• Journal of the Korean Geotechnical Society
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• v.26 no.6
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• pp.21-28
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• 2010

Decomposed granite soil is the most common type of soils. The measurement of the stress-strain-strength behavior of anisotropic decomposed granite soils is very important for the deformation and stability analysis of slopes, retaining walls, excavations. A series of unsaturated-drained triaxial compression tests were performed to know unsaturated strength properties. The sample had three different angles of the axial (major principal) direction to the sedimentation plane (compaction plane): 0, 45 and 90 degrees. The compression strain of specimens subjected to an isotropic compression was strongly influenced by the sedimentation angle. In addition, the time dependence was independent of the sedimentation angle in relation to the deformation behavior during the secondary compression process. The effect of the sedimentation angle on the triaxial compression strength and deformation was clearly shown with low confining stress. The effect of the sedimentation angle on the compressive strength and deformation was more evident in saturated specimens. A new method of predicting the shear strength of unsaturated decomposed granite soils, considering compaction angles, was proposed.

• Journal of the Korean Geosynthetics Society
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• v.19 no.2
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• pp.35-46
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• 2020

In this study, the dynamic response characteristics of the embankment model were analyzed using shaking table experiments. Laminar shear box was used to minimize the boundary effect of the model. The ratio of the vertical length to horizontal length of the slopes were 1:1, 1:1.5, and 1:2. The sensor array which is consist of 12 accelerometers was used to measure acceleration time-histories at each location of the slope model. The dynamic response characteristics of the models were analyzed for sine wave, sinesweep wave, and artificial earthquake wave in this study. The experimental results show that the dynamic response of the embankment model is increased with the slope angle. Furthermore, the experimental setup used in this study was verified with the comparative analysis between experimental results and 1-D analytical simulation on the flat ground model.

• The Journal of Engineering Geology
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• v.22 no.3
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• pp.353-363
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• 2012

The geology of Ulleung-Do is dominated by volcanic rocks with low strength and trachytic rocks with high strength but containing vertical joints that yield easily. Consequently, rockfalls along roadcuts are a major geological hazard, with the potential to affect the ring road of Ulleung-Do. In this study, we performed three types of rockfall hazard-risk assessment on the 3-km-long section of the ring road expected to have the highest possibility of rockfall. We used a rockfall ranking sheet in a roadside landslide hazard map, the Slope Stability Inspection Manual for National Highways (Japan), and a rockfall hazard rating system for inspection from the Japan Highway Public Corporation. We also employed the evaluation criteria of 'RHRS' developed by the Federal Highway Administration (FHA). An analysis of roadcuts at 27 sites with regard to geographic and geological conditions resulted in the identification of three classes of rockfall hazard (high, medium, and low). Of note, over 74% of slopes were assessed as high- and medium-class. Finally, a rockfall hazard map of the northeast region of Ulleung-Do was produced based on the evaluation results.

• Explosives and Blasting
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• v.24 no.1
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• pp.57-62
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• 2006

The typical blasting method adopted in Pasir Coal Mine is a surface blasting technique with a single free face. It means that there is only one free face, which is usually the ground surface. This kind of blasting method is easy to use but inevitably causes enormous ground vibrations, which, in turn, can affect the stability of the slopes comprising the various boundaries of the open pit mine. In addition, the method also has the problem of lowering the blast efficiency compared to other methods such as bench blasting methods or ones with more than two free faces. In this respect, a project was launched to develop a new blasting method that is suitable for controling the ground vibration and enhancing the blast efficiency. As a part of the project, authors investigated the current blasting method as well as the overall pit developing process in the mine, and established some important guidelines that should be observed during the whole development process. This paper presents the details of the typical blasting pattern and the pit developing method in the mine, and suggests the guidelines determined from the results of the observations.

• Geomechanics and Engineering
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• v.14 no.4
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• pp.307-314
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• 2018

Strength of loess that experienced cyclic freeze and thaw is of great significance for evaluating stability of slopes and foundations in loess regions. This paper takes the frequently encountered loess in the Northwestern China as the study object and carried out three kinds of laboratory tests including freeze-thaw test, direct shear test and SEM test to investigate the strength behaviors of loess after cyclic freeze and thaw, and the correlation with meso-level changes in soil structure. Results show that for loess specimens at four dry densities, the cohesion decreases with freeze-thaw cycles until a residual value is reached and thus an exponential equation is proposed. Besides, little change in the angle of internal friction was observed as freeze-thaw proceeds. This may depend on the varying of soil structure, based on which a clue can be found from the surface morphology and mesoscopic scanning of loess specimens. Clearly we observed significant changes in surface morphology of loess and it tends to aggravate at higher water contents or more cycles of freeze and thaw. Moreover, freeze-thaw cycling leads to obvious changes in the meso-structure of loess including lowering the particle aggregates and increasing both the proportion of fine particles and porosity area ratio. A damage variable dependent on the ratio of porosity area is introduced based on the continuum damage mechanics and its correlation with cohesion is discussed.

• Geomechanics and Engineering
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• v.11 no.6
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• pp.739-756
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• 2016

The shear strength reduction finite element method (SSRFEM) is a powerful tool for slope stability analysis. The factor of safety (FOS) of the slope can be easily calculated only through reducing effective cohesion (c′) and tangent of effective friction angle ($tan{\varphi}^{\prime}$) in equal proportion. However, this method may not be applicable to soil slope under wetting-drying cycles (WDCs), because the influence of WDCs on c′ and $tan{\varphi}^{\prime}$ may be different. To research the method of estimating FOS of soil slopes under WDCs, this paper presents an experimental study firstly to investigate the effects of WDCs on the parameters of shear strength and stiffness. Twelve silty clay samples were subjected to different number of WDCs and then tested with triaxial test equipment. The test results show that WDCs have a degradation effect on shear strength (${\sigma}_1-{\sigma}_3)_f$, secant modulus of elasticity ($E_s$) and c′ while little influence on ${\varphi}^{\prime}$. Hence, conventional SSRFEM which reduces c′ and $tan{\varphi}^{\prime}$ in equal proportion cannot be adopted to compute the FOS of slope under conditions of WDCs. The SSRFEM should be modified. In detail, c′ is merely reduced among shear strength parameters, and elasticity modulus is reduced correspondingly. Besides, a new approach based on sudden substantial changes in the displacement of marked nodes is proposed to identify the slope failure in SSRFEM. Finally, the modified SSRFEM is applied to compute the FOS of a slope example.

• 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.225-242
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• 2019

Rockfall failure at the access road to Seokguram were occurred due to the earthquake on September 12, 2016. A detailed investigation was carried out in order to find out the cause of the rockfall, to identify the risk of the entire sites, and to prepare proper countermeasure methods and mitigation. We checked for geological and topographical characteristics of overall slopes alongside the access road to Seokguram and made a face map. In addition, we analyzed topographical factors caused by the earthquake through calculating a degree of slope, degree of bearing, upslope contributing area, and wetness index with the use of shading relief map. As a result, we confirmed that the large rockfall occurred with a weak section. In this study, we also evaluated the overall slope stability of the entire access road to Seokguram in order to classify it into danger and caution zones depending on the risk of collapse.

• Journal of the Korean Geotechnical Society
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• v.30 no.11
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• pp.5-15
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• 2014

It is very important to design and construct slopes safely because damage cases are increasing due to slope failure. Recently, Limit Equilibrium Method (LEM) based programs are commonly used for slope designs. Though LEM can give factors of safety through simple calculation, it has a disadvantage that the sliding surface should be assumed in advance. On the other hand, the use of Finite Difference Method (FDM) is increasing since the factor of safety can be easily estimated by using shear strength reduction technique. Therefore the purpose of this study is to present a reasonable slope design methodology by comparing the two commonly used analysis approaches; LEM and FDM. To this end, the reinforcement effects of the two methods were compared in terms of the support pattern of soil nailing reinforced in the section where plane failure is anticipated. As a result, the reinforcement effects by nail angle and nail spacing turned out to be equal. Also it was found that the factor of safety increased in LEM, but not changed in FDM when the nail length increased.

• Journal of the Korean GEO-environmental Society
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• v.21 no.9
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• pp.5-14
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• 2020

This study analyzed the reinforcement effect by conducting laboratory test, model test and program analysis to utilize the surface stabilizer used for the restoration work of collapsed slopes as a reinforcing material for aging reservoirs that exhibits a curing reaction similar to cement. Based on the results of the laboratory test, a model test and program analysis were performed by applying 9% of the mixing ratio. As a result, when the surface stabilizer was used in aging reservoir, it was found that the flow of water only occurred on part of the slope and underground in reservoir. And the water flow could be reduced inside the reservoir. In addition, it was analyzed that the seepage discharge could be reduced by about 42% and the saturated area within the reservoir by about 73%, thereby securing the stability of the aged reservoir.