loadings on slope can be the external failure factors. Influences of these failure factors show different intensity according to the ground condition and are controlled by behavior characters of the slope. In this study, the soil depth ratio(SR), block size ratio(BR) and rock strength are used as the criteria to divide ground condition based on behavior characteristics. Ground condition of the slope is divided into discontinuous jointed rock mass and continuos soil-like mass, highly fractured rock mass and massive rock mass by the criteria(SR and BR). The SFi-system is a rating system to determine the slope failure index(SFi) by analyzing internal and external factors based on classification of the ground condition. The results of the SFi-system application to the real cut slopes show close relationship between the SFi value and potential or dimension of the failure. Therefore, the SFi-system can be used as a useful tool to predict and analyze the characteristic of the slope failure.

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.263-266
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• 2007

In this paper, analysis results on the failure of slope behind a Plant Complex of Gimhae due to typhoon Rusa in 2002 are introduced. The left side of the slope was reinforced by soil nails and the right side of the slope was going to construct slope reinforcement works. In the slope failure, the damage area is about $34,000m^2$, the lower width of slope failure is about 230m, the upper width of slope failure is about 50m, and the height of slope failure is about 120m. The elevation of a bedrock in the right side of the slope was lower than the left side of the slope. Due to the depth of weathered soils and weathered rocks in right side of the slope was thick, it will be expected that the effects of pore-water pressure during the rainfalls are large. For the analysis of the failure mechanism, 3-dimensional numerical analysis was carried out by FLAC-3D.

• The Journal of Engineering Geology
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• v.15 no.1
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• pp.57-66
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• 2005

The failure of cut slope and landslide sometimes come from a local downpour within a short duration in Korea. Especially, most of recent downpour converged upon a limited region and seemed the characteristics of guerilla. Characteristics of slopes failed due to local downpour are analyzed. failure mode is also analyzed with respect to the depth of soil layers and the change of groundwater level. To blow the influence factors of the slope stability during local downpour, the authors conducted field survey for failed slopes and tried to make a comparative study of 1,372 cut slope data distributed in the national road. FLAC-SLOPE(ITASCA Co.) is used to analyze slope stability with changing depth of soil layers and groundwater level. The result shows that the failed types of domestic slopes during local downpour are mainly shallow collapse and landslide. The change of soil depth and groundwater level have influenced on the stability of slopes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.10
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• pp.2810-2818
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• 2009

In order to examine the characteristic of shallow failure in cut slopes composed of weathered granite soil, this study calculated critical permeability coefficient according to rainfall characteristic in Korea, performed stability analysis according to the representative physical properties of weathered granite soil distributed in Korea such as horizontal distance to the failure surface of cut slope, slope inclination, slope height, and the depth of wetting by rainfall, and analyzed the results. In the results of analyzing critical permeability coefficient, when the local rainfall characteristic was considered, the maximum critical permeability coefficient was $7.16{\times}10^{-4}cm/sec$. We judged that shallow failure according to wetting depth should be considered when rainfall below the critical rainfall intensity lasts longer than the minimum rainfall duration in cut slopes composed of weathered granite soil, which had a critical permeability coefficient lower than the maximum critical permeability coefficient. Furthermore, using simulated failure surface, this study could understand the characteristic of shallow failure in cut slopes based on the change in slope safety factor according to horizontal distance, wetting depth, and strength parameter.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.3
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• pp.11-18
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• 1984

There are two different methods in the stability analysis of slopes depending upon the 1ocations and the types of assumed failure planes, which are the infinite slope analysis and the finite slope analysis. The infinite slope analysis is simple and easier in its application. However, since the method neglects the end effects and assumes the failure plane to be located at the shallow depth and parallel to the slope, the slopes to be analyzed by the method should be limited to a certain range. Thus, it is intended in this paper to define the infinite slopes whose stability may be analyzed by the infinite slope analysis. As a result, it is obtained that the method of infinite slope analysis may be applied to the slopes which have the ratio of the slope height to the depth of the failure plane of 9 or bigger.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.543-550
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• 2000

Rock slopes along the road or railroad are affected by temperature and therefore experienced iterative freezing-thawing process between winter and early spring. The purpose of this study is to analyze the stability of rock slopes which are influenced by the deterioration due to the freezing-thawing. The analysis is the homogenization method which evaluates the strength property of discontinuous rock mass, and as a strength failure criterion, Drucker-Prager failure criterion is used. The deterioration property of real rock is obtained by a freezing-thawing laboratory test of tuff and this property of deterioration is quantitated and used as a basic data of stability analysis for rock mass. To evaluate the deterioration depth due to the freezing-thawing in situ rock slope, one dimensional heat conductivity equation is used and as the result I can find that the depth of which is affected by a temperature. After the freezing-thawing depth of model slope is determined, we analyze the pattern of rock mass stength value of rock slope model which excesses the limit of self-load.

• Journal of the Korea institute for structural maintenance and inspection
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• v.4 no.1
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• pp.101-110
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• 2000

In case heavy rainfall is a key factor of slope failure, the failure zone is usually developed within the depth of 3~5m from the ground surface regardless of the location of the watertable. If rainfall is taken into consideration, it is general that the slope stability analysis is carried out under the assumption that the cut slope is saturated to the slope surface or the watertable elevates to a certain height so that ${\gamma}_{sat}$, the unit weight of saturated soil, is used. However, the analysis method mentioned above can't exactly simulate the variation of pore water pressure in the slope and yields different failure shape. The applicability of slope stability analysis method considering the distribution of pore water pressure within the slope with heavy rainfalls, was checked out after the stability analysis of a lage-scale cut slope in a highway construction site, where surface failure occurred with heavy rainfalls. An appropriate slope stabilization method is proposed on the base of the outcome of the analysis.