Stability Safety Factor Research Articles

Analysis of Stability Safety Factors of Gabion Weir Models against the Wall and Water Level Variation

Analysis of Stability Safety Factors of Gabion Weir Models against the Wall and Water Level Variation

Experimental Study on Repairing the Mechanical Characteristics of Oil-Contaminated Silty Clay in Ancient Dike with Modified Lime Mortar.

Flood-controlled ancient dikes play a significant role in flood control and have received widespread attention as historical and cultural symbols. Flood-controlled ancient dikes often undergo disasters, and research on their repair is receiving increasing attention from experts and scholars. This article studies the control of seepage and bank slope instability in flood-controlled ancient dikes. Starting from the repair of ancient dike materials, three types of work are carried out: a test of soil's mechanical properties, finite element numerical simulation, and repair technology research. The research results show that the soil of the ancient dike site has hardened after being contaminated with waste oil from catering. The strength index of the ancient dike soil decreases and shows brittleness when the water content is 15% and the oil content exceeds 6%. The strength index and permeability coefficient of oil-contaminated soil improved using modified lime mortar (MLM), which was achieved using the method of MLM to repair oil contaminated soil. When the MLM content was 10% and the oil content was 6%, the friction angle of the soil sample reached its maximum value. When the MLM content was the same, the higher the density of the soil sample, the greater the friction angle and cohesion and the smaller the permeability coefficient. Establishing a finite element numerical model, through comparative analysis, it was found that after MLM remediation of oil-contaminated soil, the extreme hydraulic gradient of the ancient dike decreased by 31.3%, and the extreme safety factor of the bank slope stability increased by 31.2%. MLM pressure grouting technology was used to improve the soil during the remediation of contaminated soil at the ancient dike site. Through on-site drilling inspection, the effective diffusion radius of MLM grouting was obtained, and the plane layout and grouting depth of MLM pressure grouting were determined. The on-site water injection permeability test showed that using MLM pressure grouting technology can effectively repair oil-contaminated soil in the ancient dike while reducing the permeability coefficient by 8-15%.

Searching for sliding surfaces in multi-level loess slopes based on the brachistochrone

As a key problem in slope-stability analysis, searching for potential sliding surfaces has attracted the attention of experts and scholars for a long time. However, the commonly used sliding surface curves are only considered in terms of shape approximation and lack physical significance. The search process involved in stability analysis of multi-level slopes is complex and a large amount of calculation is required. In order to solve this problem, this paper proposes a new sliding surface form based on physical interpretation of the brachistochrone, and establishes a search model for the brachistochrone sliding surface of a multi-level loess slope. At the same time, in order to further expand the search range and find a more ideal potential sliding surface curve shape and position with a lower safety factor, we recommend continuing the sliding-surface search after the brachistochrone is improved. We compared the calculation results for the position of the potential sliding surface and the stability safety factor with the corresponding results for an arc sliding surface (in combination with a calculation example) to verify its rationality. The approach offered here not only provides a new choice of sliding surface curve form for slope-stability analysis, but also significantly improves search efficiency for potential sliding surfaces of multi-level loess slopes.

Stability analysis of rock slope under Sujiaba overpass in Chongqing City based on kinematic and numeric methods

Rock slopes have the characteristics of complex geological conditions, weak structural surface development, steep slope, and great damage. In this study, the Sujiaba overpass slope in Chongqing was selected as the evaluation object, and the main stability evaluation methods of rock slope were analyzed. Combined with the special geological conditions and geographical location of the rock slope, through a geological survey, the slope was qualitatively analyzed based on the stereographic projection method, and the slope stability safety factor was calculated by using the finite element strength reduction method. FLAC3D was used to simulate the initial stress state of the unstable rock mass, the limit state stability of the unstable rock mass before bolt support, and the stability after bolt support. The simulation results show that the stability coefficients of selected unstable rock masses W1, W2, W6, and W7 under the limit state before bolt support are, respectively, 1.22, 1.80, 5.90, and 2.10. Unstable rock masses separate from the parent rock, causing a large displacement due to their instability and downward sliding. After bolt support, stability coefficients for those four unstable rock masses are 1.60, 2.40, 8.60, and 3.20, respectively. Under the same reduction coefficient, rock masses are stable and the displacement is small. The results show that the calculation results of the initial stress state of the rock slope are consistent with the theoretical understanding and field investigation. After the implementation of bolt support, the anti-sliding stability of unstable rock is obviously improved. The research results have important scientific guiding significance and practical value for revealing the failure mechanism of rock slope and analyzing the stability of unstable rock mass.

Stability Analysis of the Foundation Pit and the Twin Shield Tunnels during Adjacent Construction

Due to the rapid development of urban rail transit and the development and use of underground space, foundation pit construction near existing subway tunnels is becoming increasingly common. When adjacent foundation pit projects are being constructed, it is difficult to avoid the influence on existing subway tunnels, which threatens the safe operation of subway tunnels. Thus, this study focused on the stability of the adjacent construction of foundation pits and twin shield tunnels. The finite element limit analysis (FELA) method was used to analyze the influences of construction scheme and relative position of the twin shield tunnels and adjacent foundation pit on the global stability of adjacent construction. Based on the research results, the guidance and design for the construction scheme and relative position are provided. The stability analysis on the foundation pit during the construction process is performed. The criteria of adjacent influential partition are proposed, and the influence of various input parameters (c/γD, φ, L/D and C/D) on the global stability of adjacent construction is discussed, respectively. A new design equation of safety factor of global stability of adjacent construction is obtained by curve fitting.

Numerical investigation of liquefaction-induced settlement and instability on earth dams

Liquefaction is a phenomenon in which soil loses its bearing capacity, large settlements occur, and lateral spreading and failures may be caused. Numerous studies around the world have shown that liquefaction occurs in the alluvium foundations of earth dams. In this paper, methods of assessment and numerical analysis have been used to assess the Shourijeh reservoir dam liquefaction. According to the latest criteria, it was observed that by considering the acceleration of the maximum credible earthquake (MCE) level, the alluvial foundation of the Shourijeh dam is liquefiable in some areas. The dynamic analysis and liquefaction modelling based on linear equivalent analyses have been used. By analysing the sliding block and sliding circles based on the limit equilibrium method and the Newmark sliding block analysis, the stability safety factors of slopes for the Shourijeh dam after the earthquake have been investigated for three different earthquakes and various states of reservoir water level. The results, in addition to providing helpful information regarding the performance of earth dams against liquefaction and its effects, have shown that the settlements caused by liquefaction in the studied dam are not so large that they would cause extensive damage of the dam at the MCE level.

Instability prediction model of remaining coal pillars under remining disturbance

AbstractTo address the instability timing problem of residual coal pillars under mining disturbance, their stress migration law and instability mechanism were studied via numerical simulation, physical simulation, and engineering tests considering residual coal remining in the 3101 working face of the Shenghua Coal Industry. The results show that as the mining progresses, the stress concentrates on both sides of the remaining coal pillar and empty roadway. When the first coal pillar in front of the working face loses its bearing capacity, the stress is transmitted forward, resulting in the advanced collapse of the empty roadway roof and an excessive load on the second coal pillar in front of the working face. Additionally, the critical value prediction model of the coal pillar stability safety factor was constructed. If is less than the critical value during the repeated mining period, the remaining coal pillar must be reinforced. A hollow grouting crossed anchor is selected for coal pillar reinforcement; thus, realizing the safe mining of the remaining coal pillars. Our research results provide theoretical support for the safe secondary mining of coal in China and similar coal mines worldwide.

Dynamic behavior of gravity segmental retaining walls

AbstractThis work aims to highlight gravity segmental retaining walls with their varied advantages. The paper investigates the dynamic behavior analysis of segmental retaining walls. The stability analysis is conducted on the basis of a pseudo-static Mononobe-Okabe theory that provides safety factors against sliding and overturning failure. The results demonstrate that the crucial safety factor of internal stability is the safety factor against overturning. Moreover, the positive wall inclination angle contributes to an improvement in the stability of the segmental retaining walls and the effect of the vertical seismic coefficient on the stability can be disregarding. Finally, a new equation is proposed for the elementary design of the segmental retaining walls.

Numerical Investigation of the Upside-Down Hanging Well Combined with Curtain Grouting for Strengthening a Flood Control Ancient Levee

The ancient levees used for flood control generally exist in the rainy areas of southern China. After years of operation, the levees have lots of problems, such as leakage, swelling, and cracking, which need to be reinforced. In this paper, combined with the characteristics of river water level fluctuations, the effect of the upside-down hanging well and curtain grouting reinforcement of the ancient levee is analyzed by a numerical method, and the variation law of the levee’s stability in the flooding process before and after reinforcement is explored. The study results show that the flooding process significantly affects the pore water pressure of the filling soil between the ancient levee and the well, and has a weak impact on that behind the well, which is conducive to the levee’s stability. The horizontal displacements of the levee and the fill present the opposite change law before and after reinforcement. Before reinforcement, the maximum horizontal displacement reached 2.75 cm, and the displacement was toward the Lan River. This was caused by the deformation of the soil squeezing the levee after the water level rose, which was extremely unfavorable to the levee’s stability. After reinforcement, the levee and fill shifted away from the river, mainly due to the hydrostatic pressures caused by the rising water level. The change in the stability safety factors of the reinforced levee is basically consistent with the flood fluctuation. The minimum value of the safety factors is 1.727, the maximum value is 2.273, and the safety factor only decreases by 24.02%, which is half of the change range of the safety factors before reinforcement. The stability of the reinforced ancient levee is largely improved.

Updating Active Deformation Inventory Maps in Mining Areas by Integrating InSAR and LiDAR Datasets

Slope failures, subsidence, earthworks, consolidation of waste dumps, and erosion are typical active deformation processes that pose a significant hazard in current and abandoned mining areas, given their considerable potential to produce damage and affect the population at large. This work proves the potential of exploiting space-borne InSAR and airborne LiDAR techniques, combined with data inferred through a simple slope stability geotechnical model, to obtain and update inventory maps of active deformations in mining areas. The proposed approach is illustrated by analyzing the region of Sierra de Cartagena-La Union (Murcia), a mountainous mining area in southeast Spain. Firstly, we processed Sentinel-1 InSAR imagery acquired both in ascending and descending orbits covering the period from October 2016 to November 2021. The obtained ascending and descending deformation velocities were then separately post-processed to semi-automatically generate two active deformation areas (ADA) maps by using ADATool. Subsequently, the PS-InSAR LOS displacements of the ascending and descending tracks were decomposed into vertical and east-west components. Complementarily, open-access, and non-customized LiDAR point clouds were used to analyze surface changes and movements. Furthermore, a slope stability safety factor (SF) map was obtained over the study area adopting a simple infinite slope stability model. Finally, the InSAR-derived maps, the LiDAR-derived map, and the SF map were integrated to update a previously published landslides’ inventory map and to perform a preliminary classification of the different active deformation areas with the support of optical images and a geological map. Complementarily, a level of activity index is defined to state the reliability of the detected ADA. A total of 28, 19, 5, and 12 ADAs were identified through ascending, descending, horizontal, and vertical InSAR datasets, respectively, and 58 ADAs from the LiDAR change detection map. The subsequent preliminary classification of the ADA enabled the identification of eight areas of consolidation of waste dumps, 11 zones in which earthworks were performed, three areas affected by erosion processes, 17 landslides, two mining subsidence zone, seven areas affected by compound processes, and 23 possible false positive ADAs. The results highlight the effectiveness of these two remote sensing techniques (i.e., InSAR and LiDAR) in conjunction with simple geotechnical models and with the support of orthophotos and geological information to update inventory maps of active deformation areas in mining zones.

Stability analysis of soft–hard-interbedded anti-inclined rock slope

The instability of rock slope is still a very frequent geological disaster, which seriously affects people's life and production activities. Previous studies have mainly focused on deformation mechanism, prediction, and control of hard rock with single lithology, while there are limited studies on the theoretic computational method of the stability for soft–hard interbedded anti-inclined rock strata. In this study, a geomechanical model for the toppling failure of soft–hard-interbedded anti-inclined rock slope is established. The modes of failure for soft and hard rock strata are analyzed, the computational formula of the downward thrust for each anti-inclined rock stratum is derived, and the stability safety factor of each rock stratum is defined. A theoretical computational method for determining the potentially most dangerous failure surface of soft–hard-interbedded anti-inclined rock slope is proposed. By comparing with the existing research results, the theoretical solving method proposed in this study can well solve the location of the potentially most dangerous failure surface of soft–hard-interbedded anti-inclined rock slope. The potentially most dangerous failure surface of this kind of slope is approximately planar, and the angle between it and the normal plane of the rock strata is an acute angle within 30°. It provides theoretical support for the stability analysis of this kind of slope.

Influence of mud intercalation on the stability of seepage flow in tailings dams

Layers with low permeability are an important factor affecting the stability of tailings dams. In order to analyze the influence of the weak permeability interlayer on the seepage stability of the dam, this paper establishes a numerical analysis model of the tailings dam with the weak permeability interlayer. The seepage stability of the dam slope is calculated and analyzed for the location, thickness, number, and intervals of mud intercalation on the seepage stability of the dam slope. The weakly permeable interlayers at different locations form different saturation lines in the dam. When the weak permeability interlayer is located in the middle of the dam, the height of the saturation line is the highest, and the corresponding stability safety factor is the smallest. When the weak permeability interlayer moves up or down, the buried depth of the saturation line increases, and the safety factor increases. However, when the weak permeability interlayer is located above the drainage prism, the overall slip along the weak permeability interlayer is incidental to the increase in dam height. When the thickness of the weak permeability interlayer changes, the safety factor of the dam has a positively high significance related to the leakage. When the location of the weak permeability interlayer changes, the safety factor of the dam has no obvious correlation with the leakage. With the increase of the thickness and number of weak pemeability interlayer and the decrease of the intervals of mud intercalation, the height of the saturation line gradually increases, and the safety factor of the dam gradually decreases. Through the location of the sliding surface, it is found that the sliding surface eventually destabilizes through the lowest low-permeability interlayer.

Retracted] Uncertainty Analysis of Key Influencing Factors on Stability of Tailings Dam Body

With the continuous expansion of the mining scale of mineral resources, many tailings are produced. In order to avoid the impact of harmful substances in the tailings on the residents around the tailings pond, it is necessary to explain the stability improvement. The dam safety monitoring system is mainly composed of observation sensors, telemetry data acquisition module, industrial control network, and automatic monitoring system. Through the work of the computer, the dam observation data can be automatically collected, processed, analyzed, and calculated. This paper adopts the automated system that makes preliminary judgments and graded alarms on whether the dam’s behavior is normal or not to provide early safety warning reports for monitoring objects. In this paper, combined with a specific example of a tailings reservoir dam body, the comprehensive uncertainty method is used to analyze factors such as the height of the tailings dam, the height of the wetting line, the cohesion of the tailings soil layer, and the internal friction angle, and the stability of the dam body is calculated. The results show that the sensitivity order of the dam stability safety factor K to each factor is as follows: internal friction angle of the tailing silt layer > the height of the wetting line > dam body height > the cohesion of the tailing silt layer. The most dangerous slip surface will jump at the 19‐level subdam of the tailings pond. The remediation measures are of great significance for maintaining the ecology around the tailings pond and ensuring the personal safety of residents.

A Deterministic Method for Evaluating Safety Factor of Deep Excavation Stability against Groundwater Inrush Equivalently Considering Soil Uncertainty

In current design specifications for deep excavation, the determination of safety factors against groundwater inrush only considers the self-weight effect of soil mass at the bottom. However, the shear strength and its spatial variability in a cement-solidified bottom layer also plays an important role in safety factor estimation. Based on that, in this study, the strength reduction method was introduced into reliability analysis of deep excavation engineering, and the influence of shear strength and its spatial variability of cement-solidified soil on the stability of deep excavation is studied. Furthermore, a deterministic analysis method that can equivalently consider soil uncertainty is proposed and verified.

Effects of desert riparian vegetation roots on the riverbank retreat process in the Tarim River in China

The desert riparian vegetation zone is an important part of the riparian ecosystem. It is significant for river evolution and to channel beds owing to the reinforcement effect of the vegetation roots on the bank and resistance to erosion. The quantitative effects on toe erosion and bank collapse were first investigated to determine how vegetation roots affect the continuous retreat process of riverbanks under different water levels. The case study is the Tarim river, the degrees of riverbank stability at eight sampling sites during the 2016 and 2017 hydrological years were calculated using the bank stability and toe erosion model (BSTEM). Furthermore, the effects of six vegetation species, Populus euphratica (PE), Tamarix ramosissima (TR), Alhagi sparsifolia (AS), Nitraria tangutorum (NT), Phragmites australis (PA), and Glycyrrhiza uralensis (GU), on riverbank stability were discussed. Taking the right bank of sampling site II (Alar New Bridge) as an example, the bank stability safety factor (Fs) and collapse process under the roots of six vegetation species with different root area ratios (RARs) were calculated. The following conclusions were drawn from the results: (a) Different vegetation roots can reduce toe erosion from 0.4 % to 68.4 %, with peak effects during the dry season and recession stages; (b) The presence of near-bank vegetation roots can strongly influence bank collapse, particularly during the recession stage when water level drops rapidly; and (c) Most of the calculated Fs with the roots of all six plant species studied were higher than those without roots during four stages. Moreover, it was greater than the critical value of 1.3 in most cases. The results also indicate that banks with PE roots had the highest Fs values. By contrast, banks with NT and GU roots had the smallest Fs. As the RAR increased, the Fs values in a hydrological year increased linearly for each vegetation specie. The rate of increase order was as follows: PE > TR > NT > AS > PA > GU under a particular range of RAR (0.9 % < RAR < 1.8 %).

Probabilistic Analysis of Slope against Uncertain Soil Parameters

The purpose of this article was to investigate the influence of uncertain soil parameters on slope stability problems using the probability method. The most important soil instability is probably the inherent spatial variability of soil properties and its influence on slope safety factors. The probability method is recognized for its validity both in practice and academic research. This method of geotechnical risk management involves uncertain parameters. In this study, randomly selected uncertain parameters were combined with traditional analysis using Bishop’s simple methodology and Monte Carlo simulation. The minimum safety factor and critical slip surface of the slope stability were analyzed by Bishop’s simple method. The influence of uncertain soil parameters was analyzed by the back analysis method with Monte Carlo simulation. The calculation was controlled by a critical slip surface, and the safety factor was equal to 1. The results of the analysis show the minimum safety factor and the significant slippery surface of slope stability with the original soil strength parameters. The new soil strength parameters were recommended by Monte Carlo simulation that was used for improving the soil strength parameters in construction. In addition, probability analysis can identify an insufficient understanding of groundwater level distribution and that the assumption of a uniform distribution increases the probability of failure. Governments can use the results of water level analysis in flood warnings and flood management projects to reduce risks to life and property.

Slope stability analysis during an earthquake in flow-slide affected area of Jono Oge

On September 28th, 2018, the earthquake with a moment magnitude (Mw) 7.5 due to strike-slip Palu-Koro Fault in Central Sulawesi caused a major geological failure. In the Jono Oge area, the earthquake-induced liquefaction and flow-slide occurred on relatively flat ground with an average slope of 2%. In this paper, the safety factor for slope stability analysis was determined by shear strength reduction caused by the earthquake at the potentially liquefied soil layer, varying peak ground acceleration values, and groundwater level conditions. This analysis evaluated the potential of ground movement occurrence in Jono Oge with the condition of soil layer pre and post the Palu-Donggala earthquake that happened in 2018 using GeoStudio Slope/W geotechnical software. The analysis was conducted on the cross-section of the soil layer based on three boreholes incorporating standard penetration test (SPT) data on the study area. The analysis results showed ground movement potential because of the seismic loads and groundwater level conditions. The lower the safety factor of slope stability, the higher the ground movement potential in flow-slide affected area. This ground movement potential could trigger the occurrence of flow-slide in Jono Oge area.

Study on Stability and Ecological Restoration of Soil-Covered Rocky Slope of an Abandoned Mine on an Island in Rainy Regions

The eastern slope of the abandoned mine in the Zhoujiayuan Mountain Island area has been seriously damaged by local quarrying, which often triggers visual pollution, soil erosion, and landslides during rainfall. This paper carries out an ecological restoration of the abandoned mine based on indoor experiments and field investigation data. The paper also quantitatively analyzes the stability evolution laws of the soil-covered slope before and after the ecological restoration in the rainfall process, putting forward further slope reinforcement and ecological restoration measures. The results showed that the stability safety factor of the covered slope decreased to 0.92 after raining for 18 h, and the instability risk was very high. When the vegetation had recovered, the stability of the soil-covered slope with root system was significantly improved, and its safety factor was close to 1.15 after 64 h of continuous rainfall. Throughout the field observation conducted from 2019 to 2022, the slope of abandoned rock mines was found to be lush with restored plant diversity. After several continuous rainfall processes, neither soil erosion nor instability phenomena were found there. The study has certain reference significance for the ecological restoration of abandoned rock mines in rainy regions.

Centrifuge modeling and analytical validation of seismic amplification in a slope during earthquakes – Implications to seismic slope stability analysis

Earthquake-induced slope failure causes enormous damage to structures above and below the slope. The acceleration amplified within the slope directly degrades the stability of the slope. However, the seismic amplification characteristics within a slope during earthquakes remains poorly identified. This study explores seismic amplification of a slope during earthquakes through dynamic centrifuge tests. Comparison of the acceleration amplification patterns between a slope model and a flat ground model revealed that the acceleration was concentrated at the crest and near the slope surface. This phenomenon was verified through the analytical model developed based on a multi-degree of freedom mass-damper-spring system. In addition, the analytical model enabled the computation of the peak acceleration at each part of the slope and allowed examination of the factor of safety for slope stability. While various locations within a slope can be chosen to determine the representative acceleration as well as the free-field flat ground response, the use of the acceleration at the crest resulted in the lowest factor of safety value. Therefore, a conservative analysis would preferably use the accelerations at the crest and on the slope surface, rather than using the accelerations in a free-field flat ground. This study presents unique ground acceleration data from the well-controlled physical modeling of a slope and a simple but robust analytical model to predict seismic amplification in a slope, which provides better insight into determination of ground acceleration for slope stability analysis.

Freeze-Thaw Effect on Riverbank Stability

The stability of riverbanks in cold regions is affected by the freeze-thaw action. The freeze-thaw process causes changes in the moisture content, friction angle, and cohesiveness of the bank material. Together with the freeze-thaw effect, seepage pressure influenced by the changing water levels, and the bank slope are the key factors affecting bank stability. A limit equilibrium bank stability model considering the infiltration water pressure effect is developed and applied to the Shisifenzi section of Inner Mongolia reach of the Yellow River. Laboratory tests of field samples with moisture contents of 15%, 18%, 21%, and saturated showed that the freeze-thaw action reduced the degree of saturation by 34.37 %, 30.71%, 32.48%, and 46.23%, respectively, accompanied by reductions in the internal friction angles by 1.78%, 2.74%, 6.33%, and 5.32%. These changes resulted in a 24.35% to 29.13% reduction in the safety factor of bank stability. Together with seasonal variations in the water levels the field data showed that the bank stability safety factor in the study site increases gradually through the melting period, dry period, wet period, flooding period, and low flow period. The slope stability safety factor increases with the stage of the river but decreases with the groundwater level.