• Journal of the Korean Geotechnical Society
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• v.23 no.10
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• pp.97-107
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• 2007

Accurate evaluation of the slope stability by assuming failure block as the entire slope is considered to be apposite for the small scale slope, whereas it is not the case for the large scale slope. Hence, appropriate estimation of a failure block size is required since the safety factor and the joint strength parameters are the function of the failure block size. In this paper, the size of failure block was investigated by generating 3-dimensional rock joint system based on statistical data of joints obtained from research slope, such as joint orientation, spacing and 3-dimensional joint intensity. The result indicates that 33 potential failure blocks exist in research slope, as large as 1.4 meters at least and 38.7 meters at most, and average block height is 15.2 meters. In addition, the data obtained from 3 dimensional joint system were directly applicable to the probability analysis and 2 and 3 dimensional discontinuity analysis.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.1249-1253
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• 2007

제방은 제내지에 거주하는 인간의 재산과 삶을 방어하고, 홍수를 제어하는 가장 기본적인 수공구조물이다. 제방파괴 원인은 월류, 활동, 침식, 그리고 침투 등으로 분류되어 질 수 있다. 특히 간극수압에 의해 발생하는 침투는 제방 내부침식(internal erosion) 및 파이핑(piping) 등을 야기함으로서 제방파괴를 유도한다. 침투에 의한 제방파괴는 월류나 침식에 의한 제방파괴 유형보다 상대적으로 적으나, 다른 제방파괴 원인을 더욱 활성화 시키는 인자로 작용한다. 도시하천의 경우 높은 치수안전도를 적용하여 제방을 축조함에 따라 월류에 의한 붕괴보다 강우와 하천수의 복합요인에 의한 침투파괴가 중요한 문제로 대두되고 있다. 본 연구에서는 침투와 활동에 대한 안전성을 확보할 수 있는 침투보강기법인 단면확대기법에 대한 적용성 및 유의사항을 수치모의를 통해 검토하였다. 제방 비탈면 경사를 1:2 확대할 경우, 침투유속이 70 %정도 감소되는 것을 확인하였다. 그러나 단면확대기법은 홍수시 통수능과 제내지의 부지 확보 문제 등을 고려하여 적용하여야 하며, 도시하천에서 단면확대기법을 적용하는 데는 일정부분 한계를 가질 것으로 판단된다.

• The Journal of Engineering Geology
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• v.22 no.1
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• pp.1-13
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• 2012

The purpose of this work is to gain a better understanding of the interrelationships between geological structures and slope failure in sedimentary rocks. In the studied slopes, construction-related slope failure could only be observed on the south-dipping slopes. This indicates that slope stability may be dependent on the angular relationships between the dip direction of bedding and the orientation of the slope. Slope failure continued, post-construction, around large fault zones in the studied outcrop; these fault damage zones are, however, not easily recognized in the field. Here we suggest a new method that uses accumulated fracture density to precisely identify fault damage zones. Multiple-faced slopes are now increasingly being exposed during large-scale construction projects in South Korea. This multiple-faced slope analysis indicates that the stability of a slope should be evaluated by identifying domains, through the analysis of possible slopes and their angular relationships with bedding and other discontinuities, prior to construction. Therefore, careful consideration of geological structures such as bedding and other discontinuities, and their angular relationships during the design of cuttings through sedimentary rocks, will increase the efficiency of construction and enable the safe construction of more stable slopes that will retain their stability after construction.

• Journal of the Korean Geosynthetics Society
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• v.18 no.3
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• pp.11-22
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• 2019

This study was conducted to identify the causes of the unusually high number of rock slope failures during an expressway construction in Yangsan fault system. The shear strength (cohesion and internal friction angle) of 128 slopes of discontinuities including bedding, joint, and fault planes were re-evaluated through the examination of face mapping and back analysis. The re-evaluated values were analyzed and then compared with the existing data and values used in the design. As a result, the re-evaluated cohesion and friction angles were very low compared to the existing data and the values applied in the design. This incongruity was pointed as the primary reason for the rock slopes failures during the construction. This may be related to the inherent features of clastic sedimentary rocks in the study area, and the discontinuities in the sedimentary rocks in this region played a significant role. Especially, bedding discontinuity showed a big difference compared to the existing data. The shear strength depended on the type of discontinuity in case of clay filled in discontinuity. However, shear strength was independent on the type of discontinuity in case of shattered materials filled in discontinuity.

• Journal of the Korean Geotechnical Society
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• v.38 no.7
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• pp.39-47
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• 2022

This study aims at evaluating the stability of disaster risks, such as schools, apartments, and geotechnical structures located around slopes in urban areas. The research conducted an aerial photography analysis on where the slope of the retaining wall behind 𐩒𐩒 High School in Gwangju collapsed in August 2018 due to heavy rain. In general, the overflow of rainwater has been managed through drainage channels around slopes during the rainy season, and the surface flow of rainfall was limited due to the presence of dense forests in the area. However, when the slope collapsed, a lot of water flowed out of the ground, and the saturated surface layer ground was destroyed. To analyze the cause, the changed terrain of the upper slope area, which could not be directly identified, was photographed using unmanned aerial vehicles. Digital Elevation Model by unmanned aerial vehicle shooting was performed by analyzing the slope map, calculating the direction of rainfall and the length and width of water-logged areas. The change in the instability of the slope over time due to a 10-day rainfall was also analyzed through numerical analysis.

• The Journal of Engineering Geology
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• v.30 no.4
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• pp.673-682
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• 2020

The ground shear force at the expected failure surface and resistance force due to reinforced anchor can act as important factors according to a failure type from the stability viewpoint at a slope. Furthermore, the anchor's axial force may vary at an anchor-reinforced slope due to ground weathering, settlement, and corrosion in the incompletely anti-corrosion treated steel wire strand at a ground where the bearing plate is installed. However, in case that the resistance force of the anchor is locally lost due to the variation of the anchor's axial force, the resistance force may not play the role so that the external force tends to be transferred to the surrounding anchors, causing an increase in the tensile force in the surrounding anchors. Accordingly, a stability problem at the entire slope may occur, which requires much attention. Thus, this study proposed a method to monitor a variation trend of the tensile force of anchors installed at a slope and infer the external stability at the entire slope considering the monitoring result.

• Journal of the Korean Geotechnical Society
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• v.35 no.5
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• pp.5-19
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• 2019

Considering the natural phenomenon in which steep slopes ($65^{\circ}{\sim}85^{\circ}$) consisting of rock mass remain stable for decades, slopes steeper than 1:0.5 (the standard of slope angle for blast rock) may be applied in geotechnical conditions which are similar to those above at the design and initial construction stages. In the process of analysing the stability of a good to fair continuum rock slope that can be designed as a steep slope, a general method of estimating rock mass strength properties from design practice perspective was required. Practical and genealized engineering methods of determining the properties of a rock mass are important for a good continuum rock slope that can be designed as a steep slope. The Genealized Hoek-Brown (H-B) failure criterion and GSI (Geological Strength Index), which were revised and supplemented by Hoek et al. (2002), were assessed as rock mass characterization systems fully taking into account the effects of discontinuities, and were widely utilized as a method for calculating equivalent Mohr-Coulomb shear strength (balancing the areas) according to stress changes. The concept of calculating equivalent M-C shear strength according to the change of confining stress range was proposed, and on a slope, the equivalent shear strength changes sensitively with changes in the maximum confining stress (${{\sigma}^{\prime}}_{3max}$ or normal stress), making it difficult to use it in practical design. In this study, the method of estimating the strength properties (an iso-angle division method) that can be applied universally within the maximum confining stress range for a good to fair continuum rock mass slope is proposed by applying the H-B failure criterion. In order to assess the validity and applicability of the proposed method of estimating the shear strength (A), the rock slope, which is a study object, was selected as the type of rock (igneous, metamorphic, sedimentary) on the steep slope near the existing working design site. It is compared and analyzed with the equivalent M-C shear strength (balancing the areas) proposed by Hoek. The equivalent M-C shear strength of the balancing the areas method and iso-angle division method was estimated using the RocLab program (geotechnical properties calculation software based on the H-B failure criterion (2002)) by using the basic data of the laboratory rock triaxial compression test at the existing working design site and the face mapping of discontinuities on the rock slope of study area. The calculated equivalent M-C shear strength of the balancing the areas method was interlinked to show very large or small cohesion and internal friction angles (generally, greater than $45^{\circ}$). The equivalent M-C shear strength of the iso-angle division is in-between the equivalent M-C shear properties of the balancing the areas, and the internal friction angles show a range of $30^{\circ}$ to $42^{\circ}$. We compared and analyzed the shear strength (A) of the iso-angle division method at the study area with the shear strength (B) of the existing working design site with similar or the same grade RMR each other. The application of the proposed iso-angle division method was indirectly evaluated through the results of the stability analysis (limit equilibrium analysis and finite element analysis) applied with these the strength properties. The difference between A and B of the shear strength is about 10%. LEM results (in wet condition) showed that Fs (A) = 14.08~58.22 (average 32.9) and Fs (B) = 18.39~60.04 (average 32.2), which were similar in accordance with the same rock types. As a result of FEM, displacement (A) = 0.13~0.65 mm (average 0.27 mm) and displacement (B) = 0.14~1.07 mm (average 0.37 mm). Using the GSI and Hoek-Brown failure criterion, the significant result could be identified in the application evaluation. Therefore, the strength properties of rock mass estimated by the iso-angle division method could be applied with practical shear strength.

• Journal of the Korean GEO-environmental Society
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• v.12 no.8
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• pp.25-31
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• 2011

In recent rainy seasons, severe rain storms have caused frequent reinforced retaining wall collapses and slope sliding which have lead to casualties. In this paper, investigating cases of reinforced retaining wall failure, the causes of cracks in reinforced retaining wall and slope sliding have been examined, and a finite element analysis considering the construction phase has been done to analyze the cause and characteristics of slope sliding. As a result, reinforced retaining wall displacement has increased due to heavy rain storms and the increase size has been shown to be large. From these results, it has been analyzed that pile driving can have an effect on the collapse of reinforced retaining walls.

• Journal of the Korean Geotechnical Society
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• v.31 no.9
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• pp.5-15
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• 2015

In this study, rainfall-induced slope stability and coupling effect are investigated using hydro-mechanical finite element model. This model is developed by formulating constitutive and coupled balance equations and is verified by comparing the numerical results with field matric suction. The homogeneous soil layer (soil column) and soil slope are modeled by this model, and the results of variation in matric suction, mean effective stress, porosity, displacement, factor of safety are compared with those of staggered analysis. It is found that the vertical and horizontal displacement from coupling analysis considering change in porosity is larger than that of staggered analysis. The displacement and matric suction from coupling analysis by rainfall infiltration can affect slope instability, which shows a progressive failure behavior. The lowest factor of safety is observed under short-term rainfall. This results confirm the fact that coupling analysis is needed to design soil slope under severe rain condition.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.5
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• pp.695-705
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• 2024

As a result of Typhoon Hinnamnoh, several slope failures occurred in the Pohang region, it is necessary to perform infiltration and slope stability analyses due to the actual rainfall. In the failed sites, samples were collected, and the hydro-mechanical properties of unsaturated soil were examined. Modeling the actual behavior using a single-mode function characteristic curve was found to be inadequate, leading to the adoption of a dual-mode function characteristic curve. The dual-mode function showed better agreement with the water retention test data. We calculated the unsaturated hydraulic conductivity for single and dual modes and performed rainfall-induced infiltration analysis. The variations in saturation and pore water pressure were calculated due to rainfall for three landslide-prone areas, Stability analysis based on effective stress of unsaturated soil was conducted, and safety factors were computed over time steps. The dual-mode model successfully reproduced landslides triggered by Typhoon Hinnamnoh, while the single-mode model exhibited a minimum safety factor of 1.2-1.3, making slope failure unpredictable. The dual-mode model accurately predicted instability in the slope by appropriately accounting for pore water pressure variations during Typhoon.