Evaluation of the predictive ability of two elastic-viscoplastic constitutive models

Abstract

Two elastic-viscoplastic constitutive formulations are evaluated using laboratory and field data from Sackville, New Brunswick and Gloucester, Ontario. Both constitutive models have been implemented in a finite element program and formulated for undrained analysis and fully coupled analysis based on Biot consolidation theory. A laboratory study of the rate-sensitive behaviour of Sackville clay is described. The response of Sackville clay during consolidated anisotropic undrained (CAU) triaxial creep, CAU triaxial compression, and incremental oedometer consolidation is compared with the calculated behaviour. The comparisons demonstrate the general ability of three-parameter elastic-viscoplastic constitutive models to satisfactorily describe the rate-dependent behaviour of Sackville clay. The measured response of Gloucester clay during long-term Rowe cell consolidation tests is compared with the calculated behaviour, and the predictive ability of both constitutive formulations is evaluated using the field performance of the Gloucester case record. In undertaking the present study, the predictive ability of two elastic-viscoplastic constitutive models is examined for two soft clays. A new method of overstress measurement is introduced for elliptical yield surfaces and the importance of adopting a scalable yield surface for the constitutive modeling of soft clay is demonstrated. A model that is suitable for the study of reinforced and unreinforced embankments on soft rate-sensitive clay foundations is identified.Key words: elastic-viscoplastic, finite element analysis, overstress viscoplasticity, case study, rate-sensitive, coupled analysis.