• The Journal of Engineering Geology
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• v.17 no.4
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• pp.545-554
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• 2007

Landslides is mainly induced by a heavy rainfall, earthquake ground motion, and some other factors like soil mechanics, morphological-geological factors etc. Since the starting point of the failure seemed to be originated at a construction site in the study, it is meaningful to find out the relationship between the landslide and the construction. For this study, the slope failure factor was examined carefully to see that the original natural slope had vulnerability and that the complex ground had unstability changed by construction. A field survey was conducted on the original ground surface and filled-up ground. A laboratory test was also conducted to determine the geomechanical properties of soil samples. 2D and 3D limit equilibrium analysis with changing groundwater level were conducted at the failure depth using a seismic refraction survey. The result shows that the factor of safety is similar stability under all condition, but unstable under saturated condition.

• Smart Structures and Systems
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• v.7 no.4
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• pp.263-274
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• 2011

A reliability-based slope stability assessment method considering fluctuations in the monitored matric suction was proposed for real-time identification of slope risk. The assessment model was based on the limit equilibrium model for infinite slope failure. The first-order reliability method (FORM) was adopted to calculate the probability of slope failure, and results of the model were compared with Monte-Carlo Simulation (MCS) results to validate the accuracy and efficiency of the model. The analysis shows that a model based on Advanced First-Order Reliability Method (AFORM) generates results that are in relatively good agreement with those of the MCS, using a relatively small number of function calls. The contribution of random variables to the slope reliability index was also examined using sensitivity analysis. The results of sensitivity analysis indicate that the effective cohesion c' is a significant variable at low values of mean matric suction, whereas matric suction ($u_a-u_w$) is the most influential factor at high mean suction values. Finally, the reliability indices of an unsaturated model soil slope, which was monitored by a wireless matric suction measurement system, were illustrated as 2D images using the suggested probabilistic model.

• Geomechanics and Engineering
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• v.22 no.4
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• pp.319-328
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• 2020

This paper investigates the effect of the width of failure and tension crack (TC) on the stability of cohesive-frictional soil slopes in three dimensions. Working analytically, the slip surface and the tension crack are considered to have spheroid and cylindrical shape respectively, although the case of tension crack having planar, vertical surface is also discussed; the latter was found to return higher safety factor values. Because at the initiation of a purely rotational slide along a spheroid surface no shear forces develop inside the failure mass, the rigid body concept is conveniently used; in this respect, the validity of the rigid body concept is discussed, whilst it is supported by comparison examples. Stability tables are given for fully drained and fully saturated slopes without TC, with non-filled TC as well as with fully-filled TC. Among the main findings is that, the width of failure corresponding to the minimum safety factor value is not always infinite, but it is affected by the triggering factor for failure (e.g., water acting as pore pressures and/or as hydrostatic force in the TC). More specifically, it was found that, when a slope is near its limit equilibrium and under the influence of a triggering factor, the minimum safety factor value corresponds to a near spherical failure mechanism, even if the triggering factor (e.g., pore-water pressures) acts uniformly along the third dimension. Moreover, it was found that, the effect of tension crack is much greater when the stability of slopes is studied in three dimensions; indeed, safety factor values comparable to the 2D case are obtained.

• Journal of the Korean Geotechnical Society
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• v.28 no.6
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• pp.63-70
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• 2012

The authors discuss the effect of hydraulic conductivity on the suction profile and stability of a typical cut-slope subjected to low intensity rainfall. The initial suction value above the ground table in the unsaturated zone is assumed to be 15 kPa. The uncoupled approach of finite element and limit equilibrium method is used to evaluate the stability of the cut-slope at different elapsed times of rainfall. The finite element seepage analysis shows that the soil in the unsaturated zone always remains unsaturated during the course of low intensity rainfall. Furthermore, the slope stability remains practically unchanged so long as the wetting front remains in the unsaturated zone but it decreases noticeably when the wetting front reaches and elevates the ground water table level.

• The Journal of Engineering Geology
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• v.14 no.4 s.41
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• pp.451-460
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• 2004

The strength of sliding plane is usually assigned on the whole sliding plane with same value in 2D limit equilibrium slope stability method. However, the potential sliding plane is divided into two or three parts which have different sliding resistances. According to the calculation results of 3D slope stability analyses using 4 types of slope cutting models, marginal sliding resistance could affect the safety of slope significantly. In this calculation two kinds of the sliding plane strengths were applied differently to the parts of bottom and margin of the model slope. The effect of marginal resistance was calculated quantitatively. In case of lower sliding resistance of the bottom, the safety factor becomes low in a margin cutting model. However, in case of higher sliding resistance of the bottom, the safety factor decreased slightly in a lower part cutting model and increased in a upper margin cutting model.

• The Journal of Engineering Geology
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• v.31 no.2
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• pp.165-178
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• 2021

The influence of Soil-Water Characteristic Curve (SWCC) fitting parameters for an unsaturated natural slope was evaluated through seepage and slope stability analysis as a function of rainfall. Soil samples were collected from the study area in Jirisan National Park and the physical and mechanical characteristics of unsaturated soil layers were measured in laboratory tests. The saturation depth was calculated via seepage analysis by changing fitting parameters α, the parameter related to the Air Entry Value (AEV) and n, the parameter related to the slope of the SWCC in the range of natural conditions. Slope stability analysis using the limit equilibrium method considered the calculated depth of saturation. Results from seepage analysis for various rainfall conditions indicate the saturation depth in the soil layer suddenly increased as the fitting parameter α decreased; the saturation time for the entire soil layer also decreased. Slope stability analysis considering the calculated depth of saturation shows that the slope safety factor rapidly decreased as the fitting parameter α decreased, whereas the variation in slope safety factor was very small when n increased. Hence, fitting parameter α has a large effect on saturation depth during rainfall and therefore on slope stability, whereas slope stability is relatively unaffected by the fitting parameter n.

• Journal of the Korean Geotechnical Society
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• v.31 no.1
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• pp.47-52
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• 2015

In the slope stability analysis and design, Limit Equilibrium Method (LEM) and Shear Strength Reduction technique (SSR) are mainly used. Both methods are able to perform two and three dimensional analysis. SSR is considered to be more sensitive and more reasonable than LEM by many researchers. However, in practice LEM is still widely used because of the increase of analysis time and complexity of the model in SSR. In this study, three dimensional analysis of the protruding rock slope is performed by SSR in order to study the effects of protruding length using rock slope FLAC 3D. In this study, as results of analysis variations of the safety factor have been studied according to slope angle, slope height, the soil strength, protruding slope length projected variables. The results show that the factor of safety as more affected by the shapes of the protruding rock slope than the rock strength.

• The Journal of Engineering Geology
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• v.19 no.3
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• pp.401-408
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• 2009

Old national Road No. 59 that connects Danyang and Gagok has 35 dangerous cut slopes. It is relatively narrow and has a poor alignment. The torrential rains in 2002 and 2006 has caused numerous slope collapses, landslides and road settlements in this area. The old road's high risk level lead to the planning and construction of a new national road. During the construction of the new road in December 2006, the right side of Dugcheon Tunnel entrance has collapsed and tension cracks were observed on the district road above the tunnel. In order to determine the cause of failure, intensive field investigation and monitoring cracks were performed together with Lower Hemisphere Projection Analysis, Limit Equilibrium Analysis and Finite Difference Analysis.

• The Journal of Engineering Geology
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• v.34 no.2
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• pp.317-327
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• 2024

When a non-persistent joint system is formed in a large-scale rock slope, slope failure may occur due to presence of a the stepped sliding surface. Such a surface can be divided into joint-to-joint sliding surfaces or joint-to-rock bridge sliding surfaces. In the latter case, the rock bridge provides shear resistance parallel to the joint and tensile resistance perpendicular to the joint. The load of the sliding rock can lead to failure of the rock bridge, thereby connecting the two joints at each ends of the bridge and resulting in step-path failure of the slope. If each rock bridge on a slope has the same length, the tensile strength is lower than the shear strength, resulting in the rock bridges oriented perpendicular to the joint being more prone to failure. In addition, the smaller the ratio of discontinuity spacing to length, the greater the likelihood of step-path failure. To assess the risk of stepped sliding on a rock slope with non-persistent joints, stability analysis can be performed using limit equilibrium analysis or numerical analysis. This involves constructing a step-path failure surface through a systematic discontinuity survey and analysis.

• 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.