M. Jahanandish - Department of Civil Engineering, Shiraz University, Shiraz, Iran.
A. Eslami Haghighat - Department of Civil Engineering, Shiraz University, Shiraz, Iran.

Boundary value problems like slope stability, retaining walls and foundations comprise a large part of our problems in soil engineering. In the analysis of these problems, it is usually assumed that the direction of principal strain increments and principal stresses coincide. This assumption, known as coaxiality, has been supported by the studies of some researchers, but has been argued by others as well. The purpose of this paper is to investigate the influence of this assumption on the results of analysis of these boundary value problems. The zero extension line method has been used for this investigation. Results obtained assuming coaxiality have been compared with those in which coaxiality is not assumed. It has been concluded that result of analysis is not generally on the safe side when coaxiality is assumed.

Zero extension lines, stress characteristics, coaxiality, non-coaxiality