Failure States For Normally and Overconsolidated Soft Bangkok Clay

Extensive triaxial test data on soft Bangkok clay indicate that a unified normalized failure envelope in compression can be obtained for all states and this envelope is only dependent on the frictional component. The failure envelope on the extension side is a mirror image of the compression envelope on the mean normal stress axis. Triaxial compression and extension tests performed with a wide variety of stress paths as well as stress probing experiments inside the state boundary surface seem to confirm this single set of normalized failure envelopes. Such normalizable failure surfaces merge with the undrained stress paths of the normally consolidated states to form the state boundary surface. This would imply that for natural un-cemented deposits of soft clays, effective stress analysis could be performed successfully only with frictional mechanism in the limit state and the friction angle will vary dependent on the overconsolidation ratio. Many of the case histories in the Muar clay series of test embankments seem to give successful predictions when analysed using the CRISP Program and the limit state friction strength envelope. Similar experience is also noted in the performance of the test embankments with the Bangkok clay