PRACTICING WITH GEOSLOPE FOR DESIGN OF SLOPES

Abstract

Slope stability methods vary in their theoretical background and approach and hence the. analysis results vary depending on the used theory. At the present tine, no single analysis method is preferred over the other by agencies and therefore, the reliability of any remediation .solution to any slope failure is completely left to the engineer in charge. Most practitioners prefer one method over the other based on their familiarity with the method rather than on the conditions of the failing slope. As a result, the remediation methods are either underdesigned or overdesigned. In' reality, the mechanism of the failing slope should be studied in detail by gathering enough field data and observations in order to choose the most appropriate analysis method. It is essential that a research effort be devoted to gain better understanding of the slope failure analysis methods and to understand the weakness and strength of the methods and to point out practical aspects in the analysis procedures. This thesis deals with slope stability evolutions carried out by commonly used limit equilibrium (LE) methods. The study utilizes the GEOSLOPE software. The LIB based-, methods are compared based on the factor of safety (FOS) obtained for various load combinations. The comparison is mainly based on simplified slope geometry and assumed input parameters. Among the LE methods, the Bishop simplified (BSM) and Janbu simplified (JSM) are compared with the Morgenstern-Price method (M-PM). The latter method satisfy both force and moment, equilibriums. In addition, M-PM allows a variable interslice force function. These LE methods are well established for many years, and thus some of them are still commonly used in practice for stability analysis. Simplicity and relatively good results are the advantages of these methods. It was found that the selection of the slope stability method is critical since the accuracy of the analysis results depends on the mechanism of the failure and prediction of the most critical slip surface is influenced by the search technique. The comparative study among the LE methods shows that BSM is as good as M-PM for normal condition in circular shear surface (SS) analysis. Similarly, JSM is as good as M-PM for plane SS 111 analysis. Moreover, the study shows that BSM is insensitive to interstice forces in. circular SS analysis, whereas JSM is insensitive to interstice forces in plane SS analysis. This is true for the analyses without any external forces acting in slopes. With some external, forces, both methods nay be sensitive to the interslice farce function, and thus the analyses may result in either higher or lower FOS compared with M-PM. Even if the M-PM assumes an interstice force function in analysis, the method is found suitable, because the method satisfies both force and moment equilibrium conditions. The simplified Janbu (JSM) method gives the most conservative value of the FOS. The Autolocate SS searching method is recommended for use in LE methods of slope stability. The M-P method is recommended to use in any kind of SS analyses, including external forces, unless FE methods are available.