Decrease In Safety Factor Research Articles

Time Histories Finite Element Modelling for Irrigation Canal Stability Analysis under the Effects of Liquefaction in the Sibowi Sigi Regency, Indonesia

Abstract The Gumbasa irrigation canals are one of the water resource infrastructures damaged by the 7.5 Mw Palu-Donggala Earthquake in 2018. Canal reconstruction was performed to restore the function of the irrigation network, supllying a potential area of 8000 ha. Main canal construction is known to pass through areas with liquefaction vulnerability, and seismic factors also play a role in the stability of construction. This study discusses the stability of construction under the influence of earthquake loads on the Gumbasa irrigation main canal in the Sibowi area, Tanambulava district, Sigi Regency. The irrigation main canals are built in a landfill on a subbase soil with the potential for liquefaction. Numerical simulations were carried out using the finite element method under two conditions, namely static and dynamic conditions on soil parameters obtained from the Standard Penetration Test (N-SPT) data obtained previously. Based on the analysis results, depths of 6.5 m to 9 m have partial potential for liquefaction, with no significant decrease in safety factor (SF). In the static analysis, the SF is 1.65 and 2.13. In the dynamic analysis, the SF is 1.64 and 2.12. The vertical displacement is minimum 0.03 m and maximum 0.10 m.

A comparative slope stability analyses of heavily jointed open-pit slopes using 3D limit equilibrium and finite element methods: a case study from Bingöl, Türkiye

ABSTRACT This study investigates the slope stability of Bingöl open-pit iron mine slopes using 3D limit equilibrium and finite element methods. The pit benches are 3 m wide and 6 m high, with an overall slope angle of 38°. The geological composition comprises slightly to moderately weathered and heavily jointed phyllite, micaschist, and gneiss. Shear strength parameters were determined through back analyses of already failed sections using the Hoek-Brown failure criterion and Geological Strength Index (GSI). Factor of safety values for static and dynamic conditions were calculated using 3D limit equilibrium and 2D finite element analyses. Results show good agreement between the two methods, with benches in the northern section exhibiting a significant decrease in safety factor under dynamic conditions, indicating near-limit equilibrium slopes.

A slope management method by monitoring soil volumetric water content and its validation through numerical analysis

Landslides induced by heavy rainfall have become increasingly common in recent years. As the groundwater level rises, the safety factor of slopes tends to decrease. However, traditional monitoring methods, such as employing water-level (pressure) gauges in boreholes, require significant effort. Thus, this study proposes a slope management approach based on monitoring the volumetric water content of the ground surface. The monitored slope, approximately 20 m in height and 30 m in length, consists of topsoil mixed with grass roots and sand with a slight silt admixture, as revealed by two borehole investigations. Soil moisture meters were strategically installed at three locations along the slope (upper, middle, and lower sections) to gauge the volumetric water content. Observations indicated a sensitive increase in ground water content following rainfall. Furthermore, a three-dimensional Finite Element Method (FEM) analysis was employed to explore the correlation between rainfall (intensity and duration) and groundwater content. The FEM analysis also examined the impact of rainfall-induced changes in slope water content on the overall slope safety factor, utilizing 3D point cloud data to model the monitored slope. Qualitative agreement was observed between the monitoring and analysis results, highlighting a decrease in slope safety factor as slope water content increased. These findings underscore the potential of conveniently assessing slope safety factors based on the water content of a slope’s ground surface.

Analysing Slope Stability in Response to Blast-Induced Dynamic Loading by Pseudo-Static Approach

Regular blasting in opencast coal mines generates significant ground vibrations, impacting mine slope stability and posing risks to life and property. This study focuses on monitoring ground vibrations in an opencast coal mine through near-field monitoring and investigating the impact of blast-induced seismic loading on slope stability. The approach involves a pseudostatic method utilising Strength Reduction Factor (SRF), based on Finite Element (FE) numerical modelling software. The study examines a pit slope with a tension crack under seismic loading, varying the intensity of seismic coefficients (Ks) from 0 to 0.5. These coefficients are determined through field vibration monitoring during production blasts. In numerical modelling, seismic loading is considered in both horizontal (outward of slope face) and vertically downward (in-line with gravity). Numerical modelling incorporates dimensionless horizontal seismic coefficient (Kh) and vertical seismic coefficient (Kv), and both directions which is expressed as Seismic Coefficient Ratio (SCR) which is the ratio of Kv and Kh for interpretation of results. Although SCR induces changes in the Factor of Safety (FoS), its impact is minimal compared to seismic loading solely in the horizontal direction. Consequently, increasing SCR leads to a decrease in FoS. The study observes that Peak Ground acceleration (PGA) in the longitudinal direction has greater dominance than in the transverse direction. Additionally, the seismic wave in the horizontal direction destabilises the slope more than the corresponding vertical seismic wave. These findings are elucidated in the context of the Critical Slip Surface (CSS).

Numerical Investigation into Factors Affecting Stability of Opencast Coal Mine's Rise Side Highwall Slope

Open-pit coal mining accounts for 93% of India's total coal production, playing a significant role in meeting the nation's substantial energy needs. The success of an open-pit mine hinges on maintaining the steepest and deepest slopes that remain stable over the mine's lifespan. However, slope failure is a complex issue influenced by numerous factors. In the context of openpit coal mines, the rise side highwall involves cutting through a rock mass containing various elements like an unconsolidated weathered mantle of sandstone, sandy clay, clay, carbonaceous shale and coal. Some opencast mines within the Godavari Valley Coal Field (GVCF), India have encountered significant pit slope failures. This paper uses a numerical modelling approach aimed at effectively assessing the stability of the rise side highwall, leveraging available geotechnical data from one of GVCF's largest opencast coal mines. The research investigates the impact of seven detrimental factors on slope stability, including dynamic loading due to blasting, employing a methodical One-Factor-At-A-Time (OFAT) approach. The study utilises Rocscience Phase2 version 9.0, a Finite Element Method (FEM) based numerical modelling software to gauge the sensitivity of each factor on the Factor of Safety (FoS). The numerical modelling results indicate that there is a linear decrease in FoS corresponding to the reduction in cohesion and an exponential increase in the FoS as the angle of internal friction rises. Furthermore, the analysis reveals significant impacts on the FoS due to groundwater and seismic loading from the blasting. This approach aims to comprehensively analyse and understand the intricacies of slope stability in the specific context of open-pit coal mining.

Evaluating construction parameters of HB and CD methods for super large section tunnel: a case study

The double sidewall guide pit and centre cross diagram (CRD) methods are often used for the construction of large-section tunnels through water-rich fault fracture zones due to their long construction time and high construction cost. To shorten the construction period and save costs, the top heading and benching method (HB) and centre diaphragm (CD) can be chosen for construction. The construction parameters of the step and CD methods are optimized to ensure the surrounding rock stability and tunnel safety. By relying on the Tongzi Tunnel, we simulate the excavation of different step heights in the construction of the top heading and benching method (HB) and CD methods through numerical simulation, the laws of tunnel vault settlement, and changes in the surrounding rock stress, initial support axial force, bending moment and safety factor. The study shows that as the height of the upper step increases, the settlement of the vault and the convergence of the periphery increase, the initial support safety factor decreases, and the plastic zone of the surrounding rock increases at 30 m from the target face. The step height for the top heading and benching method (HB) of construction is optimized as follows. The ratios of the upper, middle and lower step heights are 0.45H, 0.35H and 0.2H, respectively. The CD method construction step height is optimized to the left (right) upper and left (right) lower step height ratios of 0.5H and 0.5H, respectively.

Impact of Climate Change on the Stability of the Miacher Slope, Upper Hunza, Gilgit Baltistan, Pakistan

Especially in recent years, the study of landslide phenomena is considered as very important because of the effects of climate change. The aim of this paper is to examine the stability of the slope located in Miacher Nagar village along the Hunza River (HR), using the Limit Equilibrium Method (LEM). The Miacher slope rises to a height of 900 m from the foot of the Hunza River and has a base angle of 50 degrees. Meta-sediments and quaternary recent glaciated deposits make up the majority of the slope’s composition. The slope movement of Miacher was first triggered in 1995, and was further triggered in 2010 and 2013. The slope was geologically, geomorphologically, geotechnically and geochemically investigated as well as modeled by Slope/w to determine the safety factor. Soil samples were analyzed for their geotechnical, geological and geomorphological properties. The Limit Equilibrium Method (LEM) was employed in this study to analyze the Factor of Safety (FOS) of the slope, based on assumptions of the Morgenstern and Price, Ordinary, Janbu and Bishop Methods, using the Slope/w software. Various factors, including pore water pressure, unit weight, cohesion, angle of internal friction and overburden, were examined by analyzing different scenarios. The findings showed that an increase in cohesion and angle of internal friction resulted in an increase in FOS, whereas an increase in unit weight and overburden caused a decrease in FOS. The influence of pore water pressure was positive to a certain extent, but a further increase led to a significant reduction in FOS. The results showed that the Miacher slope is currently stable, as all FOS values were greater than one, based on the existing strength parameters and simulated results obtained using Slope/w.

Study on influencing factors of slope stability and evolution law of safety factor in coal measure strata

Aiming at the influence factors and their action regulation of the slope stability in the coal measure strata of Beijing–Hong Kong & Macao Expressway, the influence characteristics of injection dip angle of rock stratum, thickness and strength parameters of the soft interlayer, slope height and size of slope angle on the slope safety factor are systematically studied by using the limit equilibrium method theory. The influence of slope height, thickness of weak interlayer and shear strength parameters on the stability of slope in coal measure strata with different dip angles is that the safety factor decreases first and then increases with the increase of strata dip angle. The minimum safety factor of slope under the action of each factor is near the strata dip angle of 30°, which indicates that the stability of slope in coal measure strata is poor when the dip angle of rock stratum is about 30°. With the increase of slope angle, the minimum safety factor decreases. However, when the slope angle is less than 40°, the slope is in a stable state and the dip angle of the strata do not affect the stability of the slope. Slopes with different slope angles have the minimum safety factor that is not affected by slope height. The difference between analytical solution and numerical solution is analyzed. The research provides a theoretical basis for the treatment of slopes in coal measure strata and has certain practical significance.

Study on the Influence of Water Level on Earth Dam Reinforced by Cut-Off Wall: A Case Study in Wujing Reservoir

The construction of a cut-off wall is a common reinforcement method for earth rock dams. At present, compared with the in-depth study on homogeneous earth dams, more and more attention is being paid to the stability and deformation of earth dams strengthened by a concrete cut-off wall. In this study, aiming at the Wujing project of the earth dam strengthened by cut-off wall, the influence of the water level rise and fall on the stability of the dam slope, the deformation of the dam body, and the crack width on dam crest were analyzed by numerical calculation and in situ measurement. The analysis results show that when the reservoir encounters a sudden drawdown, the safety factor of the dam slope decreases sharply. The faster the sudden drawdown, the faster the safety factor decreases. When the reservoir water level rises, the dam’s horizontal displacement shifts to the upstream direction, and the change of horizontal displacement of the downstream slope is significantly larger than that at the measuring point of the upstream slope. The water level of the reservoir rises, and the surface of the dam body rises, and the fluctuation of settlement deformation shows that the upstream side is larger than the downstream side, especially during the period of abrupt change in the reservoir water level. The longitudinal cracks on the dam crest show a tendency of shrinkage when the reservoir water level rises, and opening decreases with the decrease of deformation gradient increment and increases with the increase of gradient increment.

Pore-water pressure accumulation during closely spaced earthquakes: Fundão Tailings Dam

ABSTRACT This paper focuses on pore-water pressure accumulation in loose sandy tailings during three (3) earthquakes within four minutes and the accompanying decrease in effective stress to assess the dynamic stability of the Fundão Tailings Dam, which failed on 5 November 2015. Results of laboratory cyclic direct simple shear tests are used to illustrate the accumulation of pore-water pressures with closely spaced low-level cyclic events. The seismically-induced pore-water pressures in the loose sands below the left abutment downstream slope and setback area are used to estimate the decrease in factor of safety with time until failure occurred within 20–30 minutes of the earthquakes. Field cone penetration and standard penetration test conducted prior to the failure are used to calculate the factor of safety against liquefaction to estimate pore-water pressures generated during the fore, main, and aftershocks in the sandy tailings. The effective stress stability analyses utilise a liquefied shear strength ratio for the sand tailings below the left abutment downstream slope and toe of the plateau because the sand tailings reached the critical state condition due to a reduction in the effective stress. SITE LOCATION: 20.206500°S, 43.467111°W

Self-organized magnetic equilibria in tokamak plasmas with very low edge safety factor

Tokamak plasmas often exhibit self-organizing behavior in which internal modes shape the toroidal current density profile, a common example being the sawtooth instability. However, such behavior has not been studied in detail for edge safety factor below 2 due to disruptive kink instabilities that typically prevent operation in this regime. Now, steady tokamak plasmas with an edge safety factor down to 0.8 have been created in the Madison Symmetric Torus, where disruptions are prevented due to a thick, conductive wall and a feedback power supply that sustains the plasma current. Internal measurements and nonlinear magnetohydrodynamic modeling reveal a family of safety factor profiles with a central value clamped near unity as the edge safety factor decreases, indicating current profile broadening through a relaxation process. As the safety factor decreases, the magnetic fluctuations become irregular, and the electron energy confinement time decreases.

Rainfall Triggered Slope Instability Analysis with Changing Climate

Slope instability triggered by rainfall is common in tropical countries like India, where the soil of hill slopes are generally in unsaturated condition, having higher strength than in the saturated condition due to matric suction. This study aims to investigate the change in pore water pressure (PWP) with rainfall infiltration into the slope and the corresponding effect of the slope stability on different hill slopes from different regions of India. By applying rainfall on the surface of slope as a flux boundary condition, a transient seepage analysis is performed using SEEP/W, and the corresponding results in the form of PWP distribution within the slope are used as input for SLOPE/W program of Geostudio 2018 R2, to check the stability of slope. This study involves the use of CMIP5 (Coupled model intercomparision project phase 5) simulations for rainfall data of different regions for the duration of 2015–2050, 2051–2075 and 2076–2100; which is completely based on non-stationary approach (i.e., the statistics of extremes changes with time) rather than the conventional methods of extracting rainfall data that are based on stationary approach. The stability of different slopes is checked for 95 percentile rainfall intensity as well as for maximum rainfall intensity for a period of 2015–2100, and the analysis is performed for 5 days for which the duration of rainfall is considered to be 24 h. It is concluded that due to climate change, slopes which may be marginally stable under historical and present rainfall events can fail under projected precipitation estimates, and this can be understood by the results of Haflong slope stability analysis as the 30° slope, which is marginally stable under maximum rainfall intensity for the period 2015–2050 having factor of safety (FOS) value 1.0013, will fail under the maximum rainfall intensity for the period 2051–2075 and 2076–2100 having FOS value 0.9935 and 0.9989, respectively. A continuous decrease in FOS with increasing rainfall intensity is observed for all the study areas under consideration.

The geological structure effects on slopes stability and tunnels of metamorphic rocks at Poboya gold mine Palu

Poboya area has many geological structures that result in distribution of strength and stress of rocks not evenly distributed, as a result, the rock mass strength becomes disturbed and slopes become unstable. The objective of the study was to determine the geological structure effect on slope stability and tunnel conditions on metamorphic rocks at the Poboya gold mine. The study was conducted in the Mantikulore sub-district, Palu, Central Sulawesi. Lithology composing study area is metamorphic rocks consisting of gneiss and schist, therefore, the analysis was carried out on both locations which have many geological structures. Numerical analysis was performed applying the finite element method with the RS2 program assistance. The findings show that the safety factor value of the existing slope at gneiss and schist location under static loading is 4.6 and 2.72, if there is an earthquake it becomes 1.07 and 0.77. The safety factor value under static loading with the joint is 4.58 and 2.03, while under dynamic loading with joint, it becomes 0.94 and 0.64. The geological structure effect which represented by the joint gave a big impact with a decrease of safety factor at gneiss about 0.43% under static loading and 80% under dynamic loading. Meanwhile, at schist, safety factor decreased 25% under static loading and 76% under dynamic loading. For tunnel stability, the existence of joint will increase the displacement of 65% at gneiss under static loading and 84% under dynamic loading, while at schist, it increases 25% under static loading and 54% under dynamic loading. This illustrates that geological structures under dynamic loading affect significantly slope stability of Poboya gold mine.

Stability Analysis of Coal-Measure Soil Slope Based on Discrete Element Method

This paper uses the discrete element method to take the Pinglian high-speed coal-measure soil slope as the background, which uses PFC3D to calibrate the parameters, establishes the slope model, and analyzes the factors affecting the instability of the coal-measure soil slope from the granular meso-level. The results show that the discrete element method can be used to simulate the entire process of slope deformation and instability, and the sliding surface of the slope failure can be directly displayed through the displacement of the soil; the nature of the particles will affect the stability of the slope. The larger the particle size is, and the more irregular the composition of the soil particles are, the higher the safety factor of the slope is; the greater the slope is, the faster the safety factor decreases. When the slope is less than 1:0.75, the slope is relatively stable.

RETRACTED ARTICLE: Modeling study on influence of surface pore water on slope stability of mountain tunnel

In order to solve the problems of slope strength reduction and stability risks caused by excessive surface water in mountain tunnels, the influence of surface pore water on slope stability is deeply studied. This article first analyzes the seepage field of unsaturated soil. Taking the transient seepage field as the object, the distribution of the soil seepage field during the two-stage precipitation process is studied. Secondly, the existing dimensionless second-order partial differential equation is solved by Laplace transform to calculate the distribution of transient seepage field. A finite element model of rock and soil seepage field under different rainfall intensities was established, and the influence of pore water content on slope stability was quantitatively analyzed. The results show that as the anti-sliding force decreases, the pore water content increases, the pressure increases, the suction force of the matrix decreases, the shear strength decreases, and the slope safety factor decreases, which leads to the plastic deformation of the slope.

Experimental observation of low-frequency magnetohydrodynamic instabilities driven by energetic electrons in low hybrid current drive plasmas

Energetic electrons driving low-frequency magnetohydrodynamic instabilities, e.g., electron fishbone (eFB) modes and electron beta-induced Alfvén eigenmodes (eBAEs), are found in co- and counter-current drive low hybrid current drive (LHCD) plasma in HL-2A, respectively. The eBAEs are found in LHCD plasma for the first time. Two branches eFB modes are observed in the core of plasma, and they can transit from the high-frequency one to the low-frequency one continuously. The different mode structures and positions are obtained by tomography of soft x-ray arrays. The frequency jump phenomena of eFB modes are also found. Two eBAEs, with poloidal and toroidal mode numbers m/n = 3/1 and 5/2, are found in the edge of the plasma. The single m/n = 3/1 mode is found when the LHCD power (P LHCD) is 0.44 MW. The strong m/n = 5/2 mode coexists with the weak 3/1 mode when P LHCD = 0.52 MW. Although the current drive direction of LHCD is opposite to the plasma current, the two eBAEs also propagate in the electron diamagnetic drift direction poloidally, which is the same direction as the eFB modes in co-current drive LHCD plasma. With increasing P LHCD (or changed current profile), the value of the edge safety factor (q) decreases. The evolutions of the mode numbers of eBAEs may be related to changes in the edge q factors.

Geomechanical risks at underground gypsum mining

In the focus of the article is estimation of geomechanical risks during exploitation of gypsum mines. Underground extraction of gypsum is performed mainly with the use of room-and-pillar system of mining. This method provides long-term exploitation of large mine workings. The maintenance of workings in operation condition for decades is associated with existence of geomechanical risks. They potentially reduce stability of the mine workings. This negatively affects safety of personnel being underground. The long-term consequences are related to the deterioration of the ecological state of the environment. The main geomechanical processes that cause risks in the operation of gypsum mine workings are identified in the publication. Gypsum mine differs by supports installed only in a few sectors. In these conditions, the most dangerous are formation of the block structure of rock mass and stratification of the roof. Uncontrolled development of these processes can cause an emergency situation. Evolution of karst formation above the mine workings can cause caves on the day surface. Great water inflows are also a significant threat. The cases are known when separate sections in the mine field and entire mines were flooded . An approximate gradation of negative consequences as a result of the influence of each geomechanical process is presented. It is shown that a significant factor for the occurrence of geomechanical risks is the changed physical and mechanical properties of the rock mass. In this case, simulation can be used in order to quantify geomechanical risk. Its application for estimating risk of roof falls with known variation of calculated parameters is shown. The result of the simulation is the curve of probability distribution of safety factors of roof. The probability of unacceptable parameter values is calculated. The possible consequences of a gradual decrease of safety factor are taken into account. A quantitative estimate of the magnitude of geomechanical risk for a concrete project was obtained. This methodology is universal. It can be used to assess operational reliability of engineering objects under significant impact of unstable factors of natural origin. Keywords: geomechanical process, geomechanical risk, gypsum mine, safety factor, simulation.

Effect of Seepage Force on Tunnel Face Stability Using Limit Analysis with SRM

The seepage force is of importance on tunnel face stability. The formulas to determine the seepage force are introduced based on Darcy's Law. The formula of the stability safety factor containing the tunnel face of the seepage force is derived and applied to the actual tunnel engineering using the upper bound limit analysis combining with the strength reduction method. The results show that: as the water level increases, the average seepage force increases, and the safety factor decreases. If the horizontal seepage force is considered only and the vertical seepage force is ignored, the result is unsafe. The stability of the tunnel face can be improved by reducing the excavation height and adopting some reinforcement, such as grouting or rock bolt to increase the cohesion and friction angle of the rock.

Reliability Analysis of Loess Landslide Considering the Change of Groundwater Level

The reliability analysis of landslide is very important for the early warning and prevention of landslide. In this paper, Monte-Carlo method is used to analyze groundwater level, the variation coefficient of c and ϕ, and paleosol layer impact on the reliability of landslide in Jingyang South tableland. The reliability analysis results are as follows: (1) With the increase of groundwater level, the probability of landslide failure increases and the safety factor decreases. When the depth of groundwater level is 61m, the failure probability is 2.46%, and the average safety factor is 1.166; when the groundwater depth is 31.6 m, the average safety factor is 0.791, and the failure probability is 98.94%. (2) The coefficient of variation “δ” is positively related to the failure probability of landslide, and negatively related to the reliability index. When δ < 0.05, the increasing trend of failure probability and the decreasing trend of reliability index are most significant. (3) Paleosol layer has certain influence on Reliability. When the groundwater depth is less than 35.3 m, the average safety factor with paleosol layer is less than that without paleosol, but the failure probability is higher. When the groundwater depth is more than 35.3 m, it shows the opposite relationship.

Effect of variations in rainfall intensity on slope stability in Singapore

Numerous scientific evidence has given credence to the true existence and deleterious impacts of climate change. One aspect of climate change is the variations in rainfall patterns, which affect the flux boundary condition across ground surface. A possible disastrous consequence of this change is the occurrence of rainfall-induced slope failures. This paper aims to investigate the variations in rainfall patterns in Singapore and its effect on slope stability. Singapore's historical rainfall data from Seletar and Paya Lebar weather stations for the period of 1985–2009 were obtained and analysed by duration using linear regression. A general increasing trend was observed in both weather stations, with a possible shift to longer duration rainfall events, despite being statistically insignificant according to the Mann-Kendall test. Using the derived trends, projected rainfall intensities in 2050 and 2100 were used in the seepage and slope stability analyses performed on a typical residual soil slope in Singapore. A significant reduction in factor of safety was observed in the next 50 years, with only a marginal decrease in factor of safety in the subsequent 50 years. This indicates a possible detrimental effect of variations in rainfall patterns on slope stability in Singapore, especially in the next 50 years. The statistical analyses on rainfall data from Seletar and Paya Lebar weather stations for the period of 1985–2009 indicated that rainfall intensity tend to increase over the years, with a possible shift to longer duration rainfall events in the future. The stability analyses showed a significant decrease in factor of safety from 2003 to 2050 due to increase in rainfall intensity, suggesting that a climate change might have existed beyond 2009 with possibly detrimental effects to slope stability.