• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.5
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• pp.621-640
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• 2019

Quantitative stability assessment of underground cavities can be presented as a factor of safety based on the Shear Strength Reduction Method (SSRM). Also, SSRM is one of the stability evaluation methods commonly used in slope stability analysis. However, there is a lack of research that considers the relationship between the probability of occurrence of cavities in the ground and the potential failure surface of the slope at the same time. In this study, the effect of small underground cavities on the failure behavior of the slope was analyzed by using SSRM. Considering some of the glaciology studies, there is a case that suggests that there is a cavity effect inside the glacier in the condition that the glacier slides. In this study, the stability evaluation of underground cavities and slope stability analysis, where SSRM is used in geotechnical engineering field, was carried out considering simultaneous conditions. The slope stability analysis according to the shape and position change of underground cavities which are likely to occur in the lower part of a mountain road was analyzed by using SSRM in FLAC3D software and the influence of underground cavities on the slope factor of safety was confirmed. If there are underground cavities near slope potential failure surface, it will affect the calculation of a factor of safety. The results of this study are expected to be basic data on slope stability analysis with small underground cavities.

• Atmosphere
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• v.26 no.3
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• pp.401-412
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• 2016

A 3D sonic anemometer has been installed at Yongpyong alpine slope since Oct. 23th 2014 to observe the slope winds and to analyze turbulent characteristics with the change in surface cover (grass and snow) and the synoptic wind strength. Eddy covariance method has been applied to calculate the turbulent quantity after coordinate transformation of a planar-fit rotation. We have carefully selected 3 good episodes in the winter season (23 October 2014 to 28 February 2015) for each category (9 days in total), such as grass and snow covers in case of weak synoptic wind condition, and grass cover of strong synoptic wind. The diurnal variations of the slope winds were well developed like the upslope wind in the daytime and downslope wind in the nighttime for both surface covers (grass and snow) in the weak synoptic forcing, when accordingly both heat and momentum fluxes significantly increased in the daytime and decreased in the nighttime. Meanwhile, diurnal variation of heat flux was not present on the snow cover probably in associated with significant fraction of sunlight reflection due to high albedo especially during the daytime in comparison to those on the grass cover. In the strong synoptic regime, the most dominant feature at Yongpyong, only the southeasterly downslope winds were steadily generated irrespective of day and night with significant increases in momentum flux and turbulent kinetic energy as well, which could suggest that local circulations are suppressed by the synoptic scale forcing. In spite of only one season analysis applied to the limited domain, this kind of an observation-based study will provide the basis for understanding of the local wind circulation in the complex mountain domain such as Gangwon in Korea.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.4
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• pp.431-442
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• 2013

Most of previous studies have insufficiently investigated the shear behavior and fracturing characteristics, experimentally in respect to the change of size of tooth-shaped surface asperity such as length and slope angle in a broad range. This study investigates the influence of the length and slope angle of a tooth-shaped surface asperity on the fracturing characteristics and the interface shear strength by using direct shear test apparatus. A total of 36 interface direct shear tests were conducted by changing the three types of slope angle of surface asperity, four type of length, and three types of normal stress. The shape of fractured surface after the test was quantified by using a three-dimensional surface roughness measurement apparatus. Through the experimental test results, the characteristics of fractured shape of surface asperity according to the normal stress were investigated. In addition, fractured length and height were quantified at each slope angle of surface asperity under a certain normal stress condition.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.663-668
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• 2005

The present study proposed to examine the appropriateness of the ground water level condition that had a significant effect on the stability of the slopes and, for this purpose, analyzed the rise of ground water level during the rainy season by applying the average daily rainfall of Seoul for the last 30 years. The result showed that the rise of ground water level was 6.0$\sim$41.0% of the slope height, which suggests that the currently applied condition of ground water level is somewhat overestimated. In addition, the result of interpreting the stability of slopes during the rainy season, slopes were unstable in all conditions when the ground water level was at the ground surface and base failure occurred. This suggests the importance of ground water level condition in stability analysis.

• Journal of The Korean Society of Agricultural Engineers
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• v.53 no.5
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• pp.9-16
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• 2011

Curve Numbers (CN) for the combination of land use and hydrologic soil group were regionalized at Imha Watershed using Long-term Hydrologic Impact Assessment (L-THIA) coupled with SCE-UA. The L-THIA was calibrated during 1991-2000 and validated during 2001-2007 using monthly observed direct runoff data. The Nash-Sutcliffe (NS) coefficients for calibration and validation were 0.91 and 0.93, respectively, and showed high model efficiency. Based on the criteria of model calibration, both calibration and validation represented 'very good' fit with observe data. The spatial distribution of direct surface runoff by L-THIA represented runoff from Thiessen pologen at Subi and Sukbo rain gage station much higher than other area due to the combination of poor hydrologic condition (hydrologic soil C and D group) and locality heavy rainfall. As a results of hydrologic condition and treatment for land use type based on calibrated CNs, forest is recommended to be hydrologically modelled dived into deciduous, coniferous, and mixed forest due to the hydrological difference. The CNs for forest and upland showed the poor hydrologic condition. The steep slope of forest and alpine agricultural field make high runoff rate which is the poor hydrologic condition because CN method can not consider field slope. L-THIA linded with SCE-UA could generated a regionalized CNs for land use type with minimized time and effort, and maximized model's accuracy.

• The Journal of Engineering Geology
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• v.28 no.3
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• pp.489-499
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• 2018

A flume experiments was used to study the characteristics of the surface displacements and volumetric water contents (VWC) during torrential rain. The surface displacement and VWC of the granite weathered soil were measured for rainfall intensity (100, 200 mm/hr) and initial ground condition (VWC 7, 14, 26%). The test processes were also recorded by video cameras. According to the test results, The shallow failure is classified into three types: retrogressive failure, progressive failure and defined failure. In the case of retrogressive failure and progressive failure, relatively large damage could occur due to the feature that soil is deposited to the bottom of the slope. the shallow failure occurred when the VWC reached a certain value regardless of the initial soil condition. It was found that the shallow failure can be predicted through the increase patton of the VWC under the condition of the ground dry condition (VWC 7%) and the natural condition (VWC 14%). For high rainfall intensity, progressive failure predominated, and rainfall intensity above a certain level did not affect wetting front transition.

• Proceedings of the KSRS Conference
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• v.1
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• pp.504-507
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• 2006

Airborn Lidar technology has been applied to diverse applications with the advantages of accurate 3D information. Further, Lidar intensity, backscattered signal power, can provid us additional information regarding target's characteristics. Lidar intensity varies by the target reflectance, moisture condition, range, and viewing geometry. This study purposes to generate normalized airborne LiDAR intensity image considering those influential factors such as reflectance, range and geometric/topographic factors (scan angle, ground height, aspect, slope, local incidence angle: LIA). Laser points from one flight line were extracted to simplify the geometric conditions. Laser intensities of sample plots, selected by using a set of reference data and ground survey, werethen statistically analyzed with independent variables. Target reflectance, range between sensor and target, and surface slope were main factors to influence the laser intensity. Intensity of laser points was initially normalized by removing range effect only. However, microsite topographic factor, such as slope angle, was not normalized due to difficulty of automatic calculation.

• Journal of Industrial Technology
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• v.27 no.B
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• pp.193-199
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• 2007

This paper is a result of a case study about landslides at Whacheon area in Kangwondo occurred during heavy rainfall in 2006. A-day-accumulative rainfalls from July 12 to July 13 and July 15 to July 16 were 120mm and 110mm respectively. Five sites at which slope failures occurred were visited to figure out main causes of slope failures by investigating characteristics of rainfall, geological formation, topography and ground surface exploration around the boundary of the landslides. Based on the site investigation characteristics of landslide with respect to rainfall pattern, geological and topographical condition and pattern of landslide were evaluated.

• Journal of Forest and Environmental Science
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• v.26 no.3
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• pp.193-202
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• 2010

To analyze the effects of tree roots on the stability of damage slope, distributional and physical properties of five-year Pinus densiflora roots were investigated. In the composition of roots, the proportion of main root to lateral root was 1 to 9 in slope condition. Root tensile force was increased in accordance with increased proportion to diameter of Pinus densiflora roots. However, tensile strength was decreased in proportion to diameter of roots. Root shear strength showed that soil containing Pinus densiflora roots was higher than that of non-treated soils. This result shows that Pinus densiflora roots significantly stabilize the surface-soil rather than sub-soil in damage slopes.

• Geomechanics and Engineering
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• v.19 no.1
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• pp.1-9
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• 2019

Shallow failures occur frequently in both engineered and natural slopes in expansive soils. Rainfall infiltration is the most predominant triggering factor that contributes to slope failures in both expansive soils and clayey soils. However, slope failures in expansive soils have some distinct characteristics in comparison to slopes in conventional clayey soils. They typically undergo shallow failures with gentle sliding retrogression characteristics. The shallow sliding mass near the slope surface is typically in a state of unsaturated condition and will exhibit significant volume changes with increasing water content during rainfall periods. Many other properties or characteristics change such as the shear strength, matric suction including stress distribution change with respect to depth and time. All these parameters have a significant contribution to the expansive soil slopes instability and are difficult to take into consideration in slope stability analysis using traditional slope stability analysis methods based on principles of saturated soil mechanics. In this paper, commercial software VADOSE/W that can account for climatic factors is used to predict variation of matric suction with respect to time for an expansive soil cut slope in China, which is reported in the literature. The variation of factor of safety with respect to time for this slope is computed using SLOPE/W by taking account of shear strength reduction associated with loss of matric suction extending state-of-the art understanding of the mechanics of unsaturated soils.