EVALUATION OF THE STABILITY OF NATURAL SLOPES IN PLASTIC CHAMPLAIN CLAYS.

Abstract

A method of stability analysis was developed to accommodate the distinctly nonlinear nature of the strength envelopes for Champlain Sea clays in the low-stress range appropriate to stability problems. Using this method, an evaluation of natural slope failures in Champlain Sea clays was carried out based on strength characteristics determined with block samples from the sites of recent slides in Quebec. In view of some similarities in geotechnical properties and shear behavior, the strength characteristics so determined were also used to examine some of the recent slides in the Ottawa area. The results of stability analysis for eleven slides indicate that the field strength generally approaches the post-peak condition. To verify this condition, the state of stress of two slopes before sliding was determined by a finite element method accounting for work-softening behavior. The results of analysis show that the post-peak factor is very close to unity in the Quebec sites. The same observation may be applied to the slides in the Ottawa areas, provided that the post-peak strengths of the clays in these areas are verified.