Overall Factor Of Safety Research Articles

Evaluation of buoyant action of groundwater and surface water interaction on pit slope stability using hydrogeological-stratigraphic-structural assessment within the Kawere catchment of the Nsuta mine

ABSTRACT In open-pit mining operations where activities are conducted below water table or close to surface water bodies, the mine is potentially faced with dewatering and slope stability challenges. Appropriate evaluation of slope stability to obtain adequate slope safety factor has continuously been the centre of geotechnical research locally and internationally. This paper evaluates the influence of buoyant action propagated by groundwater and surface (GW-SW) interaction on pit slope designed in multi-layered fractured rock with complex hydrology using Hydrogeological-Stratigraphic-Structural Assessment (HSSA) at the Nsuta Manganese Mine in Ghana. LEM analyses of the Pit C-western slope estimated an overall factor of safety (FOS) of 1.1, probabilities of failure (POF) of 7.5% and the reliability index (RI) of 1.4 in the slope stress field. However, when the groundwater was introduced, the slope FOS was reduced to 0.13, POF of 100.0% and (RI) of 0.00 indicating failure. FEM numerical model points to the location of maximum shear strain and total displacement in the argillite zone within the rock mass. The FEM seepage analysis model estimated groundwater pore pressure data along the critical slide surfaces from the crest of the slope to the bottom of the rock slope ranging between 250 kPa and 4250 kPa with an average pore pressure of 2250 kPa within the pit slope. This proposed HSSA approach used in the study provides innovative insights into the percentage failure contribution of the individual lithologies to the overall combined lithological susceptibility of the slope under stress and groundwater failure mechanisms, pointing out Ru ratio in pit slope stability estimation as inadequate.

A Displacement-Dependent Limit-Equilibrium Slice Method for Slope Stability Analysis

Displacement and factor of safety are two crucial pieces of information about slope stability, but the traditional limit-equilibrium slice method has a significant defect; that is, it cannot reflect slope displacement. In this paper, a displacement-dependent limit-equilibrium slice method is proposed based on the soil shear constitutive model and Morgenstern–Price assumption of interslice forces to establish the relationship between the factor of safety and displacement. In addition to the overall factor of safety, point factors of safety and point displacements can also be obtained using the proposed method to characterize the displacement-dependent slope stability. The point factor of safety and shear displacement of each soil slice calculated using the proposed method are slightly higher and smaller than those calculated by the modified displacement-dependent Janbu method. The iterative process of the proposed method is simpler and more stable than that of the modified displacement-dependent Janbu method. Calculation results of four examples show that the point factors of safety at the upper and lower ends of the slide mass are generally smaller than those at the middle part of the slip body, and the shear displacement of the soil slice near the slope top is generally larger than those at the other positions. The proposed method associates the factors of safety with slope displacements, which allows us to quantitatively assess the slope stability immediately in practice by monitoring the displacements of some key points on it.

Probabilistic Evaluations of Prescribed Safety Margins in Eurocode 7 for Spread Foundations

According to the design code Eurocode 7, analysis procedures require reaching a prescribed safety margin, based on the conditions of levelling design action and design resistance. Such semi-probabilistic procedures do not result in a consistent equivalent value of the Overall Factor of Safety (OFS), neither in individual analysis nor in different tasks in geotechnical engineering. Furthermore, the implementation of different calculation approaches in Eurocode 7 also does not guarantee an equal probability of the occurrence of a relevant limit state. A comparative analysis is conducted for an example of a centrically loaded spread foundation on homogenous, isotropic, and coarse-grained soil, according to procedures in Eurocode 7, Design Approach 3. An algorithm is developed to estimate failure probability, taking into consideration the relevant statistical characteristics of each calculation parameter. A significant influence of the statistical characteristics of the relevant sample is emphasized. The degree of required modification of the equivalent Overdesign Factor (ODF) and the Overall Factor of Safety (OFS), based on the criterion of the required reliability index β and failure probability pf , is quantified.

A discrete fracture network based modeling scheme for analyzing the stability of highly fractured rock slope

Numerical investigation on stability of the rock slope with densely distributed fractures is still challenging. To overcome the large computational requirements caused by the fracture representation, material heterogeneity and mathematical nonlinearity, an efficient discrete fracture network (DFN) based modeling scheme is developed in this paper. With DFNs stochastically generated according to the statistical distributions of the fractures for resembling the natural fractured rock slope, finite element method (FEM) based strength reduction analysis is conducted for locating the critical slip surface and assessing the factor of safety, where the rock blocks are discretized as solid elements while discrete fractures are practically modeled by frictional contact interface elements. The effectiveness of the proposed approach is validated by comparison against analytical and several numerical solutions. A case study is further performed to evaluate the effects of DFN realization number and geometrical configuration on the stability of the fractured rock slope. It shows that 20 DFN realizations are sufficient to obtain a statistically convergent mean of the factor of safety. The predicted critical slip surface displays to be non-circular but linear or broken line morphology along the fracture network. The proposed numerical scheme shows to be useful and promising in investigating the deformation response and sliding failure mode in highly fractured rock slope. Massive fractures disorder the displacement distribution of the slope and influence the overall factor of safety, and the estimated factor of safety decreases with the increase ofslope height and angle, indicating the fracture distribution and slope geometric features as the prominent influential factors.

Projection of Stress on Slewing Post for Gangway Using Finite Element Method from Experimental Analysis

Slewing operation involves a heavy loading and high cyclic movements. With no windows for error, operators and engineers need to operate while maintaining the performance of slewing. Sometimes, the strength of a components changes after repaired or modified. Thus, in order to predict the performance and safety of a gangway after repaired or modifies, this paper intended to predict the factor safety of a slewing post for gangway by using combination of experiment and FEA. This study was conducted on an actual slewing that has been repaired and slightly modified. The slewing was tested on load test for up to 14752 Kg and then the stress data was compared to the FEA analysis. For further analysis, FEA was conducted at 34 tons load and the stress was projected using the factor coefficient obtained in the comparison. The findings shows that the slewing is safe to be operated at 34 tones and below as the overall factor of safety is 1.2.

Design of Planetary Gear Train for Geared Rotary Actuator

Geared Rotary Actuators are mechanically operable devices widely used in the aerospace industry so that controlled motion can be provided to secondary flight control surfaces. Their usage can be seen in a variety of applications including powered hinges for aircraft structural movements, they support aerodynamic loads in addition to the surface hinge moment, as an actuator in a linked mechanism where they supply actuation torque. Mostly GRAs are situated along with the bay door drives, and also can be used for controlling leading or trailing edge movements of the aircraft. They receive Power Drive Unit (PDU) torque via assembly of shafts and joints. From a mechanical standpoint, the GRAs can be termed as epicyclical gear reducer or compound planetary gearbox. In this work, the governing criteria and mathematical equations used to characterize GRA are discussed. SOLIDWORKS is used for part modeling of GRA. More focus will be on the speed reduction ratio calculation, determination of strength, and overall Factor of Safety (FOS) of the torque transmission unit. Thus an attempt is made to obtain the best performance parameters to meet the desired requirements of Geared Rotary Actuator.

Deformation and Stability Characteristics of Layered Rock Slope Affected by Rainfall Based on Anisotropy of Strength and Hydraulic Conductivity

The strength and hydraulic conductivity anisotropy of rock slopes have a great impact on the slope stability. This study took a layered rock slope in Pulang, Southwestern China as a case study. The strength conversion equations of the seriously weathered rock mass were proposed. Then, considering the anisotropy ratio and anisotropy angle (dip angle of bedding plane) of strength and hydraulic conductivity, the deformation and stability characteristics of rock slope were calculated and compared with field monitoring data. The results showed that the sensitivity analysis of strength and hydraulic conductivity anisotropy could successfully predict the occurrence time, horizontal displacement (HD), and the scope of the rock landslide. When the anisotropy ratio was 0.01 and the dip angle was 30°, the calculated HD and scope of the landslide were consistent with the field monitoring data, which verified the feasibility of the strength conversion equations. The maximum horizontal displacement (MHD) reached the maximum value at the dip angle of 30°, and the MHD reached the minimum value at the dip angle of 60°. When the dip angle was 30°, the overall factor of safety (FS) and the minimum factor of safety (MFS) of the rock slope were the smallest. By assuming that the layered rock slope was homogeneous, the HD and MHD would be underestimated and FS and MFS would be overestimated. The obtained results are likely to provide a theoretical basis for the prediction and monitoring of layered rock landslides.

Geotechnical and Numerical analysis of Bcharreh Landslide stability

The aim of this study is to shed light on a real stability problem within the region of Bcharreh located in North of Lebanon where roads have no protection against landslides. An attempt for landslide assessment that occurred in November 2016 is presented in order to analyse the different factors behind the landslide and find the trigger factor affecting the stability of the slope. The characterization of soil properties along the slope is done based on geotechnical investigation, and data collection. The first part of work consists of site inspection and geotechnical investigation followed by a series of laboratory tests to evaluate the mechanical properties constituting the slope, in addition to collection of topographical and hydrogeological data. The second part presents the numerical analysis where a finite element model simulating the slope conditions is generated using Plaxis 2D in order to reproduce the process of landslides, to assess slope stability and determine the overall factor of safety in both dry and wet conditions. The contribution of each causal factor in prompting soil movement is then demonstrated and explained.

Significance of Surface Eco-Protection Techniques for Cohesive Soils Slope in Selangor, Malaysia

Rapid infrastructure development in Malaysia especially in Selangor causes drastic change in landscape and clearing of more vegetated areas. This has gradually lead to slope instability problems that causes enormous loss affecting human lives, destruction of property and environment. Thus, conservation practices by incorporating vegetation to enhance slope stability is much needed alternative to the conventional technique of stabilization. Limited studies had been done in discovering the effectiveness of vegetative covers in relation to slope and soil parameters. Hence, in this paper, a parametric study is carried out to discover the relationship between some of the various vegetation species and different soil types as well as slope angles. Conventional limit equilibrium methods are applied in the analysis considering the soil shear strength parameters, unit weight of soil, as well as slope geometry. Typical scenarios of cut-slope along highways in Selangor are simulated in order to obtain comparable results from the stability assessment by means of calculating the factor of safety. The modelling showed that shallow slip failure can be prevented when sufficient number of roots of a certain tensile force interact with the slip plane, increasing the overall factor of safety of the slope. The percentage of FOS increased due to the vegetation effects can reach up to 43% with slope angles ranging between 15° and 25°. Moreover, based on the parametric study, silty soils showed more significance in contributing to the increase in FOS when incorporating vegetation.

Design of an optically accessible turbulent combustion system

In order to design the next generation of gas turbine combustors and rocket engines, understanding the flame structure at high-intensity turbulent flows is necessary. Many experimental studies have focused on flame structures at relatively low Reynolds and Damköhler numbers, which are useful but do not help to provide a deep understanding of flame behavior at gas turbine and rocket engine operating conditions. The current work is focused on the presentation of the design and development of a high-intensity (Tu = 15–30%) turbulent combustion system, which is operated at compressible flow regime from Mach numbers of 0.3 to 0.5, preheated temperatures up to 500 K, and premixed conditions in order to investigate the flame structure at high Reynolds and Damköhler numbers in the so-called thickened flame regime. The design of an optically accessible backward-facing step stabilized combustor was designed for a maximum operating pressure of 0.6 MPa. Turbulence generator grid was introduced with different blockage ratios from 54 to 67% to generate turbulence inside the combustor. Optical access was provided via quartz windows on three sides of the combustion chamber. Extensive finite element analysis was performed to verify the structural integrity of the combustor at rated conditions. In order to increase the inlet temperature of the air, a heating section is designed and presented in this paper. Separate cooling subsystem designs are also presented. A 10 kHz time-resolved particle image velocimetry system and a 3 kHz planer laser-induced fluorescence system are integrated with the system to diagnose the flow field and the flame, respectively. The combustor utilizes a UNS 316 stainless steel with a minimum wall thickness of 12.5 mm. Quartz windows were designed with a maximum thickness of 25.4 mm resulting in an overall factor of safety of 3.5.

Analysis of Road Embankment Slope Stability

The stability of earthworks (cuttings, embankments, dikes) and natural slopes is a problem that is of concern to geotechnicians, both practitioners and researchers. The disorders generated by breaking the slopes are usually spectacular, often destructive and sometimes murderers. Many methods of calculating stability have been proposed. These are differentiated by the assumptions accepted by their authors (methods of calculation in equilibrium limit, methods of calculation at break, deformation calculation methods) and the ease of their implementation (calculations using charts, automatic calculations using software), but they all agree to define an overall factor of safety according to which the stability of the studied slope is considered to be insured or compromised, or by safety factor spartial effects on the one hand, applied stresses and, on the other hand, the mechanical properties soil. Various embankment strengthening techniques have been developed. They are differentiated by the process of their realization, their cost and their durability. The main objective of this study is to present the problems of both natural and artificial slope stability on construction projects. In this regard, special emphasis is given to the sensitivity of the calculation model input parameters (soil, load), which should contribute to raising awareness about this issue, as a prerequisite to make the right decisions and optimal technical solutions in this area.

Design and analysis of a portable friction stir welding machine

Friction stir welding is a mechanism to combine two solid metals without melting. This technique is much preferred for its flexibility, energy efficient, and also environment friendly as it results in high quality welding with low shrinkage. But these machines are giant and also consume more power. In order to address this problem, a portable friction stir welding machine has been designed and analysed. In this study, a machine has been designed to weld plates of 2mm thickness at low power consumption. This could be very much beneficial for the onsite welding processes and also to weld materials of less thickness. The design was done in four stages and the fourth stage was finally analysed for 2 tonne load and the plots are also shown in results and discussion for stress, displacement, strain and factor of safety. The analysis of overall factor of safety of the portable friction stir welding machine shows that all the components are safe except the transverse drive with a Factor of safety 1.431e-001 which is considered to be safe because the applied load is double to that of the required load. The Structural static analysis also was successfully completed using Solid Works by applying 2 tonne load and the results of various parameters such as stress, displacement, strain were plotted and tabulated.

Failure Investigation at a Collapsed Deep Open Cut Slope Excavation in Soft Clay

Collapse of a 7.08-m-deep open cut excavation for the bank of a navigation lock in sensitive soft clay in Zhejiang, China, is presented in this paper. Cone penetration tests, field vane shear tests (VSTs), and traditional laboratory tests have been performed to investigate the soil properties after the collapse. According to the test results, the soft soil layers of mucky clay and muck have been found to be disturbed because of the effects of the boring holes. For bored concrete piles, the stresses release due to the cut slope, thus its shear strength is much lower than that measured from laboratory tests. The shear strength reduction technique based on a finite-element method program has been used to study the excavation behavior and overall factor of safety (FOS) of the excavated slope considering geometries of original design, later adopted schemes and soil properties associated with various test types. The computed FOS values obtained from VST results are lower than the corresponding recommended values and just a little higher than the limited value. Thus the excavated slope may easily collapse triggered by additional vehicles and surface surcharge loads. The reasons of excavation collapse can be explained as the misuse of soil properties for designers, and inadequate construction process management. The investigation of the failure provides experiences and lessons for the design and construction of similar projects in sensitive soft clay.

Evaluation of effect of basal geotextile reinforcement under embankment loading on soft marine deposits

This paper presents a case history on the performance of a coastal embankment reinforced by a layer of geotextile at the bottom of the embankment on soft marine deposits. The coastal embankment is the sea wall of the Qinshan nuclear power station on the northern side of Hangzhou bay near Shanghai, China. Monitoring of settlement and excess pore water pressure were carried out during and after embankment construction. The finite element method (FEM) was used to analyse the performance of the geotextile reinforcement and its effect on soil behaviour under the embankment loading, based on the field monitored results. Stability analyses were conducted using two approaches: c-ϕ reduction in FEM, and limit equilibrium analysis. Both field and simulation results indicate that the geotextile has an effect on reducing the vertical displacements of subsoil. However, the results show basal reinforcement cannot increase the overall factor of safety, but the factor of safety at the local position, under reinforcement, can be increased during the construction procedure, and this is due to the confinement of the soil element by the reinforcing fabric. Thus, in these circumstances, one layer of basal geotextile reinforcement can prevent sudden failure of subsoil during embankment construction.

Slope Stability Analysis Using Slice-Wise Factor of Safety

The concept of slice-wise factor of safety is introduced to investigate the state of both the whole slope and each slice. The assumption that the interslice force ratio is the same between any two slices is made and the eccentric moment of slice weight is also taken into account. Then four variables equations are formulated based on the equilibrium of forces and moment and the assumption of interslice forces, and then the slice-wise factor of safety along the slip surface can be obtained. The active and passive sections of the slope can be determined based on the distribution of factor of safety. The factor of safety of the whole slope is also defined as the ratio of the sum of antisliding force to the sum of sliding force on the slip surface. Two examples with different slip surface shapes are analysed to demonstrate the usage of the proposed method. The slice-wise factor of safety enables us to determine the sliding mechanism and pattern of a slope. The reliability is verified by comparing the overall factor of safety with that calculated by conventional methods.

A Variable-Impedance Prosthetic Socket for a Transtibial Amputee Designed from Magnetic Resonance Imaging Data

ABSTRACTThis article evaluates the design of a variable impedance prosthetic (VIPr) socket for a transtibial amputee using computer-aided design and manufacturing (CAD/CAM) processes. Compliant features are seamlessly integrated into a three-dimensional printed socket to achieve lower interface peak

Slope Stability Analysis by SSR Based on Connectivity of Plastic Zone Failure Criterion

While the elasto-plastic finite element method based on the shear strength reduction(SSR) technique is employed to analyze slope stability, the overall factor of safety computed numerically is，in a certain degree，dependent on the failure criteria used for evaluating critical instability condition of slope. In the present paper, the connectivity of plastic zone criterion is chosen with its close physical meaning to the LEM , and the farther 3D critical slip surface searching procedure is presented. The results of stability analysis of a certain initial quarry slope show that the chosen failure criterion and the 3D critical slip surface searching procedure is reasonable and can be widely applied to slope engineering practice．

Steel silos with different aspect ratios: I — Behaviour under concentric discharge

The current European standards for the design of thin-walled metal silos require the designer to use a complex combination of rules covering many different aspects of loading, structural behaviour and strength. Each individual rule was often developed autonomously, usually with implicit and undocumented conservative assumptions. When combined, the overall factor of safety of a designed silo may be significantly different from that guaranteed by the standard, making it difficult to reproduce the design rules in a numerical calculation that does not include the same implicit assumptions. This paper explores the behaviour of five thin-walled cylindrical silos with stepwise-varying wall thickness and aspect ratios varying from very squat to very slender, all custom-designed for and analysed under the EN 1991–4 concentric discharge loading condition. The aspect ratio plays a deciding role in both the behaviour and design of silos, and it is important to ascertain that a finding that is valid for one is transferable to the others. The nonlinear finite element analyses reveal that the computed load factor exceeds the partial safety factor in design by a large factor over a wide range of aspect ratio, suggesting that the overall design process is particularly conservative. The reasons for these discrepancies are explored. This paper is the first of a pair. The second paper explores the behaviour of the same set of example silos under the EN 1991–4 eccentric discharge loads, with fundamentally different conclusions.

Failure Mechanism of a Shallow Landslide at Tun-Sardon Road Cut Section of Penang Island, Malaysia

The occurrences of shallow landslides in residual soils of Penang hilly areas are common in rainy days. The failure mechanisms of a shallow landslide occurred at km 3.9 road in Tun-Sardon area of Penang Island have been simulated using two different methods of slope stability analysis. The results indicate that the failure was initiated locally inside the slope and then propagated further to induce total failure. The failure propagation was started from initial local failure zone and was driven by mobilized shear strength along the shear plane. The slope was marginally stable with an overall factor of safety of 1.32 before it failed to a rainfall event on September 6, 2008. It is found from back calculation that the rain infiltration raised the temporary water level and reduced the shearing strength of soil to a minimum level with increased pore water pressure to trigger the failure. This paper suggests further research on shallow landslide of Penang Island considering the direct rainfall infiltration effect in terms of groundwater pressure-head distribution inside the slope.

Stability Analyses of an Earth Dam Using Limit Equilibrium and Finite Element Methods

The objective of this research is to study the relationships between the stability of earth dam and its soil strength parameters. The soil strength parameters include cohesion, unit weight of soil and angle of friction. GeoStudio, commercially available software, was used to obtain the overall factor of safety using limit equilibrium method (LEM) and finite element method (FEM). Tables to show the relationships among soil strength parameters for factor of safety 1.0 and 1.5 are presented in this paper.