• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.176-183
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• 2008

This paper highlights the importance of carrying out global slope stability analysis as part of design calculations for geosynethetic walls in tiered configuration. Four design case histories were selected to examine the appropriateness of their design by performing additional slope stability analyses using the shear strength reduction method with in the frame work of finite element analysis. The results indicated that all of the walls examined, which were designed to meet the current design guide lines, did not satisfy the global slope stability requirement, and that longer reinforcements are required in the upper tiers to achieve the minimum factor of safety. Practical implications of the findings are discussed.

• Geomechanics and Engineering
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• v.34 no.2
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• pp.187-195
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• 2023

Intensive rainfall during the summer season in Korea has triggered numerous devastating landslides outside of downtown in mountainous areas. The 2D slope stability analysis that is generally used for cut slopes and embankments is inadequate to model slope failure in mountainous areas. This paper presents a new 3D slope stability formulation using the global sliding vector in the limit equilibrium method, and it uses an ellipsoidal slip surface for static and quasi-static analyses. The slip surface's flexibility of the ellipsoid shape gives a lower FS than the spherical failure shape in the Fellenius, Bishop, and Janbu's simplified methods. The increasing sub-columns of each column tend to increase the FS and converge to a steady value. The symmetrical geometric conditions of the convex turning corners do not indicate symmetrical failure of the surface in 3D analysis. Pseudo-static analysis shows that the horizontal seismic force decreases the FS and increases the mass volume at the critical failure state. The stability index takes the FS and corresponding sliding mass into consideration to assess the potential risk of slope failure in complex mountainous terrain. It is a valuable parameter for selecting a vulnerable area and evaluating the overall risk of slope failure.

• Geomechanics and Engineering
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• v.2 no.2
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• pp.125-140
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• 2010

Slope stability analysis of the right abutment of a railway bridge proposed at about 350 m above the ground level, crossing a river and connecting two huge hillocks in the Himalayas, India is presented in this paper. The site is located in a highly active seismic zone. The rock slopes are intensely jointed and the joint spacing and orientation are varying at different locations. Static slope stability of the rock slope is studied using equivalent continuum approach through the most commonly used commercial numerical tools like FLAC and SLOPE/W of GEOSTUDIO. The factor of safety for the slope under static conditions was 1.88 and it was reduced by 46% with the application of earthquake loads in pseudo-static analysis. The results obtained from the slope stability analyses confirmed the global stability of the slope. However, it is very likely that there could be possibility of wedge failures at some of the pier locations. This paper also presents the results from kinematics of right abutment slope for the wedge failure analysis based on stereographic projections. Based on the kinematics, it is recommended to flatten the slope from 50o to 43o to avoid wedge failures at all pier locations.

• Geomechanics and Engineering
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• v.19 no.2
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• pp.179-191
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• 2019

Based on the effective stress principle, a new formula for shear strength of unsaturated soil is derived under the general nonlinear Mohr-Coulomb (M-C) strength criterion to improve the classical strength criterion of unsaturated soil. Meanwhile, the simple irrigation model under steady seepage is adopted to obtain the distribution of the matrix suction or the degree of saturation (DOS) above the groundwater table in the slope. Then, combined with the improved strength criterion of unsaturated soil and the simple irrigation model under steady seepage, the limit equilibrium (LE) solutions for the unsaturated slope stability are established according to the global LE conditions of the entire sliding body with assumption of the stresses on the slip surface. Compared to the classical strength criterion of unsaturated soil, not only the cohesion soil but also the internal friction angle is affected by the matric suction or the DOS in the improved strength criterion. Moreover, the internal friction angle related to the matric suction has the nonlinear characteristics, particularly for a small of the matric suction. Thereafter, the feasibility of the present method is verified by comparison and analysis on some slope examples. Furthermore, stability charts are also drawn to quickly analyze the unsaturated slope stability.

• Journal of The Geomorphological Association of Korea
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• v.27 no.2
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• pp.81-97
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• 2020

Geopark refers to a single boundary area consisting of a collection of geosites and geotrails, which includes ecological, historical and cultural elements based on geological and geomorphological resources. To ensure the continued development and conservation of existing listed geoparks, it is necessary to carry out an environmental sensitivity analysis of the geopark components by utilizing spatial information from various scales. The objectives of this study are to analyze the environmental sensitivity in Cheongsong UNESCO global geopark in relation with slope disaster using GIS and to understand its spatial distribution in connection with geosites and geotrails. Two types of spatial database were constructed; geosites and geotrails in Cheongsong UNESCO global geopark and spatial data to perform environmental sensitivity. Potential soil loss and slope stability were analyzed to derive environmental sensitivity related to slope hazard. The results showed relatively high environmental sensitivity along the drainage network of Cheongsong UNESCO global geopark. Zonal statistics analysis was conducted for further detailed distribution of environmental sensitivity based on buffer zones of geosites and geotrails. Majority of geological sites, geological trails, Jeolgol gorge~Jusan Pond section in hiking trails, and Dalgi Mineral Spring Site~Artistic Genius Republic of Korea(Jangnankki gonghwaguk) section in road areas show relatively high slope hazard sensitivity within buffer zones.

• Journal of the Korean Geotechnical Society
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• v.24 no.9
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• pp.23-32
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• 2008

This paper presents the global stability of geosynthetic reinforced segmental retaining walls in tiered configuration. Four design cases of walls with different geometries and offset distances were analyzed based on the FHWA and NCMA design guidelines and the discrepancies between the different guidelines were identified. A series of global slope stability analyses were conducted using the limit-equilibrium analysis and the continuum mechanics based shear strength reduction method with the aim of identifying failure patterns and the associated factors of safety. The results indicated among other things that the FHWA design approach yields conservative results both in the external and internal stability calculations, i.e., lower factors of safety, than the NCMA design approach. It was also found that required reinforcement lengths are usually governed by the global slope stability requirement rather than the external stability calculations. Also shown is that the required reinforcement lengths for the upper tiers are much longer than those based on the current design guidelines.

• Journal of the Korean Geosynthetics Society
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• v.12 no.1
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• pp.109-114
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• 2013

This paper describes the global stability of the reinforced earth wall, which was collapsed by heavy rainfall. The seepage analysis was conducted to confirm the change effect of groundwater level on slope with reinforced earth wall. The seepage analysis result confirmed that the change of groundwater level is greatly influenced by rainfall. According to the change of groundwater level, the global stability analysis with reinforced earth wall was conducted based on the results of seepage analysis. The safety factor of the slope was 0.476 when the wall is collapsed firstly. The collapse cause analyzed that soil strength was weaken because the ground was saturated by continuous rainfall. Therefore, the global stability, which is considered heavy rainfall, should be conducted at design and construction of reinforced earth wall.

• Journal of the Korean Geotechnical Society
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• v.15 no.3
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• pp.27-40
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• 1999

In limit equilibrium methods(LEM), all methods employ the same definition of the safety factor as a ratio of the shear strength of the soil to the shear stress required for equilibrium, employing certain assumptions with regard to equilibrium. In addition, in the conventional finite element method of analysis, the minimum safety factor is obtained assuming certain slip surfaces after the state of stress are found. Although the stress states are obtained from the finite element method(FEM), the slope stability analysis follows the conventional method that assumes a potential slip surface. In this study, a slope stability analysis based on FEM is developed to locate the slip surface by tracking the weakest points in the slope based on the local safety factor considering the magnitude and direction of the shear stresses. It has also been applied to be compared with the slip surfaces predicted by LEM. A computer program has been developed to draw contour lines of the local safety factors automatically. This method is illustrated through a simple hypothetical slope, a natural soil slope, and a dam slope. The developed method matches very well with the conventional LEM methods, with slightly lower global safety factors.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.689-697
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• 2005

The soil nailing system at permanent slope reinforcement is used with various facing methods in Korea. Also, pressure-injected grout technique is variously applied to many structures. However, most design of the pressure-injected grout technique have been carried out empirically because of complicated mechanisms associated with the behavior of surrounding soils and the hardening process of cement grout. Therefore this study, a newly modified soil nailing technology named as the PGSN (Pressure Grouting Soil Nailing) system with fabric form is developed to increase the global stability. Up to now, the PGSN system has been estimated mainly focusing on an establishment of the design procedure. In the present study, numerical study are carried out to evaluate potential failure surface and minimum factor of safety including facing stiffness and expanded radius of cemented grout by SSR (Shear Strength Reduction) technique. Also, results of numerical analysis are carried out for the typical section of soil nails slope using $FLAC^{2D}$ program for expanded effective radius by pressure grouting.

• 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.