• Journal of the Korean Geotechnical Society
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• v.35 no.5
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• pp.31-41
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• 2019

This paper demonstrates safety factor for effective planning at initial stage by utilizing results on changes of safety factor according to various conditions of slop and examines impacts of factors that affect slope safety factors as well. Firstly, it describes shear strength which satisfies minimum allowable safety factor: 1.20 depending on height and slope. As the height increases by 5.0 m, the safety factors decrease by 0.04 while it tends to consistently reduce by approximately 20%, 30% and 40% after height goes to 10.0 m. As slope reduces by about 0.3, the safety factors increases by 0.4, which shows the rate of safety factors on slope grows by about 10%, 20% and 30% on lowering slope. When cohesion goes up by 10.0 kPa the safety factors increases by around 40% respectably while the angle of internal friction grows by $5^{\circ}$, it increases by about 8%. The rate of safety factors is identified as $Fs=3.86H^{-0.59}$, Fs = 0.43 s, Fs = 0.04 c, $Fs=0.02{\phi}$ depending on height, slope and shear strength. The safety factor with rainfall infiltration tends to increase by 18% compared to the condition of saturated surface on earth.

• Tunnel and Underground Space
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• v.24 no.3
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• pp.187-200
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• 2014

After excavation or blasting, rock properties within an excavation damaged zone can be perpetually weakened on account of stress redistribution or blasting impact. In the present study, the excavation damaged zone is applied to a rock slope. The objective of this research is to compare the mechanical stability of the rock slope depending on the presence of the damaged zone using 2-dimensional modeling and analyze factors affecting factor-of-safety. From the modeling, it was founded that the mechanical stability of the rock slope is significantly dependent on the presence of the damaged zone. In particular, factor-of-safety with a consideration of the damaged zone decreased by approximately 49.4% in comparison with no damaged zone. Factor analysis by fractional factorial design was carried out on factor-of-safety. It showed that the key parameters affecting factor-of-safety are angle of the slope, cohesion, internal friction angle and height.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11b
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• pp.213-220
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• 2000

Numerical modeling of cut slope has some limits in simulating the real slopes. In the case of 2D analysis of slope stability, it is assumed that slope is simply straight even when it is concave or convex in plan view. In this study, 3D analysis in curved shape slopes has been conducted for the comparison with 2D analysis in terms of failure mode and factor of safety. For this, 3D analysis by FLAC3D was compared with 2D analysis in plane strain condition and axi-symmetric model condition by FLAC. It was also observed how safety factors of slopes were affected by the variation of the tensile strength and cohesion, which are important variables to decide whether the slope fails or not. 2D analysis of concave slopes under plane strain condition showed much smaller safety factors by 16-40 % errors depending on the radius of curvature of slopes, compared to the more realistic values from 3D analysis. In case of convex slopes, the lower values by 7-10 % has been reported. 2D analysis of axi-symmetric model showed also smaller safety factors by 6-10 % and by 2-4 %, in case of concave and convex slopes, respectively. Such results are expected to contribute to the better understanding of failure process and could be applied for improved design of slopes.

• The Journal of Engineering Geology
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• v.30 no.4
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• pp.515-523
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• 2020

If the safety factor does not secure the safety factor suggested in the design standard at the slope design stage, the safety factor is secured by installing an anchor. Stability analysis is used to verify the effect of reinforcing the slope of the anchor, but in this process, most of the anchor construction intervals are assumed to be equal and analyzed. For economical and effective slope reinforcement, stability analysis is required by adjusting the anchor construction interval. In this study, the effect of the anchor construction interval on the change of the safety factor of the slope was identified. Stability analysis was performed by setting a virtual slope with two berms and different anchor construction intervals. As a result of the analysis, the stability of the slope is secured when the anchor spacing of the lower surface is narrowed and the anchor gaps of the upper and middle surfaces are wider than when anchors are installed at the same intervals on the upper, middle, and lower surfaces of the slope. The result was a 15% reduction in the amount of anchors. This means that, rather than reinforcing anchors at the same intervals, it is economical and effective to have an economical and effective reinforcement effect to vary the anchor construction intervals according to the slope characteristics.

• Journal of the Korean Geotechnical Society
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• v.16 no.1
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• pp.51-64
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• 2000

This paper presents a procedure of calculating a safety factor of the unsaturated slope suffering from the rainfall infiltration. The process of infiltration into a slope due to rainfall and its effect on the behavior of the soil slope are examined by using a two dimensional finite element flow-deformation coupled analysis. A factor of safety is calculated at various elapsed times after the commencement of rainfall as in the following procedure. First, stresses are estimated at each Gaussian point from the coupled finite element analysis. Then, the global stress smoothing method is applied to get a continuous stress field. Based on this stress field, a factor of safety is calculated for a specified slip surface by a stress integration scheme. Then, a search strategy is used to find out a critical slip surface which is associated with the minimum factor of safety. Some numerical examples are analyzed in order to study the effect of hydraulic conductivity on the slope stability during rain-induced infiltration. According to the results, local failure zone can be formed near the slope surface due to inhomogeneous distribution of hydraulic conductivity If the failure zone is once formed, then the region extends until a large amount of slide activates. Therefore the local failure can be neglected no longer in the stability analysis.

• Geomechanics and Engineering
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• v.33 no.1
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• pp.77-89
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• 2023

This study aims to establish the correlations between variables related to a slope during rainfall and factor of safety (FOS) and displacement using a coupling analysis method that is designed to consider both in rainfall conditions. With the recent development of measurement technologies, the approach of using the measurement data in the field has become easier. Particularly, they have been obtained in tests to determine the real-time safety and movement of a slope; however, a specific method has not been finalized. In addition, collected measurement data for recognizing the FOS and displacement in real-time with a specific relevance is difficult, and risks of uncertainty, such as in soil parameters and time, exist. In this study, the correlations between various slope-related variables (i.e., rainfall intensity, rainfall duration, angle of the slope, and mechanical properties including strength parameters of selected three types of soil; loamy sand, silt loam, sand) and the FOS and displacement are analyzed in order of seepage analysis, slope stability analysis and slope displacement analysis. Moreover, the methodology of coupling analysis is verified and a fundamental understanding of the factors that need to be considered in real-time observations is gained. The results show that the contributions of the abovementioned variables vary according to the soil type. Thus, the tendency of the displacement also differs by the soil type and variables but not same tendency with FOS. The friction angle and cohesion are negative while the rainfall duration and rainfall intensity are positive with the displacement. This suggests that understanding their correlations is necessary to determine the safety of a slope in real-time using displacement data. Additionally, databases considering rainfall conditions and a wide range of soil characteristics, including hydraulic and mechanical parameters, should be accumulated.

• Geomechanics and Engineering
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• v.15 no.4
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• pp.947-955
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• 2018

In this study, we propose a three-dimensional simplified slope stability analysis using a hybrid-type penalty method (HPM). In this method, a solid element obtained by the HPM is applied to a column that divides the slope into a lattice. Therefore, it can obtain a safety factor in the same way as simplified methods on the slip surface. Furthermore, it can obtain results (displacement and strain) that cannot be obtained by conventional limit equilibrium methods such as the Hovland method. The continuity condition of displacement between adjacent columns and between elements for each depth is considered to incorporate a penalty function and the relative displacement. For a slip surface between the bottom surface and the boundary condition to express the slip of slope, we introduce a penalty function based on the Mohr-Coulomb failure criterion. To compute the state of the slip surface, an r-min method is used in the load incremental method. Using the result of the simple three-dimensional slope stability analysis, we obtain a safety factor that is the same as the conventional method. Furthermore, the movement of the slope was calculated quantitatively and qualitatively because the displacement and strain of each element are obtained.

• Geomechanics and Engineering
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• v.14 no.1
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• pp.71-81
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• 2018

Soils are mostly nonhomogeneous and anisotropic in nature. In this study, nonhomogeneity and anisotropy of soil are taken into consideration by assuming that the cohesion increases with depth linearly and also varies with respect to direction at a particular point. A three-dimensional rotational failure mechanism is adopted, and then a three-dimensional stability analysis of slope is carried out with the failure surface in the shape of a curvilinear cone in virtue of the limit analysis method. A quasistatic approach is used to develop stability charts in nonhomogeneous and anisotropic soils. One can easily read the safety factors from the charts without the need for iterative procedures for safety factors calculation. The charts are of practical importance to prevent a plane failure in excavation slope whether it is physically constrained or not. Then the most suitable location of piles within the reinforced slope in nonhomogeneous and anisotropic soils is explored, as well as the interactions of nonhomogeneous and anisotropic coefficients on pile reinforcement effects. The results indicate that piles are more effective when they are located between the middle and the crest of the slope, and the nonhomogeneous coefficient as well as the anisotropic coefficient will not only influence the most suitable location for piles but also affect the calculated safety factor of existing reinforced slope. In addition, the two coefficients will interact with each other on the effect on slope reinforcement.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.369-376
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• 2009

Field investigation was performed right after the occurrence of debris flow at Jinbu area. Geomorphic and geotechnical characteristics were investigated and rain fall data were collected. Based on these data, seepage and slope stability analysis was performed to verify the behavior of ground water and factor of safety of the slope according to the rainfall intensity and time. As a results, the minimum value of factor of safety achieved in long time after the moment of maximum precipitation rate. And it is confirmed that the factor of safety is susceptible to ground water level rather than rainfall intensity.

• Journal of Industrial Technology
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• v.3
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• pp.53-63
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• 1983

The probability of failure is used to analyze the reliability of three dimensional slope failure, instead of conventional factor of safety. The strength parameters are assumed to be normal variated and beta variated. These are interval estimated under the specified confidence level and maximum likelihood estimation. The pseudonormal and beta random variables are generated using the uniform probability transformation method according to central limit theorem and rejection method. By means of a Monte-Carlo Simulation, the probability of failure is defined as; Pf=M/N N : Total number of trials M : Total number of failures Some of the conclusions derived from the case study include; 1. Three dimensional factors of safety are generally much higher than 2-D factors of safety. However situations appear to exist where the 3-D factor of safety can be lower than the 2-D factor of safety. 2. The F3/F2 ratio appears to be quite sensitive to c and ${\phi}$ and to the shape of the 3-D shear surface and the slope but not to be to the unit weight of soil. 3. In cases that strength parameters are assumed to be normal variated and beta variated, the relationships between safety factor and the probability of failure are fairly consistent, regardless of the shape of the 3-D shear surface and the slope. 4. As the c-value is increased, the probability of failure for the same safety factor is increased and as the ${\phi}-value$ is increased, the probability of failure for the same safety factor is decreased.