Experimental Proof of the Existence of a Bifurcation Process During the undrained test in Clay

P. Evesque: Lab MSSM, UMR 8579 CNRS, Ecole Centrale Paris, 92295 Châtenay-Malabry, France, evesque@mssmat.ecp.fr

M. Hattab : LPMM/ISGMP,UMR 7554 CNRS, Université de Metz, île de Saulcy, 57045 METZ cedex 01, France, hattab@lpmm.univ-metz.fr

Abstract: Recent papers, based on a new simple incremental modelling which assumes an "isotropic" response , predicts that the trajectory followed during an undrained compression test exhibits a bifurcation process when the stress field arrives at q=M'p', i.e. indicating a discontinuous change of solution when arriving at q=M'p'. This paper looks at experimental data on dense sample obtained at p'=c^ste, and it shows that the trajectory (p'=c^st, v=c^st) does continue to exist at and beyond the q=M'p' plane. So, this demonstrates the validity of the analysis which uses the bifurcation theory and this strengthens the proposed modelling. Indeed, this demonstrates the reality of the bifurcation process during undrained compression.

Pacs # : 5.40 ; 45.70 ; 62.20 ; 83.70.Fn

poudres & grains 12 (1), 1-4 (février 2001)