Şev stabilitesinin iki ve üç boyutlu modeller ile incelenmesi

Öz

Bu çalışmada, sonlu elemanlar yönteminin, şev stabilitesi problemlerinin analizinde uygulanabilirliği iki ve üç boyutlu modeller kullanılarak araştırılmıştır. Çalışmada, şevlerin stabilitesinin sonlu elemanlar yöntemi ile analizinde kullanılan mukavemet azaltma tekniğinden bahsedilmiş ve kumlu bir şev örneği ele alınarak göçmeye karşı güvenlik sayısı, mukavemet azaltma tekniği kullanılarak elde edilmiştir. Çalışmada iki ve üç boyutlu modellemenin sonlu elemanlar analizi üzerindeki etkileri araştırılmıştır. Ayrıca, limit denge yöntemi kullanılarak şev stabilite analizleri gerçekleştirilmiş ve elde edilen güvenlik sayıları sonlu elemanlar yöntemi ile elde edilen sonuçlarla karşılaştırılmıştır. Çalışma sonunda, üç boyutlu şev modeliyle elde edilen güvenlik sayısı değerlerinin iki boyutlu durumda elde edilen değerden daha büyük olduğu ve mukavemet azaltma tekniği ile elde edilen güvenlik sayısı değerlerinin, limit denge yöntemleri ile elde edilen güvenlik sayısı değerleriyle uyum içerisinde olduğu görülmüştür.

Anahtar Kelimeler

• Şev stabilitesi, Sonlu elemanlar yöntemi, Limit denge yöntemi, Güvenlik sayısı

Analysis of slope stability with two and three dimensional models

Abstract

In this study, the applicability of the finite element method in the analysis of slope stability problems was investigated using two and three dimensional models. Limit-equilibrium methods are the most commonly used approaches for analyzing the stability of slopes. The fundamental assumption at their core is that failure occurs through sliding of a block or mass along a slip surface. The popularity of limit-equilibrium methods is primarily due to their relative simplicity, ready ability to evaluate the sensitivity of stability to various input parameters, and the experience geotechnical engineers have acquired over the years in interpreting calculated factor of safety values. Limit-equilibrium methods require minimal input data. The factor of safety values they output help engineers to guard against uncertainties such as ignorance about the reliability of input parameters and loadings, and the possibility that identified failure mechanisms may differ from actual behaviour. As well, recommended factor of safety values for slopes and excavations generally ensure that deformations are within acceptable range. Rapid advances in computer technology and sustained development have pushed the finite element method (FEM) and other numerical analysis approaches to the forefront of geotechnical practice. Since it was first applied to geotechnical engineering in 1966, the FEM has grown tremendously in popularity, primarily due to its ability to analyze a very broad range of problems, while yielding realistic results. It can accommodate practically all kinds of geometry, and can model key aspects of material behaviour such as stress paths (construction sequence), and coupled stress-pore pressure variations. In the mid 1970s, techniques for applying the FEM to slope stability analysis started appearing in geotechnical literature. They were mostly based on an approach that flows naturally from the definition of slope factor of safety, and is now commonly referred to as the Shear Strength Reduction (SSR) technique. By definition, the factor of safety of a slope is the “ratio of actual soil shear strength to the minimum shear strength required to prevent failure,” or the factor by which soil shear strength must be reduced to bring a slope to the verge of failure (Duncan, 1996). Strength reduction technique which is used in the analysis of slope stability with finite element method is discussed and an example of sand slope was considered to obtain the factor of safety against the failure using strength reduction technique. The strenght reduction analysis was carried out with the using of the Plaxis computer programme which is solved with the finite element method. In the study, the effects of two and three dimensional models on the finite element analysis were investigated. Also, slope stability analyses were performed using limit equilibrium method and obtained results were compared with finite element results. At the end of the study, it was shown that the values of factor of safety (FS) obtained from 3D model is higher than those of 2D model and a satisfactory agreement was observed between the results obtained from limit equilibrium method.

Keywords

• Slope stability, Finite element method, Limit equilibrium method, Factor of safety