Steep Slope Stability Assessment Based on Hydrological Characteristics

Young Karb Song,Dongwook Kim 위기관리 이론과 실천 2015 Crisisonomy Vol.11 No.9

Each year, steep slope failures occur frequently because inopportune combinations of intensity and duration of rainfall trigger instability of the slopes. An Examination of effects of these two important rainfall factors on steep slope failure is a priority to prevent severe damage of properties and loss of lives resulting from slope failures. Slope failures are often triggered by a wetting band deepening caused by a decrease in matric suction due to water infiltration from the slope surfaces. The existing slope failure warning system in Korea does not reflect mechanical or hydraulic characteristics of unsaturated soils. In this study, geotechnical properties of unsaturated weathered soil, including permeability, soil-water characteristics curve, and shear strength, were examined by a series of experiments to evaluate slope stability. A procedure of steep slope failure risk evaluation is developed to reflect rainfall intensity, rainfall duration, and the mechanical and hydraulic properties of unsaturated soils.

Assessment of rock slope stability by slope mass rating (SMR): A case study for the gas flare site in Assalouyeh, South of Iran

Azarafza, Mohammad,Akgun, Haluk,Asghari-Kaljahi, Ebrahim Techno-Press 2017 Geomechanics & engineering Vol.13 No.4

Slope mass rating (SMR) is commonly used for the geomechanical classification of rock masses in an attempt to evaluate the stability of slopes. SMR is calculated from the $RMR_{89-basic}$ (basic rock mass rating) and from the characteristic features of discontinuities, and may be applied to slope stability analysis as well as to slope support recommendations. This study attempts to utilize the SMR classification system for slope stability analysis and to investigate the engineering geological conditions of the slopes and the slope stability analysis of the Gas Flare site in phases 6, 7 and 8 of the South Pars Gas Complex in Assalouyeh, south of Iran. After studying a total of twelve slopes, the results of the SMR classification system indicated that three slope failure modes, namely, wedge, plane and mass failure were possible along the slopes. In addition, the stability analyses conducted by a number of computer programs indicated that three of the slopes were stable, three of the slopes were unstable and the remaining six slopes were categorized as 'needs attention'classes.

The Slope Failure by Upward Seepage Flow in a Gradual Slope: Case Study in Sandy Slope Experiments

( Min Seok Kim ),( Young-suk Song ),( Hyun-joo Oh ),( Kyeong-su Kim ),( Choon-oh Lee ),( Sueng Won Jung ),( Yuichi Onda ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2

Slope failures are commonly occurred in steep hillslopes (>30 degrees) due to subsurface flow mechanism in soil mantle during unexpected rainfall intensity-duration. However, there were some slope failures by upward subsurface flow related with piping flow, detected at gradual hillslope (< 30 degrees) monitored under granite area, Icheon-city, Korea. The expansion of slope failure by the effect of subsurface flow were monitored at specific gradual hillslope site during 2004-2017 years. We proved its mechanism using a flume experiments with an artificial rainfall. In natural site, particularly for those slope failure which occur under intense rainfall is that from the failure surface to bedrock is saturated and has positive pore-water pressures from bedrock acting on it. In a lab test for 5 times, we observed slope failure initiation and its expansion under upward seepage direction and force (i.e. hydraulic gradient) in saturated state of soil. These subsurface flow by the seepage direction and force maybe play important role in slope failure mechanism in soil mantle of gradual slope in a granite study site.

Q-slope의 소개와 노천채탄장에서의 적용 사례

선우춘(Choon Sunwoo) 한국암반공학회 2019 터널과지하공간 Vol.29 No.5

노출 암반과 시추 코어를 특성화하고, 터널, 공동 및 광산 갱도에서 지보 및 보강 대책을 추정하기 위해 RMR 및 Q 분류법이 기술자들에 의해 널리 사용되어왔다. 사면에서의 암반분류는 SMR이 많이 사용되었지만 Q-Slope가 2015년부터 사면에 도입되었다. 지난 10년간, Q-slope라 불리는 수정된 Q시스템이 노천광산의 벤치, 도로사면 사면에 적용하기 위해 많은 저자들에 의해 시험되었다. 이 시험들을 통하여 Q-slope 값과 장기 안정 및 무지보 사면 경사각 사이에 간단한 상관관계가 있음이 나타내어 왔다. 터널이나 지하공간에서 RMR과 Q를 병용하면서 비교를 통해 상호보완 해왔던 것과 마찬가지로 사면에서도 SMR과 병행하여 Q-Slope를 사용할 수 있을 것이다. 국내에서 발표사례가 없는 Q-Slope의 사용방법과 인도네시아 Pasir 노천석탄광의 적용 예를 소개하고자 한다. The RMR and Q-system for characterizing rock mass and drilling core, and for estimating the support and reinforcement measures in mine galleries, tunnels and caverns have been widely used by engineers. SMR has been widely used in the rock mass classification for rock slope, but Q-Slope has been introduced into slopes since 2015. In the last ten years, a modified Q-system called Q-slope has been tested by the many authors for application to the benches in open pit mines and excavated road rock slopes. The results have shown that a simple correlation exists between Q-slope values and the long-term stable and unsupported slope angles. Just as RMR and Q have been used together in a tunnel or underground space and complemented by comparison, Q-Slope can be used in parallel with SMR. This paper introduces how to use Q-Slope which has not been announced in Korea and application examples of Pasir open pit coal mine in Indonesia.

식생기반재 뿜어붙이기의 비탈면 녹화이후 침식 안정성 평가 방법

길승호 ( Kil Sung-ho ) 한국환경복원기술학회(구 한국환경복원녹화기술학회) 2016 한국환경복원기술학회지 Vol.19 No.6

Slope revegetation refers to the use of vegetation and construction to protect a barren slope devastated by road and building construction. Among many revegetation strategies, hydroseeding has been widely utilized to stabilize barren slopes and has become the representative approach. Previous studies on slope stability have been conducted from a civil engineering perspective, mainly evaluating the stability of cut-slopes on solid bedrock and the use of concrete structures to stabilize devastated slopes. This study was conducted to develop a method to evaluate erosion risk of revegetated cut-slopes, based on criteria derived from previous studies. Twenty-five factors were surveyed on both on-the-spot erosion slopes and non-erosion slopes after slope revegetation to compare slope types. The scores of all non-erosion slopes exceed 80 score while erosion slopes are 80 below. Erosion slopes got the range of 68-74 score while non-erosion slopes got the range of 81-100 score in the first result which was not applied for weighted-values. The scores of all non-erosion slopes exceeded 3.10, while erosion slopes were below 3.10. Erosion slopes were in the range of 2.73-3.09, while non-erosion slopes were in the range of 3.15-3.90 in the second result, which was applied with weighted-values according to the AHP result from a previous study.

Study on Model Test of High Slope Supported by Micro-steel Pipe Piles

( Xueling Liu ),( Yuming Men ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2

The slope excavation is a commonly-used technology to expand the land space in the urban construction in the mountainous region. Due to the existence of potential slip surfaces developed in high-steep slopes, cutting will destroy initial equilibrium state within the slope body and cause a landslide. It is necessary to pre-support the slope before cutting to enhance the stability of the slope. In this research, a physical model test of using the micro-steel pipe piles to support the high and steep slope was carried out to make a comparison of the slope stabilities and deformation before and after installing the micro-steel pipe piles reinforcement. Test results show the safety factor is 0.93 in the case without using micro-steel pipe piles, and the slope failure occurred along the preset sliding surface after the slope cutting completed. For the slope supported by micro-steel pipe piles, the safety factor increased to 1.5 and no sliding trace and deformation was observed after the slope cutting. The result shows that the micro-steel pipe piles were effective in supporting the high and steep slope and restraining the slope movement, thus enhancing the stability of slope. This study provides an engineering practice for the supporting design of the high and steep slope.

Reliable Assessment of Rainfall-Induced Slope Instability

김윤기,최정찬,성주현,이승래 한국지반공학회 2009 한국지반공학회논문집 Vol.25 No.5

Many slope failures are induced by rainfall infiltration. A lot of recent researches are therefore focused on rainfall-induced slope instability and the rainfall infiltration is recognized as the important triggering factor. The rainfall infiltrates into the soil slope and makes the matric suction lost in the slope and even the positive pore water pressure develops near the surface of the slope. They decrease the resisting shear strength. In Korea, a few public institutions suggested conservative slope design guidelines that assume a fully saturated soil condition. However, this assumption is irrelevant and sometimes soil properties are misused in the slope design method to fulfill the requirement. In this study, a more relevant slope stability evaluation method is suggested to take into account the real rainfall infiltration phenomenon. Unsaturated soil properties such as shear strength, soil-water characteristic curve and permeability for Korean weathered soils were obtained by laboratory tests and also estimated by artificial neural network models. For real-time assessment of slope instability, failure warning criteria of slope based on deterministic and probabilistic analyses were introduced to complement uncertainties of field measurement data. The slope stability evaluation technique can be combined with field measurement data of important factors, such as matric suction and water content, to develop an early warning system for probably unstable slopes due to the rainfall.

Stability Analysis of Crack Slope Considering Nonlinearity and Water Pressure

Yong-xin Li,Xiao-li Yang 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.6

The soil slopes tend to induce the appearance of tension cracks at the top of slope under various factors, which poses an adverse impact on slope stability. Based on Power-Law nonlinear failure criterion, kinematical approach is adopted in this paper to investigate the effects of underground water and vertical tension cracks on stability of slopes. Notice that the tension cracks tend to propagate vertically, and thus a novel failure mechanism composed by the tension crack and logarithmic spiral shear slide plane is postulated. Theoretically, the worst position of crack propagation makes the stability factor minimal, and the failure surfaces can be obtained under different conditions through optimization. According to the proposed mechanism and nonlinear Mohr-Coulomb strength criterion, the stability factor and safety coefficient of slopes are derived. Subsequently, sensitivity analysis with respect to specific examples is conducted to analyze the influence of tension cracks, nonlinear strength parameters and pore water pressure on the slope stability. The results indicate that slope stability weakens gradually at the presence of tension cracks, and the changing degree is more evident with the increase of the slope angle. Meanwhile, nonlinear parameters have more significant impact on the safety factor with the decreasing value of the slope angle. However, the bigger the slope angle, the greater the height of tension cracks, and therefore the more obvious influence of pore water pressure on slope stability. When the slope angle approaches to be vertical, the height of tension cracks increases sharply. As a matter of fact, the height of tension cracks is highly related to geometrical conditions, strength parameters and water effect, which build a mutual relationship to determine slope stability.

침투해석을 고려한 비탈면 설계에 대한 연구

김유성,김재홍,이진광,김성수 한국지반공학회 2013 한국지반공학회논문집 Vol.29 No.1

Most of slope failures are triggered by heavy rainfall during rainy season. If the rain keeps on for the season, the water content of the ground increases and its matric suction decrease, and then the safety factor of soil slope gets lower. The change of water table level for soil slope stability dose not describe the behavior of the soil slope in real situation,hence it may be necessary to modify the design standard for slope stability in association with rain infiltration. For correct design, economical construction, and maintenance of a soil slope, unsaturated flow analysis is needed for estimation of slope instability regarding water infiltration and soil behavior on unsaturated soil slopes. The entire soil slope cannot be saturated by prolonged rainfall and wetting band depth (saturated zone) just deepens from slope surface,hence the cause of the shallow surface slide is the wetting band depth depending on rainfall duration and intensity. Therefore, the paper presents the differences between theoretical equation and numerical analysis for wetting band depth on soil surface and its safety factor, and compares the slope stability obtained from unsaturated flow analysis with that obtained from conventional slope stability analysis.

이동식 크레인 하중이 굴착사면 안정성에 미치는 영향 분석

김정곤,나예지,원정훈,Kim, Jeong Kon,Na, Ye Ji,Won, Jeong-Hun 한국안전학회 2021 한국안전학회지 Vol.36 No.5

The effect of heavy construction equipment on the excavated slope is investigated by slope stability analysis. A mobile crane with 500 kN capacity is applied as a working load to the background surface of the excavated slope, in both sandy soil and clay, designed to guarantee the safety of slope stability. Major parameters such as the distance between the edge of the slope and the mobile crane, groundwater level, and ground plate size of the mobile crane are considered. Only 23.8% and 14.3% of the analysis models with sandy soil and clay excavated slope, respectively, satisfied the slope stability. By changing the slope of the sandy soil from 1:1.0 to 1:1.2, the number of analysis models securing slope stability increased from 23.8% to 40.5%. For the clay excavated slope, the analysis models securing slope stability increased from 14.3% to 42.9% by changing slope inclination from 1:0.8 to 1:1.2. In addition, it is found that the increase in the size of the ground plate of the mobile crane increases the analysis models that secure slope stability. Therefore, it is an effective way to relax the excavated slope's inclination angle and simultaneously increase the ground plate size to guarantee stability.