Abstract
Three case studies for short term stability problem for the structures constructed on normally consolidated clays at and near failure are described in detail including discussions of the shear strength of soft clays determined by various methods currently practiced.Undrained strength to be used for stability analysis is briefly summarized and the shear strength determined by various methods are discussed as well as considerations on reliability of stability analyses. It is shown that 1) shear strength of soft clay deposits determined by the methods currently practiced is uncertain and 2) results of stability analyses evaluated using such uncertain strength values are unreliable.Results of stability analyses for the three structures constructed on normally consolidated clays at and near failure are described in detail as well as the undrained strength characteristics of the clays at the three sites. Stability analyses were carried out using the strength values from 1) the modified Bjerrum's method, 2) the SHANSEP method, 3) in-situ vane test, 4) unoconfined compression test and 5) Bjerrum's stability chart. Factors of safety obtained from each of the methods are considerably different from each other and strongly demonstrated the importance to recognize the regional variations in evaluating the proper soil behaviour.
