Papers by Keyword: Factor of Safety (FOS)

Abstract: At present, in-situ stress was not considered in Limit Equilibrium Method (LEM) of slopes, the influence of in-situ stress is very small on the stability of conventional slopes, but in deep-depressed open-pit mines, the influence should not be neglected. Formula for calculating the Factor of Safety (FOS) under the effect of horizontal in-situ stress was deduced using General Slice Method (GSM) of two-dimensional (2D) limit equilibrium method in this paper，a corresponding program SSLOPE was built, and the software was used in a deep- depressed open-pit iron mine. The results show that the FOS of the slope decreased by 20% when horizontal in-situ stress is considered, some reinforcements must be taken. Therefore, the influence of in-situ stress on slope stability should be taken into account in deep open –pit mines.

Abstract: Based on finite element analysis software ANSYS, slope stability analysis is carried out by Elastic limiting equilibrium method proposed in this paper. A series of sliding surface of the slope can be assumed firstly, and then stress field along the sliding surface is analyzed as the slope is in elastic state. The normal and tangential stresses along each sliding surface can be obtained, respectively. Then the safety factor for each slip surface can be calculated, the slip surface which the safety factor is smallest is the most dangerous sliding surface. This method is different from the previous limit equilibrium method. For the previous limit equilibrium method, the normal and tangential stresses along the sliding surface are calculated based on many assumptions. While, the limit equilibrium method proposed in this paper has fewer assumptions and clear physical meaning.

Abstract: Chen Clan academy square reconstruction project is one of the Asian Game projects. The depth of the foundation pit of the green square is about 12.1m. The difficulties of the excavation are the protection of the ancient buildings of Chen Clan academy and the surrounding buildings and the relatively short construction period. Thus, a top-down construction method was selected as the final method. For security, reliability analyses based on Taylor series technique have been performed to the factor of safety of whole stability, stability against overturning, stability against basal heave and stability against seepage. The results show that the design of the supporting structure is generally reliable, but there are also some potential safety hazards which should be noticed. The application of Taylor series technique also shows the simplification and practicality of this method.

Abstract: In this paper, it proves that the necessary and sufficient condition for the potential sliding body reaching the ultimate limit equilibrium state is that the summation of shear stresses along the sliding surface equals to that of resistant shear strength. Based on the rigorous theory analyses and derivations, it is clearly shown that the definition of factor of safety (FOS) in the slip surface stress method (SSSM) is irrelevant with the shape of slip surface. Thus, the authors demonstrate that the FOS of noncircular slip surface can also be defined as the ratio of the sum of resistant sliding force along slip surface to that of sliding force. Furthermore, the physical meaning of the FOS in the SSSM, which can be taken as the average evaluation of the strength reduction coefficient that makes the sliding body reach the ultimate limit equilibrium state along the slip surface in nature, is formulated on the basis of strength reserving theory rather than the overloading theory like that in the Limit Equilibrium Method (LEM) and the Shear Strength Reduction Method (SSRM). Finally, the factors of safety (FOS) and the locations of critical failure surfaces obtained by the SSSM, LEM and SSRM are compared for various geotechnical practices. It is found that the SSSM can achieve precise and reasonable stability assessments for the soil slopes on the basis of actual stress field. Consequently, compared with the LEM and SSRM, the SSSM is demonstrated to be effective and efficient alternative approach for routine analysis and design in geotechnical engineering practice with a high level of confidence.

Abstract: The three-dimensional shear strength reduction method is used to evaluate the stability of an idealized slope stabilized with anchors, where the soil-anchor interaction is simulated by zero-thickness three-dimensional interface elements, and the effects of the direction angle, position, spacing on the slope stability are numerical studied. The results show that the reinforcing mechanisms of anchors in slopes are to increase the shearing resistance on the slip surface，and the failure mechanism, predicted by SSR, agrees well with the critical slip circle given by Bishop’s simplified method. The better stabilizing effects can be obtained when the anchors are installed with a small angle between the anchor and the horizontal direction, and slightly closer to the slope toe.

Abstract: The impoundment and running of Three Gorges Reservoir makes the water level fluctuate between 175m and 145m, and the water level fluctuation has been leading to the seepage field variation of bank slopes, which will bring out the stability change of bank slopes. In order to obtain the relationship between the angles of dip and factors of safety of bedding rock slopes which are generalized slope models from some bedding rock slopes failure in some reservoirs, the finite element method based on Darcy seepage theory was taken to simulate the seepage field variation of this type of bedding rock slopes when exposed to water level fluctuation, then the underground water tables of the bedding rock slopes with different angles of dip were obtained, finally the factors of safety of bedding rock slopes when water level rose and fell at speed of 0.2m/d were calculated by limit equilibrium method. Through the regulation analysis of factors of safety with the increase of angles of dip of bedding rock slopes when exposed to reservoir water level fluctuation, the relationship between factors of safety and angles of dip of bedding rock slopes was obtained.

Abstract: In the analysis of slope stability, a reduction method of non-linear shear strength was applied. A power function was used to approximate the shear failure envelope which is determined by the non-linear criterion or experimental data, and then the coefficients of that function were determined by using the collocation points. The equivalent friction angles and cohesive strengths of rock as well as stress range were determined by fitting an average linear relationship to the approximate curve generated by the power function through the method of least square. Finally, an example was presented to demonstrate the superiority and feasibility of the method introduced in this paper.

Abstract: In order to implement the non-linear Hoek-Brown (HB) shear strength reduction (SSR) on commercially available softwares, this paper derives the relationship between the Drucker-prager (DP) criterion and HB criterion under the condition of plane strain. The equivalent DP parameters can be approximately estimated after serious transformations of parameters between the HB and Mohr-Coulomb (MC) yield functions. To assess the effect of dilation on the stability of slope, the non-associated flow rule, which cannot be contained in the existing limit equilibrium methods, is selected in our analysis, and the SSR-based results of a simple slope indicate that: If the angle of dilatancy ψ is taken to be zero, the factor of safety calculated by the SSR method is very close to that by the limit equilibrium method; if ψ is greater than zero, the factor of safety calculated by the SSR method is greater than that by the limit equilibrium method, and the effect of dilation on the stability of slope can be approximately described by a liner function.

Abstract: Boundary conditions have great impact on the stability of three dimensional geo-material, like slope, which is one of the oldest applications in geotechnical engineering. In order to analyze the impact of boundary condition to factor of safety of slope, the 3D stability analysis was then extended to the “rough-smooth” and “smooth-smooth” boundary. By studying slopes with the same geometric condition and shear strength parameters, the results show that the safety factors obtained from “rough-smooth” boundary are smaller than those got from “rough-smooth” boundary and bigger than those got from “smooth-smooth” boundary. The study also indicates that when the width to height ratio (W/H) of homogeneous symmetric slope satisfies certain condition, the “rough-rough” boundary equals to the “rough-smooth” boundary. The factor of safety and shape of slip surface got from these two kinds of boundary condition are of the same. Study results can give guidance for the real practice.

Abstract: The reliability analysis in this paper is implemented directly starting from the basic variables of the HoekBrown criterion. A limit state equation, in which the basic variables of the HoekBrown criterion are contained, is built by introducing the factor of safety of slope. The calculation procedures of three methods used in the reliability analysis of this paper are analyzed in detail. The stability analysis for a cut slope shows that the reliability results obtained by three methods have little differences. This paper also suggests a simple and fast method for estimating the reliability of slope stability.