Drained and Undrained Analysis for Foundations Based on Triaxial Tests

The analysis of foundations in fine grained, mostly soft soils leads to the question if either an undrained or drained analysis is appropriate to describe the ultimate limit state of a certain structure. Triaxial tests show that the undrained shear strength su is no proper soil parameter but strongly dependent on the initial conditions (OCR-value) and on the developing stress path. The analytical modelling of raft foundations in drained and undrained conditions shows the difficulties of using su based on triaxial tests. More triaxial tests and the study of different geotechnical structures are needed to give advice whether the short term behaviour (undrained) or the long term behaviour (drained) is supposed to be most critical.