ABSTRACT:
Traditional limit equilibrium formulations such as the Bishop, Spencer or Morgenstern-Price methods have some inherent weaknesses. To overcome these weaknesses, efforts have been directed at using finite element computed stresses for assessing the stability of slopes. This paper reviews and compares two methods referred to as the Strength Summation Method and the Strength Reduction Method, and concludes that the Strength Reduction Method is more suitable for serviceability (deformation) analyses while the Strength Summation Method is more suitable for stability analyses.
1 INTRODUCTION
Stability is always a key issue in the analysis, assessment or design of most earth structures. After all, the prime objective is to ensure that the structure does not collapse and/or deform to the point that it causes unmanageable property damage or in the worst case, the loss of human lives. It is by far the most common type of numerical analysis in geotechnical engineering and has become routinely used in practice. Historically, stability analyses have been completed using limiting equilibrium (LE) formulations such as the well known Bishop, Spencer and Morgenstern- Price methods. The potential sliding mass is commonly discretized into slices as shown in Figure 1. The forces on each slice, treated as a free body, are resolved to satisfy horizontal and vertical force equilibrium together with the overall moment equilibrium of the entire potential sliding mass. The factor of safety is defined as the value by which the soil strength must be reduced to achieve the limiting equilibrium condition. Limit equilibrium formulations have their shortcomings as was vividly illustrated by Krahn (2003) in the 2001 R.M. Hardy keynote address in Calgary. At the heart of the limitations is the fact that limit equilibrium formulations do not in any way consider strains and displacements so they certainly do not satisfy strain and or displacement compatibility.
