SHEAR STRENGTH IN STABILITY ANALYSIS OF SLOPES

Abstract

Slopes of cuts and embankmeznts , natural or artificial, depend for their stability entirely om the shearing strength possessed by the soil or rock of which they are composed. Stability analysis of slopes in soil mechanics includes all studies which attempt to determine whether or not the shearing strength is sufficient to prevent failure. The uncertainty in stability analysis lies primarily in the selection and determination of shear strength for the analysis and especially the shear strength of cohesive soils appears to be the most complex. As it is very diffi-oult to simulate natural conditions in testing procedures, it is impracticable to obtain from laboratory test data the shear strength which exists under natural conditions. However in recent times most of the phenomena affecting the shear strength are sufficiently well understood so that these are allowed both in the testing procedures as well as the application of the test results in the stability analysis so as to obtain maximum possible accuracy. The purpose of this dissertation is to know in the first place a clear qualitative picture of what happens to this variable of shear strength during and after construction, operation and during the various types of loadings under considera-tion. Secondly the purpose is to indicate the most critical stages from the stability point of view and to select the appropriate shear parameters and method of stability analysis. Although embankments are constructed for different purposes such asp Highways, railways, dams and levees, the present discussion will be limited to Earthen Dams only as all the critical conditions of stability occur during different stages of loading for an earth dam. Broadly the heads under which the whole discussion will be made is as under:- 1. The methods of analysing the forces that cause and resist failure in the stability of an embankment with special reference to the method of slices. 2. The methods of determining and expressing the shear strength of materials that are used in an embankment. 3. Applications of different methods of analysis and shear test results for the different conditions of stability analysis.. i) The methods of analysing the forces involved is the stability analysis of embankments are mainly methods of stress analysis similar to the method based on elastic theory, and such methods based on the principle of limit design as the ep circle method, the sliding block method, the logaritbemic spiral method and the method of slices. Here the discussion will be mainly on the method of slices which is the most valuable for the practicing Engineer at the present time. An analysis of all the forces that will be acting on a slice will also be made, in the background of which the discussion of -shear strength would be apparent.