Set of Constitutive Models for Soils Under Slow Movement

Abstract

Materially objective, rate‐type constitutive relations are presented for creeping soil. The soil is treated either as a non‐Newtonian viscous fluid or a saturated mixture of an inviscid interstitial fluid and a non‐Newtonian viscous fluid matrix. In the latter case, the effective stress is additively decomposed into a quasi‐elastic and a viscous component; the former relates the void ratio with the spherical stress and accounts for consolidation, the latter describes rate dependent deformations. Starting from stress‐stretching relations of a Reiner‐Rivlin fluid and by postulating that the stretching can only depend on nonlinear stress quantities via the second stress deviator invariant, the most general isotropic constitutive relations are deduced. Mathematical expressions which are postulated for the free phenomenological functions are calibrated with the aid of laboratory and field data. The fits that are obtained for specimens subjected to triaxial and shear tests, as well as in situ tests from Swiss landslides, prove satisfactory reproduction of the observed creep behavior.