Local Safety Factor Research Articles

Electrical resistivity tomography and statistical analysis in landslide modelling: A conceptual approach

In this paper, we propose a new approach for modelling the development of instabilities in pyroclastic covers induced by rainfall events. The approach is based on high-resolution 2D electrical resistivity tomography (ERT) and on a cellular automaton model aimed to simulate landslide events. A local and time-dependent Factor of Safety of a slope, that depends on electrical resistivity and the slope angle, is introduced. We show the results of a model run on data acquired in a test area of the Campania Region (Italy), where shallow landslides involving pyroclastic soils are very frequent and often triggered by critical rainfall events. The shown example would just emphasize the potentiality of the proposed conceptual model, which integrates geophysical and statistical analyses, in the framework of the landslide hazard, since its validation and calibration is the next step that has to be taken.

Limit equilibrium slope stability analysis using rigid finite elements

This paper revisits the interslice force assumptions associated with the method-of-slices approach to slope stability analysis. A brief review is presented on analysis procedures for this class of problem and a comparison is made between the factor of safety equations derived by Fellenius and a modified form of Bishop’s equation. A simplified rigid finite element method that takes into account progressive yielding through a sliding law is proposed, eliminating the need to provide constraint equations for the variation of interslice forces required by more advanced procedures, such as that developed by Morgenstern and Price. An example is given to demonstrate the proposed procedure and to investigate the sensitivity of the global and local factors of safety to the interslice and basal shear forces. It is demonstrated that the global factor of safety tends not to be sensitive to interslice shear forces when dealing with circular slip. For the slip circles that were analyzed, the Morgenstern and Price procedure yielded slice forces that were similar to those predicted by the proposed method, which takes into account the deformation and failure characteristics of the material comprising the slope.

Spatially resolved characterization of electrostatic fluctuations in the scrape-off layer of the CASTOR tokamak

The poloidal distribution of turbulence in the scrape-off layer (SOL) of the CASTOR tokamak is studied by means of a ring of 32 electric probes covering the whole perimeter of the poloidal cross section. Analysis of floating potential fluctuations in a SOL created in the top part of the machine by shifting the plasma downwards reveals a dominant periodic structure that propagates poloidally in the direction of the Er × B drift. Its poloidal mode number is found to be equal to the local safety factor q. Correlation and pulse propagation analyses show that this high m mode is a signature of a single long flute-like structure that is aligned with the magnetic field and snakes around the torus several times before terminating on the limiter.

An extension of 2D Janbu’s generalized procedure of slices for 3D slope stability analysis II

This paper provides a numerical approach on achieving the limit equilibrium method for 3D slope stability analysis proposed in the theoretical part of the previous paper. Some programming techniques are presented to ensure the maneuverability of the method. Three examples are introduced to illustrate the use of this method. The results are given in detail such as the local factor of safety and local potential sliding direction for a slope. As the method is an extension of 2D Janbu’s generalized procedure of slices (GPS), the results obtained by GPS for the longitudinal sections of a slope are also given for comparison with the 3D results. A practical landslide in Yunyang, the Three Gorges, of China, is also analyzed by the present method. Moreover, the proposed method has the advantages and disadvantages of GPS. The problem frequently encountered in calculation process is still about the convergency, especially in analyzing the stability of a cutting corner. Some advice on discretization is given to ensure convergence when the present method is used. However, the problem about convergency still needs to be further explored based on the rigorous theoretical background.

Landfill lining stability and integrity: the role of waste settlement

Design of landfills must consider stability both within and between elements of the lining system, within the waste and involving the sub-grade. However, the design must also consider the long-term integrity of the lining system. Stresses, and hence deformations, in both mineral and geosynthetic lining materials must be controlled to ensure preferential flow paths are not formed. An assessment of integrity requires knowledge of the interaction between components of the lining system and the waste body as it settles. This paper considers assessment of both global stability and local failure that could result in loss of lining integrity. Results are presented that demonstrate traditional limit equilibrium techniques cannot be used to assess local failure. Factors of safety relate to global stability failure (i.e. development of a continuous failure surface) and not local failure that can lead to loss of integrity. Numerical analysis techniques can be used to assess local instability. Example results are presented for typical landfill cell geometries. These demonstrate the mechanism of local failure and sensitivity of behaviour to waste properties. Local factors of safety are introduced to illustrate the likelihood of integrity failure due to loss of geomembrane protection.

Progressive failure analysis of slopes using non-vertical slices.

A limit equilibrium method for progressive failure analysis of slopes is proposed based on a technique of non-vertical slices . The local factors of safety are calculated by defining variable factor of safety instead of conventional single value factor of safety along a shear surface. Reasonable simplifying assumptions about the inter-slice forces and the line of thrust are made to render the problem statically determinate. Strain softening, though in an approximate manner, is considered in the solution procedure. The analysis of a field case history indicates that the proposed method realistically represent the behaviour of progressive failure of an actual slope. Another case study revealed that in certain conditions a reasonable solution can be obtained using non -vertical slice approach, but the vertical slice analysis does not work well in obtaining reliable results . The proposed method, which can also handle vertical slice division, enables the user to choose more appropriate results either from vertical or from non-vertical slice analyses.

Limit Equilibrium Slope Stability Assessment Considering Progressive Failure

Two different approaches, i. e. iterative procedure and load-incremental procedure are developed for the analysis of progressive failure of slopes, based on the limit equilibrium frameworks. In the former approach, self-weight of slope material together with surface load, if any, are simultaneously applied and iterative calculations are used until convergent solution is reached. On the other hand, total load including the self-weight is divided into many incremental steps, in the latter approach, and with each load-incremental step, analysis is repeated up to the final loading condition. Both procedures define local safety factor at the base of each slice to consider progressive, local failure and its evolution. Application shows that either of the procedures captures the behavior of progressive failure of slopes.

SEARCH FOR CRITICAL SLIP CIRCLE USING GENETIC ALGORITHMS

In using traditional nonlinear optimization techniques for determining the critical slip surface in slope-stability analysis there is generally some uncertainty as to robustness of the algorithms to locate the global minimum factor of safety rather than the local minimum factor of safety for complicated and non-homogeneous geological subsoil conditions. This paper describes the incorporation of a genetic algorithm methodology which is becoming increasingly popular in engineering optimization problems as it has been shown in a wide variety of problems to be suitably robust for the search not to become trapped in local optima. First, the general principles of genetic algorithms are described. The genetic algorithm procedure used to locate the critical circular slip surface is then described. The five examples presented indicate that the search strategy was suf ficiently robust and efficient to handle multi-layered soils.

Genetic algorithm search for critical slip surface in multiple-wedge stability analysis

Most procedures for determining the critical slip surface in slope-stability analysis rely on traditional nonlinear optimization techniques. The main shortcoming of these techniques is the uncertainty as to robustness of the algorithms to locate the global minimum factor of safety rather than the local minimum factor of safety for complicated and nonhomogeneous geological subsoil conditions. This paper describes the incorporation of a genetic algorithm methodology for determining the critical slip surface in multiple-wedge stability analysis. This search strategy is becoming increasingly popular in engineering optimization problems because it has been shown in a wide variety of problems to be suitably robust for the search not to become trapped in local optima. Three examples are presented to demonstrate the effectiveness of the genetic algorithm approach. The search strategy was found to be sufficiently robust to handle layered soils with weak, thin layers, and as efficient and accurate as the conventional pattern search method.Key words: critical slip surface, factor of safety, genetic algorithms, optimization, slope stability, wedge analysis.

Limit Equilibrium Slope Stability Analysis Considering Progressive Failure

This paper proposes a slope stability analysis method considering progressive failure based on the limit equilibrium principle. The softening of soil is taken into account and the slip surface of arbitary shape is adopted.Formulation of the ploblem is carried out by using the slice method, and the analysis satisfies both force and moment equilibrium conditions. The basic idea of the proposed method is to define a local factor of safety at the base of each slice. Thus, the number of unknowns increases, and the ploblem becomes more highly undeterminate than those in the conventional slice methods. In order to render the ploblem determi-nate, two simplifying assumptions about the interslice forces and the line of thrust are simultaniously made which are separatly used in the Morgenstern-Price method and the Janbu method. An overall factor of safety is introduced to evaluate the whole stability of a slope. Finally, the results of an example problem show that the proposed analysis method can reasonably represent the actual behavior of the progressive failure of cl Slopes.

Local safety factor applicable to wide range of failure criteria

Local safety factor applicable to wide range of failure criteria

Optimum material design for functionally gradient material plate

Steady thermal stresses in a plate made of a functionally gradient material (FGM) are analyzed theoretically and calculated numerically. An FGM plate composed of PSZ and Ti-6Al-4V is examined, and the temperature dependence of the material properties is considered. A local safety factor is used for evaluation of the FGM's strength. It is assumed that top and bottom surfaces of the plate are heated and kept at constant thermal boundary conditions. The pairs of the surface temperatures, for which the minimum local safety factor can be of more than one, are obtained as available temperature regions. The temperature dependence of the material properties diminishes, available temperature region as compared with that for an FGM plate without it. The available temperature region of the FGM plate is wider than that of the two-layered plate, especially for the surface temperatures which are high at the ceramic surface and low at the metal side. The influence of different mechanical boundary conditions is examined, and available temperature regions are found to be different, depending on the mechanical boundary conditions. The influence of the intermediate composition on the thermal stress reduction is also investigated in detail for the surface temperatures which are kept at 1300 K at the ceramic surface and 300K at the metal side. Appropriate intermediate composition of the FGM plate can yield the local safety factor of one or more for the four mechanical boundary conditions at once. For the two-layered plate there does not exist, however, any appropriate pair of metal and ceramic thicknesses which would yield the local safety factor of one or more for the four mechanical boundary conditions at once. The influence of the intermediate composition on the maximization of the minimum stress ratio depends on the mechanical boundary conditions. Finally, the optimal FGM plates are determined.

A Simple Method for the Analysis of Stability of Slopes in Brittle Soil

The basic idea used in limit equilibrium method, of analysing some possible states of stresses (forces) for trial slip surfaces, is further expanded by adding consideration of possible kinematics of chosen sliding bodies divided into rigid slices (wedges), so that the local factors of safety at the bases and interfaces of the slices (wedges) could be defined. This approach enables determination of the stability of slopes in brittle soil, whose shear strength is shear displacement (strain) dependent. The analyses of instabilities of two slopes, using this method, showed that the method was capable of predicting the progressive types of failures, which occurred when brittle soil was loaded non- uniformly.

破壊限接近度と局所安全率に関する考察と拡張

With a great increase in the power of digital computer, the methods of numericalanalysis for the engineering purpose have been developed in the last decades. Especially, the stress analysis is one of the most popular application of numerical methods. The calculated results of the stress analysis are usually visualized by (principal) stress contour. However, for a material of which strength dependson such as confining pressure, stress is not enough to estimate the degree of safety. In such cases, stress severity or local safety factor is used to visualizethe state of stress at any portion in the structure.In this paper, the stress severity Sv and the safety factor Sf are extended and redefined as;Sv=d/D & Sf=D/dwhere d is distance from the origin to a point (σ1, σ2, σ3) in the stress-coordinate system. If stress increases along the given stress path andreaches to the plane of failure criterion at a point (σ1', σ2'sigma;3'), Dis distance from the origin to this point.The definition of Sv & Sf are quite simple and the values of them can be easily calculated. It should be noted that failure criterion and stress path can be chosen freely and independently.The modified definition of Sv & Sf is examined comparing with the former definitions such as one by Fairhurst. It is revealed that Sv & Sf calculated following the modified definition is conformable to the former three popular ones and it can be said that the proposed definition is an extended version and upper-compatible to the former ones.

Diagnostics for investigation of magnetic reconnection in sawtooth crash on TFTR

Magnetic reconnection phenomena are documented by a set of noninvasive fast diagnostics during the crash phase of sawtooth oscillations. The electron cyclotron emission diagnostic system provides the highest resolution for measuring time evolution of electron temperature profile during a typical Tokamak Fusion Test Reactor fast sawtooth crash. The x-ray tomography also contains fast time scale information of the electron temperature profile and additionally the impurity concentration. Just before the crash, a shrinking circular hot peak and growing crescent-shaped flat island appear in the inside of the inversion radius on a bird’s-eye view of the electron temperature profile. The electron temperature gradient inside the inversion radius diminishes to nearly zero after the crash. Concomitantly, q(r) profile [q(r)=local safety factor] is measured by the motional stark effect (MSE) diagnostics to verify a magnetic field line reconnection during the sawtooth oscillation. Initial MSE data indicate that central q values increases by 5%–10% during the sawtooth crash phase even when the pressure gradient diminishes inside the q=1 region.

Finite Element Slope Stability Analysis by Shear Strength Reduction Technique

A shear strength reduction technique for finite element slope stabilityan alysis has been developed by the authors. An important orginal point in the proposed method is that the slope failure is defined according to the shear strain failure criterion. The aim of this paper is to verify the shear strength reduction technique for the finite element slope stability analysis. Are presented the detailed background behind the shear strength reduction technique, the elucidation of the physical meaning of the critical shear strength reduction ratio in regard to the total shear strain and shear strain increment for both embankment and excavation slopes and its practical application to a field test on a reinforced slope cutting. As the results, the critical shear strength reduction ratio agrees with the safety factor by the Bishop’s method if total shear strain is used for analyses of embankment slopes. In the case of the natural excavation slopes, in which total shear strain is difficult to be assessed, the safety factor can be related to the average of the local safety factors along the failure slip surface obtained by the shear strength reduction technique. The predicted behavior of the reinforced slope cutting agrees with the field test data and site observation. Agreement between the shear strength reduction technique and a modified Fellenius’ method is satisfactory. Consequently, applicability of the proposed method to practical design works is demonstrated.

Limit equilibrium method with local factors of safety for slope stability: Discussion

This is a discussion of a paper by the same title which appeared in Vol. 24, Canadian Geotechnical Journal, pp 652-656. The author of the original paper is M.M. Srbulov.

Limit equilibrium method with local factors of safety for slope stability: Reply

Limit equilibrium method with local factors of safety for slope stability: Reply

Limit equilibrium method with local factors of safety for slope stability. Note: Srbulov, M M Can Geotech JV24, N4, Nov 1987, P652–656

Limit equilibrium method with local factors of safety for slope stability. Note: Srbulov, M M Can Geotech JV24, N4, Nov 1987, P652–656

Toroidal divertor tokamak.

A plasma confinement configuration of current carrying toroidal plasma with toroidal divertors, which may have the advantages of no major disruption and good confinement, is proposed. The local rotational transform of magnetic field lines and magnetic well in the toroidal divertor are calculated in a cylindrical model. The rotational transform sharply increases near the separatrix, which induces a large shear and significant reduction of the local safety factor. Stabilization of the pressure driven and drift modes by the magnetic well through the edge plasma confinement, and stabilization of the low (m, n) current driven kink and tearing modes by line tying effects in the toroidal divertor are discussed.