Strength Parameters in Stability Analysis

Stability problems have been divided into three categories: (1) undrained (2) drained and (3) partially drained. Actually failures usually occur without significant drainage, conventional effective stress analyses give unsafe estimates of potential instability. On the other hand, the factors of safety obtained by total stress analyses are always underestimated. Therefore the so-called effective consolidation stress analysis, that treats in-situ effective stresses before failure as equal to consolidation stresses in order to evaluate variations in undrained shear strength during construction, is more rational than the above-mentioned two analyses. Inconsistencies in the conventional definition and the practical application of the angle of shearing resistance obtained from consolidated-undrained biaxial compression tests were discussed and clarified. Finally a case history was presented to illustrate the possible errors induced by the mentioned ambiguity.