Mean Factor Of Safety Research Articles

Analysis of the Influence of Groundwater Level on Slope Stability at Highwall PT. X, South Kalimantan

Mine slope design is an important part of mining operations because it is used to determine the balance between mine economy and operational safety. In the mine slope design there will also be a groundwater level design, the groundwater level is one of the triggers for a slide to occur. Therefore, this study aims to determine the effect of the groundwater level on the stability of the highwall slope cross section A-A’ as well as to determine the factor of safety value and probability of slope failure under various conditions of high groundwater levels. This research method uses quantitative methods because there are numerical data that will be used to calculate the value of slope stability. Slope stability analysis uses the “morgenstern-price” boundary equilibrium and the “monte-carlo” landslide probability. From the research results it is known that the higher the groundwater level, the lower the safety factor value because the presence of groundwater can reduce slope stability causing a decrease in soil shear strength due to increased pore water pressure. In addition, the weight of the material will increase due to the presence of groundwater, which causes the driving force on the slope to also increase. In addition, the movement of air in the soil can cause seepage forces which can affect slope stability. The lowest safety factor value is at the groundwater level 100% of the overall slope height, in conditions of 100% of the overall slope height, the deterministic safety factor value is 1.337, the mean safety factor is 1.358, and 0% hazard susceptibility.

Stability Analysis of Partially Saturated Soil Slope by Random Limit Equilibrium Method

Disregarding soil suction in computing the shear strength of unsaturated soils is widely used practice above the water table where the pore pressure is negative. Stability analysis was conducted using Rocscience Slide 2 software to evaluate matric suction contribution to the shear strength of the unsaturated soil in a slope in Hong Kong. The stability analysis resulted in a critical deterministic factor of safety for fully saturated soil and 1.2 when the matric suction is considered. Uncertainty in shear strength properties is considered by conducting multi scenarios probabilistic analysis. Lognormal distribution was assigned to the soil properties. The distribution was sampled 1000 times using Latin Hypercube method. A new sample was used to determine the safety factor in each simulation. Probability of failure (PF), mean safety factor (FSmean) and reliability index (RI) were determined in each scenario. It was shown that the most realistic results are obtained when cross correlation factors and correlation length (θ) are involved in the scenario. The study indicates that PF and RI are sensitive to a change in the correlation length less than 25 and less significant change beyond 25 m. The FSmean did not show noticeable fluctuation with the variation of correlation lengths.

Back-analysis of a rainfall-induced landslide case history using deterministic and random limit equilibrium methods

Because recurrent rainfall-induced landslide episodes mimic prior failures, this study builds a back-analysis approach to identify those prior failure events and assess the prospective slope performance going forward. Engineers use the results of this approach to project the slope performance based on the quantity of rainfall accumulation during the anticipated rainfall event. A landslide case that occurred in 2004, as a result of a typhoon event, was selected for the back-analysis procedure. Four typhon events were chosen to simulate the pore water pressure conditions, which may have caused damage of varying severity (including landslide failure) to the slope. The numerical model was initially analyzed via the deterministic limit equilibrium slope stability approach to evaluate the most critical failure surface. By adopting the Monte Carlo simulation approach, the following step assessed the random limit equilibrium slope stability on the most critical failure surfaces. The probabilistic distributions of the safety factor were then generated for each typhoon event. Subsequently, the simulation outcomes provide safety indicator values incorporating the mean safety factor, failure probability, and reliability index. From the failure probability and reliability index, a zonation approach with various site-specific performance levels were established by using the corresponding accumulated rainfall to define the exceedance threshold values for each zone. In order to confirm the site-specific performance, we compared the normalized error values acquired from the analysis technique to those measured under two recent typhoon occurrences. An acceptable consistency was attained, validating the procedure's appropriateness for future rainfall events.

Locomotor Challenges of Waterfall-Climbing Gobies during Transitions between Media.

An amphidromous goby, Sicyopterus japonicus, migrates from the ocean to upstream regions of many streams and rivers in the Pacific coasts of Japan and Taiwan. Using its mouth and fused pelvic fins (pelvic sucker), this gobiid species exhibits a rock-climbing behavior and surmounts sizable waterfalls, which block the upstream movement of many of its competitors and predators. When gobies emerge from the water to commence their climbing behavior, the change in effective density (i.e., lack of buoyancy) that occurs in this transition substantially increases the force required for adhesion. Consequently, these fish must exert adhesive suction strong enough to support their body weight against gravity during climbing on the rock surface. Suction performance for adhesion and modulatory capacity of S. japonicus were evaluated with two different sets of experimental conditions: climbing on the vertical surface with no water flow versus climbing on a 60°-inclined surface with 2 L/min flow. Individuals of S. japonicus showed 50.7% greater mean safety factor (suction force for adhesion/gravitational force) and 56.6% shorter time to reach maximum pressure differential during climbing on the 60°-inclined surface with water rushing over their bodies than during climbing on the vertical surface with no water flow. These results indicate that when climbing with drag force from flowing water, greater functional demands are imposed and therefore, S. japonicus is required to increase neuromuscular stimulation of the pelvic muscles to elevate suction performance. In addition, S. japonicus individuals at different ontogenetic stages modulate their climbing behaviors and strategies to accommodate changing functional demands as they make transitions between different inclines, as well as media, while ascending waterfalls.

Levee Fragility Behavior under Projected Future Flooding in a Warming Climate

Adaptation to climate change requires careful evaluation of infrastructure performance under future climatic extremes. This study demonstrates how a multidisciplinary approach integrating geotechnical engineering, hydrology, and climate science can be employed to quantify site-specific impacts of climate change on geotechnical infrastructure. Specifically, this paper quantifies the effects of changes in future streamflow on the performance of an earthen levee in Sacramento, California, considering multiple modes of failure. The streamflows for historical (1950–2000) and projected (2049–2099) scenarios with different recurrence intervals were derived from routed hydrological simulations driven by bias-corrected global climate models. The historical and future flood levels were then applied in a set of transient coupled finite-element seepage and limit equilibrium slope stability analyses to simulate the levee subjected to extreme streamflow. Variability in hydraulic and mechanical properties of soils was addressed using a Monte Carlo sampling method to evaluate and compare the probability of failure of the levee under different historical and future climate scenarios. Three individual modes (underseepage, uplift, and slope stability) along with lower and upper bounds for the combined mode of failure were examined. The results showed that incorporating future floods into levee failure analysis led to considerable reductions in the mean factor of safety and increases in the levee’s probability of failure, suggesting that risk assessment based on historical records can significantly underestimate the levee’s failure probability in a warming climate. Despite inherent uncertainties in future projections and substantial variability across climate models, evaluating infrastructure against projected extremes offers insights into their likely performance for the future.

A New Stability Approach using Probabilistic Profile along Direction of Excavation

Estimation of the possible instability that may be encountered in the excavation slope(s) during the planning and application steps of the rock excavation processes is an important issue in geoengineering. In this paper, a modelling method is presented for assessing the probability of wedge failure involving new permanent or temporary slope(s) along the planned excavation direction. The geostructural rock slopes including wedge blocks are determined geometrically in the first step. Here, a structural data analysis system that includes a series of filterings, sortings, and linear equations used to reveal the necessary geometric conditions for the wedge form is developed and used. The second step involves the 3D visualization and Factor of Safety (FS) using the limit equilibrium analysis of wedges on both the actual and planned new excavation surfaces. The last step is the Monte Carlo simulation, which is used in assessing the instabilities on the actual and planned new excavation surfaces. These new slope surfaces that have not yet been excavated are called the virtual structures. As a result of this work, the mean and probabilistic FS variations in the planned excavation direction are obtained as profiles. We suggest the preliminary guidelines for the mean and probability of the wedge failure in the excavation direction. The model is tested on a motorway cut slope. The FS results obtained from the Monte Carlo simulation calculations are compared with the mean results and the changes are revealed with the reasons.

Stability Analysis of Slopes with Spatially Variable Strength Properties

Natural variability of rock properties can significantly affect the strength of rock masses and factor of safety of slopes. The results of a comprehensive point load testing program showed that coefficient of variation of intact rock strength can reach unity in highly heterogeneous formations. Probabilistic numerical analysis was carried out to explore the effect of strength variability on uniaxial compressive strength of large heterogeneous samples. It was shown that mean large-scale strength decreases with increasing small-scale variability. The effect of spatial variability of strength properties on slope stability was examined using limit equilibrium and shear strength reduction methods. Both approaches gave similar results indicating that for stable slopes, increasing strength variability leads to a reduction in mean factor of safety and increase in the probability of failure. In addition, ignoring spatial variability in probabilistic slope analysis can lead to erroneous estimates of the probability of failure. Based on the results of probabilistic analyses on large heterogeneous samples and slopes, an equivalent uniaxial compressive strength can be obtained by reducing the mean strength by one-third of its standard deviation. This relationship was validated using a dataset of back-analyzed strength values in heterogeneous open pit slopes.

Evaluating stability of anisotropically deposited soil slopes

Natural soils often exhibit an anisotropic fabric pattern as a result of soil deposition, weathering or filling. This study aims to investigate the effects of spatially variable anisotropic soil fabric in a slope on its safety factor and failure mechanisms, and to identify the critical fabric orientation that is most unfavorable to the slope stability. The strength properties of colluvium (i.e., cohesion and friction angle) are modeled as random fields under two conditions (i.e., independent and negatively correlated). The study reveals that there exists a critical fabric orientation at 30° at which the mean factor of safety is the lowest and the probability of failure is the highest. The negative cross-correlation between soil shear strength properties leads to a significantly lower probability of failure, compared to the independent case. The highest proportion of deep failure mechanism is also identified at the same fabric orientation of 30°. The identified critical fabric orientation is gentler than the slope inclination. This study suggests that the conventional understanding that stratification parallel to the slope surface appears to be the most unfavorable condition leading to the lowest safety level does not hold for spatially varying soils.

The use of new intelligent techniques in designing retaining walls

The stability of retaining walls against overturning is analyzed in this study using artificial intelligence methods. Five input parameters including wall height, wall thickness, soil friction angle, soil density, and stone cement mixture density were varied and 2000 cases were considered in developing the predictive models. Using the artificial neural network (ANN) method, eight prediction models were developed and evaluated based on the coefficient of determination (R2) and the root mean square error. R2 values of 0.9740 and 0.9824 for training and testing datasets, respectively (for the best model), indicate the level of ANN capability in predicting safety factor (SF) of retaining walls. After developing the ANN model, the ant colony optimization (ACO) algorithm was used to maximize the safety factor of the wall by varying the input parameters. In fact, the best ANN model was selected to be used as a modeling function in ACO algorithm. The SF result from optimization section was obtained as 3.057 which show a significant difference from the mean SF values used in the modeling. It can be concluded that ACO may be used as a powerful optimization algorithm in optimizing SF results of retaining walls.

Worst-case spatial correlation length in probabilistic slope stability analysis

This note investigates the reliability of undrained slopes by the random finite-element method. The focus of this note is on the worst-case spatial correlation length, namely the correlation length at which the probability of slope failure reaches a maximum. It is shown that the worst-case phenomenon is most pronounced when the mean factor of safety is relatively low or the coefficient of variation is relatively high. Knowledge of the worst-case spatial correlation length is valuable, as it can be employed for conservative design in the absence of substantial soil field data.

Probabilistic and Geotechnical Modeling of an Excavation in the Outskirts of Qaen

Summary An excavation operation for the building purposes is a high-risk activity, which is done for different reasons, such as achieving an appropriate level of the earth for foundation or construction of basements. In this paper, using the Slide 6.0 program the stability of a pit wall in the outskirts of Qaen is investigated at first and then the pit wall stability after using soil nailing with various patterns is analyzed. Using back analysis, sensitivity analysis, and probabilistic analysis, this study presents a comprehensive model for analyzing pit walls, and will be useful for excavation operation in neighboring areas as well. Finally, several pit designs with acceptable safety factors have been proposed for pit excavation. Introduction Due to the growing trend of urban populations, the construction activities are increasing in central and marginal areas of cities. One of the basic concerns in these constructions is the stability of the excavated pit wall. The basic rule of judgment about the stability of a pit wall is the standard safety factor. In the traditional deterministic approach of safety factor calculation, any error or uncertainty in the soil parameters is directly reflected in the results. In recent years, the use of the probabilistic approach that provides additional measures related to the probability of failure and risk rate has become popular. In the probabilistic approach in addition to the mean safety factor, the probability of failure and reliability index are also obtained. Methodology and Approaches To perform a probabilistic analysis of a pit wall, strength properties of the soil layer and the soil density were defined as variable inputs. The coefficients of variation of these parameters according to laboratory experiments were selected. Normal and log-normal statistical distributions were used for the input variable parameters as recommended by USACE. For the efficient performance of the probabilistic analysis, Monte Carlo simulation was used. This way, and using the Slide 6.0 program, the stability of a pit wall in the outskirts of Qaen is investigated with various patterns of soil nailing as the supporting system. Results and Conclusions According to the results of this study, the soil is unstable for excavation operation and employing soil nailing technique and reducing the pit wall slope angle are appropriate steps to achieve a secure condition. Several safe pit designs have been proposed for excavating the pit.

Reliability analysis of three-dimensional rock slope

Reliability analysis is generally regarded as the most appropriate method when uncertainties are taken into account in slope designs. With the help of limit analysis, probability evaluation for three-dimensional rock slope stability was conducted based upon the Mote Carlo method. The nonlinear Hoek-Brown failure criterion was employed to reflect the practical strength characteristics of rock mass. A form of stability factor is used to perform reliability analysis for rock slopes. Results show that the variation of strength uncertainties has significant influence on probability of failure for rock slopes, as well as strength constants. It is found that the relationship between probability of failure and mean safety factor is independent of the magnitudes of input parameters but relative to the variability of variables. Due to the phenomenon, curves displaying this relationship can provide guidance for designers to obtain factor of safety according to required failure probability.

A probabilistic method for evaluating wedge stability based on blind data theory

This study proposes a probabilistic approach based on blind data theory and a k-means clustering algorithm to analyze the wedge stability problem considering multiple failure modes. The method evaluates the stability of the wedge by constructing a blind data model that can comprehensively consider the various uncertainties of the wedge parameters. The construction of the blind data evaluation model of wedge stability is described, and the blind evaluation model used to determine the wedge stability with wedge failure dominated by a prone-sliding face and double-face failure is given. The model is applied to analyze the stability of a classical double-face wedge. The results are compared with the probability of failure evaluated by a Monte-Carlo simulation, as well as the results obtained from deterministic analysis, including the mean safety factor and SWEDGE numerical analysis methods. The probability distribution for the safety factor of the wedge determined by this method is fairly consistent with those from the Monte-Carlo simulation method, verifying the reliability and efficiency of the new method. Finally, the method is applied to the stability evaluation of the wedge in Huludao city, Liaoning Province, China. The probability of safety factors less than 1 is 89.8%, and the probability that the safety factor is less than 1.2 is 100%, which is consistent with the actual situation. This result demonstrates that the blind data model for evaluating wedge stability exhibits good generalization performance.

The role of uncertainty in bedrock depth and hydraulic properties on the stability of a variably-saturated slope

We investigate the uncertainty in bedrock depth and soil hydraulic parameters on the stability of a variably-saturated slope in Rio de Janeiro, Brazil. We couple Monte Carlo simulation of a three-dimensional flow model with numerical limit analysis to calculate confidence intervals of the safety factor using a 22-day rainfall record. We evaluate the marginal and joint impact of bedrock depth and soil hydraulic uncertainty. The mean safety factor and its 95% confidence interval evolve rapidly in response to the storm events. Explicit recognition of uncertainty in the hydraulic properties and depth to bedrock increases significantly the probability of failure.

Strength of silk attachment to Ilex chinensis leaves in the tea bagworm Eumeta minuscula (Lepidoptera, Psychidae).

Silks play an important role in the life of various arthropods. A highly neglected prerequisite to make versatile use of silks is sufficient attachment to substrates. Although there have been some studies on the structure and mechanics of silk anchorages of spiders, for insects only anecdotal reports on attachment-associated spinning behaviour exist. Here, we experimentally studied the silk attachment of the pupae and last instar caterpillars of the tea bagworm Eumeta minuscula (Butler 1881) (Lepidoptera, Psychidae) to the leaves of its host plant Ilex chinensis We found that the bagworms spin attachment discs, which share some structural features with those of spiders, like a plaque consisting of numerous overlaid, looped glue-coated silk fibres and the medially attaching suspension thread. Although the glue, which coats the fibres, cannot spread and adhere very well to the leaf surface, high pull-off forces were measured, yielding a mean safety factor (force divided by the animal weight) of 385.6. Presumably, the bagworms achieve this by removal of the leaf epidermis prior to silk attachment, which exposes the underlying tissue that represents a much better bonding site. This ensures a reliable attachment during the immobile, vulnerable pupal stage. This is the first study on the biomechanics and structure of silk attachments to substrates in insects.

Fracture safety of double-porous hydroxyapatite biomaterials

Biological requirements call for substantial porosities in clinical biomaterials – challenging the mechanical integrity and strength of the latter. In this study, the authors resort to quantitative engineering principles to assess the fracture safety of double-porous hydroxyapatite ceramics: micro-computed tomography scans give access to the morphology of macropores at the submillimeter scale, as well as to voxel-specific microporosities. Advanced micromechanics of porous ceramics with needle-shaped elementary units then allows for translating voxel-specific microporosities to corresponding elasticity and strength properties, as well as to macro-to-micro scale transition (‘concentration’) tensors. These mechanical properties and tensors are fed into a large-scale finite-element model of a biomaterial granule as used for mandibular tissue regeneration. Loading the granule in splitting mode, up to physiological strain, evidences stress concentrations at the loaded poles and close to internal macropores and cracks. A parallel computing-supported subvoxel analysis of needle orientations evidences that in highly loaded regions, the intravoxel ‘single crystals’ oriented perpendicular to the loading direction undergo the most unfavorable loading. Still, only 0·6% of the finite-elements show stresses indicating failure, and the mean safety factor against fracture is as high as 7. This analysis confirms, from an engineering science viewpoint, the successful use of the investigated biomaterials in clinical practice.

Study on the Reliability of Loess Cutting Slope Considering the Variability of Soil-Water Characteristic Parameters

The complexity of the geological conditions and the non-uniformity of geotechnical material make the study of slope stability with big uncertainties, so it is necessary to analyze the reliability of slope. In this paper, firstly, the matrix suction of Malan loess in Gansu Province is measured by tension meter, and a fitted soil-water characteristic curve (SWCC) is obtained according to the empirical formula; then SWCC parameters of Malan loess such as a, n and θs (saturation volumetric water content) are thought as random variables, the method of simplified Bishop is used to calculate of slope stability, and the reliability of cutting slope of Malan loess is analyzed according to Rosenbleuth method. Through calculating, obtain mean factor of safety, failure probability and reliability index of the slope. After analyzing the relations between mean factor of safety, failure probability, reliability index and variability of parameters, the results show that, the factor of safety is 1.005 and it is stable when the variability of SWCC parameters are not considered. When variation coefficients of a, n and θs are all 0.3, the average factor of safety is 1.051, the reliability index is 10.94 and failure probability is 29.81%. It is obvious that variability of SWCC parameters has certain influence on stability of the slope. In parameters of SWCC, comparing with a and θs, the variability of n has the most important influence on the mean factor of safety and failure probability. But the corresponding reliability index is minimum (the change ratios of the mean factor of safety， failure probability and reliability index with variation coefficient of n are 0.37，3.247 and 282.0 respectively). So variation level of n should be specially taken into account in reliability analysis of the slope. This research provides an important basis for the determination of the SWCC parameters of Malan loess, the stability calculation, stability estimation and prevention sliding of loess cutting slope caused by rainfall.

The effect of surface roughness on claw and adhesive hair performance in the dock beetle Gastrophysa viridula

Abstract Natural adhesive systems are adapted to attach to rough surfaces, but the underlying mechanisms have not been fully clarified. Attachment forces for the beetle Gastrophysa viridula were recorded on epoxy casts of surfaces with different roughness using a centrifuge device. Replicas were made of standardized polishing paper with asperity sizes ranging from 0.05 to 30 μm and of dock leaves (Rumex obtusifolius). Beetles adhered with a safety factor of up to 36 times body weight on smooth substrates or on casts of leaves of their host plant. On the rough substrates, forces were much lower and a minimum at small scale roughness (0.05 μm asperity size, with a mean safety factor of 5) was observed. Removal of the claws led to a significant reduction in force for rough substrates with asperity sizes ≥ 12 μm. Attachment forces of the hairy adhesive system itself (without the claws) slightly increased from small-scale to large-scale surface roughness, but remained below the level seen on the smooth substrate. This is explained by the inability of setal tips to make full contact to the surface.

Moving on from Kirkpatrick (1994): estimating ‘safety factors’ for flying vertebrates

The most cited work (by far) to provide safety factor estimates for the wing bones of flying vertebrates is inaccurate. Kirkpatrick ([Kirkpatrick, 1994][1]) presented extremely low measurements for the material properties of wing bones and anomalous estimates of applied loading that deflate

Limit Analysis of a Stochastically Inhomogeneous Plastic Medium With Application to Plane Contact Problems

The lower and upper bound theorems of plastic limit analysis are extended to a stochastically inhomogeneous medium. The extended theorems provide bounds on the mean safety factor against plastic collapse. A three-parameter yield function is treated by introducing a spatial correlation function for uniaxial yield strength. Application of the stochastic upper-bound theorem is made to the plane problem of a truncated wedge under contact pressure. The results apply to the design of arctic structures against local ice pressure.