• Journal of the Korean Geotechnical Society
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• v.21 no.2
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• pp.127-135
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• 2005

In this paper, a numerical comparison of predictions by limit equilibrium analysis and finite difference analysis is presented for slope/soil-nail system. Special attention is given to the coupled analysis based on the explicit-finite-difference code, FLAC 2D. To this end, an internal routine (FISH) was developed to calculate a factor of safety for a soil nail slope according to shear strength reduction method. The case of coupled analyses was performed for soil nails in slope in which the soil nails response and slope stability are considered simultaneously. In this study, by using these methods, the failure surfaces and factors of safety were compared and analyzed in several cases, such as toe, middle and top of the slope, respectively. Furthermore, the coupled method based on shear strength reduction method was verified by the comparison with other analysis results.

• Journal of the Korean Society for Railway
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• v.12 no.6
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• pp.1037-1042
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• 2009

Safety regulation of railway embankment is restricted by safety factor in dry season or rainy season in Korea. Safety factor which is results from the limit equilibrium analysis is varied by various external conditions. And because it has no reflection point, it is very difficult to manage the safety of trains. Safety regulation such like warning sign, reduce speed and train stop is the best choice to reduce the damage of embankments where it is worried about occurrence of disasters. In this study, additional index is proposed to support present safety standards based on unsaturated soil mechanics and reliability analysis. It is velocity of failure probability. It has an apparent reflection point near present safety regulation. It is possible to modify the regulation for safety management and monitoring system of embankments by using this index.

• The Journal of Engineering Geology
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• v.25 no.1
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• pp.115-129
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• 2015

The cut-slope of a large-sectional tunnel portal is recognized as a potential area of weakness due to unstable stress distribution and possible permanent displacement. This paper presents a case study of a slope failure and remediation for a large-scale cut-slope at a tunnel portal. Extensive rock-slope brittle failure occurred along discontinuities in the rock mass after 46 mm of rainfall, which caused instability of the upper part of the cut-slope. Based on a geological survey and face mapping, the reason for failure is believed to be the presence of thin clay fill in discontinuities in the weathered rock mass and consequent saturationinduced joint weakening. The granite-gneiss rock mass has a high content of alkali-feldspar, indicating a vulnerability to weathering. Immediately before the slope failure, a sharp increase in displacement rate was indicated by settlement-time histories, and this observation can contribute to the safety management criteria for slope stability. In this case study, emergency remediation was performed to prevent further hazard and to facilitate reconstruction, and counterweight fill and concrete filling of voids were successfully applied. For ultimate remediation, the grid anchor-blocks were used for slope stabilization, and additional rock bolts and grouting were applied inside the tunnel. Limit-equilibrium slope stability analysis and analyses of strereographic projections confirmed the instability of the original slope and the effectiveness of reinforcing methods. After the application of reinforcing measures, instrumental monitoring indicated that the slope and the tunnel remained stable. This case study is expected to serve as a valuable reference for similar engineering cases of large-sectional slope stability.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.569-580
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• 2008

If slope height was more than 20 meters, we conducted an analysis of stereographic projection and limit equilibrium at this slope. We proposed reduction of slope face angle and reinforcement of rock bolt depending on analysis. Blasting design : Standard pattern based on result of local test blasting was made for blasting design. Vibration criterion was set for less than 3.0mm/s because of outworn buildings and inhabitants opinions. Production blasting and Controlled blasting has been done as Construction standard pattern. After Vibration Monitoring has been done, so that we can control of complement. "Bidding Document" and AASHTO 2001 "A Policy on Geometric Design of Highways and Streets" were so for design criteria of earthwork but they were different actual design criteria and left something to be desired in Afghanistan. Therefore, although "Bidding Document" and "AASHTO 2001" were basic design criteria, domestic design criteria was reflected in this design criteria for complement by discussion with supervisor. Drainage design : For stability ratio, ditch of arch block and stonework was designed by rainfall data for the 13 years and discussion with supervisor. Pavement was designed as flexible pavement. Because these days in Afghanistan postwar repair works, especially urgent repairing of roads and newly making of roads, are very highly in progress, I think that Afghanistan is the region about which our construction technical experts should have great concerns.

• The Journal of Engineering Geology
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• v.22 no.1
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• pp.83-94
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• 2012

Slopes are commonly formed both above and below roads located in mountainous terrain and along riversides. The Buk-sil site, a cut slope formed below the road, collapsed in October, 2010. A field investigation determined the causes of failure as improper drainage of valley water from the slope above the road and direct seepage of road-surface water. These factors may have accelerated the collapse via complex interaction between water and sub-surface structures such as bedding. Projection analysis of the site showed the possible involvement of plane, wedge, and toppling failure. Safety factors calculated by Limit Equilibrium Analysis for plane and wedge failure were below the standard for wet conditions. The wetness index, analyzed using topographic factors of the study area, was 9.0-10.5, which is high compared with the values calculated for nearby areas. This finding indicates a high concentration of water flow. We consider that water-flow control on the upper road is crucial for enhancing slope stability at the Buk-sil site.

• Korean Journal of Agricultural Science
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• v.23 no.1
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• pp.1-12
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• 1996

To design the safe and rational rock slope, several rock slopes of roads in Kang-won area were analyzed, and the following results were obtained ; 1. The results were analyzed by stereographic projection at the rock slope that the joint was developed. All of the sloped which were designed by standard slope of rock was not considered that the joints were unstable. 2. The relation of rainfall and slope failure, as well as the danger of failure, was very high when the maximum hourly rainfall was larger than 20mm and when there was a 2-day cumulative rainfall that was larger than 200mm. 3. In the design of rock slope, operated by the stereographic projection considering discontinuity. If turn out unstable, it should be analyzed carefully using the limit equilibrium method. 4. In the design of rock slope, it is desirable to consider the discontinuity of rock(joint, bedding, fault).

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.151-165
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• 2019

In this study, the four types of improvement methods (increase self weight and reducing sliding force etc.) were proposed depending on install location with compaction grouting to improve seismic performance of existing port structure and optimal methods by analyzing the effects of improvement (stability, constructability and economy) by theoretical and numerical methods. From the dynamic time history analysis for artificial seismic waves, the results indicated that the horizontal displacement after improvement decreased compared to before improvement, however the displacement reduction effect among improvement methods was not significantly different. Slope stability based on the strength reduction method and the limit equilibrium analysis method, it is confirmed that the passive pile method is more safe than other methods. It is due to the shear strength at the failure surface is increased. In addition, the analysis of constructability and economy showed that the reduction of earth pressure method (type 02) and the passive pile method (type 03) are excellent. However, in the case of the passive pile method is concerned that there is a shortage of design cases and the efficiency can be reduced depend on various constraints such as ground conditions.

• Journal of the Korean GEO-environmental Society
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• v.4 no.2
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• pp.77-91
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• 2003

The Hoek-Brown failure criterion for rock masses developed first in 1980 is widely accepted and has been applied in a variety of rock engineering problems including slope analyses. The failure criterion was modified over the years because rock mass strength by the original failure criterion in 1980 was overestimated. The modified failure criterion, named Generalized Hoek-Brown Failure Criterion, was proposed with a new classification called the Geological Strength Index(GSI) in 1994. Generally, Hoek-Brown failure criterion is applied in numerical analyses of rock mass behaviors using equivalent Mohr-Coulomb parameters estimated by linear regression method. But these parameters estimated by this method have some inaccuracies to be applied and to be incorporated into numerical models and limit equilibrium programs. The most important issue is that this method cannot take account of non-linear characteristics of Hoek-Brown criterion, therefore, equivalent Mohr-Coulomb parameters is used as constant values regardless of field stress distribution in rock masses. In this study, the numerical analysis on rock slope stability considering non-linear characteristics of Hoek-Brown failure criterion was carried out. Futhermore, by the latest Hoek-Brown failure criterion in 2002, the revised estimating method of equivalent Mohr-Coulomb parameters was applied and rock mass damage criterion is introduced to account for the strength reduction due to stress relaxation and blast damge in slope stability.

• Journal of the Korean Geotechnical Society
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• v.23 no.6
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• pp.97-102
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• 2007

Though the stability analysis of soil slopes widely employs the limit equilibrium method, the study on the jointed rock slopes must consider the direction of joint and the characteristics of Joint at the same time. This study analyzes the result of the change in the factors which show the characteristics of discontinuity and the shape factor of rock slopes, and so on, in an attempt to validate the propriety as to the interpretation of jointed rock slope stability which uses the general finite element program. First, the difference depending on the flow rules was compared, and the factor effect study was conducted. The selected independent variables included the direction of joint which displays the mechanical characteristics of discontinuity, adhesive cohesion, friction angle, the inclination and height of rock slope which reveal the shape of slope and surcharge load. And the horizontal displacement was numerically interpreted at the 1/3 point below the slope, a dependent variable, to compare the relative degree of factor effects. The findings of study on factor effects led to the validation that the result of horizontal displacement for each factor satisfied various engineering characteristics, making it possible to be applied to stability interpretation of jointed rock slope. A modelling is possible, which considers the application of the result of real geotechnical surveys & laboratory studies and the non-linear characteristics when designing the rock slope. In addition, the stress change which may result from the natural disaster, such as precipitation, and the construction, can be expressed. Furthermore, as the complicated rock condition and the ground supporting effect can be considered through FEM, it is considered to be very useful in making an engineering decision on the cut-slope, reinforcement and so on.

• Journal of the Korean GEO-environmental Society
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• v.20 no.5
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• pp.13-21
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• 2019

There are many cuts or natural rock slopes that remain stable for a long time in the natural environment with steep slopes ($65^{\circ}$ to $85^{\circ}$). In terms of design practice, the rock mass consisting of similar rock condition and geological structures is defined as a good continuum rock slope, and during the process of decision making angle of this rock slope, it will be important to establish the geotechnical properties estimating method of the continuum rock on the process of stability analysis in the early stages of design and construction. In this study, the stability analysis of a good continuum rock slope that can be designed as a steep slope proposed a practical method of estimating the shear strength by induced from the Hoek-Brown failure criterion, and in addition, the design applicability was evaluated through the stability analysis of steep rock slope. The existing method of estimating the shear strength was inadequate for practical use in the design, as the equivalent M-C shear strength corresponding to the H-B envelope changes sensitively, even with small variations in confining stress. To compensate for this problem, it was proposed to estimate equivalent M-C shear strength by iso-angle division method. To verify the design applicability of the iso-angle division method, the results of the safety factor and the displacement according to the change in angle of the cut slope constructed at the existing working design site were reviewed. The safety factor is FS=16~59 on the 1:0.5 slope, FS=12~52 on the 1:0.3 slope, most of which show a 10~12 percent reduction. Displacement is 0.126 to 0.975 mm on the 1:0.5 slope, 0.152 to 1.158 mm on the 1:0.3 slope, and represents an increase of 10 to 15%. This is a slightly change in normal proportion and is in good condition in terms of stability. In terms practical the working design, it was confirmed that applying the shear strength estimated by Iso-angle division method derived from the H-B failure criterion as a universal shear strength for a good continuum rock mass slope was also able to produce stable and economic results. The procedure for stability analysis using LEM (Limit Equilibrium Analysis Method) and FEM (Finite Element Analysis Method) will also be practical in the rock slope where is not distributed fault. The study was conducted by selecting the slope of study area as a good rock condition, establishing a verification for which it can be applied universal to a various rock conditions will be a research subject later on.