Influence of Destructuration of Soft Clay on Time-Dependent Settlements: Comparison of Some Elastic Viscoplastic Models

Abstract

The time-dependent settlement of soft soils following the application of surface loading may be modeled using elastic viscoplastic constitutive models to describe the soil behavior. For applied loadings that increase the stresses toward and beyond the in situ yield stress, the predicted behavior is strongly influenced by the associated breakdown of the clay structure and the way in which this is modeled. Four elastic viscoplastic models are compared and it is shown that, despite presentational differences, all calculate creep rate in fundamentally the same manner. This paper describes some predictions for a hypothetical case prediction exercise organized recently by the Norwegian Geotechnical Institute that compared different calculation methods used in settlement analyses of soft soil. The results presented here are from a one-dimensional coupled consolidation analysis implemented in a spreadsheet-based software and using a finite-element program. Parameters were obtained from an oedometer test, and the results were extrapolated over the full soil profile. Various plausible assumptions about the shape of the isotaches around yield were explored, and it is shown that the predicted long-term settlement may vary by a factor of two or more, depending on the assumptions made.